Replace PushIfAbsent by a Stack object

src/runtime/runtime-strings.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/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/conversions-inl.h"
 #include "src/isolate-inl.h"
 #include "src/regexp/jsregexp-inl.h"
@@ skipping 624 matching lines @@
   RUNTIME_ASSERT(array_length > 0);
 
   // Find total length of join result.
   int string_length = 0;
   bool is_one_byte = separator->IsOneByteRepresentation();
   bool overflow = false;
   CONVERT_NUMBER_CHECKED(int, elements_length, Int32, elements_array->length());
   RUNTIME_ASSERT(elements_length <= elements_array->elements()->length());
   RUNTIME_ASSERT((elements_length & 1) == 0);  // Even length.
   FixedArray* elements = FixedArray::cast(elements_array->elements());
-  for (int i = 0; i < elements_length; i += 2) {
-    RUNTIME_ASSERT(elements->get(i)->IsNumber());
-    CONVERT_NUMBER_CHECKED(uint32_t, position, Uint32, elements->get(i));
-    RUNTIME_ASSERT(position < array_length);
-    RUNTIME_ASSERT(elements->get(i + 1)->IsString());
-  }
-
   {
     DisallowHeapAllocation no_gc;
     for (int i = 0; i < elements_length; i += 2) {
       String* string = String::cast(elements->get(i + 1));
       int length = string->length();
       if (is_one_byte && !string->IsOneByteRepresentation()) {
         is_one_byte = false;
       }
       if (length > String::kMaxLength ||
           String::kMaxLength - length < string_length) {
@@ skipping 647 matching lines @@
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 2);
   if (!args[0]->IsString()) return isolate->heap()->undefined_value();
   if (!args[1]->IsNumber()) return isolate->heap()->undefined_value();
   if (std::isinf(args.number_at(1))) return isolate->heap()->nan_value();
   return __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
 }
 
 }  // namespace internal
 }  // namespace v8