[PATCH] D127766: [InstCombine] Fold memcmp of constant arrays and variable size

[Martin Sebor via Phabricator via llvm-commits]

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The `memcmp` simplifier is limited to folding to constants calls with constant arrays and constant sizes.  This change adds the ability to simplify `memcmp(A, B, N)` calls with constant  `A` and `B` and variable `N` to the pseudocode equivalent of

  N <= Pos ? 0 : (A < B ? -1 : B < A ? +1 : 0)

where `Pos` is the offset of the first mismatch between `A` and `B`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127766

Files:
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/memcmp-5.ll

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