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Frank Peters posted on Mon, 20 Sep 2010 21:49:33 -0400 as excerpted: |
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> After doing my periodical emerge update, I notice that gcc-4.5.1 is now |
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> unmasked and presumably stable. I also notice that a couple of new |
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> options are possible with this new release, namely Graphite and FLTO |
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> optimizations. (Actually, Graphite has been available for a while but I |
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> haven't been following gcc development too closely and only now do I |
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> become aware of it.) |
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> |
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> Does anyone have any comments on the use of Graphite and/or FLTO? Are |
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> they capable of significant improvements on a amd64 system? |
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> |
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> Supposedly FLTO will greatly increase file size and thus could be |
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> selectively enabled for only a few packages. Would building gcc itself |
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> with FLTO be advisable? |
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> |
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> There are reports that many packages fail to build with FLTO: |
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> http://blog.flameeyes.eu/2010/04/25/tinderbox-getting-friendly-with- |
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gcc-4-5 |
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> |
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> Since I have encountered little detailed discussion on this topic, I am |
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> posting my question to this list. |
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|
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Two excerpts from $equery u gcc |
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|
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- - graphite : Add support for the framework for loop optimizations |
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based on a polyhedral intermediate representation |
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|
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- - lto : Add support for link-time optimizations (unsupported, |
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use at your own risk). |
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|
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So at minimum, you'll need to enable the appropriate USE flags for those |
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features. (As you can see, I haven't.) And, link-time-optimization isn't |
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Gentoo supported at all -- probably partly as a result of flameeyes' |
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testing. |
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|
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Personally, I've been waiting for some general level documentation to come |
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across my radar before I get involved with either of these. I've been |
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running 4.5 for some time now, without issue (except that the new version |
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makes use of more instructions for certain later Intel chips, and I had a |
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problem as a result in my 32-bit chroot, trying to build for my atom based |
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netbook, until I dialed back the allowed hardware instructions to what was |
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available on my older amd opteron based build machine, gcc 4.4 apparently |
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didn't use the instructions at all, even if they were marked as |
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available), but that's partly because I've been a bit conservative in |
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enabling the newly available features such as graphite and link-time- |
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optimization. |
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|
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-- |
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Duncan - List replies preferred. No HTML msgs. |
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"Every nonfree program has a lord, a master -- |
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and if you use the program, he is your master." Richard Stallman |