diff --git a/extlibs/frontend/AntlrDriver.h b/extlibs/frontend/AntlrDriver.h
new file mode 100644
index 00000000..ee22da95
--- /dev/null
+++ b/extlibs/frontend/AntlrDriver.h
@@ -0,0 +1,20 @@
+// 包装 ANTLR4，提供简易的解析入口。
+#pragma once
+
+#include <memory>
+#include <string>
+
+#include "SysYLexer.h"
+#include "SysYParser.h"
+#include "antlr4-runtime.h"
+
+struct AntlrResult {
+  std::unique_ptr<antlr4::ANTLRInputStream> input;
+  std::unique_ptr<SysYLexer> lexer;
+  std::unique_ptr<antlr4::CommonTokenStream> tokens;
+  std::unique_ptr<SysYParser> parser;
+  antlr4::tree::ParseTree* tree = nullptr;  // owned by parser
+};
+
+// 解析指定文件，发生错误时抛出 std::runtime_error。
+AntlrResult ParseFileWithAntlr(const std::string& path);
diff --git a/extlibs/frontend/SyntaxTreePrinter.h b/extlibs/frontend/SyntaxTreePrinter.h
new file mode 100644
index 00000000..4633b5ec
--- /dev/null
+++ b/extlibs/frontend/SyntaxTreePrinter.h
@@ -0,0 +1,9 @@
+#pragma once
+
+#include <iosfwd>
+
+#include "antlr4-runtime.h"
+
+// 以树状缩进形式直接打印 ANTLR parse tree。
+void PrintSyntaxTree(antlr4::tree::ParseTree* tree, antlr4::Parser* parser,
+                     std::ostream& os);
diff --git a/extlibs/ir/IR.h b/extlibs/ir/IR.h
new file mode 100644
index 00000000..87a35e0e
--- /dev/null
+++ b/extlibs/ir/IR.h
@@ -0,0 +1,545 @@
+// 当前只支撑 i32、i32*、void 以及最小的内存/算术指令，演示用。
+//
+// 当前已经实现：
+// 1. 基础类型系统：void / i32 / i32*
+// 2. Value 体系：Value / ConstantValue / ConstantInt / Function / BasicBlock / User / GlobalValue / Instruction
+// 3. 最小指令集：Add / Alloca / Load / Store / Ret
+// 4. BasicBlock / Function / Module 三层组织结构
+// 5. IRBuilder：便捷创建常量和最小指令
+// 6. def-use 关系的轻量实现：
+//    - Instruction 保存 operand 列表
+//    - Value 保存 uses
+//    - 支持 ReplaceAllUsesWith 的简化实现
+//
+// 当前尚未实现或只做了最小占位：
+// 1. 完整类型系统：数组、函数类型、label 类型等
+// 2. 更完整的指令系统：br / condbr / call / phi / gep 等
+// 3. 更成熟的 Use 管理（例如 LLVM 风格的双向链式结构）
+// 4. 更完整的 IR verifier 和优化基础设施
+//
+// 当前需要特别说明的两个简化点：
+// 1. BasicBlock 虽然已经纳入 Value 体系，但其类型目前仍用 void 作为占位，
+//    后续如果补 label type，可以再改成更合理的块标签类型。
+// 2. ConstantValue 体系目前只实现了 ConstantInt，后续可以继续补 ConstantFloat、
+//    ConstantArray等更完整的常量种类。
+//
+// 建议的扩展顺序：
+// 1. 先补更多指令和类型
+// 2. 再补控制流相关 IR
+// 3. 最后再考虑把 Value/User/Use 进一步抽象成更完整的框架
+
+#pragma once
+
+#include <iosfwd>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+namespace ir {
+
+class Type;
+class Value;
+class User;
+class ConstantValue;
+class ConstantInt;
+class ConstantFloat;
+class GlobalValue;
+class Instruction;
+class BasicBlock;
+class Function;
+class Argument;
+class GlobalVariable;
+
+
+
+// Use 表示一个 Value 的一次使用记录。
+// 当前实现设计：
+// - value：被使用的值
+// - user：使用该值的 User
+// - operand_index：该值在 user 操作数列表中的位置
+
+class Use {
+ public:
+  Use() = default;
+  Use(Value* value, User* user, size_t operand_index)
+      : value_(value), user_(user), operand_index_(operand_index) {}
+
+  Value* GetValue() const { return value_; }
+  User* GetUser() const { return user_; }
+  size_t GetOperandIndex() const { return operand_index_; }
+
+  void SetValue(Value* value) { value_ = value; }
+  void SetUser(User* user) { user_ = user; }
+  void SetOperandIndex(size_t operand_index) { operand_index_ = operand_index; }
+
+ private:
+  Value* value_ = nullptr;
+  User* user_ = nullptr;
+  size_t operand_index_ = 0;
+};
+
+// IR 上下文：集中管理类型、常量等共享资源，便于复用与扩展。
+class Context {
+ public:
+  Context() = default;
+  ~Context();
+  // 去重创建 i32 常量。
+  ConstantInt* GetConstInt(int v);
+  ConstantFloat* GetConstFloat(double v);
+  // 去重创建 i1 常量（0 或 1）。
+  ConstantInt* GetConstBool(int v);
+
+  std::string NextTemp();
+
+ private:
+  std::unordered_map<int, std::unique_ptr<ConstantInt>> const_ints_;
+  std::unordered_map<std::string, std::unique_ptr<ConstantFloat>> const_floats_;
+  std::unordered_map<int, std::unique_ptr<ConstantInt>> const_bools_;
+  int temp_index_ = -1;
+};
+
+class Type {
+ public:
+  enum class Kind { Void, Int1, Int32, Float32, PtrInt32, PtrFloat32 };
+  explicit Type(Kind k);
+  // 使用静态共享对象获取类型。
+  // 同一类型可直接比较返回值是否相等，例如：
+  // Type::GetInt32Type() == Type::GetInt32Type()
+  static const std::shared_ptr<Type>& GetVoidType();
+  static const std::shared_ptr<Type>& GetInt1Type();
+  static const std::shared_ptr<Type>& GetInt32Type();
+  static const std::shared_ptr<Type>& GetFloat32Type();
+  static const std::shared_ptr<Type>& GetPtrInt32Type();
+  static const std::shared_ptr<Type>& GetPtrFloat32Type();
+  Kind GetKind() const;
+  bool IsVoid() const;
+  bool IsInt1() const;
+  bool IsInt32() const;
+  bool IsFloat32() const;
+  bool IsPtrInt32() const;
+  bool IsPtrFloat32() const;
+
+ private:
+  Kind kind_;
+};
+
+class Value {
+ public:
+  Value(std::shared_ptr<Type> ty, std::string name);
