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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop-interchange : Some triangular loop nests are interchanged"
href="https://bugs.llvm.org/show_bug.cgi?id=49306">49306</a>
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<tr>
<th>Summary</th>
<td>Loop-interchange : Some triangular loop nests are interchanged
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</td>
</tr>
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<th>Version</th>
<td>11.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>opt
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>flemairen6@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>$ clang -Os -mllvm -enable-loopinterchange=true traingular_fail.c && ./a.out
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
$ clang -Os -mllvm -enable-loopinterchange=false triangular_fail.c && ./a.out
0 2 7 83 0 0 9 43 0 0 0 0 0 0 0 0
$ cat triangular_fail.c
#include <stdio.h>
int foo() {
int A[4][4] = {{ 0, 0, 0, 0},
{ 0, 0, 0, 0},
{ 0, 0, 0, 0},
{ 0, 0, 0, 0}};
int B[4][4] = {{ 16, 2, 7, 83},
{ 35, 8, 9, 43},
{ 47, 123, 32, 0},
{ 21, 11, 19, 29}};
for (int i = 0; i < 4; ++i)
for (int j = 0; j < i; ++j)
A[j][i] = B[j][i];
for (int i = 0; i < 4; ++i)
for (int j = 0; j < 4; j++)
printf("%d ", A[i][j]);
printf("\n");
return 0;
}
int main() {
foo();
return 0;
}
LoopInterchange does not detect the issue with the operation `j<i` in the inner
loop, thus, breaking the program correctness.</pre>
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