xref: /freebsd/contrib/llvm-project/llvm/lib/CodeGen/LiveInterval.cpp (revision 6ba2210ee039f2f12878c217bcf058e9c8b26b29)
1 //===- LiveInterval.cpp - Live Interval Representation --------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the LiveRange and LiveInterval classes.  Given some
10 // numbering of each the machine instructions an interval [i, j) is said to be a
11 // live range for register v if there is no instruction with number j' >= j
12 // such that v is live at j' and there is no instruction with number i' < i such
13 // that v is live at i'. In this implementation ranges can have holes,
14 // i.e. a range might look like [1,20), [50,65), [1000,1001).  Each
15 // individual segment is represented as an instance of LiveRange::Segment,
16 // and the whole range is represented as an instance of LiveRange.
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #include "llvm/CodeGen/LiveInterval.h"
21 #include "LiveRangeUtils.h"
22 #include "RegisterCoalescer.h"
23 #include "llvm/ADT/ArrayRef.h"
24 #include "llvm/ADT/STLExtras.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/iterator_range.h"
28 #include "llvm/CodeGen/LiveIntervals.h"
29 #include "llvm/CodeGen/MachineBasicBlock.h"
30 #include "llvm/CodeGen/MachineInstr.h"
31 #include "llvm/CodeGen/MachineOperand.h"
32 #include "llvm/CodeGen/MachineRegisterInfo.h"
33 #include "llvm/CodeGen/SlotIndexes.h"
34 #include "llvm/CodeGen/TargetRegisterInfo.h"
35 #include "llvm/Config/llvm-config.h"
36 #include "llvm/MC/LaneBitmask.h"
37 #include "llvm/Support/Compiler.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/raw_ostream.h"
40 #include <algorithm>
41 #include <cassert>
42 #include <cstddef>
43 #include <iterator>
44 #include <utility>
45 
46 using namespace llvm;
47 
48 namespace {
49 
50 //===----------------------------------------------------------------------===//
51 // Implementation of various methods necessary for calculation of live ranges.
52 // The implementation of the methods abstracts from the concrete type of the
53 // segment collection.
54 //
55 // Implementation of the class follows the Template design pattern. The base
56 // class contains generic algorithms that call collection-specific methods,
57 // which are provided in concrete subclasses. In order to avoid virtual calls
58 // these methods are provided by means of C++ template instantiation.
59 // The base class calls the methods of the subclass through method impl(),
60 // which casts 'this' pointer to the type of the subclass.
61 //
62 //===----------------------------------------------------------------------===//
63 
64 template <typename ImplT, typename IteratorT, typename CollectionT>
65 class CalcLiveRangeUtilBase {
66 protected:
67   LiveRange *LR;
68 
69 protected:
70   CalcLiveRangeUtilBase(LiveRange *LR) : LR(LR) {}
71 
72 public:
73   using Segment = LiveRange::Segment;
74   using iterator = IteratorT;
75 
76   /// A counterpart of LiveRange::createDeadDef: Make sure the range has a
77   /// value defined at @p Def.
78   /// If @p ForVNI is null, and there is no value defined at @p Def, a new
79   /// value will be allocated using @p VNInfoAllocator.
80   /// If @p ForVNI is null, the return value is the value defined at @p Def,
81   /// either a pre-existing one, or the one newly created.
82   /// If @p ForVNI is not null, then @p Def should be the location where
83   /// @p ForVNI is defined. If the range does not have a value defined at
84   /// @p Def, the value @p ForVNI will be used instead of allocating a new
85   /// one. If the range already has a value defined at @p Def, it must be
86   /// same as @p ForVNI. In either case, @p ForVNI will be the return value.
87   VNInfo *createDeadDef(SlotIndex Def, VNInfo::Allocator *VNInfoAllocator,
88                         VNInfo *ForVNI) {
89     assert(!Def.isDead() && "Cannot define a value at the dead slot");
90     assert((!ForVNI || ForVNI->def == Def) &&
91            "If ForVNI is specified, it must match Def");
92     iterator I = impl().find(Def);
93     if (I == segments().end()) {
94       VNInfo *VNI = ForVNI ? ForVNI : LR->getNextValue(Def, *VNInfoAllocator);
95       impl().insertAtEnd(Segment(Def, Def.getDeadSlot(), VNI));
96       return VNI;
97     }
98 
99     Segment *S = segmentAt(I);
100     if (SlotIndex::isSameInstr(Def, S->start)) {
101       assert((!ForVNI || ForVNI == S->valno) && "Value number mismatch");
102       assert(S->valno->def == S->start && "Inconsistent existing value def");
103 
104       // It is possible to have both normal and early-clobber defs of the same
105       // register on an instruction. It doesn't make a lot of sense, but it is
106       // possible to specify in inline assembly.
107       //
108       // Just convert everything to early-clobber.
109       Def = std::min(Def, S->start);
110       if (Def != S->start)
111         S->start = S->valno->def = Def;
112       return S->valno;
113     }
114     assert(SlotIndex::isEarlierInstr(Def, S->start) && "Already live at def");
115     VNInfo *VNI = ForVNI ? ForVNI : LR->getNextValue(Def, *VNInfoAllocator);
116     segments().insert(I, Segment(Def, Def.getDeadSlot(), VNI));
117     return VNI;
118   }
119 
120   VNInfo *extendInBlock(SlotIndex StartIdx, SlotIndex Use) {
121     if (segments().empty())
122       return nullptr;
123     iterator I =
124       impl().findInsertPos(Segment(Use.getPrevSlot(), Use, nullptr));
125     if (I == segments().begin())
126       return nullptr;
127     --I;
128     if (I->end <= StartIdx)
129       return nullptr;
130     if (I->end < Use)
131       extendSegmentEndTo(I, Use);
132     return I->valno;
133   }
134 
135   std::pair<VNInfo*,bool> extendInBlock(ArrayRef<SlotIndex> Undefs,
136       SlotIndex StartIdx, SlotIndex Use) {
137     if (segments().empty())
138       return std::make_pair(nullptr, false);
139     SlotIndex BeforeUse = Use.getPrevSlot();
140     iterator I = impl().findInsertPos(Segment(BeforeUse, Use, nullptr));
141     if (I == segments().begin())
142       return std::make_pair(nullptr, LR->isUndefIn(Undefs, StartIdx, BeforeUse));
143     --I;
144     if (I->end <= StartIdx)
145       return std::make_pair(nullptr, LR->isUndefIn(Undefs, StartIdx, BeforeUse));
146     if (I->end < Use) {
147       if (LR->isUndefIn(Undefs, I->end, BeforeUse))
148         return std::make_pair(nullptr, true);
149       extendSegmentEndTo(I, Use);
150     }
151     return std::make_pair(I->valno, false);
152   }
153 
154   /// This method is used when we want to extend the segment specified
155   /// by I to end at the specified endpoint. To do this, we should
156   /// merge and eliminate all segments that this will overlap
157   /// with. The iterator is not invalidated.
158   void extendSegmentEndTo(iterator I, SlotIndex NewEnd) {
159     assert(I != segments().end() && "Not a valid segment!");
160     Segment *S = segmentAt(I);
161     VNInfo *ValNo = I->valno;
162 
163     // Search for the first segment that we can't merge with.
