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1 : // Copyright 2015 the V8 project authors. All rights reserved.
2 : // Use of this source code is governed by a BSD-style license that can be
3 : // found in the LICENSE file.
4 :
5 : #ifndef V8_COMPILER_BACKEND_INSTRUCTION_SCHEDULER_H_
6 : #define V8_COMPILER_BACKEND_INSTRUCTION_SCHEDULER_H_
7 :
8 : #include "src/compiler/backend/instruction.h"
9 : #include "src/zone/zone-containers.h"
10 :
11 : namespace v8 {
12 : namespace internal {
13 : namespace compiler {
14 :
15 : // A set of flags describing properties of the instructions so that the
16 : // scheduler is aware of dependencies between instructions.
17 : enum ArchOpcodeFlags {
18 : kNoOpcodeFlags = 0,
19 : kHasSideEffect = 1, // The instruction has some side effects (memory
20 : // store, function call...)
21 : kIsLoadOperation = 2, // The instruction is a memory load.
22 : kMayNeedDeoptOrTrapCheck = 4, // The instruction may be associated with a
23 : // deopt or trap check which must be run before
24 : // instruction e.g. div on Intel platform which
25 : // will raise an exception when the divisor is
26 : // zero.
27 : };
28 :
29 5 : class InstructionScheduler final : public ZoneObject {
30 : public:
31 : InstructionScheduler(Zone* zone, InstructionSequence* sequence);
32 :
33 : void StartBlock(RpoNumber rpo);
34 : void EndBlock(RpoNumber rpo);
35 :
36 : void AddInstruction(Instruction* instr);
37 : void AddTerminator(Instruction* instr);
38 :
39 : static bool SchedulerSupported();
40 :
41 : private:
42 : // A scheduling graph node.
43 : // Represent an instruction and their dependencies.
44 : class ScheduleGraphNode : public ZoneObject {
45 : public:
46 : ScheduleGraphNode(Zone* zone, Instruction* instr);
47 :
48 : // Mark the instruction represented by 'node' as a dependecy of this one.
49 : // The current instruction will be registered as an unscheduled predecessor
50 : // of 'node' (i.e. it must be scheduled before 'node').
51 : void AddSuccessor(ScheduleGraphNode* node);
52 :
53 : // Check if all the predecessors of this instruction have been scheduled.
54 : bool HasUnscheduledPredecessor() {
55 : return unscheduled_predecessors_count_ != 0;
56 : }
57 :
58 : // Record that we have scheduled one of the predecessors of this node.
59 : void DropUnscheduledPredecessor() {
60 : DCHECK_LT(0, unscheduled_predecessors_count_);
61 392522 : unscheduled_predecessors_count_--;
62 : }
63 :
64 : Instruction* instruction() { return instr_; }
65 : ZoneDeque<ScheduleGraphNode*>& successors() { return successors_; }
66 : int latency() const { return latency_; }
67 :
68 : int total_latency() const { return total_latency_; }
69 342935 : void set_total_latency(int latency) { total_latency_ = latency; }
70 :
71 : int start_cycle() const { return start_cycle_; }
72 392522 : void set_start_cycle(int start_cycle) { start_cycle_ = start_cycle; }
73 :
74 : private:
75 : Instruction* instr_;
76 : ZoneDeque<ScheduleGraphNode*> successors_;
77 :
78 : // Number of unscheduled predecessors for this node.
79 : int unscheduled_predecessors_count_;
80 :
81 : // Estimate of the instruction latency (the number of cycles it takes for
82 : // instruction to complete).
83 : int latency_;
84 :
85 : // The sum of all the latencies on the path from this node to the end of
86 : // the graph (i.e. a node with no successor).
87 : int total_latency_;
88 :
89 : // The scheduler keeps a nominal cycle count to keep track of when the
90 : // result of an instruction is available. This field is updated by the
91 : // scheduler to indicate when the value of all the operands of this
92 : // instruction will be available.
93 : int start_cycle_;
94 : };
95 :
96 : // Keep track of all nodes ready to be scheduled (i.e. all their dependencies
97 : // have been scheduled. Note that this class is inteded to be extended by
98 : // concrete implementation of the scheduling queue which define the policy
99 : // to pop node from the queue.
100 134753 : class SchedulingQueueBase {
101 : public:
102 : explicit SchedulingQueueBase(InstructionScheduler* scheduler)
103 134753 : : scheduler_(scheduler), nodes_(scheduler->zone()) {}
104 :
105 : void AddNode(ScheduleGraphNode* node);
106 :
107 : bool IsEmpty() const { return nodes_.empty(); }
108 :
109 : protected:
110 : InstructionScheduler* scheduler_;
111 : ZoneLinkedList<ScheduleGraphNode*> nodes_;
112 : };
113 :
114 : // A scheduling queue which prioritize nodes on the critical path (we look
115 : // for the instruction with the highest latency on the path to reach the end
116 : // of the graph).
