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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Binary rotation is not detected after multiplication"
href="https://llvm.org/bugs/show_bug.cgi?id=31275">31275</a>
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<tr>
<th>Summary</th>
<td>Binary rotation is not detected after multiplication
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<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>
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<th>Reporter</th>
<td>funny.falcon@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>I found that clang produces bad code for rotation after multiplication.
Although it generates good code, if multiplication is not last operation:
// Type your code here, or load an example.
#define rotl(x,n) (((x)<<(n))|((x)>>(32-(n))))
unsigned mult_rotl(unsigned num, unsigned mun) {
return rotl(num*9, 7);
}
unsigned mult_add_rotl(unsigned num, unsigned mun) {
return rotl(num*9+1, 7);
}
mult_rotl:
leal (%rdi,%rdi,8), %eax
shll $7, %edi
leal (%rdi,%rdi,8), %ecx
shrl $25, %eax
orl %ecx, %eax
retq
mult_add_rotl:
leal 1(%rdi,%rdi,8), %eax
roll $7, %eax
retq
(probably, it is llvm-optimizer's issue)</pre>
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