[compiler] Introduce code stubs for abstract equality.

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 267 matching lines @@
   // ES6 section 7.2.11 Abstract Relational Comparison step 6.
   if (!Object::ToNumber(x).ToHandle(&x) || !Object::ToNumber(y).ToHandle(&y)) {
     return Nothing<ComparisonResult>();
   }
   return Just(NumberCompare(x->Number(), y->Number()));
 }
 
 
 // static
 Maybe<bool> Object::Equals(Handle<Object> x, Handle<Object> y) {
+  // This is the generic version of Abstract Equality Comparison; a version in
+  // JavaScript land is available in the EqualStub and NotEqualStub. Whenever
+  // you change something functionality wise in here, remember to update the
+  // TurboFan code stubs as well.
   while (true) {
     if (x->IsNumber()) {
       if (y->IsNumber()) {
         return Just(NumberEquals(x, y));
       } else if (y->IsBoolean()) {
         return Just(NumberEquals(*x, Handle<Oddball>::cast(y)->to_number()));
       } else if (y->IsString()) {
         return Just(NumberEquals(x, String::ToNumber(Handle<String>::cast(y))));
       } else if (y->IsJSReceiver()) {
         if (!JSReceiver::ToPrimitive(Handle<JSReceiver>::cast(y))
@@ skipping 19473 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8