diff --git a/.vscode/settings.json b/.vscode/settings.json
index e234d5d..c40b051 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,6 +1,7 @@
 {
     "clangd.arguments": [
-        "--compile-commands-dir=${workspaceFolder}/build"
+        "--compile-commands-dir=${workspaceFolder}/build",
+        "--header-insertion=never"
     ],
     "cmake.configureOnOpen": true,
     "antlr4.rrd.saveDir": "${workspaceFolder}/build",
@@ -14,5 +15,7 @@
     "[python]": {
         "editor.defaultFormatter": "ms-python.autopep8"
     },
-    "python.formatting.provider": "none"
+    "python.formatting.provider": "none",
+    "editor.indentSize": "tabSize",
+    "editor.tabSize": 2,
 }
\ No newline at end of file
diff --git a/include/llir_instruction.h b/include/llir_instruction.h
index 946ec2f..8cfdba3 100644
--- a/include/llir_instruction.h
+++ b/include/llir_instruction.h
@@ -36,14 +36,13 @@ enum class InstTag {
   ExtractEle
 };
 
-class Instruction : public Value {
+class Instruction : public User {
 public:
   int ir_seqno = -1;
   InstTag tag;
-  std::shared_ptr<BasicBlock> parent_bb;
-  std::vector<std::shared_ptr<Value>> operand_list;
-  Instruction(InstTag inst_tag, TypePtr_t type, std::shared_ptr<BasicBlock> parent_bb)
-    : Value("", type), tag(inst_tag), parent_bb(parent_bb) {}
+  BasicBlockPtr_t parent_bb;
+  Instruction(InstTag inst_tag, TypePtr_t type, BasicBlockPtr_t parent_bb)
+    : User("", type), tag(inst_tag), parent_bb(parent_bb) {}
   virtual std::string to_string() override {
     switch (tag) {
       case InstTag::Add: return "add";
@@ -91,8 +90,8 @@ public:
   InstStore(std::shared_ptr<Value> value, std::shared_ptr<Value> pointer, std::shared_ptr<BasicBlock> parent_bb)
     : Instruction(InstTag::Store, TypeHelper::TYPE_VOID, parent_bb) {
     assert(value);
-    operand_list.push_back(value);
-    operand_list.push_back(pointer);
+    Add_Operand(value);
+    Add_Operand(pointer);
   }
 };
 
@@ -100,7 +99,7 @@ class InstLoad : public Instruction {
 public:
   InstLoad(std::shared_ptr<Value> value, TypePtr_t type, std::shared_ptr<BasicBlock> parent_bb)
     : Instruction(InstTag::Load, type, parent_bb) {
-    operand_list.push_back(value);
+    Add_Operand(value);
   }
   virtual std::string to_IR_string() override {
     std::string str = type->to_IR_string() + " %" + std::to_string(ir_seqno);
@@ -118,8 +117,8 @@ public:
     std::shared_ptr<BasicBlock> parent_bb
   )
     : Instruction(inst_tag, val_type, parent_bb) {
-    operand_list.push_back(op1);
-    operand_list.push_back(op2);
+    Add_Operand(op1);
+    Add_Operand(op2);
   }
   virtual std::string to_IR_string() override {
     std::string str = type->to_IR_string() + " %" + std::to_string(ir_seqno);
@@ -133,7 +132,7 @@ class InstZext : public Instruction {
 public:
   InstZext(std::shared_ptr<Value> op, std::shared_ptr<BasicBlock> parent_bb)
     : Instruction(InstTag::Zext, TypeHelper::TYPE_I32, parent_bb) {
-    operand_list.push_back(op);
+    Add_Operand(op);
   }
   virtual std::string to_IR_string() override {
     std::string str = type->to_IR_string() + " %" + std::to_string(ir_seqno);
@@ -146,14 +145,14 @@ public:
   // conditional branch
   InstBranch(ValuePtr_t cond, BasicBlockPtr_t true_block, BasicBlockPtr_t false_block, BasicBlockPtr_t parent_bb)
     : Instruction(InstTag::Br, TypeHelper::TYPE_VOID, parent_bb) {
-    this->operand_list.push_back(cond);
-    this->operand_list.push_back(true_block);
-    this->operand_list.push_back(false_block);
+    this->Add_Operand(cond);
+    this->Add_Operand(true_block);
+    this->Add_Operand(false_block);
   }
   // unconditional branch
   InstBranch(BasicBlockPtr_t target_block, BasicBlockPtr_t parent_bb)
     : Instruction(InstTag::Br, TypeHelper::TYPE_VOID, parent_bb) {
-    this->operand_list.push_back(target_block);
+    this->Add_Operand(target_block);
   }
 };
 
