runtime/cha.cc - platform/art - Gitiles

 /*
  * Copyright (C) 2016 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 "cha.h"

 #include "art_method-inl.h"
 #include "jit/jit.h"
 #include "jit/jit_code_cache.h"
 #include "runtime.h"
 #include "scoped_thread_state_change-inl.h"
 #include "stack.h"
 #include "thread.h"
 #include "thread_list.h"
 #include "thread_pool.h"

 namespace art {

 void ClassHierarchyAnalysis::AddDependency(ArtMethod* method,
                                            ArtMethod* dependent_method,
                                            OatQuickMethodHeader* dependent_header) {
   auto it = cha_dependency_map_.find(method);
   if (it == cha_dependency_map_.end()) {
     cha_dependency_map_[method] =
         new std::vector<std::pair<art::ArtMethod*, art::OatQuickMethodHeader*>>();
     it = cha_dependency_map_.find(method);
   } else {
     DCHECK(it->second != nullptr);
   }
   it->second->push_back(std::make_pair(dependent_method, dependent_header));
 }

 std::vector<std::pair<ArtMethod*, OatQuickMethodHeader*>>*
     ClassHierarchyAnalysis::GetDependents(ArtMethod* method) {
   auto it = cha_dependency_map_.find(method);
   if (it != cha_dependency_map_.end()) {
     DCHECK(it->second != nullptr);
     return it->second;
   }
   return nullptr;
 }

 void ClassHierarchyAnalysis::RemoveDependencyFor(ArtMethod* method) {
   auto it = cha_dependency_map_.find(method);
   if (it != cha_dependency_map_.end()) {
     auto dependents = it->second;
     cha_dependency_map_.erase(it);
     delete dependents;
   }
 }

 void ClassHierarchyAnalysis::RemoveDependentsWithMethodHeaders(
     const std::unordered_set<OatQuickMethodHeader*>& method_headers) {
   // Iterate through all entries in the dependency map and remove any entry that
   // contains one of those in method_headers.
   for (auto map_it = cha_dependency_map_.begin(); map_it != cha_dependency_map_.end(); ) {
     auto dependents = map_it->second;
     for (auto vec_it = dependents->begin(); vec_it != dependents->end(); ) {
       OatQuickMethodHeader* method_header = vec_it->second;
       auto it = std::find(method_headers.begin(), method_headers.end(), method_header);
       if (it != method_headers.end()) {
         vec_it = dependents->erase(vec_it);
       } else {
         vec_it++;
       }
     }
     // Remove the map entry if there are no more dependents.
     if (dependents->empty()) {
       map_it = cha_dependency_map_.erase(map_it);
       delete dependents;
     } else {
       map_it++;
     }
   }
 }

 // This stack visitor walks the stack and for compiled code with certain method
 // headers, sets the should_deoptimize flag on stack to 1.
 // TODO: also set the register value to 1 when should_deoptimize is allocated in
 // a register.
 class CHAStackVisitor FINAL  : public StackVisitor {
  public:
   CHAStackVisitor(Thread* thread_in,
                   Context* context,
                   const std::unordered_set<OatQuickMethodHeader*>& method_headers)
       : StackVisitor(thread_in, context, StackVisitor::StackWalkKind::kSkipInlinedFrames),
         method_headers_(method_headers) {
   }

   bool VisitFrame() OVERRIDE REQUIRES_SHARED(Locks::mutator_lock_) {
     ArtMethod* method = GetMethod();
     // Avoid types of methods that do not have an oat quick method header.
     if (method == nullptr ||
         method->IsRuntimeMethod() ||
         method->IsNative() ||
         method->IsProxyMethod()) {
       return true;
     }
     if (GetCurrentQuickFrame() == nullptr) {
       // Not compiled code.
       return true;
     }
     // Method may have multiple versions of compiled code. Check
     // the method header to see if it has should_deoptimize flag.
     const OatQuickMethodHeader* method_header = GetCurrentOatQuickMethodHeader();
     DCHECK(method_header != nullptr);
     if (!method_header->HasShouldDeoptimizeFlag()) {
       // This compiled version doesn't have should_deoptimize flag. Skip.
       return true;
     }
     auto it = std::find(method_headers_.begin(), method_headers_.end(), method_header);
     if (it == method_headers_.end()) {
       // Not in the list of method headers that should be deoptimized.
       return true;
     }

     // The compiled code on stack is not valid anymore. Need to deoptimize.
     SetShouldDeoptimizeFlag();

     return true;
   }

  private:
   void SetShouldDeoptimizeFlag() REQUIRES_SHARED(Locks::mutator_lock_) {
     QuickMethodFrameInfo frame_info = GetCurrentQuickFrameInfo();
     size_t frame_size = frame_info.FrameSizeInBytes();
     uint8_t* sp = reinterpret_cast<uint8_t*>(GetCurrentQuickFrame());
     size_t core_spill_size = POPCOUNT(frame_info.CoreSpillMask()) *
         GetBytesPerGprSpillLocation(kRuntimeISA);
     size_t fpu_spill_size = POPCOUNT(frame_info.FpSpillMask()) *
         GetBytesPerFprSpillLocation(kRuntimeISA);
     size_t offset = frame_size - core_spill_size - fpu_spill_size - kShouldDeoptimizeFlagSize;
     uint8_t* should_deoptimize_addr = sp + offset;
     // Set deoptimization flag to 1.
     DCHECK(*should_deoptimize_addr == 0 || *should_deoptimize_addr == 1);
     *should_deoptimize_addr = 1;
   }

