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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - LoopVectorizer: Can only vectorize reductions if the external user uses the “last” value in reduction cycle"
href="http://llvm.org/bugs/show_bug.cgi?id=17498">17498</a>
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<th>Summary</th>
<td>LoopVectorizer: Can only vectorize reductions if the external user uses the “last” value in reduction cycle
</td>
</tr>
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<th>Product</th>
<td>tools
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</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>
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<th>Component</th>
<td>opt
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>aschwaighofer@apple.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>See the last two examples of PR17473.
for.body3.1: ; preds = %for.body3.1,
%for.inc7
%inc613.1 = phi i32 [ 0, %for.inc7 ], [ %inc6.1, %for.body3.1 ]
%inc511.1 = phi i32 [ %inc.1, %for.inc7 ], [ %inc5.1, %for.body3.1 ]
%2 = zext i1 %tobool to i32
%inc4.1 = xor i32 %2, 1
%inc511.1.inc4.1 = add nsw i32 %inc511.1, %inc4.1
%inc5.1 = add nsw i32 %inc511.1.inc4.1, 1
%inc6.1 = add nsw i32 %inc613.1, 1
%exitcond.1 = icmp eq i32 %inc6.1, 22
br i1 %exitcond.1, label %for.inc7.1, label %for.body3.1
for.inc7.1: ; preds = %for.body3.1
%inc.2 = add nsw i32 %inc511.1.inc4.1, 2
br label %for.body3.2
And where generating this. The problem is that the external user was not using
the “last” value in the reduction. So we would loose 3 "(add 1)”s.
vector.body23: ; preds = %vector.body23,
%for.inc7
%index26 = phi i32 [ 0, %for.inc7 ], [ %index.next30, %vector.body23 ]
%vec.phi34 = phi <4 x i32> [ %7, %for.inc7 ], [ %11, %vector.body23 ]
%8 = zext <4 x i1> %broadcast.splat36 to <4 x i32>
%9 = xor <4 x i32> %8, <i32 1, i32 1, i32 1, i32 1>
%10 = add nsw <4 x i32> %vec.phi34, %9
%11 = add nsw <4 x i32> %10, <i32 1, i32 1, i32 1, i32 1>
%index.next30 = add i32 %index26, 4
%12 = icmp eq i32 %index.next30, 20
br i1 %12, label %middle.block24, label %vector.body23
middle.block24: ; preds = %vector.body23
%rdx.shuf38 = shufflevector <4 x i32> %10, <4 x i32> undef, <4 x i32> <i32 2,
i32 3, i32 undef, i32 undef></pre>
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