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[DebugInfo] Discard invalid DBG_VALUE instructions in LiveDebugVariables
Summary: This is a workaround for pr36417 https://bugs.llvm.org/show_bug.cgi?id=36417 LiveDebugVariables will now verify that the DBG_VALUE instructions are sane (prior to register allocation) by asking LIS if a virtual register used in the DBG_VALUE is live (or dead def) in the slot index before the DBG_VALUE. If it isn't sane the DBG_VALUE is discarded. One pass that was identified as introducing non-sane DBG_VALUE instructtons, when analysing pr36417, was the DAG->DAG Instruction Selection. It sometimes inserts DBG_VALUE instructions referring to a virtual register that is defined later in the same basic block. So it is a use before def kind of problem. The DBG_VALUE is typically inserted in the beginning of a basic block when this happens. The problem can be seen in the test case test/DebugInfo/X86/dbg-value-inlined-parameter.ll Reviewers: aprantl, rnk, probinson Reviewed By: aprantl Subscribers: vsk, davide, alexcrichton, Ka-Ka, eraman, llvm-commits, JDevlieghere Differential Revision: https://reviews.llvm.org/D43956 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326769 91177308-0d34-0410-b5e6-96231b3b80d8
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lines changed

3 files changed

+181
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‎lib/CodeGen/LiveDebugVariables.cpp

+37-1
Original file line numberDiff line numberDiff line change
@@ -514,6 +514,39 @@ bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
514514
return false;
515515
}
516516

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// Detect invalid DBG_VALUE instructions, with a debug-use of a virtual
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// register that hasn't been defined yet. If we do not remove those here, then
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// the re-insertion of the DBG_VALUE instruction after register allocation
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// will be incorrect.
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// TODO: If earlier passes are corrected to generate sane debug information
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// (and if the machine verifier is improved to catch this), then these checks
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// could be removed or replaced by asserts.
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bool Discard = false;
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if (MI.getOperand(0).isReg() &&
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TargetRegisterInfo::isVirtualRegister(MI.getOperand(0).getReg())) {
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const unsigned Reg = MI.getOperand(0).getReg();
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if (!LIS->hasInterval(Reg)) {
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// The DBG_VALUE is described by a virtual register that does not have a
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// live interval. Discard the DBG_VALUE.
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Discard = true;
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DEBUG(dbgs() << "Discarding debug info (no LIS interval): "
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<< Idx << " " << MI);
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} else {
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// The DBG_VALUE is only valid if either Reg is live out from Idx, or Reg
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// is defined dead at Idx (where Idx is the slot index for the instruction
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// preceeding the DBG_VALUE).
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const LiveInterval &LI = LIS->getInterval(Reg);
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LiveQueryResult LRQ = LI.Query(Idx);
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if (!LRQ.valueOutOrDead()) {
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// We have found a DBG_VALUE with the value in a virtual register that
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// is not live. Discard the DBG_VALUE.
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Discard = true;
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DEBUG(dbgs() << "Discarding debug info (reg not live): "
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<< Idx << " " << MI);
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}
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}
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}
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// Get or create the UserValue for (variable,offset) here.
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bool IsIndirect = MI.getOperand(1).isImm();
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if (IsIndirect)
@@ -522,7 +555,10 @@ bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
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const DIExpression *Expr = MI.getDebugExpression();
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UserValue *UV =
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getUserValue(Var, Expr, MI.getDebugLoc());
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UV->addDef(Idx, MI.getOperand(0), IsIndirect);
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if (!Discard)
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UV->addDef(Idx, MI.getOperand(0), IsIndirect);
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else
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UV->addDef(Idx, MachineOperand::CreateReg(0U, RegState::Debug), false);
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return true;
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}
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‎test/DebugInfo/X86/dbg-value-inlined-parameter.ll

+3-3
Original file line numberDiff line numberDiff line change
@@ -32,10 +32,10 @@
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;CHECK-NEXT: DW_AT_call_line
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;CHECK: DW_TAG_formal_parameter
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;FIXME: Linux shouldn't drop this parameter either...
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;CHECK-NOT: DW_TAG
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;DARWIN: DW_AT_abstract_origin {{.*}} "sp"
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;DARWIN: DW_TAG_formal_parameter
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;FIXME: Shouldn't drop this parameter...
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;XCHECK: DW_AT_abstract_origin {{.*}} "sp"
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;XCHECK: DW_TAG_formal_parameter
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;CHECK: DW_AT_abstract_origin {{.*}} "nums"
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;CHECK-NOT: DW_TAG_formal_parameter
4141

