xref: /freebsd/contrib/llvm-project/llvm/lib/Analysis/MemorySSA.cpp (revision dab59af3bcc7cb7ba01569d3044894b3e860ad56)
1 //===- MemorySSA.cpp - Memory SSA Builder ---------------------------------===//
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 MemorySSA class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/Analysis/MemorySSA.h"
14 #include "llvm/ADT/DenseMap.h"
15 #include "llvm/ADT/DenseMapInfo.h"
16 #include "llvm/ADT/DenseSet.h"
17 #include "llvm/ADT/DepthFirstIterator.h"
18 #include "llvm/ADT/Hashing.h"
19 #include "llvm/ADT/STLExtras.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include "llvm/ADT/StringExtras.h"
23 #include "llvm/ADT/iterator.h"
24 #include "llvm/ADT/iterator_range.h"
25 #include "llvm/Analysis/AliasAnalysis.h"
26 #include "llvm/Analysis/CFGPrinter.h"
27 #include "llvm/Analysis/IteratedDominanceFrontier.h"
28 #include "llvm/Analysis/LoopInfo.h"
29 #include "llvm/Analysis/MemoryLocation.h"
30 #include "llvm/Config/llvm-config.h"
31 #include "llvm/IR/AssemblyAnnotationWriter.h"
32 #include "llvm/IR/BasicBlock.h"
33 #include "llvm/IR/Dominators.h"
34 #include "llvm/IR/Function.h"
35 #include "llvm/IR/Instruction.h"
36 #include "llvm/IR/Instructions.h"
37 #include "llvm/IR/IntrinsicInst.h"
38 #include "llvm/IR/LLVMContext.h"
39 #include "llvm/IR/Operator.h"
40 #include "llvm/IR/PassManager.h"
41 #include "llvm/IR/Use.h"
42 #include "llvm/InitializePasses.h"
43 #include "llvm/Pass.h"
44 #include "llvm/Support/AtomicOrdering.h"
45 #include "llvm/Support/Casting.h"
46 #include "llvm/Support/CommandLine.h"
47 #include "llvm/Support/Compiler.h"
48 #include "llvm/Support/Debug.h"
49 #include "llvm/Support/ErrorHandling.h"
50 #include "llvm/Support/FormattedStream.h"
51 #include "llvm/Support/GraphWriter.h"
52 #include "llvm/Support/raw_ostream.h"
53 #include <algorithm>
54 #include <cassert>
55 #include <iterator>
56 #include <memory>
57 #include <utility>
58 
59 using namespace llvm;
60 
61 #define DEBUG_TYPE "memoryssa"
62 
63 static cl::opt<std::string>
64     DotCFGMSSA("dot-cfg-mssa",
65                cl::value_desc("file name for generated dot file"),
66                cl::desc("file name for generated dot file"), cl::init(""));
67 
68 INITIALIZE_PASS_BEGIN(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false,
69                       true)
70 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
71 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
72 INITIALIZE_PASS_END(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false,
73                     true)
74 
75 static cl::opt<unsigned> MaxCheckLimit(
76     "memssa-check-limit", cl::Hidden, cl::init(100),
77     cl::desc("The maximum number of stores/phis MemorySSA"
78              "will consider trying to walk past (default = 100)"));
79 
80 // Always verify MemorySSA if expensive checking is enabled.
81 #ifdef EXPENSIVE_CHECKS
82 bool llvm::VerifyMemorySSA = true;
83 #else
84 bool llvm::VerifyMemorySSA = false;
85 #endif
86 
87 static cl::opt<bool, true>
88     VerifyMemorySSAX("verify-memoryssa", cl::location(VerifyMemorySSA),
89                      cl::Hidden, cl::desc("Enable verification of MemorySSA."));
90 
91 const static char LiveOnEntryStr[] = "liveOnEntry";
92 
93 namespace {
94 
95 /// An assembly annotator class to print Memory SSA information in
96 /// comments.
97 class MemorySSAAnnotatedWriter : public AssemblyAnnotationWriter {
98   const MemorySSA *MSSA;
99 
100 public:
101   MemorySSAAnnotatedWriter(const MemorySSA *M) : MSSA(M) {}
102 
103   void emitBasicBlockStartAnnot(const BasicBlock *BB,
104                                 formatted_raw_ostream &OS) override {
105     if (MemoryAccess *MA = MSSA->getMemoryAccess(BB))
106       OS << "; " << *MA << "\n";
107   }
108 
109   void emitInstructionAnnot(const Instruction *I,
110                             formatted_raw_ostream &OS) override {
111     if (MemoryAccess *MA = MSSA->getMemoryAccess(I))
112       OS << "; " << *MA << "\n";
113   }
114 };
115 
116 /// An assembly annotator class to print Memory SSA information in
117 /// comments.
118 class MemorySSAWalkerAnnotatedWriter : public AssemblyAnnotationWriter {
119   MemorySSA *MSSA;
120   MemorySSAWalker *Walker;
121   BatchAAResults BAA;
122 
123 public:
124   MemorySSAWalkerAnnotatedWriter(MemorySSA *M)
125       : MSSA(M), Walker(M->getWalker()), BAA(M->getAA()) {}
126 
127   void emitBasicBlockStartAnnot(const BasicBlock *BB,
128                                 formatted_raw_ostream &OS) override {
129     if (MemoryAccess *MA = MSSA->getMemoryAccess(BB))
130       OS << "; " << *MA << "\n";
131   }
132 
133   void emitInstructionAnnot(const Instruction *I,
134                             formatted_raw_ostream &OS) override {
135     if (MemoryAccess *MA = MSSA->getMemoryAccess(I)) {
136       MemoryAccess *Clobber = Walker->getClobberingMemoryAccess(MA, BAA);
137       OS << "; " << *MA;
138       if (Clobber) {
139         OS << " - clobbered by ";
140         if (MSSA->isLiveOnEntryDef(Clobber))
141           OS << LiveOnEntryStr;
142         else
143           OS << *Clobber;
144       }
145       OS << "\n";
146     }
147   }
148 };
149 
150 } // namespace
151 
152 namespace {
153 
154 /// Our current alias analysis API differentiates heavily between calls and
155 /// non-calls, and functions called on one usually assert on the other.
156 /// This class encapsulates the distinction to simplify other code that wants
157 /// "Memory affecting instructions and related data" to use as a key.
158 /// For example, this class is used as a densemap key in the use optimizer.
159 class MemoryLocOrCall {
160 public:
161   bool IsCall = false;
162 
163   MemoryLocOrCall(MemoryUseOrDef *MUD)
164       : MemoryLocOrCall(MUD->getMemoryInst()) {}
165   MemoryLocOrCall(const MemoryUseOrDef *MUD)
166       : MemoryLocOrCall(MUD->getMemoryInst()) {}
167 
168   MemoryLocOrCall(Instruction *Inst) {
169     if (auto *C = dyn_cast<CallBase>(Inst)) {
170       IsCall = true;
171       Call = C;
172     } else {
173       IsCall = false;
174       // There is no such thing as a memorylocation for a fence inst, and it is
175       // unique in that regard.
176       if (!isa<FenceInst>(Inst))
177         Loc = MemoryLocation::get(Inst);
178     }
179   }
180 
181   explicit MemoryLocOrCall(const MemoryLocation &Loc) : Loc(Loc) {}
182 
183   const CallBase *getCall() const {
184     assert(IsCall);
185     return Call;
186   }
187 
188   MemoryLocation getLoc() const {
189     assert(!IsCall);
190     return Loc;
191   }
192 
193   bool operator==(const MemoryLocOrCall &Other) const {
194     if (IsCall != Other.IsCall)
195       return false;
196 
197     if (!IsCall)
198       return Loc == Other.Loc;
199 
200     if (Call->getCalledOperand() != Other.Call->getCalledOperand())
201       return false;
202 
203     return Call->arg_size() == Other.Call->arg_size() &&
204            std::equal(Call->arg_begin(), Call->arg_end(),
205                       Other.Call->arg_begin());
206   }
207 
208 private:
209   union {
210     const CallBase *Call;
211     MemoryLocation Loc;
212   };
213 };
214 
215 } // end anonymous namespace
216 
217 namespace llvm {
218 
219 template <> struct DenseMapInfo<MemoryLocOrCall> {
220   static inline MemoryLocOrCall getEmptyKey() {
221     return MemoryLocOrCall(DenseMapInfo<MemoryLocation>::getEmptyKey());
222   }
223 
224   static inline MemoryLocOrCall getTombstoneKey() {
225     return MemoryLocOrCall(DenseMapInfo<MemoryLocation>::getTombstoneKey());
226   }
227 
228   static unsigned getHashValue(const MemoryLocOrCall &MLOC) {
229     if (!MLOC.IsCall)
230       return hash_combine(
231           MLOC.IsCall,
232           DenseMapInfo<MemoryLocation>::getHashValue(MLOC.getLoc()));
233 
234     hash_code hash =
235         hash_combine(MLOC.IsCall, DenseMapInfo<const Value *>::getHashValue(
236                                       MLOC.getCall()->getCalledOperand()));
237 
238     for (const Value *Arg : MLOC.getCall()->args())
239       hash = hash_combine(hash, DenseMapInfo<const Value *>::getHashValue(Arg));
240     return hash;
241   }
242 
243   static bool isEqual(const MemoryLocOrCall &LHS, const MemoryLocOrCall &RHS) {
244     return LHS == RHS;
245   }
246 };
247 
248 } // end namespace llvm
249 
250 /// This does one-way checks to see if Use could theoretically be hoisted above
251 /// MayClobber. This will not check the other way around.
252 ///
253 /// This assumes that, for the purposes of MemorySSA, Use comes directly after
254 /// MayClobber, with no potentially clobbering operations in between them.
255 /// (Where potentially clobbering ops are memory barriers, aliased stores, etc.)
256 static bool areLoadsReorderable(const LoadInst *Use,
257                                 const LoadInst *MayClobber) {
258   bool VolatileUse = Use->isVolatile();
259   bool VolatileClobber = MayClobber->isVolatile();
260   // Volatile operations may never be reordered with other volatile operations.
261   if (VolatileUse && VolatileClobber)
262     return false;
263   // Otherwise, volatile doesn't matter here. From the language reference:
264   // 'optimizers may change the order of volatile operations relative to
265   // non-volatile operations.'"
266 
267   // If a load is seq_cst, it cannot be moved above other loads. If its ordering
268   // is weaker, it can be moved above other loads. We just need to be sure that
269   // MayClobber isn't an acquire load, because loads can't be moved above
270   // acquire loads.
271   //
272   // Note that this explicitly *does* allow the free reordering of monotonic (or
273   // weaker) loads of the same address.
274   bool SeqCstUse = Use->getOrdering() == AtomicOrdering::SequentiallyConsistent;
275   bool MayClobberIsAcquire = isAtLeastOrStrongerThan(MayClobber->getOrdering(),
276                                                      AtomicOrdering::Acquire);
277   return !(SeqCstUse || MayClobberIsAcquire);
278 }
279 
280 template <typename AliasAnalysisType>
281 static bool
282 instructionClobbersQuery(const MemoryDef *MD, const MemoryLocation &UseLoc,
283                          const Instruction *UseInst, AliasAnalysisType &AA) {
284   Instruction *DefInst = MD->getMemoryInst();
285   assert(DefInst && "Defining instruction not actually an instruction");
286 
287   if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) {
288     // These intrinsics will show up as affecting memory, but they are just
289     // markers, mostly.
290     //
291     // FIXME: We probably don't actually want MemorySSA to model these at all
292     // (including creating MemoryAccesses for them): we just end up inventing
293     // clobbers where they don't really exist at all. Please see D43269 for
294     // context.
295     switch (II->getIntrinsicID()) {
296     case Intrinsic::allow_runtime_check:
297     case Intrinsic::allow_ubsan_check:
298     case Intrinsic::invariant_start:
299     case Intrinsic::invariant_end:
300     case Intrinsic::assume:
301     case Intrinsic::experimental_noalias_scope_decl:
302     case Intrinsic::pseudoprobe:
303       return false;
304     case Intrinsic::dbg_declare:
305     case Intrinsic::dbg_label:
306     case Intrinsic::dbg_value:
307       llvm_unreachable("debuginfo shouldn't have associated defs!");
308     default:
309       break;
310     }
311   }
312 
313   if (auto *CB = dyn_cast_or_null<CallBase>(UseInst)) {
314     ModRefInfo I = AA.getModRefInfo(DefInst, CB);
315     return isModOrRefSet(I);
316   }
317 
318   if (auto *DefLoad = dyn_cast<LoadInst>(DefInst))
319     if (auto *UseLoad = dyn_cast_or_null<LoadInst>(UseInst))
320       return !areLoadsReorderable(UseLoad, DefLoad);
321 
322   ModRefInfo I = AA.getModRefInfo(DefInst, UseLoc);
323   return isModSet(I);
324 }
325 
326 template <typename AliasAnalysisType>
327 static bool instructionClobbersQuery(MemoryDef *MD, const MemoryUseOrDef *MU,
328                                      const MemoryLocOrCall &UseMLOC,
329                                      AliasAnalysisType &AA) {
330   // FIXME: This is a temporary hack to allow a single instructionClobbersQuery
331   // to exist while MemoryLocOrCall is pushed through places.
332   if (UseMLOC.IsCall)
333     return instructionClobbersQuery(MD, MemoryLocation(), MU->getMemoryInst(),
334                                     AA);
335   return instructionClobbersQuery(MD, UseMLOC.getLoc(), MU->getMemoryInst(),
336                                   AA);
337 }
338 
339 // Return true when MD may alias MU, return false otherwise.
340 bool MemorySSAUtil::defClobbersUseOrDef(MemoryDef *MD, const MemoryUseOrDef *MU,
341                                         AliasAnalysis &AA) {
342   return instructionClobbersQuery(MD, MU, MemoryLocOrCall(MU), AA);
343 }
344 
345 namespace {
346 
347 struct UpwardsMemoryQuery {
348   // True if our original query started off as a call
349   bool IsCall = false;
350   // The pointer location we started the query with. This will be empty if
351   // IsCall is true.
352   MemoryLocation StartingLoc;
353   // This is the instruction we were querying about.
354   const Instruction *Inst = nullptr;
355   // The MemoryAccess we actually got called with, used to test local domination
356   const MemoryAccess *OriginalAccess = nullptr;
357   bool SkipSelfAccess = false;
358 
359   UpwardsMemoryQuery() = default;
360 
361   UpwardsMemoryQuery(const Instruction *Inst, const MemoryAccess *Access)
362       : IsCall(isa<CallBase>(Inst)), Inst(Inst), OriginalAccess(Access) {
363     if (!IsCall)
364       StartingLoc = MemoryLocation::get(Inst);
365   }
366 };
367 
368 } // end anonymous namespace
369 
370 template <typename AliasAnalysisType>
371 static bool isUseTriviallyOptimizableToLiveOnEntry(AliasAnalysisType &AA,
372                                                    const Instruction *I) {
373   // If the memory can't be changed, then loads of the memory can't be
374   // clobbered.