164     iterator MergeTo = std::next(I);
165     for (; MergeTo != segments().end() && NewEnd >= MergeTo->end; ++MergeTo)
166       assert(MergeTo->valno == ValNo && "Cannot merge with differing values!");
167 
168     // If NewEnd was in the middle of a segment, make sure to get its endpoint.
169     S->end = std::max(NewEnd, std::prev(MergeTo)->end);
170 
171     // If the newly formed segment now touches the segment after it and if they
172     // have the same value number, merge the two segments into one segment.
173     if (MergeTo != segments().end() && MergeTo->start <= I->end &&
174         MergeTo->valno == ValNo) {
175       S->end = MergeTo->end;
176       ++MergeTo;
177     }
178 
179     // Erase any dead segments.
180     segments().erase(std::next(I), MergeTo);
181   }
182 
183   /// This method is used when we want to extend the segment specified
184   /// by I to start at the specified endpoint.  To do this, we should
185   /// merge and eliminate all segments that this will overlap with.
186   iterator extendSegmentStartTo(iterator I, SlotIndex NewStart) {
187     assert(I != segments().end() && "Not a valid segment!");
188     Segment *S = segmentAt(I);
189     VNInfo *ValNo = I->valno;
190 
191     // Search for the first segment that we can't merge with.
192     iterator MergeTo = I;
193     do {
194       if (MergeTo == segments().begin()) {
195         S->start = NewStart;
196         segments().erase(MergeTo, I);
197         return I;
198       }
199       assert(MergeTo->valno == ValNo && "Cannot merge with differing values!");
200       --MergeTo;
201     } while (NewStart <= MergeTo->start);
202 
203     // If we start in the middle of another segment, just delete a range and
204     // extend that segment.
205     if (MergeTo->end >= NewStart && MergeTo->valno == ValNo) {
206       segmentAt(MergeTo)->end = S->end;
207     } else {
208       // Otherwise, extend the segment right after.
209       ++MergeTo;
210       Segment *MergeToSeg = segmentAt(MergeTo);
211       MergeToSeg->start = NewStart;
212       MergeToSeg->end = S->end;
213     }
214 
215     segments().erase(std::next(MergeTo), std::next(I));
216     return MergeTo;
217   }
218 
219   iterator addSegment(Segment S) {
220     SlotIndex Start = S.start, End = S.end;
221     iterator I = impl().findInsertPos(S);
222 
223     // If the inserted segment starts in the middle or right at the end of
224     // another segment, just extend that segment to contain the segment of S.
225     if (I != segments().begin()) {
226       iterator B = std::prev(I);
227       if (S.valno == B->valno) {
228         if (B->start <= Start && B->end >= Start) {
229           extendSegmentEndTo(B, End);
230           return B;
231         }
232       } else {
233         // Check to make sure that we are not overlapping two live segments with
234         // different valno's.
235         assert(B->end <= Start &&
236                "Cannot overlap two segments with differing ValID's"
237                " (did you def the same reg twice in a MachineInstr?)");
238       }
239     }
240 
241     // Otherwise, if this segment ends in the middle of, or right next
242     // to, another segment, merge it into that segment.
243     if (I != segments().end()) {
244       if (S.valno == I->valno) {
245         if (I->start <= End) {
246           I = extendSegmentStartTo(I, Start);
247 
248           // If S is a complete superset of a segment, we may need to grow its
249           // endpoint as well.
250           if (End > I->end)
251             extendSegmentEndTo(I, End);
252           return I;
253         }
254       } else {
255         // Check to make sure that we are not overlapping two live segments with
256         // different valno's.
257         assert(I->start >= End &&
258                "Cannot overlap two segments with differing ValID's");
259       }
260     }
261 
262     // Otherwise, this is just a new segment that doesn't interact with
263     // anything.
264     // Insert it.
265     return segments().insert(I, S);
266   }
267 
268 private:
269   ImplT &impl() { return *static_cast<ImplT *>(this); }
270 
271   CollectionT &segments() { return impl().segmentsColl(); }
272 
273   Segment *segmentAt(iterator I) { return const_cast<Segment *>(&(*I)); }
274 };
275 
276 //===----------------------------------------------------------------------===//
277 //   Instantiation of the methods for calculation of live ranges
278 //   based on a segment vector.
279 //===----------------------------------------------------------------------===//
280 
281 class CalcLiveRangeUtilVector;
282 using CalcLiveRangeUtilVectorBase =
283     CalcLiveRangeUtilBase<CalcLiveRangeUtilVector, LiveRange::iterator,
284                           LiveRange::Segments>;
285 
286 class CalcLiveRangeUtilVector : public CalcLiveRangeUtilVectorBase {
287 public:
288   CalcLiveRangeUtilVector(LiveRange *LR) : CalcLiveRangeUtilVectorBase(LR) {}
289 
290 private:
291   friend CalcLiveRangeUtilVectorBase;
292 
293   LiveRange::Segments &segmentsColl() { return LR->segments; }
294 
295   void insertAtEnd(const Segment &S) { LR->segments.push_back(S); }
296 
297   iterator find(SlotIndex Pos) { return LR->find(Pos); }
298 
299   iterator findInsertPos(Segment S) { return llvm::upper_bound(*LR, S.start); }
300 };
301 
302 //===----------------------------------------------------------------------===//
303 //   Instantiation of the methods for calculation of live ranges
304 //   based on a segment set.
305 //===----------------------------------------------------------------------===//
306 
307 class CalcLiveRangeUtilSet;
308 using CalcLiveRangeUtilSetBase =
309     CalcLiveRangeUtilBase<CalcLiveRangeUtilSet, LiveRange::SegmentSet::iterator,
310                           LiveRange::SegmentSet>;
311 
312 class CalcLiveRangeUtilSet : public CalcLiveRangeUtilSetBase {
313 public:
314   CalcLiveRangeUtilSet(LiveRange *LR) : CalcLiveRangeUtilSetBase(LR) {}
315 
316 private:
317   friend CalcLiveRangeUtilSetBase;
318 
319   LiveRange::SegmentSet &segmentsColl() { return *LR->segmentSet; }
320 
321   void insertAtEnd(const Segment &S) {
322     LR->segmentSet->insert(LR->segmentSet->end(), S);
323   }
324 
325   iterator find(SlotIndex Pos) {
326     iterator I =
327         LR->segmentSet->upper_bound(Segment(Pos, Pos.getNextSlot(), nullptr));
328     if (I == LR->segmentSet->begin())
329       return I;
330     iterator PrevI = std::prev(I);
331     if (Pos < (*PrevI).end)
332       return PrevI;
333     return I;
334   }
335 
336   iterator findInsertPos(Segment S) {
337     iterator I = LR->segmentSet->upper_bound(S);
338     if (I != LR->segmentSet->end() && !(S.start < *I))
339       ++I;
340     return I;
341   }
342 };
343 
344 } // end anonymous namespace
345 
346 //===----------------------------------------------------------------------===//
347 //   LiveRange methods
348 //===----------------------------------------------------------------------===//
349 
350 LiveRange::iterator LiveRange::find(SlotIndex Pos) {
351   // This algorithm is basically std::upper_bound.
