1 // Copyright 2014 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.
5 #ifndef V8_REGISTER_ALLOCATOR_H_
6 #define V8_REGISTER_ALLOCATOR_H_
8 #include "src/compiler/instruction.h"
9 #include "src/zone-containers.h"
16 UNALLOCATED_REGISTERS,
22 // This class represents a single point of a InstructionOperand's lifetime. For
23 // each instruction there are exactly two lifetime positions: the beginning and
24 // the end of the instruction. Lifetime positions for different instructions are
26 class LifetimePosition FINAL {
28 // Return the lifetime position that corresponds to the beginning of
29 // the instruction with the given index.
30 static LifetimePosition FromInstructionIndex(int index) {
31 return LifetimePosition(index * kStep);
34 // Returns a numeric representation of this lifetime position.
35 int Value() const { return value_; }
37 // Returns the index of the instruction to which this lifetime position
39 int InstructionIndex() const {
41 return value_ / kStep;
44 // Returns true if this lifetime position corresponds to the instruction
46 bool IsInstructionStart() const { return (value_ & (kStep - 1)) == 0; }
48 // Returns the lifetime position for the start of the instruction which
49 // corresponds to this lifetime position.
50 LifetimePosition InstructionStart() const {
52 return LifetimePosition(value_ & ~(kStep - 1));
55 // Returns the lifetime position for the end of the instruction which
56 // corresponds to this lifetime position.
57 LifetimePosition InstructionEnd() const {
59 return LifetimePosition(InstructionStart().Value() + kStep / 2);
62 // Returns the lifetime position for the beginning of the next instruction.
63 LifetimePosition NextInstruction() const {
65 return LifetimePosition(InstructionStart().Value() + kStep);
68 // Returns the lifetime position for the beginning of the previous
70 LifetimePosition PrevInstruction() const {
73 return LifetimePosition(InstructionStart().Value() - kStep);
76 // Constructs the lifetime position which does not correspond to any
78 LifetimePosition() : value_(-1) {}
80 // Returns true if this lifetime positions corrensponds to some
82 bool IsValid() const { return value_ != -1; }
84 static inline LifetimePosition Invalid() { return LifetimePosition(); }
86 static inline LifetimePosition MaxPosition() {
87 // We have to use this kind of getter instead of static member due to
89 return LifetimePosition(kMaxInt);
93 static const int kStep = 2;
95 // Code relies on kStep being a power of two.
96 STATIC_ASSERT(IS_POWER_OF_TWO(kStep));
98 explicit LifetimePosition(int value) : value_(value) {}
104 // Representation of the non-empty interval [start,end[.
105 class UseInterval FINAL : public ZoneObject {
107 UseInterval(LifetimePosition start, LifetimePosition end)
108 : start_(start), end_(end), next_(nullptr) {
109 DCHECK(start.Value() < end.Value());
112 LifetimePosition start() const { return start_; }
113 LifetimePosition end() const { return end_; }
114 UseInterval* next() const { return next_; }
116 // Split this interval at the given position without effecting the
117 // live range that owns it. The interval must contain the position.
118 void SplitAt(LifetimePosition pos, Zone* zone);
120 // If this interval intersects with other return smallest position
121 // that belongs to both of them.
122 LifetimePosition Intersect(const UseInterval* other) const {
123 if (other->start().Value() < start_.Value()) return other->Intersect(this);
124 if (other->start().Value() < end_.Value()) return other->start();
125 return LifetimePosition::Invalid();
128 bool Contains(LifetimePosition point) const {
129 return start_.Value() <= point.Value() && point.Value() < end_.Value();
132 void set_start(LifetimePosition start) { start_ = start; }
133 void set_next(UseInterval* next) { next_ = next; }
135 LifetimePosition start_;
136 LifetimePosition end_;
140 DISALLOW_COPY_AND_ASSIGN(UseInterval);
144 // Representation of a use position.
145 class UsePosition FINAL : public ZoneObject {
147 UsePosition(LifetimePosition pos, InstructionOperand* operand,
148 InstructionOperand* hint);
150 InstructionOperand* operand() const { return operand_; }
151 bool HasOperand() const { return operand_ != nullptr; }
153 InstructionOperand* hint() const { return hint_; }
154 bool HasHint() const;
155 bool RequiresRegister() const;
156 bool RegisterIsBeneficial() const;
158 LifetimePosition pos() const { return pos_; }
159 UsePosition* next() const { return next_; }
161 void set_next(UsePosition* next) { next_ = next; }
163 InstructionOperand* const operand_;
164 InstructionOperand* const hint_;
165 LifetimePosition const pos_;
167 bool requires_reg_ : 1;
168 bool register_beneficial_ : 1;
171 DISALLOW_COPY_AND_ASSIGN(UsePosition);
177 // TODO(dcarney): remove this cache.
