<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/135521>135521</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [LoongArch] ADD/SUB and TLS relocation should move away from `FirstLiteralRelocationKind + offset`
        </td>
    </tr>

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

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

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

<pre>
    The current implementation of `R_LARCH_SUB{8,16,32,64}` and TLS relocation types relies on fixup kinds `FirstLiteralRelocationKind + offset` (originally intended for `.reloc` directives).  While this is clever and prevents switch cases like

```c
case fixup_...sub8:
  return ELF::R_LARCH_SUB8;
```

it needs revision.

GNU Assembler treats `.reloc` directives differently from standard relocations, notably by skipping 

* Skipping STT_SECTION adjustments (when a referenced symbol is local and satisfies certain conditions, it can be redirected to a section symbol).
* Skipping STT_TLS symbol type setting for TLS relocations.

I intend to fix a `.reloc` behavior in ELFObjectWriter (https://github.com/llvm/llvm-project/pull/135519) and notice that `llvm/test/MC/LoongArch/Relocations/relax-addsub.s` (#76433) will be broken. @MQ-mengqing 
</pre>
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