xref: /freebsd/contrib/llvm-project/llvm/lib/Analysis/MemorySSA.cpp (revision 924226fba12cc9a228c73b956e1b7fa24c60b055)
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/None.h"
20 #include "llvm/ADT/Optional.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/ADT/SmallPtrSet.h"
23 #include "llvm/ADT/SmallVector.h"
24 #include "llvm/ADT/StringExtras.h"
25 #include "llvm/ADT/iterator.h"
26 #include "llvm/ADT/iterator_range.h"
27 #include "llvm/Analysis/AliasAnalysis.h"
28 #include "llvm/Analysis/CFGPrinter.h"
29 #include "llvm/Analysis/IteratedDominanceFrontier.h"
30 #include "llvm/Analysis/MemoryLocation.h"
31 #include "llvm/Config/llvm-config.h"
32 #include "llvm/IR/AssemblyAnnotationWriter.h"
33 #include "llvm/IR/BasicBlock.h"
34 #include "llvm/IR/Dominators.h"
35 #include "llvm/IR/Function.h"
36 #include "llvm/IR/Instruction.h"
37 #include "llvm/IR/Instructions.h"
38 #include "llvm/IR/IntrinsicInst.h"
39 #include "llvm/IR/Intrinsics.h"
40 #include "llvm/IR/LLVMContext.h"
41 #include "llvm/IR/PassManager.h"
42 #include "llvm/IR/Use.h"
43 #include "llvm/InitializePasses.h"
44 #include "llvm/Pass.h"
45 #include "llvm/Support/AtomicOrdering.h"
46 #include "llvm/Support/Casting.h"
47 #include "llvm/Support/CommandLine.h"
48 #include "llvm/Support/Compiler.h"
49 #include "llvm/Support/Debug.h"
50 #include "llvm/Support/ErrorHandling.h"
51 #include "llvm/Support/FormattedStream.h"
52 #include "llvm/Support/raw_ostream.h"
53 #include <algorithm>
54 #include <cassert>
55 #include <cstdlib>
56 #include <iterator>
57 #include <memory>
58 #include <utility>
59 
60 using namespace llvm;
61 
62 #define DEBUG_TYPE "memoryssa"
63 
64 static cl::opt<std::string>
65     DotCFGMSSA("dot-cfg-mssa",
66                cl::value_desc("file name for generated dot file"),
67                cl::desc("file name for generated dot file"), cl::init(""));
68 
69 INITIALIZE_PASS_BEGIN(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false,
70                       true)
71 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
72 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
73 INITIALIZE_PASS_END(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false,
74                     true)
75 
76 INITIALIZE_PASS_BEGIN(MemorySSAPrinterLegacyPass, "print-memoryssa",
77                       "Memory SSA Printer", false, false)
78 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
79 INITIALIZE_PASS_END(MemorySSAPrinterLegacyPass, "print-memoryssa",
80                     "Memory SSA Printer", false, false)
81 
82 static cl::opt<unsigned> MaxCheckLimit(
83     "memssa-check-limit", cl::Hidden, cl::init(100),
84     cl::desc("The maximum number of stores/phis MemorySSA"
85              "will consider trying to walk past (default = 100)"));
86 
87 // Always verify MemorySSA if expensive checking is enabled.
88 #ifdef EXPENSIVE_CHECKS
89 bool llvm::VerifyMemorySSA = true;
90 #else
91 bool llvm::VerifyMemorySSA = false;
92 #endif
93 
94 static cl::opt<bool, true>
95     VerifyMemorySSAX("verify-memoryssa", cl::location(VerifyMemorySSA),
96                      cl::Hidden, cl::desc("Enable verification of MemorySSA."));
97 
98 const static char LiveOnEntryStr[] = "liveOnEntry";
99 
100 namespace {
101 
102 /// An assembly annotator class to print Memory SSA information in
103 /// comments.
104 class MemorySSAAnnotatedWriter : public AssemblyAnnotationWriter {
105   const MemorySSA *MSSA;
106 
107 public:
108   MemorySSAAnnotatedWriter(const MemorySSA *M) : MSSA(M) {}
109 
110   void emitBasicBlockStartAnnot(const BasicBlock *BB,
111                                 formatted_raw_ostream &OS) override {
112     if (MemoryAccess *MA = MSSA->getMemoryAccess(BB))
113       OS << "; " << *MA << "\n";
114   }
115 
116   void emitInstructionAnnot(const Instruction *I,
117                             formatted_raw_ostream &OS) override {
118     if (MemoryAccess *MA = MSSA->getMemoryAccess(I))
119       OS << "; " << *MA << "\n";
120   }
121 };
122 
123 /// An assembly annotator class to print Memory SSA information in
124 /// comments.
125 class MemorySSAWalkerAnnotatedWriter : public AssemblyAnnotationWriter {
126   MemorySSA *MSSA;
127   MemorySSAWalker *Walker;
128 
129 public:
130   MemorySSAWalkerAnnotatedWriter(MemorySSA *M)
131       : MSSA(M), Walker(M->getWalker()) {}
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);
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 namespace {
281 
282 struct ClobberAlias {
283   bool IsClobber;
284   Optional<AliasResult> AR;
285 };
286 
287 } // end anonymous namespace
288 
289 // Return a pair of {IsClobber (bool), AR (AliasResult)}. It relies on AR being
290 // ignored if IsClobber = false.
291 template <typename AliasAnalysisType>
292 static ClobberAlias
293 instructionClobbersQuery(const MemoryDef *MD, const MemoryLocation &UseLoc,
294                          const Instruction *UseInst, AliasAnalysisType &AA) {
295   Instruction *DefInst = MD->getMemoryInst();
296   assert(DefInst && "Defining instruction not actually an instruction");
297   Optional<AliasResult> AR;
298 
299   if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) {
300     // These intrinsics will show up as affecting memory, but they are just
301     // markers, mostly.
302     //
303     // FIXME: We probably don't actually want MemorySSA to model these at all
304     // (including creating MemoryAccesses for them): we just end up inventing
305     // clobbers where they don't really exist at all. Please see D43269 for
306     // context.
307     switch (II->getIntrinsicID()) {
308     case Intrinsic::invariant_start:
309     case Intrinsic::invariant_end:
310     case Intrinsic::assume:
311     case Intrinsic::experimental_noalias_scope_decl:
312     case Intrinsic::pseudoprobe:
313       return {false, AliasResult(AliasResult::NoAlias)};
314     case Intrinsic::dbg_addr:
315     case Intrinsic::dbg_declare:
316     case Intrinsic::dbg_label:
317     case Intrinsic::dbg_value:
318       llvm_unreachable("debuginfo shouldn't have associated defs!");
319     default:
320       break;
321     }
322   }
323 
324   if (auto *CB = dyn_cast_or_null<CallBase>(UseInst)) {
325     ModRefInfo I = AA.getModRefInfo(DefInst, CB);
326     AR = isMustSet(I) ? AliasResult::MustAlias : AliasResult::MayAlias;
327     return {isModOrRefSet(I), AR};
328   }
329 
330   if (auto *DefLoad = dyn_cast<LoadInst>(DefInst))
331     if (auto *UseLoad = dyn_cast_or_null<LoadInst>(UseInst))
332       return {!areLoadsReorderable(UseLoad, DefLoad),
333               AliasResult(AliasResult::MayAlias)};
334 
335   ModRefInfo I = AA.getModRefInfo(DefInst, UseLoc);
336   AR = isMustSet(I) ? AliasResult::MustAlias : AliasResult::MayAlias;
337   return {isModSet(I), AR};
338 }
339 
340 template <typename AliasAnalysisType>
341 static ClobberAlias instructionClobbersQuery(MemoryDef *MD,
342                                              const MemoryUseOrDef *MU,
343                                              const MemoryLocOrCall &UseMLOC,
344                                              AliasAnalysisType &AA) {
345   // FIXME: This is a temporary hack to allow a single instructionClobbersQuery
346   // to exist while MemoryLocOrCall is pushed through places.
347   if (UseMLOC.IsCall)
348     return instructionClobbersQuery(MD, MemoryLocation(), MU->getMemoryInst(),
349                                     AA);
350   return instructionClobbersQuery(MD, UseMLOC.getLoc(), MU->getMemoryInst(),
351                                   AA);
352 }
353 
354 // Return true when MD may alias MU, return false otherwise.
355 bool MemorySSAUtil::defClobbersUseOrDef(MemoryDef *MD, const MemoryUseOrDef *MU,
356                                         AliasAnalysis &AA) {
357   return instructionClobbersQuery(MD, MU, MemoryLocOrCall(MU), AA).IsClobber;
358 }
359 
360 namespace {
361 
362 struct UpwardsMemoryQuery {
363   // True if our original query started off as a call
364   bool IsCall = false;
365   // The pointer location we started the query with. This will be empty if
366   // IsCall is true.
367   MemoryLocation StartingLoc;
368   // This is the instruction we were querying about.
369   const Instruction *Inst = nullptr;
370   // The MemoryAccess we actually got called with, used to test local domination
371   const MemoryAccess *OriginalAccess = nullptr;
372   Optional<AliasResult> AR = AliasResult(AliasResult::MayAlias);
373   bool SkipSelfAccess = false;
374 
375   UpwardsMemoryQuery() = default;
376 
377   UpwardsMemoryQuery(const Instruction *Inst, const MemoryAccess *Access)
378       : IsCall(isa<CallBase>(Inst)), Inst(Inst), OriginalAccess(Access) {
379     if (!IsCall)
380       StartingLoc = MemoryLocation::get(Inst);
381   }
382 };
383 
384 } // end anonymous namespace
385 
386 template <typename AliasAnalysisType>
387 static bool isUseTriviallyOptimizableToLiveOnEntry(AliasAnalysisType &AA,
388                                                    const Instruction *I) {
389   // If the memory can't be changed, then loads of the memory can't be
390   // clobbered.
391   if (auto *LI = dyn_cast<LoadInst>(I))
392     return I->hasMetadata(LLVMContext::MD_invariant_load) ||
393            AA.pointsToConstantMemory(MemoryLocation::get(LI));
394   return false;
395 }
396 
397 /// Verifies that `Start` is clobbered by `ClobberAt`, and that nothing
398 /// inbetween `Start` and `ClobberAt` can clobbers `Start`.
399 ///
400 /// This is meant to be as simple and self-contained as possible. Because it
401 /// uses no cache, etc., it can be relatively expensive.
402 ///
403 /// \param Start     The MemoryAccess that we want to walk from.
404 /// \param ClobberAt A clobber for Start.
405 /// \param StartLoc  The MemoryLocation for Start.
406 /// \param MSSA      The MemorySSA instance that Start and ClobberAt belong to.
407 /// \param Query     The UpwardsMemoryQuery we used for our search.
408 /// \param AA        The AliasAnalysis we used for our search.
409 /// \param AllowImpreciseClobber Always false, unless we do relaxed verify.
410 
411 template <typename AliasAnalysisType>
412 LLVM_ATTRIBUTE_UNUSED static void
413 checkClobberSanity(const MemoryAccess *Start, MemoryAccess *ClobberAt,
414                    const MemoryLocation &StartLoc, const MemorySSA &MSSA,
415                    const UpwardsMemoryQuery &Query, AliasAnalysisType &AA,
416                    bool AllowImpreciseClobber = false) {
417   assert(MSSA.dominates(ClobberAt, Start) && "Clobber doesn't dominate start?");
418 
419   if (MSSA.isLiveOnEntryDef(Start)) {
420     assert(MSSA.isLiveOnEntryDef(ClobberAt) &&
421            "liveOnEntry must clobber itself");
422     return;
423   }
424 
425   bool FoundClobber = false;
426   DenseSet<ConstMemoryAccessPair> VisitedPhis;
427   SmallVector<ConstMemoryAccessPair, 8> Worklist;
428   Worklist.emplace_back(Start, StartLoc);
429   // Walk all paths from Start to ClobberAt, while looking for clobbers. If one
430   // is found, complain.
431   while (!Worklist.empty()) {
432     auto MAP = Worklist.pop_back_val();
433     // All we care about is that nothing from Start to ClobberAt clobbers Start.
434     // We learn nothing from revisiting nodes.
435     if (!VisitedPhis.insert(MAP).second)
436       continue;
437 
438     for (const auto *MA : def_chain(MAP.first)) {
439       if (MA == ClobberAt) {
440         if (const auto *MD = dyn_cast<MemoryDef>(MA)) {
441           // instructionClobbersQuery isn't essentially free, so don't use `|=`,
442           // since it won't let us short-circuit.
443           //
444           // Also, note that this can't be hoisted out of the `Worklist` loop,
445           // since MD may only act as a clobber for 1 of N MemoryLocations.
446           FoundClobber = FoundClobber || MSSA.isLiveOnEntryDef(MD);
447           if (!FoundClobber) {
448             ClobberAlias CA =
449                 instructionClobbersQuery(MD, MAP.second, Query.Inst, AA);
450             if (CA.IsClobber) {
451               FoundClobber = true;
452               // Not used: CA.AR;
453             }
454           }
455         }
456         break;
457       }
458 
459       // We should never hit liveOnEntry, unless it's the clobber.
460       assert(!MSSA.isLiveOnEntryDef(MA) && "Hit liveOnEntry before clobber?");
461 
462       if (const auto *MD = dyn_cast<MemoryDef>(MA)) {
463         // If Start is a Def, skip self.
464         if (MD == Start)
465           continue;
466 
467         assert(!instructionClobbersQuery(MD, MAP.second, Query.Inst, AA)
468                     .IsClobber &&
469                "Found clobber before reaching ClobberAt!");
470         continue;
471       }
472 
473       if (const auto *MU = dyn_cast<MemoryUse>(MA)) {
474         (void)MU;
475         assert (MU == Start &&
476                 "Can only find use in def chain if Start is a use");
477         continue;
478       }
479 
480       assert(isa<MemoryPhi>(MA));
481 
482       // Add reachable phi predecessors
483       for (auto ItB = upward_defs_begin(
484                     {const_cast<MemoryAccess *>(MA), MAP.second},
485                     MSSA.getDomTree()),
486                 ItE = upward_defs_end();
487            ItB != ItE; ++ItB)
488         if (MSSA.getDomTree().isReachableFromEntry(ItB.getPhiArgBlock()))
489           Worklist.emplace_back(*ItB);
490     }
491   }
492 
493   // If the verify is done following an optimization, it's possible that
494   // ClobberAt was a conservative clobbering, that we can now infer is not a
495   // true clobbering access. Don't fail the verify if that's the case.
