[relay][frontend] Return Module from get_workload

[zhiics]

This PR makes the relay testing frontend returns Module as the frontend parsers also return Module.

cc @tqchen @jroesch @wweic @MarisaKirisame

[jroesch]

Could we add a Python property to Module such as main so we don't have to write so much boiler plate everywhere?

[zhiics]

@jroesch Sure. I will update the rest part of the code for this PR tomorrow.

[wweic]

lgtm. marked remaining mod[mod.entry_point]

[zhiics]

@wweic Thanks. I just refactored part of the code last night. Now everything should be updated to main

[tqchen]

@zhiics @jroesch I feel we should avoid introducing the additional field mod.main, but instead, directly use mod["main"], so it is no different from getting other functions (remove one level of abstraction). We could likely remove mod.entry_func later.

[zhiics]

@jroesch do you have any comments? I am okay with either way. I can refactor to mod["main"] if you are okay as well.

[jroesch]

Tianqi and I discussed some more, he argues we should just remove and make it so there is no special main function, and we just use main as convention but allow the specification of multiple entry points in the future to passes that do liveness, etc.

Sorry for the back and forth, enjoy the holiday!

[zhiics]

@jroesch No worries.

I have one question about the updating the function for a globalvar in a module. I might miss something about the multiple entry points.

For example, we may create a module (mod) using from_expr where a main is created or directly create a module using module({"main": func}). Now if I have mod["main"] = func1, should I update the function for main, or should I keep both? I think we should just check if main is in the global list, if so, we then just update the function, right? Originally, we just update the function for entry_func

[tqchen]

@zhiics I think we should update the "main" just as if it is a normal function

[jroesch]

I think we should just treat all functions uniformly, there are a couple places where we might need to specify an entry point, and we can just default to main.