src/runtime/runtime-regexp.cc

// Copyright 2014 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/runtime/runtime-utils.h"

#include "src/arguments.h"
#include "src/conversions-inl.h"
#include "src/isolate-inl.h"
#include "src/messages.h"
#include "src/regexp/jsregexp-inl.h"
#include "src/regexp/jsregexp.h"
#include "src/string-builder.h"
#include "src/string-search.h"

namespace v8 {
namespace internal {

class CompiledReplacement {
 public:
  explicit CompiledReplacement(Zone* zone)
      : parts_(1, zone), replacement_substrings_(0, zone), zone_(zone) {}

  // Return whether the replacement is simple.
  bool Compile(Handle<String> replacement, int capture_count,
               int subject_length);

  // Use Apply only if Compile returned false.
  void Apply(ReplacementStringBuilder* builder, int match_from, int match_to,
             int32_t* match);

  // Number of distinct parts of the replacement pattern.
  int parts() { return parts_.length(); }

  Zone* zone() const { return zone_; }

 private:
  enum PartType {
    SUBJECT_PREFIX = 1,
    SUBJECT_SUFFIX,
    SUBJECT_CAPTURE,
    REPLACEMENT_SUBSTRING,
    REPLACEMENT_STRING,
    NUMBER_OF_PART_TYPES
  };

  struct ReplacementPart {
    static inline ReplacementPart SubjectMatch() {
      return ReplacementPart(SUBJECT_CAPTURE, 0);
    }
    static inline ReplacementPart SubjectCapture(int capture_index) {
      return ReplacementPart(SUBJECT_CAPTURE, capture_index);
    }
    static inline ReplacementPart SubjectPrefix() {
      return ReplacementPart(SUBJECT_PREFIX, 0);
    }
    static inline ReplacementPart SubjectSuffix(int subject_length) {
      return ReplacementPart(SUBJECT_SUFFIX, subject_length);
    }
    static inline ReplacementPart ReplacementString() {
      return ReplacementPart(REPLACEMENT_STRING, 0);
    }
    static inline ReplacementPart ReplacementSubString(int from, int to) {
      DCHECK(from >= 0);
      DCHECK(to > from);
      return ReplacementPart(-from, to);
    }

    // If tag <= 0 then it is the negation of a start index of a substring of
    // the replacement pattern, otherwise it's a value from PartType.
    ReplacementPart(int tag, int data) : tag(tag), data(data) {
      // Must be non-positive or a PartType value.
      DCHECK(tag < NUMBER_OF_PART_TYPES);
    }
    // Either a value of PartType or a non-positive number that is
    // the negation of an index into the replacement string.
    int tag;
    // The data value's interpretation depends on the value of tag:
    // tag == SUBJECT_PREFIX ||
    // tag == SUBJECT_SUFFIX:  data is unused.
    // tag == SUBJECT_CAPTURE: data is the number of the capture.
    // tag == REPLACEMENT_SUBSTRING ||
    // tag == REPLACEMENT_STRING:    data is index into array of substrings
    //                               of the replacement string.
    // tag <= 0: Temporary representation of the substring of the replacement
    //           string ranging over -tag .. data.
    //           Is replaced by REPLACEMENT_{SUB,}STRING when we create the
    //           substring objects.
    int data;
  };

