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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - opt miscompiles with "opt -O3 -flattencfg""
href="https://bugs.llvm.org/show_bug.cgi?id=37662">37662</a>
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<th>Summary</th>
<td>opt miscompiles with "opt -O3 -flattencfg"
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>Vsevolod.Livinskij@frtk.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
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<pre>Created <span class=""><a href="attachment.cgi?id=20384" name="attach_20384" title="Reproducer.">attachment 20384</a> <a href="attachment.cgi?id=20384&action=edit" title="Reproducer.">[details]</a></span>
Reproducer.
Opt produces incorrect code with opt -O3 -o func.ll func.bc -flattencfg
opt-bisect-limit points to Simplify the CFG on function
Reproducer:
<span class="quote">>$ cat func.cpp</span >
extern unsigned short a, c;
extern short *d;
extern unsigned short *e;
extern short b;
void foo() {
e = &a;
c = 0;
if (*d)
e = &c;
if (b)
e = &c;
}
<span class="quote">>$ cat driver.cpp</span >
#include <stdio.h>
short a = 6, b = 6;
unsigned short c;
unsigned short *d = &c;
short *e;
void foo();
int main() {
foo();
printf("%hd\n", *(e));
}
Error:
<span class="quote">>$ clang++ driver.cpp func.cpp
>$ ./a.out</span >
0
<span class="quote">>$ clang++ -O3 -Xclang -disable-llvm-optzns -emit-llvm -c -o func.bc func.cpp
>$ opt -O3 -o func.ll func.bc -flattencfg
>$ clang++ -c -o func.o func.ll
>$ clang++ driver.cpp func.o
>$ ./a.out</span >
6
LLVM version:
<span class="quote">>$ clang++ -v</span >
clang version 7.0.0 (trunk 333377)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /llvm/bin-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64</pre>
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