From c0cce748cc094f8d7a32b744f8d65ab351e2bb86 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Tue, 15 Jul 2025 00:12:31 +0200
Subject: [PATCH] Optimize `Array::RemoveAtKeepOrder`

---
 Source/Engine/Core/Collections/Array.h |  8 +---
 Source/Engine/Core/Memory/Memory.h     | 63 ++++++++------------------
 2 files changed, 19 insertions(+), 52 deletions(-)

diff --git a/Source/Engine/Core/Collections/Array.h b/Source/Engine/Core/Collections/Array.h
index 7cb4a3248..4f660d2a9 100644
--- a/Source/Engine/Core/Collections/Array.h
+++ b/Source/Engine/Core/Collections/Array.h
@@ -658,13 +658,7 @@ public:
         --_count;
         T* data = _allocation.Get();
         if (index < _count)
-        {
-            T* dst = data + index;
-            T* src = data + (index + 1);
-            const int32 count = _count - index;
-            for (int32 i = 0; i < count; ++i)
-                dst[i] = MoveTemp(src[i]);
-        }
+            Memory::MoveAssignItems(data + index, data + (index + 1), _count - index);
         Memory::DestructItems(data + _count, 1);
     }
 
diff --git a/Source/Engine/Core/Memory/Memory.h b/Source/Engine/Core/Memory/Memory.h
index 329ee372d..772c9fb48 100644
--- a/Source/Engine/Core/Memory/Memory.h
+++ b/Source/Engine/Core/Memory/Memory.h
@@ -104,12 +104,6 @@ public:
     {
         new(dst) T();
     }
-
-    /// <summary>
-    /// Constructs the item in the memory.
-    /// </summary>
-    /// <remarks>The optimized version is noop.</remarks>
-    /// <param name="dst">The address of the memory location to construct.</param>
     template<typename T>
     FORCE_INLINE static typename TEnableIf<TIsTriviallyConstructible<T>::Value>::Type ConstructItem(T* dst)
     {
@@ -132,13 +126,6 @@ public:
             ++(T*&)dst;
         }
     }
-
-    /// <summary>
-    /// Constructs the range of items in the memory.
-    /// </summary>
-    /// <remarks>The optimized version is noop.</remarks>
-    /// <param name="dst">The address of the first memory location to construct.</param>
-    /// <param name="count">The number of element to construct. Can be equal 0.</param>
     template<typename T>
     FORCE_INLINE static typename TEnableIf<TIsTriviallyConstructible<T>::Value>::Type ConstructItems(T* dst, int32 count)
     {
@@ -163,14 +150,6 @@ public:
             ++src;
         }
     }
-
-    /// <summary>
-    /// Constructs the range of items in the memory from the set of arguments.
-    /// </summary>
-    /// <remarks>The optimized version uses low-level memory copy.</remarks>
-    /// <param name="dst">The address of the first memory location to construct.</param>
-    /// <param name="src">The address of the first memory location to pass to the constructor.</param>
-    /// <param name="count">The number of element to construct. Can be equal 0.</param>
     template<typename T, typename U>
     FORCE_INLINE static typename TEnableIf<TIsBitwiseConstructible<T, U>::Value>::Type ConstructItems(T* dst, const U* src, int32 count)
     {
@@ -187,12 +166,6 @@ public:
     {
         dst->~T();
     }
-
-    /// <summary>
-    /// Destructs the item in the memory.
-    /// </summary>
-    /// <remarks>The optimized version is noop.</remarks>
-    /// <param name="dst">The address of the memory location to destruct.</param>
     template<typename T>
     FORCE_INLINE static typename TEnableIf<TIsTriviallyDestructible<T>::Value>::Type DestructItem(T* dst)
     {
@@ -213,13 +186,6 @@ public:
             ++dst;
         }
     }
-
-    /// <summary>
-    /// Destructs the range of items in the memory.
-    /// </summary>
-    /// <remarks>The optimized version is noop.</remarks>
-    /// <param name="dst">The address of the first memory location to destruct.</param>
-    /// <param name="count">The number of element to destruct. Can be equal 0.</param>
     template<typename T>
     FORCE_INLINE static typename TEnableIf<TIsTriviallyDestructible<T>::Value>::Type DestructItems(T* dst, int32 count)
     {
@@ -242,15 +208,7 @@ public:
             ++src;
         }
     }
-
-    /// <summary>
-    /// Copies the range of items using the assignment operator.
-    /// </summary>
-    /// <remarks>The optimized version is low-level memory copy.</remarks>
-    /// <param name="dst">The address of the first memory location to start assigning to.</param>
-    /// <param name="src">The address of the first memory location to assign from.</param>
-    /// <param name="count">The number of element to assign. Can be equal 0.</param>
-    template<typename T>
+    template<typename T, typename U>
     FORCE_INLINE static typename TEnableIf<TIsTriviallyCopyAssignable<T>::Value>::Type CopyItems(T* dst, const T* src, int32 count)
     {
         Platform::MemoryCopy(dst, src, count * sizeof(T));
@@ -273,16 +231,31 @@ public:
             ++src;
         }
     }
+    template<typename T, typename U>
+    FORCE_INLINE static typename TEnableIf<TIsBitwiseConstructible<T, U>::Value>::Type MoveItems(T* dst, U* src, int32 count)
+    {
+        Platform::MemoryCopy(dst, src, count * sizeof(U));
+    }
 
     /// <summary>
-    /// Moves the range of items in the memory from the set of arguments.
+    /// Moves the range of items using the assignment operator.
     /// </summary>
     /// <remarks>The optimized version uses low-level memory copy.</remarks>
     /// <param name="dst">The address of the first memory location to move.</param>
     /// <param name="src">The address of the first memory location to pass to the move constructor.</param>
     /// <param name="count">The number of element to move. Can be equal 0.</param>
     template<typename T, typename U>
-    FORCE_INLINE static typename TEnableIf<TIsBitwiseConstructible<T, U>::Value>::Type MoveItems(T* dst, U* src, int32 count)
+    FORCE_INLINE static typename TEnableIf<!TIsBitwiseConstructible<T, U>::Value>::Type MoveAssignItems(T* dst, U* src, int32 count)
+    {
+        while (count--)
+        {
+            *dst = MoveTemp(*src);
+            ++(T*&)dst;
+            ++src;
+        }
+    }
+    template<typename T, typename U>
+    FORCE_INLINE static typename TEnableIf<TIsBitwiseConstructible<T, U>::Value>::Type MoveAssignItems(T* dst, U* src, int32 count)
     {
         Platform::MemoryCopy(dst, src, count * sizeof(U));
     }