Anatoly Yakovenko wrote:
#include
#include int main() { int size = 1024; int ii = 0; double* v1 = malloc(sizeof(double) * (size)); double* v2 = malloc(sizeof(double) * (size)); for(ii = 0; ii < size*size; ++ii) { double _dd = cblas_ddot(0, v1, size, v2, size); } free(v1); free(v2); } Your C compiler sees that you're not using the result of cblas_ddot, so it doesn't even bother to call it. That loop never gets run. All your program does at runtime is call malloc and free twice, which is very fast :-)
C doesn't work like that :).
C compilers can do what they like ;) GCC in particular is pretty good at removing dead code, including entire loops. However it shouldn't eliminate the call to cblas_ddot unless it thinks cblas_ddot has no side effects at all, which would be surprising unless it's inlined somehow. Jules