[PATCH] Add emulated gather capability to the vectorizer

[Richard Biener <rguenther@suse.de>]

This adds a gather vectorization capability to the vectorizer
without target support by decomposing the offset vector, doing
sclar loads and then building a vector from the result.  This
is aimed mainly at cases where vectorizing the rest of the loop
offsets the cost of vectorizing the gather.

Note it's difficult to avoid vectorizing the offset load, but in
some cases later passes can turn the vector load + extract into
scalar loads, see the followup patch.

On SPEC CPU 2017 510.parest_r this improves runtime from 250s
to 219s on a Zen2 CPU which has its native gather instructions
disabled (using those the runtime instead increases to 254s)
using -Ofast -march=znver2 [-flto].  It turns out the critical
loops in this benchmark all perform gather operations.

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

Any comments?  I still plan to run this over full SPEC and
I have to apply TLC to the followup patch before I can post it.

I think neither power nor z has gather so I'm curious if the
patch helps 510.parest_r there, I'm unsure about neon/advsimd.
Both might need the followup patch - I was surprised about
the speedup without it on Zen (the followup improves runtime
to 198s there).

Thanks,
Richard.

2021-07-30  Richard Biener  <rguenther@suse.de>

	* tree-vect-data-refs.c (vect_check_gather_scatter):
	Include widening conversions only when the result is
	still handed by native gather or the current offset
	size not already matches the data size.
	Also succeed analysis in case there's no native support,
	noted by a IFN_LAST ifn and a NULL decl.
	* tree-vect-patterns.c (vect_recog_gather_scatter_pattern):
	Test for no IFN gather rather than decl gather.
	* tree-vect-stmts.c (vect_model_load_cost): Pass in the
	gather-scatter info and cost emulated gathers accordingly.
	(vect_truncate_gather_scatter_offset): Properly test for
	no IFN gather.
	(vect_use_strided_gather_scatters_p): Likewise.
	(get_load_store_type): Handle emulated gathers and its
	restrictions.
	(vectorizable_load): Likewise.  Emulate them by extracting
        scalar offsets, doing scalar loads and a vector construct.

	* gcc.target/i386/vect-gather-1.c: New testcase.
	* gfortran.dg/vect/vect-8.f90: Adjust.
---
 gcc/testsuite/gcc.target/i386/vect-gather-1.c |  18 ++++
 gcc/testsuite/gfortran.dg/vect/vect-8.f90     |   2 +-
 gcc/tree-vect-data-refs.c                     |  29 +++--
 gcc/tree-vect-patterns.c                      |   2 +-
 gcc/tree-vect-stmts.c                         | 100 ++++++++++++++++--
 5 files changed, 136 insertions(+), 15 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/vect-gather-1.c

diff --git a/gcc/testsuite/gcc.target/i386/vect-gather-1.c b/gcc/testsuite/gcc.target/i386/vect-gather-1.c
new file mode 100644
index 00000000000..134aef39666
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/vect-gather-1.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-Ofast -msse2 -fdump-tree-vect-details" } */
+
+#ifndef INDEXTYPE
+#define INDEXTYPE int
+#endif
+double vmul(INDEXTYPE *rowstart, INDEXTYPE *rowend,
+	    double *luval, double *dst)
+{
+  double res = 0;
+  for (const INDEXTYPE * col = rowstart; col != rowend; ++col, ++luval)
+        res += *luval * dst[*col];
+  return res;
+}
+
+/* With gather emulation this should be profitable to vectorize
+   even with plain SSE2.  */
+/* { dg-final { scan-tree-dump "loop vectorized" "vect" } } */
diff --git a/gcc/testsuite/gfortran.dg/vect/vect-8.f90 b/gcc/testsuite/gfortran.dg/vect/vect-8.f90
index 9994805d77f..cc1aebfbd84 100644
--- a/gcc/testsuite/gfortran.dg/vect/vect-8.f90
+++ b/gcc/testsuite/gfortran.dg/vect/vect-8.f90
@@ -706,5 +706,5 @@ END SUBROUTINE kernel
 
