[llvm-bugs] [Bug 37390] -reassociate runs forever

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37390

Davide Italiano <davide at freebsd.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Davide Italiano <davide at freebsd.org> ---
dcci at Davides-MacBook-Pro ~/w/l/llvm> git svn dcommit --interactive
Committing to https://llvm.org/svn/llvm-project/llvm/trunk ...
commit 8c88b7846a8120179850d6ba485ae731aba20982
Author: Davide Italiano <ditaliano at apple.com>
Date:   Fri May 11 08:42:01 2018 -0700

    [Reassociate] Prevent infinite loops when processing PHIs.

    Phi nodes can reside in live blocks but one of their incoming
    arguments can come from a dead block. Dead blocks and reassociate
    don't play nice together. In fact, reassociate performs an RPO
    as a first step to avoid processing dead blocks.

    The reason why Reassociate might not fixpoint when examining
    dead blocks is that the following:

      %xor0 = xor i16 %xor1, undef
      %xor1 = xor i16 %xor0, undef

    is perfectly valid LLVM IR (if it appears in a dead block),
    so the worklist algorithm keeps pushing the two instructions for
    reexamination. Note that this is not Reassociate fault, at least
    not entirely. It's llvm that has a weird definition of dominance.

    Fixes PR37390.

 create mode 100644 test/Transforms/Reassociate/infloop-deadphi.ll
Commit this patch to SVN? ([y]es (default)|[n]o|[q]uit|[a]ll): y
        A       test/Transforms/Reassociate/infloop-deadphi.ll
        M       lib/Transforms/Scalar/Reassociate.cpp
Committed r332100
        M       lib/Target/AMDGPU/AMDGPUISelLowering.cpp
        A       test/CodeGen/AMDGPU/partial-shift-shrink.ll

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