+  virtual ~Value() = default;
+  const std::shared_ptr<Type>& GetType() const;
+  const std::string& GetName() const;
+  void SetName(std::string n);
+  bool IsVoid() const;
+  bool IsInt32() const;
+  bool IsFloat32() const;
+  bool IsPtrInt32() const;
+  bool IsPtrFloat32() const;
+  bool IsConstant() const;
+  bool IsInstruction() const;
+  bool IsUser() const;
+  bool IsFunction() const;
+  void AddUse(User* user, size_t operand_index);
+  void RemoveUse(User* user, size_t operand_index);
+  const std::vector<Use>& GetUses() const;
+  void ReplaceAllUsesWith(Value* new_value);
+
+ protected:
+  std::shared_ptr<Type> type_;
+  std::string name_;
+  std::vector<Use> uses_;
+};
+
+// ConstantValue 是常量体系的基类。
+// 当前只实现了 ConstantInt，后续可继续扩展更多常量种类。
+class ConstantValue : public Value {
+ public:
+  ConstantValue(std::shared_ptr<Type> ty, std::string name = "");
+};
+
+class ConstantInt : public ConstantValue {
+ public:
+  ConstantInt(std::shared_ptr<Type> ty, int v);
+  int GetValue() const { return value_; }
+
+ private:
+  int value_{};
+};
+
+class ConstantFloat : public ConstantValue {
+ public:
+  ConstantFloat(std::shared_ptr<Type> ty, double v);
+  double GetValue() const { return value_; }
+
+ private:
+  double value_{};
+};
+
+// 后续还需要扩展更多指令类型。
+enum class Opcode {
+  Add,
+  Sub,
+  Mul,
+  Div,
+  Mod,
+  SIToFP,
+  FPToSI,
+  ZExt,
+  Eq,
+  Ne,
+  Lt,
+  Le,
+  Gt,
+  Ge,
+  Alloca,
+  Load,
+  Store,
+  GEP,
+  Call,
+  Br,
+  CondBr,
+  Ret,
+  Phi
+};
+
+// User 是所有“会使用其他 Value 作为输入”的 IR 对象的抽象基类。
+// 当前实现中只有 Instruction 继承自 User。
+class User : public Value {
+ public:
+  User(std::shared_ptr<Type> ty, std::string name);
+  size_t GetNumOperands() const;
+  Value* GetOperand(size_t index) const;
+  void SetOperand(size_t index, Value* value);
+  void AddOperand(Value* value);
+
+ private:
+  std::vector<Value*> operands_;
+};
+
+// GlobalValue 是全局值/全局变量体系的空壳占位类。
+// 当前只补齐类层次，具体初始化器、打印和链接语义后续再补。
+class GlobalValue : public User {
+ public:
+  GlobalValue(std::shared_ptr<Type> ty, std::string name);
+};
+
+class GlobalVariable : public GlobalValue {
+ public:
+  enum class StorageKind {
+    Scalar,
+    Array,
+  };
+
+  enum class ElemKind {
+    Int32,
+    Float32,
+  };
+
+  GlobalVariable(std::string name, int init_value);
+  GlobalVariable(std::string name, double init_value);
+  GlobalVariable(std::string name, size_t array_size);
+  GlobalVariable(std::string name, size_t array_size, ElemKind elem_kind);
+  GlobalVariable(std::string name, size_t array_size, const std::vector<int>& init_values);
+  GlobalVariable(std::string name, size_t array_size, const std::vector<double>& init_values);
+  StorageKind GetStorageKind() const;
+  bool IsArray() const;
+  ElemKind GetElemKind() const;
+  bool IsFloatElem() const;
+  int GetInitValue() const;
+  double GetInitFloatValue() const;
+  size_t GetArraySize() const;
+  const std::vector<int>& GetInitValues() const;
+  const std::vector<double>& GetInitFloatValues() const;
+  bool HasInitValues() const;
+
+ private:
+  StorageKind storage_kind_ = StorageKind::Scalar;
+  ElemKind elem_kind_ = ElemKind::Int32;
+  int init_value_ = 0;
+  double init_float_value_ = 0.0;
+  size_t array_size_ = 0;
+  std::vector<int> init_values_;
+  std::vector<double> init_float_values_;
+};
+
+class Instruction : public User {
+ public:
+  Instruction(Opcode op, std::shared_ptr<Type> ty, std::string name = "");
+  Opcode GetOpcode() const;
+  bool IsTerminator() const;
+  BasicBlock* GetParent() const;
+  void SetParent(BasicBlock* parent);
+
+ private:
+  Opcode opcode_;
+  BasicBlock* parent_ = nullptr;
+};
+
+class BinaryInst : public Instruction {
+ public:
+  BinaryInst(Opcode op, std::shared_ptr<Type> ty, Value* lhs, Value* rhs,
+             std::string name);
+  Value* GetLhs() const;
+  Value* GetRhs() const;
+};
+
+class CastInst : public Instruction {
+ public:
+  CastInst(Opcode op, std::shared_ptr<Type> ty, Value* operand,
+           std::string name);
+  Value* GetOperandValue() const;
+};
+
+class BranchInst : public Instruction {
+ public:
+  BranchInst(std::shared_ptr<Type> void_ty, BasicBlock* target);
+  BasicBlock* GetTarget() const;
+};
+
+class CondBranchInst : public Instruction {
+ public:
+  CondBranchInst(std::shared_ptr<Type> void_ty, Value* cond, BasicBlock* true_bb,
+                 BasicBlock* false_bb);
+  Value* GetCond() const;
+  BasicBlock* GetTrueTarget() const;
+  BasicBlock* GetFalseTarget() const;
+};
+
+class CallInst : public Instruction {
+ public:
+  CallInst(std::shared_ptr<Type> ret_ty, Function* callee,
+           const std::vector<Value*>& args, std::string name);
+  Function* GetCallee() const;
