[utf8] Rewrite NewStringFromUtf8 using Utf8::ValueOfIncremental

This is 3-4x faster than using the Utf8Decoder. This matters for proper
parse-time measurements using d8.

Change-Id: I9870e9fbe400ec022a6eeb20491c80a2a32f8519
Reviewed-on: https://chromium-review.googlesource.com/c/1451827
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59347}

src/heap/factory.cc

@@ -42,7 +42,7 @@
 #include "src/objects/stack-frame-info-inl.h"
 #include "src/objects/struct-inl.h"
 #include "src/unicode-cache.h"
-#include "src/unicode-decoder.h"
+#include "src/unicode-inl.h"
 
 namespace v8 {
 namespace internal {
@@ -670,13 +670,38 @@ MaybeHandle<String> Factory::NewStringFromUtf8(Vector<const char> string,
     return NewStringFromOneByte(Vector<const uint8_t>::cast(string), pretenure);
   }
 
-  // Non-ASCII and we need to decode.
-  auto non_ascii = string.SubVector(non_ascii_start, length);
-  Access<UnicodeCache::Utf8Decoder> decoder(
-      isolate()->unicode_cache()->utf8_decoder());
-  decoder->Reset(non_ascii);
+  std::unique_ptr<uint16_t[]> buffer(new uint16_t[length - non_ascii_start]);
+
+  const uint8_t* cursor =
+      reinterpret_cast<const uint8_t*>(&string[non_ascii_start]);
+  const uint8_t* end = reinterpret_cast<const uint8_t*>(string.end());
+
+  uint16_t* output_cursor = buffer.get();
+
+  uint32_t incomplete_char = 0;
+  unibrow::Utf8::State state = unibrow::Utf8::State::kAccept;
+
+  while (cursor < end) {
+    unibrow::uchar t =
+        unibrow::Utf8::ValueOfIncremental(&cursor, &state, &incomplete_char);
+
+    if (V8_LIKELY(t <= unibrow::Utf16::kMaxNonSurrogateCharCode)) {
+      *(output_cursor++) = static_cast<uc16>(t);  // The most frequent case.
+    } else if (t == unibrow::Utf8::kIncomplete) {
+      continue;
+    } else {
+      *(output_cursor++) = unibrow::Utf16::LeadSurrogate(t);
+      *(output_cursor++) = unibrow::Utf16::TrailSurrogate(t);
+    }
+  }
 
-  int utf16_length = static_cast<int>(decoder->Utf16Length());
+  unibrow::uchar t = unibrow::Utf8::ValueOfIncrementalFinish(&state);
+  if (t != unibrow::Utf8::kBufferEmpty) {
+    *(output_cursor++) = static_cast<uc16>(t);
+  }
+
+  DCHECK_LE(output_cursor, buffer.get() + length - non_ascii_start);
+  int utf16_length = static_cast<int>(output_cursor - buffer.get());
   DCHECK_GT(utf16_length, 0);
 
   // Allocate string.
@@ -685,15 +710,13 @@ MaybeHandle<String> Factory::NewStringFromUtf8(Vector<const char> string,
       isolate(), result,
       NewRawTwoByteString(non_ascii_start + utf16_length, pretenure), String);
 
-  // Copy ASCII portion.
+  DCHECK_LE(non_ascii_start + utf16_length, length);
+
   DisallowHeapAllocation no_gc;
   uint16_t* data = result->GetChars(no_gc);
-  for (int i = 0; i < non_ascii_start; i++) {
-    *data++ = *ascii_data++;
-  }
+  CopyChars(data, ascii_data, non_ascii_start);
+  CopyChars(data + non_ascii_start, buffer.get(), utf16_length);
 
-  // Now write the remainder.
-  decoder->WriteUtf16(data, utf16_length, non_ascii);
   return result;
 }
 

