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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - DFG AI assertions about not having to do type checks at the point of a Known use kind are unsound"
href="https://bugs.webkit.org/show_bug.cgi?id=148649">148649</a>
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<th>Summary</th>
<td>DFG AI assertions about not having to do type checks at the point of a Known use kind are unsound
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<th>Classification</th>
<td>Unclassified
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<th>Product</th>
<td>WebKit
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<th>Version</th>
<td>Other
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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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>fpizlo@apple.com
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<p>
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<pre>We often generate IR like:
Check(Int32:@x)
...
Foo(KnownInt32:@x)
It would be valid for any optimization that somehow proves the type of @x to remove the Check node entirely. But then, AI might fail on an assertion at Foo() because of the KnownInt32 use kind, if AI isn't smart enough to construct the same proof that the former optimization used for removing the Check.
The correct solution is probably to remove the compile-time assertions about Known use kinds having already been checked. It's OK for those to be debug-only JIT assertions.</pre>
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