[PATCH][RFT] Vectorization of first-order recurrences

[PATCH][RFT] Vectorization of first-order recurrences

[Richard Biener]

The following picks up the prototype by Ju-Zhe Zhong for vectorizing
first order recurrences.  That solves two TSVC missed optimization PRs.

There's a new scalar cycle def kind, vect_first_order_recurrence
and it's handling of the backedge value vectorization is complicated
by the fact that the vectorized value isn't the PHI but instead
a (series of) permute(s) shifting in the recurring value from the
previous iteration.  I've implemented this by creating both the
single vectorized PHI and the series of permutes when vectorizing
the scalar PHI but leave the backedge values in both unassigned.
The backedge values are (for the testcases) computed by a load
which is also the place after which the permutes are inserted.
That placement also restricts the cases we can handle (without
resorting to code motion).

I added both costing and SLP handling though SLP handling is
restricted to the case where a single vectorized PHI is enough.

Missing is epilogue handling - while prologue peeling would
be handled transparently by adjusting iv_phi_p the epilogue
case doesn't work with just inserting a scalar LC PHI since
that a) keeps the scalar load live and b) that loads is the
wrong one, it has to be the last, much like when we'd vectorize
the LC PHI as live operation.  Unfortunately LIVE
compute/analysis happens too early before we decide on
peeling.  When using fully masked loop vectorization the
vect-recurr-6.c works as expected though.

I have tested this on x86_64 for now, but since epilogue
handling is missing there's probably no practical cases.
My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
just fine but I didn't feel like running SPEC within SDE nor
is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
with fully masked loops succeed (minus three cases of
PR107096, caused by my WHILE_ULT prototype).

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
handle epilogues welcome.

Thanks,
Richard.

	PR tree-optimization/99409
	PR tree-optimization/99394
	* tree-vectorizer.h (vect_def_type::vect_first_order_recurrence): Add.
	(stmt_vec_info_type::recurr_info_type): Likewise.
	(vectorizable_recurr): New function.
	* tree-vect-loop.cc (vect_phi_first_order_recurrence_p): New
	function.
	(vect_analyze_scalar_cycles_1): Look for first order
	recurrences.
	(vect_analyze_loop_operations): Handle them.
	(vect_transform_loop): Likewise.
	(vectorizable_recurr): New function.
	(maybe_set_vectorized_backedge_value): Handle the backedge value
	setting in the first order recurrence PHI and the permutes.
	* tree-vect-stmts.cc (vect_analyze_stmt): Handle first order
	recurrences.
	(vect_transform_stmt): Likewise.
	(vect_is_simple_use): Likewise.
	(vect_is_simple_use): Likewise.
	* tree-vect-slp.cc (vect_get_and_check_slp_defs): Likewise.
	(vect_build_slp_tree_2): Likewise.
	(vect_schedule_scc): Handle the backedge value setting in the
	first order recurrence PHI and the permutes.

	* gcc.dg/vect/vect-recurr-1.c: New testcase.
	* gcc.dg/vect/vect-recurr-2.c: Likewise.
	* gcc.dg/vect/vect-recurr-3.c: Likewise.
	* gcc.dg/vect/vect-recurr-4.c: Likewise.
	* gcc.dg/vect/vect-recurr-5.c: Likewise.
	* gcc.dg/vect/vect-recurr-6.c: Likewise.
	* gcc.dg/vect/tsvc/vect-tsvc-s252.c: Un-XFAIL.
	* gcc.dg/vect/tsvc/vect-tsvc-s254.c: Likewise.
	* gcc.dg/vect/tsvc/vect-tsvc-s291.c: Likewise.

Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
---
 .../gcc.dg/vect/tsvc/vect-tsvc-s252.c         |   2 +-
 .../gcc.dg/vect/tsvc/vect-tsvc-s254.c         |   2 +-
 .../gcc.dg/vect/tsvc/vect-tsvc-s291.c         |   2 +-
 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c     |  38 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c     |  39 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c     |  39 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c     |  42 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c     |  43 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c     |  39 +++
 gcc/tree-vect-loop.cc                         | 286 ++++++++++++++++--
 gcc/tree-vect-slp.cc                          |  38 ++-
 gcc/tree-vect-stmts.cc                        |  17 +-
 gcc/tree-vectorizer.h                         |   4 +
 13 files changed, 563 insertions(+), 28 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c

diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
index f1302b60ae5..83eaa7a8ff5 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
@@ -40,4 +40,4 @@ int main (int argc, char **argv)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
index bdc8a01e2a5..06e9b0a849d 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
index 0b474c2e81a..91cdc121095 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
new file mode 100644
index 00000000000..6eb59fdf854
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
@@ -0,0 +1,38 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
new file mode 100644
index 00000000000..97efaaa38bc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
new file mode 100644
index 00000000000..621a5d8a257
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, signed char * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+signed char b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
new file mode 100644
index 00000000000..f6dbc494a62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
@@ -0,0 +1,42 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+	|| b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
new file mode 100644
index 00000000000..19c56df9e83
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
@@ -0,0 +1,43 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+	|| b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
new file mode 100644
index 00000000000..e7712680853
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c, int n)
+{
+  int t = *c;
+  for (int i = 0; i < n; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c, 63);
+  for (int i = 1; i < 63; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* ???  We miss epilogue handling for first order recurrences.  */
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" { target vect_fully_masked } } } */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 2536cc3cf49..b54820a960b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -529,6 +529,45 @@ vect_inner_phi_in_double_reduction_p (loop_vec_info loop_vinfo, gphi *phi)
   return false;
 }
 
+/* Returns true if Phi is a first-order recurrence. A first-order
+   recurrence is a non-reduction recurrence relation in which the value of
+   the recurrence in the current loop iteration equals a value defined in
+   the previous iteration.  */
+
+static bool
+vect_phi_first_order_recurrence_p (loop_vec_info loop_vinfo, class loop *loop,
+				   gphi *phi)
+{
+  /* Ensure the loop latch definition is from within the loop.  */
+  edge latch = loop_latch_edge (loop);
+  tree ldef = PHI_ARG_DEF_FROM_EDGE (phi, latch);
+  if (TREE_CODE (ldef) != SSA_NAME
+      || SSA_NAME_IS_DEFAULT_DEF (ldef)
+      || !flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (ldef))))
+    return false;
+
+  tree def = gimple_phi_result (phi);
+
+  /* Ensure every use_stmt of the phi node is dominated by the latch
+     definition.  */
+  imm_use_iterator imm_iter;
+  use_operand_p use_p;
+  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, def)
+    if (!is_gimple_debug (USE_STMT (use_p))
+	&& (SSA_NAME_DEF_STMT (ldef) == USE_STMT (use_p)
+	    || !vect_stmt_dominates_stmt_p (SSA_NAME_DEF_STMT (ldef),
+					    USE_STMT (use_p))))
+      return false;
+
+  /* First-order recurrence autovectorization needs shuffle vector.  */
+  tree scalar_type = TREE_TYPE (def);
+  tree vectype = get_vectype_for_scalar_type (loop_vinfo, scalar_type);
+  if (!vectype)
+    return false;
+
+  return true;
+}
+
 /* Function vect_analyze_scalar_cycles_1.
 
    Examine the cross iteration def-use cycles of scalar variables
@@ -666,6 +705,8 @@ vect_analyze_scalar_cycles_1 (loop_vec_info loop_vinfo, class loop *loop,
                 }
             }
         }
+      else if (vect_phi_first_order_recurrence_p (loop_vinfo, loop, phi))
+	STMT_VINFO_DEF_TYPE (stmt_vinfo) = vect_first_order_recurrence;
       else
         if (dump_enabled_p ())
           dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
@@ -1810,7 +1851,8 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
 
           if ((STMT_VINFO_RELEVANT (stmt_info) == vect_used_in_scope
                || STMT_VINFO_LIVE_P (stmt_info))
-              && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def)
+	      && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def
+	      && STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
 	    /* A scalar-dependence cycle that we don't support.  */
 	    return opt_result::failure_at (phi,
 					   "not vectorized:"
@@ -1831,6 +1873,11 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
 		       && ! PURE_SLP_STMT (stmt_info))
 		ok = vectorizable_reduction (loop_vinfo,
 					     stmt_info, NULL, NULL, &cost_vec);
+	      else if ((STMT_VINFO_DEF_TYPE (stmt_info)
+			== vect_first_order_recurrence)
+		       && ! PURE_SLP_STMT (stmt_info))
+		ok = vectorizable_recurr (loop_vinfo, stmt_info, NULL, NULL,
+					   &cost_vec);
             }
 
 	  /* SLP PHIs are tested by vect_slp_analyze_node_operations.  */
@@ -8267,6 +8314,183 @@ vectorizable_phi (vec_info *,
   return true;
 }
 
+/* Vectorizes first order recurrences.  */
+
+bool
+vectorizable_recurr (loop_vec_info loop_vinfo, stmt_vec_info stmt_info,
+		      gimple **vec_stmt, slp_tree slp_node,
+		      stmt_vector_for_cost *cost_vec)
+{
+  if (!loop_vinfo || !is_a<gphi *> (stmt_info->stmt))
+    return false;
+
+  gphi *phi = as_a<gphi *> (stmt_info->stmt);
+
+  /* So far we only support first-order recurrence auto-vectorization.  */
+  if (STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
+    return false;
+
+  tree vectype = STMT_VINFO_VECTYPE (stmt_info);
+  unsigned ncopies;
+  if (slp_node)
+    ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
+  else
+    ncopies = vect_get_num_copies (loop_vinfo, vectype);
+  poly_int64 nunits = TYPE_VECTOR_SUBPARTS (vectype);
+  unsigned dist = slp_node ? SLP_TREE_LANES (slp_node) : 1;
+  /* We need to be able to make progress with a single vector.  */
+  if (maybe_gt (dist * 2, nunits))
+    {
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "first order recurrence exceeds half of "
+			 "a vector\n");
+      return false;
+    }
+
+  /* First-order recurrence autovectorization needs to handle permutation
+     with indices = [nunits-1, nunits, nunits+1, ...].  */
+  vec_perm_builder sel (nunits, 1, 3);
+  for (int i = 0; i < 3; ++i)
+    sel.quick_push (nunits - dist + i);
+  vec_perm_indices indices (sel, 1, nunits * 2);
+
+  if (!vec_stmt) /* transformation not required.  */
+    {
+      if (!can_vec_perm_const_p (TYPE_MODE (vectype), TYPE_MODE (vectype),
+				 indices))
+	return false;
+
+      if (slp_node)
+	{
+	  /* We eventually need to set a vector type on invariant
+	     arguments.  */
+	  unsigned j;
+	  slp_tree child;
+	  FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (slp_node), j, child)
+	    if (!vect_maybe_update_slp_op_vectype
+		  (child, SLP_TREE_VECTYPE (slp_node)))
+	      {
+		if (dump_enabled_p ())
+		  dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+				   "incompatible vector types for "
+				   "invariants\n");
+		return false;
+	      }
+	}
+      /* The recurrence costs the initialization vector and one permute
+	 for each copy.  */
+      unsigned prologue_cost = record_stmt_cost (cost_vec, 1, scalar_to_vec,
+						 stmt_info, 0, vect_prologue);
+      unsigned inside_cost = record_stmt_cost (cost_vec, ncopies, vector_stmt,
+					       stmt_info, 0, vect_body);
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_NOTE, vect_location,
+			 "vectorizable_recurr: inside_cost = %d, "
+			 "prologue_cost = %d .\n", inside_cost,
+			 prologue_cost);
+
+      STMT_VINFO_TYPE (stmt_info) = recurr_info_type;
+      return true;
+    }
+
+  /* This is the second phase of vectorizing first-order rececurrences. An
+     overview of the transformation is described below. Suppose we have the
+     following loop.
+
+     int32_t t = 0;
+     for (int i = 0; i < n; ++i)
+       {
+	b[i] = a[i] - t;
+	t = a[i];
+      }
+
+    There is a first-order recurrence on "a". For this loop, the shorthand
+    scalar IR looks like:
+
+    scalar.preheader:
+      init = a[-1]
+      br loop.body
+
+    scalar.body:
+      i = PHI <0(scalar.preheader), i+1(scalar.body)>
+      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
+      _1 = a[i]
+      b[i] = _1 - _2
+      br cond, scalar.body, ...
+
+    In this example, _2 is a recurrence because it's value depends on the
+    previous iteration. In the first phase of vectorization, we created a
+    temporary value for _2. We now complete the vectorization and produce the
+    shorthand vector IR shown below (VF = 4).
+
+    vector.preheader:
+      vect_init = vect_cst(..., ..., ..., a[-1])
+      br vector.body
+
+    vector.body
+      i = PHI <0(vector.preheader), i+4(vector.body)>
+      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
+      vect_2 = a[i, i+1, i+2, i+3];
+      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
+      b[i, i+1, i+2, i+3] = vect_2 - vect_3
+      br cond, vector.body, middle.block
+
+    middle.block:
+      x = vect_2(3)
+      br scalar.preheader
+
+    scalar.ph:
+      s_init = PHI <x(middle.block), a[-1], otherwise>
+      br scalar.body
+
+    After execution completes the vector loop, we extract the next value of
+    the recurrence (x) to use as the initial value in the scalar loop.  */
+
+  edge pe = loop_preheader_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  basic_block bb = gimple_bb (phi);
+  tree preheader = PHI_ARG_DEF_FROM_EDGE (phi, pe);
+  tree vec_init = build_vector_from_val (vectype, preheader);
+  vec_init = vect_init_vector (loop_vinfo, stmt_info, vec_init, vectype, NULL);
+
+  /* Create the vectorized first-order PHI node.  */
+  tree vec_dest = vect_get_new_vect_var (vectype,
+					 vect_simple_var, "vec_recur_");
+  gphi *new_phi = create_phi_node (vec_dest, bb);
+  add_phi_arg (new_phi, vec_init, pe, UNKNOWN_LOCATION);
+
+  /* Insert shuffles the first-order recurrence autovectorization.
+       result = VEC_PERM <vec_recur, vect_1, index[nunits-1, nunits, ...]>.  */
+  tree perm = vect_gen_perm_mask_checked (vectype, indices);
+
+  /* Insert the required permute after the latch definition.  The
+     second and later operands are tentative and will be updated when we have
+     vectorized the latch definition.  */
+  edge le = loop_latch_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  gimple_stmt_iterator gsi2
+    = gsi_for_stmt (SSA_NAME_DEF_STMT (PHI_ARG_DEF_FROM_EDGE (phi, le)));
+  gsi_next (&gsi2);
+
+  for (unsigned i = 0; i < ncopies; ++i)
+    {
+      vec_dest = make_ssa_name (vectype);
+      gassign *vperm
+	  = gimple_build_assign (vec_dest, VEC_PERM_EXPR,
+				 i == 0 ? gimple_phi_result (new_phi) : NULL,
+				 NULL, perm);
+      vect_finish_stmt_generation (loop_vinfo, stmt_info, vperm, &gsi2);
+
+      if (slp_node)
+	SLP_TREE_VEC_STMTS (slp_node).quick_push (vperm);
+      else
+	STMT_VINFO_VEC_STMTS (stmt_info).safe_push (vperm);
+    }
+
+  if (!slp_node)
+    *vec_stmt = STMT_VINFO_VEC_STMTS (stmt_info)[0];
+  return true;
+}
+
 /* Return true if VECTYPE represents a vector that requires lowering
    by the vector lowering pass.  */
 
@@ -10223,27 +10447,53 @@ maybe_set_vectorized_backedge_value (loop_vec_info loop_vinfo,
   imm_use_iterator iter;
   use_operand_p use_p;
   FOR_EACH_IMM_USE_FAST (use_p, iter, def)
-    if (gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p)))
-      if (gimple_bb (phi)->loop_father->header == gimple_bb (phi)
-	  && (phi_info = loop_vinfo->lookup_stmt (phi))
-	  && STMT_VINFO_RELEVANT_P (phi_info)
-	  && VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
+    {
+      gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p));
+      if (!phi)
+	continue;
+      if (!(gimple_bb (phi)->loop_father->header == gimple_bb (phi)
+	    && (phi_info = loop_vinfo->lookup_stmt (phi))
+	    && STMT_VINFO_RELEVANT_P (phi_info)))
+	continue;
+      loop_p loop = gimple_bb (phi)->loop_father;
+      edge e = loop_latch_edge (loop);
+      if (PHI_ARG_DEF_FROM_EDGE (phi, e) != def)
+	continue;
+
+      if (VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
 	  && STMT_VINFO_REDUC_TYPE (phi_info) != FOLD_LEFT_REDUCTION
 	  && STMT_VINFO_REDUC_TYPE (phi_info) != EXTRACT_LAST_REDUCTION)
 	{
-	  loop_p loop = gimple_bb (phi)->loop_father;
-	  edge e = loop_latch_edge (loop);
-	  if (PHI_ARG_DEF_FROM_EDGE (phi, e) == def)
+	  vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+	  vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+	  gcc_assert (phi_defs.length () == latch_defs.length ());
+	  for (unsigned i = 0; i < phi_defs.length (); ++i)
+	    add_phi_arg (as_a <gphi *> (phi_defs[i]),
+			 gimple_get_lhs (latch_defs[i]), e,
+			 gimple_phi_arg_location (phi, e->dest_idx));
+	}
+      else if (STMT_VINFO_DEF_TYPE (phi_info) == vect_first_order_recurrence)
+	{
+	  /* For first order recurrences we have to update both uses of
+	     the latch definition, the one in the PHI node and the one
+	     in the generated VEC_PERM_EXPR.  */
+	  vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+	  vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+	  gcc_assert (phi_defs.length () == latch_defs.length ());
+	  tree phidef = gimple_assign_rhs1 (phi_defs[0]);
+	  gphi *vphi = as_a <gphi *> (SSA_NAME_DEF_STMT (phidef));
+	  for (unsigned i = 0; i < phi_defs.length (); ++i)
 	    {
-	      vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
-	      vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
-	      gcc_assert (phi_defs.length () == latch_defs.length ());
-	      for (unsigned i = 0; i < phi_defs.length (); ++i)
-		add_phi_arg (as_a <gphi *> (phi_defs[i]),
-			     gimple_get_lhs (latch_defs[i]), e,
-			     gimple_phi_arg_location (phi, e->dest_idx));
+	      gassign *perm = as_a <gassign *> (phi_defs[i]);
+	      if (i > 0)
+		gimple_assign_set_rhs1 (perm, gimple_get_lhs (latch_defs[i-1]));
+	      gimple_assign_set_rhs2 (perm, gimple_get_lhs (latch_defs[i]));
+	      update_stmt (perm);
 	    }
+	  add_phi_arg (vphi, gimple_get_lhs (latch_defs.last ()), e,
+		       gimple_phi_arg_location (phi, e->dest_idx));
 	}
+    }
 }
 
 /* Vectorize STMT_INFO if relevant, inserting any new instructions before GSI.
@@ -10652,6 +10902,7 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
+	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
 	      && ! PURE_SLP_STMT (stmt_info))
 	    {
@@ -10677,7 +10928,8 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
-	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
+	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def
+	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence)
 	      && ! PURE_SLP_STMT (stmt_info))
 	    maybe_set_vectorized_backedge_value (loop_vinfo, stmt_info);
 	}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 229f2663ebc..cea5d50da92 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -693,6 +693,7 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
 	    case vect_reduction_def:
 	    case vect_induction_def:
 	    case vect_nested_cycle:
+	    case vect_first_order_recurrence:
 	      break;
 
 	    default:
@@ -1732,7 +1733,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 	  }
 	else if (def_type == vect_reduction_def
 		 || def_type == vect_double_reduction_def
-		 || def_type == vect_nested_cycle)
+		 || def_type == vect_nested_cycle
+		 || def_type == vect_first_order_recurrence)
 	  {
 	    /* Else def types have to match.  */
 	    stmt_vec_info other_info;
@@ -1746,7 +1748,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 	      }
 	    class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
 	    /* Reduction initial values are not explicitely represented.  */
-	    if (!nested_in_vect_loop_p (loop, stmt_info))
+	    if (def_type != vect_first_order_recurrence
+		&& !nested_in_vect_loop_p (loop, stmt_info))
 	      skip_args[loop_preheader_edge (loop)->dest_idx] = true;
 	    /* Reduction chain backedge defs are filled manually.
 	       ???  Need a better way to identify a SLP reduction chain PHI.
@@ -9187,11 +9190,34 @@ vect_schedule_scc (vec_info *vinfo, slp_tree node, slp_instance instance,
 	  child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
 	  if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
 	    continue;
+	  unsigned n = SLP_TREE_VEC_STMTS (phi_node).length ();
 	  /* Simply fill all args.  */
-	  for (unsigned i = 0; i < SLP_TREE_VEC_STMTS (phi_node).length (); ++i)
-	    add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
-			 vect_get_slp_vect_def (child, i),
-			 e, gimple_phi_arg_location (phi, dest_idx));
+	  if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (phi_node))
+	      != vect_first_order_recurrence)
+	    for (unsigned i = 0; i < n; ++i)
+	      add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
+			   vect_get_slp_vect_def (child, i),
+			   e, gimple_phi_arg_location (phi, dest_idx));
+	  else
+	    {
+	      /* Unless it is a first order recurrence which needs
+		 args filled in for both the PHI node and the permutes.  */
+	      gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[0];
+	      gimple *rphi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (perm));
+	      add_phi_arg (as_a <gphi *> (rphi),
+			   vect_get_slp_vect_def (child, n - 1),
+			   e, gimple_phi_arg_location (phi, dest_idx));
+	      for (unsigned i = 0; i < n; ++i)
+		{
+		  gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[i];
+		  if (i > 0)
+		    gimple_assign_set_rhs1 (perm,
+					    vect_get_slp_vect_def (child, i - 1));
+		  gimple_assign_set_rhs2 (perm,
+					  vect_get_slp_vect_def (child, i));
+		  update_stmt (perm);
+		}
+	    }
 	}
     }
 }
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index c8d1efc45e5..4e0d75e0d75 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -11176,6 +11176,7 @@ vect_analyze_stmt (vec_info *vinfo,
          break;
 
       case vect_induction_def:
+      case vect_first_order_recurrence:
 	gcc_assert (!bb_vinfo);
 	break;
 
@@ -11234,7 +11235,9 @@ vect_analyze_stmt (vec_info *vinfo,
 	  || vectorizable_comparison (vinfo, stmt_info, NULL, NULL, node,
 				      cost_vec)
 	  || vectorizable_lc_phi (as_a <loop_vec_info> (vinfo),
-				  stmt_info, NULL, node));
+				  stmt_info, NULL, node)
+	  || vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+				   stmt_info, NULL, node, cost_vec));
   else
     {
       if (bb_vinfo)
@@ -11404,6 +11407,12 @@ vect_transform_stmt (vec_info *vinfo,
       gcc_assert (done);
       break;
 
+    case recurr_info_type:
+      done = vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+				  stmt_info, &vec_stmt, slp_node, NULL);
+      gcc_assert (done);
+      break;
+
     case phi_info_type:
       done = vectorizable_phi (vinfo, stmt_info, &vec_stmt, slp_node, NULL);
       gcc_assert (done);
@@ -11804,6 +11813,9 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
 	case vect_nested_cycle:
 	  dump_printf (MSG_NOTE, "nested cycle\n");
 	  break;
+	case vect_first_order_recurrence:
+	  dump_printf (MSG_NOTE, "first order recurrence\n");
+	  break;
 	case vect_unknown_def_type:
 	  dump_printf (MSG_NOTE, "unknown\n");
 	  break;
@@ -11852,7 +11864,8 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
       || *dt == vect_induction_def
       || *dt == vect_reduction_def
       || *dt == vect_double_reduction_def
-      || *dt == vect_nested_cycle)
+      || *dt == vect_nested_cycle
+      || *dt == vect_first_order_recurrence)
     {
       *vectype = STMT_VINFO_VECTYPE (def_stmt_info);
       gcc_assert (*vectype != NULL_TREE);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 4870c754499..016961da851 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -65,6 +65,7 @@ enum vect_def_type {
   vect_reduction_def,
   vect_double_reduction_def,
   vect_nested_cycle,
+  vect_first_order_recurrence,
   vect_unknown_def_type
 };
 
@@ -1027,6 +1028,7 @@ enum stmt_vec_info_type {
   cycle_phi_info_type,
   lc_phi_info_type,
   phi_info_type,
+  recurr_info_type,
   loop_exit_ctrl_vec_info_type
 };
 
@@ -2331,6 +2333,8 @@ extern bool vectorizable_lc_phi (loop_vec_info, stmt_vec_info,
 				 gimple **, slp_tree);
 extern bool vectorizable_phi (vec_info *, stmt_vec_info, gimple **, slp_tree,
 			      stmt_vector_for_cost *);
+extern bool vectorizable_recurr (loop_vec_info, stmt_vec_info,
+				  gimple **, slp_tree, stmt_vector_for_cost *);
 extern bool vect_emulated_vector_p (tree);
 extern bool vect_can_vectorize_without_simd_p (tree_code);
 extern bool vect_can_vectorize_without_simd_p (code_helper);
-- 
2.35.3

Re: [PATCH][RFT] Vectorization of first-order recurrences

[juzhe.zhong]

[-- Attachment #1: Type: text/plain, Size: 32549 bytes --]

Thank you so much. I will apply this patch and test it in downstream RVV GCC （12.2.0)


juzhe.zhong@rivai.ai
 
From: Richard Biener
Date: 2022-10-10 19:03
To: gcc-patches
CC: richard.sandiford; ams; juzhe.zhong
Subject: [PATCH][RFT] Vectorization of first-order recurrences
The following picks up the prototype by Ju-Zhe Zhong for vectorizing
first order recurrences.  That solves two TSVC missed optimization PRs.
 
There's a new scalar cycle def kind, vect_first_order_recurrence
and it's handling of the backedge value vectorization is complicated
by the fact that the vectorized value isn't the PHI but instead
a (series of) permute(s) shifting in the recurring value from the
previous iteration.  I've implemented this by creating both the
single vectorized PHI and the series of permutes when vectorizing
the scalar PHI but leave the backedge values in both unassigned.
The backedge values are (for the testcases) computed by a load
which is also the place after which the permutes are inserted.
That placement also restricts the cases we can handle (without
resorting to code motion).
 
