GCC generates a compile-time error if you include the intrinsics files without the right option (-msse2 or similar) enabled with the compiler. For this reason, we took care of only including the files requested by the instruction set the user has chosen.
Yes, the GCC solution is not quite the ideal one for this problem...If I, for example, want to use SSE3 but only if it is available I obviously cannot pass -msse3 because it will use SSE3 code for the whole binary (which will then of course crash on SSE2 machines) but if I do not pass -msse3 then I do not get the intrinsics at all...The "what were they thinking" question does pop up...
the usual approach of implementing a runtime-dispatching is to compile different source files for different instruction sets. tim