[PATCH] D74228: [PatternMatch] Match XOR variant of unsigned-add overflow check.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: nikic, RKSimon, lebedev.ri, spatel.
Herald added a subscriber: kristof.beyls.
Herald added a project: LLVM.

Instcombine folds (a + b <u a) to (a ^ -1 <u b) and that does not match
the expected pattern in CodeGenPerpare via UAddWithOverflow.

This causes a regression over Clang 7 on both X86 and AArch64:
https://gcc.godbolt.org/z/juhXYV

This patch extends UAddWithOverflow to also catch the XOR case, if the
XOR is only used in the ICMP. This covers just a single case, but I'd
like to make sure I am not missing anything before tackling the other
cases.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D74228

Files:
  llvm/include/llvm/IR/PatternMatch.h
  llvm/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll

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