+  size_t GetNumArgs() const;
+  Value* GetArg(size_t index) const;
+};
+
+class ReturnInst : public Instruction {
+ public:
+  ReturnInst(std::shared_ptr<Type> void_ty, Value* val = nullptr);
+  Value* GetValue() const;
+  bool HasValue() const;
+};
+
+class AllocaInst : public Instruction {
+ public:
+  AllocaInst(std::shared_ptr<Type> elem_ty, std::string name,
+             Value* count = nullptr);
+  bool IsArrayAlloca() const;
+  Value* GetCount() const;
+  std::shared_ptr<Type> GetElementType() const;
+};
+
+class GetElementPtrInst : public Instruction {
+ public:
+  GetElementPtrInst(std::shared_ptr<Type> ptr_ty, Value* base_ptr,
+                    Value* index, std::string name);
+  Value* GetBasePtr() const;
+  Value* GetIndex() const;
+};
+
+class LoadInst : public Instruction {
+ public:
+  LoadInst(std::shared_ptr<Type> val_ty, Value* ptr, std::string name);
+  Value* GetPtr() const;
+};
+
+class StoreInst : public Instruction {
+public:
+  StoreInst(std::shared_ptr<Type> void_ty, Value* val, Value* ptr);
+  Value* GetValue() const;
+  Value* GetPtr() const;
+};
+
+class PhiInst : public Instruction {
+public:
+  PhiInst(std::shared_ptr<Type> ty, std::string name);
+  AllocaInst* GetAlloca() const { return alloca_; }
+  void SetAlloca(AllocaInst* alloca) { alloca_ = alloca; }
+
+private:
+  AllocaInst* alloca_;
+};
+
+class Argument : public Value {
+ public:
+  Argument(std::shared_ptr<Type> ty, std::string name, size_t index);
+  size_t GetIndex() const;
+
+ private:
+  size_t index_ = 0;
+};
+
+// BasicBlock 已纳入 Value 体系，便于后续向更完整 IR 类图靠拢。
+// 当前其类型仍使用 void 作为占位，后续可替换为专门的 label type。
+class BasicBlock : public Value {
+ public:
+  explicit BasicBlock(std::string name);
+  Function* GetParent() const;
+  void SetParent(Function* parent);
+  bool HasTerminator() const;
+  const std::vector<std::unique_ptr<Instruction>>& GetInstructions() const;
+  const std::vector<BasicBlock*>& GetPredecessors() const;
+  const std::vector<BasicBlock*>& GetSuccessors() const;
+  std::vector<BasicBlock*>& GetMutablePredecessors() {
+    return predecessors_;
+  }
+  std::vector<BasicBlock*>& GetMutableSuccessors() {
+    return successors_;
+  }
+  template <typename T, typename... Args>
+  T* Append(Args&&... args) {
+    if (HasTerminator()) {
+      throw std::runtime_error("BasicBlock 已有 terminator，不能继续追加指令: " +
+                               name_);
+    }
+    auto inst = std::make_unique<T>(std::forward<Args>(args)...);
+    auto* ptr = inst.get();
+    ptr->SetParent(this);
+    instructions_.push_back(std::move(inst));
+    return ptr;
+  }
+  template <typename T, typename... Args>
+  T* Prepend(Args&&... args) {
+    auto inst = std::make_unique<T>(std::forward<Args>(args)...);
+    auto* ptr = inst.get();
+    ptr->SetParent(this);
+    instructions_.insert(instructions_.begin(), std::move(inst));
+    return ptr;
+  }
+  template <typename T, typename... Args>
+  T* InsertAlloca(Args&&... args) {
+    auto inst = std::make_unique<T>(std::forward<Args>(args)...);
+    auto* ptr = inst.get();
+    ptr->SetParent(this);
+    instructions_.insert(instructions_.begin() + alloca_insert_index_, std::move(inst));
+    ++alloca_insert_index_;
+    return ptr;
+  }
+  void RemoveInstruction(Instruction* inst) {
+    for (auto it = instructions_.begin(); it != instructions_.end(); ++it) {
+      if (it->get() == inst) {
+        instructions_.erase(it);
+        break;
+      }
+    }
+  }
+  std::unique_ptr<Instruction> TakeInstruction(Instruction* inst);
+  void InsertInstructionBeforeTerminator(std::unique_ptr<Instruction> inst);
+
+ private:
+  Function* parent_ = nullptr;
+  std::vector<std::unique_ptr<Instruction>> instructions_;
+  std::vector<BasicBlock*> predecessors_;
+  std::vector<BasicBlock*> successors_;
+  size_t alloca_insert_index_ = 0;
+};
+
+// Function 当前也采用了最小实现。
+// 需要特别注意：由于项目里还没有单独的 FunctionType，
+// Function 继承自 Value 后，其 type_ 目前只保存“返回类型”，
+// 并不能完整表达“返回类型 + 形参列表”这一整套函数签名。
+// 这对当前只支持 int main() 的最小 IR 足够，但后续若补普通函数、
+// 形参和调用，通常需要引入专门的函数类型表示。
+class Function : public Value {
+ public:
+  // 当前构造函数接收的也是返回类型，而不是完整函数类型。
+  Function(std::string name, std::shared_ptr<Type> ret_type,
+           bool is_external = false);
+  Argument* AddParam(const std::string& name, std::shared_ptr<Type> type);
+  const std::vector<std::unique_ptr<Argument>>& GetParams() const;
+  bool IsExternal() const;
+  BasicBlock* CreateBlock(const std::string& name);
+  BasicBlock* GetEntry();
+  const BasicBlock* GetEntry() const;
+  const std::vector<std::unique_ptr<BasicBlock>>& GetBlocks() const;
+
+ private:
+  bool is_external_ = false;
+  BasicBlock* entry_ = nullptr;
+  std::vector<std::unique_ptr<Argument>> params_;
