Originally Posted by jong357
If there is only one package that you optimize out of thousands, glibc should be it, without a doubt. Drepper and the other maintainers of glibc recommend it in fact. I wouldn't get all crazy but there is nothing wrong with:
-march=i686 -mtune=i686 -O3 -pipe
That won't affect "stability" in the slightest. In fact, the end result will have benefits over a non-optimized glibc with no adverse effects.
I could be wrong but I think that the info pages for gcc seem to be saying that -mtune isn't quite needed when you use -march because -march also implies -mcpu and that tunes the scheduling as well. As I understand it, if you use -march=i486 and -mcpu=i686 together, then -mtune=i486 might actually allow you to flip the scheduler around to favor i486 over i686.
That having been said, I don't think it's any big secret that I'm a proponent of leaving 486's by the roadside.