diff --git a/src/V3Begin.cpp b/src/V3Begin.cpp
index b4fa16a24..fa53be32f 100644
--- a/src/V3Begin.cpp
+++ b/src/V3Begin.cpp
@@ -320,7 +320,7 @@ public:
 
 //######################################################################
 
-class BeginRelinkVisitor final : public VNVisitor {
+class BeginRelinkVisitor final : public VNVisitorConst {
     // Replace tasks with new pointer
 private:
     // NODE STATE
@@ -333,13 +333,13 @@ private:
             UINFO(9, "    relinkFTask " << nodep << endl);
             nodep->name(nodep->taskp()->name());
         }
-        iterateChildren(nodep);
+        iterateChildrenConst(nodep);
     }
     void visit(AstVarRef* nodep) override {
         if (nodep->varp()->user1()) {  // It was converted
             UINFO(9, "    relinVarRef " << nodep << endl);
         }
-        iterateChildren(nodep);
+        iterateChildrenConst(nodep);
     }
     void visit(AstIfaceRefDType* nodep) override {
         // May have changed cell names
@@ -347,14 +347,14 @@ private:
         UINFO(8, "   IFACEREFDTYPE " << nodep << endl);
         if (nodep->cellp()) nodep->cellName(nodep->cellp()->name());
         UINFO(8, "       rename to " << nodep << endl);
-        iterateChildren(nodep);
+        iterateChildrenConst(nodep);
     }
     //--------------------
-    void visit(AstNode* nodep) override { iterateChildren(nodep); }
+    void visit(AstNode* nodep) override { iterateChildrenConst(nodep); }
 
 public:
     // CONSTRUCTORS
-    BeginRelinkVisitor(AstNetlist* nodep, BeginState*) { iterate(nodep); }
+    BeginRelinkVisitor(AstNetlist* nodep, BeginState*) { iterateConst(nodep); }
     ~BeginRelinkVisitor() override = default;
 };
 
diff --git a/src/V3CUse.cpp b/src/V3CUse.cpp
index 748909c2e..9b2b1ddd6 100644
--- a/src/V3CUse.cpp
+++ b/src/V3CUse.cpp
@@ -33,7 +33,7 @@ VL_DEFINE_DEBUG_FUNCTIONS;
 // Visit within a module all nodes and data types they reference, finding
 // any classes so we can make sure they are defined when Verilated code
 // compiles
-class CUseVisitor final : public VNVisitor {
+class CUseVisitor final : public VNVisitorConst {
     // NODE STATE
     //  AstNode::user1()     -> bool.  True if already visited
     const VNUser1InUse m_inuser1;
@@ -56,44 +56,44 @@ class CUseVisitor final : public VNVisitor {
     }
     void visit(AstCFunc* nodep) override {
         if (nodep->user1SetOnce()) return;
-        iterateAndNextNull(nodep->argsp());
-        iterateAndNextNull(nodep->stmtsp());
+        iterateAndNextConstNull(nodep->argsp());
+        iterateAndNextConstNull(nodep->stmtsp());
     }
     void visit(AstCCall* nodep) override { return; }
     void visit(AstCReturn* nodep) override {
         UASSERT(!nodep->user1SetOnce(), "Visited same return twice.");
-        iterate(nodep->lhsp()->dtypep());
+        iterateConst(nodep->lhsp()->dtypep());
     }
     void visit(AstNodeDType* nodep) override {
-        if (nodep->virtRefDTypep()) iterate(nodep->virtRefDTypep());
-        if (nodep->virtRefDType2p()) iterate(nodep->virtRefDType2p());
+        if (nodep->virtRefDTypep()) iterateConst(nodep->virtRefDTypep());
+        if (nodep->virtRefDType2p()) iterateConst(nodep->virtRefDType2p());
 
         // Add a CUse for every struct that requires a declaration
         AstNodeUOrStructDType* const stypep = VN_CAST(nodep->skipRefp(), NodeUOrStructDType);
         if (stypep && stypep->classOrPackagep()) {
             addNewUse(nodep, VUseType::INT_INCLUDE, stypep->classOrPackagep()->name());
-            iterateChildren(stypep);
+            iterateChildrenConst(stypep);
         } else if (AstClassRefDType* const classp = VN_CAST(nodep->skipRefp(), ClassRefDType)) {
             addNewUse(nodep, VUseType::INT_FWD_CLASS, classp->name());
         }
     }
     void visit(AstNode* nodep) override {
         if (nodep->user1SetOnce()) return;  // Process once
-        if (nodep->dtypep()) iterate(nodep->dtypep());
-        iterateChildren(nodep);
+        if (nodep->dtypep()) iterateConst(nodep->dtypep());
+        iterateChildrenConst(nodep);
     }
     void visit(AstCell* nodep) override {
         if (nodep->user1SetOnce()) return;  // Process once
         // Currently no IMP_INCLUDE because we include __Syms which has them all
         addNewUse(nodep, VUseType::INT_FWD_CLASS, nodep->modp()->name());
-        iterateChildren(nodep);
+        iterateChildrenConst(nodep);
     }
 
