[libc++] Inline fast path for exception_ptr copy constructor & destructor

libcxx/docs/ReleaseNotes/22.rst

@@ -82,6 +82,9 @@ Improvements and New Features
   iterators, resulting in a performance improvement for ``std::deque<short>`` and
   ``std::join_view<vector<vector<short>>>`` iterators.
 
+- ``std::exception_ptr`` was optimized, allowing the compiler to generate better code especially for empty
+  ``std::exception_ptr`` values.
+
 Deprecations and Removals
 -------------------------
 

libcxx/include/__configuration/availability.h

@@ -276,6 +276,12 @@
 #define _LIBCPP_AVAILABILITY_HAS_PMR _LIBCPP_INTRODUCED_IN_LLVM_16
 #define _LIBCPP_AVAILABILITY_PMR
 
+// This macro controls the availability of exception_ptr::__{inc,dec}rement_refcount
+// which are used in the inline implementations of exception_ptr's move constructor,
+// assignment operator, and destructor (see libcxx/include/__exception/exception_ptr.h).
+#define _LIBCPP_AVAILABILITY_HAS_INCREMENT_DECREMENT_REFCOUNT_EXCEPTION_PTR _LIBCPP_INTRODUCED_IN_LLVM_21
+// No attribute, since we've have a fallback implementation in the headers
+
 // These macros controls the availability of __cxa_init_primary_exception
 // in the built library, which std::make_exception_ptr might use
 // (see libcxx/include/__exception/exception_ptr.h).

libcxx/include/__exception/exception_ptr.h

@@ -17,18 +17,13 @@
 #include <__memory/construct_at.h>
 #include <__type_traits/decay.h>
 #include <__type_traits/is_pointer.h>
-#include <__utility/move.h>
-#include <__utility/swap.h>
 #include <__verbose_abort>
 #include <typeinfo>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
-_LIBCPP_PUSH_MACROS
-#include <__undef_macros>
-
 #ifndef _LIBCPP_ABI_MICROSOFT
 
 #  if _LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPTION
@@ -63,11 +58,12 @@ _LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD
 
 #ifndef _LIBCPP_ABI_MICROSOFT
 
-inline _LIBCPP_HIDE_FROM_ABI void swap(exception_ptr& __x, exception_ptr& __y) _NOEXCEPT;
-
 class _LIBCPP_EXPORTED_FROM_ABI exception_ptr {
   void* __ptr_;
 
+  static void __increment_refcount([[__gnu__::__nonnull__]] _LIBCPP_NOESCAPE void*) _NOEXCEPT;
+  static void __decrement_refcount([[__gnu__::__nonnull__]] _LIBCPP_NOESCAPE void*) _NOEXCEPT;
+
   static exception_ptr __from_native_exception_pointer(void*) _NOEXCEPT;
 
   template <class _Ep>
@@ -82,17 +78,42 @@ class _LIBCPP_EXPORTED_FROM_ABI exception_ptr {
   _LIBCPP_HIDE_FROM_ABI exception_ptr() _NOEXCEPT : __ptr_() {}
   _LIBCPP_HIDE_FROM_ABI exception_ptr(nullptr_t) _NOEXCEPT : __ptr_() {}
 
