compiler/dex/dex_to_dex_compiler.cc - platform/art - Git at Google

 /*
  * Copyright (C) 2011 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_to_dex_compiler.h"

 #include "art_field-inl.h"
 #include "art_method-inl.h"
 #include "base/logging.h"
 #include "base/mutex.h"
 #include "compiled_method.h"
 #include "dex_file-inl.h"
 #include "dex_instruction-inl.h"
 #include "driver/compiler_driver.h"
 #include "driver/dex_compilation_unit.h"
 #include "mirror/class-inl.h"
 #include "mirror/dex_cache.h"
 #include "thread-inl.h"

 namespace art {
 namespace optimizer {

 // Controls quickening activation.
 const bool kEnableQuickening = true;
 // Control check-cast elision.
 const bool kEnableCheckCastEllision = true;

 struct QuickenedInfo {
   QuickenedInfo(uint32_t pc, uint16_t index) : dex_pc(pc), dex_member_index(index) {}

   uint32_t dex_pc;
   uint16_t dex_member_index;
 };

 class DexCompiler {
  public:
   DexCompiler(art::CompilerDriver& compiler,
               const DexCompilationUnit& unit,
               DexToDexCompilationLevel dex_to_dex_compilation_level)
     : driver_(compiler),
       unit_(unit),
       dex_to_dex_compilation_level_(dex_to_dex_compilation_level) {}

   ~DexCompiler() {}

   void Compile();

   const std::vector<QuickenedInfo>& GetQuickenedInfo() const {
     return quickened_info_;
   }

  private:
   const DexFile& GetDexFile() const {
     return *unit_.GetDexFile();
   }

   bool PerformOptimizations() const {
     return dex_to_dex_compilation_level_ >= DexToDexCompilationLevel::kOptimize;
   }

   // Compiles a RETURN-VOID into a RETURN-VOID-BARRIER within a constructor where
   // a barrier is required.
   void CompileReturnVoid(Instruction* inst, uint32_t dex_pc);

   // Compiles a CHECK-CAST into 2 NOP instructions if it is known to be safe. In
   // this case, returns the second NOP instruction pointer. Otherwise, returns
   // the given "inst".
   Instruction* CompileCheckCast(Instruction* inst, uint32_t dex_pc);

   // Compiles a field access into a quick field access.
   // The field index is replaced by an offset within an Object where we can read
   // from / write to this field. Therefore, this does not involve any resolution
   // at runtime.
   // Since the field index is encoded with 16 bits, we can replace it only if the
   // field offset can be encoded with 16 bits too.
   void CompileInstanceFieldAccess(Instruction* inst, uint32_t dex_pc,
                                   Instruction::Code new_opcode, bool is_put);

   // Compiles a virtual method invocation into a quick virtual method invocation.
   // The method index is replaced by the vtable index where the corresponding
   // AbstractMethod can be found. Therefore, this does not involve any resolution
   // at runtime.
   // Since the method index is encoded with 16 bits, we can replace it only if the
   // vtable index can be encoded with 16 bits too.
   void CompileInvokeVirtual(Instruction* inst, uint32_t dex_pc,
                             Instruction::Code new_opcode, bool is_range);

   CompilerDriver& driver_;
   const DexCompilationUnit& unit_;
   const DexToDexCompilationLevel dex_to_dex_compilation_level_;

   // Filled by the compiler when quickening, in order to encode that information
   // in the .oat file. The runtime will use that information to get to the original
   // opcodes.
   std::vector<QuickenedInfo> quickened_info_;

