https://gcc.gnu.org/g:41e2fe9be1ff5ef2eafd49b30882898d26b9bf36
commit r16-3538-g41e2fe9be1ff5ef2eafd49b30882898d26b9bf36
Author: Richard Biener <rguent...@suse.de>
Date: Wed Sep 3 10:04:58 2025 +0200
tree-optimization/121758 - fix pattern stmt REDUC_IDX updating
The following fixes a corner case of pattern stmt STMT_VINFO_REDUC_IDX
updating which happens auto-magically. When a 2nd pattern sequence
uses defs from inside a prior pattern sequence then the first guess
for the lookfor can be off. This happens when for example widening
patterns use vect_get_internal_def, which looks into earlier patterns.
PR tree-optimization/121758
* tree-vect-patterns.cc (vect_mark_pattern_stmts): Try
harder to find a reduction continuation.
* gcc.dg/vect/pr121758.c: New testcase.
Diff:
---
gcc/testsuite/gcc.dg/vect/pr121758.c | 15 +++++++++++++++
gcc/tree-vect-patterns.cc | 30 ++++++++++++++++++++++++------
2 files changed, 39 insertions(+), 6 deletions(-)
diff --git a/gcc/testsuite/gcc.dg/vect/pr121758.c
b/gcc/testsuite/gcc.dg/vect/pr121758.c
new file mode 100644
index 000000000000..b27bc672588a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr121758.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+long g_2205, g_3005;
+int g_3320;
+void main()
+{
+ for (; g_2205; g_2205 += 1)
+ {
+ g_3005 = 0;
+ for (; g_3005 <= 8; g_3005 += 1)
+ g_3320 &= 611 & (unsigned char)g_3005;
+ }
+}
+
+/* { dg-final { scan-tree-dump-not "failed to update reduction index" "vect" }
} */
diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index d0bf2f9e7990..41ca0f085f0e 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -7074,14 +7074,32 @@ vect_mark_pattern_stmts (vec_info *vinfo,
{
bool found = false;
if (gimple_extract_op (s, &op))
- for (unsigned i = 0; i < op.num_ops; ++i)
- if (op.ops[i] == lookfor)
+ {
+ for (unsigned i = 0; i < op.num_ops; ++i)
+ if (op.ops[i] == lookfor)
+ {
+ STMT_VINFO_REDUC_IDX (vinfo->lookup_stmt (s)) = i;
+ lookfor = gimple_get_lhs (s);
+ found = true;
+ break;
+ }
+ /* Try harder to find a mid-entry into an earlier pattern
+ sequence. This means that the initial 'lookfor' was
+ bogus. */
+ if (!found)
{
- STMT_VINFO_REDUC_IDX (vinfo->lookup_stmt (s)) = i;
- lookfor = gimple_get_lhs (s);
- found = true;
- break;
+ for (unsigned i = 0; i < op.num_ops; ++i)
+ if (TREE_CODE (op.ops[i]) == SSA_NAME)
+ if (auto def = vinfo->lookup_def (op.ops[i]))
+ if (vect_is_reduction (def))
+ {
+ STMT_VINFO_REDUC_IDX (vinfo->lookup_stmt (s)) = i;
+ lookfor = gimple_get_lhs (s);
+ found = true;
+ break;
+ }
}
+ }
if (s == pattern_stmt)
{
if (!found && dump_enabled_p ())
