Optimize the common obfuscator pattern where ["foo","bar","baz"]

src/heap.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 824 matching lines @@
   contexts_disposed_ = 0;
 }
 
 
 void Heap::MarkCompactPrologue(bool is_compacting) {
   // At any old GC clear the keyed lookup cache to enable collection of unused
   // maps.
   isolate_->keyed_lookup_cache()->Clear();
   isolate_->context_slot_cache()->Clear();
   isolate_->descriptor_lookup_cache()->Clear();
+  StringSplitCache::Clear(string_split_cache());
 
   isolate_->compilation_cache()->MarkCompactPrologue();
 
   CompletelyClearInstanceofCache();
 
   if (is_compacting) FlushNumberStringCache();
   if (FLAG_cleanup_code_caches_at_gc) {
     polymorphic_code_cache()->set_cache(undefined_value());
   }
 
@@ skipping 1361 matching lines @@
 
   if (InitializeNumberStringCache()->IsFailure()) return false;
 
   // Allocate cache for single character ASCII strings.
   { MaybeObject* maybe_obj =
         AllocateFixedArray(String::kMaxAsciiCharCode + 1, TENURED);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_single_character_string_cache(FixedArray::cast(obj));
 
+  // Allocate cache for string split.
+  { MaybeObject* maybe_obj =
+        AllocateFixedArray(StringSplitCache::kStringSplitCacheSize, TENURED);
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  set_string_split_cache(FixedArray::cast(obj));
+
   // Allocate cache for external strings pointing to native source code.
   { MaybeObject* maybe_obj = AllocateFixedArray(Natives::GetBuiltinsCount());
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_natives_source_cache(FixedArray::cast(obj));
 
   // Handling of script id generation is in FACTORY->NewScript.
   set_last_script_id(undefined_value());
 
   // Initialize keyed lookup cache.
   isolate_->keyed_lookup_cache()->Clear();
 
   // Initialize context slot cache.
   isolate_->context_slot_cache()->Clear();
 
   // Initialize descriptor cache.
   isolate_->descriptor_lookup_cache()->Clear();
 
   // Initialize compilation cache.
   isolate_->compilation_cache()->Clear();
 
   return true;
 }
 
 
+Object* StringSplitCache::Lookup(
+    FixedArray* cache, String* string, String* pattern) {
+  if (!string->IsSymbol() || !pattern->IsSymbol()) return Smi::FromInt(0);
+  uintptr_t hash = string->Hash();
+  uintptr_t index = ((hash & (kStringSplitCacheSize - 1)) &
+      ~(kArrayEntriesPerCacheEntry - 1));
+  if (cache->get(index + kStringOffset) == string &&
+      cache->get(index + kPatternOffset) == pattern) {
+    return cache->get(index + kArrayOffset);
+  }
+  index = ((index + kArrayEntriesPerCacheEntry) & (kStringSplitCacheSize - 1));
+  if (cache->get(index + kStringOffset) == string &&
+      cache->get(index + kPatternOffset) == pattern) {
+    return cache->get(index + kArrayOffset);
+  }
+  return Smi::FromInt(0);
+}
+
+ 
+void StringSplitCache::Enter(Heap* heap,
+                             FixedArray* cache,
+                             String* string,
+                             String* pattern,
+                             FixedArray* array) {
+  if (!string->IsSymbol() || !pattern->IsSymbol()) return;
+  uintptr_t hash = string->Hash();
+  array->set_map(heap->fixed_cow_array_map());
+  uintptr_t index = ((hash & (kStringSplitCacheSize - 1)) &
+      ~(kArrayEntriesPerCacheEntry - 1));
+  if (cache->get(index + kStringOffset) == Smi::FromInt(0)) {
+    cache->set(index + kStringOffset, string);
+    cache->set(index + kPatternOffset, pattern);
+    cache->set(index + kArrayOffset, array);
+    return;
+  }
+  uintptr_t index2 =
+      ((index + kArrayEntriesPerCacheEntry) & (kStringSplitCacheSize - 1));
+  if (cache->get(index2 + kStringOffset) == Smi::FromInt(0)) {
+    cache->set(index2 + kStringOffset, string);
+    cache->set(index2 + kPatternOffset, pattern);
+    cache->set(index2 + kArrayOffset, array);
+    return;
+  }
+  cache->set(index2 + kStringOffset, Smi::FromInt(0));
+  cache->set(index2 + kPatternOffset, Smi::FromInt(0));
+  cache->set(index2 + kArrayOffset, Smi::FromInt(0));
+  cache->set(index + kStringOffset, string);
+  cache->set(index + kPatternOffset, pattern);
+  cache->set(index + kArrayOffset, array);
+  if (array->length() < 100) {  // Limit how many new symbols we want to make.
+    for (int i = 0; i < array->length(); i++) {
+      String* str = String::cast(array->get(i));
+      Object* symbol;
+      MaybeObject* maybe_symbol = heap->LookupSymbol(str);
+      if (maybe_symbol->ToObject(&symbol)) {
+        array->set(i, symbol);
+      }
+    }
+  }
+}
+
+
+void StringSplitCache::Clear(FixedArray* cache) {
+  for (int i = 0; i < kStringSplitCacheSize; i++) {
+    cache->set(i, Smi::FromInt(0));
+  }
+}
+
+
 MaybeObject* Heap::InitializeNumberStringCache() {
   // Compute the size of the number string cache based on the max heap size.
   // max_semispace_size_ == 512 KB => number_string_cache_size = 32.
   // max_semispace_size_ ==   8 MB => number_string_cache_size = 16KB.
   int number_string_cache_size = max_semispace_size_ / 512;
   number_string_cache_size = Max(32, Min(16*KB, number_string_cache_size));
   Object* obj;
   MaybeObject* maybe_obj =
       AllocateFixedArray(number_string_cache_size * 2, TENURED);
   if (maybe_obj->ToObject(&obj)) set_number_string_cache(FixedArray::cast(obj));
@@ skipping 3885 matching lines @@
 }
 
 
 void ExternalStringTable::TearDown() {
   new_space_strings_.Free();
   old_space_strings_.Free();
 }
 
 
 } }  // namespace v8::internal