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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [LoopInterchange] Support memory access requiring multiple GEPs"
href="https://bugs.llvm.org/show_bug.cgi?id=39594">39594</a>
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<th>Summary</th>
<td>[LoopInterchange] Support memory access requiring multiple GEPs
</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>Linux
</td>
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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>Loop Optimizer
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>Florian.Hahn@arm.com
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Currently LoopInterchange does only support accesses that only require a single
GEP, e.g. because all array dimensions are known statically.
We will interchange
extern unsigned Arr[1024][1024];
unsigned no_deps_interchange(unsigned k) {
unsigned sum = 0;
for (int i = 0; i < 1024; ++i)
for(int j = 0; j < 1024; ++j)
sum += Arr[j][i] + k;
return sum;
}
but we won't interchange
unsigned no_deps_interchange(unsigned **Arr, unsigned k) {
unsigned sum = 0;
for (int i = 0; i < 1024; ++i)
for(int j = 0; j < 1024; ++j)
sum += Arr[j][i] + k;
return sum;
}
because the cost model does not understand the generated address calculations.
By using SCEV for the addresses (like <a href="https://reviews.llvm.org/D35210">https://reviews.llvm.org/D35210</a>), we can
support the second case as well.</pre>
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</p>
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