RE: [sv-bc] confusion in determining the type of an self determined binary expression during evalution of type operator

From a user point of view, it seems to me that normalizing would be
easier in that my code would not have to change depending on whether I
wanted to reference bit n of an expression or an identifier. I would
only have to know its size and then the bit index would be the same for
every expression of that size, even if the exoression was just a simple
identifier.

Shalom

> -----Original Message-----
> From: Feldman, Yulik 
> Sent: Thursday, October 18, 2007 5:12 PM
> To: Gordon Vreugdenhil
> Cc: Bresticker, Shalom; sv-bc@server.eda-stds.org
> Subject: RE: [sv-bc] confusion in determining the type of an 
> self determined binary expression during evalution of type operator
> 
> Generally, I understand that both definitions (normalizing 
> and not normalizing the types) can theoretically work, and 
> thus I'll not argue too much if there is substantial 
> opposition to my point of view. But I'm interested to know 
> what the arguments for normalizing the types are.
> 
> I can understand that due to historical reasons some 
> simulators or other software tools implemented their internal 
> data structures in such a way that only normalized types can 
> be stored, and changing those data structures would mean 
> making major updates in tools' infrastructure, leading to 
> opposition to do such changes.
> 
> However, closing the eyes on historical reasons for a moment, 
> I'm not sure I understand what kind of negative effect 
> storing the original, non-normalized type information may 
> have on tool's efficiency. After all, you just need to let 
> the expression object point to the object storing the type 
> information. If the type object is the "original" one, you 
> anyway have its definition somewhere, so this object doesn't 
> consume additional memory. Also, you anyway need to store the 
> type information of the expression somehow, and I don't think 
> you could do that more compactly than storing a pointer to 
> the type object, even if the types would be normalized. From 
> performance point of view, following the pointer to the type 
> object and querying it in case of a need should be fast 
> enough for most practical needs. So it is not clear to me 
> where the supposed deficiency lies. 
> 
> Is there any other reason for considering using normalized 
> types other than unwillingness to change existing tool 
> implementations (assuming that some of them are currently 
> implementing normalization of the types)?
> 
> --Yulik.
> 
> -----Original Message-----
> From: Gordon Vreugdenhil [mailto:gordonv@model.com]
> Sent: Thursday, October 18, 2007 4:05 PM
> To: Feldman, Yulik
> Cc: Bresticker, Shalom; sv-bc@server.eda-stds.org
> Subject: Re: [sv-bc] confusion in determining the type of an 
> self determined binary expression during evalution of type operator
> 
> Feldman, Yulik wrote:
> > Yes, you're right. Maybe the example would be more persuading if I 
> > would use a typedef:
> > 
> > typedef logic base_type [3:1];
> > base_type a [4:1];
> > base_type b;
> > logic c;
> > assign b = a[3];
> > assign c = b[i];
> > 
> > Anyway, probably this example by itself is not a strong enough 
> > argument for not normalizing the types. Perhaps the other 
> argument I 
> > mentioned, to keep selects with more than one selection, 
> like a[3][1], 
> > unambiguous and similar in semantics with expressions like 
> (a[3])[i], 
> > is a stronger argument.
> > 
> > Another reason to keep the original type, is that if the type is 
> > normalized, you're practically introducing a new type to the model. 
> > For a software tool that means it should keep another object in 
> > memory, for example.
> 
> Yulik,
> 
> You are making a rather deep assumption here.  In my 
> experience with work on multiple simulator implementations, 
> the opposite is in fact true.
> It is more efficient on several fronts to assume 
> normalization everywhere.  This has been Ok to do in Verilog 
> and implementations assume various aspects of a normalized 
> model in fairly deep ways.
> 
> For those reasons, I will continue to have serious 
> reservations about this direction.
> 
> There may be some cases in which it is reasonable to require 
> more specific type information.  Steven has raised some of 
> those.  But requiring fully accurate information in various 
> places is a mine field and is a position for which you'll 
> almost certainly find substantial opposition.
> 
> Gord
> --
> --------------------------------------------------------------------
> Gordon Vreugdenhil                                503-685-0808
> Model Technology (Mentor Graphics)                gordonv@model.com
> 
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