diff --git a/include/tvm/ir_functor_ext.h b/include/tvm/ir_functor_ext.h
index 9b2632f87b3c..f7a0f2a3b61c 100644
--- a/include/tvm/ir_functor_ext.h
+++ b/include/tvm/ir_functor_ext.h
@@ -287,6 +287,265 @@ class StmtFunctor<R(const Stmt& n, Args... args)> {
 #undef EXPR_FUNCTOR_DEFAULT
 #undef STMT_FUNCTOR_DEFAULT
 
+/*!
+ * \brief ExprVisitor
+ */
+class TVM_DLL ExprVisitor :
+      public ExprFunctor<void(const Expr&)> {
+ public:
+  using ExprFunctor::operator();
+
+ protected:
+  using ExprFunctor::VisitExpr;
+  // list of functions to override.
+  void VisitExpr_(const Variable* op) override;
+  void VisitExpr_(const Load* op) override;
+  void VisitExpr_(const Let* op) override;
+  void VisitExpr_(const Call* op) override;
+  void VisitExpr_(const Add* op) override;
+  void VisitExpr_(const Sub* op) override;
+  void VisitExpr_(const Mul* op) override;
+  void VisitExpr_(const Div* op) override;
+  void VisitExpr_(const Mod* op) override;
+  void VisitExpr_(const FloorDiv* op) override;
+  void VisitExpr_(const FloorMod* op) override;
+  void VisitExpr_(const Min* op) override;
+  void VisitExpr_(const Max* op) override;
+  void VisitExpr_(const EQ* op) override;
+  void VisitExpr_(const NE* op) override;
+  void VisitExpr_(const LT* op) override;
+  void VisitExpr_(const LE* op) override;
+  void VisitExpr_(const GT* op) override;
+  void VisitExpr_(const GE* op) override;
+  void VisitExpr_(const And* op) override;
+  void VisitExpr_(const Or* op) override;
+  void VisitExpr_(const Reduce* op) override;
+  void VisitExpr_(const Cast* op) override;
+  void VisitExpr_(const Not* op) override;
+  void VisitExpr_(const Select* op) override;
+  void VisitExpr_(const Ramp* op) override;
+  void VisitExpr_(const Broadcast* op) override;
+  void VisitExpr_(const Shuffle* op) override;
+  void VisitExpr_(const IntImm* op) override;
+  void VisitExpr_(const UIntImm* op) override;
+  void VisitExpr_(const FloatImm* op) override;
+  void VisitExpr_(const StringImm* op) override;
+};
+
+/*!
+ * \brief ExprMutator that mutates expressions.
+ */
+class TVM_DLL ExprMutator :
+      protected ExprFunctor<Expr(const Expr&)> {
+ public:
+  using ExprFunctor::operator();
+
+ protected:
+  using ExprFunctor::VisitExpr;
+  // list of functions to override.
+  Expr VisitExpr_(const Variable* op) override;
+  Expr VisitExpr_(const Load* op) override;
+  Expr VisitExpr_(const Let* op) override;
+  Expr VisitExpr_(const Call* op) override;
+  Expr VisitExpr_(const Add* op) override;
+  Expr VisitExpr_(const Sub* op) override;
+  Expr VisitExpr_(const Mul* op) override;
+  Expr VisitExpr_(const Div* op) override;
+  Expr VisitExpr_(const Mod* op) override;
+  Expr VisitExpr_(const FloorDiv* op) override;
+  Expr VisitExpr_(const FloorMod* op) override;
+  Expr VisitExpr_(const Min* op) override;
+  Expr VisitExpr_(const Max* op) override;
+  Expr VisitExpr_(const EQ* op) override;
+  Expr VisitExpr_(const NE* op) override;
+  Expr VisitExpr_(const LT* op) override;
+  Expr VisitExpr_(const LE* op) override;
+  Expr VisitExpr_(const GT* op) override;
+  Expr VisitExpr_(const GE* op) override;
+  Expr VisitExpr_(const And* op) override;
+  Expr VisitExpr_(const Or* op) override;
+  Expr VisitExpr_(const Reduce* op) override;
+  Expr VisitExpr_(const Cast* op) override;
+  Expr VisitExpr_(const Not* op) override;
+  Expr VisitExpr_(const Select* op) override;
+  Expr VisitExpr_(const Ramp* op) override;
+  Expr VisitExpr_(const Broadcast* op) override;
+  Expr VisitExpr_(const Shuffle* op) override;
+  Expr VisitExpr_(const IntImm* op) override;
+  Expr VisitExpr_(const UIntImm* op) override;
+  Expr VisitExpr_(const FloatImm* op) override;
+  Expr VisitExpr_(const StringImm* op) override;
+};
+
+/*!
+ * \brief StmtVisitor.
+ */
+class TVM_DLL StmtVisitor :
+      protected StmtFunctor<void(const Stmt&)> {
+ public:
+  using StmtFunctor::operator();
+
+ protected:
+  using StmtFunctor::VisitStmt;
+  /*!
+   * \brief Visitor to Exprs, can be overriden
+   *        to do recursive changes to Exprs.
