diff --git a/src/ir/BasicBlock.cpp b/src/ir/BasicBlock.cpp
index c85d923..ef257bc 100644
--- a/src/ir/BasicBlock.cpp
+++ b/src/ir/BasicBlock.cpp
@@ -3,3 +3,22 @@
 // - 维护或可计算前驱/后继关系，用于 CFG 分析与优化
 
 #include "ir/IR.h"
+
+#include <utility>
+
+namespace ir {
+
+BasicBlock::BasicBlock(std::string name) : name_(std::move(name)) {}
+
+const std::string& BasicBlock::name() const { return name_; }
+
+bool BasicBlock::HasTerminator() const {
+  return !instructions_.empty() && instructions_.back()->IsTerminator();
+}
+
+const std::vector<std::unique_ptr<Instruction>>& BasicBlock::instructions()
+    const {
+  return instructions_;
+}
+
+}  // namespace ir
diff --git a/src/ir/Function.cpp b/src/ir/Function.cpp
index 3772494..33312b0 100644
--- a/src/ir/Function.cpp
+++ b/src/ir/Function.cpp
@@ -20,4 +20,12 @@ BasicBlock* Function::CreateBlock(const std::string& name) {
   return ptr;
 }
 
+BasicBlock* Function::entry() { return entry_; }
+
+const BasicBlock* Function::entry() const { return entry_; }
+
+const std::vector<std::unique_ptr<BasicBlock>>& Function::blocks() const {
+  return blocks_;
+}
+
 }  // namespace ir
diff --git a/src/ir/IR.h b/src/ir/IR.h
index 1f03ee1..2876333 100644
--- a/src/ir/IR.h
+++ b/src/ir/IR.h
@@ -41,8 +41,8 @@ Context& DefaultContext();
 class Type {
  public:
   enum class Kind { Void, Int32, PtrInt32 };
-  explicit Type(Kind k) : kind_(k) {}
-  Kind kind() const { return kind_; }
+  explicit Type(Kind k);
+  Kind kind() const;
   static std::shared_ptr<Type> Void();
   static std::shared_ptr<Type> Int32();
   static std::shared_ptr<Type> PtrInt32();
@@ -53,14 +53,13 @@ class Type {
 
 class Value {
  public:
-  Value(std::shared_ptr<Type> ty, std::string name)
-      : type_(std::move(ty)), name_(std::move(name)) {}
+  Value(std::shared_ptr<Type> ty, std::string name);
   virtual ~Value() = default;
-  const std::shared_ptr<Type>& type() const { return type_; }
-  const std::string& name() const { return name_; }
-  void set_name(std::string n) { name_ = std::move(n); }
-  void AddUser(Instruction* user) { users_.push_back(user); }
-  const std::vector<Instruction*>& users() const { return users_; }
+  const std::shared_ptr<Type>& type() const;
+  const std::string& name() const;
+  void set_name(std::string n);
+  void AddUser(Instruction* user);
+  const std::vector<Instruction*>& users() const;
 
  protected:
   std::shared_ptr<Type> type_;
@@ -77,16 +76,16 @@ class ConstantInt : public Value {
   int value_{};
 };
 
+// 后续还需要扩展更多指令类型。
 enum class Opcode { Add, Sub, Mul, Alloca, Load, Store, Ret };
 
 class Instruction : public Value {
  public:
-  Instruction(Opcode op, std::shared_ptr<Type> ty, std::string name = "")
-      : Value(std::move(ty), std::move(name)), opcode_(op) {}
-  Opcode opcode() const { return opcode_; }
-  bool IsTerminator() const { return opcode_ == Opcode::Ret; }
-  BasicBlock* parent() const { return parent_; }
-  void set_parent(BasicBlock* parent) { parent_ = parent; }
+  Instruction(Opcode op, std::shared_ptr<Type> ty, std::string name = "");
+  Opcode opcode() const;
+  bool IsTerminator() const;
+  BasicBlock* parent() const;
+  void set_parent(BasicBlock* parent);
 
