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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - scalar/vector operations lead to division by zero"
href="https://llvm.org/bugs/show_bug.cgi?id=27085">27085</a>
</td>
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<th>Summary</th>
<td>scalar/vector operations lead to division by zero
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.7
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>regis.portalez@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>try to compile the following code (C) using clang 3.7 (using only mem2reg pass)
typedef unsigned char char4 __attribute__ ((vector_size (4)));
char4 f1 (char4 v)
{
return v / 2;
}
this compiles down to (+ debug info):
define <4 x i8> @f1(<4 x i8> %v) {
entry:
%div = udiv <4 x i8> %v, bitcast (<1 x i32> <i32 2> to <4 x i8>)
ret <4 x i8> %div
}
according to <a href="http://llvm.org/docs/LangRef.html#bitcast-to-instruction">http://llvm.org/docs/LangRef.html#bitcast-to-instruction</a>, bitcast
instruction does not change any bit, meaning bitcast (<1 x i32> <i32 2> to <4 x
i8>) returns <2, 0, 0, 0> as char vector.
therefore the division in the original source code generates a division by
zero.
I would have expected the following IL:
define <4 x i8> @f1(<4 x i8> %v) {
entry:
%div = udiv <4 x i8> %v, <4 x i8> <i8 2, i8 2, i8 2, i8 2>
ret <4 x i8> %div
}</pre>
</div>
</p>
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