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// 公共子表达式消除（CSE）：
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// - 识别并复用重复计算的等价表达式
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// - 局部值编号：在单个基本块内消除重复计算
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#include "ir/IR.h"
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#include <cstdint>
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#include <sstream>
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#include <string>
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#include <unordered_map>
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namespace ir {
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namespace {
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// 为操作数生成唯一标识：常量使用值，否则使用指针
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std::string ValKey(Value* v) {
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if (auto* ci = dynamic_cast<ConstantInt*>(v))
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return "ci" + std::to_string(ci->GetValue());
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if (auto* cf = dynamic_cast<ConstantFloat*>(v)) {
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// 使用 IEEE 754 位表示
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union { float f; uint32_t i; } u;
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u.f = cf->GetValue();
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return "cf" + std::to_string(u.i);
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}
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// 非常量使用指针地址作为唯一标识
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std::ostringstream oss;
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oss << "p" << reinterpret_cast<uintptr_t>(v);
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return oss.str();
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}
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// 为可消除的指令生成 hash key
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std::string MakeKey(Instruction* inst) {
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switch (inst->GetOpcode()) {
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case Opcode::Add: case Opcode::Sub: case Opcode::Mul:
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case Opcode::Div: case Opcode::Mod:
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case Opcode::FAdd: case Opcode::FSub:
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case Opcode::FMul: case Opcode::FDiv: {
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auto* bin = static_cast<BinaryInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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ValKey(bin->GetLhs()) + "|" + ValKey(bin->GetRhs());
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}
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case Opcode::ICmp: {
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auto* cmp = static_cast<ICmpInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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std::to_string(static_cast<int>(cmp->GetPredicate())) + "|" +
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ValKey(cmp->GetLhs()) + "|" + ValKey(cmp->GetRhs());
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}
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case Opcode::FCmp: {
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auto* cmp = static_cast<FCmpInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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std::to_string(static_cast<int>(cmp->GetPredicate())) + "|" +
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ValKey(cmp->GetLhs()) + "|" + ValKey(cmp->GetRhs());
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}
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case Opcode::Gep: {
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auto* gep = static_cast<GepInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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ValKey(gep->GetBasePtr()) + "|" + ValKey(gep->GetIndex());
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}
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case Opcode::Load: {
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auto* ld = static_cast<LoadInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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ValKey(ld->GetPtr());
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}
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case Opcode::ZExt: {
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auto* ze = static_cast<ZExtInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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ValKey(ze->GetSrc());
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}
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case Opcode::SIToFP: {
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auto* si = static_cast<SIToFPInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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ValKey(si->GetSrc());
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}
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case Opcode::FPToSI: {
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auto* fs = static_cast<FPToSIInst*>(inst);
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return std::to_string(static_cast<int>(inst->GetOpcode())) + "|" +
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ValKey(fs->GetSrc());
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}
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default: return "";
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}
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}
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} // namespace
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bool RunCSE(Function& func) {
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bool changed = false;
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for (auto& bb : func.GetBlocks()) {
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std::unordered_map<std::string, Value*> available;
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std::vector<Instruction*> to_remove;
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for (auto& inst : bb->GetInstructions()) {
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auto* ip = inst.get();
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// Store/Call 指令可能修改内存，使之前缓存的 Load/Gep 结果失效。
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// 保守地清空整个 available 表，避免跨副作用的错误 CSE。
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if (ip->GetOpcode() == Opcode::Store ||
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ip->GetOpcode() == Opcode::Call) {
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available.clear();
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continue;
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}
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std::string key = MakeKey(ip);
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if (key.empty()) continue;
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auto it = available.find(key);
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if (it != available.end()) {
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// 找到已有的等价指令，替换使用
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ip->ReplaceAllUsesWith(it->second);
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to_remove.push_back(ip);
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changed = true;
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} else {
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available[key] = ip;
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}
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}
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for (auto* ip : to_remove) {
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for (size_t i = 0; i < ip->GetNumOperands(); ++i)
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ip->SetOperand(i, nullptr);
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ip->RemoveFromParent();
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}
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bb->SweepDeadInstructions();
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}
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return changed;
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}
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} // namespace ir
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