   DISALLOW_COPY_AND_ASSIGN(DexCompiler);
 };

 void DexCompiler::Compile() {
   DCHECK_GE(dex_to_dex_compilation_level_, DexToDexCompilationLevel::kRequired);
   const DexFile::CodeItem* code_item = unit_.GetCodeItem();
   const uint16_t* insns = code_item->insns_;
   const uint32_t insns_size = code_item->insns_size_in_code_units_;
   Instruction* inst = const_cast<Instruction*>(Instruction::At(insns));

   for (uint32_t dex_pc = 0; dex_pc < insns_size;
        inst = const_cast<Instruction*>(inst->Next()), dex_pc = inst->GetDexPc(insns)) {
     switch (inst->Opcode()) {
       case Instruction::RETURN_VOID:
         CompileReturnVoid(inst, dex_pc);
         break;

       case Instruction::CHECK_CAST:
         inst = CompileCheckCast(inst, dex_pc);
         break;

       case Instruction::IGET:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_QUICK, false);
         break;

       case Instruction::IGET_WIDE:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_WIDE_QUICK, false);
         break;

       case Instruction::IGET_OBJECT:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_OBJECT_QUICK, false);
         break;

       case Instruction::IGET_BOOLEAN:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_BOOLEAN_QUICK, false);
         break;

       case Instruction::IGET_BYTE:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_BYTE_QUICK, false);
         break;

       case Instruction::IGET_CHAR:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_CHAR_QUICK, false);
         break;

       case Instruction::IGET_SHORT:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_SHORT_QUICK, false);
         break;

       case Instruction::IPUT:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_QUICK, true);
         break;

       case Instruction::IPUT_BOOLEAN:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_BOOLEAN_QUICK, true);
         break;

       case Instruction::IPUT_BYTE:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_BYTE_QUICK, true);
         break;

       case Instruction::IPUT_CHAR:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_CHAR_QUICK, true);
         break;

       case Instruction::IPUT_SHORT:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_SHORT_QUICK, true);
         break;

       case Instruction::IPUT_WIDE:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_WIDE_QUICK, true);
         break;

       case Instruction::IPUT_OBJECT:
         CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_OBJECT_QUICK, true);
         break;

       case Instruction::INVOKE_VIRTUAL:
         CompileInvokeVirtual(inst, dex_pc, Instruction::INVOKE_VIRTUAL_QUICK, false);
         break;

       case Instruction::INVOKE_VIRTUAL_RANGE:
         CompileInvokeVirtual(inst, dex_pc, Instruction::INVOKE_VIRTUAL_RANGE_QUICK, true);
         break;

       default:
         // Nothing to do.
         break;
     }
   }
 }

 void DexCompiler::CompileReturnVoid(Instruction* inst, uint32_t dex_pc) {
   DCHECK_EQ(inst->Opcode(), Instruction::RETURN_VOID);
   if (unit_.IsConstructor()) {
     // Are we compiling a non clinit constructor which needs a barrier ?
     if (!unit_.IsStatic() &&
         driver_.RequiresConstructorBarrier(Thread::Current(), unit_.GetDexFile(),
                                            unit_.GetClassDefIndex())) {
       return;
     }
   }
   // Replace RETURN_VOID by RETURN_VOID_NO_BARRIER.
   VLOG(compiler) << "Replacing " << Instruction::Name(inst->Opcode())
                  << " by " << Instruction::Name(Instruction::RETURN_VOID_NO_BARRIER)
                  << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
                  << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
   inst->SetOpcode(Instruction::RETURN_VOID_NO_BARRIER);
 }

 Instruction* DexCompiler::CompileCheckCast(Instruction* inst, uint32_t dex_pc) {
   if (!kEnableCheckCastEllision || !PerformOptimizations()) {
     return inst;
   }
   if (!driver_.IsSafeCast(&unit_, dex_pc)) {
     return inst;
   }
   // Ok, this is a safe cast. Since the "check-cast" instruction size is 2 code
   // units and a "nop" instruction size is 1 code unit, we need to replace it by
   // 2 consecutive NOP instructions.
   // Because the caller loops over instructions by calling Instruction::Next onto
   // the current instruction, we need to return the 2nd NOP instruction. Indeed,
   // its next instruction is the former check-cast's next instruction.
   VLOG(compiler) << "Removing " << Instruction::Name(inst->Opcode())
                  << " by replacing it with 2 NOPs at dex pc "
                  << StringPrintf("0x%x", dex_pc) << " in method "
                  << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
   // We are modifying 4 consecutive bytes.
   inst->SetOpcode(Instruction::NOP);
   inst->SetVRegA_10x(0u);  // keep compliant with verifier.
   // Get to next instruction which is the second half of check-cast and replace
   // it by a NOP.
   inst = const_cast<Instruction*>(inst->Next());
   inst->SetOpcode(Instruction::NOP);
   inst->SetVRegA_10x(0u);  // keep compliant with verifier.
   return inst;
 }

