bytecode-array-writer.cc

// Copyright 2015 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/bytecode-array-writer.h"

#include "src/api-inl.h"
#include "src/interpreter/bytecode-jump-table.h"
#include "src/interpreter/bytecode-label.h"
#include "src/interpreter/bytecode-node.h"
#include "src/interpreter/bytecode-register.h"
#include "src/interpreter/bytecode-source-info.h"
#include "src/interpreter/constant-array-builder.h"
#include "src/log.h"
#include "src/objects-inl.h"

namespace v8 {
namespace internal {
namespace interpreter {

STATIC_CONST_MEMBER_DEFINITION const size_t
    BytecodeArrayWriter::kMaxSizeOfPackedBytecode;

BytecodeArrayWriter::BytecodeArrayWriter(
    Zone* zone, ConstantArrayBuilder* constant_array_builder,
    SourcePositionTableBuilder::RecordingMode source_position_mode)
    : bytecodes_(zone),
      unbound_jumps_(0),
      source_position_table_builder_(source_position_mode),
      constant_array_builder_(constant_array_builder),
      last_bytecode_(Bytecode::kIllegal),
      last_bytecode_offset_(0),
      last_bytecode_had_source_info_(false),
      elide_noneffectful_bytecodes_(FLAG_ignition_elide_noneffectful_bytecodes),
      exit_seen_in_block_(false) {
  bytecodes_.reserve(512);  // Derived via experimentation.
}

Handle<BytecodeArray> BytecodeArrayWriter::ToBytecodeArray(
    Isolate* isolate, int register_count, int parameter_count,
    Handle<ByteArray> handler_table) {
  DCHECK_EQ(0, unbound_jumps_);

  int bytecode_size = static_cast<int>(bytecodes()->size());
  int frame_size = register_count * kPointerSize;
  Handle<FixedArray> constant_pool =
      constant_array_builder()->ToFixedArray(isolate);
  Handle<ByteArray> source_position_table =
      source_position_table_builder()->ToSourcePositionTable(isolate);
  Handle<BytecodeArray> bytecode_array = isolate->factory()->NewBytecodeArray(
      bytecode_size, &bytecodes()->front(), frame_size, parameter_count,
      constant_pool);
  bytecode_array->set_handler_table(*handler_table);
  bytecode_array->set_source_position_table(*source_position_table);
  LOG_CODE_EVENT(isolate, CodeLinePosInfoRecordEvent(
                              bytecode_array->GetFirstBytecodeAddress(),
                              *source_position_table));
  return bytecode_array;
}

void BytecodeArrayWriter::Write(BytecodeNode* node) {
  DCHECK(!Bytecodes::IsJump(node->bytecode()));

  if (exit_seen_in_block_) return;  // Don't emit dead code.
  UpdateExitSeenInBlock(node->bytecode());
  MaybeElideLastBytecode(node->bytecode(), node->source_info().is_valid());

  UpdateSourcePositionTable(node);
  EmitBytecode(node);
}

void BytecodeArrayWriter::WriteJump(BytecodeNode* node, BytecodeLabel* label) {
  DCHECK(Bytecodes::IsJump(node->bytecode()));

  // TODO(rmcilroy): For forward jumps we could also mark the label as dead,
  // thereby avoiding emitting dead code when we bind the label.
  if (exit_seen_in_block_) return;  // Don't emit dead code.
  UpdateExitSeenInBlock(node->bytecode());
  MaybeElideLastBytecode(node->bytecode(), node->source_info().is_valid());

  UpdateSourcePositionTable(node);
  EmitJump(node, label);
}

void BytecodeArrayWriter::WriteSwitch(BytecodeNode* node,
                                      BytecodeJumpTable* jump_table) {
  DCHECK(Bytecodes::IsSwitch(node->bytecode()));

  // TODO(rmcilroy): For jump tables we could also mark the table as dead,
  // thereby avoiding emitting dead code when we bind the entries.
  if (exit_seen_in_block_) return;  // Don't emit dead code.
  UpdateExitSeenInBlock(node->bytecode());
  MaybeElideLastBytecode(node->bytecode(), node->source_info().is_valid());

