OpenMCL calling conventions x86 x86-64 The architectural CALL and RET instructions are not used, because CALL pushes a value onto the stack which will have an essentially arbitrary tag. It would be hard for the GC to look at that arbitrarily-tagged thing, recognize it as a pointer into a function, and then find that function. (N.B.: It looks like this may be changing. See, e.g., r6290 ff.) Therefo