Changeset 143726 in webkit

Timestamp:

Feb 22, 2013 6:39:42 AM (11 years ago)

Author:

akling@apple.com

Message:

ShareableElementData should use zero-length array for storage.
<​http://webkit.org/b/109959>

Reviewed by Anders Carlsson.

Use a zero-length Attribute array instead of always casting from void* to an array.
It was done this way originally because I didn't know we could sidestep the MSVC
build error with some #pragma hackery and a default constructor for Attribute.

• dom/Attribute.cpp:

(WebCore::Attribute::Attribute):

• dom/DocumentSharedObjectPool.cpp:

(WebCore::DocumentSharedObjectPool::cachedShareableElementDataWithAttributes):

• dom/Element.cpp:

(WebCore::sizeForShareableElementDataWithAttributeCount):
(WebCore::ShareableElementData::ShareableElementData):
(WebCore::ShareableElementData::~ShareableElementData):
(WebCore::UniqueElementData::UniqueElementData):

• dom/Element.h:

(ShareableElementData):
(WebCore::ElementData::attributeItem):

Location:

trunk/Source/WebCore

Files:

• ChangeLog (modified) (1 diff)
• dom/Attribute.h (modified) (1 diff)
• dom/DocumentSharedObjectPool.cpp (modified) (1 diff)
• dom/Element.cpp (modified) (5 diffs)
• dom/Element.h (modified) (2 diffs)

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2013-02-22  Andreas Kling  <akling@apple.com>
+
+        ShareableElementData should use zero-length array for storage.
+        <http://webkit.org/b/109959>
+
+        Reviewed by Anders Carlsson.
+
+        Use a zero-length Attribute array instead of always casting from void* to an array.
+        It was done this way originally because I didn't know we could sidestep the MSVC
+        build error with some #pragma hackery and a default constructor for Attribute.
+
+        * dom/Attribute.cpp:
+        (WebCore::Attribute::Attribute):
+        * dom/DocumentSharedObjectPool.cpp:
+        (WebCore::DocumentSharedObjectPool::cachedShareableElementDataWithAttributes):
+        * dom/Element.cpp:
+        (WebCore::sizeForShareableElementDataWithAttributeCount):
+        (WebCore::ShareableElementData::ShareableElementData):
+        (WebCore::ShareableElementData::~ShareableElementData):
+        (WebCore::UniqueElementData::UniqueElementData):
+        * dom/Element.h:
+        (ShareableElementData):
+        (WebCore::ElementData::attributeItem):
+
 2013-02-22  Andreas Kling  <akling@apple.com>
 

trunk/Source/WebCore/dom/Attribute.h

@@ -70 +70 @@
     }
 
+#if COMPILER(MSVC)
+    // NOTE: This constructor is not actually implemented, it's just defined so MSVC
+    // will let us use a zero-length array of Attributes.
+    Attribute();
+#endif
+
 private:
     QualifiedName m_name;

trunk/Source/WebCore/dom/DocumentSharedObjectPool.cpp

@@ -87 +87 @@
         return elementData.release();
 
-    cacheIterator->value = adoptPtr(new ShareableElementDataCacheEntry(ShareableElementDataCacheKey(elementData->immutableAttributeArray(), elementData->length()), elementData));
+    cacheIterator->value = adoptPtr(new ShareableElementDataCacheEntry(ShareableElementDataCacheKey(elementData->m_attributeArray, elementData->length()), elementData));
 
     return elementData.release();

trunk/Source/WebCore/dom/Element.cpp

@@ -2897 +2897 @@
 static size_t sizeForShareableElementDataWithAttributeCount(unsigned count)
 {
-    return sizeof(ShareableElementData) - sizeof(void*) + sizeof(Attribute) * count;
+    return sizeof(ShareableElementData) + sizeof(Attribute) * count;
 }
 
@@ -2915 +2915 @@
 {
     for (unsigned i = 0; i < m_arraySize; ++i)
-        new (&reinterpret_cast<Attribute*>(&m_attributeArray)[i]) Attribute(attributes[i]);
+        new (&m_attributeArray[i]) Attribute(attributes[i]);
 }
 
@@ -2921 +2921 @@
 {
     for (unsigned i = 0; i < m_arraySize; ++i)
-        (reinterpret_cast<Attribute*>(&m_attributeArray)[i]).~Attribute();
+        m_attributeArray[i].~Attribute();
 }
 
@@ -2935 +2935 @@
 
     for (unsigned i = 0; i < m_arraySize; ++i)
-        new (&reinterpret_cast<Attribute*>(&m_attributeArray)[i]) Attribute(other.m_attributeVector.at(i));
+        new (&m_attributeArray[i]) Attribute(other.m_attributeVector.at(i));
 }
 
@@ -2973 +2973 @@
     m_attributeVector.reserveCapacity(other.length());
     for (unsigned i = 0; i < other.length(); ++i)
-        m_attributeVector.uncheckedAppend(other.immutableAttributeArray()[i]);
+        m_attributeVector.uncheckedAppend(other.m_attributeArray[i]);
 }
 

trunk/Source/WebCore/dom/Element.h

@@ -120 +120 @@
 };
 
+#if COMPILER(MSVC)
+#pragma warning(push)
+#pragma warning(disable: 4200) // Disable "zero-sized array in struct/union" warning
+#endif
+
 class ShareableElementData : public ElementData {
 public:
     static PassRefPtr<ShareableElementData> createWithAttributes(const Vector<Attribute>&);
 
-    const Attribute* immutableAttributeArray() const { return reinterpret_cast<const Attribute*>(&m_attributeArray); }
-
     explicit ShareableElementData(const Vector<Attribute>&);
     explicit ShareableElementData(const UniqueElementData&);
     ~ShareableElementData();
 
-    void* m_attributeArray;
+    Attribute m_attributeArray[0];
 };
+
+#if COMPILER(MSVC)
+#pragma warning(pop)
+#endif
 
 class UniqueElementData : public ElementData {
@@ -1000 +1007 @@
     if (m_isUnique)
         return &static_cast<const UniqueElementData*>(this)->m_attributeVector.at(index);
-    return &static_cast<const ShareableElementData*>(this)->immutableAttributeArray()[index];
+    return &static_cast<const ShareableElementData*>(this)->m_attributeArray[index];
 }