diff --git a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
@@ -1094,7 +1094,7 @@
   MLocTracker *MTracker = nullptr;
 
   /// Number of the current block LiveDebugValues is stepping through.
-  unsigned CurBB;
+  unsigned CurBB = -1;
 
   /// Number of the current instruction LiveDebugValues is evaluating.
   unsigned CurInst;
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
@@ -1070,6 +1070,7 @@
       break;
     }
   }
+  assert(CurBB != -1u);
 
   LocIdxToIDNum[NewIdx] = ValNum;
   LocIdxToLocID[NewIdx] = ID;