+   * \note A common pattern is to call ExprVisitor here,
+   *       or have a class sub-class both StmtVisitor and ExprVisitor
+   *       and redirect Visit to ExprMutator::VisitExpr(Expr)
+   */
+  virtual void VisitExpr(const Expr& e) {}
+  // statement visitor
+  void VisitStmt_(const AttrStmt* op) override;
+  void VisitStmt_(const IfThenElse* op) override;
+  void VisitStmt_(const LetStmt* op) override;
+  void VisitStmt_(const For* op) override;
+  void VisitStmt_(const Allocate* op) override;
+  void VisitStmt_(const Store* op) override;
+  void VisitStmt_(const Free* op) override;
+  void VisitStmt_(const AssertStmt* op) override;
+  void VisitStmt_(const ProducerConsumer* op) override;
+  void VisitStmt_(const Provide* op) override;
+  void VisitStmt_(const Realize* op) override;
+  void VisitStmt_(const Prefetch* op) override;
+  void VisitStmt_(const Block* op) override;
+  void VisitStmt_(const Evaluate* op) override;
+};
+
+/*!
+ * \brief StmtMutator that mutates the statements.
+ */
+class TVM_DLL StmtMutator :
+      protected StmtFunctor<Stmt(const Stmt&)> {
+ public:
+  /*!
+   * \brief Mutate stmt.
+   * \param stmt The input statement to be mutated.
+   * \return The result of the call
+   * \note It is important that stmt is passed by value.
+   *       so copy on write can be triggered correctly.
+   *       do mutator(std::move(stmt)) or when copy elison is triggered.
+   */
+  Stmt operator()(Stmt stmt) {
+    allow_copy_on_write_ = true;
+    return VisitStmt(stmt);
+  }
+
+ protected:
+  // We perform copy on write optimizations on the StmtMutator
+  // so that an unique copy of parent can be mutated inplace
+  // when some of its children changed.
+  // We only do such optimization for Stmt nests(instead of Exprs) for now
+  // as Stmt's parent state is more likely remain unchanged when one of
+  // its child block changes.
+  /*!
+   * \brief Internal state to indicate whether copy on write is enabled.
+   *  COW is enabled iff all the parents of the node are unique.
+   */
+  bool allow_copy_on_write_{false};
+  /*!
+   * \brief Perform copy on write on node.
+   *
+   *  If CopyOnWrite is allowed, directly return
+   *  a strong reference to the node container.
+   *  Otherwise, return a copy of the node.
+   *
+   * \return The result object pointer.
+   */
+  template<typename TNode>
+  ObjectPtr<TNode> CopyOnWrite(const TNode* node) {
+    if (allow_copy_on_write_) {
+      // return the old node.
+      return runtime::GetObjectPtr<TNode>(const_cast<TNode*>(node));
+    } else {
+      // Make a new copy of the node.
+      // need to rely on the default copy constructor
+      return runtime::make_object<TNode>(*node);
+    }
+  }
+  /*!
+   * \brief Internal mutator that everyone calls.
+   * \note To override mutate's behavior, override VisitExpr instead.
+   * \param stmt The input stmt.
+   * \return The mutated results.
+   */
+  Stmt VisitStmt(const Stmt& stmt) override {
+    if (allow_copy_on_write_ && !stmt.unique()) {
+      allow_copy_on_write_ = false;
+      Stmt ret = StmtFunctor::VisitStmt(stmt);
+      allow_copy_on_write_ = true;
+      return ret;
+    } else {
+      return StmtFunctor::VisitStmt(stmt);
+    }
+  }
+  /*!
+   * \brief Visitor to Exprs, can be overriden
+   *        to do recursive changes to Exprs.
+   * \note A common pattern is to call ExprMutator here,
+   *       or have a class sub-class both StmtMutator and ExprMutator
+   *       and redirect Mutate to ExprMutator::Mutate(Expr)
+   */
+  virtual Expr VisitExpr(const Expr& e) {
+    return e;
+  }
+  // statement visitor
+  Stmt VisitStmt_(const AttrStmt* op) override;
+  Stmt VisitStmt_(const IfThenElse* op) override;
+  Stmt VisitStmt_(const LetStmt* op) override;
+  Stmt VisitStmt_(const For* op) override;
+  Stmt VisitStmt_(const Allocate* op) override;
+  Stmt VisitStmt_(const Store* op) override;
+  Stmt VisitStmt_(const Free* op) override;
+  Stmt VisitStmt_(const AssertStmt* op) override;
+  Stmt VisitStmt_(const ProducerConsumer* op) override;
+  Stmt VisitStmt_(const Provide* op) override;
+  Stmt VisitStmt_(const Realize* op) override;
+  Stmt VisitStmt_(const Prefetch* op) override;
+  Stmt VisitStmt_(const Block* op) override;
+  Stmt VisitStmt_(const Evaluate* op) override;
+  // internal helper.
+  class Internal;
+};
+
+/*!
+ * \brief Visitor that recursively visit stmts and exprs on them.
+ */
+class StmtExprVisitor :
+      public StmtVisitor,
+      public ExprVisitor {
+ public:
+  using StmtVisitor::operator();
+  using ExprVisitor::operator();
+
+ protected:
+  using StmtVisitor::VisitStmt;
+  using ExprVisitor::VisitExpr;
+
+  void VisitExpr(const Expr& e) override {
+    return ExprVisitor::VisitExpr(e);
+  }
+};
+
+/*!
+ * \brief Mutator that recursively mutates stmts and exprs on them.
+ */
+class StmtExprMutator :
+      public StmtMutator,
+      public ExprMutator {
+ public:
+  using StmtMutator::operator();
+  using ExprMutator::operator();
+
+ protected:
+  using StmtMutator::VisitExpr;
+  using ExprMutator::VisitExpr;
+
+  Expr VisitExpr(const Expr& e) override {
+    return ExprMutator::VisitExpr(e);
+  }
+};
+
 }  // namespace ir
 }  // namespace tvm
 #endif  // TVM_IR_FUNCTOR_EXT_H_
diff --git a/include/tvm/ir_mutator.h b/include/tvm/ir_mutator.h
index 5460ae0f4ba9..702cea3ce8fd 100644
--- a/include/tvm/ir_mutator.h
+++ b/include/tvm/ir_mutator.h
@@ -123,6 +123,7 @@ class TVM_DLL IRMutator {
   virtual Expr Mutate_(const Shuffle* op, const Expr& e);
 };
 
+
 /*!