+  std::vector<std::unique_ptr<BasicBlock>> blocks_;
+};
+
+class Module {
+ public:
+  Module() = default;
+  Context& GetContext();
+  const Context& GetContext() const;
+  // 创建函数时当前只显式传入返回类型，尚未接入完整的 FunctionType。
+  Function* CreateFunction(const std::string& name,
+                           std::shared_ptr<Type> ret_type,
+                           bool is_external = false);
+  Function* GetFunction(const std::string& name) const;
+  GlobalVariable* CreateGlobalI32(const std::string& name, int init_value);
+  GlobalVariable* CreateGlobalF32(const std::string& name, double init_value);
+  GlobalVariable* CreateGlobalArrayI32(const std::string& name,
+                                       size_t array_size);
+  GlobalVariable* CreateGlobalArrayF32(const std::string& name,
+                                       size_t array_size);
+  GlobalVariable* CreateGlobalArrayI32(const std::string& name,
+                                       size_t array_size,
+                                       const std::vector<int>& init_values);
+  GlobalVariable* CreateGlobalArrayF32(const std::string& name,
+                                       size_t array_size,
+                                       const std::vector<double>& init_values);
+  GlobalVariable* GetGlobal(const std::string& name) const;
+  const std::vector<std::unique_ptr<GlobalVariable>>& GetGlobals() const;
+  const std::vector<std::unique_ptr<Function>>& GetFunctions() const;
+
+ private:
+  Context context_;
+  std::vector<std::unique_ptr<GlobalVariable>> globals_;
+  std::vector<std::unique_ptr<Function>> functions_;
+};
+
+class IRBuilder {
+ public:
+  IRBuilder(Context& ctx, 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);
+  ConstantFloat* CreateConstFloat(double v);
+  BinaryInst* CreateBinary(Opcode op, Value* lhs, Value* rhs,
+                           const std::string& name);
+  BinaryInst* CreateAdd(Value* lhs, Value* rhs, const std::string& name);
+  BinaryInst* CreateICmp(Opcode op, Value* lhs, Value* rhs,
+                         const std::string& name);
+  CastInst* CreateSIToFP(Value* operand, const std::string& name);
+  CastInst* CreateFPToSI(Value* operand, const std::string& name);
+  CastInst* CreateZExt(Value* operand, std::shared_ptr<Type> target_ty, const std::string& name);
+  AllocaInst* CreateAlloca(std::shared_ptr<Type> elem_ty, const std::string& name,
+                           Value* count = nullptr);
+  AllocaInst* CreateAllocaI32(const std::string& name,
+                              Value* count = nullptr);
+  AllocaInst* CreateAllocaF32(const std::string& name,
+                              Value* count = nullptr);
+  LoadInst* CreateLoad(Value* ptr, const std::string& name);
+  StoreInst* CreateStore(Value* val, Value* ptr);
+  GetElementPtrInst* CreateGEP(Value* base_ptr, Value* index,
+                               const std::string& name);
+  CallInst* CreateCall(Function* callee, const std::vector<Value*>& args,
+                       const std::string& name);
+  BranchInst* CreateBr(BasicBlock* target);
+  CondBranchInst* CreateCondBr(Value* cond, BasicBlock* true_bb,
+                               BasicBlock* false_bb);
+  ReturnInst* CreateRet(Value* v);
+  ReturnInst* CreateRetVoid();
+  PhiInst* CreatePhi(std::shared_ptr<Type> ty, const std::string& name);
+
+ private:
+  Context& ctx_;
+  BasicBlock* insert_block_;
+};
+
+class IRPrinter {
+ public:
+  void Print(const Module& module, std::ostream& os);
+};
+
+}  // namespace ir
diff --git a/extlibs/irgen/IRGen.h b/extlibs/irgen/IRGen.h
new file mode 100644
index 00000000..861f6fcb
--- /dev/null
+++ b/extlibs/irgen/IRGen.h
@@ -0,0 +1,122 @@
+// 将语法树翻译为 IR。
+// 实现拆分在 IRGenFunc/IRGenStmt/IRGenExp/IRGenDecl。
+
+#pragma once
+
+#include <any>
+#include <memory>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "SysYBaseVisitor.h"
+#include "SysYParser.h"
+#include "ir/IR.h"
+#include "sem/Sema.h"
+
+namespace ir {
+class Module;
+class Function;
+class IRBuilder;
+class Value;
+}
+
+class IRGenImpl final : public SysYBaseVisitor {
+ public:
+  IRGenImpl(ir::Module& module, const SemanticContext& sema);
+
+  std::any visitCompUnit(SysYParser::CompUnitContext* ctx) override;
+  std::any visitFuncDef(SysYParser::FuncDefContext* ctx) override;
+  std::any visitBlock(SysYParser::BlockContext* ctx) override;
+  std::any visitBlockItem(SysYParser::BlockItemContext* ctx) override;
+  std::any visitDecl(SysYParser::DeclContext* ctx) override;
+  std::any visitVarDecl(SysYParser::VarDeclContext* ctx) override;
+  std::any visitStmt(SysYParser::StmtContext* ctx) override;
+  std::any visitVarDef(SysYParser::VarDefContext* ctx) override;
