[PATCH] D153453: (WIP)[MemCpyOpt] implement stack-move optimization which unify the lifetime overlapped fully copied allocas, the src is never modified or referenced

[Kohei Asano via Phabricator via llvm-commits]

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This is takeover from @pcwalton 's https://reviews.llvm.org/D140089

New transformation unifies the two allocates on the same BB if the followings are satisfied
(1) The src is fully copied to dest by memcpy, memmove or store&load.
(2) Two allocas are never captured.
(3) The src has no read and no write, from after the full copy to the end of the BB.
I think (2) is done by CaptureTracking, (3) is done by ModRef check of MemSSA.

Note: I think explicit lifetime intrinsics are not necessary to do this, although removing redundant lifetime intrinsic and inserting it are beneficial.


https://reviews.llvm.org/D153453

Files:
  llvm/include/llvm/Transforms/Scalar/MemCpyOptimizer.h
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp

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