  * \brief recursively visit the ir in post DFS order node, and transform it
  *
@@ -138,7 +139,7 @@ class TVM_DLL IRMutator {
  *          If it is not empty, preorder/postorder will only be called
  *          when the IRNode's type key is in the list.
  */
-Stmt IRTransform(const Stmt& node,
+Stmt IRTransform(Stmt node,
                  const runtime::PackedFunc& preorder,
                  const runtime::PackedFunc& postorder,
                  const Array<Expr>& only_enable = {});
diff --git a/include/tvm/node/container.h b/include/tvm/node/container.h
index d20fb288039c..0d5ab376d50a 100644
--- a/include/tvm/node/container.h
+++ b/include/tvm/node/container.h
@@ -284,6 +284,48 @@ class Array : public ObjectRef {
   inline bool empty() const {
     return size() == 0;
   }
+  /*!
+   * \brief Helper function to apply fmutate to mutate an array.
+   * \param fmutate The transformation function T -> T.
+   * \tparam F the type of the mutation function.
+   * \note This function performs copy on write optimization.
+   */
+  template<typename F>
+  inline void MutateByApply(F fmutate) {
+    ArrayNode* ptr = static_cast<ArrayNode*>(data_.get());
+    if (ptr == nullptr) return;
+    if (data_.unique()) {
+      // Copy on write optimization.
+      // Perform inplace update because this is an unique copy.
+      for (size_t i = 0; i < ptr->data.size(); ++i) {
+        // It is important to use move here
+        // to make prevent the element's ref count from increasing
+        // so fmutate itself can perform copy-on-write optimization
+        T old_elem = DowncastNoCheck<T>(std::move(ptr->data[i]));
+        T new_elem = fmutate(std::move(old_elem));
+        ptr->data[i] = std::move(new_elem);
+      }
+    } else {
+      // lazily trigger copy if there is element change.
+      ObjectPtr<ArrayNode> copy;
+      for (size_t i = 0; i < ptr->data.size(); ++i) {
+        T old_elem = DowncastNoCheck<T>(ptr->data[i]);
+        T new_elem = fmutate(old_elem);
+        if (!new_elem.same_as(ptr->data[i])) {
+          // copy the old array
+          if (copy == nullptr) {
+            copy = runtime::make_object<ArrayNode>(*ptr);
+          }
+          copy->data[i] = std::move(new_elem);
+        }
+      }
+      // replace the data with the new copy.
+      if (copy != nullptr) {
+        data_ = std::move(copy);
+      }
+    }
+  }
+
   /*! \brief specify container node */
   using ContainerType = ArrayNode;
 
diff --git a/src/pass/ir_functor.cc b/src/pass/ir_functor.cc
new file mode 100644
index 000000000000..079da756ce92
--- /dev/null
+++ b/src/pass/ir_functor.cc
@@ -0,0 +1,717 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+/*!
+ * \file ir_functor.cc
+ */
+#include <tvm/ir_functor_ext.h>
+#include <tvm/packed_func_ext.h>
+#include <tvm/ir_visitor.h>
+
+namespace tvm {
+namespace ir {
+
+// visitor to implement apply
+class IRApplyVisit :
+      public StmtExprVisitor {
+ public:
+  explicit IRApplyVisit(std::function<void(const ObjectRef&)> f) : f_(f) {}
+
+  void VisitExpr(const Expr& node) final {
+    if (visited_.count(node.get()) != 0) return;
+    visited_.insert(node.get());
+    ExprVisitor::VisitExpr(node);
+    f_(node);
+  }
+
+  void VisitStmt(const Stmt& node) final {
+    if (visited_.count(node.get()) != 0) return;
+    visited_.insert(node.get());
+    StmtVisitor::VisitStmt(node);
+    f_(node);
+  }
+
+ private:
+  std::function<void(const ObjectRef&)> f_;
+  std::unordered_set<const Object*> visited_;
+};
+
+void PostOrderVisit(const ObjectRef& node,
+                    std::function<void(const ObjectRef&)> fvisit) {
+  if (node.as<StmtNode>()) {
+    IRApplyVisit visitor(fvisit);
+    visitor(Downcast<Stmt>(node));
+  } else {
+    IRApplyVisit visitor(fvisit);
+    visitor(Downcast<Expr>(node));
+  }
+}
+
+class IRTransformer final :
+      public StmtExprMutator {
+ public:
+  IRTransformer(const runtime::PackedFunc& f_preorder,
+                const runtime::PackedFunc& f_postorder,
+                const std::unordered_set<uint32_t>& only_enable)
+      : f_preorder_(f_preorder),
+        f_postorder_(f_postorder),
+        only_enable_(only_enable) {
+  }
+  Stmt VisitStmt(const Stmt& stmt) final {
+    return MutateInternal<Stmt>(stmt, [this](const Stmt& s) {
+      return StmtMutator::VisitStmt(s);
+    });
+  }
+  Expr VisitExpr(const Expr& expr) final {
+    return MutateInternal<Expr>(expr, [this](const Expr& e) {
+      return ExprMutator::VisitExpr(e);
+    });
+  }
+
+ private:
+  template <typename T, typename F>
+  T MutateInternal(const T& node, F fmutate) {
+    if (only_enable_.size() &&
+        !only_enable_.count(node->type_index())) {
+      return fmutate(node);
+    }
+    if (f_preorder_ != nullptr) {
+      T pre = f_preorder_(node);
+      if (pre.defined()) return pre;
+    }
+    T new_node = fmutate(node);
+    if (f_postorder_ != nullptr) {
+      T post = f_postorder_(new_node);
+      if (post.defined()) return post;
+    }
+    return new_node;
+  }
+  // The functions
+  const runtime::PackedFunc& f_preorder_;
+  const runtime::PackedFunc& f_postorder_;
+  // type indices enabled.
