83 lines
3.4 KiB
Ruby
83 lines
3.4 KiB
Ruby
module Mom
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# SlotLoad is for moving data into a slot, either from another slot, or constant
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# A Slot is basically an instance variable, but it must be of known type
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#
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# The value loaded (the right hand side) can be a constant (Mom::Constant) or come from
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# another Slot (SlotDefinition)
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#
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# The Slot on the left hand side is always a SlotDefinition.
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# The only known object (*) for the left side is the current message, which is a bit like
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# the oo version of a Stack (Stack Register, Frame Pointer, ..)
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# (* off course all class objects are global, and so they are allowed too)
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#
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# A maybe not immediately obvious corrolar of this design is the total absence of
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# general external instance variable accessors. Ie only inside an object's functions
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# can a method access instance variables, because only inside the method is the type
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# guaranteed.
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# From the outside a send is neccessary, both for get and set, (which goes through the method
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# resolution and guarantees the correct method for a type), in other words perfect data hiding.
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#
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# @left: A SlotDefinition, or an array that can be passed to the constructor of the
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# SlotDefinition (see there)
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#
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# @right: A SlotDefinition with slots or a Mom::Constant
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# original_source: optinally another mom instruction that wil be passed down to created
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# risc instructions. (Because SlotLoad is often used internally in mom)
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class SlotLoad < Instruction
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attr_reader :left , :right , :original_source
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def initialize(left , right, original_source = nil)
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@left , @right = left , right
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@left = SlotDefinition.new(@left.shift , @left) if @left.is_a? Array
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@right = SlotDefinition.new(@right.shift , @right) if @right.is_a? Array
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raise "right not Mom, #{@right.to_s}" unless @right.is_a?( SlotDefinition )
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@original_source = original_source || self
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end
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def to_s
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"SlotLoad #{right} -> #{left}"
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end
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# resolve the SlotLoad to the respective risc Instructions.
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# calls sym_to_risc for most (symbols), and ConstantLoad for CacheEntry
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# after loading the right into register
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def to_risc(compiler)
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const_reg = @right.to_register(compiler , original_source)
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left_slots = @left.slots
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case @left.known_object
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when Symbol
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sym_to_risc(compiler , const_reg)
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when Parfait::CacheEntry
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left = compiler.use_reg( :CacheEntry )
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compiler.add_code Risc.load_constant(original_source, @left.known_object , left)
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compiler.add_code Risc.reg_to_slot(original_source, const_reg , left, left_slots.first)
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else
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raise "We have left #{@left.known_object}"
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end
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compiler.reset_regs
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end
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# load the data in const_reg into the slot that is named by left symbols
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# left may usually be only 3 long, as the first is known, then the second is loaded
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# with type known type (as it comes from message)
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#
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# actual lifting is done by RegisterValue resolve_and_add
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def sym_to_risc(compiler , const_reg)
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left_slots = @left.slots.dup
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raise "Not Message #{object}" unless @left.known_object == :message
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left = Risc.message_reg
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slot = left_slots.shift
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while( !left_slots.empty? )
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left = left.resolve_and_add( slot , compiler)
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slot = left_slots.shift
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end
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compiler.add_code Risc.reg_to_slot(original_source, const_reg , left, slot)
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end
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end
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end
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require_relative "slot_definition"
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