Compilers have come a long way. In the early days, compilers are not very smart, resulting in inefficient object code and wasteful memory usage. Nonetheless, a modern compiler (such as the open source GCC, GNU C compiler) can translate HLPL code to object code usually better than an average programmer can.
This is due to advances of computer science, particularly in the fields of programming languages and optimization techniques. Code generation and optimization for single processor systems is a mature field where few advances can be made. The cutting edge of code generation and optimization is now in the context of multiple parallel processors, such as in the cases of GPGPUs (general purpose graphics processing units).