[all-commits] [llvm/llvm-project] 4fb7d1: [AMDGPU] Remove implicit definition of register gr...

[Ryan Buchner via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4fb7d1953d3f72f73d580f8549838bedad031d0b
      https://github.com/llvm/llvm-project/commit/4fb7d1953d3f72f73d580f8549838bedad031d0b
  Author: Ryan Buchner <92571492+bababuck at users.noreply.github.com>
  Date:   2025-05-05 (Mon, 05 May 2025)

  Changed paths:
    M llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
    M llvm/test/CodeGen/AMDGPU/accvgpr-spill-scc-clobber.mir
    A llvm/test/CodeGen/AMDGPU/agpr-spill-copy.mir
    M llvm/test/CodeGen/AMDGPU/amdgcn.bitcast.1024bit.ll
    M llvm/test/CodeGen/AMDGPU/amdgcn.bitcast.512bit.ll
    M llvm/test/CodeGen/AMDGPU/av_spill_cross_bb_usage.mir
    M llvm/test/CodeGen/AMDGPU/pei-build-av-spill.mir
    M llvm/test/CodeGen/AMDGPU/pei-build-spill.mir
    M llvm/test/CodeGen/AMDGPU/spill-agpr-partially-undef.mir
    M llvm/test/CodeGen/AMDGPU/vgpr-spill-scc-clobber.mir

  Log Message:
  -----------
  [AMDGPU] Remove implicit definition of register group when restoring the last sub-register after a spill (#133986)

Extension of https://reviews.llvm.org/D141101 to remove the define flag
from the last stack memory access. Fixes case where COPY instructions
are used for some of the stack restoration, but the copies get optimized
away during the machine-cp pass.

Prior to this change, was possible to produce the following code:
$agpr16_agpr17_agpr18_agpr19 = SCRATCH_LOAD_DWORDX4_ST 64, 0, implicit
$exec, implicit $flat_scr, implicit-def
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
:: (load (s128) from %stack.17, align 4, addrspace 5)
$agpr20_agpr21_agpr22_agpr23 = SCRATCH_LOAD_DWORDX4_ST 80, 0, implicit
$exec, implicit $flat_scr :: (load (s128) from %stack.17 + 16, align 4,
addrspace 5)
$agpr24_agpr25_agpr26_agpr27 = SCRATCH_LOAD_DWORDX4_ST 96, 0, implicit
$exec, implicit $flat_scr :: (load (s128) from %stack.17 + 32, align 4,
addrspace 5)
$agpr31 = COPY $agpr112, implicit
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
$agpr30 = COPY $agpr208, implicit
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
$agpr28_agpr29 = SCRATCH_LOAD_DWORDX2_ST 112, 0, implicit $exec,
implicit $flat_scr, implicit-def
$agpr16_agpr17_agpr18_agpr19_agpr20_agpr21_agpr22_agpr23_agpr24_agpr25_agpr26_agpr27_agpr28_agpr29_agpr30_agpr31
:: (load (s64) from %stack.17 + 48, align 4, addrspace 5)

where `$agpr30 = COPY $agpr208` would be optimized away by `machine-cp`
pass. Instead, change to:
$agpr28_agpr29 = SCRATCH_LOAD_DWORDX2_ST 112, 0, implicit $exec,
implicit $flat_scr :: (load (s64) from %stack.17 + 48, align 4,
addrspace 5)

Fixes #131386.

Made the simple fix, but I'm not completely comfortable with this change
since the reason for the previous inclusion of `IsLastSubReg` is unclear
to me.

@krzysz00



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