Module: MilkTea::CBackend::ControlFlowEmission

Included in:
MilkTea::CBackend
Defined in:
lib/milk_tea/core/c_backend/control_flow_emission.rb

Constant Summary collapse

INVERTED_BOOLEAN_OPS = 
{
  "==" => "!=",
  "!=" => "==",
  "<"  => ">=",
  "<=" => ">",
  ">"  => "<=",
  ">=" => "<",
}.freeze

Instance Method Summary collapse

Instance Method Details

#body_has_sequential_fallthrough?(statements) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 360

def body_has_sequential_fallthrough?(statements)
  return true if statements.empty?

  !statement_prevents_sequential_fallthrough?(statements.last)
end

#body_needs_fallback_return?(statements) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 215

def body_needs_fallback_return?(statements)
  return true if statements.empty?

  !statement_prevents_c_fallthrough?(statements.last)
end

#body_terminates?(statements) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 209

def body_terminates?(statements)
  return false if statements.empty?

  statement_terminates?(statements.last)
end

#canonicalize_top_guarded_while(statement) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 131

def canonicalize_top_guarded_while(statement)
  return statement unless constant_boolean_value(statement.condition) == true
  return statement if statement.body.empty?

  break_condition = top_guard_break_condition(statement.body.first)
  return statement unless break_condition

  IR::WhileStmt.new(
    condition: invert_break_guard_condition(break_condition),
    body: statement.body.drop(1),
  )
end

#collect_used_labels(statements) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 385

def collect_used_labels(statements)
  labels = []
  collect_used_labels_from_statements(statements, labels)
  labels.uniq
end

#collect_used_labels_from_statements(statements, labels) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 391

def collect_used_labels_from_statements(statements, labels)
  statements.each do |statement|
    case statement
    when IR::BlockStmt, IR::WhileStmt, IR::ForStmt
      collect_used_labels_from_statements(statement.body, labels)
    when IR::IfStmt
      collect_used_labels_from_statements(statement.then_body, labels)
      collect_used_labels_from_statements(statement.else_body, labels) if statement.else_body
    when IR::SwitchStmt
      statement.cases.each do |switch_case|
        collect_used_labels_from_statements(switch_case.body, labels)
      end
    when IR::GotoStmt
      labels << statement.label
    end
  end
end

#constant_boolean_value(expression) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 221

def constant_boolean_value(expression)
  case expression
  when IR::BooleanLiteral
    expression.value
  when IR::Unary
    operand = constant_boolean_value(expression.operand)
    return nil if operand.nil? || expression.operator != "not"

    !operand
  when IR::Binary
    left_int = constant_integer_value(expression.left)
    right_int = constant_integer_value(expression.right)
    if !left_int.nil? && !right_int.nil?
      return left_int == right_int if expression.operator == "=="
      return left_int != right_int if expression.operator == "!="
      return left_int < right_int if expression.operator == "<"
      return left_int <= right_int if expression.operator == "<="
      return left_int > right_int if expression.operator == ">"
      return left_int >= right_int if expression.operator == ">="
    end

    left_bool = constant_boolean_value(expression.left)
    right_bool = constant_boolean_value(expression.right)
    if !left_bool.nil? && !right_bool.nil?
      return left_bool == right_bool if expression.operator == "=="
      return left_bool != right_bool if expression.operator == "!="
      return left_bool && right_bool if expression.operator == "and"
      return left_bool || right_bool if expression.operator == "or"
    end

    nil
  else
    nil
  end
end

#constant_integer_value(expression) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 257

def constant_integer_value(expression)
  case expression
  when IR::IntegerLiteral
    expression.value
  when IR::Unary
    operand = constant_integer_value(expression.operand)
    return nil if operand.nil?

