[all-commits] [llvm/llvm-project] 143be6: [AArch64][GISel] Avoid scalarizing G_IMPLICIT_DEF ...

[Dhruv Chawla via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 143be6a60186d6c1a6a298d0b7acdc1a4d69a321
      https://github.com/llvm/llvm-project/commit/143be6a60186d6c1a6a298d0b7acdc1a4d69a321
  Author: Dhruv Chawla <dhruvc at nvidia.com>
  Date:   2024-04-23 (Tue, 23 Apr 2024)

  Changed paths:
    M llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-extract-vector-elt.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-fp-arith.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-freeze.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-insert-vector-elt.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-itofp.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-load-store.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-min-max.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-phi.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-select.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-shift.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-shuffle-vector.mir
    M llvm/test/CodeGen/AArch64/GlobalISel/legalizer-info-validation.mir

  Log Message:
  -----------
  [AArch64][GISel] Avoid scalarizing G_IMPLICIT_DEF and G_FREEZE in the Legalizer (#88469)

It does not make sense to scalarize G_FREEZE as it leads to the generation
of pairs of G_UNMERGE_VALUES and G_BUILD_VECTORs which are difficult to
optimize especially when operations like G_TRUNC operate before G_FREEZE
but after G_UNMERGE_VALUES.

Instead, it is better to legalize G_FREEZE like any other vector type
would be, as it gets lowered to a COPY during instruction selection
anyways.

This is an issue that was encountered when looking at the TSVC
benchmark, where the legalization of G_FREEZE would cause generation of
unnecessary MOVs that adversely affected the performance.



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