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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - placement new null checks should be optimized away"
href="http://llvm.org/bugs/show_bug.cgi?id=22556">22556</a>
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<th>Summary</th>
<td>placement new null checks should be optimized away
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.5
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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
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>LLVM Codegen
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>vlovich@gmail.com
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Although the C++ standard address the placement-new/nullptr issue in C++17, it
would seem like the optimizer should be able to optimize away the cost
regardless, at least for vector.
Although placement new could be being called on a nullptr, it will be called
with p[i] where i is some value in [0, size() - 1].
Except for the p[0] case, p[x] where x is in [1, size() - 1] cannot be a
nullptr since pointer arithmetic is undefined behaviour for overflow.
Test-case code:
<a href="https://pastebin.mozilla.org/8625250">https://pastebin.mozilla.org/8625250</a>
More information:
<a href="http://www.reddit.com/r/cpp/comments/2v3viw/cs_placementnew_prevents_optimalcode_generation/">http://www.reddit.com/r/cpp/comments/2v3viw/cs_placementnew_prevents_optimalcode_generation/</a></pre>
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