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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang does not omit unnecessary memory allocations with -std=c++1{y,z}"
href="http://llvm.org/bugs/show_bug.cgi?id=21145">21145</a>
</td>
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<th>Summary</th>
<td>clang does not omit unnecessary memory allocations with -std=c++1{y,z}
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</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>C++1y
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>sneves@dei.uc.pt
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider the following function:
int f() {
int * x = new int(123);
int z = *x;
delete x;
return z;
}
N3664, which is implemented on clang 3.4 onward, states that the above `new`
expression is allowed not to result in an explicit allocation. However, it
appears that clang only avoids the allocation when using -std=c++98 or
-std=c++11. Here is the abridged output of `clang -std=c++11 -O3 f.cpp`:
f(): # @f()
movl $123, %eax
retq
And here is the output of `clang -std=c++1y -O3 f.cpp`:
f(): # @f()
pushq %rax
movl $4, %edi
callq operator new(unsigned long)
movl $123, (%rax)
movl $4, %esi
movq %rax, %rdi
callq operator delete(void*, unsigned long)
movl $123, %eax
popq %rdx
retq
It would seem that C++14 mode actually disables N3664, instead of enabling it.</pre>
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