[PATCH] D67178: [SCEV] Use loop guard info when computing the max BE taken count in howFarToZero.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: sanjoy.google, reames, efriedma.
Herald added subscribers: hiraditya, javed.absar.
Herald added a project: LLVM.

For some expressions, we can use information from loop guards when
we are looking for a maximum. This patch applies information from
loop guards to the expression used to compute the maximum backedge
taken count in howFarToZero. It currently replaces an unknown
expression X with UMin(X, Y), if the loop is guarded by
X ult Y.

This patch is minimal in what conditions it applies, and there
are a few TODOs to generalize.

This partly addresses PR40961. We will also need an update to
LV to address it completely.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D67178

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Transforms/LoopVectorize/AArch64/pr36032.ll
  llvm/unittests/Analysis/ScalarEvolutionTest.cpp

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