[PATCH] D116766: [SCEV] Poison-safe `UMin` expression

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: reames, nikic, mkazantsev, aqjune, rnk.
lebedev.ri added a project: LLVM.
Herald added a reviewer: bollu.
Herald added subscribers: javed.absar, hiraditya.
lebedev.ri requested review of this revision.

This is a very rough proof of concept.

As discussed in https://github.com/llvm/llvm-project/issues/53020 / https://reviews.llvm.org/D116692,
SCEV is forbidden from reasoning about 'backedge taken count'
if the branch condition is a poison-safe logical operation,
which is conservatively correct, but is severely limiting.

Instead, we should have a way to express poison blocking properties
that we want to preserve: https://alive2.llvm.org/ce/z/GQisut
That allows us to handle the patterns in question.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116766

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/include/llvm/Analysis/ScalarEvolutionDivision.h
  llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h
  llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
  llvm/test/Analysis/ScalarEvolution/exit-count-select-safe.ll
  llvm/test/Analysis/ScalarEvolution/exit-count-select.ll
  llvm/test/Transforms/IndVarSimplify/exit-count-select.ll
  polly/include/polly/Support/SCEVAffinator.h
  polly/lib/Support/SCEVAffinator.cpp
  polly/lib/Support/SCEVValidator.cpp
  polly/lib/Support/ScopHelper.cpp

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