First attempt at better cast handling

ICSharpCode.Decompiler/CSharp/Annotations.cs

@@ -80,6 +80,12 @@ namespace ICSharpCode.Decompiler.CSharp
 			return new TranslatedExpression(expression.Expression, expression.ResolveResult);
 		}
 		
+		public static TranslatedExpression WithILInstruction(this TranslatedExpression expression, ILInstruction instruction)
+		{
+			expression.Expression.AddAnnotation(instruction);
+			return expression;
+		}
+		
 		public static TranslatedExpression WithoutILInstruction(this ExpressionWithResolveResult expression)
 		{
 			return new TranslatedExpression(expression.Expression, expression.ResolveResult);

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -42,9 +42,21 @@ namespace ICSharpCode.Decompiler.CSharp
 	/// Every translated expression must have:
 	/// * an ILInstruction annotation
 	/// * a ResolveResult annotation
-	///   * The type of the ResolveResult must match the StackType of the corresponding ILInstruction.
-	///   * If the type of the ResolveResult is <c>sbyte</c> or <c>short</c>, the evaluated value of the ILInstruction
-	///     can be obtained by evaluating the C# expression and sign-extending the result to <c>int</c>.
+	/// Post-condition for Translate() calls:
+	///   * The type of the ResolveResult must match the StackType of the corresponding ILInstruction,
+	///     except that the width of integer types does not need to match (I4, I and I8 count as the same stack type here)
+	///   * Evaluating the resulting C# expression shall produce the same side effects as evaluating the ILInstruction.
+	///   * If the IL instruction has <c>ResultType == StackType.Void</c>, the C# expression may evaluate to an arbitrary type and value.
+	///   * Otherwise, evaluating the resulting C# expression shall produce a similar value as evaluating the ILInstruction.
+	///      * If the IL instruction evaluates to an integer stack type (I4, I, or I8),
+	///        the C# type of the resulting expression shall also be an integer (or enum/pointer/char/bool) type.
+	///        * If sizeof(C# type) == sizeof(IL stack type), the values must be the same.
+	///        * If sizeof(C# type) > sizeof(IL stack type), the C# value truncated to the width of the IL stack type must equal the IL value.
+	///        * If sizeof(C# type) &lt; sizeof(IL stack type), the C# value (sign/zero-)extended to the width of the IL stack type
+	///          must equal the IL value.
+	///          Whether sign or zero extension is used depends on the sign of the C# type (as determined by <c>IType.GetSign()</c>).
+	///      * If the IL instruction evaluates to a non-integer type, the C# type of the resulting expression shall match the IL stack type,
+	///        and the evaluated values shall be the same.
 	/// </remarks>
 	class ExpressionBuilder : ILVisitor<TranslatedExpression>
 	{
@@ -95,7 +107,16 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			Debug.Assert(inst != null);
 			var cexpr = inst.AcceptVisitor(this);
-			Debug.Assert(cexpr.Type.GetStackType() == inst.ResultType || cexpr.Type.Kind == TypeKind.Unknown || inst.ResultType == StackType.Void);
+			#if DEBUG
+			if (inst.ResultType != StackType.Void && cexpr.Type.Kind != TypeKind.Unknown) {
+				if (inst.ResultType.IsIntegerType()) {
+					Debug.Assert(cexpr.Type.GetStackType().IsIntegerType(), "IL instructions of integer type must convert into C# expressions of integer type");
+					Debug.Assert(cexpr.Type.GetSign() != Sign.None, "Must have a sign specified for zero/sign-extension");
+				} else {
+					Debug.Assert(cexpr.Type.GetStackType() == inst.ResultType);
+				}
+			}
+			#endif
 			return cexpr;
 		}
 		
