Don't emit -Wunused-value warnings from macro expansions.

llvm-svn: 166522

clang/lib/AST/Expr.cpp

@@ -2026,6 +2026,10 @@ bool Expr::isUnusedResultAWarning(const Expr *&WarnE, SourceLocation &Loc,
   }
   case CXXFunctionalCastExprClass:
   case CStyleCastExprClass: {
+    // Ignore casts within macro expansions.
+    if (getExprLoc().isMacroID())
+      return false;
+
     // Ignore an explicit cast to void unless the operand is a non-trivial
     // volatile lvalue.
     const CastExpr *CE = cast<CastExpr>(this);

clang/test/Sema/unused-expr.c

@@ -122,3 +122,10 @@ void f(int i, ...) {
 
 // PR8371
 int fn5() __attribute__ ((__const));
+
+// OpenSSL has some macros like this.
+#define M(a, b) (long)foo((a), (b))
+void t11(int i, int j) {
+  M(i, j);  // no warning
+}
+#undef M