Merge "[view-compiler] Support method declaration and invocation in Dex builder"

startop/view_compiler/Android.bp

@@ -16,10 +16,15 @@
 
 cc_defaults {
     name: "viewcompiler_defaults",
+    header_libs: [
+        "libbase_headers",
+    ],
     shared_libs: [
+        "libbase",
         "libdexfile",
         "slicer",
     ],
+    cppflags: ["-std=c++17"],
 }
 
 cc_library_host_static {
@@ -30,9 +35,6 @@ cc_library_host_static {
         "java_lang_builder.cc",
         "util.cc",
     ],
-    static_libs: [
-        "libbase",
-    ],
 }
 
 cc_binary_host {
@@ -42,7 +44,6 @@ cc_binary_host {
         "main.cc",
     ],
     static_libs: [
-        "libbase",
         "libtinyxml2",
         "libgflags",
         "libviewcompiler",
@@ -59,4 +60,5 @@ cc_test_host {
     static_libs: [
         "libviewcompiler",
     ],
+    test_suites: ["general-tests"],
 }

startop/view_compiler/TEST_MAPPING

@@ -1,7 +0,0 @@
-{
-  "presubmit": [
-    {
-      "name": "view-compiler-tests"
-    }
-  ]
-}

startop/view_compiler/dex_builder.cc

@@ -22,14 +22,16 @@
 #include <fstream>
 #include <memory>
 
+#define DCHECK_NOT_NULL(p) DCHECK((p) != nullptr)
+
 namespace startop {
 namespace dex {
 
 using std::shared_ptr;
 using std::string;
 
-using art::Instruction;
 using ::dex::kAccPublic;
+using Op = Instruction::Op;
 
 const TypeDescriptor TypeDescriptor::Int() { return TypeDescriptor{"I"}; };
 const TypeDescriptor TypeDescriptor::Void() { return TypeDescriptor{"V"}; };
@@ -43,6 +45,20 @@ 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;
+  }
+}
+
 void* TrackingAllocator::Allocate(size_t size) {
   std::unique_ptr<uint8_t[]> buffer = std::make_unique<uint8_t[]>(size);
   void* raw_buffer = buffer.get();
@@ -56,7 +72,7 @@ void TrackingAllocator::Free(void* ptr) { allocations_.erase(allocations_.find(p
 //
 // package dextest;
 // public class DexTest {
-//     public static int foo() { return 5; }
+//     public static int foo(String s) { return s.length(); }
 // }
 void WriteTestDexFile(const string& filename) {
   DexBuilder dex_file;
@@ -64,11 +80,17 @@ void WriteTestDexFile(const string& filename) {
   ClassBuilder cbuilder{dex_file.MakeClass("dextest.DexTest")};
   cbuilder.set_source_file("dextest.java");
 
-  MethodBuilder method{cbuilder.CreateMethod("foo", Prototype{TypeDescriptor::Int()})};
+  TypeDescriptor string_type = TypeDescriptor::FromClassname("java.lang.String");
 
-  MethodBuilder::Register r = method.MakeRegister();
-  method.BuildConst4(r, 5);
-  method.BuildReturn(r);
+  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();
 
@@ -78,6 +100,10 @@ void WriteTestDexFile(const string& 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)};
 }
@@ -119,10 +145,9 @@ ClassBuilder DexBuilder::MakeClass(const std::string& name) {
   class_def->type = type_def;
   class_def->super_class = GetOrAddType(art::DotToDescriptor("java.lang.Object"));
   class_def->access_flags = kAccPublic;
-  return ClassBuilder{this, class_def};
+  return ClassBuilder{this, name, class_def};
 }
 
-// TODO(eholk): we probably want GetOrAddString() also
 ir::Type* DexBuilder::GetOrAddType(const std::string& descriptor) {
   if (types_by_descriptor_.find(descriptor) != types_by_descriptor_.end()) {
     return types_by_descriptor_[descriptor];
@@ -158,16 +183,11 @@ std::string Prototype::Shorty() const {
   return shorty;
 }
 
