Home | History | Annotate | Download | only in cctest
      1 // Copyright 2011 the V8 project authors. All rights reserved.
      2 
      3 // Check that we can traverse very deep stacks of ConsStrings using
      4 // StringInputBuffer.  Check that Get(int) works on very deep stacks
      5 // of ConsStrings.  These operations may not be very fast, but they
      6 // should be possible without getting errors due to too deep recursion.
      7 
      8 #include <stdlib.h>
      9 
     10 #include "v8.h"
     11 
     12 #include "api.h"
     13 #include "factory.h"
     14 #include "cctest.h"
     15 #include "zone-inl.h"
     16 
     17 unsigned int seed = 123;
     18 
     19 static uint32_t gen() {
     20         uint64_t z;
     21         z = seed;
     22         z *= 279470273;
     23         z %= 4294967291U;
     24         seed = static_cast<unsigned int>(z);
     25         return static_cast<uint32_t>(seed >> 16);
     26 }
     27 
     28 
     29 using namespace v8::internal;
     30 
     31 static v8::Persistent<v8::Context> env;
     32 
     33 
     34 static void InitializeVM() {
     35   if (env.IsEmpty()) {
     36     v8::HandleScope scope;
     37     const char* extensions[] = { "v8/print" };
     38     v8::ExtensionConfiguration config(1, extensions);
     39     env = v8::Context::New(&config);
     40   }
     41   v8::HandleScope scope;
     42   env->Enter();
     43 }
     44 
     45 
     46 static const int NUMBER_OF_BUILDING_BLOCKS = 128;
     47 static const int DEEP_DEPTH = 8 * 1024;
     48 static const int SUPER_DEEP_DEPTH = 80 * 1024;
     49 
     50 
     51 class Resource: public v8::String::ExternalStringResource,
     52                 public ZoneObject {
     53  public:
     54   explicit Resource(Vector<const uc16> string): data_(string.start()) {
     55     length_ = string.length();
     56   }
     57   virtual const uint16_t* data() const { return data_; }
     58   virtual size_t length() const { return length_; }
     59 
     60  private:
     61   const uc16* data_;
     62   size_t length_;
     63 };
     64 
     65 
     66 class AsciiResource: public v8::String::ExternalAsciiStringResource,
     67                 public ZoneObject {
     68  public:
     69   explicit AsciiResource(Vector<const char> string): data_(string.start()) {
     70     length_ = string.length();
     71   }
     72   virtual const char* data() const { return data_; }
     73   virtual size_t length() const { return length_; }
     74 
     75  private:
     76   const char* data_;
     77   size_t length_;
     78 };
     79 
     80 
     81 static void InitializeBuildingBlocks(
     82     Handle<String> building_blocks[NUMBER_OF_BUILDING_BLOCKS]) {
     83   // A list of pointers that we don't have any interest in cleaning up.
     84   // If they are reachable from a root then leak detection won't complain.
     85   for (int i = 0; i < NUMBER_OF_BUILDING_BLOCKS; i++) {
     86     int len = gen() % 16;
     87     if (len > 14) {
     88       len += 1234;
     89     }
     90     switch (gen() % 4) {
     91       case 0: {
     92         uc16 buf[2000];
     93         for (int j = 0; j < len; j++) {
     94           buf[j] = gen() % 65536;
     95         }
     96         building_blocks[i] =
     97             FACTORY->NewStringFromTwoByte(Vector<const uc16>(buf, len));
     98         for (int j = 0; j < len; j++) {
     99           CHECK_EQ(buf[j], building_blocks[i]->Get(j));
    100         }
    101         break;
    102       }
    103       case 1: {
    104         char buf[2000];
    105         for (int j = 0; j < len; j++) {
