Implement IsValueInlinedInExistentialContainer

Author: augusto2112

include/swift/Remote/MetadataReader.h

@@ -690,6 +690,28 @@ class MetadataReader {
                              RemoteAddress(StartOfValue));
   }
 
+  /// Given a known-opaque existential, discover if its value is inlined in
+  /// the existential container.
+  llvm::Optional<bool>
+  isValueInlinedInExistentialContainer(RemoteAddress ExistentialAddress) {
+    // OpaqueExistentialContainer is the layout of an opaque existential.
+    // `Type` is the pointer to the metadata.
+    TargetOpaqueExistentialContainer<Runtime> Container;
+    if (!Reader->readBytes(RemoteAddress(ExistentialAddress),
+                           (uint8_t *)&Container, sizeof(Container)))
+      return None;
+    auto MetadataAddress = static_cast<StoredPointer>(Container.Type);
+    auto Metadata = readMetadata(MetadataAddress);
+    if (!Metadata)
+      return None;
+
+    auto VWT = readValueWitnessTable(MetadataAddress);
+    if (!VWT)
+      return None;
+
+    return VWT->isValueInline();
+  }
+
   /// Read a protocol from a reference to said protocol.
   template<typename Resolver>
   typename Resolver::Result readProtocol(