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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 - SLP: missed vectorization due to cost model (benchmark from SPECFP 2006)"
href="https://bugs.llvm.org/show_bug.cgi?id=52126">52126</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>SLP: missed vectorization due to cost model (benchmark from SPECFP 2006)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>433.milc
typedef struct {
double real;
double imag;
} complex;
typedef struct {
complex e[3][3];
} su3_matrix;
#define CSUM(a, b) \
{ \
(a).real += (b).real; \
(a).imag += (b).imag; \
}
#define CMUL(a, b, c) \
{ \
(c).real = (a).real * (b).real - (a).imag * (b).imag; \
(c).imag = (a).real * (b).imag + (a).imag * (b).real; \
}
void mult_su3_nn2(su3_matrix *a, su3_matrix *b, su3_matrix *c) {
int i, j, k;
complex x, y;
for (i = 0; i < 3; i++)
for (j = 0; j < 3; j++) {
x.real = x.imag = 0.0;
for (k = 0; k < 3; k++) {
CMUL(a->e[i][k], b->e[k][j], y);
CSUM(x, y);
}
c->e[i][j] = x;
}
}
Flags: -Ofast -mavx
<a href="https://godbolt.org/z/b6nq5sKaW">https://godbolt.org/z/b6nq5sKaW</a>
example.cpp:10:5: remark: the cost-model indicates that vectorization is not
beneficial [-Rpass-missed=loop-vectorize]
for(i=0;i<3;i++)
^
example.cpp:10:5: remark: the cost-model indicates that interleaving is not
beneficial [-Rpass-missed=loop-vectorize]
GCC/ICC vectorizes mult_su3_nn_unrolled. LLVM does not vectorize it with
AVX/AVX, only with -AVX512 (but does not use vaddsubpd as GCC and ICC do; GCC
recently added pattern detection for addsub to SLP vectorizer)</pre>
</div>
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