[all-commits] [llvm/llvm-project] 2549c2: Reapply "[RISCV][TTI] Extract subvector at index z...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2549c24142816073b195abc294cfc3a546ecb7a0
      https://github.com/llvm/llvm-project/commit/2549c24142816073b195abc294cfc3a546ecb7a0
  Author: Philip Reames <preames at rivosinc.com>
  Date:   2024-02-15 (Thu, 15 Feb 2024)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
    M llvm/test/Analysis/CostModel/RISCV/rvv-shuffle.ll
    M llvm/test/Analysis/CostModel/RISCV/rvv-vectorextract.ll
    M llvm/test/Analysis/CostModel/RISCV/shuffle-extract_subvector.ll

  Log Message:
  -----------
  Reapply "[RISCV][TTI] Extract subvector at index zero is free (#81751)"

This reverts commit 834d11c21541c8bf92ef598c1171e8163b69e8c7 which was
a revert of my 3a626937b1b652e3c87cd0050df9c24cc5127d3b.  I had failed
to rebase after new tests added overnight by
fc0b67e1d79d1f199687f8f06d619984d9520230.

Original commit message follows:

Extracing a subvector at index zero corresponds to a type conversion and
possibly a subregister operation. We will not emit a vslidedown. As such,
they are free.

As an aside, it looks like we're not passing an index in for cases where
the subvec type is scalable. For at least index zero, we probably should be.

Revert "Revert "[RISCV][TTI] Extract subvector at index zero is free (#81751)""