496   // We do have accesses that claim they're optimized, but could be optimized
497   // further. Updating all these can be expensive, so allow it for now (FIXME).
498   if (AllowImpreciseClobber)
499     return;
500 
501   // If ClobberAt is a MemoryPhi, we can assume something above it acted as a
502   // clobber. Otherwise, `ClobberAt` should've acted as a clobber at some point.
503   assert((isa<MemoryPhi>(ClobberAt) || FoundClobber) &&
504          "ClobberAt never acted as a clobber");
505 }
506 
507 namespace {
508 
509 /// Our algorithm for walking (and trying to optimize) clobbers, all wrapped up
510 /// in one class.
511 template <class AliasAnalysisType> class ClobberWalker {
512   /// Save a few bytes by using unsigned instead of size_t.
513   using ListIndex = unsigned;
514 
515   /// Represents a span of contiguous MemoryDefs, potentially ending in a
516   /// MemoryPhi.
517   struct DefPath {
518     MemoryLocation Loc;
519     // Note that, because we always walk in reverse, Last will always dominate
520     // First. Also note that First and Last are inclusive.
521     MemoryAccess *First;
522     MemoryAccess *Last;
523     Optional<ListIndex> Previous;
524 
525     DefPath(const MemoryLocation &Loc, MemoryAccess *First, MemoryAccess *Last,
526             Optional<ListIndex> Previous)
527         : Loc(Loc), First(First), Last(Last), Previous(Previous) {}
528 
529     DefPath(const MemoryLocation &Loc, MemoryAccess *Init,
530             Optional<ListIndex> Previous)
531         : DefPath(Loc, Init, Init, Previous) {}
532   };
533 
534   const MemorySSA &MSSA;
535   AliasAnalysisType &AA;
536   DominatorTree &DT;
537   UpwardsMemoryQuery *Query;
538   unsigned *UpwardWalkLimit;
539 
540   // Phi optimization bookkeeping:
541   // List of DefPath to process during the current phi optimization walk.
542   SmallVector<DefPath, 32> Paths;
543   // List of visited <Access, Location> pairs; we can skip paths already
544   // visited with the same memory location.
545   DenseSet<ConstMemoryAccessPair> VisitedPhis;
546   // Record if phi translation has been performed during the current phi
547   // optimization walk, as merging alias results after phi translation can
548   // yield incorrect results. Context in PR46156.
549   bool PerformedPhiTranslation = false;
550 
551   /// Find the nearest def or phi that `From` can legally be optimized to.
552   const MemoryAccess *getWalkTarget(const MemoryPhi *From) const {
553     assert(From->getNumOperands() && "Phi with no operands?");
554 
555     BasicBlock *BB = From->getBlock();
556     MemoryAccess *Result = MSSA.getLiveOnEntryDef();
557     DomTreeNode *Node = DT.getNode(BB);
558     while ((Node = Node->getIDom())) {
559       auto *Defs = MSSA.getBlockDefs(Node->getBlock());
560       if (Defs)
561         return &*Defs->rbegin();
562     }
563     return Result;
564   }
565 
566   /// Result of calling walkToPhiOrClobber.
567   struct UpwardsWalkResult {
568     /// The "Result" of the walk. Either a clobber, the last thing we walked, or
569     /// both. Include alias info when clobber found.
570     MemoryAccess *Result;
571     bool IsKnownClobber;
572     Optional<AliasResult> AR;
573   };
574 
575   /// Walk to the next Phi or Clobber in the def chain starting at Desc.Last.
576   /// This will update Desc.Last as it walks. It will (optionally) also stop at
577   /// StopAt.
578   ///
579   /// This does not test for whether StopAt is a clobber
580   UpwardsWalkResult
581   walkToPhiOrClobber(DefPath &Desc, const MemoryAccess *StopAt = nullptr,
582                      const MemoryAccess *SkipStopAt = nullptr) const {
583     assert(!isa<MemoryUse>(Desc.Last) && "Uses don't exist in my world");
584     assert(UpwardWalkLimit && "Need a valid walk limit");
585     bool LimitAlreadyReached = false;
586     // (*UpwardWalkLimit) may be 0 here, due to the loop in tryOptimizePhi. Set
587     // it to 1. This will not do any alias() calls. It either returns in the
588     // first iteration in the loop below, or is set back to 0 if all def chains
589     // are free of MemoryDefs.
590     if (!*UpwardWalkLimit) {
591       *UpwardWalkLimit = 1;
592       LimitAlreadyReached = true;
593     }
594 
595     for (MemoryAccess *Current : def_chain(Desc.Last)) {
596       Desc.Last = Current;
597       if (Current == StopAt || Current == SkipStopAt)
598         return {Current, false, AliasResult(AliasResult::MayAlias)};
599 
600       if (auto *MD = dyn_cast<MemoryDef>(Current)) {
601         if (MSSA.isLiveOnEntryDef(MD))
602           return {MD, true, AliasResult(AliasResult::MustAlias)};
603 
604         if (!--*UpwardWalkLimit)
605           return {Current, true, AliasResult(AliasResult::MayAlias)};
606 
607         ClobberAlias CA =
608             instructionClobbersQuery(MD, Desc.Loc, Query->Inst, AA);
609         if (CA.IsClobber)
610           return {MD, true, CA.AR};
611       }
612     }
613 
614     if (LimitAlreadyReached)
615       *UpwardWalkLimit = 0;
616 
617     assert(isa<MemoryPhi>(Desc.Last) &&
618            "Ended at a non-clobber that's not a phi?");
619     return {Desc.Last, false, AliasResult(AliasResult::MayAlias)};
620   }
621 
622   void addSearches(MemoryPhi *Phi, SmallVectorImpl<ListIndex> &PausedSearches,
623                    ListIndex PriorNode) {
624     auto UpwardDefsBegin = upward_defs_begin({Phi, Paths[PriorNode].Loc}, DT,
625                                              &PerformedPhiTranslation);
626     auto UpwardDefs = make_range(UpwardDefsBegin, upward_defs_end());
627     for (const MemoryAccessPair &P : UpwardDefs) {
628       PausedSearches.push_back(Paths.size());
629       Paths.emplace_back(P.second, P.first, PriorNode);
630     }
631   }
632 
633   /// Represents a search that terminated after finding a clobber. This clobber
634   /// may or may not be present in the path of defs from LastNode..SearchStart,
635   /// since it may have been retrieved from cache.
636   struct TerminatedPath {
637     MemoryAccess *Clobber;
638     ListIndex LastNode;
639   };
640 
641   /// Get an access that keeps us from optimizing to the given phi.
642   ///
643   /// PausedSearches is an array of indices into the Paths array. Its incoming
644   /// value is the indices of searches that stopped at the last phi optimization
645   /// target. It's left in an unspecified state.
646   ///
647   /// If this returns None, NewPaused is a vector of searches that terminated
648   /// at StopWhere. Otherwise, NewPaused is left in an unspecified state.
649   Optional<TerminatedPath>
650   getBlockingAccess(const MemoryAccess *StopWhere,
651                     SmallVectorImpl<ListIndex> &PausedSearches,
652                     SmallVectorImpl<ListIndex> &NewPaused,
653                     SmallVectorImpl<TerminatedPath> &Terminated) {
654     assert(!PausedSearches.empty() && "No searches to continue?");
655 
656     // BFS vs DFS really doesn't make a difference here, so just do a DFS with
657     // PausedSearches as our stack.
658     while (!PausedSearches.empty()) {
659       ListIndex PathIndex = PausedSearches.pop_back_val();
660       DefPath &Node = Paths[PathIndex];
661 
662       // If we've already visited this path with this MemoryLocation, we don't
663       // need to do so again.
664       //
665       // NOTE: That we just drop these paths on the ground makes caching
666       // behavior sporadic. e.g. given a diamond:
667       //  A
668       // B C
669       //  D
670       //
671       // ...If we walk D, B, A, C, we'll only cache the result of phi
672       // optimization for A, B, and D; C will be skipped because it dies here.
673       // This arguably isn't the worst thing ever, since:
674       //   - We generally query things in a top-down order, so if we got below D
675       //     without needing cache entries for {C, MemLoc}, then chances are
676       //     that those cache entries would end up ultimately unused.
677       //   - We still cache things for A, so C only needs to walk up a bit.
678       // If this behavior becomes problematic, we can fix without a ton of extra
679       // work.
680       if (!VisitedPhis.insert({Node.Last, Node.Loc}).second) {
681         if (PerformedPhiTranslation) {
682           // If visiting this path performed Phi translation, don't continue,
683           // since it may not be correct to merge results from two paths if one
684           // relies on the phi translation.
685           TerminatedPath Term{Node.Last, PathIndex};
686           return Term;
687         }
688         continue;
689       }
690 
691       const MemoryAccess *SkipStopWhere = nullptr;
692       if (Query->SkipSelfAccess && Node.Loc == Query->StartingLoc) {
693         assert(isa<MemoryDef>(Query->OriginalAccess));
694         SkipStopWhere = Query->OriginalAccess;
695       }
696 
697       UpwardsWalkResult Res = walkToPhiOrClobber(Node,
698                                                  /*StopAt=*/StopWhere,
699                                                  /*SkipStopAt=*/SkipStopWhere);
700       if (Res.IsKnownClobber) {
701         assert(Res.Result != StopWhere && Res.Result != SkipStopWhere);
702 
703         // If this wasn't a cache hit, we hit a clobber when walking. That's a
704         // failure.
705         TerminatedPath Term{Res.Result, PathIndex};
706         if (!MSSA.dominates(Res.Result, StopWhere))
707           return Term;
708 
709         // Otherwise, it's a valid thing to potentially optimize to.
710         Terminated.push_back(Term);
711         continue;
712       }
713 
714       if (Res.Result == StopWhere || Res.Result == SkipStopWhere) {
715         // We've hit our target. Save this path off for if we want to continue
716         // walking. If we are in the mode of skipping the OriginalAccess, and
717         // we've reached back to the OriginalAccess, do not save path, we've
718         // just looped back to self.
719         if (Res.Result != SkipStopWhere)
720           NewPaused.push_back(PathIndex);
721         continue;
722       }
723 
724       assert(!MSSA.isLiveOnEntryDef(Res.Result) && "liveOnEntry is a clobber");
725       addSearches(cast<MemoryPhi>(Res.Result), PausedSearches, PathIndex);
726     }
727 
728     return None;
729   }
730 
731   template <typename T, typename Walker>
732   struct generic_def_path_iterator
733       : public iterator_facade_base<generic_def_path_iterator<T, Walker>,
734                                     std::forward_iterator_tag, T *> {
735     generic_def_path_iterator() {}
736     generic_def_path_iterator(Walker *W, ListIndex N) : W(W), N(N) {}
737 
738     T &operator*() const { return curNode(); }
739 
740     generic_def_path_iterator &operator++() {
741       N = curNode().Previous;
742       return *this;
743     }
744 
745     bool operator==(const generic_def_path_iterator &O) const {
746       if (N.hasValue() != O.N.hasValue())
747         return false;
748       return !N.hasValue() || *N == *O.N;
749     }
750 
751   private:
752     T &curNode() const { return W->Paths[*N]; }
753 
754     Walker *W = nullptr;
755     Optional<ListIndex> N = None;
756   };
757 
758   using def_path_iterator = generic_def_path_iterator<DefPath, ClobberWalker>;
759   using const_def_path_iterator =
760       generic_def_path_iterator<const DefPath, const ClobberWalker>;
761 
762   iterator_range<def_path_iterator> def_path(ListIndex From) {
763     return make_range(def_path_iterator(this, From), def_path_iterator());
764   }
765 
766   iterator_range<const_def_path_iterator> const_def_path(ListIndex From) const {
767     return make_range(const_def_path_iterator(this, From),
768                       const_def_path_iterator());
769   }
770 
771   struct OptznResult {
772     /// The path that contains our result.
773     TerminatedPath PrimaryClobber;
774     /// The paths that we can legally cache back from, but that aren't
775     /// necessarily the result of the Phi optimization.
776     SmallVector<TerminatedPath, 4> OtherClobbers;
777   };
778 
779   ListIndex defPathIndex(const DefPath &N) const {
780     // The assert looks nicer if we don't need to do &N
781     const DefPath *NP = &N;
782     assert(!Paths.empty() && NP >= &Paths.front() && NP <= &Paths.back() &&
783            "Out of bounds DefPath!");
784     return NP - &Paths.front();
785   }
786 
787   /// Try to optimize a phi as best as we can. Returns a SmallVector of Paths
788   /// that act as legal clobbers. Note that this won't return *all* clobbers.
789   ///
790   /// Phi optimization algorithm tl;dr:
791   ///   - Find the earliest def/phi, A, we can optimize to
792   ///   - Find if all paths from the starting memory access ultimately reach A
793   ///     - If not, optimization isn't possible.
794   ///     - Otherwise, walk from A to another clobber or phi, A'.
795   ///       - If A' is a def, we're done.
796   ///       - If A' is a phi, try to optimize it.
797   ///
798   /// A path is a series of {MemoryAccess, MemoryLocation} pairs. A path
799   /// terminates when a MemoryAccess that clobbers said MemoryLocation is found.
800   OptznResult tryOptimizePhi(MemoryPhi *Phi, MemoryAccess *Start,
801                              const MemoryLocation &Loc) {
802     assert(Paths.empty() && VisitedPhis.empty() && !PerformedPhiTranslation &&
803            "Reset the optimization state.");
804 
805     Paths.emplace_back(Loc, Start, Phi, None);
806     // Stores how many "valid" optimization nodes we had prior to calling
807     // addSearches/getBlockingAccess. Necessary for caching if we had a blocker.
