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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang does not optimize simple code"
href="https://bugs.llvm.org/show_bug.cgi?id=33023">33023</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Clang does not optimize simple code
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>4.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Windows NT
</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>C++14
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>vladon@yandex-team.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>===
#include <stdlib.h>
struct Vec {
int len;
int* data;
};
inline int get(struct Vec* vec, int i) {
if (i < vec->len) {
return vec->data[i];
} else {
abort();
}
}
int sum5(struct Vec* vec) {
return get(vec, 0) + get(vec, 1) + get(vec, 2) + get(vec, 3) + get(vec, 4)
+ get(vec, 5);
}
===
See <a href="https://godbolt.org/g/WywyK3">https://godbolt.org/g/WywyK3</a>
But it optimizes this:
===
#include <stdlib.h>
struct Vec {
int len;
int* data;
};
inline int get(struct Vec* vec, int i) {
if (i < vec->len) {
return vec->data[i];
} else {
abort();
}
}
int sum5(struct Vec* vec) {
return get(vec, 5) + get(vec, 4) + get(vec, 3) + get(vec, 2) + get(vec, 1)
+ get(vec, 0);
}
===
See <a href="https://godbolt.org/g/L5TjyT">https://godbolt.org/g/L5TjyT</a>
Or this:
===
#include <stdlib.h>
struct Vec {
int len;
int* data;
};
inline int get(struct Vec* vec, int i) {
if (i < vec->len) {
return vec->data[i];
} else {
abort();
}
}
int sum5(struct Vec* vec) {
int sum = 0;
for (int i = 0; i < 6; ++i)
sum += get(vec, i);
return sum;
}
===
See <a href="https://godbolt.org/g/gldaXb">https://godbolt.org/g/gldaXb</a></pre>
</div>
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