<deque>: Fix single-element insertion of deque

stl/inc/deque

@@ -871,13 +871,48 @@ public:
         _STL_VERIFY(_Off <= _Mysize(), "deque emplace iterator outside range");
 #endif // _ITERATOR_DEBUG_LEVEL == 2
 
-        if (_Off <= _Mysize() / 2) { // closer to front, push to front then rotate
-            emplace_front(_STD forward<_Valty>(_Val)...);
-            _STD rotate(begin(), _Next_iter(begin()), begin() + static_cast<difference_type>(1 + _Off));
-        } else { // closer to back, push to back then rotate
-            emplace_back(_STD forward<_Valty>(_Val)...);
-            _STD rotate(begin() + static_cast<difference_type>(_Off), _Prev_iter(end()), end());
+        constexpr bool _Uses_move_assignment =
+            disjunction_v<is_nothrow_move_assignable<value_type>, negation<is_copy_assignable<value_type>>>;
+
+        _Orphan_all();
+        if (_Off == 0) { // at the beginning
+            _Emplace_front_internal(_STD forward<_Valty>(_Val)...);
+        } else if (_Off <= _Mysize() / 2) { // closer to front, push to front then rotate
+            auto& _Al = _Getal();
+            _Alloc_temporary2<_Alty> _Obj(_Al, _STD forward<_Valty>(_Val)...); // handle aliasing
+
+            auto _Old_unwrapped_begin = _Unchecked_begin();
+            auto _Old_unwrapped_where = _Old_unwrapped_begin + static_cast<difference_type>(_Off);
+
+            _Emplace_front_internal(_STD move_if_noexcept(*_Old_unwrapped_begin));
+            if constexpr (_Uses_move_assignment) {
+                _STD _Move_unchecked(_STD _Next_iter(_Old_unwrapped_begin), _Old_unwrapped_where, _Old_unwrapped_begin);
+                *_STD _Prev_iter(_Old_unwrapped_where) = _STD move(_Obj._Get_value());
+            } else {
+                _STD _Copy_unchecked(_STD _Next_iter(_Old_unwrapped_begin), _Old_unwrapped_where, _Old_unwrapped_begin);
+                *_STD _Prev_iter(_Old_unwrapped_where) = _STD as_const(_Obj._Get_value());
+            }
+        } else if (_Off != _Mysize()) { // closer to back, push to back then rotate
+            auto& _Al = _Getal();
+            _Alloc_temporary2<_Alty> _Obj(_Al, _STD forward<_Valty>(_Val)...); // handle aliasing
+
+            auto _Old_unwrapped_end   = _Unchecked_end();
+            auto _Old_unwrapped_where = _Unchecked_begin() + static_cast<difference_type>(_Off);
+
+            _Emplace_back_internal(_STD move_if_noexcept(*_STD _Prev_iter(_Old_unwrapped_end)));
+            if constexpr (_Uses_move_assignment) {
+                (void) _STD _Move_backward_unchecked(
+                    _Old_unwrapped_where, _STD _Prev_iter(_Old_unwrapped_end), _Old_unwrapped_end);
+                *_Old_unwrapped_where = _STD move(_Obj._Get_value());
+            } else {
+                (void) _STD _Copy_backward_unchecked(
+                    _Old_unwrapped_where, _STD _Prev_iter(_Old_unwrapped_end), _Old_unwrapped_end);
+                *_Old_unwrapped_where = _STD as_const(_Obj._Get_value());
+            }
+        } else { // at the end
+            _Emplace_back_internal(_STD forward<_Valty>(_Val)...);
         }
+
         return begin() + static_cast<difference_type>(_Off);
     }
 
@@ -1267,21 +1302,7 @@ public:
     }
 
     iterator insert(const_iterator _Where, const _Ty& _Val) {
-        size_type _Off = static_cast<size_type>(_Where - begin());
-
-#if _ITERATOR_DEBUG_LEVEL == 2
-        _STL_VERIFY(_Off <= _Mysize(), "deque insert iterator outside range");
-#endif // _ITERATOR_DEBUG_LEVEL == 2
-
-        if (_Off <= _Mysize() / 2) { // closer to front, push to front then copy
-            push_front(_Val);
-            _STD rotate(begin(), _Next_iter(begin()), begin() + static_cast<difference_type>(1 + _Off));
-        } else { // closer to back, push to back then copy
-            push_back(_Val);
-            _STD rotate(begin() + static_cast<difference_type>(_Off), _Prev_iter(end()), end());
-        }
-
-        return begin() + static_cast<difference_type>(_Off);
+        return emplace(_Where, _Val);
     }
 
     iterator insert(const_iterator _Where, _CRT_GUARDOVERFLOW size_type _Count, const _Ty& _Val) {

tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp

@@ -3,13 +3,14 @@
 
 #include <cassert>
 #include <deque>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
 #include <vector>
 
 using namespace std;
 
-void test_391805();
-
-int main() {
+void test_push_back_pop_front() {
     deque<int> d;
 
     for (int n = 0; n < 1000; ++n) {
@@ -31,8 +32,6 @@ int main() {
             assert(d[i] == *v[i]);
         }
     }
-
-    test_391805();
 }
 