  private:
   Opcode opcode_;
@@ -97,8 +96,8 @@ class BinaryInst : public Instruction {
  public:
   BinaryInst(Opcode op, std::shared_ptr<Type> ty, Value* lhs, Value* rhs,
              std::string name);
-  Value* lhs() const { return lhs_; }
-  Value* rhs() const { return rhs_; }
+  Value* lhs() const;
+  Value* rhs() const;
 
  private:
   Value* lhs_;
@@ -108,7 +107,7 @@ class BinaryInst : public Instruction {
 class ReturnInst : public Instruction {
  public:
   explicit ReturnInst(Value* val);
-  Value* value() const { return value_; }
+  Value* value() const;
 
  private:
   Value* value_;
@@ -122,7 +121,7 @@ class AllocaInst : public Instruction {
 class LoadInst : public Instruction {
  public:
   LoadInst(Value* ptr, std::string name);
-  Value* ptr() const { return ptr_; }
+  Value* ptr() const;
 
  private:
   Value* ptr_;
@@ -131,8 +130,8 @@ class LoadInst : public Instruction {
 class StoreInst : public Instruction {
  public:
   StoreInst(Value* val, Value* ptr);
-  Value* value() const { return value_; }
-  Value* ptr() const { return ptr_; }
+  Value* value() const;
+  Value* ptr() const;
 
  private:
   Value* value_;
@@ -141,14 +140,10 @@ class StoreInst : public Instruction {
 
 class BasicBlock {
  public:
-  explicit BasicBlock(std::string name) : name_(std::move(name)) {}
-  const std::string& name() const { return name_; }
-  bool HasTerminator() const {
-    return !instructions_.empty() && instructions_.back()->IsTerminator();
-  }
-  const std::vector<std::unique_ptr<Instruction>>& instructions() const {
-    return instructions_;
-  }
+  explicit BasicBlock(std::string name);
+  const std::string& name() const;
+  bool HasTerminator() const;
+  const std::vector<std::unique_ptr<Instruction>>& instructions() const;
   template <typename T, typename... Args>
   T* Append(Args&&... args) {
     if (HasTerminator()) {
@@ -172,11 +167,9 @@ class Function : public Value {
   // 允许显式指定返回类型，便于后续扩展多种函数签名。
   Function(std::string name, std::shared_ptr<Type> ret_type);
   BasicBlock* CreateBlock(const std::string& name);
-  BasicBlock* entry() { return entry_; }
-  const BasicBlock* entry() const { return entry_; }
-  const std::vector<std::unique_ptr<BasicBlock>>& blocks() const {
-    return blocks_;
-  }
+  BasicBlock* entry();
+  const BasicBlock* entry() const;
+  const std::vector<std::unique_ptr<BasicBlock>>& blocks() const;
 
  private:
   BasicBlock* entry_ = nullptr;
@@ -188,9 +181,7 @@ class Module {
   // 创建函数时显式传入返回类型，便于在 IRGen 中根据语法树信息选择类型。
   Function* CreateFunction(const std::string& name,
                            std::shared_ptr<Type> ret_type);
-  const std::vector<std::unique_ptr<Function>>& functions() const {
-    return functions_;
-  }
+  const std::vector<std::unique_ptr<Function>>& functions() const;
 
  private:
   std::vector<std::unique_ptr<Function>> functions_;
@@ -198,17 +189,15 @@ class Module {
 
 class IRBuilder {
  public:
-  explicit IRBuilder(BasicBlock* bb) : insertBlock_(bb) {}
-  void SetInsertPoint(BasicBlock* bb) { insertBlock_ = bb; }
-  BasicBlock* GetInsertBlock() const { return insertBlock_; }
+  explicit IRBuilder(BasicBlock* bb);
+  void SetInsertPoint(BasicBlock* bb);
+  BasicBlock* GetInsertBlock() const;
 