    return operand if expression.operator == "+"
    return -operand if expression.operator == "-"

    nil
  else
    nil
  end
end

#contains_visible_loop_exit?(statements) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 366

def contains_visible_loop_exit?(statements)
  statements.any? do |statement|
    case statement
    when IR::BreakStmt, IR::GotoStmt
      true
    when IR::BlockStmt
      contains_visible_loop_exit?(statement.body)
    when IR::IfStmt
      contains_visible_loop_exit?(statement.then_body) || (statement.else_body && contains_visible_loop_exit?(statement.else_body))
    when IR::SwitchStmt
      statement.cases.any? { |switch_case| contains_visible_loop_exit?(switch_case.body) }
    when IR::WhileStmt, IR::ForStmt
      false
    else
      false
    end
  end
end

#emit_if_statement(statement, level, function:, used_labels:, loop_continue_label: nil, loop_break_label: nil) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 171

def emit_if_statement(statement, level, function:, used_labels:, loop_continue_label: nil, loop_break_label: nil)
  indent = INDENT * level

  case constant_boolean_value(statement.condition)
  when true
    return emit_statement(IR::BlockStmt.new(body: statement.then_body), level, function:, used_labels:, loop_continue_label:, loop_break_label:)
  when false
    return [] unless statement.else_body && !statement.else_body.empty?

    return emit_statement(IR::BlockStmt.new(body: statement.else_body), level, function:, used_labels:, loop_continue_label:, loop_break_label:)
  end

  lines = ["#{indent}if (#{emit_expression(statement.condition)}) {"]
  lines.concat(emit_statement_sequence(statement.then_body, level + 1, function:, used_labels:, loop_continue_label:, loop_break_label:))

  nested_else_if = nested_else_if_statement(statement.else_body)
  if nested_else_if
    nested_lines = emit_if_statement(nested_else_if, level, function:, used_labels:, loop_continue_label:, loop_break_label:)
    lines << "#{indent}} else #{nested_lines.first.sub(/^#{Regexp.escape(indent)}/, "") }"
    lines.concat(nested_lines.drop(1))
    return lines
  end

  if statement.else_body && !statement.else_body.empty?
    lines << "#{indent}} else {"
    lines.concat(emit_statement_sequence(statement.else_body, level + 1, function:, used_labels:, loop_continue_label:, loop_break_label:))
  end
  lines << "#{indent}}"
  lines
end

#emit_switch_as_if_statement(statement, level, function:, used_labels:, loop_continue_label:, loop_break_label:) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 96

def emit_switch_as_if_statement(statement, level, function:, used_labels:, loop_continue_label:, loop_break_label:)
  explicit_cases = statement.cases.select { |switch_case| switch_case.is_a?(IR::SwitchCase) }
  default_case = statement.cases.find { |switch_case| switch_case.is_a?(IR::SwitchDefaultCase) }

  condition, then_body, else_body = if default_case
    explicit_case = explicit_cases.first
    [
      IR::Binary.new(operator: "==", left: statement.expression, right: explicit_case.value, type: nil),
      strip_terminal_switch_break(explicit_case.body),
      strip_terminal_switch_break(default_case.body),
    ]
  else
    [
      IR::Binary.new(operator: "==", left: statement.expression, right: explicit_cases.first.value, type: nil),
      strip_terminal_switch_break(explicit_cases.first.body),
      strip_terminal_switch_break(explicit_cases.last.body),
    ]
  end

  emit_if_statement(
    IR::IfStmt.new(condition:, then_body:, else_body:),
    level,
    function:,
    used_labels:,
    loop_continue_label:,
    loop_break_label:,
  )
end

#invert_break_guard_condition(expression) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 152

def invert_break_guard_condition(expression)
  case expression
  when IR::BooleanLiteral
    IR::BooleanLiteral.new(value: !expression.value, type: expression.type)
  when IR::Unary
    return expression.operand if expression.operator == "not"
  when IR::Binary
    if (operator = inverted_boolean_operator(expression.operator))
      return IR::Binary.new(operator:, left: expression.left, right: expression.right, type: expression.type)
    end
  end

