diff --git a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
@@ -1225,26 +1225,63 @@
     }
   }
 
-  /// Explicitly terminate variable locations based on \p mloc. Creates undef
-  /// DBG_VALUEs for any variables that were located there, and clears
-  /// #ActiveMLoc / #ActiveVLoc tracking information for that location.
-  void clobberMloc(LocIdx MLoc, MachineBasicBlock::iterator Pos) {
-    assert(MTracker->isSpill(MLoc));
+  /// Account for a location \p mloc being clobbered. Examine the variable
+  /// locations that will be terminated: and try to recover them by using
+  /// another location. Optionally, given \p MakeUndef, emit a DBG_VALUE to
+  /// explicitly terminate a location if it can't be recovered.
+  void clobberMloc(LocIdx MLoc, MachineBasicBlock::iterator Pos,
+                   bool MakeUndef = true) {
     auto ActiveMLocIt = ActiveMLocs.find(MLoc);
     if (ActiveMLocIt == ActiveMLocs.end())
       return;
 
+    // What was the old variable value?
+    ValueIDNum OldValue = VarLocs[MLoc.asU64()];
     VarLocs[MLoc.asU64()] = ValueIDNum::EmptyValue;
 
+    // Examine the remaining variable locations: if we can find the same value
+    // again, we can recover the location.
+    Optional<LocIdx> NewLoc = None;
+    for (auto Loc : MTracker->locations())
+      if (Loc.Value == OldValue)
+        NewLoc = Loc.Idx;
+
+    // If there is no location, and we weren't asked to make the variable
+    // explicitly undef, then stop here.
+    if (!NewLoc && !MakeUndef)
+      return;
+
+    // Examine all the variables based on this location.
+    DenseSet<DebugVariable> NewMLocs;
     for (auto &Var : ActiveMLocIt->second) {
       auto ActiveVLocIt = ActiveVLocs.find(Var);
-      // Create an undef. We can't feed in a nullptr DIExpression alas,
-      // so use the variables last expression. Pass None as the location.
+      // Re-state the variable location: if there's no replacement then NewLoc
+      // is None and a $noreg DBG_VALUE will be created. Otherwise, a DBG_VALUE
+      // identifying the alternative location will be emitted.
       const DIExpression *Expr = ActiveVLocIt->second.Properties.DIExpr;
       DbgValueProperties Properties(Expr, false);
-      PendingDbgValues.push_back(MTracker->emitLoc(None, Var, Properties));
-      ActiveVLocs.erase(ActiveVLocIt);
+      PendingDbgValues.push_back(MTracker->emitLoc(NewLoc, Var, Properties));
+
+      // Update machine locations <=> variable locations maps. Defer updating
+      // ActiveMLocs to avoid invalidaing the ActiveMLocIt iterator.
+      if (!NewLoc) {
+        ActiveVLocs.erase(ActiveVLocIt);
+      } else {
+        ActiveVLocIt->second.Loc = *NewLoc;
+        NewMLocs.insert(Var);
+      }
     }
+
+    // Commit any deferred ActiveMLoc changes.
+    if (!NewMLocs.empty())
+      for (auto &Var : NewMLocs)
+        ActiveMLocs[*NewLoc].insert(Var);
+
+    // We lazily track what locations have which values; if we've found a new
+    // location for the clobbered value, remember it.
+    if (NewLoc)
+      VarLocs[NewLoc->asU64()] = OldValue;
+
     flushDbgValues(Pos, nullptr);
 
     ActiveMLocIt->second.clear();
@@ -1899,6 +1936,32 @@
 
   for (auto *MO : RegMaskPtrs)
     MTracker->writeRegMask(MO, CurBB, CurInst);
+
+  if (!TTracker)
+    return;
+
+  // When committing variable values to locations: tell transfer tracker that
+  // we've clobbered things. It may be able to recover the variable from a
+  // different location.
+
+  // Inform TTracker about any direct clobbers.
+  for (uint32_t DeadReg : DeadRegs) {
+    LocIdx Loc = MTracker->lookupOrTrackRegister(DeadReg);
+    TTracker->clobberMloc(Loc, MI.getIterator(), false);
+  }
+
+  // Look for any clobbers performed by a register mask. Only test locations
+  // that are actually being tracked.
+  for (auto L : MTracker->locations()) {
+    // Stack locations can't be clobbered by regmasks.
+    if (MTracker->isSpill(L.Idx))
+      continue;
+
+    Register Reg = MTracker->LocIdxToLocID[L.Idx];
+    for (auto *MO : RegMaskPtrs)
+      if (MO->clobbersPhysReg(Reg))
+        TTracker->clobberMloc(L.Idx, MI.getIterator(), false);
+  }
 }
 
