Last Modified
2018-10-18 23:59:53 -0500


The new bytecode

We will reimplement VM to use 8bit instruction code. By bytecode, we mean real byte code. The whole purpose is reducing the memory consumption of mruby VM.


Instructions are bytes. There can be 256 instructions. Currently we have 94 instructions. Instructions can take 0 to 3 operands.


The size of operands can be either 8bits, 16bits or 24bits. In the table.1 below, the second field describes the size (and sign) of operands.

First two byte operands may be extended to 16bit. When those byte operands are bigger than 256, the instruction will be prefixed by OP_EXT1 (means 1st operand is 16bit) or OP_EXT2 (means 2nd operand is 16bit) or OP_EXT3 (means 1st and 2nd operands are 16bit).

For instructions marked by ', OP_EXT1 can be prefixed. For those with ", either OP_EXT1 or OP_EXT2 or OP_EXT2 can be prefixed.

table.1 Instruction Table

|Instruction Name |Operand type |Semantics
|—————–|————-|—————– |OP_NOP | - |
|OP_MOVE“ |BB |R(a) = R(b)
|OP_LOADL” |BB |R(a) = Pool(b)
|OP_LOADI“ |BsB |R(a) = mrb_int(b) |OP_LOADI_0' |B |R(a) = 0 |OP_LOADI_1' |B |R(a) = 1 |OP_LOADI_2' |B |R(a) = 2 |OP_LOADI_3' |B |R(a) = 3 |OP_LOADSYM” |BB |R(a) = Syms(b) |OP_LOADNIL' |B |R(a) = nil |OP_LOADSELF' |B |R(a) = self |OP_LOADT' |B |R(a) = true |OP_LOADF' |B |R(a) = false |OP_GETGV“ |BB |R(a) = getglobal(Syms(b)) |OP_SETGV” |BB |setglobal(Syms(b), R(a)) |OP_GETSV“ |BB |R(a) = Special |OP_SETSV” |BB |Special = R(a) |OP_GETIV“ |BB |R(a) = ivget(Syms(b)) |OP_SETIV” |BB |ivset(Syms(b),R(a)) |OP_GETCV“ |BB |R(a) = cvget(Syms(b)) |OP_SETCV” |BB |cvset(Syms(b),R(a)) |OP_GETCONST“ |BB |R(a) = constget(Syms(b)) |OP_SETCONST” |BB |constset(Syms(b),R(a)) |OP_GETMCNST“ |BB |R(a) = R(a)::Syms(b) |OP_SETMCNST” |BB |R(a+1)::Syms(b) = R(a) |OP_GETUPVAR' |BBB |R(a) = uvget(b,c) |OP_SETUPVAR' |BBB |uvset(b,c,R(a)) |OP_JMP |S |pc+=a |OP_JMPIF' |SB |if R(b) pc+=a |OP_JMPNOT' |SB |if !R(b) pc+=a |OP_ONERR |sS |rescue_push(pc+a) |OP_EXCEPT' |B |R(a) = exc |OP_RESCUE“ |BB |R(b) = R(a).isa?