375   if (auto *LI = dyn_cast<LoadInst>(I)) {
376     return I->hasMetadata(LLVMContext::MD_invariant_load) ||
377            !isModSet(AA.getModRefInfoMask(MemoryLocation::get(LI)));
378   }
379   return false;
380 }
381 
382 /// Verifies that `Start` is clobbered by `ClobberAt`, and that nothing
383 /// inbetween `Start` and `ClobberAt` can clobbers `Start`.
384 ///
385 /// This is meant to be as simple and self-contained as possible. Because it
386 /// uses no cache, etc., it can be relatively expensive.
387 ///
388 /// \param Start     The MemoryAccess that we want to walk from.
389 /// \param ClobberAt A clobber for Start.
390 /// \param StartLoc  The MemoryLocation for Start.
391 /// \param MSSA      The MemorySSA instance that Start and ClobberAt belong to.
392 /// \param Query     The UpwardsMemoryQuery we used for our search.
393 /// \param AA        The AliasAnalysis we used for our search.
394 /// \param AllowImpreciseClobber Always false, unless we do relaxed verify.
395 
396 LLVM_ATTRIBUTE_UNUSED static void
397 checkClobberSanity(const MemoryAccess *Start, MemoryAccess *ClobberAt,
398                    const MemoryLocation &StartLoc, const MemorySSA &MSSA,
399                    const UpwardsMemoryQuery &Query, BatchAAResults &AA,
400                    bool AllowImpreciseClobber = false) {
401   assert(MSSA.dominates(ClobberAt, Start) && "Clobber doesn't dominate start?");
402 
403   if (MSSA.isLiveOnEntryDef(Start)) {
404     assert(MSSA.isLiveOnEntryDef(ClobberAt) &&
405            "liveOnEntry must clobber itself");
406     return;
407   }
408 
409   bool FoundClobber = false;
410   DenseSet<ConstMemoryAccessPair> VisitedPhis;
411   SmallVector<ConstMemoryAccessPair, 8> Worklist;
412   Worklist.emplace_back(Start, StartLoc);
413   // Walk all paths from Start to ClobberAt, while looking for clobbers. If one
414   // is found, complain.
415   while (!Worklist.empty()) {
416     auto MAP = Worklist.pop_back_val();
417     // All we care about is that nothing from Start to ClobberAt clobbers Start.
418     // We learn nothing from revisiting nodes.
419     if (!VisitedPhis.insert(MAP).second)
420       continue;
421 
422     for (const auto *MA : def_chain(MAP.first)) {
423       if (MA == ClobberAt) {
424         if (const auto *MD = dyn_cast<MemoryDef>(MA)) {
425           // instructionClobbersQuery isn't essentially free, so don't use `|=`,
426           // since it won't let us short-circuit.
427           //
428           // Also, note that this can't be hoisted out of the `Worklist` loop,
429           // since MD may only act as a clobber for 1 of N MemoryLocations.
430           FoundClobber = FoundClobber || MSSA.isLiveOnEntryDef(MD);
431           if (!FoundClobber) {
432             if (instructionClobbersQuery(MD, MAP.second, Query.Inst, AA))
433               FoundClobber = true;
434           }
435         }
436         break;
437       }
438 
439       // We should never hit liveOnEntry, unless it's the clobber.
440       assert(!MSSA.isLiveOnEntryDef(MA) && "Hit liveOnEntry before clobber?");
441 
442       if (const auto *MD = dyn_cast<MemoryDef>(MA)) {
443         // If Start is a Def, skip self.
444         if (MD == Start)
445           continue;
446 
447         assert(!instructionClobbersQuery(MD, MAP.second, Query.Inst, AA) &&
448                "Found clobber before reaching ClobberAt!");
449         continue;
450       }
451 
452       if (const auto *MU = dyn_cast<MemoryUse>(MA)) {
453         (void)MU;
454         assert (MU == Start &&
455                 "Can only find use in def chain if Start is a use");
456         continue;
457       }
458 
459       assert(isa<MemoryPhi>(MA));
460 
461       // Add reachable phi predecessors
462       for (auto ItB = upward_defs_begin(
463                     {const_cast<MemoryAccess *>(MA), MAP.second},
464                     MSSA.getDomTree()),
465                 ItE = upward_defs_end();
466            ItB != ItE; ++ItB)
467         if (MSSA.getDomTree().isReachableFromEntry(ItB.getPhiArgBlock()))
468           Worklist.emplace_back(*ItB);
469     }
470   }
471 
472   // If the verify is done following an optimization, it's possible that
473   // ClobberAt was a conservative clobbering, that we can now infer is not a
474   // true clobbering access. Don't fail the verify if that's the case.
475   // We do have accesses that claim they're optimized, but could be optimized
476   // further. Updating all these can be expensive, so allow it for now (FIXME).
477   if (AllowImpreciseClobber)
478     return;
479 
480   // If ClobberAt is a MemoryPhi, we can assume something above it acted as a
481   // clobber. Otherwise, `ClobberAt` should've acted as a clobber at some point.
482   assert((isa<MemoryPhi>(ClobberAt) || FoundClobber) &&
483          "ClobberAt never acted as a clobber");
484 }
485 
486 namespace {
487 
488 /// Our algorithm for walking (and trying to optimize) clobbers, all wrapped up
489 /// in one class.
490 class ClobberWalker {
491   /// Save a few bytes by using unsigned instead of size_t.
492   using ListIndex = unsigned;
493 
494   /// Represents a span of contiguous MemoryDefs, potentially ending in a
495   /// MemoryPhi.
496   struct DefPath {
497     MemoryLocation Loc;
498     // Note that, because we always walk in reverse, Last will always dominate
499     // First. Also note that First and Last are inclusive.
500     MemoryAccess *First;
501     MemoryAccess *Last;
502     std::optional<ListIndex> Previous;
503 
504     DefPath(const MemoryLocation &Loc, MemoryAccess *First, MemoryAccess *Last,
505             std::optional<ListIndex> Previous)
506         : Loc(Loc), First(First), Last(Last), Previous(Previous) {}
507 
508     DefPath(const MemoryLocation &Loc, MemoryAccess *Init,
509             std::optional<ListIndex> Previous)
510         : DefPath(Loc, Init, Init, Previous) {}
511   };
512 
513   const MemorySSA &MSSA;
514   DominatorTree &DT;
515   BatchAAResults *AA;
516   UpwardsMemoryQuery *Query;
517   unsigned *UpwardWalkLimit;
518 
519   // Phi optimization bookkeeping:
520   // List of DefPath to process during the current phi optimization walk.
521   SmallVector<DefPath, 32> Paths;
522   // List of visited <Access, Location> pairs; we can skip paths already
523   // visited with the same memory location.
524   DenseSet<ConstMemoryAccessPair> VisitedPhis;
525 
526   /// Find the nearest def or phi that `From` can legally be optimized to.
527   const MemoryAccess *getWalkTarget(const MemoryPhi *From) const {
528     assert(From->getNumOperands() && "Phi with no operands?");
529 
530     BasicBlock *BB = From->getBlock();
531     MemoryAccess *Result = MSSA.getLiveOnEntryDef();
532     DomTreeNode *Node = DT.getNode(BB);
533     while ((Node = Node->getIDom())) {
534       auto *Defs = MSSA.getBlockDefs(Node->getBlock());
535       if (Defs)
536         return &*Defs->rbegin();
537     }
538     return Result;
539   }
540 
541   /// Result of calling walkToPhiOrClobber.
542   struct UpwardsWalkResult {
543     /// The "Result" of the walk. Either a clobber, the last thing we walked, or
544     /// both. Include alias info when clobber found.
545     MemoryAccess *Result;
546     bool IsKnownClobber;
547   };
548 
549   /// Walk to the next Phi or Clobber in the def chain starting at Desc.Last.
550   /// This will update Desc.Last as it walks. It will (optionally) also stop at
551   /// StopAt.
552   ///
553   /// This does not test for whether StopAt is a clobber
554   UpwardsWalkResult
555   walkToPhiOrClobber(DefPath &Desc, const MemoryAccess *StopAt = nullptr,
556                      const MemoryAccess *SkipStopAt = nullptr) const {
557     assert(!isa<MemoryUse>(Desc.Last) && "Uses don't exist in my world");
558     assert(UpwardWalkLimit && "Need a valid walk limit");
559     bool LimitAlreadyReached = false;
560     // (*UpwardWalkLimit) may be 0 here, due to the loop in tryOptimizePhi. Set
561     // it to 1. This will not do any alias() calls. It either returns in the
562     // first iteration in the loop below, or is set back to 0 if all def chains
563     // are free of MemoryDefs.
564     if (!*UpwardWalkLimit) {
565       *UpwardWalkLimit = 1;
566       LimitAlreadyReached = true;
567     }
568 
569     for (MemoryAccess *Current : def_chain(Desc.Last)) {
570       Desc.Last = Current;
571       if (Current == StopAt || Current == SkipStopAt)
572         return {Current, false};
573 
574       if (auto *MD = dyn_cast<MemoryDef>(Current)) {
575         if (MSSA.isLiveOnEntryDef(MD))
576           return {MD, true};
577 
578         if (!--*UpwardWalkLimit)
579           return {Current, true};
580 
581         if (instructionClobbersQuery(MD, Desc.Loc, Query->Inst, *AA))
582           return {MD, true};
583       }
584     }
585 
586     if (LimitAlreadyReached)
587       *UpwardWalkLimit = 0;
588 
589     assert(isa<MemoryPhi>(Desc.Last) &&
590            "Ended at a non-clobber that's not a phi?");
591     return {Desc.Last, false};
592   }
593 
594   void addSearches(MemoryPhi *Phi, SmallVectorImpl<ListIndex> &PausedSearches,
595                    ListIndex PriorNode) {
596     auto UpwardDefsBegin = upward_defs_begin({Phi, Paths[PriorNode].Loc}, DT);
597     auto UpwardDefs = make_range(UpwardDefsBegin, upward_defs_end());
598     for (const MemoryAccessPair &P : UpwardDefs) {
599       PausedSearches.push_back(Paths.size());
600       Paths.emplace_back(P.second, P.first, PriorNode);
601     }
602   }
603 
604   /// Represents a search that terminated after finding a clobber. This clobber
605   /// may or may not be present in the path of defs from LastNode..SearchStart,
606   /// since it may have been retrieved from cache.
607   struct TerminatedPath {
608     MemoryAccess *Clobber;
609     ListIndex LastNode;
610   };
611 
612   /// Get an access that keeps us from optimizing to the given phi.
613   ///
614   /// PausedSearches is an array of indices into the Paths array. Its incoming
615   /// value is the indices of searches that stopped at the last phi optimization
616   /// target. It's left in an unspecified state.
617   ///
618   /// If this returns std::nullopt, NewPaused is a vector of searches that
619   /// terminated at StopWhere. Otherwise, NewPaused is left in an unspecified
620   /// state.
621   std::optional<TerminatedPath>
622   getBlockingAccess(const MemoryAccess *StopWhere,
623                     SmallVectorImpl<ListIndex> &PausedSearches,
624                     SmallVectorImpl<ListIndex> &NewPaused,
625                     SmallVectorImpl<TerminatedPath> &Terminated) {
626     assert(!PausedSearches.empty() && "No searches to continue?");
627 
628     // BFS vs DFS really doesn't make a difference here, so just do a DFS with
629     // PausedSearches as our stack.
630     while (!PausedSearches.empty()) {
631       ListIndex PathIndex = PausedSearches.pop_back_val();
632       DefPath &Node = Paths[PathIndex];
633 
634       // If we've already visited this path with this MemoryLocation, we don't
635       // need to do so again.
636       //
637       // NOTE: That we just drop these paths on the ground makes caching
638       // behavior sporadic. e.g. given a diamond:
639       //  A
640       // B C
641       //  D
642       //
643       // ...If we walk D, B, A, C, we'll only cache the result of phi
644       // optimization for A, B, and D; C will be skipped because it dies here.
645       // This arguably isn't the worst thing ever, since:
646       //   - We generally query things in a top-down order, so if we got below D
647       //     without needing cache entries for {C, MemLoc}, then chances are
648       //     that those cache entries would end up ultimately unused.
649       //   - We still cache things for A, so C only needs to walk up a bit.
650       // If this behavior becomes problematic, we can fix without a ton of extra
651       // work.
652       if (!VisitedPhis.insert({Node.Last, Node.Loc}).second)
653         continue;
654 
655       const MemoryAccess *SkipStopWhere = nullptr;
656       if (Query->SkipSelfAccess && Node.Loc == Query->StartingLoc) {
657         assert(isa<MemoryDef>(Query->OriginalAccess));
658         SkipStopWhere = Query->OriginalAccess;
659       }
660 
661       UpwardsWalkResult Res = walkToPhiOrClobber(Node,
662                                                  /*StopAt=*/StopWhere,
663                                                  /*SkipStopAt=*/SkipStopWhere);
664       if (Res.IsKnownClobber) {
665         assert(Res.Result != StopWhere && Res.Result != SkipStopWhere);
666 
667         // If this wasn't a cache hit, we hit a clobber when walking. That's a
668         // failure.
669         TerminatedPath Term{Res.Result, PathIndex};
670         if (!MSSA.dominates(Res.Result, StopWhere))
671           return Term;
672 
673         // Otherwise, it's a valid thing to potentially optimize to.
674         Terminated.push_back(Term);
675         continue;
676       }
677 
678       if (Res.Result == StopWhere || Res.Result == SkipStopWhere) {
679         // We've hit our target. Save this path off for if we want to continue
680         // walking. If we are in the mode of skipping the OriginalAccess, and
681         // we've reached back to the OriginalAccess, do not save path, we've
682         // just looped back to self.
