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[DebugInfo] MachineSink: Insert undef DBG_VALUEs when sinking instructions
When we sink DBG_VALUEs between blocks, we simply move the DBG_VALUE instruction to below the sunk instruction. However, we should also mark the variable as being undef at the original location, to terminate any earlier variable location. This patch does that -- plus, if the instruction being sunk is a copy, it attempts to propagate the copy through the DBG_VALUE, replacing the destination with the source. Differential Revision: https://reviews.llvm.org/D58238
This commit is contained in:
Jeremy Morse
parent
b8042dbe2b
commit
ee50590e16
@ -736,6 +736,9 @@ static bool SinkingPreventsImplicitNullCheck(MachineInstr &MI,
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static void performSink(MachineInstr &MI, MachineBasicBlock &SuccToSinkTo,
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MachineBasicBlock::iterator InsertPos,
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SmallVectorImpl<MachineInstr *> *DbgVals = nullptr) {
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const MachineRegisterInfo &MRI = MI.getMF()->getRegInfo();
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const TargetInstrInfo &TII = *MI.getMF()->getSubtarget().getInstrInfo();
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// If debug values are provided use those, otherwise call collectDebugValues.
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SmallVector<MachineInstr *, 2> DbgValuesToSink;
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if (DbgVals)
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@ -758,13 +761,57 @@ static void performSink(MachineInstr &MI, MachineBasicBlock &SuccToSinkTo,
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SuccToSinkTo.splice(InsertPos, ParentBlock, MI,
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++MachineBasicBlock::iterator(MI));
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// Move previously adjacent debug value instructions to the insert position.
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// Sink a copy of debug users to the insert position. Mark the original
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// DBG_VALUE location as 'undef', indicating that any earlier variable
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// location should be terminated as we've optimised away the value at this
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// point.
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// If the sunk instruction is a copy, try to forward the copy instead of
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// leaving an 'undef' DBG_VALUE in the original location. Don't do this if
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// there's any subregister weirdness involved.
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for (SmallVectorImpl<MachineInstr *>::iterator DBI = DbgValuesToSink.begin(),
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DBE = DbgValuesToSink.end();
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DBI != DBE; ++DBI) {
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MachineInstr *DbgMI = *DBI;
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SuccToSinkTo.splice(InsertPos, ParentBlock, DbgMI,
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++MachineBasicBlock::iterator(DbgMI));
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MachineInstr *NewDbgMI = DbgMI->getMF()->CloneMachineInstr(*DBI);
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SuccToSinkTo.insert(InsertPos, NewDbgMI);
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// Copy DBG_VALUE operand and set the original to undef. We then check to
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// see whether this is something that can be copy-forwarded. If it isn't,
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// continue around the loop.
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MachineOperand DbgMO = DbgMI->getOperand(0);
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DbgMI->getOperand(0).setReg(0);
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const MachineOperand *SrcMO = nullptr, *DstMO = nullptr;
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if (!TII.isCopyInstr(MI, SrcMO, DstMO))
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continue;
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// Check validity of forwarding this copy.
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bool PostRA = MRI.getNumVirtRegs() == 0;
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// Trying to forward between physical and virtual registers is too hard.
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if (DbgMO.getReg().isVirtual() != SrcMO->getReg().isVirtual())
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continue;
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// Only try virtual register copy-forwarding before regalloc, and physical
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// register copy-forwarding after regalloc.
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bool arePhysRegs = !DbgMO.getReg().isVirtual();
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if (arePhysRegs != PostRA)
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continue;
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// Pre-regalloc, only forward if all subregisters agree (or there are no
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// subregs at all). More analysis might recover some forwardable copies.
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if (!PostRA && (DbgMO.getSubReg() != SrcMO->getSubReg() ||
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DbgMO.getSubReg() != DstMO->getSubReg()))
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continue;
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// Post-regalloc, we may be sinking a DBG_VALUE of a sub or super-register
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// of this copy. Only forward the copy if the DBG_VALUE operand exactly
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// matches the copy destination.
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if (PostRA && DbgMO.getReg() != DstMO->getReg())
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continue;
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DbgMI->getOperand(0).setReg(SrcMO->getReg());
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DbgMI->getOperand(0).setSubReg(SrcMO->getSubReg());
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}
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}
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@ -69,7 +69,10 @@ body: |
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: liveins: $edi
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; CHECK: DBG_VALUE $edi, $noreg, ![[BARVAR]]
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; CHECK-NEXT: DBG_VALUE $edi, $noreg, ![[ARGVAR]]
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; CHECK-NEXT: DBG_VALUE $noreg, $noreg, ![[BAZVAR]]
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; CHECK-NEXT: renamable $cl = MOV8ri 1
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; CHECK-NEXT: DBG_VALUE $noreg, $noreg, ![[FOOVAR]]
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; CHECK-NEXT: JMP_1 %bb.1
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; CHECK: bb.1.return:
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; CHECK: liveins: $cl, $edi
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105
llvm/test/DebugInfo/MIR/X86/sink-leaves-undef.mir
Normal file
105
llvm/test/DebugInfo/MIR/X86/sink-leaves-undef.mir
Normal file
@ -0,0 +1,105 @@
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# RUN: llc %s -o - -run-pass=machine-sink -mtriple=x86_64-- | FileCheck %s
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# This is a copy of test/CodeGen/X86/MachineSink-DbgValue.ll, where we
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# additionally test that when the MOV32rm defining %0 is sunk, it leaves
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# an 'undef' DBG_VALUE behind to terminate earlier location ranges.
