[PATCH] D111919: [RISCV][WebAssembly][TargetLowering] Allow expandCTLZ/expandCTTZ to rely on CTPOP expansion for vectors.

[Craig Topper via Phabricator via llvm-commits]

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Our fallback expansion for CTLZ/CTTZ relies on CTPOP. If CTPOP
isn't legal or custom for a vector type we would scalarize the
CTLZ/CTTZ. This is different than CTPOP itself which would use a
vector expansion.

This patch teaches expandCTLZ/CTTZ to rely on the vector CTPOP
expansion instead of scalarizing. To do this I had to add additional
checks to make sure the operations used by CTPOP expansions are all
supported. Some of the operations were already needed for the CTLZ/CTTZ
expansion.

This is a huge improvement to the RISCV which doesn't have a scalar
ctlz or cttz in the base ISA. I'm not sure if this is the right thing
for WebAssembly which does have scalar ctlz and cttz instructions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D111919

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/test/CodeGen/RISCV/rvv/fixed-vectors-ctlz.ll
  llvm/test/CodeGen/RISCV/rvv/fixed-vectors-cttz.ll
  llvm/test/CodeGen/WebAssembly/simd-unsupported.ll