Line data Source code
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 : V8_EXPORT_PRIVATE InstructionScheduler(Zone* zone,
32 : InstructionSequence* sequence);
33 :
34 : V8_EXPORT_PRIVATE void StartBlock(RpoNumber rpo);
35 : V8_EXPORT_PRIVATE void EndBlock(RpoNumber rpo);
36 :
37 : V8_EXPORT_PRIVATE void AddInstruction(Instruction* instr);
38 : V8_EXPORT_PRIVATE void AddTerminator(Instruction* instr);
39 :
40 : static bool SchedulerSupported();
41 :
42 : private:
43 : // A scheduling graph node.
44 : // Represent an instruction and their dependencies.
45 : class ScheduleGraphNode : public ZoneObject {
46 : public:
47 : ScheduleGraphNode(Zone* zone, Instruction* instr);
48 :
49 : // Mark the instruction represented by 'node' as a dependecy of this one.
50 : // The current instruction will be registered as an unscheduled predecessor
51 : // of 'node' (i.e. it must be scheduled before 'node').
52 : void AddSuccessor(ScheduleGraphNode* node);
53 :
54 : // Check if all the predecessors of this instruction have been scheduled.
55 : bool HasUnscheduledPredecessor() {
56 : return unscheduled_predecessors_count_ != 0;
57 : }
58 :
59 : // Record that we have scheduled one of the predecessors of this node.
60 : void DropUnscheduledPredecessor() {
61 : DCHECK_LT(0, unscheduled_predecessors_count_);
62 351770 : unscheduled_predecessors_count_--;
63 : }
64 :
65 : Instruction* instruction() { return instr_; }
66 : ZoneDeque<ScheduleGraphNode*>& successors() { return successors_; }
67 : int latency() const { return latency_; }
68 :
69 : int total_latency() const { return total_latency_; }
70 322679 : void set_total_latency(int latency) { total_latency_ = latency; }
71 :
72 : int start_cycle() const { return start_cycle_; }
73 351770 : void set_start_cycle(int start_cycle) { start_cycle_ = start_cycle; }
74 :
75 : private:
76 : Instruction* instr_;
77 : ZoneDeque<ScheduleGraphNode*> successors_;
78 :
79 : // Number of unscheduled predecessors for this node.
80 : int unscheduled_predecessors_count_;
81 :
82 : // Estimate of the instruction latency (the number of cycles it takes for
83 : // instruction to complete).
84 : int latency_;
85 :
86 : // The sum of all the latencies on the path from this node to the end of
87 : // the graph (i.e. a node with no successor).
88 : int total_latency_;
89 :
90 : // The scheduler keeps a nominal cycle count to keep track of when the
91 : // result of an instruction is available. This field is updated by the
92 : // scheduler to indicate when the value of all the operands of this
93 : // instruction will be available.
94 : int start_cycle_;
95 : };
96 :
97 : // Keep track of all nodes ready to be scheduled (i.e. all their dependencies
98 : // have been scheduled. Note that this class is inteded to be extended by
99 : // concrete implementation of the scheduling queue which define the policy
100 : // to pop node from the queue.
101 129776 : class SchedulingQueueBase {
102 : public:
103 : explicit SchedulingQueueBase(InstructionScheduler* scheduler)
104 129776 : : scheduler_(scheduler), nodes_(scheduler->zone()) {}
105 :
106 : void AddNode(ScheduleGraphNode* node);
107 :
108 : bool IsEmpty() const { return nodes_.empty(); }
109 :
110 : protected:
111 : InstructionScheduler* scheduler_;
112 : ZoneLinkedList<ScheduleGraphNode*> nodes_;
113 : };
114 :
115 : // A scheduling queue which prioritize nodes on the critical path (we look
116 : // for the instruction with the highest latency on the path to reach the end
117 : // of the graph).
118 129776 : class CriticalPathFirstQueue : public SchedulingQueueBase {
119 : public:
120 : explicit CriticalPathFirstQueue(InstructionScheduler* scheduler)
121 : : SchedulingQueueBase(scheduler) {}
122 :
123 : // Look for the best candidate to schedule, remove it from the queue and
124 : // return it.
125 : ScheduleGraphNode* PopBestCandidate(int cycle);
126 : };
127 :
128 : // A queue which pop a random node from the queue to perform stress tests on
129 : // the scheduler.
