https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118874
--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
In the
#include <coroutine>
struct B {
bool await_ready () const noexcept;
void await_suspend (std::coroutine_handle<> h) const noexcept;
void await_resume () const noexcept;
};
struct C {
struct promise_type {
const char *value;
std::suspend_never initial_suspend ();
std::suspend_always final_suspend () noexcept;
void return_value (const char *v);
void unhandled_exception ();
C get_return_object () { return C{this}; }
};
promise_type *p;
explicit C (promise_type *p) : p(p) {}
const char *get ();
};
C
bar (bool x)
{
if (x)
co_await B{};
co_return "foobar";
}
testcase (-O2 -m64 -mptr64 -fcoroutines -std=c++23) I see can_do_nrvo_p return
twice false when functype is RECORD_TYPE C,
once in get_return_object and once in bar function; the reason it returns false
is that retval is not a VAR_DECL, but TARGET_EXPR in both cases.
The coroutines.cc code refers to DECL_RESULT unconditionally then.
I think the problematic INIT_EXPR is created by
#5 0x0000000002090641 in build2 (code=INIT_EXPR, tt=<record_type
0x7fffe9a610a8 C>, arg0=<result_decl 0x7fffe9a60500>, arg1=<target_expr
0x7fffe9a7b038>) at ../../gcc/tree.cc:5199
#6 0x0000000000df98f8 in build2_loc (loc=84139394, code=INIT_EXPR,
type=<record_type 0x7fffe9a610a8 C>, arg0=<result_decl 0x7fffe9a60500>,
arg1=<target_expr 0x7fffe9a7b038>)
at ../../gcc/tree.h:4825
#7 0x000000000120f81e in cp_build_init_expr (loc=84139394, target=<result_decl
0x7fffe9a60500>, init=<target_expr 0x7fffe9a7b038>) at
../../gcc/cp/typeck2.cc:2820
#8 0x0000000000d8a860 in cp_build_init_expr (t=<result_decl 0x7fffe9a60500>,
i=<target_expr 0x7fffe9a7b038>) at ../../gcc/cp/cp-tree.h:8600
#9 0x00000000012027cb in check_return_expr (retval=<target_expr
0x7fffe9a7b038>, no_warning=0x7fffffffd14f, dangling=0x7fffffffd14e) at
../../gcc/cp/typeck.cc:11513
#10 0x0000000000e23d13 in cp_coroutine_transform::build_ramp_function
(this=0x3c0bb60) at ../../gcc/cp/coroutines.cc:5186
Obviously, for the aggregate_value_p (TREE_TYPE (TREE_TYPE
(current_function_decl)), current_function_decl) case what the code does is
what we want. But I guess as these 2 PRs show, for !aggregate_value_p we want
to just initialize a temporary VAR_DECL and then have GIMPLE_RETURN which
returns that VAR_DECL.
