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Re: gcc 4.4.1/linux 64bit: code crashes with -O3, works with -O2
On Mon, 2010-02-22 at 13:11 -0800, Andrew Pinski wrote:
> On Mon, Feb 22, 2010 at 1:06 PM, Janis Johnson <janis187@us.ibm.com> wrote:
> > If you can reproduce the problem with a small, self-contained test then
> > please file a bug report. It might be possible to issue a warning or
> > to detect that the loop should not be vectorized. If not, maybe the
> > compiler should disable vectorization for -fno-strict-aliasing.
>
> It is not an aliasing issue but an alignment issue. Anyways this is
> most likely the same as
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43009 .
Yes, that's the problem I had in mind but I was thinking about an
explicit cast to a pointer to more-aligned data in the function that has
the vector loop. There's no way to warn about the undefined behavior
when the cast is in a different source file.
It's interesting that two reports of failure due to this same undefined
behavior come so close together.
Janis