683         if (Res.Result != SkipStopWhere)
684           NewPaused.push_back(PathIndex);
685         continue;
686       }
687 
688       assert(!MSSA.isLiveOnEntryDef(Res.Result) && "liveOnEntry is a clobber");
689       addSearches(cast<MemoryPhi>(Res.Result), PausedSearches, PathIndex);
690     }
691 
692     return std::nullopt;
693   }
694 
695   template <typename T, typename Walker>
696   struct generic_def_path_iterator
697       : public iterator_facade_base<generic_def_path_iterator<T, Walker>,
698                                     std::forward_iterator_tag, T *> {
699     generic_def_path_iterator() = default;
700     generic_def_path_iterator(Walker *W, ListIndex N) : W(W), N(N) {}
701 
702     T &operator*() const { return curNode(); }
703 
704     generic_def_path_iterator &operator++() {
705       N = curNode().Previous;
706       return *this;
707     }
708 
709     bool operator==(const generic_def_path_iterator &O) const {
710       if (N.has_value() != O.N.has_value())
711         return false;
712       return !N || *N == *O.N;
713     }
714 
715   private:
716     T &curNode() const { return W->Paths[*N]; }
717 
718     Walker *W = nullptr;
719     std::optional<ListIndex> N;
720   };
721 
722   using def_path_iterator = generic_def_path_iterator<DefPath, ClobberWalker>;
723   using const_def_path_iterator =
724       generic_def_path_iterator<const DefPath, const ClobberWalker>;
725 
726   iterator_range<def_path_iterator> def_path(ListIndex From) {
727     return make_range(def_path_iterator(this, From), def_path_iterator());
728   }
729 
730   iterator_range<const_def_path_iterator> const_def_path(ListIndex From) const {
731     return make_range(const_def_path_iterator(this, From),
732                       const_def_path_iterator());
733   }
734 
735   struct OptznResult {
736     /// The path that contains our result.
737     TerminatedPath PrimaryClobber;
738     /// The paths that we can legally cache back from, but that aren't
739     /// necessarily the result of the Phi optimization.
740     SmallVector<TerminatedPath, 4> OtherClobbers;
741   };
742 
743   ListIndex defPathIndex(const DefPath &N) const {
744     // The assert looks nicer if we don't need to do &N
745     const DefPath *NP = &N;
746     assert(!Paths.empty() && NP >= &Paths.front() && NP <= &Paths.back() &&
747            "Out of bounds DefPath!");
748     return NP - &Paths.front();
749   }
750 
751   /// Try to optimize a phi as best as we can. Returns a SmallVector of Paths
752   /// that act as legal clobbers. Note that this won't return *all* clobbers.
753   ///
754   /// Phi optimization algorithm tl;dr:
755   ///   - Find the earliest def/phi, A, we can optimize to
756   ///   - Find if all paths from the starting memory access ultimately reach A
757   ///     - If not, optimization isn't possible.
758   ///     - Otherwise, walk from A to another clobber or phi, A'.
759   ///       - If A' is a def, we're done.
760   ///       - If A' is a phi, try to optimize it.
761   ///
762   /// A path is a series of {MemoryAccess, MemoryLocation} pairs. A path
763   /// terminates when a MemoryAccess that clobbers said MemoryLocation is found.
764   OptznResult tryOptimizePhi(MemoryPhi *Phi, MemoryAccess *Start,
765                              const MemoryLocation &Loc) {
766     assert(Paths.empty() && VisitedPhis.empty() &&
767            "Reset the optimization state.");
768 
769     Paths.emplace_back(Loc, Start, Phi, std::nullopt);
770     // Stores how many "valid" optimization nodes we had prior to calling
771     // addSearches/getBlockingAccess. Necessary for caching if we had a blocker.
772     auto PriorPathsSize = Paths.size();
773 
774     SmallVector<ListIndex, 16> PausedSearches;
775     SmallVector<ListIndex, 8> NewPaused;
776     SmallVector<TerminatedPath, 4> TerminatedPaths;
777 
778     addSearches(Phi, PausedSearches, 0);
779 
780     // Moves the TerminatedPath with the "most dominated" Clobber to the end of
781     // Paths.
782     auto MoveDominatedPathToEnd = [&](SmallVectorImpl<TerminatedPath> &Paths) {
783       assert(!Paths.empty() && "Need a path to move");
784       auto Dom = Paths.begin();
785       for (auto I = std::next(Dom), E = Paths.end(); I != E; ++I)
786         if (!MSSA.dominates(I->Clobber, Dom->Clobber))
787           Dom = I;
788       auto Last = Paths.end() - 1;
789       if (Last != Dom)
790         std::iter_swap(Last, Dom);
791     };
792 
793     MemoryPhi *Current = Phi;
794     while (true) {
795       assert(!MSSA.isLiveOnEntryDef(Current) &&
796              "liveOnEntry wasn't treated as a clobber?");
797 
798       const auto *Target = getWalkTarget(Current);
799       // If a TerminatedPath doesn't dominate Target, then it wasn't a legal
800       // optimization for the prior phi.
801       assert(all_of(TerminatedPaths, [&](const TerminatedPath &P) {
802         return MSSA.dominates(P.Clobber, Target);
803       }));
804 
805       // FIXME: This is broken, because the Blocker may be reported to be
806       // liveOnEntry, and we'll happily wait for that to disappear (read: never)
807       // For the moment, this is fine, since we do nothing with blocker info.
808       if (std::optional<TerminatedPath> Blocker = getBlockingAccess(
809               Target, PausedSearches, NewPaused, TerminatedPaths)) {
810 
811         // Find the node we started at. We can't search based on N->Last, since
812         // we may have gone around a loop with a different MemoryLocation.
813         auto Iter = find_if(def_path(Blocker->LastNode), [&](const DefPath &N) {
814           return defPathIndex(N) < PriorPathsSize;
815         });
816         assert(Iter != def_path_iterator());
817 
818         DefPath &CurNode = *Iter;
819         assert(CurNode.Last == Current);
820 
821         // Two things:
822         // A. We can't reliably cache all of NewPaused back. Consider a case
823         //    where we have two paths in NewPaused; one of which can't optimize
824         //    above this phi, whereas the other can. If we cache the second path
825         //    back, we'll end up with suboptimal cache entries. We can handle
826         //    cases like this a bit better when we either try to find all
827         //    clobbers that block phi optimization, or when our cache starts
828         //    supporting unfinished searches.
829         // B. We can't reliably cache TerminatedPaths back here without doing
830         //    extra checks; consider a case like:
831         //       T
832         //      / \
833         //     D   C
834         //      \ /
835         //       S
836         //    Where T is our target, C is a node with a clobber on it, D is a
837         //    diamond (with a clobber *only* on the left or right node, N), and
838         //    S is our start. Say we walk to D, through the node opposite N
839         //    (read: ignoring the clobber), and see a cache entry in the top
840         //    node of D. That cache entry gets put into TerminatedPaths. We then
841         //    walk up to C (N is later in our worklist), find the clobber, and
842         //    quit. If we append TerminatedPaths to OtherClobbers, we'll cache
843         //    the bottom part of D to the cached clobber, ignoring the clobber
844         //    in N. Again, this problem goes away if we start tracking all
845         //    blockers for a given phi optimization.
846         TerminatedPath Result{CurNode.Last, defPathIndex(CurNode)};
847         return {Result, {}};
848       }
849 
850       // If there's nothing left to search, then all paths led to valid clobbers
851       // that we got from our cache; pick the nearest to the start, and allow
852       // the rest to be cached back.
853       if (NewPaused.empty()) {
854         MoveDominatedPathToEnd(TerminatedPaths);
855         TerminatedPath Result = TerminatedPaths.pop_back_val();
856         return {Result, std::move(TerminatedPaths)};
857       }
858 
859       MemoryAccess *DefChainEnd = nullptr;
860       SmallVector<TerminatedPath, 4> Clobbers;
861       for (ListIndex Paused : NewPaused) {
862         UpwardsWalkResult WR = walkToPhiOrClobber(Paths[Paused]);
863         if (WR.IsKnownClobber)
864           Clobbers.push_back({WR.Result, Paused});
865         else
866           // Micro-opt: If we hit the end of the chain, save it.
867           DefChainEnd = WR.Result;
868       }
869 
870       if (!TerminatedPaths.empty()) {
871         // If we couldn't find the dominating phi/liveOnEntry in the above loop,
872         // do it now.
873         if (!DefChainEnd)
874           for (auto *MA : def_chain(const_cast<MemoryAccess *>(Target)))
875             DefChainEnd = MA;
876         assert(DefChainEnd && "Failed to find dominating phi/liveOnEntry");
877 
878         // If any of the terminated paths don't dominate the phi we'll try to
879         // optimize, we need to figure out what they are and quit.
880         const BasicBlock *ChainBB = DefChainEnd->getBlock();
881         for (const TerminatedPath &TP : TerminatedPaths) {
882           // Because we know that DefChainEnd is as "high" as we can go, we
883           // don't need local dominance checks; BB dominance is sufficient.
884           if (DT.dominates(ChainBB, TP.Clobber->getBlock()))
885             Clobbers.push_back(TP);
886         }
887       }
888 
889       // If we have clobbers in the def chain, find the one closest to Current
890       // and quit.
891       if (!Clobbers.empty()) {
892         MoveDominatedPathToEnd(Clobbers);
893         TerminatedPath Result = Clobbers.pop_back_val();
894         return {Result, std::move(Clobbers)};
895       }
896 
897       assert(all_of(NewPaused,
898                     [&](ListIndex I) { return Paths[I].Last == DefChainEnd; }));
899 
900       // Because liveOnEntry is a clobber, this must be a phi.
901       auto *DefChainPhi = cast<MemoryPhi>(DefChainEnd);
902 
903       PriorPathsSize = Paths.size();
904       PausedSearches.clear();
905       for (ListIndex I : NewPaused)
906         addSearches(DefChainPhi, PausedSearches, I);
907       NewPaused.clear();
908 
909       Current = DefChainPhi;
910     }
911   }
912 
913   void verifyOptResult(const OptznResult &R) const {
914     assert(all_of(R.OtherClobbers, [&](const TerminatedPath &P) {
915       return MSSA.dominates(P.Clobber, R.PrimaryClobber.Clobber);
916     }));
917   }
918 
919   void resetPhiOptznState() {
920     Paths.clear();
921     VisitedPhis.clear();
922   }
923 
924 public:
925   ClobberWalker(const MemorySSA &MSSA, DominatorTree &DT)
926       : MSSA(MSSA), DT(DT) {}
927 
928   /// Finds the nearest clobber for the given query, optimizing phis if
929   /// possible.
930   MemoryAccess *findClobber(BatchAAResults &BAA, MemoryAccess *Start,
931                             UpwardsMemoryQuery &Q, unsigned &UpWalkLimit) {
932     AA = &BAA;
933     Query = &Q;
934     UpwardWalkLimit = &UpWalkLimit;
935     // Starting limit must be > 0.
936     if (!UpWalkLimit)
937       UpWalkLimit++;
938 
939     MemoryAccess *Current = Start;
940     // This walker pretends uses don't exist. If we're handed one, silently grab
941     // its def. (This has the nice side-effect of ensuring we never cache uses)
942     if (auto *MU = dyn_cast<MemoryUse>(Start))
943       Current = MU->getDefiningAccess();
944 
945     DefPath FirstDesc(Q.StartingLoc, Current, Current, std::nullopt);
946     // Fast path for the overly-common case (no crazy phi optimization
947     // necessary)
948     UpwardsWalkResult WalkResult = walkToPhiOrClobber(FirstDesc);
949     MemoryAccess *Result;
950     if (WalkResult.IsKnownClobber) {
951       Result = WalkResult.Result;
952     } else {
953       OptznResult OptRes = tryOptimizePhi(cast<MemoryPhi>(FirstDesc.Last),
954                                           Current, Q.StartingLoc);
955       verifyOptResult(OptRes);
956       resetPhiOptznState();
957       Result = OptRes.PrimaryClobber.Clobber;
958     }
959 
960 #ifdef EXPENSIVE_CHECKS
961     if (!Q.SkipSelfAccess && *UpwardWalkLimit > 0)
962       checkClobberSanity(Current, Result, Q.StartingLoc, MSSA, Q, BAA);
963 #endif
964     return Result;
965   }
966 };
967 
968 struct RenamePassData {
969   DomTreeNode *DTN;
970   DomTreeNode::const_iterator ChildIt;
971   MemoryAccess *IncomingVal;
972 
973   RenamePassData(DomTreeNode *D, DomTreeNode::const_iterator It,
974                  MemoryAccess *M)
975       : DTN(D), ChildIt(It), IncomingVal(M) {}
976 
977   void swap(RenamePassData &RHS) {
978     std::swap(DTN, RHS.DTN);
979     std::swap(ChildIt, RHS.ChildIt);
980     std::swap(IncomingVal, RHS.IncomingVal);
981   }
982 };
983 
984 } // end anonymous namespace
985 
986 namespace llvm {
987 
988 class MemorySSA::ClobberWalkerBase {
989   ClobberWalker Walker;
990   MemorySSA *MSSA;
991 
992 public:
993   ClobberWalkerBase(MemorySSA *M, DominatorTree *D) : Walker(*M, *D), MSSA(M) {}
994 
995   MemoryAccess *getClobberingMemoryAccessBase(MemoryAccess *,
996                                               const MemoryLocation &,
997                                               BatchAAResults &, unsigned &);
998   // Third argument (bool), defines whether the clobber search should skip the
999   // original queried access. If true, there will be a follow-up query searching
1000   // for a clobber access past "self". Note that the Optimized access is not
1001   // updated if a new clobber is found by this SkipSelf search. If this
1002   // additional query becomes heavily used we may decide to cache the result.
1003   // Walker instantiations will decide how to set the SkipSelf bool.
1004   MemoryAccess *getClobberingMemoryAccessBase(MemoryAccess *, BatchAAResults &,
1005                                               unsigned &, bool,
1006                                               bool UseInvariantGroup = true);
1007 };
1008 
1009 /// A MemorySSAWalker that does AA walks to disambiguate accesses. It no
1010 /// longer does caching on its own, but the name has been retained for the
1011 /// moment.
1012 class MemorySSA::CachingWalker final : public MemorySSAWalker {
1013   ClobberWalkerBase *Walker;
1014 
1015 public:
1016   CachingWalker(MemorySSA *M, ClobberWalkerBase *W)
1017       : MemorySSAWalker(M), Walker(W) {}
1018   ~CachingWalker() override = default;
1019 
1020   using MemorySSAWalker::getClobberingMemoryAccess;
1021 
1022   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA, BatchAAResults &BAA,
1023                                           unsigned &UWL) {
1024     return Walker->getClobberingMemoryAccessBase(MA, BAA, UWL, false);
1025   }
1026   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1027                                           const MemoryLocation &Loc,
1028                                           BatchAAResults &BAA, unsigned &UWL) {
1029     return Walker->getClobberingMemoryAccessBase(MA, Loc, BAA, UWL);
1030   }
1031   // This method is not accessible outside of this file.
