I don't know what do you mean by 'bytecode'.
ISA microcode is the actual binary stream that the gpu eats. (Don't confuse it with x86's microcode which is stored inside every x86 microprocessor).
I was told that what this document refers to as microcode is actually the bytecode, so this clears it up, thank you. By the way, is there any way I could send you a private message here?