Code alignment? I mean, the different instructions change the alignment of the rest of the code.

- 64 bit register

    0:  48 c7 c1 01 00 00 00    mov    rcx,0x1

 - 32 bit register

    0:  b9 01 00 00 00          mov    ecx,0x1

It should be easy to test by adding a couple of NOPs to the fast version:

   0:  b9 01 00 00 00          mov    ecx,0x1
   5:  90                      nop
   6:  90                      nop

and see if it regresses again.

I don't have an Alder Lake to test on.