 public:
     // CONSTRUCTORS
     explicit CUseVisitor(AstNodeModule* modp)
         : m_modp(modp) {
-        iterate(modp);
+        iterateConst(modp);
 
         for (auto& used : m_didUse) {
             AstCUse* const newp = new AstCUse{used.second.first, used.second.second, used.first};
diff --git a/src/V3Expand.cpp b/src/V3Expand.cpp
index 1880404bc..057d9d5f4 100644
--- a/src/V3Expand.cpp
+++ b/src/V3Expand.cpp
@@ -37,7 +37,7 @@ VL_DEFINE_DEBUG_FUNCTIONS;
 //######################################################################
 // Find nodes with side effects, to mark as non-expandable
 
-class ExpandOkVisitor final : public VNVisitor {
+class ExpandOkVisitor final : public VNVisitorConst {
 private:
     // NODE STATE
     //  AstNode::user2()        -> bool.  Is pure (along with all children)
@@ -53,7 +53,7 @@ private:
         {
             VL_RESTORER(m_isImpure);
             m_isImpure = false;
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
             selfImpure |= m_isImpure;
             nodep->user2(selfImpure);
         }
@@ -62,7 +62,7 @@ private:
 
 public:
     // CONSTRUCTORS
-    explicit ExpandOkVisitor(AstNetlist* nodep) { iterate(nodep); }
+    explicit ExpandOkVisitor(AstNetlist* nodep) { iterateConst(nodep); }
     ~ExpandOkVisitor() = default;
 };
 
diff --git a/src/V3HierBlock.cpp b/src/V3HierBlock.cpp
index 294613e18..045647625 100644
--- a/src/V3HierBlock.cpp
+++ b/src/V3HierBlock.cpp
@@ -236,7 +236,7 @@ string V3HierBlock::commandArgsFileName(bool forCMake) const {
 
 //######################################################################
 // Collect how hierarchical blocks are used
-class HierBlockUsageCollectVisitor final : public VNVisitor {
+class HierBlockUsageCollectVisitor final : public VNVisitorConst {
     // NODE STATE
     // AstNode::user1()            -> bool. Processed
     const VNUser1InUse m_inuser1;
@@ -266,7 +266,7 @@ class HierBlockUsageCollectVisitor final : public VNVisitor {
         }
         prevGParams.swap(m_gparams);
 
-        iterateChildren(nodep);
+        iterateChildrenConst(nodep);
 
         if (nodep->hierBlock()) {
             m_planp->add(nodep, m_gparams);
@@ -280,7 +280,7 @@ class HierBlockUsageCollectVisitor final : public VNVisitor {
         // Visit used module here to know that the module is hier_block or not.
         // This visitor behaves almost depth first search
         if (AstModule* const modp = VN_CAST(nodep->modp(), Module)) {
-            iterate(modp);
+            iterateConst(modp);
             m_referred.insert(modp);
         }
         // Nothing to do for interface because hierarchical block does not exist
@@ -294,12 +294,12 @@ class HierBlockUsageCollectVisitor final : public VNVisitor {
     }
 
     void visit(AstNodeExpr*) override {}  // Accelerate
-    void visit(AstNode* nodep) override { iterateChildren(nodep); }
+    void visit(AstNode* nodep) override { iterateChildrenConst(nodep); }
 
 public:
     HierBlockUsageCollectVisitor(V3HierBlockPlan* planp, AstNetlist* netlist)
         : m_planp{planp} {
-        iterateChildren(netlist);
+        iterateChildrenConst(netlist);
     }
 };
 
diff --git a/src/V3Name.cpp b/src/V3Name.cpp
index 9825a3bac..ee1ca4571 100644
--- a/src/V3Name.cpp
+++ b/src/V3Name.cpp
@@ -30,7 +30,7 @@ VL_DEFINE_DEBUG_FUNCTIONS;
 //######################################################################
 // Name state, as a visitor of each AstNode
 
