Adding a -Wunused-value warning for expressions with side effects used in an unevaluated expression context, such as sizeof(), or decltype(). Also adds a similar warning when the expression passed to typeid() *is* evaluated, since it is equally likely that the user would expect the expression operand to be unevaluated in that case.

llvm-svn: 224465

1 files changed, 29 insertions, 1 deletions

diff --git a/clang/test/SemaCXX/warn-unused-value-cxx11.cpp b/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
index 115ddf3e02d..d929b4fd12f 100644
--- a/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
+++ b/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
@@ -1,5 +1,4 @@
 // RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -Wunused-value %s
-// expected-no-diagnostics
 
 void f() __attribute__((const));
 
@@ -13,4 +12,33 @@ auto foo(T) -> decltype(f(), bool()) { // Should not warn.
 void g() {
   foo(1);
 }
+
+void h() {
+  int i = 0;
+  (void)noexcept(++i); // expected-warning {{expression with side effects has no effect in an unevaluated context}}
+  decltype(i++) j = 0; // expected-warning {{expression with side effects has no effect in an unevaluated context}}
 }
+
+struct S {
+  S operator++(int);
+  S(int i);
+  S();
+
+  int& f();
+  S g();
+};
+
+void j() {
+  S s;
+  int i = 0;
+  (void)noexcept(s++); // Ok
+  (void)noexcept(i++); // expected-warning {{expression with side effects has no effect in an unevaluated context}}
+  (void)noexcept(i = 5); // expected-warning {{expression with side effects has no effect in an unevaluated context}}
+  (void)noexcept(s = 5); // Ok
+
+  (void)sizeof(s.f()); // Ok
+  (void)sizeof(s.f() = 5); // expected-warning {{expression with side effects has no effect in an unevaluated context}}
+  (void)noexcept(s.g() = 5); // Ok
+}
+
+}
\ No newline at end of file