diff --git a/src/relay/transforms/annotate_target.cc b/src/relay/transforms/annotate_target.cc
index bc6b4b993ae8..0997d8ffccfe 100644
--- a/src/relay/transforms/annotate_target.cc
+++ b/src/relay/transforms/annotate_target.cc
@@ -42,9 +42,9 @@ const PackedFunc* make_end_op = runtime::Registry::Get("relay.op.annotation._mak
 
 // A helper class to insert annotation boundaries for a program region that will
 // be handled by a specific compiler.
-class AnnotateTargetWrapper : public ExprMutator {
+class AnnotateTargetRewriter : public ExprRewriter {
  public:
-  explicit AnnotateTargetWrapper(Array<runtime::String> targets) : targets_(std::move(targets)) {}
+  explicit AnnotateTargetRewriter(Array<runtime::String> targets) : targets_(std::move(targets)) {}
 
   /*!
    * \brief This function annotates a compiler end and a compiler begin to all arguments.
@@ -108,29 +108,29 @@ class AnnotateTargetWrapper : public ExprMutator {
     return new_op;
   }
 
-  Expr VisitExpr_(const CallNode* cn) final {
+  Expr Rewrite_(const CallNode* pre, const Expr& post) final {
     // Supported targets for this node. The order implies the priority.
     std::vector<std::string> supported_targets;
 
-    auto op_node = cn->op.as<OpNode>();
+    auto op_node = pre->op.as<OpNode>();
 
     // This graph has annotations, meaning that this is not the first time running this pass.
-    if (op_node && cn->op == compiler_begin_op) {
+    if (op_node && pre->op == compiler_begin_op) {
       // Bypass compiler begin due to lack of target information. It will be processed
       // when the following op handling arguments.
-      CHECK_EQ(cn->args.size(), 1U);
-      return VisitExpr(cn->args[0]);
-    } else if (op_node && cn->op == compiler_end_op) {
+      CHECK_EQ(pre->args.size(), 1U);
+      return post.as<CallNode>()->args[0];
+    } else if (op_node && pre->op == compiler_end_op) {
       // Override compiler end with the new target.
-      CHECK_EQ(cn->args.size(), 1U);
-      auto input_expr = VisitExpr(cn->args[0]);
+      CHECK_EQ(pre->args.size(), 1U);
+      auto input_expr = post.as<CallNode>()->args[0];
       CHECK(op_expr_to_target_.find(input_expr) != op_expr_to_target_.end());
       return InsertAnnotation(input_expr, op_expr_to_target_[input_expr], make_end_op);
     }
 
     // Peek the first argument. If it is compiler begin then this node had annotated by
     // another target before, so we also consider that target as a supported target.
-    const CallNode* first_arg_call = cn->args[0].as<CallNode>();
+    const CallNode* first_arg_call = pre->args[0].as<CallNode>();
     if (first_arg_call && first_arg_call->op == compiler_begin_op) {
       std::string arg_target = first_arg_call->attrs.as<CompilerAttrs>()->compiler;
       if (arg_target != "default") {
@@ -142,21 +142,21 @@ class AnnotateTargetWrapper : public ExprMutator {
     if (op_node) {
       // TVM operators: Check target specific op checking function and add to supported_targets
       // if it is supported.
-      Op op = Downcast<Op>(cn->op);
+      Op op = Downcast<Op>(pre->op);
       CHECK(op.defined());
       for (const auto& target : this->targets_) {
         if (!Op::HasAttr("target." + std::string(target))) {
           continue;
         }
         auto fannotate = Op::GetAttr<FTVMAnnotateTarget>("target." + std::string(target));
-        if (fannotate.count(op) && fannotate[op](cn->attrs, cn->args)) {
+        if (fannotate.count(op) && fannotate[op](pre->attrs, pre->args)) {
           supported_targets.push_back(target);
         }
       }
-    } else if (cn->op->IsInstance<FunctionNode>()) {
+    } else if (pre->op->IsInstance<FunctionNode>()) {
       // Composite function: Add the target of a composite function to supported_targets
       // if it is in the target list.
-      Function func = Downcast<Function>(cn->op);
+      Function func = Downcast<Function>(pre->op);
       CHECK(func.defined());
 
       if (auto comp_name = func->GetAttr<String>(attr::kComposite)) {
@@ -181,23 +181,22 @@ class AnnotateTargetWrapper : public ExprMutator {
     std::string target = supported_targets[0];
 