@@ -591,28 +612,133 @@ namespace ICSharpCode.Decompiler.CSharp
 		protected internal override TranslatedExpression VisitConv(Conv inst)
 		{
 			var arg = Translate(inst.Argument);
-			if (inst.Kind == ConversionKind.StopGCTracking && arg.Type.Kind == TypeKind.ByReference) {
-				// cast to corresponding pointer type:
-				var pointerType = new PointerType(((ByReferenceType)arg.Type).ElementType);
-				arg = arg.ConvertTo(pointerType, this);
-				// if we want a native int, just return the pointer directly
-				if (inst.ResultType == StackType.I)
-					return arg;
-				// otherwise, continue converting
-			}
-			if (inst.Sign != Sign.None && arg.Type.GetSign() != inst.Sign) {
-				// we need to cast the input to a type of appropriate sign
-				var inputType = inst.Argument.ResultType.ToKnownTypeCode(inst.Sign);
-				arg = arg.ConvertTo(compilation.FindType(inputType), this);
-			}
-			var targetType = compilation.FindType(inst.TargetType.ToKnownTypeCode());
-			ExpressionWithResolveResult castExpr = arg.ConvertTo(targetType, this, inst.CheckForOverflow, addUncheckedAnnotations: false);
-			if (inst.Kind == ConversionKind.Nop || inst.Kind == ConversionKind.Truncate || inst.Kind == ConversionKind.FloatToInt
-			    || (inst.Kind == ConversionKind.ZeroExtend && arg.Type.GetSign() == Sign.Signed))
-			{
-				castExpr.Expression.AddAnnotation(inst.CheckForOverflow ? AddCheckedBlocks.CheckedAnnotation : AddCheckedBlocks.UncheckedAnnotation);
+			StackType inputStackType = inst.Argument.ResultType;
+			// Note: we're dealing with two conversions here:
+			// a) the implicit conversion from `arg.Type` to `inputStackType`
+			//    (due to the ExpressionBuilder post-condition being flexible with regards to the integer type width)
+			//    If this is a widening conversion, I'm calling the argument C# type "oversized".
+			//    If this is a narrowing conversion, I'm calling the argument C# type "undersized".
+			// b) the actual conversion instruction from `inputStackType` to `inst.TargetType`
+			
+			// Also, we need to be very careful with regards to the conversions we emit:
+			// In C#, zero vs. sign-extension depends on the input type,
+			// but in the ILAst Conv instruction it depends on the output type.
+			switch (inst.Kind) {
+				case ConversionKind.StopGCTracking:
+					if (arg.Type.Kind == TypeKind.ByReference) {
+						// cast to corresponding pointer type:
+						var pointerType = new PointerType(((ByReferenceType)arg.Type).ElementType);
+						return arg.ConvertTo(pointerType, this).WithILInstruction(inst);
+					} else {
+						Debug.Fail("ConversionKind.StopGCTracking should only be used with managed references");
+						goto default;
+					}
+				case ConversionKind.SignExtend:
+					// Sign extension is easy because it can never fail due to overflow checking.
+					
+					// We just need to ensure the input type before the conversion is signed.
+					// Also, if the argument was translated into an oversized C# type,
+					// we need to perform the truncatation to the input stack type.
+					if (arg.Type.GetSign() != Sign.Signed || arg.Type.GetSize() > inputStackType.GetSize()) {
+						// Note that an undersized C# type is handled just fine:
+						// If it is unsigned we'll zero-extend it to the width of the inputStackType here,
+						// and it is signed we just combine the two sign-extensions into a single sign-extending conversion.
+						arg = arg.ConvertTo(compilation.FindType(inputStackType.ToKnownTypeCode(Sign.Signed)), this);
+					}
+					// Then, we can just return the argument as-is: the ExpressionBuilder post-condition allows us
+					// to force our parent instruction to handle the actual sign-extension conversion.
+					// (our caller may have more information to pick a better fitting target type)
+					return arg.WithILInstruction(inst);
+				case ConversionKind.ZeroExtend:
+					// Zero extension may involve an overflow check.
+					
+					if (!inst.CheckForOverflow || inst.InputSign == Sign.Unsigned) {
+						// If overflow check cannot fail, handle this just like sign extension (except for swapped signs)
+						if (arg.Type.GetSign() != Sign.Unsigned || arg.Type.GetSize() > inputStackType.GetSize()) {
+							arg = arg.ConvertTo(compilation.FindType(inputStackType.ToKnownTypeCode(Sign.Unsigned)), this);
+						}
+						return arg.WithILInstruction(inst);
+					}
+					// Zero extension that should fail if the input type is negative.
+					// Split this conversion into steps:
+					// 1) perform input truncation if necessary, and perform unchecked cast to signed input type