-ClassBuilder::ClassBuilder(DexBuilder* parent, ir::Class* class_def)
-    : parent_(parent), class_(class_def) {}
+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::String* dex_name{parent_->GetOrAddString(name)};
-
-  auto* decl = parent_->Alloc<ir::MethodDecl>();
-  decl->name = dex_name;
-  decl->parent = class_->type;
-  decl->prototype = prototype.Encode(parent_);
+  ir::MethodDecl* decl = parent_->GetOrDeclareMethod(type_descriptor_, name, prototype).decl;
 
   return MethodBuilder{parent_, class_, decl};
 }
@@ -187,8 +207,13 @@ ir::EncodedMethod* MethodBuilder::Encode() {
   method->access_flags = kAccPublic | ::dex::kAccStatic;
 
   auto* code = dex_->Alloc<ir::Code>();
-  code->registers = num_registers_;
-  // TODO: support ins and outs
+  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;
 
@@ -197,17 +222,135 @@ ir::EncodedMethod* MethodBuilder::Encode() {
   return method;
 }
 
-MethodBuilder::Register MethodBuilder::MakeRegister() { return num_registers_++; }
+Value MethodBuilder::MakeRegister() { return Value::Local(num_registers_++); }
 
-void MethodBuilder::BuildReturn() { buffer_.push_back(Instruction::RETURN_VOID); }
+void MethodBuilder::AddInstruction(Instruction instruction) {
+  instructions_.push_back(instruction);
+}
 
-void MethodBuilder::BuildReturn(Register src) { buffer_.push_back(Instruction::RETURN | src << 8); }
+void MethodBuilder::BuildReturn() { AddInstruction(Instruction::OpNoArgs(Op::kReturn)); }
 
-void MethodBuilder::BuildConst4(Register target, int value) {
+void MethodBuilder::BuildReturn(Value src) {
+  AddInstruction(Instruction::OpWithArgs(Op::kReturn, /*destination=*/{}, src));
+}
+
+void MethodBuilder::BuildConst4(Value target, int value) {
   DCHECK_LT(value, 16);
-  // TODO: support more registers
-  DCHECK_LT(target, 16);
-  buffer_.push_back(Instruction::CONST_4 | (value << 12) | (target << 8));
+  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);
+  }
+}
+
+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);
+  }
+}
+
+size_t MethodBuilder::RegisterValue(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;
+}
+
+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

startop/view_compiler/dex_builder.h

@@ -17,7 +17,9 @@
 #define DEX_BUILDER_H_
 
 #include <map>
+#include <optional>
 #include <string>
+#include <unordered_map>
 #include <vector>
 
 #include "slicer/dex_ir.h"
@@ -45,7 +47,7 @@ class TrackingAllocator : public ::dex::Writer::Allocator {
   virtual void Free(void* ptr);
 
  private:
-  std::map<void*, std::unique_ptr<uint8_t[]>> allocations_;
+  std::unordered_map<void*, std::unique_ptr<uint8_t[]>> allocations_;
 };
 
 // Represents a DEX type descriptor.
@@ -57,11 +59,17 @@ class TypeDescriptor {
   static const TypeDescriptor Int();
   static const TypeDescriptor Void();
 
+  // Creates a type descriptor from a fully-qualified class name. For example, it turns the class
+  // name java.lang.Object into the descriptor Ljava/lang/Object.
+  static TypeDescriptor FromClassname(const std::string& name);
+
   // Return the full descriptor, such as I or Ljava/lang/Object
   const std::string& descriptor() const { return descriptor_; }
   // Return the shorty descriptor, such as I or L
   std::string short_descriptor() const { return descriptor().substr(0, 1); }
 
+  bool operator<(const TypeDescriptor& rhs) const { return descriptor_ < rhs.descriptor_; }
+
  private:
   TypeDescriptor(std::string descriptor) : descriptor_{descriptor} {}
 
