88 lines
2.6 KiB
Ruby
88 lines
2.6 KiB
Ruby
module Risc
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#
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# StandardAllocator keeps a list of registers whole names it accuires from the
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# Plaform.
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#
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# It allocates registers by going throught the instructions and dishing
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# out sequential registers.
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# Before doing that it determines live ranges, so registers can be returned
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# when not used anymore, and thus reused.
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class StandardAllocator
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def initialize( compiler , platform)
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@compiler = compiler
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@platform = platform
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@used_regs = {}
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@release_points = Hash.new( [] )
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@reg_names = (0 ... platform.num_registers).collect{|i| "r#{i-1}".to_sym }
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end
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attr_reader :used_regs , :compiler , :platform , :reg_names
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# main entry point and the whole reason for the class.
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# Allocate regs by changing the names of compiler instructions to
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# register names according to platform.
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# Ie on arm register names are r0 .. . r15 , so it keeps a list of unused
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# regs and frees regs according to live ranges
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def allocate_regs
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determine_liveness
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end
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# determines when registers can be freed
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#
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# this is done by walking the instructions backwards and saving the first
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# occurence of a register name. (The last, as we walk backwards)
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def determine_liveness
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walk_and_mark(@compiler.risc_instructions)
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end
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# First walk down, and on the way up mark register occurences, unless they
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# have been marked already
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def walk_and_mark(instruction)
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released = []
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released = walk_and_mark(instruction.next) if instruction.next
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#puts instruction.class.name
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instruction.register_names.each do |name|
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next if released.include?(name)
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@release_points[instruction] << name
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released << name
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end
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released
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end
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def used_regs_empty?
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@used_regs.empty?
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end
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def use_reg(reg)
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raise "not reg #{reg.class}" unless reg.is_a?(RegisterValue)
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@used_regs[reg.symbol] = reg
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end
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#
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def release_reg(reg)
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@used_regs.pop
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end
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def clear_used_regs
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@used_regs.clear
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end
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#helper method to calculate with register symbols
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def next_reg_use( type , extra = {} )
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int = @symbol[1,3].to_i
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raise "No more registers #{self}" if int > 11
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sym = "r#{int + 1}".to_sym
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RegisterValue.new( sym , type, extra)
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end
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# releasing a register (accuired by use_reg) makes it available for use again
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# thus avoiding possibly using too many registers
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def release_reg( reg )
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reg = reg.symbol if reg.is_a?(RegisterValue)
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raise "not symbol #{reg}:#{reg.class}" unless reg.is_a?(Symbol)
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@used_regs.delete(reg)
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end
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end
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end
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