352   // Unfortunately, std::upper_bound cannot be used with mixed types until we
353   // adopt C++0x. Many libraries can do it, but not all.
354   if (empty() || Pos >= endIndex())
355     return end();
356   iterator I = begin();
357   size_t Len = size();
358   do {
359     size_t Mid = Len >> 1;
360     if (Pos < I[Mid].end) {
361       Len = Mid;
362     } else {
363       I += Mid + 1;
364       Len -= Mid + 1;
365     }
366   } while (Len);
367   return I;
368 }
369 
370 VNInfo *LiveRange::createDeadDef(SlotIndex Def, VNInfo::Allocator &VNIAlloc) {
371   // Use the segment set, if it is available.
372   if (segmentSet != nullptr)
373     return CalcLiveRangeUtilSet(this).createDeadDef(Def, &VNIAlloc, nullptr);
374   // Otherwise use the segment vector.
375   return CalcLiveRangeUtilVector(this).createDeadDef(Def, &VNIAlloc, nullptr);
376 }
377 
378 VNInfo *LiveRange::createDeadDef(VNInfo *VNI) {
379   // Use the segment set, if it is available.
380   if (segmentSet != nullptr)
381     return CalcLiveRangeUtilSet(this).createDeadDef(VNI->def, nullptr, VNI);
382   // Otherwise use the segment vector.
383   return CalcLiveRangeUtilVector(this).createDeadDef(VNI->def, nullptr, VNI);
384 }
385 
386 // overlaps - Return true if the intersection of the two live ranges is
387 // not empty.
388 //
389 // An example for overlaps():
390 //
391 // 0: A = ...
392 // 4: B = ...
393 // 8: C = A + B ;; last use of A
394 //
395 // The live ranges should look like:
396 //
397 // A = [3, 11)
398 // B = [7, x)
399 // C = [11, y)
400 //
401 // A->overlaps(C) should return false since we want to be able to join
402 // A and C.
403 //
404 bool LiveRange::overlapsFrom(const LiveRange& other,
405                              const_iterator StartPos) const {
406   assert(!empty() && "empty range");
407   const_iterator i = begin();
408   const_iterator ie = end();
409   const_iterator j = StartPos;
410   const_iterator je = other.end();
411 
412   assert((StartPos->start <= i->start || StartPos == other.begin()) &&
413          StartPos != other.end() && "Bogus start position hint!");
414 
415   if (i->start < j->start) {
416     i = std::upper_bound(i, ie, j->start);
417     if (i != begin()) --i;
418   } else if (j->start < i->start) {
419     ++StartPos;
420     if (StartPos != other.end() && StartPos->start <= i->start) {
421       assert(StartPos < other.end() && i < end());
422       j = std::upper_bound(j, je, i->start);
423       if (j != other.begin()) --j;
424     }
425   } else {
426     return true;
427   }
428 
429   if (j == je) return false;
430 
431   while (i != ie) {
432     if (i->start > j->start) {
433       std::swap(i, j);
434       std::swap(ie, je);
435     }
436 
437     if (i->end > j->start)
438       return true;
439     ++i;
440   }
441 
442   return false;
443 }
444 
445 bool LiveRange::overlaps(const LiveRange &Other, const CoalescerPair &CP,
446                          const SlotIndexes &Indexes) const {
447   assert(!empty() && "empty range");
448   if (Other.empty())
449     return false;
450 
451   // Use binary searches to find initial positions.
452   const_iterator I = find(Other.beginIndex());
453   const_iterator IE = end();
454   if (I == IE)
455     return false;
456   const_iterator J = Other.find(I->start);
457   const_iterator JE = Other.end();
458   if (J == JE)
459     return false;
460 
461   while (true) {
462     // J has just been advanced to satisfy:
463     assert(J->end >= I->start);
464     // Check for an overlap.
465     if (J->start < I->end) {
466       // I and J are overlapping. Find the later start.
467       SlotIndex Def = std::max(I->start, J->start);
468       // Allow the overlap if Def is a coalescable copy.
469       if (Def.isBlock() ||
470           !CP.isCoalescable(Indexes.getInstructionFromIndex(Def)))
471         return true;
472     }
473     // Advance the iterator that ends first to check for more overlaps.
474     if (J->end > I->end) {
475       std::swap(I, J);
476       std::swap(IE, JE);
477     }
478     // Advance J until J->end >= I->start.
479     do
480       if (++J == JE)
481         return false;
482     while (J->end < I->start);
483   }
484 }
485 
486 /// overlaps - Return true if the live range overlaps an interval specified
487 /// by [Start, End).
488 bool LiveRange::overlaps(SlotIndex Start, SlotIndex End) const {
489   assert(Start < End && "Invalid range");
490   const_iterator I = std::lower_bound(begin(), end(), End);
491   return I != begin() && (--I)->end > Start;
492 }
493 
494 bool LiveRange::covers(const LiveRange &Other) const {
495   if (empty())
496     return Other.empty();
497 
498   const_iterator I = begin();
499   for (const Segment &O : Other.segments) {
500     I = advanceTo(I, O.start);
501     if (I == end() || I->start > O.start)
502       return false;
503 
504     // Check adjacent live segments and see if we can get behind O.end.
505     while (I->end < O.end) {
506       const_iterator Last = I;
507       // Get next segment and abort if it was not adjacent.
508       ++I;
509       if (I == end() || Last->end != I->start)
510         return false;
511     }
512   }
513   return true;
514 }
515 
516 /// ValNo is dead, remove it.  If it is the largest value number, just nuke it
517 /// (and any other deleted values neighboring it), otherwise mark it as ~1U so
518 /// it can be nuked later.
519 void LiveRange::markValNoForDeletion(VNInfo *ValNo) {
520   if (ValNo->id == getNumValNums()-1) {
521     do {
522       valnos.pop_back();
523     } while (!valnos.empty() && valnos.back()->isUnused());
524   } else {
525     ValNo->markUnused();
526   }
527 }
528 
529 /// RenumberValues - Renumber all values in order of appearance and delete the
530 /// remaining unused values.
531 void LiveRange::RenumberValues() {
532   SmallPtrSet<VNInfo*, 8> Seen;
533   valnos.clear();
534   for (const Segment &S : segments) {
535     VNInfo *VNI = S.valno;
536     if (!Seen.insert(VNI).second)
537       continue;
538     assert(!VNI->isUnused() && "Unused valno used by live segment");
539     VNI->id = (unsigned)valnos.size();
540     valnos.push_back(VNI);
541   }
542 }
543 
544 void LiveRange::addSegmentToSet(Segment S) {
545   CalcLiveRangeUtilSet(this).addSegment(S);
546 }
547 
548 LiveRange::iterator LiveRange::addSegment(Segment S) {
549   // Use the segment set, if it is available.
550   if (segmentSet != nullptr) {
551     addSegmentToSet(S);
552     return end();
553   }
554   // Otherwise use the segment vector.
