Compare-and-swap semantics in GHC

Hi, java.util.concurrent.atomic package provides two flavors of compare and set operations: compareAndSet and weakCompareAndSet. The latter does not create any happens-before orderings, so we can use it where no guarantees with respect to previous or subsequent reads and writes of any variables other than the target of the weakCompareAndSet are required. I'd like to ask if the compare-and-swap function provided by GHC runtime (cas() in includes/stg/SMP.h) is strong or weak. If it is strong, do all use cases of cas() require this semantics? Regards, Kwang Yul Seo