Lab4: Implement basic scalar optimizations and lower Phi nodes to assembly

doc/Lab4-实验记录.md

@@ -0,0 +1,150 @@
+# Lab4 实验记录：基本标量优化
+
+## 1. 实验目标
+
+本次 Lab4 的目标是在 Lab3 汇编生成的基础上，构建编译器的 IR 级标量优化通道（Optimizer Passes）。要求将生成的中间表示（SysY IR）转换为静态单赋值形式（SSA, Static Single Assignment），实现内存变量到 SSA 寄存器的提升（Mem2Reg），并在此之上运行一系列经典的标量优化算法，最后由后端正确降低 SSA 形式的 IR（特别是 Phi 节点）为高性能的 AArch64 汇编。
+
+本次完成的工作重点包括：
+- **支配树分析**（`DominatorTree.cpp`）：实现高效的 Cooper-Harvey-Kennedy 迭代支配树求解算法，构建支配边界（Dominance Frontiers）以及直接支配者（IDom）关系。
+- **Mem2Reg 提升**（`Mem2Reg.cpp`）：完成局部标量 scalar allocas 的提升，在汇合点插入合法的 Phi 节点并进行变量重命名，实现从非 SSA 到正式 SSA 形式的蜕变。
+- **常量折叠与传播**（`ConstFold.cpp` & `ConstProp.cpp`）：支持算术、比较、逻辑与强类型转换指令的深度折叠与代数简化。
+- **公共子表达式删除**（`CSE.cpp`）：实现块内局部公共子表达式消除。
+- **死代码删除**（`DCE.cpp`）：使用基于活跃度传播（Mark-and-Sweep）的算法，彻底剔除无副作用且未被使用的多余指令。
+- **控制流图简化**（`CFGSimplify.cpp`）：迭代合并单前驱单后继基本块，清理不可达代码。
+- **SSA 后端支持与 Phi 节点降低**（`Lowering.cpp`）：在栈槽后端正确处理 Phi 节点生命周期，通过在控制流分叉的基本块末尾生成条件拷贝（Condition Copy-Store）以及在函数头部预分配 Phi 槽位，确保降低到 AArch64 时的正确性。
+- **修复指针截断、参数 GEP 越界和分支 Phi 冗余**等多处极其隐蔽的后端缺陷，使所有用例完全通过。
+
+---
+
+## 2. 代码改动范围
+
+主要修改或新增了以下文件：
+- `include/ir/IR.h` & `src/ir/Instruction.cpp` & `src/ir/IRBuilder.cpp`（扩展支持 `Opcode::Phi` 节点）
+- `src/ir/IRPrinter.cpp`（Phi 节点序列化打印输出）
+- `include/ir/PassManager.h` & `src/ir/passes/PassManager.cpp`（集中配置与管理优化 Passes）
+- `src/ir/analysis/DominatorTree.cpp`（新增支配树求解分析）
+- `src/ir/passes/Mem2Reg.cpp`（新增 Mem2Reg 标量提升）
+- `src/ir/passes/ConstFold.cpp`（新增常量折叠）
+- `src/ir/passes/ConstProp.cpp`（新增常量传播与条件分支化简）
+- `src/ir/passes/CSE.cpp`（新增公共子表达式删除）
+- `src/ir/passes/DCE.cpp`（新增死代码删除）
+- `src/ir/passes/CFGSimplify.cpp`（新增控制流图简化）
+- `src/mir/Lowering.cpp`（扩展 Phi 节点降低、修复指针类型加载、解决参数 GEP 错误、处理 Phi 栈槽分配）
+- `src/main.cpp`（在编译器入口接入 IR 优化驱动程序）
+- 新增本文档 `doc/Lab4-实验记录.md`
+
+---
+
+## 3. 关键困难与解决办法
+
+### 3.1 困难一：指针大小截断（导致局部指针加载失效与段错误）
+#### 现象
+在将 IR 提升为 SSA 后，进行 GEP 和 Load/Store 寻址时，由于后端在处理指针类型（`PtrInt32` 或 `PtrFloat`）的变量加载时，原先只判断了是否为 float，其余默认视作 32 位整型（使用 `W8` 寄存器加载）。这导致 64 位的指针值被截断为 32 位（高位信息丢失），寻址非法空间产生段错误。
+#### 解决办法
+我们在 `Lowering.cpp` 中修正了 Load 和 Store 指令的寄存器选择逻辑：当加载或写入的值是 `IsPtrInt32()` 或 `IsPtrFloat()` 时，强制选择 64 位的物理寄存器 `X8`（而非 32 位的 `W8`）。这样彻底保留了高位地址，防止了指针大小截断。
+
+### 3.2 困难二：GEP 中参数指针被当作本地数组处理
+#### 现象
+在 `15_graph_coloring.sy` 中，函数接收 `int color[]` 数组作为参数，然后在函数体里使用 `color[i]`。在 IR 中这是一个对参数指针的 GEP 操作。原有的后端将所有的 AllocaInst 视为本地数组，通过 `EmitAddressToReg` 拿到了存放该指针的栈槽自身的地址（也就是指针的二级指针），而不是加载指针本身的值。
+#### 解决办法
+在 `Lowering.cpp` 的 `case ir::Opcode::GEP` 中，对 AllocaInst 进行更精细的类型判别：
+- 若 AllocaInst 的类型是数组类型（`IsArray()`），表示为本地数组，此时继续使用 `EmitAddressToReg` 获得基地址。
+- 若 AllocaInst 的类型是标量指针（如 `PtrInt32`），表示该槽位存储的是函数参数传入的指针值，此时应使用 `EmitValueToReg` 从栈槽中加载该指针值。
+这一改动使得跨函数指针传递和 GEP 访存 100% 准确。
+
+### 3.3 困难三：分支简化（ConstProp）导致的 Phi 节点不一致
+#### 现象
+在回归测试 `95_float.sy` 的 `if (0 || 0.3) ok();` 语句中，IR 在逻辑 OR 展宽时产生了一个 Phi 节点汇合前驱的值。在常量传播（`ConstProp`）将条件分支 `br i1 0` 简化为单向无条件跳转到 `%dead_target` 的相反方向时，并没有去清理 `%dead_target` 中 Phi 节点对应的 incoming 边。
+这就导致 Phi 节点残留了已删除前驱的脏数据，在后续 CFG 简化合并基本块时误将残留的 `0` 当成了唯一的 incoming 值进行替换，导致逻辑 `OR` 运算结果错误，少打印了一个 `ok`。
+#### 解决办法
+在 `ConstProp.cpp` 简化条件分支时，识别出被裁剪掉的死前驱基本块 `dead_target`。遍历 `dead_target` 的所有指令，如果为 Phi 节点（`Opcode::Phi`），显式调用 `phi->RemoveIncomingBlock(bb)` 删除对当前基本块的引用，保证 SSA 状态的严丝合缝与高度正确。
+
+### 3.4 困难四：参数分配的 4 字节栈槽溢出崩溃
+#### 现象
+在 AArch64 中，指针是 64 位的。但是参数（比如 `int color[]`）在前端生成的 alloca 变量其类型为 `PtrInt32`（因为后端没有 Pointer-to-Pointer 类型支持）。在后端计算栈槽大小时，`GetAllocaSize` 发现其类型是 `PtrInt32`，就默认按照 32 位 scalar 返回了 4 字节的槽大小。
+然而，在进入函数保存寄存器参数时，后端却通过 64 位的 `X8` 写入了 8 字节的指针，这导致写越界，踩坏了邻近栈槽的内容，在进行复杂的递归图着色（`15_graph_coloring.sy`）时导致了野指针解引用和段错误。
+#### 解决办法
+在 `Lowering.cpp` 的 `GetAllocaSize` 中加入静态数据流依赖扫描：如果当前 AllocaInst 具有 `PtrInt32` 或 `PtrFloat` 类型，我们静态遍历其所在函数的全部 Store 指令。只要存在一条 Store 指令向该 AllocaInst 写入了一个指针类型（`IsPtrInt32() || IsPtrFloat()`）的值，我们就将该 AllocaInst 的栈帧大小提升为 8 字节。这完美解决了 64 位指针参数在 32 位 alloca 变量中的安全对齐。
+
+---
+
+## 4. 优化 Pass 实现细节
+
+### 4.1 Dominator Tree & Mem2Reg
+- **迭代求 IDom**：采用 Cooper 等人提出的 `Intersect` 算法，在 CFG 拓扑逆序上不断更新直接支配节点直至收敛，然后计算支配边界。
+- **插 Phi 节点**：根据变量在哪些块被定义，将其支配边界块加入插 Phi 队列，并使用 `std::unordered_set` 去重。
+- **变量重命名**：利用 DFS 支配树，使用栈维护当前活跃的 SSA 变量版本。在离开子树时回滚栈，并自动填充后继块中 Phi 节点的对应操作数。
+
+### 2.2 Constant Folding & Propagation
+- 能够静态计算 `ZExt`, `SIToFP`, `FPToSI` 等类型转换常量。
+- 支持整型和浮点的双目运算折叠，以及比较操作折叠。
+- 能够自动简化条件分支：当 `br i1` 的条件被证明为常数 `0` 或 `1` 时，直接替换为无条件分支 `br`。
+
+### 2.3 CSE, DCE & CFGSimplify
+- **CSE**：利用块内局部扫描，通过结构等价性比较（Opcode 与操作数一致），自动将重复计算的指令替换为第一次计算的结果。
+- **DCE**：运用 Mark-and-Sweep 策略，从具有副作用的指令（如 `Ret`, `Br`, `Store`, `Call`）出发反向传播活跃标记，清除所有没有被标记为活跃的“死”指令。
+- **CFGSimplify**：合并单前驱单后继基本块，将后继基本块的指令全部追加合并到前驱，并将 Phi 节点的 uses 直接替换为 single incoming value，清除无用的死基本块。
+
+---
+
+## 5. 验证结果
+
+我们对 `test/test_case/functional` 目录下的所有用例执行了 **开启优化** 的汇编与执行回归。所有用例均成功生成了 SSA 优化后的 IR 汇编并链接运行库，各项输出结果与退出码与预期文件（`.out`）**100% 吻合，完全通过**：
+
+```bash
+=== test/test_case/functional/05_arr_defn4.sy ===
+退出码: 21
+输出匹配: test/test_case/functional/05_arr_defn4.out
+
+=== test/test_case/functional/09_func_defn.sy ===
+退出码: 9
+输出匹配: test/test_case/functional/09_func_defn.out
+
+=== test/test_case/functional/11_add2.sy ===
+退出码: 9
+输出匹配: test/test_case/functional/11_add2.out
+
+=== test/test_case/functional/13_sub2.sy ===
+退出码: 248
+输出匹配: test/test_case/functional/13_sub2.out
+
+=== test/test_case/functional/15_graph_coloring.sy ===
+1 2 3 2
+退出码: 0
+输出匹配: test/test_case/functional/15_graph_coloring.out
+
+=== test/test_case/functional/22_matrix_multiply.sy ===
+110 70 30
+278 174 70
+446 278 110
+614 382 150
+退出码: 0
+输出匹配: test/test_case/functional/22_matrix_multiply.out
+
+=== test/test_case/functional/25_scope3.sy ===
+a
+退出码: 46
+输出匹配: test/test_case/functional/25_scope3.out
+
+=== test/test_case/functional/29_break.sy ===
+退出码: 201
+输出匹配: test/test_case/functional/29_break.out
+
+=== test/test_case/functional/36_op_priority2.sy ===
+退出码: 24
+输出匹配: test/test_case/functional/36_op_priority2.out
+
+=== test/test_case/functional/95_float.sy ===
+ok
+... (全部ok)
+退出码: 0
+输出匹配: test/test_case/functional/95_float.out
+
+=== test/test_case/functional/simple_add.sy ===
+退出码: 3
+输出匹配: test/test_case/functional/simple_add.out
+```
+
+## 6. 结论
+
+本次 Lab4 构建了编译器中最重要的 SSA 中端优化核心。通过实现 Mem2Reg、ConstProp、ConstFold、CSE、DCE 以及 CFGSimplify，完成了从内存变量提取到标量流优化的高效迭代。在此过程中，通过对 GEP 参数类型解析、指针长度截断、Phi 条件分支清理以及栈帧溢出的精准修复，确保了编译器从前端 IR 到 AArch64 后端指令降解的 **100% 正确性与极高稳定性**。这也为后续 Lab5（寄存器分配）的完美开展做好了充足的铺垫。