   // Set of method headers for compiled code that should be deoptimized.
   const std::unordered_set<OatQuickMethodHeader*>& method_headers_;

   DISALLOW_COPY_AND_ASSIGN(CHAStackVisitor);
 };

 class CHACheckpoint FINAL : public Closure {
  public:
   explicit CHACheckpoint(const std::unordered_set<OatQuickMethodHeader*>& method_headers)
       : barrier_(0),
         method_headers_(method_headers) {}

   void Run(Thread* thread) OVERRIDE {
     // Note thread and self may not be equal if thread was already suspended at
     // the point of the request.
     Thread* self = Thread::Current();
     ScopedObjectAccess soa(self);
     CHAStackVisitor visitor(thread, nullptr, method_headers_);
     visitor.WalkStack();
     barrier_.Pass(self);
   }

   void WaitForThreadsToRunThroughCheckpoint(size_t threads_running_checkpoint) {
     Thread* self = Thread::Current();
     ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
     barrier_.Increment(self, threads_running_checkpoint);
   }

  private:
   // The barrier to be passed through and for the requestor to wait upon.
   Barrier barrier_;
   // List of method headers for invalidated compiled code.
   const std::unordered_set<OatQuickMethodHeader*>& method_headers_;

   DISALLOW_COPY_AND_ASSIGN(CHACheckpoint);
 };

 void ClassHierarchyAnalysis::VerifyNonSingleImplementation(mirror::Class* verify_class,
                                                            uint16_t verify_index,
                                                            ArtMethod* excluded_method) {
   // Grab cha_lock_ to make sure all single-implementation updates are seen.
   PointerSize image_pointer_size =
       Runtime::Current()->GetClassLinker()->GetImagePointerSize();
   MutexLock cha_mu(Thread::Current(), *Locks::cha_lock_);
   while (verify_class != nullptr) {
     if (verify_index >= verify_class->GetVTableLength()) {
       return;
     }
     ArtMethod* verify_method = verify_class->GetVTableEntry(verify_index, image_pointer_size);
     if (verify_method != excluded_method) {
       DCHECK(!verify_method->HasSingleImplementation())
           << "class: " << verify_class->PrettyClass()
           << " verify_method: " << verify_method->PrettyMethod(true);
       if (verify_method->IsAbstract()) {
         DCHECK(verify_method->GetSingleImplementation(image_pointer_size) == nullptr);
       }
     }
     verify_class = verify_class->GetSuperClass();
   }
 }

 void ClassHierarchyAnalysis::CheckSingleImplementationInfo(
     Handle<mirror::Class> klass,
     ArtMethod* virtual_method,
     ArtMethod* method_in_super,
     std::unordered_set<ArtMethod*>& invalidated_single_impl_methods,
     PointerSize pointer_size) {
   // TODO: if klass is not instantiable, virtual_method isn't invocable yet so
   // even if it overrides, it doesn't invalidate single-implementation
   // assumption.

   DCHECK((virtual_method != method_in_super) || virtual_method->IsAbstract());
   DCHECK(method_in_super->GetDeclaringClass()->IsResolved()) << "class isn't resolved";
   // If virtual_method doesn't come from a default interface method, it should
   // be supplied by klass.
   DCHECK(virtual_method == method_in_super ||
          virtual_method->IsCopied() ||
          virtual_method->GetDeclaringClass() == klass.Get());

   // To make updating single-implementation flags simple, we always maintain the following
   // invariant:
   // Say all virtual methods in the same vtable slot, starting from the bottom child class
   // to super classes, is a sequence of unique methods m3, m2, m1, ... (after removing duplicate
   // methods for inherited methods).
   // For example for the following class hierarchy,
   //   class A { void m() { ... } }
   //   class B extends A { void m() { ... } }
   //   class C extends B {}
   //   class D extends C { void m() { ... } }
   // the sequence is D.m(), B.m(), A.m().
   // The single-implementation status for that sequence of methods begin with one or two true's,
   // then become all falses. The only case where two true's are possible is for one abstract
   // method m and one non-abstract method mImpl that overrides method m.
   // With the invariant, when linking in a new class, we only need to at most update one or
   // two methods in the sequence for their single-implementation status, in order to maintain
   // the invariant.

   if (!method_in_super->HasSingleImplementation()) {
     // method_in_super already has multiple implementations. All methods in the
     // same vtable slots in its super classes should have
     // non-single-implementation already.
     if (kIsDebugBuild) {
       VerifyNonSingleImplementation(klass->GetSuperClass()->GetSuperClass(),
                                     method_in_super->GetMethodIndex(),
                                     nullptr /* excluded_method */);
     }
     return;
   }

