BranchLabel.cs :  » Script » IronPython » Microsoft » Scripting » Interpreter » C# / CSharp Open Source

/* ****************************************************************************
 *
 * Copyright (c) Microsoft Corporation. 
 *
 * This source code is subject to terms and conditions of the Microsoft Public License. A 
 * copy of the license can be found in the License.html file at the root of this distribution. If 
 * you cannot locate the  Microsoft Public License, please send an email to 
 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound 
 * by the terms of the Microsoft Public License.
 *
 * You must not remove this notice, or any other, from this software.
 *
 *
 * ***************************************************************************/

using System;
using System.Diagnostics;
using System.Collections.Generic;
using Microsoft.Scripting.Utils;

namespace Microsoft.Scripting.Interpreter{
    internal struct RuntimeLabel {
        public readonly int Index;
        public readonly int StackDepth;
        public readonly int ContinuationStackDepth;

        public RuntimeLabel(int index, int continuationStackDepth, int stackDepth) {
            Index = index;
            ContinuationStackDepth = continuationStackDepth;
            StackDepth = stackDepth;
        }

        public override string ToString() {
            return String.Format("->{0} C({1}) S({2})", Index, ContinuationStackDepth, StackDepth);
        }
    }

    public sealed class BranchLabel {
        internal const int UnknownIndex = Int32.MinValue;
        internal const int UnknownDepth = Int32.MinValue;

        internal int _labelIndex = UnknownIndex;
        internal int _targetIndex = UnknownIndex;
        internal int _stackDepth = UnknownDepth;
        internal int _continuationStackDepth = UnknownDepth;

        // Offsets of forward branching instructions targetting this label 
        // that need to be updated after we emit the label.
        private List<int> _forwardBranchFixups;

        public BranchLabel() {
        }

        internal int LabelIndex {
            get { return _labelIndex; }
            set { _labelIndex = value; }
        }

        internal bool HasRuntimeLabel {
            get { return _labelIndex != UnknownIndex; } 
        }

        internal int TargetIndex {
            get { return _targetIndex; }
        }

        internal RuntimeLabel ToRuntimeLabel() {
            Debug.Assert(_targetIndex != UnknownIndex && _stackDepth != UnknownDepth && _continuationStackDepth != UnknownDepth);
            return new RuntimeLabel(_targetIndex, _continuationStackDepth, _stackDepth);
        }

        internal void Mark(InstructionList instructions) {
            ContractUtils.Requires(_targetIndex == UnknownIndex && _stackDepth == UnknownDepth && _continuationStackDepth == UnknownDepth);

            _stackDepth = instructions.CurrentStackDepth;
            _continuationStackDepth = instructions.CurrentContinuationsDepth;
            _targetIndex = instructions.Count;

            if (_forwardBranchFixups != null) {
                foreach (var branchIndex in _forwardBranchFixups) {
                    FixupBranch(instructions, branchIndex);
                }
                _forwardBranchFixups = null;
            }
        }

        internal void AddBranch(InstructionList instructions, int branchIndex) {
            Debug.Assert(((_targetIndex == UnknownIndex) == (_stackDepth == UnknownDepth)));
            Debug.Assert(((_targetIndex == UnknownIndex) == (_continuationStackDepth == UnknownDepth)));

            if (_targetIndex == UnknownIndex) {
                if (_forwardBranchFixups == null) {
                    _forwardBranchFixups = new List<int>();
                }
                _forwardBranchFixups.Add(branchIndex);
            } else {
                FixupBranch(instructions, branchIndex);
            }
        }

        internal void FixupBranch(InstructionList instructions, int branchIndex) {
            Debug.Assert(_targetIndex != UnknownIndex);
            instructions.FixupBranch(branchIndex, _targetIndex - branchIndex, _continuationStackDepth, _stackDepth);
        }
    }


}