It isn't so much the decoder space, but the decoder complexity that is the disadvantage of x86 chips. The problem is that the instructions have varying lengths.

It isn't so much the decoder space, but the decoder complexity that is the disadvantage of x86 chips. The problem is that the instructions have varying lengths. Only when it has decoded an instruction, the chip knows where the next instruction starts. ARM-instructions are all the same length, so the instructions can be decoded in parallel without "knowing" the previous instruction. That lets Apple go much wider (8 instead of 4) with the instruction decoders.