Index: llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
===================================================================
--- llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -751,6 +751,24 @@
     // then one instruction.
     Sunk = sink3AddrInstruction(NewMI, RegB, mi);
 
+  // If the old instruction is debug value tracked, an update is required.
+  if (auto OldInstrNum = mi->peekDebugInstrNum()) {
+    // Sanity check.
+    assert(mi->getNumExplicitDefs() == 1);
+    assert(NewMI->getNumExplicitDefs() == 1);
+
+    // Find the old and new def location.
+    auto OldIt = mi->defs().begin();
+    auto NewIt = NewMI->defs().begin();
+    unsigned OldIdx = mi->getOperandNo(OldIt);
+    unsigned NewIdx = NewMI->getOperandNo(NewIt);
+
+    // Record that one def has been replaced by the other.
+    unsigned NewInstrNum = NewMI->getDebugInstrNum();
+    MF->makeDebugValueSubstitution(std::make_pair(OldInstrNum, OldIdx),
+                                   std::make_pair(NewInstrNum, NewIdx));
+  }
+
   MBB->erase(mi); // Nuke the old inst.
 
   if (!Sunk) {
Index: llvm/lib/Target/X86/X86FixupLEAs.cpp
===================================================================
--- llvm/lib/Target/X86/X86FixupLEAs.cpp
+++ llvm/lib/Target/X86/X86FixupLEAs.cpp
@@ -434,6 +434,7 @@
   } else
     return false;
 
+  MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI);
   MBB.erase(I);
   I = NewMI;
   return true;
@@ -469,6 +470,7 @@
       LLVM_DEBUG(dbgs() << "FixLEA: Candidate to replace:"; MBI->dump(););
       // now to replace with an equivalent LEA...
       LLVM_DEBUG(dbgs() << "FixLEA: Replaced by: "; NewMI->dump(););
+      MBB.getParent()->substituteDebugValuesForInst(*MBI, *NewMI);
       MBB.erase(MBI);
       MachineBasicBlock::iterator J =
           static_cast<MachineBasicBlock::iterator>(NewMI);
@@ -521,6 +523,7 @@
     LLVM_DEBUG(NewMI->dump(););
   }
   if (NewMI) {
+    MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI);
     MBB.erase(I);
     I = NewMI;
   }
@@ -626,6 +629,7 @@
       }
     }
 
+    MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI);
     MBB.erase(I);
     I = NewMI;
     return;
@@ -651,6 +655,7 @@
                 .add(Index);
     LLVM_DEBUG(NewMI->dump(););
 
+    MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI);
     MBB.erase(I);
     I = NewMI;
     return;
@@ -673,6 +678,7 @@
               .add(Base);
   LLVM_DEBUG(NewMI->dump(););
 
+  MBB.getParent()->substituteDebugValuesForInst(*I, *NewMI);
   MBB.erase(I);
   I = NewMI;
 }
Index: llvm/test/DebugInfo/MIR/InstrRef/twoaddr-to-threeaddr-sub.mir
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/MIR/InstrRef/twoaddr-to-threeaddr-sub.mir
@@ -0,0 +1,40 @@
+# RUN: llc -run-pass=twoaddressinstruction -mtriple=x86_64-- -o - %s -experimental-debug-variable-locations | FileCheck %s
+# 
+# Test that a new instruction (LEA) is created when the two-addr add below is
+# converted to three address; and that an appropriate substitution is created.
+# Maybe at some point we'll normalise DBG_INSTR_REFs on output, but until then,
+# lets not.
+#
+# CHECK:      debugValueSubstitutions:
+# CHECK-NEXT:  - { srcinst: 1, srcop: 0, dstinst: 2, dstop: 0 }
+#
+# CHECK:      LEA64_32r
+# CHECK-SAME: debug-instr-number 2
+#
+# CHECK:      DBG_INSTR_REF 1, 0
+---
+name:            test1
+alignment:       16
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gr32 }
+  - { id: 1, class: gr32 }
+  - { id: 2, class: gr32 }
+liveins:
+  - { reg: '$edi', virtual-reg: '%0' }
+frameInfo:
+  maxAlignment:    1
+machineFunctionInfo: {}
+body:             |
+  bb.0:
+    liveins: $edi
+
+    %0:gr32 = COPY killed $edi
+    %1:gr32 = SHL32ri killed %0, 5, implicit-def dead $eflags
+    %2:gr32 = ADD32ri8_DB killed %1, 3, implicit-def dead $eflags, debug-instr-number 1
+    DBG_INSTR_REF 1, 0
+    $eax = COPY killed %2
+    RET 0, killed $eax
+
+...
+