<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/74402>74402</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            AArch64 fails with "Don't know how to custom expand this" with illegal f16
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:AArch64
      </td>
    </tr>

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

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

<pre>
    ```
; RUN: llc -mtriple=aarch64-none-linux-gnu -mattr=-fp-armv8 < %s

define half @f16_return(float %arg) {
  %fptrunc = fptrunc float %arg to half
 ret half %fptrunc
}
```

Don't know how to custom expand this
UNREACHABLE executed at /Users/matt/src/llvm-project/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp:24529!
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJyMUsFunDAQ_ZrhYrEyYwPLgQMbglopyiFtzpUxBtwYg2yT3f59BaFJ2lMlNAwjvcd7b0Z4rwerVAnpBdI6EmsYZ1cK55WdonbufpWQ0eOhNdAK2IU8PT8Cq4gxksRTcHoxClgthJNjxmM7WxUbbddbPNiVxJMIwQGr436JhZtezwTYHQFM_cG410712ioyCtMT4LRPsh9OhdVZwHNvZhE2hHADYEEgv7yByDbsl-BWKwmwmvzpPyNImHfaA-JUOP7yDj105PXR_ON4r_VsAfNAXux8JeN83Vjl6sM8EXVbhO1IGPXh6Pnx6b66-1JdHu6Juim5BtWRXU_z7JXzgM0WCmDjnQRsjHmd4sXNP5UMx-f20i1g8124QW3Tqtrj_ei-flPmYb4qp-1wkssCrEKeYgGYRF3JuoIVIlJlktMk55wlPBpL7GTCO0k7PPOMs3PPJRfZFncvadFnkS6RIkuQphR5mvDTmaqWZ12ChZJpmxfAqZqENqdN5Wl2Q6S9X1WZc04xMqJVxu_XhNgK-aJsB6x6147bkblyN9yugwdOjfbBf7AFHYwqDwDphTaeXHUYCSD-5w4Q3xDaGDUIQ_oki1ZnyjGExQOrABvAZtBhXNuTnKdPkf-9iN3Ztq3d3O8AAAD__3Ui-Tk">