1032   MemoryAccess *getClobberingMemoryAccessWithoutInvariantGroup(
1033       MemoryAccess *MA, BatchAAResults &BAA, unsigned &UWL) {
1034     return Walker->getClobberingMemoryAccessBase(MA, BAA, UWL, false, false);
1035   }
1036 
1037   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1038                                           BatchAAResults &BAA) override {
1039     unsigned UpwardWalkLimit = MaxCheckLimit;
1040     return getClobberingMemoryAccess(MA, BAA, UpwardWalkLimit);
1041   }
1042   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1043                                           const MemoryLocation &Loc,
1044                                           BatchAAResults &BAA) override {
1045     unsigned UpwardWalkLimit = MaxCheckLimit;
1046     return getClobberingMemoryAccess(MA, Loc, BAA, UpwardWalkLimit);
1047   }
1048 
1049   void invalidateInfo(MemoryAccess *MA) override {
1050     if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1051       MUD->resetOptimized();
1052   }
1053 };
1054 
1055 class MemorySSA::SkipSelfWalker final : public MemorySSAWalker {
1056   ClobberWalkerBase *Walker;
1057 
1058 public:
1059   SkipSelfWalker(MemorySSA *M, ClobberWalkerBase *W)
1060       : MemorySSAWalker(M), Walker(W) {}
1061   ~SkipSelfWalker() override = default;
1062 
1063   using MemorySSAWalker::getClobberingMemoryAccess;
1064 
1065   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA, BatchAAResults &BAA,
1066                                           unsigned &UWL) {
1067     return Walker->getClobberingMemoryAccessBase(MA, BAA, UWL, true);
1068   }
1069   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1070                                           const MemoryLocation &Loc,
1071                                           BatchAAResults &BAA, unsigned &UWL) {
1072     return Walker->getClobberingMemoryAccessBase(MA, Loc, BAA, UWL);
1073   }
1074 
1075   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1076                                           BatchAAResults &BAA) override {
1077     unsigned UpwardWalkLimit = MaxCheckLimit;
1078     return getClobberingMemoryAccess(MA, BAA, UpwardWalkLimit);
1079   }
1080   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1081                                           const MemoryLocation &Loc,
1082                                           BatchAAResults &BAA) override {
1083     unsigned UpwardWalkLimit = MaxCheckLimit;
1084     return getClobberingMemoryAccess(MA, Loc, BAA, UpwardWalkLimit);
1085   }
1086 
1087   void invalidateInfo(MemoryAccess *MA) override {
1088     if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1089       MUD->resetOptimized();
1090   }
1091 };
1092 
1093 } // end namespace llvm
1094 
1095 void MemorySSA::renameSuccessorPhis(BasicBlock *BB, MemoryAccess *IncomingVal,
1096                                     bool RenameAllUses) {
1097   // Pass through values to our successors
1098   for (const BasicBlock *S : successors(BB)) {
1099     auto It = PerBlockAccesses.find(S);
1100     // Rename the phi nodes in our successor block
1101     if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front()))
1102       continue;
1103     AccessList *Accesses = It->second.get();
1104     auto *Phi = cast<MemoryPhi>(&Accesses->front());
1105     if (RenameAllUses) {
1106       bool ReplacementDone = false;
1107       for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I)
1108         if (Phi->getIncomingBlock(I) == BB) {
1109           Phi->setIncomingValue(I, IncomingVal);
1110           ReplacementDone = true;
1111         }
1112       (void) ReplacementDone;
1113       assert(ReplacementDone && "Incomplete phi during partial rename");
1114     } else
1115       Phi->addIncoming(IncomingVal, BB);
1116   }
1117 }
1118 
1119 /// Rename a single basic block into MemorySSA form.
1120 /// Uses the standard SSA renaming algorithm.
1121 /// \returns The new incoming value.
1122 MemoryAccess *MemorySSA::renameBlock(BasicBlock *BB, MemoryAccess *IncomingVal,
1123                                      bool RenameAllUses) {
1124   auto It = PerBlockAccesses.find(BB);
1125   // Skip most processing if the list is empty.
1126   if (It != PerBlockAccesses.end()) {
1127     AccessList *Accesses = It->second.get();
1128     for (MemoryAccess &L : *Accesses) {
1129       if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(&L)) {
1130         if (MUD->getDefiningAccess() == nullptr || RenameAllUses)
1131           MUD->setDefiningAccess(IncomingVal);
1132         if (isa<MemoryDef>(&L))
1133           IncomingVal = &L;
1134       } else {
1135         IncomingVal = &L;
1136       }
1137     }
1138   }
1139   return IncomingVal;
1140 }
1141 
1142 /// This is the standard SSA renaming algorithm.
1143 ///
1144 /// We walk the dominator tree in preorder, renaming accesses, and then filling
1145 /// in phi nodes in our successors.
1146 void MemorySSA::renamePass(DomTreeNode *Root, MemoryAccess *IncomingVal,
1147                            SmallPtrSetImpl<BasicBlock *> &Visited,
1148                            bool SkipVisited, bool RenameAllUses) {
1149   assert(Root && "Trying to rename accesses in an unreachable block");
1150 
1151   SmallVector<RenamePassData, 32> WorkStack;
1152   // Skip everything if we already renamed this block and we are skipping.
1153   // Note: You can't sink this into the if, because we need it to occur
1154   // regardless of whether we skip blocks or not.
1155   bool AlreadyVisited = !Visited.insert(Root->getBlock()).second;
1156   if (SkipVisited && AlreadyVisited)
1157     return;
1158 
1159   IncomingVal = renameBlock(Root->getBlock(), IncomingVal, RenameAllUses);
1160   renameSuccessorPhis(Root->getBlock(), IncomingVal, RenameAllUses);
1161   WorkStack.push_back({Root, Root->begin(), IncomingVal});
1162 
1163   while (!WorkStack.empty()) {
1164     DomTreeNode *Node = WorkStack.back().DTN;
1165     DomTreeNode::const_iterator ChildIt = WorkStack.back().ChildIt;
1166     IncomingVal = WorkStack.back().IncomingVal;
1167 
1168     if (ChildIt == Node->end()) {
1169       WorkStack.pop_back();
1170     } else {
1171       DomTreeNode *Child = *ChildIt;
1172       ++WorkStack.back().ChildIt;
1173       BasicBlock *BB = Child->getBlock();
1174       // Note: You can't sink this into the if, because we need it to occur
1175       // regardless of whether we skip blocks or not.
1176       AlreadyVisited = !Visited.insert(BB).second;
1177       if (SkipVisited && AlreadyVisited) {
1178         // We already visited this during our renaming, which can happen when
1179         // being asked to rename multiple blocks. Figure out the incoming val,
1180         // which is the last def.
1181         // Incoming value can only change if there is a block def, and in that
1182         // case, it's the last block def in the list.
1183         if (auto *BlockDefs = getWritableBlockDefs(BB))
1184           IncomingVal = &*BlockDefs->rbegin();
1185       } else
1186         IncomingVal = renameBlock(BB, IncomingVal, RenameAllUses);
1187       renameSuccessorPhis(BB, IncomingVal, RenameAllUses);
1188       WorkStack.push_back({Child, Child->begin(), IncomingVal});
1189     }
1190   }
1191 }
1192 
1193 /// This handles unreachable block accesses by deleting phi nodes in
1194 /// unreachable blocks, and marking all other unreachable MemoryAccess's as
1195 /// being uses of the live on entry definition.
1196 void MemorySSA::markUnreachableAsLiveOnEntry(BasicBlock *BB) {
1197   assert(!DT->isReachableFromEntry(BB) &&
1198          "Reachable block found while handling unreachable blocks");
1199 
1200   // Make sure phi nodes in our reachable successors end up with a
1201   // LiveOnEntryDef for our incoming edge, even though our block is forward
1202   // unreachable.  We could just disconnect these blocks from the CFG fully,
1203   // but we do not right now.
1204   for (const BasicBlock *S : successors(BB)) {
1205     if (!DT->isReachableFromEntry(S))
1206       continue;
1207     auto It = PerBlockAccesses.find(S);
1208     // Rename the phi nodes in our successor block
1209     if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front()))
1210       continue;
1211     AccessList *Accesses = It->second.get();
1212     auto *Phi = cast<MemoryPhi>(&Accesses->front());
1213     Phi->addIncoming(LiveOnEntryDef.get(), BB);
1214   }
1215 
1216   auto It = PerBlockAccesses.find(BB);
1217   if (It == PerBlockAccesses.end())
1218     return;
1219 
1220   auto &Accesses = It->second;
1221   for (auto AI = Accesses->begin(), AE = Accesses->end(); AI != AE;) {
1222     auto Next = std::next(AI);
1223     // If we have a phi, just remove it. We are going to replace all
1224     // users with live on entry.
1225     if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(AI))
1226       UseOrDef->setDefiningAccess(LiveOnEntryDef.get());
1227     else
1228       Accesses->erase(AI);
1229     AI = Next;
1230   }
1231 }
1232 
1233 MemorySSA::MemorySSA(Function &Func, AliasAnalysis *AA, DominatorTree *DT)
1234     : DT(DT), F(&Func), LiveOnEntryDef(nullptr), Walker(nullptr),
1235       SkipWalker(nullptr) {
1236   // Build MemorySSA using a batch alias analysis. This reuses the internal
1237   // state that AA collects during an alias()/getModRefInfo() call. This is
1238   // safe because there are no CFG changes while building MemorySSA and can
1239   // significantly reduce the time spent by the compiler in AA, because we will
1240   // make queries about all the instructions in the Function.
1241   assert(AA && "No alias analysis?");
1242   BatchAAResults BatchAA(*AA);
1243   buildMemorySSA(BatchAA, iterator_range(F->begin(), F->end()));
1244   // Intentionally leave AA to nullptr while building so we don't accidentally
1245   // use non-batch AliasAnalysis.
1246   this->AA = AA;
1247   // Also create the walker here.
1248   getWalker();
1249 }
1250 
1251 MemorySSA::MemorySSA(Loop &L, AliasAnalysis *AA, DominatorTree *DT)
1252     : DT(DT), L(&L), LiveOnEntryDef(nullptr), Walker(nullptr),
1253       SkipWalker(nullptr) {
1254   // Build MemorySSA using a batch alias analysis. This reuses the internal
1255   // state that AA collects during an alias()/getModRefInfo() call. This is
1256   // safe because there are no CFG changes while building MemorySSA and can
1257   // significantly reduce the time spent by the compiler in AA, because we will
1258   // make queries about all the instructions in the Function.
1259   assert(AA && "No alias analysis?");
1260   BatchAAResults BatchAA(*AA);
1261   buildMemorySSA(
1262       BatchAA, map_range(L.blocks(), [](const BasicBlock *BB) -> BasicBlock & {
1263         return *const_cast<BasicBlock *>(BB);
1264       }));
1265   // Intentionally leave AA to nullptr while building so we don't accidentally
1266   // use non-batch AliasAnalysis.
1267   this->AA = AA;
1268   // Also create the walker here.
1269   getWalker();
1270 }
1271 
1272 MemorySSA::~MemorySSA() {
1273   // Drop all our references
1274   for (const auto &Pair : PerBlockAccesses)
1275     for (MemoryAccess &MA : *Pair.second)
1276       MA.dropAllReferences();
1277 }
1278 
1279 MemorySSA::AccessList *MemorySSA::getOrCreateAccessList(const BasicBlock *BB) {
1280   auto Res = PerBlockAccesses.insert(std::make_pair(BB, nullptr));
1281 
1282   if (Res.second)
1283     Res.first->second = std::make_unique<AccessList>();
1284   return Res.first->second.get();
1285 }
1286 
1287 MemorySSA::DefsList *MemorySSA::getOrCreateDefsList(const BasicBlock *BB) {
1288   auto Res = PerBlockDefs.insert(std::make_pair(BB, nullptr));
1289 
1290   if (Res.second)
1291     Res.first->second = std::make_unique<DefsList>();
1292   return Res.first->second.get();
1293 }
1294 
1295 namespace llvm {
1296 
1297 /// This class is a batch walker of all MemoryUse's in the program, and points
1298 /// their defining access at the thing that actually clobbers them.  Because it
1299 /// is a batch walker that touches everything, it does not operate like the
1300 /// other walkers.  This walker is basically performing a top-down SSA renaming
1301 /// pass, where the version stack is used as the cache.  This enables it to be
1302 /// significantly more time and memory efficient than using the regular walker,
1303 /// which is walking bottom-up.
1304 class MemorySSA::OptimizeUses {
1305 public:
1306   OptimizeUses(MemorySSA *MSSA, CachingWalker *Walker, BatchAAResults *BAA,
1307                DominatorTree *DT)
1308       : MSSA(MSSA), Walker(Walker), AA(BAA), DT(DT) {}
1309 
1310   void optimizeUses();
1311 
1312 private:
1313   /// This represents where a given memorylocation is in the stack.
1314   struct MemlocStackInfo {
1315     // This essentially is keeping track of versions of the stack. Whenever
1316     // the stack changes due to pushes or pops, these versions increase.
1317     unsigned long StackEpoch;
1318     unsigned long PopEpoch;
1319     // This is the lower bound of places on the stack to check. It is equal to
1320     // the place the last stack walk ended.
1321     // Note: Correctness depends on this being initialized to 0, which densemap
1322     // does
1323     unsigned long LowerBound;
1324     const BasicBlock *LowerBoundBlock;
1325     // This is where the last walk for this memory location ended.
1326     unsigned long LastKill;
1327     bool LastKillValid;
1328   };
1329 
1330   void optimizeUsesInBlock(const BasicBlock *, unsigned long &, unsigned long &,
1331                            SmallVectorImpl<MemoryAccess *> &,
1332                            DenseMap<MemoryLocOrCall, MemlocStackInfo> &);
1333 
1334   MemorySSA *MSSA;
1335   CachingWalker *Walker;
1336   BatchAAResults *AA;
1337   DominatorTree *DT;
1338 };
1339 
1340 } // end namespace llvm
1341 
1342 /// Optimize the uses in a given block This is basically the SSA renaming
1343 /// algorithm, with one caveat: We are able to use a single stack for all
1344 /// MemoryUses.  This is because the set of *possible* reaching MemoryDefs is
1345 /// the same for every MemoryUse.  The *actual* clobbering MemoryDef is just
1346 /// going to be some position in that stack of possible ones.
1347 ///
1348 /// We track the stack positions that each MemoryLocation needs
1349 /// to check, and last ended at.  This is because we only want to check the
1350 /// things that changed since last time.  The same MemoryLocation should
1351 /// get clobbered by the same store (getModRefInfo does not use invariantness or
1352 /// things like this, and if they start, we can modify MemoryLocOrCall to
1353 /// include relevant data)
1354 void MemorySSA::OptimizeUses::optimizeUsesInBlock(
1355     const BasicBlock *BB, unsigned long &StackEpoch, unsigned long &PopEpoch,
1356     SmallVectorImpl<MemoryAccess *> &VersionStack,
1357     DenseMap<MemoryLocOrCall, MemlocStackInfo> &LocStackInfo) {
1358 
1359   /// If no accesses, nothing to do.