+  std::any visitExp(SysYParser::ExpContext* ctx) override;
+  std::any visitAddExp(SysYParser::AddExpContext* ctx) override;
+  std::any visitMulExp(SysYParser::MulExpContext* ctx) override;
+  std::any visitUnaryExp(SysYParser::UnaryExpContext* ctx) override;
+  std::any visitPrimaryExp(SysYParser::PrimaryExpContext* ctx) override;
+  std::any visitLVal(SysYParser::LValContext* ctx) override;
+  std::any visitNumber(SysYParser::NumberContext* ctx) override;
+
+ private:
+  enum class BlockFlow {
+    Continue,
+    Terminated,
+  };
+
+  BlockFlow VisitBlockItemResult(SysYParser::BlockItemContext& item);
+  ir::Value* EvalExpr(SysYParser::ExpContext& expr);
+  ir::Value* EvalBinaryOrFold(ir::Opcode op, ir::Value* lhs, ir::Value* rhs);
+  std::shared_ptr<ir::Type> ResolveBType(SysYParser::BTypeContext* btype) const;
+    int EvalConstIntExpr(SysYParser::ExpContext& expr);
+    int EvalConstIntExpr(SysYParser::ConstExpContext& expr);
+    int EvalConstIntAddExp(SysYParser::AddExpContext& expr);
+    int EvalConstIntMulExp(SysYParser::MulExpContext& expr);
+    int EvalConstIntUnaryExp(SysYParser::UnaryExpContext& expr);
+    int EvalConstIntPrimaryExp(SysYParser::PrimaryExpContext& expr);
+    double EvalConstFloatExpr(SysYParser::ConstExpContext& expr);
+    double EvalConstFloatAddExp(SysYParser::AddExpContext& expr);
+    double EvalConstFloatMulExp(SysYParser::MulExpContext& expr);
+    double EvalConstFloatUnaryExp(SysYParser::UnaryExpContext& expr);
+    double EvalConstFloatPrimaryExp(SysYParser::PrimaryExpContext& expr);
+    std::vector<int> EvalArrayExtents(
+      const std::vector<SysYParser::ConstExpContext*>& dims);
+    std::vector<int> GetArrayExtentsForDecl(SysYParser::VarDefContext* decl);
+    std::vector<int> GetArrayExtentsForConstDecl(
+      SysYParser::ConstDefContext* decl);
+    std::vector<int> GetArrayExtentsForLVal(SysYParser::LValContext& lval,
+                        bool& is_array);
+    ir::Value* BuildLinearizedIndex(
+      const std::vector<ir::Value*>& indices,
+      const std::vector<int>& extents_with_first_dim) ;
+  ir::Value* CastValueTo(ir::Value* value,
+                         const std::shared_ptr<ir::Type>& target_type);
+  ir::Value* GetLValAddress(SysYParser::LValContext& lval);
+  ir::AllocaInst* CreateEntryBlockAlloca(std::shared_ptr<ir::Type> elem_ty,
+                                         const std::string& name,
+                                         ir::Value* count = nullptr);
+  std::string NextBlockName(const std::string& prefix);
+  void EmitCondBranch(SysYParser::CondContext& cond, ir::BasicBlock* true_bb,
+                      ir::BasicBlock* false_bb);
+  void EmitLOrBranch(SysYParser::LOrExpContext& expr, ir::BasicBlock* true_bb,
+                     ir::BasicBlock* false_bb);
+  void EmitLAndBranch(SysYParser::LAndExpContext& expr, ir::BasicBlock* true_bb,
+                      ir::BasicBlock* false_bb);
+  void EmitEqBranch(SysYParser::EqExpContext& expr, ir::BasicBlock* true_bb,
+                    ir::BasicBlock* false_bb);
+  void EmitRelBranch(SysYParser::RelExpContext& expr, ir::BasicBlock* true_bb,
+                     ir::BasicBlock* false_bb);
+  ir::Value* EvalEqValue(SysYParser::EqExpContext& expr);
+  ir::Value* EvalRelValue(SysYParser::RelExpContext& expr);
+
+  ir::Module& module_;
+  const SemanticContext& sema_;
+  ir::Function* func_;
+  ir::IRBuilder builder_;
+  std::unordered_map<std::string, ir::Function*> function_map_;
+  std::unordered_map<std::string, int> const_value_map_;
+  std::vector<std::unordered_map<std::string, int>> local_const_stack_;
+  std::vector<std::unordered_map<std::string, int>> const_value_history_;
+  std::unordered_map<SysYParser::VarDefContext*, std::vector<int>>
+      array_extents_map_;
+    std::unordered_map<SysYParser::ConstDefContext*, std::vector<int>>
+      const_array_extents_map_;
+  std::unordered_map<std::string, std::vector<int>> param_array_extents_map_;
+  std::unordered_map<std::string, ir::Value*> param_storage_map_;
+  std::unordered_map<std::string, ir::Value*> param_pointer_map_;
+  std::unordered_map<SysYParser::VarDefContext*, ir::Value*> global_storage_map_;
+    std::unordered_map<SysYParser::ConstDefContext*, ir::Value*>
+      const_global_storage_map_;
+  // 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::VarDefContext*, ir::Value*> storage_map_;
+    std::unordered_map<SysYParser::ConstDefContext*, ir::Value*>
+      const_storage_map_;
+  std::vector<std::pair<ir::BasicBlock*, ir::BasicBlock*>> loop_stack_;
+  int block_index_ = 0;
+};
+
+std::unique_ptr<ir::Module> GenerateIR(SysYParser::CompUnitContext& tree,
