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<base href="http://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Loop miscompilation with -O3"
href="http://llvm.org/bugs/show_bug.cgi?id=16177">16177</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Loop miscompilation with -O3
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</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>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>eugeni.stepanov@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>$ cat 1.cc
#include <stdio.h>
class S {
public:
char x[1024];
};
S s[16];
S *p[16];
int main(void) {
for (unsigned i = 0; i != 16; ++i) {
p[i] = s + i;
}
for (unsigned i = 0; i != 16; ++i) {
printf("%p\n", p[i]);
}
return 0;
}
$ clang++ -O3 1.cc -o 1
$ ./1
0x601030
0x601030
0x601830
0x601030
0x602030
0x601030
0x602830
0x601030
0x603030
0x601030
0x603830
0x601030
0x604030
0x601030
0x604830
0x601030
loop IR:
vector.body: ; preds = %vector.body,
%vector.ph
%index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
%0 = getelementptr inbounds [16 x %class.S]* @s, i64 0, i64 %index
%1 = insertelement <2 x %class.S*> undef, %class.S* %0, i32 0
%2 = insertelement <2 x %class.S*> %1, %class.S* getelementptr ([16 x
%class.S]* @s, i64 0, i64 undef), i32 1
%3 = getelementptr inbounds [16 x %class.S*]* @p, i64 0, i64 %index
%4 = bitcast %class.S** %3 to <2 x %class.S*>*
store <2 x %class.S*> %2, <2 x %class.S*>* %4, align 16
%index.next = add i64 %index, 2
%5 = icmp eq i64 %index.next, 16
br i1 %5, label %for.cond2.preheader, label %vector.body
"undef" in "%2 =" line looks incorrect
Introduced in r182909.</pre>
</div>
</p>
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