555   return CalcLiveRangeUtilVector(this).addSegment(S);
556 }
557 
558 void LiveRange::append(const Segment S) {
559   // Check that the segment belongs to the back of the list.
560   assert(segments.empty() || segments.back().end <= S.start);
561   segments.push_back(S);
562 }
563 
564 std::pair<VNInfo*,bool> LiveRange::extendInBlock(ArrayRef<SlotIndex> Undefs,
565     SlotIndex StartIdx, SlotIndex Kill) {
566   // Use the segment set, if it is available.
567   if (segmentSet != nullptr)
568     return CalcLiveRangeUtilSet(this).extendInBlock(Undefs, StartIdx, Kill);
569   // Otherwise use the segment vector.
570   return CalcLiveRangeUtilVector(this).extendInBlock(Undefs, StartIdx, Kill);
571 }
572 
573 VNInfo *LiveRange::extendInBlock(SlotIndex StartIdx, SlotIndex Kill) {
574   // Use the segment set, if it is available.
575   if (segmentSet != nullptr)
576     return CalcLiveRangeUtilSet(this).extendInBlock(StartIdx, Kill);
577   // Otherwise use the segment vector.
578   return CalcLiveRangeUtilVector(this).extendInBlock(StartIdx, Kill);
579 }
580 
581 /// Remove the specified segment from this range.  Note that the segment must
582 /// be in a single Segment in its entirety.
583 void LiveRange::removeSegment(SlotIndex Start, SlotIndex End,
584                               bool RemoveDeadValNo) {
585   // Find the Segment containing this span.
586   iterator I = find(Start);
587   assert(I != end() && "Segment is not in range!");
588   assert(I->containsInterval(Start, End)
589          && "Segment is not entirely in range!");
590 
591   // If the span we are removing is at the start of the Segment, adjust it.
592   VNInfo *ValNo = I->valno;
593   if (I->start == Start) {
594     if (I->end == End) {
595       if (RemoveDeadValNo) {
596         // Check if val# is dead.
597         bool isDead = true;
598         for (const_iterator II = begin(), EE = end(); II != EE; ++II)
599           if (II != I && II->valno == ValNo) {
600             isDead = false;
601             break;
602           }
603         if (isDead) {
604           // Now that ValNo is dead, remove it.
605           markValNoForDeletion(ValNo);
606         }
607       }
608 
609       segments.erase(I);  // Removed the whole Segment.
610     } else
611       I->start = End;
612     return;
613   }
614 
615   // Otherwise if the span we are removing is at the end of the Segment,
616   // adjust the other way.
617   if (I->end == End) {
618     I->end = Start;
619     return;
620   }
621 
622   // Otherwise, we are splitting the Segment into two pieces.
623   SlotIndex OldEnd = I->end;
624   I->end = Start;   // Trim the old segment.
625 
626   // Insert the new one.
627   segments.insert(std::next(I), Segment(End, OldEnd, ValNo));
628 }
629 
630 /// removeValNo - Remove all the segments defined by the specified value#.
631 /// Also remove the value# from value# list.
632 void LiveRange::removeValNo(VNInfo *ValNo) {
633   if (empty()) return;
634   segments.erase(remove_if(*this, [ValNo](const Segment &S) {
635     return S.valno == ValNo;
636   }), end());
637   // Now that ValNo is dead, remove it.
638   markValNoForDeletion(ValNo);
639 }
640 
641 void LiveRange::join(LiveRange &Other,
642                      const int *LHSValNoAssignments,
643                      const int *RHSValNoAssignments,
644                      SmallVectorImpl<VNInfo *> &NewVNInfo) {
645   verify();
646 
647   // Determine if any of our values are mapped.  This is uncommon, so we want
648   // to avoid the range scan if not.
649   bool MustMapCurValNos = false;
650   unsigned NumVals = getNumValNums();
651   unsigned NumNewVals = NewVNInfo.size();
652   for (unsigned i = 0; i != NumVals; ++i) {
653     unsigned LHSValID = LHSValNoAssignments[i];
654     if (i != LHSValID ||
655         (NewVNInfo[LHSValID] && NewVNInfo[LHSValID] != getValNumInfo(i))) {
656       MustMapCurValNos = true;
657       break;
658     }
659   }
660 
661   // If we have to apply a mapping to our base range assignment, rewrite it now.
662   if (MustMapCurValNos && !empty()) {
663     // Map the first live range.
664 
665     iterator OutIt = begin();
666     OutIt->valno = NewVNInfo[LHSValNoAssignments[OutIt->valno->id]];
667     for (iterator I = std::next(OutIt), E = end(); I != E; ++I) {
668       VNInfo* nextValNo = NewVNInfo[LHSValNoAssignments[I->valno->id]];
669       assert(nextValNo && "Huh?");
670 
671       // If this live range has the same value # as its immediate predecessor,
672       // and if they are neighbors, remove one Segment.  This happens when we
673       // have [0,4:0)[4,7:1) and map 0/1 onto the same value #.
674       if (OutIt->valno == nextValNo && OutIt->end == I->start) {
675         OutIt->end = I->end;
676       } else {
677         // Didn't merge. Move OutIt to the next segment,
678         ++OutIt;
679         OutIt->valno = nextValNo;
680         if (OutIt != I) {
681           OutIt->start = I->start;
682           OutIt->end = I->end;
683         }
684       }
685     }
686     // If we merge some segments, chop off the end.
687     ++OutIt;
688     segments.erase(OutIt, end());
689   }
690 
691   // Rewrite Other values before changing the VNInfo ids.
692   // This can leave Other in an invalid state because we're not coalescing
693   // touching segments that now have identical values. That's OK since Other is
694   // not supposed to be valid after calling join();
695   for (Segment &S : Other.segments)
696     S.valno = NewVNInfo[RHSValNoAssignments[S.valno->id]];
697 
698   // Update val# info. Renumber them and make sure they all belong to this
699   // LiveRange now. Also remove dead val#'s.
700   unsigned NumValNos = 0;
701   for (unsigned i = 0; i < NumNewVals; ++i) {
702     VNInfo *VNI = NewVNInfo[i];
703     if (VNI) {
704       if (NumValNos >= NumVals)
705         valnos.push_back(VNI);
706       else
707         valnos[NumValNos] = VNI;
708       VNI->id = NumValNos++;  // Renumber val#.
709     }
710   }
711   if (NumNewVals < NumVals)
712     valnos.resize(NumNewVals);  // shrinkify
713 
714   // Okay, now insert the RHS live segments into the LHS.
715   LiveRangeUpdater Updater(this);
716   for (Segment &S : Other.segments)
717     Updater.add(S);
718 }
719 
720 /// Merge all of the segments in RHS into this live range as the specified
721 /// value number.  The segments in RHS are allowed to overlap with segments in
722 /// the current range, but only if the overlapping segments have the
723 /// specified value number.
724 void LiveRange::MergeSegmentsInAsValue(const LiveRange &RHS,
725                                        VNInfo *LHSValNo) {
726   LiveRangeUpdater Updater(this);
727   for (const Segment &S : RHS.segments)
728     Updater.add(S.start, S.end, LHSValNo);
729 }
730 
731 /// MergeValueInAsValue - Merge all of the live segments of a specific val#
732 /// in RHS into this live range as the specified value number.
