diff --git a/src/RISCv32Backend.cpp b/src/RISCv32Backend.cpp
index 86cb0cc..8d7b028 100644
--- a/src/RISCv32Backend.cpp
+++ b/src/RISCv32Backend.cpp
@@ -124,13 +124,13 @@ std::vector<std::unique_ptr<RISCv32CodeGen::DAGNode>> RISCv32CodeGen::build_dag(
     std::map<Value*, DAGNode*> value_to_node;
     static int vreg_counter = 0;
 
-    auto create_node = [&](DAGNode::NodeKind kind, Value* val = nullptr) {
-        if (val && value_to_node.find(val) != value_to_node.end()) {
+    auto create_node = [&](DAGNode::NodeKind kind, Value* val = nullptr) -> DAGNode* {
+        if (val && value_to_node.count(val) && kind != DAGNode::STORE && kind != DAGNode::RETURN && kind != DAGNode::BRANCH) {
             return value_to_node[val];
         }
         auto node = std::make_unique<DAGNode>(kind);
         node->value = val;
-        if (val && kind != DAGNode::STORE && kind != DAGNode::RETURN) {
+        if (val && kind != DAGNode::STORE && kind != DAGNode::RETURN && kind != DAGNode::BRANCH) {
             node->result_reg = "v" + std::to_string(vreg_counter++);
             value_vreg_map[val] = node->result_reg;
             value_to_node[val] = node.get();
@@ -146,51 +146,103 @@ std::vector<std::unique_ptr<RISCv32CodeGen::DAGNode>> RISCv32CodeGen::build_dag(
             auto store_node = create_node(DAGNode::STORE);
             Value* val = store->getValue();
             Value* ptr = store->getPointer();
-            DAGNode* val_node = nullptr;
-            if (auto constant = dynamic_cast<ConstantValue*>(val)) {
-                val_node = create_node(DAGNode::CONSTANT, val);
-            } else {
-                val_node = create_node(DAGNode::LOAD, val);
+            DAGNode* val_node = value_to_node.count(val) ? value_to_node[val] : nullptr;
+            if (!val_node) {
+                if (auto constant = dynamic_cast<ConstantValue*>(val)) {
+                    val_node = create_node(DAGNode::CONSTANT, val);
+                } else {
+                    val_node = create_node(DAGNode::LOAD, val);
+                }
             }
-            auto ptr_node = create_node(DAGNode::CONSTANT, ptr);
+            auto ptr_node = value_to_node.count(ptr) ? value_to_node[ptr] : create_node(DAGNode::CONSTANT, ptr);
             store_node->operands.push_back(val_node);
             store_node->operands.push_back(ptr_node);
             val_node->users.push_back(store_node);
             ptr_node->users.push_back(store_node);
         } else if (auto load = dynamic_cast<LoadInst*>(inst.get())) {
+            if (value_to_node.count(load)) continue; // CSE
             auto load_node = create_node(DAGNode::LOAD, load);
-            auto ptr_node = create_node(DAGNode::CONSTANT, load->getPointer());
+            auto ptr = load->getPointer();
+            auto ptr_node = value_to_node.count(ptr) ? value_to_node[ptr] : create_node(DAGNode::CONSTANT, ptr);
             load_node->operands.push_back(ptr_node);
             ptr_node->users.push_back(load_node);
         } else if (auto bin = dynamic_cast<BinaryInst*>(inst.get())) {
+            if (value_to_node.count(bin)) continue; // CSE
             auto bin_node = create_node(DAGNode::BINARY, bin);
-            auto lhs_node = create_node(DAGNode::LOAD, bin->getLhs());
-            auto rhs_node = create_node(DAGNode::LOAD, bin->getRhs());
+            auto lhs = bin->getLhs();
+            auto rhs = bin->getRhs();
+            auto lhs_node = value_to_node.count(lhs) ? value_to_node[lhs] : nullptr;
+            if (!lhs_node) {
+                if (auto constant = dynamic_cast<ConstantValue*>(lhs)) {
+                    lhs_node = create_node(DAGNode::CONSTANT, lhs);
+                } else {
+                    lhs_node = create_node(DAGNode::LOAD, lhs);
+                }
+            }
+            auto rhs_node = value_to_node.count(rhs) ? value_to_node[rhs] : nullptr;
+            if (!rhs_node) {
+                if (auto constant = dynamic_cast<ConstantValue*>(rhs)) {
