<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/87917>87917</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Assembler fails on capitalized instruction
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          boomanaiden154
      </td>
    </tr>
</table>

<pre>
    When `llvm-mc` (with the flags `--filetype=obj --assemble`) is run against the following assembly:
```x86
.intel_syntax noprefix
rep mov eax, 1
```
It produces a valid object file as expected. However, when `llvm-mc` is run against the same string, but with everything capitalized:
```x86
.intel_syntax noprefix
REP MOV EAX, 1
```
`llvm-mc` complains about it:
```
/tmp/test.s:2:1: error: invalid instruction mnemonic 'MOV'
REP MOV EAX, 1
^~~
```

I'm not sure if I'm missing something here, but as far as I'm aware, assembly is supposed to be capitalization agnostic.
</pre>
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