Internal speedups: Skip iterator for Termop or VarRefs.

Fix AstUCFunc being mis-labeled as a Termop.

src/V3Ast.cpp

@@ -804,7 +804,7 @@ void AstNode::checkTreeIter(AstNode* backp) {
     if (backp != this->backp()) {
 	this->v3fatalSrc("Back node inconsistent");
     }
-    if (castNodeTermop()) {
+    if (castNodeTermop() || castNodeVarRef()) {
 	// Termops have a short-circuited iterateChildren, so check usage
 	if (op1p()||op2p()||op3p()||op4p())
 	    this->v3fatalSrc("Terminal operation with non-terminals");

src/V3Ast.h

@@ -823,6 +823,9 @@ struct AstNodeTermop : public AstNodeMath {
     AstNodeTermop(FileLine* fl)
 	: AstNodeMath(fl) {}
     ASTNODE_BASE_FUNCS(NodeTermop)
+    // Know no children, and hot function, so skip iterator for speed
+    // See checkTreeIter also that asserts no children
+    void iterateChildren(AstNVisitor& v, AstNUser* vup=NULL) { }
 };
 
 struct AstNodeUniop : public AstNodeMath {
@@ -1070,6 +1073,9 @@ public:
     void hiername(const string& hn) { m_hiername = hn; }
     bool hierThis() const { return m_hierThis; }
     void hierThis(bool flag) { m_hierThis = flag; }
+    // Know no children, and hot function, so skip iterator for speed
+    // See checkTreeIter also that asserts no children
+    void iterateChildren(AstNVisitor& v, AstNUser* vup=NULL) { }
 };
 
 class AstNodePli : public AstNodeStmt {

src/V3AstNodes.h

@@ -1675,11 +1675,12 @@ struct AstTime : public AstNodeTermop {
     virtual bool same(AstNode* samep) const { return true; }
 };
 
-struct AstUCFunc : public AstNodeTermop {
+struct AstUCFunc : public AstNodeMath {
     // User's $c function
+    // Perhaps this should be a AstNodeListop; but there's only one list math right now
 public:
     AstUCFunc(FileLine* fl, AstNode* exprsp)
-	: AstNodeTermop(fl) {
+	: AstNodeMath(fl) {
 	addNOp1p(exprsp);
     }
     ASTNODE_NODE_FUNCS(UCFunc, UCFUNC)

src/V3Premit.cpp

@@ -246,6 +246,8 @@ private:
 	nodep->iterateChildren(*this); checkNode(nodep); }
     virtual void visit(AstNodeBiop* nodep, AstNUser*) {
 	nodep->iterateChildren(*this); checkNode(nodep); }
+    virtual void visit(AstUCFunc* nodep, AstNUser*) {
+	nodep->iterateChildren(*this); checkNode(nodep); }
     virtual void visit(AstSel* nodep, AstNUser*) {
 	nodep->fromp()->iterateAndNext(*this);
 	{   // Only the 'from' is part of the assignment LHS