+                    rhs_node = create_node(DAGNode::CONSTANT, rhs);
+                } else {
+                    rhs_node = create_node(DAGNode::LOAD, rhs);
+                }
+            }
             bin_node->operands.push_back(lhs_node);
             bin_node->operands.push_back(rhs_node);
             lhs_node->users.push_back(bin_node);
             rhs_node->users.push_back(bin_node);
         } else if (auto call = dynamic_cast<CallInst*>(inst.get())) {
+            if (value_to_node.count(call)) continue; // CSE
             auto call_node = create_node(DAGNode::CALL, call);
             for (auto arg : call->getArguments()) {
-                auto arg_node = create_node(DAGNode::CONSTANT, arg->getValue());
+                auto arg_val = arg->getValue();
+                auto arg_node = value_to_node.count(arg_val) ? value_to_node[arg_val] : nullptr;
+                if (!arg_node) {
+                    if (auto constant = dynamic_cast<ConstantValue*>(arg_val)) {
+                        arg_node = create_node(DAGNode::CONSTANT, arg_val);
+                    } else {
+                        arg_node = create_node(DAGNode::LOAD, arg_val);
+                    }
+                }
                 call_node->operands.push_back(arg_node);
                 arg_node->users.push_back(call_node);
             }
         } else if (auto ret = dynamic_cast<ReturnInst*>(inst.get())) {
             auto ret_node = create_node(DAGNode::RETURN);
             if (ret->hasReturnValue()) {
-                auto val_node = create_node(DAGNode::LOAD, ret->getReturnValue());
+                auto val = ret->getReturnValue();
+                auto val_node = value_to_node.count(val) ? value_to_node[val] : nullptr;
+                if (!val_node) {
+                    if (auto constant = dynamic_cast<ConstantValue*>(val)) {
+                        val_node = create_node(DAGNode::CONSTANT, val);
+                    } else {
+                        val_node = create_node(DAGNode::LOAD, val);
+                    }
+                }
                 ret_node->operands.push_back(val_node);
                 val_node->users.push_back(ret_node);
             }
         } else if (auto cond_br = dynamic_cast<CondBrInst*>(inst.get())) {
-            auto br_node = create_node(DAGNode::BRANCH);
+            auto br_node = create_node(DAGNode::BRANCH, cond_br);
             auto cond = cond_br->getCondition();
-            auto cond_node = value_to_node.count(cond) ? value_to_node[cond] : create_node(DAGNode::LOAD, cond);
-            br_node->operands.push_back(cond_node);
-            br_node->value = cond_br; // 存储 CondBrInst 以获取 then/else 块
-            cond_node->users.push_back(br_node);
+            DAGNode* cond_node = nullptr;
+            if (auto constant = dynamic_cast<ConstantValue*>(cond)) {
+                // 常量条件，直接记录分支目标
+                br_node->operands.push_back(nullptr); // 占位符，表示无条件操作数
+                br_node->inst = constant->getInt() ? "j " + cond_br->getThenBlock()->getName()
+                                                  : "j " + cond_br->getElseBlock()->getName();
+            } else {
+                cond_node = value_to_node.count(cond) ? value_to_node[cond] : nullptr;
+                if (!cond_node) {
+                    if (auto bin = dynamic_cast<BinaryInst*>(cond)) {
+                        cond_node = create_node(DAGNode::BINARY, cond);
+                    } else {
+                        cond_node = create_node(DAGNode::LOAD, cond);
+                    }
+                }
+                br_node->operands.push_back(cond_node);
+                cond_node->users.push_back(br_node);
+            }
         }
     }
 
@@ -277,7 +329,9 @@ void RISCv32CodeGen::select_instructions(DAGNode* node, const RegAllocResult& al
     if (!node->inst.empty()) return;
 
     for (auto operand : node->operands) {
-        select_instructions(operand, alloc);
+        if (operand) {
+            select_instructions(operand, alloc);