-class NameVisitor final : public VNVisitor {
+class NameVisitor final : public VNVisitorConst {
 private:
     // NODE STATE
     // Cleared on Netlist
@@ -69,7 +69,7 @@ private:
         VL_RESTORER(m_modp);
         {
             m_modp = nodep;
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
         }
     }
     // Add __PVT__ to names of local signals
@@ -82,39 +82,39 @@ private:
     }
     void visit(AstCFunc* nodep) override {
         if (!nodep->user1()) {
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
             rename(nodep, false);
         }
     }
-    void visit(AstVarRef* nodep) override { iterate(nodep->varp()); }
+    void visit(AstVarRef* nodep) override { iterateConst(nodep->varp()); }
     void visit(AstCell* nodep) override {
         if (!nodep->user1()) {
             rename(nodep, (!nodep->modp()->modPublic() && !VN_IS(nodep->modp(), ClassPackage)));
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
         }
     }
     void visit(AstMemberDType* nodep) override {
         if (!nodep->user1()) {
             rename(nodep, true);
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
         }
     }
     void visit(AstMemberSel* nodep) override {
         if (!nodep->user1()) {
             rename(nodep, true);
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
         }
     }
     void visit(AstStructSel* nodep) override {
         if (!nodep->user1()) {
             rename(nodep, true);
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
         }
     }
     void visit(AstScope* nodep) override {
         if (!nodep->user1SetOnce()) {
-            if (nodep->aboveScopep()) iterate(nodep->aboveScopep());
-            if (nodep->aboveCellp()) iterate(nodep->aboveCellp());
+            if (nodep->aboveScopep()) iterateConst(nodep->aboveScopep());
+            if (nodep->aboveCellp()) iterateConst(nodep->aboveCellp());
             // Always recompute name (as many levels above scope may have changed)
             // Same formula as V3Scope
             nodep->name(nodep->isTop()         ? "TOP"
@@ -123,16 +123,16 @@ private:
                             ? ("TOP." + m_modp->name())
                             : (nodep->aboveScopep()->name() + "." + nodep->aboveCellp()->name()));
             nodep->editCountInc();
-            iterateChildren(nodep);
+            iterateChildrenConst(nodep);
         }
     }
 
     //--------------------
-    void visit(AstNode* nodep) override { iterateChildren(nodep); }
+    void visit(AstNode* nodep) override { iterateChildrenConst(nodep); }
 
 public:
     // CONSTRUCTORS
-    explicit NameVisitor(AstNetlist* nodep) { iterate(nodep); }
+    explicit NameVisitor(AstNetlist* nodep) { iterateConst(nodep); }
     ~NameVisitor() override = default;
 };
 
diff --git a/src/V3SplitAs.cpp b/src/V3SplitAs.cpp
index 26898c676..5a386996e 100644
--- a/src/V3SplitAs.cpp
+++ b/src/V3SplitAs.cpp
@@ -32,7 +32,7 @@ VL_DEFINE_DEBUG_FUNCTIONS;
 //######################################################################
 // Find all split variables in a block
 
-class SplitAsFindVisitor final : public VNVisitor {
+class SplitAsFindVisitor final : public VNVisitorConst {
 private:
     // STATE - across all visitors
     AstVarScope* m_splitVscp = nullptr;  // Variable we want to split
@@ -49,11 +49,11 @@ private:
         // This will break if the m_splitVscp is a "ref" argument to the function,
         // but little we can do.
     }
-    void visit(AstNode* nodep) override { iterateChildren(nodep); }
+    void visit(AstNode* nodep) override { iterateChildrenConst(nodep); }
 
 public:
     // CONSTRUCTORS
-    explicit SplitAsFindVisitor(AstAlways* nodep) { iterate(nodep); }
+    explicit SplitAsFindVisitor(AstAlways* nodep) { iterateConst(nodep); }
     ~SplitAsFindVisitor() override = default;
     // METHODS
     AstVarScope* splitVscp() const { return m_splitVscp; }
diff --git a/src/V3Subst.cpp b/src/V3Subst.cpp
index 8935d3732..fc86d2492 100644
--- a/src/V3Subst.cpp
+++ b/src/V3Subst.cpp
@@ -165,7 +165,7 @@ public:
 // See if any variables have changed value since we determined subst value,
 // as a visitor of each AstNode
 
-class SubstUseVisitor final : public VNVisitor {
+class SubstUseVisitor final : public VNVisitorConst {
 private:
     // NODE STATE
     // See SubstVisitor
@@ -197,7 +197,7 @@ private:
     void visit(AstConst*) override {}  // Accelerate
     void visit(AstNode* nodep) override {
         if (!nodep->isPure()) m_ok = false;
-        iterateChildren(nodep);
+        iterateChildrenConst(nodep);
     }
 
 public:
@@ -205,7 +205,7 @@ public:
     SubstUseVisitor(AstNode* nodep, int origStep)
         : m_origStep{origStep} {
         UINFO(9, "        SubstUseVisitor " << origStep << " " << nodep << endl);
-        iterate(nodep);
+        iterateConst(nodep);
     }
     ~SubstUseVisitor() override = default;
     // METHODS