808     auto PriorPathsSize = Paths.size();
809 
810     SmallVector<ListIndex, 16> PausedSearches;
811     SmallVector<ListIndex, 8> NewPaused;
812     SmallVector<TerminatedPath, 4> TerminatedPaths;
813 
814     addSearches(Phi, PausedSearches, 0);
815 
816     // Moves the TerminatedPath with the "most dominated" Clobber to the end of
817     // Paths.
818     auto MoveDominatedPathToEnd = [&](SmallVectorImpl<TerminatedPath> &Paths) {
819       assert(!Paths.empty() && "Need a path to move");
820       auto Dom = Paths.begin();
821       for (auto I = std::next(Dom), E = Paths.end(); I != E; ++I)
822         if (!MSSA.dominates(I->Clobber, Dom->Clobber))
823           Dom = I;
824       auto Last = Paths.end() - 1;
825       if (Last != Dom)
826         std::iter_swap(Last, Dom);
827     };
828 
829     MemoryPhi *Current = Phi;
830     while (true) {
831       assert(!MSSA.isLiveOnEntryDef(Current) &&
832              "liveOnEntry wasn't treated as a clobber?");
833 
834       const auto *Target = getWalkTarget(Current);
835       // If a TerminatedPath doesn't dominate Target, then it wasn't a legal
836       // optimization for the prior phi.
837       assert(all_of(TerminatedPaths, [&](const TerminatedPath &P) {
838         return MSSA.dominates(P.Clobber, Target);
839       }));
840 
841       // FIXME: This is broken, because the Blocker may be reported to be
842       // liveOnEntry, and we'll happily wait for that to disappear (read: never)
843       // For the moment, this is fine, since we do nothing with blocker info.
844       if (Optional<TerminatedPath> Blocker = getBlockingAccess(
845               Target, PausedSearches, NewPaused, TerminatedPaths)) {
846 
847         // Find the node we started at. We can't search based on N->Last, since
848         // we may have gone around a loop with a different MemoryLocation.
849         auto Iter = find_if(def_path(Blocker->LastNode), [&](const DefPath &N) {
850           return defPathIndex(N) < PriorPathsSize;
851         });
852         assert(Iter != def_path_iterator());
853 
854         DefPath &CurNode = *Iter;
855         assert(CurNode.Last == Current);
856 
857         // Two things:
858         // A. We can't reliably cache all of NewPaused back. Consider a case
859         //    where we have two paths in NewPaused; one of which can't optimize
860         //    above this phi, whereas the other can. If we cache the second path
861         //    back, we'll end up with suboptimal cache entries. We can handle
862         //    cases like this a bit better when we either try to find all
863         //    clobbers that block phi optimization, or when our cache starts
864         //    supporting unfinished searches.
865         // B. We can't reliably cache TerminatedPaths back here without doing
866         //    extra checks; consider a case like:
867         //       T
868         //      / \
869         //     D   C
870         //      \ /
871         //       S
872         //    Where T is our target, C is a node with a clobber on it, D is a
873         //    diamond (with a clobber *only* on the left or right node, N), and
874         //    S is our start. Say we walk to D, through the node opposite N
875         //    (read: ignoring the clobber), and see a cache entry in the top
876         //    node of D. That cache entry gets put into TerminatedPaths. We then
877         //    walk up to C (N is later in our worklist), find the clobber, and
878         //    quit. If we append TerminatedPaths to OtherClobbers, we'll cache
879         //    the bottom part of D to the cached clobber, ignoring the clobber
880         //    in N. Again, this problem goes away if we start tracking all
881         //    blockers for a given phi optimization.
882         TerminatedPath Result{CurNode.Last, defPathIndex(CurNode)};
883         return {Result, {}};
884       }
885 
886       // If there's nothing left to search, then all paths led to valid clobbers
887       // that we got from our cache; pick the nearest to the start, and allow
888       // the rest to be cached back.
889       if (NewPaused.empty()) {
890         MoveDominatedPathToEnd(TerminatedPaths);
891         TerminatedPath Result = TerminatedPaths.pop_back_val();
892         return {Result, std::move(TerminatedPaths)};
893       }
894 
895       MemoryAccess *DefChainEnd = nullptr;
896       SmallVector<TerminatedPath, 4> Clobbers;
897       for (ListIndex Paused : NewPaused) {
898         UpwardsWalkResult WR = walkToPhiOrClobber(Paths[Paused]);
899         if (WR.IsKnownClobber)
900           Clobbers.push_back({WR.Result, Paused});
901         else
902           // Micro-opt: If we hit the end of the chain, save it.
903           DefChainEnd = WR.Result;
904       }
905 
906       if (!TerminatedPaths.empty()) {
907         // If we couldn't find the dominating phi/liveOnEntry in the above loop,
908         // do it now.
909         if (!DefChainEnd)
910           for (auto *MA : def_chain(const_cast<MemoryAccess *>(Target)))
911             DefChainEnd = MA;
912         assert(DefChainEnd && "Failed to find dominating phi/liveOnEntry");
913 
914         // If any of the terminated paths don't dominate the phi we'll try to
915         // optimize, we need to figure out what they are and quit.
916         const BasicBlock *ChainBB = DefChainEnd->getBlock();
917         for (const TerminatedPath &TP : TerminatedPaths) {
918           // Because we know that DefChainEnd is as "high" as we can go, we
919           // don't need local dominance checks; BB dominance is sufficient.
920           if (DT.dominates(ChainBB, TP.Clobber->getBlock()))
921             Clobbers.push_back(TP);
922         }
923       }
924 
925       // If we have clobbers in the def chain, find the one closest to Current
926       // and quit.
927       if (!Clobbers.empty()) {
928         MoveDominatedPathToEnd(Clobbers);
929         TerminatedPath Result = Clobbers.pop_back_val();
930         return {Result, std::move(Clobbers)};
931       }
932 
933       assert(all_of(NewPaused,
934                     [&](ListIndex I) { return Paths[I].Last == DefChainEnd; }));
935 
936       // Because liveOnEntry is a clobber, this must be a phi.
937       auto *DefChainPhi = cast<MemoryPhi>(DefChainEnd);
938 
939       PriorPathsSize = Paths.size();
940       PausedSearches.clear();
941       for (ListIndex I : NewPaused)
942         addSearches(DefChainPhi, PausedSearches, I);
943       NewPaused.clear();
944 
945       Current = DefChainPhi;
946     }
947   }
948 
949   void verifyOptResult(const OptznResult &R) const {
950     assert(all_of(R.OtherClobbers, [&](const TerminatedPath &P) {
951       return MSSA.dominates(P.Clobber, R.PrimaryClobber.Clobber);
952     }));
953   }
954 
955   void resetPhiOptznState() {
956     Paths.clear();
957     VisitedPhis.clear();
958     PerformedPhiTranslation = false;
959   }
960 
961 public:
962   ClobberWalker(const MemorySSA &MSSA, AliasAnalysisType &AA, DominatorTree &DT)
963       : MSSA(MSSA), AA(AA), DT(DT) {}
964 
965   AliasAnalysisType *getAA() { return &AA; }
966   /// Finds the nearest clobber for the given query, optimizing phis if
967   /// possible.
968   MemoryAccess *findClobber(MemoryAccess *Start, UpwardsMemoryQuery &Q,
969                             unsigned &UpWalkLimit) {
970     Query = &Q;
971     UpwardWalkLimit = &UpWalkLimit;
972     // Starting limit must be > 0.
973     if (!UpWalkLimit)
974       UpWalkLimit++;
975 
976     MemoryAccess *Current = Start;
977     // This walker pretends uses don't exist. If we're handed one, silently grab
978     // its def. (This has the nice side-effect of ensuring we never cache uses)
979     if (auto *MU = dyn_cast<MemoryUse>(Start))
980       Current = MU->getDefiningAccess();
981 
982     DefPath FirstDesc(Q.StartingLoc, Current, Current, None);
983     // Fast path for the overly-common case (no crazy phi optimization
984     // necessary)
985     UpwardsWalkResult WalkResult = walkToPhiOrClobber(FirstDesc);
986     MemoryAccess *Result;
987     if (WalkResult.IsKnownClobber) {
988       Result = WalkResult.Result;
989       Q.AR = WalkResult.AR;
990     } else {
991       OptznResult OptRes = tryOptimizePhi(cast<MemoryPhi>(FirstDesc.Last),
992                                           Current, Q.StartingLoc);
993       verifyOptResult(OptRes);
994       resetPhiOptznState();
995       Result = OptRes.PrimaryClobber.Clobber;
996     }
997 
998 #ifdef EXPENSIVE_CHECKS
999     if (!Q.SkipSelfAccess && *UpwardWalkLimit > 0)
1000       checkClobberSanity(Current, Result, Q.StartingLoc, MSSA, Q, AA);
1001 #endif
1002     return Result;
1003   }
1004 };
1005 
1006 struct RenamePassData {
1007   DomTreeNode *DTN;
1008   DomTreeNode::const_iterator ChildIt;
1009   MemoryAccess *IncomingVal;
1010 
1011   RenamePassData(DomTreeNode *D, DomTreeNode::const_iterator It,
1012                  MemoryAccess *M)
1013       : DTN(D), ChildIt(It), IncomingVal(M) {}
1014 
1015   void swap(RenamePassData &RHS) {
1016     std::swap(DTN, RHS.DTN);
1017     std::swap(ChildIt, RHS.ChildIt);
1018     std::swap(IncomingVal, RHS.IncomingVal);
1019   }
1020 };
1021 
1022 } // end anonymous namespace
1023 
1024 namespace llvm {
1025 
1026 template <class AliasAnalysisType> class MemorySSA::ClobberWalkerBase {
1027   ClobberWalker<AliasAnalysisType> Walker;
1028   MemorySSA *MSSA;
1029 
1030 public:
1031   ClobberWalkerBase(MemorySSA *M, AliasAnalysisType *A, DominatorTree *D)
1032       : Walker(*M, *A, *D), MSSA(M) {}
1033 
1034   MemoryAccess *getClobberingMemoryAccessBase(MemoryAccess *,
1035                                               const MemoryLocation &,
1036                                               unsigned &);
1037   // Third argument (bool), defines whether the clobber search should skip the
1038   // original queried access. If true, there will be a follow-up query searching
1039   // for a clobber access past "self". Note that the Optimized access is not
1040   // updated if a new clobber is found by this SkipSelf search. If this
1041   // additional query becomes heavily used we may decide to cache the result.
1042   // Walker instantiations will decide how to set the SkipSelf bool.
1043   MemoryAccess *getClobberingMemoryAccessBase(MemoryAccess *, unsigned &, bool,
1044                                               bool UseInvariantGroup = true);
1045 };
1046 
1047 /// A MemorySSAWalker that does AA walks to disambiguate accesses. It no
1048 /// longer does caching on its own, but the name has been retained for the
1049 /// moment.
1050 template <class AliasAnalysisType>
1051 class MemorySSA::CachingWalker final : public MemorySSAWalker {
1052   ClobberWalkerBase<AliasAnalysisType> *Walker;
1053 
1054 public:
1055   CachingWalker(MemorySSA *M, ClobberWalkerBase<AliasAnalysisType> *W)
1056       : MemorySSAWalker(M), Walker(W) {}
1057   ~CachingWalker() override = default;
1058 
1059   using MemorySSAWalker::getClobberingMemoryAccess;
1060 
1061   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA, unsigned &UWL) {
1062     return Walker->getClobberingMemoryAccessBase(MA, UWL, false);
1063   }
1064   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1065                                           const MemoryLocation &Loc,
1066                                           unsigned &UWL) {
1067     return Walker->getClobberingMemoryAccessBase(MA, Loc, UWL);
1068   }
1069   // This method is not accessible outside of this file.
1070   MemoryAccess *getClobberingMemoryAccessWithoutInvariantGroup(MemoryAccess *MA,
1071                                                                unsigned &UWL) {
1072     return Walker->getClobberingMemoryAccessBase(MA, UWL, false, false);
1073   }
1074 
1075   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA) override {
1076     unsigned UpwardWalkLimit = MaxCheckLimit;
1077     return getClobberingMemoryAccess(MA, UpwardWalkLimit);
1078   }
1079   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1080                                           const MemoryLocation &Loc) override {
1081     unsigned UpwardWalkLimit = MaxCheckLimit;
1082     return getClobberingMemoryAccess(MA, Loc, UpwardWalkLimit);
1083   }
1084 
1085   void invalidateInfo(MemoryAccess *MA) override {
1086     if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1087       MUD->resetOptimized();
1088   }
1089 };
1090 
1091 template <class AliasAnalysisType>
1092 class MemorySSA::SkipSelfWalker final : public MemorySSAWalker {
1093   ClobberWalkerBase<AliasAnalysisType> *Walker;
1094 
1095 public:
1096   SkipSelfWalker(MemorySSA *M, ClobberWalkerBase<AliasAnalysisType> *W)
1097       : MemorySSAWalker(M), Walker(W) {}
1098   ~SkipSelfWalker() override = default;
1099 
1100   using MemorySSAWalker::getClobberingMemoryAccess;
1101 
1102   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA, unsigned &UWL) {
1103     return Walker->getClobberingMemoryAccessBase(MA, UWL, true);
1104   }
1105   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1106                                           const MemoryLocation &Loc,
1107                                           unsigned &UWL) {
1108     return Walker->getClobberingMemoryAccessBase(MA, Loc, UWL);
1109   }
1110 
1111   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA) override {
1112     unsigned UpwardWalkLimit = MaxCheckLimit;
1113     return getClobberingMemoryAccess(MA, UpwardWalkLimit);
1114   }
1115   MemoryAccess *getClobberingMemoryAccess(MemoryAccess *MA,
1116                                           const MemoryLocation &Loc) override {
1117     unsigned UpwardWalkLimit = MaxCheckLimit;
1118     return getClobberingMemoryAccess(MA, Loc, UpwardWalkLimit);
1119   }
1120 
1121   void invalidateInfo(MemoryAccess *MA) override {
1122     if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1123       MUD->resetOptimized();
1124   }
1125 };
1126 
1127 } // end namespace llvm
1128 
1129 void MemorySSA::renameSuccessorPhis(BasicBlock *BB, MemoryAccess *IncomingVal,
1130                                     bool RenameAllUses) {
1131   // Pass through values to our successors
1132   for (const BasicBlock *S : successors(BB)) {
1133     auto It = PerBlockAccesses.find(S);
1134     // Rename the phi nodes in our successor block
1135     if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front()))
1136       continue;
1137     AccessList *Accesses = It->second.get();
1138     auto *Phi = cast<MemoryPhi>(&Accesses->front());
1139     if (RenameAllUses) {
1140       bool ReplacementDone = false;
1141       for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I)
1142         if (Phi->getIncomingBlock(I) == BB) {
1143           Phi->setIncomingValue(I, IncomingVal);
1144           ReplacementDone = true;
1145         }
1146       (void) ReplacementDone;
1147       assert(ReplacementDone && "Incomplete phi during partial rename");
1148     } else
1149       Phi->addIncoming(IncomingVal, BB);
1150   }
1151 }
1152 
1153 /// Rename a single basic block into MemorySSA form.
