[webkit-changes] [WebKit/WebKit] 1f8437: [JSC] Add V8 style ICU DST offset cache

[Yusuke Suzuki]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 1f84372b0336751caf1a2ae482a1331e754e6b51
      https://github.com/WebKit/WebKit/commit/1f84372b0336751caf1a2ae482a1331e754e6b51
  Author: Yusuke Suzuki <ysuzuki at apple.com>
  Date:   2023-06-16 (Fri, 16 Jun 2023)

  Changed paths:
    M Source/JavaScriptCore/runtime/JSDateMath.cpp
    M Source/JavaScriptCore/runtime/JSDateMath.h
    M Source/WTF/wtf/DateMath.cpp
    M Source/WTF/wtf/DateMath.h
    M Source/WTF/wtf/GregorianDateTime.cpp

  Log Message:
  -----------
  [JSC] Add V8 style ICU DST offset cache
https://bugs.webkit.org/show_bug.cgi?id=258186
rdar://110879575

Reviewed by Mark Lam.

This patch adds V8 style ICU DST offset cache into our DateCache.
Previously, we had one-way cache. But in some benchmarks, we observed
that frequent fallback to ICU due to cache miss. So we extend the cache
to 32-way LRU, which is what V8 is doing. So long as we hit this cache,
we do not need to query to ICU about DST offset.

* Source/JavaScriptCore/runtime/JSDateMath.cpp:
(JSC::DateCache::DSTCache::leastRecentlyUsed):
(JSC::DateCache::DSTCache::extendTheAfterCache):
(JSC::DateCache::DSTCache::localTimeOffset):
(JSC::DateCache::resetIfNecessarySlow):
(JSC::DateCache::localTimeOffset): Deleted.
* Source/JavaScriptCore/runtime/JSDateMath.h:
(JSC::LocalTimeOffsetCache::isEmpty):
(JSC::DateCache::DSTCache::DSTCache):
(JSC::DateCache::DSTCache::bumpEpoch):
(JSC::DateCache::DSTCache::reset):
(JSC::DateCache::localTimeOffset):

Canonical link: https://commits.webkit.org/265258@main