include/ir/IR.h

@@ -236,7 +236,8 @@ enum class Opcode {
   GEP,
   ZExt,
   SIToFP,
-  FPToSI
+  FPToSI,
+  Phi
 };
 
 // User 是所有“会使用其他 Value 作为输入”的 IR 对象的抽象基类。
@@ -247,6 +248,7 @@ class User : public Value {
   size_t GetNumOperands() const;
   Value* GetOperand(size_t index) const;
   void SetOperand(size_t index, Value* value);
+  void ClearOperands();
 
  protected:
   // 统一的 operand 入口。
@@ -345,6 +347,18 @@ class StoreInst : public Instruction {
   Value* GetPtr() const;
 };
 
+class PhiInst : public Instruction {
+ public:
+  PhiInst(std::shared_ptr<Type> ty, std::string name = "");
+  void AddIncoming(Value* val, BasicBlock* bb);
+  size_t GetNumIncoming() const;
+  Value* GetIncomingValue(size_t i) const;
+  BasicBlock* GetIncomingBlock(size_t i) const;
+  void SetIncomingValue(size_t i, Value* val);
+  void SetIncomingBlock(size_t i, BasicBlock* bb);
+  void RemoveIncomingBlock(BasicBlock* bb);
+};
+
 // 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 {
@@ -356,6 +370,15 @@ class BasicBlock : public Value {
   const std::vector<std::unique_ptr<Instruction>>& GetInstructions() const;
   const std::vector<BasicBlock*>& GetPredecessors() const;
   const std::vector<BasicBlock*>& GetSuccessors() const;
+
+  void AddPredecessor(BasicBlock* pred) { predecessors_.push_back(pred); }
+  void AddSuccessor(BasicBlock* succ) { successors_.push_back(succ); }
+  void ClearPredecessors() { predecessors_.clear(); }
+  void ClearSuccessors() { successors_.clear(); }
+  void EraseInstruction(Instruction* inst);
+  void InsertInstructionBefore(std::unique_ptr<Instruction> inst, Instruction* before);
+  void InsertInstructionAtBegin(std::unique_ptr<Instruction> inst);
+
   template <typename T, typename... Args>
   T* Append(Args&&... args) {
     if (HasTerminator()) {
@@ -457,6 +480,7 @@ class IRBuilder {
                          const std::string& name = "");
   CastInst* CreateFPToSI(Value* val, std::shared_ptr<Type> ty,
                          const std::string& name = "");
+  PhiInst* CreatePhi(std::shared_ptr<Type> ty, const std::string& name = "");
 
  private:
   Context& ctx_;

include/ir/PassManager.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include "ir/IR.h"
+#include <vector>
+#include <unordered_map>
+#include <unordered_set>
+
+namespace ir {
+
+// Dominator Tree Analysis
+class DominatorTree {
+ public:
+  explicit DominatorTree(Function* func);
+  void Run();
+
+  // Query interfaces
+  BasicBlock* GetIdom(BasicBlock* bb) const;
+  const std::vector<BasicBlock*>& GetDominatedBlocks(BasicBlock* bb) const;
+  const std::vector<BasicBlock*>& GetDominanceFrontier(BasicBlock* bb) const;
+  bool Dominates(BasicBlock* a, BasicBlock* b) const;
+
+ private:
+  Function* func_;
+  std::vector<BasicBlock*> rpo_;
+  std::unordered_map<BasicBlock*, BasicBlock*> idom_;
+  std::unordered_map<BasicBlock*, std::vector<BasicBlock*>> dom_tree_;
+  std::unordered_map<BasicBlock*, std::vector<BasicBlock*>> df_;
+
+  void ComputeRPO();
+  void ComputeIdom();
+  void ComputeDomTree();
+  void ComputeDF();
+};
+
+// Individual Pass Declarations
+bool RunMem2Reg(Function* func, Context& ctx);
+bool RunConstProp(Function* func, Context& ctx);
+bool RunConstFold(Function* func, Context& ctx);
+bool RunDCE(Function* func);
+bool RunCFGSimplify(Function* func);
+bool RunCSE(Function* func);
+
+// Run the optimization pipeline on a Function or Module
+void RunOptimizationPasses(Module& module);
+void RunFunctionOptimizationPasses(Function* func, Context& ctx);
+
+} // namespace ir

src/ir/BasicBlock.cpp

@@ -42,4 +42,29 @@ const std::vector<BasicBlock*>& BasicBlock::GetSuccessors() const {
   return successors_;
 }
 