1154 /// Uses the standard SSA renaming algorithm.
1155 /// \returns The new incoming value.
1156 MemoryAccess *MemorySSA::renameBlock(BasicBlock *BB, MemoryAccess *IncomingVal,
1157                                      bool RenameAllUses) {
1158   auto It = PerBlockAccesses.find(BB);
1159   // Skip most processing if the list is empty.
1160   if (It != PerBlockAccesses.end()) {
1161     AccessList *Accesses = It->second.get();
1162     for (MemoryAccess &L : *Accesses) {
1163       if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(&L)) {
1164         if (MUD->getDefiningAccess() == nullptr || RenameAllUses)
1165           MUD->setDefiningAccess(IncomingVal);
1166         if (isa<MemoryDef>(&L))
1167           IncomingVal = &L;
1168       } else {
1169         IncomingVal = &L;
1170       }
1171     }
1172   }
1173   return IncomingVal;
1174 }
1175 
1176 /// This is the standard SSA renaming algorithm.
1177 ///
1178 /// We walk the dominator tree in preorder, renaming accesses, and then filling
1179 /// in phi nodes in our successors.
1180 void MemorySSA::renamePass(DomTreeNode *Root, MemoryAccess *IncomingVal,
1181                            SmallPtrSetImpl<BasicBlock *> &Visited,
1182                            bool SkipVisited, bool RenameAllUses) {
1183   assert(Root && "Trying to rename accesses in an unreachable block");
1184 
1185   SmallVector<RenamePassData, 32> WorkStack;
1186   // Skip everything if we already renamed this block and we are skipping.
1187   // Note: You can't sink this into the if, because we need it to occur
1188   // regardless of whether we skip blocks or not.
1189   bool AlreadyVisited = !Visited.insert(Root->getBlock()).second;
1190   if (SkipVisited && AlreadyVisited)
1191     return;
1192 
1193   IncomingVal = renameBlock(Root->getBlock(), IncomingVal, RenameAllUses);
1194   renameSuccessorPhis(Root->getBlock(), IncomingVal, RenameAllUses);
1195   WorkStack.push_back({Root, Root->begin(), IncomingVal});
1196 
1197   while (!WorkStack.empty()) {
1198     DomTreeNode *Node = WorkStack.back().DTN;
1199     DomTreeNode::const_iterator ChildIt = WorkStack.back().ChildIt;
1200     IncomingVal = WorkStack.back().IncomingVal;
1201 
1202     if (ChildIt == Node->end()) {
1203       WorkStack.pop_back();
1204     } else {
1205       DomTreeNode *Child = *ChildIt;
1206       ++WorkStack.back().ChildIt;
1207       BasicBlock *BB = Child->getBlock();
1208       // Note: You can't sink this into the if, because we need it to occur
1209       // regardless of whether we skip blocks or not.
1210       AlreadyVisited = !Visited.insert(BB).second;
1211       if (SkipVisited && AlreadyVisited) {
1212         // We already visited this during our renaming, which can happen when
1213         // being asked to rename multiple blocks. Figure out the incoming val,
1214         // which is the last def.
1215         // Incoming value can only change if there is a block def, and in that
1216         // case, it's the last block def in the list.
1217         if (auto *BlockDefs = getWritableBlockDefs(BB))
1218           IncomingVal = &*BlockDefs->rbegin();
1219       } else
1220         IncomingVal = renameBlock(BB, IncomingVal, RenameAllUses);
1221       renameSuccessorPhis(BB, IncomingVal, RenameAllUses);
1222       WorkStack.push_back({Child, Child->begin(), IncomingVal});
1223     }
1224   }
1225 }
1226 
1227 /// This handles unreachable block accesses by deleting phi nodes in
1228 /// unreachable blocks, and marking all other unreachable MemoryAccess's as
1229 /// being uses of the live on entry definition.
1230 void MemorySSA::markUnreachableAsLiveOnEntry(BasicBlock *BB) {
1231   assert(!DT->isReachableFromEntry(BB) &&
1232          "Reachable block found while handling unreachable blocks");
1233 
1234   // Make sure phi nodes in our reachable successors end up with a
1235   // LiveOnEntryDef for our incoming edge, even though our block is forward
1236   // unreachable.  We could just disconnect these blocks from the CFG fully,
1237   // but we do not right now.
1238   for (const BasicBlock *S : successors(BB)) {
1239     if (!DT->isReachableFromEntry(S))
1240       continue;
1241     auto It = PerBlockAccesses.find(S);
1242     // Rename the phi nodes in our successor block
1243     if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front()))
1244       continue;
1245     AccessList *Accesses = It->second.get();
1246     auto *Phi = cast<MemoryPhi>(&Accesses->front());
1247     Phi->addIncoming(LiveOnEntryDef.get(), BB);
1248   }
1249 
1250   auto It = PerBlockAccesses.find(BB);
1251   if (It == PerBlockAccesses.end())
1252     return;
1253 
1254   auto &Accesses = It->second;
1255   for (auto AI = Accesses->begin(), AE = Accesses->end(); AI != AE;) {
1256     auto Next = std::next(AI);
1257     // If we have a phi, just remove it. We are going to replace all
1258     // users with live on entry.
1259     if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(AI))
1260       UseOrDef->setDefiningAccess(LiveOnEntryDef.get());
1261     else
1262       Accesses->erase(AI);
1263     AI = Next;
1264   }
1265 }
1266 
1267 MemorySSA::MemorySSA(Function &Func, AliasAnalysis *AA, DominatorTree *DT)
1268     : DT(DT), F(Func), LiveOnEntryDef(nullptr), Walker(nullptr),
1269       SkipWalker(nullptr) {
1270   // Build MemorySSA using a batch alias analysis. This reuses the internal
1271   // state that AA collects during an alias()/getModRefInfo() call. This is
1272   // safe because there are no CFG changes while building MemorySSA and can
1273   // significantly reduce the time spent by the compiler in AA, because we will
1274   // make queries about all the instructions in the Function.
1275   assert(AA && "No alias analysis?");
1276   BatchAAResults BatchAA(*AA);
1277   buildMemorySSA(BatchAA);
1278   // Intentionally leave AA to nullptr while building so we don't accidently
1279   // use non-batch AliasAnalysis.
1280   this->AA = AA;
1281   // Also create the walker here.
1282   getWalker();
1283 }
1284 
1285 MemorySSA::~MemorySSA() {
1286   // Drop all our references
1287   for (const auto &Pair : PerBlockAccesses)
1288     for (MemoryAccess &MA : *Pair.second)
1289       MA.dropAllReferences();
1290 }
1291 
1292 MemorySSA::AccessList *MemorySSA::getOrCreateAccessList(const BasicBlock *BB) {
1293   auto Res = PerBlockAccesses.insert(std::make_pair(BB, nullptr));
1294 
1295   if (Res.second)
1296     Res.first->second = std::make_unique<AccessList>();
1297   return Res.first->second.get();
1298 }
1299 
1300 MemorySSA::DefsList *MemorySSA::getOrCreateDefsList(const BasicBlock *BB) {
1301   auto Res = PerBlockDefs.insert(std::make_pair(BB, nullptr));
1302 
1303   if (Res.second)
1304     Res.first->second = std::make_unique<DefsList>();
1305   return Res.first->second.get();
1306 }
1307 
1308 namespace llvm {
1309 
1310 /// This class is a batch walker of all MemoryUse's in the program, and points
1311 /// their defining access at the thing that actually clobbers them.  Because it
1312 /// is a batch walker that touches everything, it does not operate like the
1313 /// other walkers.  This walker is basically performing a top-down SSA renaming
1314 /// pass, where the version stack is used as the cache.  This enables it to be
1315 /// significantly more time and memory efficient than using the regular walker,
1316 /// which is walking bottom-up.
1317 class MemorySSA::OptimizeUses {
1318 public:
1319   OptimizeUses(MemorySSA *MSSA, CachingWalker<BatchAAResults> *Walker,
1320                BatchAAResults *BAA, DominatorTree *DT)
1321       : MSSA(MSSA), Walker(Walker), AA(BAA), DT(DT) {}
1322 
1323   void optimizeUses();
1324 
1325 private:
1326   /// This represents where a given memorylocation is in the stack.
1327   struct MemlocStackInfo {
1328     // This essentially is keeping track of versions of the stack. Whenever
1329     // the stack changes due to pushes or pops, these versions increase.
1330     unsigned long StackEpoch;
1331     unsigned long PopEpoch;
1332     // This is the lower bound of places on the stack to check. It is equal to
1333     // the place the last stack walk ended.
1334     // Note: Correctness depends on this being initialized to 0, which densemap
1335     // does
1336     unsigned long LowerBound;
1337     const BasicBlock *LowerBoundBlock;
1338     // This is where the last walk for this memory location ended.
1339     unsigned long LastKill;
1340     bool LastKillValid;
1341     Optional<AliasResult> AR;
1342   };
1343 
1344   void optimizeUsesInBlock(const BasicBlock *, unsigned long &, unsigned long &,
1345                            SmallVectorImpl<MemoryAccess *> &,
1346                            DenseMap<MemoryLocOrCall, MemlocStackInfo> &);
1347 
1348   MemorySSA *MSSA;
1349   CachingWalker<BatchAAResults> *Walker;
1350   BatchAAResults *AA;
1351   DominatorTree *DT;
1352 };
1353 
1354 } // end namespace llvm
1355 
1356 /// Optimize the uses in a given block This is basically the SSA renaming
1357 /// algorithm, with one caveat: We are able to use a single stack for all
1358 /// MemoryUses.  This is because the set of *possible* reaching MemoryDefs is
1359 /// the same for every MemoryUse.  The *actual* clobbering MemoryDef is just
1360 /// going to be some position in that stack of possible ones.
1361 ///
1362 /// We track the stack positions that each MemoryLocation needs
1363 /// to check, and last ended at.  This is because we only want to check the
1364 /// things that changed since last time.  The same MemoryLocation should
1365 /// get clobbered by the same store (getModRefInfo does not use invariantness or
1366 /// things like this, and if they start, we can modify MemoryLocOrCall to
1367 /// include relevant data)
1368 void MemorySSA::OptimizeUses::optimizeUsesInBlock(
1369     const BasicBlock *BB, unsigned long &StackEpoch, unsigned long &PopEpoch,
1370     SmallVectorImpl<MemoryAccess *> &VersionStack,
1371     DenseMap<MemoryLocOrCall, MemlocStackInfo> &LocStackInfo) {
1372 
1373   /// If no accesses, nothing to do.
1374   MemorySSA::AccessList *Accesses = MSSA->getWritableBlockAccesses(BB);
1375   if (Accesses == nullptr)
1376     return;
1377 
1378   // Pop everything that doesn't dominate the current block off the stack,
1379   // increment the PopEpoch to account for this.
1380   while (true) {
1381     assert(
1382         !VersionStack.empty() &&
1383         "Version stack should have liveOnEntry sentinel dominating everything");
1384     BasicBlock *BackBlock = VersionStack.back()->getBlock();
1385     if (DT->dominates(BackBlock, BB))
1386       break;
1387     while (VersionStack.back()->getBlock() == BackBlock)
1388       VersionStack.pop_back();
1389     ++PopEpoch;
1390   }
1391 
1392   for (MemoryAccess &MA : *Accesses) {
1393     auto *MU = dyn_cast<MemoryUse>(&MA);
1394     if (!MU) {
1395       VersionStack.push_back(&MA);
1396       ++StackEpoch;
1397       continue;
1398     }
1399 
1400     if (isUseTriviallyOptimizableToLiveOnEntry(*AA, MU->getMemoryInst())) {
1401       MU->setDefiningAccess(MSSA->getLiveOnEntryDef(), true, None);
1402       continue;
1403     }
1404 
1405     MemoryLocOrCall UseMLOC(MU);
1406     auto &LocInfo = LocStackInfo[UseMLOC];
1407     // If the pop epoch changed, it means we've removed stuff from top of
1408     // stack due to changing blocks. We may have to reset the lower bound or
1409     // last kill info.
1410     if (LocInfo.PopEpoch != PopEpoch) {
1411       LocInfo.PopEpoch = PopEpoch;
1412       LocInfo.StackEpoch = StackEpoch;
1413       // If the lower bound was in something that no longer dominates us, we
1414       // have to reset it.
1415       // We can't simply track stack size, because the stack may have had
1416       // pushes/pops in the meantime.
1417       // XXX: This is non-optimal, but only is slower cases with heavily
1418       // branching dominator trees.  To get the optimal number of queries would
1419       // be to make lowerbound and lastkill a per-loc stack, and pop it until
1420       // the top of that stack dominates us.  This does not seem worth it ATM.
