pkg/compiler/lib/src/ssa/graph_builder.dart

// Copyright (c) 2016, 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.

import '../elements/elements.dart';
import '../types/types.dart';
import 'nodes.dart';

/// Base class for objects that build up an SSA graph.
///
/// This contains helpers for building the graph and tracking information about
/// the current state of the graph being built.
abstract class GraphBuilder {
  /// Holds the resulting SSA graph.
  final HGraph graph = new HGraph();

  HBasicBlock _current;

  /// The current block to add instructions to. Might be null, if we are
  /// visiting dead code, but see [isReachable].
  HBasicBlock get current => _current;

  void set current(c) {
    isReachable = c != null;
    _current = c;
  }

  /// The most recently opened block. Has the same value as [current] while
  /// the block is open, but unlike [current], it isn't cleared when the
  /// current block is closed.
  HBasicBlock lastOpenedBlock;

  /// Indicates whether the current block is dead (because it has a throw or a
  /// return further up). If this is false, then [current] may be null. If the
  /// block is dead then it may also be aborted, but for simplicity we only
  /// abort on statement boundaries, not in the middle of expressions. See
  /// [isAborted].
  bool isReachable = true;

  HParameterValue lastAddedParameter;

  Map<ParameterElement, HInstruction> parameters =
      <ParameterElement, HInstruction>{};

  HBasicBlock addNewBlock() {
    HBasicBlock block = graph.addNewBlock();
    // If adding a new block during building of an expression, it is due to
    // conditional expressions or short-circuit logical operators.
    return block;
  }

  void open(HBasicBlock block) {
    block.open();
    current = block;
    lastOpenedBlock = block;
  }

  HBasicBlock close(HControlFlow end) {
    HBasicBlock result = current;
    current.close(end);
    current = null;
    return result;
  }

  HBasicBlock closeAndGotoExit(HControlFlow end) {
    HBasicBlock result = current;
    current.close(end);
    current = null;
    result.addSuccessor(graph.exit);
    return result;
  }

  void goto(HBasicBlock from, HBasicBlock to) {
    from.close(new HGoto());
    from.addSuccessor(to);
  }

  bool isAborted() {
    return current == null;
  }

  /// Creates a new block, transitions to it from any current block, and
  /// opens the new block.
  HBasicBlock openNewBlock() {
    HBasicBlock newBlock = addNewBlock();
    if (!isAborted()) goto(current, newBlock);
    open(newBlock);
    return newBlock;
  }

  void add(HInstruction instruction) {
    current.add(instruction);
  }

  HParameterValue addParameter(Entity parameter, TypeMask type) {
    HParameterValue result = new HParameterValue(parameter, type);
    if (lastAddedParameter == null) {
      graph.entry.addBefore(graph.entry.first, result);
    } else {
      graph.entry.addAfter(lastAddedParameter, result);
    }
    lastAddedParameter = result;
    return result;
  }
}