AransentinDeiMOS – A Superoptimizer for the MOS 6502
If you assume that A * 10 isn't going to overflow, so that ASL A moves 0 into the carry flag (so no need for CLC), then instead of using the undocumented RRA opcode, you can just do:
sta $00
asl a
asl a
adc $00
asl a
This is also 7 bytes, but is faster since adc $00 is 3 cycles, vs rra $00 being 5 cycles.
The A = max(A, X) example is certainly interesting, but not very useful since it loops through the code twice (very slow) and assumes that $8a is available. The much faster obvious version only adds one byte:
stx $00
cmp $00
bcs done
txa
done:
Sure. Note that I picked those examples to demonstrate the two fairly quirky classes of things the optimizer tends to find. If the programmer has different requirements they can specify that, and it'll spit out the examples you gave (or something equivalent).
I like the idea of exhaustive search, which the simplicity of the 6502 seems ideally suited for, but the search speed seems a bit limiting. I wonder if there's not potential for more generation restriction (e.g. code can only use a specific N bytes of zero page) and heavy search pruning to speed it up? If it could generate optimal 20-30 op sequences in semi-reasonable time that'd make it very useful.