178 class InstructionOperandCache FINAL : public ZoneObject {
180 InstructionOperandCache();
182 InstructionOperand* RegisterOperand(int index) {
184 index < static_cast<int>(arraysize(general_register_operands_)));
185 return &general_register_operands_[index];
187 InstructionOperand* DoubleRegisterOperand(int index) {
189 index < static_cast<int>(arraysize(double_register_operands_)));
190 return &double_register_operands_[index];
195 general_register_operands_[RegisterConfiguration::kMaxGeneralRegisters];
197 double_register_operands_[RegisterConfiguration::kMaxDoubleRegisters];
199 DISALLOW_COPY_AND_ASSIGN(InstructionOperandCache);
203 // Representation of SSA values' live ranges as a collection of (continuous)
204 // intervals over the instruction ordering.
205 class LiveRange FINAL : public ZoneObject {
207 static const int kInvalidAssignment = 0x7fffffff;
209 LiveRange(int id, Zone* zone);
211 UseInterval* first_interval() const { return first_interval_; }
212 UsePosition* first_pos() const { return first_pos_; }
213 LiveRange* parent() const { return parent_; }
214 LiveRange* TopLevel() { return (parent_ == nullptr) ? this : parent_; }
215 const LiveRange* TopLevel() const {
216 return (parent_ == nullptr) ? this : parent_;
218 LiveRange* next() const { return next_; }
219 bool IsChild() const { return parent() != nullptr; }
220 int id() const { return id_; }
221 bool IsFixed() const { return id_ < 0; }
222 bool IsEmpty() const { return first_interval() == nullptr; }
223 // TODO(dcarney): remove this.
224 InstructionOperand* GetAssignedOperand(InstructionOperandCache* cache) const;
225 InstructionOperand GetAssignedOperand() const;
226 int assigned_register() const { return assigned_register_; }
227 int spill_start_index() const { return spill_start_index_; }
228 void set_assigned_register(int reg, InstructionOperandCache* cache);
230 bool is_phi() const { return is_phi_; }
231 void set_is_phi(bool is_phi) { is_phi_ = is_phi; }
232 bool is_non_loop_phi() const { return is_non_loop_phi_; }
233 void set_is_non_loop_phi(bool is_non_loop_phi) {
234 is_non_loop_phi_ = is_non_loop_phi;
237 // Returns use position in this live range that follows both start
238 // and last processed use position.
239 // Modifies internal state of live range!
240 UsePosition* NextUsePosition(LifetimePosition start);
242 // Returns use position for which register is required in this live
243 // range and which follows both start and last processed use position
244 // Modifies internal state of live range!
245 UsePosition* NextRegisterPosition(LifetimePosition start);
247 // Returns use position for which register is beneficial in this live
248 // range and which follows both start and last processed use position
249 // Modifies internal state of live range!
250 UsePosition* NextUsePositionRegisterIsBeneficial(LifetimePosition start);
252 // Returns use position for which register is beneficial in this live
253 // range and which precedes start.
254 UsePosition* PreviousUsePositionRegisterIsBeneficial(LifetimePosition start);
256 // Can this live range be spilled at this position.
257 bool CanBeSpilled(LifetimePosition pos);
259 // Split this live range at the given position which must follow the start of
261 // All uses following the given position will be moved from this
262 // live range to the result live range.
