Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 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_INSTRUCTION_SCHEDULER_H_ |
| 6 | #define V8_COMPILER_INSTRUCTION_SCHEDULER_H_ |
| 7 | |
| 8 | #include "src/compiler/instruction.h" |
| 9 | #include "src/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 | kIsBlockTerminator = 1, // The instruction marks the end of a basic block |
| 20 | // e.g.: jump and return instructions. |
| 21 | kHasSideEffect = 2, // The instruction has some side effects (memory |
| 22 | // store, function call...) |
| 23 | kIsLoadOperation = 4, // The instruction is a memory load. |
| 24 | }; |
| 25 | |
| 26 | |
| 27 | class InstructionScheduler final : public ZoneObject { |
| 28 | public: |
| 29 | InstructionScheduler(Zone* zone, InstructionSequence* sequence); |
| 30 | |
| 31 | void StartBlock(RpoNumber rpo); |
| 32 | void EndBlock(RpoNumber rpo); |
| 33 | |
| 34 | void AddInstruction(Instruction* instr); |
| 35 | |
| 36 | static bool SchedulerSupported(); |
| 37 | |
| 38 | private: |
| 39 | // A scheduling graph node. |
| 40 | // Represent an instruction and their dependencies. |
| 41 | class ScheduleGraphNode: public ZoneObject { |
| 42 | public: |
| 43 | ScheduleGraphNode(Zone* zone, Instruction* instr); |
| 44 | |
| 45 | // Mark the instruction represented by 'node' as a dependecy of this one. |
| 46 | // The current instruction will be registered as an unscheduled predecessor |
| 47 | // of 'node' (i.e. it must be scheduled before 'node'). |
| 48 | void AddSuccessor(ScheduleGraphNode* node); |
| 49 | |
| 50 | // Check if all the predecessors of this instruction have been scheduled. |
| 51 | bool HasUnscheduledPredecessor() { |
| 52 | return unscheduled_predecessors_count_ != 0; |
| 53 | } |
| 54 | |
| 55 | // Record that we have scheduled one of the predecessors of this node. |
| 56 | void DropUnscheduledPredecessor() { |
| 57 | DCHECK(unscheduled_predecessors_count_ > 0); |
| 58 | unscheduled_predecessors_count_--; |
| 59 | } |
| 60 | |
| 61 | Instruction* instruction() { return instr_; } |
| 62 | ZoneDeque<ScheduleGraphNode*>& successors() { return successors_; } |
| 63 | int latency() const { return latency_; } |
| 64 | |
| 65 | int total_latency() const { return total_latency_; } |
| 66 | void set_total_latency(int latency) { total_latency_ = latency; } |
| 67 | |
| 68 | int start_cycle() const { return start_cycle_; } |
| 69 | void set_start_cycle(int start_cycle) { start_cycle_ = start_cycle; } |
| 70 | |
| 71 | private: |
| 72 | Instruction* instr_; |
| 73 | ZoneDeque<ScheduleGraphNode*> successors_; |
| 74 | |
| 75 | // Number of unscheduled predecessors for this node. |
| 76 | int unscheduled_predecessors_count_; |
| 77 | |
| 78 | // Estimate of the instruction latency (the number of cycles it takes for |
| 79 | // instruction to complete). |
| 80 | int latency_; |
| 81 | |
| 82 | // The sum of all the latencies on the path from this node to the end of |
| 83 | // the graph (i.e. a node with no successor). |
| 84 | int total_latency_; |
| 85 | |
| 86 | // The scheduler keeps a nominal cycle count to keep track of when the |
| 87 | // result of an instruction is available. This field is updated by the |
| 88 | // scheduler to indicate when the value of all the operands of this |
| 89 | // instruction will be available. |
| 90 | int start_cycle_; |
| 91 | }; |
| 92 | |
Ben Murdoch | 097c5b2 | 2016-05-18 11:27:45 +0100 | [diff] [blame] | 93 | // Keep track of all nodes ready to be scheduled (i.e. all their dependencies |
| 94 | // have been scheduled. Note that this class is inteded to be extended by |
| 95 | // concrete implementation of the scheduling queue which define the policy |
| 96 | // to pop node from the queue. |
| 97 | class SchedulingQueueBase { |
| 98 | public: |
| 99 | explicit SchedulingQueueBase(InstructionScheduler* scheduler) |
| 100 | : scheduler_(scheduler), |
| 101 | nodes_(scheduler->zone()) { |
| 102 | } |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 103 | |
Ben Murdoch | 097c5b2 | 2016-05-18 11:27:45 +0100 | [diff] [blame] | 104 | void AddNode(ScheduleGraphNode* node) { |
| 105 | nodes_.push_back(node); |
| 106 | } |
| 107 | |
| 108 | bool IsEmpty() const { |
| 109 | return nodes_.empty(); |
| 110 | } |
| 111 | |
| 112 | protected: |
| 113 | InstructionScheduler* scheduler_; |
| 114 | ZoneLinkedList<ScheduleGraphNode*> nodes_; |
| 115 | }; |
| 116 | |
| 117 | // A scheduling queue which prioritize nodes on the critical path (we look |
| 118 | // for the instruction with the highest latency on the path to reach the end |
