On 5/13/25 10:30 AM, Iain Sandoe wrote:
The constraints of the c++ coroutines specification require the ramp
to construct a return object early in the function. This will be returned
at some later time. To meet the requirements of copy-elision, we need
to ensure NVRO for these objects, even when they are non-copyable or
non-movable. Special-case ramp functions to allow this.
Note that the compiler was already choosing to do NRVO in this case, it
just required the copy to be well-formed even though it's getting elided.
gcc/cp/ChangeLog:
* typeck.cc (check_return_expr): Suppress conversions for NVRO
in coroutine ramp functions.
Signed-off-by: Iain Sandoe <i...@sandoe.co.uk>
---
gcc/cp/typeck.cc | 3 +++
1 file changed, 3 insertions(+)
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 1b9fdf5b21d..d8bc3409984 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -11463,6 +11463,9 @@ check_return_expr (tree retval, bool *no_warning, bool
*dangling)
&& call_from_lambda_thunk_p (retval))
converted = true;
Let's add
/* Don't check copy-initialization for NRV in a coroutine ramp; we
implement this case as NRV, but it's specified as directly
initializing the return value from get_return_object(). */
OK with that tweak.
+ if (DECL_RAMP_FN (current_function_decl) && named_return_value_okay_p)
+ converted = true;
+
/* First convert the value to the function's return type, then
to the type of return value's location to handle the
case that functype is smaller than the valtype. */
