Nah, they license a proprietary one. There are a whole bunch of them (ICC, Digital Mars, PGI before they were acquired by Nvidia...). They generally aren't as

Nah, they license a proprietary one. There are a whole bunch of them (ICC, Digital Mars, PGI before they were acquired by Nvidia...). They generally aren't as good as GCC, but they keep your code private and copy-left licenses away from private codebases.