poly_int: vectorizable_reduction

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.

2018-01-03  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_defs_for_reduction): Treat the number
	of units as polynomial, forcibly converting it to a constant if
	vectorizable_reduction has already enforced the condition.
	(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.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r256133

1 files changed, 23 insertions, 0 deletions

diff --git a/gcc/tree.c b/gcc/tree.c
index f13e2d8..93c4654 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -1930,6 +1930,29 @@ build_vec_series (tree type, tree base, tree step)
   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);
+    }
+
+  tree_vector_builder v (index_vec_type, 1, 3);
+  for (unsigned int i = 0; i < 3; ++i)
+    v.quick_push (build_int_cstu (index_elt_type, base + i * step));
+  return v.build ();
+}
+
 /* Something has messed with the elements of CONSTRUCTOR C after it was built;
    calculate TREE_CONSTANT and TREE_SIDE_EFFECTS.  */