Implement a fast buffer allocator for Vector, HashTable and StringBuilder

Source/wtf/text/StringBuilder.cpp

Index: Source/wtf/text/StringBuilder.cpp
diff --git a/Source/wtf/text/StringBuilder.cpp b/Source/wtf/text/StringBuilder.cpp
index 9236bf6fb55526c337cbc82ed4074f5da8cbc934..29428f235d9075363b4070e525fa8886f343bdfe 100644
--- a/Source/wtf/text/StringBuilder.cpp
+++ b/Source/wtf/text/StringBuilder.cpp
@@ -36,7 +36,7 @@ namespace WTF {
 static unsigned expandedCapacity(unsigned capacity, unsigned requiredLength)
 {
     static const unsigned minimumCapacity = 16;
-    return std::max(requiredLength, std::max(minimumCapacity, capacity * 2));
+    return std::max(requiredLength, std::max(minimumCapacity, capacity * 5 / 4));
 }
 
 void StringBuilder::reifyString()
@@ -118,7 +118,7 @@ void StringBuilder::allocateBuffer(const LChar* currentCharacters, unsigned requ
 {
     ASSERT(m_is8Bit);
     // Copy the existing data into a new buffer, set result to point to the end of the existing data.
-    RefPtr<StringImpl> buffer = StringImpl::createUninitialized(requiredLength, m_bufferCharacters8);
+    RefPtr<StringImpl> buffer = StringImpl::createBufferUninitialized(requiredLength, m_bufferCharacters8, this);
     memcpy(m_bufferCharacters8, currentCharacters, static_cast<size_t>(m_length) * sizeof(LChar)); // This can't overflow.
 
     // Update the builder state.
@@ -132,7 +132,7 @@ void StringBuilder::allocateBuffer(const UChar* currentCharacters, unsigned requ
 {
     ASSERT(!m_is8Bit);
     // Copy the existing data into a new buffer, set result to point to the end of the existing data.
-    RefPtr<StringImpl> buffer = StringImpl::createUninitialized(requiredLength, m_bufferCharacters16);
+    RefPtr<StringImpl> buffer = StringImpl::createBufferUninitialized(requiredLength, m_bufferCharacters16, this);
     memcpy(m_bufferCharacters16, currentCharacters, static_cast<size_t>(m_length) * sizeof(UChar)); // This can't overflow.
 
     // Update the builder state.
@@ -146,7 +146,7 @@ void StringBuilder::allocateBufferUpConvert(const LChar* currentCharacters, unsi
 {
     ASSERT(m_is8Bit);
     // Copy the existing data into a new buffer, set result to point to the end of the existing data.
-    RefPtr<StringImpl> buffer = StringImpl::createUninitialized(requiredLength, m_bufferCharacters16);
+    RefPtr<StringImpl> buffer = StringImpl::createBufferUninitialized(requiredLength, m_bufferCharacters16, this);
     for (unsigned i = 0; i < m_length; ++i)
         m_bufferCharacters16[i] = currentCharacters[i];
 
@@ -168,10 +168,14 @@ void StringBuilder::reallocateBuffer<LChar>(unsigned requiredLength)
     ASSERT(m_buffer->is8Bit());
 
     if (m_buffer->hasOneRef()) {
-        m_buffer = StringImpl::reallocate(m_buffer.release(), requiredLength);
+        m_buffer = StringImpl::reallocate(m_buffer.release(), requiredLength, this);
         m_bufferCharacters8 = const_cast<LChar*>(m_buffer->characters8());
-    } else
+    } else {
+#if BUFFER_ALLOCATOR_DEBUG
+        fprintf(stderr, "!m_buffer->hasOneRef()\n");
+#endif
         allocateBuffer(m_buffer->characters8(), requiredLength);
+    }
 }
 
 template <>
@@ -184,10 +188,14 @@ void StringBuilder::reallocateBuffer<UChar>(unsigned requiredLength)
     if (m_buffer->is8Bit()) {
         allocateBufferUpConvert(m_buffer->characters8(), requiredLength);
     } else if (m_buffer->hasOneRef()) {
-        m_buffer = StringImpl::reallocate(m_buffer.release(), requiredLength);
+        m_buffer = StringImpl::reallocate(m_buffer.release(), requiredLength, this);
         m_bufferCharacters16 = const_cast<UChar*>(m_buffer->characters16());
-    } else
+    } else {
+#if BUFFER_ALLOCATOR_DEBUG
+        fprintf(stderr, "!m_buffer->hasOneRef()\n");
+#endif
         allocateBuffer(m_buffer->characters16(), requiredLength);
+    }
 }
 
 void StringBuilder::reserveCapacity(unsigned newCapacity)