IRGen: Fix multipayload enums with indirect cases

swift_unknownRetain does not work on indirect enum heap buffers.

The existing logic would say: oh one case is
ReferenceCounting::BridgeObject (which on its own probably would not
work with swift_unknownRetain), oh and another second case is NativeObject (for
the indirect buffer), let's use unknowRetain.

Pair the logic down to only use a single style of reference count
operation if all cases are of the same ReferenceCounting type.

rdar://40525268

Author: aschwaighofer

lib/IRGen/GenEnum.cpp

@@ -3129,15 +3129,12 @@ namespace {
                                                &refcounting)) {
           allSingleRefcount = false;
         } else if (haveRefcounting) {
-          // Different payloads have different reference counting styles.
-          if (refcounting != Refcounting) {
-            // Fall back to unknown entry points if the Objective-C runtime is
-            // available.
-            Refcounting = ReferenceCounting::Unknown;
-            // Otherwise, use value witnesses.
-            if (!IGM.ObjCInterop)
-              allSingleRefcount = false;
-          }
+          // Only support a single style of reference counting for now.
+          // swift_unknowRetain does not support the heap buffer of indirect
+          // enums. And I am not convinced that unknowRetain supports
+          // bridgedObjectRetain.
+          if (refcounting != Refcounting)
+            allSingleRefcount = false;
         } else {
           Refcounting = refcounting;
           haveRefcounting = true;

test/Interpreter/enum.swift

@@ -667,3 +667,33 @@ public func testCase(_ closure: @escaping (Int) -> ()) -> Indirect<(Int) -> ()>
 
 // CHECK: payload((Function), other: (Function))
 print(testCase({ _ in }))
+
+
+enum MultiIndirectRef {
+  case empty
+  indirect case ind(Int)
+  case collection([Int])
+}
+
+struct Container {
+  var storage : MultiIndirectRef = .empty
+
+  mutating func adoptStyle(_ s: Int) {
+    storage = .ind(s)
+  }
+}
+
+func copyStorage(_ s: Int, _ x : Container) -> Container {
+  var c = x
+  c.adoptStyle(s)
+  return c
+}
+
+func testCase() {
+  let l = Container()
+  let c = copyStorage(5, l)
+  print(c)
+}
+
+// CHECK: Container(storage: a.MultiIndirectRef.ind(5))
+testCase()