   // 构造常量、二元运算、返回指令的最小集合。
   ConstantInt* CreateConstInt(int v);
   BinaryInst* CreateBinary(Opcode op, Value* lhs, Value* rhs,
                            const std::string& name);
-  BinaryInst* CreateAdd(Value* lhs, Value* rhs, const std::string& name) {
-    return CreateBinary(Opcode::Add, lhs, rhs, name);
-  }
+  BinaryInst* CreateAdd(Value* lhs, Value* rhs, const std::string& name);
   AllocaInst* CreateAllocaI32(const std::string& name);
   LoadInst* CreateLoad(Value* ptr, const std::string& name);
   StoreInst* CreateStore(Value* val, Value* ptr);
diff --git a/src/ir/IRBuilder.cpp b/src/ir/IRBuilder.cpp
index 1812f14..58f08de 100644
--- a/src/ir/IRBuilder.cpp
+++ b/src/ir/IRBuilder.cpp
@@ -18,6 +18,12 @@ bool IsPtrInt32Type(const std::shared_ptr<Type>& ty) {
 
 }  // namespace
 
+IRBuilder::IRBuilder(BasicBlock* bb) : insertBlock_(bb) {}
+
+void IRBuilder::SetInsertPoint(BasicBlock* bb) { insertBlock_ = bb; }
+
+BasicBlock* IRBuilder::GetInsertBlock() const { return insertBlock_; }
+
 ConstantInt* IRBuilder::CreateConstInt(int v) {
   // 常量不需要挂在基本块里，由 Context 负责去重与生命周期。
   return DefaultContext().GetConstInt(v);
@@ -47,6 +53,11 @@ BinaryInst* IRBuilder::CreateBinary(Opcode op, Value* lhs, Value* rhs,
   return insertBlock_->Append<BinaryInst>(op, lhs->type(), lhs, rhs, name);
 }
 
+BinaryInst* IRBuilder::CreateAdd(Value* lhs, Value* rhs,
+                                 const std::string& name) {
+  return CreateBinary(Opcode::Add, lhs, rhs, name);
+}
+
 AllocaInst* IRBuilder::CreateAllocaI32(const std::string& name) {
   if (!insertBlock_) {
     throw std::runtime_error("IRBuilder 未设置插入点");
diff --git a/src/ir/Instruction.cpp b/src/ir/Instruction.cpp
index 596724a..a808daa 100644
--- a/src/ir/Instruction.cpp
+++ b/src/ir/Instruction.cpp
@@ -18,6 +18,17 @@ bool IsPtrInt32Type(const std::shared_ptr<Type>& ty) {
 
 }  // namespace
 
+Instruction::Instruction(Opcode op, std::shared_ptr<Type> ty, std::string name)
+    : Value(std::move(ty), std::move(name)), opcode_(op) {}
+
+Opcode Instruction::opcode() const { return opcode_; }
+
+bool Instruction::IsTerminator() const { return opcode_ == Opcode::Ret; }
+
+BasicBlock* Instruction::parent() const { return parent_; }
+
+void Instruction::set_parent(BasicBlock* parent) { parent_ = parent; }
+
 BinaryInst::BinaryInst(Opcode op, std::shared_ptr<Type> ty, Value* lhs,
                        Value* rhs, std::string name)
     : Instruction(op, std::move(ty), std::move(name)), lhs_(lhs), rhs_(rhs) {
@@ -45,6 +56,10 @@ BinaryInst::BinaryInst(Opcode op, std::shared_ptr<Type> ty, Value* lhs,
   }
 }
 
+Value* BinaryInst::lhs() const { return lhs_; }
+
+Value* BinaryInst::rhs() const { return rhs_; }
+
 ReturnInst::ReturnInst(Value* val)
     : Instruction(Opcode::Ret, Type::Void(), ""), value_(val) {
   if (!value_) {
@@ -53,6 +68,8 @@ ReturnInst::ReturnInst(Value* val)
   value_->AddUser(this);
 }
 
