Improve decompilation of ?. in generic code.

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

@@ -61,6 +61,12 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+		public interface ITest
+		{
+			int Int();
+			ITest Next();
+		}
+
 		private int GetInt()
 		{
 			return 9;
@@ -209,5 +215,20 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				c.Property = null;
 			}
 		}
+
+		private static int? GenericUnconstrainedInt<T>(T t) where T : ITest
+		{
+			return t?.Int();
+		}
+
+		private static int? GenericClassConstraintInt<T>(T t) where T : class, ITest
+		{
+			return t?.Int();
+		}
+
+		private static int? GenericStructConstraintInt<T>(T? t) where T : struct, ITest
+		{
+			return t?.Int();
+		}
 	}
 }

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NullPropagation.opt.roslyn.il

@@ -25,14 +25,14 @@
   .ver 0:0:0:0
 }
 .module NullPropagation.dll
-// MVID: {DDAB2C82-C901-450A-B55D-2D0D7BC34C48}
+// MVID: {B228D113-C048-4D76-A7D1-78312CF90769}
 .custom instance void [mscorlib]System.Security.UnverifiableCodeAttribute::.ctor() = ( 01 00 00 00 ) 
 .imagebase 0x10000000
 .file alignment 0x00000200
 .stackreserve 0x00100000
 .subsystem 0x0003       // WINDOWS_CUI
 .corflags 0x00000001    //  ILONLY
-// Image base: 0x003E0000
+// Image base: 0x03040000
 
 
 // =============== CLASS MEMBERS DECLARATION ===================
@@ -217,6 +217,21 @@
     } // end of property MyStruct::Item
   } // end of class MyStruct
 
+  .class interface abstract auto ansi nested public ITest
+  {
+    .method public hidebysig newslot abstract virtual 
+            instance int32  Int() cil managed
+    {
+    } // end of method ITest::Int
+
+    .method public hidebysig newslot abstract virtual 
+            instance class ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest 
+            Next() cil managed
+    {
+    } // end of method ITest::Next
+
+  } // end of class ITest
+
   .method private hidebysig instance int32 
           GetInt() cil managed
   {
@@ -845,6 +860,76 @@
     IL_0019:  ret
   } // end of method NullPropagation::Setter
 
