314139 2026-05-05 17:05:07 -0700 REGRESSION (297241@main): Overflow siblings at parser's max DOM tree depth get fully rendered, causing slow layout 2026-05-11 11:26:44 -0700 1 1 1 Unclassified WebKit New Bugs WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 1 zakr zakr webkit-bug-importer oldest_to_newest 2207874 0 zakr 2026-05-05 17:05:07 -0700 After 297241@main fixed the parser's DOM depth cap to trigger at exactly 512 (>= instead of >), overflow elements now land at depth 512 instead of 513. The render tree's depth check at StyleTreeResolver only skips depth > 512, so the overflow siblings now pass through and get fully styled and laid out. Content with thousands of overflow siblings for example, a Mail message embedding a crash log with many unmatched <unavailable> tags produces ~1500 sibling inline boxes at the boundary depth. Inline layout then walks the ancestor chain per box (LineBox::parentInlineBox / inlineLevelBoxAbsoluteTop), giving O(depth × N) and ~15s render times. Fix it with the following: at the maximum render tree depth, skip elements that have a previous element sibling. The single legitimate deepest element keeps its renderer; the overflow run gets none. 2207876 1 zakr 2026-05-05 17:05:27 -0700 <rdar://172219636> 2207893 2 zakr 2026-05-05 17:25:51 -0700 Pull request: https://github.com/WebKit/WebKit/pull/64319 2208356 3 ews-feeder 2026-05-06 16:37:48 -0700 Committed 312751@main (69a399de80ab): <https://commits.webkit.org/312751@main> Reviewed commits have been landed. Closing PR #64319 and removing active labels. 2209801 4 ews-feeder 2026-05-11 11:26:44 -0700 Committed 305877.486@webkitglib/2.52 (024db5335281): <https://commits.webkit.org/305877.486@webkitglib/2.52> Reviewed commits have been landed. Closing PR #64674 and removing active labels.