diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index fa62169b0b7b..388cef4d8b8a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -523,20 +523,19 @@ unsigned DwarfDebug::GetOrCreateSourceID(StringRef FileName,
     DirName = "";
 
   unsigned SrcId = SourceIdMap.size()+1;
-  std::pair<std::string, std::string> SourceName =
-      std::make_pair(FileName, DirName);
-  std::pair<std::pair<std::string, std::string>, unsigned> Entry =
-      make_pair(SourceName, SrcId);
 
-  std::map<std::pair<std::string, std::string>, unsigned>::iterator I;
-  bool NewlyInserted;
-  llvm::tie(I, NewlyInserted) = SourceIdMap.insert(Entry);
-  if (!NewlyInserted)
-    return I->second;
+  // We look up the file/dir pair by concatenating them with a zero byte.
+  SmallString<128> NamePair;
+  NamePair += DirName;
+  NamePair += '\0'; // Zero bytes are not allowed in paths.
+  NamePair += FileName;
+
+  StringMapEntry<unsigned> &Ent = SourceIdMap.GetOrCreateValue(NamePair, SrcId);
+  if (Ent.getValue() != SrcId)
+    return Ent.getValue();
 
   // Print out a .file directive to specify files for .loc directives.
-  Asm->OutStreamer.EmitDwarfFileDirective(SrcId, Entry.first.second,
-                                          Entry.first.first);
+  Asm->OutStreamer.EmitDwarfFileDirective(SrcId, DirName, FileName);
 
   return SrcId;
 }
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 8b802d2e21b9..83f30f5b446f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -26,7 +26,6 @@
 #include "llvm/ADT/UniqueVector.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/DebugLoc.h"
-#include <map>
 
 namespace llvm {
 
@@ -209,9 +208,9 @@ class DwarfDebug {
   ///
   std::vector<DIEAbbrev *> Abbreviations;
 
-  /// SourceIdMap - Source id map, i.e. pair of source filename and directory
-  /// mapped to a unique id.
-  std::map<std::pair<std::string, std::string>, unsigned> SourceIdMap;
+  /// SourceIdMap - Source id map, i.e. pair of source filename and directory,
+  /// separated by a zero byte, mapped to a unique id.
+  StringMap<unsigned> SourceIdMap;
 
   /// StringPool - A String->Symbol mapping of strings used by indirect
   /// references.