On 21/10/2020 22:14, Jonathan Wakely via Gcc-patches wrote:
The _M_add_ref_lock() and _M_add_ref_lock_nothrow() members of
_Sp_counted_base are very similar, except that the former throws an
exception when the use count is zero and the latter returns false. The
former (and its callers) can be implemented in terms of the latter.
This results in a small reduction in code size, because throwing an
exception now only happens in one place.
libstdc++-v3/ChangeLog:
* include/bits/shared_ptr.h (shared_ptr(const weak_ptr&, nothrow_t)):
Add noexcept.
* include/bits/shared_ptr_base.h (_Sp_counted_base::_M_add_ref_lock):
Remove specializations and just call _M_add_ref_lock_nothrow.
(__shared_count, __shared_ptr): Use nullptr for null pointer
constants.
(__shared_count(const __weak_count&)): Use _M_add_ref_lock_nothrow
instead of _M_add_ref_lock.
(__shared_count(const __weak_count&, nothrow_t)): Add noexcept.
(__shared_ptr::operator bool()): Add noexcept.
(__shared_ptr(const __weak_ptr&, nothrow_t)): Add noexcept.
Tested powerpc64le-linux. Committed to trunk.
Clang now complains about
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:230:5:
error: '_M_add_ref_lock_nothrow' is missing exception specification 'noexcept'
_M_add_ref_lock_nothrow()
^
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:158:7:
note: previous declaration is here
_M_add_ref_lock_nothrow() noexcept;
^
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:241:5:
error: '_M_add_ref_lock_nothrow' is missing exception specification 'noexcept'
_M_add_ref_lock_nothrow()
^
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:158:7:
note: previous declaration is here
_M_add_ref_lock_nothrow() noexcept;
^
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:255:5:
error: '_M_add_ref_lock_nothrow' is missing exception specification 'noexcept'
_M_add_ref_lock_nothrow()
^
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:158:7:
note: previous declaration is here
_M_add_ref_lock_nothrow() noexcept;
^
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:876:5:
error: exception specification in declaration does not match previous
declaration
__shared_count(const __weak_count<_Lp>& __r, std::nothrow_t) noexcept
^
~gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../include/c++/11.0.0/bits/shared_ptr_base.h:696:16:
note: previous declaration is here
explicit __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t);
^
4 errors generated.
which would be fixed with
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h
b/libstdc++-v3/include/bits/shared_ptr_base.h
index a9e1c9bb1d5..10c9c831411 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -227,7 +227,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<>
inline bool
_Sp_counted_base<_S_single>::
- _M_add_ref_lock_nothrow()
+ _M_add_ref_lock_nothrow() noexcept
{
if (_M_use_count == 0)
return false;
@@ -238,7 +238,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<>
inline bool
_Sp_counted_base<_S_mutex>::
- _M_add_ref_lock_nothrow()
+ _M_add_ref_lock_nothrow() noexcept
{
__gnu_cxx::__scoped_lock sentry(*this);
if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
@@ -252,7 +252,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<>
inline bool
_Sp_counted_base<_S_atomic>::
- _M_add_ref_lock_nothrow()
+ _M_add_ref_lock_nothrow() noexcept
{
// Perform lock-free add-if-not-zero operation.
_Atomic_word __count = _M_get_use_count();
@@ -693,7 +693,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
explicit __shared_count(const __weak_count<_Lp>& __r);
// Does not throw if __r._M_get_use_count() == 0, caller must check.
- explicit __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t);
+ explicit __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t)
noexcept;
~__shared_count() noexcept
{
