[PATCH] D158501: [WIP][MemCpyOpt] implement liveness analysis based stack-move optimization

[Kohei Asano via Phabricator via llvm-commits]

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I finally notice liveness analysis is sufficient and powerful to merge alloca,
, we might need to consider the not live out def node removal for the following cases.

  %src = alloca %struct.Foo, align 4
  %dest = alloca %struct.Foo, align 4
  call void @llvm.lifetime.start.p0(i64 12, ptr nocapture %src)
  call void @llvm.lifetime.start.p0(i64 12, ptr nocapture %dest)
  store %struct.Foo { i32 10, i32 20, i32 30 }, ptr %src
  
  call void @llvm.memcpy.p0.p0.i64(ptr align 4 %dest, ptr align 4 %src, i64 12, i1 false)
  store %struct.Foo { i32 13, i32 13, i32 13 }, ptr %dest
  %1 = call i32 @use_nocapture(ptr nocapture %src)
  call void @llvm.lifetime.end.p0(i64 12, ptr nocapture %src)
  call void @llvm.lifetime.end.p0(i64 12, ptr nocapture %dest)
  ret void

This is WIP


https://reviews.llvm.org/D158501

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

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