Steven Bosscher <[EMAIL PROTECTED]> wrote: >>> Steven Bosscher <[EMAIL PROTECTED]> wrote: >>>>> I guess the issue is what does "huge" mean, it is hard to discuss >>>>> based on loaded adjectives taking the place of data :-) >>>> >>>> Huge here means 15-20% on x86* hosts. >>> >>> I don't consider this huge for -O3. I think -O3 can be slower if it >>> achieves better code, and -funroll-loops makes it do just that. >> >> I would certainly agree, I am not sure I even find it huge for -O2. >> After all 20% compile time represents a couple of months advance >> in computer hardware (and that is true across the board, even if >> you are talking about upgrading 1990 hardware to 1991 hardware :-)) > > You must not have been paying attention to one of the most frequent > complaints about gcc, which is that it is dog slow already ;-)
It's not disabling the optimizers that you are making it faster. I believe you are missing my point. What is the GCC command line option for "try to optimize as best as you can, please, I don't care compiletime"? I believe that should be -O3. Otherwise let's make -O4. Or -O666. The only real argument I heard till now is that -funroll-loops isn't valuable without profile feedback. My experience is that it isn't true, I for sure use it for profit in my code. But it looks like the only argument that could make a difference is SPEC, and SPEC is not freely available. So I'd love if someone could SPEC -funroll-loops for me. Giovanni Bajo
