evaluate possible performance issue with current A stack implementation

From !14 (comment 2208991694):

I now realize that in functions with many A stack local values, there is a possible performance issue: LLVM may decide to spill some of these values to the system stack to reduce register pressure, but then when we do a jsr these values have to be restored from the system stack to push them to asp (by contrast, the current code generator never spills A stack values to the system stack, but always uses the A stack). To somewhat alleviate the problem, you can limit the number of A stack values that are passed as arguments / return values (the current code generator has only 3 registers for A stack values) and pass the rest in asp. I don't know how realistic a problem it is. It would be possible to let the code generator report call sites with large simulated A stacks and inspect the generated code to see if anything can be improved.