Fix actor/job/task leaks in the back deployment runtime.

When initializing an actor, job, or task, use _swift_instantiateInertHeapObject to have the OS's libswiftCore set up the object's refcounts field, to ensure we get a valid initial state.

There is no equivalent for immortal objects, but by a stroke of luck the new representation for immortal refcounts happens to set the immortal bit in the old representation.

rdar://93087343

Author: mikeash

stdlib/public/BackDeployConcurrency/Actor.h

@@ -31,11 +31,23 @@ class alignas(Alignment_DefaultActor) DefaultActor : public HeapObject {
   // destructor does not destroy the actor instance; you must call
   // swift_defaultActor_{initialize,destroy} yourself.
   constexpr DefaultActor(const HeapMetadata *metadata)
-    : HeapObject(metadata), PrivateData{} {}
+    : HeapObject(metadata), PrivateData{} {
+    initHeapObject();
+  }
 
   constexpr DefaultActor(const HeapMetadata *metadata,
                          InlineRefCounts::Immortal_t immortal)
-    : HeapObject(metadata, immortal), PrivateData{} {}
+    : HeapObject(metadata, immortal), PrivateData{} {
+    // By a lucky coincidence, the modern bit pattern for immortal objects also
+    // sets the immortal bit for older runtimes, so we don't need an immortal
+    // equivalent to initHeapObject().
+  }
+
+  void initHeapObject() {
+#ifdef SWIFT_CONCURRENCY_BACK_DEPLOYMENT
+    _swift_instantiateInertHeapObject(this, metadata);
+#endif
+  }
 
   void *PrivateData[NumWords_DefaultActor];
 };

stdlib/public/BackDeployConcurrency/Task.h

@@ -95,6 +95,7 @@ class alignas(2 * alignof(void*)) Job :
   Job(JobFlags flags, JobInvokeFunction *invoke,
       const HeapMetadata *metadata = &jobHeapMetadata)
       : HeapObject(metadata), Flags(flags), RunJob(invoke) {
+    initHeapObject();
     Voucher = voucher_copy();
     assert(!isAsyncTask() && "wrong constructor for a task");
   }
@@ -103,6 +104,7 @@ class alignas(2 * alignof(void*)) Job :
       const HeapMetadata *metadata = &jobHeapMetadata,
       bool captureCurrentVoucher = true)
       : HeapObject(metadata), Flags(flags), ResumeTask(invoke) {
+    initHeapObject();
     if (captureCurrentVoucher)
       Voucher = voucher_copy();
     assert(isAsyncTask() && "wrong constructor for a non-task job");
@@ -114,11 +116,20 @@ class alignas(2 * alignof(void*)) Job :
       const HeapMetadata *metadata, InlineRefCounts::Immortal_t immortal,
       bool captureCurrentVoucher = true)
       : HeapObject(metadata, immortal), Flags(flags), ResumeTask(invoke) {
+    // By a lucky coincidence, the modern bit pattern for immortal objects also
+    // sets the immortal bit for older runtimes, so we don't need an immortal
+    // equivalent to initHeapObject().
     if (captureCurrentVoucher)
       Voucher = voucher_copy();
     assert(isAsyncTask() && "wrong constructor for a non-task job");
   }
 
+  void initHeapObject() {
+#ifdef SWIFT_CONCURRENCY_BACK_DEPLOYMENT
+    _swift_instantiateInertHeapObject(this, metadata);
+#endif
+  }
+
   ~Job() { swift_voucher_release(Voucher); }
 
   bool isAsyncTask() const {