atomic_compare_exchange_strong and 'compare' variable

[joshchen]

hungry-birds/queue.c

Line 60 in 4116630

compare = popped;

Hi ! May I know why it needs to set 'compare' as 'popped' again here?
atomic_compare_exchange_strong doesn't change 'compare' when it returns true, does it? (https://en.cppreference.com/w/c/atomic/atomic_compare_exchange)
Is this line for some special cases? Thanks.