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Intel's compiler cripples code on AMD and VIA chips

Anti-competitive at the machine code level
Mon Jan 04 2010, 10:57

THE US Federal Trade Commission (FTC) apparently is interested in the fact that Intel's compiler deliberately cripples performance for non-Intel processors such as those made by AMD and VIA.

Writing in his blog, programming expert Agner Fog said that it appears that Chipzilla's compiler can produce different versions of pieces of code, with each version being optimised for a specific processor and/or instruction set. The system detects which CPU it's running on and chooses the optimal code path accordingly.

But it also checks what instruction sets are supported by the CPU and it also checks the vendor ID string. If the string says 'GenuineIntel' then it uses the optimal code path. If the CPU is not from Intel then, in most cases, it will use the slowest version of the code it can find.

While this is known, few Intel compiler users actually seem to know about it. Chipzilla does not say that the compiler is Intel-specific, either.

Fog said that if more programmers knew this fact they would probably use another compiler as everyone wants their code to run just as well on AMD's processors as on Intel's.

Some benchmarking programs are affected by this, up to a point where benchmark results can differ greatly depending on how a processor identifies itself.

It seems that in the fine print of the AMD settlement Intel has agreed to fix this problem. But apparently the FTC will still be interested because VIA could still be disadvantaged. µ


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