49 lines
1.6 KiB
Ruby
49 lines
1.6 KiB
Ruby
module Mom
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# A Label is the only legal target for a branch (in Mom, in Risc a BinaryCode is ok too)
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#
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# In the dynamic view (runtime) where the instructions form a graph,
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# branches fan out, Labels collect. In other words a branch is the place where
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# several roads lead off, and a Label where several roads arrive.
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#
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# A Label has a name which is mainly used for debugging.
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#
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# A Mom::Label converts one2one to a Risc::Label. So in a way it could not be more
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# simple.
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# Alas, since almost by definition several roads lead to this label, all those
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# several converted instructions must also point to the identical label on the
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# risc level.
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#
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# This is achieved by caching the created Risc::Label in an instance variable.
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# All branches that lead to this label can thus safely call the to_risc and
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# whoever calls first triggers the labels creation, but all get the same label.
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#
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# Off course some specific place still has to be responsible for actually
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# adding the label to the instruction list (usually an if/while)
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class Label < Instruction
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attr_reader :name
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def initialize(source , name)
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super(source)
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@name = name
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end
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def to_s
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"Label: #{name}"
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end
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# generate the risc label lazily
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def risc_label(compiler)
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@risc_label ||= Risc.label(self,name)
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compiler.add_constant(@risc_label.address)
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@risc_label
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end
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# add the risc_label to the compiler (instruction flow)
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# should only be called once
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def to_risc(compiler)
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compiler.add_code( risc_label(compiler) )
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end
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end
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end
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