[PATCH] D80483: [X86] Teach combineTruncatedArithmetic to push truncate through subtracts where only one of the inputs is free to truncate.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, RKSimon.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

Fix combineSubToSubus to handle the new DAG to avoid a regression.

There are still regressions in test14/test15/test16. Where it
looks like were trying to set up cases we could match to
umin+trunc+subus but the handling was never finished. The
regression here isn't unique to sub. Its a lost opportunity for
taking an AND with two truncated inputs and producing a larger
AND with a single truncate. The same thing could happen with
any other node we handle in combineTruncatedArithmetic since we
are moving the truncate up the DAG.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80483

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/psubus.ll

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