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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - a pass error, this pass never consider data overflow"
href="https://bugs.llvm.org/show_bug.cgi?id=40496">40496</a>
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<th>Summary</th>
<td>a pass error, this pass never consider data overflow
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>7.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>-New Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>witstorm@163.com
</td>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=21395" name="attach_21395" title="source code for error proof">attachment 21395</a> <a href="attachment.cgi?id=21395&action=edit" title="source code for error proof">[details]</a></span>
source code for error proof
Here have a simple program in the attachment.
Example:
#include<stdio.h>
typedef unsigned char X;
//typedef char X;
X Fb(X x, X y){return x + y;}
int main()
{
auto int ai0,ai1;
ai0 = 0;
ai1 = 2147483647;
ai0 = ai1 + Fb(63, 64);
printf("%d\n",ai0 == -2147483522);
}
If we use clang to generate .ll file by -O3, we will get wrong .ll file.
The compile command like that: clang a.c -O3 -emit-llvm -S -o aa.ll
we find the pass where did this optimize. There problem is the pass never
consider data overflow for icmp constant fold. And I find the same bug in other
passes, if you need it, just contact me by email(<a href="mailto:witstorm@163.com">witstorm@163.com</a>).
Run the code, it should print 1.</pre>
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