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Thread: GCC vs. LLVM-GCC Benchmarks

  1. #21

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    Quote Originally Posted by nanonyme View Post
    I wonder how long it takes until Gentoo migrates to clang... Faster compile speed should be crucial there.
    Gentoo maybe, but not Linux kernel. At least not now and probably not in the near future (if ever):

    http://lkml.org/lkml/2009/5/8/388

    the most interesting response IMO:

    http://lkml.org/lkml/2009/5/9/59
    Last edited by kraftman; 09-04-2009 at 03:39 PM.

  2. #22
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    It's a long, long way away from being supported on Gentoo. They are actually quite conservative when it comes to changing compilers, which makes sense when you think about it. They have to support all that code being compiled by users with different flags, and switching to a new compiler means going through every single emerge script and fixing every possible combination. Not an easy task to do, even for a gcc upgrade.

    Also, clang itself doesn't support tons of code (think the entire KDE desktop) that's not written in C. They'd almost certainly have to start out using the GCC front-end to get most things working.

    And judging by the benchmarks here, there might be a revolt among those "elite" users who stick on 50 different optimization flags to their CFLAGS in an effort to get any extra performance possible. I think the majority of Gentoo users are quite comfortable with letting the compiler work in the background for half an hour while they surf the web. Cutting that time to 20 minutes in exchange for reducing performance might not make much sense to a lot of them.
    Last edited by smitty3268; 09-04-2009 at 05:54 PM.

  3. #23
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    Quote Originally Posted by smitty3268 View Post
    lso, clang itself doesn't support tons of code (think the entire KDE desktop) that's not written in C. They'd almost certainly have to start out using the GCC front-end to get most things working.
    Errr, what on Earth does that have to do with anything? That's just like complaining Sun's Java compiler doesn't compile C. :P

  4. #24
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    Quote Originally Posted by nanonyme View Post
    Errr, what on Earth does that have to do with anything? That's just like complaining Sun's Java compiler doesn't compile C. :P
    Gentoo is hardly going to switch to a compiler that 95% of it's users can't use. That's all I meant. (95% because there are a lot of C++ packages most people use, even in GNOME).

  5. #25
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    Quote Originally Posted by nanonyme View Post
    I wonder how long it takes until Gentoo migrates to clang... Faster compile speed should be crucial there.
    I think most of the other Gentoo users agree that the speed (and correctness) of the final code counts more than the time it needs for compilation

    for me it's a bonus if it compiles faster than gcc or {insert other preferred compiler}

    if e.g. llvm-gcc was 4 times faster during compilation of code but the final code/compiled binary with gcc (without llvm) was 3 times faster during execution than llvm-gcc I'd prefer gcc over llvm-gcc any time

  6. #26
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    Nope, Gentoo users aren't interested in giving up runtime performance for build speed. Who wants software that runs slower? Only developers might find it useful.

  7. #27
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    Quote Originally Posted by nanonyme View Post
    Errr, what on Earth does that have to do with anything? That's just like complaining Sun's Java compiler doesn't compile C. :P
    GCC is not just a C-compiler...

  8. #28
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    Quote Originally Posted by yesterday View Post
    GCC is not just a C-compiler...
    This also has no relevance to anything whatsoever. I didn't say anyone would be giving up GCC. Mostly whether they'll set CC="clang" or whatever the binary is.

  9. #29
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    Default Full comparison.

    I would love to see LLVM, GCC, and the Intel compiler go head to head. It is an interesting discussion as to what optimization is more important to an end users.
    My opinion is that for many applications code size is more important than code speed. If the program is faster than the user then the code size will come into play. Quicker to load, uses less ram and so on. For other applications it is code speed.
    That is one of the reasons I am not all that fond of 100% 64bit environments. ls does not need to use 64 bit pointers!

  10. #30
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    Quote Originally Posted by lwatcdr View Post
    I would love to see LLVM, GCC, and the Intel compiler go head to head. It is an interesting discussion as to what optimization is more important to an end users.
    My opinion is that for many applications code size is more important than code speed. If the program is faster than the user then the code size will come into play. Quicker to load, uses less ram and so on. For other applications it is code speed.
    That is one of the reasons I am not all that fond of 100% 64bit environments. ls does not need to use 64 bit pointers!
    code size!=less resources

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