<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/96362>96362</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [compiler-rt] Clarify support for windows
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          h-vetinari
      </td>
    </tr>
</table>

<pre>
    In https://github.com/llvm/llvm-project/commit/0318ce8552896df7b180ee5481463eada65c755e, @AaronBallman added the following to the [C status page](https://clang.llvm.org/c_status.html) for support of `<complex.h>`:
> `_Complex` support requires an underlying support library such as compiler-rt to provide functions like `__divsc3`, but compiler-rt is not supported on Windows.

The following discussion ensued in the corresponding [PR](https://github.com/llvm/llvm-project/pull/88161):
> > @h-vetinari: I'm surprised about the "compiler-rt is not supported on windows" comment - in our distribution, we've been building compiler-rt on windows for years, and I don't remember significant issues.
> > 
> > It's true that `__divsc3` is not available _without_ compiler-rt (i.e. just relying on the msvc runtime libraries), but together with compiler-rt these things are generally possible? Note that a similar [situation](https://github.com/llvm/llvm-project/issues/54596) exists on `osx-arm` for example - in certain situations, linking `compiler-rt` is unavoidable.
>
> @AaronBallman: CC @petrhosek as compiler-rt CRT code owner -- is compiler-rt officially supported for Windows? The official documentation does not mention it under platform support: https://compiler-rt.llvm.org/

That statement of lack of support was now reiterated in https://github.com/llvm/llvm-project/commit/918ef312d1fda56ff783f3974b5a193542e5497c, and so I thought I'd open this issue to discuss.

In [conda-forge](https://conda-forge.org), we've been building and shipping compiler-rt since LLVM 9.0, and I'm not aware of fundamental issues that render the runtime unusable. To the contrary, it's been a [required](https://github.com/conda-forge/flang-feedstock/blob/main/recipe/meta.yaml#L54-57) component to get our flang-support for windows off the ground (which itself was a very [long story](https://labs.quansight.org/blog/building-scipy-with-flang)).

As such, I'd very much like for compiler-rt to stay _at least as usable_ as it has been over the last 5 years, even if perhaps the support may not be on par with other platforms. Better still would be explicit support of course. :)
</pre>
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