deps: update V8 to 7.6.303.28

PR-URL: https://github.com/nodejs/node/pull/28016
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann (רפאל פלחי) <refack@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>

1 files changed, 242 insertions, 0 deletions

diff --git a/deps/v8/src/codegen/source-position-table.cc b/deps/v8/src/codegen/source-position-table.cc
new file mode 100644
index 0000000000..6c0aa36b27
--- /dev/null
+++ b/deps/v8/src/codegen/source-position-table.cc
@@ -0,0 +1,242 @@
+// Copyright 2016 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/codegen/source-position-table.h"
+
+#include "src/objects/objects-inl.h"
+#include "src/objects/objects.h"
+
+namespace v8 {
+namespace internal {
+
+// We'll use a simple encoding scheme to record the source positions.
+// Conceptually, each position consists of:
+// - code_offset: An integer index into the BytecodeArray or code.
+// - source_position: An integer index into the source string.
+// - position type: Each position is either a statement or an expression.
+//
+// The basic idea for the encoding is to use a variable-length integer coding,
+// where each byte contains 7 bits of payload data, and 1 'more' bit that
+// determines whether additional bytes follow. Additionally:
+// - we record the difference from the previous position,
+// - we just stuff one bit for the type into the code offset,
+// - we write least-significant bits first,
+// - we use zig-zag encoding to encode both positive and negative numbers.
+
+namespace {
+
+// Each byte is encoded as MoreBit | ValueBits.
+class MoreBit : public BitField8<bool, 7, 1> {};
+class ValueBits : public BitField8<unsigned, 0, 7> {};
+
+// Helper: Add the offsets from 'other' to 'value'. Also set is_statement.
+void AddAndSetEntry(PositionTableEntry& value,
+                    const PositionTableEntry& other) {
+  value.code_offset += other.code_offset;
+  value.source_position += other.source_position;
+  value.is_statement = other.is_statement;
+}
+
+// Helper: Subtract the offsets from 'other' from 'value'.
+void SubtractFromEntry(PositionTableEntry& value,
+                       const PositionTableEntry& other) {
+  value.code_offset -= other.code_offset;
+  value.source_position -= other.source_position;
+}
+
+// Helper: Encode an integer.
+template <typename T>
+void EncodeInt(std::vector<byte>& bytes, T value) {
+  using unsigned_type = typename std::make_unsigned<T>::type;
+  // Zig-zag encoding.
+  static const int kShift = sizeof(T) * kBitsPerByte - 1;
+  value = ((static_cast<unsigned_type>(value) << 1) ^ (value >> kShift));
+  DCHECK_GE(value, 0);
+  unsigned_type encoded = static_cast<unsigned_type>(value);
+  bool more;
+  do {
+    more = encoded > ValueBits::kMax;
+    byte current =
+        MoreBit::encode(more) | ValueBits::encode(encoded & ValueBits::kMask);
+    bytes.push_back(current);
+    encoded >>= ValueBits::kSize;
+  } while (more);
+}
+
+// Encode a PositionTableEntry.
+void EncodeEntry(std::vector<byte>& bytes, const PositionTableEntry& entry) {
+  // We only accept ascending code offsets.
+  DCHECK_GE(entry.code_offset, 0);
+  // Since code_offset is not negative, we use sign to encode is_statement.
+  EncodeInt(bytes,
+            entry.is_statement ? entry.code_offset : -entry.code_offset - 1);
+  EncodeInt(bytes, entry.source_position);
+}
+
+// Helper: Decode an integer.
+template <typename T>
+T DecodeInt(Vector<const byte> bytes, int* index) {
+  byte current;
+  int shift = 0;
+  T decoded = 0;
+  bool more;
+  do {
+    current = bytes[(*index)++];
+    decoded |= static_cast<typename std::make_unsigned<T>::type>(
+                   ValueBits::decode(current))
+               << shift;
+    more = MoreBit::decode(current);
+    shift += ValueBits::kSize;
+  } while (more);
+  DCHECK_GE(decoded, 0);
+  decoded = (decoded >> 1) ^ (-(decoded & 1));
+  return decoded;
+}
+
+void DecodeEntry(Vector<const byte> bytes, int* index,
+                 PositionTableEntry* entry) {
+  int tmp = DecodeInt<int>(bytes, index);
+  if (tmp >= 0) {
+    entry->is_statement = true;
+    entry->code_offset = tmp;
+  } else {
+    entry->is_statement = false;
+    entry->code_offset = -(tmp + 1);
+  }
+  entry->source_position = DecodeInt<int64_t>(bytes, index);
+}
+
+Vector<const byte> VectorFromByteArray(ByteArray byte_array) {
+  return Vector<const byte>(byte_array.GetDataStartAddress(),
+                            byte_array.length());
+}
+
+#ifdef ENABLE_SLOW_DCHECKS