+  .method private hidebysig static valuetype [mscorlib]System.Nullable`1<int32> 
+          GenericUnconstrainedInt<(ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest) T>(!!T t) cil managed
+  {
+    // Code size       37 (0x25)
+    .maxstack  1
+    .locals init (valuetype [mscorlib]System.Nullable`1<int32> V_0)
+    IL_0000:  ldarg.0
+    IL_0001:  box        !!T
+    IL_0006:  brtrue.s   IL_0012
+
+    IL_0008:  ldloca.s   V_0
+    IL_000a:  initobj    valuetype [mscorlib]System.Nullable`1<int32>
+    IL_0010:  ldloc.0
+    IL_0011:  ret
+
+    IL_0012:  ldarga.s   t
+    IL_0014:  constrained. !!T
+    IL_001a:  callvirt   instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest::Int()
+    IL_001f:  newobj     instance void valuetype [mscorlib]System.Nullable`1<int32>::.ctor(!0)
+    IL_0024:  ret
+  } // end of method NullPropagation::GenericUnconstrainedInt
+
+  .method private hidebysig static valuetype [mscorlib]System.Nullable`1<int32> 
+          GenericClassConstraintInt<class (ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest) T>(!!T t) cil managed
+  {
+    // Code size       31 (0x1f)
+    .maxstack  2
+    .locals init (valuetype [mscorlib]System.Nullable`1<int32> V_0)
+    IL_0000:  ldarg.0
+    IL_0001:  box        !!T
+    IL_0006:  dup
+    IL_0007:  brtrue.s   IL_0014
+
+    IL_0009:  pop
+    IL_000a:  ldloca.s   V_0
+    IL_000c:  initobj    valuetype [mscorlib]System.Nullable`1<int32>
+    IL_0012:  ldloc.0
+    IL_0013:  ret
+
+    IL_0014:  callvirt   instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest::Int()
+    IL_0019:  newobj     instance void valuetype [mscorlib]System.Nullable`1<int32>::.ctor(!0)
+    IL_001e:  ret
+  } // end of method NullPropagation::GenericClassConstraintInt
+
+  .method private hidebysig static valuetype [mscorlib]System.Nullable`1<int32> 
+          GenericStructConstraintInt<valuetype .ctor (ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest, [mscorlib]System.ValueType) T>(valuetype [mscorlib]System.Nullable`1<!!T> t) cil managed
+  {
+    // Code size       46 (0x2e)
+    .maxstack  1
+    .locals init (valuetype [mscorlib]System.Nullable`1<int32> V_0,
+             !!T V_1)
+    IL_0000:  ldarga.s   t
+    IL_0002:  call       instance bool valuetype [mscorlib]System.Nullable`1<!!T>::get_HasValue()
+    IL_0007:  brtrue.s   IL_0013
+
+    IL_0009:  ldloca.s   V_0
+    IL_000b:  initobj    valuetype [mscorlib]System.Nullable`1<int32>
+    IL_0011:  ldloc.0
+    IL_0012:  ret
+
+    IL_0013:  ldarga.s   t
+    IL_0015:  call       instance !0 valuetype [mscorlib]System.Nullable`1<!!T>::GetValueOrDefault()
+    IL_001a:  stloc.1
+    IL_001b:  ldloca.s   V_1
+    IL_001d:  constrained. !!T
+    IL_0023:  callvirt   instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest::Int()
+    IL_0028:  newobj     instance void valuetype [mscorlib]System.Nullable`1<int32>::.ctor(!0)
+    IL_002d:  ret
+  } // end of method NullPropagation::GenericStructConstraintInt
+
   .method public hidebysig specialname rtspecialname 
           instance void  .ctor() cil managed
   {

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NullPropagation.roslyn.il

@@ -25,14 +25,14 @@
   .ver 0:0:0:0
 }
 .module NullPropagation.dll
-// MVID: {252A7D2B-A310-4825-9B38-400B4B7D3296}
+// MVID: {AC5F707E-C73C-480F-9B50-4CCACD230B55}
 .custom instance void [mscorlib]System.Security.UnverifiableCodeAttribute::.ctor() = ( 01 00 00 00 ) 
 .imagebase 0x10000000
 .file alignment 0x00000200
 .stackreserve 0x00100000
 .subsystem 0x0003       // WINDOWS_CUI
 .corflags 0x00000001    //  ILONLY
-// Image base: 0x03130000
+// Image base: 0x04950000
 
 
 // =============== CLASS MEMBERS DECLARATION ===================
@@ -263,6 +263,21 @@
     } // end of property MyStruct::Item
   } // end of class MyStruct
 
+  .class interface abstract auto ansi nested public ITest
+  {
+    .method public hidebysig newslot abstract virtual 
+            instance int32  Int() cil managed
+    {
+    } // end of method ITest::Int
+
+    .method public hidebysig newslot abstract virtual 
+            instance class ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest 
+            Next() cil managed
+    {
+    } // end of method ITest::Next
+
+  } // end of class ITest
+
   .method private hidebysig instance int32 
           GetInt() cil managed
   {
@@ -1005,6 +1020,94 @@
     IL_002a:  ret
   } // end of method NullPropagation::Setter
 
