Bug 254959

Summary: Optimize WTF::Bitmap::forEachSetBit to use hardware intrinsics when available
Product: WebKit Reporter: David Degazio <d_degazio>
Component: Web Template FrameworkAssignee: David Degazio <d_degazio>
Status: RESOLVED FIXED    
Severity: Normal CC: webkit-bug-importer
Priority: P2 Keywords: InRadar
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   

Description David Degazio 2023-04-03 17:21:15 PDT 
rdar://107584830

Currently, when iterating over the bits of a WTF::Bitmap, we manually iterate bit by bit. On x86_64 and ARM64 however, we should generally have access to bit-counting instructions in hardware. This means instead of doing one iteration for every 1 or 0 bit, we still do one iteration for every 1 bit, but skip up to a word of 0 bits at a time. This can massively reduce iteration time especially for sparse bitmaps.
Comment 1 David Degazio 2023-04-03 17:26:11 PDT 
Pull request: https://github.com/WebKit/WebKit/pull/12349
Comment 2 EWS 2023-04-04 17:46:16 PDT 
Committed 262602@main (316ccf979869): <https://commits.webkit.org/262602@main>

Reviewed commits have been landed. Closing PR #12349 and removing active labels.