<deque>: Fix single-element insertion of deque (#4022)

Co-authored-by: Stephan T. Lavavej <[email protected]>

stl/inc/deque

@@ -1112,13 +1112,35 @@ 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());
+        _Orphan_all();
+        if (_Off == 0) { // at the beginning
+            _Emplace_front_internal(_STD forward<_Valty>(_Val)...);
+        } else if (_Off == _Mysize()) { // at the end
+            _Emplace_back_internal(_STD forward<_Valty>(_Val)...);
+        } else {
+            _Alloc_temporary2<_Alty> _Obj(_Getal(), _STD forward<_Valty>(_Val)...); // handle aliasing
+
+            if (_Off <= _Mysize() / 2) { // closer to front
+                _Emplace_front_internal(_STD move(*_Unchecked_begin()));
+
+                auto _Moving_dst       = _STD _Next_iter(_Unchecked_begin());
+                auto _Moving_src_begin = _STD _Next_iter(_Moving_dst);
+                auto _Moving_src_end   = _Moving_dst + static_cast<difference_type>(_Off);
+
+                auto _Moving_dst_end = _STD _Move_unchecked(_Moving_src_begin, _Moving_src_end, _Moving_dst);
+                *_Moving_dst_end     = _STD move(_Obj._Get_value());
+            } else { // closer to back
+                _Emplace_back_internal(_STD move(*_STD _Prev_iter(_Unchecked_end())));
+
+                auto _Moving_dst_end   = _STD _Prev_iter(_Unchecked_end());
+                auto _Moving_src_end   = _STD _Prev_iter(_Moving_dst_end);
+                auto _Moving_src_begin = _Unchecked_begin() + static_cast<difference_type>(_Off);
+
+                _STD _Move_backward_unchecked(_Moving_src_begin, _Moving_src_end, _Moving_dst_end);
+                *_Moving_src_begin = _STD move(_Obj._Get_value());
+            }
         }
+
         return begin() + static_cast<difference_type>(_Off);
     }
 

tests/std/tests/Dev10_860421_deque_push_back_pop_front/test.cpp

@@ -1,15 +1,16 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <algorithm>
 #include <cassert>
 #include <deque>
+#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 +46,224 @@ 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 ThrowingConstructionTag {
+    explicit ThrowingConstructionTag() = default;
+};
+
+struct UniqueError {
+    explicit UniqueError() = default;
+};
+
+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(ThrowingConstructionTag) {
+        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 // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
+    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 // ^^^ !_HAS_CXX20 ^^^
+
+    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(), 33);
+        assert(it == d.begin());
+        assert(d.front() == NonswappableMovable{33});
+    }
+    {
+        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});
+    }
+    {
+        auto it = d.emplace(d.end(), 2023);
+        assert(it == d.end() - Diff{1});
+        assert(d.back() == NonswappableMovable{2023});
+    }
+    {
+        static constexpr int correct[] = {33, 0, 1, 42, 2, 3, 4, 5, 6, 1729, 7, 8, 9, 2023};
+        auto comp = [](const NonswappableMovable& lhs, const int rhs) { return lhs == NonswappableMovable{rhs}; };
+        assert(equal(d.begin(), d.end(), begin(correct), end(correct), comp));
+    }
+
+    const auto d_orig = d;
+    try {
+        d.emplace_front(ThrowingConstructionTag{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace_back(ThrowingConstructionTag{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.begin(), ThrowingConstructionTag{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.begin() + Diff{2}, ThrowingConstructionTag{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.end() - Diff{2}, ThrowingConstructionTag{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+
+    try {
+        d.emplace(d.end(), ThrowingConstructionTag{});
+        assert(false);
+    } catch (const UniqueError&) {
+    }
+    assert(d == d_orig);
+}
+
+class ThrowingMovable {
+public:
+    ThrowingMovable() = default;
+    ThrowingMovable(ThrowingMovable&&) {
+        throw UniqueError{};
+    }
+    ThrowingMovable(const ThrowingMovable&) = default;
+
+    explicit ThrowingMovable(int n) noexcept : payload{n} {}
+
+    ThrowingMovable& operator=(ThrowingMovable&&) {
+        throw UniqueError{};
+    }
+    ThrowingMovable& operator=(const ThrowingMovable&) = default;
+
+#if _HAS_CXX20
+    friend bool operator==(const ThrowingMovable&, const ThrowingMovable&) = default;
+#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
+    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 // ^^^ !_HAS_CXX20 ^^^
+
+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);
+    }
+
+    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(), 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);
+
+    try {
+        d.emplace(d.end(), 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();
+}