src/parsing/scanner-character-streams.cc

@@ -514,23 +514,38 @@ bool Utf8ExternalStreamingStream::SkipToPosition(size_t position) {
   unibrow::Utf8::State state = chunk.start.state;
   uint32_t incomplete_char = chunk.start.incomplete_char;
   size_t it = current_.pos.bytes - chunk.start.bytes;
-  size_t chars = chunk.start.chars;
-  while (it < chunk.length && chars < position) {
-    unibrow::uchar t = unibrow::Utf8::ValueOfIncremental(
-        chunk.data[it], &it, &state, &incomplete_char);
-    if (t == kUtf8Bom && current_.pos.chars == 0) {
-      // BOM detected at beginning of the stream. Don't copy it.
-    } else if (t != unibrow::Utf8::kIncomplete) {
+  const uint8_t* cursor = &chunk.data[it];
+  const uint8_t* end = &chunk.data[chunk.length];
+
+  size_t chars = current_.pos.chars;
+
+  if (V8_UNLIKELY(current_.pos.bytes < 3 && chars == 0)) {
+    while (cursor < end) {
+      unibrow::uchar t =
+          unibrow::Utf8::ValueOfIncremental(&cursor, &state, &incomplete_char);
+      if (t == unibrow::Utf8::kIncomplete) continue;
+      if (t != kUtf8Bom) {
+        chars++;
+        if (t > unibrow::Utf16::kMaxNonSurrogateCharCode) chars++;
+      }
+      break;
+    }
+  }
+
+  while (cursor < end && chars < position) {
+    unibrow::uchar t =
+        unibrow::Utf8::ValueOfIncremental(&cursor, &state, &incomplete_char);
+    if (t != unibrow::Utf8::kIncomplete) {
       chars++;
       if (t > unibrow::Utf16::kMaxNonSurrogateCharCode) chars++;
     }
   }
 
-  current_.pos.bytes += it;
+  current_.pos.bytes = chunk.start.bytes + (cursor - chunk.data);
   current_.pos.chars = chars;
   current_.pos.incomplete_char = incomplete_char;
   current_.pos.state = state;
-  current_.chunk_no += (it == chunk.length);
+  current_.chunk_no += (cursor == end);
 
   return current_.pos.chars == position;
 }
@@ -544,8 +559,8 @@ void Utf8ExternalStreamingStream::FillBufferFromCurrentChunk() {
 
   // The buffer_ is writable, but buffer_*_ members are const. So we get a
   // non-const pointer into buffer that points to the same char as buffer_end_.
-  uint16_t* cursor = buffer_ + (buffer_end_ - buffer_start_);
-  DCHECK_EQ(cursor, buffer_end_);
+  uint16_t* output_cursor = buffer_ + (buffer_end_ - buffer_start_);
+  DCHECK_EQ(output_cursor, buffer_end_);
 
   unibrow::Utf8::State state = current_.pos.state;
   uint32_t incomplete_char = current_.pos.incomplete_char;
@@ -556,7 +571,7 @@ void Utf8ExternalStreamingStream::FillBufferFromCurrentChunk() {
     unibrow::uchar t = unibrow::Utf8::ValueOfIncrementalFinish(&state);
     if (t != unibrow::Utf8::kBufferEmpty) {
       DCHECK_EQ(t, unibrow::Utf8::kBadChar);
-      *cursor = static_cast<uc16>(t);
+      *output_cursor = static_cast<uc16>(t);
       buffer_end_++;
       current_.pos.chars++;
       current_.pos.incomplete_char = 0;
@@ -566,30 +581,50 @@ void Utf8ExternalStreamingStream::FillBufferFromCurrentChunk() {
   }
 
   size_t it = current_.pos.bytes - chunk.start.bytes;
-  while (it < chunk.length && cursor + 1 < buffer_start_ + kBufferSize) {
-    unibrow::uchar t = unibrow::Utf8::ValueOfIncremental(
-        chunk.data[it], &it, &state, &incomplete_char);
-    if (V8_LIKELY(t < kUtf8Bom)) {
-      *(cursor++) = static_cast<uc16>(t);  // The by most frequent case.
+  const uint8_t* cursor = chunk.data + it;
+  const uint8_t* end = chunk.data + chunk.length;
+
+  // Deal with possible BOM.
+  if (V8_UNLIKELY(current_.pos.bytes < 3 && current_.pos.chars == 0)) {
+    while (cursor < end) {
+      unibrow::uchar t =
+          unibrow::Utf8::ValueOfIncremental(&cursor, &state, &incomplete_char);
+      if (V8_LIKELY(t < kUtf8Bom)) {
+        *(output_cursor++) = static_cast<uc16>(t);  // The most frequent case.
+      } else if (t == unibrow::Utf8::kIncomplete) {
+        continue;
+      } else if (t == kUtf8Bom) {
+        // BOM detected at beginning of the stream. Don't copy it.
+      } else if (t <= unibrow::Utf16::kMaxNonSurrogateCharCode) {
+        *(output_cursor++) = static_cast<uc16>(t);
+      } else {
+        *(output_cursor++) = unibrow::Utf16::LeadSurrogate(t);
+        *(output_cursor++) = unibrow::Utf16::TrailSurrogate(t);
+      }
+      break;
+    }
+  }
+
+  while (cursor < end && output_cursor + 1 < buffer_start_ + kBufferSize) {
+    unibrow::uchar t =
+        unibrow::Utf8::ValueOfIncremental(&cursor, &state, &incomplete_char);
+    if (V8_LIKELY(t < unibrow::Utf16::kMaxNonSurrogateCharCode)) {
+      *(output_cursor++) = static_cast<uc16>(t);  // The most frequent case.
     } else if (t == unibrow::Utf8::kIncomplete) {
       continue;
-    } else if (t == kUtf8Bom && current_.pos.bytes + it == 3) {
-      // BOM detected at beginning of the stream. Don't copy it.
-    } else if (t <= unibrow::Utf16::kMaxNonSurrogateCharCode) {
-      *(cursor++) = static_cast<uc16>(t);
     } else {
-      *(cursor++) = unibrow::Utf16::LeadSurrogate(t);
-      *(cursor++) = unibrow::Utf16::TrailSurrogate(t);
+      *(output_cursor++) = unibrow::Utf16::LeadSurrogate(t);
+      *(output_cursor++) = unibrow::Utf16::TrailSurrogate(t);
     }
   }
 
