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On 04/27/14 02:58 AM, Martin Vaeth wrote: |
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> Rich Freeman <rich0@g.o> wrote: |
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>> FWIW the list of packages I have issues with include: |
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> Not sure whether this is the right place to post it. |
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It's interesting to see that rather lengthy list. From a compiler |
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engineer perspective I'd like to toss in my opinion |
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Compiler flags are typically meant to do one or two things. Improve |
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performance or reduce binary (code size). Pragmatically nobody gives a |
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f* if grep has been optimized to the max since it's usually not the |
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bottleneck. Having LTO and whole program optimizations turned on for |
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every package will probably not give you a noticeably faster system, but |
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will certainly slow your build down. (Due to rather large link times) |
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The packages which it really *should* be turned on for - anything which |
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is computationally complex, Fortran and stuff where performance matters. |
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I don't know gcc's LTO or what it's capable of, but in our compiler it |
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would also potentially improve large c++ applications a lot. (It should |
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help inline more aggressively and remove c++ layer overhead). In |
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practice though - the most important c++ applications tend to be too |
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huge and end up hitting bugs. They will also typically be very very long |
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link times. (I've seen 30+ minutes - system specs and all things being |
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relative of course..) |
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Go ping the gentoo-science guys and get their feedback - they may have |
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the most experience with this... |
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Not to be a smart-ass, but will someone start a thread on global PGO |
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(profile guided optimizations) next? imho it would be interesting and |
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great to have some general training data already contributed next to the |
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ebuilds. For the science stuff I wouldn't recommend it, but who knows.. |
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