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[PHIElimination] Fix bug around $noreg assignment #146320

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Merged
merged 1 commit into from
Jun 30, 2025
+54 −2
Merged

[PHIElimination] Fix bug around $noreg assignment #146320

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5 changes: 3 additions & 2 deletions llvm/lib/CodeGen/PHIElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -582,8 +582,9 @@ void PHIEliminationImpl::LowerPHINode(MachineBasicBlock &MBB,
}

// Reuse an existing copy in the block if possible.
if (MachineInstr *DefMI = MRI->getUniqueVRegDef(SrcReg)) {
if (DefMI->isCopy() && DefMI->getParent() == &opBlock &&
if (IncomingReg.isVirtual()) {
MachineInstr *DefMI = MRI->getUniqueVRegDef(SrcReg);
if (DefMI && DefMI->isCopy() && DefMI->getParent() == &opBlock &&
MRI->use_empty(SrcReg)) {
DefMI->getOperand(0).setReg(IncomingReg);
continue;
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51 changes: 51 additions & 0 deletions llvm/test/CodeGen/AArch64/PHIElimination-reuse-copy.mir
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Expand Up @@ -66,3 +66,54 @@ body: |
%b:gpr32 = PHI %a:gpr32, %bb.1, undef %undef:gpr32, %bb.0
...

---
name: copy_to_dead
tracksRegLiveness: true
body: |
; CHECK-LABEL: name: copy_to_dead
; CHECK: bb.0:
; CHECK-NEXT: successors: %bb.2(0x40000000), %bb.1(0x40000000)
; CHECK-NEXT: liveins: $wzr, $xzr
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr32 = COPY $wzr
; CHECK-NEXT: dead [[COPY1:%[0-9]+]]:gpr64 = COPY $xzr
; CHECK-NEXT: TBZW killed [[COPY]], 0, %bb.2
; CHECK-NEXT: B %bb.1
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: bb.1:
; CHECK-NEXT: successors: %bb.2(0x80000000)
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: [[DEF:%[0-9]+]]:gpr64 = IMPLICIT_DEF
; CHECK-NEXT: [[DEF1:%[0-9]+]]:gpr64 = IMPLICIT_DEF
; CHECK-NEXT: B %bb.2
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: bb.2:
; CHECK-NEXT: successors: %bb.1(0x80000000)
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: [[DEF2:%[0-9]+]]:gpr64 = IMPLICIT_DEF
; CHECK-NEXT: [[DEF3:%[0-9]+]]:gpr64 = IMPLICIT_DEF
; CHECK-NEXT: B %bb.1
bb.0:
liveins: $wzr, $xzr

%9:gpr32 = COPY $wzr
dead %5:gpr64 = COPY $xzr
TBZW killed %9:gpr32, 0, %bb.2
B %bb.1

bb.1:
successors: %bb.2(0x80000000); %bb.2(100.00%)

dead %1:gpr64 = PHI undef %3:gpr64, %bb.2, undef %5:gpr64, %bb.0
dead %2:gpr64 = PHI undef %4:gpr64, %bb.2, undef %5:gpr64, %bb.0
B %bb.2

bb.2:
successors: %bb.1(0x80000000); %bb.1(100.00%)

dead %3:gpr64 = PHI undef %1:gpr64, %bb.1, undef %5:gpr64, %bb.0
dead %4:gpr64 = PHI undef %2:gpr64, %bb.1, undef %5:gpr64, %bb.0
B %bb.1

...

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