I believe you're correct about Open64, but it was an interesting examples of a compiler when I was researching them last, particularly its usage of WHIRL [1]. It's a similar approach as used by GCC and LLVM with their front, middle and back-end approach, although I can't quite remember if it pioneered that approach or not.
So u say, LLVM or whatever is insane because it's large. so what do u think about QBE[0] ?
BCPL's O-Code is far different from LLVM bytecode. O-Code was little more than a virtual stack machine. Very similar to Forth, though slightly more complicated.
I could be wrong, but isn't Open64 more or less dead? The only thing I can think of that actually uses it (CUDA) isn't best-in-class.