  template <typename Char>
  bool ParseReplacementPattern(ZoneList<ReplacementPart>* parts,
                               Vector<Char> characters, int capture_count,
                               int subject_length, Zone* zone) {
    int length = characters.length();
    int last = 0;
    for (int i = 0; i < length; i++) {
      Char c = characters[i];
      if (c == '$') {
        int next_index = i + 1;
        if (next_index == length) {  // No next character!
          break;
        }
        Char c2 = characters[next_index];
        switch (c2) {
          case '$':
            if (i > last) {
              // There is a substring before. Include the first "$".
              parts->Add(
                  ReplacementPart::ReplacementSubString(last, next_index),
                  zone);
              last = next_index + 1;  // Continue after the second "$".
            } else {
              // Let the next substring start with the second "$".
              last = next_index;
            }
            i = next_index;
            break;
          case '`':
            if (i > last) {
              parts->Add(ReplacementPart::ReplacementSubString(last, i), zone);
            }
            parts->Add(ReplacementPart::SubjectPrefix(), zone);
            i = next_index;
            last = i + 1;
            break;
          case '\'':
            if (i > last) {
              parts->Add(ReplacementPart::ReplacementSubString(last, i), zone);
            }
            parts->Add(ReplacementPart::SubjectSuffix(subject_length), zone);
            i = next_index;
            last = i + 1;
            break;
          case '&':
            if (i > last) {
              parts->Add(ReplacementPart::ReplacementSubString(last, i), zone);
            }
            parts->Add(ReplacementPart::SubjectMatch(), zone);
            i = next_index;
            last = i + 1;
            break;
          case '0':
          case '1':
          case '2':
          case '3':
          case '4':
          case '5':
          case '6':
          case '7':
          case '8':
          case '9': {
            int capture_ref = c2 - '0';
            if (capture_ref > capture_count) {
              i = next_index;
              continue;
            }
            int second_digit_index = next_index + 1;
            if (second_digit_index < length) {
              // Peek ahead to see if we have two digits.
              Char c3 = characters[second_digit_index];
              if ('0' <= c3 && c3 <= '9') {  // Double digits.
                int double_digit_ref = capture_ref * 10 + c3 - '0';
                if (double_digit_ref <= capture_count) {
                  next_index = second_digit_index;
                  capture_ref = double_digit_ref;
                }
              }
            }
            if (capture_ref > 0) {
              if (i > last) {
                parts->Add(ReplacementPart::ReplacementSubString(last, i),
                           zone);
              }
              DCHECK(capture_ref <= capture_count);
              parts->Add(ReplacementPart::SubjectCapture(capture_ref), zone);
              last = next_index + 1;
            }
            i = next_index;
            break;
          }
          default:
            i = next_index;
            break;
        }
      }
    }
    if (length > last) {
      if (last == 0) {
        // Replacement is simple.  Do not use Apply to do the replacement.
        return true;
      } else {
        parts->Add(ReplacementPart::ReplacementSubString(last, length), zone);
      }
    }
    return false;
  }

  ZoneList<ReplacementPart> parts_;
  ZoneList<Handle<String> > replacement_substrings_;
  Zone* zone_;
};


bool CompiledReplacement::Compile(Handle<String> replacement, int capture_count,
                                  int subject_length) {
  {
    DisallowHeapAllocation no_gc;
    String::FlatContent content = replacement->GetFlatContent();
    DCHECK(content.IsFlat());
    bool simple = false;
    if (content.IsOneByte()) {
      simple = ParseReplacementPattern(&parts_, content.ToOneByteVector(),
                                       capture_count, subject_length, zone());
    } else {
      DCHECK(content.IsTwoByte());
      simple = ParseReplacementPattern(&parts_, content.ToUC16Vector(),
                                       capture_count, subject_length, zone());
    }
    if (simple) return true;
  }

  Isolate* isolate = replacement->GetIsolate();
  // Find substrings of replacement string and create them as String objects.
  int substring_index = 0;
  for (int i = 0, n = parts_.length(); i < n; i++) {
    int tag = parts_[i].tag;
    if (tag <= 0) {  // A replacement string slice.
      int from = -tag;
      int to = parts_[i].data;
      replacement_substrings_.Add(
          isolate->factory()->NewSubString(replacement, from, to), zone());
      parts_[i].tag = REPLACEMENT_SUBSTRING;
      parts_[i].data = substring_index;
      substring_index++;
    } else if (tag == REPLACEMENT_STRING) {
      replacement_substrings_.Add(replacement, zone());
      parts_[i].data = substring_index;
      substring_index++;
    }
  }
  return false;
}


void CompiledReplacement::Apply(ReplacementStringBuilder* builder,
                                int match_from, int match_to, int32_t* match) {
  DCHECK_LT(0, parts_.length());
  for (int i = 0, n = parts_.length(); i < n; i++) {
    ReplacementPart part = parts_[i];
    switch (part.tag) {
      case SUBJECT_PREFIX:
        if (match_from > 0) builder->AddSubjectSlice(0, match_from);
        break;
      case SUBJECT_SUFFIX: {
        int subject_length = part.data;
        if (match_to < subject_length) {
          builder->AddSubjectSlice(match_to, subject_length);
        }
        break;
      }
      case SUBJECT_CAPTURE: {
        int capture = part.data;
        int from = match[capture * 2];
        int to = match[capture * 2 + 1];
        if (from >= 0 && to > from) {
          builder->AddSubjectSlice(from, to);
        }
        break;
      }
      case REPLACEMENT_SUBSTRING:
      case REPLACEMENT_STRING:
        builder->AddString(replacement_substrings_[part.data]);
        break;
      default:
        UNREACHABLE();
    }
  }
}