 ! { dg-final { scan-tree-dump-times "vectorized 24 loops" 1 "vect" { target aarch64_sve } } }
 ! { dg-final { scan-tree-dump-times "vectorized 23 loops" 1 "vect" { target { aarch64*-*-* && { ! aarch64_sve } } } } }
-! { dg-final { scan-tree-dump-times "vectorized 2\[23\] loops" 1 "vect" { target { vect_intdouble_cvt && { ! aarch64*-*-* } } } } }
+! { dg-final { scan-tree-dump-times "vectorized 2\[234\] loops" 1 "vect" { target { vect_intdouble_cvt && { ! aarch64*-*-* } } } } }
 ! { dg-final { scan-tree-dump-times "vectorized 17 loops" 1 "vect" { target { { ! vect_intdouble_cvt } && { ! aarch64*-*-* } } } } }
diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index 6995efba899..0279e75fa8e 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -4007,8 +4007,26 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
 	      continue;
 	    }
 
-	  if (TYPE_PRECISION (TREE_TYPE (op0))
-	      < TYPE_PRECISION (TREE_TYPE (off)))
+	  /* Include the conversion if it is widening and we're using
+	     the IFN path or the target can handle the converted from
+	     offset or the current size is not already the same as the
+	     data vector element size.  */
+	  if ((TYPE_PRECISION (TREE_TYPE (op0))
+	       < TYPE_PRECISION (TREE_TYPE (off)))
+	      && ((!use_ifn_p
+		   && (DR_IS_READ (dr)
+		       ? (targetm.vectorize.builtin_gather
+			  && targetm.vectorize.builtin_gather (vectype,
+							       TREE_TYPE (op0),
+							       scale))
+		       : (targetm.vectorize.builtin_scatter
+			  && targetm.vectorize.builtin_scatter (vectype,
+								TREE_TYPE (op0),
+								scale))))
+		  || (!use_ifn_p
+		      && !operand_equal_p (TYPE_SIZE (TREE_TYPE (off)),
+					   TYPE_SIZE (TREE_TYPE (vectype)),
+					   0))))
 	    {
 	      off = op0;
 	      offtype = TREE_TYPE (off);
@@ -4036,7 +4054,8 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
       if (!vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr), masked_p,
 				     vectype, memory_type, offtype, scale,
 				     &ifn, &offset_vectype))
-	return false;
+	ifn = IFN_LAST;
+      decl = NULL_TREE;
     }
   else
     {
@@ -4050,10 +4069,6 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
 	  if (targetm.vectorize.builtin_scatter)
 	    decl = targetm.vectorize.builtin_scatter (vectype, offtype, scale);
 	}
-
-      if (!decl)
-	return false;
-
       ifn = IFN_LAST;
       /* The offset vector type will be read from DECL when needed.  */
       offset_vectype = NULL_TREE;
diff --git a/gcc/tree-vect-patterns.c b/gcc/tree-vect-patterns.c
index 743fd3f5414..25de97bd9b0 100644
--- a/gcc/tree-vect-patterns.c
+++ b/gcc/tree-vect-patterns.c
@@ -4811,7 +4811,7 @@ vect_recog_gather_scatter_pattern (vec_info *vinfo,
      function for the gather/scatter operation.  */
   gather_scatter_info gs_info;
   if (!vect_check_gather_scatter (stmt_info, loop_vinfo, &gs_info)
-      || gs_info.decl)
+      || gs_info.ifn == IFN_LAST)
     return NULL;
 