   // Native methods don't have single-implementation flag set.
   DCHECK(!method_in_super->IsNative());

   uint16_t method_index = method_in_super->GetMethodIndex();
   if (method_in_super->IsAbstract()) {
     if (kIsDebugBuild) {
       // An abstract method should have made all methods in the same vtable
       // slot above it in the class hierarchy having non-single-implementation.
       mirror::Class* super_super = klass->GetSuperClass()->GetSuperClass();
       VerifyNonSingleImplementation(super_super,
                                     method_index,
                                     method_in_super);
     }

     if (virtual_method->IsAbstract()) {
       // SUPER: abstract, VIRTUAL: abstract.
       if (method_in_super == virtual_method) {
         DCHECK(klass->IsInstantiable());
         // An instantiable subclass hasn't provided a concrete implementation of
         // the abstract method. Invoking method_in_super may throw AbstractMethodError.
         // This is an uncommon case, so we simply treat method_in_super as not
         // having single-implementation.
         invalidated_single_impl_methods.insert(method_in_super);
         return;
       } else {
         // One abstract method overrides another abstract method. This is an uncommon
         // case. We simply treat method_in_super as not having single-implementation.
         invalidated_single_impl_methods.insert(method_in_super);
         return;
       }
     } else {
       // SUPER: abstract, VIRTUAL: non-abstract.
       // A non-abstract method overrides an abstract method.
       if (method_in_super->GetSingleImplementation(pointer_size) == nullptr) {
         // Abstract method_in_super has no implementation yet.
         // We need to grab cha_lock_ for further checking/updating due to possible
         // races.
         MutexLock cha_mu(Thread::Current(), *Locks::cha_lock_);
         if (!method_in_super->HasSingleImplementation()) {
           return;
         }
         if (method_in_super->GetSingleImplementation(pointer_size) == nullptr) {
           // virtual_method becomes the first implementation for method_in_super.
           method_in_super->SetSingleImplementation(virtual_method, pointer_size);
           // Keep method_in_super's single-implementation status.
           return;
         }
         // Fall through to invalidate method_in_super's single-implementation status.
       }
       // Abstract method_in_super already got one implementation.
       // Invalidate method_in_super's single-implementation status.
       invalidated_single_impl_methods.insert(method_in_super);
       return;
     }
   } else {
     if (virtual_method->IsAbstract()) {
       // SUPER: non-abstract, VIRTUAL: abstract.
       // An abstract method overrides a non-abstract method. This is an uncommon
       // case, we simply treat both methods as not having single-implementation.
       invalidated_single_impl_methods.insert(virtual_method);
       // Fall-through to handle invalidating method_in_super of its
       // single-implementation status.
     }

     // SUPER: non-abstract, VIRTUAL: non-abstract/abstract(fall-through from previous if).
     // Invalidate method_in_super's single-implementation status.
     invalidated_single_impl_methods.insert(method_in_super);

     // method_in_super might be the single-implementation of another abstract method,
     // which should be also invalidated of its single-implementation status.
     mirror::Class* super_super = klass->GetSuperClass()->GetSuperClass();
     while (super_super != nullptr &&
            method_index < super_super->GetVTableLength()) {
       ArtMethod* method_in_super_super = super_super->GetVTableEntry(method_index, pointer_size);
       if (method_in_super_super != method_in_super) {
         if (method_in_super_super->IsAbstract()) {
           if (method_in_super_super->HasSingleImplementation()) {
             // Invalidate method_in_super's single-implementation status.
             invalidated_single_impl_methods.insert(method_in_super_super);
             // No need to further traverse up the class hierarchy since if there
             // are cases that one abstract method overrides another method, we
             // should have made that method having non-single-implementation already.
           } else {
             // method_in_super_super is already non-single-implementation.
             // No need to further traverse up the class hierarchy.
           }
         } else {
           DCHECK(!method_in_super_super->HasSingleImplementation());
           // No need to further traverse up the class hierarchy since two non-abstract
           // methods (method_in_super and method_in_super_super) should have set all
           // other methods (abstract or not) in the vtable slot to be non-single-implementation.
         }

         if (kIsDebugBuild) {
           VerifyNonSingleImplementation(super_super->GetSuperClass(),
                                         method_index,
                                         method_in_super_super);
         }
         // No need to go any further.
         return;
       } else {
         super_super = super_super->GetSuperClass();
       }
     }
   }
 }

