[PATCH] D139785: [InstCombine] preserve signbit semantics of NAN with fold to fabs

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
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As discussed in (issue #59279)[https://github.com/llvm/llvm-project/issues/59279], we want fneg/fabs to conform to the IEEE-754 spec for signbit operations. Those functions produce a deterministic signbit even for NAN values where the signbit is meaningless, so we gate this transform with "nnan" in addition to "nsz":
(X > 0.0) ? X : -X --> fabs(X)

The code change is a one-liner, but we have lots of tests diffs because there are many variations of the basic pattern.


https://reviews.llvm.org/D139785

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/fabs.ll
  llvm/test/Transforms/InstCombine/fneg-fabs.ll
  llvm/test/Transforms/InstCombine/fneg.ll

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