[backend]为图着色引入保底修复

src/backend/RISCv64/CMakeLists.txt

@@ -5,6 +5,7 @@ add_library(riscv64_backend_lib STATIC
     RISCv64ISel.cpp
     RISCv64LLIR.cpp
     RISCv64RegAlloc.cpp
+    RISCv64LinearScan.cpp
     Handler/CalleeSavedHandler.cpp
     Handler/LegalizeImmediates.cpp
     Handler/PrologueEpilogueInsertion.cpp

src/backend/RISCv64/RISCv64LinearScan.cpp

@@ -0,0 +1,459 @@
+#include "RISCv64LinearScan.h"
+#include "RISCv64LLIR.h"
+#include "RISCv64ISel.h"
+#include <iostream>
+#include <set>
+
+extern int DEBUG;
+
+namespace sysy {
+
+RISCv64LinearScan::RISCv64LinearScan(MachineFunction* mfunc)
+    : MFunc(mfunc), 
+      ISel(mfunc->getISel()),
+      vreg_type_map(ISel->getVRegTypeMap()) {
+    
+    // 初始化可用的物理寄存器池，与图着色版本保持一致
+    // 整数寄存器
+    allocable_int_regs = {
+        PhysicalReg::T0, PhysicalReg::T1, PhysicalReg::T2, PhysicalReg::T3, PhysicalReg::T4, /*T5保留作为大立即数加载寄存器*/ PhysicalReg::T6,
+        PhysicalReg::A0, PhysicalReg::A1, PhysicalReg::A2, PhysicalReg::A3, PhysicalReg::A4, PhysicalReg::A5, PhysicalReg::A6, PhysicalReg::A7,
+        PhysicalReg::S1, PhysicalReg::S2, PhysicalReg::S3, PhysicalReg::S4, PhysicalReg::S5, PhysicalReg::S6, PhysicalReg::S7,
+        PhysicalReg::S8, PhysicalReg::S9, PhysicalReg::S10, PhysicalReg::S11,
+    };
+    // 浮点寄存器
+    allocable_fp_regs = {
+        PhysicalReg::F0, PhysicalReg::F1, PhysicalReg::F2, PhysicalReg::F3, PhysicalReg::F4, PhysicalReg::F5, PhysicalReg::F6, PhysicalReg::F7,
+        PhysicalReg::F10, PhysicalReg::F11, PhysicalReg::F12, PhysicalReg::F13, PhysicalReg::F14, PhysicalReg::F15, PhysicalReg::F16, PhysicalReg::F17,
+        PhysicalReg::F8, PhysicalReg::F9, PhysicalReg::F18, PhysicalReg::F19, PhysicalReg::F20, PhysicalReg::F21, PhysicalReg::F22,
+        PhysicalReg::F23, PhysicalReg::F24, PhysicalReg::F25, PhysicalReg::F26, PhysicalReg::F27,
+        PhysicalReg::F28, PhysicalReg::F29, PhysicalReg::F30, PhysicalReg::F31,
+    };
+    // 新增：识别所有通过寄存器传递的参数，并建立vreg到物理寄存器(preg)的映射
+    // 这等同于图着色算法中的“预着色”步骤。
+    if (MFunc->getFunc()) {
+        int int_arg_idx = 0;
+        int fp_arg_idx = 0;
+        for (Argument* arg : MFunc->getFunc()->getArguments()) {
+            unsigned arg_vreg = ISel->getVReg(arg);
+            if (arg->getType()->isFloat()) {
+                if (fp_arg_idx < 8) { // fa0-fa7
+                    auto preg = static_cast<PhysicalReg>(static_cast<int>(PhysicalReg::F10) + fp_arg_idx);
+                    abi_vreg_map[arg_vreg] = preg;
+                    fp_arg_idx++;
+                }
+            } else { // 整数或指针
+                if (int_arg_idx < 8) { // a0-a7
+                    auto preg = static_cast<PhysicalReg>(static_cast<int>(PhysicalReg::A0) + int_arg_idx);
+                    abi_vreg_map[arg_vreg] = preg;
+                    int_arg_idx++;
+                }
+            }
+        }
+    }
+}
+
+void RISCv64LinearScan::run() {
+    if (DEBUG) std::cerr << "===== Running Linear Scan Register Allocation for function: " << MFunc->getName() << " =====\n";
+    
+    bool changed = true;
+    while(changed) {
+        // 1. 准备阶段
+        linearizeBlocks();
+        computeLiveIntervals();
+        
+        // 2. 执行线性扫描
+        changed = linearScan();
+
+        // 3. 如果有溢出，重写代码，然后下一轮重新开始
+        if (changed) {
+            rewriteProgram();
+            if (DEBUG) std::cerr << "--- Spilling detected, re-running linear scan ---\n";
+        }
+    }
+
+    // 4. 将最终分配结果应用到机器指令
+    applyAllocation();
+    // 5. 收集用到的被调用者保存寄存器
