startop/view_compiler/dex_builder.cc - LeafOS-Project/android_frameworks_base - Gitiles

 /*
  * Copyright (C) 2018 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "dex_builder.h"

 #include "dex/descriptors_names.h"

 #include <fstream>
 #include <memory>

 #define DCHECK_NOT_NULL(p) DCHECK((p) != nullptr)

 namespace startop {
 namespace dex {

 using std::shared_ptr;
 using std::string;

 using ::dex::kAccPublic;
 using Op = Instruction::Op;

 const TypeDescriptor TypeDescriptor::Int() { return TypeDescriptor{"I"}; };
 const TypeDescriptor TypeDescriptor::Void() { return TypeDescriptor{"V"}; };

 namespace {
 // From https://source.android.com/devices/tech/dalvik/dex-format#dex-file-magic
 constexpr uint8_t kDexFileMagic[]{0x64, 0x65, 0x78, 0x0a, 0x30, 0x33, 0x38, 0x00};

 // Strings lengths can be 32 bits long, but encoded as LEB128 this can take up to five bytes.
 constexpr size_t kMaxEncodedStringLength{5};

 }  // namespace

 std::ostream& operator<<(std::ostream& out, const Instruction::Op& opcode) {
   switch (opcode) {
     case Instruction::Op::kReturn:
       out << "kReturn";
       return out;
     case Instruction::Op::kMove:
       out << "kMove";
       return out;
     case Instruction::Op::kInvokeVirtual:
       out << "kInvokeVirtual";
       return out;
     case Instruction::Op::kBindLabel:
       out << "kBindLabel";
       return out;
     case Instruction::Op::kBranchEqz:
       out << "kBranchEqz";
       return out;
   }
 }

 void* TrackingAllocator::Allocate(size_t size) {
   std::unique_ptr<uint8_t[]> buffer = std::make_unique<uint8_t[]>(size);
   void* raw_buffer = buffer.get();
   allocations_[raw_buffer] = std::move(buffer);
   return raw_buffer;
 }

 void TrackingAllocator::Free(void* ptr) { allocations_.erase(allocations_.find(ptr)); }

 // Write out a DEX file that is basically:
 //
 // package dextest;
 // public class DexTest {
 //     public static int foo(String s) { return s.length(); }
 // }
 void WriteTestDexFile(const string& filename) {
   DexBuilder dex_file;

   ClassBuilder cbuilder{dex_file.MakeClass("dextest.DexTest")};
   cbuilder.set_source_file("dextest.java");

   TypeDescriptor string_type = TypeDescriptor::FromClassname("java.lang.String");

   MethodBuilder method{cbuilder.CreateMethod("foo", Prototype{TypeDescriptor::Int(), string_type})};

   Value result = method.MakeRegister();

   MethodDeclData string_length =
       dex_file.GetOrDeclareMethod(string_type, "length", Prototype{TypeDescriptor::Int()});

   method.AddInstruction(Instruction::InvokeVirtual(string_length.id, result, Value::Parameter(0)));
   method.BuildReturn(result);

   method.Encode();

   slicer::MemView image{dex_file.CreateImage()};

   std::ofstream out_file(filename);
   out_file.write(image.ptr<const char>(), image.size());
 }

 TypeDescriptor TypeDescriptor::FromClassname(const std::string& name) {
   return TypeDescriptor{art::DotToDescriptor(name.c_str())};
 }

 DexBuilder::DexBuilder() : dex_file_{std::make_shared<ir::DexFile>()} {
   dex_file_->magic = slicer::MemView{kDexFileMagic, sizeof(kDexFileMagic)};
 }

 slicer::MemView DexBuilder::CreateImage() {
   ::dex::Writer writer(dex_file_);
   size_t image_size{0};
   ::dex::u1* image = writer.CreateImage(&allocator_, &image_size);
   return slicer::MemView{image, image_size};
 }

 ir::String* DexBuilder::GetOrAddString(const std::string& string) {
   ir::String*& entry = strings_[string];

   if (entry == nullptr) {
     // Need to encode the length and then write out the bytes, including 1 byte for null terminator
     auto buffer = std::make_unique<uint8_t[]>(string.size() + kMaxEncodedStringLength + 1);
     uint8_t* string_data_start = ::dex::WriteULeb128(buffer.get(), string.size());

     size_t header_length =
         reinterpret_cast<uintptr_t>(string_data_start) - reinterpret_cast<uintptr_t>(buffer.get());

     auto end = std::copy(string.begin(), string.end(), string_data_start);
     *end = '\0';

     entry = Alloc<ir::String>();
     // +1 for null terminator
     entry->data = slicer::MemView{buffer.get(), header_length + string.size() + 1};
     string_data_.push_back(std::move(buffer));
   }
   return entry;
 }

