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// 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.
#ifndef V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_
#define V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_
#include "src/base/compiler-specific.h"
#include "src/globals.h"
#include "src/interpreter/bytecode-register-allocator.h"
namespace v8 {
namespace internal {
namespace interpreter {
// An optimization stage for eliminating unnecessary transfers between
// registers. The bytecode generator uses temporary registers
// liberally for correctness and convenience and this stage removes
// transfers that are not required and preserves correctness.
class V8_EXPORT_PRIVATE BytecodeRegisterOptimizer final
: public NON_EXPORTED_BASE(BytecodeRegisterAllocator::Observer),
public NON_EXPORTED_BASE(ZoneObject) {
public:
class BytecodeWriter {
public:
BytecodeWriter() = default;
virtual ~BytecodeWriter() = default;
// Called to emit a register transfer bytecode.
virtual void EmitLdar(Register input) = 0;
virtual void EmitStar(Register output) = 0;
virtual void EmitMov(Register input, Register output) = 0;
private:
DISALLOW_COPY_AND_ASSIGN(BytecodeWriter);
};
BytecodeRegisterOptimizer(Zone* zone,
BytecodeRegisterAllocator* register_allocator,
int fixed_registers_count, int parameter_count,
BytecodeWriter* bytecode_writer);
~BytecodeRegisterOptimizer() override = default;
// Perform explicit register transfer operations.
void DoLdar(Register input) {
// TODO(rmcilroy): Avoid treating accumulator loads as clobbering the
// accumulator until the value is actually materialized in the accumulator.
RegisterInfo* input_info = GetRegisterInfo(input);
RegisterTransfer(input_info, accumulator_info_);
}
void DoStar(Register output) {
RegisterInfo* output_info = GetRegisterInfo(output);
RegisterTransfer(accumulator_info_, output_info);
}
void DoMov(Register input, Register output) {
RegisterInfo* input_info = GetRegisterInfo(input);
RegisterInfo* output_info = GetRegisterInfo(output);
RegisterTransfer(input_info, output_info);
}
// Materialize all live registers and flush equivalence sets.
void Flush();
bool EnsureAllRegistersAreFlushed() const;
// Prepares for |bytecode|.
template <Bytecode bytecode, AccumulatorUse accumulator_use>
V8_INLINE void PrepareForBytecode() {
if (Bytecodes::IsJump(bytecode) || Bytecodes::IsSwitch(bytecode) ||
bytecode == Bytecode::kDebugger ||
bytecode == Bytecode::kSuspendGenerator ||
bytecode == Bytecode::kResumeGenerator) {
// All state must be flushed before emitting
// - a jump bytecode (as the register equivalents at the jump target
// aren't known)
// - a switch bytecode (as the register equivalents at the switch targets
// aren't known)
// - a call to the debugger (as it can manipulate locals and parameters),
// - a generator suspend (as this involves saving all registers).
// - a generator register restore.
Flush();
}
// Materialize the accumulator if it is read by the bytecode. The
// accumulator is special and no other register can be materialized
// in it's place.
if (BytecodeOperands::ReadsAccumulator(accumulator_use)) {
Materialize(accumulator_info_);
}
// Materialize an equivalent to the accumulator if it will be
// clobbered when the bytecode is dispatched.
if (BytecodeOperands::WritesAccumulator(accumulator_use)) {
PrepareOutputRegister(accumulator_);
}
}
// Prepares |reg| for being used as an output operand.
void PrepareOutputRegister(Register reg);
// Prepares registers in |reg_list| for being used as an output operand.
void PrepareOutputRegisterList(RegisterList reg_list);
// Returns an equivalent register to |reg| to be used as an input operand.
Register GetInputRegister(Register reg);
// Returns an equivalent register list to |reg_list| to be used as an input
// operand.
RegisterList GetInputRegisterList(RegisterList reg_list);
int maxiumum_register_index() const { return max_register_index_; }
private:
static const uint32_t kInvalidEquivalenceId;
class RegisterInfo;
// BytecodeRegisterAllocator::Observer interface.
void RegisterAllocateEvent(Register reg) override;
void RegisterListAllocateEvent(RegisterList reg_list) override;
void RegisterListFreeEvent(RegisterList reg) override;
// Update internal state for register transfer from |input| to |output|
void RegisterTransfer(RegisterInfo* input, RegisterInfo* output);
// Emit a register transfer bytecode from |input| to |output|.
void OutputRegisterTransfer(RegisterInfo* input, RegisterInfo* output);
void CreateMaterializedEquivalent(RegisterInfo* info);
RegisterInfo* GetMaterializedEquivalent(RegisterInfo* info);
RegisterInfo* GetMaterializedEquivalentNotAccumulator(RegisterInfo* info);
void Materialize(RegisterInfo* info);
void AddToEquivalenceSet(RegisterInfo* set_member,
RegisterInfo* non_set_member);
void PushToRegistersNeedingFlush(RegisterInfo* reg);
// Methods for finding and creating metadata for each register.
RegisterInfo* GetRegisterInfo(Register reg) {
size_t index = GetRegisterInfoTableIndex(reg);
DCHECK_LT(index, register_info_table_.size());
return register_info_table_[index];
}
RegisterInfo* GetOrCreateRegisterInfo(Register reg) {
size_t index = GetRegisterInfoTableIndex(reg);
return index < register_info_table_.size() ? register_info_table_[index]
: NewRegisterInfo(reg);
}
RegisterInfo* NewRegisterInfo(Register reg) {
size_t index = GetRegisterInfoTableIndex(reg);
DCHECK_GE(index, register_info_table_.size());
GrowRegisterMap(reg);
return register_info_table_[index];
}
void GrowRegisterMap(Register reg);
bool RegisterIsTemporary(Register reg) const {
return reg >= temporary_base_;
}
bool RegisterIsObservable(Register reg) const {
return reg != accumulator_ && !RegisterIsTemporary(reg);
}
static Register OperandToRegister(uint32_t operand) {
return Register::FromOperand(static_cast<int32_t>(operand));
}
size_t GetRegisterInfoTableIndex(Register reg) const {
return static_cast<size_t>(reg.index() + register_info_table_offset_);
}
Register RegisterFromRegisterInfoTableIndex(size_t index) const {
return Register(static_cast<int>(index) - register_info_table_offset_);
}
uint32_t NextEquivalenceId() {
equivalence_id_++;
// TODO(rmcilroy): use the same type for these and remove static_cast.
CHECK_NE(static_cast<size_t>(equivalence_id_), kInvalidEquivalenceId);
return equivalence_id_;
}
void AllocateRegister(RegisterInfo* info);
Zone* zone() { return zone_; }
const Register accumulator_;
RegisterInfo* accumulator_info_;
const Register temporary_base_;
int max_register_index_;
// Direct mapping to register info.
ZoneVector<RegisterInfo*> register_info_table_;
int register_info_table_offset_;
ZoneDeque<RegisterInfo*> registers_needing_flushed_;
// Counter for equivalence sets identifiers.
int equivalence_id_;
BytecodeWriter* bytecode_writer_;
bool flush_required_;
Zone* zone_;
DISALLOW_COPY_AND_ASSIGN(BytecodeRegisterOptimizer);
};
} // namespace interpreter
} // namespace internal
} // namespace v8
#endif // V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_