Use AstNode::addHereThisAsNext in a few places

src/V3Depth.cpp

@@ -68,10 +68,7 @@ private:
         // Put assignment before the referencing statement
         AstAssign* const assp = new AstAssign{
             nodep->fileline(), new AstVarRef{nodep->fileline(), varp, VAccess::WRITE}, nodep};
-        VNRelinker linker2;
-        m_stmtp->unlinkFrBack(&linker2);
-        assp->addNext(m_stmtp);
-        linker2.relink(assp);
+        m_stmtp->addHereThisAsNext(assp);
     }
 
     // VISITORS

src/V3Expand.cpp

@@ -82,10 +82,7 @@ private:
 
     static void insertBefore(AstNode* placep, AstNode* newp) {
         newp->user1(1);  // Already processed, don't need to re-iterate
-        VNRelinker linker;
-        placep->unlinkFrBack(&linker);
-        newp->addNext(placep);
-        linker.relink(newp);
+        placep->addHereThisAsNext(newp);
     }
     static void replaceWithDelete(AstNode* nodep, AstNode* newp) {
         newp->user1(1);  // Already processed, don't need to re-iterate

src/V3Premit.cpp

@@ -109,10 +109,7 @@ private:
         } else if (m_inTracep) {
             m_inTracep->addPrecondsp(newp);
         } else if (m_stmtp) {
-            VNRelinker linker;
-            m_stmtp->unlinkFrBack(&linker);
-            newp->addNext(m_stmtp);
-            linker.relink(newp);
+            m_stmtp->addHereThisAsNext(newp);
         } else {
             newp->v3fatalSrc("No statement insertion point.");
         }