fix(ast): 删掉ast结构

src/irgen/IRGenStmt.cpp

@@ -1,19 +1,26 @@
-// 语句翻译模块：
-// - 处理 if/while/return 等控制流构造
-// - 负责基本块创建、分支跳转与控制流收束
-
 #include "irgen/IRGen.h"
 
 #include <stdexcept>
 
-#include "ast/AstNodes.h"
+#include "SysYParser.h"
 #include "ir/IR.h"
 
-void IRGenImpl::GenStmt(const ast::Stmt& stmt) {
-  if (auto ret = dynamic_cast<const ast::ReturnStmt*>(&stmt)) {
-    ir::Value* v = GenExpr(*ret->value);
-    builder_.CreateRet(v);
+void IRGenImpl::GenStmt(SysYParser::StmtContext& stmt) {
+  if (stmt.varDecl()) {
+    GenVarDecl(*stmt.varDecl());
+    return;
+  }
+  if (stmt.returnStmt()) {
+    GenReturnStmt(*stmt.returnStmt());
     return;
   }
   throw std::runtime_error("[irgen] 暂不支持的语句类型");
 }
+
+void IRGenImpl::GenReturnStmt(SysYParser::ReturnStmtContext& ret) {
+  if (!ret.exp()) {
+    throw std::runtime_error("[irgen] return 缺少表达式");
+  }
+  ir::Value* v = GenExpr(*ret.exp());
+  builder_.CreateRet(v);
+}