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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 - InstCombine - invalid transformation"
href="https://bugs.llvm.org/show_bug.cgi?id=34037">34037</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>InstCombine - invalid transformation
</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>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>babokin@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>clang trunk, rev 309831, x86_64.
Valid, UB-free test case, -O2 produce different output.
Opt-bisect points to InstCombine.
<span class="quote">> cat f.cpp</span >
#include <stdio.h>
long j = 0, p = 0;
unsigned k = 4, r = 0;
unsigned long m = 0;
static long cc = 0;
static unsigned short dd = 0;;
void fn1() {
long a = (~(m & r) | j) << 29;
cc = ((a - dd) * k) & (unsigned short)p;
}
int main() {
p = dd = 7;
fn1();
printf("%ld\n", cc);
}
<span class="quote">> clang -O0 f.cpp -o out; ./out</span >
4
<span class="quote">> clang -O2 f.cpp -o out; ./out</span >
0</pre>
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