1360   MemorySSA::AccessList *Accesses = MSSA->getWritableBlockAccesses(BB);
1361   if (Accesses == nullptr)
1362     return;
1363 
1364   // Pop everything that doesn't dominate the current block off the stack,
1365   // increment the PopEpoch to account for this.
1366   while (true) {
1367     assert(
1368         !VersionStack.empty() &&
1369         "Version stack should have liveOnEntry sentinel dominating everything");
1370     BasicBlock *BackBlock = VersionStack.back()->getBlock();
1371     if (DT->dominates(BackBlock, BB))
1372       break;
1373     while (VersionStack.back()->getBlock() == BackBlock)
1374       VersionStack.pop_back();
1375     ++PopEpoch;
1376   }
1377 
1378   for (MemoryAccess &MA : *Accesses) {
1379     auto *MU = dyn_cast<MemoryUse>(&MA);
1380     if (!MU) {
1381       VersionStack.push_back(&MA);
1382       ++StackEpoch;
1383       continue;
1384     }
1385 
1386     if (MU->isOptimized())
1387       continue;
1388 
1389     MemoryLocOrCall UseMLOC(MU);
1390     auto &LocInfo = LocStackInfo[UseMLOC];
1391     // If the pop epoch changed, it means we've removed stuff from top of
1392     // stack due to changing blocks. We may have to reset the lower bound or
1393     // last kill info.
1394     if (LocInfo.PopEpoch != PopEpoch) {
1395       LocInfo.PopEpoch = PopEpoch;
1396       LocInfo.StackEpoch = StackEpoch;
1397       // If the lower bound was in something that no longer dominates us, we
1398       // have to reset it.
1399       // We can't simply track stack size, because the stack may have had
1400       // pushes/pops in the meantime.
1401       // XXX: This is non-optimal, but only is slower cases with heavily
1402       // branching dominator trees.  To get the optimal number of queries would
1403       // be to make lowerbound and lastkill a per-loc stack, and pop it until
1404       // the top of that stack dominates us.  This does not seem worth it ATM.
1405       // A much cheaper optimization would be to always explore the deepest
1406       // branch of the dominator tree first. This will guarantee this resets on
1407       // the smallest set of blocks.
1408       if (LocInfo.LowerBoundBlock && LocInfo.LowerBoundBlock != BB &&
1409           !DT->dominates(LocInfo.LowerBoundBlock, BB)) {
1410         // Reset the lower bound of things to check.
1411         // TODO: Some day we should be able to reset to last kill, rather than
1412         // 0.
1413         LocInfo.LowerBound = 0;
1414         LocInfo.LowerBoundBlock = VersionStack[0]->getBlock();
1415         LocInfo.LastKillValid = false;
1416       }
1417     } else if (LocInfo.StackEpoch != StackEpoch) {
1418       // If all that has changed is the StackEpoch, we only have to check the
1419       // new things on the stack, because we've checked everything before.  In
1420       // this case, the lower bound of things to check remains the same.
1421       LocInfo.PopEpoch = PopEpoch;
1422       LocInfo.StackEpoch = StackEpoch;
1423     }
1424     if (!LocInfo.LastKillValid) {
1425       LocInfo.LastKill = VersionStack.size() - 1;
1426       LocInfo.LastKillValid = true;
1427     }
1428 
1429     // At this point, we should have corrected last kill and LowerBound to be
1430     // in bounds.
1431     assert(LocInfo.LowerBound < VersionStack.size() &&
1432            "Lower bound out of range");
1433     assert(LocInfo.LastKill < VersionStack.size() &&
1434            "Last kill info out of range");
1435     // In any case, the new upper bound is the top of the stack.
1436     unsigned long UpperBound = VersionStack.size() - 1;
1437 
1438     if (UpperBound - LocInfo.LowerBound > MaxCheckLimit) {
1439       LLVM_DEBUG(dbgs() << "MemorySSA skipping optimization of " << *MU << " ("
1440                         << *(MU->getMemoryInst()) << ")"
1441                         << " because there are "
1442                         << UpperBound - LocInfo.LowerBound
1443                         << " stores to disambiguate\n");
1444       // Because we did not walk, LastKill is no longer valid, as this may
1445       // have been a kill.
1446       LocInfo.LastKillValid = false;
1447       continue;
1448     }
1449     bool FoundClobberResult = false;
1450     unsigned UpwardWalkLimit = MaxCheckLimit;
1451     while (UpperBound > LocInfo.LowerBound) {
1452       if (isa<MemoryPhi>(VersionStack[UpperBound])) {
1453         // For phis, use the walker, see where we ended up, go there.
1454         // The invariant.group handling in MemorySSA is ad-hoc and doesn't
1455         // support updates, so don't use it to optimize uses.
1456         MemoryAccess *Result =
1457             Walker->getClobberingMemoryAccessWithoutInvariantGroup(
1458                 MU, *AA, UpwardWalkLimit);
1459         // We are guaranteed to find it or something is wrong.
1460         while (VersionStack[UpperBound] != Result) {
1461           assert(UpperBound != 0);
1462           --UpperBound;
1463         }
1464         FoundClobberResult = true;
1465         break;
1466       }
1467 
1468       MemoryDef *MD = cast<MemoryDef>(VersionStack[UpperBound]);
1469       if (instructionClobbersQuery(MD, MU, UseMLOC, *AA)) {
1470         FoundClobberResult = true;
1471         break;
1472       }
1473       --UpperBound;
1474     }
1475 
1476     // At the end of this loop, UpperBound is either a clobber, or lower bound
1477     // PHI walking may cause it to be < LowerBound, and in fact, < LastKill.
1478     if (FoundClobberResult || UpperBound < LocInfo.LastKill) {
1479       MU->setDefiningAccess(VersionStack[UpperBound], true);
1480       LocInfo.LastKill = UpperBound;
1481     } else {
1482       // Otherwise, we checked all the new ones, and now we know we can get to
1483       // LastKill.
1484       MU->setDefiningAccess(VersionStack[LocInfo.LastKill], true);
1485     }
1486     LocInfo.LowerBound = VersionStack.size() - 1;
1487     LocInfo.LowerBoundBlock = BB;
1488   }
1489 }
1490 
1491 /// Optimize uses to point to their actual clobbering definitions.
1492 void MemorySSA::OptimizeUses::optimizeUses() {
1493   SmallVector<MemoryAccess *, 16> VersionStack;
1494   DenseMap<MemoryLocOrCall, MemlocStackInfo> LocStackInfo;
1495   VersionStack.push_back(MSSA->getLiveOnEntryDef());
1496 
1497   unsigned long StackEpoch = 1;
1498   unsigned long PopEpoch = 1;
1499   // We perform a non-recursive top-down dominator tree walk.
1500   for (const auto *DomNode : depth_first(DT->getRootNode()))
1501     optimizeUsesInBlock(DomNode->getBlock(), StackEpoch, PopEpoch, VersionStack,
1502                         LocStackInfo);
1503 }
1504 
1505 void MemorySSA::placePHINodes(
1506     const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks) {
1507   // Determine where our MemoryPhi's should go
1508   ForwardIDFCalculator IDFs(*DT);
1509   IDFs.setDefiningBlocks(DefiningBlocks);
1510   SmallVector<BasicBlock *, 32> IDFBlocks;
1511   IDFs.calculate(IDFBlocks);
1512 
1513   // Now place MemoryPhi nodes.
1514   for (auto &BB : IDFBlocks)
1515     createMemoryPhi(BB);
1516 }
1517 
1518 template <typename IterT>
1519 void MemorySSA::buildMemorySSA(BatchAAResults &BAA, IterT Blocks) {
1520   // We create an access to represent "live on entry", for things like
1521   // arguments or users of globals, where the memory they use is defined before
1522   // the beginning of the function. We do not actually insert it into the IR.
1523   // We do not define a live on exit for the immediate uses, and thus our
1524   // semantics do *not* imply that something with no immediate uses can simply
1525   // be removed.
1526   BasicBlock &StartingPoint = *Blocks.begin();
1527   LiveOnEntryDef.reset(new MemoryDef(StartingPoint.getContext(), nullptr,
1528                                      nullptr, &StartingPoint, NextID++));
1529 
1530   // We maintain lists of memory accesses per-block, trading memory for time. We
1531   // could just look up the memory access for every possible instruction in the
1532   // stream.
1533   SmallPtrSet<BasicBlock *, 32> DefiningBlocks;
1534   // Go through each block, figure out where defs occur, and chain together all
1535   // the accesses.
1536   for (BasicBlock &B : Blocks) {
1537     bool InsertIntoDef = false;
1538     AccessList *Accesses = nullptr;
1539     DefsList *Defs = nullptr;
1540     for (Instruction &I : B) {
1541       MemoryUseOrDef *MUD = createNewAccess(&I, &BAA);
1542       if (!MUD)
1543         continue;
1544 
1545       if (!Accesses)
1546         Accesses = getOrCreateAccessList(&B);
1547       Accesses->push_back(MUD);
1548       if (isa<MemoryDef>(MUD)) {
1549         InsertIntoDef = true;
1550         if (!Defs)
1551           Defs = getOrCreateDefsList(&B);
1552         Defs->push_back(*MUD);
1553       }
1554     }
1555     if (InsertIntoDef)
1556       DefiningBlocks.insert(&B);
1557   }
1558   placePHINodes(DefiningBlocks);
1559 
1560   // Now do regular SSA renaming on the MemoryDef/MemoryUse. Visited will get
1561   // filled in with all blocks.
1562   SmallPtrSet<BasicBlock *, 16> Visited;
1563   if (L) {
1564     // Only building MemorySSA for a single loop. placePHINodes may have
1565     // inserted a MemoryPhi in the loop's preheader. As this is outside the
1566     // scope of the loop, set them to LiveOnEntry.
1567     if (auto *P = getMemoryAccess(L->getLoopPreheader())) {
1568       for (Use &U : make_early_inc_range(P->uses()))
1569         U.set(LiveOnEntryDef.get());
1570       removeFromLists(P);
1571     }
1572     // Now rename accesses in the loop. Populate Visited with the exit blocks of
1573     // the loop, to limit the scope of the renaming.
1574     SmallVector<BasicBlock *> ExitBlocks;
1575     L->getExitBlocks(ExitBlocks);
1576     Visited.insert(ExitBlocks.begin(), ExitBlocks.end());
1577     renamePass(DT->getNode(L->getLoopPreheader()), LiveOnEntryDef.get(),
1578                Visited);
1579   } else {
1580     renamePass(DT->getRootNode(), LiveOnEntryDef.get(), Visited);
1581   }
1582 
1583   // Mark the uses in unreachable blocks as live on entry, so that they go
1584   // somewhere.
1585   for (auto &BB : Blocks)
1586     if (!Visited.count(&BB))
1587       markUnreachableAsLiveOnEntry(&BB);
1588 }
1589 
1590 MemorySSAWalker *MemorySSA::getWalker() { return getWalkerImpl(); }
1591 
1592 MemorySSA::CachingWalker *MemorySSA::getWalkerImpl() {
1593   if (Walker)
1594     return Walker.get();
1595 
1596   if (!WalkerBase)
1597     WalkerBase = std::make_unique<ClobberWalkerBase>(this, DT);
1598 
1599   Walker = std::make_unique<CachingWalker>(this, WalkerBase.get());
1600   return Walker.get();
1601 }
1602 
1603 MemorySSAWalker *MemorySSA::getSkipSelfWalker() {
1604   if (SkipWalker)
1605     return SkipWalker.get();
1606 
1607   if (!WalkerBase)
1608     WalkerBase = std::make_unique<ClobberWalkerBase>(this, DT);
1609 
1610   SkipWalker = std::make_unique<SkipSelfWalker>(this, WalkerBase.get());
1611   return SkipWalker.get();
1612  }
1613 
1614 
1615 // This is a helper function used by the creation routines. It places NewAccess
1616 // into the access and defs lists for a given basic block, at the given
1617 // insertion point.
1618 void MemorySSA::insertIntoListsForBlock(MemoryAccess *NewAccess,
1619                                         const BasicBlock *BB,
1620                                         InsertionPlace Point) {
1621   auto *Accesses = getOrCreateAccessList(BB);
1622   if (Point == Beginning) {
1623     // If it's a phi node, it goes first, otherwise, it goes after any phi
1624     // nodes.
1625     if (isa<MemoryPhi>(NewAccess)) {
1626       Accesses->push_front(NewAccess);
1627       auto *Defs = getOrCreateDefsList(BB);
1628       Defs->push_front(*NewAccess);
1629     } else {
1630       auto AI = find_if_not(
1631           *Accesses, [](const MemoryAccess &MA) { return isa<MemoryPhi>(MA); });
1632       Accesses->insert(AI, NewAccess);
1633       if (!isa<MemoryUse>(NewAccess)) {
1634         auto *Defs = getOrCreateDefsList(BB);
1635         auto DI = find_if_not(
1636             *Defs, [](const MemoryAccess &MA) { return isa<MemoryPhi>(MA); });
1637         Defs->insert(DI, *NewAccess);
1638       }
1639     }
1640   } else {
1641     Accesses->push_back(NewAccess);
1642     if (!isa<MemoryUse>(NewAccess)) {
1643       auto *Defs = getOrCreateDefsList(BB);
1644       Defs->push_back(*NewAccess);
1645     }
1646   }
1647   BlockNumberingValid.erase(BB);
1648 }
1649 
1650 void MemorySSA::insertIntoListsBefore(MemoryAccess *What, const BasicBlock *BB,
1651                                       AccessList::iterator InsertPt) {
1652   auto *Accesses = getWritableBlockAccesses(BB);
1653   bool WasEnd = InsertPt == Accesses->end();
1654   Accesses->insert(AccessList::iterator(InsertPt), What);
1655   if (!isa<MemoryUse>(What)) {
1656     auto *Defs = getOrCreateDefsList(BB);
1657     // If we got asked to insert at the end, we have an easy job, just shove it
1658     // at the end. If we got asked to insert before an existing def, we also get
1659     // an iterator. If we got asked to insert before a use, we have to hunt for
1660     // the next def.
1661     if (WasEnd) {
1662       Defs->push_back(*What);
1663     } else if (isa<MemoryDef>(InsertPt)) {
1664       Defs->insert(InsertPt->getDefsIterator(), *What);
1665     } else {
1666       while (InsertPt != Accesses->end() && !isa<MemoryDef>(InsertPt))
1667         ++InsertPt;
1668       // Either we found a def, or we are inserting at the end
1669       if (InsertPt == Accesses->end())
1670         Defs->push_back(*What);
1671       else
1672         Defs->insert(InsertPt->getDefsIterator(), *What);
1673     }
1674   }
1675   BlockNumberingValid.erase(BB);
1676 }
1677 
1678 void MemorySSA::prepareForMoveTo(MemoryAccess *What, BasicBlock *BB) {
1679   // Keep it in the lookup tables, remove from the lists
1680   removeFromLists(What, false);
1681 
1682   // Note that moving should implicitly invalidate the optimized state of a
1683   // MemoryUse (and Phis can't be optimized). However, it doesn't do so for a
1684   // MemoryDef.
