[PATCH] D87877: [InstCombine] Fix errno bug in pow expansion to sqrt

[Hubert Tong via Phabricator via llvm-commits]

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A conversion from `pow` to `sqrt` shall not call an `errno`-setting `sqrt` with -infinity: the `sqrt` will set `EDOM` where the `pow` call would not.

This patch avoids the erroneous (pun not intended) transformation by applying the restrictions discussed in the thread for https://lists.llvm.org/pipermail/llvm-dev/2020-September/145051.html.

The existing tests are updated (depending on emphasis in the checks for
library calls, avoidance of overlap, and overall coverage):

- to add `ninf`, retaining the intended library call,
- to use the intrinsic, retaining the use of `select`, or
- to expect the replacement to not occur.

The following is tested:

- The pow intrinsic folds to a select instruction to handle -infinity.
- The pow library call folds, with `ninf`, to `sqrt` without the select instruction associated with handling -infinity.
- The pow library call does not fold to `sqrt` without `ninf`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D87877

Files:
  llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/pow-1.ll
  llvm/test/Transforms/InstCombine/pow-sqrt.ll
  llvm/test/Transforms/InstCombine/win-math.ll

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