<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/85876>85876</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            MemorySanitizer false positive when using __builtin_convertvector
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            compiler-rt:msan,
            false-positive
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          philnik777
      </td>
    </tr>
</table>

<pre>
    ```c++
template <class T>
using vec __attribute__((__ext_vector_type__(4))) = T;

void use(vec<bool> val) {}

int main() {
  auto val = vec<int>{0, 1, 2, 3};
  use(__builtin_convertvector(val, vec<bool>));
}
```
causes msan to fail with
```
==1==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x55d07d68881c in main /app/example.cpp:9:3
    #1 0x7f56abc29d8f (/lib/x86_64-linux-gnu/libc.so.6+0x29d8f) (BuildId: c289da5071a3399de893d2af81d6a30c62646e1e)
    #2 0x7f56abc29e3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e3f) (BuildId: c289da5071a3399de893d2af81d6a30c62646e1e)
    #3 0x55d07d5ee2f4 in _start (/app/output.s+0x322f4)

SUMMARY: MemorySanitizer: use-of-uninitialized-value /app/example.cpp:9:3 in main
Exiting
```
https://godbolt.org/z/TaeWE46Pq
</pre>
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