I don't know what to tell you, but that is how sequential code works. Sure you can find some instruction level parallelism in the code and your optimizer may be able to do it across function boundaries, but that is mostly a happy accident. Meanwhile HDLs are the exact opposite. Parallel by default and you have to build sequential execution yourself. What is needed for both HLS and parallel programming is a parallel by default hybrid language that makes it easy to write both sequential and parallel code.