  UpdateSourcePositionTable(node);
  EmitSwitch(node, jump_table);
}

void BytecodeArrayWriter::BindLabel(BytecodeLabel* label) {
  size_t current_offset = bytecodes()->size();
  if (label->is_forward_target()) {
    // An earlier jump instruction refers to this label. Update it's location.
    PatchJump(current_offset, label->offset());
    // Now treat as if the label will only be back referred to.
  }
  label->bind_to(current_offset);
  InvalidateLastBytecode();
  exit_seen_in_block_ = false;  // Starting a new basic block.
}

void BytecodeArrayWriter::BindLabel(const BytecodeLabel& target,
                                    BytecodeLabel* label) {
  DCHECK(!label->is_bound());
  DCHECK(target.is_bound());
  if (label->is_forward_target()) {
    // An earlier jump instruction refers to this label. Update it's location.
    PatchJump(target.offset(), label->offset());
    // Now treat as if the label will only be back referred to.
  }
  label->bind_to(target.offset());
  InvalidateLastBytecode();
  // exit_seen_in_block_ was reset when target was bound, so shouldn't be
  // changed here.
}

void BytecodeArrayWriter::BindJumpTableEntry(BytecodeJumpTable* jump_table,
                                             int case_value) {
  DCHECK(!jump_table->is_bound(case_value));

  size_t current_offset = bytecodes()->size();
  size_t relative_jump = current_offset - jump_table->switch_bytecode_offset();

  constant_array_builder()->SetJumpTableSmi(
      jump_table->ConstantPoolEntryFor(case_value),
      Smi::FromInt(static_cast<int>(relative_jump)));
  jump_table->mark_bound(case_value);

  InvalidateLastBytecode();
  exit_seen_in_block_ = false;  // Starting a new basic block.
}

void BytecodeArrayWriter::UpdateSourcePositionTable(
    const BytecodeNode* const node) {
  int bytecode_offset = static_cast<int>(bytecodes()->size());
  const BytecodeSourceInfo& source_info = node->source_info();
  if (source_info.is_valid()) {
    source_position_table_builder()->AddPosition(
        bytecode_offset, SourcePosition(source_info.source_position()),
        source_info.is_statement());
  }
}

void BytecodeArrayWriter::UpdateExitSeenInBlock(Bytecode bytecode) {
  switch (bytecode) {
    case Bytecode::kReturn:
    case Bytecode::kThrow:
    case Bytecode::kReThrow:
    case Bytecode::kAbort:
    case Bytecode::kJump:
    case Bytecode::kJumpConstant:
    case Bytecode::kSuspendGenerator:
      exit_seen_in_block_ = true;
      break;
    default:
      break;
  }
}

void BytecodeArrayWriter::MaybeElideLastBytecode(Bytecode next_bytecode,
                                                 bool has_source_info) {
  if (!elide_noneffectful_bytecodes_) return;

  // If the last bytecode loaded the accumulator without any external effect,
  // and the next bytecode clobbers this load without reading the accumulator,
  // then the previous bytecode can be elided as it has no effect.
  if (Bytecodes::IsAccumulatorLoadWithoutEffects(last_bytecode_) &&
      Bytecodes::GetAccumulatorUse(next_bytecode) == AccumulatorUse::kWrite &&
      (!last_bytecode_had_source_info_ || !has_source_info)) {
    DCHECK_GT(bytecodes()->size(), last_bytecode_offset_);
    bytecodes()->resize(last_bytecode_offset_);
    // If the last bytecode had source info we will transfer the source info
    // to this bytecode.
    has_source_info |= last_bytecode_had_source_info_;
  }
  last_bytecode_ = next_bytecode;
  last_bytecode_had_source_info_ = has_source_info;
  last_bytecode_offset_ = bytecodes()->size();
}

void BytecodeArrayWriter::InvalidateLastBytecode() {
  last_bytecode_ = Bytecode::kIllegal;
}

void BytecodeArrayWriter::EmitBytecode(const BytecodeNode* const node) {
  DCHECK_NE(node->bytecode(), Bytecode::kIllegal);

