pkg/vm/lib/transformations/type_flow/summary.dart

// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

/// Type flow summary of a member, function or initializer.
library vm.transformations.type_flow.summary;

import 'dart:core' hide Type;

import 'package:kernel/ast.dart' hide Statement, StatementVisitor;

import 'calls.dart';
import 'types.dart';
import 'utils.dart';

abstract class CallHandler {
  Type applyCall(
      Call callSite, Selector selector, Args<Type> args, bool isResultUsed);
}

/// Base class for all statements in a summary.
abstract class Statement extends TypeExpr {
  /// Index of this statement in the [Summary].
  int index = -1;

  @override
  Type getComputedType(List<Type> types) {
    final type = types[index];
    assertx(type != null);
    return type;
  }

  String get name => "t$index";

  @override
  String toString() => name;

  /// Prints body of this statement.
  String dump();

  /// Visit this statement by calling a corresponding [visitor] method.
  void accept(StatementVisitor visitor);

  /// Execute this statement and compute its resulting type.
  Type apply(List<Type> computedTypes, TypeHierarchy typeHierarchy,
      CallHandler callHandler);
}

/// Statement visitor.
class StatementVisitor {
  void visitDefault(TypeExpr expr) {}

  void visitParameter(Parameter expr) => visitDefault(expr);
  void visitNarrow(Narrow expr) => visitDefault(expr);
  void visitJoin(Join expr) => visitDefault(expr);
  void visitCall(Call expr) => visitDefault(expr);
}

/// Input parameter of the summary.
class Parameter extends Statement {
  final String _name;
  final Type staticType;
  Type defaultValue;
  Type _argumentType = const EmptyType();

  Parameter(this._name, this.staticType);

  String get name => _name != null ? "%$_name" : super.name;

  @override
  void accept(StatementVisitor visitor) => visitor.visitParameter(this);

  @override
  String dump() => "$name = _Parameter #$index [$staticType]";

  @override
  Type apply(List<Type> computedTypes, TypeHierarchy typeHierarchy,
          CallHandler callHandler) =>
      throw 'Unable to apply _Parameter';

  Type get argumentType => _argumentType;

  void _observeArgumentType(Type argType, TypeHierarchy typeHierarchy) {
    _argumentType = _argumentType.union(argType, typeHierarchy);
  }
}

/// Narrows down [arg] to [type].
class Narrow extends Statement {
  TypeExpr arg;
  Type type;

  Narrow(this.arg, this.type);

  @override
  void accept(StatementVisitor visitor) => visitor.visitNarrow(this);

  @override
  String dump() => "$name = _Narrow ($arg to $type)";

  @override
  Type apply(List<Type> computedTypes, TypeHierarchy typeHierarchy,
          CallHandler callHandler) =>
      arg.getComputedType(computedTypes).intersection(type, typeHierarchy);
}

/// Joins values from multiple sources. Its type is a union of [values].
class Join extends Statement {
  final String _name;
  final DartType staticType;
  final List<TypeExpr> values = <TypeExpr>[]; // TODO(alexmarkov): Set

  Join(this._name, this.staticType);

  String get name => _name ?? super.name;

  @override
  void accept(StatementVisitor visitor) => visitor.visitJoin(this);

  @override
  String dump() => "$name = _Join [$staticType] (${values.join(", ")})";

  @override
  Type apply(List<Type> computedTypes, TypeHierarchy typeHierarchy,
      CallHandler callHandler) {
    Type type = null;
    assertx(values.isNotEmpty);
    for (var value in values) {
      final valueType = value.getComputedType(computedTypes);
      type = type != null ? type.union(valueType, typeHierarchy) : valueType;
    }
    return type;
  }
}

/// Call site.
class Call extends Statement {
  final Selector selector;
  final Args<TypeExpr> args;

  Call(this.selector, this.args);

  @override
  void accept(StatementVisitor visitor) => visitor.visitCall(this);

  @override
  String dump() => "$name${isResultUsed ? '*' : ''} = _Call $selector $args";

  @override
  Type apply(List<Type> computedTypes, TypeHierarchy typeHierarchy,
      CallHandler callHandler) {
    final List<Type> argTypes = new List<Type>(args.values.length);
    for (int i = 0; i < args.values.length; i++) {
      final Type type = args.values[i].getComputedType(computedTypes);
      if (type == const EmptyType()) {
        debugPrint("Optimized call with empty arg");
        return const EmptyType();
      }
      argTypes[i] = type;
    }
    setReachable();
    if (selector is! DirectSelector) {
      _observeReceiverType(argTypes[0]);
    }
    final Type result = callHandler.applyCall(this, selector,
        new Args<Type>(argTypes, names: args.names), isResultUsed);
    if (isResultUsed) {
      _observeResultType(result, typeHierarchy);
    }
    return result;
  }