 ClassBuilder DexBuilder::MakeClass(const std::string& name) {
   auto* class_def = Alloc<ir::Class>();
   ir::Type* type_def = GetOrAddType(art::DotToDescriptor(name.c_str()));
   type_def->class_def = class_def;

   class_def->type = type_def;
   class_def->super_class = GetOrAddType(art::DotToDescriptor("java.lang.Object"));
   class_def->access_flags = kAccPublic;
   return ClassBuilder{this, name, class_def};
 }

 ir::Type* DexBuilder::GetOrAddType(const std::string& descriptor) {
   if (types_by_descriptor_.find(descriptor) != types_by_descriptor_.end()) {
     return types_by_descriptor_[descriptor];
   }

   ir::Type* type = Alloc<ir::Type>();
   type->descriptor = GetOrAddString(descriptor);
   types_by_descriptor_[descriptor] = type;
   return type;
 }

 ir::Proto* Prototype::Encode(DexBuilder* dex) const {
   auto* proto = dex->Alloc<ir::Proto>();
   proto->shorty = dex->GetOrAddString(Shorty());
   proto->return_type = dex->GetOrAddType(return_type_.descriptor());
   if (param_types_.size() > 0) {
     proto->param_types = dex->Alloc<ir::TypeList>();
     for (const auto& param_type : param_types_) {
       proto->param_types->types.push_back(dex->GetOrAddType(param_type.descriptor()));
     }
   } else {
     proto->param_types = nullptr;
   }
   return proto;
 }

 std::string Prototype::Shorty() const {
   std::string shorty;
   shorty.append(return_type_.short_descriptor());
   for (const auto& type_descriptor : param_types_) {
     shorty.append(type_descriptor.short_descriptor());
   }
   return shorty;
 }

 ClassBuilder::ClassBuilder(DexBuilder* parent, const std::string& name, ir::Class* class_def)
     : parent_(parent), type_descriptor_{TypeDescriptor::FromClassname(name)}, class_(class_def) {}

 MethodBuilder ClassBuilder::CreateMethod(const std::string& name, Prototype prototype) {
   ir::MethodDecl* decl = parent_->GetOrDeclareMethod(type_descriptor_, name, prototype).decl;

   return MethodBuilder{parent_, class_, decl};
 }

 void ClassBuilder::set_source_file(const string& source) {
   class_->source_file = parent_->GetOrAddString(source);
 }

 MethodBuilder::MethodBuilder(DexBuilder* dex, ir::Class* class_def, ir::MethodDecl* decl)
     : dex_{dex}, class_{class_def}, decl_{decl} {}

 ir::EncodedMethod* MethodBuilder::Encode() {
   auto* method = dex_->Alloc<ir::EncodedMethod>();
   method->decl = decl_;

   // TODO: make access flags configurable
   method->access_flags = kAccPublic | ::dex::kAccStatic;

   auto* code = dex_->Alloc<ir::Code>();
   DCHECK_NOT_NULL(decl_->prototype);
   size_t const num_args =
       decl_->prototype->param_types != nullptr ? decl_->prototype->param_types->types.size() : 0;
   code->registers = num_registers_ + num_args;
   code->ins_count = num_args;
   code->outs_count = decl_->prototype->return_type == dex_->GetOrAddType("V") ? 0 : 1;
   EncodeInstructions();
   code->instructions = slicer::ArrayView<const ::dex::u2>(buffer_.data(), buffer_.size());
   method->code = code;

   class_->direct_methods.push_back(method);

   return method;
 }

 Value MethodBuilder::MakeRegister() { return Value::Local(num_registers_++); }

 Value MethodBuilder::MakeLabel() {
   labels_.push_back({});
   return Value::Label(labels_.size() - 1);
 }

 void MethodBuilder::AddInstruction(Instruction instruction) {
   instructions_.push_back(instruction);
 }

 void MethodBuilder::BuildReturn() { AddInstruction(Instruction::OpNoArgs(Op::kReturn)); }

