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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [Polly - AST Generation] Use != for upper loop bound"
href="https://bugs.llvm.org/show_bug.cgi?id=32997">32997</a>
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<th>Summary</th>
<td>[Polly - AST Generation] Use != for upper loop bound
</td>
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<th>Product</th>
<td>Polly
</td>
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<th>Version</th>
<td>unspecified
</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
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<th>Component</th>
<td>isl
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<th>Assignee</th>
<td>polly-dev@googlegroups.com
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<th>Reporter</th>
<td>tobias@grosser.es
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Currently the isl AST generator derives
for (long i = LB; i <= UB; i++)
A[i]
for most loops. An alternative would be to generate
for (long i = LB; i != UB + 1; i++)
A[i]
In the second version a value of LB that is strictly larger than UB + 1 will
cause i to eventually overflow. As we know this is not valid (and we annotate i
in Polly with NSW), the IR carries the information that such an overflow can
never happen
and consequently that LB must be smaller or equal to UB + 1.
LLVM and its -indvars pass prefers the second alternative precisely for this
reason.
We should consider to generate IR with the above type.</pre>
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