@@ -161,7 +160,7 @@ class InstReturn : public Instruction {
 public:
   InstReturn(ValuePtr_t ret_val, BasicBlockPtr_t parent_bb)
     : Instruction(InstTag::Ret, TypeHelper::TYPE_VOID, parent_bb) {
-    this->operand_list.push_back(ret_val);
+    this->Add_Operand(ret_val);
   }
   InstReturn(BasicBlockPtr_t parent_bb) : Instruction(InstTag::Ret, TypeHelper::TYPE_VOID, parent_bb) {}
 };
@@ -171,8 +170,10 @@ class InstCall : public Instruction {
 public:
   InstCall(FunctionPtr_t func, const std::vector<ValuePtr_t> &args, BasicBlockPtr_t parent_bb)
     : Instruction(InstTag::Call, func->get_type()->return_type, parent_bb) {
-    operand_list.push_back(func);
-    operand_list.insert(operand_list.end(), args.begin(), args.end());
+    Add_Operand(func);
+    for (auto arg : args) {
+      Add_Operand(arg);
+    }
   }
   virtual std::string to_IR_string() override {
     if (Type::isType<VoidType>(type)) {
@@ -203,8 +204,10 @@ public:
       aim_to = nullptr;
     }
     element_type = extract_type(pointer, indices);
-    operand_list.push_back(pointer);
-    operand_list.insert(operand_list.end(), indices.begin(), indices.end());
+    Add_Operand(pointer);
+    for (auto index : indices) {
+      Add_Operand(index);
+    }
   }
 
   virtual std::string to_IR_string() override {
diff --git a/include/llir_type.h b/include/llir_type.h
index f87d54f..cf62da8 100644
--- a/include/llir_type.h
+++ b/include/llir_type.h
@@ -6,6 +6,9 @@
 #include <vector>
 namespace antlrSysY {
 
+class Type;
+typedef std::shared_ptr<Type> TypePtr_t;
+
 class Type {
 public:
   enum class TypeTag {
@@ -82,8 +85,6 @@ public:
   }
 };
 
-typedef std::shared_ptr<Type> TypePtr_t;
-
 class TypeHelper {
 public:
   static bool isIntegerType(TypePtr_t type) {
diff --git a/include/llir_value.h b/include/llir_value.h
index 2d6065e..d308de2 100644
--- a/include/llir_value.h
+++ b/include/llir_value.h
@@ -9,13 +9,29 @@
 #include <shared_mutex>
 #include <string>
 #include <vector>
+#include <tuple>
 
 namespace antlrSysY {
 
+class Value;
+class BasicBlock;
+class User;
+class Function;
+class Instruction;
+typedef std::shared_ptr<Value> ValuePtr_t;
+typedef std::shared_ptr<BasicBlock> BasicBlockPtr_t;
+typedef std::shared_ptr<Function> FunctionPtr_t;
+typedef std::shared_ptr<User> UserPtr_t;
+typedef std::shared_ptr<Instruction> InstructionPtr_t;
+typedef std::tuple<ValuePtr_t, UserPtr_t, int> UseEdge_t;
+//                  Define, User, operand-index
+
 class Value {
 public:
   std::string name;
   TypePtr_t type;
+  std::list<UseEdge_t> use_list;
+
   Value(const std::string &name, TypePtr_t type) : name(name), type(type) {}
   virtual ~Value() = default;
 
@@ -46,8 +62,16 @@ public:
   }
 };
 
+
 class User : public Value {
 public:
+  std::vector<ValuePtr_t> operand_list;
+
+  User(const std::string &name, TypePtr_t type) : Value(name, type) {}
+  void Add_Operand(ValuePtr_t op) {
+    operand_list.push_back(op);
+    use_list.push_back({op, std::make_shared<User>(this), operand_list.size()});
+  }
 };
 
 class BasicBlock;
@@ -96,15 +120,19 @@ public:
   BasicBlockListNode_t itr;
   std::list<std::shared_ptr<BasicBlock>> successors;
   std::list<std::shared_ptr<BasicBlock>> predecessors;
+
+  BasicBlockPtr_t idomer;
+  std::list<BasicBlockPtr_t> idomee_list;
+  std::list<BasicBlockPtr_t> domer_list;
+  std::list<BasicBlockPtr_t> dom_frontier;
+  int dom_level;
+  int _dom_helper_index;
+
   BasicBlock(const std::string &name, std::shared_ptr<Function> parent) : Value(name, TypeHelper::TYPE_LABEL) {
     this->parent = parent;
   }
 };
 
-typedef std::shared_ptr<Value> ValuePtr_t;
-typedef std::shared_ptr<BasicBlock> BasicBlockPtr_t;
-typedef std::shared_ptr<Function> FunctionPtr_t;
-
 class Constant : public Value {
 public:
   Constant(const std::string &name, TypePtr_t type) : Value(name, type) {}
diff --git a/include/pass.h b/include/pass.h
index 808e1d8..c066dd9 100644
--- a/include/pass.h
+++ b/include/pass.h
@@ -12,4 +12,10 @@ public:
   virtual void run(const Module &module) = 0;
 };
 
