80 lines
3.3 KiB
Ruby
80 lines
3.3 KiB
Ruby
module Mom
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# SlotLoad is an abstract base class for moving data into a slot
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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 PC (program Counter)
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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 purpose 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: Either a SlotDefinition or a Constant
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#
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class SlotLoad < Instruction
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attr_reader :left , :right
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def initialize(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 )#or right.is_a? Mom::Constant
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@left , @right = left , right
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end
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def to_risc(compiler)
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type = @right.respond_to?(:ct_type) ? @right.ct_type : :int
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right = compiler.use_reg( type )
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case @right.known_object
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when Constant
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const = Risc.load_constant(self, @right , right)
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when Symbol
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const = Risc::SlotToReg.new( self , Risc.message_reg ,
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Risc.resolve_to_index(:message , @right.slots[0]), right)
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puts "more slots #{@right.slots}" if @right.slots.length > 1
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else
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raise "We have a #{@right} #{@right.known_object}"
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end
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case @left.known_object
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when Symbol
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left = Risc.message_reg
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left_index = Risc.resolve_to_index(@left.known_object , @left.slots.first)
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when Parfait::CacheEntry
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left = compiler.use_reg( :int )
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left_index = Risc.resolve_to_index(:cache_entry , @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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const << Risc.reg_to_slot(self, right , left, left_index)
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compiler.release_reg(left) unless @left.known_object.is_a?(Symbol)
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compiler.release_reg(right)
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return const
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end
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end
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class SlotDefinition
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attr_reader :known_object , :slots
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# is an array of symbols, that specifies the first the object, and then the Slot.
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# The first element is either a known type name (Capitalized symbol of the class name) ,
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# or the symbol :message
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# And subsequent symbols must be instance variables on the previous type.
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# Examples: [:message , :receiver] or [:Space : :next_message]
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def initialize( object , slots)
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@known_object , @slots = object , slots
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slot = [slot] unless slot.is_a?(Array)
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raise "Not known #{slots}" unless object
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end
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end
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end
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