compiler/optimizing/inliner.cc

/*
 * Copyright (C) 2014 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 "inliner.h"

#include "art_method-inl.h"
#include "builder.h"
#include "class_linker.h"
#include "constant_folding.h"
#include "dead_code_elimination.h"
#include "driver/compiler_driver-inl.h"
#include "driver/dex_compilation_unit.h"
#include "instruction_simplifier.h"
#include "mirror/class_loader.h"
#include "mirror/dex_cache.h"
#include "nodes.h"
#include "reference_type_propagation.h"
#include "register_allocator.h"
#include "ssa_phi_elimination.h"
#include "scoped_thread_state_change.h"
#include "thread.h"
#include "dex/verified_method.h"
#include "dex/verification_results.h"

namespace art {

static constexpr int kMaxInlineCodeUnits = 18;
static constexpr int kDepthLimit = 3;

void HInliner::Run() {
  if (graph_->IsDebuggable()) {
    // For simplicity, we currently never inline when the graph is debuggable. This avoids
    // doing some logic in the runtime to discover if a method could have been inlined.
    return;
  }
  const GrowableArray<HBasicBlock*>& blocks = graph_->GetReversePostOrder();
  HBasicBlock* next_block = blocks.Get(0);
  for (size_t i = 0; i < blocks.Size(); ++i) {
    // Because we are changing the graph when inlining, we need to remember the next block.
    // This avoids doing the inlining work again on the inlined blocks.
    if (blocks.Get(i) != next_block) {
      continue;
    }
    HBasicBlock* block = next_block;
    next_block = (i == blocks.Size() - 1) ? nullptr : blocks.Get(i + 1);
    for (HInstruction* instruction = block->GetFirstInstruction(); instruction != nullptr;) {
      HInstruction* next = instruction->GetNext();
      HInvoke* call = instruction->AsInvoke();
      // As long as the call is not intrinsified, it is worth trying to inline.
      if (call != nullptr && call->GetIntrinsic() == Intrinsics::kNone) {
        // We use the original invoke type to ensure the resolution of the called method
        // works properly.
        if (!TryInline(call, call->GetDexMethodIndex(), call->GetOriginalInvokeType())) {
          if (kIsDebugBuild) {
            std::string callee_name =
                PrettyMethod(call->GetDexMethodIndex(), *outer_compilation_unit_.GetDexFile());
            bool should_inline = callee_name.find("$inline$") != std::string::npos;
            CHECK(!should_inline) << "Could not inline " << callee_name;
          }
        }
      }
      instruction = next;
    }
  }
}

static bool IsMethodOrDeclaringClassFinal(ArtMethod* method)
    SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
  return method->IsFinal() || method->GetDeclaringClass()->IsFinal();
}

/**
 * Given the `resolved_method` looked up in the dex cache, try to find
 * the actual runtime target of an interface or virtual call.
 * Return nullptr if the runtime target cannot be proven.
 */
static ArtMethod* FindVirtualOrInterfaceTarget(HInvoke* invoke, ArtMethod* resolved_method)
    SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
  if (IsMethodOrDeclaringClassFinal(resolved_method)) {
    // No need to lookup further, the resolved method will be the target.
    return resolved_method;
  }

  HInstruction* receiver = invoke->InputAt(0);
  if (receiver->IsNullCheck()) {
    // Due to multiple levels of inlining within the same pass, it might be that
    // null check does not have the reference type of the actual receiver.
    receiver = receiver->InputAt(0);
  }
  ReferenceTypeInfo info = receiver->GetReferenceTypeInfo();
  if (info.IsTop()) {
    // We have no information on the receiver.
    return nullptr;
  } else if (!info.IsExact()) {
    // We currently only support inlining with known receivers.
    // TODO: Remove this check, we should be able to inline final methods
    // on unknown receivers.
    return nullptr;
  } else if (info.GetTypeHandle()->IsInterface()) {
    // Statically knowing that the receiver has an interface type cannot
    // help us find what is the target method.
    return nullptr;
  }

  ClassLinker* cl = Runtime::Current()->GetClassLinker();
  size_t pointer_size = cl->GetImagePointerSize();
  if (invoke->IsInvokeInterface()) {
    resolved_method = info.GetTypeHandle()->FindVirtualMethodForInterface(
        resolved_method, pointer_size);
  } else {
    DCHECK(invoke->IsInvokeVirtual());
    resolved_method = info.GetTypeHandle()->FindVirtualMethodForVirtual(
        resolved_method, pointer_size);
  }

  if (resolved_method == nullptr) {
    // The information we had on the receiver was not enough to find
    // the target method. Since we check above the exact type of the receiver,
    // the only reason this can happen is an IncompatibleClassChangeError.
    return nullptr;
  } else if (resolved_method->IsAbstract()) {
    // The information we had on the receiver was not enough to find
    // the target method. Since we check above the exact type of the receiver,
    // the only reason this can happen is an IncompatibleClassChangeError.
    return nullptr;
  } else if (IsMethodOrDeclaringClassFinal(resolved_method)) {
    // A final method has to be the target method.
    return resolved_method;
  } else if (info.IsExact()) {
    // If we found a method and the receiver's concrete type is statically
    // known, we know for sure the target.
    return resolved_method;
  } else {
    // Even if we did find a method, the receiver type was not enough to
    // statically find the runtime target.
    return nullptr;
  }
}

bool HInliner::TryInline(HInvoke* invoke_instruction,
                         uint32_t method_index,
                         InvokeType invoke_type) const {
  ScopedObjectAccess soa(Thread::Current());
  const DexFile& caller_dex_file = *caller_compilation_unit_.GetDexFile();
  VLOG(compiler) << "Try inlining " << PrettyMethod(method_index, caller_dex_file);

