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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [JSC] Make array iteration methods faster"
href="https://bugs.webkit.org/show_bug.cgi?id=153738">153738</a>
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<th>Summary</th>
<td>[JSC] Make array iteration methods faster
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<th>Classification</th>
<td>Unclassified
</td>
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<th>Product</th>
<td>WebKit
</td>
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<th>Version</th>
<td>WebKit Nightly Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>Normal
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<th>Priority</th>
<td>P2
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<th>Component</th>
<td>JavaScriptCore
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<th>Assignee</th>
<td>webkit-unassigned@lists.webkit.org
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<th>Reporter</th>
<td>utatane.tea@gmail.com
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<p>
<div>
<pre>Seeing DFG dump, (unfortunately!) Array iteration methods (like forEach) performs Double Comparison on loop condition!
This is because,
1. Poor toInteger implementation
We should convert @Number(...) to NumberUse edge filtering. And implementing isFinite in JS is better (If value is speculated as Int32, we can purge many conditions!)
Like, (Number.isFinite)
function isFinite(value)
{
return value === Infinity || value === -Infinity;
}
And, (global).isFinite
function isFinite(value)
{
var numberValue = @Number(value); // This should be converted to edge filtering.
return numberValue === Infinity || numberValue === -Infinity;
}
Handling NumberConstructor::info() in DFGByteCodeParser.cpp makes it easy I think. And to ensure more high performance implementation, introducing @toNumber bytecode intrinsic (that emits to_number bytecode) may also be good.
2. maxSafeInteger = 0x1FFFFFFFFFFFFF
Now, in toLength, we have a chance to return maxSafeInteger (This is represented as double). It is unfortunate, because it makes the result value double rep.
One plan is,
When comparing value < maxSafeInteger, and if we know value is Int32, value < maxSafeInteger becomes always true.
So we can purge this comparison and maxSafeInteger. It makes the result value Int32.
How about this?</pre>
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