It also assumes you know how to write loops if they need to be fast (which frankly hasn't really mattered at the O/S level, esp on modern hardware),

so it won't "optimise" essential code out of your program by miscalculating the ranges during "aggressive-loop-optimisation".

No doubt it could be better, but it could easily be worse.

The executable is also finite size, not unbounded-but-finite.

For a compiler of a language the size and complexity of C (without some ANSI crud), I think it's not far off a size comparable to the language complexity

(although it could be a bit smaller); meanwhile, by treating "compiling C" as a subset problem of "compiling C++", gcc and especially clang are vast whales whistling at the wrong frequency for the problem.