> Because icc's performance isn't great on non-intel cpus?

I'm not sure that's true. I think it still out-performs gcc on AMD chips.

It's definitely possible. I haven't seen any benchmarks myself. I just remembered hearing that ICC purposefully produced crippled code on amd cpus. (http://www.amd.com/us-en/assets/content_type/DownloadableAss...).

The relevant section: Intel has designed its compiler purposely to degrade performance when a program is run on an AMD platform. To achieve this, Intel designed the compiler to compile code along several alternate code paths. Some paths are executed when the program runs on an Intel platform and others are executed when the program is operated on a computer with an AMD microprocessor. (The choice of code path is determined when the program is started, using a feature known as "CPUID" which identifies the computer’s microprocessor.) By design, the code paths were not created equally. If the program detects a "Genuine Intel" microprocessor, it executes a fully optimized code path and operates with the maximum efficiency. However, if the program detects an "Authentic AMD" microprocessor, it executes a different code path that will degrade the program’s performance or cause it to crash.

I think the main reasons are ideological (icc isn't free as in beer) and practical (ICC doesn't work on a huge number of architectures or os's that gcc does).