Fix support for prefix opcodes (#304)

Fixes #303

+semver:fix

Author: hazzik

src/DelegateDecompiler.Tests/Issue298.cs

@@ -10,28 +10,46 @@ public class Issue298 : DecompilerTestsBase
     [Test]
     public void TestNotConstrained()
     {
-        static int NotConstrained<T>(T value) where T : ITestInterface => ((ITestInterface)value).Value;
-
-        Expression<Func<TestClass, int>> expected = value => value.Value;
-        Test(NotConstrained, expected);
+        static int Actual<T>(T value) where T : ITestInterface => ((ITestInterface)value).Field;
+        
+        Test(Actual<TestClass>,
+            value => value.Field,
+            value => ((ITestInterface)value).Field
+        );
     }
 
     [Test]
     public void TestConstrained()
     {
-        static int Constrained<T>(T value) where T : ITestInterface => value.Value;
+        static int Actual<T>(T value) where T : ITestInterface => value.Field;
 
-        Expression<Func<TestClass, int>> expected = value => value.Value;
-        Test(Constrained, expected);
+        Test(Actual<ITestInterface>, value => value.Field);
+        Test(Actual<TestClass>, value => value.Field);
     }
 
+#if NET6_0_OR_GREATER
+    [Test]
+    public void TestConstrainedDefaultImplementation()
+    {
+        static int Actual<T>(T value, int i) where T : ITestInterface => value.Method(i);
+        static Expression<Func<T, int, int>> Expected<T>() where T : ITestInterface => (value, i) => value.Method(i);
+
+        Test(Actual, Expected<ITestInterface>());
+        Test(Actual, Expected<TestClass>());
+    }
+#endif
+
     interface ITestInterface
     {
-        public int Value { get; }
+        public int Field { get; }
+
+#if NET6_0_OR_GREATER
+        public int Method(int i) => i;
+#endif
     }
 
     class TestClass : ITestInterface
     {
-        public int Value { get; set; }
+        public int Field { get; set; }
     }
 }

src/DelegateDecompiler/Processor.cs

@@ -145,9 +145,10 @@ static int ProcessInstruction(ProcessorState state, Instruction instruction)
         {
             Debug.WriteLine(instruction);
 
-            if (instruction.OpCode == OpCodes.Nop || 
+            if (instruction.OpCode == OpCodes.Nop ||
                 instruction.OpCode == OpCodes.Break ||
                 instruction.OpCode == OpCodes.Ret ||
+                instruction.OpCode.OpCodeType == OpCodeType.Prefix ||
                 instruction.OpCode.FlowControl == FlowControl.Branch)
             {
                 // Do nothing

src/DelegateDecompiler/Processors/ConvertTypeProcessor.cs

@@ -10,20 +10,16 @@ internal class ConvertTypeProcessor : IProcessor
     {
         public static void Register(Dictionary<OpCode, IProcessor> processors)
         {
-            processors.Register(new ConvertTypeProcessor(), 
-                OpCodes.Castclass, 
+            processors.Register(new ConvertTypeProcessor(),
+                OpCodes.Castclass,
                 OpCodes.Unbox,
-                OpCodes.Unbox_Any,
-                OpCodes.Constrained);
+                OpCodes.Unbox_Any);
         }
 
         public void Process(ProcessorState state, Instruction instruction)
         {
             var expression = state.Stack.Pop();
-            var targetType = (Type)instruction.Operand;
-            state.Stack.Push(expression.Type != targetType
-                ? Expression.Convert(expression, targetType)
-                : expression);
+            state.Stack.Push(Expression.Convert(expression, (Type)instruction.Operand));
         }
     }
 }