     // Visit and mutate arguments after the target of this op has been determined.
-    auto new_call = Downcast<Call>(ExprMutator::VisitExpr_(cn));
+    Call post_call = Downcast<Call>(post);
 
     // Add annotations to each arg.
-    auto target_n_args = AnnotateArgs(new_call->args, target);
+    auto target_n_args = AnnotateArgs(post_call->args, target);
     Array<Expr> compiler_begins = std::get<1>(target_n_args);
-    Call call = Call(new_call->op, compiler_begins, new_call->attrs);
-    call->checked_type_ = cn->checked_type_;
+    Call new_call = Call(post_call->op, compiler_begins, post_call->attrs);
+    new_call->checked_type_ = pre->checked_type_;
 
     // Update the target map.
-    op_expr_to_target_[call] = target;
+    op_expr_to_target_[new_call] = target;
 
-    return std::move(call);
+    return new_call;
   }
 
-  Expr VisitExpr_(const TupleNode* op) final {
-    auto new_e = ExprMutator::VisitExpr_(op);
-    auto expr = Downcast<Tuple>(new_e);
+  Expr Rewrite_(const TupleNode* op, const Expr& post) final {
+    auto expr = Downcast<Tuple>(post);
 
     auto target_n_args = AnnotateArgs(expr->fields);
     auto new_expr = Tuple(std::get<1>(target_n_args));
@@ -205,9 +204,8 @@ class AnnotateTargetWrapper : public ExprMutator {
     return std::move(new_expr);
   }
 
-  Expr VisitExpr_(const TupleGetItemNode* op) final {
-    auto new_e = ExprMutator::VisitExpr_(op);
-    auto expr = Downcast<TupleGetItem>(new_e);
+  Expr Rewrite_(const TupleGetItemNode* op, const Expr& post) final {
+    auto expr = Downcast<TupleGetItem>(post);
 
     auto target_n_args = AnnotateArgs(Array<Expr>({expr->tuple}));
     auto new_expr = TupleGetItem(std::get<1>(target_n_args)[0], expr->index);
@@ -215,7 +213,7 @@ class AnnotateTargetWrapper : public ExprMutator {
     return std::move(new_expr);
   }
 
-  Expr VisitExpr_(const FunctionNode* fn) final {
+  Expr Rewrite_(const FunctionNode* fn, const Expr& post) final {
     Function func;
     Expr new_body;
     // don't step into composite functions
@@ -223,8 +221,7 @@ class AnnotateTargetWrapper : public ExprMutator {
       func = GetRef<Function>(fn);
       new_body = func->body;
     } else {
-      auto new_e = ExprMutator::VisitExpr_(fn);
-      func = Downcast<Function>(new_e);
+      func = Downcast<Function>(post);
       new_body = func->body;
       if (op_expr_to_target_.find(func->body) != op_expr_to_target_.end()) {
         new_body = InsertAnnotation(func->body, op_expr_to_target_[func->body], make_end_op);
@@ -234,9 +231,8 @@ class AnnotateTargetWrapper : public ExprMutator {
     return Function(func->params, new_body, func->ret_type, func->type_params, func->attrs);
   }
 
-  Expr VisitExpr_(const LetNode* op) final {
-    auto new_e = ExprMutator::VisitExpr_(op);
-    auto let = Downcast<Let>(new_e);
+  Expr Rewrite_(const LetNode* op, const Expr& post) final {
+    auto let = Downcast<Let>(post);
 
     auto target_n_args = AnnotateArgs({let->value, let->body});
     auto new_expr = Let(let->var, std::get<1>(target_n_args)[0], std::get<1>(target_n_args)[1]);
@@ -244,9 +240,8 @@ class AnnotateTargetWrapper : public ExprMutator {
     return std::move(new_expr);
   }
 
-  Expr VisitExpr_(const IfNode* op) final {
-    auto new_e = ExprMutator::VisitExpr_(op);
-    auto expr = Downcast<If>(new_e);
+  Expr Rewrite_(const IfNode* op, const Expr& post) final {
+    auto expr = Downcast<If>(post);
 
     auto target_n_args = AnnotateArgs({expr->cond, expr->true_branch, expr->false_branch});
     CHECK_EQ(std::get<1>(target_n_args).size(), 3U);
@@ -256,9 +251,8 @@ class AnnotateTargetWrapper : public ExprMutator {
     return std::move(new_expr);
   }
 
