[webkit-changes] [WebKit/WebKit] 5e5e74: [JSC] Handle Array with -1 in super common case

[Yusuke Suzuki]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 5e5e7445e5ce0a8e5f9b846c57b2d65c64cd6f51
      https://github.com/WebKit/WebKit/commit/5e5e7445e5ce0a8e5f9b846c57b2d65c64cd6f51
  Author: Yusuke Suzuki <ysuzuki at apple.com>
  Date:   2024-02-22 (Thu, 22 Feb 2024)

  Changed paths:
    A JSTests/microbenchmarks/array-negative-one.js
    A JSTests/stress/array-negative-one-instance.js
    A JSTests/stress/array-negative-one-prototype.js
    A JSTests/stress/array-negative-one-prototype2.js
    M Source/JavaScriptCore/dfg/DFGOperations.cpp
    M Source/JavaScriptCore/jit/JITOperations.cpp
    M Source/JavaScriptCore/llint/LLIntSlowPaths.cpp
    M Source/JavaScriptCore/runtime/CommonIdentifiers.cpp
    M Source/JavaScriptCore/runtime/CommonIdentifiers.h
    M Source/JavaScriptCore/runtime/JSArray.h
    M Source/JavaScriptCore/runtime/JSArrayInlines.h
    M Source/JavaScriptCore/runtime/JSGlobalObject.cpp
    M Source/JavaScriptCore/runtime/JSGlobalObject.h

  Log Message:
  -----------
  [JSC] Handle Array with -1 in super common case
https://bugs.webkit.org/show_bug.cgi?id=269901
rdar://123429794

Reviewed by Justin Michaud.

`array[-1]` access is actually common. For example,

    while (item = array[--i]) {
        ...
    }

code is written in the wild and using `array[-1]` => undefined access as a stop condition.
We should have enough fast access for that. In this patch, we set up `-1` property watchpoint for Array.prototype and Object.prototype,
and skip property lookup when we are just accessing normal Array's -1. We could improve this more generic way, but it looks like, most of cases
are just covered by this. Let's start with simple one.

                                   ToT                     Patched

    array-negative-one       29.5545+-0.6586     ^     15.6126+-0.5059        ^ definitely 1.8930x faster

* JSTests/microbenchmarks/array-negative-one.js: Added.
(shouldBe):
(t):
* JSTests/stress/array-negative-one-instance.js: Added.
(shouldBe):
(t):
* JSTests/stress/array-negative-one-prototype.js: Added.
(shouldBe):
(t):
* JSTests/stress/array-negative-one-prototype2.js: Added.
(shouldBe):
(t):
* Source/JavaScriptCore/dfg/DFGOperations.cpp:
(JSC::DFG::getByValCellInt):
(JSC::DFG::JSC_DEFINE_JIT_OPERATION):
* Source/JavaScriptCore/jit/JITOperations.cpp:
(JSC::getByVal):
(JSC::getByValWithThis):
* Source/JavaScriptCore/llint/LLIntSlowPaths.cpp:
(JSC::LLInt::getByVal):
* Source/JavaScriptCore/runtime/CommonIdentifiers.cpp:
(JSC::CommonIdentifiers::CommonIdentifiers):
* Source/JavaScriptCore/runtime/CommonIdentifiers.h:
* Source/JavaScriptCore/runtime/JSArray.h:
* Source/JavaScriptCore/runtime/JSArrayInlines.h:
(JSC::JSArray::definitelyNegativeOneMiss const):
* Source/JavaScriptCore/runtime/JSGlobalObject.cpp:
(JSC::setupAbsenceAdaptiveWatchpoint):
(JSC::JSGlobalObject::init):
* Source/JavaScriptCore/runtime/JSGlobalObject.h:
(JSC::JSGlobalObject::arrayNegativeOneWatchpointSet):

Canonical link: https://commits.webkit.org/275179@main



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