 void InstrRefBasedLDV::performCopy(Register SrcRegNum, Register DstRegNum) {
@@ -2046,8 +2109,12 @@
 
     if (TTracker) {
       Optional<LocIdx> MLoc = MTracker->getSpillMLoc(*Loc);
-      if (MLoc)
+      if (MLoc) {
+        // Un-set this location before clobbering, so that we don't salvage
+        // the variable location back to the same place.
+        MTracker->setMLoc(*MLoc, ValueIDNum::EmptyValue);
         TTracker->clobberMloc(*MLoc, MI.getIterator());
+      }
     }
   }
 
@@ -2162,6 +2229,15 @@
   if (EmulateOldLDV && SrcReg != DestReg)
     MTracker->defReg(SrcReg, CurBB, CurInst);
 
+  // Finally, the copy might have clobbered variables based on the destination
+  // register. Tell TTracker about it, in case a backup location exists.
+  if (TTracker) {
+    for (MCRegAliasIterator RAI(DestReg, TRI, true); RAI.isValid(); ++RAI) {
+      LocIdx ClobberedLoc = MTracker->getRegMLoc(*RAI);
+      TTracker->clobberMloc(ClobberedLoc, MI.getIterator(), false);
+    }
+  }
+
   return true;
 }
 
diff --git a/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
--- a/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
@@ -14,6 +14,7 @@
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetMachine.h"
 
 /// \file LiveDebugValues.cpp
@@ -33,6 +34,12 @@
 
 using namespace llvm;
 
+static cl::opt<bool>
+    ForceInstrRefLDV("force-instr-ref-livedebugvalues", cl::Hidden,
+                     cl::desc("Use instruction-ref based LiveDebugValues with "
+                              "normal DBG_VALUE inputs"),
+                     cl::init(false));
+
 /// Generic LiveDebugValues pass. Calls through to VarLocBasedLDV or
 /// InstrRefBasedLDV to perform location propagation, via the LDVImpl
 /// base class.
@@ -87,6 +94,9 @@
       InstrRefBased = TM.Options.ValueTrackingVariableLocations;
     }
 
+    // Allow the user to force selection of InstrRef LDV.
+    InstrRefBased |= ForceInstrRefLDV;
+
     if (InstrRefBased)
       TheImpl = llvm::makeInstrRefBasedLiveDebugValues();
     else
diff --git a/llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_instrref_tolocs.mir b/llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_instrref_tolocs.mir
--- a/llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_instrref_tolocs.mir
+++ b/llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_instrref_tolocs.mir
@@ -42,7 +42,7 @@
 
     $rbx = COPY killed $rax, debug-location !17
     $rax = MOV64ri 1, debug-location !17
-    ; Presently, this COPY isn't followed. Dealing with that is future work.
+    ; CHECK: DBG_VALUE $rbx, $noreg
 