  Bytecode bytecode = node->bytecode();
  OperandScale operand_scale = node->operand_scale();

  if (operand_scale != OperandScale::kSingle) {
    Bytecode prefix = Bytecodes::OperandScaleToPrefixBytecode(operand_scale);
    bytecodes()->push_back(Bytecodes::ToByte(prefix));
  }
  bytecodes()->push_back(Bytecodes::ToByte(bytecode));

  const uint32_t* const operands = node->operands();
  const int operand_count = node->operand_count();
  const OperandSize* operand_sizes =
      Bytecodes::GetOperandSizes(bytecode, operand_scale);
  for (int i = 0; i < operand_count; ++i) {
    switch (operand_sizes[i]) {
      case OperandSize::kNone:
        UNREACHABLE();
        break;
      case OperandSize::kByte:
        bytecodes()->push_back(static_cast<uint8_t>(operands[i]));
        break;
      case OperandSize::kShort: {
        uint16_t operand = static_cast<uint16_t>(operands[i]);
        const uint8_t* raw_operand = reinterpret_cast<const uint8_t*>(&operand);
        bytecodes()->push_back(raw_operand[0]);
        bytecodes()->push_back(raw_operand[1]);
        break;
      }
      case OperandSize::kQuad: {
        const uint8_t* raw_operand =
            reinterpret_cast<const uint8_t*>(&operands[i]);
        bytecodes()->push_back(raw_operand[0]);
        bytecodes()->push_back(raw_operand[1]);
        bytecodes()->push_back(raw_operand[2]);
        bytecodes()->push_back(raw_operand[3]);
        break;
      }
    }
  }
}

// static
Bytecode GetJumpWithConstantOperand(Bytecode jump_bytecode) {
  switch (jump_bytecode) {
    case Bytecode::kJump:
      return Bytecode::kJumpConstant;
    case Bytecode::kJumpIfTrue:
      return Bytecode::kJumpIfTrueConstant;
    case Bytecode::kJumpIfFalse:
      return Bytecode::kJumpIfFalseConstant;
    case Bytecode::kJumpIfToBooleanTrue:
      return Bytecode::kJumpIfToBooleanTrueConstant;
    case Bytecode::kJumpIfToBooleanFalse:
      return Bytecode::kJumpIfToBooleanFalseConstant;
    case Bytecode::kJumpIfNull:
      return Bytecode::kJumpIfNullConstant;
    case Bytecode::kJumpIfNotNull:
      return Bytecode::kJumpIfNotNullConstant;
    case Bytecode::kJumpIfUndefined:
      return Bytecode::kJumpIfUndefinedConstant;
    case Bytecode::kJumpIfNotUndefined:
      return Bytecode::kJumpIfNotUndefinedConstant;
    case Bytecode::kJumpIfJSReceiver:
      return Bytecode::kJumpIfJSReceiverConstant;
    default:
      UNREACHABLE();
  }
}