I added both costing and SLP handling though SLP handling is
restricted to the case where a single vectorized PHI is enough.
 
Missing is epilogue handling - while prologue peeling would
be handled transparently by adjusting iv_phi_p the epilogue
case doesn't work with just inserting a scalar LC PHI since
that a) keeps the scalar load live and b) that loads is the
wrong one, it has to be the last, much like when we'd vectorize
the LC PHI as live operation.  Unfortunately LIVE
compute/analysis happens too early before we decide on
peeling.  When using fully masked loop vectorization the
vect-recurr-6.c works as expected though.
 
I have tested this on x86_64 for now, but since epilogue
handling is missing there's probably no practical cases.
My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
just fine but I didn't feel like running SPEC within SDE nor
is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
with fully masked loops succeed (minus three cases of
PR107096, caused by my WHILE_ULT prototype).
 
Bootstrapped and tested on x86_64-unknown-linux-gnu.
 
Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
handle epilogues welcome.
 
Thanks,
Richard.
 
PR tree-optimization/99409
PR tree-optimization/99394
* tree-vectorizer.h (vect_def_type::vect_first_order_recurrence): Add.
(stmt_vec_info_type::recurr_info_type): Likewise.
(vectorizable_recurr): New function.
* tree-vect-loop.cc (vect_phi_first_order_recurrence_p): New
function.
(vect_analyze_scalar_cycles_1): Look for first order
recurrences.
(vect_analyze_loop_operations): Handle them.
(vect_transform_loop): Likewise.
(vectorizable_recurr): New function.
(maybe_set_vectorized_backedge_value): Handle the backedge value
setting in the first order recurrence PHI and the permutes.
* tree-vect-stmts.cc (vect_analyze_stmt): Handle first order
recurrences.
(vect_transform_stmt): Likewise.
(vect_is_simple_use): Likewise.
(vect_is_simple_use): Likewise.
* tree-vect-slp.cc (vect_get_and_check_slp_defs): Likewise.
(vect_build_slp_tree_2): Likewise.
(vect_schedule_scc): Handle the backedge value setting in the
first order recurrence PHI and the permutes.
 
* gcc.dg/vect/vect-recurr-1.c: New testcase.
* gcc.dg/vect/vect-recurr-2.c: Likewise.
* gcc.dg/vect/vect-recurr-3.c: Likewise.
* gcc.dg/vect/vect-recurr-4.c: Likewise.
* gcc.dg/vect/vect-recurr-5.c: Likewise.
* gcc.dg/vect/vect-recurr-6.c: Likewise.
* gcc.dg/vect/tsvc/vect-tsvc-s252.c: Un-XFAIL.
* gcc.dg/vect/tsvc/vect-tsvc-s254.c: Likewise.
* gcc.dg/vect/tsvc/vect-tsvc-s291.c: Likewise.
 
Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
---
.../gcc.dg/vect/tsvc/vect-tsvc-s252.c         |   2 +-
.../gcc.dg/vect/tsvc/vect-tsvc-s254.c         |   2 +-
.../gcc.dg/vect/tsvc/vect-tsvc-s291.c         |   2 +-
gcc/testsuite/gcc.dg/vect/vect-recurr-1.c     |  38 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-2.c     |  39 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-3.c     |  39 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-4.c     |  42 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-5.c     |  43 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-6.c     |  39 +++
gcc/tree-vect-loop.cc                         | 286 ++++++++++++++++--
gcc/tree-vect-slp.cc                          |  38 ++-
gcc/tree-vect-stmts.cc                        |  17 +-
gcc/tree-vectorizer.h                         |   4 +
13 files changed, 563 insertions(+), 28 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
 
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
index f1302b60ae5..83eaa7a8ff5 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
@@ -40,4 +40,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
index bdc8a01e2a5..06e9b0a849d 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
index 0b474c2e81a..91cdc121095 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
new file mode 100644
index 00000000000..6eb59fdf854
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
@@ -0,0 +1,38 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
new file mode 100644
index 00000000000..97efaaa38bc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
new file mode 100644
index 00000000000..621a5d8a257
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, signed char * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+signed char b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
new file mode 100644
index 00000000000..f6dbc494a62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
@@ -0,0 +1,42 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+ || b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
new file mode 100644
index 00000000000..19c56df9e83
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
@@ -0,0 +1,43 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+ || b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
new file mode 100644
index 00000000000..e7712680853
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c, int n)
+{
+  int t = *c;
+  for (int i = 0; i < n; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c, 63);
+  for (int i = 1; i < 63; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* ???  We miss epilogue handling for first order recurrences.  */
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" { target vect_fully_masked } } } */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 2536cc3cf49..b54820a960b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -529,6 +529,45 @@ vect_inner_phi_in_double_reduction_p (loop_vec_info loop_vinfo, gphi *phi)
   return false;
}
+/* Returns true if Phi is a first-order recurrence. A first-order
+   recurrence is a non-reduction recurrence relation in which the value of
+   the recurrence in the current loop iteration equals a value defined in
+   the previous iteration.  */
+
+static bool
+vect_phi_first_order_recurrence_p (loop_vec_info loop_vinfo, class loop *loop,
+    gphi *phi)
+{
+  /* Ensure the loop latch definition is from within the loop.  */
+  edge latch = loop_latch_edge (loop);
+  tree ldef = PHI_ARG_DEF_FROM_EDGE (phi, latch);
+  if (TREE_CODE (ldef) != SSA_NAME
+      || SSA_NAME_IS_DEFAULT_DEF (ldef)
+      || !flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (ldef))))
+    return false;
+
+  tree def = gimple_phi_result (phi);
+
+  /* Ensure every use_stmt of the phi node is dominated by the latch
+     definition.  */
+  imm_use_iterator imm_iter;
+  use_operand_p use_p;
+  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, def)
+    if (!is_gimple_debug (USE_STMT (use_p))
+ && (SSA_NAME_DEF_STMT (ldef) == USE_STMT (use_p)
+     || !vect_stmt_dominates_stmt_p (SSA_NAME_DEF_STMT (ldef),
+     USE_STMT (use_p))))
+      return false;
+
+  /* First-order recurrence autovectorization needs shuffle vector.  */
+  tree scalar_type = TREE_TYPE (def);
+  tree vectype = get_vectype_for_scalar_type (loop_vinfo, scalar_type);
+  if (!vectype)
+    return false;
+
+  return true;
+}
+
/* Function vect_analyze_scalar_cycles_1.
    Examine the cross iteration def-use cycles of scalar variables
@@ -666,6 +705,8 @@ vect_analyze_scalar_cycles_1 (loop_vec_info loop_vinfo, class loop *loop,
                 }
             }
         }
+      else if (vect_phi_first_order_recurrence_p (loop_vinfo, loop, phi))
+ STMT_VINFO_DEF_TYPE (stmt_vinfo) = vect_first_order_recurrence;
       else
         if (dump_enabled_p ())
           dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
@@ -1810,7 +1851,8 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
           if ((STMT_VINFO_RELEVANT (stmt_info) == vect_used_in_scope
                || STMT_VINFO_LIVE_P (stmt_info))
-              && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def)
+       && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def
+       && STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
    /* A scalar-dependence cycle that we don't support.  */
    return opt_result::failure_at (phi,
   "not vectorized:"
@@ -1831,6 +1873,11 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
       && ! PURE_SLP_STMT (stmt_info))
ok = vectorizable_reduction (loop_vinfo,
     stmt_info, NULL, NULL, &cost_vec);
+       else if ((STMT_VINFO_DEF_TYPE (stmt_info)
+ == vect_first_order_recurrence)
+        && ! PURE_SLP_STMT (stmt_info))
+ ok = vectorizable_recurr (loop_vinfo, stmt_info, NULL, NULL,
+    &cost_vec);
             }
  /* SLP PHIs are tested by vect_slp_analyze_node_operations.  */
@@ -8267,6 +8314,183 @@ vectorizable_phi (vec_info *,
   return true;
}
+/* Vectorizes first order recurrences.  */
+
+bool
+vectorizable_recurr (loop_vec_info loop_vinfo, stmt_vec_info stmt_info,
+       gimple **vec_stmt, slp_tree slp_node,
+       stmt_vector_for_cost *cost_vec)
+{
+  if (!loop_vinfo || !is_a<gphi *> (stmt_info->stmt))
+    return false;
+
+  gphi *phi = as_a<gphi *> (stmt_info->stmt);
+
+  /* So far we only support first-order recurrence auto-vectorization.  */
+  if (STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
+    return false;
+
+  tree vectype = STMT_VINFO_VECTYPE (stmt_info);
+  unsigned ncopies;
+  if (slp_node)
+    ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
+  else
+    ncopies = vect_get_num_copies (loop_vinfo, vectype);
+  poly_int64 nunits = TYPE_VECTOR_SUBPARTS (vectype);
+  unsigned dist = slp_node ? SLP_TREE_LANES (slp_node) : 1;
+  /* We need to be able to make progress with a single vector.  */
+  if (maybe_gt (dist * 2, nunits))
+    {
+      if (dump_enabled_p ())
+ dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+ "first order recurrence exceeds half of "
+ "a vector\n");
+      return false;
+    }
+
+  /* First-order recurrence autovectorization needs to handle permutation
+     with indices = [nunits-1, nunits, nunits+1, ...].  */
+  vec_perm_builder sel (nunits, 1, 3);
+  for (int i = 0; i < 3; ++i)
+    sel.quick_push (nunits - dist + i);
+  vec_perm_indices indices (sel, 1, nunits * 2);
+
+  if (!vec_stmt) /* transformation not required.  */
+    {
+      if (!can_vec_perm_const_p (TYPE_MODE (vectype), TYPE_MODE (vectype),
+ indices))
+ return false;
+
+      if (slp_node)
+ {
+   /* We eventually need to set a vector type on invariant
+      arguments.  */
+   unsigned j;
+   slp_tree child;
+   FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (slp_node), j, child)
+     if (!vect_maybe_update_slp_op_vectype
+   (child, SLP_TREE_VECTYPE (slp_node)))
+       {
+ if (dump_enabled_p ())
+   dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+    "incompatible vector types for "
+    "invariants\n");
+ return false;
+       }
+ }
+      /* The recurrence costs the initialization vector and one permute
+ for each copy.  */
+      unsigned prologue_cost = record_stmt_cost (cost_vec, 1, scalar_to_vec,
+ stmt_info, 0, vect_prologue);
+      unsigned inside_cost = record_stmt_cost (cost_vec, ncopies, vector_stmt,
+        stmt_info, 0, vect_body);
+      if (dump_enabled_p ())
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "vectorizable_recurr: inside_cost = %d, "
+ "prologue_cost = %d .\n", inside_cost,
+ prologue_cost);
+
+      STMT_VINFO_TYPE (stmt_info) = recurr_info_type;
+      return true;
+    }
+
+  /* This is the second phase of vectorizing first-order rececurrences. An
+     overview of the transformation is described below. Suppose we have the
+     following loop.
+
+     int32_t t = 0;
+     for (int i = 0; i < n; ++i)
+       {
+ b[i] = a[i] - t;
+ t = a[i];
+      }
+
+    There is a first-order recurrence on "a". For this loop, the shorthand
+    scalar IR looks like:
+
+    scalar.preheader:
+      init = a[-1]
+      br loop.body
+
+    scalar.body:
+      i = PHI <0(scalar.preheader), i+1(scalar.body)>
+      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
+      _1 = a[i]
+      b[i] = _1 - _2
+      br cond, scalar.body, ...
+
+    In this example, _2 is a recurrence because it's value depends on the
+    previous iteration. In the first phase of vectorization, we created a
+    temporary value for _2. We now complete the vectorization and produce the
+    shorthand vector IR shown below (VF = 4).
+
+    vector.preheader:
+      vect_init = vect_cst(..., ..., ..., a[-1])
+      br vector.body
+
+    vector.body
+      i = PHI <0(vector.preheader), i+4(vector.body)>
+      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
+      vect_2 = a[i, i+1, i+2, i+3];
+      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
+      b[i, i+1, i+2, i+3] = vect_2 - vect_3
+      br cond, vector.body, middle.block
+
+    middle.block:
+      x = vect_2(3)
+      br scalar.preheader
+
+    scalar.ph:
+      s_init = PHI <x(middle.block), a[-1], otherwise>
+      br scalar.body
+
+    After execution completes the vector loop, we extract the next value of
+    the recurrence (x) to use as the initial value in the scalar loop.  */
+
+  edge pe = loop_preheader_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  basic_block bb = gimple_bb (phi);
+  tree preheader = PHI_ARG_DEF_FROM_EDGE (phi, pe);
+  tree vec_init = build_vector_from_val (vectype, preheader);
+  vec_init = vect_init_vector (loop_vinfo, stmt_info, vec_init, vectype, NULL);
+
+  /* Create the vectorized first-order PHI node.  */
+  tree vec_dest = vect_get_new_vect_var (vectype,
+ vect_simple_var, "vec_recur_");
+  gphi *new_phi = create_phi_node (vec_dest, bb);
+  add_phi_arg (new_phi, vec_init, pe, UNKNOWN_LOCATION);
+
+  /* Insert shuffles the first-order recurrence autovectorization.
+       result = VEC_PERM <vec_recur, vect_1, index[nunits-1, nunits, ...]>.  */
+  tree perm = vect_gen_perm_mask_checked (vectype, indices);
+
+  /* Insert the required permute after the latch definition.  The
+     second and later operands are tentative and will be updated when we have
+     vectorized the latch definition.  */
+  edge le = loop_latch_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  gimple_stmt_iterator gsi2
+    = gsi_for_stmt (SSA_NAME_DEF_STMT (PHI_ARG_DEF_FROM_EDGE (phi, le)));
+  gsi_next (&gsi2);
+
+  for (unsigned i = 0; i < ncopies; ++i)
+    {
+      vec_dest = make_ssa_name (vectype);
+      gassign *vperm
+   = gimple_build_assign (vec_dest, VEC_PERM_EXPR,
+ i == 0 ? gimple_phi_result (new_phi) : NULL,
+ NULL, perm);
+      vect_finish_stmt_generation (loop_vinfo, stmt_info, vperm, &gsi2);
+
+      if (slp_node)
+ SLP_TREE_VEC_STMTS (slp_node).quick_push (vperm);
+      else
+ STMT_VINFO_VEC_STMTS (stmt_info).safe_push (vperm);
+    }
+
+  if (!slp_node)
+    *vec_stmt = STMT_VINFO_VEC_STMTS (stmt_info)[0];
+  return true;
+}
+
/* Return true if VECTYPE represents a vector that requires lowering
    by the vector lowering pass.  */
@@ -10223,27 +10447,53 @@ maybe_set_vectorized_backedge_value (loop_vec_info loop_vinfo,
   imm_use_iterator iter;
   use_operand_p use_p;
   FOR_EACH_IMM_USE_FAST (use_p, iter, def)
-    if (gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p)))
-      if (gimple_bb (phi)->loop_father->header == gimple_bb (phi)
-   && (phi_info = loop_vinfo->lookup_stmt (phi))
-   && STMT_VINFO_RELEVANT_P (phi_info)
-   && VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
+    {
+      gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p));
+      if (!phi)
+ continue;
+      if (!(gimple_bb (phi)->loop_father->header == gimple_bb (phi)
+     && (phi_info = loop_vinfo->lookup_stmt (phi))
+     && STMT_VINFO_RELEVANT_P (phi_info)))
+ continue;
+      loop_p loop = gimple_bb (phi)->loop_father;
+      edge e = loop_latch_edge (loop);
+      if (PHI_ARG_DEF_FROM_EDGE (phi, e) != def)
+ continue;
+
+      if (VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
  && STMT_VINFO_REDUC_TYPE (phi_info) != FOLD_LEFT_REDUCTION
  && STMT_VINFO_REDUC_TYPE (phi_info) != EXTRACT_LAST_REDUCTION)
{
-   loop_p loop = gimple_bb (phi)->loop_father;
-   edge e = loop_latch_edge (loop);
-   if (PHI_ARG_DEF_FROM_EDGE (phi, e) == def)
+   vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+   vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+   gcc_assert (phi_defs.length () == latch_defs.length ());
+   for (unsigned i = 0; i < phi_defs.length (); ++i)
+     add_phi_arg (as_a <gphi *> (phi_defs[i]),
+ gimple_get_lhs (latch_defs[i]), e,
+ gimple_phi_arg_location (phi, e->dest_idx));
+ }
+      else if (STMT_VINFO_DEF_TYPE (phi_info) == vect_first_order_recurrence)
+ {
+   /* For first order recurrences we have to update both uses of
+      the latch definition, the one in the PHI node and the one
+      in the generated VEC_PERM_EXPR.  */
+   vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+   vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+   gcc_assert (phi_defs.length () == latch_defs.length ());
+   tree phidef = gimple_assign_rhs1 (phi_defs[0]);
+   gphi *vphi = as_a <gphi *> (SSA_NAME_DEF_STMT (phidef));
+   for (unsigned i = 0; i < phi_defs.length (); ++i)
    {
-       vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
-       vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
-       gcc_assert (phi_defs.length () == latch_defs.length ());
-       for (unsigned i = 0; i < phi_defs.length (); ++i)
- add_phi_arg (as_a <gphi *> (phi_defs[i]),
-      gimple_get_lhs (latch_defs[i]), e,
-      gimple_phi_arg_location (phi, e->dest_idx));
+       gassign *perm = as_a <gassign *> (phi_defs[i]);
+       if (i > 0)
+ gimple_assign_set_rhs1 (perm, gimple_get_lhs (latch_defs[i-1]));
+       gimple_assign_set_rhs2 (perm, gimple_get_lhs (latch_defs[i]));
+       update_stmt (perm);
    }
+   add_phi_arg (vphi, gimple_get_lhs (latch_defs.last ()), e,
+        gimple_phi_arg_location (phi, e->dest_idx));
}
+    }
}
/* Vectorize STMT_INFO if relevant, inserting any new instructions before GSI.
@@ -10652,6 +10902,7 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
      && ! PURE_SLP_STMT (stmt_info))
    {
@@ -10677,7 +10928,8 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
-        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence)
      && ! PURE_SLP_STMT (stmt_info))
    maybe_set_vectorized_backedge_value (loop_vinfo, stmt_info);
}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 229f2663ebc..cea5d50da92 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -693,6 +693,7 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
    case vect_reduction_def:
    case vect_induction_def:
    case vect_nested_cycle:
+     case vect_first_order_recurrence:
      break;
    default:
@@ -1732,7 +1733,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
  }
else if (def_type == vect_reduction_def
|| def_type == vect_double_reduction_def
- || def_type == vect_nested_cycle)
+ || def_type == vect_nested_cycle
+ || def_type == vect_first_order_recurrence)
  {
    /* Else def types have to match.  */
    stmt_vec_info other_info;
@@ -1746,7 +1748,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
      }
    class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
    /* Reduction initial values are not explicitely represented.  */
-     if (!nested_in_vect_loop_p (loop, stmt_info))
+     if (def_type != vect_first_order_recurrence
+ && !nested_in_vect_loop_p (loop, stmt_info))
      skip_args[loop_preheader_edge (loop)->dest_idx] = true;
    /* Reduction chain backedge defs are filled manually.
       ???  Need a better way to identify a SLP reduction chain PHI.
@@ -9187,11 +9190,34 @@ vect_schedule_scc (vec_info *vinfo, slp_tree node, slp_instance instance,
  child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
  if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
    continue;
+   unsigned n = SLP_TREE_VEC_STMTS (phi_node).length ();
  /* Simply fill all args.  */
-   for (unsigned i = 0; i < SLP_TREE_VEC_STMTS (phi_node).length (); ++i)
-     add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
- vect_get_slp_vect_def (child, i),
- e, gimple_phi_arg_location (phi, dest_idx));
+   if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (phi_node))
+       != vect_first_order_recurrence)
+     for (unsigned i = 0; i < n; ++i)
+       add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
+    vect_get_slp_vect_def (child, i),
+    e, gimple_phi_arg_location (phi, dest_idx));
+   else
+     {
+       /* Unless it is a first order recurrence which needs
+ args filled in for both the PHI node and the permutes.  */
+       gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[0];
+       gimple *rphi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (perm));
+       add_phi_arg (as_a <gphi *> (rphi),
+    vect_get_slp_vect_def (child, n - 1),
+    e, gimple_phi_arg_location (phi, dest_idx));
+       for (unsigned i = 0; i < n; ++i)
+ {
+   gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[i];
+   if (i > 0)
+     gimple_assign_set_rhs1 (perm,
+     vect_get_slp_vect_def (child, i - 1));
+   gimple_assign_set_rhs2 (perm,
+   vect_get_slp_vect_def (child, i));
+   update_stmt (perm);
+ }
+     }
}
     }
}
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index c8d1efc45e5..4e0d75e0d75 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -11176,6 +11176,7 @@ vect_analyze_stmt (vec_info *vinfo,
          break;
       case vect_induction_def:
+      case vect_first_order_recurrence:
gcc_assert (!bb_vinfo);
break;
@@ -11234,7 +11235,9 @@ vect_analyze_stmt (vec_info *vinfo,
  || vectorizable_comparison (vinfo, stmt_info, NULL, NULL, node,
      cost_vec)
  || vectorizable_lc_phi (as_a <loop_vec_info> (vinfo),
-   stmt_info, NULL, node));
+   stmt_info, NULL, node)
+   || vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+    stmt_info, NULL, node, cost_vec));
   else
     {
       if (bb_vinfo)
@@ -11404,6 +11407,12 @@ vect_transform_stmt (vec_info *vinfo,
       gcc_assert (done);
       break;
+    case recurr_info_type:
+      done = vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+   stmt_info, &vec_stmt, slp_node, NULL);
+      gcc_assert (done);
+      break;
+
     case phi_info_type:
       done = vectorizable_phi (vinfo, stmt_info, &vec_stmt, slp_node, NULL);
       gcc_assert (done);
@@ -11804,6 +11813,9 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
case vect_nested_cycle:
  dump_printf (MSG_NOTE, "nested cycle\n");
  break;
+ case vect_first_order_recurrence:
+   dump_printf (MSG_NOTE, "first order recurrence\n");
+   break;
case vect_unknown_def_type:
  dump_printf (MSG_NOTE, "unknown\n");
  break;
@@ -11852,7 +11864,8 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
       || *dt == vect_induction_def
       || *dt == vect_reduction_def
       || *dt == vect_double_reduction_def
-      || *dt == vect_nested_cycle)
+      || *dt == vect_nested_cycle
+      || *dt == vect_first_order_recurrence)
     {
       *vectype = STMT_VINFO_VECTYPE (def_stmt_info);
       gcc_assert (*vectype != NULL_TREE);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 4870c754499..016961da851 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -65,6 +65,7 @@ enum vect_def_type {
   vect_reduction_def,
   vect_double_reduction_def,
   vect_nested_cycle,
+  vect_first_order_recurrence,
   vect_unknown_def_type
};
@@ -1027,6 +1028,7 @@ enum stmt_vec_info_type {
   cycle_phi_info_type,
   lc_phi_info_type,
   phi_info_type,
+  recurr_info_type,
   loop_exit_ctrl_vec_info_type
};
@@ -2331,6 +2333,8 @@ extern bool vectorizable_lc_phi (loop_vec_info, stmt_vec_info,
gimple **, slp_tree);
extern bool vectorizable_phi (vec_info *, stmt_vec_info, gimple **, slp_tree,
      stmt_vector_for_cost *);
+extern bool vectorizable_recurr (loop_vec_info, stmt_vec_info,
+   gimple **, slp_tree, stmt_vector_for_cost *);
extern bool vect_emulated_vector_p (tree);
extern bool vect_can_vectorize_without_simd_p (tree_code);
extern bool vect_can_vectorize_without_simd_p (code_helper);
-- 
2.35.3
 

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Andrew Stubbs]

On 10/10/2022 12:03, Richard Biener wrote:
> The following picks up the prototype by Ju-Zhe Zhong for vectorizing
> first order recurrences.  That solves two TSVC missed optimization PRs.
> 
> There's a new scalar cycle def kind, vect_first_order_recurrence
> and it's handling of the backedge value vectorization is complicated
> by the fact that the vectorized value isn't the PHI but instead
> a (series of) permute(s) shifting in the recurring value from the
> previous iteration.  I've implemented this by creating both the
> single vectorized PHI and the series of permutes when vectorizing
> the scalar PHI but leave the backedge values in both unassigned.
> The backedge values are (for the testcases) computed by a load
> which is also the place after which the permutes are inserted.
> That placement also restricts the cases we can handle (without
> resorting to code motion).
> 
> I added both costing and SLP handling though SLP handling is
> restricted to the case where a single vectorized PHI is enough.
> 
> Missing is epilogue handling - while prologue peeling would
> be handled transparently by adjusting iv_phi_p the epilogue
> case doesn't work with just inserting a scalar LC PHI since
> that a) keeps the scalar load live and b) that loads is the
> wrong one, it has to be the last, much like when we'd vectorize
> the LC PHI as live operation.  Unfortunately LIVE
> compute/analysis happens too early before we decide on
> peeling.  When using fully masked loop vectorization the
> vect-recurr-6.c works as expected though.
> 
> I have tested this on x86_64 for now, but since epilogue
> handling is missing there's probably no practical cases.
> My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
> just fine but I didn't feel like running SPEC within SDE nor
> is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
> with fully masked loops succeed (minus three cases of
> PR107096, caused by my WHILE_ULT prototype).
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
> 
> Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
> handle epilogues welcome.

The testcases all produce correct code on GCN and pass the execution tests.

The code isn't terribly optimal because we don't have a two-input 
permutation instruction, so we permute each half separately and 
vec_merge the results. In this case the first vector is always a no-op 
permutation so that's wasted cycles. We'd really want a vector rotate 
and write-lane (or the other way around). I think the special-case 
permutations can be recognised and coded into the backend, but I don't 
know if we can easily tell that the first vector is just a bunch of 
duplicates, when it's not constant.

