https://gcc.gnu.org/g:68e692eed9e8e8c47d83586ee08f40c27fa3a78d
commit r16-3389-g68e692eed9e8e8c47d83586ee08f40c27fa3a78d
Author: Richard Biener <rguent...@suse.de>
Date: Tue Aug 26 10:34:01 2025 +0200
tree-optimization/121659 - bogus swap of reduction operands
The following addresses a bogus swapping of SLP operands of a
reduction operation which gets STMT_VINFO_REDUC_IDX out of sync
with the SLP operand order. In fact the most obvious mistake is
that we simply swap operands even on the first stmt even when
there's no difference in the comparison operators (for == and !=
at least). But there are more latent issues that I noticed and
fixed up in the process.
PR tree-optimization/121659
* tree-vect-slp.cc (vect_build_slp_tree_1): Do not allow
matching up comparison operators by swapping if that would
disturb STMT_VINFO_REDUC_IDX. Make sure to only
actually mark operands for swapping when there was a
mismatch and we're not processing the first stmt.
* gcc.dg/vect/pr121659.c: New testcase.
Diff:
---
gcc/testsuite/gcc.dg/vect/pr121659.c | 11 +++++++++++
gcc/tree-vect-slp.cc | 11 ++++++++---
2 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/gcc/testsuite/gcc.dg/vect/pr121659.c
b/gcc/testsuite/gcc.dg/vect/pr121659.c
new file mode 100644
index 000000000000..19d5f8c37f37
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr121659.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+
+_Bool a;
+void b(_Bool c[][3])
+{
+ for (short d = 0; d < 100; d++)
+ for (int e = 1; e < 21; e += 4)
+ a ^= !c[1][1];
+ for (;;)
+ ;
+}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 3081251eba8a..2df9d2b3c6d2 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -1389,7 +1389,9 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char
*swap,
&& (TREE_CODE_CLASS (tree_code (first_stmt_code))
== tcc_comparison)
&& (swap_tree_comparison (tree_code (first_stmt_code))
- == tree_code (rhs_code))))
+ == tree_code (rhs_code))
+ && (first_reduc_idx == -1
+ || REDUC_GROUP_FIRST_ELEMENT (stmt_info))))
|| (ldst_p
&& (STMT_VINFO_GROUPED_ACCESS (stmt_info)
!= STMT_VINFO_GROUPED_ACCESS (first_stmt_info)))
@@ -1605,8 +1607,11 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char
*swap,
}
}
- if (rhs_code.is_tree_code ()
- && TREE_CODE_CLASS ((tree_code)rhs_code) == tcc_comparison
+ if (i != 0
+ && first_stmt_code != rhs_code
+ && first_stmt_code.is_tree_code ()
+ && rhs_code.is_tree_code ()
+ && TREE_CODE_CLASS ((tree_code)first_stmt_code) == tcc_comparison
&& (swap_tree_comparison ((tree_code)first_stmt_code)
== (tree_code)rhs_code))
swap[i] = 1;