733 /// The segments in RHS are allowed to overlap with segments in the
734 /// current range, it will replace the value numbers of the overlaped
735 /// segments with the specified value number.
736 void LiveRange::MergeValueInAsValue(const LiveRange &RHS,
737                                     const VNInfo *RHSValNo,
738                                     VNInfo *LHSValNo) {
739   LiveRangeUpdater Updater(this);
740   for (const Segment &S : RHS.segments)
741     if (S.valno == RHSValNo)
742       Updater.add(S.start, S.end, LHSValNo);
743 }
744 
745 /// MergeValueNumberInto - This method is called when two value nubmers
746 /// are found to be equivalent.  This eliminates V1, replacing all
747 /// segments with the V1 value number with the V2 value number.  This can
748 /// cause merging of V1/V2 values numbers and compaction of the value space.
749 VNInfo *LiveRange::MergeValueNumberInto(VNInfo *V1, VNInfo *V2) {
750   assert(V1 != V2 && "Identical value#'s are always equivalent!");
751 
752   // This code actually merges the (numerically) larger value number into the
753   // smaller value number, which is likely to allow us to compactify the value
754   // space.  The only thing we have to be careful of is to preserve the
755   // instruction that defines the result value.
756 
757   // Make sure V2 is smaller than V1.
758   if (V1->id < V2->id) {
759     V1->copyFrom(*V2);
760     std::swap(V1, V2);
761   }
762 
763   // Merge V1 segments into V2.
764   for (iterator I = begin(); I != end(); ) {
765     iterator S = I++;
766     if (S->valno != V1) continue;  // Not a V1 Segment.
767 
768     // Okay, we found a V1 live range.  If it had a previous, touching, V2 live
769     // range, extend it.
770     if (S != begin()) {
771       iterator Prev = S-1;
772       if (Prev->valno == V2 && Prev->end == S->start) {
773         Prev->end = S->end;
774 
775         // Erase this live-range.
776         segments.erase(S);
777         I = Prev+1;
778         S = Prev;
779       }
780     }
781 
782     // Okay, now we have a V1 or V2 live range that is maximally merged forward.
783     // Ensure that it is a V2 live-range.
784     S->valno = V2;
785 
786     // If we can merge it into later V2 segments, do so now.  We ignore any
787     // following V1 segments, as they will be merged in subsequent iterations
788     // of the loop.
789     if (I != end()) {
790       if (I->start == S->end && I->valno == V2) {
791         S->end = I->end;
792         segments.erase(I);
793         I = S+1;
794       }
795     }
796   }
797 
798   // Now that V1 is dead, remove it.
799   markValNoForDeletion(V1);
800 
801   return V2;
802 }
803 
804 void LiveRange::flushSegmentSet() {
805   assert(segmentSet != nullptr && "segment set must have been created");
806   assert(
807       segments.empty() &&
808       "segment set can be used only initially before switching to the array");
809   segments.append(segmentSet->begin(), segmentSet->end());
810   segmentSet = nullptr;
811   verify();
812 }
813 
814 bool LiveRange::isLiveAtIndexes(ArrayRef<SlotIndex> Slots) const {
815   ArrayRef<SlotIndex>::iterator SlotI = Slots.begin();
816   ArrayRef<SlotIndex>::iterator SlotE = Slots.end();
817 
818   // If there are no regmask slots, we have nothing to search.
819   if (SlotI == SlotE)
820     return false;
821 
822   // Start our search at the first segment that ends after the first slot.
823   const_iterator SegmentI = find(*SlotI);
824   const_iterator SegmentE = end();
825 
826   // If there are no segments that end after the first slot, we're done.
827   if (SegmentI == SegmentE)
828     return false;
829 
830   // Look for each slot in the live range.
831   for ( ; SlotI != SlotE; ++SlotI) {
832     // Go to the next segment that ends after the current slot.
833     // The slot may be within a hole in the range.
834     SegmentI = advanceTo(SegmentI, *SlotI);
835     if (SegmentI == SegmentE)
836       return false;
837 
838     // If this segment contains the slot, we're done.
839     if (SegmentI->contains(*SlotI))
840       return true;
841     // Otherwise, look for the next slot.
842   }
843 
844   // We didn't find a segment containing any of the slots.
845   return false;
846 }
847 
848 void LiveInterval::freeSubRange(SubRange *S) {
849   S->~SubRange();
850   // Memory was allocated with BumpPtr allocator and is not freed here.
851 }
852 
853 void LiveInterval::removeEmptySubRanges() {
854   SubRange **NextPtr = &SubRanges;
855   SubRange *I = *NextPtr;
856   while (I != nullptr) {
857     if (!I->empty()) {
858       NextPtr = &I->Next;
859       I = *NextPtr;
860       continue;
861     }
862     // Skip empty subranges until we find the first nonempty one.
863     do {
864       SubRange *Next = I->Next;
865       freeSubRange(I);
866       I = Next;
867     } while (I != nullptr && I->empty());
868     *NextPtr = I;
869   }
870 }
871 
872 void LiveInterval::clearSubRanges() {
873   for (SubRange *I = SubRanges, *Next; I != nullptr; I = Next) {
874     Next = I->Next;
875     freeSubRange(I);
876   }
877   SubRanges = nullptr;
878 }
879 
880 /// For each VNI in \p SR, check whether or not that value defines part
881 /// of the mask describe by \p LaneMask and if not, remove that value
882 /// from \p SR.
883 static void stripValuesNotDefiningMask(unsigned Reg, LiveInterval::SubRange &SR,
884                                        LaneBitmask LaneMask,
885                                        const SlotIndexes &Indexes,
886                                        const TargetRegisterInfo &TRI,
887                                        unsigned ComposeSubRegIdx) {
888   // Phys reg should not be tracked at subreg level.
889   // Same for noreg (Reg == 0).
890   if (!Register::isVirtualRegister(Reg) || !Reg)
891     return;
892   // Remove the values that don't define those lanes.
893   SmallVector<VNInfo *, 8> ToBeRemoved;
894   for (VNInfo *VNI : SR.valnos) {
895     if (VNI->isUnused())
896       continue;
897     // PHI definitions don't have MI attached, so there is nothing
898     // we can use to strip the VNI.
899     if (VNI->isPHIDef())
900       continue;
901     const MachineInstr *MI = Indexes.getInstructionFromIndex(VNI->def);
902     assert(MI && "Cannot find the definition of a value");
903     bool hasDef = false;
904     for (ConstMIBundleOperands MOI(*MI); MOI.isValid(); ++MOI) {
905       if (!MOI->isReg() || !MOI->isDef())
906         continue;
907       if (MOI->getReg() != Reg)
908         continue;
909       LaneBitmask OrigMask = TRI.getSubRegIndexLaneMask(MOI->getSubReg());
910       LaneBitmask ExpectedDefMask =
911           ComposeSubRegIdx
912               ? TRI.composeSubRegIndexLaneMask(ComposeSubRegIdx, OrigMask)
913               : OrigMask;
914       if ((ExpectedDefMask & LaneMask).none())
915         continue;
916       hasDef = true;
917       break;
918     }
919 
920     if (!hasDef)
921       ToBeRemoved.push_back(VNI);
922   }
923   for (VNInfo *VNI : ToBeRemoved)
924     SR.removeValNo(VNI);
925 
926   // If the subrange is empty at this point, the MIR is invalid. Do not assert
927   // and let the verifier catch this case.
