[DebugInfo] Emit comments for DBG_LABEL in AsmPrinter.

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

static bool emitDebugValueComment(const MachineInstr *MI, AsmPrinter &AP) {
   if (MemLoc)
     OS << '+' << Offset << ']';
 
   // NOTE: Want this comment at start of line, don't emit with AddComment.
   AP.OutStreamer->emitRawComment(OS.str());
   return true;
 }
 
+/// emitDebugLabelComment - This method handles the target-independent form
+/// of DBG_LABEL, returning true if it was able to do so.  A false return
+/// means the target will need to handle MI in EmitInstruction.
+static bool emitDebugLabelComment(const MachineInstr *MI, AsmPrinter &AP) {
+  // This code handles only the 1-operand target-independent form.
+  if (MI->getNumOperands() != 1)
+    return false;
+
+  SmallString<128> Str;
+  raw_svector_ostream OS(Str);
+  OS << "DEBUG_LABEL: ";
+
+  const DILabel *V = MI->getDebugLabel();
+  if (auto *SP = dyn_cast<DISubprogram>(V->getScope())) {
+    StringRef Name = SP->getName();
+    if (!Name.empty())
+      OS << Name << ":";
+  }
+  OS << V->getName();
+
+  // NOTE: Want this comment at start of line, don't emit with AddComment.
+  AP.OutStreamer->emitRawComment(OS.str());
+  return true;
+}
+
 AsmPrinter::CFIMoveType AsmPrinter::needsCFIMoves() const {
   if (MAI->getExceptionHandlingType() == ExceptionHandling::DwarfCFI &&
       MF->getFunction().needsUnwindTableEntry())
     return CFI_M_EH;
 
   if (MMI->hasDebugInfo())
     return CFI_M_Debug;
 
for (auto &MI : MBB) {
         EmitInlineAsm(&MI);
         break;
       case TargetOpcode::DBG_VALUE:
         if (isVerbose()) {
           if (!emitDebugValueComment(&MI, *this))
             EmitInstruction(&MI);
         }
         break;
+      case TargetOpcode::DBG_LABEL:
+  if (isVerbose()) {
+    if (!emitDebugLabelComment(&MI, *this))
+      EmitInstruction(&MI);
+  }
+  break;
       case TargetOpcode::IMPLICIT_DEF:
         if (isVerbose()) emitImplicitDef(&MI);
         break;
       case TargetOpcode::KILL:
         if (isVerbose()) emitKill(&MI, *this);
         break;
       default:
         EmitInstruction(&MI);