Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: fda0e1e0c823a562297b0741b65a93d0f426c877
https://github.com/WebKit/WebKit/commit/fda0e1e0c823a562297b0741b65a93d0f426c877
Author: Sosuke Suzuki <[email protected]>
Date: 2026-01-04 (Sun, 04 Jan 2026)
Changed paths:
M Source/WTF/wtf/CMakeLists.txt
M Source/WTF/wtf/text/StringImpl.cpp
M Source/WTF/wtf/text/StringImpl.h
M Source/WTF/wtf/unicode/UTF8Conversion.cpp
M Tools/TestWebKitAPI/Tests/WTF/WTFString.cpp
Log Message:
-----------
[WTF] Use simdutf for UTF-16 to UTF-8 conversion
https://bugs.webkit.org/show_bug.cgi?id=304916
Reviewed by Yusuke Suzuki.
Add SIMD optimization for UTF-16 to UTF-8 conversion using simdutf library.
This improves performance for non-ASCII strings while remaining neutral for
ASCII strings.
Benchmark results (µs per iteration, lower is better):
Type Length Orig(µs) SIMD(µs) Speedup
----- ------ -------- -------- -------
ASCII 5 0.1794 0.1184 1.52x
ASCII 10 0.1350 0.1277 1.06x
ASCII 20 0.1484 0.1454 1.02x
ASCII 50 0.2668 0.1895 1.41x
ASCII 100 0.3188 0.2364 1.35x
ASCII 500 0.6034 0.5830 1.04x
ASCII 1000 1.0247 1.0153 1.01x
JP 5 0.2474 0.1542 1.60x
JP 10 0.3662 0.1847 1.98x
JP 20 0.5966 0.3289 1.81x
JP 50 1.2413 0.5773 2.15x
JP 100 2.5593 0.6513 3.93x
JP 500 11.0678 2.2777 4.86x
JP 1000 22.2872 4.0778 5.46x
Note: ASCII results show some variance in speedup ratios due to fast
execution times, but are effectively neutral. The optimization primarily
benefits non-ASCII text (Japanese, Chinese, emoji, etc.) with 2-5x speedup.
* Source/WTF/wtf/CMakeLists.txt:
Add unicode/UTF8Conversion.cpp to SIMD warning suppression list.
* Source/WTF/wtf/text/StringImpl.cpp:
(WTF::StringImpl::utf8ForCharactersIntoBuffer): Add SIMD fast path.
(WTF::StringImpl::utf8LengthFromUTF16): Added. Calculate exact UTF-8 length
using simdutf.
(WTF::StringImpl::tryConvertUTF16ToUTF8): Added. Try SIMD conversion and
return notFound on failure.
* Source/WTF/wtf/text/StringImpl.h:
(WTF::StringImpl::tryGetUTF8ForCharacters): Use exact buffer sizing with
utf8LengthFromUTF16 and SIMD conversion with tryConvertUTF16ToUTF8.
* Source/WTF/wtf/unicode/UTF8Conversion.cpp:
(WTF::Unicode::convert): Add SIMD fast path for UTF-16 to UTF-8 conversion.
Check buffer size before SIMD conversion to avoid overflow when caller
provides insufficient buffer.
Canonical link: https://commits.webkit.org/305091@main
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