263 void SplitAt(LifetimePosition position, LiveRange* result, Zone* zone);
265 RegisterKind Kind() const { return kind_; }
266 bool HasRegisterAssigned() const {
267 return assigned_register_ != kInvalidAssignment;
269 bool IsSpilled() const { return spilled_; }
271 InstructionOperand* current_hint_operand() const {
272 DCHECK(current_hint_operand_ == FirstHint());
273 return current_hint_operand_;
275 InstructionOperand* FirstHint() const {
276 UsePosition* pos = first_pos_;
277 while (pos != nullptr && !pos->HasHint()) pos = pos->next();
278 if (pos != nullptr) return pos->hint();
282 LifetimePosition Start() const {
284 return first_interval()->start();
287 LifetimePosition End() const {
289 return last_interval_->end();
292 enum class SpillType { kNoSpillType, kSpillOperand, kSpillRange };
293 SpillType spill_type() const { return spill_type_; }
294 InstructionOperand* GetSpillOperand() const {
295 return spill_type_ == SpillType::kSpillOperand ? spill_operand_ : nullptr;
297 SpillRange* GetSpillRange() const {
298 return spill_type_ == SpillType::kSpillRange ? spill_range_ : nullptr;
300 bool HasNoSpillType() const { return spill_type_ == SpillType::kNoSpillType; }
301 bool HasSpillOperand() const {
302 return spill_type_ == SpillType::kSpillOperand;
304 bool HasSpillRange() const { return spill_type_ == SpillType::kSpillRange; }
306 void SpillAtDefinition(Zone* zone, int gap_index,
307 InstructionOperand* operand);
308 void SetSpillOperand(InstructionOperand* operand);
309 void SetSpillRange(SpillRange* spill_range);
310 void CommitSpillOperand(InstructionOperand* operand);
311 void CommitSpillsAtDefinition(InstructionSequence* sequence,
312 InstructionOperand* operand);
314 void SetSpillStartIndex(int start) {
315 spill_start_index_ = Min(start, spill_start_index_);
318 bool ShouldBeAllocatedBefore(const LiveRange* other) const;
319 bool CanCover(LifetimePosition position) const;
320 bool Covers(LifetimePosition position);
321 LifetimePosition FirstIntersection(LiveRange* other);
323 // Add a new interval or a new use position to this live range.
324 void EnsureInterval(LifetimePosition start, LifetimePosition end, Zone* zone);
325 void AddUseInterval(LifetimePosition start, LifetimePosition end, Zone* zone);
326 void AddUsePosition(LifetimePosition pos, InstructionOperand* operand,
327 InstructionOperand* hint, Zone* zone);
329 // Shorten the most recently added interval by setting a new start.
330 void ShortenTo(LifetimePosition start);
333 // True if target overlaps an existing interval.
334 bool HasOverlap(UseInterval* target) const;
339 struct SpillAtDefinitionList;
341 void ConvertUsesToOperand(InstructionOperand* op);
342 UseInterval* FirstSearchIntervalForPosition(LifetimePosition position) const;
343 void AdvanceLastProcessedMarker(UseInterval* to_start_of,
344 LifetimePosition but_not_past) const;
346 // TODO(dcarney): pack this structure better.
350 bool is_non_loop_phi_;
352 int assigned_register_;
353 UseInterval* last_interval_;
354 UseInterval* first_interval_;
355 UsePosition* first_pos_;
358 // This is used as a cache, it doesn't affect correctness.
359 mutable UseInterval* current_interval_;
360 UsePosition* last_processed_use_;
361 // This is used as a cache, it's invalid outside of BuildLiveRanges.
362 InstructionOperand* current_hint_operand_;
363 int spill_start_index_;
364 SpillType spill_type_;
366 InstructionOperand* spill_operand_;
367 SpillRange* spill_range_;
369 SpillAtDefinitionList* spills_at_definition_;
371 friend class RegisterAllocator; // Assigns to kind_.
373 DISALLOW_COPY_AND_ASSIGN(LiveRange);
377 class SpillRange FINAL : public ZoneObject {
379 SpillRange(LiveRange* range, Zone* zone);
381 UseInterval* interval() const { return use_interval_; }
382 RegisterKind Kind() const { return live_ranges_[0]->Kind(); }
383 bool IsEmpty() const { return live_ranges_.empty(); }
384 bool TryMerge(SpillRange* other);
385 void SetOperand(InstructionOperand* op);
388 LifetimePosition End() const { return end_position_; }
389 ZoneVector<LiveRange*>& live_ranges() { return live_ranges_; }
390 bool IsIntersectingWith(SpillRange* other) const;
391 // Merge intervals, making sure the use intervals are sorted
392 void MergeDisjointIntervals(UseInterval* other);
394 ZoneVector<LiveRange*> live_ranges_;
395 UseInterval* use_interval_;
396 LifetimePosition end_position_;
398 DISALLOW_COPY_AND_ASSIGN(SpillRange);
402 class RegisterAllocator FINAL : public ZoneObject {
404 explicit RegisterAllocator(const RegisterConfiguration* config,
405 Zone* local_zone, Frame* frame,
406 InstructionSequence* code,
407 const char* debug_name = nullptr);
409 const ZoneVector<LiveRange*>& live_ranges() const { return live_ranges_; }
410 const ZoneVector<LiveRange*>& fixed_live_ranges() const {
411 return fixed_live_ranges_;
413 const ZoneVector<LiveRange*>& fixed_double_live_ranges() const {
414 return fixed_double_live_ranges_;
416 InstructionSequence* code() const { return code_; }
417 // This zone is for datastructures only needed during register allocation.
418 Zone* local_zone() const { return local_zone_; }
420 // Phase 1 : insert moves to account for fixed register operands.
