[PATCH] D73058: [LoopRotate] add ability repeat loop rotation until non-deoptimizing exit is found

[Fedor Sergeev via Phabricator via llvm-commits]

fedor.sergeev created this revision.
fedor.sergeev added reviewers: skatkov, asbirlea, reames, fhahn.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

In case of loops with multiple exit where all-but-one exit are deoptimizing
it might happen that the first rotation will end up with latch having a deoptimizing
exit. This makes the loop unsuitable for trip-count analysis (say, getLoopEstimatedTripCount)
as well as for loop transformations that know how to handle multple deoptimizing exits.

It pretty much means that canonical form in multple-deoptimizing-exits case should be
with non-deoptimizing exit at latch.
Teach loop-rotation to reach this canonical form by repeating rotation.

-loop-rotate-multi option introduced to control this behavior, currently enabled by default.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73058

Files:
  llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
  llvm/test/Transforms/LoopRotate/multiple-deopt-exits.ll

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