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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Graph::methodOfGettingAValueProfileFor() should be returning the profile for operand node."
href="https://bugs.webkit.org/show_bug.cgi?id=164600">164600</a>
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<th>Summary</th>
<td>Graph::methodOfGettingAValueProfileFor() should be returning the profile for operand node.
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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>WebKit Nightly Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
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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>mark.lam@apple.com
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<pre>Currently, Graph::methodOfGettingAValueProfileFor() assumes that the operand DFG node that it is provided with always has a different origin than the node that is using that operand. For example, in a DFG graph that looks like this:
a: ...
b: ArithAdd(@a, ...)
... when emitting speculation checks on @a for the ArithAdd node at @b, Graph::methodOfGettingAValueProfileFor() is passed @a, and expects @a's to originate from a different bytecode than @b.
However, op_negate can be compiled into the following series of nodes:
a: BooleanToNumber(...)
b: DoubleRep(@a)
c: ArithNegate(@b)
All 3 nodes maps to the same op_negate bytecode i.e. they have the same origin. When the speculativeJIT does a speculationCheck in DoubleRep, it calls Graph::methodOfGettingAValueProfileFor() to get the ArithProfile for the BooleanToNumber node. But because all 3 nodes have the same origin, Graph::methodOfGettingAValueProfileFor() erroneously returns the ArithProfile for the op_negate. Subsequently, the OSR exit ramp will modify the ArithProfile of the op_negate and corrupt its profile. Instead, what the OSR exit ramp should be doing is update the ArithProfile of op_negate's operand i.e. BooleanToNumber's operand in this case.
The fix is to always pass the current node we're generating code for (in addition to the operand node) to Graph::methodOfGettingAValueProfileFor(). This way, we can determine if the profile is valid if and only if the current node and its operand node does not have the same origin.</pre>
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