[Bug c/56083] Vectorizer uses xor/movlps/movhps rather than movups

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56083

--- Comment #3 from Uros Bizjak <ubizjak at gmail dot com> 2013-01-23 16:23:47 UTC ---
(In reply to comment #2)

> Uros, I completely agree, but note that the PR also mentions this line:
> 
> xorps    %xmm0, %xmm0
> 
> which appears rather useless since the low and high parts are overwritten on
> the next 2 lines. Is this done on purpose to kill dependencies or something? Or
> is it a missed optimization? (simplify-rtx (or another place) is indeed missing
> a few things in that area)

IIRC, this insn is emitted to break dependency chain for %xmm0 register.
Processor is not _that_ smart ;)