@@ -82,11 +90,98 @@ class Prototype {
   // Get the shorty descriptor, such as VII for (Int, Int) -> Void
   std::string Shorty() const;
 
+  bool operator<(const Prototype& rhs) const {
+    return std::make_tuple(return_type_, param_types_) <
+           std::make_tuple(rhs.return_type_, rhs.param_types_);
+  }
+
  private:
   const TypeDescriptor return_type_;
   const std::vector<TypeDescriptor> param_types_;
 };
 
+// Represents a DEX register or constant. We separate regular registers and parameters
+// because we will not know the real parameter id until after all instructions
+// have been generated.
+class Value {
+ public:
+  static constexpr Value Local(size_t id) { return Value{id, Kind::kLocalRegister}; }
+  static constexpr Value Parameter(size_t id) { return Value{id, Kind::kParameter}; }
+  static constexpr Value Immediate(size_t value) { return Value{value, Kind::kImmediate}; }
+
+  bool is_register() const { return kind_ == Kind::kLocalRegister; }
+  bool is_parameter() const { return kind_ == Kind::kParameter; }
+  bool is_immediate() const { return kind_ == Kind::kImmediate; }
+
+  size_t value() const { return value_; }
+
+ private:
+  enum class Kind { kLocalRegister, kParameter, kImmediate };
+
+  const size_t value_;
+  const Kind kind_;
+
+  constexpr Value(size_t value, Kind kind) : value_{value}, kind_{kind} {}
+};
+
+// A virtual instruction. We convert these to real instructions in MethodBuilder::Encode.
+// Virtual instructions are needed to keep track of information that is not known until all of the
+// code is generated. This information includes things like how many local registers are created and
+// branch target locations.
+class Instruction {
+ public:
+  // The operation performed by this instruction. These are virtual instructions that do not
+  // correspond exactly to DEX instructions.
+  enum class Op { kReturn, kMove, kInvokeVirtual };
+
+  ////////////////////////
+  // Named Constructors //
+  ////////////////////////
+
+  // For instructions with no return value and no arguments.
+  static inline Instruction OpNoArgs(Op opcode) {
+    return Instruction{opcode, /*method_id*/ 0, /*dest*/ {}};
+  }
+  // For most instructions, which take some number of arguments and have an optional return value.
+  template <typename... T>
+  static inline Instruction OpWithArgs(Op opcode, std::optional<const Value> dest, T... args) {
+    return Instruction{opcode, /*method_id*/ 0, dest, args...};
+  }
+  // For method calls.
+  template <typename... T>
+  static inline Instruction InvokeVirtual(size_t method_id, std::optional<const Value> dest,
+                                          Value this_arg, T... args) {
+    return Instruction{Op::kInvokeVirtual, method_id, dest, this_arg, args...};
+  }
+
+  ///////////////
+  // Accessors //
+  ///////////////
+
+  Op opcode() const { return opcode_; }
+  size_t method_id() const { return method_id_; }
+  const std::optional<const Value>& dest() const { return dest_; }
+  const std::vector<const Value>& args() const { return args_; }
+
+ private:
+  inline Instruction(Op opcode, size_t method_id, std::optional<const Value> dest)
+      : opcode_{opcode}, method_id_{method_id}, dest_{dest}, args_{} {}
+
+  template <typename... T>
+  inline constexpr Instruction(Op opcode, size_t method_id, std::optional<const Value> dest,
+                               T... args)
+      : opcode_{opcode}, method_id_{method_id}, dest_{dest}, args_{args...} {}
+
+  const Op opcode_;
+  // The index of the method to invoke, for kInvokeVirtual and similar opcodes.
+  const size_t method_id_{0};
+  const std::optional<const Value> dest_;
+  const std::vector<const Value> args_;
+};
+
+// Needed for CHECK_EQ, DCHECK_EQ, etc.
+std::ostream& operator<<(std::ostream& out, const Instruction::Op& opcode);
+
 // Tools to help build methods and their bodies.
 class MethodBuilder {
  public:
@@ -95,42 +190,53 @@ class MethodBuilder {
   // Encode the method into DEX format.
   ir::EncodedMethod* Encode();
 
