Fix #1747: Stack overflow when decompiling a `bool` -> `bool?` conversion.

ICSharpCode.Decompiler.Tests/TestCases/Correctness/OverloadResolution.cs

@@ -33,6 +33,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Correctness
 			ConstructorTest();
 			TestIndexer();
 			Issue1281();
+			Issue1747();
 		}
 
 		#region ConstructorTest
@@ -203,6 +204,37 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Correctness
 		}
 		#endregion
 
+		#region NullableValueTypes
+		private static void Issue1747()
+		{
+			Console.WriteLine("Issue1747:");
+			M1747(null);
+			M1747(true);
+			M1747(false);
+			M1747((bool?)true);
+			M1747((bool?)false);
+			Console.WriteLine("Issue1747, non-constant:");
+			bool b = Get<bool>();
+			M1747(b);
+			M1747((bool?)b);
+		}
+
+		private static void M1747(bool b)
+		{
+			Console.WriteLine("bool=" + b);
+		}
+
+		private static void M1747(bool? b)
+		{
+			Console.WriteLine("bool?=" + b);
+		}
+
+		static T Get<T>()
+		{
+			return default(T);
+		}
+		#endregion
+
 		#region IndexerTests
 		static void TestIndexer()
 		{

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -285,7 +285,8 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			IType utype = NullableType.GetUnderlyingType(type);
 			IType targetUType = NullableType.GetUnderlyingType(targetType);
-			if (type.IsKnownType(KnownTypeCode.Boolean) && targetUType.GetStackType().IsIntegerType()) {
+			if (type.IsKnownType(KnownTypeCode.Boolean) && !targetUType.IsKnownType(KnownTypeCode.Boolean)
+				&& targetUType.GetStackType().IsIntegerType()) {
 				// convert from boolean to integer (or enum)
 				return new ConditionalExpression(
 					this.Expression,