The Bytecode::Interpreter will push a global call frame if needed,
and it needs to make sure that call frame survives until the end
of the Interpreter::run() function.
If there's a current Bytecode::Interpreter in action, ScriptFunction
will now compile itself into bytecode and execute in that context.
This patch also adds the Return bytecode instruction so that we can
actually return values from called functions. :^)
Return values are propagated from callee to caller via the caller's
$0 register. Bytecode::Interpreter now keeps a stack of register
"windows". These are not very efficient, but it should be pretty
straightforward to convert them to e.g a sliding register window
architecture later on.
This is pretty dang cool! :^)
This introduces two new instructions: Jump and JumpIfFalse.
Jumps are made to a Bytecode::Label, which is a simple object that
represents a location in the bytecode stream.
Note that you may not always know the target of a jump when adding the
jump instruction itself, but we can just update the instruction later
on during codegen once we know where the jump target is.
The Bytecode::Interpreter now implements jumping via a jump slot that
gets checked after each instruction to see if a jump is pending.
If not, we just increment the PC as usual.
This patch begins the work of implementing JavaScript execution in a
bytecode VM instead of an AST tree-walk interpreter.
It's probably quite naive, but we have to start somewhere.
The basic idea is that you call Bytecode::Generator::generate() on an
AST node and it hands you back a Bytecode::Block filled with
instructions that can then be interpreted by a Bytecode::Interpreter.
This first version only implements two instructions: Load and Add. :^)
Each bytecode block has infinity registers, and the interpreter resizes
its register file to fit the block being executed.
Two new `js` options are added in this patch as well:
`-d` will dump the generated bytecode
`-b` will execute the generated bytecode
Note that unless `-d` and/or `-b` are specified, none of the bytecode
related stuff in LibJS runs at all. This is implemented in parallel
with the existing AST interpreter. :^)