    106           buf[j] = gen() % 128;
    107         }
    108         building_blocks[i] =
    109             FACTORY->NewStringFromAscii(Vector<const char>(buf, len));
    110         for (int j = 0; j < len; j++) {
    111           CHECK_EQ(buf[j], building_blocks[i]->Get(j));
    112         }
    113         break;
    114       }
    115       case 2: {
    116         uc16* buf = ZONE->NewArray<uc16>(len);
    117         for (int j = 0; j < len; j++) {
    118           buf[j] = gen() % 65536;
    119         }
    120         Resource* resource = new Resource(Vector<const uc16>(buf, len));
    121         building_blocks[i] = FACTORY->NewExternalStringFromTwoByte(resource);
    122         for (int j = 0; j < len; j++) {
    123           CHECK_EQ(buf[j], building_blocks[i]->Get(j));
    124         }
    125         break;
    126       }
    127       case 3: {
    128         char* buf = NewArray<char>(len);
    129         for (int j = 0; j < len; j++) {
    130           buf[j] = gen() % 128;
    131         }
    132         building_blocks[i] =
    133             FACTORY->NewStringFromAscii(Vector<const char>(buf, len));
    134         for (int j = 0; j < len; j++) {
    135           CHECK_EQ(buf[j], building_blocks[i]->Get(j));
    136         }
    137         DeleteArray<char>(buf);
    138         break;
    139       }
    140     }
    141   }
    142 }
    143 
    144 
    145 static Handle<String> ConstructLeft(
    146     Handle<String> building_blocks[NUMBER_OF_BUILDING_BLOCKS],
    147     int depth) {
    148   Handle<String> answer = FACTORY->NewStringFromAscii(CStrVector(""));
    149   for (int i = 0; i < depth; i++) {
    150     answer = FACTORY->NewConsString(
    151         answer,
    152         building_blocks[i % NUMBER_OF_BUILDING_BLOCKS]);
    153   }
    154   return answer;
    155 }
    156 
    157 
    158 static Handle<String> ConstructRight(
    159     Handle<String> building_blocks[NUMBER_OF_BUILDING_BLOCKS],
    160     int depth) {
    161   Handle<String> answer = FACTORY->NewStringFromAscii(CStrVector(""));
    162   for (int i = depth - 1; i >= 0; i--) {
    163     answer = FACTORY->NewConsString(
    164         building_blocks[i % NUMBER_OF_BUILDING_BLOCKS],
    165         answer);
    166   }
    167   return answer;
    168 }
    169 
    170 
    171 static Handle<String> ConstructBalancedHelper(
    172     Handle<String> building_blocks[NUMBER_OF_BUILDING_BLOCKS],
    173     int from,
    174     int to) {
    175   CHECK(to > from);
    176   if (to - from == 1) {
    177     return building_blocks[from % NUMBER_OF_BUILDING_BLOCKS];
    178   }
    179   if (to - from == 2) {
    180     return FACTORY->NewConsString(
    181         building_blocks[from % NUMBER_OF_BUILDING_BLOCKS],
    182         building_blocks[(from+1) % NUMBER_OF_BUILDING_BLOCKS]);
    183   }
    184   Handle<String> part1 =
    185     ConstructBalancedHelper(building_blocks, from, from + ((to - from) / 2));
    186   Handle<String> part2 =
    187     ConstructBalancedHelper(building_blocks, from + ((to - from) / 2), to);
    188   return FACTORY->NewConsString(part1, part2);
    189 }
    190 
    191 
    192 static Handle<String> ConstructBalanced(
    193     Handle<String> building_blocks[NUMBER_OF_BUILDING_BLOCKS]) {
    194   return ConstructBalancedHelper(building_blocks, 0, DEEP_DEPTH);
    195 }
    196 
    197 
    198 static StringInputBuffer buffer;
    199 
    200 
    201 static void Traverse(Handle<String> s1, Handle<String> s2) {
    202   int i = 0;
    203   buffer.Reset(*s1);
    204   StringInputBuffer buffer2(*s2);
    205   while (buffer.has_more()) {
