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Allow machine dce to remove uses in the same instruction

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Machine DCE cannot remove a dead definition if there are non-dbg uses.
A use however can be in the same instruction:

  dead %0 = INST %0

Such instructions sometimes created by Detect dead lanes pass.

Allow this instruction to be deleted despite the use if the only use
belongs to the same instruction.

Differential Revision: https://reviews.llvm.org/D59565

llvm-svn: 356619
This commit is contained in:
Stanislav Mekhanoshin 2019-03-20 21:42:05 +00:00
parent 3a74e8400f
commit 5ffc2d960d
2 changed files with 60 additions and 3 deletions
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8
lib/CodeGen/DeadMachineInstructionElim.cpp
View File

@ -81,9 +81,11 @@ bool DeadMachineInstructionElim::isDead(const MachineInstr *MI) const {
if (LivePhysRegs.test(Reg) || MRI->isReserved(Reg))
return false;
} else {
if (!MRI->use_nodbg_empty(Reg))
// This def has a non-debug use. Don't delete the instruction!
return false;
for (const MachineInstr &Use : MRI->use_nodbg_instructions(Reg)) {
if (&Use != MI)
// This def has a non-debug use. Don't delete the instruction!
return false;
}
}
}
}

55
test/CodeGen/AMDGPU/dead-mi-use-same-intr.mir Normal file
View File

@ -0,0 +1,55 @@
# RUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs -run-pass dead-mi-elimination -o - %s | FileCheck -check-prefix=GCN %s
# GCN-LABEL: name: dead_undef
# GCN: bb.0:
# GCN-NEXT: S_ENDPGM 0
---
name: dead_undef
tracksRegLiveness: true
registers:
- { id: 0, class: vgpr_32 }
- { id: 1, class: vgpr_32 }
- { id: 2, class: vgpr_32 }
body: |
bb.0:
%0 = IMPLICIT_DEF
%1 = IMPLICIT_DEF
dead %2:vgpr_32 = V_MAC_F32_e32 %0:vgpr_32, %1:vgpr_32, undef %2:vgpr_32, implicit $exec
S_ENDPGM 0
# GCN-LABEL: name: dead_defined
# GCN: bb.0:
# GCN-NEXT: S_ENDPGM 0
---
name: dead_defined
tracksRegLiveness: true
registers:
- { id: 0, class: vgpr_32 }
- { id: 1, class: vgpr_32 }
- { id: 2, class: vgpr_32 }
body: |
bb.0:
%0 = IMPLICIT_DEF
%1 = IMPLICIT_DEF
%2 = IMPLICIT_DEF
dead %2:vgpr_32 = V_MAC_F32_e32 %0:vgpr_32, %1:vgpr_32, %2:vgpr_32, implicit $exec
S_ENDPGM 0
# Probably this dead mac can be removed anyway.
# GCN-LABEL: name: dead_def_live_use
# GCN: dead %2:vgpr_32 = V_MAC_F32_e32 %0, %1, %2, implicit $exec
---
name: dead_def_live_use
tracksRegLiveness: true
registers:
- { id: 0, class: vgpr_32 }
- { id: 1, class: vgpr_32 }
- { id: 2, class: vgpr_32 }
body: |
bb.0:
%0 = IMPLICIT_DEF
%1 = IMPLICIT_DEF
%2 = IMPLICIT_DEF
GLOBAL_STORE_DWORD undef $vgpr0_vgpr1, %2, 0, 0, 0, implicit $exec
dead %2:vgpr_32 = V_MAC_F32_e32 %0:vgpr_32, %1:vgpr_32, %2:vgpr_32, implicit $exec
S_ENDPGM 0