projectExistential: Use the metadata field offset as size comparison

It's more accurate to use the offset of the "metadata field" of the
existential's RecordTypeInfo when projecting an existential
during remote reflection.

Author: bitjammer

include/swift/Reflection/ReflectionContext.h

@@ -149,19 +149,19 @@ class ReflectionContext
     // container. If it doesn't, the first word is a pointer to a heap box.
     case RecordKind::Existential: {
       auto Fields = ExistentialRecordTI->getFields();
-      auto Metadata = std::find_if(Fields.begin(), Fields.end(),
+      auto ExistentialMetadataField = std::find_if(Fields.begin(), Fields.end(),
                                    [](const FieldInfo &FI) -> bool {
         return FI.Name.compare("metadata") == 0;
       });
-      if (Metadata == Fields.end())
+      if (ExistentialMetadataField == Fields.end())
         return false;
 
       // Get the metadata pointer for the contained instance type.
       // This is equivalent to:
       // auto PointerArray = reinterpret_cast<uintptr_t*>(ExistentialAddress);
       // uintptr_t MetadataAddress = PointerArray[Offset];
       auto MetadataAddressAddress
-        = RemoteAddress(ExistentialAddress + Metadata->Offset);
+        = RemoteAddress(ExistentialAddress + ExistentialMetadataField->Offset);
 
       StoredPointer MetadataAddress = 0;
       if (!getReader().readInteger(MetadataAddressAddress, &MetadataAddress))
@@ -177,7 +177,7 @@ class ReflectionContext
       if (!InstanceTI)
         return false;
 
-      if (InstanceTI->getSize() < ExistentialRecordTI->getSize()) {
+      if (InstanceTI->getSize() <= ExistentialMetadataField->Offset) {
         // The value fits in the existential container, so it starts at the
         // start of the container.
         *OutInstanceAddress = ExistentialAddress;