+					if (arg.Type.GetSize() > inputStackType.GetSize() || arg.Type.GetSign() != inst.InputSign) {
+						arg = arg.ConvertTo(compilation.FindType(inputStackType.ToKnownTypeCode(inst.InputSign)), this);
+					}
+					// 2) perform sign conversion to unsigned with overflow check (input zero/sign extension can be combined with this step),
+					arg = arg.ConvertTo(compilation.FindType(inputStackType.ToKnownTypeCode(Sign.Unsigned)), this, true);
+					// 3) leave the actual zero extension to our caller.
+					return arg.WithILInstruction(inst);
+				case ConversionKind.Nop:
+					// Conversion between two types of same size; possibly sign-changing; may involve overflow checking.
+					if (!inst.CheckForOverflow || inst.InputSign == inst.TargetType.GetSign()) {
+						// a true nop: no need to generate any C# code
+						return arg.WithILInstruction(inst);
+					}
+					// sign-changing, overflow-checking conversion
+					
+					// If the input conversion is a truncation, we need to perform it (without overflow-checking).
+					// If the argument has a different type than that expected by the overflow check,
+					// we need to ensure we use the correct input type.
+					if (arg.Type.GetSize() > inputStackType.GetSize() || arg.Type.GetSign() != inst.InputSign) {
+						arg = arg.ConvertTo(compilation.FindType(inputStackType.ToKnownTypeCode(inst.InputSign)), this);
+					}
+					// Note that an input conversion that is a sign/zero-extension can be combined with the
+					// overflow-checking conversion
+					
+					goto default; // Perform the actual overflow-checking conversion
+				case ConversionKind.Truncate:
+					// Note: there are three sizes involved here:
+					// A = arg.Type.GetSize()
+					// B = inputStackType.GetSize()
+					// C = inst.TargetType.GetSize().
+					// We know that C <= B (otherwise this wouldn't be the truncation case).
+					// 1) If C < B < A, we just combine the two truncations into one.
+					// 2) If C < B = A, there's no input conversion, just the truncation
+					// 3) If C <= A < B, all the extended bits get removed again by the truncation.
+					// 4) If A < C < B, some extended bits remain even after truncation.
+					// In cases 1-3, the overall conversion is a truncation or no-op.
+					// In case 4, the overall conversion is a zero/sign extension, but to a smaller
+					// size than the original conversion.
+					if (!inst.CheckForOverflow) {
+						// Truncation without overflow check.
+						
+						if (inst.TargetType.IsSmallIntegerType()) {
+							// If the target type is a small integer type, IL will implicitly sign- or zero-extend
+							// the result after the truncation back to StackType.I4.
+							// (which means there's actually 3 conversions involved!)
+							
+							if (arg.Type.GetSize() <= inst.TargetType.GetSize() && arg.Type.GetSign() == inst.TargetType.GetSign()) {
+								// There's no actual truncation involved, and the result of the Conv instruciton is extended
+								// the same way as the original instruction
+								// -> we can return arg directly
+								return arg.WithILInstruction(inst);
+							} else {
+								// We need to actually truncate; *or* we need to change the sign for the remaining extension to I4.
+								goto default; // Emit simple cast to inst.TargetType
+							}
+						} else {
+							Debug.Assert(inst.TargetType.GetSize() == inst.ResultType.GetSize());
+							// For non-small integer types, we can let the whole unchecked truncation
+							// get handled by our caller (using the ExpressionBuilder post-condition).
+							
+							// Case 4 (left-over extension from implicit conversion) can also be handled by our caller.
+							return arg.WithILInstruction(inst);
+						}
+					}
+					// Truncation with overflow check
+					// Similar to nop-case: perform input truncation without overflow checking + ensure correct input sign.
+					if (arg.Type.GetSize() > inputStackType.GetSize() || arg.Type.GetSign() != inst.InputSign) {
+						arg = arg.ConvertTo(compilation.FindType(inputStackType.ToKnownTypeCode(inst.InputSign)), this);
+					}
+					goto default; // perform cast with overflow-check
+				case ConversionKind.IntToFloat: // TODO: handle these conversions correctly
+				case ConversionKind.FloatToInt:
+				case ConversionKind.FloatPrecisionChange:
+				default:
+					return arg.ConvertTo(compilation.FindType(inst.TargetType.ToKnownTypeCode()), this, inst.CheckForOverflow)
+						.WithILInstruction(inst);
 			}
-			return castExpr.WithILInstruction(inst);
 		}
 		