     DBG_INSTR_REF 2, 0, !16, !DIExpression(), debug-location !17
     ; No instruction is labelled with the number "2". This should produce an
diff --git a/llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_recover_clobbers.mir b/llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_recover_clobbers.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_recover_clobbers.mir
@@ -0,0 +1,100 @@
+--- |
+  ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - -force-instr-ref-livedebugvalues=1 -emulate-old-livedebugvalues=0 | FileCheck %s -implicit-check-not=DBG_VALUE
+
+  ;; When using instruction referencing LiveDebugValues, when a register gets
+  ;; clobbered, we should transfer variable locations to backup locations, if
+  ;; one is available.
+  ;; I've written this test in terms of DBG_VALUEs rather than DBG_INSTR_REFs
+  ;; as this is purely a LiveDebugValues feature, and should work without the
+  ;; need to use any other instructoin referencing work.
+
+  declare i32 @use() local_unnamed_addr;
+
+  define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
+  entry:
+    br label %bb1, !dbg !17
+  bb1:
+    br label %bb2, !dbg !17
+  bb2:
+    br label %bb3, !dbg !17
+  bb3:
+    br label %bb3, !dbg !17
+  bb4:
+    br label %bb3, !dbg !17
+  bb5:
+    ret i32 0, !dbg !17
+  }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!7, !8, !9, !10}
+  !llvm.ident = !{!11}
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, debugInfoForProfiling: true, nameTableKind: None)
+  !1 = !DIFile(filename: "main.cpp", directory: "F:\")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
+  !5 = distinct !DIGlobalVariable(name: "start", scope: !0, file: !1, line: 4, type: !6, isLocal: false, isDefinition: true)
+  !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !7 = !{i32 2, !"Dwarf Version", i32 4}
+  !8 = !{i32 2, !"Debug Info Version", i32 3}
+  !9 = !{i32 1, !"wchar_size", i32 2}
+  !10 = !{i32 7, !"PIC Level", i32 2}
+  !11 = !{!"clang version 10.0.0"}
+  !12 = distinct !DISubprogram(name: "bb_to_bb", linkageName: "bb_to_bb", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!6, !6}
+  !15 = !{!16}
+  !16 = !DILocalVariable(name: "myVar", scope: !12, file: !1, line: 7, type: !6)
+  !17 = !DILocation(line: 10, scope: !12)
+
+...
+---
+name: _Z8bb_to_bb
+stack:
+  - { id: 0, type: spill-slot, offset: -12, size: 4, alignment: 4 }
+body:  |
+  bb.0.entry:
+    $eax = MOV32ri 0, debug-location !17
+    $eax = COPY $ebx
+    DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+    ;; Over-write eax, we should recover its location as being in ebx.
+    $eax = MOV32ri 0, debug-location !17
+
+    ; CHECK:      DBG_VALUE $eax
+    ; CHECK-NEXT: $eax = MOV32ri 0
+    ; CHECK-NEXT: DBG_VALUE $ebx
+
+    ;; The same should occur for spills.
+    $ebx = MOV32ri 2, debug-location !17
+    MOV32mr $rsp, 1, _, -12, _, killed $ebx :: (store 4 into %stack.0)
+    DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+    $ebx = MOV32ri 0, debug-location !17
+
+    ; CHECK-NEXT: $ebx = MOV32ri 2
+    ; CHECK-NEXT: MOV32mr $rsp
+    ; CHECK-NEXT: DBG_VALUE $ebx
+    ; CHECK-NEXT: $ebx = MOV32ri
+    ; CHECK-NEXT: DBG_VALUE $rsp
+
+    ;; Now test copies and register masks.
+    $eax = COPY $ebx
+    DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+    ;; Overwrite ebx with a copy.
+    $ecx = MOV32ri 1, debug-location !17
+    $ebx = COPY $ecx
+
+    ; CHECK:      DBG_VALUE $ebx
+    ; CHECK-NEXT: $ecx = MOV32ri
+    ; CHECK-NEXT: $ebx = COPY
+    ; CHECK-NEXT: DBG_VALUE $eax
+
+    ;; Similarly, with a register mask
+    $ebx = COPY $eax
+    CALL64pcrel32 @use, csr_64, implicit $rsp, implicit $edi, implicit-def $rsp, debug-location !17
+
+    ; CHECK-NEXT: $ebx = COPY $eax
+    ; CHECK-NEXT: CALL64pcrel32
+    ; CHECK-NEXT: DBG_VALUE $ebx
+
+    RETQ $eax, debug-location !17
+...
diff --git a/llvm/test/DebugInfo/MIR/X86/livedebugvalues_load_in_loop.mir b/llvm/test/DebugInfo/MIR/X86/livedebugvalues_load_in_loop.mir
--- a/llvm/test/DebugInfo/MIR/X86/livedebugvalues_load_in_loop.mir
+++ b/llvm/test/DebugInfo/MIR/X86/livedebugvalues_load_in_loop.mir
@@ -11,6 +11,7 @@
 
   ; CHECK-LABEL: bb.0.entry:
   ; CHECK:       DBG_VALUE $rdi, $noreg, !16, !DIExpression()
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
   ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
   ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()