+Value* ReturnInst::value() const { return value_; }
+
 AllocaInst::AllocaInst(std::string name)
     : Instruction(Opcode::Alloca, Type::PtrInt32(), std::move(name)) {}
 
@@ -67,6 +84,8 @@ LoadInst::LoadInst(Value* ptr, std::string name)
   ptr_->AddUser(this);
 }
 
+Value* LoadInst::ptr() const { return ptr_; }
+
 StoreInst::StoreInst(Value* val, Value* ptr)
     : Instruction(Opcode::Store, Type::Void(), ""), value_(val), ptr_(ptr) {
   if (!value_) {
@@ -85,4 +104,8 @@ StoreInst::StoreInst(Value* val, Value* ptr)
   ptr_->AddUser(this);
 }
 
+Value* StoreInst::value() const { return value_; }
+
+Value* StoreInst::ptr() const { return ptr_; }
+
 }  // namespace ir
diff --git a/src/ir/Module.cpp b/src/ir/Module.cpp
index 92ca9df..0a2df76 100644
--- a/src/ir/Module.cpp
+++ b/src/ir/Module.cpp
@@ -12,4 +12,8 @@ Function* Module::CreateFunction(const std::string& name,
   return functions_.back().get();
 }
 
+const std::vector<std::unique_ptr<Function>>& Module::functions() const {
+  return functions_;
+}
+
 }  // namespace ir
diff --git a/src/ir/Type.cpp b/src/ir/Type.cpp
index dc6501b..4712485 100644
--- a/src/ir/Type.cpp
+++ b/src/ir/Type.cpp
@@ -6,6 +6,10 @@
 
 namespace ir {
 
+Type::Type(Kind k) : kind_(k) {}
+
+Type::Kind Type::kind() const { return kind_; }
+
 std::shared_ptr<Type> Type::Void() { return DefaultContext().Void(); }
 
 std::shared_ptr<Type> Type::Int32() { return DefaultContext().Int32(); }
diff --git a/src/ir/Value.cpp b/src/ir/Value.cpp
index e544895..9bd2fa7 100644
--- a/src/ir/Value.cpp
+++ b/src/ir/Value.cpp
@@ -5,6 +5,19 @@
 
 namespace ir {
 
+Value::Value(std::shared_ptr<Type> ty, std::string name)
+    : type_(std::move(ty)), name_(std::move(name)) {}
+
+const std::shared_ptr<Type>& Value::type() const { return type_; }
+
+const std::string& Value::name() const { return name_; }
+
+void Value::set_name(std::string n) { name_ = std::move(n); }
+
+void Value::AddUser(Instruction* user) { users_.push_back(user); }
+
+const std::vector<Instruction*>& Value::users() const { return users_; }
+
 ConstantInt::ConstantInt(int v) : Value(Type::Int32(), ""), value_(v) {}
 
 }  // namespace ir
diff --git a/src/irgen/IRGen.h b/src/irgen/IRGen.h
index d3c9d28..f05d63f 100644
--- a/src/irgen/IRGen.h
+++ b/src/irgen/IRGen.h
@@ -9,6 +9,7 @@
 
 #include "SysYParser.h"
 #include "ir/IR.h"
+#include "sem/Sema.h"
 
 namespace antlr4 {
 namespace tree {
@@ -25,7 +26,7 @@ class Value;
 
 class IRGenImpl {
  public:
-  explicit IRGenImpl(ir::Module& module);
+  IRGenImpl(ir::Module& module, const SemanticContext& sema);
 
   void Gen(SysYParser::CompUnitContext& cu);
 
@@ -43,10 +44,12 @@ class IRGenImpl {
   ir::Value* GenPrimary(SysYParser::PrimaryContext& primary);
 
   ir::Module& module_;
+  const SemanticContext& sema_;
   ir::Function* func_;
   ir::IRBuilder builder_;
-  // 当前只维护函数级局部变量表；若后续引入嵌套块作用域，需要改成作用域栈。
-  std::unordered_map<std::string, ir::Value*> locals_;
+  // 名称绑定由 Sema 负责；IRGen 只维护“声明 -> 存储槽位”的代码生成状态。
+  std::unordered_map<SysYParser::VarDeclContext*, ir::Value*> storage_map_;
 };
 
