[webkit-changes] [WebKit/WebKit] 4cf7b6: Speed up JSNodeList indexing

[Chris Dumez]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 4cf7b61be1fa78f8578e5f4262145fd22656fcd8
      https://github.com/WebKit/WebKit/commit/4cf7b61be1fa78f8578e5f4262145fd22656fcd8
  Author: Chris Dumez <cdumez at apple.com>
  Date:   2023-03-22 (Wed, 22 Mar 2023)

  Changed paths:
    M Source/WebCore/bindings/scripts/CodeGeneratorJS.pm
    M Source/WebCore/bindings/scripts/IDLAttributes.json
    M Source/WebCore/bindings/scripts/test/JS/JSTestEventTarget.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestIndexedSetterNoIdentifier.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestIndexedSetterThrowingException.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestIndexedSetterWithIdentifier.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestNamedAndIndexedSetterNoIdentifier.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestNamedAndIndexedSetterThrowingException.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestNamedAndIndexedSetterWithIdentifier.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestNamedDeleterWithIndexedGetter.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestNamedSetterWithIndexedGetter.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestNamedSetterWithIndexedGetterAndSetter.cpp
    M Source/WebCore/bindings/scripts/test/JS/JSTestObj.cpp
    M Source/WebCore/css/typedom/CSSUnparsedValue.cpp
    M Source/WebCore/css/typedom/CSSUnparsedValue.h
    M Source/WebCore/css/typedom/CSSUnparsedValue.idl
    M Source/WebCore/css/typedom/numeric/CSSNumericArray.cpp
    M Source/WebCore/css/typedom/numeric/CSSNumericArray.h
    M Source/WebCore/css/typedom/transform/CSSTransformValue.cpp
    M Source/WebCore/css/typedom/transform/CSSTransformValue.h
    M Source/WebCore/svg/SVGLengthList.idl
    M Source/WebCore/svg/SVGNumberList.idl
    M Source/WebCore/svg/SVGPathSegList.idl
    M Source/WebCore/svg/SVGPointList.idl
    M Source/WebCore/svg/SVGStringList.idl
    M Source/WebCore/svg/SVGTransformList.idl

  Log Message:
  -----------
  Speed up JSNodeList indexing
https://bugs.webkit.org/show_bug.cgi?id=254190

Reviewed by Ryosuke Niwa.

Speed up JSNodeList indexing by generating more efficient JS bindings code.

The generated bindings code looked like:
```
if (index < list->length())
    return toJS(list->item(index));
```

This was a bit inefficient in the common case since `item()` would repeat the
bounds check and return null when out of bounds. It was even more unfortunate
for NodeList since both `length()` and `item()` are virtual.

As a result, I updated the bindings generator to generate:
```
if (auto item = list->item(index); LIKELY(!!item))
    return toJS(WTFMove(item));
```

This avoids the duplicates out-of-bounds checks and results in a single virtual
function call for JSNodeList instead of 2.

Only a few SVG list types still use the old logic since they may throw in some
cases, as per the specification. This is very unusual but supported via a new
[RaisesException] in the IDL.

Some other types had logic that would throw an exception when out of bounds but
this logic could never be triggered because the JS bindings were already doing
a bounds check before calling `item()`. I updated those types to return null
instead.

* Source/WebCore/bindings/scripts/CodeGeneratorJS.pm:
(GenerateIndexedGetter):
(GenerateGetOwnPropertySlot):
(GenerateGetOwnPropertySlotByIndex):
* Source/WebCore/bindings/scripts/IDLAttributes.json:
* Source/WebCore/css/typedom/CSSUnparsedValue.cpp:
(WebCore::CSSUnparsedValue::item):
* Source/WebCore/css/typedom/CSSUnparsedValue.h:
* Source/WebCore/css/typedom/CSSUnparsedValue.idl:
* Source/WebCore/css/typedom/numeric/CSSNumericArray.cpp:
(WebCore::CSSNumericArray::item):
* Source/WebCore/css/typedom/numeric/CSSNumericArray.h:
* Source/WebCore/css/typedom/transform/CSSTransformValue.cpp:
(WebCore::CSSTransformValue::item):
* Source/WebCore/css/typedom/transform/CSSTransformValue.h:
* Source/WebCore/svg/SVGLengthList.idl:
* Source/WebCore/svg/SVGNumberList.idl:
* Source/WebCore/svg/SVGPathSegList.idl:
* Source/WebCore/svg/SVGPointList.idl:
* Source/WebCore/svg/SVGStringList.idl:
* Source/WebCore/svg/SVGTransformList.idl:

Canonical link: https://commits.webkit.org/261988@main