421 void MeetRegisterConstraints();
423 // Phase 2: deconstruct SSA by inserting moves in successors and the headers
424 // of blocks containing phis.
427 // Phase 3: compute liveness of all virtual register.
428 void BuildLiveRanges();
429 bool ExistsUseWithoutDefinition();
431 // Phase 4: compute register assignments.
432 void AllocateGeneralRegisters();
433 void AllocateDoubleRegisters();
435 // Phase 5: assign spill splots.
436 void AssignSpillSlots();
438 // Phase 6: commit assignment.
439 void CommitAssignment();
441 // Phase 7: compute values for pointer maps.
442 void PopulatePointerMaps(); // TODO(titzer): rename to PopulateReferenceMaps.
444 // Phase 8: reconnect split ranges with moves.
445 void ConnectRanges();
447 // Phase 9: insert moves to connect ranges across basic blocks.
448 void ResolveControlFlow();
451 int GetVirtualRegister() { return code()->NextVirtualRegister(); }
453 // Checks whether the value of a given virtual register is a reference.
454 // TODO(titzer): rename this to IsReference.
455 bool HasTaggedValue(int virtual_register) const;
457 // Returns the register kind required by the given virtual register.
458 RegisterKind RequiredRegisterKind(int virtual_register) const;
460 // This zone is for InstructionOperands and moves that live beyond register
462 Zone* code_zone() const { return code()->zone(); }
464 BitVector* assigned_registers() { return assigned_registers_; }
465 BitVector* assigned_double_registers() { return assigned_double_registers_; }
471 void AllocateRegisters();
472 bool CanEagerlyResolveControlFlow(const InstructionBlock* block) const;
473 bool SafePointsAreInOrder() const;
475 // Liveness analysis support.
476 BitVector* ComputeLiveOut(const InstructionBlock* block);
477 void AddInitialIntervals(const InstructionBlock* block, BitVector* live_out);
478 bool IsOutputRegisterOf(Instruction* instr, int index);
479 bool IsOutputDoubleRegisterOf(Instruction* instr, int index);
480 void ProcessInstructions(const InstructionBlock* block, BitVector* live);
481 void MeetRegisterConstraints(const InstructionBlock* block);
482 void MeetConstraintsBetween(Instruction* first, Instruction* second,
484 void MeetRegisterConstraintsForLastInstructionInBlock(
485 const InstructionBlock* block);
486 void ResolvePhis(const InstructionBlock* block);
488 // Helper methods for building intervals.
489 InstructionOperand* AllocateFixed(UnallocatedOperand* operand, int pos,
491 LiveRange* LiveRangeFor(InstructionOperand* operand);
492 void Define(LifetimePosition position, InstructionOperand* operand,
493 InstructionOperand* hint);
494 void Use(LifetimePosition block_start, LifetimePosition position,
495 InstructionOperand* operand, InstructionOperand* hint);
496 void AddGapMove(int index, GapInstruction::InnerPosition position,
497 InstructionOperand* from, InstructionOperand* to);
499 // Helper methods for updating the life range lists.
500 void AddToActive(LiveRange* range);
501 void AddToInactive(LiveRange* range);
502 void AddToUnhandledSorted(LiveRange* range);
503 void AddToUnhandledUnsorted(LiveRange* range);
504 void SortUnhandled();
505 bool UnhandledIsSorted();
506 void ActiveToHandled(LiveRange* range);
507 void ActiveToInactive(LiveRange* range);
508 void InactiveToHandled(LiveRange* range);
509 void InactiveToActive(LiveRange* range);
511 // Helper methods for allocating registers.
512 bool TryReuseSpillForPhi(LiveRange* range);
513 bool TryAllocateFreeReg(LiveRange* range);
514 void AllocateBlockedReg(LiveRange* range);
515 SpillRange* AssignSpillRangeToLiveRange(LiveRange* range);
517 // Live range splitting helpers.
519 // Split the given range at the given position.
520 // If range starts at or after the given position then the
521 // original range is returned.
522 // Otherwise returns the live range that starts at pos and contains
523 // all uses from the original range that follow pos. Uses at pos will
524 // still be owned by the original range after splitting.
525 LiveRange* SplitRangeAt(LiveRange* range, LifetimePosition pos);
527 // Split the given range in a position from the interval [start, end].
528 LiveRange* SplitBetween(LiveRange* range, LifetimePosition start,
529 LifetimePosition end);
531 // Find a lifetime position in the interval [start, end] which
532 // is optimal for splitting: it is either header of the outermost
533 // loop covered by this interval or the latest possible position.