‎test/DebugInfo/X86/live-debug-vars-discard-invalid.mir

+141
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,141 @@
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# RUN: llc -mtriple=x86_64-linux-gnu -start-before greedy -stop-after virtregrewriter -o - %s | FileCheck %s
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--- |
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; ModuleID = '<stdin>'
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source_filename = "test/DebugInfo/X86/dbg-value-inlined-parameter.ll"
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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-darwin"
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%struct.S1 = type { float*, i32 }
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@p = common global %struct.S1 zeroinitializer, align 8, !dbg !0
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; Function Attrs: nounwind optsize ssp
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define void @foobar() !dbg !15 {
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entry:
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tail call void @llvm.dbg.value(metadata %struct.S1* @p, metadata !18, metadata !DIExpression()) , !dbg !25
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ret void, !dbg !32
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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) #2
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!llvm.dbg.cu = !{!2}
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!llvm.module.flags = !{!14}
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!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
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!1 = !DIGlobalVariable(name: "p", scope: !2, file: !3, line: 14, type: !6, isLocal: false, isDefinition: true)
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!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 2.9 (trunk 125693)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !4, globals: !5, imports: !4)
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!3 = !DIFile(filename: "nm2.c", directory: "/private/tmp")
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!4 = !{}
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!5 = !{!0}
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!6 = !DIDerivedType(tag: DW_TAG_typedef, name: "S1", scope: !2, file: !3, line: 4, baseType: !7)
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!7 = !DICompositeType(tag: DW_TAG_structure_type, name: "S1", scope: !2, file: !3, line: 1, size: 128, align: 64, elements: !8)
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!8 = !{!9, !12}
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!9 = !DIDerivedType(tag: DW_TAG_member, name: "m", scope: !3, file: !3, line: 2, baseType: !10, size: 64, align: 64)
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!10 = !DIDerivedType(tag: DW_TAG_pointer_type, scope: !2, baseType: !11, size: 64, align: 64)
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!11 = !DIBasicType(name: "float", size: 32, align: 32, encoding: DW_ATE_float)
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!12 = !DIDerivedType(tag: DW_TAG_member, name: "nums", scope: !3, file: !3, line: 3, baseType: !13, size: 32, align: 32, offset: 64)
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!13 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
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!14 = !{i32 1, !"Debug Info Version", i32 3}
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!15 = distinct !DISubprogram(name: "foobar", scope: !3, file: !3, line: 15, type: !16, isLocal: false, isDefinition: true, virtualIndex: 6, isOptimized: true, unit: !2)
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!16 = !DISubroutineType(types: !17)
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!17 = !{null}
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!18 = !DILocalVariable(name: "sp", arg: 1, scope: !19, file: !3, line: 7, type: !24)
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!19 = distinct !DISubprogram(name: "foo", scope: !3, file: !3, line: 8, type: !20, isLocal: false, isDefinition: true, scopeLine: 8, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, unit: !2, variables: !22)
46+
!20 = !DISubroutineType(types: !21)
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!21 = !{!13}
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!22 = !{!18, !23}
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!23 = !DILocalVariable(name: "nums", arg: 2, scope: !19, file: !3, line: 7, type: !13)
50+
!24 = !DIDerivedType(tag: DW_TAG_pointer_type, scope: !2, baseType: !6, size: 64, align: 64)