Andrew

Re: Re: [PATCH][RFT] Vectorization of first-order recurrences

[钟居哲]

[-- Attachment #1: Type: text/plain, Size: 3546 bytes --]

RVV also doesn't have a two-input permutation instructions (unlike ARM SVE has tbl instructions) and 
RVV needs about 4 instructions to handle this permutation, it still improve performance a lot.
I think backend should handle this. Because this first-order recurrence loop vectorizer always generates the
special permuation index = [vl-1, vl, vl+1,. ......]  (This index sequence pattern is just following LLVM). 
If the backend doesn't want this permuation happens, just recognize this index pattern and disable it.


juzhe.zhong@rivai.ai
 
From: Andrew Stubbs
Date: 2022-10-10 21:57
To: Richard Biener; gcc-patches@gcc.gnu.org
CC: richard.sandiford@arm.com; juzhe.zhong@rivai.ai
Subject: Re: [PATCH][RFT] Vectorization of first-order recurrences
On 10/10/2022 12:03, Richard Biener wrote:
> The following picks up the prototype by Ju-Zhe Zhong for vectorizing
> first order recurrences.  That solves two TSVC missed optimization PRs.
> 
> There's a new scalar cycle def kind, vect_first_order_recurrence
> and it's handling of the backedge value vectorization is complicated
> by the fact that the vectorized value isn't the PHI but instead
> a (series of) permute(s) shifting in the recurring value from the
> previous iteration.  I've implemented this by creating both the
> single vectorized PHI and the series of permutes when vectorizing
> the scalar PHI but leave the backedge values in both unassigned.
> The backedge values are (for the testcases) computed by a load
> which is also the place after which the permutes are inserted.
> That placement also restricts the cases we can handle (without
> resorting to code motion).
> 
> I added both costing and SLP handling though SLP handling is
> restricted to the case where a single vectorized PHI is enough.
> 
> Missing is epilogue handling - while prologue peeling would
> be handled transparently by adjusting iv_phi_p the epilogue
> case doesn't work with just inserting a scalar LC PHI since
> that a) keeps the scalar load live and b) that loads is the
> wrong one, it has to be the last, much like when we'd vectorize
> the LC PHI as live operation.  Unfortunately LIVE
> compute/analysis happens too early before we decide on
> peeling.  When using fully masked loop vectorization the
> vect-recurr-6.c works as expected though.
> 
> I have tested this on x86_64 for now, but since epilogue
> handling is missing there's probably no practical cases.
> My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
> just fine but I didn't feel like running SPEC within SDE nor
> is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
> with fully masked loops succeed (minus three cases of
> PR107096, caused by my WHILE_ULT prototype).
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
> 
> Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
> handle epilogues welcome.
 
The testcases all produce correct code on GCN and pass the execution tests.
 
The code isn't terribly optimal because we don't have a two-input 
permutation instruction, so we permute each half separately and 
vec_merge the results. In this case the first vector is always a no-op 
permutation so that's wasted cycles. We'd really want a vector rotate 
and write-lane (or the other way around). I think the special-case 
permutations can be recognised and coded into the backend, but I don't 
know if we can easily tell that the first vector is just a bunch of 
duplicates, when it's not constant.
 
Andrew
 

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Richard Biener]

On Mon, 10 Oct 2022, Andrew Stubbs wrote:

> On 10/10/2022 12:03, Richard Biener wrote:
> > The following picks up the prototype by Ju-Zhe Zhong for vectorizing
> > first order recurrences.  That solves two TSVC missed optimization PRs.
> > 
> > There's a new scalar cycle def kind, vect_first_order_recurrence
> > and it's handling of the backedge value vectorization is complicated
> > by the fact that the vectorized value isn't the PHI but instead
> > a (series of) permute(s) shifting in the recurring value from the
> > previous iteration.  I've implemented this by creating both the
> > single vectorized PHI and the series of permutes when vectorizing
> > the scalar PHI but leave the backedge values in both unassigned.
> > The backedge values are (for the testcases) computed by a load
> > which is also the place after which the permutes are inserted.
> > That placement also restricts the cases we can handle (without
> > resorting to code motion).
> > 
> > I added both costing and SLP handling though SLP handling is
> > restricted to the case where a single vectorized PHI is enough.
> > 
> > Missing is epilogue handling - while prologue peeling would
> > be handled transparently by adjusting iv_phi_p the epilogue
> > case doesn't work with just inserting a scalar LC PHI since
> > that a) keeps the scalar load live and b) that loads is the
> > wrong one, it has to be the last, much like when we'd vectorize
> > the LC PHI as live operation.  Unfortunately LIVE
> > compute/analysis happens too early before we decide on
> > peeling.  When using fully masked loop vectorization the
> > vect-recurr-6.c works as expected though.
> > 
> > I have tested this on x86_64 for now, but since epilogue
> > handling is missing there's probably no practical cases.
> > My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
> > just fine but I didn't feel like running SPEC within SDE nor
> > is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
> > with fully masked loops succeed (minus three cases of
> > PR107096, caused by my WHILE_ULT prototype).
> > 
> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> > 
> > Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
> > handle epilogues welcome.
> 
> The testcases all produce correct code on GCN and pass the execution tests.
> 
> The code isn't terribly optimal because we don't have a two-input permutation
> instruction, so we permute each half separately and vec_merge the results. In
> this case the first vector is always a no-op permutation so that's wasted
> cycles. We'd really want a vector rotate and write-lane (or the other way
> around). I think the special-case permutations can be recognised and coded
> into the backend, but I don't know if we can easily tell that the first vector
> is just a bunch of duplicates, when it's not constant.

It's not actually a bunch of duplicates in all but the first iteration.
But what you can recognize is that we're only using lane N - 1 of the
first vector, so you could model the permute as extract last
+ shift in scalar (the extracted lane).  IIRC VLA vector targets usually
have something like shift the vector and set the low lane from a
scalar?  The extract lane N - 1 might be more difficult but then
a rotate plus extracting lane 0 might work as well.

So yes, I think special-casing this constant permutation makes most
sense.

Richard.

Re: [PATCH][RFT] Vectorization of first-order recurrences

[juzhe.zhong]

[-- Attachment #1: Type: text/plain, Size: 32842 bytes --]

Hi, I apply this patch in RVV downstrean. Tested it with a lot of vector benchmark. It overal has a greate performance gain.
Maybe the last thing to merge this patch is wait for Richard Sandiford test it in ARM SVE?

By the way, would you mind sharing the case list that GCC failed to vectorize but Clang succeed ? 
I am familiar with LLVM. I think I can do this job.
Thanks.


juzhe.zhong@rivai.ai
 
From: Richard Biener
Date: 2022-10-10 19:03
To: gcc-patches
CC: richard.sandiford; ams; juzhe.zhong
Subject: [PATCH][RFT] Vectorization of first-order recurrences
The following picks up the prototype by Ju-Zhe Zhong for vectorizing
first order recurrences.  That solves two TSVC missed optimization PRs.
 
There's a new scalar cycle def kind, vect_first_order_recurrence
and it's handling of the backedge value vectorization is complicated
by the fact that the vectorized value isn't the PHI but instead
a (series of) permute(s) shifting in the recurring value from the
previous iteration.  I've implemented this by creating both the
single vectorized PHI and the series of permutes when vectorizing
the scalar PHI but leave the backedge values in both unassigned.
The backedge values are (for the testcases) computed by a load
which is also the place after which the permutes are inserted.
That placement also restricts the cases we can handle (without
resorting to code motion).
 
I added both costing and SLP handling though SLP handling is
restricted to the case where a single vectorized PHI is enough.
 
Missing is epilogue handling - while prologue peeling would
be handled transparently by adjusting iv_phi_p the epilogue
case doesn't work with just inserting a scalar LC PHI since
that a) keeps the scalar load live and b) that loads is the
wrong one, it has to be the last, much like when we'd vectorize
the LC PHI as live operation.  Unfortunately LIVE
compute/analysis happens too early before we decide on
peeling.  When using fully masked loop vectorization the
vect-recurr-6.c works as expected though.
 
I have tested this on x86_64 for now, but since epilogue
handling is missing there's probably no practical cases.
My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
just fine but I didn't feel like running SPEC within SDE nor
is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
with fully masked loops succeed (minus three cases of
PR107096, caused by my WHILE_ULT prototype).
 
Bootstrapped and tested on x86_64-unknown-linux-gnu.
 
Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
handle epilogues welcome.
 
Thanks,
Richard.
 
PR tree-optimization/99409
PR tree-optimization/99394
* tree-vectorizer.h (vect_def_type::vect_first_order_recurrence): Add.
(stmt_vec_info_type::recurr_info_type): Likewise.
(vectorizable_recurr): New function.
* tree-vect-loop.cc (vect_phi_first_order_recurrence_p): New
function.
(vect_analyze_scalar_cycles_1): Look for first order
recurrences.
(vect_analyze_loop_operations): Handle them.
(vect_transform_loop): Likewise.
(vectorizable_recurr): New function.
(maybe_set_vectorized_backedge_value): Handle the backedge value
setting in the first order recurrence PHI and the permutes.
* tree-vect-stmts.cc (vect_analyze_stmt): Handle first order
recurrences.
(vect_transform_stmt): Likewise.
(vect_is_simple_use): Likewise.
(vect_is_simple_use): Likewise.
* tree-vect-slp.cc (vect_get_and_check_slp_defs): Likewise.
(vect_build_slp_tree_2): Likewise.
(vect_schedule_scc): Handle the backedge value setting in the
first order recurrence PHI and the permutes.
 
* gcc.dg/vect/vect-recurr-1.c: New testcase.
* gcc.dg/vect/vect-recurr-2.c: Likewise.
* gcc.dg/vect/vect-recurr-3.c: Likewise.
* gcc.dg/vect/vect-recurr-4.c: Likewise.
* gcc.dg/vect/vect-recurr-5.c: Likewise.
* gcc.dg/vect/vect-recurr-6.c: Likewise.
* gcc.dg/vect/tsvc/vect-tsvc-s252.c: Un-XFAIL.
* gcc.dg/vect/tsvc/vect-tsvc-s254.c: Likewise.
* gcc.dg/vect/tsvc/vect-tsvc-s291.c: Likewise.
 
Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
---
.../gcc.dg/vect/tsvc/vect-tsvc-s252.c         |   2 +-
.../gcc.dg/vect/tsvc/vect-tsvc-s254.c         |   2 +-
.../gcc.dg/vect/tsvc/vect-tsvc-s291.c         |   2 +-
gcc/testsuite/gcc.dg/vect/vect-recurr-1.c     |  38 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-2.c     |  39 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-3.c     |  39 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-4.c     |  42 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-5.c     |  43 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-6.c     |  39 +++
gcc/tree-vect-loop.cc                         | 286 ++++++++++++++++--
gcc/tree-vect-slp.cc                          |  38 ++-
gcc/tree-vect-stmts.cc                        |  17 +-
gcc/tree-vectorizer.h                         |   4 +
13 files changed, 563 insertions(+), 28 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
 
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
index f1302b60ae5..83eaa7a8ff5 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
@@ -40,4 +40,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
index bdc8a01e2a5..06e9b0a849d 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
index 0b474c2e81a..91cdc121095 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
new file mode 100644
index 00000000000..6eb59fdf854
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
@@ -0,0 +1,38 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
new file mode 100644
index 00000000000..97efaaa38bc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
new file mode 100644
index 00000000000..621a5d8a257
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, signed char * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+signed char b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
new file mode 100644
index 00000000000..f6dbc494a62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
@@ -0,0 +1,42 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+ || b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
new file mode 100644
index 00000000000..19c56df9e83
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
@@ -0,0 +1,43 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+ || b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
new file mode 100644
index 00000000000..e7712680853
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c, int n)
+{
+  int t = *c;
+  for (int i = 0; i < n; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c, 63);
+  for (int i = 1; i < 63; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* ???  We miss epilogue handling for first order recurrences.  */
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" { target vect_fully_masked } } } */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 2536cc3cf49..b54820a960b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -529,6 +529,45 @@ vect_inner_phi_in_double_reduction_p (loop_vec_info loop_vinfo, gphi *phi)
   return false;
}
+/* Returns true if Phi is a first-order recurrence. A first-order
+   recurrence is a non-reduction recurrence relation in which the value of
+   the recurrence in the current loop iteration equals a value defined in
+   the previous iteration.  */
+
+static bool
+vect_phi_first_order_recurrence_p (loop_vec_info loop_vinfo, class loop *loop,
+    gphi *phi)
+{
+  /* Ensure the loop latch definition is from within the loop.  */
+  edge latch = loop_latch_edge (loop);
+  tree ldef = PHI_ARG_DEF_FROM_EDGE (phi, latch);
+  if (TREE_CODE (ldef) != SSA_NAME
+      || SSA_NAME_IS_DEFAULT_DEF (ldef)
+      || !flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (ldef))))
+    return false;
+
+  tree def = gimple_phi_result (phi);
+
+  /* Ensure every use_stmt of the phi node is dominated by the latch
+     definition.  */
+  imm_use_iterator imm_iter;
+  use_operand_p use_p;
+  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, def)
+    if (!is_gimple_debug (USE_STMT (use_p))
+ && (SSA_NAME_DEF_STMT (ldef) == USE_STMT (use_p)
+     || !vect_stmt_dominates_stmt_p (SSA_NAME_DEF_STMT (ldef),
+     USE_STMT (use_p))))
+      return false;
+
+  /* First-order recurrence autovectorization needs shuffle vector.  */
+  tree scalar_type = TREE_TYPE (def);
+  tree vectype = get_vectype_for_scalar_type (loop_vinfo, scalar_type);
+  if (!vectype)
+    return false;
+
+  return true;
+}
+
/* Function vect_analyze_scalar_cycles_1.
    Examine the cross iteration def-use cycles of scalar variables
@@ -666,6 +705,8 @@ vect_analyze_scalar_cycles_1 (loop_vec_info loop_vinfo, class loop *loop,
                 }
             }
         }
+      else if (vect_phi_first_order_recurrence_p (loop_vinfo, loop, phi))
+ STMT_VINFO_DEF_TYPE (stmt_vinfo) = vect_first_order_recurrence;
       else
         if (dump_enabled_p ())
           dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
@@ -1810,7 +1851,8 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
           if ((STMT_VINFO_RELEVANT (stmt_info) == vect_used_in_scope
                || STMT_VINFO_LIVE_P (stmt_info))
-              && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def)
+       && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def
+       && STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
    /* A scalar-dependence cycle that we don't support.  */
    return opt_result::failure_at (phi,
   "not vectorized:"
@@ -1831,6 +1873,11 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
       && ! PURE_SLP_STMT (stmt_info))
ok = vectorizable_reduction (loop_vinfo,
     stmt_info, NULL, NULL, &cost_vec);
+       else if ((STMT_VINFO_DEF_TYPE (stmt_info)
+ == vect_first_order_recurrence)
+        && ! PURE_SLP_STMT (stmt_info))
+ ok = vectorizable_recurr (loop_vinfo, stmt_info, NULL, NULL,
+    &cost_vec);
             }
  /* SLP PHIs are tested by vect_slp_analyze_node_operations.  */
@@ -8267,6 +8314,183 @@ vectorizable_phi (vec_info *,
   return true;
}
+/* Vectorizes first order recurrences.  */
+
+bool
+vectorizable_recurr (loop_vec_info loop_vinfo, stmt_vec_info stmt_info,
+       gimple **vec_stmt, slp_tree slp_node,
+       stmt_vector_for_cost *cost_vec)
+{
+  if (!loop_vinfo || !is_a<gphi *> (stmt_info->stmt))
+    return false;
+
+  gphi *phi = as_a<gphi *> (stmt_info->stmt);
+
+  /* So far we only support first-order recurrence auto-vectorization.  */
+  if (STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
+    return false;
+
+  tree vectype = STMT_VINFO_VECTYPE (stmt_info);
+  unsigned ncopies;
+  if (slp_node)
+    ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
+  else
+    ncopies = vect_get_num_copies (loop_vinfo, vectype);
+  poly_int64 nunits = TYPE_VECTOR_SUBPARTS (vectype);
+  unsigned dist = slp_node ? SLP_TREE_LANES (slp_node) : 1;
+  /* We need to be able to make progress with a single vector.  */
+  if (maybe_gt (dist * 2, nunits))
+    {
+      if (dump_enabled_p ())
+ dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+ "first order recurrence exceeds half of "
+ "a vector\n");
+      return false;
+    }
+
+  /* First-order recurrence autovectorization needs to handle permutation
+     with indices = [nunits-1, nunits, nunits+1, ...].  */
+  vec_perm_builder sel (nunits, 1, 3);
+  for (int i = 0; i < 3; ++i)
+    sel.quick_push (nunits - dist + i);
+  vec_perm_indices indices (sel, 1, nunits * 2);
+
+  if (!vec_stmt) /* transformation not required.  */
+    {
+      if (!can_vec_perm_const_p (TYPE_MODE (vectype), TYPE_MODE (vectype),
+ indices))
+ return false;
+
+      if (slp_node)
+ {
+   /* We eventually need to set a vector type on invariant
+      arguments.  */
+   unsigned j;
+   slp_tree child;
+   FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (slp_node), j, child)
+     if (!vect_maybe_update_slp_op_vectype
+   (child, SLP_TREE_VECTYPE (slp_node)))
+       {
+ if (dump_enabled_p ())
+   dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+    "incompatible vector types for "
+    "invariants\n");
+ return false;
+       }
+ }
+      /* The recurrence costs the initialization vector and one permute
+ for each copy.  */
+      unsigned prologue_cost = record_stmt_cost (cost_vec, 1, scalar_to_vec,
+ stmt_info, 0, vect_prologue);
+      unsigned inside_cost = record_stmt_cost (cost_vec, ncopies, vector_stmt,
+        stmt_info, 0, vect_body);
+      if (dump_enabled_p ())
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "vectorizable_recurr: inside_cost = %d, "
+ "prologue_cost = %d .\n", inside_cost,
+ prologue_cost);
+
+      STMT_VINFO_TYPE (stmt_info) = recurr_info_type;
+      return true;
+    }
+
+  /* This is the second phase of vectorizing first-order rececurrences. An
+     overview of the transformation is described below. Suppose we have the
+     following loop.
+
+     int32_t t = 0;
+     for (int i = 0; i < n; ++i)
+       {
+ b[i] = a[i] - t;
+ t = a[i];
+      }
+
+    There is a first-order recurrence on "a". For this loop, the shorthand
+    scalar IR looks like:
+
+    scalar.preheader:
+      init = a[-1]
+      br loop.body
+
+    scalar.body:
+      i = PHI <0(scalar.preheader), i+1(scalar.body)>
+      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
+      _1 = a[i]
+      b[i] = _1 - _2
+      br cond, scalar.body, ...
+
+    In this example, _2 is a recurrence because it's value depends on the
+    previous iteration. In the first phase of vectorization, we created a
+    temporary value for _2. We now complete the vectorization and produce the
+    shorthand vector IR shown below (VF = 4).
+
+    vector.preheader:
+      vect_init = vect_cst(..., ..., ..., a[-1])
+      br vector.body
+
+    vector.body
+      i = PHI <0(vector.preheader), i+4(vector.body)>
+      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
+      vect_2 = a[i, i+1, i+2, i+3];
+      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
+      b[i, i+1, i+2, i+3] = vect_2 - vect_3
+      br cond, vector.body, middle.block
+
+    middle.block:
+      x = vect_2(3)
+      br scalar.preheader
+
+    scalar.ph:
+      s_init = PHI <x(middle.block), a[-1], otherwise>
+      br scalar.body
+
+    After execution completes the vector loop, we extract the next value of
+    the recurrence (x) to use as the initial value in the scalar loop.  */
+
+  edge pe = loop_preheader_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  basic_block bb = gimple_bb (phi);
+  tree preheader = PHI_ARG_DEF_FROM_EDGE (phi, pe);
+  tree vec_init = build_vector_from_val (vectype, preheader);
+  vec_init = vect_init_vector (loop_vinfo, stmt_info, vec_init, vectype, NULL);
+
+  /* Create the vectorized first-order PHI node.  */
+  tree vec_dest = vect_get_new_vect_var (vectype,
+ vect_simple_var, "vec_recur_");
+  gphi *new_phi = create_phi_node (vec_dest, bb);
+  add_phi_arg (new_phi, vec_init, pe, UNKNOWN_LOCATION);
+
+  /* Insert shuffles the first-order recurrence autovectorization.
+       result = VEC_PERM <vec_recur, vect_1, index[nunits-1, nunits, ...]>.  */
+  tree perm = vect_gen_perm_mask_checked (vectype, indices);
+
+  /* Insert the required permute after the latch definition.  The
+     second and later operands are tentative and will be updated when we have
+     vectorized the latch definition.  */
+  edge le = loop_latch_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  gimple_stmt_iterator gsi2
+    = gsi_for_stmt (SSA_NAME_DEF_STMT (PHI_ARG_DEF_FROM_EDGE (phi, le)));
+  gsi_next (&gsi2);
+
+  for (unsigned i = 0; i < ncopies; ++i)
+    {
+      vec_dest = make_ssa_name (vectype);
+      gassign *vperm
+   = gimple_build_assign (vec_dest, VEC_PERM_EXPR,
+ i == 0 ? gimple_phi_result (new_phi) : NULL,
+ NULL, perm);
+      vect_finish_stmt_generation (loop_vinfo, stmt_info, vperm, &gsi2);
+
+      if (slp_node)
+ SLP_TREE_VEC_STMTS (slp_node).quick_push (vperm);
+      else
+ STMT_VINFO_VEC_STMTS (stmt_info).safe_push (vperm);
+    }
+
+  if (!slp_node)
+    *vec_stmt = STMT_VINFO_VEC_STMTS (stmt_info)[0];
+  return true;
+}
+
/* Return true if VECTYPE represents a vector that requires lowering
    by the vector lowering pass.  */
@@ -10223,27 +10447,53 @@ maybe_set_vectorized_backedge_value (loop_vec_info loop_vinfo,
   imm_use_iterator iter;
   use_operand_p use_p;
   FOR_EACH_IMM_USE_FAST (use_p, iter, def)
-    if (gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p)))
-      if (gimple_bb (phi)->loop_father->header == gimple_bb (phi)
-   && (phi_info = loop_vinfo->lookup_stmt (phi))
-   && STMT_VINFO_RELEVANT_P (phi_info)
-   && VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
+    {
+      gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p));
+      if (!phi)
+ continue;
+      if (!(gimple_bb (phi)->loop_father->header == gimple_bb (phi)
+     && (phi_info = loop_vinfo->lookup_stmt (phi))
+     && STMT_VINFO_RELEVANT_P (phi_info)))
+ continue;
+      loop_p loop = gimple_bb (phi)->loop_father;
+      edge e = loop_latch_edge (loop);
+      if (PHI_ARG_DEF_FROM_EDGE (phi, e) != def)
+ continue;
+
+      if (VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
  && STMT_VINFO_REDUC_TYPE (phi_info) != FOLD_LEFT_REDUCTION
  && STMT_VINFO_REDUC_TYPE (phi_info) != EXTRACT_LAST_REDUCTION)
{
-   loop_p loop = gimple_bb (phi)->loop_father;
-   edge e = loop_latch_edge (loop);
-   if (PHI_ARG_DEF_FROM_EDGE (phi, e) == def)
+   vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+   vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+   gcc_assert (phi_defs.length () == latch_defs.length ());
+   for (unsigned i = 0; i < phi_defs.length (); ++i)
+     add_phi_arg (as_a <gphi *> (phi_defs[i]),
+ gimple_get_lhs (latch_defs[i]), e,
+ gimple_phi_arg_location (phi, e->dest_idx));
+ }
+      else if (STMT_VINFO_DEF_TYPE (phi_info) == vect_first_order_recurrence)
+ {
+   /* For first order recurrences we have to update both uses of
+      the latch definition, the one in the PHI node and the one
+      in the generated VEC_PERM_EXPR.  */
+   vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+   vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+   gcc_assert (phi_defs.length () == latch_defs.length ());
+   tree phidef = gimple_assign_rhs1 (phi_defs[0]);
+   gphi *vphi = as_a <gphi *> (SSA_NAME_DEF_STMT (phidef));
+   for (unsigned i = 0; i < phi_defs.length (); ++i)
    {
-       vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
-       vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
-       gcc_assert (phi_defs.length () == latch_defs.length ());
-       for (unsigned i = 0; i < phi_defs.length (); ++i)
- add_phi_arg (as_a <gphi *> (phi_defs[i]),
-      gimple_get_lhs (latch_defs[i]), e,
-      gimple_phi_arg_location (phi, e->dest_idx));
+       gassign *perm = as_a <gassign *> (phi_defs[i]);
+       if (i > 0)
+ gimple_assign_set_rhs1 (perm, gimple_get_lhs (latch_defs[i-1]));
+       gimple_assign_set_rhs2 (perm, gimple_get_lhs (latch_defs[i]));
+       update_stmt (perm);
    }
+   add_phi_arg (vphi, gimple_get_lhs (latch_defs.last ()), e,
+        gimple_phi_arg_location (phi, e->dest_idx));
}
+    }
}
/* Vectorize STMT_INFO if relevant, inserting any new instructions before GSI.
@@ -10652,6 +10902,7 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
      && ! PURE_SLP_STMT (stmt_info))
    {
@@ -10677,7 +10928,8 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
-        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence)
      && ! PURE_SLP_STMT (stmt_info))
    maybe_set_vectorized_backedge_value (loop_vinfo, stmt_info);
}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 229f2663ebc..cea5d50da92 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -693,6 +693,7 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
    case vect_reduction_def:
    case vect_induction_def:
    case vect_nested_cycle:
+     case vect_first_order_recurrence:
      break;
    default:
@@ -1732,7 +1733,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
  }
else if (def_type == vect_reduction_def
|| def_type == vect_double_reduction_def
- || def_type == vect_nested_cycle)
+ || def_type == vect_nested_cycle
+ || def_type == vect_first_order_recurrence)
  {
    /* Else def types have to match.  */
    stmt_vec_info other_info;
@@ -1746,7 +1748,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
      }
    class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
    /* Reduction initial values are not explicitely represented.  */
-     if (!nested_in_vect_loop_p (loop, stmt_info))
+     if (def_type != vect_first_order_recurrence
+ && !nested_in_vect_loop_p (loop, stmt_info))
      skip_args[loop_preheader_edge (loop)->dest_idx] = true;
    /* Reduction chain backedge defs are filled manually.
       ???  Need a better way to identify a SLP reduction chain PHI.
@@ -9187,11 +9190,34 @@ vect_schedule_scc (vec_info *vinfo, slp_tree node, slp_instance instance,
  child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
  if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
    continue;
+   unsigned n = SLP_TREE_VEC_STMTS (phi_node).length ();
  /* Simply fill all args.  */
-   for (unsigned i = 0; i < SLP_TREE_VEC_STMTS (phi_node).length (); ++i)
-     add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
- vect_get_slp_vect_def (child, i),
- e, gimple_phi_arg_location (phi, dest_idx));
+   if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (phi_node))
+       != vect_first_order_recurrence)
+     for (unsigned i = 0; i < n; ++i)
+       add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
+    vect_get_slp_vect_def (child, i),
+    e, gimple_phi_arg_location (phi, dest_idx));
+   else
+     {
+       /* Unless it is a first order recurrence which needs
+ args filled in for both the PHI node and the permutes.  */
+       gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[0];
+       gimple *rphi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (perm));
+       add_phi_arg (as_a <gphi *> (rphi),
+    vect_get_slp_vect_def (child, n - 1),
+    e, gimple_phi_arg_location (phi, dest_idx));
+       for (unsigned i = 0; i < n; ++i)
+ {
+   gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[i];
+   if (i > 0)
+     gimple_assign_set_rhs1 (perm,
+     vect_get_slp_vect_def (child, i - 1));
+   gimple_assign_set_rhs2 (perm,
+   vect_get_slp_vect_def (child, i));
+   update_stmt (perm);
+ }
+     }
}
     }
}
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index c8d1efc45e5..4e0d75e0d75 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -11176,6 +11176,7 @@ vect_analyze_stmt (vec_info *vinfo,
          break;
       case vect_induction_def:
+      case vect_first_order_recurrence:
gcc_assert (!bb_vinfo);
break;
@@ -11234,7 +11235,9 @@ vect_analyze_stmt (vec_info *vinfo,
  || vectorizable_comparison (vinfo, stmt_info, NULL, NULL, node,
      cost_vec)
  || vectorizable_lc_phi (as_a <loop_vec_info> (vinfo),
-   stmt_info, NULL, node));
+   stmt_info, NULL, node)
+   || vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+    stmt_info, NULL, node, cost_vec));
   else
     {
       if (bb_vinfo)
@@ -11404,6 +11407,12 @@ vect_transform_stmt (vec_info *vinfo,
       gcc_assert (done);
       break;
+    case recurr_info_type:
+      done = vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+   stmt_info, &vec_stmt, slp_node, NULL);
+      gcc_assert (done);
+      break;
+
     case phi_info_type:
       done = vectorizable_phi (vinfo, stmt_info, &vec_stmt, slp_node, NULL);
       gcc_assert (done);
@@ -11804,6 +11813,9 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
case vect_nested_cycle:
  dump_printf (MSG_NOTE, "nested cycle\n");
  break;
+ case vect_first_order_recurrence:
+   dump_printf (MSG_NOTE, "first order recurrence\n");
+   break;
case vect_unknown_def_type:
  dump_printf (MSG_NOTE, "unknown\n");
  break;
@@ -11852,7 +11864,8 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
       || *dt == vect_induction_def
       || *dt == vect_reduction_def
       || *dt == vect_double_reduction_def
-      || *dt == vect_nested_cycle)
+      || *dt == vect_nested_cycle
+      || *dt == vect_first_order_recurrence)
     {
       *vectype = STMT_VINFO_VECTYPE (def_stmt_info);
       gcc_assert (*vectype != NULL_TREE);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 4870c754499..016961da851 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -65,6 +65,7 @@ enum vect_def_type {
   vect_reduction_def,
   vect_double_reduction_def,
   vect_nested_cycle,
+  vect_first_order_recurrence,
   vect_unknown_def_type
};
@@ -1027,6 +1028,7 @@ enum stmt_vec_info_type {
   cycle_phi_info_type,
   lc_phi_info_type,
   phi_info_type,
+  recurr_info_type,
   loop_exit_ctrl_vec_info_type
};
@@ -2331,6 +2333,8 @@ extern bool vectorizable_lc_phi (loop_vec_info, stmt_vec_info,
gimple **, slp_tree);
extern bool vectorizable_phi (vec_info *, stmt_vec_info, gimple **, slp_tree,
      stmt_vector_for_cost *);
+extern bool vectorizable_recurr (loop_vec_info, stmt_vec_info,
+   gimple **, slp_tree, stmt_vector_for_cost *);
extern bool vect_emulated_vector_p (tree);
extern bool vect_can_vectorize_without_simd_p (tree_code);
extern bool vect_can_vectorize_without_simd_p (code_helper);
-- 
2.35.3
 

