[Async CC] Add AsyncFunctionPointer to vtable.

Author: nate-chandler

lib/IRGen/GenMeta.cpp

@@ -3119,8 +3119,12 @@ namespace {
       // The class is fragile. Emit a direct reference to the vtable entry.
       llvm::Constant *ptr;
       if (entry) {
-        ptr = IGM.getAddrOfSILFunction(entry->getImplementation(),
-                                       NotForDefinition);
+        if (entry->getImplementation()->isAsync()) {
+          ptr = IGM.getAddrOfAsyncFunctionPointer(entry->getImplementation());
+        } else {
+          ptr = IGM.getAddrOfSILFunction(entry->getImplementation(),
+                                         NotForDefinition);
+        }
       } else {
         // The method is removed by dead method elimination.
         // It should be never called. We add a pointer to an error function.