+                                       const SemanticContext& sema);
diff --git a/extlibs/mir/MIR.h b/extlibs/mir/MIR.h
new file mode 100644
index 00000000..dabbd02c
--- /dev/null
+++ b/extlibs/mir/MIR.h
@@ -0,0 +1,414 @@
+#pragma once
+
+#include <initializer_list>
+#include <iosfwd>
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace ir
+{
+  class Module;
+}
+
+namespace mir
+{
+
+  class MIRContext
+  {
+  public:
+    MIRContext() = default;
+  };
+
+  MIRContext &DefaultContext();
+
+  enum class PhysReg
+  {
+    W0,
+    W1,
+    W2,
+    W3,
+    W4,
+    W5,
+    W6,
+    W7,
+    W8,
+    W9,
+    W10,
+    W11,
+    W12,
+    W13,
+    W14,
+    W15,
+    W16,
+    W17,
+    W18,
+    W19,
+    W20,
+    W21,
+    W22,
+    W23,
+    W24,
+    W25,
+    W26,
+    W27,
+    W28,
+    W29,
+    W30,
+    X0,
+    X1,
+    X2,
+    X3,
+    X4,
+    X5,
+    X6,
+    X7,
+    X8,
+    X9,
+    X10,
+    X11,
+    X12,
+    X13,
+    X14,
+    X15,
+    X16,
+    X17,
+    X18,
+    X19,
+    X20,
+    X21,
+    X22,
+    X23,
+    X24,
+    X25,
+    X26,
+    X27,
+    X28,
+    X29,
+    X30,
+    S0,
+    S1,
+    S2,
+    S3,
+    S4,
+    S5,
+    S6,
+    S7,
+    S8,
+    S9,
+    S10,
+    S11,
+    S12,
+    S13,
+    S14,
+    S15,
+    S16,
+    S17,
+    S18,
+    S19,
+    S20,
+    S21,
+    S22,
+    S23,
+    S24,
+    S25,
+    S26,
+    S27,
+    S28,
+    S29,
+    S30,
+    S31,
+    XZR,
+    SP,
+    WZR
+  };
+
+  const char *PhysRegName(PhysReg reg);
+
+  enum class VRegClass
+  {
+    Int,
+    Float,
+    Ptr
+  };
+
+  enum class Opcode
+  {
+    Prologue,
+    Epilogue,
+    MovImm,
+    LoadStack,
+    StoreStack,
+    LoadStackAddr,
+    LoadGlobal,
+    StoreGlobal,
+    LoadGlobalAddr,
+    LoadMem,
+    StoreMem,
+    AddRR,
+    SubRR,
+    MulRR,
+    DivRR,
+    ModRR,
+    AndRR,
+    OrRR,
+    XorRR,
+    ShlRR,
+    ShrRR,
+    AsrRR,
+    Asr64RR,
+    Uxtw,
+    Sxtw,
+    CmpRR,
+    CmpImm,
+    FCmpRR,
+    CSet,
+    Csel,
+    Smull,
+    Msub,
+    NegRR,
+    FAddRR,
+    FSubRR,
+    FMulRR,
+    FDivRR,
+    Scvtf,
+    FCvtzs,
+    FMovWS,
+    Br,
+    CondBr,
+    Call,
+    Ret,
+    LoadAddr,
+    MovReg,
+  };
+
+  enum class CondCode
+  {
+    EQ,
+    NE,
+    LT,
+    LE,
+    GT,
+    GE
+  };
+
+  class Operand
+  {
+  public:
+    enum class Kind
+    {
+      Reg,
+      VReg,
+      Imm,
+      FrameIndex,
+      Label,
+      Symbol
+    };
+
+    static Operand Reg(PhysReg reg);
+    static Operand VReg(int id, VRegClass vreg_class);
+    static Operand Imm(int value);
+    static Operand FrameIndex(int index);
+    static Operand Label(int label_id);
+    static Operand Symbol(std::string symbol);
+
+    Kind GetKind() const { return kind_; }
+    PhysReg GetReg() const { return reg_; }
+    int GetImm() const { return imm_; }
+    int GetFrameIndex() const { return imm_; }
+    int GetLabel() const { return imm_; }
+    const std::string &GetSymbol() const { return symbol_; }
+    int GetVRegId() const { return imm_; }
+    VRegClass GetVRegClass() const { return vreg_class_; }
+
+  private:
+    Operand(Kind kind, PhysReg reg, int imm,
+            VRegClass vreg_class = VRegClass::Int, std::string symbol = "");
+
+    Kind kind_;
+    PhysReg reg_;
+    int imm_;
+    std::string symbol_;
+    VRegClass vreg_class_;
+  };
+
+  class MachineInstr
+  {
+  public:
+    MachineInstr(Opcode opcode, std::vector<Operand> operands = {});
+
+    Opcode GetOpcode() const { return opcode_; }
+    const std::vector<Operand> &GetOperands() const { return operands_; }
+    std::vector<Operand> &GetOperands() { return operands_; }
+
+  private:
+    Opcode opcode_;
+    std::vector<Operand> operands_;
+  };
+
+  struct FrameSlot
+  {
+    int index = 0;
+    int size = 4;
+    int offset = 0;
+    bool is_stack_arg = false;
+    bool is_callee_stack_arg = false;
+  };
+
+  class MachineBasicBlock
+  {
+  public:
+    explicit MachineBasicBlock(std::string name, int label_id = -1);
+
+    const std::string &GetName() const { return name_; }
+    int GetLabelId() const { return label_id_; }
+    void SetLabelId(int label_id) { label_id_ = label_id; }
+
+    std::vector<MachineInstr> &GetInstructions() { return instructions_; }
+    const std::vector<MachineInstr> &GetInstructions() const { return instructions_; }
+
+    MachineInstr &Append(Opcode opcode,
+                         std::initializer_list<Operand> operands = {});
+
+  private:
+    std::string name_;
+    int label_id_ = -1;
+    std::vector<MachineInstr> instructions_;
+  };
+
+  class MachineFunction
+  {
+  public:
+    explicit MachineFunction(std::string name);
+
