Add support for Open instance delegate on valuetype methods

- Generalize the ability to get an non-unboxing function pointer from an unboxing stub function pointer from being part of constrainedcall support to being general purpose.
- Add path thru OpenMethodResolver which uses the above generalization
- Adjust parameter checking around delegate construction from a MethodInfo to be correct in this case
- Tweak calling convention converter to avoid asserts that would fire in this case, and to use the value in the ref parameter directly.
- A minor refactoring of CallingConventions.cs to make TypeHandle creation involving byref EETypes correct, and to provide an external to typeloader api which can express if a type is to be returned via a retbuffer. This change is not used in the current code, but the factoring appears to be an improvement

[tfs-changeset: 1659735]

2 files changed, 12 insertions, 2 deletions

diff --git a/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/MethodInvokers/InstanceMethodInvoker.cs b/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/MethodInvokers/InstanceMethodInvoker.cs
index 9d8f1a123..208ca22fe 100644
--- a/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/MethodInvokers/InstanceMethodInvoker.cs
+++ b/src/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/MethodInvokers/InstanceMethodInvoker.cs
@@ -50,9 +50,19 @@ namespace Internal.Reflection.Execution.MethodInvokers
         {
             if (isOpen)
             {
+                MethodInfo methodInfo = (MethodInfo)MethodInvokeInfo.MethodInfo;
+
+                short resolveType = OpenMethodResolver.OpenNonVirtualResolve;
+
+                if (methodInfo.DeclaringType.IsValueType && !methodInfo.IsStatic)
+                {
+                    // Open instance method for valuetype
+                    resolveType = OpenMethodResolver.OpenNonVirtualResolveLookthruUnboxing;
+                }
+
                 return RuntimeAugments.CreateDelegate(
                     delegateType,
-                    new OpenMethodResolver(_declaringTypeHandle, MethodInvokeInfo.LdFtnResult, default(GCHandle), 0).ToIntPtr(),
+                    new OpenMethodResolver(_declaringTypeHandle, MethodInvokeInfo.LdFtnResult, default(GCHandle), 0, resolveType).ToIntPtr(),
                     target,
                     isStatic: isStatic,
                     isOpen: isOpen);
diff --git a/src/System.Private.Reflection.Execution/src/Internal/Reflection/Extensions/NonPortable/DelegateMethodInfoRetriever.cs b/src/System.Private.Reflection.Execution/src/Internal/Reflection/Extensions/NonPortable/DelegateMethodInfoRetriever.cs
index 5f2d2c4e2..eccf479f6 100644
--- a/src/System.Private.Reflection.Execution/src/Internal/Reflection/Extensions/NonPortable/DelegateMethodInfoRetriever.cs
+++ b/src/System.Private.Reflection.Execution/src/Internal/Reflection/Extensions/NonPortable/DelegateMethodInfoRetriever.cs
@@ -40,7 +40,7 @@ namespace Internal.Reflection.Extensions.NonPortable
                 if (isOpenResolver)
                 {
                     OpenMethodResolver* resolver = (OpenMethodResolver*)originalLdFtnResult;
-                    if (resolver->ResolverType == OpenMethodResolver.OpenNonVirtualResolve)
+                    if (resolver->IsOpenNonVirtualResolve)
                     {
                         originalLdFtnResult = resolver->CodePointer;
                         // And go on to do normal ldftn processing.