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