[PATCH] tree-optimization/101462 - fix signedness of reused reduction vector

[Richard Biener <rguenther@suse.de>]

This fixes the partial reduction of the reused reduction vector to
carried out in the correct sign and the correctly signed vector
recorded for the skip edge use.

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

2021-07-16  Richard Biener  <rguenther@suse.de>

	* tree-vect-loop.c (vect_transform_cycle_phi): Correct sign
	conversion issues with the partial reduction of the reused
	vector accumulator.
---
 gcc/tree-vect-loop.c | 36 +++++++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index fc3dab0d143..00a57b2ba62 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -7706,21 +7706,35 @@ vect_transform_cycle_phi (loop_vec_info loop_vinfo,
   if (auto *accumulator = reduc_info->reused_accumulator)
     {
       tree def = accumulator->reduc_input;
-      unsigned int nreduc;
-      bool res = constant_multiple_p (TYPE_VECTOR_SUBPARTS (TREE_TYPE (def)),
-				      TYPE_VECTOR_SUBPARTS (vectype_out),
-				      &nreduc);
-      gcc_assert (res);
-      if (nreduc != 1)
-	{
-	  /* Reduce the single vector to a smaller one.  */
+      if (!useless_type_conversion_p (vectype_out, TREE_TYPE (def)))
+	{
+	  unsigned int nreduc;
+	  bool res = constant_multiple_p (TYPE_VECTOR_SUBPARTS
+					    (TREE_TYPE (def)),
+					  TYPE_VECTOR_SUBPARTS (vectype_out),
+					  &nreduc);
+	  gcc_assert (res);
 	  gimple_seq stmts = NULL;
-	  def = vect_create_partial_epilog (def, vectype_out,
-					    STMT_VINFO_REDUC_CODE (reduc_info),
-					    &stmts);
+	  /* Reduce the single vector to a smaller one.  */
+	  if (nreduc != 1)
+	    {
+	      /* Perform the reduction in the appropriate type.  */
+	      tree rvectype = vectype_out;
+	      if (!useless_type_conversion_p (TREE_TYPE (vectype_out),
+					      TREE_TYPE (TREE_TYPE (def))))
+		rvectype = build_vector_type (TREE_TYPE (TREE_TYPE (def)),
+					      TYPE_VECTOR_SUBPARTS
+						(vectype_out));
+	      def = vect_create_partial_epilog (def, rvectype,
+						STMT_VINFO_REDUC_CODE
+						  (reduc_info),
+						&stmts);
+	    }
 	  /* Adjust the input so we pick up the partially reduced value
 	     for the skip edge in vect_create_epilog_for_reduction.  */
 	  accumulator->reduc_input = def;
+	  if (!useless_type_conversion_p (vectype_out, TREE_TYPE (def)))
+	    def = gimple_convert (&stmts, vectype_out, def);
 	  if (loop_vinfo->main_loop_edge)
 	    {
 	      /* While we'd like to insert on the edge this will split
-- 
2.26.2