coroutines: Ensure the ramp return object is checked (PR93443).

As the PR shows, there is a pathway through the code where the
no_warning value is not set, which corresponds to a missing check
of the ramp return when it was constructed from the 'get return
object'  Fixed by ensuring that the check of the return value is
carried out for both return cases.

gcc/cp/ChangeLog:

2020-01-27  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/93443
	* coroutines.cc (morph_fn_to_coro): Check the ramp return
	value when it is constructed from the 'get return object'.

gcc/cp/ChangeLog

+2020-01-27  Iain Sandoe  <iain@sandoe.co.uk>
+
+	PR c++/93443
+	* coroutines.cc (morph_fn_to_coro): Check the ramp return
+	value when it is constructed from the 'get return object'.
+
 2020-01-27  Nathan Sidwell  <nathan@acm.org>
 
 	PR c++/91826

gcc/cp/coroutines.cc

@@ -3526,14 +3526,9 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
 
   /* Switch to using 'input_location' as the loc, since we're now more
      logically doing things related to the end of the function.  */
-  /* done, we just need the return value.  */
-  bool no_warning;
-  if (same_type_p (TREE_TYPE (gro), fn_return_type))
-    {
-      /* Already got the result.  */
-      r = check_return_expr (DECL_RESULT (orig), &no_warning);
-    }
-  else
+
+  /* The ramp is done, we just need the return value.  */
+  if (!same_type_p (TREE_TYPE (gro), fn_return_type))
     {
       /* construct the return value with a single GRO param.  */
       vec<tree, va_gc> *args = make_tree_vector_single (gro);
@@ -3545,6 +3540,13 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
       add_stmt (r);
       release_tree_vector (args);
     }
+  /* Else the GRO is the return and we already built it in place.  */
+
+  bool no_warning;
+  r = check_return_expr (DECL_RESULT (orig), &no_warning);
+  if (error_operand_p (r) && warn_return_type)
+    /* Suppress -Wreturn-type for the ramp.  */
+    TREE_NO_WARNING (orig) = true;
 
   r = build_stmt (input_location, RETURN_EXPR, DECL_RESULT (orig));
   TREE_NO_WARNING (r) |= no_warning;