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Subject: [Bug target/38708] [4.4 Regression] Revision 137646 caused gcc.c-torture/execute/memset-[23].c fail with -mtune=pentiumpro
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------- Comment #5 from jakub at gcc dot gnu dot org  2009-01-03 08:46 -------
There are several issues.  One is what H.J. mentioned, seen e.g. on:
char buf[8] __attribute__((aligned));
char A = 'A';
int len = 1;

void __attribute__((noinline))
check (void)
{
  if (__builtin_memcmp (buf, "\0\0A\0\0\0\0\0", 8))
    __builtin_abort ();
}

int
main ()
{
  __builtin_memset (buf + 2, A, len);
  check ();
  return 0;
}
with -O -mtune=pentium-m -m32.  This can be fixed by adding
max_size = smallest_pow2_greater_than (max_size - 1); at the start of
expand_setmem_epilogue_via_loop.  But another testcase with the same options
that still fails is:
char buf[8] __attribute__((aligned)) = "AAAAAAAA";
char A = 'A';
int len = 4;

void __attribute__((noinline))
check (void)
{
  if (__builtin_memcmp (buf, "AAAA\0\0\0\0", 8))
    __builtin_abort ();
}

int
main ()
{
  __builtin_memset (buf + 4, '\0', len);
  check ();
  return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38708