+    const std::string &GetName() const { return name_; }
+
+    MachineBasicBlock &GetEntry() { return *entry_; }
+    const MachineBasicBlock &GetEntry() const { return *entry_; }
+
+    MachineBasicBlock *GetEntryPtr() { return entry_; }
+    const MachineBasicBlock *GetEntryPtr() const { return entry_; }
+
+    MachineBasicBlock &CreateBlock(std::string name);
+    MachineBasicBlock *FindBlock(const std::string &name);
+    const MachineBasicBlock *FindBlock(const std::string &name) const;
+
+    std::vector<std::unique_ptr<MachineBasicBlock>> &GetBlocks()
+    {
+      return blocks_;
+    }
+    const std::vector<std::unique_ptr<MachineBasicBlock>> &GetBlocks() const
+    {
+      return blocks_;
+    }
+
+    int CreateLabel();
+
+    int CreateFrameIndex(int size = 4);
+    int CreateStackArgFrameIndex(int size = 4);
+    int CreateCalleeStackArgFrameIndex(int size = 4);
+    FrameSlot &GetFrameSlot(int index);
+    const FrameSlot &GetFrameSlot(int index) const;
+    const std::vector<FrameSlot> &GetFrameSlots() const { return frame_slots_; }
+    std::vector<FrameSlot> &GetFrameSlots() { return frame_slots_; }
+
+    int GetFrameSize() const { return frame_size_; }
+    void SetFrameSize(int size) { frame_size_ = size; }
+
+    int CreateVReg(VRegClass vreg_class);
+    VRegClass GetVRegClass(int vreg_id) const;
+    int GetNumVRegs() const { return static_cast<int>(vreg_classes_.size()); }
+
+    void AddCalleeSavedReg(PhysReg reg);
+    const std::vector<PhysReg> &GetCalleeSavedRegs() const { return callee_saved_regs_; }
+
+  private:
+    std::string name_;
+    std::vector<std::unique_ptr<MachineBasicBlock>> blocks_;
+    MachineBasicBlock *entry_ = nullptr;
+
+    std::vector<FrameSlot> frame_slots_;
+    int frame_size_ = 0;
+    int next_label_id_ = 0;
+
+    std::vector<VRegClass> vreg_classes_;
+    std::vector<PhysReg> callee_saved_regs_;
+  };
+
+  struct MachineGlobal
+  {
+    enum class Kind
+    {
+      I32Scalar,
+      I32Array
+    };
+
+    std::string name;
+    Kind kind = Kind::I32Scalar;
+    int init_value = 0;
+    size_t array_size = 0;
+    std::vector<int> init_values;
+  };
+
+  class MachineModule
+  {
+  public:
+    MachineModule() = default;
+
+    MachineFunction &CreateFunction(std::string name);
+    MachineFunction *GetFunction(const std::string &name);
+    const MachineFunction *GetFunction(const std::string &name) const;
+
+    std::vector<std::unique_ptr<MachineFunction>> &GetFunctions()
+    {
+      return functions_;
+    }
+    const std::vector<std::unique_ptr<MachineFunction>> &GetFunctions() const
+    {
+      return functions_;
+    }
+
+    void AddGlobalI32(std::string name, int init_value)
+    {
+      MachineGlobal g;
+      g.name = std::move(name);
+      g.kind = MachineGlobal::Kind::I32Scalar;
+      g.init_value = init_value;
+      globals_.push_back(std::move(g));
+    }
+
+    void AddGlobalArrayI32(std::string name, size_t array_size,
+                           std::vector<int> init_values = {})
+    {
+      MachineGlobal g;
+      g.name = std::move(name);
+      g.kind = MachineGlobal::Kind::I32Array;
+      g.array_size = array_size;
+      g.init_values = std::move(init_values);
+      globals_.push_back(std::move(g));
+    }
+
+    std::vector<MachineGlobal> &GetGlobals() { return globals_; }
+    const std::vector<MachineGlobal> &GetGlobals() const { return globals_; }
+
+  private:
+    std::vector<std::unique_ptr<MachineFunction>> functions_;
+    std::vector<MachineGlobal> globals_;
+  };
+
+  std::unique_ptr<MachineModule> LowerModuleToMIR(const ir::Module &module);
+  std::unique_ptr<MachineFunction> LowerToMIR(const ir::Module &module);
+
+  void RunRegAlloc(MachineFunction &function);
+  void RunRegAlloc(MachineModule &module);
+
+  void RunFrameLowering(MachineFunction &function);
+  void RunFrameLowering(MachineModule &module);
+
+  void RunPeephole(MachineFunction &function);
+  void RunPeephole(MachineModule &module);
+
+  void PrintAsm(const MachineFunction &function, std::ostream &os);
+  void PrintAsm(const MachineModule &module, std::ostream &os);
+
+} // namespace mir
diff --git a/extlibs/sem/Sema.h b/extlibs/sem/Sema.h
new file mode 100644
index 00000000..5a677fd0
--- /dev/null
+++ b/extlibs/sem/Sema.h
@@ -0,0 +1,92 @@
+// 基于语法树的语义检查与名称绑定。
+#pragma once
+
+#include <unordered_map>
+
+#include "SysYParser.h"
+
+class SemanticContext {
+ public:
+  void BindVarUse(SysYParser::LValContext* use,
+                  SysYParser::VarDefContext* decl) {
+    var_uses_[use] = decl;
+  }
+
+  SysYParser::VarDefContext* ResolveVarUse(
+      const SysYParser::LValContext* use) const {
+    auto it = var_uses_.find(use);
