Robert Dewar <[EMAIL PROTECTED]> writes: >> Including loop unrolling to -O2 is IMNSHO a bad idea, as loop unrolling >> increases code size, sometimes a lot. And the distinction between -O2 >> and -O3 is exactly in the space-for-speed tradeoffs.
>That's certainly a valid way of defining the difference (and certainly >used to be the case in the old days when the principle extra optimization >was inlining) But even -O2 makes several space-for-speed optimisations (multiply by shifting and adding, align jump targets, etc), so this cannot define the difference between -O2 and -O3. It is more quantitative in nature: -O2 only generates bigger code where the payoff in speed is almost certain, which is not always the case for unrolling/inlining. Still, more and more projects seem to be switching to -Os for everything which could be interpreted as both a consequence of the inevitable bloating of large programs but also as a dissatisfaction with what -O2/3 does to the code. Or maybe they are wisening up and actually using the option that has been there all along.
