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[MachineCopyPropagation] Recognise and delete no-op moves produced after forwarded uses #129889

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Merged
merged 6 commits into from
Mar 10, 2025
Merged

[MachineCopyPropagation] Recognise and delete no-op moves produced after forwarded uses #129889

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32d1aa1
[RISCV][test] Add test case showing case where machine copy propagati…
asb Mar 5, 2025
03e255f
[MachineCopyPropagation] Recognise and delete no-op moves produced af…
asb Mar 5, 2025
d209c13
Formatting fix
asb Mar 5, 2025
c0498f8
Don't delete apparent no-op if src==def is a reserved reg
asb Mar 7, 2025
a9ff08e
Merge remote-tracking branch 'origin/main' into 2025q1-machinecopypro…
asb Mar 9, 2025
85468c1
Merge remote-tracking branch 'origin/main' into 2025q1-machinecopypro…
asb Mar 10, 2025
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13 changes: 13 additions & 0 deletions llvm/lib/CodeGen/MachineCopyPropagation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -971,6 +971,19 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {

forwardUses(MI);

// It's possible that the previous transformation has resulted in a no-op
// register move (i.e. one where source and destination registers are the
// same and are not referring to a reserved register). If so, delete it.
CopyOperands = isCopyInstr(MI, *TII, UseCopyInstr);
if (CopyOperands &&
CopyOperands->Source->getReg() == CopyOperands->Destination->getReg() &&
!MRI->isReserved(CopyOperands->Source->getReg())) {
MI.eraseFromParent();
NumDeletes++;
Changed = true;
continue;
}

// Not a copy.
SmallVector<Register, 4> Defs;
const MachineOperand *RegMask = nullptr;
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1 change: 0 additions & 1 deletion llvm/test/CodeGen/RISCV/GlobalISel/constbarrier-rv32.ll
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Expand Up @@ -38,7 +38,6 @@ define void @constant_fold_barrier_i128(ptr %p) {
; RV32-NEXT: seqz a7, a6
; RV32-NEXT: and a1, a7, a1
; RV32-NEXT: add a7, a4, zero
; RV32-NEXT: add a5, a5, zero
; RV32-NEXT: sltu a4, a4, a4
; RV32-NEXT: or a1, a3, a1
; RV32-NEXT: add a7, a7, a1
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1 change: 0 additions & 1 deletion llvm/test/CodeGen/RISCV/GlobalISel/constbarrier-rv64.ll
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Expand Up @@ -26,7 +26,6 @@ define i128 @constant_fold_barrier_i128(i128 %x) {
; RV64-NEXT: and a0, a0, a2
; RV64-NEXT: add a0, a0, a2
; RV64-NEXT: sltu a2, a0, a2
; RV64-NEXT: add a1, a1, zero
; RV64-NEXT: add a1, a1, a2
; RV64-NEXT: ret
entry:
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2 changes: 0 additions & 2 deletions llvm/test/CodeGen/RISCV/machine-copyprop-noop-removal.mir
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Expand Up @@ -3,7 +3,6 @@

## This test was added to capture a case where MachineCopyPropagation risks
## leaving a no-op register move (add, x0, reg).
## FIXME: No-op register move is left behind after machine-cp.

---
name: ham
Expand All @@ -22,7 +21,6 @@ body: |
; CHECK-NEXT: liveins: $x10
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: $x11 = ADDI $x0, 0
; CHECK-NEXT: renamable $x10 = ADD $x0, killed renamable $x10
; CHECK-NEXT: BEQ renamable $x10, $x0, %bb.4
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: bb.2:
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1 change: 0 additions & 1 deletion llvm/test/CodeGen/RISCV/sextw-removal.ll
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Expand Up @@ -1352,7 +1352,6 @@ define signext i32 @sextw_sh2add(i1 zeroext %0, ptr %1, i32 signext %2, i32 sign
; NOREMOVAL-LABEL: sextw_sh2add:
; NOREMOVAL: # %bb.0:
; NOREMOVAL-NEXT: sh2add a2, a2, a3
; NOREMOVAL-NEXT: mv a2, a2
; NOREMOVAL-NEXT: beqz a0, .LBB22_2
; NOREMOVAL-NEXT: # %bb.1:
; NOREMOVAL-NEXT: sw a2, 0(a1)
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