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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Optimizer breaks compare for the negation of the signed integer -0x80000000"
href="https://bugs.llvm.org/show_bug.cgi?id=44680">44680</a>
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<th>Summary</th>
<td>Optimizer breaks compare for the negation of the signed integer -0x80000000
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>unspecified
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>info@artsoft.nl
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=23065" name="attach_23065" title="simple program to reproduce the bug">attachment 23065</a> <a href="attachment.cgi?id=23065&action=edit" title="simple program to reproduce the bug">[details]</a></span>
simple program to reproduce the bug
The following 2 lines of code:
int NaN = -0x80000000;
printf ( "%d < 0 : %s\n", -NaN, (-NaN) < 0 ? "true" : "false" );
Correctly prints when build without optimizations:
-2147483648 < 0 : true
But incorrectly prints when build with -O1 or higher:
-2147483648 < 0 : false
_______________________________________________
-0x80000000 has no positive counterpart as 0x7FFFFFFF is the max positive
value of an int32. So when you negate -0x80000000 it remains -0x80000000.
I think the optimizer rewrites the statement "( -Nan ) < 0" to "Nan > 0", but
this changes the result.</pre>
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