+class PassMem2Reg : public Pass { 
+public:
+  PassMem2Reg() : Pass("mem2reg") {}
+  virtual void run(const Module &module) override;
+};
+
 } // namespace antlrSysY
\ No newline at end of file
diff --git a/src/dominance_algo.cpp b/src/dominance_algo.cpp
new file mode 100644
index 0000000..7b6c88c
--- /dev/null
+++ b/src/dominance_algo.cpp
@@ -0,0 +1,106 @@
+#include "llir.h"
+#include "visitor.h"
+#include <bitset>
+
+namespace antlrSysY {
+
+static void _bitwise_and(std::vector<bool>& op1, const std::vector<bool>& op2) {
+  for (int i = 0; i < op1.size(); ++ i) {
+    op1[i] = op1[i] & op2[i];
+  }
+}
+
+static void _bitwise_set(std::vector<bool>& op1, int l, int r,bool val) {
+  for (int i = l; i < r; ++ i) {
+    op1[i] = val;
+  }
+}
+
+static void _gen_dom_level(BasicBlockPtr_t bb, int level) {
+  bb->dom_level = level;
+  for (auto succ : bb->idomee_list) {
+    _gen_dom_level(succ, level + 1);
+  }
+}
+
+void gen_dominance(FunctionPtr_t func) {
+  // 编译器设计 2E 352 | Engineering A Compiler P479
+  // Note: n \in Dom(n)
+  // Basic iterative idea: Dom(n) = {n} union (intersect Dom(pred(n)))
+  std::vector<std::vector<bool>> domers;
+  std::vector<BasicBlockPtr_t> bb_list;
+  const int N = func->bb_list.size();
+  auto itr = func->bb_list.begin();
+  for (auto basicblock : func->bb_list) {
+    basicblock->idomee_list.clear();
+    basicblock->domer_list.clear();
+    domers.push_back({});
+    domers.back().resize(N, true); // Dom(i) <- N
+    basicblock->_dom_helper_index = bb_list.size();
+    bb_list.push_back(basicblock);
+  }
+  _bitwise_set(domers[0], 1, N, false); // Dom(0) <- {0}
+
+  bool changed = true;
+  while (changed) {
+    changed = false;
+    int i = 0;
+    for (int i = 1; i < N; ++ i) {
+      auto cur_bb = bb_list[i];
+      std::vector<bool> temp(true, N);
+      // temp = {i} union (intersect Dom(j)), j in pred(i)
+      for (auto pred : cur_bb->predecessors) {
+        _bitwise_and(temp, domers[pred->_dom_helper_index]);
+      }
+      temp[i] = true;
+      // if temp != Dom(i)
+      if (!(temp == domers[i])) {
+        domers[i] = temp; // Dom(i) <- temp
+        changed = true;   // changed <- true
+      }
+    }
+  }
+  // set each basicblock's domer
+  for (int i = 0; i < N; ++ i) {
+    for (int j = 0; j < N; ++ j) {
+      if (domers[i][j]) {
+        bb_list[i]->domer_list.push_back(bb_list[j]);
+      }
+    }
+  }
+  // get domees and immediate domer
+  for (int i = 0; i < N; ++ i) {
+    for (auto domer1 : bb_list[i]->domer_list) {
+      if (domer1 == bb_list[i])
+        continue;
+      bool flag = true;
+      // if dom(i)[j] dom dom(i)[k], it cannot be the immediate domer of i
+      for (auto domer2 : bb_list[i]->domer_list) {
+        if (domer2 == bb_list[i] || domer2 == domer1)
+          continue;
+        if (std::find(domer2->domer_list.begin(), domer2->domer_list.end(), domer1) != domer2->domer_list.end()) {
+          flag = false;
+          break;
+        }
+      }
+      if (flag) {
+        bb_list[i]->idomer = domer1;
+        domer1->idomee_list.push_back(bb_list[i]);
+        break;
+      }
+    }
+  }
+  _gen_dom_level(bb_list[0], 0);
+}
+
+void gen_dominance_frontier(FunctionPtr_t func) {
+  // 编译器设计 2E 368
+  // for all node in CFG: DF(n) <- Empty
+  for (auto bb : func->bb_list) {
+    bb->dom_frontier.clear();
+  }
+  // for all node in CFG:
+
+}
+
+}
\ No newline at end of file
diff --git a/src/pass_mem2reg.cpp b/src/pass_mem2reg.cpp
new file mode 100644
index 0000000..aab4496
--- /dev/null
+++ b/src/pass_mem2reg.cpp
@@ -0,0 +1,14 @@
+#include "passes.h"
+#include "llir.h"
+#include "common.h"
+
+namespace antlrSysY {
+
+void PassMem2Reg::run(const Module& module) {
+  for (auto func : module.function_list) {
+    if (func->is_libfunc()) continue;
+    
+  }
+}
+
+}
\ No newline at end of file