    206     CHECK(buffer2.has_more());
    207     uint16_t c = buffer.GetNext();
    208     CHECK_EQ(c, buffer2.GetNext());
    209     i++;
    210   }
    211   CHECK_EQ(s1->length(), i);
    212   CHECK_EQ(s2->length(), i);
    213 }
    214 
    215 
    216 static void TraverseFirst(Handle<String> s1, Handle<String> s2, int chars) {
    217   int i = 0;
    218   buffer.Reset(*s1);
    219   StringInputBuffer buffer2(*s2);
    220   while (buffer.has_more() && i < chars) {
    221     CHECK(buffer2.has_more());
    222     uint16_t c = buffer.GetNext();
    223     CHECK_EQ(c, buffer2.GetNext());
    224     i++;
    225   }
    226   s1->Get(s1->length() - 1);
    227   s2->Get(s2->length() - 1);
    228 }
    229 
    230 
    231 TEST(Traverse) {
    232   printf("TestTraverse\n");
    233   InitializeVM();
    234   v8::HandleScope scope;
    235   Handle<String> building_blocks[NUMBER_OF_BUILDING_BLOCKS];
    236   ZoneScope zone(Isolate::Current(), DELETE_ON_EXIT);
    237   InitializeBuildingBlocks(building_blocks);
    238   Handle<String> flat = ConstructBalanced(building_blocks);
    239   FlattenString(flat);
    240   Handle<String> left_asymmetric = ConstructLeft(building_blocks, DEEP_DEPTH);
    241   Handle<String> right_asymmetric = ConstructRight(building_blocks, DEEP_DEPTH);
    242   Handle<String> symmetric = ConstructBalanced(building_blocks);
    243   printf("1\n");
    244   Traverse(flat, symmetric);
    245   printf("2\n");
    246   Traverse(flat, left_asymmetric);
    247   printf("3\n");
    248   Traverse(flat, right_asymmetric);
    249   printf("4\n");
    250   Handle<String> left_deep_asymmetric =
    251       ConstructLeft(building_blocks, SUPER_DEEP_DEPTH);
    252   Handle<String> right_deep_asymmetric =
    253       ConstructRight(building_blocks, SUPER_DEEP_DEPTH);
    254   printf("5\n");
    255   TraverseFirst(left_asymmetric, left_deep_asymmetric, 1050);
    256   printf("6\n");
    257   TraverseFirst(left_asymmetric, right_deep_asymmetric, 65536);
    258   printf("7\n");
    259   FlattenString(left_asymmetric);
    260   printf("10\n");
    261   Traverse(flat, left_asymmetric);
    262   printf("11\n");
    263   FlattenString(right_asymmetric);
    264   printf("12\n");
    265   Traverse(flat, right_asymmetric);
    266   printf("14\n");
    267   FlattenString(symmetric);
    268   printf("15\n");
    269   Traverse(flat, symmetric);
    270   printf("16\n");
    271   FlattenString(left_deep_asymmetric);
    272   printf("18\n");
    273 }
    274 
    275 
    276 static const int DEEP_ASCII_DEPTH = 100000;
    277 
    278 
    279 TEST(DeepAscii) {
    280   printf("TestDeepAscii\n");
    281   InitializeVM();
    282   v8::HandleScope scope;
    283 
    284   char* foo = NewArray<char>(DEEP_ASCII_DEPTH);
    285   for (int i = 0; i < DEEP_ASCII_DEPTH; i++) {
    286     foo[i] = "foo "[i % 4];
    287   }
    288   Handle<String> string =
    289       FACTORY->NewStringFromAscii(Vector<const char>(foo, DEEP_ASCII_DEPTH));
    290   Handle<String> foo_string = FACTORY->NewStringFromAscii(CStrVector("foo"));
    291   for (int i = 0; i < DEEP_ASCII_DEPTH; i += 10) {
    292     string = FACTORY->NewConsString(string, foo_string);
    293   }
    294   Handle<String> flat_string = FACTORY->NewConsString(string, foo_string);
    295   FlattenString(flat_string);
    296 
    297   for (int i = 0; i < 500; i++) {
    298     TraverseFirst(flat_string, string, DEEP_ASCII_DEPTH);
    299   }
    300   DeleteArray<char>(foo);
    301 }
    302 
    303 
    304 TEST(Utf8Conversion) {
    305   // Smoke test for converting strings to utf-8.