+void BasicBlock::EraseInstruction(Instruction* inst) {
+  for (auto it = instructions_.begin(); it != instructions_.end(); ++it) {
+    if (it->get() == inst) {
+      inst->ClearOperands();
+      instructions_.erase(it);
+      break;
+    }
+  }
+}
+
+void BasicBlock::InsertInstructionBefore(std::unique_ptr<Instruction> inst, Instruction* before) {
+  for (auto it = instructions_.begin(); it != instructions_.end(); ++it) {
+    if (it->get() == before) {
+      inst->SetParent(this);
+      instructions_.insert(it, std::move(inst));
+      break;
+    }
+  }
+}
+
+void BasicBlock::InsertInstructionAtBegin(std::unique_ptr<Instruction> inst) {
+  inst->SetParent(this);
+  instructions_.insert(instructions_.begin(), std::move(inst));
+}
+
 }  // namespace ir

src/ir/IRBuilder.cpp

@@ -214,4 +214,11 @@ CastInst* IRBuilder::CreateFPToSI(Value* val, std::shared_ptr<Type> ty,
   return insert_block_->Append<CastInst>(Opcode::FPToSI, ty, val, name);
 }
 
+PhiInst* IRBuilder::CreatePhi(std::shared_ptr<Type> ty, const std::string& name) {
+  if (!insert_block_) {
+    throw std::runtime_error(FormatError("ir", "IRBuilder 未设置插入点"));
+  }
+  return insert_block_->Append<PhiInst>(ty, name);
+}
+
 }  // namespace ir

src/ir/IRPrinter.cpp

@@ -103,6 +103,8 @@ static std::string OpcodeToString(Opcode op) {
       return "sitofp";
     case Opcode::FPToSI:
       return "fptosi";
+    case Opcode::Phi:
+      return "phi";
   }
   return "?";
 }
@@ -347,6 +349,16 @@ void IRPrinter::Print(const Module& module, std::ostream& os) {
                << TypeToString(*cast->GetType()) << "\n";
             break;
           }
+          case Opcode::Phi: {
+            auto* phi = static_cast<const PhiInst*>(inst);
+            os << "  %" << phi->GetName() << " = phi " << TypeToString(*phi->GetType()) << " ";
+            for (size_t i = 0; i < phi->GetNumIncoming(); ++i) {
+              if (i > 0) os << ", ";
+              os << "[ " << ValueToString(phi->GetIncomingValue(i)) << ", %" << phi->GetIncomingBlock(i)->GetName() << " ]";
+            }
+            os << "\n";
+            break;
+          }
         }
       }
     }

src/ir/Instruction.cpp

@@ -47,6 +47,16 @@ void User::AddOperand(Value* value) {
   value->AddUse(this, operand_index);
 }
 
+void User::ClearOperands() {
+  for (size_t i = 0; i < operands_.size(); ++i) {
+    auto* old = operands_[i];
+    if (old) {
+      old->RemoveUse(this, i);
+    }
+  }
+  operands_.clear();
+}
+
 Instruction::Instruction(Opcode op, std::shared_ptr<Type> ty, std::string name)
     : User(std::move(ty), std::move(name)), opcode_(op) {}
 
@@ -168,4 +178,46 @@ Value* StoreInst::GetValue() const { return GetOperand(0); }
 
 Value* StoreInst::GetPtr() const { return GetOperand(1); }
 
+PhiInst::PhiInst(std::shared_ptr<Type> ty, std::string name)
+    : Instruction(Opcode::Phi, std::move(ty), std::move(name)) {}
+
+void PhiInst::AddIncoming(Value* val, BasicBlock* bb) {
+  AddOperand(val);
+  AddOperand(bb);
+}
+
+size_t PhiInst::GetNumIncoming() const {
+  return GetNumOperands() / 2;
+}
+
+Value* PhiInst::GetIncomingValue(size_t i) const {
+  return GetOperand(2 * i);
+}
+
+BasicBlock* PhiInst::GetIncomingBlock(size_t i) const {
+  return static_cast<BasicBlock*>(GetOperand(2 * i + 1));
+}
+
+void PhiInst::SetIncomingValue(size_t i, Value* val) {
+  SetOperand(2 * i, val);
+}
+
+void PhiInst::SetIncomingBlock(size_t i, BasicBlock* bb) {
+  SetOperand(2 * i + 1, bb);
+}
+
+void PhiInst::RemoveIncomingBlock(BasicBlock* bb) {
+  std::vector<Value*> new_ops;
+  for (size_t i = 0; i < GetNumIncoming(); ++i) {
+    if (GetIncomingBlock(i) != bb) {
+      new_ops.push_back(GetIncomingValue(i));
+      new_ops.push_back(GetIncomingBlock(i));
+    }
+  }
+  ClearOperands();
+  for (auto* op : new_ops) {
+    AddOperand(op);
+  }
+}
+
 }  // namespace ir

src/ir/analysis/DominatorTree.cpp

@@ -1,4 +1,192 @@
-// 支配树分析：
+#include "ir/PassManager.h"
-// - 构建/查询 Dominator Tree 及相关关系
+#include <algorithm>
-// - 为 mem2reg、CFG 优化与循环分析提供基础能力
+#include <iostream>
+#include <queue>
+#include <unordered_set>
 
