<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/67950>67950</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Aarch64] Backend Bugs
        </td>
    </tr>

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

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

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

<pre>
    I separate the bug report #67787  since the report has distinct bugs.

Clang takes incorrect arm syntax and silently change registers.

```
$ cat buggy2.s
    sxtw X0, X2
    sxth X0, X4
    sxtb X0, X6

$ ./bin/clang -c --target=aarch64-linux-eabi  buggy2.s -o buggy2.o

$ objdump -d buggy2.o

Disassembly of section .text:

0000000000000000 <.text>:
   0:   93407c40        sxtw    x0, w2
   4:   93403c80        sxth     x0, w4
   8:   93401cc0        sxtb    x0, w6

```

In case of S2, D2 registers, Clang produces error message.
```
$ cat buggy2.s
    sxtw X0, X2
    sxth X0, S2
    sxtb X0, D2

$/bin/clang -c --target=aarch64-linux-eabi  buggy2.s -o buggy2.o
buggy2.s:2:14: error: invalid operand for instruction
    sxth X0, S2
 ^
buggy2.s:3:14: error: invalid operand for instruction
    sxtb X0, D2
             ^
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJysVMty8ywMfRq80dhD5PvCi7RpZrrupluMFZvWgQzgJnn7f3BuTf5ON1-ZDAFx0EE6soRzqtdEDcufWL6KxOQHY5u98q1Vuo9a0x2bV3C0E1Z4Aj8QtFMPlnbGemCYFmVZlQBOaXk6Ph8NwkGnnFda-nDFJYyvGF-e5udR6B68-CQHSktjLUkPwm7BHbUXBxC6A6dG0n48ghyE7oPnXjlP9t4VK_j5d9piBlLMlP0RE3eyAgC4g9_DO2f4DO94Zx4u5uzO3F7MxR0fZpAwXLdKM1zLOZBYQhx7YXvyLF0JYeVQZPGo9HSISbQKrs-B2FzW5tGraT-6abuDuPsRslJOOEfbdjyC2YAj6ZXRkHg6eJYuv0P5wwCWPp9xL1coAPB5U9dpxkuZcWC8DllivD7Mke9vecpu0FRWF-jAeA1n7C151Q27kPKCbW9ui98EnOdXDVI4CoG-Ybizwpv-YX-qoJ013STJAVlrLGzJOdFT8ueV8YY_VsYKHzT8w7q4PjNdIkuXiyDAKcywUPpLjKoDsyMbvpWNsaC083aaq-L3IFj-8j-O9N84HjMC38eV76pI1DVpV6e1iKhZFHWBmOXFIhoaUdKmrqjLK6w2RZ2lWLaCZy3JRV5jlUWqQY7pgnPkOda4SDosEWVVSY64kaJlGaetUGMyjl_bxNg-Us5N1BRlnfNoFC2Nbm53iJr2MB8yxND9bBPuxKFbsYyPynl38-KVH-c-uTzJyPIVPAn5SbqDp6l30WTHZvB-F7LJcM1w3Ss_TG0izZbhOjg6_8U7az5Ieobrmd4xXM_P-y8AAP__GX6YGw">