+  const std::unordered_set<uint32_t>& only_enable_;
+};
+
+Stmt IRTransform(Stmt ir_node,
+                 const runtime::PackedFunc& f_preorder,
+                 const runtime::PackedFunc& f_postorder,
+                 const Array<Expr>& only_enable) {
+  std::unordered_set<uint32_t> only_type_index;
+  for (Expr s : only_enable) {
+    only_type_index.insert(Object::TypeKey2Index(s.as<StringImm>()->value.c_str()));
+  }
+  IRTransformer transform(f_preorder, f_postorder, only_type_index);
+  return transform(std::move(ir_node));
+}
+
+// Implementation of Visitors
+template<typename T, typename F>
+inline void VisitArray(const Array<T>& arr, F fvisit) {
+  for (size_t i = 0; i < arr.size(); i++) {
+    fvisit(arr[i]);
+  }
+}
+
+void StmtVisitor::VisitStmt_(const LetStmt* op) {
+  this->VisitExpr(op->value);
+  this->VisitStmt(op->body);
+}
+
+void StmtVisitor::VisitStmt_(const AttrStmt* op) {
+  this->VisitExpr(op->value);
+  this->VisitStmt(op->body);
+}
+
+void StmtVisitor::VisitStmt_(const For* op) {
+  this->VisitExpr(op->min);
+  this->VisitExpr(op->extent);
+  this->VisitStmt(op->body);
+}
+
+void StmtVisitor::VisitStmt_(const Allocate* op) {
+  VisitArray(op->extents, [this](const Expr& e) { this->VisitExpr(e); });
+  this->VisitStmt(op->body);
+  this->VisitExpr(op->condition);
+  if (op->new_expr.defined()) {
+    this->VisitExpr(op->new_expr);
+  }
+}
+
+void StmtVisitor::VisitStmt_(const Store* op) {
+  this->VisitExpr(op->value);
+  this->VisitExpr(op->index);
+  this->VisitExpr(op->predicate);
+}
+
+void StmtVisitor::VisitStmt_(const IfThenElse* op) {
+  this->VisitExpr(op->condition);
+  this->VisitStmt(op->then_case);
+  if (op->else_case.defined()) {
+    this->VisitStmt(op->else_case);
+  }
+}
+
+void StmtVisitor::VisitStmt_(const Free* op) {}
+
+void StmtVisitor::VisitStmt_(const AssertStmt* op) {
+  this->VisitExpr(op->condition);
+  this->VisitExpr(op->message);
+  this->VisitStmt(op->body);
+}
+
+void StmtVisitor::VisitStmt_(const ProducerConsumer* op) {
+  this->VisitStmt(op->body);
+}
+
+void StmtVisitor::VisitStmt_(const Provide* op) {
+  VisitArray(op->args, [this](const Expr& e) { this->VisitExpr(e); });
+  this->VisitExpr(op->value);
+}
+
+void StmtVisitor::VisitStmt_(const Realize* op) {
+  VisitArray(op->bounds, [this](const Range& r) {
+      this->VisitExpr(r->min);
+      this->VisitExpr(r->extent);
+    });
+  this->VisitStmt(op->body);
+  this->VisitExpr(op->condition);
+}
+
+void StmtVisitor::VisitStmt_(const Prefetch* op) {
+  VisitArray(op->bounds, [this](const Range& r) {
+      this->VisitExpr(r->min);
+      this->VisitExpr(r->extent);
+    });
+}
+
+void StmtVisitor::VisitStmt_(const Block* op) {
+  this->VisitStmt(op->first);
+  this->VisitStmt(op->rest);
+}
+
+void StmtVisitor::VisitStmt_(const Evaluate* op) {
+  this->VisitExpr(op->value);
+}
+
+void ExprVisitor::VisitExpr_(const Variable* op) {}
+
+void ExprVisitor::VisitExpr_(const Load* op) {
+  this->VisitExpr(op->index);
+  this->VisitExpr(op->predicate);
+}
+
+void ExprVisitor::VisitExpr_(const Let* op) {
+  this->VisitExpr(op->value);
+  this->VisitExpr(op->body);
+}
+
+void ExprVisitor::VisitExpr_(const Call* op) {
+  VisitArray(op->args, [this](const Expr& e) { this->VisitExpr(e); });
+}
+
+#define DEFINE_BINOP_VISIT_(OP)                           \
+  void ExprVisitor::VisitExpr_(const OP* op) {            \
+    this->VisitExpr(op->a);                               \
+    this->VisitExpr(op->b);                               \
+  }
+
+DEFINE_BINOP_VISIT_(Add);
+DEFINE_BINOP_VISIT_(Sub);
+DEFINE_BINOP_VISIT_(Mul);
+DEFINE_BINOP_VISIT_(Div);
+DEFINE_BINOP_VISIT_(Mod);
+DEFINE_BINOP_VISIT_(FloorDiv);
+DEFINE_BINOP_VISIT_(FloorMod);
+DEFINE_BINOP_VISIT_(Min);
+DEFINE_BINOP_VISIT_(Max);
+DEFINE_BINOP_VISIT_(EQ);
+DEFINE_BINOP_VISIT_(NE);
+DEFINE_BINOP_VISIT_(LT);
+DEFINE_BINOP_VISIT_(LE);
+DEFINE_BINOP_VISIT_(GT);
+DEFINE_BINOP_VISIT_(GE);
+DEFINE_BINOP_VISIT_(And);
+DEFINE_BINOP_VISIT_(Or);
+
+void ExprVisitor::VisitExpr_(const IntImm* op) {}
+void ExprVisitor::VisitExpr_(const UIntImm* op) {}
+void ExprVisitor::VisitExpr_(const FloatImm* op) {}
+void ExprVisitor::VisitExpr_(const StringImm* op) {}
+
+void ExprVisitor::VisitExpr_(const Reduce* op) {
+  VisitArray(op->axis, [this](const IterVar& r) {
+      this->VisitExpr(r->dom->min);
+      this->VisitExpr(r->dom->extent);
+    });
+  VisitArray(op->source, [this](const Expr& e) { this->VisitExpr(e); });
+  this->VisitExpr(op->condition);
+}
+
+void ExprVisitor::VisitExpr_(const Cast* op) {
+  this->VisitExpr(op->value);
+}
+
+void ExprVisitor::VisitExpr_(const Not* op) {
+  this->VisitExpr(op->a);
+}
+
+void ExprVisitor::VisitExpr_(const Select* op) {
+  this->VisitExpr(op->condition);