-  Expr VisitExpr_(const RefCreateNode* op) final {
-    auto new_e = ExprMutator::VisitExpr_(op);
-    auto expr = Downcast<RefCreate>(new_e);
+  Expr Rewrite_(const RefCreateNode* op, const Expr& post) final {
+    auto expr = Downcast<RefCreate>(post);
 
     auto target_n_args = AnnotateArgs(Array<Expr>({expr->value}));
     auto new_expr = RefCreate(std::get<1>(target_n_args)[0]);
@@ -266,9 +260,8 @@ class AnnotateTargetWrapper : public ExprMutator {
     return std::move(new_expr);
   }
 
-  Expr VisitExpr_(const RefReadNode* op) final {
-    auto new_e = ExprMutator::VisitExpr_(op);
-    auto expr = Downcast<RefRead>(new_e);
+  Expr Rewrite_(const RefReadNode* op, const Expr& post) final {
+    auto expr = Downcast<RefRead>(post);
 
     auto target_n_args = AnnotateArgs(Array<Expr>({expr->ref}));
     auto new_expr = RefRead(std::get<1>(target_n_args)[0]);
@@ -276,9 +269,8 @@ class AnnotateTargetWrapper : public ExprMutator {
     return std::move(new_expr);
   }
 
-  Expr VisitExpr_(const RefWriteNode* op) final {
-    auto new_e = ExprMutator::VisitExpr_(op);
-    auto expr = Downcast<RefWrite>(new_e);
+  Expr Rewrite_(const RefWriteNode* op, const Expr& post) final {
+    auto expr = Downcast<RefWrite>(post);
 
     auto target_n_args = AnnotateArgs(Array<Expr>({expr->ref, expr->value}));
     auto new_expr = RefWrite(std::get<1>(target_n_args)[0], std::get<1>(target_n_args)[1]);
@@ -294,7 +286,8 @@ class AnnotateTargetWrapper : public ExprMutator {
 };
 
 Expr AnnotateTarget(const Expr& expr, const Array<runtime::String>& targets) {
-  return AnnotateTargetWrapper(targets).Mutate(expr);
+  auto rewriter = AnnotateTargetRewriter(targets);
+  return PostOrderRewrite(expr, &rewriter);
 }
 
 }  // namespace annotate_target
diff --git a/src/relay/transforms/merge_compiler_regions.cc b/src/relay/transforms/merge_compiler_regions.cc
index 601be0f96bc4..cb7bd8c6b3aa 100644
--- a/src/relay/transforms/merge_compiler_regions.cc
+++ b/src/relay/transforms/merge_compiler_regions.cc
@@ -140,11 +140,11 @@ class RegionMerger : public ExprVisitor {
   std::unordered_map<int, std::unordered_set<int>> region_restrictions_;
 };
 
-class MergeAnnotations : public ExprMutator {
+class MergeAnnotations : public ExprRewriter {
  public:
   explicit MergeAnnotations(AnnotatedRegionSet regions) : regions_(regions) {}
 
-  Expr VisitExpr_(const CallNode* call) final {
+  Expr Rewrite_(const CallNode* call, const Expr& post) final {
     // Merge annotations which are now internal to a region.
     // This happens if we see a compiler begin next to a
     // compiler end and they're both in the same region.
@@ -154,11 +154,12 @@ class MergeAnnotations : public ExprMutator {
         auto region1 = regions_->GetRegion(GetRef<Call>(call));
         auto region2 = regions_->GetRegion(arg);
         if (region1 == region2) {
-          return VisitExpr(arg->args[0]);
+          auto post_arg = post.as<CallNode>()->args[0];
+          return post_arg.as<CallNode>()->args[0];
         }
       }
     }
-    return ExprMutator::VisitExpr_(call);
+    return post;
   }
 
  private:
@@ -175,7 +176,7 @@ Expr MergeCompilerRegions(const Expr& expr) {
 
   // Remove annotations that are not in the region boundaries.
   MergeAnnotations merge_anno(regions);
-  return merge_anno.Mutate(expr);
+  return PostOrderRewrite(expr, &merge_anno);
 }
 
 }  // namespace merge_compiler_region