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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Interpreter project is up to 15% slower with clang 13"
href="https://bugs.llvm.org/show_bug.cgi?id=51857">51857</a>
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<th>Summary</th>
<td>Interpreter project is up to 15% slower with clang 13
</td>
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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>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>chfast@gmail.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>I maintain a relatively simple interpreter project (single main function with
big switch statement).
I tested clang 13 RC and it gives 0-15% slowdown depending on the workload. In
none of the cases the clang 13 is faster than clang 12.
I tried to look at generated assembly and LLVM IR but I cannot stop anything
interesting there. Maybe just that clang 13 produces smaller code probably due
to better register allocation / spilling.
Also perf tool does not show anything specific.
I'm happy to provide additional data if you can tell we where to start and what
would be useful.
I also started bisecting LLVM from 12.x to 13.x. So far I have found single
commit that decreases performance by ~6%:
[LVI] Don't bail on overdefined value in select
<a href="https://github.com/llvm/llvm-project/commit/72e0846ef87d0d3b5960238bc47fc0cc6f04d848">https://github.com/llvm/llvm-project/commit/72e0846ef87d0d3b5960238bc47fc0cc6f04d848</a>
<a href="https://reviews.llvm.org/rG72e0846ef87d0d3b5960238bc47fc0cc6f04d848">https://reviews.llvm.org/rG72e0846ef87d0d3b5960238bc47fc0cc6f04d848</a></pre>
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</p>
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