Well, sometimes it's fun. Other times it's utterly horrible. gcc doesn't always do a wonderful job and the maintainers sometimes just don't seem to care - induction variable optimizations and gcse were broken in 4.2 and 4.3 and the issue was left unfixed, with clear examples of obvious FAIL on simple and performance-critical inner loops.

However, this doesn't apply so much to OS code, which doesn't have nearly as much opportunity for micro-architectural shenanigans either way. Typically something like -Os does a good job of handling operating system style code.

Hand-coding OS asm remains a fine example of pointless tedium for the most part. There are clear places where you absolutely need asm, of course, but writing stuff in asm that can be perfectly well done in C is like cleaning out the barracks room bathroom with a toothbrush.

This was one of the early innovations of UNIX (high level language use), so there's something wildly anachronistic about this guy's suggestion. It's like suggesting that you rebuild grandpa's Studebaker so that it can be drawn by a team of horses.