void FindOneByteStringIndices(Vector<const uint8_t> subject, uint8_t pattern,
                              ZoneList<int>* indices, unsigned int limit,
                              Zone* zone) {
  DCHECK(limit > 0);
  // Collect indices of pattern in subject using memchr.
  // Stop after finding at most limit values.
  const uint8_t* subject_start = subject.start();
  const uint8_t* subject_end = subject_start + subject.length();
  const uint8_t* pos = subject_start;
  while (limit > 0) {
    pos = reinterpret_cast<const uint8_t*>(
        memchr(pos, pattern, subject_end - pos));
    if (pos == NULL) return;
    indices->Add(static_cast<int>(pos - subject_start), zone);
    pos++;
    limit--;
  }
}


void FindTwoByteStringIndices(const Vector<const uc16> subject, uc16 pattern,
                              ZoneList<int>* indices, unsigned int limit,
                              Zone* zone) {
  DCHECK(limit > 0);
  const uc16* subject_start = subject.start();
  const uc16* subject_end = subject_start + subject.length();
  for (const uc16* pos = subject_start; pos < subject_end && limit > 0; pos++) {
    if (*pos == pattern) {
      indices->Add(static_cast<int>(pos - subject_start), zone);
      limit--;
    }
  }
}


template <typename SubjectChar, typename PatternChar>
void FindStringIndices(Isolate* isolate, Vector<const SubjectChar> subject,
                       Vector<const PatternChar> pattern,
                       ZoneList<int>* indices, unsigned int limit, Zone* zone) {
  DCHECK(limit > 0);
  // Collect indices of pattern in subject.
  // Stop after finding at most limit values.
  int pattern_length = pattern.length();
  int index = 0;
  StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
  while (limit > 0) {
    index = search.Search(subject, index);
    if (index < 0) return;
    indices->Add(index, zone);
    index += pattern_length;
    limit--;
  }
}


void FindStringIndicesDispatch(Isolate* isolate, String* subject,
                               String* pattern, ZoneList<int>* indices,
                               unsigned int limit, Zone* zone) {
  {
    DisallowHeapAllocation no_gc;
    String::FlatContent subject_content = subject->GetFlatContent();
    String::FlatContent pattern_content = pattern->GetFlatContent();
    DCHECK(subject_content.IsFlat());
    DCHECK(pattern_content.IsFlat());
    if (subject_content.IsOneByte()) {
      Vector<const uint8_t> subject_vector = subject_content.ToOneByteVector();
      if (pattern_content.IsOneByte()) {
        Vector<const uint8_t> pattern_vector =
            pattern_content.ToOneByteVector();
        if (pattern_vector.length() == 1) {
          FindOneByteStringIndices(subject_vector, pattern_vector[0], indices,
                                   limit, zone);
        } else {
          FindStringIndices(isolate, subject_vector, pattern_vector, indices,
                            limit, zone);
        }
      } else {
        FindStringIndices(isolate, subject_vector,
                          pattern_content.ToUC16Vector(), indices, limit, zone);
      }
    } else {
      Vector<const uc16> subject_vector = subject_content.ToUC16Vector();
      if (pattern_content.IsOneByte()) {
        Vector<const uint8_t> pattern_vector =
            pattern_content.ToOneByteVector();
        if (pattern_vector.length() == 1) {
          FindTwoByteStringIndices(subject_vector, pattern_vector[0], indices,
                                   limit, zone);
        } else {
          FindStringIndices(isolate, subject_vector, pattern_vector, indices,
                            limit, zone);
        }
      } else {
        Vector<const uc16> pattern_vector = pattern_content.ToUC16Vector();
        if (pattern_vector.length() == 1) {
          FindTwoByteStringIndices(subject_vector, pattern_vector[0], indices,
                                   limit, zone);
        } else {
          FindStringIndices(isolate, subject_vector, pattern_vector, indices,
                            limit, zone);
        }
      }
    }
  }
}


template <typename ResultSeqString>
MUST_USE_RESULT static Object* StringReplaceGlobalAtomRegExpWithString(
    Isolate* isolate, Handle<String> subject, Handle<JSRegExp> pattern_regexp,
    Handle<String> replacement, Handle<JSArray> last_match_info) {
  DCHECK(subject->IsFlat());
  DCHECK(replacement->IsFlat());

  ZoneScope zone_scope(isolate->runtime_zone());
  ZoneList<int> indices(8, zone_scope.zone());
  DCHECK_EQ(JSRegExp::ATOM, pattern_regexp->TypeTag());
  String* pattern =
      String::cast(pattern_regexp->DataAt(JSRegExp::kAtomPatternIndex));
  int subject_len = subject->length();
  int pattern_len = pattern->length();
  int replacement_len = replacement->length();