+  .method private hidebysig static valuetype [mscorlib]System.Nullable`1<int32> 
+          GenericUnconstrainedInt<(ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest) T>(!!T t) cil managed
+  {
+    // Code size       43 (0x2b)
+    .maxstack  1
+    .locals init (valuetype [mscorlib]System.Nullable`1<int32> V_0,
+             valuetype [mscorlib]System.Nullable`1<int32> V_1)
+    IL_0000:  nop
+    IL_0001:  ldarg.0
+    IL_0002:  box        !!T
+    IL_0007:  brtrue.s   IL_0014
+
+    IL_0009:  ldloca.s   V_0
+    IL_000b:  initobj    valuetype [mscorlib]System.Nullable`1<int32>
+    IL_0011:  ldloc.0
+    IL_0012:  br.s       IL_0026
+
+    IL_0014:  ldarga.s   t
+    IL_0016:  constrained. !!T
+    IL_001c:  callvirt   instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest::Int()
+    IL_0021:  newobj     instance void valuetype [mscorlib]System.Nullable`1<int32>::.ctor(!0)
+    IL_0026:  stloc.1
+    IL_0027:  br.s       IL_0029
+
+    IL_0029:  ldloc.1
+    IL_002a:  ret
+  } // end of method NullPropagation::GenericUnconstrainedInt
+
+  .method private hidebysig static valuetype [mscorlib]System.Nullable`1<int32> 
+          GenericClassConstraintInt<class (ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest) T>(!!T t) cil managed
+  {
+    // Code size       37 (0x25)
+    .maxstack  2
+    .locals init (valuetype [mscorlib]System.Nullable`1<int32> V_0,
+             valuetype [mscorlib]System.Nullable`1<int32> V_1)
+    IL_0000:  nop
+    IL_0001:  ldarg.0
+    IL_0002:  box        !!T
+    IL_0007:  dup
+    IL_0008:  brtrue.s   IL_0016
+
+    IL_000a:  pop
+    IL_000b:  ldloca.s   V_0
+    IL_000d:  initobj    valuetype [mscorlib]System.Nullable`1<int32>
+    IL_0013:  ldloc.0
+    IL_0014:  br.s       IL_0020
+
+    IL_0016:  callvirt   instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest::Int()
+    IL_001b:  newobj     instance void valuetype [mscorlib]System.Nullable`1<int32>::.ctor(!0)
+    IL_0020:  stloc.1
+    IL_0021:  br.s       IL_0023
+
+    IL_0023:  ldloc.1
+    IL_0024:  ret
+  } // end of method NullPropagation::GenericClassConstraintInt
+
+  .method private hidebysig static valuetype [mscorlib]System.Nullable`1<int32> 
+          GenericStructConstraintInt<valuetype .ctor (ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest, [mscorlib]System.ValueType) T>(valuetype [mscorlib]System.Nullable`1<!!T> t) cil managed
+  {
+    // Code size       52 (0x34)
+    .maxstack  1
+    .locals init (valuetype [mscorlib]System.Nullable`1<int32> V_0,
+             !!T V_1,
+             valuetype [mscorlib]System.Nullable`1<int32> V_2)
+    IL_0000:  nop
+    IL_0001:  ldarga.s   t
+    IL_0003:  call       instance bool valuetype [mscorlib]System.Nullable`1<!!T>::get_HasValue()
+    IL_0008:  brtrue.s   IL_0015
+
+    IL_000a:  ldloca.s   V_0
+    IL_000c:  initobj    valuetype [mscorlib]System.Nullable`1<int32>
+    IL_0012:  ldloc.0
+    IL_0013:  br.s       IL_002f
+
+    IL_0015:  ldarga.s   t
+    IL_0017:  call       instance !0 valuetype [mscorlib]System.Nullable`1<!!T>::GetValueOrDefault()
+    IL_001c:  stloc.1
+    IL_001d:  ldloca.s   V_1
+    IL_001f:  constrained. !!T
+    IL_0025:  callvirt   instance int32 ICSharpCode.Decompiler.Tests.TestCases.Pretty.NullPropagation/ITest::Int()
+    IL_002a:  newobj     instance void valuetype [mscorlib]System.Nullable`1<int32>::.ctor(!0)
+    IL_002f:  stloc.2
+    IL_0030:  br.s       IL_0032
+
+    IL_0032:  ldloc.2
+    IL_0033:  ret
+  } // end of method NullPropagation::GenericStructConstraintInt
+
   .method public hidebysig specialname rtspecialname 
           instance void  .ctor() cil managed
   {

