[PATCH] D134178: [SCEV] Calculate PHI range based on its underlying values instead of just its inputs

[Dmitry Makogon via Phabricator via llvm-commits]

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This teaches SCEV to calculate range of a PHI as a union of its underlying values ranges.
Currently we do it by uniting ranges of its inputs, but there are cases where two or more PHIs
are cycled so such approach would give the full range.
This uses PhiValues analysis to get underlying values for PHIs and then unite their ranges.


https://reviews.llvm.org/D134178

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/lib/CodeGen/SafeStack.cpp
  llvm/test/Analysis/ScalarEvolution/cycled_phis.ll
  llvm/test/Analysis/ScalarEvolution/unknown_phis.ll

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