RE: [sv-ac] Make (b, v = e)[->2] legal in next 201X version?

Hi Ben, Scott,

I believe (b[->m], v=e) is different than what Ben wanted.
I guess, though, (b[->1] ##0 (v=e))[*m] is.
It's not that simple, but perhaps better let one use it, then add rewrites with controversial unwrappings.

Dana

From: owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] On Behalf Of Little, Scott
Sent: Wednesday, December 21, 2011 10:40 AM
To: ben@systemverilog.us; sv-ac@eda-stds.org; Korchemny, Dmitry
Subject: RE: [sv-ac] Make (b, v = e)[->2] legal in next 201X version?

Hi Ben,

It seems like your rewrite isn't quite equivalent. Annex F defines the equivalence as:

b[->m] == (!b [*0:$] ##1 b)[*m]

A sequence of b with length m would satisfy the goto and the above rewrite. I believe that your rewrite requires an alternation of b and !b.

The syntax (b[->m], v=e) is legal. Does that not do what you want?

Thanks,
Scott

From: owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] On Behalf Of ben cohen
Sent: Tuesday, December 20, 2011 8:48 PM
To: sv-ac@eda-stds.org; Korchemny, Dmitry
Subject: [sv-ac] Make (b, v = e)[->2] legal in next 201X version?

In reference to: http://verificationguild.com/modules.php?name=Forums&file=viewtopic&t=4356
The following is currently illegal in SVA:
   (b, v = e)[->2]
as that is equivalent to:
((!b, v = e)##[0:$](b, v = e))[*2]
and the update of v when !b==1 is not desired.

Question to this group: Do we want in the next LRM update to allow such a structure
(b, v = e)[->2] , but with the definition that it be equivalent to:
((!b)##[0:$](b, v = e))[*2] , meaning that the sequence match item is only updated when there is a match of the variable.

Do you feel that this is important?
Ben Cohen

A bit more info about the rule: The consecutive repetition operator can be applied to general sequence expressions, but the goto repetition and nonconsecutive repetition operators can be applied only to boolean expressions. In particular, goto repetition and nonconsecutive repetition cannot be applied to a boolean expression to which a sequence match item has been attached. For example,
Code:

// the following is a legal sequence expression:
  (b[->1], v = e)[*2]
  // but the following is illegal:
  (b, v = e)[->2]

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