Bug#267206: gcc-3.4: vector op code generation regression

[Daniel Jacobowitz <dan@debian.org>]

On Sat, Aug 21, 2004 at 02:27:17PM -0500, Matthew Dempsky wrote:
> Daniel Jacobowitz <dan@debian.org> writes:
> 
> > On Sat, Aug 21, 2004 at 12:44:03AM -0500, Matthew Dempsky wrote:
> >> No warning, but the generated code seems incorrect (or at least a
> >> regression from 3.3) unless ((int *)&val)[x] isn't the correct
> >> portable way to access a vector element, but there doesn't seem to be
> >> an alternative that I've been able to deduce (and the documentation
> >> doesn't list any).
> >
> > It isn't correct.  Use a union; you're violating the strict-aliasing
> > rules.
> 
> Alright, I tried changing print_v4si to this (rest of the code the
> same):
> 
>     static void
>     print_v4si (const char * name, v4si val)
>     {
>       union foo
>       {
>         v4si vector;
>         int array[4];
>       } l;
>       int x;
>     
>       l.vector = val;
>     
>       printf ("%s:\n", name);
>       for (x = 0; x < 4; ++x)
>         printf ("  vals[%d] = %d\n", x, l.array[x]);
>       printf ("\n");
>     }
> 
> And it still generates bogus values for the third and fourth vector
> elements.  I also just noticed that compiling with -march=athlon-xp
> causes all of the values to be zero.
> 
> Or did I still not get the strict aliasing rules right?
> (-Wstrict-aliasing doesn't seem to generate a warning with either old
> or new code either.)

I'm not sure - I'd have to take a look at the generated code.

-- 
Daniel Jacobowitz