[PATCH] D46278: [AArch64] Fold B = csel A, A into B = COPY A

[Francis Visoiu Mistrih via Phabricator via llvm-commits]

thegameg created this revision.
thegameg added reviewers: t.p.northover, aemerson, eli.friedman, gberry.
Herald added subscribers: jkorous, kristof.beyls, rengolin.
Herald added a reviewer: javed.absar.

I found the following pattern in the LLVM test suite + SPEC 93 times:

  csel B, A, A

I see that in some places after MachineCSE runs, we end up with things like:

  %5:gpr32 = CSELWr %1, %1, 12, implicit $nzcv

In this case, a COPY would be much better.

I added support for `optimizeSelect` in `AArch64InstrInfo`, which is called by the `PeepholeOptimizer`.


https://reviews.llvm.org/D46278

Files:
  lib/Target/AArch64/AArch64InstrFormats.td
  lib/Target/AArch64/AArch64InstrInfo.cpp
  lib/Target/AArch64/AArch64InstrInfo.h
  test/CodeGen/AArch64/csel-same-source.mir

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