+    MFunc->getFrameInfo().vreg_to_preg_map = this->vreg_to_preg_map;
+    collectUsedCalleeSavedRegs();
+
+    if (DEBUG) std::cerr << "===== Finished Linear Scan Register Allocation =====\n\n";
+}
+
+// 步骤 1.1: 对基本块进行线性化，这里我们简单地按现有顺序排列
+void RISCv64LinearScan::linearizeBlocks() {
+    linear_order_blocks.clear();
+    for (auto& mbb : MFunc->getBlocks()) {
+        linear_order_blocks.push_back(mbb.get());
+    }
+}
+
+// 步骤 1.2: 计算活跃区间
+void RISCv64LinearScan::computeLiveIntervals() {
+    instr_numbering.clear();
+    live_intervals.clear();
+    unhandled.clear();
+
+    // a. 对所有指令进行线性编号
+    int num = 0;
+    for (auto* mbb : linear_order_blocks) {
+        for (auto& instr : mbb->getInstructions()) {
+            instr_numbering[instr.get()] = num;
+            num += 2; // 指令编号间隔为2，方便在溢出重写时插入指令
+        }
+    }
+
+    // b. (新逻辑) 遍历所有指令，记录每个vreg首次和末次出现的位置
+    std::map<unsigned, std::pair<int, int>> vreg_ranges; // vreg -> {first_instr_num, last_instr_num}
+
+    for (auto* mbb : linear_order_blocks) {
+        for (auto& instr_ptr : mbb->getInstructions()) {
+            const MachineInstr* instr = instr_ptr.get();
+            int instr_num = instr_numbering.at(instr);
+            std::set<unsigned> use, def;
+            getInstrUseDef(instr, use, def);
+            
+            // 合并use和def集合，获取本条指令涉及的所有vreg
+            auto all_vregs = use;
+            all_vregs.insert(def.begin(), def.end());
+
+            // 更新每个vreg的区间边界
+            for (unsigned vreg : all_vregs) {
+                if (vreg_ranges.find(vreg) == vreg_ranges.end()) {
+                    // 第一次见到这个vreg，记录首次和末次位置
+                    vreg_ranges[vreg] = {instr_num, instr_num};
+                } else {
+                    // 更新末次位置
+                    vreg_ranges[vreg].second = std::max(vreg_ranges[vreg].second, instr_num);
+                }
+            }
+        }
+    }
+
+    // c. 根据记录的边界，创建LiveInterval对象
+    for (auto const& [vreg, range] : vreg_ranges) {
+        live_intervals.emplace(vreg, LiveInterval(vreg));
+        live_intervals.at(vreg).start = range.first;
+        live_intervals.at(vreg).end = range.second;
+    }
+
+    // d. 将所有计算出的活跃区间放入 unhandled 列表
+    for (auto& pair : live_intervals) {
+        unhandled.push_back(&pair.second);
+    }
+    std::sort(unhandled.begin(), unhandled.end(), [](const LiveInterval* a, const LiveInterval* b){
+        return a->start < b->start;
+    });
+}
+
+// 步骤 2: 线性扫描主算法
+bool RISCv64LinearScan::linearScan() {
+    // 初始化/重置状态
+    active.clear();
+    spilled_vregs.clear();
+    vreg_to_preg_map.clear();
+    free_int_regs.clear();
+    free_fp_regs.clear();
+    free_int_regs.insert(allocable_int_regs.begin(), allocable_int_regs.end());
+    free_fp_regs.insert(allocable_fp_regs.begin(), allocable_fp_regs.end());
+
+    // 1. 将ABI参数的vreg直接分配给其固定的物理寄存器
+    vreg_to_preg_map.insert(abi_vreg_map.begin(), abi_vreg_map.end());
+
+    // 2. 从unhandled列表中移除这些ABI参数区间，并将其加入active列表
+    std::vector<LiveInterval*> normal_unhandled;
+    for(LiveInterval* interval : unhandled) {
+        if(abi_vreg_map.count(interval->vreg)) {
+            // 这是一个ABI参数区间，它已经被“预分配”
+            active.push_back(interval);
+            // 从空闲池中移除对应的物理寄存器
+            PhysicalReg preg = abi_vreg_map.at(interval->vreg);
+            if (isFPVReg(interval->vreg)) {
+                free_fp_regs.erase(preg);
+            } else {
+                free_int_regs.erase(preg);
+            }
+        } else {
