Small number optimization in bytecode

[SuperFola]

(let i 0) (print i) in ArkScript generates the following bytecode

Version:   3.0.15
Timestamp: 1620651845
SHA256:    eb4587372d295f8db6314323142f64d46961f38f4d0d07f2c259710b45043

Symbols table (length: 1)
0) i

Constants table (length: 1)
0) (Number) 0.000000

Code segment 0 (length: 16)
0 LOAD_CONST (Number) 0.000000
3 LET i
6 LOAD_SYMBOL i
9 BUILTIN print
12 CALL (1)
15 HALT

We're not interested in the print itself, I added it to avoid dealing with the optimizer (which would have optimized away the variable and generated an empty bytecode file), we are interested in the LOAD_CONST (Number) 0.000000. It's taking 1 byte for the instruction and 2 more for the index of the constant, thus 3 bytes to load a constant from a space somewhere in memory, push it on a stack, and later pop it and store it in i.

The whole thing is just loading the constant table and then searching it for a specific one (this is O(1) because the table is contiguous and we have the constant's id) is pretty heavy for such a small value. So much work for a 0.

Proposal

What I'm suggesting now, is introducing a special instruction, fused with a number. Since instructions are on 1 byte, we have 1 bit for the instruction and 7 free bits for the number (from 0 to 127).

Limitations

We are limited to numbers between 0 and 127, the other will have to be kept in the constant table as before. Though we could change our interpretation to store numbers between -64 and 63 so that common negative numbers can use this optimization (eg -1 and -2).

Also this is drastically limiting the number of instructions we can have, from 256 to 128, I don't think we will suffer from this, since we only have 44 different instructions currently. If this is considered as a loss, we can agree on something less aggresive, such as LOAD_SMALL_NUM <number on 1 byte, maybe 2>

Summary

Idea 1

Add a special instruction LOAD_SMALL_NUM, with value 0x80 (0b1000'0000), with its argument being located on its low bits.

Idea 2-1

Add a new instruction LOAD_SMALL_NUM, taking a 1 byte number (between -128 and 127).

Idea 2-2

Add a new instruction LOAD_SMALL_NUM, taking a 2 bytes number (between -32768 and 32767).