While it is very common to use C as the canonical fast language, it has some warts that really hinders the compiler from doing optimizations. The main one is of

While it is very common to use C as the canonical fast language, it has some warts that really hinders the compiler from doing optimizations. The main one is of course pointer aliasing. This, for example, stops the compiler from unrolling loops that operate on two different arrays, since it can not know if they are the same. Among people doing heavy numerical computation Fortran still seems to be very much entrenched as the "fast language".