[regexp] Match spec semantics in AdvanceStringIndex

src/builtins/builtins-regexp.cc

 // Copyright 2016 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/builtins/builtins-utils.h"
 #include "src/builtins/builtins.h"
 
 #include "src/code-factory.h"
 #include "src/regexp/jsregexp.h"
 #include "src/regexp/regexp-utils.h"
@@ skipping 1382 matching lines @@
   while (string_index < length) {
     RETURN_FAILURE_ON_EXCEPTION(
         isolate, RegExpUtils::SetLastIndex(isolate, splitter, string_index));
 
     Handle<Object> result;
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
         isolate, result, RegExpUtils::RegExpExec(isolate, splitter, string,
                                                  factory->undefined_value()));
 
     if (result->IsNull(isolate)) {
-      string_index += RegExpUtils::AdvanceStringIndex(isolate, string,
-                                                      string_index, unicode);
+      string_index = RegExpUtils::AdvanceStringIndex(isolate, string,
+                                                     string_index, unicode);
       continue;
     }
 
     // TODO(jgruber): Extract toLength of some property into function.
     Handle<Object> last_index_obj;
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
         isolate, last_index_obj, RegExpUtils::GetLastIndex(isolate, splitter));
 
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
         isolate, last_index_obj, Object::ToLength(isolate, last_index_obj));
     const int last_index = Handle<Smi>::cast(last_index_obj)->value();
 
     const int end = std::min(last_index, length);
     if (end == prev_string_index) {
-      string_index += RegExpUtils::AdvanceStringIndex(isolate, string,
-                                                      string_index, unicode);
+      string_index = RegExpUtils::AdvanceStringIndex(isolate, string,
+                                                     string_index, unicode);
       continue;
     }
 
     {
       Handle<String> substr =
           factory->NewSubString(string, prev_string_index, string_index);
       elems = FixedArray::SetAndGrow(elems, num_elems++, substr);
       if (num_elems == limit) {
         return *NewJSArrayWithElements(isolate, elems, num_elems);
       }
@@ skipping 277 matching lines @@
   {
     Node* const match_elements = a->LoadElements(match_indices);
     Node* result = ConstructNewResultFromMatchInfo(isolate, a, context,
                                                    match_elements, string);
     a->Return(result);
   }
 }
 
 }  // namespace internal
 }  // namespace v8