<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/109075>109075</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Clang] -Wnan-infinity-disabled is annoying in SIMD code
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

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

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

<pre>
    The `-Wnan-infinity-disabled` warning added in Clang 18 is annoying when working with SIMD.  The kinds of programs that use SIMD code often enable `-ffast-math` for the same reason SIMD is being used in the first place.  The warning being enabled by default interferes with libraries.  libc++ itself would trigger the warning in `#include <limits>` if Clang weren't suppressing warnings in system headers.

Example of SIMD code that trips up the warning (stripped from the original):

```
#include <immintrin.h>

#define FLOAT_TRUE_MASK (-__builtin_nanf("0x3FFFFF"))

__m128 TestFunction(__m128 v)
{
 return _mm_and_ps(v, _mm_setr_ps(FLOAT_TRUE_MASK, 0.0f, FLOAT_TRUE_MASK, 0.0f));
}
```

Yes, it's undefined behavior, but it's also a common thing to do in SIMD code.  This isn't a bug, just a coding annoyance.

By the way, it's nice that Clang sees through the masking and just does `vxorps` + `vblendps`.  It recognized `0xFFFFFFFF` despite coming from floating-point.
</pre>
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