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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [Regression] Quadratic module build time due to Preprocessor::LeaveSubmodule"
href="https://llvm.org/bugs/show_bug.cgi?id=24667">24667</a>
</td>
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<tr>
<th>Summary</th>
<td>[Regression] Quadratic module build time due to Preprocessor::LeaveSubmodule
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Modules
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>chisophugis@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=14809" name="attach_14809" title="Test script exhibiting quadratic module build time with ToT.">attachment 14809</a> <a href="attachment.cgi?id=14809&action=edit" title="Test script exhibiting quadratic module build time with ToT.">[details]</a></span>
Test script exhibiting quadratic module build time with ToT.
Consider:
module foo {
header "foo1.h"
header "foo2.h"
......
}
foo<n>.h:
#pragma once
#define FOO_<n>
Preprocessor::LeaveSubmodule does O(# macros in submodule) work every time it
leaves a header. This results in quadratic build times, a regression from clang
3.6
The attached script shows the following times for different values of N with
ToT:
(N) (time)
128 0.0208690166473
256 0.0294139385223
512 0.0603349208832
1024 0.158221006393
2048 0.521872997284
4096 1.93269181252
8192 7.92222499847
Same thing but for clang 3.6:
128 0.0171859264374
256 0.0209867954254
512 0.0306701660156
1024 0.0452530384064
2048 0.0781750679016
4096 0.141057014465
8192 0.270556926727</pre>
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