Implement -Wself-assign, which warns on code such as:
int x = 42;
x = x; // Warns here.
The warning avoids macro expansions, templates, user-defined assignment
operators, and volatile types, so false positives are expected to be low.
The common (mis-)use of this code pattern is to silence unused variable
warnings, but a more idiomatic way of doing that is '(void)x;'.
A follow-up to this will add a note and fix-it hint suggesting this
replacement in cases where the StmtExpr consists precisely of the self
assignment.
llvm-svn: 122804
diff --git a/clang/test/SemaCXX/warn-self-assign.cpp b/clang/test/SemaCXX/warn-self-assign.cpp
new file mode 100644
index 0000000..fcdb2ab
--- /dev/null
+++ b/clang/test/SemaCXX/warn-self-assign.cpp
@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -fsyntax-only -Wself-assign -verify %s
+
+void f() {
+ int a = 42, b = 42;
+ a = a; // expected-warning{{explicitly assigning}}
+ b = b; // expected-warning{{explicitly assigning}}
+ a = b;
+ b = a = b;
+ a = a = a; // expected-warning{{explicitly assigning}}
+ a = b = b = a;
+}
+
+// Dummy type.
+struct S {};
+
+void false_positives() {
+#define OP =
+#define LHS a
+#define RHS a
+ int a = 42;
+ // These shouldn't warn due to the use of the preprocessor.
+ a OP a;
+ LHS = a;
+ a = RHS;
+ LHS OP RHS;
+#undef OP
+#undef LHS
+#undef RHS
+
+ S s;
+ s = s; // Not a builtin assignment operator, no warning.
+
+ // Volatile stores aren't side-effect free.
+ volatile int vol_a;
+ vol_a = vol_a;
+ volatile int &vol_a_ref = vol_a;
+ vol_a_ref = vol_a_ref;
+}
+
+template <typename T> void g() {
+ T a;
+ a = a; // May or may not be a builtin assignment operator, no warning.
+}
+void instantiate() {
+ g<int>();
+ g<S>();
+}