From 502626eecb5bbd658f3dc516d2d46ad1aed55a90 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 19 Jan 2020 12:15:43 +0100
Subject: [PATCH] AK: Teach Vector::insert() to use memmove() for trivial types

---
 AK/Tests/TestVector.cpp | 18 ++++++++++++++++++
 AK/Vector.h             | 17 ++++++++++++++---
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/AK/Tests/TestVector.cpp b/AK/Tests/TestVector.cpp
index 68c7582ef8e..74f31667420 100644
--- a/AK/Tests/TestVector.cpp
+++ b/AK/Tests/TestVector.cpp
@@ -295,4 +295,22 @@ TEST_CASE(nonnullownptrvector)
     EXPECT_EQ(objects.size(), 2);
 }
 
+TEST_CASE(insert_trivial)
+{
+    Vector<int> ints;
+    ints.append(0);
+    ints.append(10);
+    ints.append(20);
+    ints.append(30);
+    ints.append(40);
+    ints.insert(2, 15);
+    EXPECT_EQ(ints.size(), 6);
+    EXPECT_EQ(ints[0], 0);
+    EXPECT_EQ(ints[1], 10);
+    EXPECT_EQ(ints[2], 15);
+    EXPECT_EQ(ints[3], 20);
+    EXPECT_EQ(ints[4], 30);
+    EXPECT_EQ(ints[5], 40);
+}
+
 TEST_MAIN(Vector)
diff --git a/AK/Vector.h b/AK/Vector.h
index 37f970c0a7c..6cb2cac4e5c 100644
--- a/AK/Vector.h
+++ b/AK/Vector.h
@@ -94,6 +94,8 @@ class TypedTransfer {
 public:
     static void move(T* destination, T* source, size_t count)
     {
+        if (!count)
+            return;
         if constexpr (Traits<T>::is_trivial()) {
             memmove(destination, source, count * sizeof(T));
             return;
@@ -104,6 +106,8 @@ public:
 
     static void copy(T* destination, const T* source, size_t count)
     {
+        if (!count)
+            return;
         if constexpr (Traits<T>::is_trivial()) {
             memmove(destination, source, count * sizeof(T));
             return;
@@ -114,6 +118,9 @@ public:
 
     static bool compare(const T* a, const T* b, size_t count)
     {
+        if (!count)
+            return true;
+
         if constexpr (Traits<T>::is_trivial())
             return !memcmp(a, b, count * sizeof(T));
 
@@ -335,9 +342,13 @@ public:
             return append(move(value));
         grow_capacity(size() + 1);
         ++m_size;
-        for (int i = size() - 1; i > index; --i) {
-            new (slot(i)) T(move(at(i - 1)));
-            at(i - 1).~T();
+        if constexpr (Traits<T>::is_trivial()) {
+            TypedTransfer<T>::move(slot(index + 1), slot(index), m_size - index - 1);
+        } else {
+            for (int i = size() - 1; i > index; --i) {
+                new (slot(i)) T(move(at(i - 1)));
+                at(i - 1).~T();
+            }
         }
         new (slot(index)) T(move(value));
     }