You're right, I should have been more specific. By "implementation defined", I actually meant "platform-defined", not "compiler-implementation defined". So, ba

You're right, I should have been more specific. By "implementation defined", I actually meant "platform-defined", not "compiler-implementation defined". So, basically, only the native code emitter would take these behaviors into account, and could do whatever (e.g. emulate, crash, emit instructions and hope for the best, ...). But the rest of the compiler pipeline (optimisations) would still need to treat the code as valid.