Merge pull request swiftlang#39775 from nate-chandler/ownership/used-dagnodeworklist-in-visittransitiveendborrows

Used DAGNodeWorklist in visitTransitiveEndBorrows.

Author: atrick

lib/SIL/Utils/OwnershipUtils.cpp

@@ -1438,11 +1438,11 @@ void swift::findTransitiveReborrowBaseValuePairs(
 void swift::visitTransitiveEndBorrows(
     BorrowedValue beginBorrow,
     function_ref<void(EndBorrowInst *)> visitEndBorrow) {
-  SmallSetVector<SILValue, 4> worklist;
+  DAGNodeWorklist<SILValue, 4> worklist;
   worklist.insert(beginBorrow.value);
 
   while (!worklist.empty()) {
-    auto val = worklist.pop_back_val();
+    auto val = worklist.pop();
     for (auto *consumingUse : val->getConsumingUses()) {
       auto *consumingUser = consumingUse->getUser();
       if (auto *branch = dyn_cast<BranchInst>(consumingUser)) {

test/SILOptimizer/dead_code_elimination_nontrivial_ossa.sil

@@ -652,3 +652,30 @@ bb4(%3 : @owned $Klass):
   return %res : $()
 }
 
+// CHECK-LABEL: sil [ossa] @looping_borrow : $@convention(thin) () -> () {
+// CHECK-NOT:     destroy_value
+// CHECK-LABEL: } // end sil function 'looping_borrow'
+sil [ossa] @looping_borrow : $@convention(thin) () -> () {
+entry:
+  %instance_1 = enum $FakeOptional<Klass>, #FakeOptional.none!enumelt
+  %lifetime_1 = begin_borrow [lexical] %instance_1 : $FakeOptional<Klass>
+  br loop_entry(%instance_1 : $FakeOptional<Klass>, %lifetime_1 : $FakeOptional<Klass>)
+
+loop_entry(%18 : @owned $FakeOptional<Klass>, %19 : @guaranteed $FakeOptional<Klass>):
+  br loop_body
+
+loop_body:
+  cond_br undef, loop_back, loop_exit
+
+loop_back:
+  br loop_entry(%18 : $FakeOptional<Klass>, %19 : $FakeOptional<Klass>)
+
+loop_exit:
+  end_borrow %19 : $FakeOptional<Klass>
+  destroy_value %18 : $FakeOptional<Klass>
+  br exit
+
+exit:
+  %retval = tuple ()
+  return %retval : $()
+}