[PATCH] D129753: [SCEV] Prove condition invariance via context

[Max Kazantsev via Phabricator via llvm-commits]

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Contextual knowledge may be used to prove invariance of some conditions.
For example, in this case:

  ; %len >= 0
  guard(%iv = {start,+,1}<nuw> <s %len)
  guard(%iv = {start,+,1}<nuw> <u %len)

the 2nd check always fails if `start` is negative and always passes otherwise.

It looks like there is more opportunities of this kind that are still to be implemented.


https://reviews.llvm.org/D129753

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
  llvm/test/Transforms/IndVarSimplify/cycled_phis.ll
  llvm/test/Transforms/IndVarSimplify/outer_phi.ll

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