+  this->VisitExpr(op->true_value);
+  this->VisitExpr(op->false_value);
+}
+
+void ExprVisitor::VisitExpr_(const Ramp* op) {
+  this->VisitExpr(op->base);
+  this->VisitExpr(op->stride);
+}
+
+void ExprVisitor::VisitExpr_(const Shuffle* op) {
+  VisitArray(op->indices, [this](const Expr& e) { this->VisitExpr(e); });
+  VisitArray(op->vectors, [this](const Expr& e) { this->VisitExpr(e); });
+}
+
+void ExprVisitor::VisitExpr_(const Broadcast* op) {
+  this->VisitExpr(op->value);
+}
+
+// Implementation of mutators
+template<typename T, typename F>
+inline Array<T> MutateArray(const Array<T>& arr,
+                            F fmutate,
+                            bool allow_copy_on_write = false) {
+  if (allow_copy_on_write) {
+    // if we allow copy on write, we can directly
+    // call the inplace mutate function.
+    const_cast<Array<T>&>(arr).MutateByApply(fmutate);
+    return arr;
+  } else {
+    Array<T> copy = arr;
+    copy.MutateByApply(fmutate);
+    return copy;
+  }
+}
+
+class StmtMutator::Internal {
+ public:
+  static Array<Expr> Mutate(StmtMutator* self, const Array<Expr>& arr) {
+    auto fmutate = [self](const Expr& e) { return self->VisitExpr(e); };
+    return MutateArray(arr, fmutate, self->allow_copy_on_write_);
+  }
+
+  static Array<Stmt> Mutate(StmtMutator* self, const Array<Stmt>& arr) {
+    auto fmutate = [self](const Stmt& s) { return self->VisitStmt(s); };
+    return MutateArray(arr, fmutate, self->allow_copy_on_write_);
+  }
+
+  static Array<Range> Mutate(StmtMutator* self, const Array<Range>& arr) {
+    auto fmutate = [self](const Range& r) {
+      Expr min = self->VisitExpr(r->min);
+      Expr extent = self->VisitExpr(r->extent);
+      if (min.same_as(r->min) && extent.same_as(r->extent)) {
+        return r;
+      } else {
+        return Range::make_by_min_extent(min, extent);
+      }
+    };
+    return MutateArray(arr, fmutate, self->allow_copy_on_write_);
+  }
+};
+
+Stmt StmtMutator::VisitStmt_(const AttrStmt* op) {
+  Expr value = this->VisitExpr(op->value);
+  Stmt body = this->VisitStmt(op->body);
+  if (value.same_as(op->value) &&
+      body.same_as(op->body)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->value = std::move(value);
+    n->body = std::move(body);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const LetStmt* op) {
+  Expr value = this->VisitExpr(op->value);
+  Stmt body = this->VisitStmt(op->body);
+  if (value.same_as(op->value) &&
+      body.same_as(op->body)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->value = std::move(value);
+    n->body = std::move(body);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const For* op) {
+  Expr min = this->VisitExpr(op->min);
+  Expr extent = this->VisitExpr(op->extent);
+  Stmt body = this->VisitStmt(op->body);
+  if (min.same_as(op->min) &&
+      extent.same_as(op->extent) &&
+      body.same_as(op->body)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->min = std::move(min);
+    n->extent = std::move(extent);
+    n->body = std::move(body);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Allocate* op) {
+  Array<Expr> extents = Internal::Mutate(this, op->extents);
+  Stmt body = this->VisitStmt(op->body);
+  Expr condition = this->VisitExpr(op->condition);
+  Expr new_expr;
+  if (op->new_expr.defined()) {
+    new_expr = this->VisitExpr(op->new_expr);
+  }
+  if (extents.same_as(op->extents) &&
+      body.same_as(op->body) &&
+      condition.same_as(op->condition) &&
+      new_expr.same_as(op->new_expr)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->extents = std::move(extents);
+    n->body = std::move(body);
+    n->condition = std::move(condition);
+    n->new_expr = std::move(new_expr);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const IfThenElse* op) {
+  Expr condition = this->VisitExpr(op->condition);
+  Stmt then_case = this->VisitStmt(op->then_case);
+  Stmt else_case;
+  if (op->else_case.defined()) {
+    else_case = this->VisitStmt(op->else_case);
+  }
+  if (condition.same_as(op->condition) &&
+      then_case.same_as(op->then_case) &&
+      else_case.same_as(op->else_case)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->condition = std::move(condition);
+    n->then_case = std::move(then_case);
+    n->else_case = std::move(then_case);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Store* op) {
+  Expr value = this->VisitExpr(op->value);
+  Expr index = this->VisitExpr(op->index);
+  Expr predicate = this->VisitExpr(op->predicate);
+  if (value.same_as(op->value) &&
+      index.same_as(op->index) &&
+      predicate.same_as(op->predicate)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->value = std::move(value);
+    n->index = std::move(index);