1421       // A much cheaper optimization would be to always explore the deepest
1422       // branch of the dominator tree first. This will guarantee this resets on
1423       // the smallest set of blocks.
1424       if (LocInfo.LowerBoundBlock && LocInfo.LowerBoundBlock != BB &&
1425           !DT->dominates(LocInfo.LowerBoundBlock, BB)) {
1426         // Reset the lower bound of things to check.
1427         // TODO: Some day we should be able to reset to last kill, rather than
1428         // 0.
1429         LocInfo.LowerBound = 0;
1430         LocInfo.LowerBoundBlock = VersionStack[0]->getBlock();
1431         LocInfo.LastKillValid = false;
1432       }
1433     } else if (LocInfo.StackEpoch != StackEpoch) {
1434       // If all that has changed is the StackEpoch, we only have to check the
1435       // new things on the stack, because we've checked everything before.  In
1436       // this case, the lower bound of things to check remains the same.
1437       LocInfo.PopEpoch = PopEpoch;
1438       LocInfo.StackEpoch = StackEpoch;
1439     }
1440     if (!LocInfo.LastKillValid) {
1441       LocInfo.LastKill = VersionStack.size() - 1;
1442       LocInfo.LastKillValid = true;
1443       LocInfo.AR = AliasResult::MayAlias;
1444     }
1445 
1446     // At this point, we should have corrected last kill and LowerBound to be
1447     // in bounds.
1448     assert(LocInfo.LowerBound < VersionStack.size() &&
1449            "Lower bound out of range");
1450     assert(LocInfo.LastKill < VersionStack.size() &&
1451            "Last kill info out of range");
1452     // In any case, the new upper bound is the top of the stack.
1453     unsigned long UpperBound = VersionStack.size() - 1;
1454 
1455     if (UpperBound - LocInfo.LowerBound > MaxCheckLimit) {
1456       LLVM_DEBUG(dbgs() << "MemorySSA skipping optimization of " << *MU << " ("
1457                         << *(MU->getMemoryInst()) << ")"
1458                         << " because there are "
1459                         << UpperBound - LocInfo.LowerBound
1460                         << " stores to disambiguate\n");
1461       // Because we did not walk, LastKill is no longer valid, as this may
1462       // have been a kill.
1463       LocInfo.LastKillValid = false;
1464       continue;
1465     }
1466     bool FoundClobberResult = false;
1467     unsigned UpwardWalkLimit = MaxCheckLimit;
1468     while (UpperBound > LocInfo.LowerBound) {
1469       if (isa<MemoryPhi>(VersionStack[UpperBound])) {
1470         // For phis, use the walker, see where we ended up, go there.
1471         // The invariant.group handling in MemorySSA is ad-hoc and doesn't
1472         // support updates, so don't use it to optimize uses.
1473         MemoryAccess *Result =
1474             Walker->getClobberingMemoryAccessWithoutInvariantGroup(
1475                 MU, UpwardWalkLimit);
1476         // We are guaranteed to find it or something is wrong.
1477         while (VersionStack[UpperBound] != Result) {
1478           assert(UpperBound != 0);
1479           --UpperBound;
1480         }
1481         FoundClobberResult = true;
1482         break;
1483       }
1484 
1485       MemoryDef *MD = cast<MemoryDef>(VersionStack[UpperBound]);
1486       ClobberAlias CA = instructionClobbersQuery(MD, MU, UseMLOC, *AA);
1487       if (CA.IsClobber) {
1488         FoundClobberResult = true;
1489         LocInfo.AR = CA.AR;
1490         break;
1491       }
1492       --UpperBound;
1493     }
1494 
1495     // Note: Phis always have AliasResult AR set to MayAlias ATM.
1496 
1497     // At the end of this loop, UpperBound is either a clobber, or lower bound
1498     // PHI walking may cause it to be < LowerBound, and in fact, < LastKill.
1499     if (FoundClobberResult || UpperBound < LocInfo.LastKill) {
1500       // We were last killed now by where we got to
1501       if (MSSA->isLiveOnEntryDef(VersionStack[UpperBound]))
1502         LocInfo.AR = None;
1503       MU->setDefiningAccess(VersionStack[UpperBound], true, LocInfo.AR);
1504       LocInfo.LastKill = UpperBound;
1505     } else {
1506       // Otherwise, we checked all the new ones, and now we know we can get to
1507       // LastKill.
1508       MU->setDefiningAccess(VersionStack[LocInfo.LastKill], true, LocInfo.AR);
1509     }
1510     LocInfo.LowerBound = VersionStack.size() - 1;
1511     LocInfo.LowerBoundBlock = BB;
1512   }
1513 }
1514 
1515 /// Optimize uses to point to their actual clobbering definitions.
1516 void MemorySSA::OptimizeUses::optimizeUses() {
1517   SmallVector<MemoryAccess *, 16> VersionStack;
1518   DenseMap<MemoryLocOrCall, MemlocStackInfo> LocStackInfo;
1519   VersionStack.push_back(MSSA->getLiveOnEntryDef());
1520 
1521   unsigned long StackEpoch = 1;
1522   unsigned long PopEpoch = 1;
1523   // We perform a non-recursive top-down dominator tree walk.
1524   for (const auto *DomNode : depth_first(DT->getRootNode()))
1525     optimizeUsesInBlock(DomNode->getBlock(), StackEpoch, PopEpoch, VersionStack,
1526                         LocStackInfo);
1527 }
1528 
1529 void MemorySSA::placePHINodes(
1530     const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks) {
1531   // Determine where our MemoryPhi's should go
1532   ForwardIDFCalculator IDFs(*DT);
1533   IDFs.setDefiningBlocks(DefiningBlocks);
1534   SmallVector<BasicBlock *, 32> IDFBlocks;
1535   IDFs.calculate(IDFBlocks);
1536 
1537   // Now place MemoryPhi nodes.
1538   for (auto &BB : IDFBlocks)
1539     createMemoryPhi(BB);
1540 }
1541 
1542 void MemorySSA::buildMemorySSA(BatchAAResults &BAA) {
1543   // We create an access to represent "live on entry", for things like
1544   // arguments or users of globals, where the memory they use is defined before
1545   // the beginning of the function. We do not actually insert it into the IR.
1546   // We do not define a live on exit for the immediate uses, and thus our
1547   // semantics do *not* imply that something with no immediate uses can simply
1548   // be removed.
1549   BasicBlock &StartingPoint = F.getEntryBlock();
1550   LiveOnEntryDef.reset(new MemoryDef(F.getContext(), nullptr, nullptr,
1551                                      &StartingPoint, NextID++));
1552 
1553   // We maintain lists of memory accesses per-block, trading memory for time. We
1554   // could just look up the memory access for every possible instruction in the
1555   // stream.
1556   SmallPtrSet<BasicBlock *, 32> DefiningBlocks;
1557   // Go through each block, figure out where defs occur, and chain together all
1558   // the accesses.
1559   for (BasicBlock &B : F) {
1560     bool InsertIntoDef = false;
1561     AccessList *Accesses = nullptr;
1562     DefsList *Defs = nullptr;
1563     for (Instruction &I : B) {
1564       MemoryUseOrDef *MUD = createNewAccess(&I, &BAA);
1565       if (!MUD)
1566         continue;
1567 
1568       if (!Accesses)
1569         Accesses = getOrCreateAccessList(&B);
1570       Accesses->push_back(MUD);
1571       if (isa<MemoryDef>(MUD)) {
1572         InsertIntoDef = true;
1573         if (!Defs)
1574           Defs = getOrCreateDefsList(&B);
1575         Defs->push_back(*MUD);
1576       }
1577     }
1578     if (InsertIntoDef)
1579       DefiningBlocks.insert(&B);
1580   }
1581   placePHINodes(DefiningBlocks);
1582 
1583   // Now do regular SSA renaming on the MemoryDef/MemoryUse. Visited will get
1584   // filled in with all blocks.
1585   SmallPtrSet<BasicBlock *, 16> Visited;
1586   renamePass(DT->getRootNode(), LiveOnEntryDef.get(), Visited);
1587 
1588   ClobberWalkerBase<BatchAAResults> WalkerBase(this, &BAA, DT);
1589   CachingWalker<BatchAAResults> WalkerLocal(this, &WalkerBase);
1590   OptimizeUses(this, &WalkerLocal, &BAA, DT).optimizeUses();
1591 
1592   // Mark the uses in unreachable blocks as live on entry, so that they go
1593   // somewhere.
1594   for (auto &BB : F)
1595     if (!Visited.count(&BB))
1596       markUnreachableAsLiveOnEntry(&BB);
1597 }
1598 
1599 MemorySSAWalker *MemorySSA::getWalker() { return getWalkerImpl(); }
1600 
1601 MemorySSA::CachingWalker<AliasAnalysis> *MemorySSA::getWalkerImpl() {
1602   if (Walker)
1603     return Walker.get();
1604 
1605   if (!WalkerBase)
1606     WalkerBase =
1607         std::make_unique<ClobberWalkerBase<AliasAnalysis>>(this, AA, DT);
1608 
1609   Walker =
1610       std::make_unique<CachingWalker<AliasAnalysis>>(this, WalkerBase.get());
1611   return Walker.get();
1612 }
1613 
1614 MemorySSAWalker *MemorySSA::getSkipSelfWalker() {
1615   if (SkipWalker)
1616     return SkipWalker.get();
1617 
1618   if (!WalkerBase)
1619     WalkerBase =
1620         std::make_unique<ClobberWalkerBase<AliasAnalysis>>(this, AA, DT);
1621 
1622   SkipWalker =
1623       std::make_unique<SkipSelfWalker<AliasAnalysis>>(this, WalkerBase.get());
1624   return SkipWalker.get();
1625  }
1626 
1627 
1628 // This is a helper function used by the creation routines. It places NewAccess
1629 // into the access and defs lists for a given basic block, at the given
1630 // insertion point.
1631 void MemorySSA::insertIntoListsForBlock(MemoryAccess *NewAccess,
1632                                         const BasicBlock *BB,
1633                                         InsertionPlace Point) {
1634   auto *Accesses = getOrCreateAccessList(BB);
1635   if (Point == Beginning) {
1636     // If it's a phi node, it goes first, otherwise, it goes after any phi
1637     // nodes.
1638     if (isa<MemoryPhi>(NewAccess)) {
1639       Accesses->push_front(NewAccess);
1640       auto *Defs = getOrCreateDefsList(BB);
1641       Defs->push_front(*NewAccess);
1642     } else {
1643       auto AI = find_if_not(
1644           *Accesses, [](const MemoryAccess &MA) { return isa<MemoryPhi>(MA); });
1645       Accesses->insert(AI, NewAccess);
1646       if (!isa<MemoryUse>(NewAccess)) {
1647         auto *Defs = getOrCreateDefsList(BB);
1648         auto DI = find_if_not(
1649             *Defs, [](const MemoryAccess &MA) { return isa<MemoryPhi>(MA); });
1650         Defs->insert(DI, *NewAccess);
1651       }
1652     }
1653   } else {
1654     Accesses->push_back(NewAccess);
1655     if (!isa<MemoryUse>(NewAccess)) {
1656       auto *Defs = getOrCreateDefsList(BB);
1657       Defs->push_back(*NewAccess);
1658     }
1659   }
1660   BlockNumberingValid.erase(BB);
1661 }
1662 
1663 void MemorySSA::insertIntoListsBefore(MemoryAccess *What, const BasicBlock *BB,
1664                                       AccessList::iterator InsertPt) {
1665   auto *Accesses = getWritableBlockAccesses(BB);
1666   bool WasEnd = InsertPt == Accesses->end();
1667   Accesses->insert(AccessList::iterator(InsertPt), What);
1668   if (!isa<MemoryUse>(What)) {
1669     auto *Defs = getOrCreateDefsList(BB);
1670     // If we got asked to insert at the end, we have an easy job, just shove it
1671     // at the end. If we got asked to insert before an existing def, we also get
1672     // an iterator. If we got asked to insert before a use, we have to hunt for
1673     // the next def.
1674     if (WasEnd) {
1675       Defs->push_back(*What);
1676     } else if (isa<MemoryDef>(InsertPt)) {
1677       Defs->insert(InsertPt->getDefsIterator(), *What);
1678     } else {
1679       while (InsertPt != Accesses->end() && !isa<MemoryDef>(InsertPt))
1680         ++InsertPt;
1681       // Either we found a def, or we are inserting at the end
1682       if (InsertPt == Accesses->end())
1683         Defs->push_back(*What);
1684       else
1685         Defs->insert(InsertPt->getDefsIterator(), *What);
1686     }
1687   }
1688   BlockNumberingValid.erase(BB);
1689 }
1690 
1691 void MemorySSA::prepareForMoveTo(MemoryAccess *What, BasicBlock *BB) {
1692   // Keep it in the lookup tables, remove from the lists
1693   removeFromLists(What, false);
1694 
1695   // Note that moving should implicitly invalidate the optimized state of a
1696   // MemoryUse (and Phis can't be optimized). However, it doesn't do so for a
1697   // MemoryDef.
1698   if (auto *MD = dyn_cast<MemoryDef>(What))
1699     MD->resetOptimized();
1700   What->setBlock(BB);
1701 }
1702 
1703 // Move What before Where in the IR.  The end result is that What will belong to
1704 // the right lists and have the right Block set, but will not otherwise be
1705 // correct. It will not have the right defining access, and if it is a def,
1706 // things below it will not properly be updated.
