[Bug tree-optimization/46315] [4.5 Regression] gcc-4.5.1 -O2 -fno-strict-overflow causes bad code generation

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46315

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-11-12 14:56:54 UTC ---
loop-header copying is where things start to be different.

In the end the asm doesn't make much sense:

parse_ranged.clone.0:
.LFB2:
        .cfi_startproc
        leaq    2(%rdi), %rdx
        movq    %rdi, %rax
...
        leal    (%rdx,%rdx,4), %edx
        movb    $2, %al
        leal    (%rcx,%rdx,2), %edx
.L2:
        testq   %rax, %rax
        je      .L7
        cmpl    $60, %edx
        movl    $0, %edx
        cmovge  %rdx, %rax
        ret

so we might end up returning literal 2.


Reduced testcase:

static char const *
parse_ranged (char const *s, int digits)
{
  int n = 0;
  char const *lim = s + digits;
  while (s < lim)
    {
      unsigned d = *s++ - '0';
      if (9 < d)
        return 0;
      n = 10 * n + d;
    }
  return s && 0 <= n && n <= 59 ? s : 0;
}
extern void abort (void);
int main()
{
  const char *s = "10092240";

  s = parse_ranged (s, 2);
  s = parse_ranged (s, 2);
  s = parse_ranged (s, 2);
  s = parse_ranged (s, 2);
  if (!s || *s != '\0')
    abort();
  return 0;
}