bytecode-array-writer.cc

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// 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/api-inl.h"
#include "src/heap/local-factory-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-source-info.h"
#include "src/interpreter/constant-array-builder.h"
#include "src/interpreter/handler-table-builder.h"
#include "src/objects/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_(zone, 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_(
          v8_flags.ignition_elide_noneffectful_bytecodes),
      exit_seen_in_block_(false) {
  bytecodes_.reserve(512);  // Derived via experimentation.
}
 
template <typename IsolateT>
Handle<BytecodeArray> BytecodeArrayWriter::ToBytecodeArray(
    IsolateT* isolate, int register_count, uint16_t parameter_count,
    uint16_t max_arguments, DirectHandle<TrustedByteArray> handler_table) {
  DCHECK_EQ(0, unbound_jumps_);
 
  int bytecode_size = static_cast<int>(bytecodes()->size());
  int frame_size = register_count * kSystemPointerSize;
  DirectHandle<TrustedFixedArray> constant_pool =
      constant_array_builder()->ToFixedArray(isolate);
  Handle<BytecodeArray> bytecode_array = isolate->factory()->NewBytecodeArray(
      bytecode_size, &bytecodes()->front(), frame_size, parameter_count,
      max_arguments, constant_pool, handler_table);
  return bytecode_array;
}
 
template EXPORT_TEMPLATE_DEFINE(V8_EXPORT_PRIVATE)
    Handle<BytecodeArray> BytecodeArrayWriter::ToBytecodeArray(
        Isolate* isolate, int register_count, uint16_t parameter_count,
        uint16_t max_arguments, DirectHandle<TrustedByteArray> handler_table);
template EXPORT_TEMPLATE_DEFINE(V8_EXPORT_PRIVATE)
    Handle<BytecodeArray> BytecodeArrayWriter::ToBytecodeArray(
        LocalIsolate* isolate, int register_count, uint16_t parameter_count,
        uint16_t max_arguments, DirectHandle<TrustedByteArray> handler_table);
 
template <typename IsolateT>
DirectHandle<TrustedByteArray> BytecodeArrayWriter::ToSourcePositionTable(
    IsolateT* isolate) {
  DCHECK(!source_position_table_builder_.Lazy());
  DirectHandle<TrustedByteArray> source_position_table =
      source_position_table_builder_.Omit()
          ? isolate->factory()->empty_trusted_byte_array()
          : source_position_table_builder_.ToSourcePositionTable(isolate);
  return source_position_table;
}
 
template EXPORT_TEMPLATE_DEFINE(V8_EXPORT_PRIVATE)
    DirectHandle<TrustedByteArray> BytecodeArrayWriter::ToSourcePositionTable(
        Isolate* isolate);
template EXPORT_TEMPLATE_DEFINE(V8_EXPORT_PRIVATE)
    DirectHandle<TrustedByteArray> BytecodeArrayWriter::ToSourcePositionTable(
        LocalIsolate* isolate);
 
#ifdef DEBUG
int BytecodeArrayWriter::CheckBytecodeMatches(Tagged<BytecodeArray> bytecode) {
  int mismatches = false;
  int bytecode_size = static_cast<int>(bytecodes()->size());
  const uint8_t* bytecode_ptr = &bytecodes()->front();
  if (bytecode_size != bytecode->length()) mismatches = true;
 
  // If there's a mismatch only in the length of the bytecode (very unlikely)
  // then the first mismatch will be the first extra bytecode.
  int first_mismatch = std::min(bytecode_size, bytecode->length());
  for (int i = 0; i < first_mismatch; ++i) {
    if (bytecode_ptr[i] != bytecode->get(i)) {
      mismatches = true;
      first_mismatch = i;
      break;
    }
  }
 
  if (mismatches) {
    return first_mismatch;
  }
  return -1;
}
#endif
 
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::IsForwardJump(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);
  EmitJump(node, label);
}
 
void BytecodeArrayWriter::WriteJumpLoop(BytecodeNode* node,
                                        BytecodeLoopHeader* loop_header) {
  DCHECK_EQ(node->bytecode(), Bytecode::kJumpLoop);
 
  if (exit_seen_in_block_) return;  // Don't emit dead code.
  UpdateExitSeenInBlock(node->bytecode());
  MaybeElideLastBytecode(node->bytecode(), node->source_info().is_valid());
 
  UpdateSourcePositionTable(node);
  EmitJumpLoop(node, loop_header);
}
 
void BytecodeArrayWriter::WriteSwitch(BytecodeNode* node,
                                      BytecodeJumpTable* jump_table) {
  DCHECK(Bytecodes::IsSwitch(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);
  EmitSwitch(node, jump_table);
}
 
void BytecodeArrayWriter::BindLabel(BytecodeLabel* label) {
  DCHECK(label->has_referrer_jump());
  size_t current_offset = bytecodes()->size();
  // Update the jump instruction's location.
  PatchJump(current_offset, label->jump_offset());
  label->bind();
  StartBasicBlock();
}
 
void BytecodeArrayWriter::BindLoopHeader(BytecodeLoopHeader* loop_header) {
  size_t current_offset = bytecodes()->size();
  loop_header->bind_to(current_offset);
  // Don't start a basic block when the entire loop is dead.
  if (exit_seen_in_block_) return;
  StartBasicBlock();
}
 