+// These symbols are still exported from the library to prevent ABI breakage.
+#  if defined(_LIBCPP_BUILDING_LIBRARY) || !_LIBCPP_AVAILABILITY_HAS_INCREMENT_DECREMENT_REFCOUNT_EXCEPTION_PTR
   exception_ptr(const exception_ptr&) _NOEXCEPT;
+  exception_ptr& operator=(const exception_ptr&) _NOEXCEPT;
+  ~exception_ptr() _NOEXCEPT;
+#  else  // defined(_LIBCPP_BUILDING_LIBRARY) || !_LIBCPP_AVAILABILITY_HAS_INCREMENT_DECREMENT_REFCOUNT_EXCEPTION_PTR
+  _LIBCPP_HIDE_FROM_ABI exception_ptr(const exception_ptr& __other) _NOEXCEPT : __ptr_(__other.__ptr_) {
+    if (__ptr_)
+      __increment_refcount(__ptr_);
+  }
+  _LIBCPP_HIDE_FROM_ABI exception_ptr& operator=(const exception_ptr& __other) _NOEXCEPT {
+    if (__ptr_ == __other.__ptr_)
+      return *this;
+    if (__other.__ptr_)
+      __increment_refcount(__other.__ptr_);
+    if (__ptr_)
+      __decrement_refcount(__ptr_);
+    __ptr_ = __other.__ptr_;
+    return *this;
+  }
+  _LIBCPP_HIDE_FROM_ABI ~exception_ptr() _NOEXCEPT {
+    if (__ptr_)
+      __decrement_refcount(__ptr_);
+  }
+#  endif // defined(_LIBCPP_BUILDING_LIBRARY) || !_LIBCPP_AVAILABILITY_HAS_INCREMENT_DECREMENT_REFCOUNT_EXCEPTION_PTR
+
   _LIBCPP_HIDE_FROM_ABI exception_ptr(exception_ptr&& __other) _NOEXCEPT : __ptr_(__other.__ptr_) {
     __other.__ptr_ = nullptr;
   }
-  exception_ptr& operator=(const exception_ptr&) _NOEXCEPT;
   _LIBCPP_HIDE_FROM_ABI exception_ptr& operator=(exception_ptr&& __other) _NOEXCEPT {
-    exception_ptr __tmp(std::move(__other));
-    std::swap(__tmp, *this);
+    if (__ptr_)
+      __decrement_refcount(__ptr_);
+    __ptr_         = __other.__ptr_;
+    __other.__ptr_ = nullptr;
     return *this;
   }
-  ~exception_ptr() _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return __ptr_ != nullptr; }
 
@@ -104,16 +125,10 @@ class _LIBCPP_EXPORTED_FROM_ABI exception_ptr {
     return !(__x == __y);
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI void swap(exception_ptr& __x, exception_ptr& __y) _NOEXCEPT;
-
   friend _LIBCPP_EXPORTED_FROM_ABI exception_ptr current_exception() _NOEXCEPT;
   friend _LIBCPP_EXPORTED_FROM_ABI void rethrow_exception(exception_ptr);
 };
 
-inline _LIBCPP_HIDE_FROM_ABI void swap(exception_ptr& __x, exception_ptr& __y) _NOEXCEPT {
-  std::swap(__x.__ptr_, __y.__ptr_);
-}
-
 #  if _LIBCPP_HAS_EXCEPTIONS
 #    if _LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPTION
 template <class _Ep>
@@ -223,6 +238,4 @@ _LIBCPP_HIDE_FROM_ABI exception_ptr make_exception_ptr(_Ep __e) _NOEXCEPT {
 #endif // _LIBCPP_ABI_MICROSOFT
 _LIBCPP_END_UNVERSIONED_NAMESPACE_STD
 
-_LIBCPP_POP_MACROS
-
 #endif // _LIBCPP___EXCEPTION_EXCEPTION_PTR_H

libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -858,6 +858,8 @@
 {'is_defined': True, 'name': '__ZNSt13bad_exceptionD0Ev', 'type': 'I'}
 {'is_defined': True, 'name': '__ZNSt13bad_exceptionD1Ev', 'type': 'I'}
 {'is_defined': True, 'name': '__ZNSt13bad_exceptionD2Ev', 'type': 'I'}
+{'is_defined': True, 'name': '__ZNSt13exception_ptr20__decrement_refcountEPv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '__ZNSt13exception_ptr20__increment_refcountEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt13exception_ptrC1ERKS_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt13exception_ptrC2ERKS_', 'type': 'FUNC'}

libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -494,6 +494,8 @@
 {'is_defined': True, 'name': '_ZNSt13bad_exceptionD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13bad_exceptionD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13bad_exceptionD2Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__decrement_refcountEPv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__increment_refcountEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC1ERKS_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC2ERKS_', 'type': 'FUNC'}

libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -250,6 +250,8 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD0Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD1Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD2Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptr20__decrement_refcountEPv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptr20__increment_refcountEPv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptrC1ERKS_', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptrC2ERKS_', 'storage_mapping_class': 'DS', 'type': 'FUNC'}

libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -250,6 +250,8 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD0Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD1Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD2Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptr20__decrement_refcountEPv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptr20__increment_refcountEPv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptrC1ERKS_', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt13exception_ptrC2ERKS_', 'storage_mapping_class': 'DS', 'type': 'FUNC'}

libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -857,6 +857,8 @@
 {'is_defined': True, 'name': '__ZNSt13bad_exceptionD0Ev', 'type': 'I'}
 {'is_defined': True, 'name': '__ZNSt13bad_exceptionD1Ev', 'type': 'I'}
 {'is_defined': True, 'name': '__ZNSt13bad_exceptionD2Ev', 'type': 'I'}
+{'is_defined': True, 'name': '__ZNSt13exception_ptr20__decrement_refcountEPv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '__ZNSt13exception_ptr20__increment_refcountEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt13exception_ptrC1ERKS_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt13exception_ptrC2ERKS_', 'type': 'FUNC'}

libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -494,6 +494,8 @@
 {'is_defined': True, 'name': '_ZNSt13bad_exceptionD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13bad_exceptionD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13bad_exceptionD2Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__decrement_refcountEPv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__increment_refcountEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC1ERKS_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC2ERKS_', 'type': 'FUNC'}

libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -525,6 +525,8 @@
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD2Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__decrement_refcountEPv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__increment_refcountEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC1ERKS_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC2ERKS_', 'type': 'FUNC'}

libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist

@@ -523,6 +523,8 @@
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD2Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__decrement_refcountEPv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__increment_refcountEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC1ERKS_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC2ERKS_', 'type': 'FUNC'}

libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist

@@ -494,6 +494,8 @@
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD0Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt12experimental19bad_optional_accessD2Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__decrement_refcountEPv', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt13exception_ptr20__increment_refcountEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptr31__from_native_exception_pointerEPv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC1ERKS_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt13exception_ptrC2ERKS_', 'type': 'FUNC'}

libcxx/modules/std/exception.inc

@@ -18,7 +18,6 @@ export namespace std {
   using std::rethrow_exception;
   using std::rethrow_if_nested;
   using std::set_terminate;
-  using std::swap;
   using std::terminate;
   using std::terminate_handler;
   using std::throw_with_nested;

libcxx/src/exception.cpp

@@ -25,12 +25,15 @@ using namespace __cxxabiv1;
 #elif defined(_LIBCPPABI_VERSION)
 #  include "support/runtime/exception_libcxxabi.ipp"
 #  include "support/runtime/exception_pointer_cxxabi.ipp"
+#  include "support/runtime/exception_pointer_refcounted.ipp"
 #elif defined(LIBCXXRT)
 #  include "support/runtime/exception_libcxxrt.ipp"
 #  include "support/runtime/exception_pointer_cxxabi.ipp"
+#  include "support/runtime/exception_pointer_refcounted.ipp"
 #elif defined(__GLIBCXX__)
 #  include "support/runtime/exception_glibcxx.ipp"
 #  include "support/runtime/exception_pointer_glibcxx.ipp"
+#  include "support/runtime/exception_pointer_refcounted.ipp"
 #else
 #  include "include/atomic_support.h"
 #  include "support/runtime/exception_fallback.ipp"

libcxx/src/support/runtime/exception_pointer_cxxabi.ipp

@@ -13,27 +13,12 @@
 
 namespace std {
 
-exception_ptr::~exception_ptr() noexcept { __cxa_decrement_exception_refcount(__ptr_); }
-
-exception_ptr::exception_ptr(const exception_ptr& other) noexcept : __ptr_(other.__ptr_) {
-  __cxa_increment_exception_refcount(__ptr_);
-}
-
-exception_ptr& exception_ptr::operator=(const exception_ptr& other) noexcept {
-  if (__ptr_ != other.__ptr_) {
-    __cxa_increment_exception_refcount(other.__ptr_);
-    __cxa_decrement_exception_refcount(__ptr_);
-    __ptr_ = other.__ptr_;
-  }
-  return *this;
+void exception_ptr::__increment_refcount([[__gnu__::__nonnull__]] _LIBCPP_NOESCAPE void* __ptr) noexcept {
+  __cxa_increment_exception_refcount(__ptr);
 }
 
