[PATCH] D154289: [Reassociate] Keep flags for more unchanged operations

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: nikic, spatel.
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Reassociation destroys nsw/nuw flags from BinOps that are changed. If the expression in at the end of a tree that was altered, but didn't change itself the flags do not need to be removed though. For example, if %a, %b and %c are reassociated in

  %x = add nsw i32 %a, %c
  %y = add nsw i32 %x, %b
  %z = add nsw i32 %y, %d

The value of %y and so `add %y %d` remains the same, and %z needn't drop the nsw flags.
https://alive2.llvm.org/ce/z/_juAiV


https://reviews.llvm.org/D154289

Files:
  llvm/lib/Transforms/Scalar/Reassociate.cpp
  llvm/test/Transforms/Reassociate/cse-pairs.ll
  llvm/test/Transforms/Reassociate/local-cse.ll

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