[PATCH] D116332: [ConstantFold] Make icmp of gep fold offset based

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
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We can fold an equality or unsigned icmp between `base+offset1` and `base+offset2` with inbounds offsets by comparison the offsets directly.

This replaces a pair of specialized folds that tried to reason based on the GEP structure instead. One of those folds was plain wrong (because it does not account for negative offsets), while the other is unnecessarily complicated and limited (e.g. it will fail with bitcasts involved).

The disadvantage of this change is that it requires data layout, so the fold is no longer performed by datalayout-independent constant folding. I don't think this is a loss in practice, but it does regress the ConstantExprFold.ll test, which checks folding without running any passes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116332

Files:
  llvm/lib/Analysis/ConstantFolding.cpp
  llvm/lib/IR/ConstantFold.cpp
  llvm/test/Assembler/ConstantExprFold.ll
  llvm/test/Transforms/InstSimplify/ConstProp/icmp-global.ll

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