Use stack for first scope in VariableSizedHandleScope

VariableSizedHandleScope commonly doesn't have that many handles,
avoid doing an allocation for those cases.

Test: test-art-host
Change-Id: Iaf6c502723a239b1a2e861152efa37f4ef66431b

2 files changed, 7 insertions, 4 deletions

diff --git a/runtime/handle_scope-inl.h b/runtime/handle_scope-inl.h
index 6d8a05dcd2..90cf5970dd 100644
--- a/runtime/handle_scope-inl.h
+++ b/runtime/handle_scope-inl.h
@@ -211,16 +211,18 @@ inline MutableHandle<MirrorType> VariableSizedHandleScope::NewHandle(ObjPtr<Mirr
 
 inline VariableSizedHandleScope::VariableSizedHandleScope(Thread* const self)
     : BaseHandleScope(self->GetTopHandleScope()),
-      self_(self) {
-  current_scope_ = new LocalScopeType(/*link=*/ nullptr);
+      self_(self),
+      current_scope_(&first_scope_),
+      first_scope_(/*link=*/ nullptr) {
   self_->PushHandleScope(this);
 }
 
 inline VariableSizedHandleScope::~VariableSizedHandleScope() {
   BaseHandleScope* top_handle_scope = self_->PopHandleScope();
   DCHECK_EQ(top_handle_scope, this);
-  while (current_scope_ != nullptr) {
-    LocalScopeType* next = reinterpret_cast<LocalScopeType*>(current_scope_->GetLink());
+  // Don't delete first_scope_ since it is not heap allocated.
+  while (current_scope_ != &first_scope_) {
+    LocalScopeType* next = down_cast<LocalScopeType*>(current_scope_->GetLink());
     delete current_scope_;
     current_scope_ = next;
   }
diff --git a/runtime/handle_scope.h b/runtime/handle_scope.h
index 61f99b03c9..b173453df0 100644
--- a/runtime/handle_scope.h
+++ b/runtime/handle_scope.h
@@ -271,6 +271,7 @@ class VariableSizedHandleScope : public BaseHandleScope {
   using LocalScopeType = FixedSizeHandleScope<kNumReferencesPerScope>;
   static_assert(sizeof(LocalScopeType) <= kMaxLocalScopeSize, "Unexpected size of LocalScopeType");
   LocalScopeType* current_scope_;
+  LocalScopeType first_scope_;
 
   DISALLOW_COPY_AND_ASSIGN(VariableSizedHandleScope);
 };