Class: Fisk::CFG

Inherits:
Struct
  • Object
show all
Defined in:
lib/fisk/basic_block.rb

Defined Under Namespace

Classes: BasicBlock

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Attribute Details

#blocks ⇒ Object

Returns the value of attribute blocks

Returns:

  • (Object) —

    the current value of blocks



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# File 'lib/fisk/basic_block.rb', line 2

def blocks
  @blocks
end

#variables ⇒ Object

Returns the value of attribute variables

Returns:

  • (Object) —

    the current value of variables



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# File 'lib/fisk/basic_block.rb', line 2

def variables
  @variables
end

Class Method Details

.build(instructions) ⇒ Object 



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# File 'lib/fisk/basic_block.rb', line 22

def self.build instructions
  blocks = []
  bb_index = 0

  chunks = instructions.chunk { |insn|
    if insn.label?
      # start a new block here
      bb_index += 1
    end

    ret_idx = bb_index

    if insn.jump?
      # end the block here
      bb_index += 1
    end

    ret_idx
  }.to_a

  chunk_name = ->(chunk_id, insns) {
    if insns.first.label?
      insns.first.name
    else
      :"bb_#{chunk_id}"
    end
  }

  jump_targets = {}
  wants_target = []
  insn_idx = 0

  chunks.each_with_index do |(chunk_id, insns), idx|
    prev_block = blocks.last

    name = chunk_name.(chunk_id, insns)

    next_chunk_id, next_insns = chunks[idx + 1]

    outgoing = []

    if next_chunk_id
      outgoing << chunk_name.(next_chunk_id, next_insns)
    end

    bb = BasicBlock.new(name, insns)
    bb.pred = []
    bb.start_point = insn_idx
    insn_idx += insns.length
    bb.end_point = insn_idx - 1

    if bb.jump?
      target_name = bb.jump_name

      # if we need to jump backwards, the label should already be filled in.
      # Otherwise we need to find the block later (we're jumping forward)
      if jump_targets[target_name]
        jt = jump_targets[target_name]
        bb.jump = jt
        jt.pred << bb
      else
        wants_target << bb
      end
    end

    jump_targets[bb.name] = bb

    if prev_block
      prev_block.fall = bb
      bb.pred << prev_block
    end

    blocks << bb
  end

  # fill in any forward jumps
  wants_target.each { |bb|
    jt = jump_targets[bb.jump_name]
    bb.jump = jt
    jt.pred << bb
  }

  variables = live_variables blocks

  CFG.new variables, blocks
end

.live_variables(blocks) ⇒ Object 



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# File 'lib/fisk/basic_block.rb', line 109

def self.live_variables blocks
  seen = Set.new

  blocks.each do |block|
    used = Set.new
    defd = Set.new

    block.insns.each do |insn|
      if insn.has_temp_registers?
        insn.temp_registers.each do |reg|
          defd << reg unless seen.include?(reg)
          used << reg unless defd.include?(reg)
          seen << reg
        end
      end
    end

    block.use = used.to_a
    block.def = defd.to_a
    block.in  = []
    block.out = []
  end

  worklist = blocks.dup
  while block = worklist.pop
    block.out = block.succ.inject([]) { |out_registers, succ_block|
      out_registers | succ_block.in
    }
    ins = block.in | block.use | (block.out - block.def)

    if ins == block.in
      # Done with this block!
      block.live.each do |live_register|
        live_register.end_point ||= block.end_point

        if live_register.start_point > block.start_point
          live_register.start_point = block.start_point
        end

        if live_register.end_point < block.end_point
          live_register.end_point = block.end_point
        end
      end
    else
      block.in = ins
      worklist.concat(block.pred)
    end
  end

  seen
end