   /* Convert the mask to the right form.  */
diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
index 05085e1b110..9d51b476db6 100644
--- a/gcc/tree-vect-stmts.c
+++ b/gcc/tree-vect-stmts.c
@@ -1084,6 +1084,7 @@ static void
 vect_model_load_cost (vec_info *vinfo,
 		      stmt_vec_info stmt_info, unsigned ncopies, poly_uint64 vf,
 		      vect_memory_access_type memory_access_type,
+		      gather_scatter_info *gs_info,
 		      slp_tree slp_node,
 		      stmt_vector_for_cost *cost_vec)
 {
@@ -1172,9 +1173,17 @@ vect_model_load_cost (vec_info *vinfo,
   if (memory_access_type == VMAT_ELEMENTWISE
       || memory_access_type == VMAT_GATHER_SCATTER)
     {
-      /* N scalar loads plus gathering them into a vector.  */
       tree vectype = STMT_VINFO_VECTYPE (stmt_info);
       unsigned int assumed_nunits = vect_nunits_for_cost (vectype);
+      if (memory_access_type == VMAT_GATHER_SCATTER
+	  && gs_info->ifn == IFN_LAST && !gs_info->decl)
+	/* For emulated gathers N offset vector element extracts
+	   (we assume the scalar scaling and ptr + offset add is consumed by
+	   the load).  */
+	inside_cost += record_stmt_cost (cost_vec, ncopies * assumed_nunits,
+					 vec_to_scalar, stmt_info, 0,
+					 vect_body);
+      /* N scalar loads plus gathering them into a vector.  */
       inside_cost += record_stmt_cost (cost_vec,
 				       ncopies * assumed_nunits,
 				       scalar_load, stmt_info, 0, vect_body);
@@ -1184,7 +1193,9 @@ vect_model_load_cost (vec_info *vinfo,
 			&inside_cost, &prologue_cost, 
 			cost_vec, cost_vec, true);
   if (memory_access_type == VMAT_ELEMENTWISE
-      || memory_access_type == VMAT_STRIDED_SLP)
+      || memory_access_type == VMAT_STRIDED_SLP
+      || (memory_access_type == VMAT_GATHER_SCATTER
+	  && gs_info->ifn == IFN_LAST && !gs_info->decl))
     inside_cost += record_stmt_cost (cost_vec, ncopies, vec_construct,
 				     stmt_info, 0, vect_body);
 
@@ -1866,7 +1877,8 @@ vect_truncate_gather_scatter_offset (stmt_vec_info stmt_info,
       tree memory_type = TREE_TYPE (DR_REF (dr));
       if (!vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr), masked_p,
 				     vectype, memory_type, offset_type, scale,
-				     &gs_info->ifn, &gs_info->offset_vectype))
+				     &gs_info->ifn, &gs_info->offset_vectype)
+	  || gs_info->ifn == IFN_LAST)
 	continue;
 
       gs_info->decl = NULL_TREE;
@@ -1901,7 +1913,7 @@ vect_use_strided_gather_scatters_p (stmt_vec_info stmt_info,
 				    gather_scatter_info *gs_info)
 {
   if (!vect_check_gather_scatter (stmt_info, loop_vinfo, gs_info)
-      || gs_info->decl)
+      || gs_info->ifn == IFN_LAST)
     return vect_truncate_gather_scatter_offset (stmt_info, loop_vinfo,
 						masked_p, gs_info);
 
@@ -2355,6 +2367,27 @@ get_load_store_type (vec_info  *vinfo, stmt_vec_info stmt_info,
 			     vls_type == VLS_LOAD ? "gather" : "scatter");
 	  return false;
 	}
+      else if (gs_info->ifn == IFN_LAST && !gs_info->decl)
+	{
+	  if (vls_type != VLS_LOAD)
+	    {
+	      if (dump_enabled_p ())
+		dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+				 "unsupported emulated scatter.\n");
+	      return false;
+	    }
+	  else if (!TYPE_VECTOR_SUBPARTS (vectype).is_constant ()
+		   || !known_eq (TYPE_VECTOR_SUBPARTS (vectype),
+				 TYPE_VECTOR_SUBPARTS
+				   (gs_info->offset_vectype)))
+	    {
+	      if (dump_enabled_p ())
+		dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+				 "unsupported vector types for emulated "
+				 "gather.\n");
+	      return false;
+	    }
+	}
       /* Gather-scatter accesses perform only component accesses, alignment
 	 is irrelevant for them.  */
       *alignment_support_scheme = dr_unaligned_supported;
@@ -8692,6 +8725,15 @@ vectorizable_load (vec_info *vinfo,
 			     "unsupported access type for masked load.\n");
 	  return false;
 	}
+      else if (memory_access_type == VMAT_GATHER_SCATTER
+	       && gs_info.ifn == IFN_LAST
+	       && !gs_info.decl)
+	{
+	  if (dump_enabled_p ())
+	    dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			     "unsupported masked emulated gather.\n");
+	  return false;
+	}
     }
 
