Itanium does this automatically. You declare what registers you're using in the the function prologue and it handles popping/pushing/renaming. No register window exceptions too.
Sadly it's dead now. In a cruel twist of fate, Intel killed it off shortly before we found out about all the speculative execution attacks and found that everything else is horrifically vulnerable.
It's inherently not vulnerable to the Spectre/Meltdown family of attacks. They rely on speculative, out-of-order execution on modern CPUs, but Itanium is an in-order core with very limited (and software-controlled) speculation.
It's actually not vulnerable to a bunch of other attacks as well (e.g. a buffer overflow cannot overwrite the return address on Itanium).