130 0 : class StressSchedulerQueue : public SchedulingQueueBase {
131 : public:
132 : explicit StressSchedulerQueue(InstructionScheduler* scheduler)
133 : : SchedulingQueueBase(scheduler) {}
134 :
135 : ScheduleGraphNode* PopBestCandidate(int cycle);
136 :
137 : private:
138 : Isolate* isolate() { return scheduler_->isolate(); }
139 : };
140 :
141 : // Perform scheduling for the current block specifying the queue type to
142 : // use to determine the next best candidate.
143 : template <typename QueueType>
144 : void ScheduleBlock();
145 :
146 : // Return the scheduling properties of the given instruction.
147 : V8_EXPORT_PRIVATE int GetInstructionFlags(const Instruction* instr) const;
148 : int GetTargetInstructionFlags(const Instruction* instr) const;
149 :
150 : // Check whether the given instruction has side effects (e.g. function call,
151 : // memory store).
152 : bool HasSideEffect(const Instruction* instr) const {
153 186527 : return (GetInstructionFlags(instr) & kHasSideEffect) != 0;
154 : }
155 :
156 : // Return true if the instruction is a memory load.
157 : bool IsLoadOperation(const Instruction* instr) const {
158 119588 : return (GetInstructionFlags(instr) & kIsLoadOperation) != 0;
159 : }
160 :
161 : // The scheduler will not move the following instructions before the last
162 : // deopt/trap check:
163 : // * loads (this is conservative)
164 : // * instructions with side effect
165 : // * other deopts/traps
166 : // Any other instruction can be moved, apart from those that raise exceptions
167 : // on specific inputs - these are filtered out by the deopt/trap check.
168 : bool MayNeedDeoptOrTrapCheck(const Instruction* instr) const {
169 10 : return (GetInstructionFlags(instr) & kMayNeedDeoptOrTrapCheck) != 0;
170 : }
171 :
172 : // Return true if the instruction cannot be moved before the last deopt or
173 : // trap point we encountered.
174 10 : bool DependsOnDeoptOrTrap(const Instruction* instr) const {
175 15 : return MayNeedDeoptOrTrapCheck(instr) || instr->IsDeoptimizeCall() ||
176 15 : instr->IsTrap() || HasSideEffect(instr) || IsLoadOperation(instr);
177 : }
178 :
179 : // Identify nops used as a definition point for live-in registers at
180 : // function entry.
181 192903 : bool IsFixedRegisterParameter(const Instruction* instr) const {
182 103836 : return (instr->arch_opcode() == kArchNop) && (instr->OutputCount() == 1) &&
183 207070 : (instr->OutputAt(0)->IsUnallocated()) &&
184 : (UnallocatedOperand::cast(instr->OutputAt(0))
185 7785 : ->HasFixedRegisterPolicy() ||
186 : UnallocatedOperand::cast(instr->OutputAt(0))
187 192903 : ->HasFixedFPRegisterPolicy());
188 : }
189 :
190 : void ComputeTotalLatencies();
191 :
192 : static int GetInstructionLatency(const Instruction* instr);
193 :
194 : Zone* zone() { return zone_; }
195 : InstructionSequence* sequence() { return sequence_; }
196 : Isolate* isolate() { return sequence()->isolate(); }
197 :
198 : Zone* zone_;
199 : InstructionSequence* sequence_;
200 : ZoneVector<ScheduleGraphNode*> graph_;
201 :
202 : friend class InstructionSchedulerTester;
203 :
204 : // Last side effect instruction encountered while building the graph.
205 : ScheduleGraphNode* last_side_effect_instr_;
206 :
207 : // Set of load instructions encountered since the last side effect instruction
208 : // which will be added as predecessors of the next instruction with side
209 : // effects.
210 : ZoneVector<ScheduleGraphNode*> pending_loads_;
211 :
212 : // Live-in register markers are nop instructions which are emitted at the
213 : // beginning of a basic block so that the register allocator will find a
214 : // defining instruction for live-in values. They must not be moved.
215 : // All these nops are chained together and added as a predecessor of every
216 : // other instructions in the basic block.
217 : ScheduleGraphNode* last_live_in_reg_marker_;
218 :
219 : // Last deoptimization or trap instruction encountered while building the
220 : // graph.
221 : ScheduleGraphNode* last_deopt_or_trap_;
222 :
223 : // Keep track of definition points for virtual registers. This is used to
224 : // record operand dependencies in the scheduling graph.
225 : ZoneMap<int32_t, ScheduleGraphNode*> operands_map_;
226 : };
227 :
228 : } // namespace compiler
229 : } // namespace internal
230 : } // namespace v8
231 :
232 : #endif // V8_COMPILER_BACKEND_INSTRUCTION_SCHEDULER_H_
|
