Class: MilkTea::ControlFlow::ConstantPropagation

Inherits:
Object
  • Object
show all
Defined in:
lib/milk_tea/core/control_flow/constant_propagation.rb

Defined Under Namespace

Classes: ConstVal, Result

Constant Summary collapse

UNDEF = 
:undef
NAC = 
:nac

Class Method Summary collapse

Class Method Details

.constant_value_of(expr, in_state, binding_resolution: nil, strict_binding_ids: false) ⇒ Object 



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# File 'lib/milk_tea/core/control_flow/constant_propagation.rb', line 124

def self.constant_value_of(expr, in_state, binding_resolution: nil, strict_binding_ids: false)
  result = send(:eval_expr_const, expr, in_state, binding_resolution:, strict_binding_ids:)
  result.is_a?(ConstVal) ? result.value : nil
end

.eval_assignment_const(statement, in_state, binding_resolution:, strict_binding_ids:) ⇒ Object 



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# File 'lib/milk_tea/core/control_flow/constant_propagation.rb', line 74

def self.eval_assignment_const(statement, in_state, binding_resolution:, strict_binding_ids:)
  return NAC unless statement.target.is_a?(AST::Identifier)

  rhs = eval_expr_const(statement.value, in_state, binding_resolution:, strict_binding_ids:)
  return NAC unless rhs.is_a?(ConstVal)

  return rhs if statement.operator == "="

  lhs = eval_expr_const(statement.target, in_state, binding_resolution:, strict_binding_ids:)
  return NAC unless lhs.is_a?(ConstVal)

  begin
    v = case statement.operator
    when "+="  then lhs.value + rhs.value
    when "-="  then lhs.value - rhs.value
    when "*="  then lhs.value * rhs.value
    when "/="  then rhs.value.zero? ? (return NAC) : lhs.value / rhs.value
    when "%="  then rhs.value.zero? ? (return NAC) : lhs.value % rhs.value
    when "&="  then lhs.value & rhs.value
    when "|="  then lhs.value | rhs.value
    when "^="  then lhs.value ^ rhs.value
    when "<<=" then lhs.value << rhs.value
    when ">>=" then lhs.value >> rhs.value
    else return NAC
    end
    ConstVal.new(v)
  rescue ZeroDivisionError, RangeError
    NAC
  end
end

.eval_const(statement, _write, in_state, binding_resolution:, strict_binding_ids:) ⇒ Object 



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# File 'lib/milk_tea/core/control_flow/constant_propagation.rb', line 63

def self.eval_const(statement, _write, in_state, binding_resolution:, strict_binding_ids:)
  case statement
  when AST::LocalDecl
    eval_expr_const(statement.value, in_state, binding_resolution:, strict_binding_ids:)
  when AST::Assignment
    eval_assignment_const(statement, in_state, binding_resolution:, strict_binding_ids:)
  else
    NAC
  end
end

.eval_expr_const(expr, state, binding_resolution:, strict_binding_ids:) ⇒ Object 



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# File 'lib/milk_tea/core/control_flow/constant_propagation.rb', line 105

def self.eval_expr_const(expr, state, binding_resolution:, strict_binding_ids:)
  return NAC if expr.nil?

  value = ConstEval.evaluate(
    expr,
    resolve_identifier: lambda do |identifier_expression|
      key = identifier_key(identifier_expression, binding_resolution:, strict_binding_ids:)
      next unless key

      state_value = state[key]
      state_value.is_a?(ConstVal) ? state_value.value : nil
    end,
    resolve_member_access: nil,
  )
  value.nil? ? NAC : ConstVal.new(value)
rescue CompileTime::Error
  NAC
end

.identifier_key(identifier_expression, binding_resolution:, strict_binding_ids:) ⇒ Object 



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# File 'lib/milk_tea/core/control_flow/constant_propagation.rb', line 129

def self.identifier_key(identifier_expression, binding_resolution:, strict_binding_ids:)
  if binding_resolution && (id = binding_resolution.identifier_binding_ids[identifier_expression.object_id])
    return id
  end

  return nil if strict_binding_ids

  identifier_expression.name
end

.join_lattice(a, b) ⇒ Object 



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# File 'lib/milk_tea/core/control_flow/constant_propagation.rb', line 55

def self.join_lattice(a, b)
  return b if a == UNDEF
  return a if b == UNDEF
  return NAC if a == NAC || b == NAC

  a == b ? a : NAC
end

.solve(graph, binding_resolution: nil, strict_binding_ids: false) ⇒ Object 



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# File 'lib/milk_tea/core/control_flow/constant_propagation.rb', line 23

def self.solve(graph, binding_resolution: nil, strict_binding_ids: false)
  result = Dataflow.solve(
    graph,
    direction: :forward,
    initial: -> { {} },
    join: lambda do |states|
      return {} if states.empty?

      states.reduce do |acc, state|
        keys = acc.keys | state.keys
        keys.each_with_object({}) do |k, merged|
          a = acc[k]   || UNDEF
          b = state[k] || UNDEF
          merged[k] = join_lattice(a, b)
        end
      end
    end,
    transfer: lambda do |node, in_state|
      out = in_state.dup
      node.writes_info.each do |write|
        key = write[:binding_key]
        val = eval_const(node.statement, write, in_state, binding_resolution:, strict_binding_ids:)
        out[key] = val
      end
      out
    end,
    boundary_in: { graph.entry_id => {} }
  )

  Result.new(in_states: result.in_states, out_states: result.out_states)
end