  ArtMethod* resolved_method = nullptr;
  {
    // Don't keep this handle scope on stack, otherwise we cannot do a reference type
    // propagation while inlining.
    StackHandleScope<2> hs(soa.Self());
    Handle<mirror::DexCache> dex_cache(
        hs.NewHandle(caller_compilation_unit_.GetClassLinker()->FindDexCache(caller_dex_file)));
    Handle<mirror::ClassLoader> class_loader(hs.NewHandle(
        soa.Decode<mirror::ClassLoader*>(caller_compilation_unit_.GetClassLoader())));
    resolved_method = compiler_driver_->ResolveMethod(
        soa, dex_cache, class_loader, &caller_compilation_unit_, method_index, invoke_type);
  }

  if (resolved_method == nullptr) {
    VLOG(compiler) << "Method cannot be resolved " << PrettyMethod(method_index, caller_dex_file);
    return false;
  }

  if (!invoke_instruction->IsInvokeStaticOrDirect()) {
    resolved_method = FindVirtualOrInterfaceTarget(invoke_instruction, resolved_method);
    if (resolved_method == nullptr) {
      VLOG(compiler) << "Interface or virtual call to "
                     << PrettyMethod(method_index, caller_dex_file)
                     << "could not be statically determined";
      return false;
    }
  }

  bool same_dex_file = true;
  const DexFile& outer_dex_file = *outer_compilation_unit_.GetDexFile();
  if (resolved_method->GetDexFile()->GetLocation().compare(outer_dex_file.GetLocation()) != 0) {
    same_dex_file = false;
  }

  const DexFile::CodeItem* code_item = resolved_method->GetCodeItem();

  if (code_item == nullptr) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " is not inlined because it is native";
    return false;
  }

  if (code_item->insns_size_in_code_units_ > kMaxInlineCodeUnits) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " is too big to inline";
    return false;
  }

  if (code_item->tries_size_ != 0) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " is not inlined because of try block";
    return false;
  }

  uint16_t class_def_idx = resolved_method->GetDeclaringClass()->GetDexClassDefIndex();
  if (!compiler_driver_->IsMethodVerifiedWithoutFailures(
        resolved_method->GetDexMethodIndex(), class_def_idx, *resolved_method->GetDexFile())) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " couldn't be verified, so it cannot be inlined";
    return false;
  }

  if (resolved_method->ShouldNotInline()) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " was already flagged as non inlineable";
    return false;
  }

  if (invoke_instruction->IsInvokeStaticOrDirect() &&
      invoke_instruction->AsInvokeStaticOrDirect()->IsStaticWithImplicitClinitCheck()) {
    // Case of a static method that cannot be inlined because it implicitly
    // requires an initialization check of its declaring class.
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " is not inlined because it is static and requires a clinit"
                   << " check that cannot be emitted due to Dex cache limitations";
    return false;
  }

  if (!TryBuildAndInline(resolved_method, invoke_instruction, method_index, same_dex_file)) {
    return false;
  }

  VLOG(compiler) << "Successfully inlined " << PrettyMethod(method_index, caller_dex_file);
  MaybeRecordStat(kInlinedInvoke);
  return true;
}

bool HInliner::TryBuildAndInline(ArtMethod* resolved_method,
                                 HInvoke* invoke_instruction,
                                 uint32_t method_index,
                                 bool same_dex_file) const {
  ScopedObjectAccess soa(Thread::Current());
  const DexFile::CodeItem* code_item = resolved_method->GetCodeItem();
  const DexFile& caller_dex_file = *caller_compilation_unit_.GetDexFile();

  DexCompilationUnit dex_compilation_unit(
    nullptr,
    caller_compilation_unit_.GetClassLoader(),
    caller_compilation_unit_.GetClassLinker(),
    *resolved_method->GetDexFile(),
    code_item,
    resolved_method->GetDeclaringClass()->GetDexClassDefIndex(),
    resolved_method->GetDexMethodIndex(),
    resolved_method->GetAccessFlags(),
    nullptr);

  bool requires_ctor_barrier = false;

  if (dex_compilation_unit.IsConstructor()) {
    // If it's a super invocation and we already generate a barrier there's no need
    // to generate another one.
    // We identify super calls by looking at the "this" pointer. If its value is the
    // same as the local "this" pointer then we must have a super invocation.
    bool is_super_invocation = invoke_instruction->InputAt(0)->IsParameterValue()
        && invoke_instruction->InputAt(0)->AsParameterValue()->IsThis();
    if (is_super_invocation && graph_->ShouldGenerateConstructorBarrier()) {
      requires_ctor_barrier = false;
    } else {
      Thread* self = Thread::Current();
      requires_ctor_barrier = compiler_driver_->RequiresConstructorBarrier(self,
          dex_compilation_unit.GetDexFile(),
          dex_compilation_unit.GetClassDefIndex());
    }
  }