 void DexCompiler::CompileInstanceFieldAccess(Instruction* inst,
                                              uint32_t dex_pc,
                                              Instruction::Code new_opcode,
                                              bool is_put) {
   if (!kEnableQuickening || !PerformOptimizations()) {
     return;
   }
   uint32_t field_idx = inst->VRegC_22c();
   MemberOffset field_offset(0u);
   bool is_volatile;
   bool fast_path = driver_.ComputeInstanceFieldInfo(field_idx, &unit_, is_put,
                                                     &field_offset, &is_volatile);
   if (fast_path && !is_volatile && IsUint<16>(field_offset.Int32Value())) {
     VLOG(compiler) << "Quickening " << Instruction::Name(inst->Opcode())
                    << " to " << Instruction::Name(new_opcode)
                    << " by replacing field index " << field_idx
                    << " by field offset " << field_offset.Int32Value()
                    << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
                    << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
     // We are modifying 4 consecutive bytes.
     inst->SetOpcode(new_opcode);
     // Replace field index by field offset.
     inst->SetVRegC_22c(static_cast<uint16_t>(field_offset.Int32Value()));
     quickened_info_.push_back(QuickenedInfo(dex_pc, field_idx));
   }
 }

 void DexCompiler::CompileInvokeVirtual(Instruction* inst, uint32_t dex_pc,
                                        Instruction::Code new_opcode, bool is_range) {
   if (!kEnableQuickening || !PerformOptimizations()) {
     return;
   }
   uint32_t method_idx = is_range ? inst->VRegB_3rc() : inst->VRegB_35c();
   MethodReference target_method(&GetDexFile(), method_idx);
   InvokeType invoke_type = kVirtual;
   InvokeType original_invoke_type = invoke_type;
   int vtable_idx;
   uintptr_t direct_code;
   uintptr_t direct_method;
   // TODO: support devirtualization.
   const bool kEnableDevirtualization = false;
   bool fast_path = driver_.ComputeInvokeInfo(&unit_, dex_pc,
                                              false, kEnableDevirtualization,
                                              &invoke_type,
                                              &target_method, &vtable_idx,
                                              &direct_code, &direct_method);
   if (fast_path && original_invoke_type == invoke_type) {
     if (vtable_idx >= 0 && IsUint<16>(vtable_idx)) {
       VLOG(compiler) << "Quickening " << Instruction::Name(inst->Opcode())
                      << "(" << PrettyMethod(method_idx, GetDexFile(), true) << ")"
                      << " to " << Instruction::Name(new_opcode)
                      << " by replacing method index " << method_idx
                      << " by vtable index " << vtable_idx
                      << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
                      << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
       // We are modifying 4 consecutive bytes.
       inst->SetOpcode(new_opcode);
       // Replace method index by vtable index.
       if (is_range) {
         inst->SetVRegB_3rc(static_cast<uint16_t>(vtable_idx));
       } else {
         inst->SetVRegB_35c(static_cast<uint16_t>(vtable_idx));
       }
       quickened_info_.push_back(QuickenedInfo(dex_pc, method_idx));
     }
   }
 }