| 119 | // of the graph). |
| 120 | class CriticalPathFirstQueue : public SchedulingQueueBase { |
| 121 | public: |
| 122 | explicit CriticalPathFirstQueue(InstructionScheduler* scheduler) |
| 123 | : SchedulingQueueBase(scheduler) { } |
| 124 | |
| 125 | // Look for the best candidate to schedule, remove it from the queue and |
| 126 | // return it. |
| 127 | ScheduleGraphNode* PopBestCandidate(int cycle); |
| 128 | |
| 129 | private: |
| 130 | // Compare the two nodes and return true if node1 is a better candidate than |
| 131 | // node2 (i.e. node1 should be scheduled before node2). |
| 132 | bool CompareNodes(ScheduleGraphNode *node1, ScheduleGraphNode *node2) const; |
| 133 | }; |
| 134 | |
| 135 | // A queue which pop a random node from the queue to perform stress tests on |
| 136 | // the scheduler. |
| 137 | class StressSchedulerQueue : public SchedulingQueueBase { |
| 138 | public: |
| 139 | explicit StressSchedulerQueue(InstructionScheduler* scheduler) |
| 140 | : SchedulingQueueBase(scheduler) { } |
| 141 | |
| 142 | ScheduleGraphNode* PopBestCandidate(int cycle); |
| 143 | |
| 144 | private: |
| 145 | Isolate *isolate() { |
| 146 | return scheduler_->isolate(); |
| 147 | } |
| 148 | }; |
| 149 | |
| 150 | // Perform scheduling for the current block specifying the queue type to |
| 151 | // use to determine the next best candidate. |
| 152 | template <typename QueueType> |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 153 | void ScheduleBlock(); |
| 154 | |
| 155 | // Return the scheduling properties of the given instruction. |
| 156 | int GetInstructionFlags(const Instruction* instr) const; |
| 157 | int GetTargetInstructionFlags(const Instruction* instr) const; |
| 158 | |
| 159 | // Return true if instr2 uses any value defined by instr1. |
| 160 | bool HasOperandDependency(const Instruction* instr1, |
| 161 | const Instruction* instr2) const; |
| 162 | |
| 163 | // Return true if the instruction is a basic block terminator. |
| 164 | bool IsBlockTerminator(const Instruction* instr) const; |
| 165 | |
| 166 | // Check whether the given instruction has side effects (e.g. function call, |
| 167 | // memory store). |
| 168 | bool HasSideEffect(const Instruction* instr) const { |
| 169 | return GetInstructionFlags(instr) & kHasSideEffect; |
| 170 | } |
| 171 | |
| 172 | // Return true if the instruction is a memory load. |
| 173 | bool IsLoadOperation(const Instruction* instr) const { |
| 174 | return GetInstructionFlags(instr) & kIsLoadOperation; |
| 175 | } |
| 176 | |
| 177 | // Identify nops used as a definition point for live-in registers at |
| 178 | // function entry. |
| 179 | bool IsFixedRegisterParameter(const Instruction* instr) const { |
| 180 | return (instr->arch_opcode() == kArchNop) && |
| 181 | (instr->OutputCount() == 1) && |
| 182 | (instr->OutputAt(0)->IsUnallocated()) && |
| 183 | UnallocatedOperand::cast(instr->OutputAt(0))->HasFixedRegisterPolicy(); |
| 184 | } |
| 185 | |
| 186 | void ComputeTotalLatencies(); |
| 187 | |
| 188 | static int GetInstructionLatency(const Instruction* instr); |
| 189 | |
| 190 | Zone* zone() { return zone_; } |
| 191 | InstructionSequence* sequence() { return sequence_; } |
Ben Murdoch | 097c5b2 | 2016-05-18 11:27:45 +0100 | [diff] [blame] | 192 | Isolate* isolate() { return sequence()->isolate(); } |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 193 | |
| 194 | Zone* zone_; |
| 195 | InstructionSequence* sequence_; |
| 196 | ZoneVector<ScheduleGraphNode*> graph_; |
| 197 | |
| 198 | // Last side effect instruction encountered while building the graph. |
| 199 | ScheduleGraphNode* last_side_effect_instr_; |
| 200 | |
| 201 | // Set of load instructions encountered since the last side effect instruction |
| 202 | // which will be added as predecessors of the next instruction with side |
| 203 | // effects. |
| 204 | ZoneVector<ScheduleGraphNode*> pending_loads_; |
| 205 | |
| 206 | // Live-in register markers are nop instructions which are emitted at the |
| 207 | // beginning of a basic block so that the register allocator will find a |
| 208 | // defining instruction for live-in values. They must not be moved. |
| 209 | // All these nops are chained together and added as a predecessor of every |
| 210 | // other instructions in the basic block. |
| 211 | ScheduleGraphNode* last_live_in_reg_marker_; |
| 212 | }; |
| 213 | |
| 214 | } // namespace compiler |
| 215 | } // namespace internal |
| 216 | } // namespace v8 |
| 217 | |
| 218 | #endif // V8_COMPILER_INSTRUCTION_SCHEDULER_H_ |