 		protected internal override TranslatedExpression VisitCall(Call inst)

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -20,6 +20,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using ICSharpCode.Decompiler.CSharp.Transforms;
 using ICSharpCode.NRefactory.CSharp;
 using ICSharpCode.NRefactory.Semantics;
 using ICSharpCode.NRefactory.TypeSystem;
@@ -89,6 +90,7 @@ namespace ICSharpCode.Decompiler.CSharp
 	/// TranslatedExpression as a separate type is still useful to ensure that no case in the expression builder
 	/// forgets to add the annotation.
 	/// </remarks>
+	[DebuggerDisplay("{Expression} : {ResolveResult}")]
 	struct TranslatedExpression
 	{
 		public readonly Expression Expression;
@@ -153,32 +155,74 @@ namespace ICSharpCode.Decompiler.CSharp
 			throw new ArgumentException("descendant must be a descendant of the current node");
 		}
 		
-		public TranslatedExpression ConvertTo(IType targetType, ExpressionBuilder expressionBuilder, bool checkForOverflow = false, bool addUncheckedAnnotations = true)
+		/// <summary>
+		/// Adds casts (if necessary) to convert this expression to the specified target type.
+		/// </summary>
+		/// <remarks>
+		/// If the target type is narrower than the source type, the value is truncated.
+		/// If the target type is wider than the source type, the value is sign- or zero-extended based on the
+		/// sign of the source type.
+		/// This fits with the ExpressionBuilder's post-condition, so e.g. an assignment can simply
+		/// call <c>Translate(stloc.Value).ConvertTo(stloc.Variable.Type)</c> and have the overall C# semantics match the IL semantics.
+		/// </remarks>
+		public TranslatedExpression ConvertTo(IType targetType, ExpressionBuilder expressionBuilder, bool checkForOverflow = false)
 		{
 			var type = this.Type;
 			if (type.Equals(targetType))
 				return this;
 			var compilation = expressionBuilder.compilation;
+			if (type.IsKnownType(KnownTypeCode.Boolean) && targetType.GetStackType().IsIntegerType()) {
+				// convert from boolean to integer (or enum)
+				return new ConditionalExpression(
+					this.Expression,
+					LdcI4(compilation, 1).ConvertTo(targetType, expressionBuilder, checkForOverflow),
+					LdcI4(compilation, 0).ConvertTo(targetType, expressionBuilder, checkForOverflow)
+				).WithoutILInstruction().WithRR(new ResolveResult(targetType));
+			}
+			// Special-case IntPtr and UIntPtr: they behave slightly weird, e.g. converting to them always checks for overflow,
+			// but converting from them never checks for overflow.
+			if (checkForOverflow && type.IsKnownType(KnownTypeCode.IntPtr) && !targetType.IsKnownType(KnownTypeCode.Int64)) {
+				// Convert through `long` instead.
+				return this.ConvertTo(compilation.FindType(KnownTypeCode.Int64), expressionBuilder, checkForOverflow)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow);
+			} else if (checkForOverflow && type.IsKnownType(KnownTypeCode.UIntPtr) && !targetType.IsKnownType(KnownTypeCode.UInt64)) {
+				// Convert through `ulong` instead.
+				return this.ConvertTo(compilation.FindType(KnownTypeCode.UInt64), expressionBuilder, checkForOverflow)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow);
+			}
+			
 			if (targetType.IsKnownType(KnownTypeCode.Boolean)) {
 				// convert to boolean through byte, to simulate the truncation to 8 bits
-				return this.ConvertTo(compilation.FindType(KnownTypeCode.Byte), expressionBuilder, checkForOverflow, addUncheckedAnnotations)
+				return this.ConvertTo(compilation.FindType(KnownTypeCode.Byte), expressionBuilder, checkForOverflow)
 					.ConvertToBoolean(expressionBuilder);
 			}
-			if ((targetType.IsKnownType(KnownTypeCode.IntPtr) || targetType.IsKnownType(KnownTypeCode.UIntPtr)) && type.Kind != TypeKind.Pointer) {
-				// (u)long -> IntPtr/UIntPtr casts in C# throw overflow exceptions, even in unchecked context.
-				// To avoid those, convert via void*.
-				return this.ConvertTo(new PointerType(compilation.FindType(KnownTypeCode.Void)), expressionBuilder, checkForOverflow, addUncheckedAnnotations)
-					.ConvertTo(targetType, expressionBuilder, checkForOverflow, addUncheckedAnnotations);
+			if ((targetType.IsKnownType(KnownTypeCode.IntPtr) || targetType.IsKnownType(KnownTypeCode.UIntPtr))
+			    && type.Kind != TypeKind.Pointer && !checkForOverflow)
+			{
+				// (u)long -> (U)IntPtr casts in C# can throw overflow exceptions in 32-bit mode, even in unchecked context.
+				// To avoid those, convert via `void*`.
