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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 - `add nsw` + `sadd.with.overflow` with constants should fold"
href="https://bugs.llvm.org/show_bug.cgi?id=38146">38146</a>
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<th>Summary</th>
<td>`add nsw` + `sadd.with.overflow` with constants should fold
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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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>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>me22.ca@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>```
%3 = add nsw i32 %1, 7
%4 = tail call { i32, i1 } @llvm.sadd.with.overflow.i32(i32 %3, i32 13)
```
should be folded to
```
%4 = tail call { i32, i1 } @llvm.sadd.with.overflow.i32(i32 %1, i32 20)
```
Repro in clang: <a href="https://godbolt.org/g/DM5Gq9">https://godbolt.org/g/DM5Gq9</a>
```
#include <optional>
std::optional<int> test_nsw_sadd_fold(int num) {
num += 7;
int r;
if (__builtin_sadd_overflow(num, 13, &r)) {
return {};
}
return r;
}
```
Cases for `.add_nsw(C1).sadd_overflow(C2)`:
- Same sign can be folded to a single overflow call
- Opposite signs with |C2|>|C1| can be folded to a single overflow call
- Opposite signs with |C2|<=|C1| can be folded to a single nsw call
(Similarly, just simpler, for `.add_nuw(C1).uadd_overflow(C2)`.)</pre>
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