[all-commits] [llvm/llvm-project] 06daa5: [AArch64] Don't remove free sext_inreg(vector_extr...

[David Green via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 06daa515b27029885826833a5626937355abc4a1
      https://github.com/llvm/llvm-project/commit/06daa515b27029885826833a5626937355abc4a1
  Author: David Green <david.green at arm.com>
  Date:   2023-02-27 (Mon, 27 Feb 2023)

  Changed paths:
    M llvm/include/llvm/CodeGen/TargetLowering.h
    M llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/lib/Target/AArch64/AArch64ISelLowering.h
    M llvm/test/CodeGen/AArch64/extract-sext-zext.ll

  Log Message:
  -----------
  [AArch64] Don't remove free sext_inreg(vector_extract(x)) if it leads to multiple extracts

If we have sext_inreg(vector_extract(x)) but the top bits are not used, DAG
will try to remove the sext_inreg, using vector_extract(x) directly. This can
lead to multiple uses of both sext_inreg(vector_extract(x)) and
vector_extract(x), leading to the generation of both umov and smov extracts.
This adds a target hook to prevent that under AArch64 where the sext_inreg can
be considered free if there are multiple uses of the sext and no uses of the
vector_extract. This helps fix a small regression from D144550.

Differential Revision: https://reviews.llvm.org/D144850