This. AArch64 is far more than a simple "ARM, but with 64-bit addresses" change, most obviously predicated instructions are gone (which is a big deal for OoOE)

This. AArch64 is far more than a simple "ARM, but with 64-bit addresses" change, most obviously predicated instructions are gone (which is a big deal for OoOE) and exceptions are vastly simpler.