assembly-tool/de4dot/de4dot.blocks/Block.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 {
	public class Block : BaseBlock {
		List<Instr> instructions = new List<Instr>();

		// List of all explicit (non-fall-through) targets. It's just one if it's a normal
		// branch, but if it's a switch, it could be many targets.
		List<Block> targets;

		// This is the fall through Block (non branch instructions)
		Block fallThrough;

		// All blocks that fall through or branches to this block
		List<Block> sources = new List<Block>();

		public Block FallThrough {
			get => fallThrough;
			set => fallThrough = value;
		}

		public List<Block> Targets {
			get => targets;
			set => targets = value;
		}

		public List<Block> Sources => sources;

		public Instr FirstInstr {
			get {
				if (instructions.Count == 0)
					Add(new Instr(OpCodes.Nop.ToInstruction()));
				return instructions[0];
			}
		}

		public Instr LastInstr {
			get {
				if (instructions.Count == 0)
					Add(new Instr(OpCodes.Nop.ToInstruction()));
				return instructions[instructions.Count - 1];
			}
		}

		public void Add(Instr instr) => instructions.Add(instr);
		public void Insert(int index, Instruction instr) => instructions.Insert(index, new Instr(instr));

		public List<Instr> Instructions => instructions;

		// If last instr is a br/br.s, removes it and replaces it with a fall through
		public void RemoveLastBr() {
			if (!LastInstr.IsBr())
				return;

			if (fallThrough != null || (LastInstr.Operand != null && (targets == null || targets.Count != 1)))
				throw new ApplicationException("Invalid block state when last instr is a br/br.s");
			fallThrough = LastInstr.Operand != null ? targets[0] : null;
			targets = null;
			instructions.RemoveAt(instructions.Count - 1);
		}

		public void Replace(int index, int num, Instruction instruction) {
			if (num <= 0)
				throw new ArgumentOutOfRangeException("num");
			Remove(index, num);
			instructions.Insert(index, new Instr(instruction));
		}

		public void Remove(int index, int num) {
			if (index + num > instructions.Count)
				throw new ApplicationException("Overflow");
			if (num > 0 && index + num == instructions.Count && LastInstr.IsConditionalBranch())
				DisconnectFromFallThroughAndTargets();
			instructions.RemoveRange(index, num);
		}

		public void Remove(IEnumerable<int> indexes) {
			var instrsToDelete = new List<int>(Utils.Unique(indexes));
			instrsToDelete.Sort();
			instrsToDelete.Reverse();
			foreach (var index in instrsToDelete)
				Remove(index, 1);
		}

		// Replace the last instructions with a branch to target
		public void ReplaceLastInstrsWithBranch(int numInstrs, Block target) {
			if (numInstrs < 0 || numInstrs > instructions.Count)
				throw new ApplicationException("Invalid numInstrs to replace with branch");
			if (target == null)
				throw new ApplicationException("Invalid new target, it's null");

			DisconnectFromFallThroughAndTargets();
			if (numInstrs > 0)
				instructions.RemoveRange(instructions.Count - numInstrs, numInstrs);
			fallThrough = target;
			target.sources.Add(this);
		}

		public void ReplaceLastNonBranchWithBranch(int numInstrs, Block target) {
			if (LastInstr.IsBr())
				numInstrs++;
			ReplaceLastInstrsWithBranch(numInstrs, target);
		}

		public void ReplaceBccWithBranch(bool isTaken) => ReplaceLastInstrsWithBranch(1, isTaken ? targets[0] : fallThrough);

		public void ReplaceSwitchWithBranch(Block target) {
			if (LastInstr.OpCode.Code != Code.Switch)
				throw new ApplicationException("Last instruction is not a switch");
			ReplaceLastInstrsWithBranch(1, target);
		}

		public void SetNewFallThrough(Block newFallThrough) {
			DisconnectFromFallThrough();
			fallThrough = newFallThrough;
			newFallThrough.sources.Add(this);
		}

		public void SetNewTarget(int index, Block newTarget) {
			DisconnectFromBlock(targets[index]);
			targets[index] = newTarget;
			newTarget.sources.Add(this);
		}

		public void RemoveDeadBlock() {
			if (sources.Count != 0)
				throw new ApplicationException("Trying to remove a non-dead block");
			RemoveGuaranteedDeadBlock();
		}

