[PATCH] [GVN} don't propagate equality comparisons of FP zero (PR22376)

[hfinkel at anl.gov]

In http://reviews.llvm.org/D7257#115372, @spatel wrote:

> In http://reviews.llvm.org/D7257#115344, @rnk wrote:
>
> > Don't we have FP math flags for this? See FastMathFlags::noSignedZeros(). Looks like we don't have those on fcmp instrs, though.
> >
> > We should consider doing this folding if signed zeros are disabled.
>
>
> I thought about making this conditional on the IR-level FMF, but as you noted, they don't apply to fcmp (or intrinsics; see http://llvm.org/bugs/show_bug.cgi?id=21290 ). So until we get FMF fixed, we'd have to rely on a function-level attribute (unsafe-fp-math I think; I don't see an NSZ equivalent).
>
> Ok, if I just put a 'ToDo' comment in this patch for this?


Yes, add a FIXME for this.  LGTM.


http://reviews.llvm.org/D7257

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