[ir] Add nodiscard to get_loop_guard/get_if_guard (#2377)

* [ir] Add nodiscard to get_loop_guard/get_if_guard

* [skip ci] enforce code format

* code format...

* [skip ci] enforce code format

* Revert "enforce code format"

This reverts commit 21a932b

Co-authored-by: Taichi Gardener <taichigardener@gmail.com>

taichi/ir/ir_builder.h

@@ -90,10 +90,10 @@ class IRBuilder {
   };
 
   template <typename XStmt>
-  LoopGuard get_loop_guard(XStmt *loop) {
+  [[nodiscard]] LoopGuard get_loop_guard(XStmt *loop) {
     return LoopGuard(*this, loop);
   }
-  IfGuard get_if_guard(IfStmt *if_stmt, bool true_branch) {
+  [[nodiscard]] IfGuard get_if_guard(IfStmt *if_stmt, bool true_branch) {
     return IfGuard(*this, if_stmt, true_branch);
   }
 
@@ -192,7 +192,7 @@ class IRBuilder {
 
   // Print values and strings. Arguments can be Stmt* or std::string.
   template <typename... Args>
-  PrintStmt *create_print(Args &&... args) {
+  PrintStmt *create_print(Args &&...args) {
     return insert(Stmt::make_typed<PrintStmt>(std::forward<Args>(args)...));
   }