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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Inefficient code generated for matrix initialization loop"
href="https://bugs.llvm.org/show_bug.cgi?id=47705">47705</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Inefficient code generated for matrix initialization loop
</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>All
</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>florian_hahn@apple.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>As reported on the mailing list
(<a href="http://lists.llvm.org/pipermail/llvm-dev/2020-September/145367.html">http://lists.llvm.org/pipermail/llvm-dev/2020-September/145367.html</a>) and
discord, GCC beats LLVM on the code below by 4x reportedly
<a href="https://godbolt.org/z/4G1rh1">https://godbolt.org/z/4G1rh1</a>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MILLION 1000000
struct Matrix {
float E[4][4];
};
int main(void) {
Matrix identity =
{
{{1, 0, 0, 0},
{0, 1, 0, 0},
{0, 0, 1, 0},
{0, 0, 0, 1}}
};
int matrix_count = 10 * MILLION;
Matrix *matrices = (Matrix *) malloc(matrix_count * sizeof(Matrix));
clock_t begin = clock();
for (int run = 0; run < 25; ++run) {
for (int i = 0; i < matrix_count; ++i) {
matrices[i] = identity;
}
}
clock_t end = clock();
printf("Value Check: %f\n", matrices[matrix_count / 2].E[2][2]);
printf("Time in seconds: %f\n", (double)(end - begin) / CLOCKS_PER_SEC);
}</pre>
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