928 }
929 
930 void LiveInterval::refineSubRanges(
931     BumpPtrAllocator &Allocator, LaneBitmask LaneMask,
932     std::function<void(LiveInterval::SubRange &)> Apply,
933     const SlotIndexes &Indexes, const TargetRegisterInfo &TRI,
934     unsigned ComposeSubRegIdx) {
935   LaneBitmask ToApply = LaneMask;
936   for (SubRange &SR : subranges()) {
937     LaneBitmask SRMask = SR.LaneMask;
938     LaneBitmask Matching = SRMask & LaneMask;
939     if (Matching.none())
940       continue;
941 
942     SubRange *MatchingRange;
943     if (SRMask == Matching) {
944       // The subrange fits (it does not cover bits outside \p LaneMask).
945       MatchingRange = &SR;
946     } else {
947       // We have to split the subrange into a matching and non-matching part.
948       // Reduce lanemask of existing lane to non-matching part.
949       SR.LaneMask = SRMask & ~Matching;
950       // Create a new subrange for the matching part
951       MatchingRange = createSubRangeFrom(Allocator, Matching, SR);
952       // Now that the subrange is split in half, make sure we
953       // only keep in the subranges the VNIs that touch the related half.
954       stripValuesNotDefiningMask(reg(), *MatchingRange, Matching, Indexes, TRI,
955                                  ComposeSubRegIdx);
956       stripValuesNotDefiningMask(reg(), SR, SR.LaneMask, Indexes, TRI,
957                                  ComposeSubRegIdx);
958     }
959     Apply(*MatchingRange);
960     ToApply &= ~Matching;
961   }
962   // Create a new subrange if there are uncovered bits left.
963   if (ToApply.any()) {
964     SubRange *NewRange = createSubRange(Allocator, ToApply);
965     Apply(*NewRange);
966   }
967 }
968 
969 unsigned LiveInterval::getSize() const {
970   unsigned Sum = 0;
971   for (const Segment &S : segments)
972     Sum += S.start.distance(S.end);
973   return Sum;
974 }
975 
976 void LiveInterval::computeSubRangeUndefs(SmallVectorImpl<SlotIndex> &Undefs,
977                                          LaneBitmask LaneMask,
978                                          const MachineRegisterInfo &MRI,
979                                          const SlotIndexes &Indexes) const {
980   assert(Register::isVirtualRegister(reg()));
981   LaneBitmask VRegMask = MRI.getMaxLaneMaskForVReg(reg());
982   assert((VRegMask & LaneMask).any());
983   const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
984   for (const MachineOperand &MO : MRI.def_operands(reg())) {
985     if (!MO.isUndef())
986       continue;
987     unsigned SubReg = MO.getSubReg();
988     assert(SubReg != 0 && "Undef should only be set on subreg defs");
989     LaneBitmask DefMask = TRI.getSubRegIndexLaneMask(SubReg);
990     LaneBitmask UndefMask = VRegMask & ~DefMask;
991     if ((UndefMask & LaneMask).any()) {
992       const MachineInstr &MI = *MO.getParent();
993       bool EarlyClobber = MO.isEarlyClobber();
994       SlotIndex Pos = Indexes.getInstructionIndex(MI).getRegSlot(EarlyClobber);
995       Undefs.push_back(Pos);
996     }
997   }
998 }
999 
1000 raw_ostream& llvm::operator<<(raw_ostream& OS, const LiveRange::Segment &S) {
1001   return OS << '[' << S.start << ',' << S.end << ':' << S.valno->id << ')';
1002 }
1003 
1004 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1005 LLVM_DUMP_METHOD void LiveRange::Segment::dump() const {
1006   dbgs() << *this << '\n';
1007 }
1008 #endif
1009 
1010 void LiveRange::print(raw_ostream &OS) const {
1011   if (empty())
1012     OS << "EMPTY";
1013   else {
1014     for (const Segment &S : segments) {
1015       OS << S;
1016       assert(S.valno == getValNumInfo(S.valno->id) && "Bad VNInfo");
1017     }
1018   }
1019 
1020   // Print value number info.
1021   if (getNumValNums()) {
1022     OS << "  ";
1023     unsigned vnum = 0;
1024     for (const_vni_iterator i = vni_begin(), e = vni_end(); i != e;
1025          ++i, ++vnum) {
1026       const VNInfo *vni = *i;
1027       if (vnum) OS << ' ';
1028       OS << vnum << '@';
1029       if (vni->isUnused()) {
1030         OS << 'x';
1031       } else {
1032         OS << vni->def;
1033         if (vni->isPHIDef())
1034           OS << "-phi";
1035       }
1036     }
1037   }
1038 }
1039 
1040 void LiveInterval::SubRange::print(raw_ostream &OS) const {
1041   OS << " L" << PrintLaneMask(LaneMask) << ' '
1042      << static_cast<const LiveRange&>(*this);
1043 }
1044 
1045 void LiveInterval::print(raw_ostream &OS) const {
1046   OS << printReg(reg()) << ' ';
1047   super::print(OS);
1048   // Print subranges
1049   for (const SubRange &SR : subranges())
1050     OS << SR;
1051   OS << " weight:" << Weight;
1052 }
1053 
1054 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1055 LLVM_DUMP_METHOD void LiveRange::dump() const {
1056   dbgs() << *this << '\n';
1057 }
1058 
1059 LLVM_DUMP_METHOD void LiveInterval::SubRange::dump() const {
1060   dbgs() << *this << '\n';
1061 }
1062 
1063 LLVM_DUMP_METHOD void LiveInterval::dump() const {
1064   dbgs() << *this << '\n';
1065 }
1066 #endif
1067 
1068 #ifndef NDEBUG
1069 void LiveRange::verify() const {
1070   for (const_iterator I = begin(), E = end(); I != E; ++I) {
1071     assert(I->start.isValid());
1072     assert(I->end.isValid());
1073     assert(I->start < I->end);
1074     assert(I->valno != nullptr);
1075     assert(I->valno->id < valnos.size());
1076     assert(I->valno == valnos[I->valno->id]);
1077     if (std::next(I) != E) {
1078       assert(I->end <= std::next(I)->start);
1079       if (I->end == std::next(I)->start)
1080         assert(I->valno != std::next(I)->valno);
1081     }
1082   }
1083 }
1084 
1085 void LiveInterval::verify(const MachineRegisterInfo *MRI) const {
1086   super::verify();
1087 
1088   // Make sure SubRanges are fine and LaneMasks are disjunct.
1089   LaneBitmask Mask;
1090   LaneBitmask MaxMask = MRI != nullptr ? MRI->getMaxLaneMaskForVReg(reg())
1091                                        : LaneBitmask::getAll();
1092   for (const SubRange &SR : subranges()) {
1093     // Subrange lanemask should be disjunct to any previous subrange masks.