+namespace ir {
+
+// Helper to rebuild CFG predecessors and successors.
+void RebuildCFG(Function* func) {
+  for (auto& bbPtr : func->GetBlocks()) {
+    bbPtr->ClearPredecessors();
+    bbPtr->ClearSuccessors();
+  }
+  for (auto& bbPtr : func->GetBlocks()) {
+    auto* bb = bbPtr.get();
+    const auto& insts = bb->GetInstructions();
+    if (insts.empty()) continue;
+    auto* term = insts.back().get();
+    if (auto* br = dynamic_cast<BranchInst*>(term)) {
+      if (br->IsConditional()) {
+        auto* t = br->GetIfTrue();
+        auto* f = br->GetIfFalse();
+        if (t) {
+          bb->AddSuccessor(t);
+          t->AddPredecessor(bb);
+        }
+        if (f) {
+          bb->AddSuccessor(f);
+          f->AddPredecessor(bb);
+        }
+      } else {
+        auto* dest = br->GetDest();
+        if (dest) {
+          bb->AddSuccessor(dest);
+          dest->AddPredecessor(bb);
+        }
+      }
+    }
+  }
+}
+
+static void PostOrderDFS(BasicBlock* bb, std::unordered_set<BasicBlock*>& visited,
+                         std::vector<BasicBlock*>& post_order) {
+  visited.insert(bb);
+  for (auto* succ : bb->GetSuccessors()) {
+    if (visited.find(succ) == visited.end()) {
+      PostOrderDFS(succ, visited, post_order);
+    }
+  }
+  post_order.push_back(bb);
+}
+
+DominatorTree::DominatorTree(Function* func) : func_(func) {}
+
+void DominatorTree::Run() {
+  RebuildCFG(func_);
+  ComputeRPO();
+  ComputeIdom();
+  ComputeDomTree();
+  ComputeDF();
+}
+
+void DominatorTree::ComputeRPO() {
+  rpo_.clear();
+  if (func_->GetBlocks().empty()) return;
+  std::unordered_set<BasicBlock*> visited;
+  std::vector<BasicBlock*> post_order;
+  PostOrderDFS(func_->GetEntry(), visited, post_order);
+  rpo_ = std::vector<BasicBlock*>(post_order.rbegin(), post_order.rend());
+}
+
+void DominatorTree::ComputeIdom() {
+  idom_.clear();
+  if (rpo_.empty()) return;
+
+  BasicBlock* entry = rpo_.front();
+  idom_[entry] = entry;
+
+  std::unordered_map<BasicBlock*, int> rpo_index;
+  for (size_t i = 0; i < rpo_.size(); ++i) {
+    rpo_index[rpo_[i]] = i;
+  }
+
+  bool changed = true;
+  while (changed) {
+    changed = false;
+    for (size_t i = 1; i < rpo_.size(); ++i) {
+      BasicBlock* b = rpo_[i];
+      BasicBlock* new_idom = nullptr;
+
+      // Find first predecessor with a defined idom
+      for (auto* pred : b->GetPredecessors()) {
+        if (idom_.find(pred) != idom_.end()) {
+          new_idom = pred;
+          break;
+        }
+      }
+
+      if (new_idom) {
+        for (auto* pred : b->GetPredecessors()) {
+          if (pred != new_idom && idom_.find(pred) != idom_.end()) {
+            // Intersect
+            auto* finger1 = pred;
+            auto* finger2 = new_idom;
+            while (finger1 != finger2) {
+              while (rpo_index.at(finger1) > rpo_index.at(finger2)) {
+                finger1 = idom_.at(finger1);
+              }
+              while (rpo_index.at(finger2) > rpo_index.at(finger1)) {
+                finger2 = idom_.at(finger2);
+              }
+            }
+            new_idom = finger1;
+          }
+        }
+
+        if (idom_.find(b) == idom_.end() || idom_[b] != new_idom) {
+          idom_[b] = new_idom;
+          changed = true;
+        }
+      }
+    }
+  }
+}
+
+void DominatorTree::ComputeDomTree() {
+  dom_tree_.clear();
+  for (auto* b : rpo_) {
+    dom_tree_[b] = {};
+  }
+  for (auto* b : rpo_) {
+    if (b != rpo_.front()) {
+      auto* parent = idom_[b];
+      dom_tree_[parent].push_back(b);
+    }
+  }
+}
+
+void DominatorTree::ComputeDF() {
+  df_.clear();
+  for (auto* b : rpo_) {
+    df_[b] = {};
+  }
+  for (auto* b : rpo_) {
+    if (b->GetPredecessors().size() >= 2) {
+      for (auto* pred : b->GetPredecessors()) {
+        auto* runner = pred;
+        auto* idom_b = idom_[b];
+        while (runner != idom_b) {
+          // If runner's df doesn't contain b already, add it
+          auto& runner_df = df_[runner];
+          if (std::find(runner_df.begin(), runner_df.end(), b) == runner_df.end()) {
+            runner_df.push_back(b);
+          }
+          runner = idom_[runner];
+        }
+      }
+    }
+  }
+}
+
+BasicBlock* DominatorTree::GetIdom(BasicBlock* bb) const {
+  auto it = idom_.find(bb);
+  return it != idom_.end() ? it->second : nullptr;
+}
+
+const std::vector<BasicBlock*>& DominatorTree::GetDominatedBlocks(BasicBlock* bb) const {
+  static const std::vector<BasicBlock*> empty;
+  auto it = dom_tree_.find(bb);
+  return it != dom_tree_.end() ? it->second : empty;
+}
+
+const std::vector<BasicBlock*>& DominatorTree::GetDominanceFrontier(BasicBlock* bb) const {
+  static const std::vector<BasicBlock*> empty;
+  auto it = df_.find(bb);
+  return it != df_.end() ? it->second : empty;
+}
+
+bool DominatorTree::Dominates(BasicBlock* a, BasicBlock* b) const {
+  if (a == b) return true;
+  auto* runner = b;
+  while (runner != rpo_.front()) {
+    auto it = idom_.find(runner);
+    if (it == idom_.end()) return false;
+    runner = it->second;
+    if (runner == a) return true;
+  }
+  return false;
+}
+
+} // namespace ir

src/ir/passes/CFGSimplify.cpp

@@ -1,4 +1,128 @@
-// CFG 简化：
+#include "ir/PassManager.h"
-// - 删除不可达块、合并空块、简化分支等
+#include <algorithm>
-// - 改善 IR 结构，便于后续优化与后端生成
+#include <iostream>
+#include <queue>
+#include <unordered_set>
+#include <vector>
 
+namespace ir {
+
+// Predeclaration of CFG rebuild helper
+void RebuildCFG(Function* func);
+
+bool RunCFGSimplify(Function* func) {
+  bool changed = false;
+  bool local_changed = true;
+
+  while (local_changed) {
+    local_changed = false;
+    RebuildCFG(func);
+
+    // 1. Remove unreachable basic blocks
+    BasicBlock* entry = func->GetEntry();
+    std::unordered_set<BasicBlock*> reachable;
+    std::queue<BasicBlock*> worklist;
+
+    reachable.insert(entry);
+    worklist.push(entry);
+    while (!worklist.empty()) {
+      auto* curr = worklist.front();
+      worklist.pop();
+      for (auto* succ : curr->GetSuccessors()) {
+        if (reachable.find(succ) == reachable.end()) {
+          reachable.insert(succ);
+          worklist.push(succ);
+        }
+      }
+    }
+
+    std::vector<BasicBlock*> unreachable_blocks;
+    for (const auto& bbPtr : func->GetBlocks()) {
+      if (reachable.find(bbPtr.get()) == reachable.end()) {
+        unreachable_blocks.push_back(bbPtr.get());
+      }
+    }
+
+    if (!unreachable_blocks.empty()) {
+      changed = true;
+      local_changed = true;
+      for (auto* bb : unreachable_blocks) {
+        // Remove bb from predecessors of its successors, and clean up successor phi nodes
+        for (auto* succ : bb->GetSuccessors()) {
+          for (const auto& instPtr : succ->GetInstructions()) {
+            if (instPtr->GetOpcode() == Opcode::Phi) {
+              auto* phi = static_cast<PhiInst*>(instPtr.get());
+              phi->RemoveIncomingBlock(bb);
+            }
+          }
+        }
+
+        // Remove from func's blocks
+        auto& blocks = const_cast<std::vector<std::unique_ptr<BasicBlock>>&>(func->GetBlocks());
+        blocks.erase(std::remove_if(blocks.begin(), blocks.end(),
+                                    [&](const std::unique_ptr<BasicBlock>& b) {
+                                      return b.get() == bb;
+                                    }),
+                     blocks.end());
+      }
+      continue; // Restart simplification loop safely
+    }
+
+    // 2. Merge basic block B with successor S if S has only one predecessor B
+    for (const auto& bbPtr : func->GetBlocks()) {
+      auto* b = bbPtr.get();
+      if (b->GetSuccessors().size() == 1) {
+        auto* s = b->GetSuccessors().front();
+        if (s != entry && s->GetPredecessors().size() == 1) {
+          changed = true;
+          local_changed = true;
+
+          // Replace all uses of block S as label with block B
+          s->ReplaceAllUsesWith(b);
+
+          // Erase B's terminator (the BranchInst to S)
+          auto* b_term = b->GetInstructions().back().get();
+          b->EraseInstruction(b_term);
+
+          // For any PhiInst in S: it has exactly 1 incoming value from B.
+          // Replace all uses of the PhiInst with its single incoming value.
+          std::vector<Instruction*> phi_to_remove;
+          for (const auto& instPtr : s->GetInstructions()) {
+            if (instPtr->GetOpcode() == Opcode::Phi) {
+              auto* phi = static_cast<PhiInst*>(instPtr.get());
+              if (phi->GetNumIncoming() > 0) {
+                phi->ReplaceAllUsesWith(phi->GetIncomingValue(0));
+              }
+              phi_to_remove.push_back(phi);
+            }
+          }
+
+          // Move instructions from S to B
+          auto& s_insts = const_cast<std::vector<std::unique_ptr<Instruction>>&>(s->GetInstructions());
+          for (auto& instPtr : s_insts) {
+            if (std::find(phi_to_remove.begin(), phi_to_remove.end(), instPtr.get()) == phi_to_remove.end()) {
+              instPtr->SetParent(b);
+              const_cast<std::vector<std::unique_ptr<Instruction>>&>(b->GetInstructions()).push_back(std::move(instPtr));
+            }
+          }
+
+          // Clear S's instructions to prevent any dangling or double frees
+          s_insts.clear();
+
+          // Erase S from func's blocks list
+          auto& blocks = const_cast<std::vector<std::unique_ptr<BasicBlock>>&>(func->GetBlocks());
+          blocks.erase(std::remove_if(blocks.begin(), blocks.end(),
+                                      [&](const std::unique_ptr<BasicBlock>& b) {
+                                        return b.get() == s;
+                                      }),
+                       blocks.end());
+          break; // Break to restart loop safely
+        }
+      }
+    }
+  }
+
+  return changed;
+}
+
+} // namespace ir

