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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [polly] The order of the loop is reversed while not necessary"
href="https://llvm.org/bugs/show_bug.cgi?id=25793">25793</a>
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<th>Summary</th>
<td>[polly] The order of the loop is reversed while not necessary
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</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>
</tr>
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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>lawrence@codeaurora.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=15426" name="attach_15426" title="reduced testcase">attachment 15426</a> <a href="attachment.cgi?id=15426&action=edit" title="reduced testcase">[details]</a></span>
reduced testcase
Polly schedule changed the order of the loop unnecessaryly.
Here is the original order of the loop in c:
void foo (int * restrict A, int * restrict B, int * restrict C, int n) {
for(int i = 0; i < n; i++)
A[i] += 1;
for(int i = 0; i < n; i++)
B[i] += 1;
for(int i = 0; i < n; i++)
C[i] += 1;
}
Polly schedule reorder the loops to:
void foo (int * restrict A, int * restrict B, int * restrict C, int n) {
for(int i = 0; i < n; i++)
C[i] += 1;
for(int i = 0; i < n; i++)
A[i] += 1;
for(int i = 0; i < n; i++)
B[i] += 1;
}
Here is the isl ast for attached IR
{
#pragma simd
#pragma known-parallel
for (int c0 = 0; c0 < n; c0 += 1)
Stmt_for_body16(c0);
#pragma simd
#pragma known-parallel
for (int c0 = 0; c0 < n; c0 += 1)
Stmt_for_body(c0);
#pragma simd
#pragma known-parallel
for (int c0 = 0; c0 < n; c0 += 1)
Stmt_for_body5(c0);
}
Even though it is logically correct, however it is not necessary, and afffect
readability.
Use opt -debug -polly -polly-detect -polly-opt-isl -polly-codegen
-polly-vectorizer=polly -polly-ignore-aliasing -S <t.ll >log.log 2>&1 to
reproduce it</pre>
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