Add -Wpessimizing-move and -Wredundant-move warnings.

-Wpessimizing-move warns when a call to std::move would prevent copy elision
if the argument was not wrapped in a call.  This happens when moving a local
variable in a return statement when the variable is the same type as the
return type or using a move to create a new object from a temporary object.

-Wredundant-move warns when an implicit move would already be made, so the
std::move call is not needed, such as when moving a local variable in a return
that is different from the return type.

Differential Revision: http://reviews.llvm.org/D7633

llvm-svn: 236075

1 files changed, 203 insertions, 0 deletions

diff --git a/clang/test/SemaCXX/warn-pessmizing-move.cpp b/clang/test/SemaCXX/warn-pessmizing-move.cpp
new file mode 100644
index 00000000000..6b49944f287
--- /dev/null
+++ b/clang/test/SemaCXX/warn-pessmizing-move.cpp
@@ -0,0 +1,203 @@
+// RUN: %clang_cc1 -fsyntax-only -Wpessimizing-move -std=c++11 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wpessimizing-move -std=c++11 -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+
+// definitions for std::move
+namespace std {
+inline namespace foo {
+template <class T> struct remove_reference { typedef T type; };
+template <class T> struct remove_reference<T&> { typedef T type; };
+template <class T> struct remove_reference<T&&> { typedef T type; };
+
+template <class T> typename remove_reference<T>::type &&move(T &&t);
+}
+}
+
+struct A {};
+struct B {
+  B() {}
+  B(A) {}
+};
+
+A test1(A a1) {
+  A a2;
+  return a1;
+  return a2;
+  return std::move(a1);
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:22-[[@LINE-4]]:23}:""
+  return std::move(a2);
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:22-[[@LINE-4]]:23}:""
+}
+
+B test2(A a1, B b1) {
+  // Object is different than return type so don't warn.
+  A a2;
+  return a1;
+  return a2;
+  return std::move(a1);
+  return std::move(a2);
+
+  B b2;
+  return b1;
+  return b2;
+  return std::move(b1);
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:22-[[@LINE-4]]:23}:""
+  return std::move(b2);
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:22-[[@LINE-4]]:23}:""
+}
+
+A global_a;
+A test3() {
+  // Don't warn when object is not local.
+  return global_a;
+  return std::move(global_a);
+  static A static_a;
+  return static_a;
+  return std::move(static_a);
+
+}
+
+A test4() {
+  return A();
+  return test3();
+
+  return std::move(A());
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:23-[[@LINE-4]]:24}:""
+  return std::move(test3());
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:27-[[@LINE-4]]:28}:""
+}
+
+void test5(A) {
+  test5(A());
+  test5(test4());
+
+  test5(std::move(A()));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:9-[[@LINE-3]]:19}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:22-[[@LINE-4]]:23}:""
+  test5(std::move(test4()));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:9-[[@LINE-3]]:19}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:26-[[@LINE-4]]:27}:""
+}
+
+void test6() {
+  A a1 = A();
+  A a2 = test3();
+
+  A a3 = std::move(A());
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:23-[[@LINE-4]]:24}:""
+  A a4 = std::move(test3());
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:27-[[@LINE-4]]:28}:""
+}
+
+A test7() {
+  A a1 = std::move(A());
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:23-[[@LINE-4]]:24}:""
+  A a2 = std::move((A()));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:25-[[@LINE-4]]:26}:""
+  A a3 = (std::move(A()));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:11-[[@LINE-3]]:21}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:24-[[@LINE-4]]:25}:""
+  A a4 = (std::move((A())));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:11-[[@LINE-3]]:21}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:26-[[@LINE-4]]:27}:""
+
+  return std::move(a1);
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:22-[[@LINE-4]]:23}:""
+  return std::move((a1));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:24-[[@LINE-4]]:25}:""
+  return (std::move(a1));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:11-[[@LINE-3]]:21}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:23-[[@LINE-4]]:24}:""
+  return (std::move((a1)));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:11-[[@LINE-3]]:21}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:25-[[@LINE-4]]:26}:""
+}
+
+#define wrap1(x) x
+#define wrap2(x) x
+
+// Macro test.  Since the std::move call is outside the macro, it is
+// safe to suggest a fix-it.
+A test8(A a) {
+  return std::move(a);
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:21-[[@LINE-4]]:22}:""
+  return std::move(wrap1(a));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:28-[[@LINE-4]]:29}:""
+  return std::move(wrap1(wrap2(a)));
+  // expected-warning@-1{{prevents copy elision}}
+  // expected-note@-2{{remove std::move call}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:10-[[@LINE-3]]:20}:""
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:35-[[@LINE-4]]:36}:""
+}
+
+#define test9            \
+  A test9(A a) {         \
+    return std::move(a); \
+  }
+
+// Macro test.  The std::call is inside the macro, so no fix-it is suggested.
+test9
+// expected-warning@-1{{prevents copy elision}}
+// CHECK-NOT: fix-it
+
+#define return_a return std::move(a)
+
+// Macro test.  The std::call is inside the macro, so no fix-it is suggested.
+A test10(A a) {
+  return_a;
+  // expected-warning@-1{{prevents copy elision}}
+  // CHECK-NOT: fix-it
+}