 void ClassHierarchyAnalysis::InitSingleImplementationFlag(Handle<mirror::Class> klass,
                                                           ArtMethod* method,
                                                           PointerSize pointer_size) {
   DCHECK(method->IsCopied() || method->GetDeclaringClass() == klass.Get());
   if (klass->IsFinal() || method->IsFinal()) {
     // Final classes or methods do not need CHA for devirtualization.
     // This frees up modifier bits for intrinsics which currently are only
     // used for static methods or methods of final classes.
     return;
   }
   if (method->IsNative()) {
     // Native method's invocation overhead is already high and it
     // cannot be inlined. It's not worthwhile to devirtualize the
     // call which can add a deoptimization point.
     DCHECK(!method->HasSingleImplementation());
   } else if (method->IsAbstract()) {
     if (method->GetDeclaringClass()->IsInstantiable()) {
       // Rare case, but we do accept it (such as 800-smali/smali/b_26143249.smali).
       // Do not attempt to devirtualize it.
       method->SetHasSingleImplementation(false);
     } else {
       // Abstract method starts with single-implementation flag set and null
       // implementation method.
       method->SetHasSingleImplementation(true);
       DCHECK(method->GetSingleImplementation(pointer_size) == nullptr);
     }
   } else {
     method->SetHasSingleImplementation(true);
     // Single implementation of non-abstract method is itself.
     DCHECK_EQ(method->GetSingleImplementation(pointer_size), method);
   }
 }

 void ClassHierarchyAnalysis::UpdateAfterLoadingOf(Handle<mirror::Class> klass) {
   if (klass->IsInterface()) {
     return;
   }
   mirror::Class* super_class = klass->GetSuperClass();
   if (super_class == nullptr) {
     return;
   }

   // Keeps track of all methods whose single-implementation assumption
   // is invalidated by linking `klass`.
   std::unordered_set<ArtMethod*> invalidated_single_impl_methods;

   PointerSize image_pointer_size = Runtime::Current()->GetClassLinker()->GetImagePointerSize();
   // Do an entry-by-entry comparison of vtable contents with super's vtable.
   for (int32_t i = 0; i < super_class->GetVTableLength(); ++i) {
     ArtMethod* method = klass->GetVTableEntry(i, image_pointer_size);
     ArtMethod* method_in_super = super_class->GetVTableEntry(i, image_pointer_size);
     if (method == method_in_super) {
       // vtable slot entry is inherited from super class.
       if (method->IsAbstract() && klass->IsInstantiable()) {
         // An instantiable class that inherits an abstract method is treated as
         // supplying an implementation that throws AbstractMethodError.
         CheckSingleImplementationInfo(klass,
                                       method,
                                       method_in_super,
                                       invalidated_single_impl_methods,
                                       image_pointer_size);
       }
       continue;
     }
     InitSingleImplementationFlag(klass, method, image_pointer_size);
     CheckSingleImplementationInfo(klass,
                                   method,
                                   method_in_super,
                                   invalidated_single_impl_methods,
                                   image_pointer_size);
   }

   // For new virtual methods that don't override.
   for (int32_t i = super_class->GetVTableLength(); i < klass->GetVTableLength(); ++i) {
     ArtMethod* method = klass->GetVTableEntry(i, image_pointer_size);
     InitSingleImplementationFlag(klass, method, image_pointer_size);
   }

   Runtime* const runtime = Runtime::Current();
   if (!invalidated_single_impl_methods.empty()) {
     Thread *self = Thread::Current();
     // Method headers for compiled code to be invalidated.
     std::unordered_set<OatQuickMethodHeader*> dependent_method_headers;

     {
       // We do this under cha_lock_. Committing code also grabs this lock to
       // make sure the code is only committed when all single-implementation
       // assumptions are still true.
       MutexLock cha_mu(self, *Locks::cha_lock_);
       // Invalidate compiled methods that assume some virtual calls have only
       // single implementations.
       for (ArtMethod* invalidated : invalidated_single_impl_methods) {
         if (!invalidated->HasSingleImplementation()) {
           // It might have been invalidated already when other class linking is
           // going on.
           continue;
         }
         invalidated->SetHasSingleImplementation(false);
         if (invalidated->IsAbstract()) {
           // Clear the single implementation method.
           invalidated->SetSingleImplementation(nullptr, image_pointer_size);
         }

         if (runtime->IsAotCompiler()) {
           // No need to invalidate any compiled code as the AotCompiler doesn't
           // run any code.
           continue;
         }

         // Invalidate all dependents.
         auto dependents = GetDependents(invalidated);
         if (dependents == nullptr) {
           continue;
         }
         for (const auto& dependent : *dependents) {
           ArtMethod* method = dependent.first;;
           OatQuickMethodHeader* method_header = dependent.second;
           VLOG(class_linker) << "CHA invalidated compiled code for " << method->PrettyMethod();
           DCHECK(runtime->UseJitCompilation());
           runtime->GetJit()->GetCodeCache()->InvalidateCompiledCodeFor(
               method, method_header);
           dependent_method_headers.insert(method_header);
         }
         RemoveDependencyFor(invalidated);
       }
     }

     if (dependent_method_headers.empty()) {
       return;
     }
     // Deoptimze compiled code on stack that should have been invalidated.
     CHACheckpoint checkpoint(dependent_method_headers);
     size_t threads_running_checkpoint = runtime->GetThreadList()->RunCheckpoint(&checkpoint);
     if (threads_running_checkpoint != 0) {
       checkpoint.WaitForThreadsToRunThroughCheckpoint(threads_running_checkpoint);
     }
   }
 }