+            // 这是一个普通区间，留待后续处理
+            normal_unhandled.push_back(interval);
+        }
+    }
+    unhandled = normal_unhandled; // 更新unhandled列表，只包含普通区间
+
+    // 3. 对active列表（现在只包含ABI参数）按结束点排序
+    std::sort(active.begin(), active.end(), [](const LiveInterval* a, const LiveInterval* b){
+        return a->end < b->end;
+    });
+    
+    for (LiveInterval* current : unhandled) {
+        // a. 检查并释放 active 列表中已经结束的区间
+        std::vector<LiveInterval*> new_active;
+        for (LiveInterval* active_interval : active) {
+            if (active_interval->end < current->start) {
+                // 此区间已结束，释放其物理寄存器
+                PhysicalReg preg = vreg_to_preg_map.at(active_interval->vreg);
+                if (isFPVReg(active_interval->vreg)) free_fp_regs.insert(preg);
+                else free_int_regs.insert(preg);
+            } else {
+                new_active.push_back(active_interval);
+            }
+        }
+        active = new_active;
+
+        // b. 尝试为当前区间分配寄存器
+        chooseRegForInterval(current);
+    }
+    return !spilled_vregs.empty();
+}
+
+void RISCv64LinearScan::chooseRegForInterval(LiveInterval* current) {
+    bool is_fp = isFPVReg(current->vreg);
+    auto& free_regs = is_fp ? free_fp_regs : free_int_regs;
+    
+    if (!free_regs.empty()) {
+        // 有可用寄存器
+        PhysicalReg preg = *free_regs.begin();
+        free_regs.erase(free_regs.begin());
+        vreg_to_preg_map[current->vreg] = preg;
+        active.push_back(current);
+        // 保持 active 列表按结束点排序
+        std::sort(active.begin(), active.end(), [](const LiveInterval* a, const LiveInterval* b){
+            return a->end < b->end;
+        });
+    } else {
+        // 没有可用寄存器，需要溢出
+        spillAtInterval(current);
+    }
+}
+
+void RISCv64LinearScan::spillAtInterval(LiveInterval* current) {
+    // 启发式：比较当前区间和 active 列表中结束点最晚的区间
+    LiveInterval* spill_candidate = active.back(); // active已按end排序，最后一个就是结束最晚的
+    
+    if (spill_candidate->end > current->end) {
+        // active中的区间结束得更晚，溢出它
+        PhysicalReg preg = vreg_to_preg_map.at(spill_candidate->vreg);
+        
+        // 将被溢出区间的物理寄存器分配给当前区间
+        vreg_to_preg_map[current->vreg] = preg;
+        
+        // 更新 active 列表
+        active.pop_back(); // 移除被溢出的
+        active.push_back(current); // 加入当前的
+        std::sort(active.begin(), active.end(), [](const LiveInterval* a, const LiveInterval* b){
+            return a->end < b->end;
+        });
+
+        spilled_vregs.insert(spill_candidate->vreg);
+        if(DEBUG) std::cerr << "  Spilling vreg" << spill_candidate->vreg << " to make room for vreg" << current->vreg << "\n";
+    } else {
+        // 当前区间结束得更晚，直接溢出当前区间
+        spilled_vregs.insert(current->vreg);
+        if(DEBUG) std::cerr << "  Spilling current vreg" << current->vreg << "\n";
+    }
+}
+
+
+// 步骤 3: 重写程序，插入溢出代码
+void RISCv64LinearScan::rewriteProgram() {
+    StackFrameInfo& frame_info = MFunc->getFrameInfo();
+    int spill_offset = frame_info.locals_size; // 溢出区域接在局部变量之后
+
+    for (unsigned vreg : spilled_vregs) {
+        if (frame_info.spill_offsets.count(vreg)) continue; // 避免重复分配
+        
+        int size = isFPVReg(vreg) ? 4 : (vreg_type_map.at(vreg)->isPointer() ? 8 : 4);
+        spill_offset += size;
+        spill_offset = (spill_offset + 7) & ~7; // 8字节对齐
+        frame_info.spill_offsets[vreg] = -(16 + spill_offset);
+    }
+    frame_info.spill_size = spill_offset - frame_info.locals_size;
+
+    for (auto& mbb : MFunc->getBlocks()) {
