Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 8339909e6ce15eb0070e5ec79871bff7e7c76148
https://github.com/WebKit/WebKit/commit/8339909e6ce15eb0070e5ec79871bff7e7c76148
Author: Sosuke Suzuki <[email protected]>
Date: 2026-07-21 (Tue, 21 Jul 2026)
Changed paths:
A JSTests/microbenchmarks/object-spread-small-clone.js
M Source/JavaScriptCore/runtime/JSObject.h
M Source/JavaScriptCore/runtime/ObjectConstructorInlines.h
Log Message:
-----------
[JSC] Avoid zero-filling and `gcSafeMemcpy` in `tryCreateObjectViaCloning`
https://bugs.webkit.org/show_bug.cgi?id=319850
Reviewed by Yusuke Suzuki.
tryCreateObjectViaCloning, which implements the fast path of object spread `{
...source }`,
was creating a JSFinalObject via createWithButterfly, which zero-fills the
inline storage in
its constructor, and then copying source's inline storage over it with
gcSafeMemcpy. Since the
zero-filled values are always overwritten by source's values, that memset is
pure waste.
This patch adds a JSFinalObject constructor (and
createWithButterflyCopyingInlineStorage)
which initializes the inline storage by copying from another object's inline
storage instead
of zero-filling it. Because the new object is not exposed to anyone until this
function
returns, the copy does not need to be gcSafeMemcpy either. Also, DeferGC and
the out-of-line
capacity computation are now only performed when source actually has
out-of-line properties.
Baseline Patched
object-spread-small-clone 11.7545+-0.1951 ^
9.9040+-0.2022 ^ definitely 1.1868x faster
clone-objects-via-spread-first 17.8918+-0.1675
17.5364+-0.3234 might be 1.0203x faster
clone-objects-via-spread 16.5543+-0.2060
16.3735+-0.1780 might be 1.0110x faster
Test: JSTests/microbenchmarks/object-spread-small-clone.js
* JSTests/microbenchmarks/object-spread-small-clone.js: Added.
* Source/JavaScriptCore/runtime/JSObject.h:
(JSC::JSFinalObject::createWithButterflyCopyingInlineStorage):
* Source/JavaScriptCore/runtime/ObjectConstructorInlines.h:
(JSC::tryCreateObjectViaCloning):
Canonical link: https://commits.webkit.org/317659@main
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