  IR::Unary.new(operator: "not", operand: expression, type: expression.type)
end

#inverted_boolean_operator(operator) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 167

def inverted_boolean_operator(operator)
  INVERTED_BOOLEAN_OPS[operator]
end

#loop_break_label_name(statements, remaining_statements) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 25

def loop_break_label_name(statements, remaining_statements)
  return if remaining_statements.empty?

  label = remaining_statements.first
  return unless label.is_a?(IR::LabelStmt)
  return unless statements_reference_label?(statements, label.name)

  label.name
end

#loop_continue_label_name(statements) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 15

def loop_continue_label_name(statements)
  return if statements.empty?

  label = statements.last
  return unless label.is_a?(IR::LabelStmt)
  return unless label.name.include?("loop_continue")

  label.name
end

#nested_else_if_statement(else_body) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 202

def nested_else_if_statement(else_body)
  return unless else_body && else_body.length == 1

  nested = else_body.first
  nested if nested.is_a?(IR::IfStmt)
end

#statement_needs_explicit_break_label_after_emission?(statement, label_name, loop_break_label_active:) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 61

def statement_needs_explicit_break_label_after_emission?(statement, label_name, loop_break_label_active:)
  case statement
  when IR::BlockStmt, IR::IfStmt
    then_body = statement.is_a?(IR::IfStmt) ? statement.then_body : statement.body
    else_body = statement.is_a?(IR::IfStmt) ? statement.else_body : nil
    statements_need_explicit_break_label_after_emission?(then_body, label_name, loop_break_label_active:) ||
      (else_body && statements_need_explicit_break_label_after_emission?(else_body, label_name, loop_break_label_active:))
  when IR::WhileStmt, IR::ForStmt
    statements_need_explicit_break_label_after_emission?(statement.body, label_name, loop_break_label_active: false)
  when IR::SwitchStmt
    return false unless statement_references_label?(statement, label_name)

    active = loop_break_label_active && switch_emittable_as_if?(statement, loop_break_label: label_name)
    statements_need_explicit_break_label_after_emission?(
      statement.cases.flat_map(&:body),
      label_name,
      loop_break_label_active: active,
    )
  when IR::GotoStmt
    statement.label == label_name && !loop_break_label_active
  else
    false
  end
end

#statement_prevents_c_fallthrough?(statement) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 293

def statement_prevents_c_fallthrough?(statement)
  case statement
  when IR::ReturnStmt
    true
  when IR::BlockStmt
    !body_needs_fallback_return?(statement.body)
  when IR::IfStmt
    statement.else_body && !body_needs_fallback_return?(statement.then_body) && !body_needs_fallback_return?(statement.else_body)
  when IR::SwitchStmt
    switch_statement_prevents_outer_fallthrough?(statement)
  when IR::WhileStmt
    constant_boolean_value(statement.condition) == true && !contains_visible_loop_exit?(statement.body)
  else
    false
  end
end

#statement_prevents_sequential_fallthrough?(statement) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 310

def statement_prevents_sequential_fallthrough?(statement)
  case statement
  when IR::ReturnStmt, IR::BreakStmt, IR::ContinueStmt, IR::GotoStmt
    true
  when IR::BlockStmt
    !body_has_sequential_fallthrough?(statement.body)
  when IR::IfStmt
    statement.else_body && !body_has_sequential_fallthrough?(statement.then_body) && !body_has_sequential_fallthrough?(statement.else_body)
  when IR::SwitchStmt
    switch_statement_prevents_outer_fallthrough?(statement)
  when IR::WhileStmt
    constant_boolean_value(statement.condition) == true && !contains_visible_loop_exit?(statement.body)
  else
    false
  end
end

