ILSpy/ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

// Copyright (c) 2014 Daniel Grunwald
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System.Diagnostics;
using ICSharpCode.NRefactory.Semantics;
using ICSharpCode.NRefactory.Utils;
using ICSharpCode.Decompiler.IL;
using ICSharpCode.NRefactory.CSharp;
using ICSharpCode.NRefactory.TypeSystem;
using System;
using System.Collections.Generic;
using System.Linq;

namespace ICSharpCode.Decompiler.CSharp
{
	class StatementBuilder : ILVisitor<Statement>
	{
		readonly ExpressionBuilder exprBuilder;
		readonly IMethod currentMethod;

		public StatementBuilder(ITypeResolveContext decompilationContext, IMethod currentMethod)
		{
			Debug.Assert(decompilationContext != null && currentMethod != null);
			this.exprBuilder = new ExpressionBuilder(decompilationContext);
			this.currentMethod = currentMethod;
		}
		
		public Statement Convert(ILInstruction inst)
		{
			return inst.AcceptVisitor(this);
		}

		public BlockStatement ConvertAsBlock(ILInstruction inst)
		{
			Statement stmt = Convert(inst);
			return stmt as BlockStatement ?? new BlockStatement { stmt };
		}

		protected override Statement Default(ILInstruction inst)
		{
			return new ExpressionStatement(exprBuilder.Translate(inst));
		}
		
		protected internal override Statement VisitNop(Nop inst)
		{
			return new EmptyStatement();
		}
		
		protected internal override Statement VisitVoid(ICSharpCode.Decompiler.IL.Void inst)
		{
			return new ExpressionStatement(exprBuilder.Translate(inst.Argument));
		}

		protected internal override Statement VisitIfInstruction(IfInstruction inst)
		{
			var condition = exprBuilder.TranslateCondition(inst.Condition);
			var trueStatement = Convert(inst.TrueInst);
			var falseStatement = inst.FalseInst.OpCode == OpCode.Nop ? null : Convert(inst.FalseInst);
			return new IfElseStatement(condition, trueStatement, falseStatement);
		}

		CaseLabel CreateTypedCaseLabel(long i, IType type)
		{
			object value;
			if (type.IsKnownType(KnownTypeCode.Boolean)) {
				value = i != 0;
			} else if (type.Kind == TypeKind.Enum) {
				var enumType = type.GetDefinition().EnumUnderlyingType;
				value = CSharpPrimitiveCast.Cast(ReflectionHelper.GetTypeCode(enumType), i, true);
			} else {
				value = CSharpPrimitiveCast.Cast(ReflectionHelper.GetTypeCode(type), i, true);
			}
			return new CaseLabel(exprBuilder.ConvertConstantValue(new ConstantResolveResult(type, value)));
		}
		
		protected internal override Statement VisitSwitchInstruction(SwitchInstruction inst)
		{
			var value = exprBuilder.Translate(inst.Value);
			var stmt = new SwitchStatement() { Expression = value };	
			foreach (var section in inst.Sections) {
				var astSection = new ICSharpCode.NRefactory.CSharp.SwitchSection();
				astSection.CaseLabels.AddRange(section.Labels.Range().Select(i => CreateTypedCaseLabel(i, value.Type)));
				astSection.Statements.Add(Convert(section.Body));
				stmt.SwitchSections.Add(astSection);
			}
			return stmt;
		}
		
		/// <summary>Target block that a 'continue;' statement would jump to</summary>
		Block continueTarget;
		/// <summary>Number of ContinueStatements that were created for the current continueTarget</summary>
		int continueCount;
		
		protected internal override Statement VisitBranch(Branch inst)
		{
			if (inst.TargetBlock == continueTarget) {
				continueCount++;
				return new ContinueStatement();
			}
			return new GotoStatement(inst.TargetLabel);
		}
		
		/// <summary>Target container that a 'break;' statement would break out of</summary>
		BlockContainer breakTarget;
		/// <summary>Dictionary from BlockContainer to label name for 'goto of_container';</summary>
		readonly Dictionary<BlockContainer, string> endContainerLabels = new Dictionary<BlockContainer, string>();
		
		protected internal override Statement VisitLeave(Leave inst)
		{
			if (inst.TargetContainer == breakTarget)
				return new BreakStatement();
			string label;
			if (!endContainerLabels.TryGetValue(inst.TargetContainer, out label)) {
				label = "end_" + inst.TargetLabel;
				endContainerLabels.Add(inst.TargetContainer, label);
			}
			return new GotoStatement(label);
		}
		
		protected internal override Statement VisitThrow(Throw inst)
		{
			return new ThrowStatement(exprBuilder.Translate(inst.Argument));
		}
		
		protected internal override Statement VisitReturn(Return inst)
		{
			if (inst.ReturnValue == null)
				return new ReturnStatement();
			return new ReturnStatement(exprBuilder.Translate(inst.ReturnValue).ConvertTo(currentMethod.ReturnType, exprBuilder));
		}