 CompiledMethod* ArtCompileDEX(
     CompilerDriver* driver,
     const DexFile::CodeItem* code_item,
     uint32_t access_flags,
     InvokeType invoke_type ATTRIBUTE_UNUSED,
     uint16_t class_def_idx,
     uint32_t method_idx,
     jobject class_loader,
     const DexFile& dex_file,
     DexToDexCompilationLevel dex_to_dex_compilation_level) {
   DCHECK(driver != nullptr);
   if (dex_to_dex_compilation_level != DexToDexCompilationLevel::kDontDexToDexCompile) {
     ScopedObjectAccess soa(Thread::Current());
     StackHandleScope<1> hs(soa.Self());
     ClassLinker* const class_linker = Runtime::Current()->GetClassLinker();
     art::DexCompilationUnit unit(nullptr, class_loader, class_linker,
                                  dex_file, code_item, class_def_idx, method_idx, access_flags,
                                  driver->GetVerifiedMethod(&dex_file, method_idx),
                                  hs.NewHandle(class_linker->FindDexCache(soa.Self(), dex_file)));
     art::optimizer::DexCompiler dex_compiler(*driver, unit, dex_to_dex_compilation_level);
     dex_compiler.Compile();
     if (dex_compiler.GetQuickenedInfo().empty()) {
       // No need to create a CompiledMethod if there are no quickened opcodes.
       return nullptr;
     }

     // Create a `CompiledMethod`, with the quickened information in the vmap table.
     Leb128EncodingVector<> builder;
     for (QuickenedInfo info : dex_compiler.GetQuickenedInfo()) {
       builder.PushBackUnsigned(info.dex_pc);
       builder.PushBackUnsigned(info.dex_member_index);
     }
     InstructionSet instruction_set = driver->GetInstructionSet();
     if (instruction_set == kThumb2) {
       // Don't use the thumb2 instruction set to avoid the one off code delta.
       instruction_set = kArm;
     }
     return CompiledMethod::SwapAllocCompiledMethod(
         driver,
         instruction_set,
         ArrayRef<const uint8_t>(),                   // no code
         0,
         0,
         0,
         ArrayRef<const SrcMapElem>(),                // src_mapping_table
         ArrayRef<const uint8_t>(),                   // mapping_table
         ArrayRef<const uint8_t>(builder.GetData()),  // vmap_table
         ArrayRef<const uint8_t>(),                   // gc_map
         ArrayRef<const uint8_t>(),                   // cfi data
         ArrayRef<const LinkerPatch>());
   }
   return nullptr;
 }

 }  // namespace optimizer

 }  // namespace art
	/*
	* Copyright (C) 2011 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_to_dex_compiler.h"

	#include "art_field-inl.h"
	#include "art_method-inl.h"
	#include "base/logging.h"
	#include "base/mutex.h"
	#include "compiled_method.h"
	#include "dex_file-inl.h"
	#include "dex_instruction-inl.h"
	#include "driver/compiler_driver.h"
	#include "driver/dex_compilation_unit.h"
	#include "mirror/class-inl.h"
	#include "mirror/dex_cache.h"
	#include "thread-inl.h"

	namespace art {
	namespace optimizer {

	// Controls quickening activation.
	const bool kEnableQuickening = true;
	// Control check-cast elision.
	const bool kEnableCheckCastEllision = true;

	struct QuickenedInfo {
	QuickenedInfo(uint32_t pc, uint16_t index) : dex_pc(pc), dex_member_index(index) {}

	uint32_t dex_pc;
	uint16_t dex_member_index;
	};

	class DexCompiler {
	public:
	DexCompiler(art::CompilerDriver& compiler,
	const DexCompilationUnit& unit,
	DexToDexCompilationLevel dex_to_dex_compilation_level)
	: driver_(compiler),
	unit_(unit),
	dex_to_dex_compilation_level_(dex_to_dex_compilation_level) {}

	~DexCompiler() {}

	void Compile();

	const std::vector<QuickenedInfo>& GetQuickenedInfo() const {
	return quickened_info_;
	}

	private:
	const DexFile& GetDexFile() const {
	return *unit_.GetDexFile();
	}

	bool PerformOptimizations() const {
	return dex_to_dex_compilation_level_ >= DexToDexCompilationLevel::kOptimize;
	}

	// Compiles a RETURN-VOID into a RETURN-VOID-BARRIER within a constructor where
	// a barrier is required.
	void CompileReturnVoid(Instruction* inst, uint32_t dex_pc);

