fix(frontend): 规范一下前端实现

src/antlr4/SysY.g4

@@ -10,16 +10,24 @@ compUnit
     ;
 
 funcDef
-    : Int Main L_PAREN R_PAREN block
+    : Int Ident L_PAREN R_PAREN block
     ;
 
 block
-    : L_BRACE stmt* R_BRACE
+    : L_BRACE blockItem* R_BRACE
     ;
 
-stmt
+blockItem
+    : decl
+    | stmt
+    ;
+
+decl
     : varDecl
-    | returnStmt
+    ;
+
+stmt
+    : returnStmt
     ;
 
 varDecl
@@ -46,7 +54,6 @@ primary
 
 Int     : 'int';
 Return  : 'return';
-Main    : 'main';
 
 AddOp   : '+';
 Assign  : '=';

src/frontend/AntlrDriver.cpp

@@ -12,6 +12,10 @@
 
 namespace {
 
+bool HasParsePrefix(const std::string& msg) {
+  return msg.rfind("[parse]", 0) == 0;
+}
+
 class ParseErrorListener : public antlr4::BaseErrorListener {
  public:
   void syntaxError(antlr4::Recognizer* /*recognizer*/, antlr4::Token* /*offendingSymbol*/,
@@ -49,6 +53,9 @@ AntlrResult ParseFileWithAntlr(const std::string& path) {
   } catch (const std::exception& ex) {
     const std::string msg = ex.what();
     if (!msg.empty()) {
+      if (HasParsePrefix(msg)) {
+        throw;
+      }
       throw std::runtime_error("[parse] 暂不支持的语法/词法 - " + msg);
     }
     if (auto* tok = parser->getCurrentToken()) {

src/ir/IR.h

@@ -23,7 +23,7 @@ class Context {
   const std::shared_ptr<Type>& PtrInt32();
   // 去重创建 i32 常量。
   ConstantInt* GetConstInt(int v);
-  // 生成临时名称，如 %t0、%t1 ...
+ 
   std::string NextTemp();
 
  private:

src/ir/IRBuilder.cpp

@@ -6,6 +6,13 @@
 #include <stdexcept>
 
 namespace ir {
+namespace {
+
+bool IsArithmeticType(const std::shared_ptr<Type>& ty) {
+  return ty && ty->kind() == Type::Kind::Int32;
+}
+
+}  // namespace
 
 ConstantInt* IRBuilder::CreateConstInt(int v) {
   // 常量不需要挂在基本块里，由 Context 负责去重与生命周期。
@@ -17,7 +24,23 @@ BinaryInst* IRBuilder::CreateBinary(Opcode op, Value* lhs, Value* rhs,
   if (!insertBlock_) {
     throw std::runtime_error("IRBuilder 未设置插入点");
   }
-  return insertBlock_->Append<BinaryInst>(op, Type::Int32(), lhs, rhs, name);
+  if (!lhs) {
+    throw std::runtime_error("IRBuilder::CreateBinary 缺少 lhs");
+  }
+  if (!rhs) {
+    throw std::runtime_error("IRBuilder::CreateBinary 缺少 rhs");
+  }
+  if (op != Opcode::Add) {
+    throw std::runtime_error("IRBuilder::CreateBinary 当前只支持 Add");
+  }
+  if (!lhs->type() || !rhs->type() ||
+      lhs->type()->kind() != rhs->type()->kind()) {
+    throw std::runtime_error("IRBuilder::CreateBinary 操作数类型不匹配");
+  }
+  if (!IsArithmeticType(lhs->type())) {
+    throw std::runtime_error("IRBuilder::CreateBinary 当前只支持 i32 二元运算");
+  }
+  return insertBlock_->Append<BinaryInst>(op, lhs->type(), lhs, rhs, name);
 }
 
