Index: lib/Sema/SemaTemplateInstantiate.cpp
===================================================================
--- lib/Sema/SemaTemplateInstantiate.cpp
+++ lib/Sema/SemaTemplateInstantiate.cpp
@@ -1512,7 +1512,7 @@
 }
 
 static bool NeedsInstantiationAsFunctionType(TypeSourceInfo *T) {
-  if (T->getType()->isInstantiationDependentType() || 
+  if (T->getType()->isInstantiationDependentType() ||
       T->getType()->isVariablyModifiedType())
     return true;
 
@@ -1522,22 +1522,12 @@
 
   FunctionProtoTypeLoc FP = TL.castAs<FunctionProtoTypeLoc>();
   for (unsigned I = 0, E = FP.getNumParams(); I != E; ++I) {
-    ParmVarDecl *P = FP.getParam(I);
-
     // This must be synthesized from a typedef.
-    if (!P) continue;
-
-    // The parameter's type as written might be dependent even if the
-    // decayed type was not dependent.
-    if (TypeSourceInfo *TSInfo = P->getTypeSourceInfo())
-      if (TSInfo->getType()->isInstantiationDependentType())
-        return true;
+    if (!FP.getParam(I)) continue;
 
-    // TODO: currently we always rebuild expressions.  When we
-    // properly get lazier about this, we should use the same
-    // logic to avoid rebuilding prototypes here.
-    if (P->hasDefaultArg())
-      return true;
+    // If there are any parameters, a new TypeSourceInfo that refers to the
+    // instantiated parameters must be built.
+    return true;
   }
 
   return false;
@@ -1556,7 +1546,7 @@
   assert(!ActiveTemplateInstantiations.empty() &&
          "Cannot perform an instantiation without some context on the "
          "instantiation stack");
-  
+
   if (!NeedsInstantiationAsFunctionType(T))
     return T;