Revert "Handlify concat string and substring."

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 2e4ef44ecdcd8fe1dd7b467043e497ee1ca99b6c..30932093be4763c09ebbe8b1498192ab8cbd5cee 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3774,6 +3774,262 @@ 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();
+  } else 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);
+  }
+
+  // Make an attempt to flatten the buffer to reduce access time.
+  buffer = buffer->TryFlattenGetString();
+
+  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();