When creating LookupResults, see through UsingDecls. Fixes PR4450.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@74258 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index e6f3d9e..4d25f5b 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -325,7 +325,9 @@
   if (ObjCCompatibleAliasDecl *Alias 
         = dyn_cast_or_null<ObjCCompatibleAliasDecl>(D))
     D = Alias->getClassInterface();
-
+  if (UsingDecl *UD = dyn_cast_or_null<UsingDecl>(D))
+    D = UD->getTargetDecl();
+  
   LookupResult Result;
   Result.StoredKind = (D && isa<OverloadedFunctionDecl>(D))?
     OverloadedDeclSingleDecl : SingleDecl;
@@ -358,7 +360,9 @@
   if (ObjCCompatibleAliasDecl *Alias 
         = dyn_cast_or_null<ObjCCompatibleAliasDecl>(D))
     D = Alias->getClassInterface();
-    
+  if (UsingDecl *UD = dyn_cast_or_null<UsingDecl>(D))
+    D = UD->getTargetDecl();
+
   Result.StoredKind = SingleDecl;
   Result.First = reinterpret_cast<uintptr_t>(D);
   Result.Last = 0;
diff --git a/test/SemaCXX/using-decl-pr4450.cpp b/test/SemaCXX/using-decl-pr4450.cpp
new file mode 100644
index 0000000..c3d5b83
--- /dev/null
+++ b/test/SemaCXX/using-decl-pr4450.cpp
@@ -0,0 +1,15 @@
+// RUN: clang-cc -fsyntax-only -verify %s
+
+namespace A {
+  void g();
+}
+
+namespace X {
+  using A::g; 
+}
+
+void h()
+{
+  A::g();
+  X::g();
+}