<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/156560>156560</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Reorder ARM disassembler decode functions to eliminate forward declarations
        </td>
    </tr>

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

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

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

<pre>
    In https://github.com/llvm/llvm-project/pull/154802, we refactored the decoder emitter to move the common functions generated by the decoder emitter into a new header file: MCDecoder.h. This includes the function `fieldFromInstruction`.

Prior to that, decoder functions that called `fieldFromInstruction` had to be declared before including the generated GenDisassembler.inc file (as the generated code references them) and then defined after that so that they can find use the `fieldFromInstruction` function which is in the generated code:

```
static DecodeStatus DecodeXYX(...);
#include "GenDisassembler.inc"
static DecodeStatus DecodeXYZ(...) {
   Z = fieldFromInstruction()
}
```

Now that `fieldFromInstruction` is in a common header, we can do away with the need to forward declare these functions:

```
#include "MCDecoder.h"

static DecodeStatus DecodeXYZ(...) {
   Z = fieldFromInstruction()
}
#include "GenDisassembler.inc"
```

For most other targets, doing this generates a diff that looks just like this (include AArch64). For some other targets, this requires a little more rearrangement to get rid of all forward declarations, and then the diff becomes too complex. This includes the ARM disassembler. Hence, for ARM, we need to this in N steps so that in each step the diff is a simple code motion and looks like that. This issue is to track that.
</pre>
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