[webkit-changes] [WebKit/WebKit] e4568f: [JSC] Add StringSplitCache

[Yusuke Suzuki]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: e4568fa804be7b5d0c9fd788a3885faf1e6d2284
      https://github.com/WebKit/WebKit/commit/e4568fa804be7b5d0c9fd788a3885faf1e6d2284
  Author: Yusuke Suzuki <ysuzuki at apple.com>
  Date:   2023-05-31 (Wed, 31 May 2023)

  Changed paths:
    M Source/JavaScriptCore/CMakeLists.txt
    M Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
    M Source/JavaScriptCore/heap/Heap.cpp
    M Source/JavaScriptCore/runtime/ArgList.h
    M Source/JavaScriptCore/runtime/StringPrototype.cpp
    A Source/JavaScriptCore/runtime/StringSplitCache.h
    A Source/JavaScriptCore/runtime/StringSplitCacheInlines.h
    M Source/JavaScriptCore/runtime/VM.cpp
    M Source/JavaScriptCore/runtime/VM.h

  Log Message:
  -----------
  [JSC] Add StringSplitCache
https://bugs.webkit.org/show_bug.cgi?id=257530
rdar://problem/110053165

Reviewed by Justin Michaud.

This patch adds String#split cache, inspired from V8's string split cache.
It is common in the real world code that splitting a literal string with a literal
separator because of readability, and it can be done multiple times instead of doing it globally.
Instead of repeatedly splitting and re-generating strings again and again, we can safely cache the result.
This patch caches result as JSImmutableButterfly when the both subject and separator are atom strings.
In String#split operation, also, instead of generating substrings and extending butterfly, we just compute
offset of substrings. And then finally generating JSImmutableButterfly / JSArray with repeated substrings.
This avoids wasteful intermediate butterfly allocations.

* Source/JavaScriptCore/CMakeLists.txt:
* Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj:
* Source/JavaScriptCore/heap/Heap.cpp:
(JSC::Heap::finalize):
* Source/JavaScriptCore/runtime/ArgList.h:
(JSC::ArgList::ArgList):
* Source/JavaScriptCore/runtime/StringPrototype.cpp:
(JSC::splitStringByOneCharacterImpl):
(JSC::JSC_DEFINE_HOST_FUNCTION):
* Source/JavaScriptCore/runtime/StringSplitCache.h: Added.
(JSC::StringSplitCache::clear):
* Source/JavaScriptCore/runtime/StringSplitCacheInlines.h: Added.
(JSC::StringSplitCache::get):
(JSC::StringSplitCache::set):
* Source/JavaScriptCore/runtime/VM.cpp:
(JSC::VM::VM):
* Source/JavaScriptCore/runtime/VM.h:

Canonical link: https://commits.webkit.org/264749@main