Index: llvm/lib/CodeGen/LiveDebugVariables.cpp
===================================================================
--- llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -394,6 +394,11 @@
   LiveIntervals *LIS;
   const TargetRegisterInfo *TRI;
 
+  using StashedInstrRef =
+      std::tuple<unsigned, unsigned, const DILocalVariable *,
+                 const DIExpression *, DebugLoc>;
+  std::map<SlotIndex, std::vector<StashedInstrRef>> StashedInstrReferences;
+
   /// Whether emitDebugValues is called.
   bool EmitDone = false;
 
@@ -430,6 +435,16 @@
   /// \returns True if the DBG_VALUE instruction should be deleted.
   bool handleDebugValue(MachineInstr &MI, SlotIndex Idx);
 
+  /// Track a DBG_INSTR_REF. This needs to be removed from the MachineFunction
+  /// during regalloc -- but there's no need to maintain live ranges, as we
+  /// refer to a value rather than a location.
+  ///
+  /// \param MI DBG_INSTR_REF instruction
+  /// \param Idx Last valid SlotIndex before instruction
+  ///
+  /// \returns True if the DBG_VALUE instruction should be deleted.
+  bool handleDebugInstrRef(MachineInstr &MI, SlotIndex Idx);
+
   /// Add DBG_LABEL instruction to UserLabel.
   ///
   /// \param MI DBG_LABEL instruction
@@ -458,6 +473,7 @@
   /// Release all memory.
   void clear() {
     MF = nullptr;
+    StashedInstrReferences.clear();
     userValues.clear();
     userLabels.clear();
     virtRegToEqClass.clear();
@@ -665,6 +681,19 @@
   return true;
 }
 
+bool LDVImpl::handleDebugInstrRef(MachineInstr &MI, SlotIndex Idx) {
+  assert(MI.isDebugRef());
+  unsigned InstrNum = MI.getOperand(0).getImm();
+  unsigned OperandNum = MI.getOperand(1).getImm();
+  auto *Var = MI.getDebugVariable();
+  auto *Expr = MI.getDebugExpression();
+  auto &DL = MI.getDebugLoc();
+  StashedInstrRef Stashed =
+      std::make_tuple(InstrNum, OperandNum, Var, Expr, DL);
+  StashedInstrReferences[Idx].push_back(Stashed);
+  return true;
+}
+
 bool LDVImpl::handleDebugLabel(MachineInstr &MI, SlotIndex Idx) {
   // DBG_LABEL label
   if (MI.getNumOperands() != 1 || !MI.getOperand(0).isMetadata()) {
@@ -712,6 +741,7 @@
         // Only handle DBG_VALUE in handleDebugValue(). Skip all other
         // kinds of debug instructions.
         if ((MBBI->isDebugValue() && handleDebugValue(*MBBI, Idx)) ||
+            (MBBI->isDebugRef() && handleDebugInstrRef(*MBBI, Idx)) ||
             (MBBI->isDebugLabel() && handleDebugLabel(*MBBI, Idx))) {
           MBBI = MBB->erase(MBBI);
           Changed = true;
@@ -1434,6 +1464,28 @@
     LLVM_DEBUG(userLabel->print(dbgs(), TRI));
     userLabel->emitDebugLabel(*LIS, *TII);
   }
+
+  LLVM_DEBUG(dbgs() << "********** EMITTING INSTR REFERENCES **********\n");
+
+  // Re-insert any DBG_INSTR_REFs back in the position they were. Ordering
+  // is preserved by vector.
+  auto Slots = LIS->getSlotIndexes();
+  const MCInstrDesc &RefII = TII->get(TargetOpcode::DBG_INSTR_REF);
+  for (auto &P : StashedInstrReferences) {
+    const SlotIndex &Idx = P.first;
+    auto *MBB = Slots->getMBBFromIndex(Idx);
+    MachineBasicBlock::iterator insertPos = findInsertLocation(MBB, Idx, *LIS);
+    for (auto &Stashed : P.second) {
+      auto MIB = BuildMI(*MF, std::get<4>(Stashed), RefII);
+      MIB.addImm(std::get<0>(Stashed));
+      MIB.addImm(std::get<1>(Stashed));
+      MIB.addMetadata(std::get<2>(Stashed));
+      MIB.addMetadata(std::get<3>(Stashed));
+      MachineInstr *New = MIB;
+      MBB->insert(insertPos, New);
+    }
+  }
+
   EmitDone = true;
 }
 