-exception_ptr exception_ptr::__from_native_exception_pointer(void* __e) noexcept {
-  exception_ptr ptr;
-  ptr.__ptr_ = __e;
-  __cxa_increment_exception_refcount(ptr.__ptr_);
-
-  return ptr;
+void exception_ptr::__decrement_refcount([[__gnu__::__nonnull__]] _LIBCPP_NOESCAPE void* __ptr) noexcept {
+  __cxa_decrement_exception_refcount(__ptr);
 }
 
 nested_exception::nested_exception() noexcept : __ptr_(current_exception()) {}

libcxx/src/support/runtime/exception_pointer_glibcxx.ipp

@@ -11,10 +11,9 @@
 // it uses to implement std::exception_ptr (which it declares as an alias of
 // std::__exception_ptr::exception_ptr) is not directly exported to clients. So
 // we have little choice but to hijack std::__exception_ptr::exception_ptr's
-// (which fortunately has the same layout as our std::exception_ptr) copy
-// constructor, assignment operator and destructor (which are part of its
-// stable ABI), and its rethrow_exception(std::__exception_ptr::exception_ptr)
-// function.
+// _M_addref and _M_release and its rethrow_exception function. Fortunately,
+// glibcxx's exception_ptr has the same layout as our exception_ptr and we can
+// reinterpret_cast between the two.
 
 namespace std {
 
@@ -23,34 +22,20 @@ namespace __exception_ptr {
 struct exception_ptr {
   void* __ptr_;
 
-  explicit exception_ptr(void*) noexcept;
-  exception_ptr(const exception_ptr&) noexcept;
-  exception_ptr& operator=(const exception_ptr&) noexcept;
-  ~exception_ptr() noexcept;
+  void _M_addref() noexcept;
+  void _M_release() noexcept;
 };
 
 } // namespace __exception_ptr
 
 [[noreturn]] void rethrow_exception(__exception_ptr::exception_ptr);
 
-exception_ptr::~exception_ptr() noexcept { reinterpret_cast<__exception_ptr::exception_ptr*>(this)->~exception_ptr(); }
-
-exception_ptr::exception_ptr(const exception_ptr& other) noexcept : __ptr_(other.__ptr_) {
-  new (reinterpret_cast<void*>(this))
-      __exception_ptr::exception_ptr(reinterpret_cast<const __exception_ptr::exception_ptr&>(other));
-}
-
-exception_ptr& exception_ptr::operator=(const exception_ptr& other) noexcept {
-  *reinterpret_cast<__exception_ptr::exception_ptr*>(this) =
-      reinterpret_cast<const __exception_ptr::exception_ptr&>(other);
-  return *this;
+void exception_ptr::__increment_refcount([[__gnu__::__nonnull__]] _LIBCPP_NOESCAPE void* __ptr) noexcept {
+  reinterpret_cast<__exception_ptr::exception_ptr*>(this)->_M_addref();
 }
 
-exception_ptr exception_ptr::__from_native_exception_pointer(void* __e) noexcept {
-  exception_ptr ptr{};
-  new (reinterpret_cast<void*>(&ptr)) __exception_ptr::exception_ptr(__e);
-
-  return ptr;
+void exception_ptr::__decrement_refcount([[__gnu__::__nonnull__]] _LIBCPP_NOESCAPE void* __ptr) noexcept {
+  reinterpret_cast<__exception_ptr::exception_ptr*>(this)->_M_release();
 }
 
 nested_exception::nested_exception() noexcept : __ptr_(current_exception()) {}

libcxx/src/support/runtime/exception_pointer_refcounted.ipp

@@ -0,0 +1,37 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Provides the common functionality shared between cxxabi and glibcxx.
+
+namespace std {
+
+exception_ptr exception_ptr::__from_native_exception_pointer(void* __e) noexcept {
+  exception_ptr ptr;
+  ptr.__ptr_ = __e;
+  __increment_refcount(ptr.__ptr_);
+
+  return ptr;
+}
+
+exception_ptr::~exception_ptr() noexcept { __decrement_refcount(__ptr_); }
+
+exception_ptr::exception_ptr(const exception_ptr& other) noexcept : __ptr_(other.__ptr_) {
+  __increment_refcount(__ptr_);
+}
+
+exception_ptr& exception_ptr::operator=(const exception_ptr& other) noexcept {
+  if (__ptr_ != other.__ptr_) {
+    __increment_refcount(other.__ptr_);
+    __decrement_refcount(__ptr_);
+    __ptr_ = other.__ptr_;
+  }
+  return *this;
+}
+
+} // namespace std