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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - NPM inliner does not perform alloca merging"
href="https://bugs.llvm.org/show_bug.cgi?id=47909">47909</a>
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<th>Summary</th>
<td>NPM inliner does not perform alloca merging
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>aeubanks@google.com
</td>
</tr>
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<th>CC</th>
<td>alina.sbirlea@gmail.com, davidxl@google.com, htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, rnk@google.com
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<th>Blocks</th>
<td>46649
</td>
</tr></table>
<p>
<div>
<pre>The NPM inliner does not perform alloca merging. Lifetimes can help mitigate
the issue of not reusing stack slots when inlining multiple functions, but they
are not emitted at -O0. If we have something like
void a(void*);
__attribute__((always_inline)) void b() {
long long l[10000];
a(l);
}
void c() {
b();
b();
b();
b();
b();
b();
b();
b();
b();
b();
b();
b();
b();
}
the stack usage in c() is much much larger under the NPM than in the legacy PM
under -O0.
<a href="https://godbolt.org/z/bWaWvv">https://godbolt.org/z/bWaWvv</a></pre>
</div>
</p>
<div id="referenced">
<hr style="border: 1px dashed #969696">
<b>Referenced Bugs:</b>
<ul>
<li>
[<a class="bz_bug_link
bz_status_NEW "
title="NEW - Change default pass manager to new pass manager"
href="https://bugs.llvm.org/show_bug.cgi?id=46649">Bug 46649</a>] Change default pass manager to new pass manager
</li>
</ul>
</div>
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