dart2js cps: Refactor tracking of side effects.

pkg/compiler/lib/src/cps_ir/effects.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.
+library dart2js.cps_ir.effects;
+
+import 'dart:typed_data';
+import '../universe/side_effects.dart' show SideEffects;
+
+/// Bitmasks for tracking non-local side effects and dependencies.
+///
+/// All effects must be attributed to an effect area.  The `other` area is a
+/// catch-all for any effect that does not belong to any of the specific areas;
+/// this includes external effects such as printing to the console.
+class Effects {
+  // Effect areas.
+  // These are bit positions, not bit masks. They are private because it is
+  // otherwise easy to mistake them for bitmasks.
+  static const int _staticField = 0;
+  static const int _instanceField = 1;
+  static const int _indexableContent = 2;
+  static const int _indexableLength = 3;
+  static const int _other = 4;
+  static const int numberOfEffectAreas = 5;
+
+  // Bitmasks for computation that modifies state in a given area.
+  static const int _changes = 1;
+  static const int changesStaticField = _changes << _staticField;
+  static const int changesInstanceField = _changes << _instanceField;
+  static const int changesIndexableContent = _changes << _indexableContent;
+  static const int changesIndexableLength = _changes << _indexableLength;
+  static const int changesOther = _changes << _other;

[Siggi Cherem (dart-lang), 2016/02/17 20:53:23]

I didn't see the `other` area used anywhere in the different phases. What's the
purpose you have in mind for it?

[asgerf, 2016/02/29 12:48:17]

It's just to ensure that these bits form a proper partition of all effects.

E.g. so "effects == 0" actually guarantees that there are no non-local side
effects.

+
+  static const int changesAll =
+      changesStaticField |
+      changesInstanceField |
+      changesIndexableContent |
+      changesIndexableLength |
+      changesOther;
+
+  // Bitmasks for computation that depends on state in a given area.
+  static const int _depends = 1 << numberOfEffectAreas;
+  static const int dependsOnStaticField = _depends << _staticField;
+  static const int dependsOnInstanceField = _depends << _instanceField;
+  static const int dependsOnIndexableContent = _depends << _indexableContent;
+  static const int dependsOnIndexableLength = _depends << _indexableLength;
+  static const int dependsOnOther = _depends << _other;
+
+  static const int dependsOnAll =
+      dependsOnStaticField |
+      dependsOnInstanceField |
+      dependsOnIndexableContent |
+      dependsOnIndexableLength |
+      dependsOnOther;
+
+  static const int all = changesAll | dependsOnAll;
+  static const int none = 0;
+
+  static int _changesArea(int effectArea) => _changes << effectArea;
+
+  static int _dependsOnArea(int effectArea) => _depends << effectArea;
+
+  static int changesToDepends(int changesFlags) {
+    return (changesFlags & changesAll) << numberOfEffectAreas;
+  }
+
+  static int dependsToChanges(int dependsFlags) {
+    return (dependsFlags & dependsOnAll) >> numberOfEffectAreas;
+  }
+
+  /// Converts [SideEffects] from a JS annotation or type inference to the
+  /// more fine-grained flag set.
+  //
+  // TODO(asgerf): Once we finalize the set of flags to use, unify the two
+  //               systems.
+  static int from(SideEffects fx) {
+    int result = 0;
+    if (fx.changesInstanceProperty()) {
+      result |= changesInstanceField;
+    }
+    if (fx.changesStaticProperty()) {
+      result |= changesStaticField;
+    }
+    if (fx.changesIndex()) {
+      result |= changesIndexableContent | changesIndexableLength;
+    }
+    if (fx.hasSideEffects()) {
+      result |= changesOther;
+    }
+    if (fx.dependsOnInstancePropertyStore()) {
+      result |= dependsOnInstanceField;
+    }
+    if (fx.dependsOnStaticPropertyStore()) {
+      result |= dependsOnStaticField;
+    }
+    if (fx.dependsOnIndexStore()) {
+      result |= dependsOnIndexableContent | dependsOnIndexableLength;
+    }
+    if (fx.dependsOnSomething()) {
+      result |= dependsOnOther;
+    }
+    return result;
+  }
+}
+
+/// Creates fresh IDs to ensure effect numbers do not clash with each other.
+class EffectNumberer {
+  int _id = 0;
+  int next() => ++_id;
+
+  /// Special effect number that can be used in place for an effect area that
+  /// is irrelevant for a computation.
+  ///
+  /// This value is never returned by [next].
+  static const int none = 0;
+}
+
+/// A mutable vector of effect numbers, one for each effect area.
+///
+/// Effect numbers are used to identify regions of code wherein the given
+/// effect area is unmodified.
+class EffectNumbers {
+  final Int32List _effectNumbers = new Int32List(Effects.numberOfEffectAreas);
+
+  EffectNumbers._zero();
+
+  EffectNumbers.fresh(EffectNumberer numberer) {
+    reset(numberer);
+  }
+
+  EffectNumbers copy() {
+    return new EffectNumbers._zero().._effectNumbers.setAll(0, _effectNumbers);
+  }
+
+  int operator[](int i) => _effectNumbers[i];
+
+  void operator[]=(int i, int value) {
+    _effectNumbers[i] = value;
+  }
+
+  int get staticField => _effectNumbers[Effects._staticField];
+  int get instanceField => _effectNumbers[Effects._instanceField];
+  int get indexableContent => _effectNumbers[Effects._indexableContent];
+  int get indexableLength => _effectNumbers[Effects._indexableLength];
+  int get other => _effectNumbers[Effects._other];
+
+  void set staticField(int n) {
+    _effectNumbers[Effects._staticField] = n;
+  }
+  void set instanceField(int n) {
+    _effectNumbers[Effects._instanceField] = n;
+  }
+  void set indexableContent(int n) {
+    _effectNumbers[Effects._indexableContent] = n;
+  }
+  void set indexableLength(int n) {
+    _effectNumbers[Effects._indexableLength] = n;
+  }
+  void set other(int n) {
+    _effectNumbers[Effects._other] = n;
+  }
+
+  void reset(EffectNumberer numberer) {
+    for (int i = 0; i < Effects.numberOfEffectAreas; ++i) {
+      _effectNumbers[i] = numberer.next();
+    }
+  }
+
+  void join(EffectNumberer numberer, EffectNumbers other) {
+    for (int i = 0; i < Effects.numberOfEffectAreas; ++i) {
+      if (_effectNumbers[i] != other._effectNumbers[i]) {
+        _effectNumbers[i] = numberer.next();
+      }
+    }
+  }
+
+  void change(EffectNumberer numberer, int changeFlags) {
+    for (int i = 0; i < Effects.numberOfEffectAreas; ++i) {
+      if (changeFlags & Effects._changesArea(i) != 0) {
+        _effectNumbers[i] = numberer.next();
+      }
+    }
+  }
+
+  /// Builds a vector where all entries that are not depended on are replaced
+  /// by [EffectNumberer.none].
+  //
+  // TODO(asgerf): Use this in GVN to simplify the dispatching code.
+  List<int> getDependencies(int dependsFlags) {
+    Int32List copy = new Int32List.fromList(_effectNumbers);
+    for (int i = 0; i < Effects.numberOfEffectAreas; ++i) {
+      if (dependsFlags & Effects._dependsOnArea(i) == 0) {
+        copy[i] = EffectNumberer.none;
+      }
+    }
+    return copy;
+  }
+}