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_COMPILER_OPTIMIZING_ESCAPE_H_
18 #define ART_COMPILER_OPTIMIZING_ESCAPE_H_
19
20 namespace art {
21
22 class HInstruction;
23
24 /*
25 * Methods related to escape analysis, i.e. determining whether an object
26 * allocation is visible outside ('escapes') its immediate method context.
27 */
28
29 // A visitor for seeing all instructions escape analysis considers escaping.
30 // Called with each user of the reference passed to 'VisitEscapes'. Return true
31 // to continue iteration and false to stop.
32 class EscapeVisitor {
33 public:
~EscapeVisitor()34 virtual ~EscapeVisitor() {}
35 virtual bool Visit(HInstruction* escape) = 0;
operator()36 bool operator()(HInstruction* user) {
37 return Visit(user);
38 }
39 };
40
41 // An explicit EscapeVisitor for lambdas
42 template <typename F>
43 class LambdaEscapeVisitor final : public EscapeVisitor {
44 public:
LambdaEscapeVisitor(F f)45 explicit LambdaEscapeVisitor(F f) : func_(f) {}
Visit(HInstruction * escape)46 bool Visit(HInstruction* escape) override {
47 return func_(escape);
48 }
49
50 private:
51 F func_;
52 };
53
54 // This functor is used with the escape-checking functions. If the NoEscape
55 // function returns true escape analysis will consider 'user' to not have
56 // escaped 'reference'. This allows clients with additional information to
57 // supplement the escape-analysis. If the NoEscape function returns false then
58 // the normal escape-checking code will be used to determine whether or not
59 // 'reference' escapes.
60 class NoEscapeCheck {
61 public:
~NoEscapeCheck()62 virtual ~NoEscapeCheck() {}
63 virtual bool NoEscape(HInstruction* reference, HInstruction* user) = 0;
operator()64 bool operator()(HInstruction* ref, HInstruction* user) {
65 return NoEscape(ref, user);
66 }
67 };
68
69 // An explicit NoEscapeCheck for use with c++ lambdas.
70 template <typename F>
71 class LambdaNoEscapeCheck final : public NoEscapeCheck {
72 public:
LambdaNoEscapeCheck(F f)73 explicit LambdaNoEscapeCheck(F f) : func_(f) {}
NoEscape(HInstruction * ref,HInstruction * user)74 bool NoEscape(HInstruction* ref, HInstruction* user) override {
75 return func_(ref, user);
76 }
77
78 private:
79 F func_;
80 };
81
82 /*
83 * Performs escape analysis on the given instruction, typically a reference to an
84 * allocation. The method assigns true to parameter 'is_singleton' if the reference
85 * is the only name that can refer to its value during the lifetime of the method,
86 * meaning that the reference is not aliased with something else, is not stored to
87 * heap memory, and not passed to another method. In addition, the method assigns
88 * true to parameter 'is_singleton_and_not_returned' if the reference is a singleton
89 * and not returned to the caller and to parameter 'is_singleton_and_not_deopt_visible'
90 * if the reference is a singleton and not used as an environment local of an
91 * HDeoptimize instruction (clients of the final value must run after BCE to ensure
92 * all such instructions have been introduced already).
93 *
94 * Note that being visible to a HDeoptimize instruction does not count for ordinary
95 * escape analysis, since switching between compiled code and interpreted code keeps
96 * non escaping references restricted to the lifetime of the method and the thread
97 * executing it. This property only concerns optimizations that are interested in
98 * escape analysis with respect to the *compiled* code (such as LSE).
99 *
100 * When set, the no_escape function is applied to any use of the allocation instruction
101 * prior to any built-in escape analysis. This allows clients to define better escape
102 * analysis in certain case-specific circumstances. If 'no_escape(reference, user)'
103 * returns true, the user is assumed *not* to cause any escape right away. The return
104 * value false means the client cannot provide a definite answer and built-in escape
105 * analysis is applied to the user instead.
106 */
107 void CalculateEscape(HInstruction* reference,
108 NoEscapeCheck& no_escape,
109 /*out*/ bool* is_singleton,
110 /*out*/ bool* is_singleton_and_not_returned,
111 /*out*/ bool* is_singleton_and_not_deopt_visible);
112
CalculateEscape(HInstruction * reference,bool (* no_escape_fn)(HInstruction *,HInstruction *),bool * is_singleton,bool * is_singleton_and_not_returned,bool * is_singleton_and_not_deopt_visible)113 inline void CalculateEscape(HInstruction* reference,
114 bool (*no_escape_fn)(HInstruction*, HInstruction*),
115 /*out*/ bool* is_singleton,
116 /*out*/ bool* is_singleton_and_not_returned,
117 /*out*/ bool* is_singleton_and_not_deopt_visible) {
118 LambdaNoEscapeCheck esc(no_escape_fn);
119 LambdaNoEscapeCheck noop_esc([](HInstruction*, HInstruction*) { return false; });
120 CalculateEscape(reference,
121 no_escape_fn == nullptr ? static_cast<NoEscapeCheck&>(noop_esc) : esc,
122 is_singleton,
123 is_singleton_and_not_returned,
124 is_singleton_and_not_deopt_visible);
125 }
126
127 /*
128 * Performs escape analysis and visits each escape of the reference. Does not try to calculate any
129 * overall information about the method. Escapes are calculated in the same way as CalculateEscape.
130 *
131 * The escape_visitor should return true to continue visiting, false otherwise.
132 */
133 void VisitEscapes(HInstruction* reference, EscapeVisitor& escape_visitor);
134
135 /*
136 * Convenience method for testing the singleton and not returned properties at once.
137 * Callers should be aware that this method invokes the full analysis at each call.
138 */
139 bool DoesNotEscape(HInstruction* reference, NoEscapeCheck& no_escape);
140
DoesNotEscape(HInstruction * reference,bool (* no_escape_fn)(HInstruction *,HInstruction *))141 inline bool DoesNotEscape(HInstruction* reference,
142 bool (*no_escape_fn)(HInstruction*, HInstruction*)) {
143 LambdaNoEscapeCheck<typeof(no_escape_fn)> esc(no_escape_fn);
144 return DoesNotEscape(reference, esc);
145 }
146
147 } // namespace art
148
149 #endif // ART_COMPILER_OPTIMIZING_ESCAPE_H_
150