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Richard Sandiford]

Richard Biener <rguenther@suse.de> writes:
> On Mon, 10 Oct 2022, Andrew Stubbs wrote:
>> On 10/10/2022 12:03, Richard Biener wrote:
>> > The following picks up the prototype by Ju-Zhe Zhong for vectorizing
>> > first order recurrences.  That solves two TSVC missed optimization PRs.
>> > 
>> > There's a new scalar cycle def kind, vect_first_order_recurrence
>> > and it's handling of the backedge value vectorization is complicated
>> > by the fact that the vectorized value isn't the PHI but instead
>> > a (series of) permute(s) shifting in the recurring value from the
>> > previous iteration.  I've implemented this by creating both the
>> > single vectorized PHI and the series of permutes when vectorizing
>> > the scalar PHI but leave the backedge values in both unassigned.
>> > The backedge values are (for the testcases) computed by a load
>> > which is also the place after which the permutes are inserted.
>> > That placement also restricts the cases we can handle (without
>> > resorting to code motion).
>> > 
>> > I added both costing and SLP handling though SLP handling is
>> > restricted to the case where a single vectorized PHI is enough.
>> > 
>> > Missing is epilogue handling - while prologue peeling would
>> > be handled transparently by adjusting iv_phi_p the epilogue
>> > case doesn't work with just inserting a scalar LC PHI since
>> > that a) keeps the scalar load live and b) that loads is the
>> > wrong one, it has to be the last, much like when we'd vectorize
>> > the LC PHI as live operation.  Unfortunately LIVE
>> > compute/analysis happens too early before we decide on
>> > peeling.  When using fully masked loop vectorization the
>> > vect-recurr-6.c works as expected though.
>> > 
>> > I have tested this on x86_64 for now, but since epilogue
>> > handling is missing there's probably no practical cases.
>> > My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
>> > just fine but I didn't feel like running SPEC within SDE nor
>> > is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
>> > with fully masked loops succeed (minus three cases of
>> > PR107096, caused by my WHILE_ULT prototype).
>> > 
>> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
>> > 
>> > Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
>> > handle epilogues welcome.
>> 
>> The testcases all produce correct code on GCN and pass the execution tests.
>> 
>> The code isn't terribly optimal because we don't have a two-input permutation
>> instruction, so we permute each half separately and vec_merge the results. In
>> this case the first vector is always a no-op permutation so that's wasted
>> cycles. We'd really want a vector rotate and write-lane (or the other way
>> around). I think the special-case permutations can be recognised and coded
>> into the backend, but I don't know if we can easily tell that the first vector
>> is just a bunch of duplicates, when it's not constant.
>
> It's not actually a bunch of duplicates in all but the first iteration.
> But what you can recognize is that we're only using lane N - 1 of the
> first vector, so you could model the permute as extract last
> + shift in scalar (the extracted lane).  IIRC VLA vector targets usually
> have something like shift the vector and set the low lane from a
> scalar?

Yeah.

> The extract lane N - 1 might be more difficult but then
> a rotate plus extracting lane 0 might work as well.

I guess for SVE we should probably use SPLICE, which joins two vectors
and uses a predicate to select the first element that should be extracted.

Unfortunately we don't have a way of representing "last bit set, all other
bits clear" as a constant though, so I guess it'll have to be hidden
behind unspecs.

I meant to start SVE tests running once I'd finished for the day yesterday,
but forgot, sorry.  Will try to test today.

On the patch:

+  /* This is the second phase of vectorizing first-order rececurrences. An
+     overview of the transformation is described below. Suppose we have the
+     following loop.
+
+     int32_t t = 0;
+     for (int i = 0; i < n; ++i)
+       {
+	b[i] = a[i] - t;
+	t = a[i];
+      }
+
+    There is a first-order recurrence on "a". For this loop, the shorthand
+    scalar IR looks like:
+
+    scalar.preheader:
+      init = a[-1]
+      br loop.body
+
+    scalar.body:
+      i = PHI <0(scalar.preheader), i+1(scalar.body)>
+      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
+      _1 = a[i]
+      b[i] = _1 - _2
+      br cond, scalar.body, ...
+
+    In this example, _2 is a recurrence because it's value depends on the
+    previous iteration. In the first phase of vectorization, we created a
+    temporary value for _2. We now complete the vectorization and produce the
+    shorthand vector IR shown below (VF = 4).
+
+    vector.preheader:
+      vect_init = vect_cst(..., ..., ..., a[-1])
+      br vector.body
+
+    vector.body
+      i = PHI <0(vector.preheader), i+4(vector.body)>
+      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
+      vect_2 = a[i, i+1, i+2, i+3];
+      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
+      b[i, i+1, i+2, i+3] = vect_2 - vect_3
+      br cond, vector.body, middle.block
+
+    middle.block:
+      x = vect_2(3)
+      br scalar.preheader
+
+    scalar.ph:
+      s_init = PHI <x(middle.block), a[-1], otherwise>
+      br scalar.body
+
+    After execution completes the vector loop, we extract the next value of
+    the recurrence (x) to use as the initial value in the scalar loop.  */

Looks like a[-1] should be zero in the example (or t should be initialised
to a[-1]).

Thanks,
Richard

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Richard Sandiford]

Richard Biener <rguenther@suse.de> writes:
> +  /* First-order recurrence autovectorization needs to handle permutation
> +     with indices = [nunits-1, nunits, nunits+1, ...].  */
> +  vec_perm_builder sel (nunits, 1, 3);
> +  for (int i = 0; i < 3; ++i)
> +    sel.quick_push (nunits - dist + i);
> +  vec_perm_indices indices (sel, 1, nunits * 2);

Should be:

  vec_perm_indices indices (sel, 2, nunits);

With that change, the patch passes testing on SVE.  vect-recurr-6.c
fails to vectorise, but I think that's because SVE doesn't yet support
the required permute.

Thanks,
Richard

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Richard Biener]

On Tue, 11 Oct 2022, Richard Sandiford wrote:

> Richard Biener <rguenther@suse.de> writes:
> > On Mon, 10 Oct 2022, Andrew Stubbs wrote:
> >> On 10/10/2022 12:03, Richard Biener wrote:
> >> > The following picks up the prototype by Ju-Zhe Zhong for vectorizing
> >> > first order recurrences.  That solves two TSVC missed optimization PRs.
> >> > 
> >> > There's a new scalar cycle def kind, vect_first_order_recurrence
> >> > and it's handling of the backedge value vectorization is complicated
> >> > by the fact that the vectorized value isn't the PHI but instead
> >> > a (series of) permute(s) shifting in the recurring value from the
> >> > previous iteration.  I've implemented this by creating both the
> >> > single vectorized PHI and the series of permutes when vectorizing
> >> > the scalar PHI but leave the backedge values in both unassigned.
> >> > The backedge values are (for the testcases) computed by a load
> >> > which is also the place after which the permutes are inserted.
> >> > That placement also restricts the cases we can handle (without
> >> > resorting to code motion).
> >> > 
> >> > I added both costing and SLP handling though SLP handling is
> >> > restricted to the case where a single vectorized PHI is enough.
> >> > 
> >> > Missing is epilogue handling - while prologue peeling would
> >> > be handled transparently by adjusting iv_phi_p the epilogue
> >> > case doesn't work with just inserting a scalar LC PHI since
> >> > that a) keeps the scalar load live and b) that loads is the
> >> > wrong one, it has to be the last, much like when we'd vectorize
> >> > the LC PHI as live operation.  Unfortunately LIVE
> >> > compute/analysis happens too early before we decide on
> >> > peeling.  When using fully masked loop vectorization the
> >> > vect-recurr-6.c works as expected though.
> >> > 
> >> > I have tested this on x86_64 for now, but since epilogue
> >> > handling is missing there's probably no practical cases.
> >> > My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
> >> > just fine but I didn't feel like running SPEC within SDE nor
> >> > is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
> >> > with fully masked loops succeed (minus three cases of
> >> > PR107096, caused by my WHILE_ULT prototype).
> >> > 
> >> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> >> > 
> >> > Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
> >> > handle epilogues welcome.
> >> 
> >> The testcases all produce correct code on GCN and pass the execution tests.
> >> 
> >> The code isn't terribly optimal because we don't have a two-input permutation
> >> instruction, so we permute each half separately and vec_merge the results. In
> >> this case the first vector is always a no-op permutation so that's wasted
> >> cycles. We'd really want a vector rotate and write-lane (or the other way
> >> around). I think the special-case permutations can be recognised and coded
> >> into the backend, but I don't know if we can easily tell that the first vector
> >> is just a bunch of duplicates, when it's not constant.
> >
> > It's not actually a bunch of duplicates in all but the first iteration.
> > But what you can recognize is that we're only using lane N - 1 of the
> > first vector, so you could model the permute as extract last
> > + shift in scalar (the extracted lane).  IIRC VLA vector targets usually
> > have something like shift the vector and set the low lane from a
> > scalar?
> 
> Yeah.
> 
> > The extract lane N - 1 might be more difficult but then
> > a rotate plus extracting lane 0 might work as well.
> 
> I guess for SVE we should probably use SPLICE, which joins two vectors
> and uses a predicate to select the first element that should be extracted.
> 
> Unfortunately we don't have a way of representing "last bit set, all other
> bits clear" as a constant though, so I guess it'll have to be hidden
> behind unspecs.
> 
> I meant to start SVE tests running once I'd finished for the day yesterday,
> but forgot, sorry.  Will try to test today.
> 
> On the patch:
> 
> +  /* This is the second phase of vectorizing first-order rececurrences. An
> +     overview of the transformation is described below. Suppose we have the
> +     following loop.
> +
> +     int32_t t = 0;
> +     for (int i = 0; i < n; ++i)
> +       {
> +	b[i] = a[i] - t;
> +	t = a[i];
> +      }
> +
> +    There is a first-order recurrence on "a". For this loop, the shorthand
> +    scalar IR looks like:
> +
> +    scalar.preheader:
> +      init = a[-1]
> +      br loop.body
> +
> +    scalar.body:
> +      i = PHI <0(scalar.preheader), i+1(scalar.body)>
> +      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
> +      _1 = a[i]
> +      b[i] = _1 - _2
> +      br cond, scalar.body, ...
> +
> +    In this example, _2 is a recurrence because it's value depends on the
> +    previous iteration. In the first phase of vectorization, we created a
> +    temporary value for _2. We now complete the vectorization and produce the
> +    shorthand vector IR shown below (VF = 4).
> +
> +    vector.preheader:
> +      vect_init = vect_cst(..., ..., ..., a[-1])
> +      br vector.body
> +
> +    vector.body
> +      i = PHI <0(vector.preheader), i+4(vector.body)>
> +      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
> +      vect_2 = a[i, i+1, i+2, i+3];
> +      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
> +      b[i, i+1, i+2, i+3] = vect_2 - vect_3
> +      br cond, vector.body, middle.block
> +
> +    middle.block:
> +      x = vect_2(3)
> +      br scalar.preheader
> +
> +    scalar.ph:
> +      s_init = PHI <x(middle.block), a[-1], otherwise>
> +      br scalar.body
> +
> +    After execution completes the vector loop, we extract the next value of
> +    the recurrence (x) to use as the initial value in the scalar loop.  */
> 
> Looks like a[-1] should be zero in the example (or t should be initialised
> to a[-1]).

Indeed.  I've promoted the comment to function level and adjusted it
to reflect what is done now (I've missed to update it from Ju-Zhes
prototype).  I have also applied your correctness fix.

Re-bootstrap and regtest running on x86_64-unknown-linux-gnu.

OK (given limited x86 test quality)?

Thanks,
Richard.

From 054bb007b09334402f018a4b2b65aef150cd8182 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Thu, 6 Oct 2022 13:56:09 +0200
Subject: [PATCH] Vectorization of first-order recurrences
To: gcc-patches@gcc.gnu.org

The following picks up the prototype by Ju-Zhe Zhong for vectorizing
first order recurrences.  That solves two TSVC missed optimization PRs.

There's a new scalar cycle def kind, vect_first_order_recurrence
and it's handling of the backedge value vectorization is complicated
by the fact that the vectorized value isn't the PHI but instead
a (series of) permute(s) shifting in the recurring value from the
previous iteration.  I've implemented this by creating both the
single vectorized PHI and the series of permutes when vectorizing
the scalar PHI but leave the backedge values in both unassigned.
The backedge values are (for the testcases) computed by a load
which is also the place after which the permutes are inserted.
That placement also restricts the cases we can handle (without
resorting to code motion).

I added both costing and SLP handling though SLP handling is
restricted to the case where a single vectorized PHI is enough.

Missing is epilogue handling - while prologue peeling would
be handled transparently by adjusting iv_phi_p the epilogue
case doesn't work with just inserting a scalar LC PHI since
that a) keeps the scalar load live and b) that loads is the
wrong one, it has to be the last, much like when we'd vectorize
the LC PHI as live operation.  Unfortunately LIVE
compute/analysis happens too early before we decide on
peeling.  When using fully masked loop vectorization the
vect-recurr-6.c works as expected though.

I have tested this on x86_64 for now, but since epilogue
handling is missing there's probably no practical cases.
My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
just fine but I didn't feel like running SPEC within SDE nor
is the WHILE_ULT patch complete enough.

	PR tree-optimization/99409
	PR tree-optimization/99394
	* tree-vectorizer.h (vect_def_type::vect_first_order_recurrence): Add.
	(stmt_vec_info_type::recurr_info_type): Likewise.
	(vectorizable_recurr): New function.
	* tree-vect-loop.cc (vect_phi_first_order_recurrence_p): New
	function.
	(vect_analyze_scalar_cycles_1): Look for first order
	recurrences.
	(vect_analyze_loop_operations): Handle them.
	(vect_transform_loop): Likewise.
	(vectorizable_recurr): New function.
	(maybe_set_vectorized_backedge_value): Handle the backedge value
	setting in the first order recurrence PHI and the permutes.
	* tree-vect-stmts.cc (vect_analyze_stmt): Handle first order
	recurrences.
	(vect_transform_stmt): Likewise.
	(vect_is_simple_use): Likewise.
	(vect_is_simple_use): Likewise.
	* tree-vect-slp.cc (vect_get_and_check_slp_defs): Likewise.
	(vect_build_slp_tree_2): Likewise.
	(vect_schedule_scc): Handle the backedge value setting in the
	first order recurrence PHI and the permutes.

	* gcc.dg/vect/vect-recurr-1.c: New testcase.
	* gcc.dg/vect/vect-recurr-2.c: Likewise.
	* gcc.dg/vect/vect-recurr-3.c: Likewise.
	* gcc.dg/vect/vect-recurr-4.c: Likewise.
	* gcc.dg/vect/vect-recurr-5.c: Likewise.
	* gcc.dg/vect/vect-recurr-6.c: Likewise.
	* gcc.dg/vect/tsvc/vect-tsvc-s252.c: Un-XFAIL.
	* gcc.dg/vect/tsvc/vect-tsvc-s254.c: Likewise.
	* gcc.dg/vect/tsvc/vect-tsvc-s291.c: Likewise.

Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
---
 .../gcc.dg/vect/tsvc/vect-tsvc-s252.c         |   2 +-
 .../gcc.dg/vect/tsvc/vect-tsvc-s254.c         |   2 +-
 .../gcc.dg/vect/tsvc/vect-tsvc-s291.c         |   2 +-
 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c     |  38 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c     |  39 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c     |  39 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c     |  42 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c     |  43 +++
 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c     |  39 +++
 gcc/tree-vect-loop.cc                         | 281 ++++++++++++++++--
 gcc/tree-vect-slp.cc                          |  38 ++-
 gcc/tree-vect-stmts.cc                        |  17 +-
 gcc/tree-vectorizer.h                         |   4 +
 13 files changed, 558 insertions(+), 28 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
 create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c

diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
index f1302b60ae5..83eaa7a8ff5 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
@@ -40,4 +40,4 @@ int main (int argc, char **argv)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
index bdc8a01e2a5..06e9b0a849d 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
index 0b474c2e81a..91cdc121095 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
new file mode 100644
index 00000000000..6eb59fdf854
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
@@ -0,0 +1,38 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
new file mode 100644
index 00000000000..97efaaa38bc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
new file mode 100644
index 00000000000..621a5d8a257
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, signed char * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+signed char b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
new file mode 100644
index 00000000000..f6dbc494a62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
@@ -0,0 +1,42 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+	|| b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
new file mode 100644
index 00000000000..19c56df9e83
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
@@ -0,0 +1,43 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+	|| b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
new file mode 100644
index 00000000000..e7712680853
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c, int n)
+{
+  int t = *c;
+  for (int i = 0; i < n; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c, 63);
+  for (int i = 1; i < 63; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* ???  We miss epilogue handling for first order recurrences.  */
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" { target vect_fully_masked } } } */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 98a943d8a4b..63e86540d12 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -529,6 +529,45 @@ vect_inner_phi_in_double_reduction_p (loop_vec_info loop_vinfo, gphi *phi)
   return false;
 }
 
+/* Returns true if Phi is a first-order recurrence. A first-order
+   recurrence is a non-reduction recurrence relation in which the value of
+   the recurrence in the current loop iteration equals a value defined in
+   the previous iteration.  */
+
+static bool
+vect_phi_first_order_recurrence_p (loop_vec_info loop_vinfo, class loop *loop,
+				   gphi *phi)
+{
+  /* Ensure the loop latch definition is from within the loop.  */
+  edge latch = loop_latch_edge (loop);
+  tree ldef = PHI_ARG_DEF_FROM_EDGE (phi, latch);
+  if (TREE_CODE (ldef) != SSA_NAME
+      || SSA_NAME_IS_DEFAULT_DEF (ldef)
+      || !flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (ldef))))
+    return false;
+
+  tree def = gimple_phi_result (phi);
+
+  /* Ensure every use_stmt of the phi node is dominated by the latch
+     definition.  */
+  imm_use_iterator imm_iter;
+  use_operand_p use_p;
+  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, def)
+    if (!is_gimple_debug (USE_STMT (use_p))
+	&& (SSA_NAME_DEF_STMT (ldef) == USE_STMT (use_p)
+	    || !vect_stmt_dominates_stmt_p (SSA_NAME_DEF_STMT (ldef),
+					    USE_STMT (use_p))))
+      return false;
+
+  /* First-order recurrence autovectorization needs shuffle vector.  */
+  tree scalar_type = TREE_TYPE (def);
+  tree vectype = get_vectype_for_scalar_type (loop_vinfo, scalar_type);
+  if (!vectype)
+    return false;
+
+  return true;
+}
+
 /* Function vect_analyze_scalar_cycles_1.
 
