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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - regression of bit manipulation optimization for certain bit positions"
href="https://llvm.org/bugs/show_bug.cgi?id=28466">28466</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>regression of bit manipulation optimization for certain bit positions
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.8
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nowak-llvm@tepeserwery.pl
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>f1 and f2 have the same meaning but produce different code - f2 is not
correctly optimized and this happens only with bits 7, 15 and 31.
3.7.1 didn't have this problem.
unsigned int f1(unsigned int v) {
unsigned int r = (v & 0x80u) ? v : (v | 0x80u);
return r;
}
unsigned int f2(unsigned int v) {
unsigned int r;
if (v & 0x80u) {
r = v;
} else {
r = v | 0x80u;
}
return r;
}
unsigned int f3(unsigned int v) {
unsigned int r;
if (v & 0x40u) {
r = v;
} else {
r = v | 0x40u;
}
return r;
}
f1(unsigned int): # @f1(unsigned int)
orl $128, %edi
movl %edi, %eax
f2(unsigned int): # @f2(unsigned int)
movl %edi, %eax
orl $128, %eax
testb %dil, %dil
cmovsl %edi, %eax
f3(unsigned int): # @f3(unsigned int)
orl $64, %edi
movl %edi, %eax</pre>
</div>
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