<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=http://email.email.llvm.org/c/eJylk8FuozAQhp_GXEZBxgRCDhySZiP10AutetjLytgDuCV2ZJtUefsdSLqrrfaw0koW1sjj__88M7ROX-tnd0J4c20Ai6hRQ-c8yIuPxl5ZvmP8wPj9m6XwMErbw27_-CUNhhjPYc4XR1q9Umlvp9T5nqIP825oo-wVHTCRN6gnhfrHy3x5kRYpPEn_Dg1nm29NVoD0CB4D-gshGQus5HsTX1FF8t29Ng32JkT0j7Zzs22-6zE29wt0GJiolLMhkq4ajMXjZFU0jpRE-USMW1K8eecpvAxIfrPnSdorDNJrUG6uxhQQXAdNBtJqwgO8oL9-zPlMPMDHYNQAYXDTqKFFUAPVh65FB_fKkcttLeEnNiy0_Xf0jkAvzmgiArbZ06Pj5O1naYHlRzLfwFzjJmP5npIOf9V6wdP5X7TKmxb_Q-sL5nopCcgQ8NSOZHF_oUaS8XzlsyK9ZSa6zvU238pETnFwvm7RhsFwniWTH-svY2HiMLWpcicKxvHyua3O3r1Rayk0IUxIzTsW-brYJkOdddW62GheoFZZl-tKV1ipslOyFG0n1skoWxxDzYo9E6KV6h2tJkeaEYpZcUj-n8LUggvBM1HxvCiLKs3zQikyV9sMtyVu2JrjSZoxnXXmqU98vUi2E03imo_UqPD7kOpqevrdFmgijCaOSzBDFwd4ns5n5-Ovxmm8GIUhWbDqheknuYsrPA>53459</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [AVR] Support avrtiny devices
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          benshi001
      </td>
    </tr>
</table>

<pre>
    Some jobs needed for avrtiny:

1. Clang ABI for avrtiny: https://gcc.gnu.org/wiki/avr-gcc#Reduced_Tiny
2. Mark R0~R15 are reserved in `BitVector AVRRegisterInfo::getReservedRegs(const MachineFunction &MF)`
3. There are many hard coded use of R1 and R0 everywhere, which should be changed to 
```
Register getRegZero(void) { return avrtiny ? R17 : R1; }
Register getRegTemp(void) { return avrtiny ? R16 : R0; }
```
4. The assembler should deny r0-r15.

</pre>
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