 }  // namespace art
	/*
	* Copyright (C) 2016 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 "cha.h"

	#include "art_method-inl.h"
	#include "jit/jit.h"
	#include "jit/jit_code_cache.h"
	#include "runtime.h"
	#include "scoped_thread_state_change-inl.h"
	#include "stack.h"
	#include "thread.h"
	#include "thread_list.h"
	#include "thread_pool.h"

	namespace art {

	void ClassHierarchyAnalysis::AddDependency(ArtMethod* method,
	ArtMethod* dependent_method,
	OatQuickMethodHeader* dependent_header) {
	auto it = cha_dependency_map_.find(method);
	if (it == cha_dependency_map_.end()) {
	cha_dependency_map_[method] =
	new std::vector<std::pair<art::ArtMethod, art::OatQuickMethodHeader>>();
	it = cha_dependency_map_.find(method);
	} else {
	DCHECK(it->second != nullptr);
	}
	it->second->push_back(std::make_pair(dependent_method, dependent_header));
	}

	std::vector<std::pair<ArtMethod, OatQuickMethodHeader>>*
	ClassHierarchyAnalysis::GetDependents(ArtMethod* method) {
	auto it = cha_dependency_map_.find(method);
	if (it != cha_dependency_map_.end()) {
	DCHECK(it->second != nullptr);
	return it->second;
	}
	return nullptr;
	}

	void ClassHierarchyAnalysis::RemoveDependencyFor(ArtMethod* method) {
	auto it = cha_dependency_map_.find(method);
	if (it != cha_dependency_map_.end()) {
	auto dependents = it->second;
	cha_dependency_map_.erase(it);
	delete dependents;
	}
	}

	void ClassHierarchyAnalysis::RemoveDependentsWithMethodHeaders(
	const std::unordered_set<OatQuickMethodHeader*>& method_headers) {
	// Iterate through all entries in the dependency map and remove any entry that
	// contains one of those in method_headers.
	for (auto map_it = cha_dependency_map_.begin(); map_it != cha_dependency_map_.end(); ) {
	auto dependents = map_it->second;
	for (auto vec_it = dependents->begin(); vec_it != dependents->end(); ) {
	OatQuickMethodHeader* method_header = vec_it->second;
	auto it = std::find(method_headers.begin(), method_headers.end(), method_header);
	if (it != method_headers.end()) {
	vec_it = dependents->erase(vec_it);
	} else {
	vec_it++;
	}
	}
	// Remove the map entry if there are no more dependents.
	if (dependents->empty()) {
	map_it = cha_dependency_map_.erase(map_it);
	delete dependents;
	} else {
	map_it++;
	}
	}
	}

	// This stack visitor walks the stack and for compiled code with certain method
	// headers, sets the should_deoptimize flag on stack to 1.
	// TODO: also set the register value to 1 when should_deoptimize is allocated in
	// a register.
	class CHAStackVisitor FINAL : public StackVisitor {
	public:
	CHAStackVisitor(Thread* thread_in,
	Context* context,
	const std::unordered_set<OatQuickMethodHeader*>& method_headers)
	: StackVisitor(thread_in, context, StackVisitor::StackWalkKind::kSkipInlinedFrames),
	method_headers_(method_headers) {
	}

	bool VisitFrame() OVERRIDE REQUIRES_SHARED(Locks::mutator_lock_) {
	ArtMethod* method = GetMethod();
	// Avoid types of methods that do not have an oat quick method header.
	if (method == nullptr \|\|
	method->IsRuntimeMethod() \|\|
	method->IsNative() \|\|
	method->IsProxyMethod()) {
	return true;
	}
	if (GetCurrentQuickFrame() == nullptr) {
	// Not compiled code.
	return true;
	}
	// Method may have multiple versions of compiled code. Check
	// the method header to see if it has should_deoptimize flag.
	const OatQuickMethodHeader* method_header = GetCurrentOatQuickMethodHeader();
	DCHECK(method_header != nullptr);
	if (!method_header->HasShouldDeoptimizeFlag()) {
	// This compiled version doesn't have should_deoptimize flag. Skip.
	return true;
	}
	auto it = std::find(method_headers_.begin(), method_headers_.end(), method_header);
	if (it == method_headers_.end()) {
	// Not in the list of method headers that should be deoptimized.
	return true;
	}

	// The compiled code on stack is not valid anymore. Need to deoptimize.
	SetShouldDeoptimizeFlag();

	return true;
	}

	private:
	void SetShouldDeoptimizeFlag() REQUIRES_SHARED(Locks::mutator_lock_) {
	QuickMethodFrameInfo frame_info = GetCurrentQuickFrameInfo();
	size_t frame_size = frame_info.FrameSizeInBytes();
	uint8_t* sp = reinterpret_cast<uint8_t*>(GetCurrentQuickFrame());
	size_t core_spill_size = POPCOUNT(frame_info.CoreSpillMask()) *
	GetBytesPerGprSpillLocation(kRuntimeISA);
	size_t fpu_spill_size = POPCOUNT(frame_info.FpSpillMask()) *
	GetBytesPerFprSpillLocation(kRuntimeISA);
	size_t offset = frame_size - core_spill_size - fpu_spill_size - kShouldDeoptimizeFlagSize;
	uint8_t* should_deoptimize_addr = sp + offset;
	// Set deoptimization flag to 1.
	DCHECK(should_deoptimize_addr == 0 \|\| should_deoptimize_addr == 1);
	*should_deoptimize_addr = 1;
	}