	// Compiles a CHECK-CAST into 2 NOP instructions if it is known to be safe. In
	// this case, returns the second NOP instruction pointer. Otherwise, returns
	// the given "inst".
	Instruction* CompileCheckCast(Instruction* inst, uint32_t dex_pc);

	// Compiles a field access into a quick field access.
	// The field index is replaced by an offset within an Object where we can read
	// from / write to this field. Therefore, this does not involve any resolution
	// at runtime.
	// Since the field index is encoded with 16 bits, we can replace it only if the
	// field offset can be encoded with 16 bits too.
	void CompileInstanceFieldAccess(Instruction* inst, uint32_t dex_pc,
	Instruction::Code new_opcode, bool is_put);

	// Compiles a virtual method invocation into a quick virtual method invocation.
	// The method index is replaced by the vtable index where the corresponding
	// AbstractMethod can be found. Therefore, this does not involve any resolution
	// at runtime.
	// Since the method index is encoded with 16 bits, we can replace it only if the
	// vtable index can be encoded with 16 bits too.
	void CompileInvokeVirtual(Instruction* inst, uint32_t dex_pc,
	Instruction::Code new_opcode, bool is_range);

	CompilerDriver& driver_;
	const DexCompilationUnit& unit_;
	const DexToDexCompilationLevel dex_to_dex_compilation_level_;

	// Filled by the compiler when quickening, in order to encode that information
	// in the .oat file. The runtime will use that information to get to the original
	// opcodes.
	std::vector<QuickenedInfo> quickened_info_;

	DISALLOW_COPY_AND_ASSIGN(DexCompiler);
	};

	void DexCompiler::Compile() {
	DCHECK_GE(dex_to_dex_compilation_level_, DexToDexCompilationLevel::kRequired);
	const DexFile::CodeItem* code_item = unit_.GetCodeItem();
	const uint16_t* insns = code_item->insns_;
	const uint32_t insns_size = code_item->insns_size_in_code_units_;
	Instruction* inst = const_cast<Instruction*>(Instruction::At(insns));

	for (uint32_t dex_pc = 0; dex_pc < insns_size;
	inst = const_cast<Instruction*>(inst->Next()), dex_pc = inst->GetDexPc(insns)) {
	switch (inst->Opcode()) {
	case Instruction::RETURN_VOID:
	CompileReturnVoid(inst, dex_pc);
	break;

	case Instruction::CHECK_CAST:
	inst = CompileCheckCast(inst, dex_pc);
	break;

	case Instruction::IGET:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_QUICK, false);
	break;

	case Instruction::IGET_WIDE:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_WIDE_QUICK, false);
	break;

	case Instruction::IGET_OBJECT:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_OBJECT_QUICK, false);
	break;

	case Instruction::IGET_BOOLEAN:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_BOOLEAN_QUICK, false);
	break;

	case Instruction::IGET_BYTE:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_BYTE_QUICK, false);
	break;

	case Instruction::IGET_CHAR:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_CHAR_QUICK, false);
	break;

	case Instruction::IGET_SHORT:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IGET_SHORT_QUICK, false);
	break;

	case Instruction::IPUT:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_QUICK, true);
	break;

	case Instruction::IPUT_BOOLEAN:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_BOOLEAN_QUICK, true);
	break;

	case Instruction::IPUT_BYTE:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_BYTE_QUICK, true);
	break;

	case Instruction::IPUT_CHAR:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_CHAR_QUICK, true);
	break;

	case Instruction::IPUT_SHORT:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_SHORT_QUICK, true);
	break;

	case Instruction::IPUT_WIDE:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_WIDE_QUICK, true);
	break;

	case Instruction::IPUT_OBJECT:
	CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_OBJECT_QUICK, true);
	break;

	case Instruction::INVOKE_VIRTUAL:
	CompileInvokeVirtual(inst, dex_pc, Instruction::INVOKE_VIRTUAL_QUICK, false);
	break;

	case Instruction::INVOKE_VIRTUAL_RANGE:
	CompileInvokeVirtual(inst, dex_pc, Instruction::INVOKE_VIRTUAL_RANGE_QUICK, true);
	break;

