[070/nnn] poly_int: vectorizable_reduction

[Richard Sandiford <richard.sandiford@linaro.org>]

This patch makes vectorizable_reduction cope with variable-length vectors.
We can handle the simple case of an inner loop reduction for which
the target has native support for the epilogue operation.  For now we
punt on other cases, but patches after the main SVE submission allow
SLP and double reductions too.


2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree.h (build_index_vector): Declare.
	* tree.c (build_index_vector): New function.
	* tree-vect-loop.c (get_initial_def_for_reduction): Treat the number
	of units as polynomial, forcibly converting it to a constant if
	vectorizable_reduction has already enforced the condition.
	(get_initial_defs_for_reduction): Likewise.
	(vect_create_epilog_for_reduction): Likewise.  Use build_index_vector
	to create a {1,2,3,...} vector.
	(vectorizable_reduction): Treat the number of units as polynomial.
	Choose vectype_in based on the largest scalar element size rather
	than the smallest number of units.  Enforce the restrictions
	relied on above.

Index: gcc/tree.h
===================================================================
--- gcc/tree.h	2017-10-23 17:22:32.736226191 +0100
+++ gcc/tree.h	2017-10-23 17:22:35.831905077 +0100
@@ -4050,6 +4050,7 @@ extern tree build_vector (tree, vec<tree
 extern tree build_vector_from_ctor (tree, vec<constructor_elt, va_gc> *);
 extern tree build_vector_from_val (tree, tree);
 extern tree build_vec_series (tree, tree, tree);
+extern tree build_index_vector (tree, poly_uint64, poly_uint64);
 extern void recompute_constructor_flags (tree);
 extern void verify_constructor_flags (tree);
 extern tree build_constructor (tree, vec<constructor_elt, va_gc> *);
Index: gcc/tree.c
===================================================================
--- gcc/tree.c	2017-10-23 17:22:32.734226398 +0100
+++ gcc/tree.c	2017-10-23 17:22:35.830905181 +0100
@@ -1974,6 +1974,37 @@ build_vec_series (tree type, tree base,
   return build2 (VEC_SERIES_EXPR, type, base, step);
 }
 
+/* Return a vector with the same number of units and number of bits
+   as VEC_TYPE, but in which the elements are a linear series of unsigned
+   integers { BASE, BASE + STEP, BASE + STEP * 2, ... }.  */
+
+tree
+build_index_vector (tree vec_type, poly_uint64 base, poly_uint64 step)
+{
+  tree index_vec_type = vec_type;
+  tree index_elt_type = TREE_TYPE (vec_type);
+  poly_uint64 nunits = TYPE_VECTOR_SUBPARTS (vec_type);
+  if (!INTEGRAL_TYPE_P (index_elt_type) || !TYPE_UNSIGNED (index_elt_type))
+    {
+      index_elt_type = build_nonstandard_integer_type
+	(GET_MODE_BITSIZE (SCALAR_TYPE_MODE (index_elt_type)), true);
+      index_vec_type = build_vector_type (index_elt_type, nunits);
+    }
+
+  unsigned HOST_WIDE_INT count;
+  if (nunits.is_constant (&count))
+    {
+      auto_vec<tree, 32> v (count);
+      for (unsigned int i = 0; i < count; ++i)
+	v.quick_push (build_int_cstu (index_elt_type, base + i * step));
+      return build_vector (index_vec_type, v);
+    }
+
+  return build_vec_series (index_vec_type,
+			   build_int_cstu (index_elt_type, base),
+			   build_int_cstu (index_elt_type, step));
+}
+
 /* Something has messed with the elements of CONSTRUCTOR C after it was built;
    calculate TREE_CONSTANT and TREE_SIDE_EFFECTS.  */
 
Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c	2017-10-23 17:22:32.727227124 +0100
+++ gcc/tree-vect-loop.c	2017-10-23 17:22:35.829905285 +0100
@@ -3997,11 +3997,10 @@ get_initial_def_for_reduction (gimple *s
   struct loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
   tree scalar_type = TREE_TYPE (init_val);
   tree vectype = get_vectype_for_scalar_type (scalar_type);
-  int nunits;
+  poly_uint64 nunits;
   enum tree_code code = gimple_assign_rhs_code (stmt);
   tree def_for_init;
   tree init_def;
-  int i;
   bool nested_in_vect_loop = false;
   REAL_VALUE_TYPE real_init_val = dconst0;
   int int_init_val = 0;
@@ -4082,9 +4081,13 @@ get_initial_def_for_reduction (gimple *s
 	else
 	  {
 	    /* Option2: the first element is INIT_VAL.  */
-	    auto_vec<tree, 32> elts (nunits);
+
+	    /* Enforced by vectorizable_reduction (which disallows double
+	       reductions with variable-length vectors).  */
+	    unsigned int count = nunits.to_constant ();
+	    auto_vec<tree, 32> elts (count);
 	    elts.quick_push (init_val);
-	    for (i = 1; i < nunits; ++i)
+	    for (unsigned int i = 1; i < count; ++i)
 	      elts.quick_push (def_for_init);
 	    init_def = gimple_build_vector (&stmts, vectype, elts);
 	  }
@@ -4144,6 +4147,8 @@ get_initial_defs_for_reduction (slp_tree
 
   vector_type = STMT_VINFO_VECTYPE (stmt_vinfo);
   scalar_type = TREE_TYPE (vector_type);
+  /* vectorizable_reduction has already rejected SLP reductions on
+     variable-length vectors.  */
   nunits = TYPE_VECTOR_SUBPARTS (vector_type);
 
   gcc_assert (STMT_VINFO_DEF_TYPE (stmt_vinfo) == vect_reduction_def);
@@ -4510,8 +4515,7 @@ vect_create_epilog_for_reduction (vec<tr
   if (STMT_VINFO_VEC_REDUCTION_TYPE (stmt_info) == COND_REDUCTION)
     {
       tree indx_before_incr, indx_after_incr;
-      int nunits_out = TYPE_VECTOR_SUBPARTS (vectype);
-      int k;
+      poly_uint64 nunits_out = TYPE_VECTOR_SUBPARTS (vectype);
 
       gimple *vec_stmt = STMT_VINFO_VEC_STMT (stmt_info);
       gcc_assert (gimple_assign_rhs_code (vec_stmt) == VEC_COND_EXPR);
@@ -4527,10 +4531,7 @@ vect_create_epilog_for_reduction (vec<tr
 	 vector size (STEP).  */
 
       /* Create a {1,2,3,...} vector.  */
-      auto_vec<tree, 32> vtemp (nunits_out);
-      for (k = 0; k < nunits_out; ++k)
-	vtemp.quick_push (build_int_cst (cr_index_scalar_type, k + 1));
-      tree series_vect = build_vector (cr_index_vector_type, vtemp);
+      tree series_vect = build_index_vector (cr_index_vector_type, 1, 1);
 
       /* Create a vector of the step value.  */
       tree step = build_int_cst (cr_index_scalar_type, nunits_out);
@@ -4911,8 +4912,11 @@ vect_create_epilog_for_reduction (vec<tr
       tree data_eltype = TREE_TYPE (TREE_TYPE (new_phi_result));
       tree idx_eltype = TREE_TYPE (TREE_TYPE (induction_index));
       unsigned HOST_WIDE_INT el_size = tree_to_uhwi (TYPE_SIZE (idx_eltype));
-      unsigned HOST_WIDE_INT v_size
-	= el_size * TYPE_VECTOR_SUBPARTS (TREE_TYPE (induction_index));
+      poly_uint64 nunits = TYPE_VECTOR_SUBPARTS (TREE_TYPE (induction_index));
+      /* Enforced by vectorizable_reduction, which ensures we have target
+	 support before allowing a conditional reduction on variable-length
+	 vectors.  */
+      unsigned HOST_WIDE_INT v_size = el_size * nunits.to_constant ();
       tree idx_val = NULL_TREE, val = NULL_TREE;
       for (unsigned HOST_WIDE_INT off = 0; off < v_size; off += el_size)
 	{
@@ -5024,6 +5028,9 @@ vect_create_epilog_for_reduction (vec<tr
     {
       bool reduce_with_shift = have_whole_vector_shift (mode);
       int element_bitsize = tree_to_uhwi (bitsize);
+      /* Enforced by vectorizable_reduction, which disallows SLP reductions
+	 for variable-length vectors and also requires direct target support
+	 for loop reductions.  */
       int vec_size_in_bits = tree_to_uhwi (TYPE_SIZE (vectype));
       tree vec_temp;
 