void BytecodeArrayWriter::PatchJumpWith8BitOperand(size_t jump_location,
                                                   int delta) {
  Bytecode jump_bytecode = Bytecodes::FromByte(bytecodes()->at(jump_location));
  DCHECK(Bytecodes::IsForwardJump(jump_bytecode));
  DCHECK(Bytecodes::IsJumpImmediate(jump_bytecode));
  DCHECK_EQ(Bytecodes::GetOperandType(jump_bytecode, 0), OperandType::kUImm);
  DCHECK_GT(delta, 0);
  size_t operand_location = jump_location + 1;
  DCHECK_EQ(bytecodes()->at(operand_location), k8BitJumpPlaceholder);
  if (Bytecodes::ScaleForUnsignedOperand(delta) == OperandScale::kSingle) {
    // The jump fits within the range of an UImm8 operand, so cancel
    // the reservation and jump directly.
    constant_array_builder()->DiscardReservedEntry(OperandSize::kByte);
    bytecodes()->at(operand_location) = static_cast<uint8_t>(delta);
  } else {
    // The jump does not fit within the range of an UImm8 operand, so
    // commit reservation putting the offset into the constant pool,
    // and update the jump instruction and operand.
    size_t entry = constant_array_builder()->CommitReservedEntry(
        OperandSize::kByte, Smi::FromInt(delta));
    DCHECK_EQ(Bytecodes::SizeForUnsignedOperand(static_cast<uint32_t>(entry)),
              OperandSize::kByte);
    jump_bytecode = GetJumpWithConstantOperand(jump_bytecode);
    bytecodes()->at(jump_location) = Bytecodes::ToByte(jump_bytecode);
    bytecodes()->at(operand_location) = static_cast<uint8_t>(entry);
  }
}

void BytecodeArrayWriter::PatchJumpWith16BitOperand(size_t jump_location,
                                                    int delta) {
  Bytecode jump_bytecode = Bytecodes::FromByte(bytecodes()->at(jump_location));
  DCHECK(Bytecodes::IsForwardJump(jump_bytecode));
  DCHECK(Bytecodes::IsJumpImmediate(jump_bytecode));
  DCHECK_EQ(Bytecodes::GetOperandType(jump_bytecode, 0), OperandType::kUImm);
  DCHECK_GT(delta, 0);
  size_t operand_location = jump_location + 1;
  uint8_t operand_bytes[2];
  if (Bytecodes::ScaleForUnsignedOperand(delta) <= OperandScale::kDouble) {
    // The jump fits within the range of an Imm16 operand, so cancel
    // the reservation and jump directly.
    constant_array_builder()->DiscardReservedEntry(OperandSize::kShort);
    WriteUnalignedUInt16(reinterpret_cast<Address>(operand_bytes),
                         static_cast<uint16_t>(delta));
  } else {
    // The jump does not fit within the range of an Imm16 operand, so
    // commit reservation putting the offset into the constant pool,
    // and update the jump instruction and operand.
    size_t entry = constant_array_builder()->CommitReservedEntry(
        OperandSize::kShort, Smi::FromInt(delta));
    jump_bytecode = GetJumpWithConstantOperand(jump_bytecode);
    bytecodes()->at(jump_location) = Bytecodes::ToByte(jump_bytecode);
    WriteUnalignedUInt16(reinterpret_cast<Address>(operand_bytes),
                         static_cast<uint16_t>(entry));
  }
  DCHECK(bytecodes()->at(operand_location) == k8BitJumpPlaceholder &&
         bytecodes()->at(operand_location + 1) == k8BitJumpPlaceholder);
  bytecodes()->at(operand_location++) = operand_bytes[0];
  bytecodes()->at(operand_location) = operand_bytes[1];
}

void BytecodeArrayWriter::PatchJumpWith32BitOperand(size_t jump_location,
                                                    int delta) {
  DCHECK(Bytecodes::IsJumpImmediate(
      Bytecodes::FromByte(bytecodes()->at(jump_location))));
  constant_array_builder()->DiscardReservedEntry(OperandSize::kQuad);
  uint8_t operand_bytes[4];
  WriteUnalignedUInt32(reinterpret_cast<Address>(operand_bytes),
                       static_cast<uint32_t>(delta));
  size_t operand_location = jump_location + 1;
  DCHECK(bytecodes()->at(operand_location) == k8BitJumpPlaceholder &&
         bytecodes()->at(operand_location + 1) == k8BitJumpPlaceholder &&
         bytecodes()->at(operand_location + 2) == k8BitJumpPlaceholder &&
         bytecodes()->at(operand_location + 3) == k8BitJumpPlaceholder);
  bytecodes()->at(operand_location++) = operand_bytes[0];
  bytecodes()->at(operand_location++) = operand_bytes[1];
  bytecodes()->at(operand_location++) = operand_bytes[2];
  bytecodes()->at(operand_location) = operand_bytes[3];
}