+    return it == var_uses_.end() ? nullptr : it->second;
+  }
+
+  void BindConstArrayUse(SysYParser::LValContext* use,
+                         SysYParser::ConstDefContext* decl) {
+    const_array_uses_[use] = decl;
+  }
+
+  SysYParser::ConstDefContext* ResolveConstArrayUse(
+      const SysYParser::LValContext* use) const {
+    auto it = const_array_uses_.find(use);
+    return it == const_array_uses_.end() ? nullptr : it->second;
+  }
+
+  void BindConstScalarUse(SysYParser::LValContext* use,
+                          SysYParser::ConstDefContext* decl) {
+    const_scalar_uses_[use] = decl;
+  }
+
+  SysYParser::ConstDefContext* ResolveConstScalarUse(
+      const SysYParser::LValContext* use) const {
+    auto it = const_scalar_uses_.find(use);
+    return it == const_scalar_uses_.end() ? nullptr : it->second;
+  }
+
+  void BindConstUse(SysYParser::LValContext* use, int value) {
+    const_uses_[use] = value;
+  }
+
+  const int* ResolveConstUse(const SysYParser::LValContext* use) const {
+    auto it = const_uses_.find(use);
+    return it == const_uses_.end() ? nullptr : &it->second;
+  }
+
+  void BindConstFloatUse(SysYParser::LValContext* use, double value) {
+    const_float_uses_[use] = value;
+  }
+
+  const double* ResolveConstFloatUse(const SysYParser::LValContext* use) const {
+    auto it = const_float_uses_.find(use);
+    return it == const_float_uses_.end() ? nullptr : &it->second;
+  }
+
+  void BindCallUse(SysYParser::UnaryExpContext* call,
+                   SysYParser::FuncDefContext* decl) {
+    call_uses_[call] = decl;
+  }
+
+  SysYParser::FuncDefContext* ResolveCallUse(
+      const SysYParser::UnaryExpContext* call) const {
+    auto it = call_uses_.find(call);
+    return it == call_uses_.end() ? nullptr : it->second;
+  }
+
+ private:
+  std::unordered_map<const SysYParser::LValContext*,
+                     SysYParser::VarDefContext*>
+      var_uses_;
+  std::unordered_map<const SysYParser::LValContext*, int> const_uses_;
+  std::unordered_map<const SysYParser::LValContext*, double> const_float_uses_;
+  std::unordered_map<const SysYParser::LValContext*,
+                     SysYParser::ConstDefContext*>
+      const_array_uses_;
+  std::unordered_map<const SysYParser::LValContext*,
+                     SysYParser::ConstDefContext*>
+      const_scalar_uses_;
+  std::unordered_map<const SysYParser::UnaryExpContext*,
+                     SysYParser::FuncDefContext*>
+      call_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
+SemanticContext RunSema(SysYParser::CompUnitContext& comp_unit);
diff --git a/extlibs/sem/SymbolTable.h b/extlibs/sem/SymbolTable.h
new file mode 100644
index 00000000..61275509
--- /dev/null
+++ b/extlibs/sem/SymbolTable.h
@@ -0,0 +1,22 @@
+// 极简符号表：记录局部变量定义点。
+#pragma once
+
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "SysYParser.h"
+
+class SymbolTable {
+ public:
+  void EnterScope();
+  void ExitScope();
+  void Add(const std::string& name, SysYParser::VarDefContext* decl);
+  bool ContainsInCurrent(const std::string& name) const;
+  bool Contains(const std::string& name) const;
+  SysYParser::VarDefContext* Lookup(const std::string& name) const;
+
+ private:
+  std::vector<std::unordered_map<std::string, SysYParser::VarDefContext*>>
+      scopes_;
+};
diff --git a/extlibs/utils/CLI.h b/extlibs/utils/CLI.h
new file mode 100644
index 00000000..a06106b6
--- /dev/null
+++ b/extlibs/utils/CLI.h
@@ -0,0 +1,17 @@
+// 命令行解析：支持比赛要求的 -S -o -O1 格式
+#pragma once
+
+#include <string>
+
+struct CLIOptions {
+  std::string input;
+  std::string output;          // -o 指定的输出文件路径
+  bool emit_parse_tree = false;
+  bool emit_ir = false;
+  bool emit_asm = false;
+  bool show_help = false;
+  bool optimize = false;       // -O 或 -O1
+  int opt_level = 0;           // 优化级别: 0, 1, 2, 3
+};
+
+CLIOptions ParseCLI(int argc, char** argv);
diff --git a/extlibs/utils/Log.h b/extlibs/utils/Log.h
new file mode 100644
index 00000000..303f1a11
--- /dev/null
+++ b/extlibs/utils/Log.h
@@ -0,0 +1,20 @@
+// 轻量日志接口。
+#pragma once
+
+#include <cstddef>
+#include <exception>
+#include <iosfwd>
+#include <string>
+#include <string_view>
+
+void LogInfo(std::string_view msg, std::ostream& os);
+void LogError(std::string_view msg, std::ostream& os);
+
+std::string FormatError(std::string_view stage, std::string_view msg);
+std::string FormatErrorAt(std::string_view stage, std::size_t line,
+                          std::size_t column, std::string_view msg);
+bool HasErrorPrefix(std::string_view msg, std::string_view stage);
+void PrintException(std::ostream& os, const std::exception& ex);
+
+// 打印命令行帮助信息（用于 `compiler --help`）。
+void PrintHelp(std::ostream& os);