[PATCH] D91755: [GlobalISel] Combine icmp eq/ne (ext (icmp cc, x, y)), true/false)

[Jessica Paquette via Phabricator via llvm-commits]

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This implements the following combines:

  icmp ne ([sz]ext (icmp cc, x, y)), 0) -> icmp cc, x, y
  icmp eq, ([sz]ext (icmp cc x, y)), 0) -> icmp inv(cc), x, y
  icmp ne, (zext (icmp cc, x, y)), 1) -> icmp inv(cc), x, y
  icmp eq, (zext (icmp cc, x, y)), 1) -> icmp cc, x, y
  icmp ne, (sext (icmp cc, x, y)), -1) -> icmp inv(cc), x, y
  icmp eq, (sext (icmp cc, x, y)), -1) -> icmp cc, x, y

This is similar to a combine in `TargetLowering::SimplifySetCC`.

IR example: https://godbolt.org/z/qzx81v


https://reviews.llvm.org/D91755

Files:
  llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
  llvm/include/llvm/Target/GlobalISel/Combine.td
  llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-ext-icmp.mir

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