 AllocaInst* IRBuilder::CreateAllocaI32(const std::string& name) {

src/irgen/IRGen.h

@@ -32,6 +32,8 @@ class IRGenImpl {
  private:
   void GenFuncDef(SysYParser::FuncDefContext& func);
   void GenBlock(SysYParser::BlockContext& block);
+  bool GenBlockItem(SysYParser::BlockItemContext& item);
+  void GenDecl(SysYParser::DeclContext& decl);
   bool GenStmt(SysYParser::StmtContext& stmt);
   void GenVarDecl(SysYParser::VarDeclContext& decl);
   void GenReturnStmt(SysYParser::ReturnStmtContext& ret);

src/irgen/IRGenDecl.cpp

@@ -6,15 +6,34 @@
 #include "ir/IR.h"
 
 void IRGenImpl::GenBlock(SysYParser::BlockContext& block) {
-  for (auto* stmt : block.stmt()) {
-    if (stmt) {
-      if (GenStmt(*stmt)) {
+  for (auto* item : block.blockItem()) {
+    if (item) {
+      if (GenBlockItem(*item)) {
         break;
       }
     }
   }
 }
 
+bool IRGenImpl::GenBlockItem(SysYParser::BlockItemContext& item) {
+  if (item.decl()) {
+    GenDecl(*item.decl());
+    return false;
+  }
+  if (item.stmt()) {
+    return GenStmt(*item.stmt());
+  }
+  throw std::runtime_error("[irgen] 暂不支持的 blockItem 类型");
+}
+
+void IRGenImpl::GenDecl(SysYParser::DeclContext& decl) {
+  if (decl.varDecl()) {
+    GenVarDecl(*decl.varDecl());
+    return;
+  }
+  throw std::runtime_error("[irgen] 暂不支持的声明类型");
+}
+
 void IRGenImpl::GenVarDecl(SysYParser::VarDeclContext& decl) {
   const std::string name = decl.Ident()->getText();
   if (locals_.find(name) != locals_.end()) {

src/irgen/IRGenFunc.cpp

@@ -19,8 +19,11 @@ void IRGenImpl::GenFuncDef(SysYParser::FuncDefContext& func) {
   if (!func.block()) {
     throw std::runtime_error("[irgen] 函数体为空");
   }
+  if (!func.Ident()) {
+    throw std::runtime_error("[irgen] 缺少函数名");
+  }
 
-  func_ = module_.CreateFunction("main", ir::Type::Int32());
+  func_ = module_.CreateFunction(func.Ident()->getText(), ir::Type::Int32());
   builder_.SetInsertPoint(func_->entry());
   locals_.clear();
 

src/sem/Sema.cpp

@@ -48,14 +48,27 @@ void RunSema(SysYParser::CompUnitContext& comp_unit) {
   if (!func || !func->block()) {
     throw std::runtime_error("[sema] 缺少 main 函数定义");
   }
+  if (!func->Ident() || func->Ident()->getText() != "main") {
+    throw std::runtime_error("[sema] 入口函数必须命名为 main");
+  }
 
   SymbolTable table;
+  bool seen_return = false;
+
+  const auto& items = func->block()->blockItem();
+  if (items.empty()) {
+    throw std::runtime_error("[sema] main 函数不能为空，且必须以 return 结束");
+  }
 
-  for (auto* stmt : func->block()->stmt()) {
-    if (!stmt) {
+  for (size_t i = 0; i < items.size(); ++i) {
+    auto* item = items[i];
+    if (!item) {
       continue;
     }
-    if (auto* decl = stmt->varDecl()) {
+    if (seen_return) {
+      throw std::runtime_error("[sema] return 必须是 main 函数中的最后一条语句");
+    }
+    if (auto* decl = item->decl() ? item->decl()->varDecl() : nullptr) {
       const std::string name = decl->Ident()->getText();
       if (table.Contains(name)) {
         throw std::runtime_error("[sema] 重复定义变量: " + name);
@@ -66,10 +79,19 @@ void RunSema(SysYParser::CompUnitContext& comp_unit) {
       table.Add(name);
       continue;
     }
-    if (auto* ret = stmt->returnStmt()) {
+    if (auto* stmt = item->stmt(); stmt && stmt->returnStmt()) {
+      auto* ret = stmt->returnStmt();
       CheckExpr(*ret->exp(), table);
-      break;
+      seen_return = true;
+      if (i + 1 != items.size()) {
+        throw std::runtime_error("[sema] return 必须是 main 函数中的最后一条语句");
+      }
+      continue;
     }
-    throw std::runtime_error("[sema] 暂不支持的语句类型");
+    throw std::runtime_error("[sema] 暂不支持的 blockItem 类型");
+  }
+
+  if (!seen_return) {
+    throw std::runtime_error("[sema] main 函数必须包含 return 语句");
   }
 }