1 /*
2 * Copyright (C) 2017 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 #include "slicer/control_flow_graph.h"
18 #include "slicer/chronometer.h"
19
20 namespace lir {
21
Finish()22 std::vector<BasicBlock> BasicBlocksVisitor::Finish() {
23 // the .dex format specification has the following constraint:
24 //
25 // B17 The last reachable instruction of a method must either be a
26 // backwards goto or branch, a return, or a throw instruction. It must not
27 // be possible to leave the insns array at the bottom. 4.8.2.20
28 //
29 // NOTE: this is a very aggressive check though since in the LIR we also
30 // have labels, annotations, directives, etc. For example it's possible to have
31 // debug annotations (.line, .endlocal, ...) after the last bytecode.
32 //
33 SLICER_WEAK_CHECK(state_ == State::Outside);
34 SLICER_CHECK(state_ != State::BlockBody);
35 current_block_.region = {};
36 state_ = State::Outside;
37 return std::move(basic_blocks_);
38 }
39
Visit(Bytecode * bytecode)40 bool BasicBlocksVisitor::Visit(Bytecode* bytecode) {
41 switch (state_) {
42 case State::Outside:
43 StartBlock(bytecode);
44 state_ = State::BlockBody;
45 break;
46 case State::BlockHeader:
47 state_ = State::BlockBody;
48 break;
49 case State::BlockBody:
50 // inside basic block body, nothing to do.
51 break;
52 }
53
54 // terminate the current block?
55 bool terminate_block = false;
56 const auto flags = dex::GetFlagsFromOpcode(bytecode->opcode);
57 if (model_exceptions_) {
58 constexpr auto exit_instr_flags =
59 dex::kBranch |
60 dex::kSwitch |
61 dex::kThrow |
62 dex::kReturn;
63 terminate_block = (flags & exit_instr_flags) != 0;
64 } else {
65 constexpr auto exit_instr_flags =
66 dex::kBranch |
67 dex::kSwitch |
68 dex::kReturn;
69 terminate_block = bytecode->opcode == dex::OP_THROW || (flags & exit_instr_flags) != 0;
70 }
71 if (terminate_block) {
72 EndBlock(bytecode);
73 }
74
75 return true;
76 }
77
Visit(Label * label)78 bool BasicBlocksVisitor::Visit(Label* label) {
79 switch (state_) {
80 case State::Outside:
81 StartBlock(label);
82 break;
83 case State::BlockBody:
84 EndBlock(label->prev);
85 StartBlock(label);
86 break;
87 case State::BlockHeader:
88 break;
89 }
90 return true;
91 }
92
HandleAnnotation(Instruction * instr)93 bool BasicBlocksVisitor::HandleAnnotation(Instruction* instr) {
94 if (state_ == State::Outside) {
95 StartBlock(instr);
96 }
97 return true;
98 }
99
SkipInstruction(Instruction * instr)100 bool BasicBlocksVisitor::SkipInstruction(Instruction* instr) {
101 if (state_ != State::Outside) {
102 EndBlock(instr->prev);
103 }
104 return true;
105 }
106
StartBlock(Instruction * instr)107 void BasicBlocksVisitor::StartBlock(Instruction* instr) {
108 assert(instr != nullptr);
109 assert(state_ == State::Outside);
110 // mark the location of the "first" instruction,
111 // "last" will be set when we end the basic block.
112 current_block_.region.first = instr;
113 current_block_.region.last = nullptr;
114 state_ = State::BlockHeader;
115 }
116
EndBlock(Instruction * instr)117 void BasicBlocksVisitor::EndBlock(Instruction* instr) {
118 assert(instr != nullptr);
119 if (state_ == State::BlockBody) {
120 ++current_block_.id;
121 assert(current_block_.region.first != nullptr);
122 current_block_.region.last = instr;
123 basic_blocks_.push_back(current_block_);
124 } else {
125 assert(state_ == State::BlockHeader);
126 }
127 current_block_.region = {};
128 state_ = State::Outside;
129 }
130
CreateBasicBlocks(bool model_exceptions)131 void ControlFlowGraph::CreateBasicBlocks(bool model_exceptions) {
132 BasicBlocksVisitor visitor(model_exceptions);
133 for (auto instr : code_ir->instructions) {
134 instr->Accept(&visitor);
135 }
136 basic_blocks = visitor.Finish();
137 }
138
139 } // namespace lir
140