Reland "Handlify concat string and substring."

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 6921bb653f8a97c905fcc0800736c5044e6e38d4..d4ae9893008aeea9bf5a4561bab3ac4ae409a0d1 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3794,264 +3794,6 @@ MaybeObject* Heap::AllocateJSMessageObject(String* type,
 }
 
 
-
-// Returns true for a character in a range.  Both limits are inclusive.
-static inline bool Between(uint32_t character, uint32_t from, uint32_t to) {
-  // This makes uses of the the unsigned wraparound.
-  return character - from <= to - from;
-}
-
-
-MUST_USE_RESULT static inline MaybeObject* MakeOrFindTwoCharacterString(
-    Heap* heap,
-    uint16_t c1,
-    uint16_t c2) {
-  String* result;
-  // Numeric strings have a different hash algorithm not known by
-  // LookupTwoCharsStringIfExists, so we skip this step for such strings.
-  if ((!Between(c1, '0', '9') || !Between(c2, '0', '9')) &&
-      heap->string_table()->LookupTwoCharsStringIfExists(c1, c2, &result)) {
-    return result;
-  // Now we know the length is 2, we might as well make use of that fact
-  // when building the new string.
-  } else if (static_cast<unsigned>(c1 | c2) <= String::kMaxOneByteCharCodeU) {
-    // We can do this.
-    ASSERT(IsPowerOf2(String::kMaxOneByteCharCodeU + 1));  // because of this.
-    Object* result;
-    { MaybeObject* maybe_result = heap->AllocateRawOneByteString(2);
-      if (!maybe_result->ToObject(&result)) return maybe_result;
-    }
-    uint8_t* dest = SeqOneByteString::cast(result)->GetChars();
-    dest[0] = static_cast<uint8_t>(c1);
-    dest[1] = static_cast<uint8_t>(c2);
-    return result;
-  } else {
-    Object* result;
-    { MaybeObject* maybe_result = heap->AllocateRawTwoByteString(2);
-      if (!maybe_result->ToObject(&result)) return maybe_result;
-    }
-    uc16* dest = SeqTwoByteString::cast(result)->GetChars();
-    dest[0] = c1;
-    dest[1] = c2;
-    return result;
-  }
-}
-
-
-MaybeObject* Heap::AllocateConsString(String* first, String* second) {
-  int first_length = first->length();
-  if (first_length == 0) {
-    return second;
-  }
-
-  int second_length = second->length();
-  if (second_length == 0) {
-    return first;
-  }
-
-  int length = first_length + second_length;
-
-  // Optimization for 2-byte strings often used as keys in a decompression
-  // dictionary.  Check whether we already have the string in the string
-  // table to prevent creation of many unneccesary strings.
-  if (length == 2) {
-    uint16_t c1 = first->Get(0);
-    uint16_t c2 = second->Get(0);
-    return MakeOrFindTwoCharacterString(this, c1, c2);
-  }
-
-  bool first_is_one_byte = first->IsOneByteRepresentation();
-  bool second_is_one_byte = second->IsOneByteRepresentation();
-  bool is_one_byte = first_is_one_byte && second_is_one_byte;
-  // Make sure that an out of memory exception is thrown if the length
-  // of the new cons string is too large.
-  if (length > String::kMaxLength || length < 0) {
-    isolate()->context()->mark_out_of_memory();
-    return Failure::OutOfMemoryException(0x4);
-  }
-
-  bool is_one_byte_data_in_two_byte_string = false;
-  if (!is_one_byte) {
-    // At least one of the strings uses two-byte representation so we
-    // can't use the fast case code for short ASCII strings below, but
-    // we can try to save memory if all chars actually fit in ASCII.
-    is_one_byte_data_in_two_byte_string =
-        first->HasOnlyOneByteChars() && second->HasOnlyOneByteChars();
-    if (is_one_byte_data_in_two_byte_string) {
-      isolate_->counters()->string_add_runtime_ext_to_ascii()->Increment();
-    }
-  }
-
-  // If the resulting string is small make a flat string.
-  if (length < ConsString::kMinLength) {
-    // Note that neither of the two inputs can be a slice because:
-    STATIC_ASSERT(ConsString::kMinLength <= SlicedString::kMinLength);
-    ASSERT(first->IsFlat());
-    ASSERT(second->IsFlat());
-    if (is_one_byte) {
-      Object* result;
-      { MaybeObject* maybe_result = AllocateRawOneByteString(length);
-        if (!maybe_result->ToObject(&result)) return maybe_result;
-      }
-      // Copy the characters into the new object.
-      uint8_t* dest = SeqOneByteString::cast(result)->GetChars();
-      // Copy first part.
-      const uint8_t* src;
-      if (first->IsExternalString()) {
-        src = ExternalAsciiString::cast(first)->GetChars();
-      } else {
-        src = SeqOneByteString::cast(first)->GetChars();
-      }
-      for (int i = 0; i < first_length; i++) *dest++ = src[i];
-      // Copy second part.
-      if (second->IsExternalString()) {
-        src = ExternalAsciiString::cast(second)->GetChars();
-      } else {
-        src = SeqOneByteString::cast(second)->GetChars();
-      }
-      for (int i = 0; i < second_length; i++) *dest++ = src[i];
-      return result;
-    } else {
-      if (is_one_byte_data_in_two_byte_string) {
-        Object* result;
-        { MaybeObject* maybe_result = AllocateRawOneByteString(length);
-          if (!maybe_result->ToObject(&result)) return maybe_result;
-        }
-        // Copy the characters into the new object.
