Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 8e15aeeee3bc2d5257fec145a08f5532ae7447d7
https://github.com/WebKit/WebKit/commit/8e15aeeee3bc2d5257fec145a08f5532ae7447d7
Author: Sosuke Suzuki <[email protected]>
Date: 2026-07-04 (Sat, 04 Jul 2026)
Changed paths:
A JSTests/microbenchmarks/throw-new-error-from-deep-frames.js
A JSTests/microbenchmarks/throw-preallocated-error-from-deep-frames.js
A JSTests/microbenchmarks/throw-sentinel-from-deep-frames.js
M Source/JavaScriptCore/interpreter/Interpreter.h
M Source/JavaScriptCore/interpreter/InterpreterInlines.h
M Source/JavaScriptCore/interpreter/StackVisitor.cpp
M Source/JavaScriptCore/interpreter/StackVisitor.h
M Source/JavaScriptCore/interpreter/VMEntryRecord.h
M Source/JavaScriptCore/jit/RegisterSet.cpp
M Source/JavaScriptCore/jit/RegisterSet.h
Log Message:
-----------
[JSC] Improve exception unwinding performance
https://bugs.webkit.org/show_bug.cgi?id=318292
Reviewed by Yusuke Suzuki.
I noticed that JSC is significantly slower than V8 at unwinding when an
exception is thrown from a deep call stack. Profiling shows that most of
the time is spent in per-frame callee-save bookkeeping during
Interpreter::unwind.
This patch applies three independent optimizations:
1. Make StackVisitor::Frame::calleeSaveRegistersForUnwinding() return
const RegisterAtOffsetList* instead of std::optional<RegisterAtOffsetList>.
Every list it returns is a long-lived object, so there is no need to
heap-allocate and free a copy for every unwound frame.
2. Add an m_vmEntryRecord field to UnwindFunctorBase, computed once in the
constructor, instead of calling vmEntryRecord() on every call to
copyCalleeSavesToEntryFrameCalleeSavesBuffer.
3. Use a prebuilt table (RegisterSet::vmCalleeSaveBufferSlotsByRegIndex())
that maps Reg::index() to the register's slot in the entry frame
callee-save buffer, instead of doing a binary search per register.
This turns each lookup from O(log n) into O(1).
Baseline
Patched
throw-new-error-from-deep-frames 176.5424+-0.9251 ^
129.7769+-1.6492 ^ definitely 1.3604x faster
throw-preallocated-error-from-deep-frames
265.7363+-2.6056 ^
175.6531+-2.0253 ^ definitely 1.5128x faster
throw-sentinel-from-deep-frames 266.3385+-1.5604 ^
176.2640+-1.5277 ^ definitely 1.5110x faster
Tests: JSTests/microbenchmarks/throw-new-error-from-deep-frames.js
JSTests/microbenchmarks/throw-preallocated-error-from-deep-frames.js
JSTests/microbenchmarks/throw-sentinel-from-deep-frames.js
* JSTests/microbenchmarks/throw-new-error-from-deep-frames.js: Added.
(thrower):
(i.catch):
* JSTests/microbenchmarks/throw-preallocated-error-from-deep-frames.js: Added.
(thrower):
(i.catch):
* JSTests/microbenchmarks/throw-sentinel-from-deep-frames.js: Added.
(thrower):
(i.catch):
* Source/JavaScriptCore/interpreter/Interpreter.h:
(JSC::UnwindFunctorBase::UnwindFunctorBase): Deleted.
* Source/JavaScriptCore/interpreter/InterpreterInlines.h:
(JSC::UnwindFunctorBase::UnwindFunctorBase):
(JSC::UnwindFunctorBase::copyCalleeSavesToEntryFrameCalleeSavesBuffer const):
* Source/JavaScriptCore/interpreter/StackVisitor.cpp:
(JSC::StackVisitor::Frame::calleeSaveRegistersForUnwinding):
* Source/JavaScriptCore/interpreter/StackVisitor.h:
* Source/JavaScriptCore/jit/RegisterSet.cpp:
(JSC::RegisterSet::vmCalleeSaveBufferSlotsByRegIndex):
* Source/JavaScriptCore/jit/RegisterSet.h:
Canonical link: https://commits.webkit.org/316511@main
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