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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [SLP] Failure to account for truncating stores in MinVF calculation"
href="https://bugs.llvm.org/show_bug.cgi?id=46983">46983</a>
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<th>Summary</th>
<td>[SLP] Failure to account for truncating stores in MinVF calculation
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
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<th>CC</th>
<td>a.bataev@hotmail.com, anton.a.afanasyev@gmail.com, llvm-bugs@lists.llvm.org
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<th>Blocks</th>
<td>46968
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<p>
<div>
<pre>Noticed while investigating [<a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed SLP vectorization with umin/umax"
href="show_bug.cgi?id=46968">Bug #46968</a>]
<a href="https://godbolt.org/z/T9Mna8">https://godbolt.org/z/T9Mna8</a>
The MinVF calculation in SLPVectorizerPass::vectorizeStoreChain is based off
the
number of storesize elements that fix in the vector register:
const unsigned MinVF = R.getMinVecRegSize() / Sz;
But this means we fail to account for cases where we are truncating the result
just prior to the store.
Sz is set by:
unsigned BoUpSLP::getVectorElementSize(Value *V) {
// If V is a store, just return the width of the stored value without
// traversing the expression tree. This is the common case.
if (auto *Store = dyn_cast<StoreInst>(V))
return DL->getTypeSizeInBits(Store->getValueOperand()->getType());
...
}
So we may be able to just check for truncates feeding stores in the StoreInst
case.</pre>
</div>
</p>
<div id="referenced">
<hr style="border: 1px dashed #969696">
<b>Referenced Bugs:</b>
<ul>
<li>
[<a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed SLP vectorization with umin/umax"
href="https://bugs.llvm.org/show_bug.cgi?id=46968">Bug 46968</a>] Missed SLP vectorization with umin/umax
</li>
</ul>
</div>
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