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Thread: R600 Gallium3D Disables LLVM Back-End By Default

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  1. #1
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    Default R600 Gallium3D Disables LLVM Back-End By Default

    Phoronix: R600 Gallium3D Disables LLVM Back-End By Default

    AMD has decided to disable the LLVM compiler back-end by default within the R600 era Gallium3D graphics driver...

    http://www.phoronix.com/vr.php?view=MTY2NjI

  2. #2
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    Does this means less performance? And are we talking about mesa 10.2?, because its not explained.
    Last edited by edoantonioco; 04-16-2014 at 10:57 PM.

  3. #3
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    Quote Originally Posted by edoantonioco View Post
    Does this means less performance? And are we talking about mesa 10.2?, because its not explained.
    It means worse performance, but better compatibility. And yes, we're talking about Mesa 10.2. Any change to Mesa that isn't a bug fix is assumed to be for the next version.

  4. #4
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    Quote Originally Posted by Plombo View Post
    It means worse performance, but better compatibility. And yes, we're talking about Mesa 10.2. Any change to Mesa that isn't a bug fix is assumed to be for the next version.
    Are you sure there's a performance hit ? My recollection was that Vadim's "sb" option was running at about the same speed as llvm, and I believe it was enabled by default.

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    Quote Originally Posted by bridgman View Post
    Are you sure there's a performance hit ? My recollection was that Vadim's "sb" option was running at about the same speed as llvm, and I believe it was enabled by default.
    Ah, you're probably right. I had forgotten about Vadim's compiler.

  6. #6
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    On my previous a10-5800k APU, Vadim's SB compiler was much better than llvm. I tested it a lot.

  7. #7
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    Some time ago in mesa 9.2 there was a new feature (the r600 back-end) that bring better performance, but it was disabled by default (enabled by default in 10.0). I activate that feature with
    R600_DEBUG=sb,nollvm
    and the performance was better, but if I did this
    R600_DEBUG=sb
    the performance was even better.
    That means than the LLVM stuff meant more performance. Thats why I was curious about how the performance would be affected now than the feature is going to be disabled.

  8. #8
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    Quote Originally Posted by edoantonioco View Post
    Does this means less performance?
    That depends on the hardware I guess. On my card (HD 6950) LLVM causes more stuttering.

    Quote Originally Posted by bridgman View Post
    My recollection was that Vadim's "sb" option was running at about the same speed as llvm, and I believe it was enabled by default.
    But Vadim's "sb" option can be enabled with LLVM, too. IIRC it's a shader optimization that happens after the shader has been compiled.

  9. #9
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    Does this also mean that r600 will never get FOSS OpenCL ?? (when and if ready)

  10. #10
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    " --enable-r600-llvm-compiler [...] but now not even that will disable the compiler back-end by default for this driver." IMHO it should say enable not disable otherwise I fail to find logical conclusion from that statement.

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