[PATCH] D105723: [LSR] Do not hoist IV if it is not post increment case. PR43678

[Serguei Katkov via Phabricator via llvm-commits]

skatkov created this revision.
skatkov added reviewers: efriedma, mkazantsev, ebrevnov, reames, qcolombet.
Herald added subscribers: javed.absar, hiraditya.
skatkov requested review of this revision.
Herald added a project: LLVM.

Hosting IV in SCEV expander of non post-increment IV seems unprofitable.
Moreover it is dangerous as it might appear that the SCEV represents an instruction
which LSR plans to update to replace its operand. In this case instruction to change is hoisted
while the value to replace operand will be expanded in the older place.
It ends up with incorrect SSA form.

Two attached tests shows the bad behavior.


https://reviews.llvm.org/D105723

Files:
  llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
  llvm/test/Transforms/LoopStrengthReduce/pr43678-2.ll
  llvm/test/Transforms/LoopStrengthReduce/pr43678.ll

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