RE: [sv-ec] inline constraints -- things are not really quite right yet (perhaps)

I am extremely uncomfortable with this.

The wildcard import rules are already complicated and difficult
for users to understand. Now you are proposing to make a long
list of exceptions to the wild card import rules, places where
wild card imports do not work. 

This may make it easier to implement, but it does not simplify the 
language. It just makes the wild card import mechanism more 
complicated and difficult for users to understand. There now
are a set of rules for how it works, and then set of exceptions
to the rules where wild card import will not work.

I think this is moving in the wrong direction.  

> -----Original Message-----
> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On 
> Behalf Of Gordon Vreugdenhil
> Sent: Tuesday, November 06, 2007 7:40 PM
> To: SV_EC List
> Subject: [sv-ec] inline constraints -- things are not really 
> quite right yet (perhaps)
> 
> 
> In the discussion regarding inline constraints, I am now Ok 
> with the fact that there exists a mechanism for forcing a 
> reference to resolve in an outwards manner.
> 
> That isn't really very "tight" though.
> 
> Given the following:
> 
>     package p;
>        int x;
>     endpackage
>     module m #(parameter type T);
>        T c = new;
>        initial c.randomize with {x < y} ;
>        int x;
>     endmodule
> 
> 
> We still have the latent error problem that I am pretty unhappy about.
> 
> Yes, the user *could* (if aware of the possible issue), write 
> the constraint as either:
>        initial c.randomize with {local::x < y} ; or
>        initial c.randomize with {local::c.x < y} ; depending 
> on which way "x" is supposed to resolve.
> 
> However, the bare "x < y" is still legal but only if "x" 
> binds as c.x.  If "x" doesn't bind in that manner, too bad, 
> you get a latent import error at elaboration time.
> 
> This still disturbs me in terms of how robust separately 
> compiled designs can be without a huge level of paranoia on 
> the part of the author.
> 
> Since most users indicated at least some level of preference 
> for fairly static handling, could we refine things a bit?
> 
> How about the following:
>    1) local::x  resolves outside the constraint and is sufficient
>       for wildcard import
>    2) local::c.x  (indirectly) forces resolution into the object
>    3) a bare "x" binds either way but is not sufficient for a
>       wildcard import.
> 
> (3) is kind of like what we do with .* references -- it can 
> bind to something that is there, but can't impact import 
> relationships.
> This means that a separate compilation cannot have later 
> declarations be invalidated by latent imports -- if the user 
> wants to allow a "both ways" resolution, they can do a direct 
> import of the name.  Any conflicting declaration errors are 
> then caught early.
> Otherwise, the name must resolve into the object.  
> Fortunately, that can even be quite easily checked (for 
> non-hierarchical references) and warned about by an implementation.
> 
> Since "local::x" would be sufficient for wildcard import, I 
> think we can then cover all the bases.
> 
> I realize that this might be slightly incompatible, but I 
> don't think it is sufficiently incompatible to prevent 
> serious consideration.
> 
> I don't know if any real users are relying on assumed import 
> behavior right now.  If so, that would definitely be good 
> input to hear.
> 
> This direction would certainly satisfy my desire for avoiding 
> latent import conflicts while posing (I think) a fairly 
> minimal compatibility issue.
> 
> Gord.
> --
> --------------------------------------------------------------------
> Gordon Vreugdenhil                                503-685-0808
> Model Technology (Mentor Graphics)                gordonv@model.com
> 
> 
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