[gcc r16-9457] tree-optimization/126404 - fixup conversion detection in reductions

https://gcc.gnu.org/g:8801728ac99a19763df4851e682f1cacfe7975fc

commit r16-9457-g8801728ac99a19763df4851e682f1cacfe7975fc
Author: Richard Biener <[email protected]>
Date:   Mon Jul 27 19:24:32 2026 +0200

    tree-optimization/126404 - fixup conversion detection in reductions
    
    The following makes sure to check the pattern stmt against being a
    conversion to skip but the original stmt for a mismatch in code.
    
            PR tree-optimization/126404
            * tree-vect-slp.cc (vect_analyze_slp_reduc_chain): Fixup
            conversion detection.
    
            * gcc.dg/vect/vect-pr126404.c: New testcase.
    
    (cherry picked from commit 3cd23c9fd60854cd9d160ce3b341a819025bfeb8)

Diff:
---
 gcc/testsuite/gcc.dg/vect/vect-pr126404.c | 14 ++++++++++++++
 gcc/tree-vect-slp.cc                      |  7 ++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/vect-pr126404.c b/gcc/testsuite/gcc.dg/vect/vect-pr126404.c
new file mode 100644
index 000000000000..4657d34baf38
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-pr126404.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+
+unsigned ff(int g7)
+{
+  int v3 = 8;
+  int ob13;
+  int ov14;
+  do {
+      ob13 = __builtin_add_overflow(2, g7, &ov14);
+      g7 = 0;
+      v3 = __builtin_ctz(v3);
+  } while (ob13);
+  return v3;
+}
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index c114c5d6175e..48bfd87f8961 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -4237,7 +4237,7 @@ vect_analyze_slp_reduc_chain (loop_vec_info vinfo,
   do
     {
       stmt_vec_info stmt = next_stmt;
-      gimple_match_op op;
+      gimple_match_op op, orig_op;
       if (!gimple_extract_op (STMT_VINFO_STMT (stmt), &op))
 	gcc_unreachable ();
       tree reduc_def = gimple_arg (STMT_VINFO_STMT (stmt),
@@ -4245,14 +4245,15 @@ vect_analyze_slp_reduc_chain (loop_vec_info vinfo,
       next_stmt = vect_stmt_to_vectorize (vinfo->lookup_def (reduc_def));
       gcc_assert (is_a <gphi *> (STMT_VINFO_STMT (next_stmt))
 		  || STMT_VINFO_REDUC_IDX (next_stmt) != -1);
-      if (!gimple_extract_op (STMT_VINFO_STMT (vect_orig_stmt (stmt)), &op))
+      if (!gimple_extract_op (STMT_VINFO_STMT (vect_orig_stmt (stmt)),
+			      &orig_op))
 	gcc_unreachable ();
       if (CONVERT_EXPR_CODE_P (op.code)
 	  && tree_nop_conversion_p (op.type, TREE_TYPE (op.ops[0]))
 	  && (first
 	      || is_a <gphi *> (STMT_VINFO_STMT (next_stmt))))
 	;
-      else if (code != op.code)
+      else if (code != orig_op.code)
 	{
 	  fail = true;
 	  break;