[PATCH] D129155: [InstCombine][SimplifyLibCalls] convert sqrt libcalls with "nnan" to sqrt intrinsics

[Sanjay Patel via Phabricator via llvm-commits]

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If a sqrt call has "nnan", that implies that the input argument is never negative because sqrt of {negative number} --> NAN.
If the argument is never negative, then we can assume that errno is not written, so the call can be translated to the LLVM intrinsic.

This affects codegen for targets like x86 that have a sqrt instruction, but we still have to conservatively assume that a libcall may be needed to set errno as shown in issue #52620 <https://github.com/llvm/llvm-project/issues/52620>.

This patch won't solve that example - we will need to extend this to use `CannotBeOrderedLessThanZero` or similar, enhance that analysis for new operators, and deal with `llvm.assume` too.


https://reviews.llvm.org/D129155

Files:
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/pow-4.ll
  llvm/test/Transforms/InstCombine/pow-sqrt.ll
  llvm/test/Transforms/InstCombine/sqrt.ll

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