[gcc r16-6979] testsuite: Add testcase for already fixed PR [PR123753]

[Jakub Jelinek]

https://gcc.gnu.org/g:d52669acc6829c93270b9014af7a681dbd694c39

commit r16-6979-gd52669acc6829c93270b9014af7a681dbd694c39
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Jan 22 13:54:08 2026 +0100

    testsuite: Add testcase for already fixed PR [PR123753]
    
    This testcase started to ICE with r16-6671, since r16-6741
    it has been miscompiled and finally fixed with r16-6976.
    
    2026-01-22  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/123753
            * gcc.c-torture/execute/pr123753.c: New test.

Diff:
---
 gcc/testsuite/gcc.c-torture/execute/pr123753.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr123753.c b/gcc/testsuite/gcc.c-torture/execute/pr123753.c
new file mode 100644
index 000000000000..e3d403d95ad8
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr123753.c
@@ -0,0 +1,25 @@
+/* PR tree-optimization/123753 */
+
+typedef int V __attribute__((__vector_size__ (8)));
+typedef short W __attribute__((__vector_size__ (8)));
+
+union { unsigned short u[4]; W w; } u;
+V v;
+
+V
+foo ()
+{
+  u.w--;
+  V r = v + u.u[0];
+  return r;
+}
+
+int
+main ()
+{
+  if (sizeof (int) != 4 || sizeof (short) != 2)
+    return 0;
+  V x = foo ();
+  if (x[0] != (unsigned short) -1 || x[1] != (unsigned short) -1)
+    __builtin_abort ();
+}