-  // Registers are just represented by their number.
-  using Register = size_t;
-
   // Create a new register to be used to storing values. Note that these are not SSA registers, like
   // might be expected in similar code generators. This does no liveness tracking or anything, so
   // it's up to the caller to reuse registers as appropriate.
-  Register MakeRegister();
+  Value MakeRegister();
 
   /////////////////////////////////
   // Instruction builder methods //
   /////////////////////////////////
 
+  void AddInstruction(Instruction instruction);
+
   // return-void
   void BuildReturn();
-  void BuildReturn(Register src);
+  void BuildReturn(Value src);
   // const/4
-  void BuildConst4(Register target, int value);
+  void BuildConst4(Value target, int value);
 
   // TODO: add builders for more instructions
 
  private:
+  void EncodeInstructions();
+  void EncodeInstruction(const Instruction& instruction);
+  void EncodeReturn(const Instruction& instruction);
+  void EncodeMove(const Instruction& instruction);
+  void EncodeInvokeVirtual(const Instruction& instruction);
+
+  // Converts a register or parameter to its DEX register number.
+  size_t RegisterValue(Value value) const;
+
   DexBuilder* dex_;
   ir::Class* class_;
   ir::MethodDecl* decl_;
 
-  // A buffer to hold instructions we are generating.
+  // A list of the instructions we will eventually encode.
+  std::vector<Instruction> instructions_;
+
+  // A buffer to hold instructions that have been encoded.
   std::vector<::dex::u2> buffer_;
 
   // How many registers we've allocated
-  size_t num_registers_;
+  size_t num_registers_{0};
 };
 
 // A helper to build class definitions.
 class ClassBuilder {
  public:
-  ClassBuilder(DexBuilder* parent, ir::Class* class_def);
+  ClassBuilder(DexBuilder* parent, const std::string& name, ir::Class* class_def);
 
   void set_source_file(const std::string& source);
 
@@ -139,8 +245,15 @@ class ClassBuilder {
   MethodBuilder CreateMethod(const std::string& name, Prototype prototype);
 
  private:
-  DexBuilder* parent_;
-  ir::Class* class_;
+  DexBuilder* const parent_;
+  const TypeDescriptor type_descriptor_;
+  ir::Class* const class_;
+};
+
+// Keeps track of information needed to manipulate or call a method.
+struct MethodDeclData {
+  size_t id;
+  ir::MethodDecl* decl;
 };
 
 // Builds Dex files from scratch.
@@ -163,10 +276,19 @@ class DexBuilder {
   ClassBuilder MakeClass(const std::string& name);
 
   // Add a type for the given descriptor, or return the existing one if it already exists.
-  // See the TypeDescriptor class for help generating these.
+  // See the TypeDescriptor class for help generating these. GetOrAddType can be used to declare
+  // imported classes.
   ir::Type* GetOrAddType(const std::string& descriptor);
 
+  // Returns the method id for the method, creating it if it has not been created yet.
+  const MethodDeclData& GetOrDeclareMethod(TypeDescriptor type, const std::string& name,
+                                           Prototype prototype);
+
  private:
+  // Looks up the ir::Proto* corresponding to this given prototype, or creates one if it does not
+  // exist.
+  ir::Proto* GetOrEncodeProto(Prototype prototype);
+
   std::shared_ptr<ir::DexFile> dex_file_;
 
   // allocator_ is needed to be able to encode the image.
@@ -177,10 +299,29 @@ class DexBuilder {
   std::vector<std::unique_ptr<uint8_t[]>> string_data_;
 
