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diff --git a/libcxx/include/__utility/exception_guard.h b/libcxx/include/__utility/exception_guard.h
new file mode 100644
index 000000000000..737d1a69c971
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+++ b/libcxx/include/__utility/exception_guard.h
@@ -0,0 +1,128 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___UTILITY_TRANSACTION_H
+#define _LIBCPP___UTILITY_TRANSACTION_H
+
+#include <__assert>
+#include <__config>
+#include <__type_traits/is_nothrow_move_constructible.h>
+#include <__utility/exchange.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// __exception_guard is a helper class for writing code with the strong exception guarantee.
+//
+// When writing code that can throw an exception, one can store rollback instructions in an
+// exception guard so that if an exception is thrown at any point during the lifetime of the
+// exception guard, it will be rolled back automatically. When the exception guard is done, one
+// must mark it as being complete so it isn't rolled back when the exception guard is destroyed.
+//
+// Exception guards are not default constructible, they can't be copied or assigned to, but
+// they can be moved around for convenience.
+//
+// __exception_guard is a no-op in -fno-exceptions mode to produce better code-gen. This means
+// that we don't provide the strong exception guarantees. However, Clang doesn't generate cleanup
+// code with exceptions disabled, so even if we wanted to provide the strong exception guarantees
+// we couldn't. This is also only relevant for constructs with a stack of
+// -fexceptions > -fno-exceptions > -fexceptions code, since the exception can't be caught where
+// exceptions are disabled. While -fexceptions > -fno-exceptions is quite common
+// (e.g. libc++.dylib > -fno-exceptions), having another layer with exceptions enabled seems a lot
+// less common, especially one that tries to catch an exception through -fno-exceptions code.
+//
+// __exception_guard can help greatly simplify code that would normally be cluttered by
+// `#if _LIBCPP_NO_EXCEPTIONS`. For example:
+//
+//    template <class Iterator, class Size, class OutputIterator>
+//    Iterator uninitialized_copy_n(Iterator iter, Size n, OutputIterator out) {
+//        typedef typename iterator_traits<Iterator>::value_type value_type;
+//        __exception_guard guard([start=out, &out] {
+//            std::destroy(start, out);
+//        });
+//
+//        for (; n > 0; ++iter, ++out, --n) {
+//            ::new ((void*)std::addressof(*out)) value_type(*iter);
+//        }
+//        guard.__complete();
+//        return out;
+//    }
+//
+
+#ifndef _LIBCPP_NO_EXCEPTIONS
+template <class _Rollback>
+struct __exception_guard {
+  __exception_guard() = delete;
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit __exception_guard(_Rollback __rollback)
+      : __rollback_(std::move(__rollback)), __completed_(false) {}
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __exception_guard(__exception_guard&& __other)
+      _NOEXCEPT_(is_nothrow_move_constructible<_Rollback>::value)
+      : __rollback_(std::move(__other.__rollback_)), __completed_(__other.__completed_) {
+    __other.__completed_ = true;
+  }
+
+  __exception_guard(__exception_guard const&)            = delete;
+  __exception_guard& operator=(__exception_guard const&) = delete;
+  __exception_guard& operator=(__exception_guard&&)      = delete;
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __complete() _NOEXCEPT { __completed_ = true; }
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__exception_guard() {
+    if (!__completed_)
+      __rollback_();
+  }
+
+private:
+  _Rollback __rollback_;
+  bool __completed_;
+};
+#else  // _LIBCPP_NO_EXCEPTIONS
+template <class _Rollback>
+struct __exception_guard {
+  __exception_guard() = delete;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_NODEBUG explicit __exception_guard(_Rollback) {}
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_NODEBUG __exception_guard(__exception_guard&& __other)
+      _NOEXCEPT_(is_nothrow_move_constructible<_Rollback>::value)
+      : __completed_(__other.__completed_) {
+    __other.__completed_ = true;
+  }
+
+  __exception_guard(__exception_guard const&)            = delete;
+  __exception_guard& operator=(__exception_guard const&) = delete;
+  __exception_guard& operator=(__exception_guard&&)      = delete;
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_NODEBUG void __complete() _NOEXCEPT {
+    __completed_ = true;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_NODEBUG ~__exception_guard() {
+    _LIBCPP_ASSERT(__completed_, "__exception_guard not completed with exceptions disabled");
+  }
+
+private:
+  bool __completed_ = false;
+};
+#endif // _LIBCPP_NO_EXCEPTIONS
+
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(__exception_guard);
+
+template <class _Rollback>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __exception_guard<_Rollback> __make_exception_guard(_Rollback __rollback) {
+  return __exception_guard<_Rollback>(std::move(__rollback));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___UTILITY_TRANSACTION_H