Fix #1828, Fix #2290: Ensure base references have the correct type and are turned into this references and casted if necessary

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -2487,9 +2487,11 @@ namespace ICSharpCode.Decompiler.CSharp
 			{
 				if (ShouldUseBaseReference())
 				{
+					var baseReferenceType = resolver.CurrentTypeDefinition.DirectBaseTypes
+						.FirstOrDefault(t => t.Kind != TypeKind.Interface);
 					return new BaseReferenceExpression()
 						.WithILInstruction(target)
-						.WithRR(new ThisResolveResult(memberDeclaringType, nonVirtualInvocation));
+						.WithRR(new ThisResolveResult(baseReferenceType ?? memberDeclaringType, nonVirtualInvocation));
 				}
 				else
 				{

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -452,6 +452,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				// perform remaining pointer cast, if necessary
 				return pointerExpr.ConvertTo(targetType, expressionBuilder);
 			}
+			Expression expr;
 			if (targetType.Kind == TypeKind.ByReference)
 			{
 				if (NormalizeTypeVisitor.TypeErasure.EquivalentTypes(targetType, this.Type))
@@ -481,7 +482,6 @@ namespace ICSharpCode.Decompiler.CSharp
 				// Convert from integer/pointer to reference.
 				// First, convert to the corresponding pointer type:
 				var arg = this.ConvertTo(new PointerType(elementType), expressionBuilder, checkForOverflow);
-				Expression expr;
 				ResolveResult elementRR;
 				if (arg.Expression is UnaryOperatorExpression unary && unary.Operator == UnaryOperatorType.AddressOf)
 				{
@@ -561,7 +561,11 @@ namespace ICSharpCode.Decompiler.CSharp
 					return this;
 				}
 			}
-			var castExpr = new CastExpression(expressionBuilder.ConvertType(targetType), Expression);
+			// BaseReferenceExpression must not be used with CastExpressions
+			expr = Expression is BaseReferenceExpression
+				? new ThisReferenceExpression().WithILInstruction(this.ILInstructions)
+				: Expression;
+			var castExpr = new CastExpression(expressionBuilder.ConvertType(targetType), expr);
 			bool needsCheckAnnotation = targetUType.GetStackType().IsIntegerType();
 			if (needsCheckAnnotation)
 			{