From: Richard Biener <rguenther@suse.de>
Date: Thu, 27 Jun 2024 09:26:08 +0000 (+0200)
Subject: tree-optimization/115669 - fix SLP reduction association
X-Git-Tag: releases/gcc-12.5.0~367
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=882f7e53a7664f2c76b10dc020e720ba9f55f022;p=thirdparty%2Fgcc.git

tree-optimization/115669 - fix SLP reduction association

The following avoids associating a reduction path as that might
get STMT_VINFO_REDUC_IDX out-of-sync with the SLP operand order.
This is a latent issue with SLP reductions but now easily exposed
as we're doing single-lane SLP reductions.

When we achieved SLP only we can move and update this meta-data.

	PR tree-optimization/115669
	* tree-vect-slp.cc (vect_build_slp_tree_2): Do not reassociate
	chains that participate in a reduction.

	* gcc.dg/vect/pr115669.c: New testcase.

(cherry picked from commit 7886830bb45c4f5dca0496d4deae9a45204d78f5)
---

diff --git a/gcc/testsuite/gcc.dg/vect/pr115669.c b/gcc/testsuite/gcc.dg/vect/pr115669.c
new file mode 100644
index 000000000000..361a17a64e68
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr115669.c
@@ -0,0 +1,22 @@
+/* { dg-additional-options "-fwrapv" } */
+
+#include "tree-vect.h"
+
+int a = 10;
+unsigned b;
+long long c[100];
+int foo()
+{
+  long long *d = c;
+  for (short e = 0; e < a; e++)
+    b += ~(d ? d[e] : 0);
+  return b;
+}
+
+int main()
+{
+  check_vect ();
+  if (foo () != -10)
+    abort ();
+  return 0;
+}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 19cab93761c9..0462fa01020d 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -1825,6 +1825,9 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
   else if (is_a <loop_vec_info> (vinfo)
 	   /* ???  We don't handle !vect_internal_def defs below.  */
 	   && STMT_VINFO_DEF_TYPE (stmt_info) == vect_internal_def
+	   /* ???  Do not associate a reduction, this will wreck REDUC_IDX
+	      mapping as long as that exists on the stmt_info level.  */
+	   && STMT_VINFO_REDUC_IDX (stmt_info) == -1
 	   && is_gimple_assign (stmt_info->stmt)
 	   && (associative_tree_code (gimple_assign_rhs_code (stmt_info->stmt))
 	       || gimple_assign_rhs_code (stmt_info->stmt) == MINUS_EXPR)