Fix #3322: Add missing checks for equality comparison

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -130,6 +130,7 @@
     <Compile Include="ProjectDecompiler\TargetFrameworkTests.cs" />
     <Compile Include="TestAssemblyResolver.cs" />
     <Compile Include="TestCases\ILPretty\MonoFixed.cs" />
+    <Compile Include="TestCases\Pretty\Comparisons.cs" />
     <None Include="TestCases\VBPretty\VBAutomaticEvents.vb" />
     <Compile Include="TestCases\VBPretty\VBAutomaticEvents.cs" />
     <Compile Include="TestCases\VBPretty\VBNonGenericForEach.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -586,6 +586,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public async Task Comparisons([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions);
+		}
+
 		[Test]
 		public async Task ConstantsTests([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{

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

@@ -0,0 +1,18 @@
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public class Comparisons
+	{
+		private class A
+		{
+		}
+
+		private class B
+		{
+		}
+
+		private bool CompareUnrelatedNeedsCast(A a, B b)
+		{
+			return (object)a == b;
+		}
+	}
+}

ICSharpCode.Decompiler/CSharp/Resolver/CSharpResolver.cs

@@ -805,7 +805,10 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 					}
 					if (op == BinaryOperatorType.Equality || op == BinaryOperatorType.InEquality)
 					{
-						if (lhsType.IsReferenceType == true && rhsType.IsReferenceType == true)
+						if (lhsType.IsReferenceType == true && rhsType.IsReferenceType == true
+							&& (conversions.IdentityConversion(lhsType, rhsType)
+								|| conversions.ExplicitConversion(lhsType, rhsType).IsReferenceConversion
+								|| conversions.ExplicitConversion(rhsType, lhsType).IsReferenceConversion))
 						{
 							// If it's a reference comparison
 							if (op == BinaryOperatorType.Equality)