Index: cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp
===================================================================
--- cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp
+++ cfe/trunk/lib/Driver/ToolChains/CommonArgs.cpp
@@ -464,8 +464,12 @@
       CmdArgs.push_back(
           Args.MakeArgString("-plugin-opt=cs-profile-path=default_%m.profraw"));
   } else if (ProfileUseArg) {
+    SmallString<128> Path(
+        ProfileUseArg->getNumValues() == 0 ? "" : ProfileUseArg->getValue());
+    if (Path.empty() || llvm::sys::fs::is_directory(Path))
+      llvm::sys::path::append(Path, "default.profdata");
     CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=cs-profile-path=") +
-                                         ProfileUseArg->getValue()));
+                                         Path));
   }
 
   // Need this flag to turn on new pass manager via Gold plugin.
Index: cfe/trunk/test/Driver/cspgo-lto.c
===================================================================
--- cfe/trunk/test/Driver/cspgo-lto.c
+++ cfe/trunk/test/Driver/cspgo-lto.c
@@ -0,0 +1,6 @@
+// RUN: touch %t.o
+//
+// RUN: %clang -target x86_64-unknown-linux -### %t.o -flto=thin \
+// RUN:   -fprofile-use 2>&1 | FileCheck %s
+
+// CHECK: -plugin-opt=cs-profile-path=default.profdata