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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - 'dereferenceable' not treated as implying 'nonnull'?"
href="https://bugs.llvm.org/show_bug.cgi?id=46876">46876</a>
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<th>Summary</th>
<td>'dereferenceable' not treated as implying 'nonnull'?
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<th>Product</th>
<td>libraries
</td>
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<tr>
<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
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>richard-llvm@metafoo.co.uk
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>In this C++ testcase:
int f(int &v, int k) {
int a = 0;
for (int n = 0; n != k; ++n) {
a += v;
}
return a;
}
... LLVM is able to optimize away the branch and produce 'return k * v;'
In this similar C testcase:
int f(int arr[static 1], int k) {
int a = 0;
for (int n = 0; n != k; ++n) {
a += *arr;
}
return a;
}
... LLVM leaves behind the branch.
The only relevant difference between the IR emitted for the two testcases
appears to be that in the C++ case we emit the 'v' parameter as 'nonnull
dereferenceable(4)', whereas in the C case we emit the 'arr' parameter as only
'dereferenceable(4)', not 'nonnull'.
But 'dereferenceable(N)' is supposed to imply 'nonnull' in the default address
space, so that presumably shouldn't make any difference!</pre>
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</p>
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