[PATCH] D52432: [PowerPC] Remove self-copies in pre-emit peephole

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai created this revision.
nemanjai added reviewers: hfinkel, echristo, kbarton, jsji.

There are occasionally instances where AADB rewrites registers in such a way that a reg-reg copy becomes a self-copy. Such an instruction is obviously redundant and can be removed. This patch does precisely that.

Note that this will not remove various `nop`'s that we insert (which are themselves just self-copies). The reason those are left alone is that all of them have their own opcodes (that just encode to a self-copy).

What prompted this patch is the fact that these self-copies sometimes end up using registers that make the instruction a priority-setting nop, thereby having a significant effect on performance.


Repository:
  rL LLVM

https://reviews.llvm.org/D52432

Files:
  lib/Target/PowerPC/PPCPreEmitPeephole.cpp
  test/CodeGen/PowerPC/remove-self-copies.mir

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