Generate interface lists for necessary EETypes

The compiler can generate two kinds of `MethodTable` structures: constructed and unconstructed. The constructed one has a fully populated vtable and GCInfo and is required whenever the object type could be allocated on the heap. The unconstructed one is generated for all other scenarios as a size optimization.

We were previously also skipping emission of the interface list in the unconstructed case. But interface list might be required for variant casting. We could introduce yet another `MethodTable` kind for this specific scenario, but it doesn't seem to warrant the complexity.

Emitting interface list for all types is a less than 0.1% size regression for the Todos app. It is a 0.5% size regression for Hello World. That part is unfortunate. It's mostly due to the useless numeric interfaces. We can get this size back if we do dotnet#66716 and start trimming interface lists.

Fixes dotnet#95574.

Author: MichalStrehovsky

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/CanonicalEETypeNode.cs

@@ -29,7 +29,7 @@ public CanonicalEETypeNode(NodeFactory factory, TypeDesc type) : base(factory, t
 
         public override bool StaticDependenciesAreComputed => true;
         public override bool IsShareable => IsTypeNodeShareable(_type);
-        protected override bool EmitVirtualSlotsAndInterfaces => true;
+        protected override bool EmitVirtualSlots => true;
         public override bool ShouldSkipEmittingObjectNode(NodeFactory factory) => false;
 
         protected override DependencyList ComputeNonRelocationBasedDependencies(NodeFactory factory)

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/ConstructedEETypeNode.cs

@@ -20,7 +20,7 @@ public ConstructedEETypeNode(NodeFactory factory, TypeDesc type) : base(factory,
 
         public override bool ShouldSkipEmittingObjectNode(NodeFactory factory) => false;
 
-        protected override bool EmitVirtualSlotsAndInterfaces => true;
+        protected override bool EmitVirtualSlots => true;
 
         protected override DependencyList ComputeNonRelocationBasedDependencies(NodeFactory factory)
         {

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/EETypeNode.cs

@@ -97,7 +97,7 @@ public EETypeNode(NodeFactory factory, TypeDesc type)
             _writableDataNode = SupportsWritableData(factory.Target) && !_type.IsCanonicalSubtype(CanonicalFormKind.Any) ? new WritableDataNode(this) : null;
             _hasConditionalDependenciesFromMetadataManager = factory.MetadataManager.HasConditionalDependenciesDueToEETypePresence(type);
 
-            if (EmitVirtualSlotsAndInterfaces)
+            if (EmitVirtualSlots)
                 _virtualMethodAnalysisFlags = AnalyzeVirtualMethods(type);
 
             factory.TypeSystemContext.EnsureLoadableType(type);
@@ -201,7 +201,7 @@ protected bool MightHaveInterfaceDispatchMap(NodeFactory factory)
         {
             if (!_mightHaveInterfaceDispatchMap.HasValue)
             {
-                _mightHaveInterfaceDispatchMap = EmitVirtualSlotsAndInterfaces && InterfaceDispatchMapNode.MightHaveInterfaceDispatchMap(_type, factory);
+                _mightHaveInterfaceDispatchMap = EmitVirtualSlots && InterfaceDispatchMapNode.MightHaveInterfaceDispatchMap(_type, factory);
             }
 
             return _mightHaveInterfaceDispatchMap.Value;
@@ -238,7 +238,7 @@ protected override ObjectNodeSection GetDehydratedSection(NodeFactory factory)
         public static int GetMinimumObjectSize(TypeSystemContext typeSystemContext)
             => typeSystemContext.Target.PointerSize * 3;
 
-        protected virtual bool EmitVirtualSlotsAndInterfaces => false;
+        protected virtual bool EmitVirtualSlots => false;
 
         public override bool InterestingForDynamicDependencyAnalysis
             => (_virtualMethodAnalysisFlags & VirtualMethodAnalysisFlags.InterestingForDynamicDependencies) != 0;
@@ -305,7 +305,7 @@ public sealed override bool HasConditionalStaticDependencies
                     return true;
                 }
 
-                if (!EmitVirtualSlotsAndInterfaces)
+                if (!EmitVirtualSlots)
                     return false;
 
                 // Since the vtable is dependency driven, generate conditional static dependencies for
@@ -373,7 +373,7 @@ public sealed override IEnumerable<CombinedDependencyListEntry> GetConditionalSt
                     "Information about static bases for type with template"));
             }
 
-            if (!EmitVirtualSlotsAndInterfaces)
+            if (!EmitVirtualSlots)
                 return result;
 
             DefType defType = _type.GetClosestDefType();
@@ -586,7 +586,7 @@ protected override DependencyList ComputeNonRelocationBasedDependencies(NodeFact
             // emitting it.
             dependencies.Add(new DependencyListEntry(_optionalFieldsNode, "Optional fields"));
 
-            if (EmitVirtualSlotsAndInterfaces)
+            if (EmitVirtualSlots)
             {
                 if (!_type.IsArrayTypeWithoutGenericInterfaces())
                 {
@@ -677,7 +677,7 @@ protected override ObjectData GetDehydratableData(NodeFactory factory, bool relo
 
             objData.EmitInt(_type.GetHashCode());
 
