Distinguish queue dimensions from `null` expressions

Queue dimensions use a `PENull` expression as an internal marker for `$`.
This also represents a source `null` expression, so declarations such as:

    integer value[null:2];

are accepted and elaborated as bounded queues.

Use a dedicated `PEQueueDimension` marker for queue dimensions. This lets
source `null` expressions follow normal range expression validation while
preserving the existing representation of dynamic and fixed dimensions.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

PExpr.h

@@ -635,6 +635,12 @@ class PENull : public PExpr {
                                      unsigned flags) const override;
 };
 
+// Internal marker for the '$' in a queue dimension.
+class PEQueueDimension : public PExpr {
+    public:
+      void dump(std::ostream&) const override;
+};
+
 class PENumber : public PExpr {
 
     public:

elab_type.cc

@@ -374,9 +374,8 @@ ivl_type_t elaborate_array_type(Design *des, NetScope *scope,
 		  type = elaborate_darray_check_type(des, li, type, "Dynamic array");
 		  type = new netdarray_t(type);
 		  continue;
-	    } else if (dynamic_cast<PENull*>(lidx)) {
-		    // Special case: Detect the mark for a QUEUE declaration,
-		    // which is the dimensions [null:max_idx].
+	    } else if (dynamic_cast<PEQueueDimension*>(lidx)) {
+		    // Special case: Detect the mark for a QUEUE declaration.
 		  type = elaborate_static_array_type(des, li, type, dimensions);
 		  type = elaborate_queue_type(des, scope, li, type, ridx);
 		  continue;

netmisc.cc

@@ -1087,7 +1087,7 @@ bool evaluate_range(Design*des, NetScope*scope, const LineInfo*li,
                     "An unsized dimension is not allowed here." << endl;
             dimension_ok = false;
             des->errors += 1;
-      } else if (dynamic_cast<PENull*>(range.first)) {
+      } else if (dynamic_cast<PEQueueDimension*>(range.first)) {
             cerr << li->get_fileline() << ": error: "
                     "A queue dimension is not allowed here." << endl;
             dimension_ok = false;

parse.y

@@ -3197,7 +3197,7 @@ variable_dimension /* IEEE1800-2005: A.2.5 */
   | '[' '$' ']'
       { // SystemVerilog queue
 	list<pform_range_t> *tmp = new std::list<pform_range_t>;
-	pform_range_t index (new PENull,0);
+	pform_range_t index (new PEQueueDimension,0);
 	pform_requires_sv(@$, "Queue declaration");
 	tmp->push_back(index);
 	$$ = tmp;
@@ -3205,7 +3205,7 @@ variable_dimension /* IEEE1800-2005: A.2.5 */
   | '[' '$' ':' expression ']'
       { // SystemVerilog queue with a max size
 	list<pform_range_t> *tmp = new std::list<pform_range_t>;
-	pform_range_t index (new PENull,$4);
+	pform_range_t index (new PEQueueDimension,$4);
 	pform_requires_sv(@$, "Queue declaration");
 	tmp->push_back(index);
 	$$ = tmp;

pform_dump.cc

@@ -506,6 +506,11 @@ void PENull::dump(ostream&out) const
       out << "null";
 }
 
+void PEQueueDimension::dump(ostream&out) const
+{
+      out << "$";
+}
+
 void PENumber::dump(ostream&out) const
 {
       out << value();

pform_types.h

@@ -91,8 +91,12 @@ typedef std::pair<perm_string, unsigned> pform_ident_t;
  *       second = 0
  *
  *   [ $ ] -- Queue type
- *       first = PENull
+ *       first = PEQueueDimension
  *       second = 0
+ *
+ *   [ $ : <expr> ] -- Bounded queue type
+ *       first = PEQueueDimension
+ *       second = <expr>
  */
 typedef std::pair<PExpr*,PExpr*> pform_range_t;