[PATCH] D116804: [x86] use SETCC_CARRY instead of SBB node for select lowering

[Sanjay Patel via Phabricator via llvm-commits]

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This is a suggested follow-up to D116765 <https://reviews.llvm.org/D116765> (and diffs are on top of that patch). This removes a clear of the register operand, so it is better for code size, but it does potentially create a false register dependency on surrounding code.

The asm results match what I was expecting, but I'm not exactly sure how this works. Given that the node is called SETCC_CARRY and documented as:

  // Same as SETCC except it's materialized with a sbb and the value is all
  // one's or all zero's.
  SETCC_CARRY, // R = carry_bit ? ~0 : 0

...why does it require a parameter for X86::COND_B? I changed that parameter in an experimental patch, and it didn't alter the asm.


https://reviews.llvm.org/D116804

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/pr35972.ll
  llvm/test/CodeGen/X86/sdiv_fix_sat.ll
  llvm/test/CodeGen/X86/select.ll
  llvm/test/CodeGen/X86/shl-crash-on-legalize.ll
  llvm/test/CodeGen/X86/umul_fix_sat.ll

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