Shrink WebCore::Pair
Created attachment 344550 [details] Patch
Before +0 < 40> Pair +0 < 8> __vtbl_ptr_type * _vptr +8 < 4> WTF::RefCounted<WebCore::Pair> WTF::RefCounted<WebCore::Pair> +8 < 4> WTF::RefCountedBase WTF::RefCountedBase +8 < 4> unsigned int m_refCount +12 < 4> <PADDING: 4 bytes> +16 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_first +16 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType m_ptr +24 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_second +24 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType m_ptr +32 < 4> WebCore::Pair::IdenticalValueEncoding m_encoding +36 < 4> <PADDING: 4 bytes> Total byte size: 40 Total pad bytes: 8 Padding percentage: 20.00 % After 24$ $ ./Tools/Scripts/dump-class-layout -c Release WebCore Pair +0 < 32> Pair +0 < 8> __vtbl_ptr_type * _vptr +8 < 4> WTF::RefCounted<WebCore::Pair> WTF::RefCounted<WebCore::Pair> +8 < 4> WTF::RefCountedBase WTF::RefCountedBase +8 < 4> unsigned int m_refCount +12 < 1> WebCore::Pair::IdenticalValueEncoding m_encoding +13 < 3> <PADDING: 3 bytes> +16 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_first +16 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType m_ptr +24 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_second +24 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType m_ptr Total byte size: 32 Total pad bytes: 3 Padding percentage: 9.38 %
(In reply to Simon Fraser (smfr) from comment #2) > Before > +0 < 40> Pair > +0 < 8> __vtbl_ptr_type * _vptr > +8 < 4> WTF::RefCounted<WebCore::Pair> WTF::RefCounted<WebCore::Pair> > +8 < 4> WTF::RefCountedBase WTF::RefCountedBase > +8 < 4> unsigned int m_refCount > +12 < 4> <PADDING: 4 bytes> > +16 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, > WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_first > +16 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType > m_ptr > +24 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, > WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_second > +24 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType > m_ptr > +32 < 4> WebCore::Pair::IdenticalValueEncoding m_encoding > +36 < 4> <PADDING: 4 bytes> > Total byte size: 40 > Total pad bytes: 8 > Padding percentage: 20.00 % > > > After > 24$ $ ./Tools/Scripts/dump-class-layout -c Release WebCore Pair > +0 < 32> Pair > +0 < 8> __vtbl_ptr_type * _vptr > +8 < 4> WTF::RefCounted<WebCore::Pair> WTF::RefCounted<WebCore::Pair> > +8 < 4> WTF::RefCountedBase WTF::RefCountedBase > +8 < 4> unsigned int m_refCount > +12 < 1> WebCore::Pair::IdenticalValueEncoding m_encoding > +13 < 3> <PADDING: 3 bytes> > +16 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, > WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_first > +16 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType > m_ptr > +24 < 8> WTF::RefPtr<WebCore::CSSPrimitiveValue, > WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue> > m_second > +24 < 8> WTF::DumbPtrTraits<WebCore::CSSPrimitiveValue>::StorageType > m_ptr > Total byte size: 32 > Total pad bytes: 3 > Padding percentage: 9.38 % Pair is a final class. And it only inherits RefCounted<Pair>. So, if we remove `virtual ~Pair()`, I think we can drop vtable pointer further!
Comment on attachment 344550 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=344550&action=review > Source/WebCore/ChangeLog:8 > + Move m_encoding to pick in with m_refCount, shrinking the class from 40 to 32 bytes. Do you mean 'pack' here?
Comment on attachment 344550 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=344550&action=review > Source/WebCore/css/Pair.h:33 > class Pair final : public RefCounted<Pair> { I think Yusuke is right that we should drop the virtual destructor here. We do not need a vtable.
Will fix.
https://trac.webkit.org/changeset/233652/webkit
<rdar://problem/41984422>