[string] Add a fast path to String.p.replace

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 <memory>
 #include <sstream>
@@ skipping 11422 matching lines @@
     Vector<const uint8_t> pat_vector = search_content.ToOneByteVector();
     return SearchString<const uint8_t>(isolate, receiver_content, pat_vector,
                                        start_index);
   }
   Vector<const uc16> pat_vector = search_content.ToUC16Vector();
   return SearchString<const uc16>(isolate, receiver_content, pat_vector,
                                   start_index);
 }
 
 MaybeHandle<String> String::GetSubstitution(Isolate* isolate, Match* match,
-                                            Handle<String> replacement) {
+                                            Handle<String> replacement,
+                                            int start_index) {
   DCHECK_IMPLIES(match->HasNamedCaptures(), FLAG_harmony_regexp_named_captures);
+  DCHECK_GE(start_index, 0);
 
   Factory* factory = isolate->factory();
 
   const int replacement_length = replacement->length();
   const int captures_length = match->CaptureCount();
 
   replacement = String::Flatten(replacement);
 
   Handle<String> dollar_string =
       factory->LookupSingleCharacterStringFromCode('$');
-  int next_dollar_ix = String::IndexOf(isolate, replacement, dollar_string, 0);
+  int next_dollar_ix =
+      String::IndexOf(isolate, replacement, dollar_string, start_index);
   if (next_dollar_ix < 0) {
     return replacement;
   }
 
   IncrementalStringBuilder builder(isolate);
 
   if (next_dollar_ix > 0) {
     builder.AppendString(factory->NewSubString(replacement, 0, next_dollar_ix));
   }
 
@@ skipping 8985 matching lines @@
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 
 }  // namespace internal
 }  // namespace v8