[Unity][UX][Tweak] Make it an error to mark a function private and specify a global symbol

[slyubomirsky]

A small follow-up to #15140, which was merged before I could make this addition: This change throws an error if a function has been annotated as private but the user manually specifies the global symbol. Since it is a contradiction to do so, it is best to detect this error rather than have it silently work (with the effect of actually making the function public).

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• cc @quic-sanirudh _{See #10317 for details}

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[tvm-bot]

Thanks for contributing to TVM! Please refer to the contributing guidelines https://tvm.apache.org/docs/contribute/ for useful information and tips. Please request code reviews from Reviewers by @-ing them in a comment.

• cc @quic-sanirudh _{See #10317 for details}

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[junrushao]

This is a really cool addition! A bit off the topic: do you think we should sugar the global_symbol attribute to make it part of the decorator? For example,

@R.function(global_symbol=True) # implies the global symbol name as "my_relax_func"
def my_relax_func: ...
@I.prim_func(global_symbol=True) # implies the global symbol name as "my_relax_func"
def my_tir_func: ...
@I.prim_func # implies the private symbol
def my_private_func: ...

[slyubomirsky]

Having syntax sugar for global symbol might make sense. However, as established in the last PR, I think we would prefer for the default not to be private

@tqchen Any thoughts on this suggestion?

[junrushao]

in fact default not being private sounds better to me :-)

[tqchen]

I agree, we would go for default not private