Index: lld/trunk/COFF/Driver.h
===================================================================
--- lld/trunk/COFF/Driver.h
+++ lld/trunk/COFF/Driver.h
@@ -16,6 +16,7 @@
 #include "lld/Common/Reproduce.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Option/Arg.h"
@@ -127,6 +128,8 @@
   std::list<std::function<void()>> TaskQueue;
   std::vector<StringRef> FilePaths;
   std::vector<MemoryBufferRef> Resources;
+
+  llvm::StringSet<> DirectivesExports;
 };
 
 // Functions below this line are defined in DriverUtils.cpp.
Index: lld/trunk/COFF/Driver.cpp
===================================================================
--- lld/trunk/COFF/Driver.cpp
+++ lld/trunk/COFF/Driver.cpp
@@ -245,6 +245,13 @@
       Config->Entry = addUndefined(mangle(Arg->getValue()));
       break;
     case OPT_export: {
+      // If a common header file contains dllexported function
+      // declarations, many object files may end up with having the
+      // same /EXPORT options. In order to save cost of parsing them,
+      // we dedup them first.
+      if (!DirectivesExports.insert(Arg->getValue()).second)
+        break;
+
       Export E = parseExport(Arg->getValue());
       if (Config->Machine == I386 && Config->MinGW) {
         if (!isDecorated(E.Name))