Can somebody shed some light on it, why embedded companies (speak Microchip etc) have not switched to clang/llvm? It must cost them quite a bit to maintain their own compiler stack and it is not very good.

Fun example: a customer of mine initialized a variable within a loop and that resulting program just didn't work as expected (which it did with the same code on my desktop with gcc). As soon as he moved the variable out of the loop the program worked as expected.