+    n->predicate = std::move(predicate);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Provide* op) {
+  Array<Expr> args = Internal::Mutate(this, op->args);
+  Expr value = this->VisitExpr(op->value);
+  if (args.same_as(op->args) &&
+      value.same_as(op->value)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->args = std::move(args);
+    n->value = std::move(value);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Realize* op) {
+  Region bounds = Internal::Mutate(this, op->bounds);
+  Stmt body = this->VisitStmt(op->body);
+  Expr condition = this->VisitExpr(op->condition);
+  if (bounds.same_as(op->bounds) &&
+      body.same_as(op->body) &&
+      condition.same_as(op->condition)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->bounds = std::move(bounds);
+    n->body = std::move(body);
+    n->condition = std::move(condition);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Prefetch* op) {
+  Region bounds = Internal::Mutate(this, op->bounds);
+  if (bounds.same_as(op->bounds)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->bounds = std::move(bounds);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Block* op) {
+  Stmt first = this->VisitStmt(op->first);
+  Stmt rest = this->VisitStmt(op->rest);
+  if (first.same_as(op->first) &&
+      rest.same_as(op->rest)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->first = std::move(first);
+    n->rest = std::move(rest);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const AssertStmt* op) {
+  Expr condition = this->VisitExpr(op->condition);
+  Expr message = this->VisitExpr(op->message);
+  Stmt body = this->VisitStmt(op->body);
+
+  if (condition.same_as(op->condition) &&
+      message.same_as(op->message) &&
+      body.same_as(op->body)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->condition = std::move(condition);
+    n->message = std::move(message);
+    n->body = std::move(body);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const ProducerConsumer* op) {
+  Stmt body = this->VisitStmt(op->body);
+  if (body.same_as(op->body)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->body = std::move(body);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Evaluate* op) {
+  Expr value = this->VisitExpr(op->value);
+  if (value.same_as(op->value)) {
+    return GetRef<Stmt>(op);
+  } else {
+    auto n = CopyOnWrite(op);
+    n->value = std::move(value);
+    return Stmt(n);
+  }
+}
+
+Stmt StmtMutator::VisitStmt_(const Free* op) {
+  return GetRef<Stmt>(op);
+}
+
+
+Expr ExprMutator::VisitExpr_(const Variable* op) {
+  return GetRef<Expr>(op);
+}
+
+Expr ExprMutator::VisitExpr_(const Load* op) {
+  Expr index = this->VisitExpr(op->index);
+  Expr predicate = this->VisitExpr(op->predicate);
+  if (index.same_as(op->index) && predicate.same_as(op->predicate)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Load::make(op->dtype, op->buffer_var, index, predicate);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Let* op) {
+  Expr value = this->VisitExpr(op->value);
+  Expr body = this->VisitExpr(op->body);
+  if (value.same_as(op->value) &&
+      body.same_as(op->body)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Let::make(op->var, value, body);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Call* op) {
+  auto fmutate = [this](const Expr& e) { return this->VisitExpr(e); };
+  Array<Expr> args = MutateArray(op->args, fmutate);
+
+  if (args.same_as(op->args)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Call::make(op->dtype,
+                      op->name,
+                      args,
+                      op->call_type,
+                      op->func,
+                      op->value_index);
+  }
+}
+
+#define DEFINE_OP_RETURN_SELF_EXPR_MUTATE_(OP)                    \
+  Expr ExprMutator::VisitExpr_(const OP *op) {                    \
+    return GetRef<Expr>(op);                                      \
+  }
+
+DEFINE_OP_RETURN_SELF_EXPR_MUTATE_(IntImm)
+DEFINE_OP_RETURN_SELF_EXPR_MUTATE_(UIntImm)
+DEFINE_OP_RETURN_SELF_EXPR_MUTATE_(FloatImm)
+DEFINE_OP_RETURN_SELF_EXPR_MUTATE_(StringImm)
+
+#define DEFINE_BIOP_EXPR_MUTATE_(OP)                                    \
+  Expr ExprMutator::VisitExpr_(const OP* op) {                          \
+    Expr a = this->VisitExpr(op->a);                                    \
+    Expr b = this->VisitExpr(op->b);                                    \
+    if (a.same_as(op->a) &&                                             \
+        b.same_as(op->b)) {                                             \
+      return GetRef<Expr>(op);                                          \
+    } else {                                                            \