    Examine the cross iteration def-use cycles of scalar variables
@@ -666,6 +705,8 @@ vect_analyze_scalar_cycles_1 (loop_vec_info loop_vinfo, class loop *loop,
                 }
             }
         }
+      else if (vect_phi_first_order_recurrence_p (loop_vinfo, loop, phi))
+	STMT_VINFO_DEF_TYPE (stmt_vinfo) = vect_first_order_recurrence;
       else
         if (dump_enabled_p ())
           dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
@@ -1810,7 +1851,8 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
 
           if ((STMT_VINFO_RELEVANT (stmt_info) == vect_used_in_scope
                || STMT_VINFO_LIVE_P (stmt_info))
-              && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def)
+	      && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def
+	      && STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
 	    /* A scalar-dependence cycle that we don't support.  */
 	    return opt_result::failure_at (phi,
 					   "not vectorized:"
@@ -1831,6 +1873,11 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
 		       && ! PURE_SLP_STMT (stmt_info))
 		ok = vectorizable_reduction (loop_vinfo,
 					     stmt_info, NULL, NULL, &cost_vec);
+	      else if ((STMT_VINFO_DEF_TYPE (stmt_info)
+			== vect_first_order_recurrence)
+		       && ! PURE_SLP_STMT (stmt_info))
+		ok = vectorizable_recurr (loop_vinfo, stmt_info, NULL, NULL,
+					   &cost_vec);
             }
 
 	  /* SLP PHIs are tested by vect_slp_analyze_node_operations.  */
@@ -8290,6 +8337,178 @@ vectorizable_phi (vec_info *,
   return true;
 }
 
+/* Vectorizes first order recurrences.  An overview of the transformation
+   is described below. Suppose we have the following loop.
+
+     int t = 0;
+     for (int i = 0; i < n; ++i)
+       {
+	 b[i] = a[i] - t;
+	 t = a[i];
+       }
+
+   There is a first-order recurrence on 'a'. For this loop, the scalar IR
+   looks (simplified) like:
+
+    scalar.preheader:
+      init = 0;
+
+    scalar.body:
+      i = PHI <0(scalar.preheader), i+1(scalar.body)>
+      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
+      _1 = a[i]
+      b[i] = _1 - _2
+      if (i < n) goto scalar.body
+
+   In this example, _2 is a recurrence because it's value depends on the
+   previous iteration.  We vectorize this as (VF = 4)
+
+    vector.preheader:
+      vect_init = vect_cst(..., ..., ..., 0)
+
+    vector.body
+      i = PHI <0(vector.preheader), i+4(vector.body)>
+      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
+      vect_2 = a[i, i+1, i+2, i+3];
+      vect_3 = vec_perm (vect_1, vect_2, { 3, 4, 5, 6 })
+      b[i, i+1, i+2, i+3] = vect_2 - vect_3
+      if (..) goto vector.body
+
+   In this function, vectorizable_recurr, we code generate both the
+   vector PHI node and the permute since those together compute the
+   vectorized value of the scalar PHI.  We do not yet have the
+   backedge value to fill in there nor into the vec_perm.  Those
+   are filled in maybe_set_vectorized_backedge_value and
+   vect_schedule_scc.
+
+   TODO:  Since the scalar loop does not have a use of the recurrence
+   outside of the loop the natural way to implement peeling via
+   vectorizing the live value doesn't work.  For now peeling of loops
+   with a recurrence is not implemented.  For SLP the supported cases
+   are restricted to those requiring a single vector recurrence PHI.  */
+
+bool
+vectorizable_recurr (loop_vec_info loop_vinfo, stmt_vec_info stmt_info,
+		     gimple **vec_stmt, slp_tree slp_node,
+		     stmt_vector_for_cost *cost_vec)
+{
+  if (!loop_vinfo || !is_a<gphi *> (stmt_info->stmt))
+    return false;
+
+  gphi *phi = as_a<gphi *> (stmt_info->stmt);
+
+  /* So far we only support first-order recurrence auto-vectorization.  */
+  if (STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
+    return false;
+
+  tree vectype = STMT_VINFO_VECTYPE (stmt_info);
+  unsigned ncopies;
+  if (slp_node)
+    ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
+  else
+    ncopies = vect_get_num_copies (loop_vinfo, vectype);
+  poly_int64 nunits = TYPE_VECTOR_SUBPARTS (vectype);
+  unsigned dist = slp_node ? SLP_TREE_LANES (slp_node) : 1;
+  /* We need to be able to make progress with a single vector.  */
+  if (maybe_gt (dist * 2, nunits))
+    {
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "first order recurrence exceeds half of "
+			 "a vector\n");
+      return false;
+    }
+
+  /* First-order recurrence autovectorization needs to handle permutation
+     with indices = [nunits-1, nunits, nunits+1, ...].  */
+  vec_perm_builder sel (nunits, 1, 3);
+  for (int i = 0; i < 3; ++i)
+    sel.quick_push (nunits - dist + i);
+  vec_perm_indices indices (sel, 2, nunits);
+
+  if (!vec_stmt) /* transformation not required.  */
+    {
+      if (!can_vec_perm_const_p (TYPE_MODE (vectype), TYPE_MODE (vectype),
+				 indices))
+	return false;
+
+      if (slp_node)
+	{
+	  /* We eventually need to set a vector type on invariant
+	     arguments.  */
+	  unsigned j;
+	  slp_tree child;
+	  FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (slp_node), j, child)
+	    if (!vect_maybe_update_slp_op_vectype
+		  (child, SLP_TREE_VECTYPE (slp_node)))
+	      {
+		if (dump_enabled_p ())
+		  dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+				   "incompatible vector types for "
+				   "invariants\n");
+		return false;
+	      }
+	}
+      /* The recurrence costs the initialization vector and one permute
+	 for each copy.  */
+      unsigned prologue_cost = record_stmt_cost (cost_vec, 1, scalar_to_vec,
+						 stmt_info, 0, vect_prologue);
+      unsigned inside_cost = record_stmt_cost (cost_vec, ncopies, vector_stmt,
+					       stmt_info, 0, vect_body);
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_NOTE, vect_location,
+			 "vectorizable_recurr: inside_cost = %d, "
+			 "prologue_cost = %d .\n", inside_cost,
+			 prologue_cost);
+
+      STMT_VINFO_TYPE (stmt_info) = recurr_info_type;
+      return true;
+    }
+
+  edge pe = loop_preheader_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  basic_block bb = gimple_bb (phi);
+  tree preheader = PHI_ARG_DEF_FROM_EDGE (phi, pe);
+  tree vec_init = build_vector_from_val (vectype, preheader);
+  vec_init = vect_init_vector (loop_vinfo, stmt_info, vec_init, vectype, NULL);
+
+  /* Create the vectorized first-order PHI node.  */
+  tree vec_dest = vect_get_new_vect_var (vectype,
+					 vect_simple_var, "vec_recur_");
+  gphi *new_phi = create_phi_node (vec_dest, bb);
+  add_phi_arg (new_phi, vec_init, pe, UNKNOWN_LOCATION);
+
+  /* Insert shuffles the first-order recurrence autovectorization.
+       result = VEC_PERM <vec_recur, vect_1, index[nunits-1, nunits, ...]>.  */
+  tree perm = vect_gen_perm_mask_checked (vectype, indices);
+
+  /* Insert the required permute after the latch definition.  The
+     second and later operands are tentative and will be updated when we have
+     vectorized the latch definition.  */
+  edge le = loop_latch_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  gimple_stmt_iterator gsi2
+    = gsi_for_stmt (SSA_NAME_DEF_STMT (PHI_ARG_DEF_FROM_EDGE (phi, le)));
+  gsi_next (&gsi2);
+
+  for (unsigned i = 0; i < ncopies; ++i)
+    {
+      vec_dest = make_ssa_name (vectype);
+      gassign *vperm
+	  = gimple_build_assign (vec_dest, VEC_PERM_EXPR,
+				 i == 0 ? gimple_phi_result (new_phi) : NULL,
+				 NULL, perm);
+      vect_finish_stmt_generation (loop_vinfo, stmt_info, vperm, &gsi2);
+
+      if (slp_node)
+	SLP_TREE_VEC_STMTS (slp_node).quick_push (vperm);
+      else
+	STMT_VINFO_VEC_STMTS (stmt_info).safe_push (vperm);
+    }
+
+  if (!slp_node)
+    *vec_stmt = STMT_VINFO_VEC_STMTS (stmt_info)[0];
+  return true;
+}
+
 /* Return true if VECTYPE represents a vector that requires lowering
    by the vector lowering pass.  */
 
@@ -10242,27 +10461,53 @@ maybe_set_vectorized_backedge_value (loop_vec_info loop_vinfo,
   imm_use_iterator iter;
   use_operand_p use_p;
   FOR_EACH_IMM_USE_FAST (use_p, iter, def)
-    if (gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p)))
-      if (gimple_bb (phi)->loop_father->header == gimple_bb (phi)
-	  && (phi_info = loop_vinfo->lookup_stmt (phi))
-	  && STMT_VINFO_RELEVANT_P (phi_info)
-	  && VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
+    {
+      gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p));
+      if (!phi)
+	continue;
+      if (!(gimple_bb (phi)->loop_father->header == gimple_bb (phi)
+	    && (phi_info = loop_vinfo->lookup_stmt (phi))
+	    && STMT_VINFO_RELEVANT_P (phi_info)))
+	continue;
+      loop_p loop = gimple_bb (phi)->loop_father;
+      edge e = loop_latch_edge (loop);
+      if (PHI_ARG_DEF_FROM_EDGE (phi, e) != def)
+	continue;
+
+      if (VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
 	  && STMT_VINFO_REDUC_TYPE (phi_info) != FOLD_LEFT_REDUCTION
 	  && STMT_VINFO_REDUC_TYPE (phi_info) != EXTRACT_LAST_REDUCTION)
 	{
-	  loop_p loop = gimple_bb (phi)->loop_father;
-	  edge e = loop_latch_edge (loop);
-	  if (PHI_ARG_DEF_FROM_EDGE (phi, e) == def)
+	  vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+	  vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+	  gcc_assert (phi_defs.length () == latch_defs.length ());
+	  for (unsigned i = 0; i < phi_defs.length (); ++i)
+	    add_phi_arg (as_a <gphi *> (phi_defs[i]),
+			 gimple_get_lhs (latch_defs[i]), e,
+			 gimple_phi_arg_location (phi, e->dest_idx));
+	}
+      else if (STMT_VINFO_DEF_TYPE (phi_info) == vect_first_order_recurrence)
+	{
+	  /* For first order recurrences we have to update both uses of
+	     the latch definition, the one in the PHI node and the one
+	     in the generated VEC_PERM_EXPR.  */
+	  vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+	  vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+	  gcc_assert (phi_defs.length () == latch_defs.length ());
+	  tree phidef = gimple_assign_rhs1 (phi_defs[0]);
+	  gphi *vphi = as_a <gphi *> (SSA_NAME_DEF_STMT (phidef));
+	  for (unsigned i = 0; i < phi_defs.length (); ++i)
 	    {
-	      vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
-	      vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
-	      gcc_assert (phi_defs.length () == latch_defs.length ());
-	      for (unsigned i = 0; i < phi_defs.length (); ++i)
-		add_phi_arg (as_a <gphi *> (phi_defs[i]),
-			     gimple_get_lhs (latch_defs[i]), e,
-			     gimple_phi_arg_location (phi, e->dest_idx));
+	      gassign *perm = as_a <gassign *> (phi_defs[i]);
+	      if (i > 0)
+		gimple_assign_set_rhs1 (perm, gimple_get_lhs (latch_defs[i-1]));
+	      gimple_assign_set_rhs2 (perm, gimple_get_lhs (latch_defs[i]));
+	      update_stmt (perm);
 	    }
+	  add_phi_arg (vphi, gimple_get_lhs (latch_defs.last ()), e,
+		       gimple_phi_arg_location (phi, e->dest_idx));
 	}
+    }
 }
 
 /* Vectorize STMT_INFO if relevant, inserting any new instructions before GSI.
@@ -10671,6 +10916,7 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
+	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
 	      && ! PURE_SLP_STMT (stmt_info))
 	    {
@@ -10696,7 +10942,8 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
 	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
-	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
+	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def
+	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence)
 	      && ! PURE_SLP_STMT (stmt_info))
 	    maybe_set_vectorized_backedge_value (loop_vinfo, stmt_info);
 	}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 229f2663ebc..cea5d50da92 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -693,6 +693,7 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
 	    case vect_reduction_def:
 	    case vect_induction_def:
 	    case vect_nested_cycle:
+	    case vect_first_order_recurrence:
 	      break;
 
 	    default:
@@ -1732,7 +1733,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 	  }
 	else if (def_type == vect_reduction_def
 		 || def_type == vect_double_reduction_def
-		 || def_type == vect_nested_cycle)
+		 || def_type == vect_nested_cycle
+		 || def_type == vect_first_order_recurrence)
 	  {
 	    /* Else def types have to match.  */
 	    stmt_vec_info other_info;
@@ -1746,7 +1748,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 	      }
 	    class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
 	    /* Reduction initial values are not explicitely represented.  */
-	    if (!nested_in_vect_loop_p (loop, stmt_info))
+	    if (def_type != vect_first_order_recurrence
+		&& !nested_in_vect_loop_p (loop, stmt_info))
 	      skip_args[loop_preheader_edge (loop)->dest_idx] = true;
 	    /* Reduction chain backedge defs are filled manually.
 	       ???  Need a better way to identify a SLP reduction chain PHI.
@@ -9187,11 +9190,34 @@ vect_schedule_scc (vec_info *vinfo, slp_tree node, slp_instance instance,
 	  child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
 	  if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
 	    continue;
+	  unsigned n = SLP_TREE_VEC_STMTS (phi_node).length ();
 	  /* Simply fill all args.  */
-	  for (unsigned i = 0; i < SLP_TREE_VEC_STMTS (phi_node).length (); ++i)
-	    add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
-			 vect_get_slp_vect_def (child, i),
-			 e, gimple_phi_arg_location (phi, dest_idx));
+	  if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (phi_node))
+	      != vect_first_order_recurrence)
+	    for (unsigned i = 0; i < n; ++i)
+	      add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
+			   vect_get_slp_vect_def (child, i),
+			   e, gimple_phi_arg_location (phi, dest_idx));
+	  else
+	    {
+	      /* Unless it is a first order recurrence which needs
+		 args filled in for both the PHI node and the permutes.  */
+	      gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[0];
+	      gimple *rphi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (perm));
+	      add_phi_arg (as_a <gphi *> (rphi),
+			   vect_get_slp_vect_def (child, n - 1),
+			   e, gimple_phi_arg_location (phi, dest_idx));
+	      for (unsigned i = 0; i < n; ++i)
+		{
+		  gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[i];
+		  if (i > 0)
+		    gimple_assign_set_rhs1 (perm,
+					    vect_get_slp_vect_def (child, i - 1));
+		  gimple_assign_set_rhs2 (perm,
+					  vect_get_slp_vect_def (child, i));
+		  update_stmt (perm);
+		}
+	    }
 	}
     }
 }
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index c8d1efc45e5..4e0d75e0d75 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -11176,6 +11176,7 @@ vect_analyze_stmt (vec_info *vinfo,
          break;
 
       case vect_induction_def:
+      case vect_first_order_recurrence:
 	gcc_assert (!bb_vinfo);
 	break;
 
@@ -11234,7 +11235,9 @@ vect_analyze_stmt (vec_info *vinfo,
 	  || vectorizable_comparison (vinfo, stmt_info, NULL, NULL, node,
 				      cost_vec)
 	  || vectorizable_lc_phi (as_a <loop_vec_info> (vinfo),
-				  stmt_info, NULL, node));
+				  stmt_info, NULL, node)
+	  || vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+				   stmt_info, NULL, node, cost_vec));
   else
     {
       if (bb_vinfo)
@@ -11404,6 +11407,12 @@ vect_transform_stmt (vec_info *vinfo,
       gcc_assert (done);
       break;
 
+    case recurr_info_type:
+      done = vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+				  stmt_info, &vec_stmt, slp_node, NULL);
+      gcc_assert (done);
+      break;
+
     case phi_info_type:
       done = vectorizable_phi (vinfo, stmt_info, &vec_stmt, slp_node, NULL);
       gcc_assert (done);
@@ -11804,6 +11813,9 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
 	case vect_nested_cycle:
 	  dump_printf (MSG_NOTE, "nested cycle\n");
 	  break;
+	case vect_first_order_recurrence:
+	  dump_printf (MSG_NOTE, "first order recurrence\n");
+	  break;
 	case vect_unknown_def_type:
 	  dump_printf (MSG_NOTE, "unknown\n");
 	  break;
@@ -11852,7 +11864,8 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
       || *dt == vect_induction_def
       || *dt == vect_reduction_def
       || *dt == vect_double_reduction_def
-      || *dt == vect_nested_cycle)
+      || *dt == vect_nested_cycle
+      || *dt == vect_first_order_recurrence)
     {
       *vectype = STMT_VINFO_VECTYPE (def_stmt_info);
       gcc_assert (*vectype != NULL_TREE);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 4870c754499..016961da851 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -65,6 +65,7 @@ enum vect_def_type {
   vect_reduction_def,
   vect_double_reduction_def,
   vect_nested_cycle,
+  vect_first_order_recurrence,
   vect_unknown_def_type
 };
 
@@ -1027,6 +1028,7 @@ enum stmt_vec_info_type {
   cycle_phi_info_type,
   lc_phi_info_type,
   phi_info_type,
+  recurr_info_type,
   loop_exit_ctrl_vec_info_type
 };
 
@@ -2331,6 +2333,8 @@ extern bool vectorizable_lc_phi (loop_vec_info, stmt_vec_info,
 				 gimple **, slp_tree);
 extern bool vectorizable_phi (vec_info *, stmt_vec_info, gimple **, slp_tree,
 			      stmt_vector_for_cost *);
+extern bool vectorizable_recurr (loop_vec_info, stmt_vec_info,
+				  gimple **, slp_tree, stmt_vector_for_cost *);
 extern bool vect_emulated_vector_p (tree);
 extern bool vect_can_vectorize_without_simd_p (tree_code);
 extern bool vect_can_vectorize_without_simd_p (code_helper);
-- 
2.35.3

Re: Re: [PATCH][RFT] Vectorization of first-order recurrences

[juzhe.zhong]

[-- Attachment #1: Type: text/plain, Size: 38935 bytes --]

LGTM.



juzhe.zhong@rivai.ai
 
From: Richard Biener
Date: 2022-10-14 15:07
To: Richard Sandiford
CC: Andrew Stubbs; gcc-patches; juzhe.zhong
Subject: Re: [PATCH][RFT] Vectorization of first-order recurrences
On Tue, 11 Oct 2022, Richard Sandiford wrote:
 
> Richard Biener <rguenther@suse.de> writes:
> > On Mon, 10 Oct 2022, Andrew Stubbs wrote:
> >> On 10/10/2022 12:03, Richard Biener wrote:
> >> > The following picks up the prototype by Ju-Zhe Zhong for vectorizing
> >> > first order recurrences.  That solves two TSVC missed optimization PRs.
> >> > 
> >> > There's a new scalar cycle def kind, vect_first_order_recurrence
> >> > and it's handling of the backedge value vectorization is complicated
> >> > by the fact that the vectorized value isn't the PHI but instead
> >> > a (series of) permute(s) shifting in the recurring value from the
> >> > previous iteration.  I've implemented this by creating both the
> >> > single vectorized PHI and the series of permutes when vectorizing
> >> > the scalar PHI but leave the backedge values in both unassigned.
> >> > The backedge values are (for the testcases) computed by a load
> >> > which is also the place after which the permutes are inserted.
> >> > That placement also restricts the cases we can handle (without
> >> > resorting to code motion).
> >> > 
> >> > I added both costing and SLP handling though SLP handling is
> >> > restricted to the case where a single vectorized PHI is enough.
> >> > 
> >> > Missing is epilogue handling - while prologue peeling would
> >> > be handled transparently by adjusting iv_phi_p the epilogue
> >> > case doesn't work with just inserting a scalar LC PHI since
> >> > that a) keeps the scalar load live and b) that loads is the
> >> > wrong one, it has to be the last, much like when we'd vectorize
> >> > the LC PHI as live operation.  Unfortunately LIVE
> >> > compute/analysis happens too early before we decide on
> >> > peeling.  When using fully masked loop vectorization the
> >> > vect-recurr-6.c works as expected though.
> >> > 
> >> > I have tested this on x86_64 for now, but since epilogue
> >> > handling is missing there's probably no practical cases.
> >> > My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
> >> > just fine but I didn't feel like running SPEC within SDE nor
> >> > is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
> >> > with fully masked loops succeed (minus three cases of
> >> > PR107096, caused by my WHILE_ULT prototype).
> >> > 
> >> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
> >> > 
> >> > Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
> >> > handle epilogues welcome.
> >> 
> >> The testcases all produce correct code on GCN and pass the execution tests.
> >> 
> >> The code isn't terribly optimal because we don't have a two-input permutation
> >> instruction, so we permute each half separately and vec_merge the results. In
> >> this case the first vector is always a no-op permutation so that's wasted
> >> cycles. We'd really want a vector rotate and write-lane (or the other way
> >> around). I think the special-case permutations can be recognised and coded
> >> into the backend, but I don't know if we can easily tell that the first vector
> >> is just a bunch of duplicates, when it's not constant.
> >
> > It's not actually a bunch of duplicates in all but the first iteration.
> > But what you can recognize is that we're only using lane N - 1 of the
> > first vector, so you could model the permute as extract last
> > + shift in scalar (the extracted lane).  IIRC VLA vector targets usually
> > have something like shift the vector and set the low lane from a
> > scalar?
> 
> Yeah.
> 
> > The extract lane N - 1 might be more difficult but then
> > a rotate plus extracting lane 0 might work as well.
> 
> I guess for SVE we should probably use SPLICE, which joins two vectors
> and uses a predicate to select the first element that should be extracted.
> 
> Unfortunately we don't have a way of representing "last bit set, all other
> bits clear" as a constant though, so I guess it'll have to be hidden
> behind unspecs.
> 
> I meant to start SVE tests running once I'd finished for the day yesterday,
> but forgot, sorry.  Will try to test today.
> 
> On the patch:
> 
> +  /* This is the second phase of vectorizing first-order rececurrences. An
> +     overview of the transformation is described below. Suppose we have the
> +     following loop.
> +
> +     int32_t t = 0;
> +     for (int i = 0; i < n; ++i)
> +       {
> + b[i] = a[i] - t;
> + t = a[i];
> +      }
> +
> +    There is a first-order recurrence on "a". For this loop, the shorthand
> +    scalar IR looks like:
> +
> +    scalar.preheader:
> +      init = a[-1]
> +      br loop.body
> +
> +    scalar.body:
> +      i = PHI <0(scalar.preheader), i+1(scalar.body)>
> +      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
> +      _1 = a[i]
> +      b[i] = _1 - _2
> +      br cond, scalar.body, ...
> +
> +    In this example, _2 is a recurrence because it's value depends on the
> +    previous iteration. In the first phase of vectorization, we created a
> +    temporary value for _2. We now complete the vectorization and produce the
> +    shorthand vector IR shown below (VF = 4).
> +
> +    vector.preheader:
> +      vect_init = vect_cst(..., ..., ..., a[-1])
> +      br vector.body
> +
> +    vector.body
> +      i = PHI <0(vector.preheader), i+4(vector.body)>
> +      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
> +      vect_2 = a[i, i+1, i+2, i+3];
> +      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
> +      b[i, i+1, i+2, i+3] = vect_2 - vect_3
> +      br cond, vector.body, middle.block
> +
> +    middle.block:
> +      x = vect_2(3)
> +      br scalar.preheader
> +
> +    scalar.ph:
> +      s_init = PHI <x(middle.block), a[-1], otherwise>
> +      br scalar.body
> +
> +    After execution completes the vector loop, we extract the next value of
> +    the recurrence (x) to use as the initial value in the scalar loop.  */
> 
> Looks like a[-1] should be zero in the example (or t should be initialised
> to a[-1]).
 
Indeed.  I've promoted the comment to function level and adjusted it
to reflect what is done now (I've missed to update it from Ju-Zhes
prototype).  I have also applied your correctness fix.
 
Re-bootstrap and regtest running on x86_64-unknown-linux-gnu.
 
OK (given limited x86 test quality)?
 
Thanks,
Richard.
 
From 054bb007b09334402f018a4b2b65aef150cd8182 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Thu, 6 Oct 2022 13:56:09 +0200
Subject: [PATCH] Vectorization of first-order recurrences
To: gcc-patches@gcc.gnu.org
 
The following picks up the prototype by Ju-Zhe Zhong for vectorizing
first order recurrences.  That solves two TSVC missed optimization PRs.
 
There's a new scalar cycle def kind, vect_first_order_recurrence
and it's handling of the backedge value vectorization is complicated
by the fact that the vectorized value isn't the PHI but instead
a (series of) permute(s) shifting in the recurring value from the
previous iteration.  I've implemented this by creating both the
single vectorized PHI and the series of permutes when vectorizing
the scalar PHI but leave the backedge values in both unassigned.
The backedge values are (for the testcases) computed by a load
which is also the place after which the permutes are inserted.
That placement also restricts the cases we can handle (without
resorting to code motion).
 
I added both costing and SLP handling though SLP handling is
restricted to the case where a single vectorized PHI is enough.
 
Missing is epilogue handling - while prologue peeling would
be handled transparently by adjusting iv_phi_p the epilogue
case doesn't work with just inserting a scalar LC PHI since
that a) keeps the scalar load live and b) that loads is the
wrong one, it has to be the last, much like when we'd vectorize
the LC PHI as live operation.  Unfortunately LIVE
compute/analysis happens too early before we decide on
peeling.  When using fully masked loop vectorization the
vect-recurr-6.c works as expected though.
 
I have tested this on x86_64 for now, but since epilogue
handling is missing there's probably no practical cases.
My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
just fine but I didn't feel like running SPEC within SDE nor
is the WHILE_ULT patch complete enough.
 
PR tree-optimization/99409
PR tree-optimization/99394
* tree-vectorizer.h (vect_def_type::vect_first_order_recurrence): Add.
(stmt_vec_info_type::recurr_info_type): Likewise.
(vectorizable_recurr): New function.
* tree-vect-loop.cc (vect_phi_first_order_recurrence_p): New
function.
(vect_analyze_scalar_cycles_1): Look for first order
recurrences.
(vect_analyze_loop_operations): Handle them.
(vect_transform_loop): Likewise.
(vectorizable_recurr): New function.
(maybe_set_vectorized_backedge_value): Handle the backedge value
setting in the first order recurrence PHI and the permutes.
* tree-vect-stmts.cc (vect_analyze_stmt): Handle first order
recurrences.
(vect_transform_stmt): Likewise.
(vect_is_simple_use): Likewise.
(vect_is_simple_use): Likewise.
* tree-vect-slp.cc (vect_get_and_check_slp_defs): Likewise.
(vect_build_slp_tree_2): Likewise.
(vect_schedule_scc): Handle the backedge value setting in the
first order recurrence PHI and the permutes.
 
* gcc.dg/vect/vect-recurr-1.c: New testcase.
* gcc.dg/vect/vect-recurr-2.c: Likewise.
* gcc.dg/vect/vect-recurr-3.c: Likewise.
* gcc.dg/vect/vect-recurr-4.c: Likewise.
* gcc.dg/vect/vect-recurr-5.c: Likewise.
* gcc.dg/vect/vect-recurr-6.c: Likewise.
* gcc.dg/vect/tsvc/vect-tsvc-s252.c: Un-XFAIL.
* gcc.dg/vect/tsvc/vect-tsvc-s254.c: Likewise.
* gcc.dg/vect/tsvc/vect-tsvc-s291.c: Likewise.
 
Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
---
.../gcc.dg/vect/tsvc/vect-tsvc-s252.c         |   2 +-
.../gcc.dg/vect/tsvc/vect-tsvc-s254.c         |   2 +-
.../gcc.dg/vect/tsvc/vect-tsvc-s291.c         |   2 +-
gcc/testsuite/gcc.dg/vect/vect-recurr-1.c     |  38 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-2.c     |  39 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-3.c     |  39 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-4.c     |  42 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-5.c     |  43 +++
gcc/testsuite/gcc.dg/vect/vect-recurr-6.c     |  39 +++
gcc/tree-vect-loop.cc                         | 281 ++++++++++++++++--
gcc/tree-vect-slp.cc                          |  38 ++-
gcc/tree-vect-stmts.cc                        |  17 +-
gcc/tree-vectorizer.h                         |   4 +
13 files changed, 558 insertions(+), 28 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
 
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
index f1302b60ae5..83eaa7a8ff5 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
@@ -40,4 +40,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
index bdc8a01e2a5..06e9b0a849d 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
index 0b474c2e81a..91cdc121095 100644
--- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
+++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
@@ -39,4 +39,4 @@ int main (int argc, char **argv)
   return 0;
}
-/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
new file mode 100644
index 00000000000..6eb59fdf854
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
@@ -0,0 +1,38 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
new file mode 100644
index 00000000000..97efaaa38bc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
new file mode 100644
index 00000000000..621a5d8a257
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, signed char * __restrict__ b, int * __restrict__ c)
+{
+  int t = *c;
+  for (int i = 0; i < 64; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64];
+signed char b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 1; i < 64; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
new file mode 100644
index 00000000000..f6dbc494a62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
@@ -0,0 +1,42 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+ || b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
new file mode 100644
index 00000000000..19c56df9e83
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
@@ -0,0 +1,43 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
+{
+  int t1 = *c;
+  int t2 = *c;
+  for (int i = 0; i < 64; i+=2)
+    {
+      b[i] = a[i] - t1;
+      t1 = a[i];
+      b[i+1] = a[i+1] - t2;
+      t2 = a[i+1];
+    }
+}
+
+int a[64];
+short b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c);
+  for (int i = 2; i < 64; i+=2)
+    if (b[i] != a[i] - a[i-2]
+ || b[i+1] != a[i+1] - a[i-1])
+      abort ();
+  if (b[0] != -7 || b[1] != -6)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
new file mode 100644
index 00000000000..e7712680853
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
@@ -0,0 +1,39 @@
+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+void __attribute__((noipa))
+foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c, int n)
+{
+  int t = *c;
+  for (int i = 0; i < n; ++i)
+    {
+      b[i] = a[i] - t;
+      t = a[i];
+    }
+}
+
+int a[64], b[64];
+
+int
+main ()
+{
+  check_vect ();
+  for (int i = 0; i < 64; ++i)
+    {
+      a[i] = i;
+      __asm__ volatile ("" ::: "memory");
+    }
+  int c = 7;
+  foo (a, b, &c, 63);
+  for (int i = 1; i < 63; ++i)
+    if (b[i] != a[i] - a[i-1])
+      abort ();
+  if (b[0] != -7)
+    abort ();
+  return 0;
+}
+
+/* ???  We miss epilogue handling for first order recurrences.  */
+/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" { target vect_fully_masked } } } */
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 98a943d8a4b..63e86540d12 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -529,6 +529,45 @@ vect_inner_phi_in_double_reduction_p (loop_vec_info loop_vinfo, gphi *phi)
   return false;
}
+/* Returns true if Phi is a first-order recurrence. A first-order
+   recurrence is a non-reduction recurrence relation in which the value of
+   the recurrence in the current loop iteration equals a value defined in
+   the previous iteration.  */
+
+static bool
+vect_phi_first_order_recurrence_p (loop_vec_info loop_vinfo, class loop *loop,
+    gphi *phi)
+{
+  /* Ensure the loop latch definition is from within the loop.  */
+  edge latch = loop_latch_edge (loop);
+  tree ldef = PHI_ARG_DEF_FROM_EDGE (phi, latch);
+  if (TREE_CODE (ldef) != SSA_NAME
+      || SSA_NAME_IS_DEFAULT_DEF (ldef)
+      || !flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (ldef))))
+    return false;
+
+  tree def = gimple_phi_result (phi);
+
+  /* Ensure every use_stmt of the phi node is dominated by the latch
+     definition.  */
+  imm_use_iterator imm_iter;
+  use_operand_p use_p;
+  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, def)
+    if (!is_gimple_debug (USE_STMT (use_p))
+ && (SSA_NAME_DEF_STMT (ldef) == USE_STMT (use_p)
+     || !vect_stmt_dominates_stmt_p (SSA_NAME_DEF_STMT (ldef),
+     USE_STMT (use_p))))
+      return false;
+
+  /* First-order recurrence autovectorization needs shuffle vector.  */
+  tree scalar_type = TREE_TYPE (def);
+  tree vectype = get_vectype_for_scalar_type (loop_vinfo, scalar_type);
+  if (!vectype)
+    return false;
+
+  return true;
+}
+
/* Function vect_analyze_scalar_cycles_1.
    Examine the cross iteration def-use cycles of scalar variables
@@ -666,6 +705,8 @@ vect_analyze_scalar_cycles_1 (loop_vec_info loop_vinfo, class loop *loop,
                 }
             }
         }
+      else if (vect_phi_first_order_recurrence_p (loop_vinfo, loop, phi))
+ STMT_VINFO_DEF_TYPE (stmt_vinfo) = vect_first_order_recurrence;
       else
         if (dump_enabled_p ())
           dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
@@ -1810,7 +1851,8 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
           if ((STMT_VINFO_RELEVANT (stmt_info) == vect_used_in_scope
                || STMT_VINFO_LIVE_P (stmt_info))
-              && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def)
+       && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def
+       && STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
    /* A scalar-dependence cycle that we don't support.  */
    return opt_result::failure_at (phi,
   "not vectorized:"
@@ -1831,6 +1873,11 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
       && ! PURE_SLP_STMT (stmt_info))
ok = vectorizable_reduction (loop_vinfo,
     stmt_info, NULL, NULL, &cost_vec);
+       else if ((STMT_VINFO_DEF_TYPE (stmt_info)
+ == vect_first_order_recurrence)
+        && ! PURE_SLP_STMT (stmt_info))
+ ok = vectorizable_recurr (loop_vinfo, stmt_info, NULL, NULL,
+    &cost_vec);
             }
  /* SLP PHIs are tested by vect_slp_analyze_node_operations.  */
@@ -8290,6 +8337,178 @@ vectorizable_phi (vec_info *,
   return true;
}
+/* Vectorizes first order recurrences.  An overview of the transformation
+   is described below. Suppose we have the following loop.
+
+     int t = 0;
+     for (int i = 0; i < n; ++i)
+       {
+ b[i] = a[i] - t;
+ t = a[i];
+       }
+
+   There is a first-order recurrence on 'a'. For this loop, the scalar IR
+   looks (simplified) like:
+
+    scalar.preheader:
+      init = 0;
+
+    scalar.body:
+      i = PHI <0(scalar.preheader), i+1(scalar.body)>
+      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
+      _1 = a[i]
+      b[i] = _1 - _2
+      if (i < n) goto scalar.body
+
+   In this example, _2 is a recurrence because it's value depends on the
+   previous iteration.  We vectorize this as (VF = 4)
+
+    vector.preheader:
+      vect_init = vect_cst(..., ..., ..., 0)
+
+    vector.body
+      i = PHI <0(vector.preheader), i+4(vector.body)>
+      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
+      vect_2 = a[i, i+1, i+2, i+3];
+      vect_3 = vec_perm (vect_1, vect_2, { 3, 4, 5, 6 })
+      b[i, i+1, i+2, i+3] = vect_2 - vect_3
+      if (..) goto vector.body
+
+   In this function, vectorizable_recurr, we code generate both the
+   vector PHI node and the permute since those together compute the
+   vectorized value of the scalar PHI.  We do not yet have the
+   backedge value to fill in there nor into the vec_perm.  Those
+   are filled in maybe_set_vectorized_backedge_value and
+   vect_schedule_scc.
+
+   TODO:  Since the scalar loop does not have a use of the recurrence
+   outside of the loop the natural way to implement peeling via
+   vectorizing the live value doesn't work.  For now peeling of loops
+   with a recurrence is not implemented.  For SLP the supported cases
+   are restricted to those requiring a single vector recurrence PHI.  */
+
+bool
+vectorizable_recurr (loop_vec_info loop_vinfo, stmt_vec_info stmt_info,
+      gimple **vec_stmt, slp_tree slp_node,
+      stmt_vector_for_cost *cost_vec)
+{
+  if (!loop_vinfo || !is_a<gphi *> (stmt_info->stmt))
+    return false;
+
+  gphi *phi = as_a<gphi *> (stmt_info->stmt);
+
+  /* So far we only support first-order recurrence auto-vectorization.  */
+  if (STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
+    return false;
+
+  tree vectype = STMT_VINFO_VECTYPE (stmt_info);
+  unsigned ncopies;
+  if (slp_node)
+    ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
+  else
+    ncopies = vect_get_num_copies (loop_vinfo, vectype);
+  poly_int64 nunits = TYPE_VECTOR_SUBPARTS (vectype);
+  unsigned dist = slp_node ? SLP_TREE_LANES (slp_node) : 1;
+  /* We need to be able to make progress with a single vector.  */
+  if (maybe_gt (dist * 2, nunits))
+    {
+      if (dump_enabled_p ())
+ dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+ "first order recurrence exceeds half of "
+ "a vector\n");
+      return false;
+    }
+
+  /* First-order recurrence autovectorization needs to handle permutation
+     with indices = [nunits-1, nunits, nunits+1, ...].  */
+  vec_perm_builder sel (nunits, 1, 3);
+  for (int i = 0; i < 3; ++i)
+    sel.quick_push (nunits - dist + i);
+  vec_perm_indices indices (sel, 2, nunits);
+
+  if (!vec_stmt) /* transformation not required.  */
+    {
+      if (!can_vec_perm_const_p (TYPE_MODE (vectype), TYPE_MODE (vectype),
+ indices))
+ return false;
+
+      if (slp_node)
+ {
+   /* We eventually need to set a vector type on invariant
+      arguments.  */
+   unsigned j;
+   slp_tree child;
+   FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (slp_node), j, child)
+     if (!vect_maybe_update_slp_op_vectype
+   (child, SLP_TREE_VECTYPE (slp_node)))
+       {
+ if (dump_enabled_p ())
+   dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+    "incompatible vector types for "
+    "invariants\n");
+ return false;
+       }
+ }
+      /* The recurrence costs the initialization vector and one permute
+ for each copy.  */
+      unsigned prologue_cost = record_stmt_cost (cost_vec, 1, scalar_to_vec,
+ stmt_info, 0, vect_prologue);
+      unsigned inside_cost = record_stmt_cost (cost_vec, ncopies, vector_stmt,
+        stmt_info, 0, vect_body);
+      if (dump_enabled_p ())
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "vectorizable_recurr: inside_cost = %d, "
+ "prologue_cost = %d .\n", inside_cost,
+ prologue_cost);
+
+      STMT_VINFO_TYPE (stmt_info) = recurr_info_type;
+      return true;
+    }
+
+  edge pe = loop_preheader_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  basic_block bb = gimple_bb (phi);
+  tree preheader = PHI_ARG_DEF_FROM_EDGE (phi, pe);
+  tree vec_init = build_vector_from_val (vectype, preheader);
+  vec_init = vect_init_vector (loop_vinfo, stmt_info, vec_init, vectype, NULL);
+
+  /* Create the vectorized first-order PHI node.  */
+  tree vec_dest = vect_get_new_vect_var (vectype,
+ vect_simple_var, "vec_recur_");
+  gphi *new_phi = create_phi_node (vec_dest, bb);
+  add_phi_arg (new_phi, vec_init, pe, UNKNOWN_LOCATION);
+
+  /* Insert shuffles the first-order recurrence autovectorization.
+       result = VEC_PERM <vec_recur, vect_1, index[nunits-1, nunits, ...]>.  */
+  tree perm = vect_gen_perm_mask_checked (vectype, indices);
+
+  /* Insert the required permute after the latch definition.  The
+     second and later operands are tentative and will be updated when we have
+     vectorized the latch definition.  */
+  edge le = loop_latch_edge (LOOP_VINFO_LOOP (loop_vinfo));
+  gimple_stmt_iterator gsi2
+    = gsi_for_stmt (SSA_NAME_DEF_STMT (PHI_ARG_DEF_FROM_EDGE (phi, le)));
+  gsi_next (&gsi2);
+
+  for (unsigned i = 0; i < ncopies; ++i)
+    {
+      vec_dest = make_ssa_name (vectype);
+      gassign *vperm
+   = gimple_build_assign (vec_dest, VEC_PERM_EXPR,
+ i == 0 ? gimple_phi_result (new_phi) : NULL,
+ NULL, perm);
+      vect_finish_stmt_generation (loop_vinfo, stmt_info, vperm, &gsi2);
+
+      if (slp_node)
+ SLP_TREE_VEC_STMTS (slp_node).quick_push (vperm);
+      else
+ STMT_VINFO_VEC_STMTS (stmt_info).safe_push (vperm);
+    }
+
+  if (!slp_node)
+    *vec_stmt = STMT_VINFO_VEC_STMTS (stmt_info)[0];
+  return true;
+}
+
/* Return true if VECTYPE represents a vector that requires lowering
    by the vector lowering pass.  */
@@ -10242,27 +10461,53 @@ maybe_set_vectorized_backedge_value (loop_vec_info loop_vinfo,
   imm_use_iterator iter;
   use_operand_p use_p;
   FOR_EACH_IMM_USE_FAST (use_p, iter, def)
-    if (gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p)))
-      if (gimple_bb (phi)->loop_father->header == gimple_bb (phi)
-   && (phi_info = loop_vinfo->lookup_stmt (phi))
-   && STMT_VINFO_RELEVANT_P (phi_info)
-   && VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
+    {
+      gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p));
+      if (!phi)
+ continue;
+      if (!(gimple_bb (phi)->loop_father->header == gimple_bb (phi)
+     && (phi_info = loop_vinfo->lookup_stmt (phi))
+     && STMT_VINFO_RELEVANT_P (phi_info)))
+ continue;
+      loop_p loop = gimple_bb (phi)->loop_father;
+      edge e = loop_latch_edge (loop);
+      if (PHI_ARG_DEF_FROM_EDGE (phi, e) != def)
+ continue;
+
+      if (VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
  && STMT_VINFO_REDUC_TYPE (phi_info) != FOLD_LEFT_REDUCTION
  && STMT_VINFO_REDUC_TYPE (phi_info) != EXTRACT_LAST_REDUCTION)
{
-   loop_p loop = gimple_bb (phi)->loop_father;
-   edge e = loop_latch_edge (loop);
-   if (PHI_ARG_DEF_FROM_EDGE (phi, e) == def)
+   vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+   vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+   gcc_assert (phi_defs.length () == latch_defs.length ());
+   for (unsigned i = 0; i < phi_defs.length (); ++i)
+     add_phi_arg (as_a <gphi *> (phi_defs[i]),
+ gimple_get_lhs (latch_defs[i]), e,
+ gimple_phi_arg_location (phi, e->dest_idx));
+ }
+      else if (STMT_VINFO_DEF_TYPE (phi_info) == vect_first_order_recurrence)
+ {
+   /* For first order recurrences we have to update both uses of
+      the latch definition, the one in the PHI node and the one
+      in the generated VEC_PERM_EXPR.  */
+   vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
+   vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
+   gcc_assert (phi_defs.length () == latch_defs.length ());
+   tree phidef = gimple_assign_rhs1 (phi_defs[0]);
+   gphi *vphi = as_a <gphi *> (SSA_NAME_DEF_STMT (phidef));
+   for (unsigned i = 0; i < phi_defs.length (); ++i)
    {
-       vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
-       vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
-       gcc_assert (phi_defs.length () == latch_defs.length ());
-       for (unsigned i = 0; i < phi_defs.length (); ++i)
- add_phi_arg (as_a <gphi *> (phi_defs[i]),
-      gimple_get_lhs (latch_defs[i]), e,
-      gimple_phi_arg_location (phi, e->dest_idx));
+       gassign *perm = as_a <gassign *> (phi_defs[i]);
+       if (i > 0)
+ gimple_assign_set_rhs1 (perm, gimple_get_lhs (latch_defs[i-1]));
+       gimple_assign_set_rhs2 (perm, gimple_get_lhs (latch_defs[i]));
+       update_stmt (perm);
    }
+   add_phi_arg (vphi, gimple_get_lhs (latch_defs.last ()), e,
+        gimple_phi_arg_location (phi, e->dest_idx));
}
+    }
}
/* Vectorize STMT_INFO if relevant, inserting any new instructions before GSI.
@@ -10671,6 +10916,7 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
      && ! PURE_SLP_STMT (stmt_info))
    {
@@ -10696,7 +10942,8 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
-        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def
+        || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence)
      && ! PURE_SLP_STMT (stmt_info))
    maybe_set_vectorized_backedge_value (loop_vinfo, stmt_info);
}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 229f2663ebc..cea5d50da92 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -693,6 +693,7 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
    case vect_reduction_def:
    case vect_induction_def:
    case vect_nested_cycle:
+     case vect_first_order_recurrence:
      break;
    default:
@@ -1732,7 +1733,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
  }
else if (def_type == vect_reduction_def
|| def_type == vect_double_reduction_def
- || def_type == vect_nested_cycle)
+ || def_type == vect_nested_cycle
+ || def_type == vect_first_order_recurrence)
  {
    /* Else def types have to match.  */
    stmt_vec_info other_info;
@@ -1746,7 +1748,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
      }
    class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
    /* Reduction initial values are not explicitely represented.  */
-     if (!nested_in_vect_loop_p (loop, stmt_info))
+     if (def_type != vect_first_order_recurrence
+ && !nested_in_vect_loop_p (loop, stmt_info))
      skip_args[loop_preheader_edge (loop)->dest_idx] = true;
    /* Reduction chain backedge defs are filled manually.
       ???  Need a better way to identify a SLP reduction chain PHI.
@@ -9187,11 +9190,34 @@ vect_schedule_scc (vec_info *vinfo, slp_tree node, slp_instance instance,
  child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
  if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
    continue;
+   unsigned n = SLP_TREE_VEC_STMTS (phi_node).length ();
  /* Simply fill all args.  */
-   for (unsigned i = 0; i < SLP_TREE_VEC_STMTS (phi_node).length (); ++i)
-     add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
- vect_get_slp_vect_def (child, i),
- e, gimple_phi_arg_location (phi, dest_idx));
+   if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (phi_node))
+       != vect_first_order_recurrence)
+     for (unsigned i = 0; i < n; ++i)
+       add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
+    vect_get_slp_vect_def (child, i),
+    e, gimple_phi_arg_location (phi, dest_idx));
+   else
+     {
+       /* Unless it is a first order recurrence which needs
+ args filled in for both the PHI node and the permutes.  */
+       gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[0];
+       gimple *rphi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (perm));
+       add_phi_arg (as_a <gphi *> (rphi),
+    vect_get_slp_vect_def (child, n - 1),
+    e, gimple_phi_arg_location (phi, dest_idx));
+       for (unsigned i = 0; i < n; ++i)
+ {
+   gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[i];
+   if (i > 0)
+     gimple_assign_set_rhs1 (perm,
+     vect_get_slp_vect_def (child, i - 1));
+   gimple_assign_set_rhs2 (perm,
+   vect_get_slp_vect_def (child, i));
+   update_stmt (perm);
+ }
+     }
}
     }
}
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index c8d1efc45e5..4e0d75e0d75 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -11176,6 +11176,7 @@ vect_analyze_stmt (vec_info *vinfo,
          break;
       case vect_induction_def:
+      case vect_first_order_recurrence:
gcc_assert (!bb_vinfo);
break;
@@ -11234,7 +11235,9 @@ vect_analyze_stmt (vec_info *vinfo,
  || vectorizable_comparison (vinfo, stmt_info, NULL, NULL, node,
      cost_vec)
  || vectorizable_lc_phi (as_a <loop_vec_info> (vinfo),
-   stmt_info, NULL, node));
+   stmt_info, NULL, node)
+   || vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+    stmt_info, NULL, node, cost_vec));
   else
     {
       if (bb_vinfo)
@@ -11404,6 +11407,12 @@ vect_transform_stmt (vec_info *vinfo,
       gcc_assert (done);
       break;
+    case recurr_info_type:
+      done = vectorizable_recurr (as_a <loop_vec_info> (vinfo),
+   stmt_info, &vec_stmt, slp_node, NULL);
+      gcc_assert (done);
+      break;
+
     case phi_info_type:
       done = vectorizable_phi (vinfo, stmt_info, &vec_stmt, slp_node, NULL);
       gcc_assert (done);
@@ -11804,6 +11813,9 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
case vect_nested_cycle:
  dump_printf (MSG_NOTE, "nested cycle\n");
  break;
+ case vect_first_order_recurrence:
+   dump_printf (MSG_NOTE, "first order recurrence\n");
+   break;
case vect_unknown_def_type:
  dump_printf (MSG_NOTE, "unknown\n");
  break;
@@ -11852,7 +11864,8 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
       || *dt == vect_induction_def
       || *dt == vect_reduction_def
       || *dt == vect_double_reduction_def
-      || *dt == vect_nested_cycle)
+      || *dt == vect_nested_cycle
+      || *dt == vect_first_order_recurrence)
     {
       *vectype = STMT_VINFO_VECTYPE (def_stmt_info);
       gcc_assert (*vectype != NULL_TREE);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 4870c754499..016961da851 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -65,6 +65,7 @@ enum vect_def_type {
   vect_reduction_def,
   vect_double_reduction_def,
   vect_nested_cycle,
+  vect_first_order_recurrence,
   vect_unknown_def_type
};
@@ -1027,6 +1028,7 @@ enum stmt_vec_info_type {
   cycle_phi_info_type,
   lc_phi_info_type,
   phi_info_type,
+  recurr_info_type,
   loop_exit_ctrl_vec_info_type
};
@@ -2331,6 +2333,8 @@ extern bool vectorizable_lc_phi (loop_vec_info, stmt_vec_info,
gimple **, slp_tree);
extern bool vectorizable_phi (vec_info *, stmt_vec_info, gimple **, slp_tree,
      stmt_vector_for_cost *);
+extern bool vectorizable_recurr (loop_vec_info, stmt_vec_info,
+   gimple **, slp_tree, stmt_vector_for_cost *);
extern bool vect_emulated_vector_p (tree);
extern bool vect_can_vectorize_without_simd_p (tree_code);
extern bool vect_can_vectorize_without_simd_p (code_helper);
-- 
2.35.3
 
 

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Andrew Stubbs]

On 14/10/2022 08:07, Richard Biener wrote:
> On Tue, 11 Oct 2022, Richard Sandiford wrote:
> 
>> Richard Biener <rguenther@suse.de> writes:
>>> On Mon, 10 Oct 2022, Andrew Stubbs wrote:
>>>> On 10/10/2022 12:03, Richard Biener wrote:
>>>>> The following picks up the prototype by Ju-Zhe Zhong for vectorizing
>>>>> first order recurrences.  That solves two TSVC missed optimization PRs.
>>>>>
>>>>> There's a new scalar cycle def kind, vect_first_order_recurrence
>>>>> and it's handling of the backedge value vectorization is complicated
>>>>> by the fact that the vectorized value isn't the PHI but instead
>>>>> a (series of) permute(s) shifting in the recurring value from the
>>>>> previous iteration.  I've implemented this by creating both the
>>>>> single vectorized PHI and the series of permutes when vectorizing
>>>>> the scalar PHI but leave the backedge values in both unassigned.
>>>>> The backedge values are (for the testcases) computed by a load
>>>>> which is also the place after which the permutes are inserted.
>>>>> That placement also restricts the cases we can handle (without
>>>>> resorting to code motion).
>>>>>
>>>>> I added both costing and SLP handling though SLP handling is
>>>>> restricted to the case where a single vectorized PHI is enough.
>>>>>
>>>>> Missing is epilogue handling - while prologue peeling would
>>>>> be handled transparently by adjusting iv_phi_p the epilogue
>>>>> case doesn't work with just inserting a scalar LC PHI since
>>>>> that a) keeps the scalar load live and b) that loads is the
>>>>> wrong one, it has to be the last, much like when we'd vectorize
>>>>> the LC PHI as live operation.  Unfortunately LIVE
>>>>> compute/analysis happens too early before we decide on
>>>>> peeling.  When using fully masked loop vectorization the
>>>>> vect-recurr-6.c works as expected though.
>>>>>
>>>>> I have tested this on x86_64 for now, but since epilogue
>>>>> handling is missing there's probably no practical cases.
>>>>> My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
>>>>> just fine but I didn't feel like running SPEC within SDE nor
>>>>> is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
>>>>> with fully masked loops succeed (minus three cases of
>>>>> PR107096, caused by my WHILE_ULT prototype).
>>>>>
>>>>> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>>>>>
>>>>> Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
>>>>> handle epilogues welcome.
>>>>
>>>> The testcases all produce correct code on GCN and pass the execution tests.
>>>>
>>>> The code isn't terribly optimal because we don't have a two-input permutation
>>>> instruction, so we permute each half separately and vec_merge the results. In
>>>> this case the first vector is always a no-op permutation so that's wasted
>>>> cycles. We'd really want a vector rotate and write-lane (or the other way
>>>> around). I think the special-case permutations can be recognised and coded
>>>> into the backend, but I don't know if we can easily tell that the first vector
>>>> is just a bunch of duplicates, when it's not constant.
>>>
>>> It's not actually a bunch of duplicates in all but the first iteration.
>>> But what you can recognize is that we're only using lane N - 1 of the
>>> first vector, so you could model the permute as extract last
>>> + shift in scalar (the extracted lane).  IIRC VLA vector targets usually
>>> have something like shift the vector and set the low lane from a
>>> scalar?
>>
>> Yeah.
>>
>>> The extract lane N - 1 might be more difficult but then
>>> a rotate plus extracting lane 0 might work as well.
>>
>> I guess for SVE we should probably use SPLICE, which joins two vectors
>> and uses a predicate to select the first element that should be extracted.
>>
>> Unfortunately we don't have a way of representing "last bit set, all other
>> bits clear" as a constant though, so I guess it'll have to be hidden
>> behind unspecs.
>>
>> I meant to start SVE tests running once I'd finished for the day yesterday,
>> but forgot, sorry.  Will try to test today.
>>
>> On the patch:
>>
>> +  /* This is the second phase of vectorizing first-order rececurrences. An
>> +     overview of the transformation is described below. Suppose we have the
>> +     following loop.
>> +
>> +     int32_t t = 0;
>> +     for (int i = 0; i < n; ++i)
>> +       {
>> +	b[i] = a[i] - t;
>> +	t = a[i];
>> +      }
>> +
>> +    There is a first-order recurrence on "a". For this loop, the shorthand
>> +    scalar IR looks like:
>> +
>> +    scalar.preheader:
>> +      init = a[-1]
>> +      br loop.body
>> +
>> +    scalar.body:
>> +      i = PHI <0(scalar.preheader), i+1(scalar.body)>
>> +      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
>> +      _1 = a[i]
>> +      b[i] = _1 - _2
>> +      br cond, scalar.body, ...
>> +
>> +    In this example, _2 is a recurrence because it's value depends on the
>> +    previous iteration. In the first phase of vectorization, we created a
>> +    temporary value for _2. We now complete the vectorization and produce the
>> +    shorthand vector IR shown below (VF = 4).
>> +
>> +    vector.preheader:
>> +      vect_init = vect_cst(..., ..., ..., a[-1])
>> +      br vector.body
>> +
>> +    vector.body
>> +      i = PHI <0(vector.preheader), i+4(vector.body)>
>> +      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
>> +      vect_2 = a[i, i+1, i+2, i+3];
>> +      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
>> +      b[i, i+1, i+2, i+3] = vect_2 - vect_3
>> +      br cond, vector.body, middle.block
>> +
>> +    middle.block:
>> +      x = vect_2(3)
>> +      br scalar.preheader
>> +
>> +    scalar.ph:
>> +      s_init = PHI <x(middle.block), a[-1], otherwise>
>> +      br scalar.body
>> +
>> +    After execution completes the vector loop, we extract the next value of
>> +    the recurrence (x) to use as the initial value in the scalar loop.  */
>>
>> Looks like a[-1] should be zero in the example (or t should be initialised
>> to a[-1]).
> 
> Indeed.  I've promoted the comment to function level and adjusted it
> to reflect what is done now (I've missed to update it from Ju-Zhes
> prototype).  I have also applied your correctness fix.
> 
> Re-bootstrap and regtest running on x86_64-unknown-linux-gnu.
> 
> OK (given limited x86 test quality)?

