RE: [sv-bc] declaration vs reference order issue

Dave,

 

This has been discussed in the past - in the context of randomize-with
and package imports. The only consistent way to deal with the 2 cases
that Daniel shows is to resolve all class references to the class, that
is, in the two examples, an undecorated 'i' always refers to the one
inside the class - both cases should display 2. This is similar to the
way in which C++ handles class members: undecorated references to class
members always resolve within the class, regardless of the declaration
order. And, like SV, C++ also has a declaration-before use rule for
other identifiers. BTW, don't forget that resolving names in classes
must also consider the inheritance hierarchy, for example:

 

int v = 1;

 

class B;

  static int v = 2;

endclass

 

class C extends B;

  static int w = v;            // this 'v' resolves to the base class
B::v (2)

endclass

 

On another note, whether the compiler is a single-pass or multiple-pass
is definitely an implementation issue that should not be mandated by the
LRM. I recall that Mark Hartoog had proposed a scheme that would support
all this, but I don't see it in the text.

 

            Arturo

 

From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of
Rich, Dave
Sent: Thursday, September 04, 2008 8:49 AM
To: Daniel Mlynek; sv-bc@eda-stds.org
Cc: Mirek Forczek; Piotr Winter; Sergei Zaychenko
Subject: RE: [sv-bc] declaration vs reference order issue

 

Mantis 2106 added to 6.21

 

A variable declaration shall precede any simple reference
(non-hierarchical) to that variable. 

 

So there can be no tool dependence on this issue. Customers certainly do
not like when code compiles on one simulator and not on another. The
begrudgingly accept order of evaluation dependencies only if a single
implementation cannot guarantee ordering.

 

For case 2, I thought we had added text that defines the search rules
from the point of the source code, but I can't seem to find it. But
given the rule above, there's no way $display(i) can refer to this.i and
display 2.

 

Dave

 

 

 

________________________________

From: owner-sv-bc@server.eda.org [mailto:owner-sv-bc@server.eda.org] On
Behalf Of Daniel Mlynek
Sent: Thursday, September 04, 2008 2:53 AM
To: sv-bc@server.eda-stds.org
Cc: 'Mirek Forczek'; 'Piotr Winter'; 'Sergei Zaychenko'
Subject: [sv-bc] declaration vs reference order issue

 

CASE1:

Does LRM defines rules on how tool should behave if reference to an
identifier which is unknown at this point of source code.  Idetnifier is
delcared later in code (case1). LRM specifies that both single pass
parser and multi pass parser may be used for parsing SV code (LRM:"
Implementations may execute compilation in one or more passes") It is
obvious that single pass compiler will fail on case like below, while
mutli pass can handle with that. So this should be tool dependend if
CASE would pass compilation?

 

2nd case is connected - what should happend if in current scope and in
higher scope there is an identifier declared. But in current scope
declaration is place in code after reference - so which one should be
printed by case2. Is it defined or tool dependend?

 

LRM:22.9 says:"If an identifier is referenced directly (without a
hierarchical path) within a task, function, named block, or generate
block, it shall be declared either within the task, function, named
block, or generate block locally or within a module, interface, program,
task, function, named block, or generate block that is higher in the
same branch of the name tree that contains the task, function, named
block, or generate block. If it is declared locally, then the local item
shall be used; if not, the search shall continue upward until an item by
that name is found or until a module,  interface, or program boundary is
encountered."

So imho in both cases "2" should be displayed

 

 

 

CASE1:  

module top;

 

   class nested;
       function new ();
              $display(i);    //  displaying "i" - this should be a
failure - as i is unkcnown since here, or 2 shoudl be displayed?
      endfunction
      int i = 2;               // local member "i"
   endclass

 

   nested n_inst = new();

 

endmodule

 

CASE2:

module top;
    bit [2:0] i = 0;   // static member "i"

 

   class nested;
       function new ();
              $display(i);    //  displaying "i" - which i would be
displayed - ???????????????
      endfunction
      int i = 2;               // local member "i"
   endclass

 

   nested n_inst = new();

 

endmodule

 

 

 

DANiel


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