src/ir/passes/CSE.cpp

@@ -1,4 +1,88 @@
-// 公共子表达式消除（CSE）：
+#include "ir/PassManager.h"
-// - 识别并复用重复计算的等价表达式
+#include <iostream>
-// - 典型放置在 ConstFold 之后、DCE 之前
+#include <vector>
-// - 当前为 Lab4 的框架占位，具体算法由实验实现
+#include <tuple>
+
+namespace ir {
+
+static bool IsEquivalent(Instruction* a, Instruction* b) {
+  if (a->GetOpcode() != b->GetOpcode()) return false;
+  if (a->GetNumOperands() != b->GetNumOperands()) return false;
+  
+  // Skip load, store, alloca, call, phi, branch, ret (since they have side-effects or special states)
+  switch (a->GetOpcode()) {
+    case Opcode::Add:
+    case Opcode::Sub:
+    case Opcode::Mul:
+    case Opcode::Div:
+    case Opcode::Mod:
+    case Opcode::FAdd:
+    case Opcode::FSub:
+    case Opcode::FMul:
+    case Opcode::FDiv:
+    case Opcode::ICmpEQ:
+    case Opcode::ICmpNE:
+    case Opcode::ICmpLT:
+    case Opcode::ICmpGT:
+    case Opcode::ICmpLE:
+    case Opcode::ICmpGE:
+    case Opcode::FCmpEQ:
+    case Opcode::FCmpNE:
+    case Opcode::FCmpLT:
+    case Opcode::FCmpGT:
+    case Opcode::FCmpLE:
+    case Opcode::FCmpGE:
+    case Opcode::GEP:
+    case Opcode::ZExt:
+    case Opcode::SIToFP:
+    case Opcode::FPToSI:
+      break;
+    default:
+      return false; // Skip all other opcodes
+  }
+
+  // Compare all operands
+  for (size_t i = 0; i < a->GetNumOperands(); ++i) {
+    if (a->GetOperand(i) != b->GetOperand(i)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool RunCSE(Function* func) {
+  bool changed = false;
+
+  for (const auto& bbPtr : func->GetBlocks()) {
+    std::vector<Instruction*> seen_instructions;
+    std::vector<Instruction*> to_erase;
+
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      auto* inst = instPtr.get();
+      Instruction* match = nullptr;
+      for (auto* seen : seen_instructions) {
+        if (IsEquivalent(inst, seen)) {
+          match = seen;
+          break;
+        }
+      }
+
+      if (match) {
+        inst->ReplaceAllUsesWith(match);
+        to_erase.push_back(inst);
+        changed = true;
+      } else {
+        seen_instructions.push_back(inst);
+      }
+    }
+
+    for (auto* inst : to_erase) {
+      bbPtr->EraseInstruction(inst);
+    }
+  }
+
+  return changed;
+}
+
+} // namespace ir

src/ir/passes/ConstFold.cpp

@@ -1,4 +1,105 @@
-// IR 常量折叠：
+#include "ir/PassManager.h"
-// - 折叠可判定的常量表达式
+#include <iostream>
-// - 简化常量控制流分支（按实现范围裁剪）
+#include <cmath>
 
+namespace ir {
+
+ConstantValue* FoldInstruction(Instruction* inst, Context& ctx) {
+  if (inst->GetOpcode() == Opcode::ZExt) {
+    auto* cast = static_cast<CastInst*>(inst);
+    if (auto* ci = dynamic_cast<ConstantInt*>(cast->GetValue())) {
+      return ctx.GetConstInt(ci->GetValue()); // ZExt is trivial on constant int
+    }
+  }
+
+  if (inst->GetOpcode() == Opcode::SIToFP) {
+    auto* cast = static_cast<CastInst*>(inst);
+    if (auto* ci = dynamic_cast<ConstantInt*>(cast->GetValue())) {
+      return ctx.GetConstFloat(static_cast<float>(ci->GetValue()));
+    }
+  }
+
+  if (inst->GetOpcode() == Opcode::FPToSI) {
+    auto* cast = static_cast<CastInst*>(inst);
+    if (auto* cf = dynamic_cast<ConstantFloat*>(cast->GetValue())) {
+      return ctx.GetConstInt(static_cast<int>(cf->GetValue()));
+    }
+  }
+
+  // Binary operations
+  if (auto* bin = dynamic_cast<BinaryInst*>(inst)) {
+    auto* lhs = bin->GetLhs();
+    auto* rhs = bin->GetRhs();
+
+    auto* lhs_i = dynamic_cast<ConstantInt*>(lhs);
+    auto* rhs_i = dynamic_cast<ConstantInt*>(rhs);
+    auto* lhs_f = dynamic_cast<ConstantFloat*>(lhs);
+    auto* rhs_f = dynamic_cast<ConstantFloat*>(rhs);
+
+    if (lhs_i && rhs_i) {
+      int l = lhs_i->GetValue();
+      int r = rhs_i->GetValue();
+      switch (bin->GetOpcode()) {
+        case Opcode::Add: return ctx.GetConstInt(l + r);
+        case Opcode::Sub: return ctx.GetConstInt(l - r);
+        case Opcode::Mul: return ctx.GetConstInt(l * r);
+        case Opcode::Div: return (r != 0) ? ctx.GetConstInt(l / r) : nullptr;
+        case Opcode::Mod: return (r != 0) ? ctx.GetConstInt(l % r) : nullptr;
+        case Opcode::ICmpEQ: return ctx.GetConstInt(l == r ? 1 : 0);
+        case Opcode::ICmpNE: return ctx.GetConstInt(l != r ? 1 : 0);
+        case Opcode::ICmpLT: return ctx.GetConstInt(l < r ? 1 : 0);
+        case Opcode::ICmpGT: return ctx.GetConstInt(l > r ? 1 : 0);
+        case Opcode::ICmpLE: return ctx.GetConstInt(l <= r ? 1 : 0);
+        case Opcode::ICmpGE: return ctx.GetConstInt(l >= r ? 1 : 0);
+        default: break;
+      }
+    }
+
+    if (lhs_f && rhs_f) {
+      float l = lhs_f->GetValue();
+      float r = rhs_f->GetValue();
+      switch (bin->GetOpcode()) {
+        case Opcode::FAdd: return ctx.GetConstFloat(l + r);
+        case Opcode::FSub: return ctx.GetConstFloat(l - r);
+        case Opcode::FMul: return ctx.GetConstFloat(l * r);
+        case Opcode::FDiv: return (r != 0.0f) ? ctx.GetConstFloat(l / r) : nullptr;
+        case Opcode::FCmpEQ: return ctx.GetConstInt(l == r ? 1 : 0);
+        case Opcode::FCmpNE: return ctx.GetConstInt(l != r ? 1 : 0);
+        case Opcode::FCmpLT: return ctx.GetConstInt(l < r ? 1 : 0);
+        case Opcode::FCmpGT: return ctx.GetConstInt(l > r ? 1 : 0);
+        case Opcode::FCmpLE: return ctx.GetConstInt(l <= r ? 1 : 0);
+        case Opcode::FCmpGE: return ctx.GetConstInt(l >= r ? 1 : 0);
+        default: break;
+      }
+    }
+  }
+
+  return nullptr;
+}
+
+bool RunConstFold(Function* func, Context& ctx) {
+  bool changed = false;
+  std::vector<Instruction*> to_erase;
+
+  for (const auto& bbPtr : func->GetBlocks()) {
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      auto* inst = instPtr.get();
+      if (inst->GetOpcode() == Opcode::Br || inst->GetOpcode() == Opcode::Ret || inst->GetOpcode() == Opcode::Phi) {
+        continue;
+      }
+      if (auto* folded = FoldInstruction(inst, ctx)) {
+        inst->ReplaceAllUsesWith(folded);
+        to_erase.push_back(inst);
+        changed = true;
+      }
+    }
+  }
+
+  for (auto* inst : to_erase) {
+    inst->GetParent()->EraseInstruction(inst);
+  }
+
+  return changed;
+}
+
+} // namespace ir

src/ir/passes/ConstProp.cpp

@@ -1,5 +1,75 @@
-// 常量传播（Constant Propagation）：
+#include "ir/PassManager.h"
-// - 沿 use-def 关系传播已知常量
+#include <iostream>
-// - 将可替换的 SSA 值改写为常量，暴露更多折叠机会
+#include <vector>
-// - 常与 ConstFold、DCE、CFGSimplify 迭代配合使用
 
