[PATCH] D138808: [AArch64] use CNT for ISD::popcnt and ISD::parity if available

[Ties Stuij via Phabricator via llvm-commits]

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These are the two places where we explicitly want to use cnt in
SelectionDAG when feature CSSC is available: ISD::popcnt and ISD::parity

For both, we need to make sure we're emitting optimized code for i32 (and
lower), i64 and i128. The most optimal way is of course using the GPR CNT
instruction. If we don't have CSSC, but we do have neon, we'll use floating
point CNT. If all fails, we'll fall back on the general GPR popcnt and parity
implementations.

spec:
https://developer.arm.com/documentation/ddi0602/2022-09/Base-Instructions/CNT--Count-bits-


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138808

Files:
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/lib/Target/AArch64/AArch64InstrInfo.td
  llvm/test/CodeGen/AArch64/arm64-popcnt.ll
  llvm/test/CodeGen/AArch64/ctpop-nonean.ll
  llvm/test/CodeGen/AArch64/parity.ll

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