It's still slow on -O0, it's slow because it doesn't approach the problem of compiling a complete program the right way, like these old compilers did. The fact that everything is a file, the fact that every single header needs to /searched for/ then /compiled/ millions of times, and optimized later on, without context; that is the problem.

I wrote applications that were shipped on millions of computers in the 90s and I didn't have to make hard choices for building, the debug version were quicker to build sure, but the Release versions weren't a chore to make, and I was often building PPC/68k/debug/release in one go.

Also, this is a ridiculous defence of autoshit stuff. It hasn't been needed for well over 20 years, it's only purpose is self propagation where "oh I need autoconf blah because otherwise I can't build everywhere" where there is so much standardisation these days that there are MOSTLY TWO choices for nix systems. Not only that but it fails* all the time, on embedded for example; it doesn't 'save' and give you portability, it just gives you a false assurance that you are doing 'the right thing' by using it, while it's broken is many other ways.

More often than not, you can replace all that garbage with a 1/2 page Makefile. Who the hell needs to check wether the compiler /works/ or strdup /exists/ and all that idiocy. Or add dependencies for stuff while 'pkg-config' exists anyway. Who the hell actually /needs/ 'libtool' when there's about (perhaps) 3 ways of making a shared library on a unix system? And who the hell want or have the time to go and debug some stupid arcane 'm4' file to fix the weird problems that comes up?

Disclaimer: I build embedded distros for fun and profit, I deal with that stuff /all the time/ and most of my 'compile time' for distros is not even spent actually 'compiling' stuff, it's spent in the 'configure' stage, and 90% of my time fixing portability problem isn't in the code, it's in the autoshit stuff that somehow breaks in some new, interesting way.