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The disclaimer about non-Intel processors is necessary, but sad. The dirty tricks they pulled with their compiler creating slow code on AMD processors are reall

The disclaimer about non-Intel processors is necessary, but sad. The dirty tricks they pulled with their compiler creating slow code on AMD processors are really underhanded.

garenp 13y ago
"Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel" Right, because Intel should spend their finite resources buying every imaginable Intel-compatible CPU from other vendors just to test and qualify them for the Intel compiler.
- frandroid 13y ago
  1) "Finite resources", when talking about Intel, is a relative concept. 2) As mentioned above, Intel has a history of undermining compilation on non-Intel processors. It's not just a question of passively not spending time testing on other CPUs.
- wmf 13y ago
  Right, because Intel should spend their finite resources buying every imaginable Intel-compatible CPU from other vendors just to test and qualify them for the Intel compiler. That's not what people are asking. Removing the code that sabotages performance on non-Intel processors would be trivial for Intel to do and would benefit users enormously.
  - garenp 13y ago
    Not generating model-specific code for a processor that doesn't match your CPUID table is hardly what I'd call "sabotaging."
    - mikeash 13y ago
      Ignoring the results of feature checking when on a competitor's CPU is, though, and that's what they do.
      - garenp 13y ago
        So they should just then believe what another third-party vendor CPU says, and ship the compiler and hope for the best? Not what I would do. I would only enable specific optimizations when I could guarantee the output would be optimal or a given model. "Hope is not a plan."
        raverbashing 13y ago
        "So they should just then believe what another third-party vendor CPU says" Of course. This is obvious, if you had any idea about what you were talking about. " I would only enable specific optimizations when I could guarantee the output would be optimal or a given model." You can do that with compiler flags, ever heard of them?
        hdevalence 13y ago
        Yes, they should. If your CPU lies about its feature support, there are far, far, far bigger problems for the end user than whether a binary is optimal or not.
        ponce 13y ago
        I remember earlier AMD processors, supporting SSE1 (with the CPUID bit on), but this was so slow to be unusable in practice, slower than general instructions. In this case, the optimal thing to do was not to use these instructions despite the processors claiming support.
        wmf 13y ago
        I'd argue that the optimal thing for a compiler to do is to use SSE when the processor supports it... and then the optimal thing for customers to do is not buy processors that run reasonable code slowly.
    - oomkiller 13y ago
      Traditionally (with ICC) the criticism has been that it just checks the vendor string for "GenuineIntel" instead of actually checking for feature support with CPUID. People just want the option to be able to just check just for feature support.
      - garenp 13y ago
        A given "feature" does not behave identically on different CPUs. To generate optimal code, you need to know which model is being targeted to make codegen decisions. It is simply not reasonable to expect Intel to do the work on their compiler to figure that all out and test it for competing vendor chips. If you want more, use a different compiler, period. $VENDOR spends money on their compiler to support their chips, not to appease every whining, butt-hurt user on the Interwebz that thinks $BIGCO owes them something on a competing chip.
      - Marat_Dukhan 13y ago
        There are such options. Just use -mavx instead of -xAVX and it will compile for any AVX-compatible processor.
      - simula67 13y ago
        Will that make the compiler code harder to maintain ?
- ANTSANTS 13y ago
  http://www.agner.org/optimize/blog/read.php?i=49 http://www.agner.org/optimize/blog/read.php?i=49 It's not that the engineers behind ICC failed to take the architectures of non-Intel processors into account, it's that it intentionally uses a slow path on non-Intel processors that cripples performance. We're talking assuming that the CPU doesn't support SIMD bad here. If you use virtualization to make your CPUID vendor string look like "GenuineIntel", or modify the executable to remove the Intel processor check, the "Intel optimized" builds run just as fast (barring relative processor strengths) on comparable AMD processors. This matters because: Until this became public, Intel gave no mention or disclaimer of suboptimal performance for ICC-generated code on non-Intel processors. News outlets did and probably still do use ICC-generated binaries for benchmarking, giving an unfair marketing advantage to Intel processors ("Look how poorly this AMD CPU runs this binary we specifically designed to function horribly on their CPU! Buy Intel today!") Almost no one is aware of this.
TwoBit 13y ago
Well it cost them some business, because some companies wouldn't use it due to performing poorly on other processors. I can't see how it would be beneficial for them to cripple AMD performance.
- orik 13y ago
  It's a none issue. This compiler is for OSx only, and I can't even remember the last time Apple released an OSx machine that's had AuthenticAMD.
Lockal 13y ago
They are adding this page/slide to everything, that is connected with Intel CPU (probably after that case with AMD mis-optimization, but I am not sure, if it was the first appearance of this page). For example, if they release a new instruction set, even if there are no alternatives in AMD world, Intel would add this page. Treat this like a boilerplate.
- xooyoozoo 13y ago
  It's 100% boilerplate. The whole "handicapping" debate that pops up every ICC thread is likely several years out of date (not that I don't expect to see it again and again for the next decade or two). Case in point, take bench completion time on a Xeon supercomputer [1]. Compare that to relative completion time on an Opteron supercomputer [2] (for both, lower is better). If that's Intel's compiler handicapping AMD performance, I wonder what GCC is trying to do? [1]: http://www.nersc.gov/users/computational-systems/edison/performance-and-optimization/compiler-comparisons/choosing-a-compiler-on-edison/ http://www.nersc.gov/users/computational-systems/edison/perf... [2]: http://www.nersc.gov/assets/_resampled/resizedimage730421-hopcmp1013.jpg http://www.nersc.gov/assets/_resampled/resizedimage730421-ho...
sitkack 13y ago
They still do this.