void BytecodeArrayWriter::PatchJump(size_t jump_target, size_t jump_location) {
  Bytecode jump_bytecode = Bytecodes::FromByte(bytecodes()->at(jump_location));
  int delta = static_cast<int>(jump_target - jump_location);
  int prefix_offset = 0;
  OperandScale operand_scale = OperandScale::kSingle;
  if (Bytecodes::IsPrefixScalingBytecode(jump_bytecode)) {
    // If a prefix scaling bytecode is emitted the target offset is one
    // less than the case of no prefix scaling bytecode.
    delta -= 1;
    prefix_offset = 1;
    operand_scale = Bytecodes::PrefixBytecodeToOperandScale(jump_bytecode);
    jump_bytecode =
        Bytecodes::FromByte(bytecodes()->at(jump_location + prefix_offset));
  }

  DCHECK(Bytecodes::IsJump(jump_bytecode));
  switch (operand_scale) {
    case OperandScale::kSingle:
      PatchJumpWith8BitOperand(jump_location, delta);
      break;
    case OperandScale::kDouble:
      PatchJumpWith16BitOperand(jump_location + prefix_offset, delta);
      break;
    case OperandScale::kQuadruple:
      PatchJumpWith32BitOperand(jump_location + prefix_offset, delta);
      break;
    default:
      UNREACHABLE();
  }
  unbound_jumps_--;
}

void BytecodeArrayWriter::EmitJump(BytecodeNode* node, BytecodeLabel* label) {
  DCHECK(Bytecodes::IsJump(node->bytecode()));
  DCHECK_EQ(0u, node->operand(0));

  size_t current_offset = bytecodes()->size();

  if (label->is_bound()) {
    CHECK_GE(current_offset, label->offset());
    CHECK_LE(current_offset, static_cast<size_t>(kMaxUInt32));
    // Label has been bound already so this is a backwards jump.
    uint32_t delta = static_cast<uint32_t>(current_offset - label->offset());
    OperandScale operand_scale = Bytecodes::ScaleForUnsignedOperand(delta);
    if (operand_scale > OperandScale::kSingle) {
      // Adjust for scaling byte prefix for wide jump offset.
      delta += 1;
    }
    DCHECK_EQ(Bytecode::kJumpLoop, node->bytecode());
    node->update_operand0(delta);
  } else {
    // The label has not yet been bound so this is a forward reference
    // that will be patched when the label is bound. We create a
    // reservation in the constant pool so the jump can be patched
    // when the label is bound. The reservation means the maximum size
    // of the operand for the constant is known and the jump can
    // be emitted into the bytecode stream with space for the operand.
    unbound_jumps_++;
    label->set_referrer(current_offset);
    OperandSize reserved_operand_size =
        constant_array_builder()->CreateReservedEntry();
    DCHECK_NE(Bytecode::kJumpLoop, node->bytecode());
    switch (reserved_operand_size) {
      case OperandSize::kNone:
        UNREACHABLE();
        break;
      case OperandSize::kByte:
        node->update_operand0(k8BitJumpPlaceholder);
        break;
      case OperandSize::kShort:
        node->update_operand0(k16BitJumpPlaceholder);
        break;
      case OperandSize::kQuad:
        node->update_operand0(k32BitJumpPlaceholder);
        break;
    }
  }
  EmitBytecode(node);
}

void BytecodeArrayWriter::EmitSwitch(BytecodeNode* node,
                                     BytecodeJumpTable* jump_table) {
  DCHECK(Bytecodes::IsSwitch(node->bytecode()));

  size_t current_offset = bytecodes()->size();
  if (node->operand_scale() > OperandScale::kSingle) {
    // Adjust for scaling byte prefix.
    current_offset += 1;
  }
  jump_table->set_switch_bytecode_offset(current_offset);

  EmitBytecode(node);
}

}  // namespace interpreter
}  // namespace internal
}  // namespace v8