Question regarding expected behaviour when user-defined top-module identifier is provided

[TooMuchDakka]

Section 2.1 "Module and Signal declarations" of RevLib 2.0.1 states:
"The top-module of a program is defined by the special identifier main. If no module with this name exists, the last module declared is used instead by convention."

While looking through the code of the synthesis base class implementation the following lines raised the question:

auto mainModule = get<std::string>(settings, "main_module", std::string());

// get the main module
Module::ptr main;

if (!mainModule.empty()) {
    main = program.findModule(mainModule);
    if (!main) {
        std::cerr << "Program has no module: " << mainModule << "\n";
        return false;
    }
} else {
    main = program.findModule("main");
    if (!main) {
        main = program.modules().front();
    }
}

• It seems that currently the user is able to specify the expected identifier of the top-module via the syrec::Settings class. Is this a custom extension since this is not specified in RevLib?
• A SyReC program for which no module matching the user defined top-module identifier is found cannot be synthesized which differs from the behaviour when no expected top-module identifier is defined and no module with identifier "main" is found. Is this expected behaviour?

[burgholzer]

Just some quick comments.

• the spec of RevLib is fairly old and has hardly been worked on in the last years. Not everything in there is fully fleshed out or polished. Some aspects definitely deserve improvements.
• the first point seems reasonable to me, even though it is not fully compliant with the spec. Although I'd be fairly open a PR adjusting the code to follow the spec more closely.
• I would say no, and would consider that a technical limitation of the current code. PRs welcome. 🙏

[TooMuchDakka]

@burgholzer I would have defined the process of finding the top-module of a SyReC program in the parser and synthesizer as follows:

1. If the expected top-module identifier was defined in the configuration (for the parser in syrec::ReadProgramSettings, for the synthesizer in syrec::Properties) find the first module matching this identifier. This implies that at most one module with such matching identifier is allowed to exist, if zero or more than one matching module is found then report an error. We do not continue to 2. since the top-module identifier was explicitly set by the user while in 2. it was implicitly defined.
2. If no top-module identifier was defined in the configuration, find the first module with identifier main. Only one module with such identifer is allowed to exist. Otherwise, report an error if more than on matching module was found.
3. Select the last defined module of the SyReC program as top-module.

[burgholzer]

Sounds like a reasonable approach to me 👍🏻