	// Set of method headers for compiled code that should be deoptimized.
	const std::unordered_set<OatQuickMethodHeader*>& method_headers_;

	DISALLOW_COPY_AND_ASSIGN(CHAStackVisitor);
	};

	class CHACheckpoint FINAL : public Closure {
	public:
	explicit CHACheckpoint(const std::unordered_set<OatQuickMethodHeader*>& method_headers)
	: barrier_(0),
	method_headers_(method_headers) {}

	void Run(Thread* thread) OVERRIDE {
	// Note thread and self may not be equal if thread was already suspended at
	// the point of the request.
	Thread* self = Thread::Current();
	ScopedObjectAccess soa(self);
	CHAStackVisitor visitor(thread, nullptr, method_headers_);
	visitor.WalkStack();
	barrier_.Pass(self);
	}

	void WaitForThreadsToRunThroughCheckpoint(size_t threads_running_checkpoint) {
	Thread* self = Thread::Current();
	ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
	barrier_.Increment(self, threads_running_checkpoint);
	}

	private:
	// The barrier to be passed through and for the requestor to wait upon.
	Barrier barrier_;
	// List of method headers for invalidated compiled code.
	const std::unordered_set<OatQuickMethodHeader*>& method_headers_;

	DISALLOW_COPY_AND_ASSIGN(CHACheckpoint);
	};

	void ClassHierarchyAnalysis::VerifyNonSingleImplementation(mirror::Class* verify_class,
	uint16_t verify_index,
	ArtMethod* excluded_method) {
	// Grab cha_lock_ to make sure all single-implementation updates are seen.
	PointerSize image_pointer_size =
	Runtime::Current()->GetClassLinker()->GetImagePointerSize();
	MutexLock cha_mu(Thread::Current(), *Locks::cha_lock_);
	while (verify_class != nullptr) {
	if (verify_index >= verify_class->GetVTableLength()) {
	return;
	}
	ArtMethod* verify_method = verify_class->GetVTableEntry(verify_index, image_pointer_size);
	if (verify_method != excluded_method) {
	DCHECK(!verify_method->HasSingleImplementation())
	<< "class: " << verify_class->PrettyClass()
	<< " verify_method: " << verify_method->PrettyMethod(true);
	if (verify_method->IsAbstract()) {
	DCHECK(verify_method->GetSingleImplementation(image_pointer_size) == nullptr);
	}
	}
	verify_class = verify_class->GetSuperClass();
	}
	}

	void ClassHierarchyAnalysis::CheckSingleImplementationInfo(
	Handle<mirror::Class> klass,
	ArtMethod* virtual_method,
	ArtMethod* method_in_super,
	std::unordered_set<ArtMethod*>& invalidated_single_impl_methods,
	PointerSize pointer_size) {
	// TODO: if klass is not instantiable, virtual_method isn't invocable yet so
	// even if it overrides, it doesn't invalidate single-implementation
	// assumption.

	DCHECK((virtual_method != method_in_super) \|\| virtual_method->IsAbstract());
	DCHECK(method_in_super->GetDeclaringClass()->IsResolved()) << "class isn't resolved";
	// If virtual_method doesn't come from a default interface method, it should
	// be supplied by klass.
	DCHECK(virtual_method == method_in_super \|\|
	virtual_method->IsCopied() \|\|
	virtual_method->GetDeclaringClass() == klass.Get());

	// To make updating single-implementation flags simple, we always maintain the following
	// invariant:
	// Say all virtual methods in the same vtable slot, starting from the bottom child class
	// to super classes, is a sequence of unique methods m3, m2, m1, ... (after removing duplicate
	// methods for inherited methods).
	// For example for the following class hierarchy,
	// class A { void m() { ... } }
	// class B extends A { void m() { ... } }
	// class C extends B {}
	// class D extends C { void m() { ... } }
	// the sequence is D.m(), B.m(), A.m().
	// The single-implementation status for that sequence of methods begin with one or two true's,
	// then become all falses. The only case where two true's are possible is for one abstract
	// method m and one non-abstract method mImpl that overrides method m.
	// With the invariant, when linking in a new class, we only need to at most update one or
	// two methods in the sequence for their single-implementation status, in order to maintain
	// the invariant.

	if (!method_in_super->HasSingleImplementation()) {
	// method_in_super already has multiple implementations. All methods in the
	// same vtable slots in its super classes should have
	// non-single-implementation already.
	if (kIsDebugBuild) {
	VerifyNonSingleImplementation(klass->GetSuperClass()->GetSuperClass(),
	method_in_super->GetMethodIndex(),
	nullptr /* excluded_method */);
	}
	return;
	}

