Merge pull request #3425 from ElektroKill/fix/issue3423

Improve generation of not equals check

Author: siegfriedpammer

ICSharpCode.Decompiler.Tests/TestCases/Pretty/EnumTests.cs

@@ -1,4 +1,4 @@
-// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
 // 
 // 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
@@ -28,6 +28,12 @@ public enum SimpleEnum
 			Item2
 		}
 
+		public enum NoZero
+		{
+			Item1 = 1,
+			Item2
+		}
+
 		public enum OutOfOrderMembers
 		{
 			Item1 = 1,
@@ -135,5 +141,18 @@ public object PreservingTypeWhenBoxedTwoEnum()
 		{
 			return AttributeTargets.Class | AttributeTargets.Delegate;
 		}
+
+		public void EnumInNotZeroCheck(SimpleEnum value, NoZero value2)
+		{
+			if (value != SimpleEnum.Item1)
+			{
+				Console.WriteLine();
+			}
+
+			if (value2 != 0)
+			{
+				Console.WriteLine();
+			}
+		}
 	}
 }

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -1,4 +1,4 @@
-// Copyright (c) 2014 Daniel Grunwald
+// 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
@@ -731,6 +731,17 @@ public TranslatedExpression ConvertToBoolean(ExpressionBuilder expressionBuilder
 					.WithRR(new OperatorResolveResult(boolType, System.Linq.Expressions.ExpressionType.NotEqual,
 													  this.ResolveResult, nullRef.ResolveResult));
 			}
+			else if (Type.Kind == TypeKind.Enum && Type.GetDefinition() is { } typeDef &&
+					 typeDef.Fields.Any(f => f.GetConstantValue() is { } val && (ulong)CSharpPrimitiveCast.Cast(TypeCode.UInt64, val, false) == 0L))
+			{
+				var zero = expressionBuilder
+					.ConvertConstantValue(new ConstantResolveResult(Type, 0), allowImplicitConversion: true);
+				var op = negate ? BinaryOperatorType.Equality : BinaryOperatorType.InEquality;
+				return new BinaryOperatorExpression(Expression, op, zero.Expression)
+					.WithoutILInstruction()
+					.WithRR(new OperatorResolveResult(boolType, System.Linq.Expressions.ExpressionType.NotEqual,
+						this.ResolveResult, zero.ResolveResult));
+			}
 			else
 			{
 				var zero = new PrimitiveExpression(0)