I fully expect apples M1 chip to get a spectre type vulnerability at some point and then any improvements it had will disappear.
Any speculation around memory accesses will yield this.
Also, In dougallj's code [1] the zero of registers should be superfluous so it is assumed the function below is needed to make the experiments run stably by claiming ownership of the registers as part of a general anti-speculation security mechanism.
static int add_prep(uint32_t *ibuf, int instr_type);
The M1 explainer [2] has lot of interesting ideas like this contained inside it.
[1] https://gist.github.com/dougallj/5bafb113492047c865c0c8cfbc9...