-std::unique_ptr<ir::Module> GenerateIR(antlr4::tree::ParseTree* tree);
+std::unique_ptr<ir::Module> GenerateIR(SysYParser::CompUnitContext& tree,
+                                       const SemanticContext& sema);
diff --git a/src/irgen/IRGenDecl.cpp b/src/irgen/IRGenDecl.cpp
index 948c72f..72c8cfb 100644
--- a/src/irgen/IRGenDecl.cpp
+++ b/src/irgen/IRGenDecl.cpp
@@ -36,12 +36,11 @@ void IRGenImpl::GenDecl(SysYParser::DeclContext& decl) {
 }
 
 void IRGenImpl::GenVarDecl(SysYParser::VarDeclContext& decl) {
-  const std::string name = decl.Ident()->getText();
-  if (locals_.find(name) != locals_.end()) {
-    throw std::runtime_error("[irgen] 重复定义变量: " + name);
+  if (storage_map_.find(&decl) != storage_map_.end()) {
+    throw std::runtime_error("[irgen] 声明重复生成存储槽位");
   }
   auto* slot = builder_.CreateAllocaI32(ir::DefaultContext().NextTemp());
-  locals_[name] = slot;
+  storage_map_[&decl] = slot;
 
   ir::Value* init = nullptr;
   if (decl.exp()) {
diff --git a/src/irgen/IRGenDriver.cpp b/src/irgen/IRGenDriver.cpp
index 014b60a..aaeb297 100644
--- a/src/irgen/IRGenDriver.cpp
+++ b/src/irgen/IRGenDriver.cpp
@@ -4,21 +4,12 @@
 #include <stdexcept>
 
 #include "SysYParser.h"
-#include "antlr4-runtime.h"
 #include "ir/IR.h"
 
-std::unique_ptr<ir::Module> GenerateIR(antlr4::tree::ParseTree* tree) {
-  if (!tree) {
-    throw std::runtime_error("[irgen] 语法树为空");
-  }
-
-  auto* cu = dynamic_cast<SysYParser::CompUnitContext*>(tree);
-  if (!cu) {
-    throw std::runtime_error("[irgen] 语法树根节点不是 compUnit");
-  }
-
+std::unique_ptr<ir::Module> GenerateIR(SysYParser::CompUnitContext& tree,
+                                       const SemanticContext& sema) {
   auto module = std::make_unique<ir::Module>();
-  IRGenImpl gen(*module);
-  gen.Gen(*cu);
+  IRGenImpl gen(*module, sema);
+  gen.Gen(tree);
   return module;
 }
diff --git a/src/irgen/IRGenExp.cpp b/src/irgen/IRGenExp.cpp
index e62ca91..a7c7292 100644
--- a/src/irgen/IRGenExp.cpp
+++ b/src/irgen/IRGenExp.cpp
@@ -33,10 +33,15 @@ ir::Value* IRGenImpl::GenPrimary(SysYParser::PrimaryContext& primary) {
     return ir::DefaultContext().GetConstInt(std::stoi(primary.Number()->getText()));
   }
   if (primary.Ident()) {
-    const std::string name = primary.Ident()->getText();
-    auto it = locals_.find(name);
-    if (it == locals_.end()) {
-      throw std::runtime_error("[irgen] 变量未找到: " + name);
+    auto* decl = sema_.ResolveVarUse(&primary);
+    if (!decl) {
+      throw std::runtime_error("[irgen] 变量使用缺少语义绑定: " +
+                               primary.Ident()->getText());
+    }
+    auto it = storage_map_.find(decl);
+    if (it == storage_map_.end()) {
+      throw std::runtime_error("[irgen] 变量声明缺少存储槽位: " +
+                               primary.Ident()->getText());
     }
     return builder_.CreateLoad(it->second, ir::DefaultContext().NextTemp());
   }
diff --git a/src/irgen/IRGenFunc.cpp b/src/irgen/IRGenFunc.cpp
index 4c0500a..8b2edc8 100644
--- a/src/irgen/IRGenFunc.cpp
+++ b/src/irgen/IRGenFunc.cpp
@@ -19,8 +19,8 @@ void VerifyFunctionStructure(const ir::Function& func) {
 
