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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 - The vector stopped when the referencing order was changed"
href="https://bugs.llvm.org/show_bug.cgi?id=43398">43398</a>
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</tr>
<tr>
<th>Summary</th>
<td>The vector stopped when the referencing order was changed
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>fj8765ah@aa.jp.fujitsu.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The vector stopped when the referencing order was changed.
I think that NG.c can be vectorized.
$ clang -O3 OK.c -Rpass=vector -S -Rpass-analysis=vector
OK.c:14:7: remark: vectorized loop (vectorization width: 4, interleaved count:
2) [-Rpass=loop-vectorize]
for(j=1 ; j<jmax-1 ; j++)
^
$ clang -O3 NG.c -Rpass=vector -S -Rpass-analysis=vector
NG.c:17:13: remark: loop not vectorized: value that could not be identified as
reduction is used outside the loop [-Rpass-analysis=loop-vectorize]
+ p[i ][j ] // difference1
^
- OK.c
#define IMAX 257
#define JMAX 257
extern float p[IMAX][JMAX];
extern float q[IMAX][JMAX];
extern int imax, jmax;
void
foo()
{
int i,j,k,n;
for(i=1 ; i<imax-1 ; i++)
for(j=1 ; j<jmax-1 ; j++)
q[i][j]
= p[i+1][j ]
+ p[i ][j+1] // Reference1
+ p[i ][j ] // Reference2
;
}
- NG.ｃ
#define IMAX 257
#define JMAX 257
extern float p[IMAX][JMAX];
extern float q[IMAX][JMAX];
extern int imax, jmax;
void
foo()
{
int i,j,k,n;
for(i=1 ; i<imax-1 ; i++)
for(j=1 ; j<jmax-1 ; j++)
q[i][j]
= p[i+1][j ]
+ p[i ][j ] // Reference2
+ p[i ][j+1] // Reference1
;
}</pre>
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