1094     assert((Mask & SR.LaneMask).none());
1095     Mask |= SR.LaneMask;
1096 
1097     // subrange mask should not contained in maximum lane mask for the vreg.
1098     assert((Mask & ~MaxMask).none());
1099     // empty subranges must be removed.
1100     assert(!SR.empty());
1101 
1102     SR.verify();
1103     // Main liverange should cover subrange.
1104     assert(covers(SR));
1105   }
1106 }
1107 #endif
1108 
1109 //===----------------------------------------------------------------------===//
1110 //                           LiveRangeUpdater class
1111 //===----------------------------------------------------------------------===//
1112 //
1113 // The LiveRangeUpdater class always maintains these invariants:
1114 //
1115 // - When LastStart is invalid, Spills is empty and the iterators are invalid.
1116 //   This is the initial state, and the state created by flush().
1117 //   In this state, isDirty() returns false.
1118 //
1119 // Otherwise, segments are kept in three separate areas:
1120 //
1121 // 1. [begin; WriteI) at the front of LR.
1122 // 2. [ReadI; end) at the back of LR.
1123 // 3. Spills.
1124 //
1125 // - LR.begin() <= WriteI <= ReadI <= LR.end().
1126 // - Segments in all three areas are fully ordered and coalesced.
1127 // - Segments in area 1 precede and can't coalesce with segments in area 2.
1128 // - Segments in Spills precede and can't coalesce with segments in area 2.
1129 // - No coalescing is possible between segments in Spills and segments in area
1130 //   1, and there are no overlapping segments.
1131 //
1132 // The segments in Spills are not ordered with respect to the segments in area
1133 // 1. They need to be merged.
1134 //
1135 // When they exist, Spills.back().start <= LastStart,
1136 //                 and WriteI[-1].start <= LastStart.
1137 
1138 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1139 void LiveRangeUpdater::print(raw_ostream &OS) const {
1140   if (!isDirty()) {
1141     if (LR)
1142       OS << "Clean updater: " << *LR << '\n';
1143     else
1144       OS << "Null updater.\n";
1145     return;
1146   }
1147   assert(LR && "Can't have null LR in dirty updater.");
1148   OS << " updater with gap = " << (ReadI - WriteI)
1149      << ", last start = " << LastStart
1150      << ":\n  Area 1:";
1151   for (const auto &S : make_range(LR->begin(), WriteI))
1152     OS << ' ' << S;
1153   OS << "\n  Spills:";
1154   for (unsigned I = 0, E = Spills.size(); I != E; ++I)
1155     OS << ' ' << Spills[I];
1156   OS << "\n  Area 2:";
1157   for (const auto &S : make_range(ReadI, LR->end()))
1158     OS << ' ' << S;
1159   OS << '\n';
1160 }
1161 
1162 LLVM_DUMP_METHOD void LiveRangeUpdater::dump() const {
1163   print(errs());
1164 }
1165 #endif
1166 
1167 // Determine if A and B should be coalesced.
1168 static inline bool coalescable(const LiveRange::Segment &A,
1169                                const LiveRange::Segment &B) {
1170   assert(A.start <= B.start && "Unordered live segments.");
1171   if (A.end == B.start)
1172     return A.valno == B.valno;
1173   if (A.end < B.start)
1174     return false;
1175   assert(A.valno == B.valno && "Cannot overlap different values");
1176   return true;
1177 }
1178 
1179 void LiveRangeUpdater::add(LiveRange::Segment Seg) {
1180   assert(LR && "Cannot add to a null destination");
1181 
1182   // Fall back to the regular add method if the live range
1183   // is using the segment set instead of the segment vector.
1184   if (LR->segmentSet != nullptr) {
1185     LR->addSegmentToSet(Seg);
1186     return;
1187   }
1188 
1189   // Flush the state if Start moves backwards.
1190   if (!LastStart.isValid() || LastStart > Seg.start) {
1191     if (isDirty())
1192       flush();
1193     // This brings us to an uninitialized state. Reinitialize.
1194     assert(Spills.empty() && "Leftover spilled segments");
1195     WriteI = ReadI = LR->begin();
1196   }
1197 
1198   // Remember start for next time.
1199   LastStart = Seg.start;
1200 
1201   // Advance ReadI until it ends after Seg.start.
1202   LiveRange::iterator E = LR->end();
1203   if (ReadI != E && ReadI->end <= Seg.start) {
1204     // First try to close the gap between WriteI and ReadI with spills.
1205     if (ReadI != WriteI)
1206       mergeSpills();
1207     // Then advance ReadI.
1208     if (ReadI == WriteI)
1209       ReadI = WriteI = LR->find(Seg.start);
1210     else
1211       while (ReadI != E && ReadI->end <= Seg.start)
1212         *WriteI++ = *ReadI++;
1213   }
1214 
1215   assert(ReadI == E || ReadI->end > Seg.start);
1216 
1217   // Check if the ReadI segment begins early.
1218   if (ReadI != E && ReadI->start <= Seg.start) {
1219     assert(ReadI->valno == Seg.valno && "Cannot overlap different values");
1220     // Bail if Seg is completely contained in ReadI.
1221     if (ReadI->end >= Seg.end)
1222       return;
1223     // Coalesce into Seg.
1224     Seg.start = ReadI->start;
1225     ++ReadI;
1226   }
1227 
1228   // Coalesce as much as possible from ReadI into Seg.
1229   while (ReadI != E && coalescable(Seg, *ReadI)) {
1230     Seg.end = std::max(Seg.end, ReadI->end);
1231     ++ReadI;
1232   }
1233 
1234   // Try coalescing Spills.back() into Seg.
1235   if (!Spills.empty() && coalescable(Spills.back(), Seg)) {
1236     Seg.start = Spills.back().start;
1237     Seg.end = std::max(Spills.back().end, Seg.end);
1238     Spills.pop_back();
1239   }
1240 
1241   // Try coalescing Seg into WriteI[-1].
1242   if (WriteI != LR->begin() && coalescable(WriteI[-1], Seg)) {
1243     WriteI[-1].end = std::max(WriteI[-1].end, Seg.end);
1244     return;
1245   }
1246 
1247   // Seg doesn't coalesce with anything, and needs to be inserted somewhere.
1248   if (WriteI != ReadI) {
1249     *WriteI++ = Seg;
1250     return;
1251   }
1252 
1253   // Finally, append to LR or Spills.
1254   if (WriteI == E) {
1255     LR->segments.push_back(Seg);
1256     WriteI = ReadI = LR->end();
1257   } else
1258     Spills.push_back(Seg);
1259 }
1260 
1261 // Merge as many spilled segments as possible into the gap between WriteI
1262 // and ReadI. Advance WriteI to reflect the inserted instructions.
1263 void LiveRangeUpdater::mergeSpills() {
1264   // Perform a backwards merge of Spills and [SpillI;WriteI).
