Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 1d355c27ea88a9e50184d16b7a76adb1ed6492bb
https://github.com/WebKit/WebKit/commit/1d355c27ea88a9e50184d16b7a76adb1ed6492bb
Author: Yijia Huang <[email protected]>
Date: 2026-07-28 (Tue, 28 Jul 2026)
Changed paths:
A JSTests/microbenchmarks/json-stringify-short-strings-upconvert.js
M Source/JavaScriptCore/runtime/JSONObject.cpp
M Source/WTF/wtf/MathExtras.h
M Tools/TestWebKitAPI/Tests/WTF/MathExtras.cpp
Log Message:
-----------
[JSC] Add an 8-byte SWAR fast path to JSON.stringify's stringCopyUpconvert
for short strings
https://bugs.webkit.org/show_bug.cgi?id=320419
rdar://183378922
Reviewed by Yusuke Suzuki.
stringCopyUpconvert() is stringCopySameType()'s Latin1-to-char16_t upconvert
sibling and has the same gap: a scalar byte-at-a-time fallback and a 16-byte
SIMD fast path, but nothing in between, so strings shorter than 16 bytes
always took the scalar loop.
Add the same 8-byte SWAR tier. Widening 4 packed Latin1 bytes into 4
char16_t lanes needs an extra step beyond stringCopySameType's plain copy,
so this adds WTF::zeroExtendBytesToHalfwords(), a small bit-doubling
"spread" helper, and reuses it instead of an 8-instruction unrolled
extract-and-store loop.
ToT
Patched
json-stringify-short-strings-upconvert 174.2817+-5.1099 ^
144.8684+-5.8863 ^ definitely 1.2030x faster
Tests: JSTests/microbenchmarks/json-stringify-short-strings-upconvert.js
Tools/TestWebKitAPI/Tests/WTF/MathExtras.cpp
Canonical link: https://commits.webkit.org/318078@main
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