[Speex-dev] SSE bug on Win32 with GCC 4.2.1

[Duane Storey]

Actually, it might just be an OS "feature"..  On most linux and mac
platforms, the memory managers align memory on proper boundaries -- this
doesn't occur on most versions of windows.  I don't have all the code in
front of me, but it's possible that it's simply a side effect of windows not
aligning the memory, and an implicit assumption in the speex code that it
will have proper alignment.


On 8/20/07, Thorvald Natvig <speex at natvig.com> wrote:
>
> Jean-Marc Valin wrote:
> >> I recently found a .. weird bug on Win32 SSE with GCC 4.2.1.
> >>
> >> In libspeex/cb_search_sse.h, the following union is used:
> >>
> >> union {
> >>    float __a[4];
> >>    __m128 __v;
> >>  } __u;
> >>
> >> For some odd reason, this particular version of GCC will not 16-byte
> >> align the union. IE; the alignment requirement of __v isn't propagated.
> >> Changing it into this:
> >>
> >>  union {
> >>    float __a[4];
> >>    __m128 __v;
> >>  } __u __attribute__((aligned(16)));
> >>
> >> And it works again. This is definitely a GCC bug, but I thought I'd
> >> mention it here in case others have similar problems.
> >
> > That's, euh... "interesting". Did you submit a bug report to the gcc
> > team? I guess I could add your code as a workaround (do you know what
> > version started supporting that attribute?) until it's fixed. I just
> > find it amazing how many bugs in gcc Speex has managed to trigger. I
> > believe this is at least the third one related to SSE (one in 3.4, one
> > in 4.1).
> >
> >       Jean-Marc
>
> It's supported on at least GCC 3.2, but it is very GCC specific and
> breaks horribly with any other compiler.
>
> However, I think this might be "local" to the windows versions of gcc
> 4.2. I'll install GCC on a few more platforms and try to verify it.
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