Index: llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
===================================================================
--- llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -804,7 +804,7 @@
       DbgMI = nullptr;
     }
 
-    if (MI.isDebugValue()) {
+    if (MI.isDebugValue() || MI.isDebugRef()) {
       DbgMI = &MI;
       continue;
     }
Index: llvm/test/DebugInfo/MIR/InstrRef/survives-livedebugvars.mir
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/MIR/InstrRef/survives-livedebugvars.mir
@@ -0,0 +1,142 @@
+# RUN: llc -start-after=phi-node-elimination -stop-after=virtregrewriter %s -mtriple=x86_64-unknown-unknown -o - -experimental-debug-variable-locations | FileCheck %s
+# RUN: llc -O0 -start-after=phi-node-elimination -stop-after=regallocfast %s -mtriple=x86_64-unknown-unknown -o - -experimental-debug-variable-locations | FileCheck %s --check-prefix=FASTREG
+#
+# Test that DBG_INSTR_REFs can pass through livedebugvariables to the end of
+# regalloc without problem. Program body copied from
+# livedebugvars-crossbb-interval.mir.
+#
+# CHECK-LABEL: bb.0:
+# CHECK:       DBG_INSTR_REF 1, 0
+# CHECK-NEXT:  JMP_1
+# CHECK-LABEL: bb.1:
+# CHECK:       DBG_INSTR_REF 2, 0
+# CHECK-NEXT:  JMP_1
+# CHECK-LABEL: bb.2:
+# CHECK:       DBG_INSTR_REF 3, 0
+# CHECK-NEXT:  CALL64pcrel32
+# CHECK-LABEL: bb.3:
+# CHECK:       DBG_INSTR_REF 4, 0
+# CHECK-NEXT:  JMP_1
+#
+#
+# The fast register allocator puts some spills in -- these are no-ops as far
+# as the slot indexes are concerned. It doesn't matter which side of spills
+# the DBG_INSTR_REF lands on.
+#
+# FASTREG-LABEL: bb.0:
+# FASTREG:       DBG_INSTR_REF 1, 0
+# FASTREG-NEXT:  MOV64mr
+# FASTREG-NEXT:  MOV32mr
+# FASTREG-NEXT:  JMP_1
+# FASTREG-LABEL: bb.1:
+# FASTREG:       DBG_INSTR_REF 2, 0
+# FASTREG-NEXT:  JMP_1
+# FASTREG-LABEL: bb.2:
+# FASTREG:       DBG_INSTR_REF 3, 0
+# FASTREG-NEXT:  CALL64pcrel32
+# FASTREG-LABEL: bb.3:
+# FASTREG:       MOV32rm
+# FASTREG-NEXT:  DBG_INSTR_REF 4, 0
+# FASTREG-NEXT:  MOV32mr
+# FASTREG-NEXT:  JMP_1
+# FASTREG-LABEL: bb.4:
+# FASTREG:       DBG_INSTR_REF 5, 0
+# FASTREG-NEXT:  RETQ
+
+--- |
+  ; ModuleID = 'tmp.ll'
+  source_filename = "tmp.ll"
+  target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+  
+  %struct.a = type { i32 }
+  
+  ; Function Attrs: nounwind ssp
+  define i32 @bar() !dbg !4 {
+    ret i32 0, !dbg !18
+  }
+  
+  declare i32 @foo();
+
+  ; Function Attrs: nounwind readnone speculatable willreturn
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+  
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3}
+  
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "asdf", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2)
+  !1 = !DIFile(filename: "bar.c", directory: "asdf")
+  !2 = !{}
+  !3 = !{i32 1, !"Debug Info Version", i32 3}