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!25 = !DILocation(line: 7, column: 13, scope: !19, inlinedAt: !26)
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!26 = !DILocation(line: 16, column: 3, scope: !27)
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!27 = distinct !DILexicalBlock(scope: !15, file: !3, line: 15, column: 15)
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!32 = !DILocation(line: 17, column: 1, scope: !27)
55+
56+
...
57+
---
58+
name: foobar
59+
tracksRegLiveness: true
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body: |
61+
bb.0:
62+
%1:gr64 = IMPLICIT_DEF
63+
%2:gr64 = IMPLICIT_DEF
64+
65+
bb.1:
66+
; This DBG_VALUE will be discarded (use before def of %0).
67+
DBG_VALUE debug-use %0, debug-use $noreg, !18, !DIExpression(), debug-location !25
68+
%0:gr64 = IMPLICIT_DEF
69+
%0:gr64 = IMPLICIT_DEF
70+
%0:gr64 = IMPLICIT_DEF
71+
%0:gr64 = IMPLICIT_DEF
72+
73+
bb.2:
74+
; This DBG_VALUE will be discarded (%1 is defined earlier, but it is not live in, so we do not know where %1 is stored).
75+
DBG_VALUE debug-use %1, debug-use $noreg, !18, !DIExpression(), debug-location !25
76+
%1:gr64 = IMPLICIT_DEF
77+
%1:gr64 = IMPLICIT_DEF
78+
%1:gr64 = IMPLICIT_DEF
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%1:gr64 = IMPLICIT_DEF
80+
; This DBG_VALUE is kept, even if %1 is dead, it was defined in the prev instruction,
81+
; so the value should be available for as long as the register allocated to %1 is live.
82+
DBG_VALUE debug-use %1, debug-use $noreg, !18, !DIExpression(), debug-location !25
83+
84+
bb.3:
85+
%1:gr64 = IMPLICIT_DEF
86+
DBG_VALUE 0, debug-use $noreg, !23, !DIExpression(), debug-location !25
87+
; This DBG_VALUE is kept, even if %1 is dead, it was defined in the prev non-dbg instruction,
88+
; so the value should be available for as long as the register allocated to %1 is live.
89+
DBG_VALUE debug-use %1, debug-use $noreg, !18, !DIExpression(), debug-location !25
90+
91+
bb.4:
92+
; All DBG_VALUEs here should survive. %2 is livein as it was defined in bb.0, and it has use/def in the BTS64rr instruction.
93+
DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
94+
%2:gr64 = BTS64rr %2, 0, implicit-def $eflags
95+
DBG_VALUE 0, debug-use $noreg, !23, !DIExpression(), debug-location !25
96+
DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
97+
%2:gr64 = BTS64rr %2, 0, implicit-def $eflags
98+
DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
99+
%2:gr64 = BTS64rr %2, 0, implicit-def $eflags
100+
DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
101+
102+
bb.5:
103+
RET 0, debug-location !32
104+
...
105+
106+
# CHECK-LABEL: name: foobar
107+
108+
# CHECK-LABEL: bb.1:
109+
## After solving https://bugs.llvm.org/show_bug.cgi?id=36579 we expect to get a
110+
## DBG_VALUE debug-use $noreg
111+
## here.
112+
# CHECK-NOT: DBG_VALUE
113+
114+
# CHECK-LABEL: bb.2:
115+
## After solving https://bugs.llvm.org/show_bug.cgi?id=36579 we expect to get a
116+
## DBG_VALUE debug-use $noreg
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## here.
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# CHECK-NOT: DBG_VALUE
119+
# CHECK: dead renamable $rcx = IMPLICIT_DEF
120+
# CHECK-NEXT: dead renamable $rcx = IMPLICIT_DEF
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# CHECK-NEXT: dead renamable $rcx = IMPLICIT_DEF
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# CHECK-NEXT: dead renamable $rcx = IMPLICIT_DEF
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# CHECK-NEXT: DBG_VALUE debug-use $rcx, debug-use $noreg, !18, !DIExpression()
124+
125+
# CHECK-LABEL: bb.3:
126+
# CHECK: dead renamable $rcx = IMPLICIT_DEF
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# CHECK-NEXT: DBG_VALUE 0, debug-use $noreg, !23, !DIExpression()
128+
# CHECK-NEXT: DBG_VALUE debug-use $rcx, debug-use $noreg, !18, !DIExpression()
129+
130+
# CHECK-LABEL: bb.4:
131+
# CHECK: liveins: $rax
132+
# CHECK: DBG_VALUE debug-use $rax, debug-use $noreg, !18, !DIExpression()
133+
# CHECK-NEXT: renamable $rax = BTS64rr killed renamable $rax, 0, implicit-def $eflags
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# CHECK-NEXT: DBG_VALUE 0, debug-use $noreg, !23, !DIExpression()
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# CHECK-NEXT: DBG_VALUE debug-use $rax, debug-use $noreg, !18, !DIExpression()
136+
# CHECK-NEXT: renamable $rax = BTS64rr killed renamable $rax, 0, implicit-def $eflags
137+
# CHECK-NEXT: DBG_VALUE debug-use $rax, debug-use $noreg, !18, !DIExpression()
138+
# CHECK-NEXT: dead renamable $rax = BTS64rr killed renamable $rax, 0, implicit-def $eflags
139+
140+
# CHECK-LABEL: bb.5:
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# CHECK-NEXT: RET 0

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