+      return OP::make(a, b);                                            \
+    }                                                                   \
+  }
+
+DEFINE_BIOP_EXPR_MUTATE_(Add);
+DEFINE_BIOP_EXPR_MUTATE_(Sub);
+DEFINE_BIOP_EXPR_MUTATE_(Mul);
+DEFINE_BIOP_EXPR_MUTATE_(Div);
+DEFINE_BIOP_EXPR_MUTATE_(Mod);
+DEFINE_BIOP_EXPR_MUTATE_(FloorDiv);
+DEFINE_BIOP_EXPR_MUTATE_(FloorMod);
+DEFINE_BIOP_EXPR_MUTATE_(Min);
+DEFINE_BIOP_EXPR_MUTATE_(Max);
+DEFINE_BIOP_EXPR_MUTATE_(EQ);
+DEFINE_BIOP_EXPR_MUTATE_(NE);
+DEFINE_BIOP_EXPR_MUTATE_(LT);
+DEFINE_BIOP_EXPR_MUTATE_(LE);
+DEFINE_BIOP_EXPR_MUTATE_(GT);
+DEFINE_BIOP_EXPR_MUTATE_(GE);
+DEFINE_BIOP_EXPR_MUTATE_(And);
+DEFINE_BIOP_EXPR_MUTATE_(Or);
+
+Expr ExprMutator::VisitExpr_(const Reduce* op) {
+  auto fitervar =  [this](const IterVar& v) {
+    Range r = v->dom;
+    Expr min = this->VisitExpr(r->min);
+    Expr extent = this->VisitExpr(r->extent);
+    if (min.same_as(r->min) &&
+        extent.same_as(r->extent)) {
+      return v;
+    } else {
+      return IterVarNode::make(
+          Range::make_by_min_extent(min, extent),
+          v->var, v->iter_type, v->thread_tag);
+    }
+  };
+  Array<IterVar> axis = MutateArray(op->axis, fitervar);
+
+  auto fexpr = [this](const Expr& e) { return this->VisitExpr(e); };
+  Array<Expr> source = MutateArray(op->source, fexpr);
+
+  Expr condition = this->VisitExpr(op->condition);
+
+  if (axis.same_as(op->axis) &&
+      source.same_as(op->source) &&
+      condition.same_as(op->condition)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Reduce::make(
+      op->combiner, source, axis, condition, op->value_index);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Cast* op) {
+  Expr value = this->VisitExpr(op->value);
+  if (value.same_as(op->value)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Cast::make(op->dtype, value);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Not* op) {
+  Expr a = this->VisitExpr(op->a);
+  if (a.same_as(op->a)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Not::make(a);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Select* op) {
+  Expr condition = this->VisitExpr(op->condition);
+  Expr true_value = this->VisitExpr(op->true_value);
+  Expr false_value = this->VisitExpr(op->false_value);
+  if (condition.same_as(op->condition) &&
+      true_value.same_as(op->true_value) &&
+      false_value.same_as(op->false_value)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Select::make(condition, true_value, false_value);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Ramp* op) {
+  Expr base = this->VisitExpr(op->base);
+  Expr stride = this->VisitExpr(op->stride);
+  if (base.same_as(op->base) &&
+      stride.same_as(op->stride)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Ramp::make(base, stride, op->lanes);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Broadcast* op) {
+  Expr value = this->VisitExpr(op->value);
+  if (value.same_as(op->value)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Broadcast::make(value, op->lanes);
+  }
+}
+
+Expr ExprMutator::VisitExpr_(const Shuffle* op) {
+  auto fexpr = [this](const Expr& e) { return this->VisitExpr(e); };
+  auto vectors = MutateArray(op->vectors, fexpr);
+  if (vectors.same_as(op->vectors)) {
+    return GetRef<Expr>(op);
+  } else {
+    return Shuffle::make(vectors, op->indices);
+  }
+}
+
+}  // namespace ir
+}  // namespace tvm
diff --git a/src/pass/ir_mutator.cc b/src/pass/ir_mutator.cc
index b300989dd2fd..5ba29fc0b6e9 100644
--- a/src/pass/ir_mutator.cc
+++ b/src/pass/ir_mutator.cc
@@ -28,59 +28,6 @@
 namespace tvm {
 namespace ir {
 
-class IRTransformer final : public IRMutator {
- public:
-  IRTransformer(const runtime::PackedFunc& f_preorder,
-                const runtime::PackedFunc& f_postorder,
-                const std::unordered_set<uint32_t>& only_enable)
-      : f_preorder_(f_preorder),
-        f_postorder_(f_postorder),
-        only_enable_(only_enable) {
-  }
-  Stmt Mutate(Stmt stmt) final {
-    return MutateInternal<Stmt>(stmt);
-  }
-  Expr Mutate(Expr expr) final {
-    return MutateInternal<Expr>(expr);
-  }
-
- private:
-  template <typename T>
-  T MutateInternal(T node) {
-    if (only_enable_.size() &&
-        !only_enable_.count(node->type_index())) {
-      return IRMutator::Mutate(node);
-    }
-    if (f_preorder_ != nullptr) {
-      T pre = f_preorder_(node);
-      if (pre.defined()) return pre;
-    }
-    node = IRMutator::Mutate(node);
-    if (f_postorder_ != nullptr) {
-      T post = f_postorder_(node);
-      if (post.defined()) return post;
-    }
-    return node;
-  }
-  // The functions
-  const runtime::PackedFunc& f_preorder_;
-  const runtime::PackedFunc& f_postorder_;
-  // type indices enabled.
