anchor.diff:          b = b._previous;
         }
       }
  -    while (imports.isNotEmpty) {
  -      result = result._add(imports.removeLast());
  +
  +    // Add merged elements back in reverse order. It is tempting to pop them off
  +    // with `removeLast()` but that causes measurable shrinking reallocations.
  +    for (int i = imports.length - 1; i >= 0; i--) {
  +      result = result._add(imports[i]);
       }
       return result;
     }
  
positive.code:   }
  
    /// Links to other import sets in the lattice by adding one import.
    final Map<_DeferredImport, ImportSet> _transitions = {};
  
    ImportSet.empty()
        : _import = null,
  
negative.code: import 'universe/use.dart';
  import 'universe/world_impact.dart'
      show ImpactUseCase, WorldImpact, WorldImpactVisitorImpl;
  import 'util/maplet.dart';
  import 'util/util.dart' show makeUnique;
  import 'world.dart' show KClosedWorld;
  
  