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[AArch64] Drop flags from BSP pseudos #151856

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[AArch64] Drop flags from BSP pseudos #151856

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6 changes: 4 additions & 2 deletions llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1242,8 +1242,10 @@ bool AArch64ExpandPseudo::expandMI(MachineBasicBlock &MBB,
.addReg(DstReg,
RegState::Define |
getRenamableRegState(MI.getOperand(0).isRenamable()))
.add(MI.getOperand(1))
.add(MI.getOperand(1));
.addReg(MI.getOperand(1).getReg(),
getRenamableRegState(MI.getOperand(1).isRenamable()))
.addReg(MI.getOperand(1).getReg(),
getRenamableRegState(MI.getOperand(1).isRenamable()));
auto I2 =
BuildMI(MBB, MBBI, MI.getDebugLoc(),
TII->get(Opcode == AArch64::BSPv8i8 ? AArch64::BSLv8i8
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22 changes: 21 additions & 1 deletion llvm/test/CodeGen/AArch64/bsp_implicit_ops.mir
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Expand Up @@ -13,7 +13,7 @@ body: |
; CHECK-LABEL: name: BSL_COPY
; CHECK: liveins: $q20, $q21, $q22, $q23, $q6, $q1, $q7
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: renamable $q2 = ORRv16i8 killed renamable $q20, killed renamable $q20
; CHECK-NEXT: renamable $q2 = ORRv16i8 renamable $q20, renamable $q20
; CHECK-NEXT: renamable $q2 = BSLv16i8 killed renamable $q2, renamable $q21, renamable $q6, implicit killed $q21_q22_q23, implicit killed $q0_q1_q2_q3, implicit-def $q0_q1_q2_q3
; CHECK-NEXT: $q22 = ORRv16i8 $q0, killed $q0
; CHECK-NEXT: $q23 = ORRv16i8 $q1, killed $q1
Expand Down Expand Up @@ -96,3 +96,23 @@ body: |
$q25 = ORRv16i8 $q3, killed $q3
RET_ReallyLR implicit $q22
...
---
name: DoubleOp
tracksRegLiveness: true
body: |
bb.0.entry:
liveins: $q2

; CHECK-LABEL: name: DoubleOp
; CHECK: liveins: $q2
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: renamable $q0 = MOVIv8i16 1, 0
; CHECK-NEXT: renamable $q1 = ORRv16i8 renamable $q2, renamable $q2
; CHECK-NEXT: renamable $q1 = BSLv16i8 killed renamable $q1, renamable $q2, renamable $q0
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@rj-jesus rj-jesus Aug 5, 2025 •
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Would it be worth preserving the kill flag when the MOV's operand isn't needed elsewhere, like in BSL_COPY above, and propagating it down to the BSL in other cases (for example, killing q2 here)?

; CHECK-NEXT: renamable $q0 = SQADDv8i16 killed renamable $q1, killed renamable $q0
; CHECK-NEXT: RET undef $lr, implicit $q0
renamable $q0 = MOVIv8i16 1, 0
renamable $q1 = BSPv16i8 killed renamable $q2, renamable $q2, renamable $q0
renamable $q0 = SQADDv8i16 killed renamable $q1, killed renamable $q0
RET_ReallyLR implicit $q0
...