-  const std::unordered_set<uint32_t>& only_enable_;
-};
-
-Stmt IRTransform(const Stmt& ir_node,
-                 const runtime::PackedFunc& f_preorder,
-                 const runtime::PackedFunc& f_postorder,
-                 const Array<Expr>& only_enable) {
-  std::unordered_set<uint32_t> only_type_index;
-  for (Expr s : only_enable) {
-    only_type_index.insert(Object::TypeKey2Index(s.as<StringImm>()->value.c_str()));
-  }
-  return IRTransformer(f_preorder, f_postorder, only_type_index)
-      .Mutate(ir_node);
-}
-
 IRMutator::FMutateExpr& IRMutator::vtable_expr() {  // NOLINT(*)
   static FMutateExpr inst; return inst;
 }
diff --git a/src/pass/ir_visitor.cc b/src/pass/ir_visitor.cc
index 467cd5de2ef7..af6ea5252166 100644
--- a/src/pass/ir_visitor.cc
+++ b/src/pass/ir_visitor.cc
@@ -26,26 +26,6 @@
 
 namespace tvm {
 namespace ir {
-// visitor to implement apply
-class IRApplyVisit : public IRVisitor {
- public:
-  explicit IRApplyVisit(std::function<void(const ObjectRef&)> f) : f_(f) {}
-
-  void Visit(const ObjectRef& node) final {
-    if (visited_.count(node.get()) != 0) return;
-    visited_.insert(node.get());
-    IRVisitor::Visit(node);
-    f_(node);
-  }
-
- private:
-  std::function<void(const ObjectRef&)> f_;
-  std::unordered_set<const Object*> visited_;
-};
-
-void PostOrderVisit(const ObjectRef& node, std::function<void(const ObjectRef&)> fvisit) {
-  IRApplyVisit(fvisit).Visit(node);
-}
 
 IRVisitor::FVisit& IRVisitor::vtable() {  // NOLINT(*)
   static FVisit inst; return inst;
diff --git a/tests/cpp/ir_functor_test.cc b/tests/cpp/ir_functor_test.cc
index 5636958a5b26..5f0860153587 100644
--- a/tests/cpp/ir_functor_test.cc
+++ b/tests/cpp/ir_functor_test.cc
@@ -31,7 +31,6 @@ TEST(IRF, Basic) {
   auto z = x + 1;
 
   NodeFunctor<int(const ObjectRef& n, int b)> f;
-  LOG(INFO) << "x";
   f.set_dispatch<Variable>([](const ObjectRef& n, int b) {
       return b;
     });
@@ -101,6 +100,98 @@ TEST(IRF, ExprVisit) {
   CHECK_EQ(v.count, 1);
 }
 
+
+TEST(IRF, StmtVisitor) {
+  using namespace tvm;
+  using namespace tvm::ir;
+  Var x("x");
+  class MyVisitor
+      : public StmtExprVisitor {
+   public:
+    int count = 0;
+    // implementation
+    void VisitExpr_(const Variable* op) final {
+      ++count;
+    }
+  };
+  MyVisitor v;
+  auto fmaketest = [&]() {
+    auto z = x + 1;
+    Stmt body = Evaluate::make(z);
+    Var buffer("b", DataType::Handle());
+    return Allocate::make(buffer, DataType::Float(32), {z, z}, const_true(), body);
+  };
+  v(fmaketest());
+  CHECK_EQ(v.count, 3);
+}
+
+TEST(IRF, StmtMutator) {
+  using namespace tvm;
+  using namespace tvm::ir;
+  Var x("x");
+
+  class MyVisitor
+      : public ir::StmtMutator,
+        public ir::ExprMutator {
+   public:
+    using StmtMutator::operator();
+    using ExprMutator::operator();
+
+   protected:
+    // implementation
+    Expr VisitExpr_(const Add* op) final {
+      return op->a;
+    }
+    Expr VisitExpr(const Expr& expr) final {
+      return ExprMutator::VisitExpr(expr);
+    }
+  };
+  auto fmaketest = [&]() {
+    auto z = x + 1;
+    Stmt body = Evaluate::make(z);
+    Var buffer("b", DataType::Handle());
+    return Allocate::make(buffer, DataType::Float(32), {1, z}, const_true(), body);
+  };
+
+  MyVisitor v;
+  {
+    auto body = fmaketest();
+    Stmt body2 = Evaluate::make(1);
+    Stmt bref = body.as<Allocate>()->body;
+    auto* extentptr = body.as<Allocate>()->extents.get();
+    Array<Stmt> arr{std::move(body), body2, body2};
+    auto* arrptr = arr.get();
+    arr.MutateByApply([&](Stmt s) { return v(std::move(s)); });
+    CHECK(arr.get() == arrptr);
+    // inplace update body
+    CHECK(arr[0].as<Allocate>()->extents[1].same_as(x));
+    CHECK(arr[0].as<Allocate>()->extents.get() == extentptr);
+    // copy because there is additional refs
+    CHECK(!arr[0].as<Allocate>()->body.same_as(bref));
+    CHECK(arr[0].as<Allocate>()->body.as<Evaluate>()->value.same_as(x));
+    CHECK(bref.as<Evaluate>()->value.as<Add>());
+  }
+  {
+    Array<Stmt> arr{fmaketest()};
+    // mutate array get reference by another one, triiger copy.
+    Array<Stmt> arr2 = arr;
+    auto* arrptr = arr.get();
+    arr.MutateByApply([&](Stmt s) { return v(std::move(s)); });
+    CHECK(arr.get() != arrptr);
+    CHECK(arr[0].as<Allocate>()->extents[1].same_as(x));
+    CHECK(!arr2[0].as<Allocate>()->extents[1].same_as(x));
+    // mutate but no content change.
+    arr2 = arr;
+    arr.MutateByApply([&](Stmt s) { return v(std::move(s)); });
+    CHECK(arr2.get() == arr.get());
+  }
+  {
+    auto body = Evaluate::make(Call::make(DataType::Int(32), "xyz", {x + 1}, Call::Extern));
+    auto res = v(std::move(body));
+    CHECK(res.as<Evaluate>()->value.as<Call>()->args[0].same_as(x));
+  }
+}
+
 int main(int argc, char ** argv) {
   testing::InitGoogleTest(&argc, argv);
   testing::FLAGS_gtest_death_test_style = "threadsafe";