117 134753 : class CriticalPathFirstQueue : public SchedulingQueueBase {
118 : public:
119 : explicit CriticalPathFirstQueue(InstructionScheduler* scheduler)
120 : : SchedulingQueueBase(scheduler) {}
121 :
122 : // Look for the best candidate to schedule, remove it from the queue and
123 : // return it.
124 : ScheduleGraphNode* PopBestCandidate(int cycle);
125 : };
126 :
127 : // A queue which pop a random node from the queue to perform stress tests on
128 : // the scheduler.
129 0 : class StressSchedulerQueue : public SchedulingQueueBase {
130 : public:
131 : explicit StressSchedulerQueue(InstructionScheduler* scheduler)
132 : : SchedulingQueueBase(scheduler) {}
133 :
134 : ScheduleGraphNode* PopBestCandidate(int cycle);
135 :
136 : private:
137 : Isolate* isolate() { return scheduler_->isolate(); }
138 : };
139 :
140 : // Perform scheduling for the current block specifying the queue type to
141 : // use to determine the next best candidate.
142 : template <typename QueueType>
143 : void ScheduleBlock();
144 :
145 : // Return the scheduling properties of the given instruction.
146 : int GetInstructionFlags(const Instruction* instr) const;
147 : int GetTargetInstructionFlags(const Instruction* instr) const;
148 :
149 : // Check whether the given instruction has side effects (e.g. function call,
150 : // memory store).
151 : bool HasSideEffect(const Instruction* instr) const {
152 201839 : return (GetInstructionFlags(instr) & kHasSideEffect) != 0;
153 : }
154 :
155 : // Return true if the instruction is a memory load.
156 : bool IsLoadOperation(const Instruction* instr) const {
157 128233 : return (GetInstructionFlags(instr) & kIsLoadOperation) != 0;
158 : }
159 :
160 : // The scheduler will not move the following instructions before the last
161 : // deopt/trap check:
162 : // * loads (this is conservative)
163 : // * instructions with side effect
164 : // * other deopts/traps
165 : // Any other instruction can be moved, apart from those that raise exceptions
166 : // on specific inputs - these are filtered out by the deopt/trap check.
167 : bool MayNeedDeoptOrTrapCheck(const Instruction* instr) const {
168 10 : return (GetInstructionFlags(instr) & kMayNeedDeoptOrTrapCheck) != 0;
169 : }
170 :
171 : // Return true if the instruction cannot be moved before the last deopt or
172 : // trap point we encountered.
173 10 : bool DependsOnDeoptOrTrap(const Instruction* instr) const {
174 15 : return MayNeedDeoptOrTrapCheck(instr) || instr->IsDeoptimizeCall() ||
175 15 : instr->IsTrap() || HasSideEffect(instr) || IsLoadOperation(instr);
176 : }
177 :
178 : // Identify nops used as a definition point for live-in registers at
179 : // function entry.
180 208182 : bool IsFixedRegisterParameter(const Instruction* instr) const {
181 101646 : return (instr->arch_opcode() == kArchNop) && (instr->OutputCount() == 1) &&
182 222790 : (instr->OutputAt(0)->IsUnallocated()) &&
183 : (UnallocatedOperand::cast(instr->OutputAt(0))
184 8259 : ->HasFixedRegisterPolicy() ||
185 : UnallocatedOperand::cast(instr->OutputAt(0))
186 208182 : ->HasFixedFPRegisterPolicy());
187 : }
188 :
189 : void ComputeTotalLatencies();
190 :
191 : static int GetInstructionLatency(const Instruction* instr);
192 :
193 : Zone* zone() { return zone_; }
194 : InstructionSequence* sequence() { return sequence_; }
195 : Isolate* isolate() { return sequence()->isolate(); }
196 :
197 : Zone* zone_;
198 : InstructionSequence* sequence_;
199 : ZoneVector<ScheduleGraphNode*> graph_;
200 :
201 : friend class InstructionSchedulerTester;
202 :
203 : // Last side effect instruction encountered while building the graph.
204 : ScheduleGraphNode* last_side_effect_instr_;
205 :
206 : // Set of load instructions encountered since the last side effect instruction
207 : // which will be added as predecessors of the next instruction with side
208 : // effects.
209 : ZoneVector<ScheduleGraphNode*> pending_loads_;
210 :
211 : // Live-in register markers are nop instructions which are emitted at the
212 : // beginning of a basic block so that the register allocator will find a
213 : // defining instruction for live-in values. They must not be moved.
214 : // All these nops are chained together and added as a predecessor of every
215 : // other instructions in the basic block.
216 : ScheduleGraphNode* last_live_in_reg_marker_;
217 :
218 : // Last deoptimization or trap instruction encountered while building the
219 : // graph.
220 : ScheduleGraphNode* last_deopt_or_trap_;
221 :
222 : // Keep track of definition points for virtual registers. This is used to
223 : // record operand dependencies in the scheduling graph.
224 : ZoneMap<int32_t, ScheduleGraphNode*> operands_map_;
225 : };
226 :
227 : } // namespace compiler
228 : } // namespace internal
229 : } // namespace v8
230 :
231 : #endif // V8_COMPILER_BACKEND_INSTRUCTION_SCHEDULER_H_
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