[PATCH] D63660: [InstCombine] squash is-power-of-2 that uses ctpop

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: lebedev.ri, nikic, xbolva00.
Herald added subscribers: hiraditya, mcrosier.
Herald added a project: LLVM.

This is another intermediate IR step towards solving PR42314:
https://bugs.llvm.org/show_bug.cgi?id=42314

We can test if a value is power-of-2-or-0 using ctpop(X) < 2, so combining that with a non-zero check of the input is the same as testing if exactly 1 bit is set:

  (X != 0) && (ctpop(X) u< 2) --> ctpop(X) == 1


https://reviews.llvm.org/D63660

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  llvm/test/Transforms/InstCombine/ispow2.ll

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