 void MethodBuilder::BuildReturn(Value src) {
   AddInstruction(Instruction::OpWithArgs(Op::kReturn, /*destination=*/{}, src));
 }

 void MethodBuilder::BuildConst4(Value target, int value) {
   DCHECK_LT(value, 16);
   AddInstruction(Instruction::OpWithArgs(Op::kMove, target, Value::Immediate(value)));
 }

 void MethodBuilder::EncodeInstructions() {
   buffer_.clear();
   for (const auto& instruction : instructions_) {
     EncodeInstruction(instruction);
   }
 }

 void MethodBuilder::EncodeInstruction(const Instruction& instruction) {
   switch (instruction.opcode()) {
     case Instruction::Op::kReturn:
       return EncodeReturn(instruction);
     case Instruction::Op::kMove:
       return EncodeMove(instruction);
     case Instruction::Op::kInvokeVirtual:
       return EncodeInvokeVirtual(instruction);
     case Instruction::Op::kBindLabel:
       return BindLabel(instruction.args()[0]);
     case Instruction::Op::kBranchEqz:
       return EncodeBranch(art::Instruction::IF_EQZ, instruction);
   }
 }

 void MethodBuilder::EncodeReturn(const Instruction& instruction) {
   DCHECK_EQ(Instruction::Op::kReturn, instruction.opcode());
   DCHECK(!instruction.dest().has_value());
   if (instruction.args().size() == 0) {
     buffer_.push_back(art::Instruction::RETURN_VOID);
   } else {
     DCHECK(instruction.args().size() == 1);
     size_t source = RegisterValue(instruction.args()[0]);
     buffer_.push_back(art::Instruction::RETURN | source << 8);
   }
 }

 void MethodBuilder::EncodeMove(const Instruction& instruction) {
   DCHECK_EQ(Instruction::Op::kMove, instruction.opcode());
   DCHECK(instruction.dest().has_value());
   DCHECK(instruction.dest()->is_register() || instruction.dest()->is_parameter());
   DCHECK_EQ(1, instruction.args().size());

   const Value& source = instruction.args()[0];

   if (source.is_immediate()) {
     // TODO: support more registers
     DCHECK_LT(RegisterValue(*instruction.dest()), 16);
     DCHECK_LT(source.value(), 16);
     buffer_.push_back(art::Instruction::CONST_4 | (source.value() << 12) |
                       (RegisterValue(*instruction.dest()) << 8));
   } else {
     UNIMPLEMENTED(FATAL);
   }
 }

 void MethodBuilder::EncodeInvokeVirtual(const Instruction& instruction) {
   DCHECK_EQ(Instruction::Op::kInvokeVirtual, instruction.opcode());

   // TODO: support more than one argument (i.e. the this argument) and change this to DCHECK_GE
   DCHECK_EQ(1, instruction.args().size());

   const Value& this_arg = instruction.args()[0];

   size_t real_reg = RegisterValue(this_arg) & 0xf;
   buffer_.push_back(1 << 12 | art::Instruction::INVOKE_VIRTUAL);
   buffer_.push_back(instruction.method_id());
   buffer_.push_back(real_reg);

   if (instruction.dest().has_value()) {
     real_reg = RegisterValue(*instruction.dest());
     buffer_.push_back(real_reg << 8 | art::Instruction::MOVE_RESULT);
   }
 }

 // Encodes a conditional branch that tests a single argument.
 void MethodBuilder::EncodeBranch(art::Instruction::Code op, const Instruction& instruction) {
   const auto& args = instruction.args();
   const auto& test_value = args[0];
   const auto& branch_target = args[1];
   CHECK_EQ(2, args.size());
   CHECK(test_value.is_variable());
   CHECK(branch_target.is_label());

   size_t instruction_offset = buffer_.size();
   buffer_.push_back(op | (RegisterValue(test_value) << 8));
   size_t field_offset = buffer_.size();
   buffer_.push_back(LabelValue(branch_target, instruction_offset, field_offset));
 }

 size_t MethodBuilder::RegisterValue(const Value& value) const {
   if (value.is_register()) {
     return value.value();
   } else if (value.is_parameter()) {
     return value.value() + num_registers_;
   }
   DCHECK(false && "Must be either a parameter or a register");
   return 0;
 }

 void MethodBuilder::BindLabel(const Value& label_id) {
   CHECK(label_id.is_label());

