[PATCH] D135970: [InstCombine] try to determine "exact" for sdiv

[Sanjay Patel via Phabricator via llvm-commits]

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If the divisor is a power-of-2 or negative-power-of-2 and the dividend is known to have >= trailing zeros than the divisor, the division is exact:
https://alive2.llvm.org/ce/z/UGBksM (general proof)
https://alive2.llvm.org/ce/z/D4yPS- (examples based on regression tests)

This isn't the most direct optimization (we could create ashr in these examples instead of relying on existing folds for exact divides), but it's possible that there's a more general constraint than just a pow2 divisor, so this might be extended in the future.

This should solve issue #58348 <https://github.com/llvm/llvm-project/issues/58348>.


https://reviews.llvm.org/D135970

Files:
  llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
  llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll
  llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll

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