(R(b)) |OP_POPERR |B |a.times{rescue_pop()} |OP_RAISE' |B |raise(R(a)) |OP_EPUSH' |B |ensure_push(SEQ) |OP_EPOP |B |A.times{ensure_pop().call} |OP_SENDV” |BB |R(a) = call(R(a),Syms(b),R(a+1)) |OP_SENDVB“ |BB |R(a) = call(R(a),Syms(b),R(a+1),&R(a+2)) |OP_SEND” |BBB |R(a) = call(R(a),Syms(b),R(a+1),…,R(a+c)) |OP_SENDB“ |BBB |R(a) = call(R(a),Syms(Bx),R(a+1),…,R(a+c),&R(a+c+1)) |OP_CALL' |B |R(a) =, frame.argv) |OP_SUPER' |BB |R(a) = super(R(a+1),… ,R(a+b+1)) |OP_ARGARY' |BS |R(a) = argument array (16=5:1:5:1:4) |OP_ENTER |W |arg setup according to flags (23=5:5:1:5:5:1:1) |OP_KARG” |BB |R(a) = kdict # todo |OP_KARG2“ |BB |R(a) = kdict; kdict.rm(Syms(b)) # todo |OP_RETURN' |B |return R(a) (normal) |OP_RETURN_BLK' |B |return R(a) (in-block return) |OP_BREAK' |B |break R(a) |OP_BLKPUSH' |BS |R(a) = block (16=5:1:5:1:4) |OP_ADD” |BB |R(a) = R(a)+R(a+1) (Syms=:+) |OP_ADDI“ |BBB |R(a) = R(a)+mrb_int© (Syms=:+) |OP_SUB” |BB |R(a) = R(a)-R(a+1) (Syms=:-) |OP_SUBI“ |BB |R(a) = R(a)-C (Syms=:-) |OP_MUL” |BB |R(a) = R(a)R(a+1) (Syms=:) |OP_DIV“ |BB |R(a) = R(a)/R(a+1) (Syms=:/) |OP_EQ” |BB |R(a) = R(a)==R(a+1) (Syms=:==) |OP_LT“ |BB |R(a) = R(a)<R(a+1) (Syms=:<) |OP_LE” |BB |R(a) = R(a)<=R(a+1) (Syms=:<=) |OP_GT“ |BB |R(a) = R(a)>R(a+1) (Syms=:>) |OP_GE” |BB |R(a) = R(a)>=R(a+1) (Syms=:>=) |OP_ARRAY' |BB |R(a) = ary_new(R(a),R(a+1)..R(a+b)) |OP_ARRAY2“ |BB |R(a) = ary_new(R(b),R(b+1)..R(b+c)) |OP_ARYCAT' |B |ary_cat(R(a),R(a+1)) |OP_ARYPUSH' |B |ary_push(R(a),R(a+1)) |OP_AREF' |BB |R(a) = R(a) |OP_ASET' |BB |R(a) = R(a+1) |OP_APOST' |BB |*R(a),R(A+1)..R(A+C) = R(a) |OP_STRING” |BB |R(a) = str_dup(Lit(b)) |OP_STRCAT' |B |str_cat(R(a),R(a+1)) |OP_HASH' |BB |R(a) = hash_new(R(a),R(a+1)..R(a+b)) |OP_HASHADD' |BB |R(a) = hash_push(R(a),R(a+1)..R(a+b)) |OP_LAMBDA“ |BB |R(a) = lambda(SEQ,OP_L_LAMBDA) |OP_BLOCK” |BB |R(a) = lambda(SEQ,OP_L_BLOCK) |OP_METHOD“ |BB |R(a) = lambda(SEQ,OP_L_METHOD) |OP_RANGE_INC' |B |R(a) = range_new(R(a),R(a+1),FALSE) |OP_RANGE_EXC' |B |R(a) = range_new(R(a),R(a+1),TRUE) |OP_OCLASS' |B |R(a) = ::Object |OP_CLASS” |BB |R(a) = newclass(R(a),Syms(b),R(a+1)) |OP_MODULE“ |BB |R(a) = newmodule(R(a),Syms(b)) |OP_EXEC” |BB |R(a) = blockexec(R(a),SEQ) |OP_DEF“ |BB |R(a).newmethod(Syms(b),R(a+1)) |OP_ALIAS' |B |alias_method(R(a),R(a+1),R(a+2)) |OP_UNDEF” |BB |undef_method(R(a),Syms(b)) |OP_SCLASS' |B |R(a) = R(a).singleton_class |OP_TCLASS' |B |R(a) = target_class |OP_ERR' |B |raise(RuntimeError, Lit(Bx)) |OP_EXT1 |- |make 1st operand 16bit |OP_EXT2 |- |make 2nd operand 16bit |OP_EXT3 |- |make 1st and 2nd operands 16bit |OP_STOP |- |stop VM