Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 02b44f2ad986575436f69f51863b556cbd460180
https://github.com/WebKit/WebKit/commit/02b44f2ad986575436f69f51863b556cbd460180
Author: Sosuke Suzuki <[email protected]>
Date: 2026-07-03 (Fri, 03 Jul 2026)
Changed paths:
A JSTests/microbenchmarks/string-split-empty-long.js
A JSTests/microbenchmarks/string-split-empty-short.js
A JSTests/stress/string-split-empty-single-character-index-of.js
M Source/JavaScriptCore/dfg/DFGOperations.cpp
M Source/JavaScriptCore/runtime/ArrayPrototype.cpp
M Source/JavaScriptCore/runtime/StringPrototype.cpp
Log Message:
-----------
[JSC] Skip Latin-1 single-character atomization in `s.split('')`
https://bugs.webkit.org/show_bug.cgi?id=318510
Reviewed by Yusuke Suzuki.
The empty-separator fast path of s.split("") atomizes every resulting
character through toIdentifier / DeferGC / atomStringToJSStringMap
.ensureValue,
even though Latin-1 single characters are already
atom-backed SmallStrings cells. This patch skips that block for Latin-1
characters.
Skipping alone would break the Array.prototype.indexOf onlyAtomStrings
fast path, which treats absence from atomStringToJSStringMap as absence
from the array. To prevent that, indexOf now treats a single Latin-1
character search as potentially present and falls through to the
pointer-comparison scan.
string-split-empty-long 45.4817+-1.1086 ^ 14.8687+-0.3740 ^ definitely
3.0589x faster
string-split-empty-short 38.2363+-1.1574 ^ 16.1969+-0.1237 ^ definitely
2.3607x faster
No regression on the indexOf microbenchmarks that now always scan:
atom-string-array-split-empty-index-of-not-found 0.8349+-0.0327
0.8123+-0.0378 might be 1.0278x faster
atom-string-array-split-empty-index-of-found 1.0105+-0.0291 ^
0.9138+-0.0307 ^ definitely 1.1058x faster
Tests: JSTests/microbenchmarks/string-split-empty-long.js
JSTests/microbenchmarks/string-split-empty-short.js
JSTests/stress/string-split-empty-single-character-index-of.js
* JSTests/microbenchmarks/string-split-empty-long.js: Added.
(test):
* JSTests/microbenchmarks/string-split-empty-short.js: Added.
(test):
* JSTests/stress/string-split-empty-single-character-index-of.js: Added.
(shouldBe):
* Source/JavaScriptCore/dfg/DFGOperations.cpp:
(JSC::DFG::JSC_DEFINE_JIT_OPERATION):
* Source/JavaScriptCore/runtime/ArrayPrototype.cpp:
(JSC::JSC_DEFINE_HOST_FUNCTION):
* Source/JavaScriptCore/runtime/StringPrototype.cpp:
(JSC::stringSplitFast):
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