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--- |
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target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-apple-macosx10.7.0"
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; Function Attrs: nounwind readonly ssp uwtable
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define i32 @foo(i32 %i, i32* nocapture %c) !dbg !4 {
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call void @llvm.dbg.value(metadata i32 %i, metadata !9, metadata !DIExpression()), !dbg !14
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%ab = load i32, i32* %c, align 1, !dbg !15
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call void @llvm.dbg.value(metadata i32* %c, metadata !10, metadata !DIExpression()), !dbg !16
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call void @llvm.dbg.value(metadata i32 %ab, metadata !12, metadata !DIExpression()), !dbg !15
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%cd = icmp eq i32 %i, 42, !dbg !17
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br i1 %cd, label %bb1, label %bb2, !dbg !17
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bb1: ; preds = %0
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%gh = add nsw i32 %ab, 2, !dbg !18
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br label %bb2, !dbg !18
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bb2: ; preds = %bb1, %0
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%.0 = phi i32 [ %gh, %bb1 ], [ 0, %0 ]
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ret i32 %.0, !dbg !19
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}
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; Function Attrs: nounwind readnone speculatable
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declare void @llvm.dbg.value(metadata, metadata, metadata)
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; Function Attrs: nounwind
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declare void @llvm.stackprotector(i8*, i8**)
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "Apple clang version 3.0 (tags/Apple/clang-211.10.1) (based on LLVM 3.0svn)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2)
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!1 = !DIFile(filename: "a.c", directory: "/private/tmp")
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!2 = !{}
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!3 = !{i32 1, !"Debug Info Version", i32 3}
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!4 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 2, type: !5, virtualIndex: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
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!5 = !DISubroutineType(types: !6)
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!6 = !{!7}
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!7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
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!8 = !{!9, !10, !12}
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!9 = !DILocalVariable(name: "i", arg: 1, scope: !4, file: !1, line: 2, type: !7)
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!10 = !DILocalVariable(name: "c", arg: 2, scope: !4, file: !1, line: 2, type: !11)
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!11 = !DIDerivedType(tag: DW_TAG_pointer_type, scope: !0, baseType: !7, size: 64, align: 64)
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!12 = !DILocalVariable(name: "a", scope: !13, file: !1, line: 3, type: !7)
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!13 = distinct !DILexicalBlock(scope: !4, file: !1, line: 2, column: 25)
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!14 = !DILocation(line: 2, column: 13, scope: !4)
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!15 = !DILocation(line: 3, column: 14, scope: !13)
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!16 = !DILocation(line: 2, column: 22, scope: !4)
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!17 = !DILocation(line: 4, column: 3, scope: !13)
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!18 = !DILocation(line: 5, column: 5, scope: !13)
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!19 = !DILocation(line: 7, column: 1, scope: !13)
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; CHECK: ![[VARNUM:[0-9]+]] = !DILocalVariable(name: "a",
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...
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---
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name: foo
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alignment: 4
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tracksRegLiveness: true
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registers:
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- { id: 0, class: gr32 }
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- { id: 1, class: gr32 }
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- { id: 2, class: gr32 }
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- { id: 3, class: gr32 }
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- { id: 4, class: gr64 }
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- { id: 5, class: gr32 }
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- { id: 6, class: gr32 }
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liveins:
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- { reg: '$edi', virtual-reg: '%3' }
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- { reg: '$rsi', virtual-reg: '%4' }
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body: |
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bb.0 (%ir-block.0):
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successors: %bb.1, %bb.2
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liveins: $edi, $rsi
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; CHECK-LABEL: bb.0 (%ir-block.0):
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; CHECK: DBG_VALUE $noreg, $noreg, ![[VARNUM]]
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DBG_VALUE $edi, $noreg, !9, !DIExpression(), debug-location !14
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DBG_VALUE $rsi, $noreg, !10, !DIExpression(), debug-location !16
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%4:gr64 = COPY $rsi
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DBG_VALUE %4, $noreg, !10, !DIExpression(), debug-location !16
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%3:gr32 = COPY $edi
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DBG_VALUE %3, $noreg, !9, !DIExpression(), debug-location !14
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%0:gr32 = MOV32rm %4, 1, $noreg, 0, $noreg, debug-location !15 :: (load 4 from %ir.c, align 1)
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DBG_VALUE %0, $noreg, !12, !DIExpression(), debug-location !15
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%5:gr32 = MOV32r0 implicit-def dead $eflags
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%6:gr32 = SUB32ri8 %3, 42, implicit-def $eflags, debug-location !17
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JCC_1 %bb.2, 5, implicit $eflags, debug-location !17
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JMP_1 %bb.1, debug-location !17
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bb.1.bb1:
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; CHECK-LABEL: bb.1.bb1:
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; CHECK: %[[VREG:[0-9]+]]:gr32 = MOV32rm
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; CHECK-NEXT: DBG_VALUE %[[VREG]], $noreg, ![[VARNUM]]
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; CHECK-NEXT: ADD32ri8
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%1:gr32 = nsw ADD32ri8 %0, 2, implicit-def dead $eflags, debug-location !18
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bb.2.bb2:
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%2:gr32 = PHI %5, %bb.0, %1, %bb.1
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$eax = COPY %2, debug-location !19
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RET 0, $eax, debug-location !19
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...
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