<xmemory>: Unify overloads of _Allocate and _Deallocate with if constexpr (#4432)

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

Author: frederick-vs-ja

stl/inc/xmemory

@@ -190,21 +190,21 @@ inline void _Adjust_manually_vector_aligned(void*& _Ptr, size_t& _Bytes) {
 }
 #endif // defined(_M_IX86) || defined(_M_X64)
 
-#ifdef __cpp_aligned_new
-template <size_t _Align, class _Traits = _Default_allocate_traits,
-    enable_if_t<(_Align > __STDCPP_DEFAULT_NEW_ALIGNMENT__), int> = 0>
+template <size_t _Align, class _Traits = _Default_allocate_traits>
 __declspec(allocator) _CONSTEXPR20 void* _Allocate(const size_t _Bytes) {
-    // allocate _Bytes when __cpp_aligned_new && _Align > __STDCPP_DEFAULT_NEW_ALIGNMENT__
+    // allocate _Bytes
     if (_Bytes == 0) {
         return nullptr;
     }
 
 #if _HAS_CXX20 // TRANSITION, GH-1532
     if (_STD is_constant_evaluated()) {
         return _Traits::_Allocate(_Bytes);
-    } else
+    }
 #endif // _HAS_CXX20
-    {
+
+#ifdef __cpp_aligned_new
+    if constexpr (_Align > __STDCPP_DEFAULT_NEW_ALIGNMENT__) {
         size_t _Passed_align = _Align;
 #if defined(_M_IX86) || defined(_M_X64)
         if (_Bytes >= _Big_allocation_threshold) {
@@ -213,75 +213,52 @@ __declspec(allocator) _CONSTEXPR20 void* _Allocate(const size_t _Bytes) {
         }
 #endif // defined(_M_IX86) || defined(_M_X64)
         return _Traits::_Allocate_aligned(_Bytes, _Passed_align);
-    }
-}
-
-template <size_t _Align, enable_if_t<(_Align > __STDCPP_DEFAULT_NEW_ALIGNMENT__), int> = 0>
-_CONSTEXPR20 void _Deallocate(void* _Ptr, const size_t _Bytes) noexcept {
-    // deallocate storage allocated by _Allocate when __cpp_aligned_new && _Align > __STDCPP_DEFAULT_NEW_ALIGNMENT__
-#if _HAS_CXX20 // TRANSITION, GH-1532
-    if (_STD is_constant_evaluated()) {
-        ::operator delete(_Ptr);
     } else
-#endif // _HAS_CXX20
+#endif // defined(__cpp_aligned_new)
     {
-        size_t _Passed_align = _Align;
 #if defined(_M_IX86) || defined(_M_X64)
-        if (_Bytes >= _Big_allocation_threshold) { // boost the alignment of big allocations to help autovectorization
-            _Passed_align = (_STD max)(_Align, _Big_allocation_alignment);
-        }
-#endif // defined(_M_IX86) || defined(_M_X64)
-        ::operator delete(_Ptr, _Bytes, align_val_t{_Passed_align});
-    }
-}
-
-#define _HAS_ALIGNED_NEW 1
-#else // ^^^ defined(__cpp_aligned_new) / !defined(__cpp_aligned_new) vvv
-#define _HAS_ALIGNED_NEW 0
-#endif // ^^^ !defined(__cpp_aligned_new) ^^^
-
-template <size_t _Align, class _Traits = _Default_allocate_traits,
-    enable_if_t<(!_HAS_ALIGNED_NEW || _Align <= __STDCPP_DEFAULT_NEW_ALIGNMENT__), int> = 0>
-__declspec(allocator) _CONSTEXPR20 void* _Allocate(const size_t _Bytes) {
-    // allocate _Bytes when !_HAS_ALIGNED_NEW || _Align <= __STDCPP_DEFAULT_NEW_ALIGNMENT__
-#if defined(_M_IX86) || defined(_M_X64)
-#if _HAS_CXX20 // TRANSITION, GH-1532
-    if (!_STD is_constant_evaluated())
-#endif // _HAS_CXX20
-    {
-        if (_Bytes >= _Big_allocation_threshold) { // boost the alignment of big allocations to help autovectorization
+        if (_Bytes >= _Big_allocation_threshold) {
+            // boost the alignment of big allocations to help autovectorization
             return _Allocate_manually_vector_aligned<_Traits>(_Bytes);
         }
-    }
 #endif // defined(_M_IX86) || defined(_M_X64)
-
-    if (_Bytes != 0) {
         return _Traits::_Allocate(_Bytes);
     }
-
-    return nullptr;
 }
 
-template <size_t _Align, enable_if_t<(!_HAS_ALIGNED_NEW || _Align <= __STDCPP_DEFAULT_NEW_ALIGNMENT__), int> = 0>
+template <size_t _Align>
 _CONSTEXPR20 void _Deallocate(void* _Ptr, size_t _Bytes) noexcept {
-    // deallocate storage allocated by _Allocate when !_HAS_ALIGNED_NEW || _Align <= __STDCPP_DEFAULT_NEW_ALIGNMENT__
+    // deallocate storage allocated by _Allocate
 #if _HAS_CXX20 // TRANSITION, GH-1532
     if (_STD is_constant_evaluated()) {
         ::operator delete(_Ptr);
-    } else
+        return;
+    }
 #endif // _HAS_CXX20
+
+#ifdef __cpp_aligned_new
+    if constexpr (_Align > __STDCPP_DEFAULT_NEW_ALIGNMENT__) {
+        size_t _Passed_align = _Align;
+#if defined(_M_IX86) || defined(_M_X64)
+        if (_Bytes >= _Big_allocation_threshold) {
+            // boost the alignment of big allocations to help autovectorization
+            _Passed_align = (_STD max)(_Align, _Big_allocation_alignment);
+        }
+#endif // defined(_M_IX86) || defined(_M_X64)
+        ::operator delete(_Ptr, _Bytes, align_val_t{_Passed_align});
+    } else
+#endif // defined(__cpp_aligned_new)
     {
 #if defined(_M_IX86) || defined(_M_X64)
-        if (_Bytes >= _Big_allocation_threshold) { // boost the alignment of big allocations to help autovectorization
+        if (_Bytes >= _Big_allocation_threshold) {
+            // boost the alignment of big allocations to help autovectorization
             _Adjust_manually_vector_aligned(_Ptr, _Bytes);
         }
 #endif // defined(_M_IX86) || defined(_M_X64)
         ::operator delete(_Ptr, _Bytes);
     }
 }
 
-#undef _HAS_ALIGNED_NEW
-
 template <class _Ptr, class _Ty>
 using _Rebind_pointer_t = typename pointer_traits<_Ptr>::template rebind<_Ty>;