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[InstCombine] fold fneg into constant operand of fmul/fdiv

Authored by spatel on Aug 7 2018, 4:29 PM.



I think this is the missing IR fold noted in D50195, but AFAICT, we don't need any fast-math to enable the transform. FP negation can always be folded into an fmul/fdiv constant to eliminate the fneg.

I've limited this to one-use to ensure that we are eliminating an instruction rather than replacing fneg by a potentially expensive fdiv or fmul.

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spatel created this revision.Aug 7 2018, 4:29 PM

Looked it over in detail, the transformations all track.
LGTM, up to you if you want second set of eyes.

spatel accepted this revision.Aug 8 2018, 7:28 AM

Marking as accepted here on Phab to avoid unknown state when committing.

This revision is now accepted and ready to land.Aug 8 2018, 7:28 AM
This revision was automatically updated to reflect the committed changes.