I've tested it on amdgcn and the vect-recurr tests all pass.

However the tsvc tests all fail because there's no definition of "struct 
timeval" without an "include <sys/time.h>". If I add that then they pass 
too. (Curiously, the timeval variables don't appear to be used anywhere, 
which is lucky because amdgcn doesn't have a working gettimeofday function.)

I can't claim any insight into the patch itself.

Andrew

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Richard Biener]

On Fri, 14 Oct 2022, Andrew Stubbs wrote:

> On 14/10/2022 08:07, Richard Biener wrote:
> > On Tue, 11 Oct 2022, Richard Sandiford wrote:
> > 
> >> Richard Biener <rguenther@suse.de> writes:
> >>> On Mon, 10 Oct 2022, Andrew Stubbs wrote:
> >>>> On 10/10/2022 12:03, Richard Biener wrote:
> >>>>> The following picks up the prototype by Ju-Zhe Zhong for vectorizing
> >>>>> first order recurrences.  That solves two TSVC missed optimization PRs.
> >>>>>
> >>>>> There's a new scalar cycle def kind, vect_first_order_recurrence
> >>>>> and it's handling of the backedge value vectorization is complicated
> >>>>> by the fact that the vectorized value isn't the PHI but instead
> >>>>> a (series of) permute(s) shifting in the recurring value from the
> >>>>> previous iteration.  I've implemented this by creating both the
> >>>>> single vectorized PHI and the series of permutes when vectorizing
> >>>>> the scalar PHI but leave the backedge values in both unassigned.
> >>>>> The backedge values are (for the testcases) computed by a load
> >>>>> which is also the place after which the permutes are inserted.
> >>>>> That placement also restricts the cases we can handle (without
> >>>>> resorting to code motion).
> >>>>>
> >>>>> I added both costing and SLP handling though SLP handling is
> >>>>> restricted to the case where a single vectorized PHI is enough.
> >>>>>
> >>>>> Missing is epilogue handling - while prologue peeling would
> >>>>> be handled transparently by adjusting iv_phi_p the epilogue
> >>>>> case doesn't work with just inserting a scalar LC PHI since
> >>>>> that a) keeps the scalar load live and b) that loads is the
> >>>>> wrong one, it has to be the last, much like when we'd vectorize
> >>>>> the LC PHI as live operation.  Unfortunately LIVE
> >>>>> compute/analysis happens too early before we decide on
> >>>>> peeling.  When using fully masked loop vectorization the
> >>>>> vect-recurr-6.c works as expected though.
> >>>>>
> >>>>> I have tested this on x86_64 for now, but since epilogue
> >>>>> handling is missing there's probably no practical cases.
> >>>>> My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
> >>>>> just fine but I didn't feel like running SPEC within SDE nor
> >>>>> is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
> >>>>> with fully masked loops succeed (minus three cases of
> >>>>> PR107096, caused by my WHILE_ULT prototype).
> >>>>>
> >>>>> Bootstrapped and tested on x86_64-unknown-linux-gnu.
> >>>>>
> >>>>> Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
> >>>>> handle epilogues welcome.
> >>>>
> >>>> The testcases all produce correct code on GCN and pass the execution
> >>>> tests.
> >>>>
> >>>> The code isn't terribly optimal because we don't have a two-input
> >>>> permutation
> >>>> instruction, so we permute each half separately and vec_merge the
> >>>> results. In
> >>>> this case the first vector is always a no-op permutation so that's wasted
> >>>> cycles. We'd really want a vector rotate and write-lane (or the other way
> >>>> around). I think the special-case permutations can be recognised and
> >>>> coded
> >>>> into the backend, but I don't know if we can easily tell that the first
> >>>> vector
> >>>> is just a bunch of duplicates, when it's not constant.
> >>>
> >>> It's not actually a bunch of duplicates in all but the first iteration.
> >>> But what you can recognize is that we're only using lane N - 1 of the
> >>> first vector, so you could model the permute as extract last
> >>> + shift in scalar (the extracted lane).  IIRC VLA vector targets usually
> >>> have something like shift the vector and set the low lane from a
> >>> scalar?
> >>
> >> Yeah.
> >>
> >>> The extract lane N - 1 might be more difficult but then
> >>> a rotate plus extracting lane 0 might work as well.
> >>
> >> I guess for SVE we should probably use SPLICE, which joins two vectors
> >> and uses a predicate to select the first element that should be extracted.
> >>
> >> Unfortunately we don't have a way of representing "last bit set, all other
> >> bits clear" as a constant though, so I guess it'll have to be hidden
> >> behind unspecs.
> >>
> >> I meant to start SVE tests running once I'd finished for the day yesterday,
> >> but forgot, sorry.  Will try to test today.
> >>
> >> On the patch:
> >>
> >> +  /* This is the second phase of vectorizing first-order rececurrences. An
> >> +     overview of the transformation is described below. Suppose we have
> >> the
> >> +     following loop.
> >> +
> >> +     int32_t t = 0;
> >> +     for (int i = 0; i < n; ++i)
> >> +       {
> >> +	b[i] = a[i] - t;
> >> +	t = a[i];
> >> +      }
> >> +
> >> +    There is a first-order recurrence on "a". For this loop, the shorthand
> >> +    scalar IR looks like:
> >> +
> >> +    scalar.preheader:
> >> +      init = a[-1]
> >> +      br loop.body
> >> +
> >> +    scalar.body:
> >> +      i = PHI <0(scalar.preheader), i+1(scalar.body)>
> >> +      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
> >> +      _1 = a[i]
> >> +      b[i] = _1 - _2
> >> +      br cond, scalar.body, ...
> >> +
> >> +    In this example, _2 is a recurrence because it's value depends on the
> >> +    previous iteration. In the first phase of vectorization, we created a
> >> +    temporary value for _2. We now complete the vectorization and produce
> >> the
> >> +    shorthand vector IR shown below (VF = 4).
> >> +
> >> +    vector.preheader:
> >> +      vect_init = vect_cst(..., ..., ..., a[-1])
> >> +      br vector.body
> >> +
> >> +    vector.body
> >> +      i = PHI <0(vector.preheader), i+4(vector.body)>
> >> +      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
> >> +      vect_2 = a[i, i+1, i+2, i+3];
> >> +      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
> >> +      b[i, i+1, i+2, i+3] = vect_2 - vect_3
> >> +      br cond, vector.body, middle.block
> >> +
> >> +    middle.block:
> >> +      x = vect_2(3)
> >> +      br scalar.preheader
> >> +
> >> +    scalar.ph:
> >> +      s_init = PHI <x(middle.block), a[-1], otherwise>
> >> +      br scalar.body
> >> +
> >> +    After execution completes the vector loop, we extract the next value
> >> of
> >> +    the recurrence (x) to use as the initial value in the scalar loop.  */
> >>
> >> Looks like a[-1] should be zero in the example (or t should be initialised
> >> to a[-1]).
> > 
> > Indeed.  I've promoted the comment to function level and adjusted it
> > to reflect what is done now (I've missed to update it from Ju-Zhes
> > prototype).  I have also applied your correctness fix.
> > 
> > Re-bootstrap and regtest running on x86_64-unknown-linux-gnu.
> > 
> > OK (given limited x86 test quality)?
> 
> I've tested it on amdgcn and the vect-recurr tests all pass.
> 
> However the tsvc tests all fail because there's no definition of "struct
> timeval" without an "include <sys/time.h>". If I add that then they pass too.
> (Curiously, the timeval variables don't appear to be used anywhere, which is
> lucky because amdgcn doesn't have a working gettimeofday function.)

Ah, that's probably from tsvc.h which is included by all tests which
uses struct timeval but doesn't include any header defining it.  It
also looks like the members are unused.

Martin - can you have a look into that issue?

Thanks,
Richard.

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Richard Sandiford]

Richard Biener <rguenther@suse.de> writes:
> On Tue, 11 Oct 2022, Richard Sandiford wrote:
>
>> Richard Biener <rguenther@suse.de> writes:
>> > On Mon, 10 Oct 2022, Andrew Stubbs wrote:
>> >> On 10/10/2022 12:03, Richard Biener wrote:
>> >> > The following picks up the prototype by Ju-Zhe Zhong for vectorizing
>> >> > first order recurrences.  That solves two TSVC missed optimization PRs.
>> >> > 
>> >> > There's a new scalar cycle def kind, vect_first_order_recurrence
>> >> > and it's handling of the backedge value vectorization is complicated
>> >> > by the fact that the vectorized value isn't the PHI but instead
>> >> > a (series of) permute(s) shifting in the recurring value from the
>> >> > previous iteration.  I've implemented this by creating both the
>> >> > single vectorized PHI and the series of permutes when vectorizing
>> >> > the scalar PHI but leave the backedge values in both unassigned.
>> >> > The backedge values are (for the testcases) computed by a load
>> >> > which is also the place after which the permutes are inserted.
>> >> > That placement also restricts the cases we can handle (without
>> >> > resorting to code motion).
>> >> > 
>> >> > I added both costing and SLP handling though SLP handling is
>> >> > restricted to the case where a single vectorized PHI is enough.
>> >> > 
>> >> > Missing is epilogue handling - while prologue peeling would
>> >> > be handled transparently by adjusting iv_phi_p the epilogue
>> >> > case doesn't work with just inserting a scalar LC PHI since
>> >> > that a) keeps the scalar load live and b) that loads is the
>> >> > wrong one, it has to be the last, much like when we'd vectorize
>> >> > the LC PHI as live operation.  Unfortunately LIVE
>> >> > compute/analysis happens too early before we decide on
>> >> > peeling.  When using fully masked loop vectorization the
>> >> > vect-recurr-6.c works as expected though.
>> >> > 
>> >> > I have tested this on x86_64 for now, but since epilogue
>> >> > handling is missing there's probably no practical cases.
>> >> > My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
>> >> > just fine but I didn't feel like running SPEC within SDE nor
>> >> > is the WHILE_ULT patch complete enough.  Builds of SPEC 2k7
>> >> > with fully masked loops succeed (minus three cases of
>> >> > PR107096, caused by my WHILE_ULT prototype).
>> >> > 
>> >> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
>> >> > 
>> >> > Testing with SVE, GCN or RVV appreciated, ideas how to cleanly
>> >> > handle epilogues welcome.
>> >> 
>> >> The testcases all produce correct code on GCN and pass the execution tests.
>> >> 
>> >> The code isn't terribly optimal because we don't have a two-input permutation
>> >> instruction, so we permute each half separately and vec_merge the results. In
>> >> this case the first vector is always a no-op permutation so that's wasted
>> >> cycles. We'd really want a vector rotate and write-lane (or the other way
>> >> around). I think the special-case permutations can be recognised and coded
>> >> into the backend, but I don't know if we can easily tell that the first vector
>> >> is just a bunch of duplicates, when it's not constant.
>> >
>> > It's not actually a bunch of duplicates in all but the first iteration.
>> > But what you can recognize is that we're only using lane N - 1 of the
>> > first vector, so you could model the permute as extract last
>> > + shift in scalar (the extracted lane).  IIRC VLA vector targets usually
>> > have something like shift the vector and set the low lane from a
>> > scalar?
>> 
>> Yeah.
>> 
>> > The extract lane N - 1 might be more difficult but then
>> > a rotate plus extracting lane 0 might work as well.
>> 
>> I guess for SVE we should probably use SPLICE, which joins two vectors
>> and uses a predicate to select the first element that should be extracted.
>> 
>> Unfortunately we don't have a way of representing "last bit set, all other
>> bits clear" as a constant though, so I guess it'll have to be hidden
>> behind unspecs.
>> 
>> I meant to start SVE tests running once I'd finished for the day yesterday,
>> but forgot, sorry.  Will try to test today.
>> 
>> On the patch:
>> 
>> +  /* This is the second phase of vectorizing first-order rececurrences. An
>> +     overview of the transformation is described below. Suppose we have the
>> +     following loop.
>> +
>> +     int32_t t = 0;
>> +     for (int i = 0; i < n; ++i)
>> +       {
>> +	b[i] = a[i] - t;
>> +	t = a[i];
>> +      }
>> +
>> +    There is a first-order recurrence on "a". For this loop, the shorthand
>> +    scalar IR looks like:
>> +
>> +    scalar.preheader:
>> +      init = a[-1]
>> +      br loop.body
>> +
>> +    scalar.body:
>> +      i = PHI <0(scalar.preheader), i+1(scalar.body)>
>> +      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
>> +      _1 = a[i]
>> +      b[i] = _1 - _2
>> +      br cond, scalar.body, ...
>> +
>> +    In this example, _2 is a recurrence because it's value depends on the
>> +    previous iteration. In the first phase of vectorization, we created a
>> +    temporary value for _2. We now complete the vectorization and produce the
>> +    shorthand vector IR shown below (VF = 4).
>> +
>> +    vector.preheader:
>> +      vect_init = vect_cst(..., ..., ..., a[-1])
>> +      br vector.body
>> +
>> +    vector.body
>> +      i = PHI <0(vector.preheader), i+4(vector.body)>
>> +      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
>> +      vect_2 = a[i, i+1, i+2, i+3];
>> +      vect_3 = vector(vect_1(3), vect_2(0, 1, 2))
>> +      b[i, i+1, i+2, i+3] = vect_2 - vect_3
>> +      br cond, vector.body, middle.block
>> +
>> +    middle.block:
>> +      x = vect_2(3)
>> +      br scalar.preheader
>> +
>> +    scalar.ph:
>> +      s_init = PHI <x(middle.block), a[-1], otherwise>
>> +      br scalar.body
>> +
>> +    After execution completes the vector loop, we extract the next value of
>> +    the recurrence (x) to use as the initial value in the scalar loop.  */
>> 
>> Looks like a[-1] should be zero in the example (or t should be initialised
>> to a[-1]).
>
> Indeed.  I've promoted the comment to function level and adjusted it
> to reflect what is done now (I've missed to update it from Ju-Zhes
> prototype).  I have also applied your correctness fix.
>
> Re-bootstrap and regtest running on x86_64-unknown-linux-gnu.
>
> OK (given limited x86 test quality)?

LGTM FWIW.