		// Removes a block that has been guaranteed to be dead. This method won't verify
		// that it really is dead.
		public void RemoveGuaranteedDeadBlock() {
			DisconnectFromFallThroughAndTargets();
			Parent = null;
		}

		void DisconnectFromFallThroughAndTargets() {
			DisconnectFromFallThrough();
			DisconnectFromTargets();
		}

		void DisconnectFromFallThrough() {
			if (fallThrough != null) {
				DisconnectFromBlock(fallThrough);
				fallThrough = null;
			}
		}

		void DisconnectFromTargets() {
			if (targets != null) {
				foreach (var target in targets)
					DisconnectFromBlock(target);
				targets = null;
			}
		}

		void DisconnectFromBlock(Block target) {
			if (!target.sources.Remove(this))
				throw new ApplicationException("Could not remove the block from its target block");
		}

		public int CountTargets() {
			int count = fallThrough != null ? 1 : 0;
			if (targets != null)
				count += targets.Count;
			return count;
		}

		// Returns the target iff it has only ONE target. Else it returns null.
		public Block GetOnlyTarget() {
			if (CountTargets() != 1)
				return null;
			if (fallThrough != null)
				return fallThrough;
			return targets[0];
		}

		// Returns all targets. FallThrough (if not null) is always returned first!
		public IEnumerable<Block> GetTargets() {
			if (fallThrough != null)
				yield return fallThrough;
			if (targets != null) {
				foreach (var block in targets)
					yield return block;
			}
		}

		// Returns true iff other is the only block in Sources
		public bool IsOnlySource(Block other) => sources.Count == 1 && sources[0] == other;

		// Returns true if we can merge other with this
		public bool CanMerge(Block other) => CanAppend(other) && other.IsOnlySource(this);

		// Merge two blocks into one
		public void Merge(Block other) {
			if (!CanMerge(other))
				throw new ApplicationException("Can't merge the two blocks!");
			Append(other);
			other.DisconnectFromFallThroughAndTargets();
			other.Parent = null;
		}

		public bool CanAppend(Block other) {
			if (other == null || other == this || GetOnlyTarget() != other)
				return false;
			// If it's eg. a leave, then don't merge them since it clears the stack.
			return LastInstr.IsBr() || Instr.IsFallThrough(LastInstr.OpCode);
		}

		public void Append(Block other) {
			if (!CanAppend(other))
				throw new ApplicationException("Can't append the block!");

			RemoveLastBr();		// Get rid of last br/br.s if present

			var newInstructions = new List<Instr>(instructions.Count + other.instructions.Count);
			AddInstructions(newInstructions, instructions, false);
			AddInstructions(newInstructions, other.instructions, true);
			instructions = newInstructions;

			DisconnectFromFallThroughAndTargets();
			if (other.targets != null)
				targets = new List<Block>(other.targets);
			else
				targets = null;
			fallThrough = other.fallThrough;
			UpdateSources();
		}

		void AddInstructions(IList<Instr> dest, IList<Instr> instrs, bool clone) {
			for (int i = 0; i < instrs.Count; i++) {
				var instr = instrs[i];
				if (instr.OpCode != OpCodes.Nop)
					dest.Add(clone ? new Instr(instr.Instruction.Clone()) : instr);
			}
		}

		// Update each target's Sources property. Must only be called if this isn't in the
		// Sources list!
		public void UpdateSources() {
			if (fallThrough != null)
				fallThrough.sources.Add(this);
			if (targets != null) {
				foreach (var target in targets)
					target.sources.Add(this);
			}
		}

		// Returns true if it falls through
		public bool IsFallThrough() => targets == null && fallThrough != null;

		public bool CanFlipConditionalBranch() => LastInstr.CanFlipConditionalBranch();

		public void FlipConditionalBranch() {
			if (fallThrough == null || targets == null || targets.Count != 1)
				throw new ApplicationException("Invalid bcc block state");
			LastInstr.FlipConditonalBranch();
			var oldFallThrough = fallThrough;
			fallThrough = targets[0];
			targets[0] = oldFallThrough;
		}

		// Returns true if it's a conditional branch
		public bool IsConditionalBranch() => LastInstr.IsConditionalBranch();

		public bool IsNopBlock() {
			if (!IsFallThrough())
				return false;
			foreach (var instr in instructions) {
				if (instr.OpCode.Code != Code.Nop)
					return false;
			}
			return true;
		}
	}
}