DwarfDebug: Store the filename/dirname pair as a zero-separated string in a stringmap, instead of using a highly inefficient std::map of a pair of std::strings.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152541 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.h b/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 8b802d2..83f30f5 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/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 @@
   ///
   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.