[Bug target/58320] New: [4.7 / 4.8 / 4.9 Regression] code used in autoconf test fails with -O2, works with -O0

[doko at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58320

            Bug ID: 58320
           Summary: [4.7 / 4.8 / 4.9 Regression] code used in autoconf
                    test fails with -O2, works with -O0
           Product: gcc
           Version: 4.7.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: doko at gcc dot gnu.org

seen on arm-linux-gnueabihf, as part of an autoconf test in librep:

$ cat stack.c 
#include <stdlib.h>

void inner (char *foo) {
  char bar;
  exit (!(foo >= &bar));
}

void main () {
  char foo;
  inner (&foo);
}

$ gcc-4.6 -o conftest -O2 stack.c && ./conftest ; echo $?
0
$ gcc-4.7 -o conftest -O2 stack.c && ./conftest ; echo $?
1
$ gcc-4.8 -o conftest -O2 stack.c && ./conftest ; echo $?
1
$ gcc-4.8 -o conftest -O0 stack.c && ./conftest ; echo $?
0