[PATCH] D148001: [LICM] Reassociate & hoist add/sub expressions

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
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LICM could reassociate mixed variant/invariant comparison/arithmetic operations
and hoist invariant parts out of loop if it can prove that they can be computed
without overflow. Motivating example here:

  INV1 - VAR1 < INV2

can be turned into

  VAR > INV1 - INV2

if we can prove no-signed-overflow here. Then `INV1 - INV2` can be computed
out of loop, so we save one arithmetic operation in-loop.

I tried to make it as general as possible in this patch. For some reason it only
works when no-overflow facts are known from non-contextual facts, but this
is maybe a limitation of SCEV. It can be a subject of further improvement in
SCEV.


https://reviews.llvm.org/D148001

Files:
  llvm/lib/Transforms/Scalar/LICM.cpp
  llvm/test/Transforms/LICM/hoist-add-sub.ll

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