[sv-bc] Task export in interface modports

I know this is way too late for the current PAR, and maybe 
someone's already turned out all the lights at sv-bc, but 
I'd appreciate any input on this issue where the LRM
appears silent and existing implementations disagree.

Consider a module that exports a different task to 
each of several ports of the same interface.modport type:

interface I();
  modport mp(export task T());
  initial begin
    $display("interface %m calls T()");
    T();
  end
endinterface : I
//
module M(I.mp p, I.mp q);
  task p.T();
    $display("called %m through p.T()");
  endtask
  task q.T();
    $display("called %m through q.T()");
  endtask
endmodule : M
//
module top;
  I i_p();
  I i_q();
  M m(i_p.mp, i_q.mp);
endmodule : top

Is this legal?  Depending on your mental model of
task export, you might think that each instance of
interface I has some sort of reference to the exported 
task, which itself resides within the module; or, 
alternatively, you might imagine that the task is 
effectively rewritten into the body of the interface.

If you take the former view (reference-to-task), as
one simulator seems to do, then all is well.  Its 
output from the code above is what I would hope for:
  interface top.i_p calls T()
  called top.m.p.T through p.T()
  interface top.i_q calls T()
  called top.m.q.T through q.T()

If you take the latter view (exported task is rewritten
into the interface) then the code is illegal because
it attempts to write two different tasks T() into
the same interface.  I can see that this might be a
reasonable interpretation if you think of the interface
as having an "extern" task declaration; but, in that case,
surely the task body should be named
  interface_name::task_name
rather than
  port_name.task_name

Mysteriously, the simulator that complains about 
this code will accept a slightly altered version
in which the exporting module's ports are of 
generic interface type:

  module M(interface.mp p, interface.mp q);

and it then gives the following output:
  interface top.i_p calls T()
  called top.m.T through p.T()
  interface top.i_q calls T()
  called top.m.T through q.T()

Note the different result from %m within the exported task.
I can't make much sense of this.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is not just an academic exercise; there are real,
useful scenarios in which I need to know what is correct.

Other things that might affect the answer, but don't
seem to change anything in the two simulators I tried:
- having the exported task be "automatic";
- parameterizing the two interface instances differently.

Thanks in advance
-- 
Jonathan Bromley
Consultant

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