+        auto& instrs = mbb->getInstructions();
+        std::vector<std::unique_ptr<MachineInstr>> new_instrs;
+
+        for (auto it = instrs.begin(); it != instrs.end(); ++it) {
+            auto& instr = *it;
+            std::set<unsigned> use, def;
+            getInstrUseDef(instr.get(), use, def);
+
+            // 为每个溢出的 use 创建 load
+            for (unsigned old_vreg : use) {
+                if (spilled_vregs.count(old_vreg)) {
+                    Type* type = vreg_type_map.at(old_vreg);
+                    unsigned new_temp_vreg = ISel->getNewVReg(type);
+                    
+                    RVOpcodes load_op = isFPVReg(old_vreg) ? RVOpcodes::FLW : (type->isPointer() ? RVOpcodes::LD : RVOpcodes::LW);
+                    auto load = std::make_unique<MachineInstr>(load_op);
+                    load->addOperand(std::make_unique<RegOperand>(new_temp_vreg));
+                    load->addOperand(std::make_unique<MemOperand>(
+                        std::make_unique<RegOperand>(PhysicalReg::S0),
+                        std::make_unique<ImmOperand>(frame_info.spill_offsets.at(old_vreg))
+                    ));
+                    new_instrs.push_back(std::move(load));
+
+                    // 替换原指令中的 use
+                    for(auto& op : instr->getOperands()) {
+                        if(op->getKind() == MachineOperand::KIND_REG) {
+                            auto reg_op = static_cast<RegOperand*>(op.get());
+                            if(reg_op->isVirtual() && reg_op->getVRegNum() == old_vreg) {
+                                reg_op->setVRegNum(new_temp_vreg);
+                            }
+                        } else if(op->getKind() == MachineOperand::KIND_MEM) {
+                            auto mem_op = static_cast<MemOperand*>(op.get());
+                            auto base_reg = mem_op->getBase();
+                            if(base_reg->isVirtual() && base_reg->getVRegNum() == old_vreg) {
+                                base_reg->setVRegNum(new_temp_vreg);
+                            }
+                        }
+                    }
+                }
+            }
+            
+            new_instrs.push_back(std::move(instr));
+
+            // 为每个溢出的 def 创建 store
+            for (unsigned old_vreg : def) {
+                if (spilled_vregs.count(old_vreg)) {
+                    Type* type = vreg_type_map.at(old_vreg);
+                    unsigned new_temp_vreg = ISel->getNewVReg(type);
+
+                    // 替换原指令中的 def
+                    for(auto& op : new_instrs.back()->getOperands()) {
+                         if(op->getKind() == MachineOperand::KIND_REG) {
+                            auto reg_op = static_cast<RegOperand*>(op.get());
+                            if(reg_op->isVirtual() && reg_op->getVRegNum() == old_vreg) {
+                                reg_op->setVRegNum(new_temp_vreg);
+                            }
+                        }
+                    }
+
+                    RVOpcodes store_op = isFPVReg(old_vreg) ? RVOpcodes::FSW : (type->isPointer() ? RVOpcodes::SD : RVOpcodes::SW);
+                    auto store = std::make_unique<MachineInstr>(store_op);
+                    store->addOperand(std::make_unique<RegOperand>(new_temp_vreg));
+                    store->addOperand(std::make_unique<MemOperand>(
+                        std::make_unique<RegOperand>(PhysicalReg::S0),
+                        std::make_unique<ImmOperand>(frame_info.spill_offsets.at(old_vreg))