  FindStringIndicesDispatch(isolate, *subject, pattern, &indices, 0xffffffff,
                            zone_scope.zone());

  int matches = indices.length();
  if (matches == 0) return *subject;

  // Detect integer overflow.
  int64_t result_len_64 = (static_cast<int64_t>(replacement_len) -
                           static_cast<int64_t>(pattern_len)) *
                              static_cast<int64_t>(matches) +
                          static_cast<int64_t>(subject_len);
  int result_len;
  if (result_len_64 > static_cast<int64_t>(String::kMaxLength)) {
    STATIC_ASSERT(String::kMaxLength < kMaxInt);
    result_len = kMaxInt;  // Provoke exception.
  } else {
    result_len = static_cast<int>(result_len_64);
  }

  int subject_pos = 0;
  int result_pos = 0;

  MaybeHandle<SeqString> maybe_res;
  if (ResultSeqString::kHasOneByteEncoding) {
    maybe_res = isolate->factory()->NewRawOneByteString(result_len);
  } else {
    maybe_res = isolate->factory()->NewRawTwoByteString(result_len);
  }
  Handle<SeqString> untyped_res;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, untyped_res, maybe_res);
  Handle<ResultSeqString> result = Handle<ResultSeqString>::cast(untyped_res);

  for (int i = 0; i < matches; i++) {
    // Copy non-matched subject content.
    if (subject_pos < indices.at(i)) {
      String::WriteToFlat(*subject, result->GetChars() + result_pos,
                          subject_pos, indices.at(i));
      result_pos += indices.at(i) - subject_pos;
    }

    // Replace match.
    if (replacement_len > 0) {
      String::WriteToFlat(*replacement, result->GetChars() + result_pos, 0,
                          replacement_len);
      result_pos += replacement_len;
    }

    subject_pos = indices.at(i) + pattern_len;
  }
  // Add remaining subject content at the end.
  if (subject_pos < subject_len) {
    String::WriteToFlat(*subject, result->GetChars() + result_pos, subject_pos,
                        subject_len);
  }

  int32_t match_indices[] = {indices.at(matches - 1),
                             indices.at(matches - 1) + pattern_len};
  RegExpImpl::SetLastMatchInfo(last_match_info, subject, 0, match_indices);

  return *result;
}


MUST_USE_RESULT static Object* StringReplaceGlobalRegExpWithString(
    Isolate* isolate, Handle<String> subject, Handle<JSRegExp> regexp,
    Handle<String> replacement, Handle<JSArray> last_match_info) {
  DCHECK(subject->IsFlat());
  DCHECK(replacement->IsFlat());

  int capture_count = regexp->CaptureCount();
  int subject_length = subject->length();

  // CompiledReplacement uses zone allocation.
  ZoneScope zone_scope(isolate->runtime_zone());
  CompiledReplacement compiled_replacement(zone_scope.zone());
  bool simple_replace =
      compiled_replacement.Compile(replacement, capture_count, subject_length);

  // Shortcut for simple non-regexp global replacements
  if (regexp->TypeTag() == JSRegExp::ATOM && simple_replace) {
    if (subject->HasOnlyOneByteChars() && replacement->HasOnlyOneByteChars()) {
      return StringReplaceGlobalAtomRegExpWithString<SeqOneByteString>(
          isolate, subject, regexp, replacement, last_match_info);
    } else {
      return StringReplaceGlobalAtomRegExpWithString<SeqTwoByteString>(
          isolate, subject, regexp, replacement, last_match_info);
    }
  }

  RegExpImpl::GlobalCache global_cache(regexp, subject, true, isolate);
  if (global_cache.HasException()) return isolate->heap()->exception();

  int32_t* current_match = global_cache.FetchNext();
  if (current_match == NULL) {
    if (global_cache.HasException()) return isolate->heap()->exception();
    return *subject;
  }

  // Guessing the number of parts that the final result string is built
  // from. Global regexps can match any number of times, so we guess
  // conservatively.
  int expected_parts = (compiled_replacement.parts() + 1) * 4 + 1;
  ReplacementStringBuilder builder(isolate->heap(), subject, expected_parts);

