<html>
<head>
<base href="https://llvm.org/bugs/" />
</head>
<body><span class="vcard"><a class="email" href="mailto:david.majnemer@gmail.com" title="David Majnemer <david.majnemer@gmail.com>"> <span class="fn">David Majnemer</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - The add instruction is incorrectly folded into icmp when there is an overflow by instcombine"
href="https://llvm.org/bugs/show_bug.cgi?id=25986">bug 25986</a>
<br>
<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr>
<tr>
<td style="text-align:right;">CC</td>
<td>
</td>
<td>david.majnemer@gmail.com
</td>
</tr>
<tr>
<td style="text-align:right;">Component</td>
<td>new bugs
</td>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>INVALID
</td>
</tr>
<tr>
<td style="text-align:right;">Product</td>
<td>new-bugs
</td>
<td>libraries
</td>
</tr></table>
<p>
<div>
<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - The add instruction is incorrectly folded into icmp when there is an overflow by instcombine"
href="https://llvm.org/bugs/show_bug.cgi?id=25986#c1">Comment # 1</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - The add instruction is incorrectly folded into icmp when there is an overflow by instcombine"
href="https://llvm.org/bugs/show_bug.cgi?id=25986">bug 25986</a>
from <span class="vcard"><a class="email" href="mailto:david.majnemer@gmail.com" title="David Majnemer <david.majnemer@gmail.com>"> <span class="fn">David Majnemer</span></a>
</span></b>
<pre>Hi Yuanrui,
I do not believe InstCombine is wrong here.
The value you chose for '%j' is 'i32 2147483647'.
The add instruction in '%inc' is 'add nsw i32 %j, 1'. Notice the 'nsw' flag on
the add instruction, it means that '%inc' is poison if it sign overflows or
sign underflows (see <a href="http://llvm.org/docs/LangRef.html#poisonvalues">http://llvm.org/docs/LangRef.html#poisonvalues</a>)
This means that we have the following dynamic values:
%j = i32 2147483647
%inc = i32 poison
%cmp = i1 poison
%conv = i32 poison
If you want signed overflow/underflow to be well defined, remove the nsw flag
from the add instruction.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>