[PATCH] D63958: [SDAG] commute setcc operands to match a subtract

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: craig.topper, RKSimon, efriedma, jpienaar.
Herald added subscribers: jsji, hiraditya, javed.absar, mcrosier.
Herald added a project: LLVM.

If we have:

  R = sub X, Y
  P = cmp Y, X

...then flipping the operands in the compare instruction can allow using a subtract that sets compare flags.

Motivated by diffs in D58875 <https://reviews.llvm.org/D58875> - not sure if this changes anything there, but this seems like a good thing independent of that.

I've never seen Lanai code before this, so I don't know whether that change is good, bad, or even correct.


https://reviews.llvm.org/D63958

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/test/CodeGen/AArch64/arm64-shrink-wrapping.ll
  llvm/test/CodeGen/AArch64/cgp-usubo.ll
  llvm/test/CodeGen/Lanai/sub-cmp-peephole.ll
  llvm/test/CodeGen/X86/jump_sign.ll
  llvm/test/CodeGen/X86/psubus.ll

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