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Thread: Compiler related: Intel's code slower on AMD-CPUs?!

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    Member Vacon's Avatar
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    Compiler related: Intel's code slower on AMD-CPUs?!

    Hello everyone,

    since every now and then a thread deals with the question which compiler is more practical than the other, maybe here is an interesting link:
    http://www.swallowtail.org/naughty-intel.html
    Since I have no experience in programming / compiling I give to the audience to decide or test.
    In short: Intel compilers check on which CPU the code runs and slow down on AMD
    Edit: ok, nothing brand-new, but found on 7-zip's forum:
    http://sourceforge.net/forum/forum.p...forum_id=45797

    Best regards!
    Last edited by Vacon; 9th May 2008 at 16:17.

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    The Founder encode's Avatar
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    Quote Originally Posted by Vacon View Post
    Intel's code slower on AMD-CPUs?!
    In short: Intel compilers check on which CPU the code runs and slow down on AMD
    I doubt it. Intel Compiler can generate native code - without CPU detection/code selection. Furthermore, in Intel's Optimization Guide you may find which options to use with each processor or processor group, including AMD CPUs. Concluding, Intel has optimizations for Generic/AMD processors as well as it's own Intel-oriented...

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    Administrator Shelwien's Avatar
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    That's kinda expected... Probably, the whole compiler is made to improve CPU selling by making use of their new instruction sets which other compilers don't.
    Instead you should say thanks that they didn't insert some less identifiable brakes.

    1. Read section 12.1 from http://agner.org/optimize/optimizing_cpp.pdf
    2. I just compile my executables with /QxN without any patches,
    because its better to use separate binaries for different CPUs anyway... Imho /Qax switches cause too much code caching problems.
    3. Intel's math library is bloated, and anyway its a bad practice to directly use the math.h functions in internal loops.

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    I've seen it before. people using hacks on the compiler to get the propper code executed on AMD cpu's

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    /me always use iccpatch for icc builds.

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    Quote Originally Posted by encode View Post
    I doubt it. Intel Compiler can generate native code - without CPU detection/code selection.
    Well, yes, ICC _can_ do it, but usually doesn't. This article is mainly about Intel Fortran Compiler, but author adds ICC behaves completely the same way...
    Last edited by Black_Fox; 10th May 2008 at 18:03.
    I am... Black_Fox... my discontinued benchmark
    "No one involved in computers would ever say that a certain amount of memory is enough for all time? I keep bumping into that silly quotation attributed to me that says 640K of memory is enough. There's never a citation; the quotation just floats like a rumor, repeated again and again." -- Bill Gates

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