[Bug tree-optimization/26763] [4.1 Regression] wrong final value of induction variable calculated

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #9 from rguenther at suse dot de  2006-04-03 16:59 -------
Subject: Re:  [4.1 Regression] wrong final value
 of induction variable calculated

On Mon, 3 Apr 2006, rakdver at gcc dot gnu dot org wrote:

> (In reply to comment #6)
> > I believe c-common.c:pointer_int_sum is wrong in relying on pointer overflow
> > during conversion of the integer offset to an unsigned pointer.  I'm sending
> > a patch that fixes this for comments.
> 
> The patch seems a bit too conservative to me; perhaps just always comparing the
> offsets as signed could work?

I'm not a language lawyer here - and as this is the second (or third) 
patch to this folding to correct problems I'd rather be safe than sorry 
this time.  I'm sure jsm can construct a testcase where comparing offsets
as signed leads to wrong code.  Maybe

char *memory = 0;

int foo(void)
{
  return memory + 0x80000000 < memory;
}

int main()
{
  if (foo())
    abort ();
}

i.e. have a mapping >2Gb on a 32bit machine.  A corner case, but valid I 
guess.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26763