   LabelData& label = labels_[label_id.value()];
   CHECK(!label.bound_address.has_value());

   label.bound_address = buffer_.size();

   // patch any forward references to this label.
   for (const auto& ref : label.references) {
     buffer_[ref.field_offset] = *label.bound_address - ref.instruction_offset;
   }
   // No point keeping these around anymore.
   label.references.clear();
 }

 ::dex::u2 MethodBuilder::LabelValue(const Value& label_id, size_t instruction_offset,
                                     size_t field_offset) {
   CHECK(label_id.is_label());
   LabelData& label = labels_[label_id.value()];

   // Short-circuit if the label is already bound.
   if (label.bound_address.has_value()) {
     return *label.bound_address - instruction_offset;
   }

   // Otherwise, save a reference to where we need to back-patch later.
   label.references.push_front(LabelReference{instruction_offset, field_offset});
   return 0;
 }

 const MethodDeclData& DexBuilder::GetOrDeclareMethod(TypeDescriptor type, const std::string& name,
                                                      Prototype prototype) {
   MethodDeclData& entry = method_id_map_[{type, name, prototype}];

   if (entry.decl == nullptr) {
     // This method has not already been declared, so declare it.
     ir::MethodDecl* decl = dex_file_->Alloc<ir::MethodDecl>();
     // The method id is the last added method.
     size_t id = dex_file_->methods.size() - 1;

     ir::String* dex_name{GetOrAddString(name)};
     decl->name = dex_name;
     decl->parent = GetOrAddType(type.descriptor());
     decl->prototype = GetOrEncodeProto(prototype);

     // update the index -> ir node map (see tools/dexter/slicer/dex_ir_builder.cc)
     auto new_index = dex_file_->methods_indexes.AllocateIndex();
     auto& ir_node = dex_file_->methods_map[new_index];
     SLICER_CHECK(ir_node == nullptr);
     ir_node = decl;
     decl->orig_index = new_index;

     entry = {id, decl};
   }

   return entry;
 }

 ir::Proto* DexBuilder::GetOrEncodeProto(Prototype prototype) {
   ir::Proto*& ir_proto = proto_map_[prototype];
   if (ir_proto == nullptr) {
     ir_proto = prototype.Encode(this);
   }
   return ir_proto;
 }

 }  // namespace dex
 }  // namespace startop
	/*
	* Copyright (C) 2018 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "dex_builder.h"

	#include "dex/descriptors_names.h"

	#include <fstream>
	#include <memory>

	#define DCHECK_NOT_NULL(p) DCHECK((p) != nullptr)

	namespace startop {
	namespace dex {

	using std::shared_ptr;
	using std::string;

	using ::dex::kAccPublic;
	using Op = Instruction::Op;

	const TypeDescriptor TypeDescriptor::Int() { return TypeDescriptor{"I"}; };
	const TypeDescriptor TypeDescriptor::Void() { return TypeDescriptor{"V"}; };

	namespace {
	// From https://source.android.com/devices/tech/dalvik/dex-format#dex-file-magic
	constexpr uint8_t kDexFileMagic[]{0x64, 0x65, 0x78, 0x0a, 0x30, 0x33, 0x38, 0x00};

	// Strings lengths can be 32 bits long, but encoded as LEB128 this can take up to five bytes.
	constexpr size_t kMaxEncodedStringLength{5};

	} // namespace

	std::ostream& operator<<(std::ostream& out, const Instruction::Op& opcode) {
	switch (opcode) {
	case Instruction::Op::kReturn:
	out << "kReturn";
	return out;
	case Instruction::Op::kMove:
	out << "kMove";
	return out;
	case Instruction::Op::kInvokeVirtual:
	out << "kInvokeVirtual";
	return out;
	case Instruction::Op::kBindLabel:
	out << "kBindLabel";
	return out;
	case Instruction::Op::kBranchEqz:
	out << "kBranchEqz";
	return out;
	}
	}

	void* TrackingAllocator::Allocate(size_t size) {
	std::unique_ptr<uint8_t[]> buffer = std::make_unique<uint8_t[]>(size);
	void* raw_buffer = buffer.get();
	allocations_[raw_buffer] = std::move(buffer);
	return raw_buffer;
	}

	void TrackingAllocator::Free(void* ptr) { allocations_.erase(allocations_.find(ptr)); }

	// Write out a DEX file that is basically:
	//
	// package dextest;
	// public class DexTest {
	// public static int foo(String s) { return s.length(); }
	// }
	void WriteTestDexFile(const string& filename) {
	DexBuilder dex_file;

