[all-commits] [llvm/llvm-project] b7166e: [RISCV] Combine extract_vector_elt followed by VFM...

[Craig Topper via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b7166e252448187f69fe7838b77cfaa1e6982e36
      https://github.com/llvm/llvm-project/commit/b7166e252448187f69fe7838b77cfaa1e6982e36
  Author: Craig Topper <craig.topper at sifive.com>
  Date:   2023-01-24 (Tue, 24 Jan 2023)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/test/CodeGen/RISCV/rvv/fixed-vectors-reduction-fp-vp.ll
    M llvm/test/CodeGen/RISCV/rvv/fixed-vectors-reduction-fp.ll
    M llvm/test/CodeGen/RISCV/rvv/vreductions-fp-vp.ll

  Log Message:
  -----------
  [RISCV] Combine extract_vector_elt followed by VFMV_S_F_VL.

If we're extracting an element and inserting into a undef vector
with the same number of elements, we can use the original vector.

This pattern occurs around reductions that have been cascaded
together.

This can be generalized to wider/narrow vectors by using
insert_subvector/extract_subvector, but we don't have lit tests
for that case currently.

We can also support non-undef before by using a slide or vmv.v.v

Reviewed By: reames

Differential Revision: https://reviews.llvm.org/D142264