+        }
     }
 
     switch (node->kind) {
@@ -298,38 +352,65 @@ void RISCv32CodeGen::select_instructions(DAGNode* node, const RegAllocResult& al
             break;
         }
         case DAGNode::LOAD: {
+            if (node->operands.empty() || !node->operands[0]) {
+                if (auto constant = dynamic_cast<ConstantValue*>(node->value)) {
+                    node->inst = "li " + node->result_reg + ", " + std::to_string(constant->getInt());
+                }
+                break;
+            }
             auto ptr = node->operands[0]->value;
+            if (!ptr) break;
             if (alloc.stack_map.count(ptr)) {
                 int offset = alloc.stack_map.at(ptr);
                 node->inst = "lw " + node->result_reg + ", " + std::to_string(offset) + "(s0)";
             } else {
                 auto ptr_reg = node->operands[0]->result_reg;
-                node->inst = "lw " + node->result_reg + ", 0(" + ptr_reg + ")";
+                if (!ptr_reg.empty()) {
+                    node->inst = "lw " + node->result_reg + ", 0(" + ptr_reg + ")";
+                }
             }
             break;
         }
         case DAGNode::STORE: {
+            if (node->operands.size() < 2 || !node->operands[0] || !node->operands[1]) break;
             auto val = node->operands[0]->value;
             auto ptr = node->operands[1]->value;
-            auto val_reg = node->operands[0]->result_reg;
+            if (!val || !ptr) break;
             if (alloc.stack_map.count(ptr)) {
                 int offset = alloc.stack_map.at(ptr);
-                node->inst = "sw " + val_reg + ", " + std::to_string(offset) + "(s0)";
+                if (auto constant = dynamic_cast<ConstantValue*>(val)) {
+                    // 直接存储常量
+                    node->inst = "li t0, " + std::to_string(constant->getInt()) + "\nsw t0, " + std::to_string(offset) + "(s0)";
+                } else {
+                    auto val_reg = node->operands[0]->result_reg;
+                    if (!val_reg.empty()) {
+                        node->inst = "sw " + val_reg + ", " + std::to_string(offset) + "(s0)";
+                    }
+                }
             } else {
                 auto ptr_reg = node->operands[1]->result_reg;
-                node->inst = "sw " + val_reg + ", 0(" + ptr_reg + ")";
+                auto val_reg = node->operands[0]->result_reg;
+                if (!ptr_reg.empty() && !val_reg.empty()) {
+                    node->inst = "sw " + val_reg + ", 0(" + ptr_reg + ")";
+                }
             }
             break;
         }
         case DAGNode::BINARY: {
+            if (node->operands.size() < 2 || !node->operands[0] || !node->operands[1]) break;
             auto bin = dynamic_cast<BinaryInst*>(node->value);
+            if (!bin) break;
             auto lhs_reg = node->operands[0]->result_reg;
             auto rhs_reg = node->operands[1]->result_reg;
+            if (lhs_reg.empty() || rhs_reg.empty()) break;
             std::string opcode;
             switch (bin->getKind()) {
                 case BinaryInst::kAdd: opcode = "add"; break;
                 case BinaryInst::kSub: opcode = "sub"; break;
                 case BinaryInst::kMul: opcode = "mul"; break;
+                case BinaryInst::kICmpEQ:
+                    node->inst = "sub " + node->result_reg + ", " + lhs_reg + ", " + rhs_reg + "\nseqz " + node->result_reg + ", " + node->result_reg;
+                    return;
                 default: break;
             }
             if (!opcode.empty()) {
@@ -338,10 +419,14 @@ void RISCv32CodeGen::select_instructions(DAGNode* node, const RegAllocResult& al
             break;
         }
         case DAGNode::CALL: {
+            if (!node->value) break;
             auto call = dynamic_cast<CallInst*>(node->value);
+            if (!call) break;
             std::string insts;
             for (size_t i = 0; i < node->operands.size() && i < 8; ++i) {
