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  • GCC vs. LLVM-GCC Benchmarks

    Phoronix: GCC vs. LLVM-GCC Benchmarks

    Last Friday we published Mac OS X 10.6 benchmarks and then on Monday they were joined by Ubuntu 9.10 vs. Mac OS X 10.6 benchmarks. One of the requests that has come up since publishing those articles are to carry out a set of tests comparing the performance of LLVM and LLVM-GCC. With Apple's Snow Leopard release, some parts of the operating system were built using LLVM-GCC for optimized performance, although this compiler is not yet matured. In this article we have a set of 12 benchmarks comparing GCC to LLVM-GCC.

    http://www.phoronix.com/vr.php?view=14164

  • #2
    Originally posted by phoronix View Post
    Phoronix: GCC vs. LLVM-GCC Benchmarks

    Last Friday we published Mac OS X 10.6 benchmarks and then on Monday they were joined by Ubuntu 9.10 vs. Mac OS X 10.6 benchmarks. One of the requests that has come up since publishing those articles are to carry out a set of tests comparing the performance of LLVM and LLVM-GCC. With Apple's Snow Leopard release, some parts of the operating system were built using LLVM-GCC for optimized performance, although this compiler is not yet matured. In this article we have a set of 12 benchmarks comparing GCC to LLVM-GCC.

    http://www.phoronix.com/vr.php?view=14164
    This is one, I think, important note from the release notes (for LLVM 2.5 and the appropriate LLVM-GCC):

    * In this release, the GCC inliner is completely disabled. Previously the GCC inliner was used to handle always-inline functions and other cases. This caused problems with code size growth, and it is completely disabled in this release.

    I think this may have a huge impact on your tested benchmark.

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    • #3
      Ouch, LLVM-GCC was beaten solidly here. Any guesses as to why? Wasn't LLVM supposed to be much faster?

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      • #4
        Originally posted by BlackStar View Post
        Ouch, LLVM-GCC was beaten solidly here. Any guesses as to why? Wasn't LLVM supposed to be much faster?
        Couple of factors I would guess comes into play. LLVM is fairly young in development and the biggest improvements so far as performance concerning LLVM is the time to compile. Unfortunately we haven't seen any of those compile times in the tests.

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        • #5
          Originally posted by deanjo View Post
          Couple of factors I would guess comes into play. LLVM is fairly young in development and the biggest improvements so far as performance concerning LLVM is the time to compile. Unfortunately we haven't seen any of those compile times in the tests.
          Plus you won't see any speed advantage because phoronix is using the gcc frontend.

          edit : s/backend/frontend/
          Last edited by Rip-Rip; 09-04-2009, 09:47 AM.

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          • #6
            next up we will be testing LLVM/Clang to see how that performs.
            Shouldn't make any difference, Clang is just the frontend, right?

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            • #7
              Originally posted by Rip-Rip View Post
              Plus you won't see any speed advantage because phoronix is using the gcc backend.
              Hum, LLVM-GCC combines GCC frontend with LLVM backend (optimizer and code generator).

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              • #8
                Originally posted by tettamanti View Post
                Hum, LLVM-GCC combines GCC frontend with LLVM backend (optimizer and code generator).
                Thanks, I've edited (in fact, I wanted to write frontend...).

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                • #9
                  Originally posted by deanjo View Post
                  Couple of factors I would guess comes into play. LLVM is fairly young in development and the biggest improvements so far as performance concerning LLVM is the time to compile. Unfortunately we haven't seen any of those compile times in the tests.
                  Someone mentioned there could be only one core used when comes to GCC and Ubuntu vs OS X benchmarks. Btw. I heard GCC is optimized to be good at some benchmarks, but I wonder if its better results have reflection in reality.

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                  • #10
                    I've been playing with Clang, and it really is very cool. Compile times are a lot better than GCC, and error messages are far more clear. I'm really glad Apple are funding development for it!

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