	ClassBuilder cbuilder{dex_file.MakeClass("dextest.DexTest")};
	cbuilder.set_source_file("dextest.java");

	TypeDescriptor string_type = TypeDescriptor::FromClassname("java.lang.String");

	MethodBuilder method{cbuilder.CreateMethod("foo", Prototype{TypeDescriptor::Int(), string_type})};

	Value result = method.MakeRegister();

	MethodDeclData string_length =
	dex_file.GetOrDeclareMethod(string_type, "length", Prototype{TypeDescriptor::Int()});

	method.AddInstruction(Instruction::InvokeVirtual(string_length.id, result, Value::Parameter(0)));
	method.BuildReturn(result);

	method.Encode();

	slicer::MemView image{dex_file.CreateImage()};

	std::ofstream out_file(filename);
	out_file.write(image.ptr<const char>(), image.size());
	}

	TypeDescriptor TypeDescriptor::FromClassname(const std::string& name) {
	return TypeDescriptor{art::DotToDescriptor(name.c_str())};
	}

	DexBuilder::DexBuilder() : dex_file_{std::make_shared<ir::DexFile>()} {
	dex_file_->magic = slicer::MemView{kDexFileMagic, sizeof(kDexFileMagic)};
	}

	slicer::MemView DexBuilder::CreateImage() {
	::dex::Writer writer(dex_file_);
	size_t image_size{0};
	::dex::u1* image = writer.CreateImage(&allocator_, &image_size);
	return slicer::MemView{image, image_size};
	}

	ir::String* DexBuilder::GetOrAddString(const std::string& string) {
	ir::String*& entry = strings_[string];

	if (entry == nullptr) {
	// Need to encode the length and then write out the bytes, including 1 byte for null terminator
	auto buffer = std::make_unique<uint8_t[]>(string.size() + kMaxEncodedStringLength + 1);
	uint8_t* string_data_start = ::dex::WriteULeb128(buffer.get(), string.size());

	size_t header_length =
	reinterpret_cast<uintptr_t>(string_data_start) - reinterpret_cast<uintptr_t>(buffer.get());

	auto end = std::copy(string.begin(), string.end(), string_data_start);
	*end = '\0';

	entry = Alloc<ir::String>();
	// +1 for null terminator
	entry->data = slicer::MemView{buffer.get(), header_length + string.size() + 1};
	string_data_.push_back(std::move(buffer));
	}
	return entry;
	}

	ClassBuilder DexBuilder::MakeClass(const std::string& name) {
	auto* class_def = Alloc<ir::Class>();
	ir::Type* type_def = GetOrAddType(art::DotToDescriptor(name.c_str()));
	type_def->class_def = class_def;

	class_def->type = type_def;
	class_def->super_class = GetOrAddType(art::DotToDescriptor("java.lang.Object"));
	class_def->access_flags = kAccPublic;
	return ClassBuilder{this, name, class_def};
	}

	ir::Type* DexBuilder::GetOrAddType(const std::string& descriptor) {
	if (types_by_descriptor_.find(descriptor) != types_by_descriptor_.end()) {
	return types_by_descriptor_[descriptor];
	}

	ir::Type* type = Alloc<ir::Type>();
	type->descriptor = GetOrAddString(descriptor);
	types_by_descriptor_[descriptor] = type;
	return type;
	}

	ir::Proto* Prototype::Encode(DexBuilder* dex) const {
	auto* proto = dex->Alloc<ir::Proto>();
	proto->shorty = dex->GetOrAddString(Shorty());
	proto->return_type = dex->GetOrAddType(return_type_.descriptor());
	if (param_types_.size() > 0) {
	proto->param_types = dex->Alloc<ir::TypeList>();
	for (const auto& param_type : param_types_) {
	proto->param_types->types.push_back(dex->GetOrAddType(param_type.descriptor()));
	}
	} else {
	proto->param_types = nullptr;
	}
	return proto;
	}

	std::string Prototype::Shorty() const {
	std::string shorty;
	shorty.append(return_type_.short_descriptor());
	for (const auto& type_descriptor : param_types_) {
	shorty.append(type_descriptor.short_descriptor());
	}
	return shorty;
	}

