// Copyright (c) .NET Foundation and contributors. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
using System;
using System.Collections.Generic;
using Mono.Cecil.Cil;
 
namespace Mono.Linker.Dataflow
{
	static class ScannerExtensions
	{
		public static bool IsControlFlowInstruction (in this OpCode opcode)
		{
			return opcode.FlowControl == FlowControl.Branch
				|| opcode.FlowControl == FlowControl.Cond_Branch
				|| (opcode.FlowControl == FlowControl.Return && opcode.Code != Code.Ret);
		}
 
		public static HashSet<int> ComputeBranchTargets (this MethodIL methodIL)
		{
			HashSet<int> branchTargets = new HashSet<int> ();
			foreach (Instruction operation in methodIL.Instructions) {
				if (!operation.OpCode.IsControlFlowInstruction ())
					continue;
				object value = operation.Operand;
				if (value is Instruction inst) {
					branchTargets.Add (inst.Offset);
				} else if (value is Instruction[] instructions) {
					foreach (Instruction switchLabel in instructions) {
						branchTargets.Add (switchLabel.Offset);
					}
				}
			}
			foreach (ExceptionHandler einfo in methodIL.ExceptionHandlers) {
				if (einfo.HandlerType == ExceptionHandlerType.Filter) {
					branchTargets.Add (einfo.FilterStart.Offset);
				}
				branchTargets.Add (einfo.HandlerStart.Offset);
			}
			return branchTargets;
		}
	}
 
}