<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/121122>121122</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [amdgpu] Using fp128 fails with unsupported libcalls
        </td>
    </tr>

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

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

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

<pre>
    `fp128` seems to work fine in arguments and return values, but trying to do computations like `fmul` or `fdiv` fails:
```llvm
target triple = "amdgcn-amd-amdhsa"

define fp128 @fp128(fp128 %a, fp128 %b) {
  %res = fmul fp128 %a, %b
  ret fp128 %res
}
```
results in
```
LLVM ERROR: unsupported libcall legalization
Stack dump:
…
#10 llvm::SITargetLowering::LowerCall(llvm::TargetLowering::CallLoweringInfo&, llvm::SmallVectorImpl<llvm::SDValue>&) const llvm-project/llvm/lib/Target/AMDGPU/SIISelLowering.cpp:3877:34
```

I assume this is expected.
I encountered this while trying to compile Rust code, see also https://github.com/rust-lang/compiler-builtins/pull/737.
</pre>
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