You are always at the mercy of the compiler, unless you use intrinsics or assembly directly (and then it's debatable whether what you are writing is really "C")

You are always at the mercy of the compiler, unless you use intrinsics or assembly directly (and then it's debatable whether what you are writing is really "C"). C compilers are pretty good, but there are things they cannot do. For example, ISPC[1] is a low-level language that is very similar to C, but which makes it straightforward for the compiler to use vector instructions very aggressively - far more than any existing C compiler would be able to. [1]: https://ispc.github.io/ https://ispc.github.io/