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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Microsoft mangling takes forever with large, deeply nested templates"
href="https://bugs.llvm.org/show_bug.cgi?id=34356">34356</a>
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<th>Summary</th>
<td>Microsoft mangling takes forever with large, deeply nested templates
</td>
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<th>Product</th>
<td>clang
</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
</td>
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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
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>george.burgess.iv@gmail.com
</td>
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<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Split from <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - clang is 36.5 times slower than gcc"
href="show_bug.cgi?id=29160">https://bugs.llvm.org/show_bug.cgi?id=29160</a>, in hopes of making a
more targeted bug.
To reproduce, compile the test-case from said bug with:
$ clang -target i686-windows -fms-compatibility -fmsc-version=1700 tc.cpp
-DCHUNKS=N
(for values of N >= 15).
Looks like, as we approach -DCHUNKS=42, we're building up more and more massive
(>100MB) strings so we can potentially discard them and use a backreference
instead. (In particular, we do this in the `isTemplate()` branch in
MicrosoftCXXNameMangler::mangleUnqualifiedName). Blindly caching these sped up
execution time substantially (DCHUNKS=42 ran in ~5 minutes, instead of 35), but
also made clang use 21GB of RAM. This doesn't seem ideal.
I thought 100MB strings sounded large, but when I asked clang to -ast-dump the
program, I killed it after 2 hours and >200GB of output. So...</pre>
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