Ciaran McCreesh wrote:
How much of that is memory bound? Of the things that aren't, how many aren't written in assembly anyway? Of those things, what proportion of the runtime is spent in those areas? If you double the speed of something that takes up 2% of the overall execution time, you can't measure the improvement. Or looking at it the other way -- is there any reason to believe that using icc (which can end up being a substantial pain in the arse, given the way it tries to use gcc's c++ headers but doesn't support some of the extensions or quirks that g++ does) will provide a genuine gain for people who aren't already doing clever profile-directed trickery anyway? The problem with -O3 is that function inlining can lead to a substantial cache hit. Unless you're using profile-directed optimisations, which Gentoo doesn't support, it's extremely hit and miss as to whether O3 helps or hurts.
I agree with all of the above. Gentoo is about choice, so if people want to make ICC work well more power to them. I agree that it would be hard to make it THE ONLY system compiler. For those who do try it I'd be really interested in their findings.
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