+                    ));
+                    new_instrs.push_back(std::move(store));
+                }
+            }
+        }
+        instrs = std::move(new_instrs);
+    }
+}
+
+
+// 步骤 4: 应用最终分配结果
+void RISCv64LinearScan::applyAllocation() {
+    for (auto& mbb : MFunc->getBlocks()) {
+        for (auto& instr_ptr : mbb->getInstructions()) {
+            for (auto& op_ptr : instr_ptr->getOperands()) {
+                if (op_ptr->getKind() == MachineOperand::KIND_REG) {
+                    auto reg_op = static_cast<RegOperand*>(op_ptr.get());
+                    if (reg_op->isVirtual()) {
+                        unsigned vreg = reg_op->getVRegNum();
+                        if (vreg_to_preg_map.count(vreg)) {
+                            reg_op->setPReg(vreg_to_preg_map.at(vreg));
+                        } else {
+                            // 如果一个vreg最终没有颜色，这通常意味着它是一个短生命周期的临时变量
+                            // 在溢出重写中产生，但在下一轮分配前就被优化掉了。
+                            // 或者是一个从未被使用的定义。
+                            // 给他一个临时寄存器以防万一。
+                            reg_op->setPReg(PhysicalReg::T5); 
+                        }
+                    }
+                } else if (op_ptr->getKind() == MachineOperand::KIND_MEM) {
+                    auto mem_op = static_cast<MemOperand*>(op_ptr.get());
+                    auto reg_op = mem_op->getBase();
+                    if (reg_op->isVirtual()) {
+                        unsigned vreg = reg_op->getVRegNum();
+                        if (vreg_to_preg_map.count(vreg)) {
+                            reg_op->setPReg(vreg_to_preg_map.at(vreg));
+                        } else {
+                            reg_op->setPReg(PhysicalReg::T5);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+// 辅助函数: 获取指令的use/def集合 (仅虚拟寄存器)
+void RISCv64LinearScan::getInstrUseDef(const MachineInstr* instr, std::set<unsigned>& use, std::set<unsigned>& def) {
+    // 这个函数与图着色版本中的 getInstrUseDef 逻辑完全相同，此处直接复用
+    auto opcode = instr->getOpcode();
+    const auto& operands = instr->getOperands();
+
+    static const std::map<RVOpcodes, std::pair<std::vector<int>, std::vector<int>>> op_info = {
+        {RVOpcodes::ADD, {{0}, {1, 2}}}, {RVOpcodes::SUB, {{0}, {1, 2}}}, {RVOpcodes::MUL, {{0}, {1, 2}}},
+        {RVOpcodes::DIV, {{0}, {1, 2}}}, {RVOpcodes::REM, {{0}, {1, 2}}}, {RVOpcodes::ADDW, {{0}, {1, 2}}},
+        {RVOpcodes::SUBW, {{0}, {1, 2}}}, {RVOpcodes::MULW, {{0}, {1, 2}}}, {RVOpcodes::DIVW, {{0}, {1, 2}}},
+        {RVOpcodes::REMW, {{0}, {1, 2}}}, {RVOpcodes::SLT, {{0}, {1, 2}}}, {RVOpcodes::SLTU, {{0}, {1, 2}}},
+        {RVOpcodes::ADDI, {{0}, {1}}}, {RVOpcodes::ADDIW, {{0}, {1}}}, {RVOpcodes::XORI, {{0}, {1}}},
+        {RVOpcodes::SLTI, {{0}, {1}}}, {RVOpcodes::SLTIU, {{0}, {1}}}, {RVOpcodes::LB, {{0}, {}}},
+        {RVOpcodes::LH, {{0}, {}}}, {RVOpcodes::LW, {{0}, {}}}, {RVOpcodes::LD, {{0}, {}}},
+        {RVOpcodes::LBU, {{0}, {}}}, {RVOpcodes::LHU, {{0}, {}}}, {RVOpcodes::LWU, {{0}, {}}},
+        {RVOpcodes::FLW, {{0}, {}}}, {RVOpcodes::FLD, {{0}, {}}}, {RVOpcodes::SB, {{}, {0, 1}}},
+        {RVOpcodes::SH, {{}, {0, 1}}}, {RVOpcodes::SW, {{}, {0, 1}}}, {RVOpcodes::SD, {{}, {0, 1}}},
+        {RVOpcodes::FSW, {{}, {0, 1}}}, {RVOpcodes::FSD, {{}, {0, 1}}}, {RVOpcodes::BEQ, {{}, {0, 1}}},
+        {RVOpcodes::BNE, {{}, {0, 1}}}, {RVOpcodes::BLT, {{}, {0, 1}}}, {RVOpcodes::BGE, {{}, {0, 1}}},
+        {RVOpcodes::JALR, {{0}, {1}}}, {RVOpcodes::LI, {{0}, {}}}, {RVOpcodes::LA, {{0}, {}}},