Thanks,
Richard

>
> Thanks,
> Richard.
>
> From 054bb007b09334402f018a4b2b65aef150cd8182 Mon Sep 17 00:00:00 2001
> From: Richard Biener <rguenther@suse.de>
> Date: Thu, 6 Oct 2022 13:56:09 +0200
> Subject: [PATCH] Vectorization of first-order recurrences
> To: gcc-patches@gcc.gnu.org
>
> The following picks up the prototype by Ju-Zhe Zhong for vectorizing
> first order recurrences.  That solves two TSVC missed optimization PRs.
>
> There's a new scalar cycle def kind, vect_first_order_recurrence
> and it's handling of the backedge value vectorization is complicated
> by the fact that the vectorized value isn't the PHI but instead
> a (series of) permute(s) shifting in the recurring value from the
> previous iteration.  I've implemented this by creating both the
> single vectorized PHI and the series of permutes when vectorizing
> the scalar PHI but leave the backedge values in both unassigned.
> The backedge values are (for the testcases) computed by a load
> which is also the place after which the permutes are inserted.
> That placement also restricts the cases we can handle (without
> resorting to code motion).
>
> I added both costing and SLP handling though SLP handling is
> restricted to the case where a single vectorized PHI is enough.
>
> Missing is epilogue handling - while prologue peeling would
> be handled transparently by adjusting iv_phi_p the epilogue
> case doesn't work with just inserting a scalar LC PHI since
> that a) keeps the scalar load live and b) that loads is the
> wrong one, it has to be the last, much like when we'd vectorize
> the LC PHI as live operation.  Unfortunately LIVE
> compute/analysis happens too early before we decide on
> peeling.  When using fully masked loop vectorization the
> vect-recurr-6.c works as expected though.
>
> I have tested this on x86_64 for now, but since epilogue
> handling is missing there's probably no practical cases.
> My prototype WHILE_ULT AVX512 patch can handle vect-recurr-6.c
> just fine but I didn't feel like running SPEC within SDE nor
> is the WHILE_ULT patch complete enough.
>
> 	PR tree-optimization/99409
> 	PR tree-optimization/99394
> 	* tree-vectorizer.h (vect_def_type::vect_first_order_recurrence): Add.
> 	(stmt_vec_info_type::recurr_info_type): Likewise.
> 	(vectorizable_recurr): New function.
> 	* tree-vect-loop.cc (vect_phi_first_order_recurrence_p): New
> 	function.
> 	(vect_analyze_scalar_cycles_1): Look for first order
> 	recurrences.
> 	(vect_analyze_loop_operations): Handle them.
> 	(vect_transform_loop): Likewise.
> 	(vectorizable_recurr): New function.
> 	(maybe_set_vectorized_backedge_value): Handle the backedge value
> 	setting in the first order recurrence PHI and the permutes.
> 	* tree-vect-stmts.cc (vect_analyze_stmt): Handle first order
> 	recurrences.
> 	(vect_transform_stmt): Likewise.
> 	(vect_is_simple_use): Likewise.
> 	(vect_is_simple_use): Likewise.
> 	* tree-vect-slp.cc (vect_get_and_check_slp_defs): Likewise.
> 	(vect_build_slp_tree_2): Likewise.
> 	(vect_schedule_scc): Handle the backedge value setting in the
> 	first order recurrence PHI and the permutes.
>
> 	* gcc.dg/vect/vect-recurr-1.c: New testcase.
> 	* gcc.dg/vect/vect-recurr-2.c: Likewise.
> 	* gcc.dg/vect/vect-recurr-3.c: Likewise.
> 	* gcc.dg/vect/vect-recurr-4.c: Likewise.
> 	* gcc.dg/vect/vect-recurr-5.c: Likewise.
> 	* gcc.dg/vect/vect-recurr-6.c: Likewise.
> 	* gcc.dg/vect/tsvc/vect-tsvc-s252.c: Un-XFAIL.
> 	* gcc.dg/vect/tsvc/vect-tsvc-s254.c: Likewise.
> 	* gcc.dg/vect/tsvc/vect-tsvc-s291.c: Likewise.
>
> Co-authored-by: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
> ---
>  .../gcc.dg/vect/tsvc/vect-tsvc-s252.c         |   2 +-
>  .../gcc.dg/vect/tsvc/vect-tsvc-s254.c         |   2 +-
>  .../gcc.dg/vect/tsvc/vect-tsvc-s291.c         |   2 +-
>  gcc/testsuite/gcc.dg/vect/vect-recurr-1.c     |  38 +++
>  gcc/testsuite/gcc.dg/vect/vect-recurr-2.c     |  39 +++
>  gcc/testsuite/gcc.dg/vect/vect-recurr-3.c     |  39 +++
>  gcc/testsuite/gcc.dg/vect/vect-recurr-4.c     |  42 +++
>  gcc/testsuite/gcc.dg/vect/vect-recurr-5.c     |  43 +++
>  gcc/testsuite/gcc.dg/vect/vect-recurr-6.c     |  39 +++
>  gcc/tree-vect-loop.cc                         | 281 ++++++++++++++++--
>  gcc/tree-vect-slp.cc                          |  38 ++-
>  gcc/tree-vect-stmts.cc                        |  17 +-
>  gcc/tree-vectorizer.h                         |   4 +
>  13 files changed, 558 insertions(+), 28 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
>
> diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
> index f1302b60ae5..83eaa7a8ff5 100644
> --- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
> +++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s252.c
> @@ -40,4 +40,4 @@ int main (int argc, char **argv)
>    return 0;
>  }
>  
> -/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
> +/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
> index bdc8a01e2a5..06e9b0a849d 100644
> --- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
> +++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s254.c
> @@ -39,4 +39,4 @@ int main (int argc, char **argv)
>    return 0;
>  }
>  
> -/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
> +/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
> index 0b474c2e81a..91cdc121095 100644
> --- a/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
> +++ b/gcc/testsuite/gcc.dg/vect/tsvc/vect-tsvc-s291.c
> @@ -39,4 +39,4 @@ int main (int argc, char **argv)
>    return 0;
>  }
>  
> -/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { xfail *-*-* } } } */
> +/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
> new file mode 100644
> index 00000000000..6eb59fdf854
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-1.c
> @@ -0,0 +1,38 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target vect_int } */
> +
> +#include "tree-vect.h"
> +
> +void __attribute__((noipa))
> +foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
> +{
> +  int t = *c;
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      b[i] = a[i] - t;
> +      t = a[i];
> +    }
> +}
> +
> +int a[64], b[64];
> +
> +int
> +main ()
> +{
> +  check_vect ();
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      a[i] = i;
> +      __asm__ volatile ("" ::: "memory");
> +    }
> +  int c = 7;
> +  foo (a, b, &c);
> +  for (int i = 1; i < 64; ++i)
> +    if (b[i] != a[i] - a[i-1])
> +      abort ();
> +  if (b[0] != -7)
> +    abort ();
> +  return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
> new file mode 100644
> index 00000000000..97efaaa38bc
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-2.c
> @@ -0,0 +1,39 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target vect_int } */
> +
> +#include "tree-vect.h"
> +
> +void __attribute__((noipa))
> +foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
> +{
> +  int t = *c;
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      b[i] = a[i] - t;
> +      t = a[i];
> +    }
> +}
> +
> +int a[64];
> +short b[64];
> +
> +int
> +main ()
> +{
> +  check_vect ();
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      a[i] = i;
> +      __asm__ volatile ("" ::: "memory");
> +    }
> +  int c = 7;
> +  foo (a, b, &c);
> +  for (int i = 1; i < 64; ++i)
> +    if (b[i] != a[i] - a[i-1])
> +      abort ();
> +  if (b[0] != -7)
> +    abort ();
> +  return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
> new file mode 100644
> index 00000000000..621a5d8a257
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-3.c
> @@ -0,0 +1,39 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target vect_int } */
> +
> +#include "tree-vect.h"
> +
> +void __attribute__((noipa))
> +foo (int * __restrict__ a, signed char * __restrict__ b, int * __restrict__ c)
> +{
> +  int t = *c;
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      b[i] = a[i] - t;
> +      t = a[i];
> +    }
> +}
> +
> +int a[64];
> +signed char b[64];
> +
> +int
> +main ()
> +{
> +  check_vect ();
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      a[i] = i;
> +      __asm__ volatile ("" ::: "memory");
> +    }
> +  int c = 7;
> +  foo (a, b, &c);
> +  for (int i = 1; i < 64; ++i)
> +    if (b[i] != a[i] - a[i-1])
> +      abort ();
> +  if (b[0] != -7)
> +    abort ();
> +  return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
> new file mode 100644
> index 00000000000..f6dbc494a62
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-4.c
> @@ -0,0 +1,42 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target vect_int } */
> +
> +#include "tree-vect.h"
> +
> +void __attribute__((noipa))
> +foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c)
> +{
> +  int t1 = *c;
> +  int t2 = *c;
> +  for (int i = 0; i < 64; i+=2)
> +    {
> +      b[i] = a[i] - t1;
> +      t1 = a[i];
> +      b[i+1] = a[i+1] - t2;
> +      t2 = a[i+1];
> +    }
> +}
> +
> +int a[64], b[64];
> +
> +int
> +main ()
> +{
> +  check_vect ();
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      a[i] = i;
> +      __asm__ volatile ("" ::: "memory");
> +    }
> +  int c = 7;
> +  foo (a, b, &c);
> +  for (int i = 2; i < 64; i+=2)
> +    if (b[i] != a[i] - a[i-2]
> +	|| b[i+1] != a[i+1] - a[i-1])
> +      abort ();
> +  if (b[0] != -7 || b[1] != -6)
> +    abort ();
> +  return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
> new file mode 100644
> index 00000000000..19c56df9e83
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-5.c
> @@ -0,0 +1,43 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target vect_int } */
> +
> +#include "tree-vect.h"
> +
> +void __attribute__((noipa))
> +foo (int * __restrict__ a, short * __restrict__ b, int * __restrict__ c)
> +{
> +  int t1 = *c;
> +  int t2 = *c;
> +  for (int i = 0; i < 64; i+=2)
> +    {
> +      b[i] = a[i] - t1;
> +      t1 = a[i];
> +      b[i+1] = a[i+1] - t2;
> +      t2 = a[i+1];
> +    }
> +}
> +
> +int a[64];
> +short b[64];
> +
> +int
> +main ()
> +{
> +  check_vect ();
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      a[i] = i;
> +      __asm__ volatile ("" ::: "memory");
> +    }
> +  int c = 7;
> +  foo (a, b, &c);
> +  for (int i = 2; i < 64; i+=2)
> +    if (b[i] != a[i] - a[i-2]
> +	|| b[i+1] != a[i+1] - a[i-1])
> +      abort ();
> +  if (b[0] != -7 || b[1] != -6)
> +    abort ();
> +  return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
> new file mode 100644
> index 00000000000..e7712680853
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/vect-recurr-6.c
> @@ -0,0 +1,39 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target vect_int } */
> +
> +#include "tree-vect.h"
> +
> +void __attribute__((noipa))
> +foo (int * __restrict__ a, int * __restrict__ b, int * __restrict__ c, int n)
> +{
> +  int t = *c;
> +  for (int i = 0; i < n; ++i)
> +    {
> +      b[i] = a[i] - t;
> +      t = a[i];
> +    }
> +}
> +
> +int a[64], b[64];
> +
> +int
> +main ()
> +{
> +  check_vect ();
> +  for (int i = 0; i < 64; ++i)
> +    {
> +      a[i] = i;
> +      __asm__ volatile ("" ::: "memory");
> +    }
> +  int c = 7;
> +  foo (a, b, &c, 63);
> +  for (int i = 1; i < 63; ++i)
> +    if (b[i] != a[i] - a[i-1])
> +      abort ();
> +  if (b[0] != -7)
> +    abort ();
> +  return 0;
> +}
> +
> +/* ???  We miss epilogue handling for first order recurrences.  */
> +/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" { target vect_fully_masked } } } */
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index 98a943d8a4b..63e86540d12 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -529,6 +529,45 @@ vect_inner_phi_in_double_reduction_p (loop_vec_info loop_vinfo, gphi *phi)
>    return false;
>  }
>  
> +/* Returns true if Phi is a first-order recurrence. A first-order
> +   recurrence is a non-reduction recurrence relation in which the value of
> +   the recurrence in the current loop iteration equals a value defined in
> +   the previous iteration.  */
> +
> +static bool
> +vect_phi_first_order_recurrence_p (loop_vec_info loop_vinfo, class loop *loop,
> +				   gphi *phi)
> +{
> +  /* Ensure the loop latch definition is from within the loop.  */
> +  edge latch = loop_latch_edge (loop);
> +  tree ldef = PHI_ARG_DEF_FROM_EDGE (phi, latch);
> +  if (TREE_CODE (ldef) != SSA_NAME
> +      || SSA_NAME_IS_DEFAULT_DEF (ldef)
> +      || !flow_bb_inside_loop_p (loop, gimple_bb (SSA_NAME_DEF_STMT (ldef))))
> +    return false;
> +
> +  tree def = gimple_phi_result (phi);
> +
> +  /* Ensure every use_stmt of the phi node is dominated by the latch
> +     definition.  */
> +  imm_use_iterator imm_iter;
> +  use_operand_p use_p;
> +  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, def)
> +    if (!is_gimple_debug (USE_STMT (use_p))
> +	&& (SSA_NAME_DEF_STMT (ldef) == USE_STMT (use_p)
> +	    || !vect_stmt_dominates_stmt_p (SSA_NAME_DEF_STMT (ldef),
> +					    USE_STMT (use_p))))
> +      return false;
> +
> +  /* First-order recurrence autovectorization needs shuffle vector.  */
> +  tree scalar_type = TREE_TYPE (def);
> +  tree vectype = get_vectype_for_scalar_type (loop_vinfo, scalar_type);
> +  if (!vectype)
> +    return false;
> +
> +  return true;
> +}
> +
>  /* Function vect_analyze_scalar_cycles_1.
>  
>     Examine the cross iteration def-use cycles of scalar variables
> @@ -666,6 +705,8 @@ vect_analyze_scalar_cycles_1 (loop_vec_info loop_vinfo, class loop *loop,
>                  }
>              }
>          }
> +      else if (vect_phi_first_order_recurrence_p (loop_vinfo, loop, phi))
> +	STMT_VINFO_DEF_TYPE (stmt_vinfo) = vect_first_order_recurrence;
>        else
>          if (dump_enabled_p ())
>            dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> @@ -1810,7 +1851,8 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
>  
>            if ((STMT_VINFO_RELEVANT (stmt_info) == vect_used_in_scope
>                 || STMT_VINFO_LIVE_P (stmt_info))
> -              && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def)
> +	      && STMT_VINFO_DEF_TYPE (stmt_info) != vect_induction_def
> +	      && STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
>  	    /* A scalar-dependence cycle that we don't support.  */
>  	    return opt_result::failure_at (phi,
>  					   "not vectorized:"
> @@ -1831,6 +1873,11 @@ vect_analyze_loop_operations (loop_vec_info loop_vinfo)
>  		       && ! PURE_SLP_STMT (stmt_info))
>  		ok = vectorizable_reduction (loop_vinfo,
>  					     stmt_info, NULL, NULL, &cost_vec);
> +	      else if ((STMT_VINFO_DEF_TYPE (stmt_info)
> +			== vect_first_order_recurrence)
> +		       && ! PURE_SLP_STMT (stmt_info))
> +		ok = vectorizable_recurr (loop_vinfo, stmt_info, NULL, NULL,
> +					   &cost_vec);
>              }
>  
>  	  /* SLP PHIs are tested by vect_slp_analyze_node_operations.  */
> @@ -8290,6 +8337,178 @@ vectorizable_phi (vec_info *,
>    return true;
>  }
>  
> +/* Vectorizes first order recurrences.  An overview of the transformation
> +   is described below. Suppose we have the following loop.
> +
> +     int t = 0;
> +     for (int i = 0; i < n; ++i)
> +       {
> +	 b[i] = a[i] - t;
> +	 t = a[i];
> +       }
> +
> +   There is a first-order recurrence on 'a'. For this loop, the scalar IR
> +   looks (simplified) like:
> +
> +    scalar.preheader:
> +      init = 0;
> +
> +    scalar.body:
> +      i = PHI <0(scalar.preheader), i+1(scalar.body)>
> +      _2 = PHI <(init(scalar.preheader), <_1(scalar.body)>
> +      _1 = a[i]
> +      b[i] = _1 - _2
> +      if (i < n) goto scalar.body
> +
> +   In this example, _2 is a recurrence because it's value depends on the
> +   previous iteration.  We vectorize this as (VF = 4)
> +
> +    vector.preheader:
> +      vect_init = vect_cst(..., ..., ..., 0)
> +
> +    vector.body
> +      i = PHI <0(vector.preheader), i+4(vector.body)>
> +      vect_1 = PHI <vect_init(vector.preheader), v2(vector.body)>
> +      vect_2 = a[i, i+1, i+2, i+3];
> +      vect_3 = vec_perm (vect_1, vect_2, { 3, 4, 5, 6 })
> +      b[i, i+1, i+2, i+3] = vect_2 - vect_3
> +      if (..) goto vector.body
> +
> +   In this function, vectorizable_recurr, we code generate both the
> +   vector PHI node and the permute since those together compute the
> +   vectorized value of the scalar PHI.  We do not yet have the
> +   backedge value to fill in there nor into the vec_perm.  Those
> +   are filled in maybe_set_vectorized_backedge_value and
> +   vect_schedule_scc.
> +
> +   TODO:  Since the scalar loop does not have a use of the recurrence
> +   outside of the loop the natural way to implement peeling via
> +   vectorizing the live value doesn't work.  For now peeling of loops
> +   with a recurrence is not implemented.  For SLP the supported cases
> +   are restricted to those requiring a single vector recurrence PHI.  */
> +
> +bool
> +vectorizable_recurr (loop_vec_info loop_vinfo, stmt_vec_info stmt_info,
> +		     gimple **vec_stmt, slp_tree slp_node,
> +		     stmt_vector_for_cost *cost_vec)
> +{
> +  if (!loop_vinfo || !is_a<gphi *> (stmt_info->stmt))
> +    return false;
> +
> +  gphi *phi = as_a<gphi *> (stmt_info->stmt);
> +
> +  /* So far we only support first-order recurrence auto-vectorization.  */
> +  if (STMT_VINFO_DEF_TYPE (stmt_info) != vect_first_order_recurrence)
> +    return false;
> +
> +  tree vectype = STMT_VINFO_VECTYPE (stmt_info);
> +  unsigned ncopies;
> +  if (slp_node)
> +    ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
> +  else
> +    ncopies = vect_get_num_copies (loop_vinfo, vectype);
> +  poly_int64 nunits = TYPE_VECTOR_SUBPARTS (vectype);
> +  unsigned dist = slp_node ? SLP_TREE_LANES (slp_node) : 1;
> +  /* We need to be able to make progress with a single vector.  */
> +  if (maybe_gt (dist * 2, nunits))
> +    {
> +      if (dump_enabled_p ())
> +	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> +			 "first order recurrence exceeds half of "
> +			 "a vector\n");
> +      return false;
> +    }
> +
> +  /* First-order recurrence autovectorization needs to handle permutation
> +     with indices = [nunits-1, nunits, nunits+1, ...].  */
> +  vec_perm_builder sel (nunits, 1, 3);
> +  for (int i = 0; i < 3; ++i)
> +    sel.quick_push (nunits - dist + i);
> +  vec_perm_indices indices (sel, 2, nunits);
> +
> +  if (!vec_stmt) /* transformation not required.  */
> +    {
> +      if (!can_vec_perm_const_p (TYPE_MODE (vectype), TYPE_MODE (vectype),
> +				 indices))
> +	return false;
> +
> +      if (slp_node)
> +	{
> +	  /* We eventually need to set a vector type on invariant
> +	     arguments.  */
> +	  unsigned j;
> +	  slp_tree child;
> +	  FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (slp_node), j, child)
> +	    if (!vect_maybe_update_slp_op_vectype
> +		  (child, SLP_TREE_VECTYPE (slp_node)))
> +	      {
> +		if (dump_enabled_p ())
> +		  dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> +				   "incompatible vector types for "
> +				   "invariants\n");
> +		return false;
> +	      }
> +	}
> +      /* The recurrence costs the initialization vector and one permute
> +	 for each copy.  */
> +      unsigned prologue_cost = record_stmt_cost (cost_vec, 1, scalar_to_vec,
> +						 stmt_info, 0, vect_prologue);
> +      unsigned inside_cost = record_stmt_cost (cost_vec, ncopies, vector_stmt,
> +					       stmt_info, 0, vect_body);
> +      if (dump_enabled_p ())
> +	dump_printf_loc (MSG_NOTE, vect_location,
> +			 "vectorizable_recurr: inside_cost = %d, "
> +			 "prologue_cost = %d .\n", inside_cost,
> +			 prologue_cost);
> +
> +      STMT_VINFO_TYPE (stmt_info) = recurr_info_type;
> +      return true;
> +    }
> +
> +  edge pe = loop_preheader_edge (LOOP_VINFO_LOOP (loop_vinfo));
> +  basic_block bb = gimple_bb (phi);
> +  tree preheader = PHI_ARG_DEF_FROM_EDGE (phi, pe);
> +  tree vec_init = build_vector_from_val (vectype, preheader);
> +  vec_init = vect_init_vector (loop_vinfo, stmt_info, vec_init, vectype, NULL);
> +
> +  /* Create the vectorized first-order PHI node.  */
> +  tree vec_dest = vect_get_new_vect_var (vectype,
> +					 vect_simple_var, "vec_recur_");
> +  gphi *new_phi = create_phi_node (vec_dest, bb);
> +  add_phi_arg (new_phi, vec_init, pe, UNKNOWN_LOCATION);
> +
> +  /* Insert shuffles the first-order recurrence autovectorization.
> +       result = VEC_PERM <vec_recur, vect_1, index[nunits-1, nunits, ...]>.  */
> +  tree perm = vect_gen_perm_mask_checked (vectype, indices);
> +
> +  /* Insert the required permute after the latch definition.  The
> +     second and later operands are tentative and will be updated when we have
> +     vectorized the latch definition.  */
> +  edge le = loop_latch_edge (LOOP_VINFO_LOOP (loop_vinfo));
> +  gimple_stmt_iterator gsi2
> +    = gsi_for_stmt (SSA_NAME_DEF_STMT (PHI_ARG_DEF_FROM_EDGE (phi, le)));
> +  gsi_next (&gsi2);
> +
> +  for (unsigned i = 0; i < ncopies; ++i)
> +    {
> +      vec_dest = make_ssa_name (vectype);
> +      gassign *vperm
> +	  = gimple_build_assign (vec_dest, VEC_PERM_EXPR,
> +				 i == 0 ? gimple_phi_result (new_phi) : NULL,
> +				 NULL, perm);
> +      vect_finish_stmt_generation (loop_vinfo, stmt_info, vperm, &gsi2);
> +
> +      if (slp_node)
> +	SLP_TREE_VEC_STMTS (slp_node).quick_push (vperm);
> +      else
> +	STMT_VINFO_VEC_STMTS (stmt_info).safe_push (vperm);
> +    }
> +
> +  if (!slp_node)
> +    *vec_stmt = STMT_VINFO_VEC_STMTS (stmt_info)[0];
> +  return true;
> +}
> +
>  /* Return true if VECTYPE represents a vector that requires lowering
>     by the vector lowering pass.  */
>  
> @@ -10242,27 +10461,53 @@ maybe_set_vectorized_backedge_value (loop_vec_info loop_vinfo,
>    imm_use_iterator iter;
>    use_operand_p use_p;
>    FOR_EACH_IMM_USE_FAST (use_p, iter, def)
> -    if (gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p)))
> -      if (gimple_bb (phi)->loop_father->header == gimple_bb (phi)
> -	  && (phi_info = loop_vinfo->lookup_stmt (phi))
> -	  && STMT_VINFO_RELEVANT_P (phi_info)
> -	  && VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
> +    {
> +      gphi *phi = dyn_cast <gphi *> (USE_STMT (use_p));
> +      if (!phi)
> +	continue;
> +      if (!(gimple_bb (phi)->loop_father->header == gimple_bb (phi)
> +	    && (phi_info = loop_vinfo->lookup_stmt (phi))
> +	    && STMT_VINFO_RELEVANT_P (phi_info)))
> +	continue;
> +      loop_p loop = gimple_bb (phi)->loop_father;
> +      edge e = loop_latch_edge (loop);
> +      if (PHI_ARG_DEF_FROM_EDGE (phi, e) != def)
> +	continue;
> +
> +      if (VECTORIZABLE_CYCLE_DEF (STMT_VINFO_DEF_TYPE (phi_info))
>  	  && STMT_VINFO_REDUC_TYPE (phi_info) != FOLD_LEFT_REDUCTION
>  	  && STMT_VINFO_REDUC_TYPE (phi_info) != EXTRACT_LAST_REDUCTION)
>  	{
> -	  loop_p loop = gimple_bb (phi)->loop_father;
> -	  edge e = loop_latch_edge (loop);
> -	  if (PHI_ARG_DEF_FROM_EDGE (phi, e) == def)
> +	  vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
> +	  vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
> +	  gcc_assert (phi_defs.length () == latch_defs.length ());
> +	  for (unsigned i = 0; i < phi_defs.length (); ++i)
> +	    add_phi_arg (as_a <gphi *> (phi_defs[i]),
> +			 gimple_get_lhs (latch_defs[i]), e,
> +			 gimple_phi_arg_location (phi, e->dest_idx));
> +	}
> +      else if (STMT_VINFO_DEF_TYPE (phi_info) == vect_first_order_recurrence)
> +	{
> +	  /* For first order recurrences we have to update both uses of
> +	     the latch definition, the one in the PHI node and the one
> +	     in the generated VEC_PERM_EXPR.  */
> +	  vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
> +	  vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
> +	  gcc_assert (phi_defs.length () == latch_defs.length ());
> +	  tree phidef = gimple_assign_rhs1 (phi_defs[0]);
> +	  gphi *vphi = as_a <gphi *> (SSA_NAME_DEF_STMT (phidef));
> +	  for (unsigned i = 0; i < phi_defs.length (); ++i)
>  	    {
> -	      vec<gimple *> &phi_defs = STMT_VINFO_VEC_STMTS (phi_info);
> -	      vec<gimple *> &latch_defs = STMT_VINFO_VEC_STMTS (def_stmt_info);
> -	      gcc_assert (phi_defs.length () == latch_defs.length ());
> -	      for (unsigned i = 0; i < phi_defs.length (); ++i)
> -		add_phi_arg (as_a <gphi *> (phi_defs[i]),
> -			     gimple_get_lhs (latch_defs[i]), e,
> -			     gimple_phi_arg_location (phi, e->dest_idx));
> +	      gassign *perm = as_a <gassign *> (phi_defs[i]);
> +	      if (i > 0)
> +		gimple_assign_set_rhs1 (perm, gimple_get_lhs (latch_defs[i-1]));
> +	      gimple_assign_set_rhs2 (perm, gimple_get_lhs (latch_defs[i]));
> +	      update_stmt (perm);
>  	    }
> +	  add_phi_arg (vphi, gimple_get_lhs (latch_defs.last ()), e,
> +		       gimple_phi_arg_location (phi, e->dest_idx));
>  	}
> +    }
>  }
>  
>  /* Vectorize STMT_INFO if relevant, inserting any new instructions before GSI.
> @@ -10671,6 +10916,7 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
>  	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
>  	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
>  	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
> +	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence
>  	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
>  	      && ! PURE_SLP_STMT (stmt_info))
>  	    {
> @@ -10696,7 +10942,8 @@ vect_transform_loop (loop_vec_info loop_vinfo, gimple *loop_vectorized_call)
>  	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
>  	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def
>  	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_nested_cycle
> -	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def)
> +	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def
> +	       || STMT_VINFO_DEF_TYPE (stmt_info) == vect_first_order_recurrence)
>  	      && ! PURE_SLP_STMT (stmt_info))
>  	    maybe_set_vectorized_backedge_value (loop_vinfo, stmt_info);
>  	}
> diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
> index 229f2663ebc..cea5d50da92 100644
> --- a/gcc/tree-vect-slp.cc
> +++ b/gcc/tree-vect-slp.cc
> @@ -693,6 +693,7 @@ vect_get_and_check_slp_defs (vec_info *vinfo, unsigned char swap,
>  	    case vect_reduction_def:
>  	    case vect_induction_def:
>  	    case vect_nested_cycle:
> +	    case vect_first_order_recurrence:
>  	      break;
>  
>  	    default:
> @@ -1732,7 +1733,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
>  	  }
>  	else if (def_type == vect_reduction_def
>  		 || def_type == vect_double_reduction_def
> -		 || def_type == vect_nested_cycle)
> +		 || def_type == vect_nested_cycle
> +		 || def_type == vect_first_order_recurrence)
>  	  {
>  	    /* Else def types have to match.  */
>  	    stmt_vec_info other_info;
> @@ -1746,7 +1748,8 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
>  	      }
>  	    class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
>  	    /* Reduction initial values are not explicitely represented.  */
> -	    if (!nested_in_vect_loop_p (loop, stmt_info))
> +	    if (def_type != vect_first_order_recurrence
> +		&& !nested_in_vect_loop_p (loop, stmt_info))
>  	      skip_args[loop_preheader_edge (loop)->dest_idx] = true;
>  	    /* Reduction chain backedge defs are filled manually.
>  	       ???  Need a better way to identify a SLP reduction chain PHI.
> @@ -9187,11 +9190,34 @@ vect_schedule_scc (vec_info *vinfo, slp_tree node, slp_instance instance,
>  	  child = SLP_TREE_CHILDREN (phi_node)[dest_idx];
>  	  if (!child || SLP_TREE_DEF_TYPE (child) != vect_internal_def)
>  	    continue;
> +	  unsigned n = SLP_TREE_VEC_STMTS (phi_node).length ();
>  	  /* Simply fill all args.  */
> -	  for (unsigned i = 0; i < SLP_TREE_VEC_STMTS (phi_node).length (); ++i)
> -	    add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
> -			 vect_get_slp_vect_def (child, i),
> -			 e, gimple_phi_arg_location (phi, dest_idx));
> +	  if (STMT_VINFO_DEF_TYPE (SLP_TREE_REPRESENTATIVE (phi_node))
> +	      != vect_first_order_recurrence)
> +	    for (unsigned i = 0; i < n; ++i)
> +	      add_phi_arg (as_a <gphi *> (SLP_TREE_VEC_STMTS (phi_node)[i]),
> +			   vect_get_slp_vect_def (child, i),
> +			   e, gimple_phi_arg_location (phi, dest_idx));
> +	  else
> +	    {
> +	      /* Unless it is a first order recurrence which needs
> +		 args filled in for both the PHI node and the permutes.  */
> +	      gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[0];
> +	      gimple *rphi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (perm));
> +	      add_phi_arg (as_a <gphi *> (rphi),
> +			   vect_get_slp_vect_def (child, n - 1),
> +			   e, gimple_phi_arg_location (phi, dest_idx));
> +	      for (unsigned i = 0; i < n; ++i)
> +		{
> +		  gimple *perm = SLP_TREE_VEC_STMTS (phi_node)[i];
> +		  if (i > 0)
> +		    gimple_assign_set_rhs1 (perm,
> +					    vect_get_slp_vect_def (child, i - 1));
> +		  gimple_assign_set_rhs2 (perm,
> +					  vect_get_slp_vect_def (child, i));
> +		  update_stmt (perm);
> +		}
> +	    }
>  	}
>      }
>  }
> diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
> index c8d1efc45e5..4e0d75e0d75 100644
> --- a/gcc/tree-vect-stmts.cc
> +++ b/gcc/tree-vect-stmts.cc
> @@ -11176,6 +11176,7 @@ vect_analyze_stmt (vec_info *vinfo,
>           break;
>  
>        case vect_induction_def:
> +      case vect_first_order_recurrence:
>  	gcc_assert (!bb_vinfo);
>  	break;
>  
> @@ -11234,7 +11235,9 @@ vect_analyze_stmt (vec_info *vinfo,
>  	  || vectorizable_comparison (vinfo, stmt_info, NULL, NULL, node,
>  				      cost_vec)
>  	  || vectorizable_lc_phi (as_a <loop_vec_info> (vinfo),
> -				  stmt_info, NULL, node));
> +				  stmt_info, NULL, node)
> +	  || vectorizable_recurr (as_a <loop_vec_info> (vinfo),
> +				   stmt_info, NULL, node, cost_vec));
>    else
>      {
>        if (bb_vinfo)
> @@ -11404,6 +11407,12 @@ vect_transform_stmt (vec_info *vinfo,
>        gcc_assert (done);
>        break;
>  
> +    case recurr_info_type:
> +      done = vectorizable_recurr (as_a <loop_vec_info> (vinfo),
> +				  stmt_info, &vec_stmt, slp_node, NULL);
> +      gcc_assert (done);
> +      break;
> +
>      case phi_info_type:
>        done = vectorizable_phi (vinfo, stmt_info, &vec_stmt, slp_node, NULL);
>        gcc_assert (done);
> @@ -11804,6 +11813,9 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
>  	case vect_nested_cycle:
>  	  dump_printf (MSG_NOTE, "nested cycle\n");
>  	  break;
> +	case vect_first_order_recurrence:
> +	  dump_printf (MSG_NOTE, "first order recurrence\n");
> +	  break;
>  	case vect_unknown_def_type:
>  	  dump_printf (MSG_NOTE, "unknown\n");
>  	  break;
> @@ -11852,7 +11864,8 @@ vect_is_simple_use (tree operand, vec_info *vinfo, enum vect_def_type *dt,
>        || *dt == vect_induction_def
>        || *dt == vect_reduction_def
>        || *dt == vect_double_reduction_def
> -      || *dt == vect_nested_cycle)
> +      || *dt == vect_nested_cycle
> +      || *dt == vect_first_order_recurrence)
>      {
>        *vectype = STMT_VINFO_VECTYPE (def_stmt_info);
>        gcc_assert (*vectype != NULL_TREE);
> diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
> index 4870c754499..016961da851 100644
> --- a/gcc/tree-vectorizer.h
> +++ b/gcc/tree-vectorizer.h
> @@ -65,6 +65,7 @@ enum vect_def_type {
>    vect_reduction_def,
>    vect_double_reduction_def,
>    vect_nested_cycle,
> +  vect_first_order_recurrence,
>    vect_unknown_def_type
>  };
>  
> @@ -1027,6 +1028,7 @@ enum stmt_vec_info_type {
>    cycle_phi_info_type,
>    lc_phi_info_type,
>    phi_info_type,
> +  recurr_info_type,
>    loop_exit_ctrl_vec_info_type
>  };
>  
> @@ -2331,6 +2333,8 @@ extern bool vectorizable_lc_phi (loop_vec_info, stmt_vec_info,
>  				 gimple **, slp_tree);
>  extern bool vectorizable_phi (vec_info *, stmt_vec_info, gimple **, slp_tree,
>  			      stmt_vector_for_cost *);
> +extern bool vectorizable_recurr (loop_vec_info, stmt_vec_info,
> +				  gimple **, slp_tree, stmt_vector_for_cost *);
>  extern bool vect_emulated_vector_p (tree);
>  extern bool vect_can_vectorize_without_simd_p (tree_code);
>  extern bool vect_can_vectorize_without_simd_p (code_helper);

Re: [PATCH][RFT] Vectorization of first-order recurrences

[Richard Biener]

On Tue, 11 Oct 2022, juzhe.zhong@rivai.ai wrote:

> Hi, I apply this patch in RVV downstrean. Tested it with a lot of vector benchmark. It overal has a greate performance gain.
> Maybe the last thing to merge this patch is wait for Richard Sandiford test it in ARM SVE?
> 
> By the way, would you mind sharing the case list that GCC failed to vectorize but Clang succeed ? 
> I am familiar with LLVM. I think I can do this job.

Sure - for (most of?) the TSVC tests GCC is failing to vectorize there
should be a bugzilla open.  So if you have TSVC tests that LLVM can
vectorize but GCC can not then check if there is a bugzilla open.
If so, note that LLVM can vectorize, if not, open one.

I have now pushed the change.

Thanks,
Richard.