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Thread: R600 Gallium3D Disables LLVM Back-End By Default

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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

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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.

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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.

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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.

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

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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.

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

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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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    Quote Originally Posted by 89c51 View Post
    Does this also mean that r600 will never get FOSS OpenCL ?? (when and if ready)
    No, it just disables the LLVM backend for the shader compiler. OpenCL is a different thing.

    Quote Originally Posted by ryszardzonk View Post
    " --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.
    The statement is correct. If you compile mesa without --enable-r600-llvm-compiler you can't enable it at all. If you compile with --enable-r600-llvm-compiler it is still disabled by default but you're able to enable it with R600_DEBUG=llvm

    //EDIT: In other words: --enable-r600-llvm-compiler compiles the support in (this is a compile-time switch) while R600_DEBUG=llvm enables it at runtime (it is a runtime switch).
    Last edited by TAXI; 04-17-2014 at 07:18 AM.

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