1685   if (auto *MD = dyn_cast<MemoryDef>(What))
1686     MD->resetOptimized();
1687   What->setBlock(BB);
1688 }
1689 
1690 // Move What before Where in the IR.  The end result is that What will belong to
1691 // the right lists and have the right Block set, but will not otherwise be
1692 // correct. It will not have the right defining access, and if it is a def,
1693 // things below it will not properly be updated.
1694 void MemorySSA::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
1695                        AccessList::iterator Where) {
1696   prepareForMoveTo(What, BB);
1697   insertIntoListsBefore(What, BB, Where);
1698 }
1699 
1700 void MemorySSA::moveTo(MemoryAccess *What, BasicBlock *BB,
1701                        InsertionPlace Point) {
1702   if (isa<MemoryPhi>(What)) {
1703     assert(Point == Beginning &&
1704            "Can only move a Phi at the beginning of the block");
1705     // Update lookup table entry
1706     ValueToMemoryAccess.erase(What->getBlock());
1707     bool Inserted = ValueToMemoryAccess.insert({BB, What}).second;
1708     (void)Inserted;
1709     assert(Inserted && "Cannot move a Phi to a block that already has one");
1710   }
1711 
1712   prepareForMoveTo(What, BB);
1713   insertIntoListsForBlock(What, BB, Point);
1714 }
1715 
1716 MemoryPhi *MemorySSA::createMemoryPhi(BasicBlock *BB) {
1717   assert(!getMemoryAccess(BB) && "MemoryPhi already exists for this BB");
1718   MemoryPhi *Phi = new MemoryPhi(BB->getContext(), BB, NextID++);
1719   // Phi's always are placed at the front of the block.
1720   insertIntoListsForBlock(Phi, BB, Beginning);
1721   ValueToMemoryAccess[BB] = Phi;
1722   return Phi;
1723 }
1724 
1725 MemoryUseOrDef *MemorySSA::createDefinedAccess(Instruction *I,
1726                                                MemoryAccess *Definition,
1727                                                const MemoryUseOrDef *Template,
1728                                                bool CreationMustSucceed) {
1729   assert(!isa<PHINode>(I) && "Cannot create a defined access for a PHI");
1730   MemoryUseOrDef *NewAccess = createNewAccess(I, AA, Template);
1731   if (CreationMustSucceed)
1732     assert(NewAccess != nullptr && "Tried to create a memory access for a "
1733                                    "non-memory touching instruction");
1734   if (NewAccess) {
1735     assert((!Definition || !isa<MemoryUse>(Definition)) &&
1736            "A use cannot be a defining access");
1737     NewAccess->setDefiningAccess(Definition);
1738   }
1739   return NewAccess;
1740 }
1741 
1742 // Return true if the instruction has ordering constraints.
1743 // Note specifically that this only considers stores and loads
1744 // because others are still considered ModRef by getModRefInfo.
1745 static inline bool isOrdered(const Instruction *I) {
1746   if (auto *SI = dyn_cast<StoreInst>(I)) {
1747     if (!SI->isUnordered())
1748       return true;
1749   } else if (auto *LI = dyn_cast<LoadInst>(I)) {
1750     if (!LI->isUnordered())
1751       return true;
1752   }
1753   return false;
1754 }
1755 
1756 /// Helper function to create new memory accesses
1757 template <typename AliasAnalysisType>
1758 MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I,
1759                                            AliasAnalysisType *AAP,
1760                                            const MemoryUseOrDef *Template) {
1761   // The assume intrinsic has a control dependency which we model by claiming
1762   // that it writes arbitrarily. Debuginfo intrinsics may be considered
1763   // clobbers when we have a nonstandard AA pipeline. Ignore these fake memory
1764   // dependencies here.
1765   // FIXME: Replace this special casing with a more accurate modelling of
1766   // assume's control dependency.
1767   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
1768     switch (II->getIntrinsicID()) {
1769     default:
1770       break;
1771     case Intrinsic::allow_runtime_check:
1772     case Intrinsic::allow_ubsan_check:
1773     case Intrinsic::assume:
1774     case Intrinsic::experimental_noalias_scope_decl:
1775     case Intrinsic::pseudoprobe:
1776       return nullptr;
1777     }
1778   }
1779 
1780   // Using a nonstandard AA pipelines might leave us with unexpected modref
1781   // results for I, so add a check to not model instructions that may not read
1782   // from or write to memory. This is necessary for correctness.
1783   if (!I->mayReadFromMemory() && !I->mayWriteToMemory())
1784     return nullptr;
1785 
1786   bool Def, Use;
1787   if (Template) {
1788     Def = isa<MemoryDef>(Template);
1789     Use = isa<MemoryUse>(Template);
1790 #if !defined(NDEBUG)
1791     ModRefInfo ModRef = AAP->getModRefInfo(I, std::nullopt);
1792     bool DefCheck, UseCheck;
1793     DefCheck = isModSet(ModRef) || isOrdered(I);
1794     UseCheck = isRefSet(ModRef);
1795     // Memory accesses should only be reduced and can not be increased since AA
1796     // just might return better results as a result of some transformations.
1797     assert((Def == DefCheck || !DefCheck) &&
1798            "Memory accesses should only be reduced");
1799     if (!Def && Use != UseCheck) {
1800       // New Access should not have more power than template access
1801       assert(!UseCheck && "Invalid template");
1802     }
1803 #endif
1804   } else {
1805     // Find out what affect this instruction has on memory.
1806     ModRefInfo ModRef = AAP->getModRefInfo(I, std::nullopt);
1807     // The isOrdered check is used to ensure that volatiles end up as defs
1808     // (atomics end up as ModRef right now anyway).  Until we separate the
1809     // ordering chain from the memory chain, this enables people to see at least
1810     // some relative ordering to volatiles.  Note that getClobberingMemoryAccess
1811     // will still give an answer that bypasses other volatile loads.  TODO:
1812     // Separate memory aliasing and ordering into two different chains so that
1813     // we can precisely represent both "what memory will this read/write/is
1814     // clobbered by" and "what instructions can I move this past".
1815     Def = isModSet(ModRef) || isOrdered(I);
1816     Use = isRefSet(ModRef);
1817   }
1818 
1819   // It's possible for an instruction to not modify memory at all. During
1820   // construction, we ignore them.
1821   if (!Def && !Use)
1822     return nullptr;
1823 
1824   MemoryUseOrDef *MUD;
1825   if (Def) {
1826     MUD = new MemoryDef(I->getContext(), nullptr, I, I->getParent(), NextID++);
1827   } else {
1828     MUD = new MemoryUse(I->getContext(), nullptr, I, I->getParent());
1829     if (isUseTriviallyOptimizableToLiveOnEntry(*AAP, I)) {
1830       MemoryAccess *LiveOnEntry = getLiveOnEntryDef();
1831       MUD->setOptimized(LiveOnEntry);
1832     }
1833   }
1834   ValueToMemoryAccess[I] = MUD;
1835   return MUD;
1836 }
1837 
1838 /// Properly remove \p MA from all of MemorySSA's lookup tables.
1839 void MemorySSA::removeFromLookups(MemoryAccess *MA) {
1840   assert(MA->use_empty() &&
1841          "Trying to remove memory access that still has uses");
1842   BlockNumbering.erase(MA);
1843   if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1844     MUD->setDefiningAccess(nullptr);
1845   // Invalidate our walker's cache if necessary
1846   if (!isa<MemoryUse>(MA))
1847     getWalker()->invalidateInfo(MA);
1848 
1849   Value *MemoryInst;
1850   if (const auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1851     MemoryInst = MUD->getMemoryInst();
1852   else
1853     MemoryInst = MA->getBlock();
1854 
1855   auto VMA = ValueToMemoryAccess.find(MemoryInst);
1856   if (VMA->second == MA)
1857     ValueToMemoryAccess.erase(VMA);
1858 }
1859 
1860 /// Properly remove \p MA from all of MemorySSA's lists.
1861 ///
1862 /// Because of the way the intrusive list and use lists work, it is important to
1863 /// do removal in the right order.
1864 /// ShouldDelete defaults to true, and will cause the memory access to also be
1865 /// deleted, not just removed.
1866 void MemorySSA::removeFromLists(MemoryAccess *MA, bool ShouldDelete) {
1867   BasicBlock *BB = MA->getBlock();
1868   // The access list owns the reference, so we erase it from the non-owning list
1869   // first.
1870   if (!isa<MemoryUse>(MA)) {
1871     auto DefsIt = PerBlockDefs.find(BB);
1872     std::unique_ptr<DefsList> &Defs = DefsIt->second;
1873     Defs->remove(*MA);
1874     if (Defs->empty())
1875       PerBlockDefs.erase(DefsIt);
1876   }
1877 
1878   // The erase call here will delete it. If we don't want it deleted, we call
1879   // remove instead.
1880   auto AccessIt = PerBlockAccesses.find(BB);
1881   std::unique_ptr<AccessList> &Accesses = AccessIt->second;
1882   if (ShouldDelete)
1883     Accesses->erase(MA);
1884   else
1885     Accesses->remove(MA);
1886 
1887   if (Accesses->empty()) {
1888     PerBlockAccesses.erase(AccessIt);
1889     BlockNumberingValid.erase(BB);
1890   }
1891 }
1892 
1893 void MemorySSA::print(raw_ostream &OS) const {
1894   MemorySSAAnnotatedWriter Writer(this);
1895   Function *F = this->F;
1896   if (L)
1897     F = L->getHeader()->getParent();
1898   F->print(OS, &Writer);
1899 }
1900 
1901 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1902 LLVM_DUMP_METHOD void MemorySSA::dump() const { print(dbgs()); }
1903 #endif
1904 
1905 void MemorySSA::verifyMemorySSA(VerificationLevel VL) const {
1906 #if !defined(NDEBUG) && defined(EXPENSIVE_CHECKS)
1907   VL = VerificationLevel::Full;
1908 #endif
1909 
1910 #ifndef NDEBUG
1911   if (F) {
1912     auto Blocks = iterator_range(F->begin(), F->end());
1913     verifyOrderingDominationAndDefUses(Blocks, VL);
1914     verifyDominationNumbers(Blocks);
1915     if (VL == VerificationLevel::Full)
1916       verifyPrevDefInPhis(Blocks);
1917   } else {
1918     assert(L && "must either have loop or function");
1919     auto Blocks =
1920         map_range(L->blocks(), [](const BasicBlock *BB) -> BasicBlock & {
1921           return *const_cast<BasicBlock *>(BB);
1922         });
1923     verifyOrderingDominationAndDefUses(Blocks, VL);
1924     verifyDominationNumbers(Blocks);
1925     if (VL == VerificationLevel::Full)
1926       verifyPrevDefInPhis(Blocks);
1927   }
1928 #endif
1929   // Previously, the verification used to also verify that the clobberingAccess
1930   // cached by MemorySSA is the same as the clobberingAccess found at a later
1931   // query to AA. This does not hold true in general due to the current fragility
1932   // of BasicAA which has arbitrary caps on the things it analyzes before giving
1933   // up. As a result, transformations that are correct, will lead to BasicAA
1934   // returning different Alias answers before and after that transformation.
1935   // Invalidating MemorySSA is not an option, as the results in BasicAA can be so
1936   // random, in the worst case we'd need to rebuild MemorySSA from scratch after
1937   // every transformation, which defeats the purpose of using it. For such an
1938   // example, see test4 added in D51960.
1939 }
1940 
1941 template <typename IterT>
1942 void MemorySSA::verifyPrevDefInPhis(IterT Blocks) const {
1943   for (const BasicBlock &BB : Blocks) {
1944     if (MemoryPhi *Phi = getMemoryAccess(&BB)) {
1945       for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I) {
1946         auto *Pred = Phi->getIncomingBlock(I);
1947         auto *IncAcc = Phi->getIncomingValue(I);
1948         // If Pred has no unreachable predecessors, get last def looking at
1949         // IDoms. If, while walkings IDoms, any of these has an unreachable
1950         // predecessor, then the incoming def can be any access.
1951         if (auto *DTNode = DT->getNode(Pred)) {
1952           while (DTNode) {
1953             if (auto *DefList = getBlockDefs(DTNode->getBlock())) {
1954               auto *LastAcc = &*(--DefList->end());
1955               assert(LastAcc == IncAcc &&
1956                      "Incorrect incoming access into phi.");
1957               (void)IncAcc;
1958               (void)LastAcc;
1959               break;
1960             }
1961             DTNode = DTNode->getIDom();
1962           }
1963         } else {
1964           // If Pred has unreachable predecessors, but has at least a Def, the
1965           // incoming access can be the last Def in Pred, or it could have been
1966           // optimized to LoE. After an update, though, the LoE may have been
1967           // replaced by another access, so IncAcc may be any access.
1968           // If Pred has unreachable predecessors and no Defs, incoming access
1969           // should be LoE; However, after an update, it may be any access.
1970         }
1971       }
1972     }
1973   }
1974 }
1975 
1976 /// Verify that all of the blocks we believe to have valid domination numbers
1977 /// actually have valid domination numbers.
1978 template <typename IterT>
1979 void MemorySSA::verifyDominationNumbers(IterT Blocks) const {
1980   if (BlockNumberingValid.empty())
1981     return;
1982 
1983   SmallPtrSet<const BasicBlock *, 16> ValidBlocks = BlockNumberingValid;
1984   for (const BasicBlock &BB : Blocks) {
1985     if (!ValidBlocks.count(&BB))
1986       continue;
1987 
1988     ValidBlocks.erase(&BB);
1989 
1990     const AccessList *Accesses = getBlockAccesses(&BB);
1991     // It's correct to say an empty block has valid numbering.
1992     if (!Accesses)
1993       continue;
1994 
1995     // Block numbering starts at 1.
1996     unsigned long LastNumber = 0;
1997     for (const MemoryAccess &MA : *Accesses) {
1998       auto ThisNumberIter = BlockNumbering.find(&MA);
1999       assert(ThisNumberIter != BlockNumbering.end() &&
2000              "MemoryAccess has no domination number in a valid block!");
2001 
2002       unsigned long ThisNumber = ThisNumberIter->second;
2003       assert(ThisNumber > LastNumber &&
2004              "Domination numbers should be strictly increasing!");
2005       (void)LastNumber;
2006       LastNumber = ThisNumber;
2007     }
2008   }
2009 
2010   assert(ValidBlocks.empty() &&
2011          "All valid BasicBlocks should exist in F -- dangling pointers?");
2012 }
2013 
2014 /// Verify ordering: the order and existence of MemoryAccesses matches the
2015 /// order and existence of memory affecting instructions.
