[coroutines] Fix unused warning on result of co_yield.

This patch follows up on r328602, which fixed the spurious unused
result warning for `co_await`.

llvm-svn: 328607

2 files changed, 21 insertions, 3 deletions

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 3cb0013c9bf..57c8850ba91 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2050,7 +2050,8 @@ bool Expr::isUnusedResultAWarning(const Expr *&WarnE, SourceLocation &Loc,
     return cast<GenericSelectionExpr>(this)->getResultExpr()->
       isUnusedResultAWarning(WarnE, Loc, R1, R2, Ctx);
   case CoawaitExprClass:
-    return cast<CoawaitExpr>(this)->getResumeExpr()->
+  case CoyieldExprClass:
+    return cast<CoroutineSuspendExpr>(this)->getResumeExpr()->
       isUnusedResultAWarning(WarnE, Loc, R1, R2, Ctx);
   case ChooseExprClass:
     return cast<ChooseExpr>(this)->getChosenSubExpr()->
diff --git a/clang/test/SemaCXX/coroutines.cpp b/clang/test/SemaCXX/coroutines.cpp
index 308e70e054a..c09ca570636 100644
--- a/clang/test/SemaCXX/coroutines.cpp
+++ b/clang/test/SemaCXX/coroutines.cpp
@@ -1338,7 +1338,6 @@ bad_coroutine_calls_with_no_matching_constructor(int, int) {
 
 } // namespace CoroHandleMemberFunctionTest
 
-
 class awaitable_no_unused_warn {
 public:
   using handle_type = std::experimental::coroutine_handle<>;
@@ -1357,7 +1356,25 @@ public:
   int await_resume() { return 1; }
 };
 
-void test_unused_warning() {
+template <class Await>
+struct check_warning_promise {
+  coro<check_warning_promise> get_return_object();
+  Await initial_suspend();
+  Await final_suspend();
+  Await yield_value(int);
+  void return_void();
+  void unhandled_exception();
+};
+
+
+coro<check_warning_promise<awaitable_no_unused_warn>>
+test_no_unused_warning() {
   co_await awaitable_no_unused_warn();
+  co_yield 42;
+}
+
+coro<check_warning_promise<awaitable_unused_warn>>
+test_unused_warning() {
   co_await awaitable_unused_warn(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  co_yield 42; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
 }