    306   InitializeVM();
    307   v8::HandleScope handle_scope;
    308   // A simple ascii string
    309   const char* ascii_string = "abcdef12345";
    310   int len =
    311       v8::String::New(ascii_string,
    312                       StrLength(ascii_string))->Utf8Length();
    313   CHECK_EQ(StrLength(ascii_string), len);
    314   // A mixed ascii and non-ascii string
    315   // U+02E4 -> CB A4
    316   // U+0064 -> 64
    317   // U+12E4 -> E1 8B A4
    318   // U+0030 -> 30
    319   // U+3045 -> E3 81 85
    320   const uint16_t mixed_string[] = {0x02E4, 0x0064, 0x12E4, 0x0030, 0x3045};
    321   // The characters we expect to be output
    322   const unsigned char as_utf8[11] = {0xCB, 0xA4, 0x64, 0xE1, 0x8B, 0xA4, 0x30,
    323       0xE3, 0x81, 0x85, 0x00};
    324   // The number of bytes expected to be written for each length
    325   const int lengths[12] = {0, 0, 2, 3, 3, 3, 6, 7, 7, 7, 10, 11};
    326   const int char_lengths[12] = {0, 0, 1, 2, 2, 2, 3, 4, 4, 4, 5, 5};
    327   v8::Handle<v8::String> mixed = v8::String::New(mixed_string, 5);
    328   CHECK_EQ(10, mixed->Utf8Length());
    329   // Try encoding the string with all capacities
    330   char buffer[11];
    331   const char kNoChar = static_cast<char>(-1);
    332   for (int i = 0; i <= 11; i++) {
    333     // Clear the buffer before reusing it
    334     for (int j = 0; j < 11; j++)
    335       buffer[j] = kNoChar;
    336     int chars_written;
    337     int written = mixed->WriteUtf8(buffer, i, &chars_written);
    338     CHECK_EQ(lengths[i], written);
    339     CHECK_EQ(char_lengths[i], chars_written);
    340     // Check that the contents are correct
    341     for (int j = 0; j < lengths[i]; j++)
    342       CHECK_EQ(as_utf8[j], static_cast<unsigned char>(buffer[j]));
    343     // Check that the rest of the buffer hasn't been touched
    344     for (int j = lengths[i]; j < 11; j++)
    345       CHECK_EQ(kNoChar, buffer[j]);
    346   }
    347 }
    348 
    349 
    350 TEST(ExternalShortStringAdd) {
    351   ZoneScope zone(Isolate::Current(), DELETE_ON_EXIT);
    352 
    353   InitializeVM();
    354   v8::HandleScope handle_scope;
    355 
    356   // Make sure we cover all always-flat lengths and at least one above.
    357   static const int kMaxLength = 20;
    358   CHECK_GT(kMaxLength, i::ConsString::kMinLength);
    359 
    360   // Allocate two JavaScript arrays for holding short strings.
    361   v8::Handle<v8::Array> ascii_external_strings =
    362       v8::Array::New(kMaxLength + 1);
    363   v8::Handle<v8::Array> non_ascii_external_strings =
    364       v8::Array::New(kMaxLength + 1);
    365 
    366   // Generate short ascii and non-ascii external strings.
    367   for (int i = 0; i <= kMaxLength; i++) {
    368     char* ascii = ZONE->NewArray<char>(i + 1);
    369     for (int j = 0; j < i; j++) {
    370       ascii[j] = 'a';
    371     }
    372     // Terminating '\0' is left out on purpose. It is not required for external
    373     // string data.
    374     AsciiResource* ascii_resource =
    375         new AsciiResource(Vector<const char>(ascii, i));
    376     v8::Local<v8::String> ascii_external_string =
    377         v8::String::NewExternal(ascii_resource);
    378 
    379     ascii_external_strings->Set(v8::Integer::New(i), ascii_external_string);
    380     uc16* non_ascii = ZONE->NewArray<uc16>(i + 1);
    381     for (int j = 0; j < i; j++) {
    382       non_ascii[j] = 0x1234;
    383     }
    384     // Terminating '\0' is left out on purpose. It is not required for external
    385     // string data.
    386     Resource* resource = new Resource(Vector<const uc16>(non_ascii, i));
    387     v8::Local<v8::String> non_ascii_external_string =
    388       v8::String::NewExternal(resource);
    389     non_ascii_external_strings->Set(v8::Integer::New(i),
    390                                     non_ascii_external_string);
    391   }
    392 
    393   // Add the arrays with the short external strings in the global object.
    394   v8::Handle<v8::Object> global = env->Global();
    395   global->Set(v8_str("external_ascii"), ascii_external_strings);
    396   global->Set(v8_str("external_non_ascii"), non_ascii_external_strings);
    397   global->Set(v8_str("max_length"), v8::Integer::New(kMaxLength));
    398 
    399   // Add short external ascii and non-ascii strings checking the result.