  // Number of parts added by compiled replacement plus preceeding
  // string and possibly suffix after last match.  It is possible for
  // all components to use two elements when encoded as two smis.
  const int parts_added_per_loop = 2 * (compiled_replacement.parts() + 2);

  int prev = 0;

  do {
    builder.EnsureCapacity(parts_added_per_loop);

    int start = current_match[0];
    int end = current_match[1];

    if (prev < start) {
      builder.AddSubjectSlice(prev, start);
    }

    if (simple_replace) {
      builder.AddString(replacement);
    } else {
      compiled_replacement.Apply(&builder, start, end, current_match);
    }
    prev = end;

    current_match = global_cache.FetchNext();
  } while (current_match != NULL);

  if (global_cache.HasException()) return isolate->heap()->exception();

  if (prev < subject_length) {
    builder.EnsureCapacity(2);
    builder.AddSubjectSlice(prev, subject_length);
  }

  RegExpImpl::SetLastMatchInfo(last_match_info, subject, capture_count,
                               global_cache.LastSuccessfulMatch());

  Handle<String> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result, builder.ToString());
  return *result;
}


template <typename ResultSeqString>
MUST_USE_RESULT static Object* StringReplaceGlobalRegExpWithEmptyString(
    Isolate* isolate, Handle<String> subject, Handle<JSRegExp> regexp,
    Handle<JSArray> last_match_info) {
  DCHECK(subject->IsFlat());

  // Shortcut for simple non-regexp global replacements
  if (regexp->TypeTag() == JSRegExp::ATOM) {
    Handle<String> empty_string = isolate->factory()->empty_string();
    if (subject->IsOneByteRepresentation()) {
      return StringReplaceGlobalAtomRegExpWithString<SeqOneByteString>(
          isolate, subject, regexp, empty_string, last_match_info);
    } else {
      return StringReplaceGlobalAtomRegExpWithString<SeqTwoByteString>(
          isolate, subject, regexp, empty_string, last_match_info);
    }
  }

  RegExpImpl::GlobalCache global_cache(regexp, subject, true, isolate);
  if (global_cache.HasException()) return isolate->heap()->exception();

  int32_t* current_match = global_cache.FetchNext();
  if (current_match == NULL) {
    if (global_cache.HasException()) return isolate->heap()->exception();
    return *subject;
  }

  int start = current_match[0];
  int end = current_match[1];
  int capture_count = regexp->CaptureCount();
  int subject_length = subject->length();

  int new_length = subject_length - (end - start);
  if (new_length == 0) return isolate->heap()->empty_string();

  Handle<ResultSeqString> answer;
  if (ResultSeqString::kHasOneByteEncoding) {
    answer = Handle<ResultSeqString>::cast(
        isolate->factory()->NewRawOneByteString(new_length).ToHandleChecked());
  } else {
    answer = Handle<ResultSeqString>::cast(
        isolate->factory()->NewRawTwoByteString(new_length).ToHandleChecked());
  }

  int prev = 0;
  int position = 0;

  do {
    start = current_match[0];
    end = current_match[1];
    if (prev < start) {
      // Add substring subject[prev;start] to answer string.
      String::WriteToFlat(*subject, answer->GetChars() + position, prev, start);
      position += start - prev;
    }
    prev = end;

    current_match = global_cache.FetchNext();
  } while (current_match != NULL);

  if (global_cache.HasException()) return isolate->heap()->exception();

  RegExpImpl::SetLastMatchInfo(last_match_info, subject, capture_count,
                               global_cache.LastSuccessfulMatch());

  if (prev < subject_length) {
    // Add substring subject[prev;length] to answer string.
    String::WriteToFlat(*subject, answer->GetChars() + position, prev,
                        subject_length);
    position += subject_length - prev;
  }

  if (position == 0) return isolate->heap()->empty_string();

  // Shorten string and fill
  int string_size = ResultSeqString::SizeFor(position);
  int allocated_string_size = ResultSeqString::SizeFor(new_length);
  int delta = allocated_string_size - string_size;

  answer->set_length(position);
  if (delta == 0) return *answer;

  Address end_of_string = answer->address() + string_size;
  Heap* heap = isolate->heap();

  // The trimming is performed on a newly allocated object, which is on a
  // fresly allocated page or on an already swept page. Hence, the sweeper
  // thread can not get confused with the filler creation. No synchronization
  // needed.
  // TODO(hpayer): We should shrink the large object page if the size
  // of the object changed significantly.
  if (!heap->lo_space()->Contains(*answer)) {
    heap->CreateFillerObjectAt(end_of_string, delta);
  }
  heap->AdjustLiveBytes(*answer, -delta, Heap::CONCURRENT_TO_SWEEPER);
  return *answer;
}


RUNTIME_FUNCTION(Runtime_StringReplaceGlobalRegExpWithString) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 4);

