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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ExitValue rewrite in IndVarSimplify may introduce extra spills and instructions at no benefit"
href="https://bugs.llvm.org/show_bug.cgi?id=42965">42965</a>
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<th>Summary</th>
<td>ExitValue rewrite in IndVarSimplify may introduce extra spills and instructions at no benefit
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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>All
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<th>Status</th>
<td>NEW
</td>
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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>Loop Optimizer
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>d.maljutin@yandex.ru
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=22369" name="attach_22369" title="C code showing the issue">attachment 22369</a> <a href="attachment.cgi?id=22369&action=edit" title="C code showing the issue">[details]</a></span>
C code showing the issue
When there is a chain of calculations on some variable in a loop which is then
used outside, IndVarSimplify may rewrite its exit value to be independent from
loop adding index computations to the loop header.
When the loop body is big enough (e.g. due to unswitching of nested loops),
this increases register pressure and may lead to spills/reloads.
The example can be seen here: <a href="https://godbolt.org/z/_wxzut">https://godbolt.org/z/_wxzut</a> (the code can also
be found in the attachments).</pre>
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