Allow connecting module instance using implicit named port connections.

This is part of the 1800-2009 standard (Section 23.3.2.3) and allows
ports of module instances to be declared like:

modname instance(.foo, .bar);

instead of

modname instead(.foo(foo), .bar(bar));

The only tricky part about this is the implicit port connection shall
not create an implicit net declaration.  To make this happen, the path
of least resistance was to add a bool to PEIdent indicating that it
should not implicitely create a net.

This does not rely on the generation flag to be 2009, following the
trend that new port naming convention (like ANSI style ports) work
regardless of the generation.

PExpr.cc

@@ -258,11 +258,12 @@ const verireal& PEFNumber::value() const
 }
 
 PEIdent::PEIdent(const pform_name_t&that)
-: path_(that)
+: path_(that), no_implicit_sig_(false)
 {
 }
 
-PEIdent::PEIdent(perm_string s)
+PEIdent::PEIdent(perm_string s, bool no_implicit_sig)
+: no_implicit_sig_(no_implicit_sig)
 {
       path_.push_back(name_component_t(s));
 }
@@ -273,9 +274,13 @@ PEIdent::~PEIdent()
 
 void PEIdent::declare_implicit_nets(LexicalScope*scope, NetNet::Type type)
 {
-        /* We create an implicit wire if this is a simple identifier and
+        /* We create an implicit wire if:
-           if an identifier of that name has not already been declared in
+	   - this is a simple identifier
-           any enclosing scope. */
+           - an identifier of that name has not already been declared in
+             any enclosing scope.
+	   - this is not an implicit named port connection */
+     if (no_implicit_sig_)
+	    return;
      if ((path_.size() == 1) && (path_.front().index.size() == 0)) {
             perm_string name = path_.front().name;
             LexicalScope*ss = scope;

PExpr.h

@@ -255,7 +255,7 @@ class PEFNumber : public PExpr {
 class PEIdent : public PExpr {
 
     public:
-      explicit PEIdent(perm_string);
+      explicit PEIdent(perm_string, bool no_implicit_sig=false);
       explicit PEIdent(const pform_name_t&);
       ~PEIdent();
 
@@ -298,6 +298,7 @@ class PEIdent : public PExpr {
 
     private:
       pform_name_t path_;
+      bool no_implicit_sig_;
 
     private:
 	// Common functions to calculate parts of part/bit

parse.y

@@ -3101,6 +3101,14 @@ port_name
 		  delete[]$2;
 		  $$ = tmp;
 		}
+	| '.' IDENTIFIER
+		{ named_pexpr_t*tmp = new named_pexpr_t;
+		  tmp->name = lex_strings.make($2);
+		  tmp->parm = new PEIdent(lex_strings.make($2), true);
+		  FILE_NAME(tmp->parm, @1);
+		  delete[]$2;
+		  $$ = tmp;
+		}
 	;
 
 port_name_list