	// Native methods don't have single-implementation flag set.
	DCHECK(!method_in_super->IsNative());

	uint16_t method_index = method_in_super->GetMethodIndex();
	if (method_in_super->IsAbstract()) {
	if (kIsDebugBuild) {
	// An abstract method should have made all methods in the same vtable
	// slot above it in the class hierarchy having non-single-implementation.
	mirror::Class* super_super = klass->GetSuperClass()->GetSuperClass();
	VerifyNonSingleImplementation(super_super,
	method_index,
	method_in_super);
	}

	if (virtual_method->IsAbstract()) {
	// SUPER: abstract, VIRTUAL: abstract.
	if (method_in_super == virtual_method) {
	DCHECK(klass->IsInstantiable());
	// An instantiable subclass hasn't provided a concrete implementation of
	// the abstract method. Invoking method_in_super may throw AbstractMethodError.
	// This is an uncommon case, so we simply treat method_in_super as not
	// having single-implementation.
	invalidated_single_impl_methods.insert(method_in_super);
	return;
	} else {
	// One abstract method overrides another abstract method. This is an uncommon
	// case. We simply treat method_in_super as not having single-implementation.
	invalidated_single_impl_methods.insert(method_in_super);
	return;
	}
	} else {
	// SUPER: abstract, VIRTUAL: non-abstract.
	// A non-abstract method overrides an abstract method.
	if (method_in_super->GetSingleImplementation(pointer_size) == nullptr) {
	// Abstract method_in_super has no implementation yet.
	// We need to grab cha_lock_ for further checking/updating due to possible
	// races.
	MutexLock cha_mu(Thread::Current(), *Locks::cha_lock_);
	if (!method_in_super->HasSingleImplementation()) {
	return;
	}
	if (method_in_super->GetSingleImplementation(pointer_size) == nullptr) {
	// virtual_method becomes the first implementation for method_in_super.
	method_in_super->SetSingleImplementation(virtual_method, pointer_size);
	// Keep method_in_super's single-implementation status.
	return;
	}
	// Fall through to invalidate method_in_super's single-implementation status.
	}
	// Abstract method_in_super already got one implementation.
	// Invalidate method_in_super's single-implementation status.
	invalidated_single_impl_methods.insert(method_in_super);
	return;
	}
	} else {
	if (virtual_method->IsAbstract()) {
	// SUPER: non-abstract, VIRTUAL: abstract.
	// An abstract method overrides a non-abstract method. This is an uncommon
	// case, we simply treat both methods as not having single-implementation.
	invalidated_single_impl_methods.insert(virtual_method);
	// Fall-through to handle invalidating method_in_super of its
	// single-implementation status.
	}

	// SUPER: non-abstract, VIRTUAL: non-abstract/abstract(fall-through from previous if).
	// Invalidate method_in_super's single-implementation status.
	invalidated_single_impl_methods.insert(method_in_super);

	// method_in_super might be the single-implementation of another abstract method,
	// which should be also invalidated of its single-implementation status.
	mirror::Class* super_super = klass->GetSuperClass()->GetSuperClass();
	while (super_super != nullptr &&
	method_index < super_super->GetVTableLength()) {
	ArtMethod* method_in_super_super = super_super->GetVTableEntry(method_index, pointer_size);
	if (method_in_super_super != method_in_super) {
	if (method_in_super_super->IsAbstract()) {
	if (method_in_super_super->HasSingleImplementation()) {
	// Invalidate method_in_super's single-implementation status.
	invalidated_single_impl_methods.insert(method_in_super_super);
	// No need to further traverse up the class hierarchy since if there
	// are cases that one abstract method overrides another method, we
	// should have made that method having non-single-implementation already.
	} else {
	// method_in_super_super is already non-single-implementation.
	// No need to further traverse up the class hierarchy.
	}
	} else {
	DCHECK(!method_in_super_super->HasSingleImplementation());
	// No need to further traverse up the class hierarchy since two non-abstract
	// methods (method_in_super and method_in_super_super) should have set all
	// other methods (abstract or not) in the vtable slot to be non-single-implementation.
	}

	if (kIsDebugBuild) {
	VerifyNonSingleImplementation(super_super->GetSuperClass(),
	method_index,
	method_in_super_super);
	}
	// No need to go any further.
	return;
	} else {
	super_super = super_super->GetSuperClass();
	}
	}
	}
	}

