Use source position table for unoptimized code.

src/interpreter/source-position-table.cc

-// 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/interpreter/source-position-table.h"
-
-#include "src/objects-inl.h"
-#include "src/objects.h"
-
-namespace v8 {
-namespace internal {
-namespace interpreter {
-
-// We'll use a simple encoding scheme to record the source positions.
-// Conceptually, each position consists of:
-// - bytecode_offset: An integer index into the BytecodeArray
-// - 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 bytecode 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.bytecode_offset += other.bytecode_offset;
-  value.source_position += other.source_position;
-  value.is_statement = other.is_statement;
-}
-
-// Helper: Substract the offsets from 'other' from 'value'.
-void SubtractFromEntry(PositionTableEntry& value,
-                       const PositionTableEntry& other) {
-  value.bytecode_offset -= other.bytecode_offset;
-  value.source_position -= other.source_position;
-}
-
-// Helper: Encode an integer.
-void EncodeInt(ZoneVector<byte>& bytes, int value) {
-  // Zig-zag encoding.
-  static const int kShift = kIntSize * kBitsPerByte - 1;
-  value = ((value << 1) ^ (value >> kShift));
-  DCHECK_GE(value, 0);
-  unsigned int encoded = static_cast<unsigned int>(value);
-  bool more;
-  do {
-    more = encoded > ValueBits::kMax;
-    bytes.push_back(MoreBit::encode(more) |
-                    ValueBits::encode(encoded & ValueBits::kMask));
-    encoded >>= ValueBits::kSize;
-  } while (more);
-}
-
-// Encode a PositionTableEntry.
-void EncodeEntry(ZoneVector<byte>& bytes, const PositionTableEntry& entry) {
-  // We only accept ascending bytecode offsets.
-  DCHECK(entry.bytecode_offset >= 0);
-  // Since bytecode_offset is not negative, we use sign to encode is_statement.
-  EncodeInt(bytes, entry.is_statement ? entry.bytecode_offset
-                                      : -entry.bytecode_offset - 1);
-  EncodeInt(bytes, entry.source_position);
-}
-
-// Helper: Decode an integer.
-void DecodeInt(ByteArray* bytes, int* index, int* v) {
-  byte current;
-  int shift = 0;
-  int decoded = 0;
-  bool more;
-  do {
-    current = bytes->get((*index)++);
-    decoded |= ValueBits::decode(current) << shift;
-    more = MoreBit::decode(current);
-    shift += ValueBits::kSize;
-  } while (more);
-  DCHECK_GE(decoded, 0);
-  decoded = (decoded >> 1) ^ (-(decoded & 1));
-  *v = decoded;
-}
-
-void DecodeEntry(ByteArray* bytes, int* index, PositionTableEntry* entry) {
-  int tmp;
-  DecodeInt(bytes, index, &tmp);
-  if (tmp >= 0) {
-    entry->is_statement = true;
-    entry->bytecode_offset = tmp;
-  } else {
-    entry->is_statement = false;
-    entry->bytecode_offset = -(tmp + 1);
-  }
-  DecodeInt(bytes, index, &entry->source_position);
-}
-
-}  // namespace
-
-void SourcePositionTableBuilder::AddPosition(size_t bytecode_offset,
-                                             int source_position,
-                                             bool is_statement) {
-  int offset = static_cast<int>(bytecode_offset);
-  AddEntry({offset, source_position, is_statement});
-}
-
-void SourcePositionTableBuilder::AddEntry(const PositionTableEntry& entry) {
-  PositionTableEntry tmp(entry);
-  SubtractFromEntry(tmp, previous_);
-  EncodeEntry(bytes_, tmp);
-  previous_ = entry;
-
-  if (entry.is_statement) {
-    LOG_CODE_EVENT(isolate_, CodeLinePosInfoAddStatementPositionEvent(
-                                 jit_handler_data_, entry.bytecode_offset,
-                                 entry.source_position));
-  }
-  LOG_CODE_EVENT(isolate_, CodeLinePosInfoAddPositionEvent(
-                               jit_handler_data_, entry.bytecode_offset,
-                               entry.source_position));
-
-#ifdef ENABLE_SLOW_DCHECKS
-  raw_entries_.push_back(entry);
-#endif
-}
-
-Handle<ByteArray> SourcePositionTableBuilder::ToSourcePositionTable() {
-  if (bytes_.empty()) return isolate_->factory()->empty_byte_array();
-
-  Handle<ByteArray> table = isolate_->factory()->NewByteArray(
-      static_cast<int>(bytes_.size()), TENURED);
-
-  MemCopy(table->GetDataStartAddress(), &*bytes_.begin(), bytes_.size());
-
-#ifdef ENABLE_SLOW_DCHECKS
-  // Brute force testing: Record all positions and decode
-  // the entire table to verify they are identical.
-  auto raw = raw_entries_.begin();
-  for (SourcePositionTableIterator encoded(*table); !encoded.done();
-       encoded.Advance(), raw++) {
-    DCHECK(raw != raw_entries_.end());
-    DCHECK_EQ(encoded.bytecode_offset(), raw->bytecode_offset);
-    DCHECK_EQ(encoded.source_position(), raw->source_position);
-    DCHECK_EQ(encoded.is_statement(), raw->is_statement);
-  }
-  DCHECK(raw == raw_entries_.end());
-#endif
-
-  return table;
-}
-
-SourcePositionTableIterator::SourcePositionTableIterator(ByteArray* byte_array)
-    : table_(byte_array), index_(0), current_() {
-  Advance();
-}
-
-void SourcePositionTableIterator::Advance() {
-  DCHECK(!done());
-  DCHECK(index_ >= 0 && index_ <= table_->length());
-  if (index_ == table_->length()) {
-    index_ = kDone;
-  } else {
-    PositionTableEntry tmp;
-    DecodeEntry(table_, &index_, &tmp);
-    AddAndSetEntry(current_, tmp);
-  }
-}
-
-}  // namespace interpreter
-}  // namespace internal
-}  // namespace v8