[webkit-changes] [WebKit/WebKit] 641608: Optimize the CSSVariableData constructor

[Chris Dumez]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 641608e9630336fbbd011dc072655ee83bdf7b03
      https://github.com/WebKit/WebKit/commit/641608e9630336fbbd011dc072655ee83bdf7b03
  Author: Chris Dumez <cdumez at apple.com>
  Date:   2023-09-07 (Thu, 07 Sep 2023)

  Changed paths:
    M Source/WebCore/css/CSSVariableData.cpp
    M Source/WebCore/css/CSSVariableData.h
    M Source/WebCore/css/parser/CSSParserToken.h

  Log Message:
  -----------
  Optimize the CSSVariableData constructor
https://bugs.webkit.org/show_bug.cgi?id=261285

Reviewed by Ryosuke Niwa.

Optimize the CSSVariableData constructor by:
1. Using Vector's reserveInitialCapacity() / uncheckedAppend() for m_tokens
   since we know how many tokens are present in the range.
2. Populate the m_tokens vector as we traverse the token range to append to
   the StringBuilder, instead of doing it later on.
3. Stop relying on CSSParserToken::copyWithUpdatedString() instead instead
   update characters in place in the pre-populated vector using the new
   CSSParserToken::updateCharacters(). CSSParserToken::updateCharacters()
   also takes the characters as LChar/UChar instead of StringView to avoid
   a redundant `is8Bit()` check.

* Source/WebCore/css/CSSVariableData.cpp:
(WebCore::CSSVariableData::updateBackingStringsInTokens):
(WebCore::CSSVariableData::CSSVariableData):
(WebCore::CSSVariableData::updateTokens): Deleted.
* Source/WebCore/css/CSSVariableData.h:
* Source/WebCore/css/parser/CSSParserToken.h:
(WebCore::CSSParserToken::updateCharacters):

Canonical link: https://commits.webkit.org/267753@main