  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, replacement, 2);
  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 1);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, last_match_info, 3);

  RUNTIME_ASSERT(regexp->GetFlags() & JSRegExp::kGlobal);
  RUNTIME_ASSERT(last_match_info->HasFastObjectElements());

  subject = String::Flatten(subject);

  if (replacement->length() == 0) {
    if (subject->HasOnlyOneByteChars()) {
      return StringReplaceGlobalRegExpWithEmptyString<SeqOneByteString>(
          isolate, subject, regexp, last_match_info);
    } else {
      return StringReplaceGlobalRegExpWithEmptyString<SeqTwoByteString>(
          isolate, subject, regexp, last_match_info);
    }
  }

  replacement = String::Flatten(replacement);

  return StringReplaceGlobalRegExpWithString(isolate, subject, regexp,
                                             replacement, last_match_info);
}


RUNTIME_FUNCTION(Runtime_StringSplit) {
  HandleScope handle_scope(isolate);
  DCHECK(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(String, subject, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, pattern, 1);
  CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[2]);
  RUNTIME_ASSERT(limit > 0);

  int subject_length = subject->length();
  int pattern_length = pattern->length();
  RUNTIME_ASSERT(pattern_length > 0);

  if (limit == 0xffffffffu) {
    FixedArray* last_match_cache_unused;
    Handle<Object> cached_answer(
        RegExpResultsCache::Lookup(isolate->heap(), *subject, *pattern,
                                   &last_match_cache_unused,
                                   RegExpResultsCache::STRING_SPLIT_SUBSTRINGS),
        isolate);
    if (*cached_answer != Smi::FromInt(0)) {
      // The cache FixedArray is a COW-array and can therefore be reused.
      Handle<JSArray> result = isolate->factory()->NewJSArrayWithElements(
          Handle<FixedArray>::cast(cached_answer));
      return *result;
    }
  }

  // The limit can be very large (0xffffffffu), but since the pattern
  // isn't empty, we can never create more parts than ~half the length
  // of the subject.

  subject = String::Flatten(subject);
  pattern = String::Flatten(pattern);

  static const int kMaxInitialListCapacity = 16;

  ZoneScope zone_scope(isolate->runtime_zone());

  // Find (up to limit) indices of separator and end-of-string in subject
  int initial_capacity = Min<uint32_t>(kMaxInitialListCapacity, limit);
  ZoneList<int> indices(initial_capacity, zone_scope.zone());

  FindStringIndicesDispatch(isolate, *subject, *pattern, &indices, limit,
                            zone_scope.zone());

  if (static_cast<uint32_t>(indices.length()) < limit) {
    indices.Add(subject_length, zone_scope.zone());
  }

  // The list indices now contains the end of each part to create.

  // Create JSArray of substrings separated by separator.
  int part_count = indices.length();

  Handle<JSArray> result = isolate->factory()->NewJSArray(part_count);
  JSObject::EnsureCanContainHeapObjectElements(result);
  result->set_length(Smi::FromInt(part_count));

  DCHECK(result->HasFastObjectElements());

  Handle<FixedArray> elements(FixedArray::cast(result->elements()));

  if (part_count == 1 && indices.at(0) == subject_length) {
    elements->set(0, *subject);
  } else {
    int part_start = 0;
    for (int i = 0; i < part_count; i++) {
      HandleScope local_loop_handle(isolate);
      int part_end = indices.at(i);
      Handle<String> substring =
          isolate->factory()->NewProperSubString(subject, part_start, part_end);
      elements->set(i, *substring);
      part_start = part_end + pattern_length;
    }
  }

  if (limit == 0xffffffffu) {
    if (result->HasFastObjectElements()) {
      RegExpResultsCache::Enter(isolate, subject, pattern, elements,
                                isolate->factory()->empty_fixed_array(),
                                RegExpResultsCache::STRING_SPLIT_SUBSTRINGS);
    }
  }

  return *result;
}


RUNTIME_FUNCTION(Runtime_RegExpExec) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 4);
  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, subject, 1);
  CONVERT_INT32_ARG_CHECKED(index, 2);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, last_match_info, 3);
  // Due to the way the JS calls are constructed this must be less than the
  // length of a string, i.e. it is always a Smi.  We check anyway for security.
  RUNTIME_ASSERT(index >= 0);
  RUNTIME_ASSERT(index <= subject->length());
  isolate->counters()->regexp_entry_runtime()->Increment();
  Handle<Object> result;
  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
      isolate, result,
      RegExpImpl::Exec(regexp, subject, index, last_match_info));
  return *result;
}