+				return this.ConvertTo(new PointerType(compilation.FindType(KnownTypeCode.Void)), expressionBuilder, checkForOverflow)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow);
 			}
 			if (targetType.Kind == TypeKind.Pointer && type.Kind == TypeKind.Enum) {
-				// enum to pointer: convert via underlying type
-				return this.ConvertTo(type.GetEnumUnderlyingType(), expressionBuilder, checkForOverflow, addUncheckedAnnotations)
-					.ConvertTo(targetType, expressionBuilder, checkForOverflow, addUncheckedAnnotations);
-			} else if (targetType.Kind == TypeKind.Pointer && (type.IsKnownType(KnownTypeCode.Boolean) || type.IsKnownType(KnownTypeCode.Char))) {
-				// bool/char to pointer: convert via uint
-				return this.ConvertTo(compilation.FindType(KnownTypeCode.UInt32), expressionBuilder, checkForOverflow, addUncheckedAnnotations)
-					.ConvertTo(targetType, expressionBuilder, checkForOverflow, addUncheckedAnnotations);
-			} else if (targetType.Kind == TypeKind.Pointer && type.Kind == TypeKind.ByReference && Expression is DirectionExpression) {
+				// enum to pointer: C# doesn't allow such casts
+				// -> convert via underlying type
+				return this.ConvertTo(type.GetEnumUnderlyingType(), expressionBuilder, checkForOverflow)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow);
+			} else if (targetType.Kind == TypeKind.Enum && type.Kind == TypeKind.Pointer) {
+				// pointer to enum: C# doesn't allow such casts
+				// -> convert via underlying type
+				return this.ConvertTo(targetType.GetEnumUnderlyingType(), expressionBuilder, checkForOverflow)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow);
+			}
+			if (targetType.Kind == TypeKind.Pointer && type.IsKnownType(KnownTypeCode.Char)
+			   || targetType.IsKnownType(KnownTypeCode.Char) && type.Kind == TypeKind.Pointer) {
+				// char <-> pointer: C# doesn't allow such casts
+				// -> convert via ushort
+				return this.ConvertTo(compilation.FindType(KnownTypeCode.UInt16), expressionBuilder, checkForOverflow)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow);
+			}
+			if (targetType.Kind == TypeKind.Pointer && type.Kind == TypeKind.ByReference && Expression is DirectionExpression) {
 				// convert from reference to pointer
 				Expression arg = ((DirectionExpression)Expression).Expression.Detach();
 				var pointerType = new PointerType(((ByReferenceType)type).ElementType);
@@ -192,7 +236,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				// Convert from integer/pointer to reference.
 				// First, convert to the corresponding pointer type:
 				var elementType = ((ByReferenceType)targetType).ElementType;
-				var arg = this.ConvertTo(new PointerType(elementType), expressionBuilder, checkForOverflow, addUncheckedAnnotations);
+				var arg = this.ConvertTo(new PointerType(elementType), expressionBuilder, checkForOverflow);
 				// Then dereference the pointer:
 				var derefExpr = new UnaryOperatorExpression(UnaryOperatorType.Dereference, arg.Expression);
 				var elementRR = new ResolveResult(elementType);
@@ -202,26 +246,19 @@ namespace ICSharpCode.Decompiler.CSharp
 					.WithoutILInstruction()
 					.WithRR(new ByReferenceResolveResult(elementRR, false));
 			}
-			if (type.IsKnownType(KnownTypeCode.Boolean) && targetType.GetStackType().IsIntegerType()) {
-				// convert from boolean to integer (or enum)
-				return new ConditionalExpression(
-					this.Expression,
-					LdcI4(compilation, 1).ConvertTo(targetType, expressionBuilder),
-					LdcI4(compilation, 0).ConvertTo(targetType, expressionBuilder)
-				).WithoutILInstruction().WithRR(new ResolveResult(targetType));
-			}
 			var rr = expressionBuilder.resolver.WithCheckForOverflow(checkForOverflow).ResolveCast(targetType, ResolveResult);
 			if (rr.IsCompileTimeConstant && !rr.IsError) {
 				return expressionBuilder.ConvertConstantValue(rr)
 					.WithILInstruction(this.ILInstructions);
 			}
 			if (targetType.Kind == TypeKind.Pointer && 0.Equals(ResolveResult.ConstantValue)) {
-				return new NullReferenceExpression()
+				return new NullReferenceExpression().CastTo(expressionBuilder.ConvertType(targetType))
 					.WithILInstruction(this.ILInstructions)
 					.WithRR(new ConstantResolveResult(targetType, null));
 			}
-			return Expression.CastTo(expressionBuilder.ConvertType(targetType))
-				.WithoutILInstruction().WithRR(rr);
+			var castExpr = new CastExpression(expressionBuilder.ConvertType(targetType), Expression);
+			castExpr.AddAnnotation(checkForOverflow ? AddCheckedBlocks.CheckedAnnotation : AddCheckedBlocks.UncheckedAnnotation);
+			return castExpr.WithoutILInstruction().WithRR(rr);
 		}
 		