1707 void MemorySSA::moveTo(MemoryUseOrDef *What, BasicBlock *BB,
1708                        AccessList::iterator Where) {
1709   prepareForMoveTo(What, BB);
1710   insertIntoListsBefore(What, BB, Where);
1711 }
1712 
1713 void MemorySSA::moveTo(MemoryAccess *What, BasicBlock *BB,
1714                        InsertionPlace Point) {
1715   if (isa<MemoryPhi>(What)) {
1716     assert(Point == Beginning &&
1717            "Can only move a Phi at the beginning of the block");
1718     // Update lookup table entry
1719     ValueToMemoryAccess.erase(What->getBlock());
1720     bool Inserted = ValueToMemoryAccess.insert({BB, What}).second;
1721     (void)Inserted;
1722     assert(Inserted && "Cannot move a Phi to a block that already has one");
1723   }
1724 
1725   prepareForMoveTo(What, BB);
1726   insertIntoListsForBlock(What, BB, Point);
1727 }
1728 
1729 MemoryPhi *MemorySSA::createMemoryPhi(BasicBlock *BB) {
1730   assert(!getMemoryAccess(BB) && "MemoryPhi already exists for this BB");
1731   MemoryPhi *Phi = new MemoryPhi(BB->getContext(), BB, NextID++);
1732   // Phi's always are placed at the front of the block.
1733   insertIntoListsForBlock(Phi, BB, Beginning);
1734   ValueToMemoryAccess[BB] = Phi;
1735   return Phi;
1736 }
1737 
1738 MemoryUseOrDef *MemorySSA::createDefinedAccess(Instruction *I,
1739                                                MemoryAccess *Definition,
1740                                                const MemoryUseOrDef *Template,
1741                                                bool CreationMustSucceed) {
1742   assert(!isa<PHINode>(I) && "Cannot create a defined access for a PHI");
1743   MemoryUseOrDef *NewAccess = createNewAccess(I, AA, Template);
1744   if (CreationMustSucceed)
1745     assert(NewAccess != nullptr && "Tried to create a memory access for a "
1746                                    "non-memory touching instruction");
1747   if (NewAccess) {
1748     assert((!Definition || !isa<MemoryUse>(Definition)) &&
1749            "A use cannot be a defining access");
1750     NewAccess->setDefiningAccess(Definition);
1751   }
1752   return NewAccess;
1753 }
1754 
1755 // Return true if the instruction has ordering constraints.
1756 // Note specifically that this only considers stores and loads
1757 // because others are still considered ModRef by getModRefInfo.
1758 static inline bool isOrdered(const Instruction *I) {
1759   if (auto *SI = dyn_cast<StoreInst>(I)) {
1760     if (!SI->isUnordered())
1761       return true;
1762   } else if (auto *LI = dyn_cast<LoadInst>(I)) {
1763     if (!LI->isUnordered())
1764       return true;
1765   }
1766   return false;
1767 }
1768 
1769 /// Helper function to create new memory accesses
1770 template <typename AliasAnalysisType>
1771 MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I,
1772                                            AliasAnalysisType *AAP,
1773                                            const MemoryUseOrDef *Template) {
1774   // The assume intrinsic has a control dependency which we model by claiming
1775   // that it writes arbitrarily. Debuginfo intrinsics may be considered
1776   // clobbers when we have a nonstandard AA pipeline. Ignore these fake memory
1777   // dependencies here.
1778   // FIXME: Replace this special casing with a more accurate modelling of
1779   // assume's control dependency.
1780   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
1781     switch (II->getIntrinsicID()) {
1782     default:
1783       break;
1784     case Intrinsic::assume:
1785     case Intrinsic::experimental_noalias_scope_decl:
1786     case Intrinsic::pseudoprobe:
1787       return nullptr;
1788     }
1789   }
1790 
1791   // Using a nonstandard AA pipelines might leave us with unexpected modref
1792   // results for I, so add a check to not model instructions that may not read
1793   // from or write to memory. This is necessary for correctness.
1794   if (!I->mayReadFromMemory() && !I->mayWriteToMemory())
1795     return nullptr;
1796 
1797   bool Def, Use;
1798   if (Template) {
1799     Def = isa<MemoryDef>(Template);
1800     Use = isa<MemoryUse>(Template);
1801 #if !defined(NDEBUG)
1802     ModRefInfo ModRef = AAP->getModRefInfo(I, None);
1803     bool DefCheck, UseCheck;
1804     DefCheck = isModSet(ModRef) || isOrdered(I);
1805     UseCheck = isRefSet(ModRef);
1806     assert(Def == DefCheck && (Def || Use == UseCheck) && "Invalid template");
1807 #endif
1808   } else {
1809     // Find out what affect this instruction has on memory.
1810     ModRefInfo ModRef = AAP->getModRefInfo(I, None);
1811     // The isOrdered check is used to ensure that volatiles end up as defs
1812     // (atomics end up as ModRef right now anyway).  Until we separate the
1813     // ordering chain from the memory chain, this enables people to see at least
1814     // some relative ordering to volatiles.  Note that getClobberingMemoryAccess
1815     // will still give an answer that bypasses other volatile loads.  TODO:
1816     // Separate memory aliasing and ordering into two different chains so that
1817     // we can precisely represent both "what memory will this read/write/is
1818     // clobbered by" and "what instructions can I move this past".
1819     Def = isModSet(ModRef) || isOrdered(I);
1820     Use = isRefSet(ModRef);
1821   }
1822 
1823   // It's possible for an instruction to not modify memory at all. During
1824   // construction, we ignore them.
1825   if (!Def && !Use)
1826     return nullptr;
1827 
1828   MemoryUseOrDef *MUD;
1829   if (Def)
1830     MUD = new MemoryDef(I->getContext(), nullptr, I, I->getParent(), NextID++);
1831   else
1832     MUD = new MemoryUse(I->getContext(), nullptr, I, I->getParent());
1833   ValueToMemoryAccess[I] = MUD;
1834   return MUD;
1835 }
1836 
1837 /// Properly remove \p MA from all of MemorySSA's lookup tables.
1838 void MemorySSA::removeFromLookups(MemoryAccess *MA) {
1839   assert(MA->use_empty() &&
1840          "Trying to remove memory access that still has uses");
1841   BlockNumbering.erase(MA);
1842   if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1843     MUD->setDefiningAccess(nullptr);
1844   // Invalidate our walker's cache if necessary
1845   if (!isa<MemoryUse>(MA))
1846     getWalker()->invalidateInfo(MA);
1847 
1848   Value *MemoryInst;
1849   if (const auto *MUD = dyn_cast<MemoryUseOrDef>(MA))
1850     MemoryInst = MUD->getMemoryInst();
1851   else
1852     MemoryInst = MA->getBlock();
1853 
1854   auto VMA = ValueToMemoryAccess.find(MemoryInst);
1855   if (VMA->second == MA)
1856     ValueToMemoryAccess.erase(VMA);
1857 }
1858 
1859 /// Properly remove \p MA from all of MemorySSA's lists.
1860 ///
1861 /// Because of the way the intrusive list and use lists work, it is important to
1862 /// do removal in the right order.
1863 /// ShouldDelete defaults to true, and will cause the memory access to also be
1864 /// deleted, not just removed.
1865 void MemorySSA::removeFromLists(MemoryAccess *MA, bool ShouldDelete) {
1866   BasicBlock *BB = MA->getBlock();
1867   // The access list owns the reference, so we erase it from the non-owning list
1868   // first.
1869   if (!isa<MemoryUse>(MA)) {
1870     auto DefsIt = PerBlockDefs.find(BB);
1871     std::unique_ptr<DefsList> &Defs = DefsIt->second;
1872     Defs->remove(*MA);
1873     if (Defs->empty())
1874       PerBlockDefs.erase(DefsIt);
1875   }
1876 
1877   // The erase call here will delete it. If we don't want it deleted, we call
1878   // remove instead.
1879   auto AccessIt = PerBlockAccesses.find(BB);
1880   std::unique_ptr<AccessList> &Accesses = AccessIt->second;
1881   if (ShouldDelete)
1882     Accesses->erase(MA);
1883   else
1884     Accesses->remove(MA);
1885 
1886   if (Accesses->empty()) {
1887     PerBlockAccesses.erase(AccessIt);
1888     BlockNumberingValid.erase(BB);
1889   }
1890 }
1891 
1892 void MemorySSA::print(raw_ostream &OS) const {
1893   MemorySSAAnnotatedWriter Writer(this);
1894   F.print(OS, &Writer);
1895 }
1896 
1897 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1898 LLVM_DUMP_METHOD void MemorySSA::dump() const { print(dbgs()); }
1899 #endif
1900 
1901 void MemorySSA::verifyMemorySSA(VerificationLevel VL) const {
1902 #if !defined(NDEBUG) && defined(EXPENSIVE_CHECKS)
1903   VL = VerificationLevel::Full;
1904 #endif
1905 
1906 #ifndef NDEBUG
1907   verifyOrderingDominationAndDefUses(F, VL);
1908   verifyDominationNumbers(F);
1909   if (VL == VerificationLevel::Full)
1910     verifyPrevDefInPhis(F);
1911 #endif
1912   // Previously, the verification used to also verify that the clobberingAccess
1913   // cached by MemorySSA is the same as the clobberingAccess found at a later
1914   // query to AA. This does not hold true in general due to the current fragility
1915   // of BasicAA which has arbitrary caps on the things it analyzes before giving
1916   // up. As a result, transformations that are correct, will lead to BasicAA
1917   // returning different Alias answers before and after that transformation.
1918   // Invalidating MemorySSA is not an option, as the results in BasicAA can be so
1919   // random, in the worst case we'd need to rebuild MemorySSA from scratch after
1920   // every transformation, which defeats the purpose of using it. For such an
1921   // example, see test4 added in D51960.
1922 }
1923 
1924 void MemorySSA::verifyPrevDefInPhis(Function &F) const {
1925   for (const BasicBlock &BB : F) {
1926     if (MemoryPhi *Phi = getMemoryAccess(&BB)) {
1927       for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I) {
1928         auto *Pred = Phi->getIncomingBlock(I);
1929         auto *IncAcc = Phi->getIncomingValue(I);
1930         // If Pred has no unreachable predecessors, get last def looking at
1931         // IDoms. If, while walkings IDoms, any of these has an unreachable
1932         // predecessor, then the incoming def can be any access.
1933         if (auto *DTNode = DT->getNode(Pred)) {
1934           while (DTNode) {
1935             if (auto *DefList = getBlockDefs(DTNode->getBlock())) {
1936               auto *LastAcc = &*(--DefList->end());
1937               assert(LastAcc == IncAcc &&
1938                      "Incorrect incoming access into phi.");
1939               (void)IncAcc;
1940               (void)LastAcc;
1941               break;
1942             }
1943             DTNode = DTNode->getIDom();
1944           }
1945         } else {
1946           // If Pred has unreachable predecessors, but has at least a Def, the
1947           // incoming access can be the last Def in Pred, or it could have been
1948           // optimized to LoE. After an update, though, the LoE may have been
1949           // replaced by another access, so IncAcc may be any access.
1950           // If Pred has unreachable predecessors and no Defs, incoming access
1951           // should be LoE; However, after an update, it may be any access.
1952         }
1953       }
1954     }
1955   }
1956 }
1957 
1958 /// Verify that all of the blocks we believe to have valid domination numbers
1959 /// actually have valid domination numbers.
1960 void MemorySSA::verifyDominationNumbers(const Function &F) const {
1961   if (BlockNumberingValid.empty())
1962     return;
1963 
1964   SmallPtrSet<const BasicBlock *, 16> ValidBlocks = BlockNumberingValid;
1965   for (const BasicBlock &BB : F) {
1966     if (!ValidBlocks.count(&BB))
1967       continue;
1968 
1969     ValidBlocks.erase(&BB);
1970 
1971     const AccessList *Accesses = getBlockAccesses(&BB);
1972     // It's correct to say an empty block has valid numbering.
1973     if (!Accesses)
1974       continue;
1975 
1976     // Block numbering starts at 1.
1977     unsigned long LastNumber = 0;
1978     for (const MemoryAccess &MA : *Accesses) {
1979       auto ThisNumberIter = BlockNumbering.find(&MA);
1980       assert(ThisNumberIter != BlockNumbering.end() &&
1981              "MemoryAccess has no domination number in a valid block!");
1982 
1983       unsigned long ThisNumber = ThisNumberIter->second;
1984       assert(ThisNumber > LastNumber &&
1985              "Domination numbers should be strictly increasing!");
1986       (void)LastNumber;
1987       LastNumber = ThisNumber;
1988     }
1989   }
1990 
1991   assert(ValidBlocks.empty() &&
1992          "All valid BasicBlocks should exist in F -- dangling pointers?");
1993 }
1994 
1995 /// Verify ordering: the order and existence of MemoryAccesses matches the
1996 /// order and existence of memory affecting instructions.
1997 /// Verify domination: each definition dominates all of its uses.
1998 /// Verify def-uses: the immediate use information - walk all the memory
1999 /// accesses and verifying that, for each use, it appears in the appropriate
2000 /// def's use list
2001 void MemorySSA::verifyOrderingDominationAndDefUses(Function &F,
2002                                                    VerificationLevel VL) const {
2003   // Walk all the blocks, comparing what the lookups think and what the access
2004   // lists think, as well as the order in the blocks vs the order in the access
2005   // lists.
2006   SmallVector<MemoryAccess *, 32> ActualAccesses;
2007   SmallVector<MemoryAccess *, 32> ActualDefs;
2008   for (BasicBlock &B : F) {
2009     const AccessList *AL = getBlockAccesses(&B);
2010     const auto *DL = getBlockDefs(&B);
2011     MemoryPhi *Phi = getMemoryAccess(&B);
2012     if (Phi) {
2013       // Verify ordering.
2014       ActualAccesses.push_back(Phi);
2015       ActualDefs.push_back(Phi);
2016       // Verify domination
2017       for (const Use &U : Phi->uses()) {
2018         assert(dominates(Phi, U) && "Memory PHI does not dominate it's uses");
2019         (void)U;
2020       }
2021       // Verify def-uses for full verify.
