LowerHopToActor: insert borrow scope if an optional actor value is owned

The inserted switch_enum must not consume the actor value, therefore a borrow scope is needed.
Fixes an ownership error.

Author: eeckstein

lib/SILOptimizer/Mandatory/LowerHopToActor.cpp

@@ -268,10 +268,16 @@ SILValue LowerHopToActor::emitGetExecutor(SILBuilderWithScope &B,
     return B.createStructExtract(loc, witnessCall, executorProps[0]);
   };
 
+  bool needEndBorrow = false;
   SILValue unmarkedExecutor;
   if (auto wrappedActor = actorType->getOptionalObjectType()) {
     assert(makeOptional);
 
+    if (B.hasOwnership() && actor->getOwnershipKind() == OwnershipKind::Owned) {
+      actor = B.createBeginBorrow(loc, actor);
+      needEndBorrow = true;
+    }
+
     // Unwrap the optional and call 'unownedExecutor'.
     auto *someDecl = B.getASTContext().getOptionalSomeDecl();
     auto *curBB = B.getInsertionPoint()->getParent();
@@ -323,6 +329,9 @@ SILValue LowerHopToActor::emitGetExecutor(SILBuilderWithScope &B,
   // force the actor to stay alive.
   SILValue executor = B.createMarkDependence(loc, unmarkedExecutor, actor,
                                              MarkDependenceKind::Escaping);
+  if (needEndBorrow) {
+    B.createEndBorrow(loc, actor);
+  }
 
   return executor;
 }

test/SILOptimizer/lower_hop_to_actor.sil

@@ -290,3 +290,20 @@ bb0(%0 : @guaranteed $Optional<any Actor>):
   %r = tuple ()
   return %r : $()
 }
+
+// CHECK-LABEL: sil [ossa] @optional_owned_actor :
+// CHECK:         %1 = copy_value %0
+// CHECK-NEXT:    %2 = begin_borrow %1
+// CHECK-NEXT:    switch_enum %2
+// CHECK:         mark_dependence
+// CHECK-NEXT:    end_borrow %2
+// CHECKL:      } // end sil function '@optional_owned_actor'
+sil [ossa] @optional_owned_actor : $@convention(thin) @async (@guaranteed Optional<any Actor>) -> () {
+bb0(%0 : @guaranteed $Optional<any Actor>):
+  %1 = copy_value %0
+  hop_to_executor %1
+  destroy_value %1
+  %r = tuple ()
+  return %r
+}
+