	default:
	// Nothing to do.
	break;
	}
	}
	}

	void DexCompiler::CompileReturnVoid(Instruction* inst, uint32_t dex_pc) {
	DCHECK_EQ(inst->Opcode(), Instruction::RETURN_VOID);
	if (unit_.IsConstructor()) {
	// Are we compiling a non clinit constructor which needs a barrier ?
	if (!unit_.IsStatic() &&
	driver_.RequiresConstructorBarrier(Thread::Current(), unit_.GetDexFile(),
	unit_.GetClassDefIndex())) {
	return;
	}
	}
	// Replace RETURN_VOID by RETURN_VOID_NO_BARRIER.
	VLOG(compiler) << "Replacing " << Instruction::Name(inst->Opcode())
	<< " by " << Instruction::Name(Instruction::RETURN_VOID_NO_BARRIER)
	<< " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
	<< PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
	inst->SetOpcode(Instruction::RETURN_VOID_NO_BARRIER);
	}

	Instruction* DexCompiler::CompileCheckCast(Instruction* inst, uint32_t dex_pc) {
	if (!kEnableCheckCastEllision \|\| !PerformOptimizations()) {
	return inst;
	}
	if (!driver_.IsSafeCast(&unit_, dex_pc)) {
	return inst;
	}
	// Ok, this is a safe cast. Since the "check-cast" instruction size is 2 code
	// units and a "nop" instruction size is 1 code unit, we need to replace it by
	// 2 consecutive NOP instructions.
	// Because the caller loops over instructions by calling Instruction::Next onto
	// the current instruction, we need to return the 2nd NOP instruction. Indeed,
	// its next instruction is the former check-cast's next instruction.
	VLOG(compiler) << "Removing " << Instruction::Name(inst->Opcode())
	<< " by replacing it with 2 NOPs at dex pc "
	<< StringPrintf("0x%x", dex_pc) << " in method "
	<< PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
	// We are modifying 4 consecutive bytes.
	inst->SetOpcode(Instruction::NOP);
	inst->SetVRegA_10x(0u); // keep compliant with verifier.
	// Get to next instruction which is the second half of check-cast and replace
	// it by a NOP.
	inst = const_cast<Instruction*>(inst->Next());
	inst->SetOpcode(Instruction::NOP);
	inst->SetVRegA_10x(0u); // keep compliant with verifier.
	return inst;
	}

	void DexCompiler::CompileInstanceFieldAccess(Instruction* inst,
	uint32_t dex_pc,
	Instruction::Code new_opcode,
	bool is_put) {
	if (!kEnableQuickening \|\| !PerformOptimizations()) {
	return;
	}
	uint32_t field_idx = inst->VRegC_22c();
	MemberOffset field_offset(0u);
	bool is_volatile;
	bool fast_path = driver_.ComputeInstanceFieldInfo(field_idx, &unit_, is_put,
	&field_offset, &is_volatile);
	if (fast_path && !is_volatile && IsUint<16>(field_offset.Int32Value())) {
	VLOG(compiler) << "Quickening " << Instruction::Name(inst->Opcode())
	<< " to " << Instruction::Name(new_opcode)
	<< " by replacing field index " << field_idx
	<< " by field offset " << field_offset.Int32Value()
	<< " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
	<< PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
	// We are modifying 4 consecutive bytes.
	inst->SetOpcode(new_opcode);
	// Replace field index by field offset.
	inst->SetVRegC_22c(static_cast<uint16_t>(field_offset.Int32Value()));
	quickened_info_.push_back(QuickenedInfo(dex_pc, field_idx));
	}
	}