2022       if (VL == VerificationLevel::Full) {
2023         assert(Phi->getNumOperands() == static_cast<unsigned>(std::distance(
2024                                             pred_begin(&B), pred_end(&B))) &&
2025                "Incomplete MemoryPhi Node");
2026         for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I) {
2027           verifyUseInDefs(Phi->getIncomingValue(I), Phi);
2028           assert(is_contained(predecessors(&B), Phi->getIncomingBlock(I)) &&
2029                  "Incoming phi block not a block predecessor");
2030         }
2031       }
2032     }
2033 
2034     for (Instruction &I : B) {
2035       MemoryUseOrDef *MA = getMemoryAccess(&I);
2036       assert((!MA || (AL && (isa<MemoryUse>(MA) || DL))) &&
2037              "We have memory affecting instructions "
2038              "in this block but they are not in the "
2039              "access list or defs list");
2040       if (MA) {
2041         // Verify ordering.
2042         ActualAccesses.push_back(MA);
2043         if (MemoryAccess *MD = dyn_cast<MemoryDef>(MA)) {
2044           // Verify ordering.
2045           ActualDefs.push_back(MA);
2046           // Verify domination.
2047           for (const Use &U : MD->uses()) {
2048             assert(dominates(MD, U) &&
2049                    "Memory Def does not dominate it's uses");
2050             (void)U;
2051           }
2052         }
2053         // Verify def-uses for full verify.
2054         if (VL == VerificationLevel::Full)
2055           verifyUseInDefs(MA->getDefiningAccess(), MA);
2056       }
2057     }
2058     // Either we hit the assert, really have no accesses, or we have both
2059     // accesses and an access list. Same with defs.
2060     if (!AL && !DL)
2061       continue;
2062     // Verify ordering.
2063     assert(AL->size() == ActualAccesses.size() &&
2064            "We don't have the same number of accesses in the block as on the "
2065            "access list");
2066     assert((DL || ActualDefs.size() == 0) &&
2067            "Either we should have a defs list, or we should have no defs");
2068     assert((!DL || DL->size() == ActualDefs.size()) &&
2069            "We don't have the same number of defs in the block as on the "
2070            "def list");
2071     auto ALI = AL->begin();
2072     auto AAI = ActualAccesses.begin();
2073     while (ALI != AL->end() && AAI != ActualAccesses.end()) {
2074       assert(&*ALI == *AAI && "Not the same accesses in the same order");
2075       ++ALI;
2076       ++AAI;
2077     }
2078     ActualAccesses.clear();
2079     if (DL) {
2080       auto DLI = DL->begin();
2081       auto ADI = ActualDefs.begin();
2082       while (DLI != DL->end() && ADI != ActualDefs.end()) {
2083         assert(&*DLI == *ADI && "Not the same defs in the same order");
2084         ++DLI;
2085         ++ADI;
2086       }
2087     }
2088     ActualDefs.clear();
2089   }
2090 }
2091 
2092 /// Verify the def-use lists in MemorySSA, by verifying that \p Use
2093 /// appears in the use list of \p Def.
2094 void MemorySSA::verifyUseInDefs(MemoryAccess *Def, MemoryAccess *Use) const {
2095   // The live on entry use may cause us to get a NULL def here
2096   if (!Def)
2097     assert(isLiveOnEntryDef(Use) &&
2098            "Null def but use not point to live on entry def");
2099   else
2100     assert(is_contained(Def->users(), Use) &&
2101            "Did not find use in def's use list");
2102 }
2103 
2104 /// Perform a local numbering on blocks so that instruction ordering can be
2105 /// determined in constant time.
2106 /// TODO: We currently just number in order.  If we numbered by N, we could
2107 /// allow at least N-1 sequences of insertBefore or insertAfter (and at least
2108 /// log2(N) sequences of mixed before and after) without needing to invalidate
2109 /// the numbering.
2110 void MemorySSA::renumberBlock(const BasicBlock *B) const {
2111   // The pre-increment ensures the numbers really start at 1.
2112   unsigned long CurrentNumber = 0;
2113   const AccessList *AL = getBlockAccesses(B);
2114   assert(AL != nullptr && "Asking to renumber an empty block");
2115   for (const auto &I : *AL)
2116     BlockNumbering[&I] = ++CurrentNumber;
2117   BlockNumberingValid.insert(B);
2118 }
2119 
2120 /// Determine, for two memory accesses in the same block,
2121 /// whether \p Dominator dominates \p Dominatee.
2122 /// \returns True if \p Dominator dominates \p Dominatee.
2123 bool MemorySSA::locallyDominates(const MemoryAccess *Dominator,
2124                                  const MemoryAccess *Dominatee) const {
2125   const BasicBlock *DominatorBlock = Dominator->getBlock();
2126 
2127   assert((DominatorBlock == Dominatee->getBlock()) &&
2128          "Asking for local domination when accesses are in different blocks!");
2129   // A node dominates itself.
2130   if (Dominatee == Dominator)
2131     return true;
2132 
2133   // When Dominatee is defined on function entry, it is not dominated by another
2134   // memory access.
2135   if (isLiveOnEntryDef(Dominatee))
2136     return false;
2137 
2138   // When Dominator is defined on function entry, it dominates the other memory
2139   // access.
2140   if (isLiveOnEntryDef(Dominator))
2141     return true;
2142 
2143   if (!BlockNumberingValid.count(DominatorBlock))
2144     renumberBlock(DominatorBlock);
2145 
2146   unsigned long DominatorNum = BlockNumbering.lookup(Dominator);
2147   // All numbers start with 1
2148   assert(DominatorNum != 0 && "Block was not numbered properly");
2149   unsigned long DominateeNum = BlockNumbering.lookup(Dominatee);
2150   assert(DominateeNum != 0 && "Block was not numbered properly");
2151   return DominatorNum < DominateeNum;
2152 }
2153 
2154 bool MemorySSA::dominates(const MemoryAccess *Dominator,
2155                           const MemoryAccess *Dominatee) const {
2156   if (Dominator == Dominatee)
2157     return true;
2158 
2159   if (isLiveOnEntryDef(Dominatee))
2160     return false;
2161 
2162   if (Dominator->getBlock() != Dominatee->getBlock())
2163     return DT->dominates(Dominator->getBlock(), Dominatee->getBlock());
2164   return locallyDominates(Dominator, Dominatee);
2165 }
2166 
2167 bool MemorySSA::dominates(const MemoryAccess *Dominator,
2168                           const Use &Dominatee) const {
2169   if (MemoryPhi *MP = dyn_cast<MemoryPhi>(Dominatee.getUser())) {
2170     BasicBlock *UseBB = MP->getIncomingBlock(Dominatee);
2171     // The def must dominate the incoming block of the phi.
2172     if (UseBB != Dominator->getBlock())
2173       return DT->dominates(Dominator->getBlock(), UseBB);
2174     // If the UseBB and the DefBB are the same, compare locally.
2175     return locallyDominates(Dominator, cast<MemoryAccess>(Dominatee));
2176   }
2177   // If it's not a PHI node use, the normal dominates can already handle it.
2178   return dominates(Dominator, cast<MemoryAccess>(Dominatee.getUser()));
2179 }
2180 
2181 void MemoryAccess::print(raw_ostream &OS) const {
2182   switch (getValueID()) {
2183   case MemoryPhiVal: return static_cast<const MemoryPhi *>(this)->print(OS);
2184   case MemoryDefVal: return static_cast<const MemoryDef *>(this)->print(OS);
2185   case MemoryUseVal: return static_cast<const MemoryUse *>(this)->print(OS);
2186   }
2187   llvm_unreachable("invalid value id");
2188 }
2189 
2190 void MemoryDef::print(raw_ostream &OS) const {
2191   MemoryAccess *UO = getDefiningAccess();
2192 
2193   auto printID = [&OS](MemoryAccess *A) {
2194     if (A && A->getID())
2195       OS << A->getID();
2196     else
2197       OS << LiveOnEntryStr;
2198   };
2199 
2200   OS << getID() << " = MemoryDef(";
2201   printID(UO);
2202   OS << ")";
2203 
2204   if (isOptimized()) {
2205     OS << "->";
2206     printID(getOptimized());
2207 
2208     if (Optional<AliasResult> AR = getOptimizedAccessType())
2209       OS << " " << *AR;
2210   }
2211 }
2212 
2213 void MemoryPhi::print(raw_ostream &OS) const {
2214   ListSeparator LS(",");
2215   OS << getID() << " = MemoryPhi(";
2216   for (const auto &Op : operands()) {
2217     BasicBlock *BB = getIncomingBlock(Op);
2218     MemoryAccess *MA = cast<MemoryAccess>(Op);
2219 
2220     OS << LS << '{';
2221     if (BB->hasName())
2222       OS << BB->getName();
2223     else
2224       BB->printAsOperand(OS, false);
2225     OS << ',';
2226     if (unsigned ID = MA->getID())
2227       OS << ID;
2228     else
2229       OS << LiveOnEntryStr;
2230     OS << '}';
2231   }
2232   OS << ')';
2233 }
2234 
2235 void MemoryUse::print(raw_ostream &OS) const {
2236   MemoryAccess *UO = getDefiningAccess();
2237   OS << "MemoryUse(";
2238   if (UO && UO->getID())
2239     OS << UO->getID();
2240   else
2241     OS << LiveOnEntryStr;
2242   OS << ')';
2243 
2244   if (Optional<AliasResult> AR = getOptimizedAccessType())
2245     OS << " " << *AR;
2246 }
2247 
2248 void MemoryAccess::dump() const {
2249 // Cannot completely remove virtual function even in release mode.
2250 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
2251   print(dbgs());
2252   dbgs() << "\n";
2253 #endif
2254 }
2255 
2256 char MemorySSAPrinterLegacyPass::ID = 0;
2257 
2258 MemorySSAPrinterLegacyPass::MemorySSAPrinterLegacyPass() : FunctionPass(ID) {
2259   initializeMemorySSAPrinterLegacyPassPass(*PassRegistry::getPassRegistry());
2260 }
2261 
2262 void MemorySSAPrinterLegacyPass::getAnalysisUsage(AnalysisUsage &AU) const {
2263   AU.setPreservesAll();
2264   AU.addRequired<MemorySSAWrapperPass>();
2265 }
2266 
2267 class DOTFuncMSSAInfo {
2268 private:
2269   const Function &F;
2270   MemorySSAAnnotatedWriter MSSAWriter;
2271 
2272 public:
2273   DOTFuncMSSAInfo(const Function &F, MemorySSA &MSSA)
2274       : F(F), MSSAWriter(&MSSA) {}
2275 
2276   const Function *getFunction() { return &F; }
2277   MemorySSAAnnotatedWriter &getWriter() { return MSSAWriter; }
2278 };
2279 
2280 namespace llvm {
2281 
2282 template <>
2283 struct GraphTraits<DOTFuncMSSAInfo *> : public GraphTraits<const BasicBlock *> {
2284   static NodeRef getEntryNode(DOTFuncMSSAInfo *CFGInfo) {
2285     return &(CFGInfo->getFunction()->getEntryBlock());
2286   }
2287 
2288   // nodes_iterator/begin/end - Allow iteration over all nodes in the graph
2289   using nodes_iterator = pointer_iterator<Function::const_iterator>;
2290 
2291   static nodes_iterator nodes_begin(DOTFuncMSSAInfo *CFGInfo) {
2292     return nodes_iterator(CFGInfo->getFunction()->begin());
2293   }
2294 
2295   static nodes_iterator nodes_end(DOTFuncMSSAInfo *CFGInfo) {
2296     return nodes_iterator(CFGInfo->getFunction()->end());
2297   }
2298 
2299   static size_t size(DOTFuncMSSAInfo *CFGInfo) {
2300     return CFGInfo->getFunction()->size();
2301   }
2302 };
2303 
2304 template <>
2305 struct DOTGraphTraits<DOTFuncMSSAInfo *> : public DefaultDOTGraphTraits {
2306 
2307   DOTGraphTraits(bool IsSimple = false) : DefaultDOTGraphTraits(IsSimple) {}
2308 
2309   static std::string getGraphName(DOTFuncMSSAInfo *CFGInfo) {
2310     return "MSSA CFG for '" + CFGInfo->getFunction()->getName().str() +
2311            "' function";
2312   }
2313 
2314   std::string getNodeLabel(const BasicBlock *Node, DOTFuncMSSAInfo *CFGInfo) {
2315     return DOTGraphTraits<DOTFuncInfo *>::getCompleteNodeLabel(
2316         Node, nullptr,
2317         [CFGInfo](raw_string_ostream &OS, const BasicBlock &BB) -> void {
2318           BB.print(OS, &CFGInfo->getWriter(), true, true);
2319         },
2320         [](std::string &S, unsigned &I, unsigned Idx) -> void {
2321           std::string Str = S.substr(I, Idx - I);
2322           StringRef SR = Str;
2323           if (SR.count(" = MemoryDef(") || SR.count(" = MemoryPhi(") ||
2324               SR.count("MemoryUse("))
2325             return;
2326           DOTGraphTraits<DOTFuncInfo *>::eraseComment(S, I, Idx);
2327         });
2328   }
2329 
2330   static std::string getEdgeSourceLabel(const BasicBlock *Node,
2331                                         const_succ_iterator I) {
2332     return DOTGraphTraits<DOTFuncInfo *>::getEdgeSourceLabel(Node, I);
2333   }
2334 
2335   /// Display the raw branch weights from PGO.
