[PATCH] D131492: [RISCV] Implement isMaskAndCmp0FoldingBeneficial hook

[Alex Bradbury via Phabricator via llvm-commits]

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This hook is currently only used by CodeGenPrepare, which will sink an
`and` into a block that has an `icmp 0` user of it.

This hook is less useful for RISC-V than for targets like AArch64 that
have a TBZ (test bit and branch if zero instruction), but may still be
profitable if Zbs is available and a BEXTI can be selected.

Conservatively, we return false even if Zbs is enabled for any masks
that fit in the ANDI immediate because it's possible the only use is a
branch on the result, and ANDI+BNEZ => BEXTI+BNEZ isn't a profitable
transformation.


https://reviews.llvm.org/D131492

Files:
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/lib/Target/RISCV/RISCVISelLowering.h
  llvm/test/Transforms/CodeGenPrepare/RISCV/and-mask-sink.ll

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