// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using Microsoft.CodeAnalysis.Text;

namespace Microsoft.CodeAnalysis.CodeGen
{
    internal partial class ILBuilder
    {
        /// <summary>
        /// Contains information about a label.
        /// </summary>
        private readonly struct LabelInfo
        {
            //some labels can be jumped to only with non zero stack depth.
            //all jumps must agree on the stack depth as well as if we reach the 
            //label via fall through.
            //if a label is marked before any branches to the label have been seen
            //the stack is considered to be 0.
            internal readonly int stack;
            internal readonly BasicBlock? bb;

            /// <summary>
            /// Sometimes we need to know if a label is targeted by conditional branches.
            /// For example optimizer can do optimizations of branches into outer try scopes only 
            /// if they are unconditional (because there are no conditional Leave opcodes)
            /// </summary>
            internal readonly bool targetOfConditionalBranches;

            /// <summary>
            /// Used when we see a branch, but label is not yet marked.
            /// </summary>
            internal LabelInfo(int stack, bool targetOfConditionalBranches)
                : this(null, stack, targetOfConditionalBranches)
            {
            }

            /// <summary>
            /// Used when label is marked to the code.
            /// </summary>
            internal LabelInfo(BasicBlock? bb, int stack, bool targetOfConditionalBranches)
            {
                this.stack = stack;
                this.bb = bb;
                this.targetOfConditionalBranches = targetOfConditionalBranches;
            }

            internal LabelInfo WithNewTarget(BasicBlock? bb)
            {
                return new LabelInfo(bb, this.stack, this.targetOfConditionalBranches);
            }

            internal LabelInfo SetTargetOfConditionalBranches()
            {
                return new LabelInfo(this.bb, this.stack, true);
            }
        }
    }
}
