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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [LoopAccessAnalysis / IndVarSimplify]"
href="https://bugs.llvm.org/show_bug.cgi?id=38935">38935</a>
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<th>Summary</th>
<td>[LoopAccessAnalysis / IndVarSimplify]
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<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>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Global Analyses
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>paulsson@linux.vnet.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=20876" name="attach_20876" title="reduced testcase">attachment 20876</a> <a href="attachment.cgi?id=20876&action=edit" title="reduced testcase">[details]</a></span>
reduced testcase
The reduced test case gets its loop vectorized on x86 (icelake-server),while on
SystemZ (z14), this fails (actually in the reduced test case VF 1 is selected,
but the point is that it is *possible* for only one of the targets).
On SystemZ, the IV is rewritten from i32 to i64, which seems to somehow result
in 'LAA: SCEV could not compute the loop exit count.'
It seems like a bug somewhere that when IndVarSimplify makes a transformation,
the SCEV becomes uncomputable.
Could this be something in ScalarEvolution to fix, perhaps?
opt tc_indvar_vec.ll -mtriple=i686-unknown-linux-gnu -mcpu=icelake-server -S -o
/dev/null -O3 -debug-only=loop-accesses |& grep "exit count"
opt tc_indvar_vec.ll -mtriple=systemz-unknown -mcpu=z14 -S -o /dev/null -O3
-debug-only=loop-accesses |& grep "exit count"
LAA: SCEV could not compute the loop exit count.
LAA: SCEV could not compute the loop exit count.</pre>
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