 }  // namespace
 
-IRGenImpl::IRGenImpl(ir::Module& module)
-    : module_(module), func_(nullptr), builder_(nullptr) {}
+IRGenImpl::IRGenImpl(ir::Module& module, const SemanticContext& sema)
+    : module_(module), sema_(sema), func_(nullptr), builder_(nullptr) {}
 
 void IRGenImpl::Gen(SysYParser::CompUnitContext& cu) {
   if (!cu.funcDef()) {
@@ -39,7 +39,7 @@ void IRGenImpl::GenFuncDef(SysYParser::FuncDefContext& func) {
 
   func_ = module_.CreateFunction(func.Ident()->getText(), ir::Type::Int32());
   builder_.SetInsertPoint(func_->entry());
-  locals_.clear();
+  storage_map_.clear();
 
   GenBlock(*func.block());
   // 语义正确性主要由 sema 保证，这里只兜底检查 IR 结构是否合法。
diff --git a/src/main.cpp b/src/main.cpp
index da355f6..c798420 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -30,9 +30,9 @@ int main(int argc, char** argv) {
     if (!comp_unit) {
       throw std::runtime_error("[main] 语法树根节点不是 compUnit");
     }
-    RunSema(*comp_unit);
+    auto sema = RunSema(*comp_unit);
 
-    auto module = GenerateIR(antlr.tree);
+    auto module = GenerateIR(*comp_unit, sema);
     if (opts.emit_ir) {
       ir::IRPrinter printer;
       if (need_blank_line) {
diff --git a/src/sem/Sema.cpp b/src/sem/Sema.cpp
index d64d9f0..e586036 100644
--- a/src/sem/Sema.cpp
+++ b/src/sem/Sema.cpp
@@ -7,43 +7,47 @@
 
 namespace {
 
-void CheckExpr(SysYParser::ExpContext& exp, const SymbolTable& table);
+void CheckExpr(SysYParser::ExpContext& exp, const SymbolTable& table,
+               SemanticContext& sema);
 
 void CheckPrimary(SysYParser::PrimaryContext& primary,
-                  const SymbolTable& table) {
+                  const SymbolTable& table, SemanticContext& sema) {
   if (primary.Number()) {
     return;
   }
 
   if (primary.Ident()) {
     const std::string name = primary.Ident()->getText();
-    if (!table.Contains(name)) {
+    auto* decl = table.Lookup(name);
+    if (!decl) {
       throw std::runtime_error("[sema] 使用了未定义的变量: " + name);
     }
+    sema.BindVarUse(&primary, decl);
     return;
   }
 
   if (primary.exp()) {
-    CheckExpr(*primary.exp(), table);
+    CheckExpr(*primary.exp(), table, sema);
     return;
   }
 
   throw std::runtime_error("[sema] 暂不支持的 primary 形式");
 }
 
-void CheckExpr(SysYParser::ExpContext& exp, const SymbolTable& table) {
+void CheckExpr(SysYParser::ExpContext& exp, const SymbolTable& table,
+               SemanticContext& sema) {
   if (!exp.addExp()) {
     throw std::runtime_error("[sema] 非法表达式");
   }
   const auto& terms = exp.addExp()->primary();
   for (auto* term : terms) {
-    CheckPrimary(*term, table);
+    CheckPrimary(*term, table, sema);
   }
 }
 