2016 /// Verify domination: each definition dominates all of its uses.
2017 /// Verify def-uses: the immediate use information - walk all the memory
2018 /// accesses and verifying that, for each use, it appears in the appropriate
2019 /// def's use list
2020 template <typename IterT>
2021 void MemorySSA::verifyOrderingDominationAndDefUses(IterT Blocks,
2022                                                    VerificationLevel VL) const {
2023   // Walk all the blocks, comparing what the lookups think and what the access
2024   // lists think, as well as the order in the blocks vs the order in the access
2025   // lists.
2026   SmallVector<MemoryAccess *, 32> ActualAccesses;
2027   SmallVector<MemoryAccess *, 32> ActualDefs;
2028   for (BasicBlock &B : Blocks) {
2029     const AccessList *AL = getBlockAccesses(&B);
2030     const auto *DL = getBlockDefs(&B);
2031     MemoryPhi *Phi = getMemoryAccess(&B);
2032     if (Phi) {
2033       // Verify ordering.
2034       ActualAccesses.push_back(Phi);
2035       ActualDefs.push_back(Phi);
2036       // Verify domination
2037       for (const Use &U : Phi->uses()) {
2038         assert(dominates(Phi, U) && "Memory PHI does not dominate it's uses");
2039         (void)U;
2040       }
2041       // Verify def-uses for full verify.
2042       if (VL == VerificationLevel::Full) {
2043         assert(Phi->getNumOperands() == pred_size(&B) &&
2044                "Incomplete MemoryPhi Node");
2045         for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I) {
2046           verifyUseInDefs(Phi->getIncomingValue(I), Phi);
2047           assert(is_contained(predecessors(&B), Phi->getIncomingBlock(I)) &&
2048                  "Incoming phi block not a block predecessor");
2049         }
2050       }
2051     }
2052 
2053     for (Instruction &I : B) {
2054       MemoryUseOrDef *MA = getMemoryAccess(&I);
2055       assert((!MA || (AL && (isa<MemoryUse>(MA) || DL))) &&
2056              "We have memory affecting instructions "
2057              "in this block but they are not in the "
2058              "access list or defs list");
2059       if (MA) {
2060         // Verify ordering.
2061         ActualAccesses.push_back(MA);
2062         if (MemoryAccess *MD = dyn_cast<MemoryDef>(MA)) {
2063           // Verify ordering.
2064           ActualDefs.push_back(MA);
2065           // Verify domination.
2066           for (const Use &U : MD->uses()) {
2067             assert(dominates(MD, U) &&
2068                    "Memory Def does not dominate it's uses");
2069             (void)U;
2070           }
2071         }
2072         // Verify def-uses for full verify.
2073         if (VL == VerificationLevel::Full)
2074           verifyUseInDefs(MA->getDefiningAccess(), MA);
2075       }
2076     }
2077     // Either we hit the assert, really have no accesses, or we have both
2078     // accesses and an access list. Same with defs.
2079     if (!AL && !DL)
2080       continue;
2081     // Verify ordering.
2082     assert(AL->size() == ActualAccesses.size() &&
2083            "We don't have the same number of accesses in the block as on the "
2084            "access list");
2085     assert((DL || ActualDefs.size() == 0) &&
2086            "Either we should have a defs list, or we should have no defs");
2087     assert((!DL || DL->size() == ActualDefs.size()) &&
2088            "We don't have the same number of defs in the block as on the "
2089            "def list");
2090     auto ALI = AL->begin();
2091     auto AAI = ActualAccesses.begin();
2092     while (ALI != AL->end() && AAI != ActualAccesses.end()) {
2093       assert(&*ALI == *AAI && "Not the same accesses in the same order");
2094       ++ALI;
2095       ++AAI;
2096     }
2097     ActualAccesses.clear();
2098     if (DL) {
2099       auto DLI = DL->begin();
2100       auto ADI = ActualDefs.begin();
2101       while (DLI != DL->end() && ADI != ActualDefs.end()) {
2102         assert(&*DLI == *ADI && "Not the same defs in the same order");
2103         ++DLI;
2104         ++ADI;
2105       }
2106     }
2107     ActualDefs.clear();
2108   }
2109 }
2110 
2111 /// Verify the def-use lists in MemorySSA, by verifying that \p Use
2112 /// appears in the use list of \p Def.
2113 void MemorySSA::verifyUseInDefs(MemoryAccess *Def, MemoryAccess *Use) const {
2114   // The live on entry use may cause us to get a NULL def here
2115   if (!Def)
2116     assert(isLiveOnEntryDef(Use) &&
2117            "Null def but use not point to live on entry def");
2118   else
2119     assert(is_contained(Def->users(), Use) &&
2120            "Did not find use in def's use list");
2121 }
2122 
2123 /// Perform a local numbering on blocks so that instruction ordering can be
2124 /// determined in constant time.
2125 /// TODO: We currently just number in order.  If we numbered by N, we could
2126 /// allow at least N-1 sequences of insertBefore or insertAfter (and at least
2127 /// log2(N) sequences of mixed before and after) without needing to invalidate
2128 /// the numbering.
2129 void MemorySSA::renumberBlock(const BasicBlock *B) const {
2130   // The pre-increment ensures the numbers really start at 1.
2131   unsigned long CurrentNumber = 0;
2132   const AccessList *AL = getBlockAccesses(B);
2133   assert(AL != nullptr && "Asking to renumber an empty block");
2134   for (const auto &I : *AL)
2135     BlockNumbering[&I] = ++CurrentNumber;
2136   BlockNumberingValid.insert(B);
2137 }
2138 
2139 /// Determine, for two memory accesses in the same block,
2140 /// whether \p Dominator dominates \p Dominatee.
2141 /// \returns True if \p Dominator dominates \p Dominatee.
2142 bool MemorySSA::locallyDominates(const MemoryAccess *Dominator,
2143                                  const MemoryAccess *Dominatee) const {
2144   const BasicBlock *DominatorBlock = Dominator->getBlock();
2145 
2146   assert((DominatorBlock == Dominatee->getBlock()) &&
2147          "Asking for local domination when accesses are in different blocks!");
2148   // A node dominates itself.
2149   if (Dominatee == Dominator)
2150     return true;
2151 
2152   // When Dominatee is defined on function entry, it is not dominated by another
2153   // memory access.
2154   if (isLiveOnEntryDef(Dominatee))
2155     return false;
2156 
2157   // When Dominator is defined on function entry, it dominates the other memory
2158   // access.
2159   if (isLiveOnEntryDef(Dominator))
2160     return true;
2161 
2162   if (!BlockNumberingValid.count(DominatorBlock))
2163     renumberBlock(DominatorBlock);
2164 
2165   unsigned long DominatorNum = BlockNumbering.lookup(Dominator);
2166   // All numbers start with 1
2167   assert(DominatorNum != 0 && "Block was not numbered properly");
2168   unsigned long DominateeNum = BlockNumbering.lookup(Dominatee);
2169   assert(DominateeNum != 0 && "Block was not numbered properly");
2170   return DominatorNum < DominateeNum;
2171 }
2172 
2173 bool MemorySSA::dominates(const MemoryAccess *Dominator,
2174                           const MemoryAccess *Dominatee) const {
2175   if (Dominator == Dominatee)
2176     return true;
2177 
2178   if (isLiveOnEntryDef(Dominatee))
2179     return false;
2180 
2181   if (Dominator->getBlock() != Dominatee->getBlock())
2182     return DT->dominates(Dominator->getBlock(), Dominatee->getBlock());
2183   return locallyDominates(Dominator, Dominatee);
2184 }
2185 
2186 bool MemorySSA::dominates(const MemoryAccess *Dominator,
2187                           const Use &Dominatee) const {
2188   if (MemoryPhi *MP = dyn_cast<MemoryPhi>(Dominatee.getUser())) {
2189     BasicBlock *UseBB = MP->getIncomingBlock(Dominatee);
2190     // The def must dominate the incoming block of the phi.
2191     if (UseBB != Dominator->getBlock())
2192       return DT->dominates(Dominator->getBlock(), UseBB);
2193     // If the UseBB and the DefBB are the same, compare locally.
2194     return locallyDominates(Dominator, cast<MemoryAccess>(Dominatee));
2195   }
2196   // If it's not a PHI node use, the normal dominates can already handle it.
2197   return dominates(Dominator, cast<MemoryAccess>(Dominatee.getUser()));
2198 }
2199 
2200 void MemorySSA::ensureOptimizedUses() {
2201   if (IsOptimized)
2202     return;
2203 
2204   BatchAAResults BatchAA(*AA);
2205   ClobberWalkerBase WalkerBase(this, DT);
2206   CachingWalker WalkerLocal(this, &WalkerBase);
2207   OptimizeUses(this, &WalkerLocal, &BatchAA, DT).optimizeUses();
2208   IsOptimized = true;
2209 }
2210 
2211 void MemoryAccess::print(raw_ostream &OS) const {
2212   switch (getValueID()) {
2213   case MemoryPhiVal: return static_cast<const MemoryPhi *>(this)->print(OS);
2214   case MemoryDefVal: return static_cast<const MemoryDef *>(this)->print(OS);
2215   case MemoryUseVal: return static_cast<const MemoryUse *>(this)->print(OS);
2216   }
2217   llvm_unreachable("invalid value id");
2218 }
2219 
2220 void MemoryDef::print(raw_ostream &OS) const {
2221   MemoryAccess *UO = getDefiningAccess();
2222 
2223   auto printID = [&OS](MemoryAccess *A) {
2224     if (A && A->getID())
2225       OS << A->getID();
2226     else
2227       OS << LiveOnEntryStr;
2228   };
2229 
2230   OS << getID() << " = MemoryDef(";
2231   printID(UO);
2232   OS << ")";
2233 
2234   if (isOptimized()) {
2235     OS << "->";
2236     printID(getOptimized());
2237   }
2238 }
2239 
2240 void MemoryPhi::print(raw_ostream &OS) const {
2241   ListSeparator LS(",");
2242   OS << getID() << " = MemoryPhi(";
2243   for (const auto &Op : operands()) {
2244     BasicBlock *BB = getIncomingBlock(Op);
2245     MemoryAccess *MA = cast<MemoryAccess>(Op);
2246 
2247     OS << LS << '{';
2248     if (BB->hasName())
2249       OS << BB->getName();
2250     else
2251       BB->printAsOperand(OS, false);
2252     OS << ',';
2253     if (unsigned ID = MA->getID())
2254       OS << ID;
2255     else
2256       OS << LiveOnEntryStr;
2257     OS << '}';
2258   }
2259   OS << ')';
2260 }
2261 
2262 void MemoryUse::print(raw_ostream &OS) const {
2263   MemoryAccess *UO = getDefiningAccess();
2264   OS << "MemoryUse(";
2265   if (UO && UO->getID())
2266     OS << UO->getID();
2267   else
2268     OS << LiveOnEntryStr;
2269   OS << ')';
2270 }
2271 
2272 void MemoryAccess::dump() const {
2273 // Cannot completely remove virtual function even in release mode.
2274 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
2275   print(dbgs());
2276   dbgs() << "\n";
2277 #endif
2278 }
2279 
2280 class DOTFuncMSSAInfo {
2281 private:
2282   const Function &F;
2283   MemorySSAAnnotatedWriter MSSAWriter;
2284 
2285 public:
2286   DOTFuncMSSAInfo(const Function &F, MemorySSA &MSSA)
2287       : F(F), MSSAWriter(&MSSA) {}
2288 
2289   const Function *getFunction() { return &F; }
2290   MemorySSAAnnotatedWriter &getWriter() { return MSSAWriter; }
2291 };
2292 
2293 namespace llvm {
2294 
2295 template <>
2296 struct GraphTraits<DOTFuncMSSAInfo *> : public GraphTraits<const BasicBlock *> {
2297   static NodeRef getEntryNode(DOTFuncMSSAInfo *CFGInfo) {
2298     return &(CFGInfo->getFunction()->getEntryBlock());
2299   }
2300 
2301   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
2302   using nodes_iterator = pointer_iterator<Function::const_iterator>;
2303 
2304   static nodes_iterator nodes_begin(DOTFuncMSSAInfo *CFGInfo) {
2305     return nodes_iterator(CFGInfo->getFunction()->begin());
2306   }
2307 
2308   static nodes_iterator nodes_end(DOTFuncMSSAInfo *CFGInfo) {
2309     return nodes_iterator(CFGInfo->getFunction()->end());
2310   }
2311 
2312   static size_t size(DOTFuncMSSAInfo *CFGInfo) {
2313     return CFGInfo->getFunction()->size();
2314   }
2315 };
2316 
2317 template <>
2318 struct DOTGraphTraits<DOTFuncMSSAInfo *> : public DefaultDOTGraphTraits {
2319 
2320   DOTGraphTraits(bool IsSimple = false) : DefaultDOTGraphTraits(IsSimple) {}
2321 
2322   static std::string getGraphName(DOTFuncMSSAInfo *CFGInfo) {
2323     return "MSSA CFG for '" + CFGInfo->getFunction()->getName().str() +
2324            "' function";
2325   }
2326 
2327   std::string getNodeLabel(const BasicBlock *Node, DOTFuncMSSAInfo *CFGInfo) {
2328     return DOTGraphTraits<DOTFuncInfo *>::getCompleteNodeLabel(
2329         Node, nullptr,
2330         [CFGInfo](raw_string_ostream &OS, const BasicBlock &BB) -> void {
2331           BB.print(OS, &CFGInfo->getWriter(), true, true);
2332         },
2333         [](std::string &S, unsigned &I, unsigned Idx) -> void {
2334           std::string Str = S.substr(I, Idx - I);
2335           StringRef SR = Str;
2336           if (SR.count(" = MemoryDef(") || SR.count(" = MemoryPhi(") ||
2337               SR.count("MemoryUse("))
2338             return;
2339           DOTGraphTraits<DOTFuncInfo *>::eraseComment(S, I, Idx);
2340         });
2341   }
2342 
2343   static std::string getEdgeSourceLabel(const BasicBlock *Node,
2344                                         const_succ_iterator I) {
2345     return DOTGraphTraits<DOTFuncInfo *>::getEdgeSourceLabel(Node, I);
2346   }
2347 
2348   /// Display the raw branch weights from PGO.