  HGraph* callee_graph = new (graph_->GetArena()) HGraph(
      graph_->GetArena(),
      caller_dex_file,
      method_index,
      requires_ctor_barrier,
      compiler_driver_->GetInstructionSet(),
      invoke_instruction->GetOriginalInvokeType(),
      graph_->IsDebuggable(),
      graph_->GetCurrentInstructionId());

  OptimizingCompilerStats inline_stats;
  HGraphBuilder builder(callee_graph,
                        &dex_compilation_unit,
                        &outer_compilation_unit_,
                        resolved_method->GetDexFile(),
                        compiler_driver_,
                        &inline_stats);

  if (!builder.BuildGraph(*code_item)) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " could not be built, so cannot be inlined";
    // There could be multiple reasons why the graph could not be built, including
    // unaccessible methods/fields due to using a different dex cache. We do not mark
    // the method as non-inlineable so that other callers can still try to inline it.
    return false;
  }

  if (!RegisterAllocator::CanAllocateRegistersFor(*callee_graph,
                                                  compiler_driver_->GetInstructionSet())) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " cannot be inlined because of the register allocator";
    resolved_method->SetShouldNotInline();
    return false;
  }

  if (!callee_graph->TryBuildingSsa()) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " could not be transformed to SSA";
    resolved_method->SetShouldNotInline();
    return false;
  }

  // Run simple optimizations on the graph.
  HDeadCodeElimination dce(callee_graph, stats_);
  HConstantFolding fold(callee_graph);
  ReferenceTypePropagation type_propagation(callee_graph, handles_);
  InstructionSimplifier simplify(callee_graph, stats_);

  HOptimization* optimizations[] = {
    &dce,
    &fold,
    &type_propagation,
    &simplify,
  };

  for (size_t i = 0; i < arraysize(optimizations); ++i) {
    HOptimization* optimization = optimizations[i];
    optimization->Run();
  }

  if (depth_ + 1 < kDepthLimit) {
    HInliner inliner(callee_graph,
                     outer_compilation_unit_,
                     dex_compilation_unit,
                     compiler_driver_,
                     handles_,
                     stats_,
                     depth_ + 1);
    inliner.Run();
  }

  // TODO: We should abort only if all predecessors throw. However,
  // HGraph::InlineInto currently does not handle an exit block with
  // a throw predecessor.
  HBasicBlock* exit_block = callee_graph->GetExitBlock();
  if (exit_block == nullptr) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " could not be inlined because it has an infinite loop";
    resolved_method->SetShouldNotInline();
    return false;
  }

  bool has_throw_predecessor = false;
  for (size_t i = 0, e = exit_block->GetPredecessors().Size(); i < e; ++i) {
    if (exit_block->GetPredecessors().Get(i)->GetLastInstruction()->IsThrow()) {
      has_throw_predecessor = true;
      break;
    }
  }
  if (has_throw_predecessor) {
    VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                   << " could not be inlined because one branch always throws";
    resolved_method->SetShouldNotInline();
    return false;
  }

  HReversePostOrderIterator it(*callee_graph);
  it.Advance();  // Past the entry block, it does not contain instructions that prevent inlining.
  for (; !it.Done(); it.Advance()) {
    HBasicBlock* block = it.Current();
    if (block->IsLoopHeader()) {
      VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                     << " could not be inlined because it contains a loop";
      resolved_method->SetShouldNotInline();
      return false;
    }

    for (HInstructionIterator instr_it(block->GetInstructions());
         !instr_it.Done();
         instr_it.Advance()) {
      HInstruction* current = instr_it.Current();

      if (current->IsInvokeInterface()) {
        // Disable inlining of interface calls. The cost in case of entering the
        // resolution conflict is currently too high.
        VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                       << " could not be inlined because it has an interface call.";
        resolved_method->SetShouldNotInline();
        return false;
      }

      if (!same_dex_file && current->NeedsEnvironment()) {
        VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                       << " could not be inlined because " << current->DebugName()
                       << " needs an environment and is in a different dex file";
        return false;
      }

      if (!same_dex_file && current->NeedsDexCache()) {
        VLOG(compiler) << "Method " << PrettyMethod(method_index, caller_dex_file)
                       << " could not be inlined because " << current->DebugName()
                       << " it is in a different dex file and requires access to the dex cache";
        // Do not flag the method as not-inlineable. A caller within the same
        // dex file could still successfully inline it.
        return false;
      }
    }
  }

  callee_graph->InlineInto(graph_, invoke_instruction);

  return true;
}

}  // namespace art