In an AVR assembly tutorial http://www.avr-asm-tutorial.net/avr_en/beginner/REGISTER.html#Unterschied
there was a list of notes about register usage:
Recommendation for the use of registers
Define names for registers with the .DEF directive, never use them with their direct name Rx.
If you need pointer access reserve R26 to R31 for that purpose.
16-bit-counter are best located R25:R24.
If you need to read from the program memory, e.g. fixed tables, reserve Z (R31:R30) and R0 for that purpose.
If you plan to have access to single bits within certain registers (e.g. for testing flags), use R16 to R23 for that purpose.
It's the first one that caught my eye.
Is that customary in "AVR-circles"?
I've never done that, and I guess it would "hide" the possible restrictions if alias is used.