This is purely a theory question, so, given an "infinite" time to make a trivial program, and an advanced knowledge of C and Assembly, is it really better to do something in Assembly? is "performance" lost when compiling C into Assembly (to machine code)?
By performance I mean, do modern C compilers do a bad job at certain tasks that programming directly in Assembly speeds up?
Modern C can do a better job than assembly in many cases, because keeping track of which operations can overlap and which will block others is so complex it can only be reasonably be tracked by a computer.