[ic] Avoid memory wasting when allocating names table of type feedback metadata.

src/type-feedback-vector.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/type-feedback-vector.h"
 
 #include "src/code-stubs.h"
 #include "src/ic/ic.h"
 #include "src/ic/ic-state.h"
 #include "src/objects.h"
@@ skipping 82 matching lines @@
   for (int i = 0; i < slot_kinds_length; i++) {
     array->set(kReservedIndexCount + i, Smi::FromInt(0));
   }
 
   Handle<TypeFeedbackMetadata> metadata =
       Handle<TypeFeedbackMetadata>::cast(array);
 
   // Add names to NamesTable.
   const int name_count = spec->name_count();
 
-  Handle<UnseededNumberDictionary> names =
-      UnseededNumberDictionary::New(isolate, name_count);
+  Handle<UnseededNumberDictionary> names;
+  if (name_count) {
+    names = UnseededNumberDictionary::New(
+        isolate, base::bits::RoundUpToPowerOfTwo32(name_count), TENURED,
+        USE_CUSTOM_MINIMUM_CAPACITY);
+  }
 
   int name_index = 0;
   for (int i = 0; i < slot_count; i++) {
     FeedbackVectorSlotKind kind = spec->GetKind(i);
     metadata->SetKind(FeedbackVectorSlot(i), kind);
     if (SlotRequiresName(kind)) {
       Handle<String> name = spec->GetName(name_index);
       DCHECK(!name.is_null());
       names = UnseededNumberDictionary::AtNumberPut(names, i, name);
       name_index++;
     }
   }
   DCHECK_EQ(name_count, name_index);
-  metadata->set(kNamesTableIndex, *names);
+  metadata->set(kNamesTableIndex,
+                name_count ? static_cast<Object*>(*names) : Smi::FromInt(0));
 
   // It's important that the TypeFeedbackMetadata have a COW map, since it's
   // pointed to by both a SharedFunctionInfo and indirectly by closures through
   // the TypeFeedbackVector. The serializer uses the COW map type to decide
   // this object belongs in the startup snapshot and not the partial
   // snapshot(s).
   metadata->set_map(isolate->heap()->fixed_cow_array_map());
 
   return metadata;
 }
@@ skipping 881 matching lines @@
 
 IcCheckType KeyedStoreICNexus::GetKeyType() const {
   Object* feedback = GetFeedback();
   if (feedback == *TypeFeedbackVector::MegamorphicSentinel(GetIsolate())) {
     return static_cast<IcCheckType>(Smi::cast(GetFeedbackExtra())->value());
   }
   return IsPropertyNameFeedback(feedback) ? PROPERTY : ELEMENT;
 }
 }  // namespace internal
 }  // namespace v8