[PATCH] D116765: [x86] make select lowering using SBB hack more flexible

[Sanjay Patel via Phabricator via llvm-commits]

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select (X != 0), -1, Y --> 0 - X; or (sbb), Y
select (X != 0), Y, -1 --> X - 1; or (sbb), Y

We already had these x86 carry-flag transforms, but one was over-specified to handle a "0" select arm. That's just a special-case of the more general pattern (the 'or' will be deleted if Y is zero).

This is part of solving #53006, but it misses that example because some other combine has already converted that exact pattern into math ops.


https://reviews.llvm.org/D116765

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/sdiv_fix_sat.ll
  llvm/test/CodeGen/X86/select.ll
  llvm/test/CodeGen/X86/umul_fix_sat.ll

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