[dart2js] Add properties to EnumSetDomain to simplify handling offsets.

Change-Id: I4719bf415d7b29c290d59e46c4eaf2977f3650b6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/399120
Reviewed-by: Nate Biggs <[email protected]>

Author: fishythefish

pkg/compiler/lib/src/universe/side_effects.dart

@@ -15,8 +15,9 @@ enum SideEffectsFlag {
   staticProperty,
 }
 
-final _changes = EnumSetDomain<SideEffectsFlag>(0);
-final _depends = EnumSetDomain<SideEffectsFlag>(SideEffectsFlag.values.length);
+final _changes = EnumSetDomain<SideEffectsFlag>(0, SideEffectsFlag.values);
+final _depends =
+    EnumSetDomain<SideEffectsFlag>(_changes.nextOffset, SideEffectsFlag.values);
 
 class SideEffects {
   /// Tag used for identifying serialized [SideEffects] objects in a debugging
@@ -25,9 +26,9 @@ class SideEffects {
 
   Bitset _flags = Bitset.empty();
 
-  static final Bitset allChanges = _changes.allValues(SideEffectsFlag.values);
+  static final Bitset allChanges = _changes.allValues;
 
-  static final Bitset allDepends = _depends.allValues(SideEffectsFlag.values);
+  static final Bitset allDepends = _depends.allValues;
 
   SideEffects() {
     setAllSideEffects();

pkg/compiler/lib/src/util/enumset.dart

@@ -136,12 +136,15 @@ class EnumSetDomain<E extends Enum> {
   /// is equivalent to using an [EnumSet] directly.
   final int offset;
 
-  const EnumSetDomain(this.offset);
+  final Iterable<E> values;
+
+  EnumSetDomain(this.offset, this.values);
+
+  /// When composing [EnumSetDomain]s, the [offset] to use for the next domain.
+  int get nextOffset => offset + values.length;
 
   /// Returns a bitset containing all enum values in [E].
-  /// [values] is intended to be the `values` property of the enum class.
-  Bitset allValues(Iterable<E> values) =>
-      Bitset(((1 << values.length) - 1) << offset);
+  Bitset get allValues => Bitset(((1 << values.length) - 1) << offset);
 
   /// Returns a singleton bitset containing [value].
   Bitset fromValue(E value) => value.mask(offset);