+        {RVOpcodes::MV, {{0}, {1}}}, {RVOpcodes::SEQZ, {{0}, {1}}}, {RVOpcodes::SNEZ, {{0}, {1}}},
+        {RVOpcodes::RET, {{}, {}}}, {RVOpcodes::FADD_S, {{0}, {1, 2}}}, {RVOpcodes::FSUB_S, {{0}, {1, 2}}},
+        {RVOpcodes::FMUL_S, {{0}, {1, 2}}}, {RVOpcodes::FDIV_S, {{0}, {1, 2}}}, {RVOpcodes::FEQ_S, {{0}, {1, 2}}},
+        {RVOpcodes::FLT_S, {{0}, {1, 2}}}, {RVOpcodes::FLE_S, {{0}, {1, 2}}}, {RVOpcodes::FCVT_S_W, {{0}, {1}}},
+        {RVOpcodes::FCVT_W_S, {{0}, {1}}}, {RVOpcodes::FMV_S, {{0}, {1}}}, {RVOpcodes::FMV_W_X, {{0}, {1}}},
+        {RVOpcodes::FMV_X_W, {{0}, {1}}}, {RVOpcodes::FNEG_S, {{0}, {1}}}
+    };
+    
+    auto get_vreg_id_if_virtual = [&](const MachineOperand* op, std::set<unsigned>& s) {
+        if (op->getKind() == MachineOperand::KIND_REG) {
+            auto reg_op = static_cast<const RegOperand*>(op);
+            if (reg_op->isVirtual()) s.insert(reg_op->getVRegNum());
+        } else if (op->getKind() == MachineOperand::KIND_MEM) {
+            auto mem_op = static_cast<const MemOperand*>(op);
+            auto reg_op = mem_op->getBase();
+            if (reg_op->isVirtual()) s.insert(reg_op->getVRegNum());
+        }
+    };
+
+    if (op_info.count(opcode)) {
+        const auto& info = op_info.at(opcode);
+        for (int idx : info.first) if (idx < operands.size()) get_vreg_id_if_virtual(operands[idx].get(), def);
+        for (int idx : info.second) if (idx < operands.size()) get_vreg_id_if_virtual(operands[idx].get(), use);
+        for (const auto& op : operands) if (op->getKind() == MachineOperand::KIND_MEM) get_vreg_id_if_virtual(op.get(), use);
+    } else if (opcode == RVOpcodes::CALL) {
+        if (!operands.empty() && operands[0]->getKind() == MachineOperand::KIND_REG) get_vreg_id_if_virtual(operands[0].get(), def);
+        for (size_t i = 1; i < operands.size(); ++i) if (operands[i]->getKind() == MachineOperand::KIND_REG) get_vreg_id_if_virtual(operands[i].get(), use);
+    }
+}
+
+// 辅助函数: 判断是否为浮点vreg
+bool RISCv64LinearScan::isFPVReg(unsigned vreg) const {
+    return vreg_type_map.count(vreg) && vreg_type_map.at(vreg)->isFloat();
+}
+
+// 辅助函数: 收集被使用的被调用者保存寄存器
+void RISCv64LinearScan::collectUsedCalleeSavedRegs() {
+    StackFrameInfo& frame_info = MFunc->getFrameInfo();
+    frame_info.used_callee_saved_regs.clear();
+
+    const auto& callee_saved_int = getCalleeSavedIntRegs();
+    const auto& callee_saved_fp = getCalleeSavedFpRegs();
+    std::set<PhysicalReg> callee_saved_set(callee_saved_int.begin(), callee_saved_int.end());
+    callee_saved_set.insert(callee_saved_fp.begin(), callee_saved_fp.end());
+    callee_saved_set.insert(PhysicalReg::S0); // s0总是被用作帧指针
+
+    for(const auto& pair : vreg_to_preg_map) {
+        PhysicalReg preg = pair.second;
+        if(callee_saved_set.count(preg)) {
+            frame_info.used_callee_saved_regs.insert(preg);
+        }
+    }
+}
+
+} // namespace sysy

src/backend/RISCv64/RISCv64RegAlloc.cpp

@@ -55,41 +55,12 @@ void RISCv64RegAlloc::run() {
 
     if (DEBUG) std::cerr << "===== Running Graph Coloring Register Allocation for function: " << MFunc->getName() << " =====\n";
     
-    const int MAX_ITERATIONS = 50;
-    int iteration = 0;
-    
-    while (iteration++ < MAX_ITERATIONS) {
+    while (true) {
         if (doAllocation()) {
             break;
         } else {
             rewriteProgram();
-            if (DEBUG) std::cerr << "--- Spilling detected, re-running allocation (iteration " << iteration << ") ---\n";
