Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 08d31de09e2b120d1bb2a2bb9abe97c6f3802c13
https://github.com/WebKit/WebKit/commit/08d31de09e2b120d1bb2a2bb9abe97c6f3802c13
Author: Ahmad Saleem <[email protected]>
Date: 2026-07-30 (Thu, 30 Jul 2026)
Changed paths:
M Source/WebCore/cssjit/SelectorCompiler.cpp
Log Message:
-----------
Reduce sizeof(SelectorFragment) by eliminating struct padding in the CSS JIT
https://bugs.webkit.org/show_bug.cgi?id=320628
rdar://183591712
Reviewed by Chris Dumez.
SelectorFragment had 12 bytes of padding holes on 64-bit: 3 bytes after
isRightmostOrAdjacent, 3 bytes after backtrackingFlags, and 6 bytes of tail
padding after the two trailing bools.
Give BacktrackingAction, FragmentRelation and FragmentPositionInRootFragments
an explicit uint8_t underlying type, and move matchesHasScope and
onlyMatchesLinksInQuirksMode up beside the other byte-sized members so all ten
of them pack contiguously into offsets 0-9. This moves the first pointer member
from offset 56 down to 40 and takes sizeof(SelectorFragment) from 528 to 504,
leaving only the 2 bytes of alignment padding before the first unsigned.
These three enums are used only within SelectorCompiler.cpp for bookkeeping
during compilation; none of them are encoded into the generated code, so
narrowing them has no effect on the emitted JIT code.
SelectorFragmentList is a Vector<SelectorFragment, 4>, so its inline (stack)
storage shrinks from 2144 to 2048 bytes. That saving compounds while compiling
nested functional pseudo-classes, where notFilters, matchesFilters and the
nthChildOf filter lists nest SelectorFragmentLists recursively. See the
existing FIXME about the inline capacity in this struct.
No change in behavior.
* Source/WebCore/cssjit/SelectorCompiler.cpp:
Canonical link: https://commits.webkit.org/318247@main
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