Class: Furnace::AVM2::Transform::ASTBuild

Inherits:
Object
  • Object
show all
Defined in:
lib/furnace-avm2/transform/ast_build.rb

Overview

I’m not exactly proud of this code, but it works… for now. I really should rework it if I want to expect it to work good.

Constant Summary collapse

CONDITIONAL_OPERATORS = 
[ :if_eq,  :if_false, :if_true,      :if_ge,        :if_gt,
:if_le,  :if_lt,    :if_ne,        :if_nge,       :if_ngt,
:if_nle, :if_nlt,   :if_strict_eq, :if_strict_ne, :if_true ]
CONST_OPERATORS = 
[ :integer, :double, :string, :false, :true, :nan, :undefined, :null ]

Instance Method Summary collapse

Constructor Details

#initialize(options) ⇒ ASTBuild

Returns a new instance of ASTBuild.



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# File 'lib/furnace-avm2/transform/ast_build.rb', line 12

def initialize(options)
  @validate = options[:validate] || false
  @verbose  = options[:verbose]  || false

  #@verbose = true
end

Instance Method Details

#transform(code, method) ⇒ Object 



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# File 'lib/furnace-avm2/transform/ast_build.rb', line 19

def transform(code, method)
  stack = []
  ast   = AST::Node.new(:root)

  dup         = nil
  spurious    = 0

  in_shortcut = false
  shortjump   = []
  ternary     = []

  consume = lambda do |count|
    if count == 0
      []
    elsif count <= stack.size
      stack.slice!(-count..-1)
    else
      raise "cannot consume #{count}: stack underflow with #{stack.size}"
    end
  end

  produce = lambda do |what|
    stack.push what
  end

  emit = lambda do |node|
    if @verbose
      puts "emitted:"
      puts node.to_sexp(1)
    end

    ast.children.push node
  end

  extend_complex_expr = lambda do |valid_types, expected_depth=nil|
    expr, current = consume.(2)

    if @validate
      if !valid_types.include?(expr.type)
        raise "invalid complex expr: #{expr.type} not in #{valid_types}"
      elsif expected_depth && expr.children.count != expected_depth
        raise "invalid complex expr: depth #{expr.children.count} != #{expected_depth}"
      end
    end

    expr.children << current
    produce.(expr)
  end

  finalize_complex_expr = lambda do |opcode, worklist, valid_types, expected_depth=nil, wrap_to=nil|
    while worklist.last == opcode.offset
      extend_complex_expr.(valid_types, expected_depth)

      if wrap_to
        node, *prepend = *wrap_to

        expr, = consume.(1)
        expr = AST::Node.new(node, [*prepend, expr])
        produce.(expr)
      end

      worklist.pop
    end
  end

  expand_conditionals = lambda do
    expressions = []

    while stack.any? && CONDITIONAL_OPERATORS.include?(stack.last.type)
      conditional, = consume.(1)

      jump_node = AST::Node.new(:jump_if, [ true, conditional.metadata[:offset], conditional ])
      expressions.unshift jump_node
    end

    ast.children.concat expressions
  end

  code.each do |opcode|
    if @verbose
      puts "================================"
      puts "stack: #{stack.inspect}"
      puts "shortjump: #{shortjump.inspect} ternary: #{ternary.inspect}"
      puts "opcode: #{opcode.inspect}"
    end

    finalize_complex_expr.(opcode, ternary, CONDITIONAL_OPERATORS, nil, [:ternary_if, false])
    finalize_complex_expr.(opcode, shortjump, [ :and, :or ], 1)

    if dup == 1 && (opcode.is_a?(ABC::AS3CoerceB) ||
            opcode.is_a?(ABC::AS3IfTrue) || opcode.is_a?(ABC::AS3IfFalse))
      in_shortcut  = true
      dup          = false
    end

    if in_shortcut
      if opcode.is_a?(ABC::AS3IfTrue)
        type = :or
      elsif opcode.is_a?(ABC::AS3IfFalse)
        type = :and
      elsif opcode.is_a?(ABC::AS3CoerceB)
        next
      elsif opcode.is_a?(ABC::AS3Pop)
        in_shortcut = false
        next
      elsif opcode.is_a?(ABC::AS3Jump) && opcode.body.jump_offset == 0
        # nop
        next
      else
        raise "invalid shortcut"
      end

      node = AST::Node.new(type, [], label: opcode.offset)
      node.children = consume.(1)
      produce.(node)

      shortjump.push opcode.target_offset
    elsif opcode.is_a?(ABC::AS3Swap)
      first, second = stack.pop, stack.pop
      stack.push first, second
    elsif opcode.is_a?(ABC::AS3Dup)
      node = stack.last

      if CONST_OPERATORS.include?(node.type) ||
            (node.type == :get_local && node.children.first == 0)
        dup_node = node.dup
        dup_node.metadata[:label] = opcode.offset
        produce.(dup_node)
      else
        dup ||= 0
        dup  += 1
      end
    elsif opcode.is_a?(ABC::AS3Jump)
      if opcode.body.jump_offset == 0
        node = AST::Node.new(:nop, [], label: opcode.offset)
        emit.(node)
      elsif stack.any? && !CONDITIONAL_OPERATORS.include?(stack.last.type)
        extend_complex_expr.(CONDITIONAL_OPERATORS)

        ternary.push opcode.target_offset
      else
        expand_conditionals.()

        node = AST::Node.new(opcode.ast_type, opcode.parameters, label: opcode.offset)
        emit.(node)
      end
    elsif opcode.is_a?(ABC::ControlTransferOpcode)
      node = AST::Node.new(opcode.ast_type, [], label: opcode.offset)
      node.metadata[:offset] = opcode.target_offset
      node.children = consume.(opcode.consumes)
      produce.(node)
    elsif opcode.is_a?(ABC::AS3Kill)
      # Ignore. SSA will handle that.
    else
      if dup
        spurious += 1

        save_node = AST::Node.new(:set_local, [ -spurious, *consume.(1) ])
        emit.(save_node)

        (1 + dup).times do
          load_node = AST::Node.new(:get_local, [ -spurious ])
          produce.(load_node)
        end

        dup = false
      end

      node = AST::Node.new(opcode.ast_type, [], label: opcode.offset)

      parameters = consume.(opcode.consumes)
      if opcode.consumes_context
        context = opcode.context(consume.(opcode.consumes_context))
      end

      node.children.concat context if context
      node.children.concat opcode.parameters
      node.children.concat parameters

      # All opcodes which produce 2 results--that is, dup and swap--
      # are already handled at the top.
      if opcode.produces == 0
        expand_conditionals.()
        emit.(node)
      elsif opcode.produces == 1
        produce.(node)
      end
    end
  end

  if @validate
    extracted_opcodes = []
    extract = lambda do |tree|
      extracted_opcodes.push tree.metadata[:label]
      tree.select { |c| c.is_a? Node }.each { |c| extract.(c) }
    end
  end

  ast.normalize_hierarchy!
end