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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 - Intermittent bug in opt with -O3 -newgvn"
href="https://bugs.llvm.org/show_bug.cgi?id=37676">37676</a>
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<tr>
<th>Summary</th>
<td>Intermittent bug in opt with -O3 -newgvn
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</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>enhancement
</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>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=20388" name="attach_20388" title="Reproducer.">attachment 20388</a> <a href="attachment.cgi?id=20388&action=edit" title="Reproducer.">[details]</a></span>
Reproducer.
Intermittent bug in opt with -O3 -newgvn.
It gives 2 variants of assembler for different compilations.
opt-bisect-limit points to "Global Value Numbering on function"
Reproducer:
<span class="quote">>$ cat func.c</span >
extern unsigned long long b, e, g;
extern const signed char a;
extern const unsigned c;
extern unsigned d, h;
extern signed char f, i;
extern unsigned *j;
extern unsigned long long *k;
extern signed char *l;
void foo() {
if (*k <= (8 & -b * ((1 - 8ULL) * c) ?: ~i))
f = 8 & -(b * ((1 - 8ULL) * c)) ?: i * d;
e = g ? -(8 & -b * ((1 - 8ULL) * c) ?: i * d) : 0;
if (!a) {
*l = ~0 ? 8 & -(b * ((1 - 8ULL) * c)) ?: i * d : 2022409665839104;
h = 8 & -(b * ((1ULL - 8) * c)) ? b * ((1 - 8ULL) * c) : 0;
}
if (8 & -(b * ((1ULL - 8) * c)) ? 0 : ~0)
*j = b * ((1 - 8ULL) * c);
}
<span class="quote">>$ cat driver.c</span >
#include <stdio.h>
unsigned long long b, e, g;
const signed char a = 8;
const unsigned c = 92620;
unsigned d, h, m;
signed char f, i;
unsigned *j = &m;
unsigned long long *k = &e;
signed char *l;
void foo();
int main() {
*j = 42;
foo();
printf("%u\n", *j);
}
Error:
<span class="quote">>$ clang driver.c func.c
>$ ./a.out</span >
0
<span class="quote">>$ clang -O3 -Xclang -disable-llvm-optzns -emit-llvm -c -o func.bc func.c
>$ opt -O3 -o func.ll func.bc -newgvn
>$ clang -O3 -c -o func.o func.ll
>$ clang -O3 driver.c func.o
>$ ./a.out</span >
42
LLVM version:
clang version 7.0.0 (trunk 333836)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /users/vlivinsk/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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