Make sure to flatten names before lookup. Lookup using cons strings is really slow.

Restores SortNumbers perf degrade

BUG=chromium:495949, v8:4137
LOG=n

Review URL: https://codereview.chromium.org/1177043009

Cr-Commit-Position: refs/heads/master@{#29095}

src/api.cc

@@ -3658,9 +3658,6 @@ i::MaybeHandle<i::Object> DeleteObjectProperty(
     name = i::Handle<i::String>::cast(converted);
   }
 
-  if (name->IsString()) {
-    name = i::String::Flatten(i::Handle<i::String>::cast(name));
-  }
   return i::JSReceiver::DeleteProperty(receiver, name, language_mode);
 }
 

src/lookup.h

@@ -52,7 +52,7 @@ class LookupIterator final BASE_EMBEDDED {
         interceptor_state_(InterceptorState::kUninitialized),
         property_details_(PropertyDetails::Empty()),
         isolate_(name->GetIsolate()),
-        name_(name),
+        name_(Name::Flatten(name)),
         // kMaxUInt32 isn't a valid index.
         index_(kMaxUInt32),
         receiver_(receiver),
@@ -76,7 +76,7 @@ class LookupIterator final BASE_EMBEDDED {
         interceptor_state_(InterceptorState::kUninitialized),
         property_details_(PropertyDetails::Empty()),
         isolate_(name->GetIsolate()),
-        name_(name),
+        name_(Name::Flatten(name)),
         // kMaxUInt32 isn't a valid index.
         index_(kMaxUInt32),
         receiver_(receiver),
@@ -135,6 +135,7 @@ class LookupIterator final BASE_EMBEDDED {
   static LookupIterator PropertyOrElement(
       Isolate* isolate, Handle<Object> receiver, Handle<Name> name,
       Configuration configuration = DEFAULT) {
+    name = Name::Flatten(name);
     uint32_t index;
     LookupIterator it =
         name->AsArrayIndex(&index)
@@ -147,6 +148,7 @@ class LookupIterator final BASE_EMBEDDED {
   static LookupIterator PropertyOrElement(
       Isolate* isolate, Handle<Object> receiver, Handle<Name> name,
       Handle<JSReceiver> holder, Configuration configuration = DEFAULT) {
+    name = Name::Flatten(name);
     uint32_t index;
     LookupIterator it =
         name->AsArrayIndex(&index)
@@ -155,6 +157,7 @@ class LookupIterator final BASE_EMBEDDED {
     it.name_ = name;
     return it;
   }
+
   Isolate* isolate() const { return isolate_; }
   State state() const { return state_; }
 

src/objects-inl.h

@@ -3226,6 +3226,12 @@ Handle<String> String::Flatten(Handle<String> string, PretenureFlag pretenure) {
 }
 
 
+Handle<Name> Name::Flatten(Handle<Name> name, PretenureFlag pretenure) {
+  if (name->IsSymbol()) return name;
+  return String::Flatten(Handle<String>::cast(name));
+}
+
+
 uint16_t String::Get(int index) {
   DCHECK(index >= 0 && index < length());
   switch (StringShape(this).full_representation_tag()) {

src/objects.h

@@ -8592,6 +8592,11 @@ class Name: public HeapObject {
   // If the name is private, it can only name own properties.
   inline bool IsPrivate();
 
+  // If the name is a non-flat string, this method returns a flat version of the
+  // string. Otherwise it'll just return the input.
+  static inline Handle<Name> Flatten(Handle<Name> name,
+                                     PretenureFlag pretenure = NOT_TENURED);
+
   DECLARE_CAST(Name)
 
   DECLARE_PRINTER(Name)