Bug 306383 – [appearance: base] Shrink ComputedStyleBase to free some bits for form controls pseudo elements

• Status: RESOLVED
• Resolution: FIXED
• Component: Forms

[Said Abou-Hallawa]

ComputedStyleBase has m_nonInheritedData, which is DataRef, as its first member. m_nonInheritedData has to be aligned at 8 bytes boundary. Because the CheckedPtr uses a 4-bytes counter which comes the first thing, there are 4-bytes padding between this counter and m_inheritedRareData. Similarly there are 2-bytes padding between m_nonInheritedFlags and m_inheritedRareData.

To shrink this class by using the padding bytes, m_nonInheritedFlags and m_inheritedFlags should be the first members of ComputedStyleBase. If we reserve 22 unused bits for pseudo elements in m_nonInheritedFlags, moving the m_nonInheritedFlags and m_inheritedFlags the current padding will be reduced from

Total byte size: 64
Total pad bytes: 6
Padding percentage: 10.16%

To be 

Total byte size: 64
Total pad bytes: 0
Padding percentage: 0.78 %

[Radar WebKit Bug Importer]

<rdar://problem/169048994>

[Said Abou-Hallawa]

Pull request: https://github.com/WebKit/WebKit/pull/57374

[EWS]

Committed 306352@main (653d8d23600e): <https://commits.webkit.org/306352@main>

Reviewed commits have been landed. Closing PR #57374 and removing active labels.