[runtime] Implement sidetable path for isUniquelyReferenced

https://bugs.swift.org/browse/SR-5633

Author: lorentey

stdlib/public/SwiftShims/RefCount.h

@@ -961,7 +961,7 @@ class RefCounts {
   bool isUniquelyReferenced() const {
     auto bits = refCounts.load(SWIFT_MEMORY_ORDER_CONSUME);
     if (bits.hasSideTable())
-      return false;  // FIXME: implement side table path if useful
+      return bits.getSideTable()->isUniquelyReferenced();
 
     assert(!bits.getIsDeiniting());
     return bits.isUniquelyReferenced();
@@ -1384,6 +1384,10 @@ class HeapObjectSideTableEntry {
     return refCounts.getCount();
   }
 
+  bool isUniquelyReferenced() const {
+    return refCounts.isUniquelyReferenced();
+  }
+
   bool isUniquelyReferencedOrPinned() const {
     return refCounts.isUniquelyReferencedOrPinned();
   }

test/stdlib/Builtins.swift

@@ -36,6 +36,31 @@ tests.test("_isUnique/NativeObject") {
   expectFalse(_isUnique_native(&b))
 }
 
+tests.test("_isUnique/NativeObjectWithPreviousStrongRef") {
+  var a: Builtin.NativeObject = Builtin.castToNativeObject(X())
+  expectTrue(_isUnique_native(&a))
+  var b: Builtin.NativeObject? = a
+  expectFalse(_isUnique_native(&a))
+  b = nil
+  expectTrue(_isUnique_native(&a))
+}
+
+tests.test("_isUnique/NativeObjectWithWeakRef") {
+  var a: Builtin.NativeObject = Builtin.castToNativeObject(X())
+  expectTrue(_isUnique_native(&a))
+  weak var b = a
+  expectTrue(_isUnique_native(&a))
+  expectFalse(_isUnique_native(&b))
+}
+
+tests.test("_isUnique/NativeObjectWithUnownedRef") {
+  var a: Builtin.NativeObject = Builtin.castToNativeObject(X())
+  expectTrue(_isUnique_native(&a))
+  unowned var b = a
+  expectTrue(_isUnique_native(&a))
+  expectFalse(_isUnique_native(&b))
+}
+
 tests.test("_isUniquelyReferenced/OptionalNativeObject") {
   var a: Builtin.NativeObject? = Builtin.castToNativeObject(X())
   StdlibUnittest.expectTrue(_getBool(Builtin.isUnique(&a)))