[all-commits] [llvm/llvm-project] 7e3ef7: [AMDGPU] lowerEXTRACT_VECTOR_ELT - fold from a SCA...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 7e3ef7dcd2b8201dce671237857f04a1d527d580
      https://github.com/llvm/llvm-project/commit/7e3ef7dcd2b8201dce671237857f04a1d527d580
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2022-05-07 (Sat, 07 May 2022)

  Changed paths:
    M llvm/lib/Target/AMDGPU/SIISelLowering.cpp
    M llvm/test/CodeGen/AMDGPU/insert_vector_elt.v2i16.ll
    M llvm/test/CodeGen/AMDGPU/load-lo16.ll

  Log Message:
  -----------
  [AMDGPU] lowerEXTRACT_VECTOR_ELT - fold from a SCALAR_TO_VECTOR source

As suggested by @foad on D124839

If we're extracting a vector element that originally came from a scalar_to_vector, then avoid the bitcasting of a vector type and perform the shift masking on the (any-extended) scalar source directly, making use of the fact that the upper elements of a scalar_to_vector are all undef.

Differential Revision: https://reviews.llvm.org/D125173