	ClassBuilder::ClassBuilder(DexBuilder* parent, const std::string& name, ir::Class* class_def)
	: parent_(parent), type_descriptor_{TypeDescriptor::FromClassname(name)}, class_(class_def) {}

	MethodBuilder ClassBuilder::CreateMethod(const std::string& name, Prototype prototype) {
	ir::MethodDecl* decl = parent_->GetOrDeclareMethod(type_descriptor_, name, prototype).decl;

	return MethodBuilder{parent_, class_, decl};
	}

	void ClassBuilder::set_source_file(const string& source) {
	class_->source_file = parent_->GetOrAddString(source);
	}

	MethodBuilder::MethodBuilder(DexBuilder* dex, ir::Class* class_def, ir::MethodDecl* decl)
	: dex_{dex}, class_{class_def}, decl_{decl} {}

	ir::EncodedMethod* MethodBuilder::Encode() {
	auto* method = dex_->Alloc<ir::EncodedMethod>();
	method->decl = decl_;

	// TODO: make access flags configurable
	method->access_flags = kAccPublic \| ::dex::kAccStatic;

	auto* code = dex_->Alloc<ir::Code>();
	DCHECK_NOT_NULL(decl_->prototype);
	size_t const num_args =
	decl_->prototype->param_types != nullptr ? decl_->prototype->param_types->types.size() : 0;
	code->registers = num_registers_ + num_args;
	code->ins_count = num_args;
	code->outs_count = decl_->prototype->return_type == dex_->GetOrAddType("V") ? 0 : 1;
	EncodeInstructions();
	code->instructions = slicer::ArrayView<const ::dex::u2>(buffer_.data(), buffer_.size());
	method->code = code;

	class_->direct_methods.push_back(method);

	return method;
	}

	Value MethodBuilder::MakeRegister() { return Value::Local(num_registers_++); }

	Value MethodBuilder::MakeLabel() {
	labels_.push_back({});
	return Value::Label(labels_.size() - 1);
	}

	void MethodBuilder::AddInstruction(Instruction instruction) {
	instructions_.push_back(instruction);
	}

	void MethodBuilder::BuildReturn() { AddInstruction(Instruction::OpNoArgs(Op::kReturn)); }

	void MethodBuilder::BuildReturn(Value src) {
	AddInstruction(Instruction::OpWithArgs(Op::kReturn, /destination=/{}, src));
	}

	void MethodBuilder::BuildConst4(Value target, int value) {
	DCHECK_LT(value, 16);
	AddInstruction(Instruction::OpWithArgs(Op::kMove, target, Value::Immediate(value)));
	}

	void MethodBuilder::EncodeInstructions() {
	buffer_.clear();
	for (const auto& instruction : instructions_) {
	EncodeInstruction(instruction);
	}
	}

	void MethodBuilder::EncodeInstruction(const Instruction& instruction) {
	switch (instruction.opcode()) {
	case Instruction::Op::kReturn:
	return EncodeReturn(instruction);
	case Instruction::Op::kMove:
	return EncodeMove(instruction);
	case Instruction::Op::kInvokeVirtual:
	return EncodeInvokeVirtual(instruction);
	case Instruction::Op::kBindLabel:
	return BindLabel(instruction.args()[0]);
	case Instruction::Op::kBranchEqz:
	return EncodeBranch(art::Instruction::IF_EQZ, instruction);
	}
	}

	void MethodBuilder::EncodeReturn(const Instruction& instruction) {
	DCHECK_EQ(Instruction::Op::kReturn, instruction.opcode());
	DCHECK(!instruction.dest().has_value());
	if (instruction.args().size() == 0) {
	buffer_.push_back(art::Instruction::RETURN_VOID);
	} else {
	DCHECK(instruction.args().size() == 1);
	size_t source = RegisterValue(instruction.args()[0]);
	buffer_.push_back(art::Instruction::RETURN \| source << 8);
	}
	}

	void MethodBuilder::EncodeMove(const Instruction& instruction) {
	DCHECK_EQ(Instruction::Op::kMove, instruction.opcode());
	DCHECK(instruction.dest().has_value());
	DCHECK(instruction.dest()->is_register() \|\| instruction.dest()->is_parameter());
	DCHECK_EQ(1, instruction.args().size());

	const Value& source = instruction.args()[0];

	if (source.is_immediate()) {
	// TODO: support more registers
	DCHECK_LT(RegisterValue(*instruction.dest()), 16);
	DCHECK_LT(source.value(), 16);
	buffer_.push_back(art::Instruction::CONST_4 \| (source.value() << 12) \|
	(RegisterValue(*instruction.dest()) << 8));
	} else {
	UNIMPLEMENTED(FATAL);
	}
	}

	void MethodBuilder::EncodeInvokeVirtual(const Instruction& instruction) {
	DCHECK_EQ(Instruction::Op::kInvokeVirtual, instruction.opcode());