  // --- Inferred call site information. ---

  int _flags = 0;
  Type _resultType = const EmptyType();

  static const int kMonomorphic = (1 << 0);
  static const int kPolymorphic = (1 << 1);
  static const int kNullableReceiver = (1 << 2);
  static const int kResultUsed = (1 << 3);
  static const int kReachable = (1 << 4);

  Member _monomorphicTarget;

  Member get monomorphicTarget => _monomorphicTarget;

  bool get isMonomorphic => (_flags & kMonomorphic) != 0;

  bool get isPolymorphic => (_flags & kPolymorphic) != 0;

  bool get isNullableReceiver => (_flags & kNullableReceiver) != 0;

  bool get isResultUsed => (_flags & kResultUsed) != 0;

  bool get isReachable => (_flags & kReachable) != 0;

  Type get resultType => _resultType;

  void setResultUsed() {
    _flags |= kResultUsed;
  }

  void setReachable() {
    _flags |= kReachable;
  }

  void setPolymorphic() {
    _flags = (_flags & ~kMonomorphic) | kPolymorphic;
    _monomorphicTarget = null;
  }

  void addTarget(Member target) {
    if (!isPolymorphic) {
      if (isMonomorphic) {
        if (_monomorphicTarget != target) {
          setPolymorphic();
        }
      } else {
        _flags |= kMonomorphic;
        _monomorphicTarget = target;
      }
    }
  }

  void _observeReceiverType(Type receiver) {
    if (receiver is NullableType) {
      _flags |= kNullableReceiver;
    }
  }

  void _observeResultType(Type result, TypeHierarchy typeHierarchy) {
    _resultType = _resultType.union(result, typeHierarchy);
  }
}

/// Summary is a linear sequence of statements representing a type flow in
/// one member, function or initializer.
class Summary {
  final int parameterCount;
  final int requiredParameterCount;

  List<Statement> _statements = <Statement>[];
  TypeExpr result = null;

  Summary({this.parameterCount: 0, this.requiredParameterCount: 0});

  List<Statement> get statements => _statements;

  Statement add(Statement op) {
    op.index = _statements.length;
    _statements.add(op);
    return op;
  }

  void reset() {
    _statements = <Statement>[];
  }

  @override
  String toString() {
    return _statements.map((op) => op.dump()).join("\n") +
        "\n" +
        "RESULT: ${result}";
  }

  /// Apply this summary to the given arguments and return the resulting type.
  Type apply(Args<Type> arguments, TypeHierarchy typeHierarchy,
      CallHandler callHandler) {
    // TODO(alexmarkov): take named parameters into account
    final args = arguments.positional;

    assertx(args.length >= requiredParameterCount);
    assertx(args.length <= parameterCount);

    // Interpret statements sequentially, calculating the result type
    // of each statement and putting it into the 'types' list parallel
    // to `_statements`.
    //
    // After normalization, statements can only reference preceding statements
    // (they can't have forward references or loops).
    //
    // The first `parameterCount` statements are Parameters.

    List<Type> types = new List<Type>(_statements.length);

    types.setAll(0, args);

    for (int i = 0; i < args.length; i++) {
      Parameter param = _statements[i] as Parameter;
      param._observeArgumentType(args[i], typeHierarchy);
      types[i] = args[i].intersection(param.staticType, typeHierarchy);
    }

    for (int i = args.length; i < parameterCount; i++) {
      Parameter param = _statements[i] as Parameter;
      param._observeArgumentType(param.defaultValue, typeHierarchy);
      types[i] = param.defaultValue;
      assertx(types[i] != null);
    }

    for (int i = parameterCount; i < _statements.length; i++) {
      // Test if tracing is enabled to avoid expensive message formatting.
      if (kPrintTrace) {
        tracePrint("EVAL ${_statements[i].dump()}");
      }
      types[i] = _statements[i].apply(types, typeHierarchy, callHandler);
      if (kPrintTrace) {
        tracePrint("RESULT ${types[i]}");
      }
    }

    Statistics.summariesAnalyzed++;

    return result.getComputedType(types);
  }

  Args<Type> get argumentTypes {
    final positional = new List<Type>(parameterCount);
    for (int i = 0; i < parameterCount; i++) {
      Parameter param = _statements[i] as Parameter;
      positional[i] = param.argumentType;
    }
    // TODO(alexmarkov): support named parameters
    return new Args<Type>(positional);
  }
}