2349   std::string getEdgeAttributes(const BasicBlock *Node, const_succ_iterator I,
2350                                 DOTFuncMSSAInfo *CFGInfo) {
2351     return "";
2352   }
2353 
2354   std::string getNodeAttributes(const BasicBlock *Node,
2355                                 DOTFuncMSSAInfo *CFGInfo) {
2356     return getNodeLabel(Node, CFGInfo).find(';') != std::string::npos
2357                ? "style=filled, fillcolor=lightpink"
2358                : "";
2359   }
2360 };
2361 
2362 } // namespace llvm
2363 
2364 AnalysisKey MemorySSAAnalysis::Key;
2365 
2366 MemorySSAAnalysis::Result MemorySSAAnalysis::run(Function &F,
2367                                                  FunctionAnalysisManager &AM) {
2368   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
2369   auto &AA = AM.getResult<AAManager>(F);
2370   return MemorySSAAnalysis::Result(std::make_unique<MemorySSA>(F, &AA, &DT));
2371 }
2372 
2373 bool MemorySSAAnalysis::Result::invalidate(
2374     Function &F, const PreservedAnalyses &PA,
2375     FunctionAnalysisManager::Invalidator &Inv) {
2376   auto PAC = PA.getChecker<MemorySSAAnalysis>();
2377   return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>()) ||
2378          Inv.invalidate<AAManager>(F, PA) ||
2379          Inv.invalidate<DominatorTreeAnalysis>(F, PA);
2380 }
2381 
2382 PreservedAnalyses MemorySSAPrinterPass::run(Function &F,
2383                                             FunctionAnalysisManager &AM) {
2384   auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
2385   if (EnsureOptimizedUses)
2386     MSSA.ensureOptimizedUses();
2387   if (DotCFGMSSA != "") {
2388     DOTFuncMSSAInfo CFGInfo(F, MSSA);
2389     WriteGraph(&CFGInfo, "", false, "MSSA", DotCFGMSSA);
2390   } else {
2391     OS << "MemorySSA for function: " << F.getName() << "\n";
2392     MSSA.print(OS);
2393   }
2394 
2395   return PreservedAnalyses::all();
2396 }
2397 
2398 PreservedAnalyses MemorySSAWalkerPrinterPass::run(Function &F,
2399                                                   FunctionAnalysisManager &AM) {
2400   auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
2401   OS << "MemorySSA (walker) for function: " << F.getName() << "\n";
2402   MemorySSAWalkerAnnotatedWriter Writer(&MSSA);
2403   F.print(OS, &Writer);
2404 
2405   return PreservedAnalyses::all();
2406 }
2407 
2408 PreservedAnalyses MemorySSAVerifierPass::run(Function &F,
2409                                              FunctionAnalysisManager &AM) {
2410   AM.getResult<MemorySSAAnalysis>(F).getMSSA().verifyMemorySSA();
2411 
2412   return PreservedAnalyses::all();
2413 }
2414 
2415 char MemorySSAWrapperPass::ID = 0;
2416 
2417 MemorySSAWrapperPass::MemorySSAWrapperPass() : FunctionPass(ID) {
2418   initializeMemorySSAWrapperPassPass(*PassRegistry::getPassRegistry());
2419 }
2420 
2421 void MemorySSAWrapperPass::releaseMemory() { MSSA.reset(); }
2422 
2423 void MemorySSAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
2424   AU.setPreservesAll();
2425   AU.addRequiredTransitive<DominatorTreeWrapperPass>();
2426   AU.addRequiredTransitive<AAResultsWrapperPass>();
2427 }
2428 
2429 bool MemorySSAWrapperPass::runOnFunction(Function &F) {
2430   auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
2431   auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
2432   MSSA.reset(new MemorySSA(F, &AA, &DT));
2433   return false;
2434 }
2435 
2436 void MemorySSAWrapperPass::verifyAnalysis() const {
2437   if (VerifyMemorySSA)
2438     MSSA->verifyMemorySSA();
2439 }
2440 
2441 void MemorySSAWrapperPass::print(raw_ostream &OS, const Module *M) const {
2442   MSSA->print(OS);
2443 }
2444 
2445 MemorySSAWalker::MemorySSAWalker(MemorySSA *M) : MSSA(M) {}
2446 
2447 /// Walk the use-def chains starting at \p StartingAccess and find
2448 /// the MemoryAccess that actually clobbers Loc.
2449 ///
2450 /// \returns our clobbering memory access
2451 MemoryAccess *MemorySSA::ClobberWalkerBase::getClobberingMemoryAccessBase(
2452     MemoryAccess *StartingAccess, const MemoryLocation &Loc,
2453     BatchAAResults &BAA, unsigned &UpwardWalkLimit) {
2454   assert(!isa<MemoryUse>(StartingAccess) && "Use cannot be defining access");
2455 
2456   // If location is undefined, conservatively return starting access.
2457   if (Loc.Ptr == nullptr)
2458     return StartingAccess;
2459 
2460   Instruction *I = nullptr;
2461   if (auto *StartingUseOrDef = dyn_cast<MemoryUseOrDef>(StartingAccess)) {
2462     if (MSSA->isLiveOnEntryDef(StartingUseOrDef))
2463       return StartingUseOrDef;
2464 
2465     I = StartingUseOrDef->getMemoryInst();
2466 
2467     // Conservatively, fences are always clobbers, so don't perform the walk if
2468     // we hit a fence.
2469     if (!isa<CallBase>(I) && I->isFenceLike())
2470       return StartingUseOrDef;
2471   }
2472 
2473   UpwardsMemoryQuery Q;
2474   Q.OriginalAccess = StartingAccess;
2475   Q.StartingLoc = Loc;
2476   Q.Inst = nullptr;
2477   Q.IsCall = false;
2478 
2479   // Unlike the other function, do not walk to the def of a def, because we are
2480   // handed something we already believe is the clobbering access.
2481   // We never set SkipSelf to true in Q in this method.
2482   MemoryAccess *Clobber =
2483       Walker.findClobber(BAA, StartingAccess, Q, UpwardWalkLimit);
2484   LLVM_DEBUG({
2485     dbgs() << "Clobber starting at access " << *StartingAccess << "\n";
2486     if (I)
2487       dbgs() << "  for instruction " << *I << "\n";
2488     dbgs() << "  is " << *Clobber << "\n";
2489   });
2490   return Clobber;
2491 }
2492 
2493 static const Instruction *
2494 getInvariantGroupClobberingInstruction(Instruction &I, DominatorTree &DT) {
2495   if (!I.hasMetadata(LLVMContext::MD_invariant_group) || I.isVolatile())
2496     return nullptr;
2497 
2498   // We consider bitcasts and zero GEPs to be the same pointer value. Start by
2499   // stripping bitcasts and zero GEPs, then we will recursively look at loads
2500   // and stores through bitcasts and zero GEPs.
2501   Value *PointerOperand = getLoadStorePointerOperand(&I)->stripPointerCasts();
2502 
2503   // It's not safe to walk the use list of a global value because function
2504   // passes aren't allowed to look outside their functions.
2505   // FIXME: this could be fixed by filtering instructions from outside of
2506   // current function.
2507   if (isa<Constant>(PointerOperand))
2508     return nullptr;
2509 
2510   // Queue to process all pointers that are equivalent to load operand.
2511   SmallVector<const Value *, 8> PointerUsesQueue;
2512   PointerUsesQueue.push_back(PointerOperand);
2513 
2514   const Instruction *MostDominatingInstruction = &I;
2515 
2516   // FIXME: This loop is O(n^2) because dominates can be O(n) and in worst case
2517   // we will see all the instructions. It may not matter in practice. If it
2518   // does, we will have to support MemorySSA construction and updates.
2519   while (!PointerUsesQueue.empty()) {
2520     const Value *Ptr = PointerUsesQueue.pop_back_val();
2521     assert(Ptr && !isa<GlobalValue>(Ptr) &&
2522            "Null or GlobalValue should not be inserted");
2523 
2524     for (const User *Us : Ptr->users()) {
2525       auto *U = dyn_cast<Instruction>(Us);
2526       if (!U || U == &I || !DT.dominates(U, MostDominatingInstruction))
2527         continue;
2528 
2529       // Add bitcasts and zero GEPs to queue.
2530       if (isa<BitCastInst>(U)) {
2531         PointerUsesQueue.push_back(U);
2532         continue;
2533       }
2534       if (auto *GEP = dyn_cast<GetElementPtrInst>(U)) {
2535         if (GEP->hasAllZeroIndices())
2536           PointerUsesQueue.push_back(U);
2537         continue;
2538       }
2539 
2540       // If we hit a load/store with an invariant.group metadata and the same
2541       // pointer operand, we can assume that value pointed to by the pointer
2542       // operand didn't change.
2543       if (U->hasMetadata(LLVMContext::MD_invariant_group) &&
2544           getLoadStorePointerOperand(U) == Ptr && !U->isVolatile()) {
2545         MostDominatingInstruction = U;
2546       }
2547     }
2548   }
2549   return MostDominatingInstruction == &I ? nullptr : MostDominatingInstruction;
2550 }
2551 
2552 MemoryAccess *MemorySSA::ClobberWalkerBase::getClobberingMemoryAccessBase(
2553     MemoryAccess *MA, BatchAAResults &BAA, unsigned &UpwardWalkLimit,
2554     bool SkipSelf, bool UseInvariantGroup) {
2555   auto *StartingAccess = dyn_cast<MemoryUseOrDef>(MA);
2556   // If this is a MemoryPhi, we can't do anything.
2557   if (!StartingAccess)
2558     return MA;
2559 
2560   if (UseInvariantGroup) {
2561     if (auto *I = getInvariantGroupClobberingInstruction(
2562             *StartingAccess->getMemoryInst(), MSSA->getDomTree())) {
2563       assert(isa<LoadInst>(I) || isa<StoreInst>(I));
2564 
2565       auto *ClobberMA = MSSA->getMemoryAccess(I);
2566       assert(ClobberMA);
2567       if (isa<MemoryUse>(ClobberMA))
2568         return ClobberMA->getDefiningAccess();
2569       return ClobberMA;
2570     }
2571   }
2572 
2573   bool IsOptimized = false;
2574 
2575   // If this is an already optimized use or def, return the optimized result.
2576   // Note: Currently, we store the optimized def result in a separate field,
2577   // since we can't use the defining access.
2578   if (StartingAccess->isOptimized()) {
2579     if (!SkipSelf || !isa<MemoryDef>(StartingAccess))
2580       return StartingAccess->getOptimized();
2581     IsOptimized = true;
2582   }
2583 
2584   const Instruction *I = StartingAccess->getMemoryInst();
2585   // We can't sanely do anything with a fence, since they conservatively clobber
2586   // all memory, and have no locations to get pointers from to try to
2587   // disambiguate.
2588   if (!isa<CallBase>(I) && I->isFenceLike())
2589     return StartingAccess;
2590 
2591   UpwardsMemoryQuery Q(I, StartingAccess);
2592 
2593   if (isUseTriviallyOptimizableToLiveOnEntry(BAA, I)) {
2594     MemoryAccess *LiveOnEntry = MSSA->getLiveOnEntryDef();
2595     StartingAccess->setOptimized(LiveOnEntry);
2596     return LiveOnEntry;
2597   }
2598 
2599   MemoryAccess *OptimizedAccess;
2600   if (!IsOptimized) {
2601     // Start with the thing we already think clobbers this location
2602     MemoryAccess *DefiningAccess = StartingAccess->getDefiningAccess();
2603 
2604     // At this point, DefiningAccess may be the live on entry def.
2605     // If it is, we will not get a better result.
2606     if (MSSA->isLiveOnEntryDef(DefiningAccess)) {
2607       StartingAccess->setOptimized(DefiningAccess);
2608       return DefiningAccess;
2609     }
2610 
2611     OptimizedAccess =
2612         Walker.findClobber(BAA, DefiningAccess, Q, UpwardWalkLimit);
2613     StartingAccess->setOptimized(OptimizedAccess);
2614   } else
2615     OptimizedAccess = StartingAccess->getOptimized();
2616 
2617   LLVM_DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is ");
2618   LLVM_DEBUG(dbgs() << *StartingAccess << "\n");
2619   LLVM_DEBUG(dbgs() << "Optimized Memory SSA clobber for " << *I << " is ");
2620   LLVM_DEBUG(dbgs() << *OptimizedAccess << "\n");
2621 
2622   MemoryAccess *Result;
2623   if (SkipSelf && isa<MemoryPhi>(OptimizedAccess) &&
2624       isa<MemoryDef>(StartingAccess) && UpwardWalkLimit) {
2625     assert(isa<MemoryDef>(Q.OriginalAccess));
2626     Q.SkipSelfAccess = true;
2627     Result = Walker.findClobber(BAA, OptimizedAccess, Q, UpwardWalkLimit);
2628   } else
2629     Result = OptimizedAccess;
2630 
2631   LLVM_DEBUG(dbgs() << "Result Memory SSA clobber [SkipSelf = " << SkipSelf);
2632   LLVM_DEBUG(dbgs() << "] for " << *I << " is " << *Result << "\n");
2633 
2634   return Result;
2635 }
2636 
2637 MemoryAccess *
2638 DoNothingMemorySSAWalker::getClobberingMemoryAccess(MemoryAccess *MA,
2639                                                     BatchAAResults &) {
2640   if (auto *Use = dyn_cast<MemoryUseOrDef>(MA))
2641     return Use->getDefiningAccess();
2642   return MA;
2643 }
2644 
2645 MemoryAccess *DoNothingMemorySSAWalker::getClobberingMemoryAccess(
2646     MemoryAccess *StartingAccess, const MemoryLocation &, BatchAAResults &) {
2647   if (auto *Use = dyn_cast<MemoryUseOrDef>(StartingAccess))
2648     return Use->getDefiningAccess();
2649   return StartingAccess;
2650 }
2651 
2652 void MemoryPhi::deleteMe(DerivedUser *Self) {
2653   delete static_cast<MemoryPhi *>(Self);
2654 }
2655 
2656 void MemoryDef::deleteMe(DerivedUser *Self) {
2657   delete static_cast<MemoryDef *>(Self);
2658 }
2659 
2660 void MemoryUse::deleteMe(DerivedUser *Self) {
2661   delete static_cast<MemoryUse *>(Self);
2662 }
2663 
2664 bool upward_defs_iterator::IsGuaranteedLoopInvariant(const Value *Ptr) const {
2665   auto IsGuaranteedLoopInvariantBase = [](const Value *Ptr) {
2666     Ptr = Ptr->stripPointerCasts();
2667     if (!isa<Instruction>(Ptr))
2668       return true;
2669     return isa<AllocaInst>(Ptr);
2670   };
2671 
2672   Ptr = Ptr->stripPointerCasts();
2673   if (auto *I = dyn_cast<Instruction>(Ptr)) {
2674     if (I->getParent()->isEntryBlock())
2675       return true;
2676   }
2677   if (auto *GEP = dyn_cast<GEPOperator>(Ptr)) {
2678     return IsGuaranteedLoopInvariantBase(GEP->getPointerOperand()) &&
2679            GEP->hasAllConstantIndices();
2680   }
2681   return IsGuaranteedLoopInvariantBase(Ptr);
2682 }
2683