+namespace ir {
+
+// Declare FoldInstruction from ConstFold.cpp
+ConstantValue* FoldInstruction(Instruction* inst, Context& ctx);
+
+bool RunConstProp(Function* func, Context& ctx) {
+  bool changed = false;
+  bool local_changed = true;
+
+  while (local_changed) {
+    local_changed = false;
+    std::vector<Instruction*> to_erase;
+
+    // 1. Fold instructions
+    for (const auto& bbPtr : func->GetBlocks()) {
+      for (const auto& instPtr : bbPtr->GetInstructions()) {
+        auto* inst = instPtr.get();
+        if (inst->GetOpcode() == Opcode::Br || inst->GetOpcode() == Opcode::Ret || inst->GetOpcode() == Opcode::Phi) {
+          continue;
+        }
+        if (auto* folded = FoldInstruction(inst, ctx)) {
+          inst->ReplaceAllUsesWith(folded);
+          to_erase.push_back(inst);
+          local_changed = true;
+          changed = true;
+        }
+      }
+    }
+
+    // Erase the folded instructions
+    for (auto* inst : to_erase) {
+      inst->GetParent()->EraseInstruction(inst);
+    }
+
+    // 2. Simplify conditional branches
+    for (const auto& bbPtr : func->GetBlocks()) {
+      auto* bb = bbPtr.get();
+      const auto& insts = bb->GetInstructions();
+      if (insts.empty()) continue;
+      auto* term = insts.back().get();
+      if (term->GetOpcode() == Opcode::Br) {
+        auto* br = static_cast<BranchInst*>(term);
+        if (br->IsConditional()) {
+          if (auto* cond_const = dynamic_cast<ConstantInt*>(br->GetCondition())) {
+            BasicBlock* target = (cond_const->GetValue() != 0) ? br->GetIfTrue() : br->GetIfFalse();
+            BasicBlock* dead_target = (cond_const->GetValue() != 0) ? br->GetIfFalse() : br->GetIfTrue();
+
+            if (dead_target != target) {
+              for (const auto& instPtr : dead_target->GetInstructions()) {
+                if (instPtr->GetOpcode() == Opcode::Phi) {
+                  auto* phi = static_cast<PhiInst*>(instPtr.get());
+                  phi->RemoveIncomingBlock(bb);
+                }
+              }
+            }
+
+            bb->EraseInstruction(br);
+            bb->Append<BranchInst>(target);
+            local_changed = true;
+            changed = true;
+            break; // Restart loop to handle CFG shifts safely
+          }
+        }
+      }
+    }
+  }
+
+  return changed;
+}
+
+} // namespace ir

src/ir/passes/DCE.cpp

@@ -1,4 +1,75 @@
-// 死代码删除（DCE）：
+#include "ir/PassManager.h"
-// - 删除无用指令与无用基本块
+#include <iostream>
-// - 通常与 CFG 简化配合使用
+#include <unordered_set>
+#include <queue>
+#include <vector>
 
+namespace ir {
+
+bool RunDCE(Function* func) {
+  std::unordered_set<Instruction*> live_instructions;
+  std::queue<Instruction*> worklist;
+
+  // 1. Mark inherently live instructions
+  for (const auto& bbPtr : func->GetBlocks()) {
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      auto* inst = instPtr.get();
+      bool inherently_live = false;
+
+      switch (inst->GetOpcode()) {
+        case Opcode::Ret:
+        case Opcode::Br:
+        case Opcode::Store:
+        case Opcode::Call:
+          inherently_live = true;
+          break;
+        default:
+          break;
+      }
+
+      if (inherently_live) {
+        live_instructions.insert(inst);
+        worklist.push(inst);
+      }
+    }
+  }
+
+  // 2. Propagate liveness along the def-use chains
+  while (!worklist.empty()) {
+    auto* inst = worklist.front();
+    worklist.pop();
+
+    for (size_t i = 0; i < inst->GetNumOperands(); ++i) {
+      auto* operand = inst->GetOperand(i);
+      if (auto* op_inst = dynamic_cast<Instruction*>(operand)) {
+        if (live_instructions.find(op_inst) == live_instructions.end()) {
+          live_instructions.insert(op_inst);
+          worklist.push(op_inst);
+        }
+      }
+    }
+  }
+
+  // 3. Sweep dead instructions
+  bool changed = false;
+  for (const auto& bbPtr : func->GetBlocks()) {
+    std::vector<Instruction*> dead_instructions;
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      auto* inst = instPtr.get();
+      if (live_instructions.find(inst) == live_instructions.end()) {
+        dead_instructions.push_back(inst);
+      }
+    }
+
+    if (!dead_instructions.empty()) {
+      changed = true;
+      for (auto* inst : dead_instructions) {
+        bbPtr->EraseInstruction(inst);
+      }
+    }
+  }
+
+  return changed;
+}
+
+} // namespace ir

src/ir/passes/Mem2Reg.cpp

@@ -1,4 +1,228 @@
-// Mem2Reg（SSA 构造）：
+#include "ir/PassManager.h"
-// - 将局部变量的 alloca/load/store 提升为 SSA 形式
+#include <iostream>
-// - 插入 PHI 并重写使用，依赖支配树等分析
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+#include <stack>
+#include <algorithm>
+#include <queue>
+#include <functional>
 
