icsharpcode-ILSpy/ICSharpCode.Decompiler/IL/Transforms/BlockTransform.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

using ICSharpCode.Decompiler.FlowAnalysis;
using ICSharpCode.Decompiler.IL.ControlFlow;
using ICSharpCode.Decompiler.Util;

namespace ICSharpCode.Decompiler.IL.Transforms
{
	/// <summary>
	/// Per-block IL transform.
	/// </summary>
	public interface IBlockTransform
	{
		/// <summary>
		/// Runs the transform on the specified block.
		/// 
		/// Note: the transform may only modify the specified block and its descendants,
		/// as well as any sibling blocks that are dominated by the specified block.
		/// </summary>
		void Run(Block block, BlockTransformContext context);
	}

	/// <summary>
	/// Parameter class holding various arguments for <see cref="IBlockTransform.Run"/>.
	/// </summary>
	public class BlockTransformContext : ILTransformContext
	{
		/// <summary>
		/// The block to process.
		/// </summary>
		/// <remarks>
		/// Should be identical to the <c>block</c> parameter to <c>IBlockTransform.Run</c>.
		/// </remarks>
		public Block Block { get; set; }

		/// <summary>
		/// The control flow node corresponding to the block being processed.
		/// </summary>
		/// <remarks>
		/// Identical to <c>ControlFlowGraph.GetNode(Block)</c>.
		/// Note: the control flow graph is not up-to-date, but was created at the start of the
		/// block transforms (before loop detection).
		/// </remarks>
		public ControlFlowNode ControlFlowNode { get; set; }

		/// <summary>
		/// Gets the control flow graph.
		/// 
		/// Note: the control flow graph is not up-to-date, but was created at the start of the
		/// block transforms (before loop detection).
		/// </summary>
		public ControlFlowGraph ControlFlowGraph { get; set; }

		/// <summary>
		/// Initially equal to Block.Instructions.Count indicating that nothing has been transformed yet.
		/// Set by <see cref="ConditionDetection"/> when another already transformed block is merged into
		/// the current block. Subsequent <see cref="IBlockTransform"/>s must update this value, for example,
		/// by resetting it to Block.Instructions.Count. <see cref="StatementTransform"/> will use this value to
		/// skip already transformed instructions.
		/// </summary>
		public int IndexOfFirstAlreadyTransformedInstruction { get; set; }

		public BlockTransformContext(ILTransformContext context) : base(context)
		{
		}
	}


	/// <summary>
	/// IL transform that runs a list of per-block transforms.
	/// </summary>
	public class BlockILTransform : IILTransform
	{
		public IList<IBlockTransform> PreOrderTransforms { get; } = new List<IBlockTransform>();
		public IList<IBlockTransform> PostOrderTransforms { get; } = new List<IBlockTransform>();

		bool running;

		public override string ToString()
		{
			return $"{nameof(BlockILTransform)} ({string.Join(", ", PreOrderTransforms.Concat(PostOrderTransforms).Select(t => t.GetType().Name))})";
		}

		public void Run(ILFunction function, ILTransformContext context)
		{
			if (running)
				throw new InvalidOperationException("Reentrancy detected. Transforms (and the CSharpDecompiler) are neither thread-safe nor re-entrant.");
			try
			{
				running = true;
				var blockContext = new BlockTransformContext(context);
				Debug.Assert(blockContext.Function == function);
				foreach (var container in function.Descendants.OfType<BlockContainer>().ToList())
				{
					context.CancellationToken.ThrowIfCancellationRequested();
					blockContext.ControlFlowGraph = new ControlFlowGraph(container, context.CancellationToken);
					VisitBlock(blockContext.ControlFlowGraph.GetNode(container.EntryPoint), blockContext);
				}
			}
			finally
			{
				running = false;
			}
		}

		/// <summary>
		/// Walks the dominator tree rooted at entryNode, calling the transforms on each block.
		/// </summary>
		void VisitBlock(ControlFlowNode entryNode, BlockTransformContext context)
		{
			IEnumerable<ControlFlowNode> Preorder(ControlFlowNode cfgNode)
			{
				// preorder processing:
				Block block = (Block)cfgNode.UserData;
				context.StepStartGroup(block.Label, block);

				context.ControlFlowNode = cfgNode;
				context.Block = block;
				context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
				block.RunTransforms(PreOrderTransforms, context);

				// process the children
				return cfgNode.DominatorTreeChildren;
			}

			foreach (var cfgNode in TreeTraversal.PostOrder(entryNode, Preorder))
			{
				// in post-order:
				Block block = (Block)cfgNode.UserData;
				context.ControlFlowNode = cfgNode;
				context.Block = block;
				context.IndexOfFirstAlreadyTransformedInstruction = block.Instructions.Count;
				block.RunTransforms(PostOrderTransforms, context);
				context.StepEndGroup();
			}
		}
	}
}