 // Also test Dev10-391805 "STL: Prefast error in deque".
@@ -47,3 +46,190 @@ void test_391805() {
 
     assert(d.size() == 4 && d[0] == 40 && d[1] == 30 && d[2] == 10 && d[3] == 20);
 }
+
+// Also test GH-1023 "<deque>: std::deque::insert performance"
+// - support for single-element insertion of non-swappable type, and
+// - exception safety for single-element insertion.
+
+struct ThrowingConstruction {
+    explicit ThrowingConstruction() = default;
+};
+
+class UniqueError : public std::exception {};
+
+class NonswappableMovable {
+public:
+    NonswappableMovable() = default;
+    NonswappableMovable(NonswappableMovable&& other) noexcept : payload{exchange(other.payload, -1)} {}
+    NonswappableMovable(const NonswappableMovable&) = default;
+
+    explicit NonswappableMovable(int n) noexcept : payload{n} {}
+    explicit NonswappableMovable(ThrowingConstruction) {
+        throw UniqueError{};
+    }
+
+    NonswappableMovable& operator=(NonswappableMovable&& other) noexcept {
+        payload = exchange(other.payload, -1);
+        return *this;
+    }
+    NonswappableMovable& operator=(const NonswappableMovable&) = default;
+
+#if _HAS_CXX20
+    friend bool operator==(const NonswappableMovable&, const NonswappableMovable&) = default;
+#else // ^^^ C++20 or later / C++17 or earlier
+    friend bool operator==(const NonswappableMovable& lhs, const NonswappableMovable& rhs) noexcept {
+        return lhs.payload == rhs.payload;
+    }
+
+    friend bool operator!=(const NonswappableMovable& lhs, const NonswappableMovable& rhs) noexcept {
+        return lhs.payload != rhs.payload;
+    }
+#endif // ^^^ C++17 or earlier ^^^
+
+    friend void swap(NonswappableMovable, NonswappableMovable) = delete;
+
+private:
+    int payload = -1;
+};
+
+#if _HAS_CXX17
+static_assert(!is_swappable_v<NonswappableMovable>);
+#endif // _HAS_CXX17
+
+void test_exception_safety_for_nonswappable_movable() {
+    using Diff = deque<NonswappableMovable>::difference_type;
+
+    deque<NonswappableMovable> d;
+    for (int i = 0; i < 10; ++i) {
+        d.emplace_back(i);
+    }
+
+    {
+        auto it = d.emplace(d.begin() + Diff{3}, 42);
+        assert(it == d.begin() + Diff{3});
+        assert(d[3] == NonswappableMovable{42});
+    }
+    {
+        auto it = d.emplace(d.end() - Diff{3}, 1729);
+        assert(it == d.end() - Diff{4});
+        assert(d[d.size() - 4] == NonswappableMovable{1729});
+    }
+
+    const auto d_orig = d;
+    try {
+        d.emplace_front(ThrowingConstruction{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace_back(ThrowingConstruction{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.begin() + Diff{2}, ThrowingConstruction{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.end() - Diff{2}, ThrowingConstruction{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+}
+
+class ThrowingMovable {
+public:
+    ThrowingMovable() = default;
+    ThrowingMovable(ThrowingMovable&&) {
+        throw UniqueError{};
+    }
+    ThrowingMovable(const ThrowingMovable&) noexcept = default;
+
+    explicit ThrowingMovable(int n) noexcept : payload{n} {}
+
+    ThrowingMovable& operator=(ThrowingMovable&&) {
+        throw UniqueError{};
+    }
+    ThrowingMovable& operator=(const ThrowingMovable&) noexcept = default;
+
+#if _HAS_CXX20
+    friend bool operator==(const ThrowingMovable&, const ThrowingMovable&) = default;
+#else // ^^^ C++20 or later / C++17 or earlier
+    friend bool operator==(const ThrowingMovable& lhs, const ThrowingMovable& rhs) noexcept {
+        return lhs.payload == rhs.payload;
+    }
+
+    friend bool operator!=(const ThrowingMovable& lhs, const ThrowingMovable& rhs) noexcept {
+        return lhs.payload != rhs.payload;
+    }
+#endif // ^^^ C++17 or earlier ^^^
+
+private:
+    int payload = -1;
+};
+
+void test_exception_safety_for_throwing_movable() {
+    using Diff = deque<ThrowingMovable>::difference_type;
+
+    deque<ThrowingMovable> d;
+    for (int i = 0; i < 10; ++i) {
+        d.emplace_back(i);
+    }
+
+    {
+        auto it = d.emplace(d.begin() + Diff{3}, 42);
+        assert(it == d.begin() + Diff{3});
+        assert(d[3] == ThrowingMovable{42});
+    }
+    {
+        auto it = d.emplace(d.end() - Diff{3}, 1729);
+        assert(it == d.end() - Diff{4});
+        assert(d[d.size() - 4] == ThrowingMovable{1729});
+    }
+
+    const auto d_orig = d;
+    try {
+        d.emplace_front(ThrowingMovable{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace_back(ThrowingMovable{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.begin() + Diff{2}, ThrowingMovable{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.end() - Diff{2}, ThrowingMovable{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+}
+
+int main() {
+    test_push_back_pop_front();
+
+    test_391805();
+
+    test_exception_safety_for_nonswappable_movable();
+    test_exception_safety_for_throwing_movable();
+}