[all-commits] [llvm/llvm-project] ebcb49: [AArch64][ISel] Subvector extracts can use undef f...

[Gaëtan Bossu via All-commits]

  Branch: refs/heads/users/gbossu.vector.extract.1
  Home:   https://github.com/llvm/llvm-project
  Commit: ebcb4929004ae3f08b2ca3d5d246f29aa73600e1
      https://github.com/llvm/llvm-project/commit/ebcb4929004ae3f08b2ca3d5d246f29aa73600e1
  Author: Gaëtan Bossu <gaetan.bossu at arm.com>
  Date:   2025-08-01 (Fri, 01 Aug 2025)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/test/CodeGen/AArch64/get-active-lane-mask-extract.ll
    M llvm/test/CodeGen/AArch64/sve-fixed-length-int-div.ll
    M llvm/test/CodeGen/AArch64/sve-fixed-length-int-rem.ll
    M llvm/test/CodeGen/AArch64/sve-fixed-length-masked-scatter.ll
    M llvm/test/CodeGen/AArch64/sve-fixed-length-shuffles.ll
    M llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-fp-extend-trunc.ll
    M llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-fp-to-int.ll
    M llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-int-div.ll
    M llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-int-extends.ll
    M llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-int-rem.ll
    M llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-int-to-fp.ll
    M llvm/test/CodeGen/AArch64/sve-streaming-mode-fixed-length-reductions.ll
    A llvm/test/CodeGen/AArch64/sve2-fixed-length-extract-subvector.ll

  Log Message:
  -----------
  [AArch64][ISel] Subvector extracts can use undef for second EXT input

This will later allow us to use the SVE2 constructive variant of EXT
without requiring a MOV. That is because that variant of EXT requires
two consecutive Z registers as input. As a consequence, extracting a
subvector from e.g. z2 into z0 would require:
  z3 = MOV z2
  z0 = EXT_ZZI_B { z2, z3 }, idx

With this change, the z3 part of the { z2, z3 } tuple will be marked as
undef, allowing the MOV to be simplified.

We just need to add patterns for EXT_ZZI_B now, currently only the the
destructive EXT_ZZI variant is selected.



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