[PATCH] D151736: [RISCV] Lower inserts into identity shuffles as v{,f}slide1ups

[Luke Lau via Phabricator via llvm-commits]

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Inserting an element at index 0, into a shuffle that's an identity shuffle past the first
element, can be achieved with a single v{,f}slide1up. This patch detects such shuffles with
the isIdentityMask logic and lowers it to said vslide1up.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D151736

Files:
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/test/CodeGen/RISCV/rvv/fixed-vector-shuffle-vslide1up.ll

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