The "atomic-primops" library depends on symbols such as store_load_barrier and "cas", which are defined in SMP.h. Thus the result is that if the program is linked WITHOUT "-threaded", the user gets a linker error about undefined symbols.
The specific place it's used is in the 'foreign "C"' bits of this .cmm code:
I'm trying to explore hacks that will enable me to pull in those functions during compile time, without duplicating a whole bunch of code from the RTS. But it's a fragile business.
It seems to me that some of these routines have general utility. In future versions of GHC, could we consider linking in those routines irrespective of "-threaded"?
-Ryan