#statement_references_label?(statement, label_name) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 39

def statement_references_label?(statement, label_name)
  case statement
  when IR::BlockStmt, IR::WhileStmt, IR::ForStmt
    statements_reference_label?(statement.body, label_name)
  when IR::IfStmt
    statements_reference_label?(statement.then_body, label_name) ||
      (statement.else_body && statements_reference_label?(statement.else_body, label_name))
  when IR::SwitchStmt
    statement.cases.any? { |switch_case| statements_reference_label?(switch_case.body, label_name) }
  when IR::GotoStmt
    statement.label == label_name
  else
    false
  end
end

#statement_terminates?(statement) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 274

def statement_terminates?(statement)
  case statement
  when IR::ReturnStmt
    true
  when IR::BreakStmt, IR::ContinueStmt
    true
  when IR::GotoStmt
    true
  when IR::BlockStmt
    body_terminates?(statement.body)
  when IR::IfStmt
    statement.else_body && body_terminates?(statement.then_body) && body_terminates?(statement.else_body)
  when IR::SwitchStmt
    switch_statement_prevents_outer_fallthrough?(statement)
  else
    false
  end
end

#statements_need_explicit_break_label_after_emission?(statements, label_name, loop_break_label_active:) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 55

def statements_need_explicit_break_label_after_emission?(statements, label_name, loop_break_label_active:)
  statements.any? do |statement|
    statement_needs_explicit_break_label_after_emission?(statement, label_name, loop_break_label_active:)
  end
end

#statements_reference_label?(statements, label_name) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 35

def statements_reference_label?(statements, label_name)
  statements.any? { |statement| statement_references_label?(statement, label_name) }
end

#strip_terminal_switch_break(statements) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 125

def strip_terminal_switch_break(statements)
  return statements unless statements.last.is_a?(IR::BreakStmt)

  statements[0...-1]
end

#switch_case_body_prevents_outer_fallthrough?(statements) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 333

def switch_case_body_prevents_outer_fallthrough?(statements)
  return false if statements.empty?

  switch_case_statement_prevents_outer_fallthrough?(statements.last)
end

#switch_case_statement_prevents_outer_fallthrough?(statement) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 339

def switch_case_statement_prevents_outer_fallthrough?(statement)
  case statement
  when IR::ReturnStmt, IR::ContinueStmt, IR::GotoStmt
    true
  when IR::BreakStmt
    false
  when IR::BlockStmt
    switch_case_body_prevents_outer_fallthrough?(statement.body)
  when IR::IfStmt
    statement.else_body &&
      switch_case_body_prevents_outer_fallthrough?(statement.then_body) &&
      switch_case_body_prevents_outer_fallthrough?(statement.else_body)
  when IR::SwitchStmt
    switch_statement_prevents_outer_fallthrough?(statement)
  when IR::WhileStmt
    constant_boolean_value(statement.condition) == true && !contains_visible_loop_exit?(statement.body)
  else
    false
  end
end

#switch_emittable_as_if?(statement, loop_break_label: nil) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 86

def switch_emittable_as_if?(statement, loop_break_label: nil)
  return false unless loop_break_label
  return false unless statement.exhaustive
  return false unless statement.cases.length == 2
  return false unless side_effect_free_expression?(statement.expression)
  return false unless statement_references_label?(statement, loop_break_label)

  statement.cases.count { |switch_case| switch_case.is_a?(IR::SwitchDefaultCase) } <= 1
end

#switch_statement_prevents_outer_fallthrough?(statement) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 327

def switch_statement_prevents_outer_fallthrough?(statement)
  return false unless statement.exhaustive && statement.cases.any?

  statement.cases.all? { |switch_case| switch_case_body_prevents_outer_fallthrough?(switch_case.body) }
end

#top_guard_break_condition(statement) ⇒ Object 



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# File 'lib/milk_tea/core/c_backend/control_flow_emission.rb', line 144

def top_guard_break_condition(statement)
  return unless statement.is_a?(IR::IfStmt)
  return unless statement.else_body.nil? || statement.else_body.empty?
  return unless statement.then_body.length == 1 && statement.then_body.first.is_a?(IR::BreakStmt)

  statement.condition
end