-  current_.pos.bytes = chunk.start.bytes + it;
-  current_.pos.chars += (cursor - buffer_end_);
+  current_.pos.bytes = chunk.start.bytes + (cursor - chunk.data);
+  current_.pos.chars += (output_cursor - buffer_end_);
   current_.pos.incomplete_char = incomplete_char;
   current_.pos.state = state;
-  current_.chunk_no += (it == chunk.length);
+  current_.chunk_no += (cursor == end);
 
-  buffer_end_ = cursor;
+  buffer_end_ = output_cursor;
 }
 
 bool Utf8ExternalStreamingStream::FetchChunk() {

src/unicode-inl.h

@@ -56,6 +56,53 @@ template <class T, int s> int Mapping<T, s>::CalculateValue(uchar c, uchar n,
   }
 }
 
+// Decodes UTF-8 bytes incrementally, allowing the decoding of bytes as they
+// stream in. This **must** be followed by a call to ValueOfIncrementalFinish
+// when the stream is complete, to ensure incomplete sequences are handled.
+uchar Utf8::ValueOfIncremental(const byte** cursor, State* state,
+                               Utf8IncrementalBuffer* buffer) {
+  DCHECK_NOT_NULL(buffer);
+  State old_state = *state;
+  byte next = **cursor;
+  *cursor += 1;
+
+  if (V8_LIKELY(next <= kMaxOneByteChar && old_state == State::kAccept)) {
+    DCHECK_EQ(0u, *buffer);
+    return static_cast<uchar>(next);
+  }
+
+  // So we're at the lead byte of a 2/3/4 sequence, or we're at a continuation
+  // char in that sequence.
+  Utf8DfaDecoder::Decode(next, state, buffer);
+
+  switch (*state) {
+    case State::kAccept: {
+      uchar t = *buffer;
+      *buffer = 0;
+      return t;
+    }
+
+    case State::kReject:
+      *state = State::kAccept;
+      *buffer = 0;
+
+      // If we hit a bad byte, we need to determine if we were trying to start
+      // a sequence or continue one. If we were trying to start a sequence,
+      // that means it's just an invalid lead byte and we need to continue to
+      // the next (which we already did above). If we were already in a
+      // sequence, we need to reprocess this same byte after resetting to the
+      // initial state.
+      if (old_state != State::kAccept) {
+        // We were trying to continue a sequence, so let's reprocess this byte
+        // next time.
+        *cursor -= 1;
+      }
+      return kBadChar;
+
+    default:
+      return kIncomplete;
+  }
+}
 
 unsigned Utf8::EncodeOneByte(char* str, uint8_t c) {
   static const int kMask = ~(1 << 6);

src/unicode.cc

@@ -203,62 +203,17 @@ uchar Utf8::CalculateValue(const byte* str, size_t max_length, size_t* cursor) {
   Utf8IncrementalBuffer buffer = 0;
   uchar t;
 
-  size_t i = 0;
+  const byte* start = str;
+  const byte* end = str + max_length;
+
   do {
-    t = ValueOfIncremental(str[i], &i, &state, &buffer);
-  } while (i < max_length && t == kIncomplete);
+    t = ValueOfIncremental(&str, &state, &buffer);
+  } while (str < end && t == kIncomplete);
 
-  *cursor += i;
+  *cursor += str - start;
   return (state == State::kAccept) ? t : kBadChar;
 }
 
