[PATCH] D114279: [InstSimplify] Fold X {lshr,udiv} C <u X --> true for nonzero X, non-identity C

[Erik Desjardins via Phabricator via llvm-commits]

erikdesjardins created this revision.
erikdesjardins added reviewers: nikic, lebedev.ri, spatel.
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This eliminates the bounds check in Rust code like

pub fn mid(data: &[i32]) -> i32 {

  if data.is_empty() { return 0; }
  return data[data.len()/2];

}

(from https://blog.sigplan.org/2021/11/18/undefined-behavior-deserves-a-better-reputation/)

Alive proofs:
lshr https://alive2.llvm.org/ce/z/t9Btcx
udiv https://alive2.llvm.org/ce/z/vLcbRQ


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114279

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/compare.ll

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