[rwmj]

> divide the local registers in half for boxed and unboxed values

Fondly remembers the separate address and data registers on 68000. Why didn't they go back to this approach for x86_64 (16 registers), now that no one really cares about 32 bit x86?

[aidenn0]

The conservative GC approach has worked well enough in practice that nobody is going to do the work. Also there is a performance tradeoff in non-allocating code: Sometimes you need more unboxed registers, other times you need more boxed registers so with only ~6 of each[1] you will run into register pressure.

1: 2 stacks means 2 stack pointers and 2 frame pointers leaving only 12 registers left for values; it's also possible that the SBCL ABI uses a global register for something else as well, which would leave only 11. PowerPC is a really luxurious platform in which you have 32 GPRs so even if you use 8 GPRs for various bookkeeping purposes that leaves 24 remaining, which is enough for pretty much everyone.