-// Decodes UTF-8 bytes incrementally, allowing the decoding of bytes as they
-// stream in. This **must** be followed by a call to ValueOfIncrementalFinish
-// when the stream is complete, to ensure incomplete sequences are handled.
-uchar Utf8::ValueOfIncremental(byte next, size_t* cursor, State* state,
-                               Utf8IncrementalBuffer* buffer) {
-  DCHECK_NOT_NULL(buffer);
-  State old_state = *state;
-  *cursor += 1;
-
-  if (V8_LIKELY(next <= kMaxOneByteChar && old_state == State::kAccept)) {
-    DCHECK_EQ(0u, *buffer);
-    return static_cast<uchar>(next);
-  }
-
-  // So we're at the lead byte of a 2/3/4 sequence, or we're at a continuation
-  // char in that sequence.
-  Utf8DfaDecoder::Decode(next, state, buffer);
-
-  switch (*state) {
-    case State::kAccept: {
-      uchar t = *buffer;
-      *buffer = 0;
-      return t;
-    }
-
-    case State::kReject:
-      *state = State::kAccept;
-      *buffer = 0;
-
-      // If we hit a bad byte, we need to determine if we were trying to start
-      // a sequence or continue one. If we were trying to start a sequence,
-      // that means it's just an invalid lead byte and we need to continue to
-      // the next (which we already did above). If we were already in a
-      // sequence, we need to reprocess this same byte after resetting to the
-      // initial state.
-      if (old_state != State::kAccept) {
-        // We were trying to continue a sequence, so let's reprocess this byte
-        // next time.
-        *cursor -= 1;
-      }
-      return kBadChar;
-
-    default:
-      return kIncomplete;
-  }
-}
-
 // Finishes the incremental decoding, ensuring that if an unfinished sequence
 // is left that it is replaced by a replacement char.
 uchar Utf8::ValueOfIncrementalFinish(State* state) {

src/unicode.h

@@ -163,8 +163,8 @@ class V8_EXPORT_PRIVATE Utf8 {
   static inline uchar ValueOf(const byte* str, size_t length, size_t* cursor);
 
   typedef uint32_t Utf8IncrementalBuffer;
-  static uchar ValueOfIncremental(byte next_byte, size_t* cursor, State* state,
-                                  Utf8IncrementalBuffer* buffer);
+  static inline uchar ValueOfIncremental(const byte** cursor, State* state,
+                                         Utf8IncrementalBuffer* buffer);
   static uchar ValueOfIncrementalFinish(State* state);
 
   // Excludes non-characters from the set of valid code points.

test/cctest/unicode-helpers.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "test/cctest/unicode-helpers.h"
+#include "src/unicode-inl.h"
 
 int Ucs2CharLength(unibrow::uchar c) {
   if (c == unibrow::Utf8::kIncomplete || c == unibrow::Utf8::kBufferEmpty) {
@@ -19,10 +20,9 @@ int Utf8LengthHelper(const char* s) {
   unibrow::Utf8::State state = unibrow::Utf8::State::kAccept;
 
   int length = 0;
-  size_t i = 0;
-  while (s[i] != '\0') {
-    unibrow::uchar tmp =
-        unibrow::Utf8::ValueOfIncremental(s[i], &i, &state, &buffer);
+  const uint8_t* c = reinterpret_cast<const uint8_t*>(s);
+  while (*c != '\0') {
+    unibrow::uchar tmp = unibrow::Utf8::ValueOfIncremental(&c, &state, &buffer);
     length += Ucs2CharLength(tmp);
   }
   unibrow::uchar tmp = unibrow::Utf8::ValueOfIncrementalFinish(&state);

test/unittests/unicode-unittest.cc

@@ -50,9 +50,11 @@ void DecodeIncrementally(const std::vector<byte>& bytes,
                          std::vector<unibrow::uchar>* output) {
   unibrow::Utf8::Utf8IncrementalBuffer buffer = 0;
   unibrow::Utf8::State state = unibrow::Utf8::State::kAccept;
-  for (size_t i = 0; i < bytes.size();) {
+  const byte* cursor = &bytes[0];
+  const byte* end = &bytes[bytes.size()];
+  while (cursor < end) {
     unibrow::uchar result =
-        unibrow::Utf8::ValueOfIncremental(bytes[i], &i, &state, &buffer);
+        unibrow::Utf8::ValueOfIncremental(&cursor, &state, &buffer);
     if (result != unibrow::Utf8::kIncomplete) {
       output->push_back(result);
     }