[gcc r13-2219] New testcase for uninit

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:fc1b5707faf0b607da06e9ec3437245aba69a255

commit r13-2219-gfc1b5707faf0b607da06e9ec3437245aba69a255
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Aug 26 12:56:30 2022 +0200

    New testcase for uninit
    
    The following adds a testcase that illustrates a defect in
    compute_control_dep_chain and its attempt to identify loop
    exits as special to continue walking post-dominators but failing
    to do so for following post-dominators.  On trunk there is now
    simple_control_dep_chain saving the day, avoiding the false
    positive but with GCC 12 we get a bogus diagnostic.
    
            * gcc.dg/uninit-pred-11.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/uninit-pred-11.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/uninit-pred-11.c b/gcc/testsuite/gcc.dg/uninit-pred-11.c
new file mode 100644
index 00000000000..734df379ef7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/uninit-pred-11.c
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-options "-O -Wmaybe-uninitialized" } */
+
+extern unsigned bar (void);
+extern void quux (void);
+int z;
+unsigned foo (unsigned v, int y)
+{
+  unsigned u;
+  if (v != 1)
+    u = bar ();
+
+  // Prevent the "dom" pass from changing the CFG layout based on the inference
+  // 'if (v != 1) is false then (v != 2) is true'.  (Now it would have to
+  // duplicate the loop in order to do so, which is deemed expensive.)
+  for (int i = 0; i < 10; i++)
+    quux ();
+
+  // This variation from uninit-25.c causes compute_control_dep_chain
+  // to run into a defect but simple_control_dep_chain saves us here
+  if (y)
+    z = 1;
+  if (v != 1)
+    return u;       /* { dg-bogus "may be used uninitialized" } */
+
+  return 0;
+}