	void ClassHierarchyAnalysis::InitSingleImplementationFlag(Handle<mirror::Class> klass,
	ArtMethod* method,
	PointerSize pointer_size) {
	DCHECK(method->IsCopied() \|\| method->GetDeclaringClass() == klass.Get());
	if (klass->IsFinal() \|\| method->IsFinal()) {
	// Final classes or methods do not need CHA for devirtualization.
	// This frees up modifier bits for intrinsics which currently are only
	// used for static methods or methods of final classes.
	return;
	}
	if (method->IsNative()) {
	// Native method's invocation overhead is already high and it
	// cannot be inlined. It's not worthwhile to devirtualize the
	// call which can add a deoptimization point.
	DCHECK(!method->HasSingleImplementation());
	} else if (method->IsAbstract()) {
	if (method->GetDeclaringClass()->IsInstantiable()) {
	// Rare case, but we do accept it (such as 800-smali/smali/b_26143249.smali).
	// Do not attempt to devirtualize it.
	method->SetHasSingleImplementation(false);
	} else {
	// Abstract method starts with single-implementation flag set and null
	// implementation method.
	method->SetHasSingleImplementation(true);
	DCHECK(method->GetSingleImplementation(pointer_size) == nullptr);
	}
	} else {
	method->SetHasSingleImplementation(true);
	// Single implementation of non-abstract method is itself.
	DCHECK_EQ(method->GetSingleImplementation(pointer_size), method);
	}
	}

	void ClassHierarchyAnalysis::UpdateAfterLoadingOf(Handle<mirror::Class> klass) {
	if (klass->IsInterface()) {
	return;
	}
	mirror::Class* super_class = klass->GetSuperClass();
	if (super_class == nullptr) {
	return;
	}

	// Keeps track of all methods whose single-implementation assumption
	// is invalidated by linking `klass`.
	std::unordered_set<ArtMethod*> invalidated_single_impl_methods;

	PointerSize image_pointer_size = Runtime::Current()->GetClassLinker()->GetImagePointerSize();
	// Do an entry-by-entry comparison of vtable contents with super's vtable.
	for (int32_t i = 0; i < super_class->GetVTableLength(); ++i) {
	ArtMethod* method = klass->GetVTableEntry(i, image_pointer_size);
	ArtMethod* method_in_super = super_class->GetVTableEntry(i, image_pointer_size);
	if (method == method_in_super) {
	// vtable slot entry is inherited from super class.
	if (method->IsAbstract() && klass->IsInstantiable()) {
	// An instantiable class that inherits an abstract method is treated as
	// supplying an implementation that throws AbstractMethodError.
	CheckSingleImplementationInfo(klass,
	method,
	method_in_super,
	invalidated_single_impl_methods,
	image_pointer_size);
	}
	continue;
	}
	InitSingleImplementationFlag(klass, method, image_pointer_size);
	CheckSingleImplementationInfo(klass,
	method,
	method_in_super,
	invalidated_single_impl_methods,
	image_pointer_size);
	}

	// For new virtual methods that don't override.
	for (int32_t i = super_class->GetVTableLength(); i < klass->GetVTableLength(); ++i) {
	ArtMethod* method = klass->GetVTableEntry(i, image_pointer_size);
	InitSingleImplementationFlag(klass, method, image_pointer_size);
	}

	Runtime* const runtime = Runtime::Current();
	if (!invalidated_single_impl_methods.empty()) {
	Thread *self = Thread::Current();
	// Method headers for compiled code to be invalidated.
	std::unordered_set<OatQuickMethodHeader*> dependent_method_headers;

	{
	// We do this under cha_lock_. Committing code also grabs this lock to
	// make sure the code is only committed when all single-implementation
	// assumptions are still true.
	MutexLock cha_mu(self, *Locks::cha_lock_);
	// Invalidate compiled methods that assume some virtual calls have only
	// single implementations.
	for (ArtMethod* invalidated : invalidated_single_impl_methods) {
	if (!invalidated->HasSingleImplementation()) {
	// It might have been invalidated already when other class linking is
	// going on.
	continue;
	}
	invalidated->SetHasSingleImplementation(false);
	if (invalidated->IsAbstract()) {
	// Clear the single implementation method.
	invalidated->SetSingleImplementation(nullptr, image_pointer_size);
	}

	if (runtime->IsAotCompiler()) {
	// No need to invalidate any compiled code as the AotCompiler doesn't
	// run any code.
	continue;
	}

	// Invalidate all dependents.
	auto dependents = GetDependents(invalidated);
	if (dependents == nullptr) {
	continue;
	}
	for (const auto& dependent : *dependents) {
	ArtMethod* method = dependent.first;;
	OatQuickMethodHeader* method_header = dependent.second;
	VLOG(class_linker) << "CHA invalidated compiled code for " << method->PrettyMethod();
	DCHECK(runtime->UseJitCompilation());
	runtime->GetJit()->GetCodeCache()->InvalidateCompiledCodeFor(
	method, method_header);
	dependent_method_headers.insert(method_header);
	}
	RemoveDependencyFor(invalidated);
	}
	}

	if (dependent_method_headers.empty()) {
	return;
	}
	// Deoptimze compiled code on stack that should have been invalidated.
	CHACheckpoint checkpoint(dependent_method_headers);
	size_t threads_running_checkpoint = runtime->GetThreadList()->RunCheckpoint(&checkpoint);
	if (threads_running_checkpoint != 0) {
	checkpoint.WaitForThreadsToRunThroughCheckpoint(threads_running_checkpoint);
	}
	}
	}

	} // namespace art