[flohofwoe]

That's mainly the result of optimizer passes, C itself doesn't have much to do with it.

Assembly languages actually haven't changed all that much since the 70's, but compilers have improved a lot. The output of early C compilers did indeed match the source code quite closely (and not just on the PDP-11), but even today that's true if you disable optimizations (and even with optimizations is usually pretty straightforward to map the C source to the assembly listing - if you're somewhat aware what optimizer passes in modern compilers are doing).

Of course CPU ISAs are already human-friendly abstractions over what's actually happening down in the hardware.

[sweetjuly]

C has everything to do with optimizer passes, the language definition is what allows them to happen! The fact that you get about what you'd expect on -O0 is merely incidental, the specification does not afford you this.