[PATCH] D74077: [AArch64][GlobalISel] Fold G_LSHR into test bit calculation

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
paquette added a reviewer: aemerson.
Herald added subscribers: Petar.Avramovic, hiraditya, kristof.beyls, rovka.
Herald added a project: LLVM.

Add support for walking through G_LSHR in `getTestBitReg`. Equivalent to the code in `getTestBitOperand` in AArch64ISelLowering.

  (tbz (lshr x, c), b) -> (tbz x, b+c) when b + c is < # bits in x


https://reviews.llvm.org/D74077

Files:
  llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/opt-fold-shift-tbz-tbnz.mir

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