[PATCH] use -0.0 when creating an fneg instruction

[Chris Lattner]

> On Dec 18, 2014, at 10:31 AM, Sanjay Patel <spatel at rotateright.com> wrote:
> 
> Hi hfinkel, resistor,
> 
> Simple (I hope) bug fix when generating an fneg operation in InstCombine. Backends recognize (-0.0 - X) as the canonical form for fneg and produce better code. Eg, ppc64 with 0.0:
>   lis r2, ha16(LCPI0_0)
>   lfs f0, lo16(LCPI0_0)(r2)
>   fsubs f1, f0, f1
>   blr
> 
> Vs. -0.0:
>   fneg f1, f1
>   blr
> 
> http://reviews.llvm.org/D6723

LGTM.

-Chris