    400   static const char* source =
    401     "function test() {"
    402     "  var ascii_chars = 'aaaaaaaaaaaaaaaaaaaa';"
    403     "  var non_ascii_chars = '\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234\\u1234';"  //NOLINT
    404     "  if (ascii_chars.length != max_length) return 1;"
    405     "  if (non_ascii_chars.length != max_length) return 2;"
    406     "  var ascii = Array(max_length + 1);"
    407     "  var non_ascii = Array(max_length + 1);"
    408     "  for (var i = 0; i <= max_length; i++) {"
    409     "    ascii[i] = ascii_chars.substring(0, i);"
    410     "    non_ascii[i] = non_ascii_chars.substring(0, i);"
    411     "  };"
    412     "  for (var i = 0; i <= max_length; i++) {"
    413     "    if (ascii[i] != external_ascii[i]) return 3;"
    414     "    if (non_ascii[i] != external_non_ascii[i]) return 4;"
    415     "    for (var j = 0; j < i; j++) {"
    416     "      if (external_ascii[i] !="
    417     "          (external_ascii[j] + external_ascii[i - j])) return 5;"
    418     "      if (external_non_ascii[i] !="
    419     "          (external_non_ascii[j] + external_non_ascii[i - j])) return 6;"
    420     "      if (non_ascii[i] != (non_ascii[j] + non_ascii[i - j])) return 7;"
    421     "      if (ascii[i] != (ascii[j] + ascii[i - j])) return 8;"
    422     "      if (ascii[i] != (external_ascii[j] + ascii[i - j])) return 9;"
    423     "      if (ascii[i] != (ascii[j] + external_ascii[i - j])) return 10;"
    424     "      if (non_ascii[i] !="
    425     "          (external_non_ascii[j] + non_ascii[i - j])) return 11;"
    426     "      if (non_ascii[i] !="
    427     "          (non_ascii[j] + external_non_ascii[i - j])) return 12;"
    428     "    }"
    429     "  }"
    430     "  return 0;"
    431     "};"
    432     "test()";
    433   CHECK_EQ(0, CompileRun(source)->Int32Value());
    434 }
    435 
    436 
    437 TEST(CachedHashOverflow) {
    438   // We incorrectly allowed strings to be tagged as array indices even if their
    439   // values didn't fit in the hash field.
    440   // See http://code.google.com/p/v8/issues/detail?id=728
    441   ZoneScope zone(Isolate::Current(), DELETE_ON_EXIT);
    442 
    443   InitializeVM();
    444   v8::HandleScope handle_scope;
    445   // Lines must be executed sequentially. Combining them into one script
    446   // makes the bug go away.
    447   const char* lines[] = {
    448       "var x = [];",
    449       "x[4] = 42;",
    450       "var s = \"1073741828\";",
    451       "x[s];",
    452       "x[s] = 37;",
    453       "x[4];",
    454       "x[s];",
    455       NULL
    456   };
    457 
    458   Handle<Smi> fortytwo(Smi::FromInt(42));
    459   Handle<Smi> thirtyseven(Smi::FromInt(37));
    460   Handle<Object> results[] = {
    461       FACTORY->undefined_value(),
    462       fortytwo,
    463       FACTORY->undefined_value(),
    464       FACTORY->undefined_value(),
    465       thirtyseven,
    466       fortytwo,
    467       thirtyseven  // Bug yielded 42 here.
    468   };
    469 
    470   const char* line;
    471   for (int i = 0; (line = lines[i]); i++) {
    472     printf("%s\n", line);
    473     v8::Local<v8::Value> result =
    474         v8::Script::Compile(v8::String::New(line))->Run();
    475     CHECK_EQ(results[i]->IsUndefined(), result->IsUndefined());
    476     CHECK_EQ(results[i]->IsNumber(), result->IsNumber());
    477     if (result->IsNumber()) {
    478       CHECK_EQ(Smi::cast(results[i]->ToSmi()->ToObjectChecked())->value(),
    479                result->ToInt32()->Value());
    480     }
    481   }
    482 }
    483 
    484 
    485 TEST(SliceFromCons) {
    486   FLAG_string_slices = true;
    487   InitializeVM();
    488   v8::HandleScope scope;
    489   Handle<String> string =
    490       FACTORY->NewStringFromAscii(CStrVector("parentparentparent"));
    491   Handle<String> parent = FACTORY->NewConsString(string, string);
    492   CHECK(parent->IsConsString());
    493   CHECK(!parent->IsFlat());
    494   Handle<String> slice = FACTORY->NewSubString(parent, 1, 25);
    495   // After slicing, the original string becomes a flat cons.