	void DexCompiler::CompileInvokeVirtual(Instruction* inst, uint32_t dex_pc,
	Instruction::Code new_opcode, bool is_range) {
	if (!kEnableQuickening \|\| !PerformOptimizations()) {
	return;
	}
	uint32_t method_idx = is_range ? inst->VRegB_3rc() : inst->VRegB_35c();
	MethodReference target_method(&GetDexFile(), method_idx);
	InvokeType invoke_type = kVirtual;
	InvokeType original_invoke_type = invoke_type;
	int vtable_idx;
	uintptr_t direct_code;
	uintptr_t direct_method;
	// TODO: support devirtualization.
	const bool kEnableDevirtualization = false;
	bool fast_path = driver_.ComputeInvokeInfo(&unit_, dex_pc,
	false, kEnableDevirtualization,
	&invoke_type,
	&target_method, &vtable_idx,
	&direct_code, &direct_method);
	if (fast_path && original_invoke_type == invoke_type) {
	if (vtable_idx >= 0 && IsUint<16>(vtable_idx)) {
	VLOG(compiler) << "Quickening " << Instruction::Name(inst->Opcode())
	<< "(" << PrettyMethod(method_idx, GetDexFile(), true) << ")"
	<< " to " << Instruction::Name(new_opcode)
	<< " by replacing method index " << method_idx
	<< " by vtable index " << vtable_idx
	<< " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
	<< PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
	// We are modifying 4 consecutive bytes.
	inst->SetOpcode(new_opcode);
	// Replace method index by vtable index.
	if (is_range) {
	inst->SetVRegB_3rc(static_cast<uint16_t>(vtable_idx));
	} else {
	inst->SetVRegB_35c(static_cast<uint16_t>(vtable_idx));
	}
	quickened_info_.push_back(QuickenedInfo(dex_pc, method_idx));
	}
	}
	}

	CompiledMethod* ArtCompileDEX(
	CompilerDriver* driver,
	const DexFile::CodeItem* code_item,
	uint32_t access_flags,
	InvokeType invoke_type ATTRIBUTE_UNUSED,
	uint16_t class_def_idx,
	uint32_t method_idx,
	jobject class_loader,
	const DexFile& dex_file,
	DexToDexCompilationLevel dex_to_dex_compilation_level) {
	DCHECK(driver != nullptr);
	if (dex_to_dex_compilation_level != DexToDexCompilationLevel::kDontDexToDexCompile) {
	ScopedObjectAccess soa(Thread::Current());
	StackHandleScope<1> hs(soa.Self());
	ClassLinker* const class_linker = Runtime::Current()->GetClassLinker();
	art::DexCompilationUnit unit(nullptr, class_loader, class_linker,
	dex_file, code_item, class_def_idx, method_idx, access_flags,
	driver->GetVerifiedMethod(&dex_file, method_idx),
	hs.NewHandle(class_linker->FindDexCache(soa.Self(), dex_file)));
	art::optimizer::DexCompiler dex_compiler(*driver, unit, dex_to_dex_compilation_level);
	dex_compiler.Compile();
	if (dex_compiler.GetQuickenedInfo().empty()) {
	// No need to create a CompiledMethod if there are no quickened opcodes.
	return nullptr;
	}

	// Create a `CompiledMethod`, with the quickened information in the vmap table.
	Leb128EncodingVector<> builder;
	for (QuickenedInfo info : dex_compiler.GetQuickenedInfo()) {
	builder.PushBackUnsigned(info.dex_pc);
	builder.PushBackUnsigned(info.dex_member_index);
	}
	InstructionSet instruction_set = driver->GetInstructionSet();
	if (instruction_set == kThumb2) {
	// Don't use the thumb2 instruction set to avoid the one off code delta.
	instruction_set = kArm;
	}
	return CompiledMethod::SwapAllocCompiledMethod(
	driver,
	instruction_set,
	ArrayRef<const uint8_t>(), // no code
	0,
	0,
	0,
	ArrayRef<const SrcMapElem>(), // src_mapping_table
	ArrayRef<const uint8_t>(), // mapping_table
	ArrayRef<const uint8_t>(builder.GetData()), // vmap_table
	ArrayRef<const uint8_t>(), // gc_map
	ArrayRef<const uint8_t>(), // cfi data
	ArrayRef<const LinkerPatch>());
	}
	return nullptr;
	}

	} // namespace optimizer

	} // namespace art