compiler/dex/dex_to_dex_compiler.cc

/*
 * 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 "base/logging.h"
#include "base/mutex.h"
#include "dex_file-inl.h"
#include "dex_instruction-inl.h"
#include "driver/compiler_driver.h"
#include "driver/dex_compilation_unit.h"
#include "mirror/abstract_method-inl.h"
#include "mirror/class-inl.h"
#include "mirror/dex_cache.h"
#include "mirror/field-inl.h"

namespace art {
namespace optimizer {

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

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

  ~DexCompiler() {}

  void Compile();

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

  // TODO: since the whole compilation pipeline uses a "const DexFile", we need
  // to "unconst" here. The DEX-to-DEX compiler should work on a non-const DexFile.
  DexFile& GetModifiableDexFile() {
    return *const_cast<DexFile*>(unit_.GetDexFile());
  }

  // 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_;

  DISALLOW_COPY_AND_ASSIGN(DexCompiler);
};

// Ensures write access to a part of DEX file.
//
// If a DEX file is read-only, it modifies its protection (mprotect) so it allows
// write access to the part of DEX file defined by an address and a length.
// In this case, it also takes the DexFile::modification_lock to prevent from
// concurrent protection modification from a parallel DEX-to-DEX compilation on
// the same DEX file.
// When the instance is destroyed, it recovers original protection and releases
// the lock.
// TODO: as this scoped class is similar to a MutexLock we should use annotalysis
// to capture the locking behavior.
class ScopedDexWriteAccess {
 public:
  ScopedDexWriteAccess(DexFile& dex_file, Instruction* inst,
                       size_t length)
    : dex_file_(dex_file),
      address_(reinterpret_cast<uint8_t*>(inst)),
      length_(length),
      is_read_only_(dex_file_.IsReadOnly()) {
    if (is_read_only_) {
      // We need to enable DEX write access. To avoid concurrent DEX write access
      // modification, we take the DexFile::modification_lock before.
      dex_file_.GetModificationLock().ExclusiveLock(Thread::Current());
      bool success = dex_file_.EnableWrite(address_, length_);
      DCHECK(success) << "Failed to enable DEX write access";
    }
  }

  ~ScopedDexWriteAccess() {
    DCHECK_EQ(is_read_only_, dex_file_.IsReadOnly());
    if (is_read_only_) {
      bool success = dex_file_.DisableWrite(address_, length_);
      DCHECK(success) << "Failed to disable DEX write access";
      // Now we recovered original read-only protection, we can release the
      // DexFile::modification_lock.
      dex_file_.GetModificationLock().ExclusiveUnlock(Thread::Current());
    }
  }

 private:
  DexFile& dex_file_;
  // TODO: make address_ const.
  uint8_t* address_;
  const size_t length_;
  const bool is_read_only_;

  DISALLOW_COPY_AND_ASSIGN(ScopedDexWriteAccess);
};

void DexCompiler::Compile() {
  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::IPUT:
      case Instruction::IPUT_BOOLEAN:
      case Instruction::IPUT_BYTE:
      case Instruction::IPUT_CHAR:
      case Instruction::IPUT_SHORT:
        // These opcodes have the same implementation in interpreter so group
        // them under IPUT_QUICK.
        CompileInstanceFieldAccess(inst, dex_pc, Instruction::IPUT_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(inst->Opcode() == Instruction::RETURN_VOID);
  // Are we compiling a constructor ?
  if ((unit_.GetAccessFlags() & kAccConstructor) == 0) {
    return;
  }
  // Do we need a constructor barrier ?
  if (!driver_.RequiresConstructorBarrier(Thread::Current(), unit_.GetDexFile(),
                                         unit_.GetClassDefIndex())) {
    return;
  }
  // Replace RETURN_VOID by RETURN_VOID_BARRIER.
  VLOG(compiler) << "Replacing " << Instruction::Name(inst->Opcode())
                 << " by " << Instruction::Name(Instruction::RETURN_VOID_BARRIER)
                 << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
                 << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
  ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 2u);
  inst->SetOpcode(Instruction::RETURN_VOID_BARRIER);
}

Instruction* DexCompiler::CompileCheckCast(Instruction* inst, uint32_t dex_pc) {
  if (!kEnableCheckCastEllision) {
    return inst;
  }
  MethodReference referrer(&GetDexFile(), unit_.GetDexMethodIndex());
  if (!driver_.IsSafeCast(referrer, 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.
  ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 4u);
  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) {
    return;
  }
  uint32_t field_idx = inst->VRegC_22c();
  int field_offset;
  bool is_volatile;
  bool fast_path = driver_.ComputeInstanceFieldInfo(field_idx, &unit_, field_offset,
                                                    is_volatile, is_put);
  if (fast_path && !is_volatile && IsUint(16, field_offset)) {
    VLOG(compiler) << "Quickening " << Instruction::Name(inst->Opcode())
                   << " to " << Instruction::Name(new_opcode)
                   << " by replacing field index " << field_idx
                   << " by field offset " << field_offset
                   << " at dex pc " << StringPrintf("0x%x", dex_pc) << " in method "
                   << PrettyMethod(unit_.GetDexMethodIndex(), GetDexFile(), true);
    // We are modifying 4 consecutive bytes.
    ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 4u);
    inst->SetOpcode(new_opcode);
    // Replace field index by field offset.
    inst->SetVRegC_22c(static_cast<uint16_t>(field_offset));
  }
}

void DexCompiler::CompileInvokeVirtual(Instruction* inst,
                                uint32_t dex_pc,
                                Instruction::Code new_opcode,
                                bool is_range) {
  if (!kEnableQuickening) {
    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;
  bool fast_path = driver_.ComputeInvokeInfo(&unit_, dex_pc, invoke_type,
                                             target_method, vtable_idx,
                                             direct_code, direct_method,
                                             false);
  // TODO: support devirtualization.
  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.
      ScopedDexWriteAccess sdwa(GetModifiableDexFile(), inst, 4u);
      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));
      }
    }
  }
}

}  // namespace optimizer
}  // namespace art

extern "C" art::CompiledMethod*
    ArtCompileDEX(art::CompilerDriver& compiler, const art::DexFile::CodeItem* code_item,
                  uint32_t access_flags, art::InvokeType invoke_type,
                  uint32_t class_def_idx, uint32_t method_idx, jobject class_loader,
                  const art::DexFile& dex_file) {
  art::DexCompilationUnit unit(NULL, class_loader, art::Runtime::Current()->GetClassLinker(),
                               dex_file, code_item, class_def_idx, method_idx, access_flags);
  art::optimizer::DexCompiler dex_compiler(compiler, unit);
  dex_compiler.Compile();
  return NULL;
}