Tentative implementation of string slices (hidden under the flag --string-slices).

src/runtime.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 2948 matching lines @@
   int pattern_length = pat->length();
   if (pattern_length == 0) return start_index;
 
   int subject_length = sub->length();
   if (start_index + pattern_length > subject_length) return -1;
 
   if (!sub->IsFlat()) FlattenString(sub);
   if (!pat->IsFlat()) FlattenString(pat);
 
   AssertNoAllocation no_heap_allocation;  // ensure vectors stay valid
-  // Extract flattened substrings of cons strings before determining asciiness.
-  String* seq_sub = *sub;
-  if (seq_sub->IsConsString()) seq_sub = ConsString::cast(seq_sub)->first();
-  String* seq_pat = *pat;
-  if (seq_pat->IsConsString()) seq_pat = ConsString::cast(seq_pat)->first();
 
   // dispatch on type of strings
-  if (seq_pat->IsAsciiRepresentation()) {
-    Vector<const char> pat_vector = seq_pat->ToAsciiVector();
-    if (seq_sub->IsAsciiRepresentation()) {
+  if (pat->IsAsciiRepresentationUnderneath()) {
+    Vector<const char> pat_vector = pat->ToAsciiVector();
+    if (sub->IsAsciiRepresentationUnderneath()) {
       return SearchString(isolate,
-                          seq_sub->ToAsciiVector(),
+                          sub->ToAsciiVector(),
                           pat_vector,
                           start_index);
     }
     return SearchString(isolate,
-                        seq_sub->ToUC16Vector(),
+                        sub->ToUC16Vector(),
                         pat_vector,
                         start_index);
   }
-  Vector<const uc16> pat_vector = seq_pat->ToUC16Vector();
-  if (seq_sub->IsAsciiRepresentation()) {
+  Vector<const uc16> pat_vector = pat->ToUC16Vector();
+  if (sub->IsAsciiRepresentationUnderneath()) {
     return SearchString(isolate,
-                        seq_sub->ToAsciiVector(),
+                        sub->ToAsciiVector(),
                         pat_vector,
                         start_index);
   }
   return SearchString(isolate,
-                      seq_sub->ToUC16Vector(),
+                      sub->ToUC16Vector(),
                       pat_vector,
                       start_index);
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_StringIndexOf) {
   HandleScope scope(isolate);  // create a new handle scope
   ASSERT(args.length() == 3);
 
   CONVERT_ARG_CHECKED(String, sub, 0);
@@ skipping 564 matching lines @@
   // No matches at all, return failure or exception result directly.
   return result;
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpExecMultiple) {
   ASSERT(args.length() == 4);
   HandleScope handles(isolate);
 
   CONVERT_ARG_CHECKED(String, subject, 1);
-  if (!subject->IsFlat()) { FlattenString(subject); }
+  if (!subject->IsFlat()) FlattenString(subject);
   CONVERT_ARG_CHECKED(JSRegExp, regexp, 0);
   CONVERT_ARG_CHECKED(JSArray, last_match_info, 2);
   CONVERT_ARG_CHECKED(JSArray, result_array, 3);
 
   ASSERT(last_match_info->HasFastElements());
   ASSERT(regexp->GetFlags().is_global());
   Handle<FixedArray> result_elements;
   if (result_array->HasFastElements()) {
     result_elements =
         Handle<FixedArray>(FixedArray::cast(result_array->elements()));
@@ skipping 9156 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal