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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r12-2470] libstdc++: Use __builtin_operator_new when available [PR94295] Date: Thu, 22 Jul 2021 13:43:16 +0000 (GMT) [thread overview] Message-ID: <20210722134316.545B838618F3@sourceware.org> (raw) https://gcc.gnu.org/g:c9ca352186226ae757688e160e7c6f394c9f26aa commit r12-2470-gc9ca352186226ae757688e160e7c6f394c9f26aa Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Jul 22 14:38:34 2021 +0100 libstdc++: Use __builtin_operator_new when available [PR94295] Clang provides __builtin_operator_new and __builtin_operator_delete, which have the same semantics as ::operator new and ::operator delete except that the compiler is allowed to elide calls to them. This changes std::allocator to use those built-in functions so that memory allocated by std::allocator can be optimized away when using Clang. This avoids an abstraction penalty for using std::allocator to allocate storage rather than a new-expression. Signed-off-by: Jonathan Wakely <jwakely@redhat.com> libstdc++-v3/ChangeLog: PR libstdc++/94295 * include/ext/new_allocator.h (_GLIBCXX_OPERATOR_NEW) (_GLIBCXX_OPERATOR_DELETE, _GLIBCXX_SIZED_DEALLOC): Define. (allocator::allocate, allocator::deallocate): Use new macros. Diff: --- libstdc++-v3/include/ext/new_allocator.h | 38 +++++++++++++++++++++----------- 1 file changed, 25 insertions(+), 13 deletions(-) diff --git a/libstdc++-v3/include/ext/new_allocator.h b/libstdc++-v3/include/ext/new_allocator.h index 3fb893be152..7c48c820c62 100644 --- a/libstdc++-v3/include/ext/new_allocator.h +++ b/libstdc++-v3/include/ext/new_allocator.h @@ -97,6 +97,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return std::__addressof(__x); } #endif +#if __has_builtin(__builtin_operator_new) >= 201802L +# define _GLIBCXX_OPERATOR_NEW __builtin_operator_new +# define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete +#else +# define _GLIBCXX_OPERATOR_NEW ::operator new +# define _GLIBCXX_OPERATOR_DELETE ::operator delete +#endif + // NB: __n is permitted to be 0. The C++ standard says nothing // about what the return value is when __n == 0. _GLIBCXX_NODISCARD _Tp* @@ -121,34 +129,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__) { std::align_val_t __al = std::align_val_t(alignof(_Tp)); - return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), __al)); + return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp), + __al)); } #endif - return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp))); + return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp))); } // __p is not permitted to be a null pointer. void - deallocate(_Tp* __p, size_type __t __attribute__ ((__unused__))) + deallocate(_Tp* __p, size_type __n __attribute__ ((__unused__))) { +#if __cpp_sized_deallocation +# define _GLIBCXX_SIZED_DEALLOC(p, n) (p), (n) * sizeof(_Tp) +#else +# define _GLIBCXX_SIZED_DEALLOC(p, n) (p) +#endif + #if __cpp_aligned_new if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__) { - ::operator delete(__p, -# if __cpp_sized_deallocation - __t * sizeof(_Tp), -# endif - std::align_val_t(alignof(_Tp))); + _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n), + std::align_val_t(alignof(_Tp))); return; } #endif - ::operator delete(__p -#if __cpp_sized_deallocation - , __t * sizeof(_Tp) -#endif - ); + _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n)); } +#undef _GLIBCXX_SIZED_DEALLOC +#undef _GLIBCXX_OPERATOR_DELETE +#undef _GLIBCXX_OPERATOR_NEW + #if __cplusplus <= 201703L size_type max_size() const _GLIBCXX_USE_NOEXCEPT
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