factor/vm/slot_visitor.hpp

namespace factor
{

/* Slot visitors iterate over the slots of an object, applying a functor to
each one that is a non-immediate slot. The pointer is untagged first. The
functor returns a new untagged object pointer. The return value may or may not equal the old one,
however the new pointer receives the same tag before being stored back to the
original location.

Slots storing immediate values are left unchanged and the visitor does inspect
them.

This is used by GC's copying, sweep and compact phases, and the implementation
of the become primitive.

Iteration is driven by visit_*() methods. Some of them define GC roots:
- visit_roots()
- visit_contexts() */

template<typename Visitor> struct slot_visitor {
	factor_vm *parent;
	Visitor visitor;

	explicit slot_visitor<Visitor>(factor_vm *parent_, Visitor visitor_) :
		parent(parent_), visitor(visitor_) {}

	cell visit_pointer(cell pointer);
	void visit_handle(cell *handle);
	void visit_slots(object *ptr, cell payload_start);
	void visit_slots(object *ptr);
	void visit_stack_elements(segment *region, cell *top);
	void visit_data_roots();
	void visit_bignum_roots();
	void visit_callback_roots();
	void visit_literal_table_roots();
	void visit_roots();
	void visit_contexts();
	void visit_code_block_objects(code_block *compiled);
	void visit_embedded_literals(code_block *compiled);
};

template<typename Visitor>
cell slot_visitor<Visitor>::visit_pointer(cell pointer)
{
	if(immediate_p(pointer)) return pointer;

	object *untagged = untag<object>(pointer);
	untagged = visitor(untagged);
	return RETAG(untagged,TAG(pointer));
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_handle(cell *handle)
{
	*handle = visit_pointer(*handle);
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_slots(object *ptr, cell payload_start)
{
	cell *slot = (cell *)ptr;
	cell *end = (cell *)((cell)ptr + payload_start);

	if(slot != end)
	{
		slot++;
		for(; slot < end; slot++) visit_handle(slot);
	}
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_slots(object *ptr)
{
	visit_slots(ptr,ptr->binary_payload_start());
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_stack_elements(segment *region, cell *top)
{
	for(cell *ptr = (cell *)region->start; ptr <= top; ptr++)
		visit_handle(ptr);
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_data_roots()
{
	std::vector<data_root_range>::const_iterator iter = parent->data_roots.begin();
	std::vector<data_root_range>::const_iterator end = parent->data_roots.end();

	for(; iter < end; iter++)
	{
		data_root_range r = *iter;
		for(cell index = 0; index < r.len; index++)
			visit_handle(r.start + index);
	}
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_bignum_roots()
{
	std::vector<cell>::const_iterator iter = parent->bignum_roots.begin();
	std::vector<cell>::const_iterator end = parent->bignum_roots.end();

	for(; iter < end; iter++)
	{
		cell *handle = (cell *)(*iter);

		if(*handle)
			*handle = (cell)visitor(*(object **)handle);
	}
}

template<typename Visitor>
struct callback_slot_visitor {
	callback_heap *callbacks;
	slot_visitor<Visitor> *visitor;

	explicit callback_slot_visitor(callback_heap *callbacks_, slot_visitor<Visitor> *visitor_) :
		callbacks(callbacks_), visitor(visitor_) {}

	void operator()(code_block *stub)
	{
		visitor->visit_handle(&stub->owner);
	}
};

template<typename Visitor>
void slot_visitor<Visitor>::visit_callback_roots()
{
	callback_slot_visitor<Visitor> callback_visitor(parent->callbacks,this);
	parent->callbacks->each_callback(callback_visitor);
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_literal_table_roots()
{
	std::map<code_block *, cell> *uninitialized_blocks = &parent->code->uninitialized_blocks;
	std::map<code_block *, cell>::const_iterator iter = uninitialized_blocks->begin();
	std::map<code_block *, cell>::const_iterator end = uninitialized_blocks->end();

	std::map<code_block *, cell> new_uninitialized_blocks;
	for(; iter != end; iter++)
	{
		new_uninitialized_blocks.insert(std::make_pair(
			iter->first,
			visit_pointer(iter->second)));
	}

	parent->code->uninitialized_blocks = new_uninitialized_blocks;
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_roots()
{
	visit_handle(&parent->true_object);
	visit_handle(&parent->bignum_zero);
	visit_handle(&parent->bignum_pos_one);
	visit_handle(&parent->bignum_neg_one);

	visit_data_roots();
	visit_bignum_roots();
	visit_callback_roots();
	visit_literal_table_roots();

	for(cell i = 0; i < special_object_count; i++)
		visit_handle(&parent->special_objects[i]);
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_contexts()
{
	context *ctx = parent->ctx;

	while(ctx)
	{
		visit_stack_elements(ctx->datastack_region,(cell *)ctx->datastack);
		visit_stack_elements(ctx->retainstack_region,(cell *)ctx->retainstack);

		visit_handle(&ctx->catchstack_save);
		visit_handle(&ctx->current_callback_save);

		ctx = ctx->next;
	}
}

template<typename Visitor>
struct literal_references_visitor {
	slot_visitor<Visitor> *visitor;

	explicit literal_references_visitor(slot_visitor<Visitor> *visitor_) : visitor(visitor_) {}

	void operator()(instruction_operand op)
	{
		if(op.rel_type() == RT_LITERAL)
			op.store_value(visitor->visit_pointer(op.load_value()));
	}
};

template<typename Visitor>
void slot_visitor<Visitor>::visit_code_block_objects(code_block *compiled)
{
	visit_handle(&compiled->owner);
	visit_handle(&compiled->parameters);
	visit_handle(&compiled->relocation);
}

template<typename Visitor>
void slot_visitor<Visitor>::visit_embedded_literals(code_block *compiled)
{
	if(!parent->code->uninitialized_p(compiled))
	{
		literal_references_visitor<Visitor> visitor(this);
		compiled->each_instruction_operand(visitor);
	}
}

}