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -1515,7 +1515,18 @@ namespace ICSharpCode.Decompiler.CSharp
 						translatedTarget = translatedTarget.ConvertTo(new ByReferenceType(constrainedTo ?? member.DeclaringType), this);
 					}
 					if (translatedTarget.Expression is DirectionExpression) {
+						// (ref x).member => x.member
 						translatedTarget = translatedTarget.UnwrapChild(((DirectionExpression)translatedTarget).Expression);
+					} else if (translatedTarget.Expression is UnaryOperatorExpression uoe 
+						&& uoe.Operator == UnaryOperatorType.NullConditional
+						&& uoe.Expression is DirectionExpression) {
+						// (ref x)?.member => x?.member
+						translatedTarget = translatedTarget.UnwrapChild(((DirectionExpression)uoe.Expression).Expression);
+						// note: we need to create a new ResolveResult for the null-conditional operator,
+						// using the underlying type of the input expression without the DirectionExpression
+						translatedTarget = new UnaryOperatorExpression(UnaryOperatorType.NullConditional, translatedTarget)
+							.WithRR(new ResolveResult(NullableType.GetUnderlyingType(translatedTarget.Type)))
+							.WithoutILInstruction();
 					}
 					return translatedTarget;
 				}

ICSharpCode.Decompiler/IL/Instructions.cs

@@ -102,9 +102,13 @@ namespace ICSharpCode.Decompiler.IL
 		ThreeValuedLogicAnd,
 		/// <summary>Three valued logic or. Inputs are of type bool? or I4, output is of type bool?. Unlike logic.or(), does not have short-circuiting behavior.</summary>
 		ThreeValuedLogicOr,
-		/// <summary>The input operand must be either a nullable value type or a reference type.
+		/// <summary>The input operand must be one of:
+		///   1. a nullable value type
+		///   2. a reference type
+		///   3. a managed reference to a type parameter.
 		/// If the input is non-null, evaluates to the (unwrapped) input.
-		/// If the input is null, jumps to the innermost nullable.rewrap instruction that contains this instruction.</summary>
+		/// If the input is null, jumps to the innermost nullable.rewrap instruction that contains this instruction.
+		/// In case 3 (managed reference), the dereferenced value is the input being tested, and the nullable.unwrap instruction returns the managed reference unmodified (if the value is non-null).</summary>
 		NullableUnwrap,
 		/// <summary>Serves as jump target for the nullable.unwrap instruction.
 		/// If the input evaluates normally, evaluates to the input value (wrapped in Nullable<T> if the input is a non-nullable value type).If a nullable.unwrap instruction encounters a null input and jumps to the (endpoint of the) nullable.rewrap instruction,the nullable.rewrap instruction evaluates to null.</summary>
@@ -2518,9 +2522,13 @@ namespace ICSharpCode.Decompiler.IL
 }
 namespace ICSharpCode.Decompiler.IL
 {
-	/// <summary>The input operand must be either a nullable value type or a reference type.
+	/// <summary>The input operand must be one of:
+	///   1. a nullable value type
+	///   2. a reference type
+	///   3. a managed reference to a type parameter.
 	/// If the input is non-null, evaluates to the (unwrapped) input.
-	/// If the input is null, jumps to the innermost nullable.rewrap instruction that contains this instruction.</summary>
+	/// If the input is null, jumps to the innermost nullable.rewrap instruction that contains this instruction.
+	/// In case 3 (managed reference), the dereferenced value is the input being tested, and the nullable.unwrap instruction returns the managed reference unmodified (if the value is non-null).</summary>
 	public sealed partial class NullableUnwrap : UnaryInstruction
 	{
 

