Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: fa83cf53f871966898862ed6dc7c08e51519de64
https://github.com/WebKit/WebKit/commit/fa83cf53f871966898862ed6dc7c08e51519de64
Author: Sosuke Suzuki <[email protected]>
Date: 2026-04-18 (Sat, 18 Apr 2026)
Changed paths:
A JSTests/microbenchmarks/rope-single-char-endsWith.js
A JSTests/microbenchmarks/rope-single-char-startsWith.js
A JSTests/stress/string-starts-ends-with-rope-single-char.js
M Source/JavaScriptCore/dfg/DFGOperations.cpp
M Source/JavaScriptCore/runtime/JSString.h
M Source/JavaScriptCore/runtime/JSStringInlines.h
M Source/JavaScriptCore/runtime/StringPrototype.cpp
Log Message:
-----------
[JSC] Avoid rope resolution for single-char `startsWith` / `endsWith`
https://bugs.webkit.org/show_bug.cgi?id=311891
Reviewed by Yusuke Suzuki.
When the search string is a single character and the receiver is a rope
longer than minLengthForRopeWalk, we only need one character from the
rope to answer startsWith / endsWith. Resolving the whole rope just to
read that one character is wasteful.
This patch adds JSString::tryGetCharAt(), a sibling of tryFindOneChar()
that walks at most one level of fibers and returns the character at the
requested index.
TipOfTree Patched
rope-single-char-startsWith 14.0873+-1.8901 ^ 1.5065+-0.0736
^ definitely 9.3512x faster
rope-single-char-endsWith 13.5408+-0.2436 ^ 1.5653+-0.0427
^ definitely 8.6505x faster
Tests: JSTests/microbenchmarks/rope-single-char-endsWith.js
JSTests/microbenchmarks/rope-single-char-startsWith.js
JSTests/stress/string-starts-ends-with-rope-single-char.js
* JSTests/microbenchmarks/rope-single-char-endsWith.js: Added.
(testHit):
(testMiss):
* JSTests/microbenchmarks/rope-single-char-startsWith.js: Added.
(testHit):
(testMiss):
* JSTests/stress/string-starts-ends-with-rope-single-char.js: Added.
(shouldBe):
(throw.new.Error.sw):
(throw.new.Error.ew):
(throw.new.Error):
(shouldBe.swp):
(shouldBe.ewp):
(shouldBe.sw):
(shouldBe.ew):
* Source/JavaScriptCore/dfg/DFGOperations.cpp:
(JSC::DFG::JSC_DEFINE_JIT_OPERATION):
* Source/JavaScriptCore/runtime/JSString.h:
* Source/JavaScriptCore/runtime/JSStringInlines.h:
(JSC::JSString::tryGetCharAt const):
* Source/JavaScriptCore/runtime/StringPrototype.cpp:
(JSC::JSC_DEFINE_HOST_FUNCTION):
Canonical link: https://commits.webkit.org/311521@main
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