+  !4 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 5, type: !5, virtualIndex: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+  !5 = !DISubroutineType(types: !6)
+  !6 = !{!7}
+  !7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+  !8 = !{!9, !14}
+  !9 = !DILocalVariable(name: "b", arg: 1, scope: !4, file: !1, line: 5, type: !10)
+  !10 = !DIDerivedType(tag: DW_TAG_pointer_type, scope: !0, baseType: !11, size: 64, align: 64)
+  !11 = !DICompositeType(tag: DW_TAG_structure_type, name: "a", scope: !0, file: !1, line: 1, size: 32, align: 32, elements: !12)
+  !12 = !{!13}
+  !13 = !DIDerivedType(tag: DW_TAG_member, name: "c", scope: !1, file: !1, line: 2, baseType: !7, size: 32, align: 32)
+  !14 = !DILocalVariable(name: "x", scope: !15, file: !1, line: 6, type: !7)
+  !15 = distinct !DILexicalBlock(scope: !4, file: !1, line: 5, column: 22)
+  !16 = !DILocation(line: 5, column: 19, scope: !4)
+  !17 = !DILocation(line: 6, column: 14, scope: !15)
+  !18 = !DILocation(line: 8, column: 2, scope: !15)
+  !19 = !DILocation(line: 7, column: 2, scope: !15)
+
+...
+---
+name:            bar
+alignment:       16
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gr64 }
+  - { id: 1, class: gr32 }
+  - { id: 2, class: gr64 }
+  - { id: 3, class: gr64 }
+  - { id: 4, class: gr32 }
+  - { id: 5, class: gr32 }
+  - { id: 6, class: gr32 }
+  - { id: 7, class: gr32 }
+liveins:
+  - { reg: '$rdi', virtual-reg: '%2' }
+  - { reg: '$esi', virtual-reg: '%4' }
+frameInfo:
+  hasCalls:        true
+machineFunctionInfo: {}
+body:             |
+  bb.0:
+    liveins: $rdi, $esi
+  
+    %4:gr32 = COPY $esi
+    %2:gr64 = COPY $rdi
+    %3:gr64 = COPY killed %2
+    %5:gr32 = COPY killed %4
+    DBG_INSTR_REF 1, 0, !9, !DIExpression(), debug-location !16
+    JMP_1 %bb.3
+  
+  bb.1:
+    DBG_INSTR_REF 2, 0, !9, !DIExpression(), debug-location !16
+    JMP_1 %bb.4
+  
+  bb.2:
+    ADJCALLSTACKDOWN64 0, 0, 0, implicit-def $rsp, implicit-def $eflags, implicit-def $ssp, implicit $rsp, implicit $ssp, debug-location !19
+    $edi = COPY %6, debug-location !19
+    $al = MOV8ri 0, debug-location !19
+    DBG_INSTR_REF 3, 0, !9, !DIExpression(), debug-location !16
+    CALL64pcrel32 @foo, csr_64, implicit $rsp, implicit $ssp, implicit $al, implicit $edi, implicit-def $eax, debug-location !19
+    ADJCALLSTACKUP64 0, 0, implicit-def $rsp, implicit-def $eflags, implicit-def $ssp, implicit $rsp, implicit $ssp, debug-location !19
+    %7:gr32 = COPY $eax, debug-location !19
+    JMP_1 %bb.1
+  
+  bb.3:
+    %6:gr32 = MOV32rm %3, 1, $noreg, 0, $noreg, debug-location !17
+    DBG_INSTR_REF 4, 0, !9, !DIExpression(), debug-location !16
+    JMP_1 %bb.2
+  
+  bb.4:
+    $eax = COPY %5, debug-location !18
+    DBG_INSTR_REF 5, 0, !9, !DIExpression(), debug-location !16
+    RETQ implicit $eax, debug-location !18
+
+...