As an aside: it's only relevant on microcontrollers nowadays, but ARM T32 (Thumb) code density is really good. Most instructions are 2 bytes, and it's got some clever ways to represent commonly used 32-bit values in 12 bits:
RISC-V code density is pretty good these days with Zcmp (push, pop, compressed double move) and Zcb (compressed mul, sign/zero-extend, byte load/store). There is also Zcmt but it's kind of cursed. Hopefully density will keep improving once mainstream compilers have full support for Zilsd/Zclsd (load/store pair for RV32).
T32 is a pretty good encoding but far from perfect. If they had the chance to redo it I doubt they would spend a full 1/32nd of the encoding space on asrs, for example.
https://developer.arm.com/documentation/ddi0403/d/Applicatio...