 		TranslatedExpression LdcI4(ICompilation compilation, int val)
@@ -231,11 +268,18 @@ namespace ICSharpCode.Decompiler.CSharp
 				.WithRR(new ConstantResolveResult(compilation.FindType(KnownTypeCode.Int32), val));
 		}
 		
+		/// <summary>
+		/// Converts this expression to a boolean expression.
+		/// 
+		/// Expects that the input expression is an integer expression; produces an expression
+		/// that returns <c>true</c> iff the integer value is not 0.
+		/// </summary>
 		public TranslatedExpression ConvertToBoolean(ExpressionBuilder expressionBuilder)
 		{
 			if (Type.IsKnownType(KnownTypeCode.Boolean) || Type.Kind == TypeKind.Unknown) {
 				return this;
 			}
+			Debug.Assert(Type.GetStackType().IsIntegerType());
 			IType boolType = expressionBuilder.compilation.FindType(KnownTypeCode.Boolean);
 			if (ResolveResult.IsCompileTimeConstant && ResolveResult.ConstantValue is int) {
 				bool val = (int)ResolveResult.ConstantValue != 0;

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -879,7 +879,7 @@ namespace ICSharpCode.Decompiler.IL
 			ILInstruction inst = Pop();
 			if (expectedType != inst.ResultType) {
 				if (expectedType == StackType.I && inst.ResultType == StackType.I4) {
-					inst = new Conv(inst, PrimitiveType.I, false, Sign.Signed);
+					inst = new Conv(inst, PrimitiveType.I, false, Sign.None);
 				} else {
 					Warn($"Expected {expectedType}, but got {inst.ResultType}");
 				}
@@ -892,7 +892,7 @@ namespace ICSharpCode.Decompiler.IL
 			ILInstruction inst = Pop();
 			switch (inst.ResultType) {
 				case StackType.I4:
-					return new Conv(inst, PrimitiveType.I, false, Sign.Signed);
+					return new Conv(inst, PrimitiveType.I, false, Sign.None);
 				case StackType.I:
 				case StackType.Ref:
 				case StackType.Unknown:
@@ -1087,9 +1087,9 @@ namespace ICSharpCode.Decompiler.IL
 			var left = Pop();
 			// make the implicit I4->I conversion explicit:
 			if (left.ResultType == StackType.I4 && right.ResultType == StackType.I) {
-				left = new Conv(left, PrimitiveType.I, false, Sign.Signed);
+				left = new Conv(left, PrimitiveType.I, false, Sign.None);
 			} else if (left.ResultType == StackType.I && right.ResultType == StackType.I4) {
-				right = new Conv(right, PrimitiveType.I, false, Sign.Signed);
+				right = new Conv(right, PrimitiveType.I, false, Sign.None);
 			}
 			
 			// Based on Table 4: Binary Comparison or Branch Operation
@@ -1137,7 +1137,7 @@ namespace ICSharpCode.Decompiler.IL
 					// introduce explicit comparison with 0
 					condition = new Comp(
 						negate ? ComparisonKind.Equality : ComparisonKind.Inequality,
-						Sign.None, condition, new Conv(new LdcI4(0), PrimitiveType.I, false, Sign.Signed));
+						Sign.None, condition, new Conv(new LdcI4(0), PrimitiveType.I, false, Sign.None));
 					break;
 				case StackType.I8:
 					// introduce explicit comparison with 0
@@ -1197,9 +1197,9 @@ namespace ICSharpCode.Decompiler.IL
 			if (opCode != OpCode.Shl && opCode != OpCode.Shr) {
 				// make the implicit I4->I conversion explicit:
 				if (left.ResultType == StackType.I4 && right.ResultType == StackType.I) {
-					left = new Conv(left, PrimitiveType.I, false, Sign.Signed);
+					left = new Conv(left, PrimitiveType.I, false, Sign.None);
 				} else if (left.ResultType == StackType.I && right.ResultType == StackType.I4) {
-					right = new Conv(right, PrimitiveType.I, false, Sign.Signed);
+					right = new Conv(right, PrimitiveType.I, false, Sign.None);
 				}
 			}
 			return Push(BinaryNumericInstruction.Create(opCode, left, right, checkForOverflow, sign));

ICSharpCode.Decompiler/IL/ILTypeExtensions.cs

@@ -64,6 +64,70 @@ namespace ICSharpCode.Decompiler.IL
 			return ((MetadataType)primitiveType).GetStackType();
 		}
 		