   if (!vec_stmt) /* transformation not required.  */
@@ -8725,7 +8767,7 @@ vectorizable_load (vec_info *vinfo,
 
       STMT_VINFO_TYPE (orig_stmt_info) = load_vec_info_type;
       vect_model_load_cost (vinfo, stmt_info, ncopies, vf, memory_access_type,
-			    slp_node, cost_vec);
+			    &gs_info, slp_node, cost_vec);
       return true;
     }
 
@@ -9438,7 +9480,8 @@ vectorizable_load (vec_info *vinfo,
 		    unsigned int misalign;
 		    unsigned HOST_WIDE_INT align;
 
-		    if (memory_access_type == VMAT_GATHER_SCATTER)
+		    if (memory_access_type == VMAT_GATHER_SCATTER
+			&& gs_info.ifn != IFN_LAST)
 		      {
 			tree zero = build_zero_cst (vectype);
 			tree scale = size_int (gs_info.scale);
@@ -9456,6 +9499,51 @@ vectorizable_load (vec_info *vinfo,
 			data_ref = NULL_TREE;
 			break;
 		      }
+		    else if (memory_access_type == VMAT_GATHER_SCATTER)
+		      {
+			/* Emulated gather-scatter.  */
+			gcc_assert (!final_mask);
+			unsigned HOST_WIDE_INT const_nunits
+			  = nunits.to_constant ();
+			vec<constructor_elt, va_gc> *ctor_elts;
+			vec_alloc (ctor_elts, const_nunits);
+			gimple_seq stmts = NULL;
+			tree idx_type = TREE_TYPE (TREE_TYPE (vec_offset));
+			tree scale = size_int (gs_info.scale);
+			align
+			  = get_object_alignment (DR_REF (first_dr_info->dr));
+			tree ltype = build_aligned_type (TREE_TYPE (vectype),
+							 align);
+			for (unsigned k = 0; k < const_nunits; ++k)
+			  {
+			    tree boff = size_binop (MULT_EXPR,
+						    TYPE_SIZE (idx_type),
+						    bitsize_int (k));
+			    tree idx = gimple_build (&stmts, BIT_FIELD_REF,
+						     idx_type, vec_offset,
+						     TYPE_SIZE (idx_type),
+						     boff);
+			    idx = gimple_convert (&stmts, sizetype, idx);
+			    idx = gimple_build (&stmts, MULT_EXPR,
+						sizetype, idx, scale);
+			    tree ptr = gimple_build (&stmts, PLUS_EXPR,
+						     TREE_TYPE (dataref_ptr),
+						     dataref_ptr, idx);
+			    ptr = gimple_convert (&stmts, ptr_type_node, ptr);
+			    tree elt = make_ssa_name (TREE_TYPE (vectype));
+			    tree ref = build2 (MEM_REF, ltype, ptr,
+					       build_int_cst (ref_type, 0));
+			    new_stmt = gimple_build_assign (elt, ref);
+			    gimple_seq_add_stmt (&stmts, new_stmt);
+			    CONSTRUCTOR_APPEND_ELT (ctor_elts, NULL_TREE, elt);
+			  }
+			gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
+			new_stmt = gimple_build_assign (NULL_TREE,
+							build_constructor
+							  (vectype, ctor_elts));
+			data_ref = NULL_TREE;
+			break;
+		      }
 
 		    align =
 		      known_alignment (DR_TARGET_ALIGNMENT (first_dr_info));
-- 
2.31.1