1/*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ART_RUNTIME_CHA_H_
18#define ART_RUNTIME_CHA_H_
19
20#include <unordered_map>
21#include <unordered_set>
22
23#include "base/enums.h"
24#include "base/mutex.h"
25#include "handle.h"
26#include "mirror/class.h"
27#include "oat_quick_method_header.h"
28
29namespace art {
30
31class ArtMethod;
32class LinearAlloc;
33
34/**
35 * Class Hierarchy Analysis (CHA) tries to devirtualize virtual calls into
36 * direct calls based on the info generated by analyzing class hierarchies.
37 * If a class is not subclassed, or even if it's subclassed but one of its
38 * virtual methods isn't overridden, a virtual call for that method can be
39 * changed into a direct call.
40 *
41 * Each virtual method carries a single-implementation status. The status is
42 * incrementally maintained at the end of class linking time when method
43 * overriding takes effect.
44 *
45 * Compiler takes advantage of the single-implementation info of a
46 * method. If a method A has the single-implementation flag set, the compiler
47 * devirtualizes the virtual call for method A into a direct call, and
48 * further try to inline the direct call as a result. The compiler will
49 * also register a dependency that the compiled code depends on the
50 * assumption that method A has single-implementation status.
51 *
52 * When single-implementation info is updated at the end of class linking,
53 * and if method A's single-implementation status is invalidated, all compiled
54 * code that depends on the assumption that method A has single-implementation
55 * status need to be invalidated. Method entrypoints that have this dependency
56 * will be updated as a result. Method A can later be recompiled with less
57 * aggressive assumptions.
58 *
59 * For live compiled code that's on stack, deoptmization will be initiated
60 * to force the invalidated compiled code into interpreter mode to guarantee
61 * correctness. The deoptimization mechanism used is a hybrid of
62 * synchronous and asynchronous deoptimization. The synchronous deoptimization
63 * part checks a hidden local variable flag for the method, and if true,
64 * initiates deoptimization. The asynchronous deoptimization part issues a
65 * checkpoint that walks the stack and for any compiled code on the stack
66 * that should be deoptimized, set the hidden local variable value to be true.
67 *
68 * A cha_lock_ needs to be held for updating single-implementation status,
69 * and registering/unregistering CHA dependencies. Registering CHA dependency
70 * and making compiled code visible also need to be atomic. Otherwise, we
71 * may miss invalidating CHA dependents or making compiled code visible even
72 * after it is invalidated. Care needs to be taken between cha_lock_ and
73 * JitCodeCache::lock_ to guarantee the atomicity.
74 *
75 * We base our CHA on dynamically linked class profiles instead of doing static
76 * analysis. Static analysis can be too aggressive due to dynamic class loading
77 * at runtime, and too conservative since some classes may not be really loaded
78 * at runtime.
79 */
80class ClassHierarchyAnalysis {
81 public:
82  // Types for recording CHA dependencies.
83  // For invalidating CHA dependency, we need to know both the ArtMethod and
84  // the method header. If the ArtMethod has compiled code with the method header
85  // as the entrypoint, we update the entrypoint to the interpreter bridge.
86  // We will also deoptimize frames that are currently executing the code of
87  // the method header.
88  typedef std::pair<ArtMethod*, OatQuickMethodHeader*> MethodAndMethodHeaderPair;
89  typedef std::vector<MethodAndMethodHeaderPair> ListOfDependentPairs;
90
91  ClassHierarchyAnalysis() {}
92
93  // Add a dependency that compiled code with `dependent_header` for `dependent_method`
94  // assumes that virtual `method` has single-implementation.
95  void AddDependency(ArtMethod* method,
96                     ArtMethod* dependent_method,
97                     OatQuickMethodHeader* dependent_header) REQUIRES(Locks::cha_lock_);
98
99  // Return compiled code that assumes that `method` has single-implementation.