ICSharpCode.Decompiler/IL/Instructions.tt

@@ -160,9 +160,14 @@
 			CustomClassName("ThreeValuedLogicAnd"), Binary, ResultType("O")),
 		new OpCode("3vl.logic.or", "Three valued logic or. Inputs are of type bool? or I4, output is of type bool?. Unlike logic.or(), does not have short-circuiting behavior.",
 			CustomClassName("ThreeValuedLogicOr"), Binary, ResultType("O")),
-		new OpCode("nullable.unwrap", "The input operand must be either a nullable value type or a reference type." + Environment.NewLine
+		new OpCode("nullable.unwrap", "The input operand must be one of:" + Environment.NewLine
+				+ "  1. a nullable value type" + Environment.NewLine
+				+ "  2. a reference type" + Environment.NewLine
+				+ "  3. a managed reference to a type parameter." + Environment.NewLine
 				+ "If the input is non-null, evaluates to the (unwrapped) input." + Environment.NewLine
-				+ "If the input is null, jumps to the innermost nullable.rewrap instruction that contains this instruction.",
+				+ "If the input is null, jumps to the innermost nullable.rewrap instruction that contains this instruction." + Environment.NewLine
+				+ "In case 3 (managed reference), the dereferenced value is the input being tested, and the nullable.unwrap instruction "
+				+ "returns the managed reference unmodified (if the value is non-null).",
 			Unary, CustomConstructor, CustomWriteTo, HasFlag("InstructionFlags.MayUnwrapNull")),
 		new OpCode("nullable.rewrap", "Serves as jump target for the nullable.unwrap instruction." + Environment.NewLine
 				+ "If the input evaluates normally, evaluates to the input value (wrapped in Nullable<T> if the input is a non-nullable value type)."

ICSharpCode.Decompiler/IL/Instructions/NullableInstructions.cs

@@ -32,7 +32,11 @@ namespace ICSharpCode.Decompiler.IL
 		internal override void CheckInvariant(ILPhase phase)
 		{
 			base.CheckInvariant(phase);
+			if (this.ResultType == StackType.Ref) {
+				Debug.Assert(Argument.ResultType == StackType.Ref, "nullable.unwrap expects reference to nullable type as input");
+			} else {
 				Debug.Assert(Argument.ResultType == StackType.O, "nullable.unwrap expects nullable type as input");
+			}
 			Debug.Assert(Ancestors.Any(a => a is NullableRewrap));
 		}
 

ICSharpCode.Decompiler/IL/Transforms/NullPropagationTransform.cs

@@ -176,7 +176,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 						return false; // setter/adder/remover cannot be called with ?. syntax
 					}
 					inst = call.Arguments[0];
-					if (call.Method.DeclaringType.IsReferenceType == false && inst.MatchAddressOf(out var arg)) {
+					if ((call.ConstrainedTo ?? call.Method.DeclaringType).IsReferenceType == false && inst.MatchAddressOf(out var arg)) {
 						inst = arg;
 					}
 					// ensure the access chain does not contain any 'nullable.unwrap' that aren't directly part of the chain
@@ -197,7 +197,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			bool IsValidEndOfChain()
 			{
 				if (testedVarHasReferenceType) {
-					return inst.MatchLdLoc(testedVar);
+					// either reference type (expect: ldloc(testedVar)) or unconstrained generic type (expect: ldloca(testedVar)).
+					return inst.MatchLdLocRef(testedVar);
 				} else {
 					return NullableLiftingTransform.MatchGetValueOrDefault(inst, testedVar);
 				}
@@ -219,7 +220,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			} else {
 				// Wrap varLoad in nullable.unwrap:
 				var children = varLoad.Parent.Children;
-				children[varLoad.ChildIndex] = new NullableUnwrap(testedVar.StackType, varLoad);
+				children[varLoad.ChildIndex] = new NullableUnwrap(varLoad.ResultType, varLoad);
 			}
 		}
 	}