   // Keep track of what types we've defined so we can look them up later.
-  std::map<std::string, ir::Type*> types_by_descriptor_;
+  std::unordered_map<std::string, ir::Type*> types_by_descriptor_;
+
+  struct MethodDescriptor {
+    TypeDescriptor type;
+    std::string name;
+    Prototype prototype;
+
+    inline bool operator<(const MethodDescriptor& rhs) const {
+      return std::make_tuple(type, name, prototype) <
+             std::make_tuple(rhs.type, rhs.name, rhs.prototype);
+    }
+  };
+
+  // Maps method declarations to their method index. This is needed to encode references to them.
+  // When we go to actually write the DEX file, slicer will re-assign these after correctly sorting
+  // the methods list.
+  std::map<MethodDescriptor, MethodDeclData> method_id_map_;
 
   // Keep track of what strings we've defined so we can look them up later.
-  std::map<std::string, ir::String*> strings_;
+  std::unordered_map<std::string, ir::String*> strings_;
+
+  // Keep track of already-encoded protos.
+  std::map<Prototype, ir::Proto*> proto_map_;
 };
 
 }  // namespace dex

startop/view_compiler/dex_builder_test.cc

@@ -40,6 +40,12 @@ bool EncodeAndVerify(DexBuilder* dex_file) {
   return loaded_dex_file != nullptr;
 }
 
+// Write out and verify a DEX file that corresponds to:
+//
+// package dextest;
+// public class DexTest {
+//     public static void foo() {}
+// }
 TEST(DexBuilderTest, VerifyDexWithClassMethod) {
   DexBuilder dex_file;
 
@@ -67,6 +73,12 @@ TEST(DexBuilderTest, VerifyBadDexWithClassMethod) {
   EXPECT_FALSE(EncodeAndVerify(&dex_file));
 }
 
+// Write out and verify a DEX file that corresponds to:
+//
+// package dextest;
+// public class DexTest {
+//     public static int foo() { return 5; }
+// }
 TEST(DexBuilderTest, VerifyDexReturn5) {
   DexBuilder dex_file;
 
@@ -80,3 +92,51 @@ TEST(DexBuilderTest, VerifyDexReturn5) {
 
   EXPECT_TRUE(EncodeAndVerify(&dex_file));
 }
+
+// Write out and verify a DEX file that corresponds to:
+//
+// package dextest;
+// public class DexTest {
+//     public static int foo(int x) { return x; }
+// }
+TEST(DexBuilderTest, VerifyDexReturnIntParam) {
+  DexBuilder dex_file;
+
+  auto cbuilder{dex_file.MakeClass("dextest.DexTest")};
+
+  auto method{
+      cbuilder.CreateMethod("foo", Prototype{TypeDescriptor::Int(), TypeDescriptor::Int()})};
+  method.BuildReturn(Value::Parameter(0));
+  method.Encode();
+
+  EXPECT_TRUE(EncodeAndVerify(&dex_file));
+}
+
+// Write out and verify a DEX file that corresponds to:
+//
+// package dextest;
+// public class DexTest {
+//     public static int foo(String s) { return s.length(); }
+// }
+TEST(DexBuilderTest, VerifyDexCallStringLength) {
+  DexBuilder dex_file;
+
+  auto cbuilder{dex_file.MakeClass("dextest.DexTest")};
+
+  MethodBuilder method{cbuilder.CreateMethod(
+      "foo", Prototype{TypeDescriptor::Int(), TypeDescriptor::FromClassname("java.lang.String")})};
+
+  Value result = method.MakeRegister();
+
+  MethodDeclData string_length =
+      dex_file.GetOrDeclareMethod(TypeDescriptor::FromClassname("java.lang.String"),
+                                  "length",
+                                  Prototype{TypeDescriptor::Int()});
+
+  method.AddInstruction(Instruction::InvokeVirtual(string_length.id, result, Value::Parameter(0)));
+  method.BuildReturn(result);
+
+  method.Encode();
+
+  EXPECT_TRUE(EncodeAndVerify(&dex_file));
+}