		TryCatchStatement MakeTryCatch(ILInstruction tryBlock)
		{
			var tryBlockConverted = Convert(tryBlock);
			var tryCatch = tryBlockConverted as TryCatchStatement;
			if (tryCatch != null && tryCatch.FinallyBlock.IsNull)
				return tryCatch; // extend existing try-catch
			tryCatch = new TryCatchStatement();
			tryCatch.TryBlock = tryBlockConverted as BlockStatement ?? new BlockStatement { tryBlockConverted };
			return tryCatch;
		}
		
		protected internal override Statement VisitTryCatch(TryCatch inst)
		{
			var tryCatch = new TryCatchStatement();
			tryCatch.TryBlock = ConvertAsBlock(inst.TryBlock);
			foreach (var handler in inst.Handlers) {
				var catchClause = new CatchClause();
				if (handler.Variable != null) {
					catchClause.Type = exprBuilder.ConvertType(handler.Variable.Type);
					catchClause.VariableName = handler.Variable.Name;
				}
				if (!handler.Filter.MatchLdcI4(1))
					catchClause.Condition = exprBuilder.TranslateCondition(handler.Filter);
				catchClause.Body = ConvertAsBlock(handler.Body);
				tryCatch.CatchClauses.Add(catchClause);
			}
			return tryCatch;
		}
		
		protected internal override Statement VisitTryFinally(TryFinally inst)
		{
			var tryCatch = MakeTryCatch(inst.TryBlock);
			tryCatch.FinallyBlock = ConvertAsBlock(inst.FinallyBlock);
			return tryCatch;
		}
		
		protected internal override Statement VisitTryFault(TryFault inst)
		{
			var tryCatch = new TryCatchStatement();
			tryCatch.TryBlock = ConvertAsBlock(inst.TryBlock);
			var faultBlock = ConvertAsBlock(inst.FaultBlock);
			faultBlock.InsertChildAfter(null, new Comment("try-fault"), Roles.Comment);
			faultBlock.Add(new ThrowStatement());
			tryCatch.CatchClauses.Add(new CatchClause { Body = faultBlock });
			return tryCatch;
		}

		protected internal override Statement VisitBlock(Block block)
		{
			// Block without container
			BlockStatement blockStatement = new BlockStatement();
			foreach (var inst in block.Instructions) {
				blockStatement.Add(Convert(inst));
			}
			if (block.FinalInstruction.OpCode != OpCode.Nop)
				blockStatement.Add(Convert(block.FinalInstruction));
			return blockStatement;
		}
		
		protected internal override Statement VisitBlockContainer(BlockContainer container)
		{
			if (container.EntryPoint.IncomingEdgeCount > 1) {
				var oldContinueTarget = continueTarget;
				var oldContinueCount = continueCount;
				var oldBreakTarget = breakTarget;
				continueTarget = container.EntryPoint;
				continueCount = 0;
				breakTarget = container;
				var blockStatement = ConvertBlockContainer(container);
				Debug.Assert(continueCount < container.EntryPoint.IncomingEdgeCount);
				Debug.Assert(blockStatement.Statements.First() is LabelStatement);
				if (container.EntryPoint.IncomingEdgeCount == continueCount + 1) {
					// Remove the entrypoint label if all jumps to the label were replaced with 'continue;' statements
					blockStatement.Statements.First().Remove();
				}
				continueTarget = oldContinueTarget;
				continueCount = oldContinueCount;
				breakTarget = oldBreakTarget;
				return new WhileStatement(new PrimitiveExpression(true), blockStatement);
			} else {
				return ConvertBlockContainer(container);
			}
		}
		
		BlockStatement ConvertBlockContainer(BlockContainer container)
		{
			BlockStatement blockStatement = new BlockStatement();
			foreach (var block in container.Blocks) {
				if (block.IncomingEdgeCount > 1 || block != container.EntryPoint) {
					// If there are any incoming branches to this block, add a label:
					blockStatement.Add(new LabelStatement { Label = block.Label });
				}
				foreach (var inst in block.Instructions) {
					if (inst.OpCode == OpCode.Leave && IsFinalLeave((Leave)inst)) {
						// skip the final 'leave' instruction and just fall out of the BlockStatement
						continue;
					}
					blockStatement.Add(Convert(inst));
				}
				if (block.FinalInstruction.OpCode != OpCode.Nop) {
					blockStatement.Add(Convert(block.FinalInstruction));
				}
			}
			string label;
			if (endContainerLabels.TryGetValue(container, out label)) {
				blockStatement.Add(new LabelStatement { Label = label });
			}
			return blockStatement;
		}

		static bool IsFinalLeave(Leave leave)
		{
			Block block = (Block)leave.Parent;
			if (leave.ChildIndex != block.Instructions.Count - 1 || block.FinalInstruction.OpCode != OpCode.Nop)
				return false;
			BlockContainer container = (BlockContainer)block.Parent;
			return block.ChildIndex == container.Blocks.Count - 1;
		}
	}
}