The disclaimer about non-Intel processors is necessary, but sad. The dirty tricks they pulled with their compiler creating slow code on AMD processors are really underhanded.

garenp 13y ago

"Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel" Right, because Intel should spend their finite resources buying every imaginable Intel-compatible CPU from other vendors just to test and qualify them for the Intel compiler.

frandroid 13y ago
1) "Finite resources", when talking about Intel, is a relative concept. 2) As mentioned above, Intel has a history of undermining compilation on non-Intel processors. It's not just a question of passively not spending time testing on other CPUs.
wmf 13y ago
Right, because Intel should spend their finite resources buying every imaginable Intel-compatible CPU from other vendors just to test and qualify them for the Intel compiler. That's not what people are asking. Removing the code that sabotages performance on non-Intel processors would be trivial for Intel to do and would benefit users enormously.
- garenp 13y ago
  Not generating model-specific code for a processor that doesn't match your CPUID table is hardly what I'd call "sabotaging."
  - mikeash 13y ago
    Ignoring the results of feature checking when on a competitor's CPU is, though, and that's what they do.
    - garenp 13y ago
      So they should just then believe what another third-party vendor CPU says, and ship the compiler and hope for the best? Not what I would do. I would only enable specific optimizations when I could guarantee the output would be optimal or a given model. "Hope is not a plan."
      - raverbashing 13y ago
        "So they should just then believe what another third-party vendor CPU says" Of course. This is obvious, if you had any idea about what you were talking about. " I would only enable specific optimizations when I could guarantee the output would be optimal or a given model." You can do that with compiler flags, ever heard of them?
      - hdevalence 13y ago
        Yes, they should. If your CPU lies about its feature support, there are far, far, far bigger problems for the end user than whether a binary is optimal or not.
        ponce 13y ago
        I remember earlier AMD processors, supporting SSE1 (with the CPUID bit on), but this was so slow to be unusable in practice, slower than general instructions. In this case, the optimal thing to do was not to use these instructions despite the processors claiming support.
        wmf 13y ago
        I'd argue that the optimal thing for a compiler to do is to use SSE when the processor supports it... and then the optimal thing for customers to do is not buy processors that run reasonable code slowly.
  - oomkiller 13y ago
    Traditionally (with ICC) the criticism has been that it just checks the vendor string for "GenuineIntel" instead of actually checking for feature support with CPUID. People just want the option to be able to just check just for feature support.
    - garenp 13y ago
      A given "feature" does not behave identically on different CPUs. To generate optimal code, you need to know which model is being targeted to make codegen decisions. It is simply not reasonable to expect Intel to do the work on their compiler to figure that all out and test it for competing vendor chips. If you want more, use a different compiler, period. $VENDOR spends money on their compiler to support their chips, not to appease every whining, butt-hurt user on the Interwebz that thinks $BIGCO owes them something on a competing chip.
    - Marat_Dukhan 13y ago
      There are such options. Just use -mavx instead of -xAVX and it will compile for any AVX-compatible processor.
    - simula67 13y ago
      Will that make the compiler code harder to maintain ?
ANTSANTS 13y ago
http://www.agner.org/optimize/blog/read.php?i=49 http://www.agner.org/optimize/blog/read.php?i=49 It's not that the engineers behind ICC failed to take the architectures of non-Intel processors into account, it's that it intentionally uses a slow path on non-Intel processors that cripples performance. We're talking assuming that the CPU doesn't support SIMD bad here. If you use virtualization to make your CPUID vendor string look like "GenuineIntel", or modify the executable to remove the Intel processor check, the "Intel optimized" builds run just as fast (barring relative processor strengths) on comparable AMD processors. This matters because: Until this became public, Intel gave no mention or disclaimer of suboptimal performance for ICC-generated code on non-Intel processors. News outlets did and probably still do use ICC-generated binaries for benchmarking, giving an unfair marketing advantage to Intel processors ("Look how poorly this AMD CPU runs this binary we specifically designed to function horribly on their CPU! Buy Intel today!") Almost no one is aware of this.

TwoBit 13y ago

Well it cost them some business, because some companies wouldn't use it due to performing poorly on other processors. I can't see how it would be beneficial for them to cripple AMD performance.

orik 13y ago
It's a none issue. This compiler is for OSx only, and I can't even remember the last time Apple released an OSx machine that's had AuthenticAMD.

Lockal 13y ago

They are adding this page/slide to everything, that is connected with Intel CPU (probably after that case with AMD mis-optimization, but I am not sure, if it was the first appearance of this page). For example, if they release a new instruction set, even if there are no alternatives in AMD world, Intel would add this page. Treat this like a boilerplate.

xooyoozoo 13y ago
It's 100% boilerplate. The whole "handicapping" debate that pops up every ICC thread is likely several years out of date (not that I don't expect to see it again and again for the next decade or two). Case in point, take bench completion time on a Xeon supercomputer [1]. Compare that to relative completion time on an Opteron supercomputer [2] (for both, lower is better). If that's Intel's compiler handicapping AMD performance, I wonder what GCC is trying to do? [1]: http://www.nersc.gov/users/computational-systems/edison/performance-and-optimization/compiler-comparisons/choosing-a-compiler-on-edison/ http://www.nersc.gov/users/computational-systems/edison/perf... [2]: http://www.nersc.gov/assets/_resampled/resizedimage730421-hopcmp1013.jpg http://www.nersc.gov/assets/_resampled/resizedimage730421-ho...

sitkack 13y ago

They still do this.