[PATCH] D145301: Add more efficient vector bitcast for AArch64

[Lawrence Benson via Phabricator via llvm-commits]

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Adds a custom DAG combine check for vector comparisons followed by a bitcast to a scalar value. Previously, this resulted in an expand. Now, this is done with a constant number of instructions that take one bit per vector value (via an AND mask) and perfom a horizontal add to get a single value. This is especially useful for Clang's __builtin_convertvector() to a bool vector.

Issue: https://github.com/llvm/llvm-project/issues/59829


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D145301

Files:
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/test/CodeGen/AArch64/vec-combine-compare-to-bitmask.ll

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