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 <jwak...@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.
Tested powerpc64le-linux.
The macros are ugly, but using #ifdef is unavoidable here. I think
this is less ugly than the laternative ways to do this.
Any objections to pushing this, or any better ideas for doing this?
commit f8c86589f2eab42c0888390bea7bceb8dc31d92b
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Mon Jul 19 16:43:11 2021
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 <jwak...@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 --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
