Index: lib/CodeGen/LiveDebugVariables.cpp
===================================================================
--- lib/CodeGen/LiveDebugVariables.cpp
+++ lib/CodeGen/LiveDebugVariables.cpp
@@ -1087,6 +1087,7 @@
         // index is no longer available. That means the user value is in a
         // non-existent sub-register, and %noreg is exactly what we want.
         Loc.substPhysReg(VRM.getPhys(VirtReg), TRI);
+        Loc.setIsRenamable();
       } else if (VRM.getStackSlot(VirtReg) != VirtRegMap::NO_STACK_SLOT) {
         // Retrieve the stack slot offset.
         unsigned SpillSize;
Index: lib/CodeGen/MachineCopyPropagation.cpp
===================================================================
--- lib/CodeGen/MachineCopyPropagation.cpp
+++ lib/CodeGen/MachineCopyPropagation.cpp
@@ -307,6 +307,11 @@
 bool MachineCopyPropagation::isForwardableRegClassCopy(const MachineInstr &Copy,
                                                        const MachineInstr &UseI,
                                                        unsigned UseIdx) {
+  // Debug values have no register classes to be examined
+  if (UseI.isDebugValue()) {
+    assert(UseI.getOperand(UseIdx).isReg());
+    return true;
+  }
 
   unsigned CopySrcReg = Copy.getOperand(1).getReg();
 
@@ -612,7 +617,7 @@
 
       // Update matching debug values.
       assert(MaybeDead->isCopy());
-      MaybeDead->changeDebugValuesDefReg(MaybeDead->getOperand(1).getReg());
+      //MaybeDead->changeDebugValuesDefReg(MaybeDead->getOperand(1).getReg());
 
       MaybeDead->eraseFromParent();
       Changed = true;
Index: test/CodeGen/MIR/X86/pr38773.mir
===================================================================
--- test/CodeGen/MIR/X86/pr38773.mir
+++ test/CodeGen/MIR/X86/pr38773.mir
@@ -98,7 +98,7 @@
     renamable $ecx = COPY $eax
     ; CHECK:        IDIV32r killed renamable $ecx
     ; CHECK-NEXT:   DBG_VALUE $eax, $noreg, !12, !DIExpression(), debug-location !13
-    DBG_VALUE $ecx, $noreg, !12, !DIExpression(), debug-location !13
+    DBG_VALUE renamable $ecx, $noreg, !12, !DIExpression(), debug-location !13
     $eax = COPY killed renamable $ecx
     RET 0, $eax