Handle calls to shared generic interfaces from shared generic code (#117210)

- The implementation uses the true LDVIRTFTN path for this. Since it thunks to using function pointer the perf is likely not ideal, but we will need a new generic dictionary entry kind to make this simple, and I'd like to avoid making that change to unblock progress here
- This expensive path was probably fine for use with virtual generic methods, but regular interface dispatch shouldn't be this expensive, so we'll want to fix this later

Author: davidwrighton

src/coreclr/interpreter/compiler.cpp

@@ -2888,7 +2888,7 @@ void InterpCompiler::EmitCall(CORINFO_RESOLVED_TOKEN* pConstrainedToken, bool re
             break;
 
         case CORINFO_VIRTUALCALL_LDVIRTFTN:
-            if (callInfo.sig.sigInst.methInstCount != 0)
+            if ((callInfo.sig.sigInst.methInstCount != 0) || (m_compHnd->getClassAttribs(resolvedCallToken.hClass) & CORINFO_FLG_SHAREDINST))
             {
                 assert(extraParamArgLocation == INT_MAX);
                 // We should not have a type argument for the ldvirtftn path since we don't know

src/tests/JIT/interpreter/Interpreter.cs

@@ -1889,7 +1889,7 @@ private static Type LoadType<T>()
         return typeof(T);
     }
 
-    class GenericClass<T>
+    class GenericClass<T> : IGeneric<T>
     {
         public Type GetTypeOfTInstance()
         {
@@ -1899,6 +1899,11 @@ public static Type GetTypeOfTStatic()
         {
             return typeof(T);
         }
+
+        Type IGeneric<T>.Method()
+        {
+            return typeof(T);
+        }
     }
 
     public static bool TestSharedGenerics_IsInst<T>(object o)
@@ -2216,6 +2221,11 @@ public static bool TestSharedGenerics_CallsTo()
         return true;
     }
 
+    interface IGeneric<T>
+    {
+        Type Method();
+    }
+
     public static bool TestGenerics_CallsFrom<T>()
     {
         if (LoadType<T>() != typeof(T))
@@ -2227,6 +2237,9 @@ public static bool TestGenerics_CallsFrom<T>()
         if (GenericClass<T>.GetTypeOfTStatic() != typeof(T))
             return false;
 
+        if (((IGeneric<T>)new GenericClass<T>()).Method() != typeof(T))
+            return false;
+
         return true;
     }