Properly test allocator awareness of string

Did fix some bugs in string * We were only allocating _Newcapacity in _Copy_assign. This lead to memory corruption * We were not calling _Tidy_deallocate in _Move_assign which leaked memory of lhs * We did not swap proxies in swap if one of the strings was in SSO. Breaks with stateful allocators * We always performed work in swap even if self swapping
microsoft · Aug 27, 2021 · c164242 · c164242
1 parent a5e7657
commit c164242
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Showing 2 changed files with 436 additions and 53 deletions.
diff --git a/stl/inc/xstring b/stl/inc/xstring
@@ -2871,7 +2871,7 @@ public:
     }
 
 private:
-    void _Memcpy_val_from(const basic_string& _Right) noexcept {
+    _CONSTEXPR20 void _Memcpy_val_from(const basic_string& _Right) noexcept {
         _STL_INTERNAL_CHECK(_Can_memcpy_val); // TRANSITION, if constexpr
         const auto _My_data_mem =
             reinterpret_cast<unsigned char*>(_STD addressof(_Mypair._Myval2)) + _Memcpy_val_offset;
@@ -2914,6 +2914,11 @@ private:
             _Right_data._Bx._Ptr = nullptr;
             _Swap_proxy_and_iterators(_Right);
         } else { // copy small string buffer
+#if _HAS_CXX20
+            if (_STD is_constant_evaluated()) {
+                _Construct_in_place(_Mypair._Myval2._Bx);
+            }
+#endif // _HAS_CXX20
             _Traits::copy(_My_data._Bx._Buf, _Right_data._Bx._Buf, _Right_data._Mysize + 1);
             _Right_data._Orphan_all();
         }
@@ -3017,19 +3022,25 @@ public:
     static constexpr auto npos{static_cast<size_type>(-1)};
 
 private:
-    void _Copy_assign_val_from_small(const basic_string& _Right) {
+    _CONSTEXPR20 void _Copy_assign_val_from_small(const basic_string& _Right) {
         // TRANSITION, VSO-761321; inline into only caller when that's fixed
         _Tidy_deallocate();
         if constexpr (_Can_memcpy_val) {
-            _Memcpy_val_from(_Right);
-        } else {
-            auto& _My_data    = _Mypair._Myval2;
-            auto& _Right_data = _Right._Mypair._Myval2;
-
-            _Traits::copy(_My_data._Bx._Buf, _Right_data._Bx._Buf, _Right_data._Mysize + 1);
-            _My_data._Mysize = _Right_data._Mysize;
-            _My_data._Myres  = _Right_data._Myres;
+#if _HAS_CXX20
+            if (!is_constant_evaluated())
+#endif // _HAS_CXX20
+            {
+                _Memcpy_val_from(_Right);
+                return;
+            }
         }
+
+        auto& _My_data    = _Mypair._Myval2;
+        auto& _Right_data = _Right._Mypair._Myval2;
+
+        _Traits::copy(_My_data._Bx._Buf, _Right_data._Bx._Buf, _Right_data._Mysize + 1);
+        _My_data._Mysize = _Right_data._Mysize;
+        _My_data._Myres  = _Right_data._Myres;
     }
 
     _CONSTEXPR20 void _Copy_assign(const basic_string& _Right, false_type) {