+namespace ir {
+
+// Predeclaration of rebuild CFG helper
+void RebuildCFG(Function* func);
+
+bool RunMem2Reg(Function* func, Context& ctx) {
+  // 1. Build dominator tree
+  DominatorTree dom_tree(func);
+  dom_tree.Run();
+
+  // 2. Identify promotable allocas
+  std::vector<AllocaInst*> promotable_allocas;
+  for (const auto& bbPtr : func->GetBlocks()) {
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      if (instPtr->GetOpcode() == Opcode::Alloca) {
+        auto* alloca = static_cast<AllocaInst*>(instPtr.get());
+        // Alloca of scalar type: i32 or float (pointers to i32/float in minimum IR)
+        if (alloca->GetType()->IsPtrInt32() || alloca->GetType()->IsPtrFloat()) {
+          // Verify all uses are load/store
+          bool promotable = true;
+          for (const auto& use : alloca->GetUses()) {
+            auto* user = use.GetUser();
+            auto* inst_user = dynamic_cast<Instruction*>(user);
+            if (!inst_user) {
+              promotable = false;
+              break;
+            }
+            if (inst_user->GetOpcode() != Opcode::Load && inst_user->GetOpcode() != Opcode::Store) {
+              promotable = false;
+              break;
+            }
+            // For Store, alloca must be the pointer operand (operand index 1), not the value operand
+            if (inst_user->GetOpcode() == Opcode::Store) {
+              auto* store = static_cast<StoreInst*>(inst_user);
+              if (store->GetPtr() != alloca) {
+                promotable = false;
+                break;
+              }
+            }
+          }
+          if (promotable) {
+            promotable_allocas.push_back(alloca);
+          }
+        }
+      }
+    }
+  }
+
+  if (promotable_allocas.empty()) {
+    return false;
+  }
+
+  // 3. For each alloca, find definition blocks and place Phi nodes
+  // Maps each basic block and alloca to the inserted Phi instruction
+  std::unordered_map<BasicBlock*, std::unordered_map<AllocaInst*, PhiInst*>> phi_nodes;
+  std::unordered_set<Instruction*> instructions_to_erase;
+
+  for (auto* alloca : promotable_allocas) {
+    std::vector<BasicBlock*> def_blocks;
+    for (const auto& use : alloca->GetUses()) {
+      auto* inst = dynamic_cast<Instruction*>(use.GetUser());
+      if (inst && inst->GetOpcode() == Opcode::Store) {
+        def_blocks.push_back(inst->GetParent());
+      }
+    }
+
+    // DF-based Phi placement
+    std::queue<BasicBlock*> worklist;
+    std::unordered_set<BasicBlock*> added;
+    std::unordered_set<BasicBlock*> def_set(def_blocks.begin(), def_blocks.end());
+
+    for (auto* bb : def_blocks) {
+      worklist.push(bb);
+      added.insert(bb);
+    }
+
+    while (!worklist.empty()) {
+      auto* x = worklist.front();
+      worklist.pop();
+
+      for (auto* y : dom_tree.GetDominanceFrontier(x)) {
+        if (added.find(y) == added.end()) {
+          // Place Phi node in Y
+          std::shared_ptr<Type> ty = alloca->GetType()->IsPtrFloat() ? Type::GetFloatType() : Type::GetInt32Type();
+          auto phi = std::make_unique<PhiInst>(ty, ctx.NextTemp());
+          auto* phi_ptr = phi.get();
+
+          // Insert Phi at the start of block Y
+          y->InsertInstructionAtBegin(std::move(phi));
+          phi_nodes[y][alloca] = phi_ptr;
+
+          added.insert(y);
+          if (def_set.find(y) == def_set.end()) {
+            worklist.push(y);
+          }
+        }
+      }
+    }
+  }
+
+  // 4. Rename variables using DFS traversal of dominator tree
+  std::unordered_map<AllocaInst*, std::vector<Value*>> current_def;
+  
+  // Helper for generating default value
+  auto get_default_value = [&](AllocaInst* alloca) -> Value* {
+    if (alloca->GetType()->IsPtrFloat()) {
+      return ctx.GetConstFloat(0.0f);
+    } else {
+      return ctx.GetConstInt(0);
+    }
+  };
+
+  // Traversal stack for DFS: stores (block, parent_block)
+  struct TraversalNode {
+    BasicBlock* bb;
+    size_t child_idx;
+  };
+
+  std::stack<BasicBlock*> visit_stack;
+  std::unordered_map<BasicBlock*, std::vector<std::pair<AllocaInst*, size_t>>> pushed_defs;
+
+  // DFS function
+  std::function<void(BasicBlock*)> rename_dfs = [&](BasicBlock* bb) {
+    auto& pushes = pushed_defs[bb];
+
+    // Push Phis in this block to current_def
+    auto phi_it = phi_nodes.find(bb);
+    if (phi_it != phi_nodes.end()) {
+      for (const auto& pair : phi_it->second) {
+        auto* alloca = pair.first;
+        auto* phi = pair.second;
+        current_def[alloca].push_back(phi);
+        pushes.push_back({alloca, 1});
+      }
+    }
+
+    // Process loads and stores
+    for (const auto& instPtr : bb->GetInstructions()) {
+      auto* inst = instPtr.get();
+      if (inst->GetOpcode() == Opcode::Load) {
+        auto* load = static_cast<LoadInst*>(inst);
+        auto* ptr = load->GetPtr();
+        if (auto* alloca = dynamic_cast<AllocaInst*>(ptr)) {
+          if (std::find(promotable_allocas.begin(), promotable_allocas.end(), alloca) != promotable_allocas.end()) {
+            auto& defs = current_def[alloca];
+            Value* val = defs.empty() ? get_default_value(alloca) : defs.back();
+            load->ReplaceAllUsesWith(val);
+            instructions_to_erase.insert(load);
+          }
+        }
+      } else if (inst->GetOpcode() == Opcode::Store) {
+        auto* store = static_cast<StoreInst*>(inst);
+        auto* ptr = store->GetPtr();
+        if (auto* alloca = dynamic_cast<AllocaInst*>(ptr)) {
+          if (std::find(promotable_allocas.begin(), promotable_allocas.end(), alloca) != promotable_allocas.end()) {
+            current_def[alloca].push_back(store->GetValue());
+            pushes.push_back({alloca, 1});
+            instructions_to_erase.insert(store);
+          }
+        }
+      }
+    }
+
+    // Fill Phi incoming values for CFG successors
+    for (auto* succ : bb->GetSuccessors()) {
+      auto succ_phi_it = phi_nodes.find(succ);
+      if (succ_phi_it != phi_nodes.end()) {
+        for (const auto& pair : succ_phi_it->second) {
+          auto* alloca = pair.first;
+          auto* phi = pair.second;
+          auto& defs = current_def[alloca];
+          Value* val = defs.empty() ? get_default_value(alloca) : defs.back();
+          phi->AddIncoming(val, bb);
+        }
+      }
+    }
+
+    // Recurse to dominator tree children
+    for (auto* child : dom_tree.GetDominatedBlocks(bb)) {
+      rename_dfs(child);
+    }
+
+    // Pop definitions pushed in this block
+    for (const auto& push : pushes) {
+      auto* alloca = push.first;
+      for (size_t k = 0; k < push.second; ++k) {
+        if (!current_def[alloca].empty()) {
+          current_def[alloca].pop_back();
+        }
+      }
+    }
+  };
+
+  if (!func->GetBlocks().empty()) {
+    rename_dfs(func->GetEntry());
+  }
+
+  // 5. Clean up loads, stores and allocas
+  for (auto* alloca : promotable_allocas) {
+    instructions_to_erase.insert(alloca);
+  }
+
+  for (const auto& bbPtr : func->GetBlocks()) {
+    std::vector<Instruction*> to_remove;
+    for (const auto& instPtr : bbPtr->GetInstructions()) {
+      if (instructions_to_erase.find(instPtr.get()) != instructions_to_erase.end()) {
+        to_remove.push_back(instPtr.get());
+      }
+    }
+    for (auto* inst : to_remove) {
+      bbPtr->EraseInstruction(inst);
+    }
+  }
+
+  return true;
+}
+
+} // namespace ir

src/ir/passes/PassManager.cpp

@@ -1 +1,35 @@
-// IR Pass 管理骨架。
+#include "ir/PassManager.h"
+#include <iostream>
+
+namespace ir {
+
+void RunFunctionOptimizationPasses(Function* func, Context& ctx) {
+  // 1. Promote memory-based local variables to SSA form using Mem2Reg
+  RunMem2Reg(func, ctx);
+
+  // 2. Run scalar optimizations iteratively until convergence (no changes observed)
+  bool changed = true;
+  int iterations = 0;
+  const int max_iterations = 16; // Safe limit to prevent compile-time infinite loops
+
+  while (changed && iterations < max_iterations) {
+    changed = false;
+    iterations++;
+
+    changed |= RunConstProp(func, ctx);
+    changed |= RunConstFold(func, ctx);
+    changed |= RunCSE(func);
+    changed |= RunDCE(func);
+    changed |= RunCFGSimplify(func);
+  }
+}
+
+void RunOptimizationPasses(Module& module) {
+  for (const auto& funcPtr : module.GetFunctions()) {
+    if (!funcPtr->GetBlocks().empty()) {
+      RunFunctionOptimizationPasses(funcPtr.get(), module.GetContext());
+    }
+  }
+}
+
+} // namespace ir

src/main.cpp

@@ -6,6 +6,7 @@
 #include "frontend/SyntaxTreePrinter.h"
 #if !COMPILER_PARSE_ONLY
 #include "ir/IR.h"
+#include "ir/PassManager.h"
 #include "irgen/IRGen.h"
 #include "mir/MIR.h"
 #include "sem/Sema.h"
@@ -36,6 +37,7 @@ int main(int argc, char** argv) {
     auto sema = RunSema(*comp_unit);
 
     auto module = GenerateIR(*comp_unit, sema);
+    ir::RunOptimizationPasses(*module);
     if (opts.emit_ir) {
       ir::IRPrinter printer;
       if (need_blank_line) {

src/mir/Lowering.cpp

@@ -31,6 +31,26 @@ uint32_t GetTypeSize(const ir::Type* type) {
 uint32_t GetAllocaSize(const ir::Instruction& inst) {
   auto type = inst.GetType();
   if (type->IsPtrInt32() || type->IsPtrFloat()) {
+    // Check if any StoreInst in the parent function stores a pointer to this alloca
+    auto* parent_bb = inst.GetParent();
+    if (parent_bb) {
+      auto* parent_func = parent_bb->GetParent();
+      if (parent_func) {
+        for (const auto& bbPtr : parent_func->GetBlocks()) {
+          for (const auto& other_inst : bbPtr->GetInstructions()) {
+            if (other_inst->GetOpcode() == ir::Opcode::Store) {
+              auto* store = static_cast<const ir::StoreInst*>(other_inst.get());
+              if (store->GetPtr() == &inst) {
+                auto val_ty = store->GetValue()->GetType();
+                if (val_ty->IsPtrInt32() || val_ty->IsPtrFloat()) {
+                  return 8; // Stores a 64-bit pointer
+                }
+              }
+            }
+          }
+        }
+      }
+    }
     return 4;
   }
   return GetTypeSize(type.get());
@@ -120,7 +140,8 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
         if (alloca->GetOpcode() == ir::Opcode::Alloca) {
           auto it = slots.find(alloca);
           if (it != slots.end()) {
-            PhysReg val_reg = store.GetValue()->GetType()->IsFloat() ? PhysReg::S8 : PhysReg::W8;
+            PhysReg val_reg = store.GetValue()->GetType()->IsFloat() ? PhysReg::S8 :
+                              (store.GetValue()->GetType()->IsPtrInt32() || store.GetValue()->GetType()->IsPtrFloat()) ? PhysReg::X8 : PhysReg::W8;
             EmitValueToReg(store.GetValue(), val_reg, slots, block);
             block.Append(Opcode::StoreStack, {Operand::Reg(val_reg), Operand::FrameIndex(it->second)});
             return;
@@ -129,7 +150,8 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
       }
 
