<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/69394>69394</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang] __is_trivially_relocatable isn't correct on Windows
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang,
            platform:windows,
            clang-cl
      </td>
    </tr>

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

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

<pre>
    As implemented in https://reviews.llvm.org/D119017 and https://reviews.llvm.org/D114732, the `__is_trivially_relocatable` type trait is built on top of `canPassInRegisters`, which was never meant to implement this type trait:
https://github.com/llvm/llvm-project/blob/e90ec58b132a7244bdd8d45dd482fd78fe487f37/clang/lib/AST/Type.cpp#L2649

`canPassInRegisters` is full of various size checks that have nothing to do with trivial relocatability:
https://github.com/llvm/llvm-project/blob/340d746abae18f6a69bdf4a3bbe4a46990bb755d/clang/lib/Sema/SemaDeclCXX.cpp#L6909-L6915

This means `__is_trivial_relocatability` doesn't work correctly on Windows or PS4.

There are extensive comments on the original review which I haven't read through, but it seems like the proper solution is to track trivial relocatability as a type trait, and then use that to inform whether things get passed in registers.

I think (at risk of misremembering) that I suggested the name of "canPassInRegisters", and what I think I had in mind is that we should name it something intentionally hyper-specific and low-level so that folks don't rely on it for any other purpose, but I guess that didn't work out as planned. I guess it wasn't that great of a plan in the first place.

cc @zygoloid @ssbr @zmodem @danakj
</pre>
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