[webkit-changes] [WebKit/WebKit] 4d8164: [JSC] Further optimize JSRopeString::resolveRope

[Yusuke Suzuki]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 4d816460b765acd8aef90ab474615850b91ecc35
      https://github.com/WebKit/WebKit/commit/4d816460b765acd8aef90ab474615850b91ecc35
  Author: Yusuke Suzuki <ysuzuki at apple.com>
  Date:   2023-07-14 (Fri, 14 Jul 2023)

  Changed paths:
    A JSTests/microbenchmarks/rope-resolve-recursive.js
    M Source/JavaScriptCore/runtime/JSString.cpp
    M Source/JavaScriptCore/runtime/JSString.h
    M Source/JavaScriptCore/runtime/JSStringInlines.h
    M Source/WTF/wtf/Compiler.h

  Log Message:
  -----------
  [JSC] Further optimize JSRopeString::resolveRope
https://bugs.webkit.org/show_bug.cgi?id=259203
rdar://112241674

Reviewed by Mark Lam.

This patch furhter improves JSRopeString::resolveRope and jsAtomString.

1. We crafted JSRopeString::resolveToBuffer very carefully so that it becomes tail calls well.
   This allows clang to make it loop instead of calls for recursive resolveToBuffer calls, which
   is significantly efficient. We ensure this condition is met by using MUST_TAIL_CALL C++ attribute,
   which is available in clang.
2. We tweak jsAtomString to make it better in terms of performance. It turned out these duplicate part
   is mandatory to make it super efficient, which is observed by JetStream2/WSL.

Simple rope resolution gets 3-4% improvement.

                                   ToT                     Patched

rope-resolve-recursive       21.3292+-0.6975     ^     20.5524+-0.0687        ^ definitely 1.0378x faster

* Source/JavaScriptCore/runtime/JSString.cpp:
(JSC::JSRopeString::resolveRopeInternalNoSubstring const):
* Source/JavaScriptCore/runtime/JSString.h:
* Source/JavaScriptCore/runtime/JSStringInlines.h:
(JSC::JSRopeString::resolveToBufferSlow):
(JSC::JSRopeString::resolveToBuffer):
(JSC::jsAtomString):
(JSC::JSStringFibers::JSStringFibers): Deleted.
(JSC::JSStringFibers::fiber const): Deleted.
(JSC::JSStringFibers::fiber0 const): Deleted.
(JSC::JSStringFibers::fiber1 const): Deleted.
(JSC::JSStringFibers::fiber2 const): Deleted.
(): Deleted.
* Source/WTF/wtf/Compiler.h:

Canonical link: https://commits.webkit.org/266060@main