[webkit-changes] [WebKit/WebKit] 9a163c: [WTF] Add SIMD accelerated path for string upconvert

[Yusuke Suzuki]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 9a163cadeab24a7f0217cb7c129dd27647a9e600
      https://github.com/WebKit/WebKit/commit/9a163cadeab24a7f0217cb7c129dd27647a9e600
  Author: Yusuke Suzuki <ysuzuki at apple.com>
  Date:   2022-09-20 (Tue, 20 Sep 2022)

  Changed paths:
    M Source/WTF/wtf/text/StringImpl.h
    M Source/WTF/wtf/text/StringView.h
    M Tools/TestWebKitAPI/Tests/WTF/StringView.cpp

  Log Message:
  -----------
  [WTF] Add SIMD accelerated path for string upconvert
https://bugs.webkit.org/show_bug.cgi?id=245063
rdar://problem/100108570

Reviewed by Justin Michaud and Darin Adler.

This patch adds ARM64 SIMD fast path to string upconvert operation. This optimization
is driven by the fact that we are using some time in Speedometer2.1. A/B test on AppleSilicon
showed that this patch offers Speedometer2.1 0.25% progression with 90% confidence.

In this patch, we use ld1[1] and st2[2].

[1]: https://developer.arm.com/documentation/dui0801/h/A64-SIMD-Vector-Instructions/LD1--vector--single-structure-
[2]: https://developer.arm.com/documentation/dui0801/h/A64-SIMD-Vector-Instructions/ST2--vector--multiple-structures-

* Source/WTF/wtf/text/StringImpl.h:
(WTF::StringImpl::copyCharacters):
* Source/WTF/wtf/text/StringView.h:
(WTF::StringView::UpconvertedCharacters::UpconvertedCharacters):
* Tools/TestWebKitAPI/Tests/WTF/StringView.cpp:
(TestWebKitAPI::TEST):

Canonical link: https://commits.webkit.org/254714@main