The bytecode VM is a stack-based virtual machine. Instructions operate on an implicit operand stack, pushing and popping values. This is the original execution backend for ƿit.
The compiler emits JSFunctionBytecode objects containing opcode sequences, constant pools, and debug information.
Instruction Categories
Value Loading
Opcode
Description
push_i32
Push a 32-bit immediate integer
push_const
Push a value from the constant pool
null
Push null
push_false
Push false
push_true
Push true
Stack Manipulation
Opcode
Description
drop
Remove top of stack
dup
Duplicate top of stack
dup1 / dup2 / dup3
Duplicate item at depth
swap
Swap top two items
rot3l / rot3r
Rotate top three items
insert2 / insert3
Insert top item deeper
nip
Remove second item
Variable Access
Opcode
Description
get_var
Load variable by name (pre-link)
put_var
Store variable by name (pre-link)
get_loc / put_loc
Access local variable by index
get_arg / put_arg
Access function argument by index
get_env_slot / set_env_slot
Access closure variable (post-link)
get_global_slot / set_global_slot
Access global variable (post-link)
Variable access opcodes are patched during linking. get_var instructions are rewritten to get_loc, get_env_slot, or get_global_slot depending on where the variable is resolved.
Arithmetic
Opcode
Description
add / sub / mul / div
Basic arithmetic
mod / pow
Modulo and power
neg / inc / dec
Unary operations
add_loc / inc_loc / dec_loc
Optimized local variable update
Comparison and Logic
Opcode
Description
strict_eq / strict_neq
Equality (ƿit uses strict only)
lt / lte / gt / gte
Ordered comparison
not / lnot
Logical / bitwise not
and / or / xor
Bitwise operations
Control Flow
Opcode
Description
goto
Unconditional jump
if_true / if_false
Conditional jump
goto8 / goto16
Short jumps (size-optimized)
if_true8 / if_false8
Short conditional jumps
catch
Set exception handler
Function Calls
Opcode
Description
call
Call function with N arguments
tail_call
Tail-call optimization
call_method
Call method on object
return
Return value from function
return_undef
Return null from function
throw
Throw exception (disrupt)
Property Access
Opcode
Description
get_field
Get named property
put_field
Set named property
get_array_el
Get computed property
put_array_el
Set computed property
define_field
Define property during object literal
Object Creation
Opcode
Description
object
Create new empty object
array_from
Create array from stack values
Bytecode Patching
During the link/integrate phase, symbolic variable references are resolved to concrete access instructions. This is a critical optimization — the interpreter does not perform name lookups at runtime.
A get_var "x" instruction becomes:
get_loc 3 — if x is local variable at index 3
get_env_slot 1, 5 — if x is captured from outer scope (depth 1, slot 5)
