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[InstCombine] Fix infinite loop due to bitcast <-> phi transforms #32

Merged
merged 1 commit into from
Jan 16, 2020
Merged

[InstCombine] Fix infinite loop due to bitcast <-> phi transforms #32

merged 1 commit into from
Jan 16, 2020

Commits on Jan 16, 2020

  1. [InstCombine] Fix infinite loop due to bitcast <-> phi transforms 

    Fix for https://bugs.llvm.org/show_bug.cgi?id=44245.

The optimizeBitCastFromPhi() and FoldPHIArgOpIntoPHI() end up
fighting against each other, because optimizeBitCastFromPhi()
assumes that bitcasts of loads will get folded. This doesn't
happen here, because a dangling phi node prevents the one-use
fold in https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp#L620-L628 from triggering.

This patch fixes the issue by explicitly performing the load
combine as part of the bitcast of phi transform. Other attempts
to force the load to be combined first were ultimately too
unreliable.

Differential Revision: https://reviews.llvm.org/D71164
    @nikic @tmandry
    nikic authored and tmandry committed Jan 16, 2020
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