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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Over-aggressive overflow elimination check with call to exit()"
href="https://llvm.org/bugs/show_bug.cgi?id=28012">28012</a>
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<th>Summary</th>
<td>Over-aggressive overflow elimination check with call to exit()
</td>
</tr>
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<th>Product</th>
<td>libraries
</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>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>eli.friedman@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>atrick@apple.com, llvm-bugs@lists.llvm.org, sanjoy@playingwithpointers.com
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Testcase:
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
static int will_add_overflow(int a, int x) {
return a >= INT_MIN - x;
}
void f(int a, long last_value) {
if (will_add_overflow(a, 3)) {
// Leave, and don't actually do the increment, so no UB.
printf("last_value = %ld\n", last_value);
exit(0);
}
}
void (*ff)(int, long) = f;
int main() {
int a = 0;
unsigned a_u = 0;
volatile long last_value;
do {
a_u += 3;
last_value = (long) ((int) a_u);
ff(a, last_value);
a += 3;
} while (a != 46);
return 0;
}
With clang -O0, prints "last_value = -2147483647". With clang -O2, prints
nothing. (Tested on x86-64 Linux.)
Basically the same testcase as <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - new overflow check elimination code is too good"
href="show_bug.cgi?id=27315">bug 27315</a>, except that I hid the call to exit().</pre>
</div>
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