Index: lib/CodeGen/AsmPrinter/DwarfDebug.h
===================================================================
--- lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -242,6 +242,8 @@
   /// debug info.
   DebugLoc PrevInstLoc;
   MCSymbol *PrevLabel;
+  const MachineBasicBlock *CurBB;
+  bool LastWasCall;
 
   /// This location indicates end of function prologue and beginning of
   /// function body.
Index: lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1032,7 +1032,13 @@
 
         const MDNode *Scope = DL.getScope();
         recordSourceLine(DL.getLine(), DL.getCol(), Scope, Flags);
-      } else if (UnknownLocations) {
+      } else if (UnknownLocations || PrevLabel || LastWasCall ||
+                 CurBB != MI->getParent()) {
+        // We want to ensure that any instruction starting a block or
+        // referenced from somewhere else (eg. debug information) has
+        // a source location. Instead of making up a location from the
+        // surrounding instructions, just use a line 0 location that
+        // the debugger will ignore.
         PrevInstLoc = DL;
         recordSourceLine(0, 0, nullptr, 0);
       }
@@ -1063,8 +1069,11 @@
   assert(CurMI != nullptr);
   // Don't create a new label after DBG_VALUE instructions.
   // They don't generate code.
-  if (!CurMI->isDebugValue())
+  if (!CurMI->isDebugValue()) {
     PrevLabel = nullptr;
+    CurBB = CurMI->getParent();
+    LastWasCall = CurMI->isCall();
+  }
 
   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
       LabelsAfterInsn.find(CurMI);
@@ -1207,6 +1216,8 @@
 
   PrevInstLoc = DebugLoc();
   PrevLabel = Asm->getFunctionBegin();
+  CurBB = nullptr;
+  LastWasCall = false;
 
   // Record beginning of function.
   PrologEndLoc = findPrologueEndLoc(MF);