diff --git a/taichi/transforms/auto_diff.cpp b/taichi/transforms/auto_diff.cpp
index 871f092a4a28f..798d00509a0ee 100644
--- a/taichi/transforms/auto_diff.cpp
+++ b/taichi/transforms/auto_diff.cpp
@@ -488,10 +488,9 @@ class ReverseOuterLoops : public BasicStmtVisitor {
   }
 };
 
-// Generate the adjoint version of an independent block
-
-class MakeAdjoint : public IRVisitor {
- private:
+// Base class for both reverse (make adjoint) and forward (make dual) mode
+class ADTransform : public IRVisitor {
+ protected:
   Stmt *constant(float32 x) {
     return insert<ConstStmt>(TypedConstant(x));
   }
@@ -556,6 +555,107 @@ class MakeAdjoint : public IRVisitor {
   }
 
  public:
+  virtual Stmt *insert_grad_stmt(std::unique_ptr<Stmt> &&stmt) = 0;
+
+  template <typename T, typename... Args>
+  Stmt *insert(Args &&...args) {
+    return insert_grad_stmt(Stmt::make<T>(args...));
+  }
+
+  void visit(AllocaStmt *alloca) override {
+    // do nothing.
+  }
+
+  void visit(AdStackAllocaStmt *alloca) override {
+    // do nothing.
+  }
+
+  void visit(ArgLoadStmt *stmt) override {
+    // do nothing.
+  }
+
+  void visit(LoopIndexStmt *stmt) override {
+    // do nothing.
+  }
+
+  void visit(PrintStmt *print_stmt) override {
+    // do nothing
+  }
+
+  void visit(ConstStmt *const_stmt) override {
+    // do nothing
+  }
+
+  void visit(WhileControlStmt *stmt) override {
+    TI_NOT_IMPLEMENTED
+  }
+
+  void visit(ContinueStmt *stmt) override {
+    TI_NOT_IMPLEMENTED;
+  }
+
+  void visit(WhileStmt *stmt) override {
+    TI_NOT_IMPLEMENTED
+  }
+
+  void visit(GlobalPtrStmt *stmt) override {
+    // do nothing
+  }
+
+  Stmt *load(Stmt *alloc) {
+    TI_ASSERT(alloc != nullptr);
+    if (alloc->is<AllocaStmt>()) {
+      return insert<LocalLoadStmt>(LocalAddress(alloc, 0));
+    } else {
+      // non alloca
+      return alloc;
+    }
+  }
+
+  bool gradients_stopped(GlobalLoadStmt *stmt, SNode *snode) {
+    for (auto block = stmt->parent; block; block = block->parent_block()) {
+      for (auto s : block->stop_gradients) {
+        if (s == snode) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  void visit(ElementShuffleStmt *stmt) override {
+    TI_NOT_IMPLEMENTED
+  }
+
+  void visit(AssertStmt *stmt) override {
+    // do nothing
+  }
+
+  void visit(RangeAssumptionStmt *stmt) override {
+    // do nothing
+  }
+
+  void visit(LinearizeStmt *stmt) override {
+    // do nothing
+  }
+
+  void visit(BitExtractStmt *stmt) override {
+    // do nothing
+  }
+
+  void visit(IntegerOffsetStmt *stmt) override {
+    // do nothing
+  }
+
+  void visit(RandStmt *stmt) override {
+    TI_ERROR("RandStmt not supported in AutoDiff for now.");
+  }
+};
+
+// Generate the adjoint version of an independent block
+class MakeAdjoint : public ADTransform {
+ public:
+  using ADTransform::visit;
   Block *current_block;
   Block *alloca_block;
   // Backup the forward pass (the forward pass might be modified during the
@@ -593,17 +693,12 @@ class MakeAdjoint : public IRVisitor {
     }
   }
 
-  Stmt *insert_back(std::unique_ptr<Stmt> &&stmt) {
+  Stmt *insert_grad_stmt(std::unique_ptr<Stmt> &&stmt) override {
     auto ptr = stmt.get();
     current_block->insert(std::move(stmt), -1);
     return ptr;
   }
 
-  template <typename T, typename... Args>
-  Stmt *insert(Args &&...args) {
-    return insert_back(Stmt::make<T>(args...));
-  }
-
   // Accumulate [value] to the adjoint of [primal]
   void accumulate(Stmt *primal, Stmt *value) {
     auto alloca_ = adjoint(primal);
@@ -675,22 +770,6 @@ class MakeAdjoint : public IRVisitor {
     return adjoint_stmt[stmt];
   }
 
-  void visit(AllocaStmt *alloca) override {
-    // do nothing.
-  }
-
-  void visit(AdStackAllocaStmt *alloca) override {
-    // do nothing.
-  }
-
-  void visit(ArgLoadStmt *stmt) override {
-    // do nothing.
-  }
-
-  void visit(LoopIndexStmt *stmt) override {
-    // do nothing.
-  }
-
   void visit(UnaryOpStmt *stmt) override {
     if (stmt->op_type == UnaryOpType::floor ||
         stmt->op_type == UnaryOpType::ceil) {
@@ -827,34 +906,14 @@ class MakeAdjoint : public IRVisitor {
       }
       current_block = old_current_block;
     }
-    insert_back(std::move(new_if));
-  }
-
-  void visit(PrintStmt *print_stmt) override {
-    // do nothing
-  }
-
-  void visit(ConstStmt *const_stmt) override {
-    // do nothing
-  }
-
-  void visit(WhileControlStmt *stmt) override {
-    TI_NOT_IMPLEMENTED
-  }
-
-  void visit(ContinueStmt *stmt) override {
-    TI_NOT_IMPLEMENTED;
-  }
-
-  void visit(WhileStmt *stmt) override {
-    TI_NOT_IMPLEMENTED
+    insert_grad_stmt(std::move(new_if));
   }
 
   void visit(RangeForStmt *for_stmt) override {
     auto new_for = for_stmt->clone();
     auto new_for_ptr = new_for->as<RangeForStmt>();
     new_for_ptr->reversed = !new_for_ptr->reversed;
-    insert_back(std::move(new_for));
+    insert_grad_stmt(std::move(new_for));
     const int len = new_for_ptr->body->size();
 
     for (int i = 0; i < len; i++) {
@@ -889,10 +948,6 @@ class MakeAdjoint : public IRVisitor {
     for_stmt->body->accept(this);
   }
 
-  void visit(GlobalPtrStmt *stmt) override {
-    // do nothing
-  }
-
   // Equivalent to AdStackLoadTopStmt when no stack is needed
   void visit(LocalLoadStmt *stmt) override {
     // TI_ASSERT(!needs_grad(stmt->ret_type));
@@ -999,34 +1054,6 @@ class MakeAdjoint : public IRVisitor {
     }
     stmt->parent->erase(stmt);
   }
-
-  void visit(ElementShuffleStmt *stmt) override {
-    TI_NOT_IMPLEMENTED
-  }
-
-  void visit(AssertStmt *stmt) override {
-    // do nothing
-  }
-
-  void visit(RangeAssumptionStmt *stmt) override {
-    // do nothing
-  }
-
-  void visit(LinearizeStmt *stmt) override {
-    // do nothing
-  }
-
-  void visit(BitExtractStmt *stmt) override {
-    // do nothing
-  }
-
-  void visit(IntegerOffsetStmt *stmt) override {
-    // do nothing
-  }
-
-  void visit(RandStmt *stmt) override {
-    TI_ERROR("RandStmt not supported in AutoDiff for now.");
-  }
 };
 
 class BackupSSA : public BasicStmtVisitor {