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

[gangren at google dot com]

------- Comment #5 from gangren at google dot com  2007-06-12 17:53 -------
(In reply to comment #3)
> >Do you mean that short_var + short_var is defined as 
> > (short)((unsigned short)short_var + (unsigned short)short_var)?
> 
> Kinda, because it is really defined by the C standard as:
>  (short)((int)short_var + (int)short_var)
> And then GCC's middle-end optimizes it to:
> (short)((unsigned short)short_var + (unsigned short)short_var)
> 
> *** This bug has been marked as a duplicate of 26128 ***
> 

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?


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