<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop vectorizer miscompile resulting in additional loop iteration"
href="https://bugs.llvm.org/show_bug.cgi?id=32317">32317</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Loop vectorizer miscompile resulting in additional loop iteration
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</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>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>igor@azulsystems.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Attached test case produces incorrect result when run -force-vector-width=2:
$ lli test.ll
89.000000
$ opt -S -O3 -force-vector-width=2 test.ll > test.opt.ll
$ lli test.opt.ll
90.000000
$ opt -S -O3 -force-vector-width=4 test.ll > test.opt.ll
$ lli test.opt.ll
89.000000
Looking at the output I believe that vectorizer incorrectly calculates
resulting loop value for the fFld:
vector.body:
%index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
%vec.ind = phi <2 x i64> [ <i64 4, i64 5>, %vector.ph ], [ %vec.ind.next,
%vector.body ]
%vector.recur = phi <2 x i64> [ %vector.recur.init, %vector.ph ], [ %20,
%vector.body ]
%20 = add nsw <2 x i64> %vec.ind, %broadcast.splat
%21 = shufflevector <2 x i64> %vector.recur, <2 x i64> %20, <2 x i32> <i32 1,
i32 2>
%index.next = add i64 %index, 2
%vec.ind.next = add <2 x i64> %vec.ind, <i64 2, i64 2>
%22 = icmp eq i64 %index.next, 86
br i1 %22, label %middle.block, label %vector.body, !llvm.loop !52
middle.block: ; preds = %vector.body
%cmp.n = icmp eq i64 86, 86
%vector.recur.extract = extractelement <2 x i64> %20, i32 1
br i1 %cmp.n, label %bci_64, label %scalar.ph
If in the "%vector.recur.extract" instead of the "%20" we would have used
"%vec.ind" - result would have been correct.
Attached .ll test case and roughly equivalent c code.</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>