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    Traditionally, the difference between -O2 and -O3 is that -O3 included things that sometimes sped things up and other things got a lot slower. It sounds as if the heuristics for -O3 have got better in GCC. It sounds a bit like GCC needs to move a few passes from their -O3 pipeline to -O2.

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        Talking about Gentoo, I do think it would be interesting to see which packages would benefit from these optimisations without having to manually test them one by one.