-        uint8_t* dest = SeqOneByteString::cast(result)->GetChars();
-        String::WriteToFlat(first, dest, 0, first_length);
-        String::WriteToFlat(second, dest + first_length, 0, second_length);
-        isolate_->counters()->string_add_runtime_ext_to_ascii()->Increment();
-        return result;
-      }
-
-      Object* result;
-      { MaybeObject* maybe_result = AllocateRawTwoByteString(length);
-        if (!maybe_result->ToObject(&result)) return maybe_result;
-      }
-      // Copy the characters into the new object.
-      uc16* dest = SeqTwoByteString::cast(result)->GetChars();
-      String::WriteToFlat(first, dest, 0, first_length);
-      String::WriteToFlat(second, dest + first_length, 0, second_length);
-      return result;
-    }
-  }
-
-  Map* map = (is_one_byte || is_one_byte_data_in_two_byte_string) ?
-      cons_ascii_string_map() : cons_string_map();
-
-  Object* result;
-  { MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
-    if (!maybe_result->ToObject(&result)) return maybe_result;
-  }
-
-  DisallowHeapAllocation no_gc;
-  ConsString* cons_string = ConsString::cast(result);
-  WriteBarrierMode mode = cons_string->GetWriteBarrierMode(no_gc);
-  cons_string->set_length(length);
-  cons_string->set_hash_field(String::kEmptyHashField);
-  cons_string->set_first(first, mode);
-  cons_string->set_second(second, mode);
-  return result;
-}
-
-
-MaybeObject* Heap::AllocateSubString(String* buffer,
-                                     int start,
-                                     int end,
-                                     PretenureFlag pretenure) {
-  int length = end - start;
-  if (length <= 0) {
-    return empty_string();
-  }
-
-  // Make an attempt to flatten the buffer to reduce access time.
-  buffer = buffer->TryFlattenGetString();
-
-  if (length == 1) {
-    return LookupSingleCharacterStringFromCode(buffer->Get(start));
-  } else if (length == 2) {
-    // Optimization for 2-byte strings often used as keys in a decompression
-    // dictionary.  Check whether we already have the string in the string
-    // table to prevent creation of many unnecessary strings.
-    uint16_t c1 = buffer->Get(start);
-    uint16_t c2 = buffer->Get(start + 1);
-    return MakeOrFindTwoCharacterString(this, c1, c2);
-  }
-
-  if (!FLAG_string_slices ||
-      !buffer->IsFlat() ||
-      length < SlicedString::kMinLength ||
-      pretenure == TENURED) {
-    Object* result;
-    // WriteToFlat takes care of the case when an indirect string has a
-    // different encoding from its underlying string.  These encodings may
-    // differ because of externalization.
-    bool is_one_byte = buffer->IsOneByteRepresentation();
-    { MaybeObject* maybe_result = is_one_byte
-                                  ? AllocateRawOneByteString(length, pretenure)
-                                  : AllocateRawTwoByteString(length, pretenure);
-      if (!maybe_result->ToObject(&result)) return maybe_result;
-    }
-    String* string_result = String::cast(result);
-    // Copy the characters into the new object.
-    if (is_one_byte) {
-      ASSERT(string_result->IsOneByteRepresentation());
-      uint8_t* dest = SeqOneByteString::cast(string_result)->GetChars();
-      String::WriteToFlat(buffer, dest, start, end);
-    } else {
-      ASSERT(string_result->IsTwoByteRepresentation());
-      uc16* dest = SeqTwoByteString::cast(string_result)->GetChars();
-      String::WriteToFlat(buffer, dest, start, end);
-    }
-    return result;
-  }
-
-  ASSERT(buffer->IsFlat());
-#if VERIFY_HEAP
-  if (FLAG_verify_heap) {
-    buffer->StringVerify();
-  }
-#endif
-
-  Object* result;
-  // When slicing an indirect string we use its encoding for a newly created
-  // slice and don't check the encoding of the underlying string.  This is safe
-  // even if the encodings are different because of externalization.  If an
-  // indirect ASCII string is pointing to a two-byte string, the two-byte char
-  // codes of the underlying string must still fit into ASCII (because
-  // externalization must not change char codes).
-  { Map* map = buffer->IsOneByteRepresentation()
-                 ? sliced_ascii_string_map()
-                 : sliced_string_map();
-    MaybeObject* maybe_result = Allocate(map, NEW_SPACE);
-    if (!maybe_result->ToObject(&result)) return maybe_result;
-  }
-
-  DisallowHeapAllocation no_gc;
-  SlicedString* sliced_string = SlicedString::cast(result);
-  sliced_string->set_length(length);
-  sliced_string->set_hash_field(String::kEmptyHashField);
-  if (buffer->IsConsString()) {
-    ConsString* cons = ConsString::cast(buffer);
-    ASSERT(cons->second()->length() == 0);
-    sliced_string->set_parent(cons->first());
-    sliced_string->set_offset(start);
-  } else if (buffer->IsSlicedString()) {
-    // Prevent nesting sliced strings.
-    SlicedString* parent_slice = SlicedString::cast(buffer);
-    sliced_string->set_parent(parent_slice->parent());
-    sliced_string->set_offset(start + parent_slice->offset());
-  } else {
-    sliced_string->set_parent(buffer);
-    sliced_string->set_offset(start);
-  }
-  ASSERT(sliced_string->parent()->IsSeqString() ||
-         sliced_string->parent()->IsExternalString());
-  return result;
-}
-
-
 MaybeObject* Heap::AllocateExternalStringFromAscii(
     const ExternalAsciiString::Resource* resource) {
   size_t length = resource->length();