@@ -5703,10 +5710,10 @@ vectorizable_reduction (gimple *stmt, gi
 	  if (k == 1
 	      && gimple_assign_rhs_code (reduc_stmt) == COND_EXPR)
 	    continue;
-	  tem = get_vectype_for_scalar_type (TREE_TYPE (op));
-	  if (! vectype_in
-	      || TYPE_VECTOR_SUBPARTS (tem) < TYPE_VECTOR_SUBPARTS (vectype_in))
-	    vectype_in = tem;
+	  if (!vectype_in
+	      || (GET_MODE_SIZE (SCALAR_TYPE_MODE (TREE_TYPE (vectype_in)))
+		  < GET_MODE_SIZE (SCALAR_TYPE_MODE (TREE_TYPE (op)))))
+	    vectype_in = get_vectype_for_scalar_type (TREE_TYPE (op));
 	  break;
 	}
       gcc_assert (vectype_in);
@@ -6016,6 +6023,7 @@ vectorizable_reduction (gimple *stmt, gi
   gcc_assert (ncopies >= 1);
 
   vec_mode = TYPE_MODE (vectype_in);
+  poly_uint64 nunits_out = TYPE_VECTOR_SUBPARTS (vectype_out);
 
   if (code == COND_EXPR)
     {
@@ -6205,8 +6213,8 @@ vectorizable_reduction (gimple *stmt, gi
       int scalar_precision
 	= GET_MODE_PRECISION (SCALAR_TYPE_MODE (scalar_type));
       cr_index_scalar_type = make_unsigned_type (scalar_precision);
-      cr_index_vector_type = build_vector_type
-	(cr_index_scalar_type, TYPE_VECTOR_SUBPARTS (vectype_out));
+      cr_index_vector_type = build_vector_type (cr_index_scalar_type,
+						nunits_out);
 
       optab = optab_for_tree_code (REDUC_MAX_EXPR, cr_index_vector_type,
 				   optab_default);
@@ -6215,6 +6223,15 @@ vectorizable_reduction (gimple *stmt, gi
 	epilog_reduc_code = REDUC_MAX_EXPR;
     }
 
+  if (epilog_reduc_code == ERROR_MARK && !nunits_out.is_constant ())
+    {
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "missing target support for reduction on"
+			 " variable-length vectors.\n");
+      return false;
+    }
+
   if ((double_reduc
        || STMT_VINFO_VEC_REDUCTION_TYPE (stmt_info) != TREE_CODE_REDUCTION)
       && ncopies > 1)
@@ -6226,6 +6243,27 @@ vectorizable_reduction (gimple *stmt, gi
       return false;
     }
 
+  if (double_reduc && !nunits_out.is_constant ())
+    {
+      /* The current double-reduction code creates the initial value
+	 element-by-element.  */
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "double reduction not supported for variable-length"
+			 " vectors.\n");
+      return false;
+    }
+
+  if (slp_node && !nunits_out.is_constant ())
+    {
+      /* The current SLP code creates the initial value element-by-element.  */
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "SLP reduction not supported for variable-length"
+			 " vectors.\n");
+      return false;
+    }
+
   /* In case of widenning multiplication by a constant, we update the type
      of the constant to be the type of the other operand.  We check that the
      constant fits the type in the pattern recognition pass.  */