Add back references. Since "back references" is two words...

src/interpreter-re2k.cc

 // Copyright 2008 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 262 matching lines @@
       }
       BYTECODE(LOOKUP_HI_MAP8) {
         // Look up high byte of this character in a byte map.  Use the byte as
         // an index into a table that follows this instruction immediately.
         int index = (current_char >> 8) - pc[1];
         byte map = code_base[Load32(pc + 2) + index];
         const byte* new_pc = code_base + Load32(pc + 6) + (map << 2);
         pc = code_base + Load32(new_pc);
         break;
       }
-      BYTECODE(CHECK_BACKREF)
-        UNREACHABLE();
+      BYTECODE(CHECK_NOT_BACK_REF) {
+        int from = registers[pc[1]];
+        int len = registers[pc[1] + 1] - from;
+        if (current + len > subject.length()) {
+          pc = code_base + Load32(pc + 2);
+          break;
+        } else {
+          int i;
+          for (i = 0; i < len; i++) {
+            if (subject[from + i] != subject[current + i]) {
+              pc = code_base + Load32(pc + 2);
+              break;
+            }
+          }
+          if (i < len) break;
+          current += len;
+        }
+        pc += BC_CHECK_NOT_BACK_REF_LENGTH;
         break;
-      BYTECODE(CHECK_NOT_BACKREF)
-        UNREACHABLE();
-        break;
+      }
       default:
         UNREACHABLE();
         break;
     }
   }
 }
 
 
 bool Re2kInterpreter::Match(Handle<ByteArray> code_array,
                             Handle<String> subject16,
                             int* registers,
                             int start_position) {
   ASSERT(StringShape(*subject16).IsTwoByteRepresentation());
   ASSERT(subject16->IsFlat(StringShape(*subject16)));
 
 
   AssertNoAllocation a;
   const byte* code_base = code_array->GetDataStartAddress();
   return RawMatch(code_base,
                   Vector<const uc16>(subject16->GetTwoByteData(),
                                      subject16->length()),
                   registers,
                   start_position);
 }
 
 } }  // namespace v8::internal