It's not particularly short of registers, but IIRC even aarch64 is short enough that they implemented register renaming. I agree that taking a register away is a much less pressing issue there than on the x86.
The purpose of register renaming in the AArch64 microarchitectures is to support out-of-order. By comparison, you don't find register renaming in the in-order A53.
Suppose you had enough registers, ie. so many that there's no real reason to compilers to save. In that case, you could "support" out-of-order execution by adding a couple sentences to the compiler guidance documentation for your CPU, telling them that they'll get better performance on o-o-o cores if they wait as long as practical with reusing registers.
They've tried variations of this. It takes instruction bits to describe these registers: 32 regs is 5 bits, target + src1 + src2 is 15 bits already. They've tried scratch pads. The Mill CPU's Belt is yet another approach.
https://en.wikipedia.org/wiki/Scratchpad_memory
https://millcomputing.com/
How to Use 1000 Registers
https://caltechconf.library.caltech.edu/200/
1000 registers would be 10 bits. So they tried register windows.
These are all good ideas but they get to compete. So far, I'm a huge AArch64 fan but I now see the purpose of RISC-V. I watched Chris Lattner's ASPLOS talk and it finally clicked.
I know... and it's quite interesting really, but for the purpose of this thread, I think it's safe to say that the CPU-wallahs spend considerable effort on ways to lighten or avoid register pressure, and from that I infer that all of the currently widely used CPUs do have significant pressure.
Much more on the x86 than on sane architectures, of course.
