Add an operation that checks whether we are at the start of the string.

src/interpreter-irregexp.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 347 matching lines @@
           break;
         } else {
           if (BackRefMatchesNoCase(from, current, len, subject)) {
             pc += BC_CHECK_NOT_BACK_REF_NO_CASE_LENGTH;
           } else {
             pc = code_base + Load32(pc + 2);
           }
         }
         break;
       }
+      BYTECODE(CHECK_NOT_AT_START)
+        if (current == 0) {
+          pc += BC_CHECK_NOT_AT_START_LENGTH;
+        } else {
+          pc = code_base + Load32(pc + 1);
+        }
+        break;
       default:
         UNREACHABLE();
         break;
     }
   }
 }
 
 
 bool IrregexpInterpreter::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();
   uc16 previous_char = '\n';
   Vector<const uc16> subject_vector =
       Vector<const uc16>(subject16->GetTwoByteData(), subject16->length());
   if (start_position != 0) previous_char = subject_vector[start_position - 1];
   return RawMatch(code_base,
                   subject_vector,
                   registers,
                   start_position,
                   previous_char);
 }
 
 } }  // namespace v8::internal