[gcc r16-6577] tree-optimization/123310 - wrong aggregate copy VN

[Richard Biener]

https://gcc.gnu.org/g:6225251b90056f21b5896be46ed2c3c5a823a848

commit r16-6577-g6225251b90056f21b5896be46ed2c3c5a823a848
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Jan 8 13:08:57 2026 +0100

    tree-optimization/123310 - wrong aggregate copy VN
    
    There's a typo in the check against unknown offset when processing
    an aggregate copy during VN, leading to wrong lookup.
    
            PR tree-optimization/123310
            * tree-ssa-sccvn.cc (vn_reference_lookup_3): Properly
            test against unknown offset.
    
            * gcc.dg/torture/pr123310.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr123310.c | 21 +++++++++++++++++++++
 gcc/tree-ssa-sccvn.cc                   |  2 +-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr123310.c b/gcc/testsuite/gcc.dg/torture/pr123310.c
new file mode 100644
index 000000000000..1c2dee65c8d7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr123310.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+
+struct a {
+    short b;
+} c[7], e;
+int d;
+static struct a f[3][2] = {{}, {}, 5, 5};
+void __attribute__((noipa)) g()
+{
+  for (; e.b >= 0; e.b--)
+    {
+      c[e.b + 6] = f[2][1];
+      d = c[6].b;
+    }
+}
+int main()
+{
+  g();
+  if (d != 5)
+    __builtin_abort ();
+}
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 6fda0ef60440..16343d2a407f 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -3694,7 +3694,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
 	 via extra_off.  Note this is an attempt to fixup secondary
 	 copies after we hit the !found && j == 0 case above.  */
       while (j != -1
-	     && known_ne (lhs_ops[j].off, -1U))
+	     && known_ne (lhs_ops[j].off, -1))
 	{
 	  extra_off += -lhs_ops[j].off;
 	  j--;