[ir] Add nodiscard to get_loop_guard/get_if_guard (#2377)
[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 21a932b5

Co-authored-by: Taichi Gardener <52844ac7498fba84f633481a7c3ae54491811c81@gmail.com>
yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi