CMS was written in C and translated with a custom P95/P2000 backend for good ol' GCC. However, your question is of course about a publicly available compiler.

CMS was written in C and translated with a custom P95/P2000 backend for good ol' GCC. However, your question is of course about a publicly available compiler. Well, it would be a bit tricky as the ISA was never public and the firmware tried very hard to keep the innards secret. An interesting fact was that CMS could occasionally (not always, but not rarely either) do a better job than the ahead-of-time compiler as CMS benefits from: statistics collected at runtime and can generate code under assumption without compensation code. When the assumptions are found to be violated, it can just recompile the code again. The challenge is always having the compilation overhead be [more than] paid off by the runtime gain. Sometimes it worked, others it didn't. Unfortunately, people really notice when it doesn't work which added to a negative perception of Crusoe. The conventional processors (even out-of-order) have far more predictable performance.