ForwardScanOrder.cs

/*
    Copyright (C) 2011-2015 de4dot@gmail.com

    This file is part of de4dot.

    de4dot is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    de4dot is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with de4dot.  If not, see <http://www.gnu.org/licenses/>.
*/

using System;
using System.Collections.Generic;
using dnlib.DotNet.Emit;

namespace de4dot.blocks {
	// This class makes sure that each block that is entered with a non-empty stack has at
	// least one of its source blocks sorted before itself. This is to make sure peverify
	// doesn't complain AND also to make sure dnlib sets the correct maxstack.
	class ForwardScanOrder {
		ScopeBlock scopeBlock;
		IList<BaseBlock> sorted;
		Dictionary<BaseBlock, BlockInfo> blockInfos = new Dictionary<BaseBlock, BlockInfo>();
		Dictionary<BaseBlock, bool> inNewList = new Dictionary<BaseBlock, bool>();
		List<BaseBlock> newList;

		class BlockInfo {
			BaseBlock baseBlock;
			public int stackStart = 0;
			public int stackEnd = 0;

			public BlockInfo(BaseBlock baseBlock, int stackStart) {
				this.baseBlock = baseBlock;
				this.stackStart = stackStart;
			}

			public void CalculateStackUsage() {
				var block = baseBlock as Block;
				if (block == null) {
					stackEnd = stackStart;
					return;
				}

				int stack = stackStart;
				foreach (var instr in block.Instructions)
					instr.Instruction.UpdateStack(ref stack, false);
				stackEnd = stack;
			}
		}

		public ForwardScanOrder(ScopeBlock scopeBlock, IList<BaseBlock> sorted) {
			this.scopeBlock = scopeBlock;
			this.sorted = sorted;
		}

		public List<BaseBlock> Fix() {
			CreateBlockInfos();
			CreateNewList();
			return newList;
		}

		void CreateBlockInfos() {
			int firstBlockStackStart = 0;
			if ((scopeBlock is HandlerBlock || scopeBlock is FilterHandlerBlock) &&
				scopeBlock.Parent is TryHandlerBlock tryHandlerBlock &&
				(tryHandlerBlock.HandlerType == ExceptionHandlerType.Catch || tryHandlerBlock.HandlerType == ExceptionHandlerType.Filter)) {
				firstBlockStackStart = 1;
			}
			foreach (var bb in GetStartBlocks()) {
				int stackStart = ReferenceEquals(bb, sorted[0]) ? firstBlockStackStart : 0;
				ScanBaseBlock(bb, stackStart);
			}

			// One reason for this to fail is if there are still dead blocks left. Could also
			// be a bug in the code.
			if (blockInfos.Count != sorted.Count)
				throw new ApplicationException($"Didn't add all blocks: {blockInfos.Count} vs {sorted.Count}");
		}

		IEnumerable<BaseBlock> GetStartBlocks() {
			if (sorted.Count > 0) {
				yield return sorted[0];
				foreach (var bb in sorted) {
					if (ReferenceEquals(bb, sorted[0]))
						continue;
					var block = bb as Block;
					if (block == null || block.Sources == null || IsOneSourceInAnotherScopeBlock(block))
						yield return bb;
				}
			}
		}

		bool IsOneSourceInAnotherScopeBlock(Block block) {
			foreach (var source in block.Sources) {
				if (!scopeBlock.IsOurBaseBlock(source))
					return true;
			}
			return false;
		}

		struct ScanBaseBlockState {
			public BaseBlock bb;
			public int stackStart;
			public ScanBaseBlockState(BaseBlock bb, int stackStart) {
				this.bb = bb;
				this.stackStart = stackStart;
			}
		}
		Stack<ScanBaseBlockState> scanBaseBlockStack = new Stack<ScanBaseBlockState>();
		void ScanBaseBlock(BaseBlock bb, int stackStart) {
			scanBaseBlockStack.Push(new ScanBaseBlockState(bb, stackStart));
			while (scanBaseBlockStack.Count > 0) {
				var state = scanBaseBlockStack.Pop();
				if (blockInfos.ContainsKey(state.bb) || !scopeBlock.IsOurBaseBlock(state.bb))
					continue;

				var blockInfo = new BlockInfo(state.bb, state.stackStart);
				blockInfos[state.bb] = blockInfo;

				var block = state.bb as Block;
				if (block == null) {	// i.e., if try, filter, or handler block
					// It's not important to know the exact values, so we set them both to 0.
					// Compilers must make sure the stack is empty when entering a try block.
					blockInfo.stackStart = blockInfo.stackEnd = 0;
					continue;
				}

				blockInfo.CalculateStackUsage();

				foreach (var target in block.GetTargets())
					scanBaseBlockStack.Push(new ScanBaseBlockState(target, blockInfo.stackEnd));
			}
		}

		void CreateNewList() {
			newList = new List<BaseBlock>(sorted.Count);
			foreach (var bb in sorted)
				AddToNewList(bb);
			if (newList.Count != sorted.Count)
				throw new ApplicationException($"Too many/few blocks after sorting: {newList.Count} vs {sorted.Count}");
			if (newList.Count > 0 && !ReferenceEquals(newList[0], sorted[0]))
				throw new ApplicationException("Start block is not first block after sorting");
		}

		void AddToNewList(BaseBlock bb) {
			if (inNewList.ContainsKey(bb) || !scopeBlock.IsOurBaseBlock(bb))
				return;
			inNewList[bb] = false;

			var blockInfo = blockInfos[bb];
			var block = bb as Block;
			if (blockInfo.stackStart == 0 || ReferenceEquals(bb, sorted[0]) ||
				block == null || block.Sources == null || IsInNewList(block.Sources)) {
			}
			else {
				foreach (var source in block.Sources) {
					if (!scopeBlock.IsOurBaseBlock(source))
						continue;
					int oldCount = newList.Count;
					AddToNewList(source);	// Make sure it's before this block
					if (oldCount != newList.Count)
						break;
				}
			}

			inNewList[bb] = true;
			newList.Add(bb);
		}

		bool IsInNewList(IEnumerable<Block> blocks) {
			foreach (var block in blocks) {
				if (inNewList.ContainsKey(block) && inNewList[block])
					return true;
			}
			return false;
		}
	}
}