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);
 
  StartBasicBlock();
}
 
void BytecodeArrayWriter::BindHandlerTarget(
    HandlerTableBuilder* handler_table_builder, int handler_id) {
  size_t current_offset = bytecodes()->size();
  StartBasicBlock();
  handler_table_builder->SetHandlerTarget(handler_id, current_offset);
}
 
void BytecodeArrayWriter::BindTryRegionStart(
    HandlerTableBuilder* handler_table_builder, int handler_id) {
  size_t current_offset = bytecodes()->size();
  // Try blocks don't have to be in a separate basic block, but we do have to
  // invalidate the bytecode to avoid eliding it and changing the offset.
  InvalidateLastBytecode();
  handler_table_builder->SetTryRegionStart(handler_id, current_offset);
}
 
void BytecodeArrayWriter::BindTryRegionEnd(
    HandlerTableBuilder* handler_table_builder, int handler_id) {
  // Try blocks don't have to be in a separate basic block, but we do have to
  // invalidate the bytecode to avoid eliding it and changing the offset.
  InvalidateLastBytecode();
  size_t current_offset = bytecodes()->size();
  handler_table_builder->SetTryRegionEnd(handler_id, current_offset);
}
 
void BytecodeArrayWriter::SetFunctionEntrySourcePosition(int position) {
  bool is_statement = false;
  source_position_table_builder_.AddPosition(
      kFunctionEntryBytecodeOffset, SourcePosition(position), is_statement);
}
 
void BytecodeArrayWriter::StartBasicBlock() {
  InvalidateLastBytecode();
  exit_seen_in_block_ = false;
}
 
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::kJumpLoop:
    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::GetImplicitRegisterUse(next_bytecode) ==
          ImplicitRegisterUse::kWriteAccumulator &&
      (!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();
      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::kJumpIfUndefinedOrNull:
      return Bytecode::kJumpIfUndefinedOrNullConstant;
    case Bytecode::kJumpIfJSReceiver:
      return Bytecode::kJumpIfJSReceiverConstant;
    case Bytecode::kJumpIfForInDone:
      return Bytecode::kJumpIfForInDoneConstant;
    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);
    base::WriteUnalignedValue<uint16_t>(
        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);
    base::WriteUnalignedValue<uint16_t>(
        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];
  base::WriteUnalignedValue<uint32_t>(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::EmitJumpLoop(BytecodeNode* node,
                                       BytecodeLoopHeader* loop_header) {
  DCHECK_EQ(node->bytecode(), Bytecode::kJumpLoop);
  DCHECK_EQ(0u, node->operand(0));
 
  size_t current_offset = bytecodes()->size();
 
  CHECK_GE(current_offset, loop_header->offset());
  CHECK_LE(current_offset, static_cast<size_t>(kMaxUInt32));
 
  // Update the actual jump offset now that we know the bytecode offset of both
  // the target loop header and this JumpLoop bytecode.
  //
  // The label has been bound already so this is a backwards jump.
  uint32_t delta =
      static_cast<uint32_t>(current_offset - loop_header->offset());
  // This JumpLoop bytecode itself may have a kWide or kExtraWide prefix; if
  // so, bump the delta to account for it.
  const bool emits_prefix_bytecode =
      Bytecodes::OperandScaleRequiresPrefixBytecode(node->operand_scale()) ||
      Bytecodes::OperandScaleRequiresPrefixBytecode(
          Bytecodes::ScaleForUnsignedOperand(delta));
  if (emits_prefix_bytecode) {
    static constexpr int kPrefixBytecodeSize = 1;
    delta += kPrefixBytecodeSize;
    DCHECK_EQ(Bytecodes::Size(Bytecode::kWide, OperandScale::kSingle),
              kPrefixBytecodeSize);
    DCHECK_EQ(Bytecodes::Size(Bytecode::kExtraWide, OperandScale::kSingle),
              kPrefixBytecodeSize);
  }
  node->update_operand0(delta);
  DCHECK_EQ(
      Bytecodes::OperandScaleRequiresPrefixBytecode(node->operand_scale()),
      emits_prefix_bytecode);
 
  EmitBytecode(node);
}
 
void BytecodeArrayWriter::EmitJump(BytecodeNode* node, BytecodeLabel* label) {
  DCHECK(Bytecodes::IsForwardJump(node->bytecode()));
  DCHECK_EQ(0u, node->operand(0));
 
  size_t current_offset = bytecodes()->size();
 
  // 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(
          static_cast<OperandSize>(node->operand_scale()));
  DCHECK_NE(Bytecode::kJumpLoop, node->bytecode());
  switch (reserved_operand_size) {
    case OperandSize::kNone:
      UNREACHABLE();
    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