+void CheckTableEquals(std::vector<PositionTableEntry>& raw_entries,
+                      SourcePositionTableIterator& encoded) {
+  // Brute force testing: Record all positions and decode
+  // the entire table to verify they are identical.
+  auto raw = raw_entries.begin();
+  for (; !encoded.done(); encoded.Advance(), raw++) {
+    DCHECK(raw != raw_entries.end());
+    DCHECK_EQ(encoded.code_offset(), raw->code_offset);
+    DCHECK_EQ(encoded.source_position().raw(), raw->source_position);
+    DCHECK_EQ(encoded.is_statement(), raw->is_statement);
+  }
+  DCHECK(raw == raw_entries.end());
+}
+#endif
+
+}  // namespace
+
+SourcePositionTableBuilder::SourcePositionTableBuilder(
+    SourcePositionTableBuilder::RecordingMode mode)
+    : mode_(mode), previous_() {}
+
+void SourcePositionTableBuilder::AddPosition(size_t code_offset,
+                                             SourcePosition source_position,
+                                             bool is_statement) {
+  if (Omit()) return;
+  DCHECK(source_position.IsKnown());
+  int offset = static_cast<int>(code_offset);
+  AddEntry({offset, source_position.raw(), is_statement});
+}
+
+void SourcePositionTableBuilder::AddEntry(const PositionTableEntry& entry) {
+  PositionTableEntry tmp(entry);
+  SubtractFromEntry(tmp, previous_);
+  EncodeEntry(bytes_, tmp);
+  previous_ = entry;
+#ifdef ENABLE_SLOW_DCHECKS
+  raw_entries_.push_back(entry);
+#endif
+}
+
+Handle<ByteArray> SourcePositionTableBuilder::ToSourcePositionTable(
+    Isolate* isolate) {
+  if (bytes_.empty()) return isolate->factory()->empty_byte_array();
+  DCHECK(!Omit());
+
+  Handle<ByteArray> table = isolate->factory()->NewByteArray(
+      static_cast<int>(bytes_.size()), AllocationType::kOld);
+  MemCopy(table->GetDataStartAddress(), bytes_.data(), bytes_.size());
+
+#ifdef ENABLE_SLOW_DCHECKS
+  // Brute force testing: Record all positions and decode
+  // the entire table to verify they are identical.
+  SourcePositionTableIterator it(*table, SourcePositionTableIterator::kAll);
+  CheckTableEquals(raw_entries_, it);
+  // No additional source positions after creating the table.
+  mode_ = OMIT_SOURCE_POSITIONS;
+#endif
+  return table;
+}
+
+OwnedVector<byte> SourcePositionTableBuilder::ToSourcePositionTableVector() {
+  if (bytes_.empty()) return OwnedVector<byte>();
+  DCHECK(!Omit());
+
+  OwnedVector<byte> table = OwnedVector<byte>::Of(bytes_);
+
+#ifdef ENABLE_SLOW_DCHECKS
+  // Brute force testing: Record all positions and decode
+  // the entire table to verify they are identical.
+  SourcePositionTableIterator it(table.as_vector(),
+                                 SourcePositionTableIterator::kAll);
+  CheckTableEquals(raw_entries_, it);
+  // No additional source positions after creating the table.
+  mode_ = OMIT_SOURCE_POSITIONS;
+#endif
+  return table;
+}
+
+SourcePositionTableIterator::SourcePositionTableIterator(ByteArray byte_array,
+                                                         IterationFilter filter)
+    : raw_table_(VectorFromByteArray(byte_array)), filter_(filter) {
+  Advance();
+}
+
+SourcePositionTableIterator::SourcePositionTableIterator(
+    Handle<ByteArray> byte_array, IterationFilter filter)
+    : table_(byte_array), filter_(filter) {
+  Advance();
+#ifdef DEBUG
+  // We can enable allocation because we keep the table in a handle.
+  no_gc.Release();
+#endif  // DEBUG
+}
+
+SourcePositionTableIterator::SourcePositionTableIterator(
+    Vector<const byte> bytes, IterationFilter filter)
+    : raw_table_(bytes), filter_(filter) {
+  Advance();
+#ifdef DEBUG
+  // We can enable allocation because the underlying vector does not move.
+  no_gc.Release();
+#endif  // DEBUG
+}
+
+void SourcePositionTableIterator::Advance() {
+  Vector<const byte> bytes =
+      table_.is_null() ? raw_table_ : VectorFromByteArray(*table_);
+  DCHECK(!done());
+  DCHECK(index_ >= 0 && index_ <= bytes.length());
+  bool filter_satisfied = false;
+  while (!done() && !filter_satisfied) {
+    if (index_ >= bytes.length()) {
+      index_ = kDone;
+    } else {
+      PositionTableEntry tmp;
+      DecodeEntry(bytes, &index_, &tmp);
+      AddAndSetEntry(current_, tmp);
+      SourcePosition p = source_position();
+      filter_satisfied = (filter_ == kAll) ||
+                         (filter_ == kJavaScriptOnly && p.IsJavaScript()) ||
+                         (filter_ == kExternalOnly && p.IsExternal());
+    }
+  }
+}
+
+}  // namespace internal
+}  // namespace v8