On Wed, 31 Mar 2010, Khiszinsky, Maxim wrote:
Giovanni Piero Deretta wrote
Shouldn't volatile go in the cast and not in v? It is fine if v is stored in a register, but you want the read to pMem not to be cached. What you are doing with the cast right now is casting away volatile-ness in addition of changing the type of the pointed object. The fact that it is now working is probably just due to the fact that the compiler is confused: the compiler is still free to hoist the loads from pmem, as long as all stores and loads to v (which is in the stack) are done.
Yes, I agree However, the parameter of _mm_loadl_epi64 is declared as non-volatile and casting _mm_loadl_epi64( (__m128i volatile const *) pMem ) generates error. The solution from CDS library is a workaround for MS Visual C++ compiler. I cannot invent something better now.
Second solution: use 64bit CAS to load/store 64bit values on x86. It seems too heavy for just loading/storing it isn't?
this is actually what I do in Boost.Atomic; I *think* it is cheaper than shuffling around the values between SSE and general purpose registers (it sure is cheaper than MMX considering you also have to issue emms) Regards, Helge