	// TODO: support more than one argument (i.e. the this argument) and change this to DCHECK_GE
	DCHECK_EQ(1, instruction.args().size());

	const Value& this_arg = instruction.args()[0];

	size_t real_reg = RegisterValue(this_arg) & 0xf;
	buffer_.push_back(1 << 12 \| art::Instruction::INVOKE_VIRTUAL);
	buffer_.push_back(instruction.method_id());
	buffer_.push_back(real_reg);

	if (instruction.dest().has_value()) {
	real_reg = RegisterValue(*instruction.dest());
	buffer_.push_back(real_reg << 8 \| art::Instruction::MOVE_RESULT);
	}
	}

	// Encodes a conditional branch that tests a single argument.
	void MethodBuilder::EncodeBranch(art::Instruction::Code op, const Instruction& instruction) {
	const auto& args = instruction.args();
	const auto& test_value = args[0];
	const auto& branch_target = args[1];
	CHECK_EQ(2, args.size());
	CHECK(test_value.is_variable());
	CHECK(branch_target.is_label());

	size_t instruction_offset = buffer_.size();
	buffer_.push_back(op \| (RegisterValue(test_value) << 8));
	size_t field_offset = buffer_.size();
	buffer_.push_back(LabelValue(branch_target, instruction_offset, field_offset));
	}

	size_t MethodBuilder::RegisterValue(const Value& value) const {
	if (value.is_register()) {
	return value.value();
	} else if (value.is_parameter()) {
	return value.value() + num_registers_;
	}
	DCHECK(false && "Must be either a parameter or a register");
	return 0;
	}

	void MethodBuilder::BindLabel(const Value& label_id) {
	CHECK(label_id.is_label());

	LabelData& label = labels_[label_id.value()];
	CHECK(!label.bound_address.has_value());

	label.bound_address = buffer_.size();

	// patch any forward references to this label.
	for (const auto& ref : label.references) {
	buffer_[ref.field_offset] = *label.bound_address - ref.instruction_offset;
	}
	// No point keeping these around anymore.
	label.references.clear();
	}

	::dex::u2 MethodBuilder::LabelValue(const Value& label_id, size_t instruction_offset,
	size_t field_offset) {
	CHECK(label_id.is_label());
	LabelData& label = labels_[label_id.value()];

	// Short-circuit if the label is already bound.
	if (label.bound_address.has_value()) {
	return *label.bound_address - instruction_offset;
	}

	// Otherwise, save a reference to where we need to back-patch later.
	label.references.push_front(LabelReference{instruction_offset, field_offset});
	return 0;
	}

	const MethodDeclData& DexBuilder::GetOrDeclareMethod(TypeDescriptor type, const std::string& name,
	Prototype prototype) {
	MethodDeclData& entry = method_id_map_[{type, name, prototype}];

	if (entry.decl == nullptr) {
	// This method has not already been declared, so declare it.
	ir::MethodDecl* decl = dex_file_->Alloc<ir::MethodDecl>();
	// The method id is the last added method.
	size_t id = dex_file_->methods.size() - 1;

	ir::String* dex_name{GetOrAddString(name)};
	decl->name = dex_name;
	decl->parent = GetOrAddType(type.descriptor());
	decl->prototype = GetOrEncodeProto(prototype);

	// update the index -> ir node map (see tools/dexter/slicer/dex_ir_builder.cc)
	auto new_index = dex_file_->methods_indexes.AllocateIndex();
	auto& ir_node = dex_file_->methods_map[new_index];
	SLICER_CHECK(ir_node == nullptr);
	ir_node = decl;
	decl->orig_index = new_index;

	entry = {id, decl};
	}

	return entry;
	}

	ir::Proto* DexBuilder::GetOrEncodeProto(Prototype prototype) {
	ir::Proto*& ir_proto = proto_map_[prototype];
	if (ir_proto == nullptr) {
	ir_proto = prototype.Encode(this);
	}
	return ir_proto;
	}

	} // namespace dex
	} // namespace startop