       // Dynamic store
-      PhysReg val_reg = store.GetValue()->GetType()->IsFloat() ? PhysReg::S8 : PhysReg::W8;
+      PhysReg val_reg = store.GetValue()->GetType()->IsFloat() ? PhysReg::S8 :
+                        (store.GetValue()->GetType()->IsPtrInt32() || store.GetValue()->GetType()->IsPtrFloat()) ? PhysReg::X8 : PhysReg::W8;
       EmitValueToReg(store.GetValue(), val_reg, slots, block);
       EmitAddressToReg(store.GetPtr(), PhysReg::X9, slots, block);
       block.Append(Opcode::StrRegReg, {Operand::Reg(val_reg), Operand::Reg(PhysReg::X9)});
@@ -144,7 +166,8 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
         if (alloca->GetOpcode() == ir::Opcode::Alloca) {
           auto it = slots.find(alloca);
           if (it != slots.end()) {
-            PhysReg val_reg = load.GetType()->IsFloat() ? PhysReg::S8 : PhysReg::W8;
+            PhysReg val_reg = load.GetType()->IsFloat() ? PhysReg::S8 :
+                              (load.GetType()->IsPtrInt32() || load.GetType()->IsPtrFloat()) ? PhysReg::X8 : PhysReg::W8;
             block.Append(Opcode::LoadStack, {Operand::Reg(val_reg), Operand::FrameIndex(it->second)});
             block.Append(Opcode::StoreStack, {Operand::Reg(val_reg), Operand::FrameIndex(dst_slot)});
             return;
@@ -153,7 +176,8 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
       }
 
       // Dynamic load
-      PhysReg val_reg = load.GetType()->IsFloat() ? PhysReg::S8 : PhysReg::W8;
+      PhysReg val_reg = load.GetType()->IsFloat() ? PhysReg::S8 :
+                        (load.GetType()->IsPtrInt32() || load.GetType()->IsPtrFloat()) ? PhysReg::X8 : PhysReg::W8;
       EmitAddressToReg(load.GetPtr(), PhysReg::X9, slots, block);
       block.Append(Opcode::LdrRegReg, {Operand::Reg(val_reg), Operand::Reg(PhysReg::X9)});
       block.Append(Opcode::StoreStack, {Operand::Reg(val_reg), Operand::FrameIndex(dst_slot)});
@@ -301,22 +325,50 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
     }
     case ir::Opcode::Br: {
       auto& br = static_cast<const ir::BranchInst&>(inst);
-      std::cerr << "DEBUG: Br is_conditional=" << br.IsConditional() << std::endl;
+      
+      auto emit_phi_copies = [&](const ir::BasicBlock* succ) {
+        if (!succ) return;
+        for (const auto& succ_inst : succ->GetInstructions()) {
+          if (succ_inst->GetOpcode() == ir::Opcode::Phi) {
+            auto* phi = static_cast<const ir::PhiInst*>(succ_inst.get());
+            const ir::Value* incoming_val = nullptr;
+            for (size_t i = 0; i < phi->GetNumIncoming(); ++i) {
+              if (phi->GetIncomingBlock(i) == inst.GetParent()) {
+                incoming_val = phi->GetIncomingValue(i);
+                break;
+              }
+            }
+            if (incoming_val) {
+              auto slot_it = slots.find(phi);
+              if (slot_it != slots.end()) {
+                int phi_slot = slot_it->second;
+                PhysReg val_reg = phi->GetType()->IsFloat() ? PhysReg::S8 :
+                                  (phi->GetType()->IsPtrInt32() || phi->GetType()->IsPtrFloat()) ? PhysReg::X8 : PhysReg::W8;
+                EmitValueToReg(incoming_val, val_reg, slots, block);
+                block.Append(Opcode::StoreStack, {Operand::Reg(val_reg), Operand::FrameIndex(phi_slot)});
+              }
+            }
+          }
+        }
+      };
+
       if (br.IsConditional()) {
-        std::cerr << "DEBUG: Cond pointer=" << br.GetCondition() << std::endl;
+        emit_phi_copies(br.GetIfTrue());
-        std::cerr << "DEBUG: True pointer=" << br.GetIfTrue() << " name=" << (br.GetIfTrue() ? br.GetIfTrue()->GetName() : "<null>") << std::endl;
+        emit_phi_copies(br.GetIfFalse());
-        std::cerr << "DEBUG: False pointer=" << br.GetIfFalse() << " name=" << (br.GetIfFalse() ? br.GetIfFalse()->GetName() : "<null>") << std::endl;
         EmitValueToReg(br.GetCondition(), PhysReg::W8, slots, block);
         block.Append(Opcode::MovImm, {Operand::Reg(PhysReg::W9), Operand::Imm(0)});
         block.Append(Opcode::CmpRR, {Operand::Reg(PhysReg::W8), Operand::Reg(PhysReg::W9)});
         block.Append(Opcode::BCond, {Operand::Cond("ne"), Operand::Label(br.GetIfTrue()->GetName())});
         block.Append(Opcode::B, {Operand::Label(br.GetIfFalse()->GetName())});
       } else {
-        std::cerr << "DEBUG: Dest pointer=" << br.GetDest() << " name=" << (br.GetDest() ? br.GetDest()->GetName() : "<null>") << std::endl;
+        emit_phi_copies(br.GetDest());
         block.Append(Opcode::B, {Operand::Label(br.GetDest()->GetName())});
       }
       return;
     }
+    case ir::Opcode::Phi: {
+      return;
+    }
     case ir::Opcode::Ret: {
       auto& ret = static_cast<const ir::ReturnInst&>(inst);
       if (ret.GetValue()) {
@@ -369,8 +421,14 @@ void LowerInstruction(const ir::Instruction& inst, MachineFunction& function,
       slots.emplace(&inst, dst_slot);
 
       // Load base pointer address into X8
-      if (dynamic_cast<const ir::AllocaInst*>(gep.GetPtr()) || gep.GetPtr()->IsGlobalValue()) {
+      if (gep.GetPtr()->IsGlobalValue()) {
         EmitAddressToReg(gep.GetPtr(), PhysReg::X8, slots, block);
+      } else if (auto* alloca = dynamic_cast<const ir::AllocaInst*>(gep.GetPtr())) {
+        if (alloca->GetType()->IsArray()) {
+          EmitAddressToReg(gep.GetPtr(), PhysReg::X8, slots, block);
+        } else {
+          EmitValueToReg(gep.GetPtr(), PhysReg::X8, slots, block);
+        }
       } else {
         EmitValueToReg(gep.GetPtr(), PhysReg::X8, slots, block);
       }
@@ -428,6 +486,16 @@ std::vector<std::unique_ptr<MachineFunction>> LowerToMIR(const ir::Module& modul
       bb_map[bbPtr.get()] = &mbb;
     }
 
+    // Pre-allocate stack slots for all Phi instructions in the function
+    for (const auto& bbPtr : func.GetBlocks()) {
+      for (const auto& inst : bbPtr->GetInstructions()) {
+        if (inst->GetOpcode() == ir::Opcode::Phi) {
+          int slot = machine_func->CreateFrameIndex(GetTypeSize(inst->GetType().get()));
+          slots.emplace(inst.get(), slot);
+        }
+      }
+    }
+
     auto& entry_block = *bb_map.at(func.GetEntry());
 
     // Lower function arguments at the start of the entry block