 }  // namespace
 
-void RunSema(SysYParser::CompUnitContext& comp_unit) {
+SemanticContext RunSema(SysYParser::CompUnitContext& comp_unit) {
   auto* func = comp_unit.funcDef();
   if (!func || !func->block()) {
     throw std::runtime_error("[sema] 缺少 main 函数定义");
@@ -53,6 +57,7 @@ void RunSema(SysYParser::CompUnitContext& comp_unit) {
   }
 
   SymbolTable table;
+  SemanticContext sema;
   bool seen_return = false;
 
   const auto& items = func->block()->blockItem();
@@ -74,14 +79,14 @@ void RunSema(SysYParser::CompUnitContext& comp_unit) {
         throw std::runtime_error("[sema] 重复定义变量: " + name);
       }
       if (decl->exp()) {
-        CheckExpr(*decl->exp(), table);
+        CheckExpr(*decl->exp(), table, sema);
       }
-      table.Add(name);
+      table.Add(name, decl);
       continue;
     }
     if (auto* stmt = item->stmt(); stmt && stmt->returnStmt()) {
       auto* ret = stmt->returnStmt();
-      CheckExpr(*ret->exp(), table);
+      CheckExpr(*ret->exp(), table, sema);
       seen_return = true;
       if (i + 1 != items.size()) {
         throw std::runtime_error("[sema] return 必须是 main 函数中的最后一条语句");
@@ -94,4 +99,6 @@ void RunSema(SysYParser::CompUnitContext& comp_unit) {
   if (!seen_return) {
     throw std::runtime_error("[sema] main 函数必须包含 return 语句");
   }
+
+  return sema;
 }
diff --git a/src/sem/Sema.h b/src/sem/Sema.h
index 8f9d9a7..3dcc830 100644
--- a/src/sem/Sema.h
+++ b/src/sem/Sema.h
@@ -1,9 +1,30 @@
-// 基于语法树的极简语义检查。
+// 基于语法树的极简语义检查与名称绑定。
 #pragma once
 
+#include <unordered_map>
+
 #include "SysYParser.h"
 
+class SemanticContext {
+ public:
+  void BindVarUse(SysYParser::PrimaryContext* use,
+                  SysYParser::VarDeclContext* decl) {
+    var_uses_[use] = decl;
+  }
+
+  SysYParser::VarDeclContext* ResolveVarUse(
+      const SysYParser::PrimaryContext* use) const {
+    auto it = var_uses_.find(use);
+    return it == var_uses_.end() ? nullptr : it->second;
+  }
+
+ private:
+  std::unordered_map<const SysYParser::PrimaryContext*,
+                     SysYParser::VarDeclContext*>
+      var_uses_;
+};
+
 // 目前仅检查：
 // - 变量先声明后使用
 // - 局部变量不允许重复定义
-void RunSema(SysYParser::CompUnitContext& comp_unit);
+SemanticContext RunSema(SysYParser::CompUnitContext& comp_unit);
diff --git a/src/sem/SymbolTable.h b/src/sem/SymbolTable.h
index eaf565e..06d59f4 100644
--- a/src/sem/SymbolTable.h
+++ b/src/sem/SymbolTable.h
@@ -1,16 +1,24 @@
-// 极简符号表：记录局部变量是否定义。
+// 极简符号表：记录局部变量定义点。
 #pragma once
 
 #include <string>
 #include <unordered_map>
 
+#include "SysYParser.h"
+
 class SymbolTable {
  public:
-  void Add(const std::string& name) { table_[name] = true; }
+  void Add(const std::string& name, SysYParser::VarDeclContext* decl) {
+    table_[name] = decl;
+  }
   bool Contains(const std::string& name) const {
     return table_.find(name) != table_.end();
   }
+  SysYParser::VarDeclContext* Lookup(const std::string& name) const {
+    auto it = table_.find(name);
+    return it == table_.end() ? nullptr : it->second;
+  }
 
  private:
-  std::unordered_map<std::string, bool> table_;
+  std::unordered_map<std::string, SysYParser::VarDeclContext*> table_;
 };