-            if (EmitVirtualSlotsAndInterfaces)
+            if (EmitVirtualSlots)
             {
                 // Emit VTable
                 Debug.Assert(objData.CountBytes - ((ISymbolDefinitionNode)this).Offset == GetVTableOffset(objData.TargetPointerSize));
@@ -687,23 +687,21 @@ protected override ObjectData GetDehydratableData(NodeFactory factory, bool relo
                 // Update slot count
                 int numberOfVtableSlots = virtualSlotCounter.CountSlots(ref /* readonly */ objData);
                 objData.EmitShort(vtableSlotCountReservation, checked((short)numberOfVtableSlots));
-
-                // Emit interface map
-                SlotCounter interfaceSlotCounter = SlotCounter.BeginCounting(ref /* readonly */ objData);
-                OutputInterfaceMap(factory, ref objData);
-
-                // Update slot count
-                int numberOfInterfaceSlots = interfaceSlotCounter.CountSlots(ref /* readonly */ objData);
-                objData.EmitShort(interfaceCountReservation, checked((short)numberOfInterfaceSlots));
-
             }
             else
             {
                 // If we're not emitting any slots, the number of slots is zero.
                 objData.EmitShort(vtableSlotCountReservation, 0);
-                objData.EmitShort(interfaceCountReservation, 0);
             }
 
+            // Emit interface map
+            SlotCounter interfaceSlotCounter = SlotCounter.BeginCounting(ref /* readonly */ objData);
+            OutputInterfaceMap(factory, ref objData);
+
+            // Update slot count
+            int numberOfInterfaceSlots = interfaceSlotCounter.CountSlots(ref /* readonly */ objData);
+            objData.EmitShort(interfaceCountReservation, checked((short)numberOfInterfaceSlots));
+
             OutputTypeManagerIndirection(factory, ref objData);
             OutputWritableData(factory, ref objData);
             OutputDispatchMap(factory, ref objData);
@@ -751,7 +749,7 @@ private void OutputFlags(NodeFactory factory, ref ObjectDataBuilder objData, boo
                 flags |= (uint)EETypeFlags.GenericVarianceFlag;
             }
 
-            if (EmitVirtualSlotsAndInterfaces && !_type.IsArrayTypeWithoutGenericInterfaces())
+            if (EmitVirtualSlots && !_type.IsArrayTypeWithoutGenericInterfaces())
             {
                 SealedVTableNode sealedVTable = factory.SealedVTable(_type.ConvertToCanonForm(CanonicalFormKind.Specific));
                 if (sealedVTable.BuildSealedVTableSlots(factory, relocsOnly) && sealedVTable.NumSealedVTableEntries > 0)
@@ -949,7 +947,7 @@ protected virtual void OutputRelatedType(NodeFactory factory, ref ObjectDataBuil
 
         private void OutputVirtualSlots(NodeFactory factory, ref ObjectDataBuilder objData, TypeDesc implType, TypeDesc declType, TypeDesc templateType, bool relocsOnly)
         {
-            Debug.Assert(EmitVirtualSlotsAndInterfaces);
+            Debug.Assert(EmitVirtualSlots);
 
             declType = declType.GetClosestDefType();
             templateType = templateType.ConvertToCanonForm(CanonicalFormKind.Specific);
@@ -1096,8 +1094,6 @@ protected virtual IEETypeNode GetInterfaceTypeNode(NodeFactory factory, TypeDesc
 
         protected virtual void OutputInterfaceMap(NodeFactory factory, ref ObjectDataBuilder objData)
         {
-            Debug.Assert(EmitVirtualSlotsAndInterfaces);
-
             foreach (var itf in _type.RuntimeInterfaces)
             {
                 objData.EmitPointerReloc(GetInterfaceTypeNode(factory, itf));
@@ -1150,7 +1146,7 @@ protected void OutputOptionalFields(NodeFactory factory, ref ObjectDataBuilder o
 
         private void OutputSealedVTable(NodeFactory factory, bool relocsOnly, ref ObjectDataBuilder objData)
         {
-            if (EmitVirtualSlotsAndInterfaces && !_type.IsArrayTypeWithoutGenericInterfaces())
+            if (EmitVirtualSlots && !_type.IsArrayTypeWithoutGenericInterfaces())
             {
                 // Sealed vtables have relative pointers, so to minimize size, we build sealed vtables for the canonical types
                 SealedVTableNode sealedVTable = factory.SealedVTable(_type.ConvertToCanonForm(CanonicalFormKind.Specific));

src/tests/nativeaot/SmokeTests/UnitTests/Generics.cs

@@ -54,6 +54,7 @@ internal static int Run()
         TestRefAny.Run();
         TestNullableCasting.Run();
         TestVariantCasting.Run();
+        TestVariantDispatchUnconstructedTypes.Run();
         TestMDArrayAddressMethod.Run();
         TestNativeLayoutGeneration.Run();
         TestByRefLikeVTables.Run();
@@ -1159,6 +1160,24 @@ public static void Run()
         }
     }
 
+    class TestVariantDispatchUnconstructedTypes
+    {
+        interface IFoo { }
+        class Foo : IFoo { }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        static IEnumerable<IFoo> GetFoos() => new Foo[5];
+
+        public static void Run()
+        {
+            int j = 0;
+            foreach (var f in GetFoos())
+                j++;
+            if (j != 5)
+                throw new Exception();
+        }
+    }
+
     class TestMDArrayAddressMethod
     {
         [MethodImpl(MethodImplOptions.NoInlining)]