[Bug tree-optimization/32309] Unnecessary conversion from short to unsigend short breaks vectorization

["gangren at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #7 from gangren at google dot com  2007-06-12 18:10 -------
(In reply to comment #6)
> Subject: Re:  Unnecessary conversion from short to unsigend short breaks
> vectorization
> 
> On 12 Jun 2007 17:53:19 -0000, gangren at google dot com
> <gcc-bugzilla@gcc.gnu.org> wrote:
> 
> > I'm aware of integral promotion. But not quite understand why we can optimize
> > (short)((int)short_var + (int)short_var) to (short)((unsigned short)short_var +
> > (unsigned short)short_var), but not to (short)((short)short_var +
> > (short)short_var)? Is it because unsigned short has different overflow
> > handling?
> 
> Yes, signed short has undefined overflow, while unsigned is defined as
> wrapping.
> 
> --Pinski
> 

Thanks. So even if the underlining architecture does not trigger an overflow on
signed short (like AltiVec if I remember correctly), we still need to have such
conversions? In addition, does "undefined overflow" include "no overflow"? 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32309