2336   std::string getEdgeAttributes(const BasicBlock *Node, const_succ_iterator I,
2337                                 DOTFuncMSSAInfo *CFGInfo) {
2338     return "";
2339   }
2340 
2341   std::string getNodeAttributes(const BasicBlock *Node,
2342                                 DOTFuncMSSAInfo *CFGInfo) {
2343     return getNodeLabel(Node, CFGInfo).find(';') != std::string::npos
2344                ? "style=filled, fillcolor=lightpink"
2345                : "";
2346   }
2347 };
2348 
2349 } // namespace llvm
2350 
2351 bool MemorySSAPrinterLegacyPass::runOnFunction(Function &F) {
2352   auto &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA();
2353   if (DotCFGMSSA != "") {
2354     DOTFuncMSSAInfo CFGInfo(F, MSSA);
2355     WriteGraph(&CFGInfo, "", false, "MSSA", DotCFGMSSA);
2356   } else
2357     MSSA.print(dbgs());
2358 
2359   if (VerifyMemorySSA)
2360     MSSA.verifyMemorySSA();
2361   return false;
2362 }
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 (DotCFGMSSA != "") {
2386     DOTFuncMSSAInfo CFGInfo(F, MSSA);
2387     WriteGraph(&CFGInfo, "", false, "MSSA", DotCFGMSSA);
2388   } else {
2389     OS << "MemorySSA for function: " << F.getName() << "\n";
2390     MSSA.print(OS);
2391   }
2392 
2393   return PreservedAnalyses::all();
2394 }
2395 
2396 PreservedAnalyses MemorySSAWalkerPrinterPass::run(Function &F,
2397                                                   FunctionAnalysisManager &AM) {
2398   auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
2399   OS << "MemorySSA (walker) for function: " << F.getName() << "\n";
2400   MemorySSAWalkerAnnotatedWriter Writer(&MSSA);
2401   F.print(OS, &Writer);
2402 
2403   return PreservedAnalyses::all();
2404 }
2405 
2406 PreservedAnalyses MemorySSAVerifierPass::run(Function &F,
2407                                              FunctionAnalysisManager &AM) {
2408   AM.getResult<MemorySSAAnalysis>(F).getMSSA().verifyMemorySSA();
2409 
2410   return PreservedAnalyses::all();
2411 }
2412 
2413 char MemorySSAWrapperPass::ID = 0;
2414 
2415 MemorySSAWrapperPass::MemorySSAWrapperPass() : FunctionPass(ID) {
2416   initializeMemorySSAWrapperPassPass(*PassRegistry::getPassRegistry());
2417 }
2418 
2419 void MemorySSAWrapperPass::releaseMemory() { MSSA.reset(); }
2420 
2421 void MemorySSAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
2422   AU.setPreservesAll();
2423   AU.addRequiredTransitive<DominatorTreeWrapperPass>();
2424   AU.addRequiredTransitive<AAResultsWrapperPass>();
2425 }
2426 
2427 bool MemorySSAWrapperPass::runOnFunction(Function &F) {
2428   auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
2429   auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
2430   MSSA.reset(new MemorySSA(F, &AA, &DT));
2431   return false;
2432 }
2433 
2434 void MemorySSAWrapperPass::verifyAnalysis() const {
2435   if (VerifyMemorySSA)
2436     MSSA->verifyMemorySSA();
2437 }
2438 
2439 void MemorySSAWrapperPass::print(raw_ostream &OS, const Module *M) const {
2440   MSSA->print(OS);
2441 }
2442 
2443 MemorySSAWalker::MemorySSAWalker(MemorySSA *M) : MSSA(M) {}
2444 
2445 /// Walk the use-def chains starting at \p StartingAccess and find
2446 /// the MemoryAccess that actually clobbers Loc.
2447 ///
2448 /// \returns our clobbering memory access
2449 template <typename AliasAnalysisType>
2450 MemoryAccess *
2451 MemorySSA::ClobberWalkerBase<AliasAnalysisType>::getClobberingMemoryAccessBase(
2452     MemoryAccess *StartingAccess, const MemoryLocation &Loc,
2453     unsigned &UpwardWalkLimit) {
2454   assert(!isa<MemoryUse>(StartingAccess) && "Use cannot be defining access");
2455 
2456   Instruction *I = nullptr;
2457   if (auto *StartingUseOrDef = dyn_cast<MemoryUseOrDef>(StartingAccess)) {
2458     if (MSSA->isLiveOnEntryDef(StartingUseOrDef))
2459       return StartingUseOrDef;
2460 
2461     I = StartingUseOrDef->getMemoryInst();
2462 
2463     // Conservatively, fences are always clobbers, so don't perform the walk if
2464     // we hit a fence.
2465     if (!isa<CallBase>(I) && I->isFenceLike())
2466       return StartingUseOrDef;
2467   }
2468 
2469   UpwardsMemoryQuery Q;
2470   Q.OriginalAccess = StartingAccess;
2471   Q.StartingLoc = Loc;
2472   Q.Inst = nullptr;
2473   Q.IsCall = false;
2474 
2475   // Unlike the other function, do not walk to the def of a def, because we are
2476   // handed something we already believe is the clobbering access.
2477   // We never set SkipSelf to true in Q in this method.
2478   MemoryAccess *Clobber =
2479       Walker.findClobber(StartingAccess, Q, UpwardWalkLimit);
2480   LLVM_DEBUG({
2481     dbgs() << "Clobber starting at access " << *StartingAccess << "\n";
2482     if (I)
2483       dbgs() << "  for instruction " << *I << "\n";
2484     dbgs() << "  is " << *Clobber << "\n";
2485   });
2486   return Clobber;
2487 }
2488 
2489 static const Instruction *
2490 getInvariantGroupClobberingInstruction(Instruction &I, DominatorTree &DT) {
2491   if (!I.hasMetadata(LLVMContext::MD_invariant_group) || I.isVolatile())
2492     return nullptr;
2493 
2494   // We consider bitcasts and zero GEPs to be the same pointer value. Start by
2495   // stripping bitcasts and zero GEPs, then we will recursively look at loads
2496   // and stores through bitcasts and zero GEPs.
2497   Value *PointerOperand = getLoadStorePointerOperand(&I)->stripPointerCasts();
2498 
2499   // It's not safe to walk the use list of a global value because function
2500   // passes aren't allowed to look outside their functions.
2501   // FIXME: this could be fixed by filtering instructions from outside of
2502   // current function.
2503   if (isa<Constant>(PointerOperand))
2504     return nullptr;
2505 
2506   // Queue to process all pointers that are equivalent to load operand.
2507   SmallVector<const Value *, 8> PointerUsesQueue;
2508   PointerUsesQueue.push_back(PointerOperand);
2509 
2510   const Instruction *MostDominatingInstruction = &I;
2511 
2512   // FIXME: This loop is O(n^2) because dominates can be O(n) and in worst case
2513   // we will see all the instructions. It may not matter in practice. If it
2514   // does, we will have to support MemorySSA construction and updates.
2515   while (!PointerUsesQueue.empty()) {
2516     const Value *Ptr = PointerUsesQueue.pop_back_val();
2517     assert(Ptr && !isa<GlobalValue>(Ptr) &&
2518            "Null or GlobalValue should not be inserted");
2519 
2520     for (const User *Us : Ptr->users()) {
2521       auto *U = dyn_cast<Instruction>(Us);
2522       if (!U || U == &I || !DT.dominates(U, MostDominatingInstruction))
2523         continue;
2524 
2525       // Add bitcasts and zero GEPs to queue.
2526       if (isa<BitCastInst>(U)) {
2527         PointerUsesQueue.push_back(U);
2528         continue;
2529       }
2530       if (auto *GEP = dyn_cast<GetElementPtrInst>(U)) {
2531         if (GEP->hasAllZeroIndices())
2532           PointerUsesQueue.push_back(U);
2533         continue;
2534       }
2535 
2536       // If we hit a load/store with an invariant.group metadata and the same
2537       // pointer operand, we can assume that value pointed to by the pointer
2538       // operand didn't change.
2539       if (U->hasMetadata(LLVMContext::MD_invariant_group) &&
2540           getLoadStorePointerOperand(U) == Ptr && !U->isVolatile()) {
2541         MostDominatingInstruction = U;
2542       }
2543     }
2544   }
2545   return MostDominatingInstruction == &I ? nullptr : MostDominatingInstruction;
2546 }
2547 
2548 template <typename AliasAnalysisType>
2549 MemoryAccess *
2550 MemorySSA::ClobberWalkerBase<AliasAnalysisType>::getClobberingMemoryAccessBase(
2551     MemoryAccess *MA, unsigned &UpwardWalkLimit, bool SkipSelf,
2552     bool UseInvariantGroup) {
2553   auto *StartingAccess = dyn_cast<MemoryUseOrDef>(MA);
2554   // If this is a MemoryPhi, we can't do anything.
2555   if (!StartingAccess)
2556     return MA;
2557 
2558   if (UseInvariantGroup) {
2559     if (auto *I = getInvariantGroupClobberingInstruction(
2560             *StartingAccess->getMemoryInst(), MSSA->getDomTree())) {
2561       assert(isa<LoadInst>(I) || isa<StoreInst>(I));
2562 
2563       auto *ClobberMA = MSSA->getMemoryAccess(I);
2564       assert(ClobberMA);
2565       if (isa<MemoryUse>(ClobberMA))
2566         return ClobberMA->getDefiningAccess();
2567       return ClobberMA;
2568     }
2569   }
2570 
2571   bool IsOptimized = false;
2572 
2573   // If this is an already optimized use or def, return the optimized result.
2574   // Note: Currently, we store the optimized def result in a separate field,
2575   // since we can't use the defining access.
2576   if (StartingAccess->isOptimized()) {
2577     if (!SkipSelf || !isa<MemoryDef>(StartingAccess))
2578       return StartingAccess->getOptimized();
2579     IsOptimized = true;
2580   }
2581 
2582   const Instruction *I = StartingAccess->getMemoryInst();
2583   // We can't sanely do anything with a fence, since they conservatively clobber
2584   // all memory, and have no locations to get pointers from to try to
2585   // disambiguate.
2586   if (!isa<CallBase>(I) && I->isFenceLike())
2587     return StartingAccess;
2588 
2589   UpwardsMemoryQuery Q(I, StartingAccess);
2590 
2591   if (isUseTriviallyOptimizableToLiveOnEntry(*Walker.getAA(), I)) {
2592     MemoryAccess *LiveOnEntry = MSSA->getLiveOnEntryDef();
2593     StartingAccess->setOptimized(LiveOnEntry);
2594     StartingAccess->setOptimizedAccessType(None);
2595     return LiveOnEntry;
2596   }
2597 
2598   MemoryAccess *OptimizedAccess;
2599   if (!IsOptimized) {
2600     // Start with the thing we already think clobbers this location
2601     MemoryAccess *DefiningAccess = StartingAccess->getDefiningAccess();
2602 
2603     // At this point, DefiningAccess may be the live on entry def.
2604     // If it is, we will not get a better result.
2605     if (MSSA->isLiveOnEntryDef(DefiningAccess)) {
2606       StartingAccess->setOptimized(DefiningAccess);
2607       StartingAccess->setOptimizedAccessType(None);
2608       return DefiningAccess;
2609     }
2610 
2611     OptimizedAccess = Walker.findClobber(DefiningAccess, Q, UpwardWalkLimit);
2612     StartingAccess->setOptimized(OptimizedAccess);
2613     if (MSSA->isLiveOnEntryDef(OptimizedAccess))
2614       StartingAccess->setOptimizedAccessType(None);
2615     else if (Q.AR && *Q.AR == AliasResult::MustAlias)
2616       StartingAccess->setOptimizedAccessType(
2617           AliasResult(AliasResult::MustAlias));
2618   } else
2619     OptimizedAccess = StartingAccess->getOptimized();
2620 
2621   LLVM_DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is ");
2622   LLVM_DEBUG(dbgs() << *StartingAccess << "\n");
2623   LLVM_DEBUG(dbgs() << "Optimized Memory SSA clobber for " << *I << " is ");
2624   LLVM_DEBUG(dbgs() << *OptimizedAccess << "\n");
2625 
2626   MemoryAccess *Result;
2627   if (SkipSelf && isa<MemoryPhi>(OptimizedAccess) &&
2628       isa<MemoryDef>(StartingAccess) && UpwardWalkLimit) {
2629     assert(isa<MemoryDef>(Q.OriginalAccess));
2630     Q.SkipSelfAccess = true;
2631     Result = Walker.findClobber(OptimizedAccess, Q, UpwardWalkLimit);
2632   } else
2633     Result = OptimizedAccess;
2634 
2635   LLVM_DEBUG(dbgs() << "Result Memory SSA clobber [SkipSelf = " << SkipSelf);
2636   LLVM_DEBUG(dbgs() << "] for " << *I << " is " << *Result << "\n");
2637 
2638   return Result;
2639 }
2640 
2641 MemoryAccess *
2642 DoNothingMemorySSAWalker::getClobberingMemoryAccess(MemoryAccess *MA) {
2643   if (auto *Use = dyn_cast<MemoryUseOrDef>(MA))
2644     return Use->getDefiningAccess();
2645   return MA;
2646 }
2647 
2648 MemoryAccess *DoNothingMemorySSAWalker::getClobberingMemoryAccess(
2649     MemoryAccess *StartingAccess, const MemoryLocation &) {
2650   if (auto *Use = dyn_cast<MemoryUseOrDef>(StartingAccess))
2651     return Use->getDefiningAccess();
2652   return StartingAccess;
2653 }
2654 
2655 void MemoryPhi::deleteMe(DerivedUser *Self) {
2656   delete static_cast<MemoryPhi *>(Self);
2657 }
2658 
2659 void MemoryDef::deleteMe(DerivedUser *Self) {
2660   delete static_cast<MemoryDef *>(Self);
2661 }
2662 
2663 void MemoryUse::deleteMe(DerivedUser *Self) {
2664   delete static_cast<MemoryUse *>(Self);
2665 }
2666 
2667 bool upward_defs_iterator::IsGuaranteedLoopInvariant(Value *Ptr) const {
2668   auto IsGuaranteedLoopInvariantBase = [](Value *Ptr) {
2669     Ptr = Ptr->stripPointerCasts();
2670     if (!isa<Instruction>(Ptr))
2671       return true;
2672     return isa<AllocaInst>(Ptr);
2673   };
2674 
2675   Ptr = Ptr->stripPointerCasts();
2676   if (auto *I = dyn_cast<Instruction>(Ptr)) {
2677     if (I->getParent()->isEntryBlock())
2678       return true;
2679   }
2680   if (auto *GEP = dyn_cast<GEPOperator>(Ptr)) {
2681     return IsGuaranteedLoopInvariantBase(GEP->getPointerOperand()) &&
2682            GEP->hasAllConstantIndices();
2683   }
2684   return IsGuaranteedLoopInvariantBase(Ptr);
2685 }
2686