100  const ListOfDependentPairs& GetDependents(ArtMethod* method) REQUIRES(Locks::cha_lock_);
101
102  // Remove dependency tracking for compiled code that assumes that
103  // `method` has single-implementation.
104  void RemoveAllDependenciesFor(ArtMethod* method) REQUIRES(Locks::cha_lock_);
105
106  // Remove from cha_dependency_map_ all entries that contain OatQuickMethodHeader from
107  // the given `method_headers` set.
108  // This is used when some compiled code is freed.
109  void RemoveDependentsWithMethodHeaders(
110      const std::unordered_set<OatQuickMethodHeader*>& method_headers)
111      REQUIRES(Locks::cha_lock_);
112
113  // If a given class belongs to a linear allocation that is about to be deleted, in all its
114  // superclasses and superinterfaces reset SingleImplementation fields of their methods
115  // that might be affected by the deletion.
116  // The method is intended to be called during GC before ReclaimPhase, since it gets info from
117  // Java objects that are going to be collected.
118  // For the same reason it's important to access objects without read barrier to not revive them.
119  void ResetSingleImplementationInHierarchy(ObjPtr<mirror::Class> klass,
120                                            const LinearAlloc* alloc,
121                                            PointerSize pointer_size)
122      const REQUIRES_SHARED(Locks::mutator_lock_);
123
124  // Update CHA info for methods that `klass` overrides, after loading `klass`.
125  void UpdateAfterLoadingOf(Handle<mirror::Class> klass) REQUIRES_SHARED(Locks::mutator_lock_);
126
127  // Remove all of the dependencies for a linear allocator. This is called when dex cache unloading
128  // occurs.
129  void RemoveDependenciesForLinearAlloc(const LinearAlloc* linear_alloc)
130      REQUIRES(!Locks::cha_lock_);
131
132 private:
133  void InitSingleImplementationFlag(Handle<mirror::Class> klass,
134                                    ArtMethod* method,
135                                    PointerSize pointer_size)
136      REQUIRES_SHARED(Locks::mutator_lock_);
137
138  // Check/update single-implementation info when one virtual method
139  // overrides another.
140  // `virtual_method` in `klass` overrides `method_in_super`.
141  // This may invalidate some assumptions on single-implementation.
142  // Append methods that should have their single-implementation flag invalidated
143  // to `invalidated_single_impl_methods`.
144  void CheckVirtualMethodSingleImplementationInfo(
145      Handle<mirror::Class> klass,
146      ArtMethod* virtual_method,
147      ArtMethod* method_in_super,
148      std::unordered_set<ArtMethod*>& invalidated_single_impl_methods,
149      PointerSize pointer_size)
150      REQUIRES_SHARED(Locks::mutator_lock_);
151
152  // Check/update single-implementation info when one method
153  // implements an interface method.
154  // `implementation_method` in `klass` implements `interface_method`.
155  // Append `interface_method` to `invalidated_single_impl_methods`
156  // if `interface_method` gets a new implementation.
157  void CheckInterfaceMethodSingleImplementationInfo(
158      Handle<mirror::Class> klass,
159      ArtMethod* interface_method,
160      ArtMethod* implementation_method,
161      std::unordered_set<ArtMethod*>& invalidated_single_impl_methods,
162      PointerSize pointer_size)
163      REQUIRES_SHARED(Locks::mutator_lock_);
164
165  void InvalidateSingleImplementationMethods(
166      std::unordered_set<ArtMethod*>& invalidated_single_impl_methods)
167      REQUIRES_SHARED(Locks::mutator_lock_);
168
169  // A map that maps a method to a set of compiled code that assumes that method has a
170  // single implementation, which is used to do CHA-based devirtualization.
171  std::unordered_map<ArtMethod*, ListOfDependentPairs> cha_dependency_map_
172    GUARDED_BY(Locks::cha_lock_);
173
174  DISALLOW_COPY_AND_ASSIGN(ClassHierarchyAnalysis);
175};
176
177}  // namespace art
178
179#endif  // ART_RUNTIME_CHA_H_
180