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[IndVars] Replace checks with invariants if we cannot remove them

Authored by mkazantsev on Sep 29 2020, 9:55 PM.



If we cannot prove that the check is trivially true, but can prove that it either
fails on the 1st iteration or never fails, we can replace it with first iteration check.

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mkazantsev created this revision.Sep 29 2020, 9:55 PM
Herald added a project: Restricted Project. · View Herald TranscriptSep 29 2020, 9:55 PM
mkazantsev planned changes to this revision.Sep 29 2020, 10:00 PM

Rebased, ready for review.

anna added a subscriber: anna.Nov 11 2020, 7:18 PM

Just a stylistic comment. You can have the InvariantCond as a struct with the fields: InvariantPred, InvariantLHS, InvariantRHS. I think this will make code more readable (for example, use the struct in ReplaceInvariantCond(ExitingBB, InvariantCond).


I maybe missing something. Where are we checking the "never fails in any iteration other than the first" ?


Nit: ReplaceWithInvariantCond.

skatkov added inline comments.

SE->isLoopInvariantExitCondDuringFirstIterations ?

mkazantsev added inline comments.Nov 11 2020, 9:22 PM

Yes, inside of isLoopInvariantExitCondDuringFirstIterations we effectively check that comparison against IV may be replaced with comparison against start.

skatkov accepted this revision.Nov 11 2020, 9:28 PM

lgtm with Anna's nit + please do a rebase.

This revision is now accepted and ready to land.Nov 11 2020, 9:28 PM

(InvariantPred, InvariantLHS, InvariantRHS) API is used in SCEV. I will follow-up with refactoring changing it whevever it is used.