    496   CHECK(parent->IsFlat());
    497   CHECK(slice->IsSlicedString());
    498   CHECK_EQ(SlicedString::cast(*slice)->parent(),
    499            ConsString::cast(*parent)->first());
    500   CHECK(SlicedString::cast(*slice)->parent()->IsSeqString());
    501   CHECK(slice->IsFlat());
    502 }
    503 
    504 
    505 class AsciiVectorResource : public v8::String::ExternalAsciiStringResource {
    506  public:
    507   explicit AsciiVectorResource(i::Vector<const char> vector)
    508       : data_(vector) {}
    509   virtual ~AsciiVectorResource() {}
    510   virtual size_t length() const { return data_.length(); }
    511   virtual const char* data() const { return data_.start(); }
    512  private:
    513   i::Vector<const char> data_;
    514 };
    515 
    516 
    517 TEST(SliceFromExternal) {
    518   FLAG_string_slices = true;
    519   InitializeVM();
    520   v8::HandleScope scope;
    521   AsciiVectorResource resource(
    522       i::Vector<const char>("abcdefghijklmnopqrstuvwxyz", 26));
    523   Handle<String> string = FACTORY->NewExternalStringFromAscii(&resource);
    524   CHECK(string->IsExternalString());
    525   Handle<String> slice = FACTORY->NewSubString(string, 1, 25);
    526   CHECK(slice->IsSlicedString());
    527   CHECK(string->IsExternalString());
    528   CHECK_EQ(SlicedString::cast(*slice)->parent(), *string);
    529   CHECK(SlicedString::cast(*slice)->parent()->IsExternalString());
    530   CHECK(slice->IsFlat());
    531 }
    532 
    533 
    534 TEST(TrivialSlice) {
    535   // This tests whether a slice that contains the entire parent string
    536   // actually creates a new string (it should not).
    537   FLAG_string_slices = true;
    538   InitializeVM();
    539   HandleScope scope;
    540   v8::Local<v8::Value> result;
    541   Handle<String> string;
    542   const char* init = "var str = 'abcdefghijklmnopqrstuvwxyz';";
    543   const char* check = "str.slice(0,26)";
    544   const char* crosscheck = "str.slice(1,25)";
    545 
    546   CompileRun(init);
    547 
    548   result = CompileRun(check);
    549   CHECK(result->IsString());
    550   string = v8::Utils::OpenHandle(v8::String::Cast(*result));
    551   CHECK(!string->IsSlicedString());
    552 
    553   string = FACTORY->NewSubString(string, 0, 26);
    554   CHECK(!string->IsSlicedString());
    555   result = CompileRun(crosscheck);
    556   CHECK(result->IsString());
    557   string = v8::Utils::OpenHandle(v8::String::Cast(*result));
    558   CHECK(string->IsSlicedString());
    559   CHECK_EQ("bcdefghijklmnopqrstuvwxy", *(string->ToCString()));
    560 }
    561 
    562 
    563 TEST(SliceFromSlice) {
    564   // This tests whether a slice that contains the entire parent string
    565   // actually creates a new string (it should not).
    566   FLAG_string_slices = true;
    567   InitializeVM();
    568   HandleScope scope;
    569   v8::Local<v8::Value> result;
    570   Handle<String> string;
    571   const char* init = "var str = 'abcdefghijklmnopqrstuvwxyz';";
    572   const char* slice = "var slice = str.slice(1,-1); slice";
    573   const char* slice_from_slice = "slice.slice(1,-1);";
    574 
    575   CompileRun(init);
    576   result = CompileRun(slice);
    577   CHECK(result->IsString());
    578   string = v8::Utils::OpenHandle(v8::String::Cast(*result));
    579   CHECK(string->IsSlicedString());
    580   CHECK(SlicedString::cast(*string)->parent()->IsSeqString());
    581   CHECK_EQ("bcdefghijklmnopqrstuvwxy", *(string->ToCString()));
    582 
    583   result = CompileRun(slice_from_slice);
    584   CHECK(result->IsString());
    585   string = v8::Utils::OpenHandle(v8::String::Cast(*result));
    586   CHECK(string->IsSlicedString());
    587   CHECK(SlicedString::cast(*string)->parent()->IsSeqString());
    588   CHECK_EQ("cdefghijklmnopqrstuvwx", *(string->ToCString()));
    589 }
    590