Comment by relium
The ones I remember most affecting performance were zeroing allocated memory and the Spectre/Meltdown fix. Also, the first launch of a new app is slow in order to check the signature. Whole disk encryption is pretty fast today, but probably is a bit slower than unencrypted. The original FileVault using disk images was even slower.
It's not whole-disk encryption, it's file-level encryption which is better. (more security guarantees)
Zeroing allocated memory is complicated because it also has performance benefits, since it improves compressed swap.