[PATCH] D84821: Don't transfer BitCastInst at InstCombine pass when the user of BitCast is lifetime marker

[Chuanqi Xu via Phabricator via llvm-commits]

ChuanqiXu created this revision.
ChuanqiXu added reviewers: nikic, lebedev.ri, fhahn.
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It is a usual pattern  to get the `lifetime marker` of Instruction `I`:

  SmallPtrSet<Instruction*, 4> LifetimeMarkers;
  for (User *U : I->users()) {
      if ( U is a lifetime marker)
          LifetimeMarkers.insert(U);
      if (BitCastInst* BCI=dyn_cast<BitCastInst>(U)){
          for (User* BCIUser:BCI->users())
              if (BCIUser is a lifetime marker)
                  LifetimeMarkers.insert(BCIUser);
      }
  }

In another word, the `lifetime marker` of an instruction `I` is either a user of I or a user of a user of I which is a BitCastInst. Although I don't find any rule for this pattern, I find it in a lot of codes.

However, in the InstCombine pass, it would try to transfer BitCast to a GEP when the target type of BitCast could be transferred by the source type of BitCast, which would break this pattern.

So I try to Disable the transferring process when the user of BitCast is `lifetime` marker.


https://reviews.llvm.org/D84821

Files:
  clang/test/CodeGen/aggregate-assign-call.c
  clang/test/CodeGen/temporary-lifetime-exceptions.cpp
  clang/test/CodeGenCXX/auto-var-init.cpp
  clang/test/CodeGenCXX/nrvo.cpp
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/bitcast-lifetime.ll
  llvm/test/Transforms/MemCpyOpt/memcpy-to-memset-with-lifetimes.ll

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