RUNTIME_FUNCTION(Runtime_RegExpFlags) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_CHECKED(JSRegExp, regexp, 0);
  return regexp->flags();
}


RUNTIME_FUNCTION(Runtime_RegExpSource) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_CHECKED(JSRegExp, regexp, 0);
  return regexp->source();
}


RUNTIME_FUNCTION(Runtime_RegExpConstructResult) {
  HandleScope handle_scope(isolate);
  DCHECK(args.length() == 3);
  CONVERT_SMI_ARG_CHECKED(size, 0);
  RUNTIME_ASSERT(size >= 0 && size <= FixedArray::kMaxLength);
  CONVERT_ARG_HANDLE_CHECKED(Object, index, 1);
  CONVERT_ARG_HANDLE_CHECKED(Object, input, 2);
  Handle<FixedArray> elements = isolate->factory()->NewFixedArray(size);
  Handle<Map> regexp_map(isolate->native_context()->regexp_result_map());
  Handle<JSObject> object =
      isolate->factory()->NewJSObjectFromMap(regexp_map, NOT_TENURED);
  Handle<JSArray> array = Handle<JSArray>::cast(object);
  array->set_elements(*elements);
  array->set_length(Smi::FromInt(size));
  // Write in-object properties after the length of the array.
  array->InObjectPropertyAtPut(JSRegExpResult::kIndexIndex, *index);
  array->InObjectPropertyAtPut(JSRegExpResult::kInputIndex, *input);
  return *array;
}


RUNTIME_FUNCTION(Runtime_RegExpInitializeAndCompile) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 3);
  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, source, 1);
  CONVERT_ARG_HANDLE_CHECKED(String, flags, 2);

  RETURN_FAILURE_ON_EXCEPTION(isolate,
                              JSRegExp::Initialize(regexp, source, flags));

  return *regexp;
}


// Only called from Runtime_RegExpExecMultiple so it doesn't need to maintain
// separate last match info.  See comment on that function.
template <bool has_capture>
static Object* SearchRegExpMultiple(Isolate* isolate, Handle<String> subject,
                                    Handle<JSRegExp> regexp,
                                    Handle<JSArray> last_match_array,
                                    Handle<JSArray> result_array) {
  DCHECK(subject->IsFlat());
  DCHECK_NE(has_capture, regexp->CaptureCount() == 0);

  int capture_count = regexp->CaptureCount();
  int subject_length = subject->length();

  static const int kMinLengthToCache = 0x1000;

  if (subject_length > kMinLengthToCache) {
    FixedArray* last_match_cache;
    Object* cached_answer = RegExpResultsCache::Lookup(
        isolate->heap(), *subject, regexp->data(), &last_match_cache,
        RegExpResultsCache::REGEXP_MULTIPLE_INDICES);
    if (cached_answer->IsFixedArray()) {
      int capture_registers = (capture_count + 1) * 2;
      int32_t* last_match = NewArray<int32_t>(capture_registers);
      for (int i = 0; i < capture_registers; i++) {
        last_match[i] = Smi::cast(last_match_cache->get(i))->value();
      }
      Handle<FixedArray> cached_fixed_array =
          Handle<FixedArray>(FixedArray::cast(cached_answer));
      // The cache FixedArray is a COW-array and can therefore be reused.
      JSArray::SetContent(result_array, cached_fixed_array);
      RegExpImpl::SetLastMatchInfo(last_match_array, subject, capture_count,
                                   last_match);
      DeleteArray(last_match);
      return *result_array;
    }
  }

  RegExpImpl::GlobalCache global_cache(regexp, subject, true, isolate);
  if (global_cache.HasException()) return isolate->heap()->exception();

  // Ensured in Runtime_RegExpExecMultiple.
  DCHECK(result_array->HasFastObjectElements());
  Handle<FixedArray> result_elements(
      FixedArray::cast(result_array->elements()));
  if (result_elements->length() < 16) {
    result_elements = isolate->factory()->NewFixedArrayWithHoles(16);
  }

  FixedArrayBuilder builder(result_elements);

  // Position to search from.
  int match_start = -1;
  int match_end = 0;
  bool first = true;

