[PATCH] D119929: [MemCpyOpt] Check uses of found Clobber in writtenBetween.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: asbirlea, nikic, reames.
Herald added a subscriber: hiraditya.
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Currently writtenBetween can miss clobbers of Loc between End and Clobber
if Loc is not clobbered by End itself. End's defining accesses only have
to contain defs/phis that may clobber memory clobbered by End. But
writtenBetween needs to check for all write-clobbers of Loc.

To guarantee we see all write clobbers of Loc between the found Clobber
and End, I think we have to look at all uses of Clobber between Clobber
and End.

This fixes 2 mis-compiles illustrated in
llvm/test/Transforms/MemCpyOpt/memcpy-byval-forwarding-clobbers.ll

The implementation in this patch may consider write-clobbers on paths
that do not reach End as writes between Clobber and End. There's
potential to improve this as follow-up.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D119929

Files:
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
  llvm/test/Transforms/MemCpyOpt/memcpy-byval-forwarding-clobbers.ll
  llvm/test/Transforms/MemCpyOpt/nonlocal-memcpy-memcpy.ll

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