Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -9932,9 +9932,13 @@
       Diag(FD->getLocation(), diag::warn_pure_function_definition);
 
     if (!FD->isInvalidDecl()) {
-      DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
-      DiagnoseSizeOfParametersAndReturnValue(FD->param_begin(), FD->param_end(),
-                                             FD->getReturnType(), FD);
+      // In case of cxx11, Body is null if function is marked deleted/ defaulted
+      // out-of-line. Calling these DiagnoseXXX in such cases is not useful.
+      if (Body) {
+        DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
+        DiagnoseSizeOfParametersAndReturnValue(
+            FD->param_begin(), FD->param_end(), FD->getReturnType(), FD);
+      }
 
       // If this is a constructor, we need a vtable.
       if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(FD))
Index: test/SemaCXX/cxx11-unused.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/cxx11-unused.cpp
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -std=c++11 -verify %s -Wunused-parameter
+
+// PR19303 : Make sure we don't get a unused expression warning for deleted and
+// defaulted functions
+
+// expected-no-diagnostics
+
+class A {
+public:
+  int x;
+  A() = default;
+  ~A() = default;
+  A(const A &other) = delete;
+
+  template <typename T>
+  void SetX(T x) {
+    this->x = x;
+  };
+
+  void SetX1(int x);
+};
+
+template <>
+void A::SetX(A x) = delete;
+
+class B {
+public:
+  B() = default;
+  ~B() = default;
+  B(const B &other);
+};
+
+B::B(const B &other) = default;