-                insts += "mv a" + std::to_string(i) + ", " + node->operands[i]->result_reg + "\n";
+                if (node->operands[i] && !node->operands[i]->result_reg.empty()) {
+                    insts += "mv a" + std::to_string(i) + ", " + node->operands[i]->result_reg + "\n";
+                }
             }
             insts += "jal " + call->getCallee()->getName();
             if (call->getType()->isInt() || call->getType()->isFloat()) {
@@ -351,17 +436,20 @@ void RISCv32CodeGen::select_instructions(DAGNode* node, const RegAllocResult& al
             break;
         }
         case DAGNode::RETURN: {
-            if (!node->operands.empty()) {
+            if (!node->operands.empty() && node->operands[0] && !node->operands[0]->result_reg.empty()) {
                 node->inst = "mv a0, " + node->operands[0]->result_reg;
             }
             break;
         }
         case DAGNode::BRANCH: {
             auto br = dynamic_cast<CondBrInst*>(node->value);
+            if (!br) break;
+            if (!node->inst.empty()) break; // 常量条件已预生成跳转
+            if (node->operands.empty() || !node->operands[0]) break;
             auto cond_reg = node->operands[0]->result_reg;
+            if (cond_reg.empty()) break;
             auto then_block = br->getThenBlock()->getName();
             auto else_block = br->getElseBlock()->getName();
-            // 假设条件为 true 时跳转到 then，否则到 else
             node->inst = "bnez " + cond_reg + ", " + then_block + "\nj " + else_block;
             break;
         }
@@ -371,56 +459,71 @@ void RISCv32CodeGen::select_instructions(DAGNode* node, const RegAllocResult& al
 
 // 指令发射
 void RISCv32CodeGen::emit_instructions(DAGNode* node, std::vector<std::string>& insts, const RegAllocResult& alloc) {
-    std::set<DAGNode*> emitted; // 局部变量，针对每个基本块独立
-    std::set<std::string> seen_insts; // 跟踪已发射的指令以去重
+    std::set<DAGNode*> emitted;
+    std::set<std::string> seen_insts;
 
     std::function<void(DAGNode*)> emit = [&](DAGNode* n) {
         if (!n || emitted.count(n)) return;
         emitted.insert(n);
 
         for (auto operand : n->operands) {
-            emit(operand);
+            if (operand) emit(operand);
         }
 
         if (!n->inst.empty()) {
             std::stringstream ss(n->inst);
             std::string line;
             while (std::getline(ss, line, '\n')) {
-                if (!line.empty()) {
-                    std::string new_line = line;
-                    if (!n->result_reg.empty()) {
-                        if (alloc.vreg_to_preg.count(n->result_reg)) {
-                            new_line = std::regex_replace(new_line, std::regex("\\b" + n->result_reg + "\\b"), reg_to_string(alloc.vreg_to_preg.at(n->result_reg)));
-                        } else if (alloc.stack_map.count(n->value)) {
+                // 清理空白和无效字符
+                line.erase(std::remove_if(line.begin(), line.end(), [](char c) { return std::isspace(c) || c == ':'; }), line.end());
+                if (line.empty()) continue;
+
+                std::string new_line = line;
+                // 替换结果寄存器
+                if (!n->result_reg.empty()) {
+                    if (alloc.vreg_to_preg.count(n->result_reg)) {
+                        new_line = std::regex_replace(new_line, std::regex("\\b" + n->result_reg + "\\b"), reg_to_string(alloc.vreg_to_preg.at(n->result_reg)));
+                    } else {
+                        // 如果虚拟寄存器未分配物理寄存器，使用 t0 并通过栈访问
+                        if (n->value && alloc.stack_map.count(n->value)) {
                             int offset = alloc.stack_map.at(n->value);
                             new_line = std::regex_replace(new_line, std::regex("\\b" + n->result_reg + "\\b"), "t0");
-                            std::string store = "sw t0, " + std::to_string(offset) + "(s0)";
-                            if (!seen_insts.count(store)) {
-                                insts.push_back(store);
-                                seen_insts.insert(store);
