Ensure we track MakeGenericType (#118479)

...even if there's no member access following the call.

This was found in https://github.com/dotnet/runtime/pull/118060/files#r2247963234 but the test case I'm adding is also failing in .NET 9 and doesn't require an IL-only repro to hit because all we need is a struct.

Author: MichalStrehovsky

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/HandleCallAction.cs

@@ -90,15 +90,24 @@ private partial bool TryHandleIntrinsic(
                                             }
                                         }
                                     }
-                                    else if (typeInstantiated.Instantiation.IsConstrainedToBeReferenceTypes())
-                                    {
-                                        // This will always succeed thanks to the runtime type loader
-                                    }
                                     else
                                     {
-                                        triggersWarning = true;
-                                    }
+                                        if (typeInstantiated.Instantiation.IsConstrainedToBeReferenceTypes())
+                                        {
+                                            // This will always succeed thanks to the runtime type loader
+                                        }
+                                        else
+                                        {
+                                            triggersWarning = true;
+                                        }
 
+                                        // This should technically be in the IsConstrainedToBeReferenceTypes branch above
+                                        // but we have trim warning suppressions in dotnet/runtime and elsewhere that rely on the implementation
+                                        // detail that reference type instantiations will work, even if the generic is not
+                                        // constrained to be a reference type.
+                                        // MarkType will try to come up with a reference type type loader template.
+                                        _reflectionMarker.MarkType(_diagnosticContext.Origin, typeInstantiated, "MakeGenericType");
+                                    }
                                 }
                                 else if (value == NullValue.Instance)
                                 {

src/tests/nativeaot/SmokeTests/Reflection/Reflection.cs

@@ -76,6 +76,8 @@ private static int Main()
         Test105034Regression.Run();
         TestMethodsNeededFromNativeLayout.Run();
         TestFieldAndParamMetadata.Run();
+        TestActivationWithoutConstructor.Run();
+        TestNestedMakeGeneric.Run();
 
         //
         // Mostly functionality tests
@@ -859,6 +861,60 @@ public static void Run()
         }
     }
 
+    class TestActivationWithoutConstructor
+    {
+        public static void Run()
+        {
+            {
+                object o = Activator.CreateInstance(typeof(StructForCreateInstanceDirect<>).MakeGenericType(GetTheType()));
+                if (!o.ToString().Contains(nameof(StructForCreateInstanceDirect<>)))
+                    throw new Exception();
+            }
+
+            {
+                object o = CreateInstance(typeof(StructForCreateInstanceIndirect<>).MakeGenericType(GetTheType()));
+                if (!o.ToString().Contains(nameof(StructForCreateInstanceIndirect<>)))
+                    throw new Exception();
+
+                static object CreateInstance([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type t)
+                    => Activator.CreateInstance(t);
+            }
+
+            {
+                object o = RuntimeHelpers.GetUninitializedObject(typeof(StructForGetUninitializedObject<>).MakeGenericType(GetTheType()));
+                if (!o.ToString().Contains(nameof(StructForGetUninitializedObject<>)))
+                    throw new Exception();
+            }
+
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            static Type GetTheType() => typeof(Atom);
+        }
+
+        class Atom;
+
+        struct StructForCreateInstanceDirect<T> where T : class;
+        struct StructForCreateInstanceIndirect<T> where T : class;
+        struct StructForGetUninitializedObject<T> where T : class;
+    }
+
+    class TestNestedMakeGeneric
+    {
+        class Outie<T> where T : class;
+        class Innie<T> where T : class;
+        class Atom;
+
+        public static void Run()
+        {
+            Type inner = typeof(Innie<>).MakeGenericType(GetAtom());
+            Type outer = typeof(Outie<>).MakeGenericType(inner);
+
+            Console.WriteLine(Activator.CreateInstance(outer));
+
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            static Type GetAtom() => typeof(Atom);
+        }
+    }
+
     class TestCreateDelegate
     {
         internal class Greeter