+		public static Sign GetSign(this PrimitiveType primitiveType)
+		{
+			switch (primitiveType) {
+				case PrimitiveType.I1:
+				case PrimitiveType.I2:
+				case PrimitiveType.I4:
+				case PrimitiveType.I8:
+				case PrimitiveType.R4:
+				case PrimitiveType.R8:
+				case PrimitiveType.I:
+					return Sign.Signed;
+				case PrimitiveType.U1:
+				case PrimitiveType.U2:
+				case PrimitiveType.U4:
+				case PrimitiveType.U8:
+				case PrimitiveType.U:
+					return Sign.Unsigned;
+				default:
+					return Sign.None;
+			}
+		}
+		
+		/// <summary>
+		/// Gets whether the type is a small integer type.
+		/// Small integer types are:
+		/// * bool, sbyte, byte, char, short, ushort
+		/// * any enums that have a small integer type as underlying type
+		/// </summary>
+		public static int GetSize(this PrimitiveType type)
+		{
+			switch (type) {
+				case PrimitiveType.I1:
+				case PrimitiveType.U1:
+					return 1;
+				case PrimitiveType.I2:
+				case PrimitiveType.U2:
+					return 2;
+				case PrimitiveType.I4:
+				case PrimitiveType.U4:
+				case PrimitiveType.R4:
+					return 4;
+				case PrimitiveType.I8:
+				case PrimitiveType.R8:
+				case PrimitiveType.U8:
+					return 8;
+				case PrimitiveType.I:
+				case PrimitiveType.U:
+					return TypeUtils.NativeIntSize;
+				default:
+					return 0;
+			}
+		}
+		
+		/// <summary>
+		/// Gets whether the type is a small integer type.
+		/// Small integer types are:
+		/// * bool, sbyte, byte, char, short, ushort
+		/// * any enums that have a small integer type as underlying type
+		/// </summary>
+		public static bool IsSmallIntegerType(this PrimitiveType type)
+		{
+			return GetSize(type) < 4;
+		}
+		
 		public static bool IsIntegerType(this PrimitiveType primitiveType)
 		{
 			return primitiveType.GetStackType().IsIntegerType();

ICSharpCode.Decompiler/IL/Instructions/Conv.cs

@@ -53,11 +53,12 @@ namespace ICSharpCode.Decompiler.IL
 		FloatPrecisionChange,
 		/// <summary>
 		/// Conversion of integer type to larger signed integer type.
+		/// May involve overflow checking (when converting from U4 to I on 32-bit).
 		/// </summary>
 		SignExtend,
 		/// <summary>
 		/// Conversion of integer type to larger unsigned integer type.
-		/// May involve overflow checking (when converting from a small signed type).
+		/// May involve overflow checking (when converting from a signed type).
 		/// </summary>
 		ZeroExtend,
 		/// <summary>
@@ -104,13 +105,13 @@ namespace ICSharpCode.Decompiler.IL
 		/// The input sign does not have any effect on whether the conversion zero-extends or sign-extends;
 		/// that is purely determined by the <c>TargetType</c>.
 		/// </remarks>
-		public readonly Sign Sign;
+		public readonly Sign InputSign;
 		
-		public Conv(ILInstruction argument, PrimitiveType targetType, bool checkForOverflow, Sign sign) : base(OpCode.Conv, argument)
+		public Conv(ILInstruction argument, PrimitiveType targetType, bool checkForOverflow, Sign inputSign) : base(OpCode.Conv, argument)
 		{
 			this.TargetType = targetType;
 			this.CheckForOverflow = checkForOverflow;
-			this.Sign = sign;
+			this.InputSign = inputSign;
 			this.Kind = GetConversionKind(targetType, argument.ResultType);
 			Debug.Assert(this.Kind != ConversionKind.Invalid);
 		}
@@ -207,9 +208,9 @@ namespace ICSharpCode.Decompiler.IL
 			output.Write(OpCode);
 			if (CheckForOverflow)
 				output.Write(".ovf");
-			if (Sign == Sign.Unsigned)
+			if (InputSign == Sign.Unsigned)
 				output.Write(".unsigned");
-			else if (Sign == Sign.Signed)
+			else if (InputSign == Sign.Signed)
 				output.Write(".signed");
 			output.Write(' ');
 			output.Write(Argument.ResultType);

ICSharpCode.Decompiler/Tests/RoundtripAssembly.cs

@@ -62,23 +62,19 @@ namespace ICSharpCode.Decompiler.Tests
 		}
 		
 		[Test]
-		public void Random_Tests_Implicit_Conversions()
+		public void Implicit_Conversions()
 		{
 			RunWithOutput("Random Tests\\TestCases", "ImplicitConversions.exe");
 		}
 
 		[Test]
-		public void Random_Tests_Implicit_Conversions_32()
+		public void Implicit_Conversions_32()
 		{
-			try {
-				RunWithOutput("Random Tests\\TestCases", "ImplicitConversions_32.exe");
-			} catch (AssertionException ex) {
-				Assert.Ignore(ex.Message);
-			}
+			RunWithOutput("Random Tests\\TestCases", "ImplicitConversions_32.exe");
 		}
 
