https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101406
Bug ID: 101406
Summary: shared_ptr in _S_atomic mode still uses
__atomic_add_dispatch()
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: marc.mutz at kdab dot com
Target Milestone: ---
Consider
// https://godbolt.org/z/efTW6MoEh
void test_copy(const std::shared_ptr<int> &sp)
{ auto copy = sp; }
vs.
// https://godbolt.org/z/3aoGq1f9P
void test_copy(const boost::shared_ptr<int> &sp)
{ auto copy = sp; }
In the first cast, over 70 lines of assembler are emitted, in the second,
around 30. This seems to be in large part because in
_Sp_counted_base::_M_add_ref_copy(), you're using __atomic_add_dispatch() even
if _Lp is _S_atomic. It seems to me that a specialisation of this function
template for _S_atomic calling just __atomic_add() is missing:
https://godbolt.org/z/crPz9hGe7
Probably same for the deref case, too.
