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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Add an option to allow an exhaustive search during last chance recoloring"
href="http://llvm.org/bugs/show_bug.cgi?id=18747">18747</a>
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<th>Summary</th>
<td>Add an option to allow an exhaustive search during last chance recoloring
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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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>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Register Allocator
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>qcolombet@apple.com
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Since r200883, the greedy register allocator features a last chance recoloring
mechanism.
This mechanism allows to find a valid assignment of the variables (if any) when
the regular heuristic fails.
It uses a backtracking algorithm which is currently cutoff with some heuristics
to avoid uncontrolled compile time.
There is two things to improve here:
1. When the assignment fails because of the early cutoffs, this should be
reported instead of the current obscur “ran out of registers”.
2. We should provide an option (e.g., -fexhaustive-register-search) to allow to
explore all the possibilities when the allocation failed because of a cutoffs
(which we would know thanks to 1.).
For testing the reporting in 1., one can use the test-case of r200883 and
artificially cut the search space with:
- lcr-max-depth=<uint>
- lcr-max-interf=<uint></pre>
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