[PATCH] D17475: MachineCopyPropagation: Catch copies of the form A<-B; A<-B

[Matthias Braun via llvm-commits]

MatzeB marked an inline comment as done.

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Comment at: lib/CodeGen/MachineCopyPropagation.cpp:212
@@ -193,3 +211,3 @@
       // Copy is now a candidate for deletion.
       if (!MRI->isReserved(Def))
         MaybeDeadCopies.insert(MI);
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junbuml wrote:
> Shouldn't we need to add  !MRI->isReserved(Src) as well ?
This is fine. Elminating a redundant copy of a reserved register is bad because you either write to a reserved register which may have effects you don't know about so you just cannot erase the write, or the redundant copy reads from a reserved register in which case we cannot be sure that is still has the previous value.

In the case of a dead copy reading form a reserved register we do not care though: We don't know the value that is read but nobody reads the value produced by the dead copy anyway.


Repository:
  rL LLVM

http://reviews.llvm.org/D17475