<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64700>64700</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [RISC-V] Unexpected registers in extended inline asm
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          lekcyjna123
      </td>
    </tr>
</table>

<pre>
    Hi,

I currently play around with kernels to test my RISC-V processor and I have found an behaviour which is unexpected for me. I have created small code sample:

```c
int main()
{
 unsigned int LEN = 4;
  unsigned int tab[] = {0,1,2,3};
  unsigned int buf1, buf2;
//  buf1 = 14;
  asm volatile (
                "add %[buf1], %[buf2], %[tab] \n\t"
                "addi %[buf2], %[LEN], 0 \n"
                : [buf1] "+r" (buf1),
 [buf2] "+r" (buf2)
                : [LEN]"r"(LEN),
 [tab]"r"(tab)
                : );
  return 0;
}
```

If I create an variable without any initialisation and use it as "+r" output register with this uninitialised variable. A correct code is generated if I use clang without optimisations:
```asm
 add     a2, a1, a4
        mv      a1, a3
```

But If I use a flag for optimisations (e.g. -O2) the same registers are allocated for `buf1` `LEN` and `buf2` `tab`:
```asm
        add     a0, a1, a1
        mv a1, a0
```

If I initialise buf* variables before inline assembly then everything is fine also with optimisations. Of course my inline assembly is buggy because I have specified that I use `buf1` and `buf2` as an input, while I don't do that, but using gcc this code compile correctly (via https://godbolt.org/z/er8PjY6xc).

So I would like to ask:
- Is the difference with gcc expected?
- Is there a possibility to warn about such issues?
</pre>
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