Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 67969621f7032db54f3cec3c893ff1b5bf212fcf
https://github.com/WebKit/WebKit/commit/67969621f7032db54f3cec3c893ff1b5bf212fcf
Author: Sosuke Suzuki <[email protected]>
Date: 2026-05-17 (Sun, 17 May 2026)
Changed paths:
M Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp
M Source/JavaScriptCore/dfg/DFGSpeculativeJIT.h
M Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp
Log Message:
-----------
[JSC] Inline `String#startsWith` / `String#endsWith` with constant search
string in DFG/FTL
https://bugs.webkit.org/show_bug.cgi?id=314517
Reviewed by Yusuke Suzuki.
This patch inlines StringStartsWith / StringEndsWith when the search
string is a constant, embedding its bytes as immediate operands instead
of calling into the runtime.
The comparison uses a few wide loads with overlap when the search
length isn't a power of two: load64 for >= 8 bytes, load32 for 4-7,
load16 for 2-3, load8 for 1. A 16-byte search needs at most two
load64 + cmp.
Only constant 8-bit search strings of 1-16 bytes are supported; ropes,
16-bit base strings, and variable or position-argument forms still go
through the runtime helper.
TipOfTree
Patched
string-startswith-constant 17.9727+-0.4341 ^
5.7938+-0.3102 ^ definitely 3.1021x faster
string-endswith-constant 17.3566+-1.8544 ^
6.1307+-0.2170 ^ definitely 2.8311x faster
string-startswith-constant-long 16.1837+-1.2149 ^
5.8331+-0.4844 ^ definitely 2.7744x faster
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp:
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT.h:
* Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp:
(JSC::FTL::DFG::LowerDFGToB3::compileStringStartsOrEndsWithConstant):
(JSC::FTL::DFG::LowerDFGToB3::compileStringStartsOrEndsWith):
Canonical link: https://commits.webkit.org/313394@main
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