[Bug target/80479] [7/8 Regression] strcmp() produces valgrind errors on ppc64le

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80479

Alan Modra <amodra at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amodra at gmail dot com

--- Comment #9 from Alan Modra <amodra at gmail dot com> ---
The following doesn't fail, but the strcmp optimization doesn't trigger
either..

#include <stdio.h>
#include <string.h>
#include <sys/mman.h>

int
main ()
{
#if 0
  char str1[15];
  char str2[15];
#else
  const size_t len = 65536;
  char *buf1, *buf2, *str1, *str2;

  buf1 = mmap (NULL, 2 * len, PROT_READ | PROT_WRITE,
               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  if (buf1 == MAP_FAILED)
    {
      perror ("mmap failed");
      return 0;
    }
  if (munmap (buf1 + len, len) < 0)
    {
      perror ("munmap failed");
      return 0;
    }

  buf2 = mmap (NULL, 2 * len, PROT_READ | PROT_WRITE,
               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  if (buf2 == MAP_FAILED)
    {
      perror ("mmap failed");
      return 0;
    }
  if (munmap (buf2 + len, len) < 0)
    {
      perror ("munmap failed");
      return 0;
    }
  str1 = buf1 + len - 7;
  str2 = buf2 + len - 7;
#endif
  strcpy (str1, "abcdef");
  strcpy (str2, "ABCDEF");
  return strcmp (str1, str2);
}

For the #if 1 case, valgrind is complaining about the compare of two eight byte
words read from the stack, which indeed do have one uninitialized byte past the
string terminating zero.  I don't believe it matters.  (The generated asm looks
OK to me, but that might be because my brain has shut down for the night.)