  // Two smis before and after the match, for very long strings.
  static const int kMaxBuilderEntriesPerRegExpMatch = 5;

  while (true) {
    int32_t* current_match = global_cache.FetchNext();
    if (current_match == NULL) break;
    match_start = current_match[0];
    builder.EnsureCapacity(kMaxBuilderEntriesPerRegExpMatch);
    if (match_end < match_start) {
      ReplacementStringBuilder::AddSubjectSlice(&builder, match_end,
                                                match_start);
    }
    match_end = current_match[1];
    {
      // Avoid accumulating new handles inside loop.
      HandleScope temp_scope(isolate);
      Handle<String> match;
      if (!first) {
        match = isolate->factory()->NewProperSubString(subject, match_start,
                                                       match_end);
      } else {
        match =
            isolate->factory()->NewSubString(subject, match_start, match_end);
        first = false;
      }

      if (has_capture) {
        // Arguments array to replace function is match, captures, index and
        // subject, i.e., 3 + capture count in total.
        Handle<FixedArray> elements =
            isolate->factory()->NewFixedArray(3 + capture_count);

        elements->set(0, *match);
        for (int i = 1; i <= capture_count; i++) {
          int start = current_match[i * 2];
          if (start >= 0) {
            int end = current_match[i * 2 + 1];
            DCHECK(start <= end);
            Handle<String> substring =
                isolate->factory()->NewSubString(subject, start, end);
            elements->set(i, *substring);
          } else {
            DCHECK(current_match[i * 2 + 1] < 0);
            elements->set(i, isolate->heap()->undefined_value());
          }
        }
        elements->set(capture_count + 1, Smi::FromInt(match_start));
        elements->set(capture_count + 2, *subject);
        builder.Add(*isolate->factory()->NewJSArrayWithElements(elements));
      } else {
        builder.Add(*match);
      }
    }
  }

  if (global_cache.HasException()) return isolate->heap()->exception();

  if (match_start >= 0) {
    // Finished matching, with at least one match.
    if (match_end < subject_length) {
      ReplacementStringBuilder::AddSubjectSlice(&builder, match_end,
                                                subject_length);
    }

    RegExpImpl::SetLastMatchInfo(last_match_array, subject, capture_count,
                                 global_cache.LastSuccessfulMatch());

    if (subject_length > kMinLengthToCache) {
      // Store the last successful match into the array for caching.
      // TODO(yangguo): do not expose last match to JS and simplify caching.
      int capture_registers = (capture_count + 1) * 2;
      Handle<FixedArray> last_match_cache =
          isolate->factory()->NewFixedArray(capture_registers);
      int32_t* last_match = global_cache.LastSuccessfulMatch();
      for (int i = 0; i < capture_registers; i++) {
        last_match_cache->set(i, Smi::FromInt(last_match[i]));
      }
      Handle<FixedArray> result_fixed_array = builder.array();
      result_fixed_array->Shrink(builder.length());
      // Cache the result and turn the FixedArray into a COW array.
      RegExpResultsCache::Enter(
          isolate, subject, handle(regexp->data(), isolate), result_fixed_array,
          last_match_cache, RegExpResultsCache::REGEXP_MULTIPLE_INDICES);
    }
    return *builder.ToJSArray(result_array);
  } else {
    return isolate->heap()->null_value();  // No matches at all.
  }
}


// This is only called for StringReplaceGlobalRegExpWithFunction.  This sets
// lastMatchInfoOverride to maintain the last match info, so we don't need to
// set any other last match array info.
RUNTIME_FUNCTION(Runtime_RegExpExecMultiple) {
  HandleScope handles(isolate);
  DCHECK(args.length() == 4);

  CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 0);
  CONVERT_ARG_HANDLE_CHECKED(String, subject, 1);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, last_match_info, 2);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, result_array, 3);
  RUNTIME_ASSERT(last_match_info->HasFastObjectElements());
  RUNTIME_ASSERT(result_array->HasFastObjectElements());

  subject = String::Flatten(subject);
  RUNTIME_ASSERT(regexp->GetFlags() & JSRegExp::kGlobal);

  if (regexp->CaptureCount() == 0) {
    return SearchRegExpMultiple<false>(isolate, subject, regexp,
                                       last_match_info, result_array);
  } else {
    return SearchRegExpMultiple<true>(isolate, subject, regexp, last_match_info,
                                      result_array);
  }
}


RUNTIME_FUNCTION(Runtime_RegExpExecReThrow) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 4);
  Object* exception = isolate->pending_exception();
  isolate->clear_pending_exception();
  return isolate->ReThrow(exception);
}


RUNTIME_FUNCTION(Runtime_IsRegExp) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_CHECKED(Object, obj, 0);
  return isolate->heap()->ToBoolean(obj->IsJSRegExp());
}
}  // namespace internal
}  // namespace v8