From b48b6c0caafc0ff2f5960e20fcc200e57543ccb9 Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Wed, 7 Aug 2019 11:53:21 +0200
Subject: [PATCH] Vector: Use memmove() for moving trivial types around more

This can definitely be improved with better trivial type detection and
by using the TypedTransfer template in more places.

It's a bit annoying that we can't get <type_traits> in Vector.h since
it's included in the toolchain compilation before we have libstdc++.
---
 AK/Traits.h | 12 ++++++++++++
 AK/Vector.h | 31 ++++++++++++++++++++++++++-----
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/AK/Traits.h b/AK/Traits.h
index b651a3f6350..0eaf5d3e869 100644
--- a/AK/Traits.h
+++ b/AK/Traits.h
@@ -12,32 +12,44 @@ struct GenericTraits {
 
 template<typename T>
 struct Traits : public GenericTraits<T> {
+    static constexpr bool is_trivial() { return false; }
 };
 
 template<>
 struct Traits<int> : public GenericTraits<int> {
+    static constexpr bool is_trivial() { return true; }
     static unsigned hash(int i) { return int_hash(i); }
     static void dump(int i) { kprintf("%d", i); }
 };
 
 template<>
 struct Traits<unsigned> : public GenericTraits<unsigned> {
+    static constexpr bool is_trivial() { return true; }
     static unsigned hash(unsigned u) { return int_hash(u); }
     static void dump(unsigned u) { kprintf("%u", u); }
 };
 
 template<>
 struct Traits<u16> : public GenericTraits<u16> {
+    static constexpr bool is_trivial() { return true; }
     static unsigned hash(u16 u) { return int_hash(u); }
     static void dump(u16 u) { kprintf("%u", u); }
 };
 
+template<>
+struct Traits<char> : public GenericTraits<char> {
+    static constexpr bool is_trivial() { return true; }
+    static unsigned hash(char c) { return int_hash(c); }
+    static void dump(char c) { kprintf("%c", c); }
+};
+
 template<typename T>
 struct Traits<T*> {
     static unsigned hash(const T* p)
     {
         return int_hash((unsigned)(__PTRDIFF_TYPE__)p);
     }
+    static constexpr bool is_trivial() { return true; }
     static void dump(const T* p) { kprintf("%p", p); }
     static bool equals(const T* a, const T* b) { return a == b; }
 };
diff --git a/AK/Vector.h b/AK/Vector.h
index 7daf6c54d8d..21e3aa1b916 100644
--- a/AK/Vector.h
+++ b/AK/Vector.h
@@ -63,6 +63,30 @@ private:
     int m_index { 0 };
 };
 
+template<typename T>
+class TypedTransfer {
+public:
+    static void move(T* destination, T* source, size_t count)
+    {
+        if constexpr (Traits<T>::is_trivial()) {
+            memmove(destination, source, count * sizeof(T));
+            return;
+        }
+        for (size_t i = 0; i < count; ++i)
+            new (&destination[i]) T(AK::move(source[i]));
+    }
+
+    static void copy(T* destination, const T* source, size_t count)
+    {
+        if constexpr (Traits<T>::is_trivial()) {
+            memmove(destination, source, count * sizeof(T));
+            return;
+        }
+        for (size_t i = 0; i < count; ++i)
+            new (&destination[i]) T(source[i]);
+    }
+};
+
 template<typename T, int inline_capacity = 0>
 class Vector {
 public:
@@ -379,9 +403,7 @@ public:
         }
 
         Vector tmp = move(other);
-        for (int i = 0; i < tmp.size(); ++i)
-            new (slot(i)) T(move(tmp.at(i)));
-
+        TypedTransfer<T>::move(slot(0), tmp.data(), tmp.size());
         m_size += other_size;
     }
 
@@ -390,8 +412,7 @@ public:
         if (!count)
             return;
         grow_capacity(size() + count);
-        for (int i = 0; i < count; ++i)
-            new (slot(m_size + i)) T(values[i]);
+        TypedTransfer<T>::copy(slot(m_size), values, count);
         m_size += count;
     }