[PATCH] DAGCombiner: don't duplicate (fmul x, c) when folding fneg if fneg is free

[escha]

I think the only in-tree target that uses isFNegFree is R600; should I try to come up with an R600 test case? I've never worked on that backend.


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  rL LLVM

http://reviews.llvm.org/D10277

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