534 LifetimePosition FindOptimalSplitPos(LifetimePosition start,
535 LifetimePosition end);
537 // Spill the given life range after position pos.
538 void SpillAfter(LiveRange* range, LifetimePosition pos);
540 // Spill the given life range after position [start] and up to position [end].
541 void SpillBetween(LiveRange* range, LifetimePosition start,
542 LifetimePosition end);
544 // Spill the given life range after position [start] and up to position [end].
545 // Range is guaranteed to be spilled at least until position [until].
546 void SpillBetweenUntil(LiveRange* range, LifetimePosition start,
547 LifetimePosition until, LifetimePosition end);
549 void SplitAndSpillIntersecting(LiveRange* range);
551 // If we are trying to spill a range inside the loop try to
552 // hoist spill position out to the point just before the loop.
553 LifetimePosition FindOptimalSpillingPos(LiveRange* range,
554 LifetimePosition pos);
556 void Spill(LiveRange* range);
557 bool IsBlockBoundary(LifetimePosition pos);
559 // Helper methods for resolving control flow.
560 void ResolveControlFlow(const InstructionBlock* block,
561 InstructionOperand* cur_op,
562 const InstructionBlock* pred,
563 InstructionOperand* pred_op);
565 void SetLiveRangeAssignedRegister(LiveRange* range, int reg);
567 // Return parallel move that should be used to connect ranges split at the
569 ParallelMove* GetConnectingParallelMove(LifetimePosition pos);
571 // Return the block which contains give lifetime position.
572 const InstructionBlock* GetInstructionBlock(LifetimePosition pos);
574 // Helper methods for the fixed registers.
575 int RegisterCount() const;
576 static int FixedLiveRangeID(int index) { return -index - 1; }
577 int FixedDoubleLiveRangeID(int index);
578 LiveRange* FixedLiveRangeFor(int index);
579 LiveRange* FixedDoubleLiveRangeFor(int index);
580 LiveRange* LiveRangeFor(int index);
581 GapInstruction* GetLastGap(const InstructionBlock* block);
583 const char* RegisterName(int allocation_index);
585 Instruction* InstructionAt(int index) { return code()->InstructionAt(index); }
587 Frame* frame() const { return frame_; }
588 const char* debug_name() const { return debug_name_; }
589 const RegisterConfiguration* config() const { return config_; }
590 InstructionOperandCache* operand_cache() const { return operand_cache_; }
591 ZoneVector<LiveRange*>& live_ranges() { return live_ranges_; }
592 ZoneVector<LiveRange*>& fixed_live_ranges() { return fixed_live_ranges_; }
593 ZoneVector<LiveRange*>& fixed_double_live_ranges() {
594 return fixed_double_live_ranges_;
596 ZoneVector<LiveRange*>& unhandled_live_ranges() {
597 return unhandled_live_ranges_;
599 ZoneVector<LiveRange*>& active_live_ranges() { return active_live_ranges_; }
600 ZoneVector<LiveRange*>& inactive_live_ranges() {
601 return inactive_live_ranges_;
603 ZoneVector<SpillRange*>& spill_ranges() { return spill_ranges_; }
606 PhiMapValue(PhiInstruction* phi, const InstructionBlock* block)
607 : phi(phi), block(block) {}
608 PhiInstruction* const phi;
609 const InstructionBlock* const block;
611 typedef ZoneMap<int, PhiMapValue> PhiMap;
613 Zone* const local_zone_;
615 InstructionSequence* const code_;
616 const char* const debug_name_;
618 const RegisterConfiguration* config_;
619 InstructionOperandCache* const operand_cache_;
622 // During liveness analysis keep a mapping from block id to live_in sets
623 // for blocks already analyzed.
624 ZoneVector<BitVector*> live_in_sets_;
626 // Liveness analysis results.
627 ZoneVector<LiveRange*> live_ranges_;
629 // Lists of live ranges
630 ZoneVector<LiveRange*> fixed_live_ranges_;
631 ZoneVector<LiveRange*> fixed_double_live_ranges_;
632 ZoneVector<LiveRange*> unhandled_live_ranges_;
633 ZoneVector<LiveRange*> active_live_ranges_;
634 ZoneVector<LiveRange*> inactive_live_ranges_;
635 ZoneVector<SpillRange*> spill_ranges_;
640 BitVector* assigned_registers_;
641 BitVector* assigned_double_registers_;
644 LifetimePosition allocation_finger_;
647 DISALLOW_COPY_AND_ASSIGN(RegisterAllocator);
650 } // namespace compiler
651 } // namespace internal
654 #endif // V8_REGISTER_ALLOCATOR_H_