[PATCH] D48557: [X86] Use XOR for SUB (C, X) during isel if will help fold an immediate

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, RKSimon.

Same idea as https://reviews.llvm.org/D48529, but restricted to X86 and done very late to avoid any surprises where subtract might be better for DAG combining.

This seems like the safest way to do this trick. And we consider doing it as a DAG combine later.


https://reviews.llvm.org/D48557

Files:
  lib/Target/X86/X86InstrCompiler.td
  test/CodeGen/X86/bool-math.ll
  test/CodeGen/X86/dagcombine-select.ll
  test/CodeGen/X86/extract-lowbits.ll

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