// <summary>
        //   Creates a new flow branching which is contained in `parent'.
        //   You should only pass non-null for the `block' argument if this block
        //   introduces any new variables - in this case, we need to create a new
        //   usage vector with a different size than our parent's one.
        // </summary>
        protected FlowBranching(FlowBranching parent, BranchingType type, SiblingType stype,
            Block block, Location loc)
        {
            Parent = parent;
            Block = block;
            Location = loc;
            Type = type;
            id = ++next_id;

            UsageVector vector;
            if (Block != null) {
                UsageVector parent_vector = parent != null ? parent.CurrentUsageVector : null;
                vector = new UsageVector (stype, parent_vector, Block, loc, Block.AssignableSlots);
            } else {
                vector = new UsageVector (stype, Parent.CurrentUsageVector, null, loc);
            }

            AddSibling (vector);
        }

		public FlowBranchingContinuable (FlowBranching parent, BranchingType type, SiblingType stype, Block block, Location loc)
			: base (parent, type, stype, block, loc)
		{ }

		// <summary>
		//   Creates a sibling of the current usage vector.
		// </summary>
		public virtual void CreateSibling (Block block, SiblingType type)
		{
			UsageVector vector = new UsageVector (
				type, Parent.CurrentUsageVector, block, Location);
			AddSibling (vector);

			Report.Debug (1, "  CREATED SIBLING", CurrentUsageVector);
		}

			private UsageVector (MyBitVector locals, bool is_unreachable, Block block, Location loc)
			{
				this.Type = SiblingType.Block;
				this.Location = loc;
				this.Block = block;

				this.is_unreachable = is_unreachable;

				this.locals = locals;

				id = ++next_id;

			}