-                            }
-                        }
-                    }
-                    for (auto operand : n->operands) {
-                        if (!operand->result_reg.empty()) {
-                            if (alloc.vreg_to_preg.count(operand->result_reg)) {
-                                new_line = std::regex_replace(new_line, std::regex("\\b" + operand->result_reg + "\\b"), reg_to_string(alloc.vreg_to_preg.at(operand->result_reg)));
-                            } else if (alloc.stack_map.count(operand->value)) {
-                                int offset = alloc.stack_map.at(operand->value);
-                                std::string load = "lw t0, " + std::to_string(offset) + "(s0)";
-                                if (!seen_insts.count(load)) {
-                                    insts.push_back(load);
-                                    seen_insts.insert(load);
+                            if (n->kind != DAGNode::STORE) { // 避免为 STORE 节点重复生成存储
+                                std::string store = "sw t0, " + std::to_string(offset) + "(s0)";
+                                if (!seen_insts.count(store)) {
+                                    insts.push_back(store);
+                                    seen_insts.insert(store);
                                 }
-                                new_line = std::regex_replace(new_line, std::regex("\\b" + operand->result_reg + "\\b"), "t0");
                             }
+                        } else {
+                            // 兜底：使用 t0
+                            new_line = std::regex_replace(new_line, std::regex("\\b" + n->result_reg + "\\b"), "t0");
                         }
                     }
-                    if (!seen_insts.count(new_line)) {
-                        insts.push_back(new_line);
-                        seen_insts.insert(new_line);
+                }
+                // 替换操作数寄存器
+                for (auto operand : n->operands) {
+                    if (operand && !operand->result_reg.empty()) {
+                        if (alloc.vreg_to_preg.count(operand->result_reg)) {
+                            new_line = std::regex_replace(new_line, std::regex("\\b" + operand->result_reg + "\\b"), reg_to_string(alloc.vreg_to_preg.at(operand->result_reg)));
+                        } else if (operand->value && alloc.stack_map.count(operand->value)) {
+                            int offset = alloc.stack_map.at(operand->value);
+                            std::string load = "lw t0, " + std::to_string(offset) + "(s0)";
+                            if (!seen_insts.count(load)) {
+                                insts.push_back(load);
+                                seen_insts.insert(load);
+                            }
+                            new_line = std::regex_replace(new_line, std::regex("\\b" + operand->result_reg + "\\b"), "t0");
+                        } else {
+                            // 兜底：使用 t0
+                            new_line = std::regex_replace(new_line, std::regex("\\b" + operand->result_reg + "\\b"), "t0");
+                        }
                     }
                 }
+                if (!seen_insts.count(new_line)) {
+                    insts.push_back(new_line);
+                    seen_insts.insert(new_line);
+                }
             }
         }
     };
@@ -688,9 +791,10 @@ RISCv32CodeGen::RegAllocResult RISCv32CodeGen::register_allocation(Function* fun
     // 分配溢出栈空间
     for (const auto& pair : value_vreg_map) {
         auto vreg = pair.second;
+        auto value = pair.first;
         if (result.vreg_to_preg.find(vreg) == result.vreg_to_preg.end()) {
-            if (result.stack_map.find(pair.first) == result.stack_map.end()) {
-                result.stack_map[pair.first] = stack_offset;
+            if (result.stack_map.find(value) == result.stack_map.end()) {
+                result.stack_map[value] = stack_offset;
                 stack_offset += 4;
             }
         }