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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __restrict on struct member has no effect"
href="https://bugs.llvm.org/show_bug.cgi?id=45863">45863</a>
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<th>Summary</th>
<td>__restrict on struct member has no effect
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>dsharlet@google.com
</td>
</tr>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>The following code demonstrates the issue:
const int N = 8;
void add1(const float* __restrict a, const float* __restrict b, float*
__restrict c) {
for (int i = 0; i < N; i++) {
c[i] = a[i] + b[i];
}
}
struct A {
float * __restrict x;
};
void add2(const A& a, const A& b, A& c) {
for (int i = 0; i < N; i++) {
c.x[i] = a.x[i] + b.x[i];
}
}
When compiling this with clang -S -O2 -march=native, I see a vectorized loop
for add1, but not for add2. When I look at the generated LLVM assembly, there's
no indication that the noalias attribute was applied to any of the pointers.
Adding __restrict to the function argument references does not help either (but
I wouldn't expect it to).
As far as I can tell, this is supposed to work to indicate that none of the x
pointers in add2 alias, at least in C.
I just tried this on a recently updated trunk Clang+LLVM and see the same
behavior (commit 57fb56b30e8).</pre>
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