[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]

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

--- Comment #4 from Richard Guenther  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
leaq2(%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;
}

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

[dirtyepic at gentoo dot org]

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

Ryan Hill  changed:

   What|Removed |Added

 CC||dirtyepic at gentoo dot org

--- Comment #3 from Ryan Hill  2010-11-09 04:49:54 
UTC ---
Not to rush you, but I was wondering if there will be anyone looking at this in
the near future.  I was planning on releasing 4.5.1 into the unstable branch of
our repo this week but if a patch may be soon available I'll hold off.  If
there isn't any interest I'll do the release and mask it on our hardened
profiles (which use -fno-strict-overflow by default) for now.

[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]

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

--- Comment #2 from Richard Guenther  2010-11-05 
16:47:12 UTC ---
ipa-cp triggers this but is not neccessarily at fault.  Workaround:
-fno-ipa-cp.

[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]

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

Richard Guenther  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2010.11.05 16:43:32
  Known to work||4.4.4, 4.6.0
   Target Milestone|--- |4.5.2
Summary|gcc-4.5.1 -O2   |[4.5 Regression] gcc-4.5.1
   |-fno-strict-overflow causes |-O2 -fno-strict-overflow
   |bad code generation |causes bad code generation
 Ever Confirmed|0   |1
  Known to fail||4.5.0, 4.5.1

--- Comment #1 from Richard Guenther  2010-11-05 
16:43:32 UTC ---
Confirmed.