-            
-            if (iteration >= MAX_ITERATIONS) {
-                std::cerr << "ERROR: Register allocation failed to converge after " << MAX_ITERATIONS << " iterations\n";
-                std::cerr << "  Spill worklist size: " << spillWorklist.size() << "\n";
-                std::cerr << "  Total nodes: " << (initial.size() + coloredNodes.size()) << "\n";
-                
-                // Emergency spill remaining nodes to break the loop
-                std::cerr << "  Emergency spilling remaining spill worklist nodes...\n";
-                for (unsigned node : spillWorklist) {
-                    spilledNodes.insert(node);
-                }
-                
-                // Also spill any nodes that didn't get colors
-                std::set<unsigned> uncolored;
-                for (unsigned node : initial) {
-                    if (color_map.find(node) == color_map.end()) {
-                        uncolored.insert(node);
-                    }
-                }
-                for (unsigned node : uncolored) {
-                    spilledNodes.insert(node);
-                }
-                
-                // Force completion
-                break;
-            }
+            if (DEBUG) std::cerr << "--- Spilling detected, re-running allocation ---\n";
         }
     }
 

src/include/backend/RISCv64/RISCv64LinearScan.h

@@ -0,0 +1,81 @@
+#ifndef RISCV64_LINEARSCAN_H
+#define RISCV64_LINEARSCAN_H
+
+#include "RISCv64LLIR.h"
+#include "RISCv64ISel.h"
+#include <vector>
+#include <map>
+#include <set>
+#include <algorithm>
+
+namespace sysy {
+
+// 前向声明
+class MachineBasicBlock;
+class MachineFunction;
+class RISCv64ISel;
+
+/**
+ * @brief 表示一个虚拟寄存器的活跃区间。
+ * 包含起始和结束指令编号。为了简化，我们不处理有“洞”的区间。
+ */
+struct LiveInterval {
+    unsigned vreg = 0;
+    int start = -1;
+    int end = -1;
+
+    LiveInterval(unsigned vreg) : vreg(vreg) {}
+
+    // 用于排序，按起始点从小到大
+    bool operator<(const LiveInterval& other) const {
+        return start < other.start;
+    }
+};
+
+class RISCv64LinearScan {
+public:
+    RISCv64LinearScan(MachineFunction* mfunc);
+    void run();
+
+private:
+    // --- 核心算法流程 ---
+    void linearizeBlocks();
+    void computeLiveIntervals();
+    bool linearScan();
+    void rewriteProgram();
+    void applyAllocation();
+    void chooseRegForInterval(LiveInterval* current);
+    void spillAtInterval(LiveInterval* current);
+    
+    // --- 辅助函数 ---
+    void getInstrUseDef(const MachineInstr* instr, std::set<unsigned>& use, std::set<unsigned>& def);
+    bool isFPVReg(unsigned vreg) const;
+    void collectUsedCalleeSavedRegs();
+
+    MachineFunction* MFunc;
+    RISCv64ISel* ISel;
+
+    // --- 线性扫描数据结构 ---
+    std::vector<MachineBasicBlock*> linear_order_blocks;
+    std::map<const MachineInstr*, int> instr_numbering;
+    std::map<unsigned, LiveInterval> live_intervals;
+    
+    std::vector<LiveInterval*> unhandled;
+    std::vector<LiveInterval*> active; // 活跃且已分配物理寄存器的区间
+    
+    std::set<unsigned> spilled_vregs; // 记录在本轮被决定溢出的vreg
+
+    // --- 寄存器池和分配结果 ---
+    std::vector<PhysicalReg> allocable_int_regs;
+    std::vector<PhysicalReg> allocable_fp_regs;
+    std::set<PhysicalReg> free_int_regs;
+    std::set<PhysicalReg> free_fp_regs;
+    std::map<unsigned, PhysicalReg> vreg_to_preg_map;
+    std::map<unsigned, PhysicalReg> abi_vreg_map;
+    
+    const std::map<unsigned, Type*>& vreg_type_map;
+};
+
+} // namespace sysy
+
+#endif // RISCV64_LINEARSCAN_H