QEmu ARC port - decoder implementation feedback

[Richard Henderson]

On 6/9/21 2:58 AM, Cupertino Miranda wrote:
> We started to do that and in the process we realize that the approach
> would bring us yet another encoding language description to maintain.

Why would you be maintaining another description?  Your approach below with the 
simple recursive algorithm appears to be no different.

> Also that decodetree alone would not allow us to properly disassembly
> code, still requiring to keep the initial structure.

Why is that?

The current uses of decodetree are quite complex, so I sincerely doubt that it 
cannot do the job.  You've asked no questions, nor have you described any 
problems you have encountered.

That said, decodetree was merely a suggestion based on what appeared to me to 
be a trivial automated textual rewrite of your current data set.  If you want 
to use something else that performs equally well, fine.

> So far, we did the following:
>     - converted opcodes.def to macros instead of table entries.

Sure.

>     - created a script that reads those entries and outputs macros that
> directly translate to a switch/case decision tree (example below), just
> like the ones produced by decodetree. The difference is that the switch
> will return the enum entry for the proper decoder structure instead of
> calling a translation function.

An enum result is fine, sure.

The example is not especially enlightening because you don't show the macro 
definitions, or the expansion.  Have you a link to a git repo that you can share?

>     - the script can either be contributed in C or python language as it
> is based on a simple recursive algorithm.

Either is fine.  We currently use both as build-time generators.


r~