1265   size_t GapSize = ReadI - WriteI;
1266   size_t NumMoved = std::min(Spills.size(), GapSize);
1267   LiveRange::iterator Src = WriteI;
1268   LiveRange::iterator Dst = Src + NumMoved;
1269   LiveRange::iterator SpillSrc = Spills.end();
1270   LiveRange::iterator B = LR->begin();
1271 
1272   // This is the new WriteI position after merging spills.
1273   WriteI = Dst;
1274 
1275   // Now merge Src and Spills backwards.
1276   while (Src != Dst) {
1277     if (Src != B && Src[-1].start > SpillSrc[-1].start)
1278       *--Dst = *--Src;
1279     else
1280       *--Dst = *--SpillSrc;
1281   }
1282   assert(NumMoved == size_t(Spills.end() - SpillSrc));
1283   Spills.erase(SpillSrc, Spills.end());
1284 }
1285 
1286 void LiveRangeUpdater::flush() {
1287   if (!isDirty())
1288     return;
1289   // Clear the dirty state.
1290   LastStart = SlotIndex();
1291 
1292   assert(LR && "Cannot add to a null destination");
1293 
1294   // Nothing to merge?
1295   if (Spills.empty()) {
1296     LR->segments.erase(WriteI, ReadI);
1297     LR->verify();
1298     return;
1299   }
1300 
1301   // Resize the WriteI - ReadI gap to match Spills.
1302   size_t GapSize = ReadI - WriteI;
1303   if (GapSize < Spills.size()) {
1304     // The gap is too small. Make some room.
1305     size_t WritePos = WriteI - LR->begin();
1306     LR->segments.insert(ReadI, Spills.size() - GapSize, LiveRange::Segment());
1307     // This also invalidated ReadI, but it is recomputed below.
1308     WriteI = LR->begin() + WritePos;
1309   } else {
1310     // Shrink the gap if necessary.
1311     LR->segments.erase(WriteI + Spills.size(), ReadI);
1312   }
1313   ReadI = WriteI + Spills.size();
1314   mergeSpills();
1315   LR->verify();
1316 }
1317 
1318 unsigned ConnectedVNInfoEqClasses::Classify(const LiveRange &LR) {
1319   // Create initial equivalence classes.
1320   EqClass.clear();
1321   EqClass.grow(LR.getNumValNums());
1322 
1323   const VNInfo *used = nullptr, *unused = nullptr;
1324 
1325   // Determine connections.
1326   for (const VNInfo *VNI : LR.valnos) {
1327     // Group all unused values into one class.
1328     if (VNI->isUnused()) {
1329       if (unused)
1330         EqClass.join(unused->id, VNI->id);
1331       unused = VNI;
1332       continue;
1333     }
1334     used = VNI;
1335     if (VNI->isPHIDef()) {
1336       const MachineBasicBlock *MBB = LIS.getMBBFromIndex(VNI->def);
1337       assert(MBB && "Phi-def has no defining MBB");
1338       // Connect to values live out of predecessors.
1339       for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
1340            PE = MBB->pred_end(); PI != PE; ++PI)
1341         if (const VNInfo *PVNI = LR.getVNInfoBefore(LIS.getMBBEndIdx(*PI)))
1342           EqClass.join(VNI->id, PVNI->id);
1343     } else {
1344       // Normal value defined by an instruction. Check for two-addr redef.
1345       // FIXME: This could be coincidental. Should we really check for a tied
1346       // operand constraint?
1347       // Note that VNI->def may be a use slot for an early clobber def.
1348       if (const VNInfo *UVNI = LR.getVNInfoBefore(VNI->def))
1349         EqClass.join(VNI->id, UVNI->id);
1350     }
1351   }
1352 
1353   // Lump all the unused values in with the last used value.
1354   if (used && unused)
1355     EqClass.join(used->id, unused->id);
1356 
1357   EqClass.compress();
1358   return EqClass.getNumClasses();
1359 }
1360 
1361 void ConnectedVNInfoEqClasses::Distribute(LiveInterval &LI, LiveInterval *LIV[],
1362                                           MachineRegisterInfo &MRI) {
1363   // Rewrite instructions.
1364   for (MachineRegisterInfo::reg_iterator RI = MRI.reg_begin(LI.reg()),
1365                                          RE = MRI.reg_end();
1366        RI != RE;) {
1367     MachineOperand &MO = *RI;
1368     MachineInstr *MI = RI->getParent();
1369     ++RI;
1370     const VNInfo *VNI;
1371     if (MI->isDebugValue()) {
1372       // DBG_VALUE instructions don't have slot indexes, so get the index of
1373       // the instruction before them. The value is defined there too.
1374       SlotIndex Idx = LIS.getSlotIndexes()->getIndexBefore(*MI);
1375       VNI = LI.Query(Idx).valueOut();
1376     } else {
1377       SlotIndex Idx = LIS.getInstructionIndex(*MI);
1378       LiveQueryResult LRQ = LI.Query(Idx);
1379       VNI = MO.readsReg() ? LRQ.valueIn() : LRQ.valueDefined();
1380     }
1381     // In the case of an <undef> use that isn't tied to any def, VNI will be
1382     // NULL. If the use is tied to a def, VNI will be the defined value.
1383     if (!VNI)
1384       continue;
1385     if (unsigned EqClass = getEqClass(VNI))
1386       MO.setReg(LIV[EqClass - 1]->reg());
1387   }
1388 
1389   // Distribute subregister liveranges.
1390   if (LI.hasSubRanges()) {
1391     unsigned NumComponents = EqClass.getNumClasses();
1392     SmallVector<unsigned, 8> VNIMapping;
1393     SmallVector<LiveInterval::SubRange*, 8> SubRanges;
1394     BumpPtrAllocator &Allocator = LIS.getVNInfoAllocator();
1395     for (LiveInterval::SubRange &SR : LI.subranges()) {
1396       // Create new subranges in the split intervals and construct a mapping
1397       // for the VNInfos in the subrange.
1398       unsigned NumValNos = SR.valnos.size();
1399       VNIMapping.clear();
1400       VNIMapping.reserve(NumValNos);
1401       SubRanges.clear();
1402       SubRanges.resize(NumComponents-1, nullptr);
1403       for (unsigned I = 0; I < NumValNos; ++I) {
1404         const VNInfo &VNI = *SR.valnos[I];
1405         unsigned ComponentNum;
1406         if (VNI.isUnused()) {
1407           ComponentNum = 0;
1408         } else {
1409           const VNInfo *MainRangeVNI = LI.getVNInfoAt(VNI.def);
1410           assert(MainRangeVNI != nullptr
1411                  && "SubRange def must have corresponding main range def");
1412           ComponentNum = getEqClass(MainRangeVNI);
1413           if (ComponentNum > 0 && SubRanges[ComponentNum-1] == nullptr) {
1414             SubRanges[ComponentNum-1]
1415               = LIV[ComponentNum-1]->createSubRange(Allocator, SR.LaneMask);
1416           }
1417         }
1418         VNIMapping.push_back(ComponentNum);
1419       }
1420       DistributeRange(SR, SubRanges.data(), VNIMapping);
1421     }
1422     LI.removeEmptySubRanges();
1423   }
1424 
1425   // Distribute main liverange.
1426   DistributeRange(LI, LIV, EqClass);
1427 }
1428