 		[Test]
-		public void Random_Tests_Explicit_Conversions()
+		public void Explicit_Conversions()
 		{
 			try {
 				RunWithOutput("Random Tests\\TestCases", "ExplicitConversions.exe");
@@ -88,7 +84,7 @@ namespace ICSharpCode.Decompiler.Tests
 		}
 
 		[Test]
-		public void Random_Tests_Explicit_Conversions_32()
+		public void Explicit_Conversions_32()
 		{
 			try {
 				RunWithOutput("Random Tests\\TestCases", "ExplicitConversions_32.exe");

ICSharpCode.Decompiler/TypeSystem/TypeUtils.cs

@@ -24,14 +24,26 @@ namespace ICSharpCode.Decompiler
 {
 	public static class TypeUtils
 	{
-		static int GetNativeSize(IType type)
+		public const int NativeIntSize = 6; // between 4 (Int32) and 8 (Int64)
+		
+		/// <summary>
+		/// Gets the size (in bytes) of the input type.
+		/// Returns <c>NativeIntSize</c> for pointer-sized types.
+		/// Returns 0 for structs and other types of unknown size.
+		/// </summary>
+		public static int GetSize(this IType type)
 		{
-			const int NativeIntSize = 6; // between 4 (Int32) and 8 (Int64)
-			if (type.Kind == TypeKind.Pointer)
-				return NativeIntSize;
+			switch (type.Kind) {
+				case TypeKind.Pointer:
+				case TypeKind.ByReference:
+				case TypeKind.Class:
+					return NativeIntSize;
+				case TypeKind.Enum:
+					type = type.GetEnumUnderlyingType();
+					break;
+			}
 			
-			var typeForConstant = (type.Kind == TypeKind.Enum) ? type.GetDefinition().EnumUnderlyingType : type;
-			var typeDef = typeForConstant.GetDefinition();
+			var typeDef = type.GetDefinition();
 			if (typeDef == null)
 				return 0;
 			switch (typeDef.KnownTypeCode) {
@@ -58,9 +70,33 @@ namespace ICSharpCode.Decompiler
 			return 0;
 		}
 		
+		/// <summary>
+		/// Gets the size of the input stack type.
+		/// </summary>
+		/// <returns>
+		/// * 4 for <c>I4</c>,
+		/// * 8 for <c>I8</c>,
+		/// * <c>NativeIntSize</c> for <c>I</c> and <c>Ref</c>,
+		/// * 0 otherwise (O, F, Void, Unknown).
+		/// </returns>
+		public static int GetSize(this StackType type)
+		{
+			switch (type) {
+				case StackType.I4:
+					return 4;
+				case StackType.I8:
+					return 8;
+				case StackType.I:
+				case StackType.Ref:
+					return NativeIntSize;
+				default:
+					return 0;
+			}
+		}
+		
 		public static IType GetLargerType(IType type1, IType type2)
 		{
-			return GetNativeSize(type1) >= GetNativeSize(type2) ? type1 : type2;
+			return GetSize(type1) >= GetSize(type2) ? type1 : type2;
 		}
 		
 		/// <summary>
@@ -71,7 +107,7 @@ namespace ICSharpCode.Decompiler
 		/// </summary>
 		public static bool IsSmallIntegerType(this IType type)
 		{
-			return GetNativeSize(type) < 4;
+			return GetSize(type) < 4;
 		}
 		
 		/// <summary>
@@ -114,7 +150,7 @@ namespace ICSharpCode.Decompiler
 			// 2) Both types are integer types of equal size
 			StackType memoryStackType = memoryType.GetStackType();
 			StackType accessStackType = accessType.GetStackType();
-			return memoryStackType == accessStackType && memoryStackType.IsIntegerType() && GetNativeSize(memoryType) == GetNativeSize(accessType);
+			return memoryStackType == accessStackType && memoryStackType.IsIntegerType() && GetSize(memoryType) == GetSize(accessType);
 		}
 
 		/// <summary>
@@ -174,12 +210,14 @@ namespace ICSharpCode.Decompiler
 		/// <remarks>
 		/// Integer types (including IntPtr/UIntPtr) return the sign as expected.
 		/// Floating point types and <c>decimal</c> are considered to be signed.
-		/// <c>char</c> and <c>bool</c> are unsigned.
+		/// <c>char</c>, <c>bool</c> and pointer types (e.g. <c>void*</c>) are unsigned.
 		/// Enums have a sign based on their underlying type.
 		/// All other types return <c>Sign.None</c>.
 		/// </remarks>
 		public static Sign GetSign(this IType type)
 		{
+			if (type.Kind == TypeKind.Pointer)
+				return Sign.Unsigned;
 			var typeDef = type.GetEnumUnderlyingType().GetDefinition();
 			if (typeDef == null)
 				return Sign.None;