xref: /llvm-project/llvm/lib/Transforms/Scalar/MergedLoadStoreMotion.cpp (revision d7708773288c4f33bf98c724f7a486b5973b8cc6)
1 //===- MergedLoadStoreMotion.cpp - merge and hoist/sink load/stores -------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //! \file
11 //! \brief This pass performs merges of loads and stores on both sides of a
12 //  diamond (hammock). It hoists the loads and sinks the stores.
13 //
14 // The algorithm iteratively hoists two loads to the same address out of a
15 // diamond (hammock) and merges them into a single load in the header. Similar
16 // it sinks and merges two stores to the tail block (footer). The algorithm
17 // iterates over the instructions of one side of the diamond and attempts to
18 // find a matching load/store on the other side. It hoists / sinks when it
19 // thinks it safe to do so.  This optimization helps with eg. hiding load
20 // latencies, triggering if-conversion, and reducing static code size.
21 //
22 //===----------------------------------------------------------------------===//
23 //
24 //
25 // Example:
26 // Diamond shaped code before merge:
27 //
28 //            header:
29 //                     br %cond, label %if.then, label %if.else
30 //                        +                    +
31 //                       +                      +
32 //                      +                        +
33 //            if.then:                         if.else:
34 //               %lt = load %addr_l               %le = load %addr_l
35 //               <use %lt>                        <use %le>
36 //               <...>                            <...>
37 //               store %st, %addr_s               store %se, %addr_s
38 //               br label %if.end                 br label %if.end
39 //                     +                         +
40 //                      +                       +
41 //                       +                     +
42 //            if.end ("footer"):
43 //                     <...>
44 //
45 // Diamond shaped code after merge:
46 //
47 //            header:
48 //                     %l = load %addr_l
49 //                     br %cond, label %if.then, label %if.else
50 //                        +                    +
51 //                       +                      +
52 //                      +                        +
53 //            if.then:                         if.else:
54 //               <use %l>                         <use %l>
55 //               <...>                            <...>
56 //               br label %if.end                 br label %if.end
57 //                      +                        +
58 //                       +                      +
59 //                        +                    +
60 //            if.end ("footer"):
61 //                     %s.sink = phi [%st, if.then], [%se, if.else]
62 //                     <...>
63 //                     store %s.sink, %addr_s
64 //                     <...>
65 //
66 //
67 //===----------------------- TODO -----------------------------------------===//
68 //
69 // 1) Generalize to regions other than diamonds
70 // 2) Be more aggressive merging memory operations
71 // Note that both changes require register pressure control
72 //
73 //===----------------------------------------------------------------------===//
74 
75 #include "llvm/Transforms/Scalar/MergedLoadStoreMotion.h"
76 #include "llvm/ADT/Statistic.h"
77 #include "llvm/Analysis/AliasAnalysis.h"
78 #include "llvm/Analysis/CFG.h"
79 #include "llvm/Analysis/GlobalsModRef.h"
80 #include "llvm/Analysis/Loads.h"
81 #include "llvm/Analysis/MemoryBuiltins.h"
82 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
83 #include "llvm/Analysis/ValueTracking.h"
84 #include "llvm/IR/Metadata.h"
85 #include "llvm/IR/PatternMatch.h"
86 #include "llvm/Support/Debug.h"
87 #include "llvm/Support/raw_ostream.h"
88 #include "llvm/Transforms/Scalar.h"
89 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
90 #include "llvm/Transforms/Utils/SSAUpdater.h"
91 
92 using namespace llvm;
93 
94 #define DEBUG_TYPE "mldst-motion"
95 
96 //===----------------------------------------------------------------------===//
97 //                         MergedLoadStoreMotion Pass
98 //===----------------------------------------------------------------------===//
99 class MergedLoadStoreMotion {
100   MemoryDependenceResults *MD = nullptr;
101   AliasAnalysis *AA = nullptr;
102 
103   // The mergeLoad/Store algorithms could have Size0 * Size1 complexity,
104   // where Size0 and Size1 are the #instructions on the two sides of
105   // the diamond. The constant chosen here is arbitrary. Compiler Time
106   // Control is enforced by the check Size0 * Size1 < MagicCompileTimeControl.
107   const int MagicCompileTimeControl = 250;
108 
109 public:
110   bool run(Function &F, MemoryDependenceResults *MD, AliasAnalysis &AA);
111 
112 private:
113   ///
114   /// \brief Remove instruction from parent and update memory dependence
115   /// analysis.
116   ///
117   void removeInstruction(Instruction *Inst);
118   BasicBlock *getDiamondTail(BasicBlock *BB);
119   bool isDiamondHead(BasicBlock *BB);
120   // Routines for hoisting loads
121   bool isLoadHoistBarrierInRange(const Instruction &Start,
122                                  const Instruction &End, LoadInst *LI,
123                                  bool SafeToLoadUnconditionally);
124   LoadInst *canHoistFromBlock(BasicBlock *BB, LoadInst *LI);
125   void hoistInstruction(BasicBlock *BB, Instruction *HoistCand,
126                         Instruction *ElseInst);
127   bool isSafeToHoist(Instruction *I) const;
128   bool hoistLoad(BasicBlock *BB, LoadInst *HoistCand, LoadInst *ElseInst);
129   bool mergeLoads(BasicBlock *BB);
130   // Routines for sinking stores
131   StoreInst *canSinkFromBlock(BasicBlock *BB, StoreInst *SI);
132   PHINode *getPHIOperand(BasicBlock *BB, StoreInst *S0, StoreInst *S1);
133   bool isStoreSinkBarrierInRange(const Instruction &Start,
134                                  const Instruction &End, MemoryLocation Loc);
135   bool sinkStore(BasicBlock *BB, StoreInst *SinkCand, StoreInst *ElseInst);
136   bool mergeStores(BasicBlock *BB);
137 };
138 
139 ///
140 /// \brief Remove instruction from parent and update memory dependence analysis.
141 ///
142 void MergedLoadStoreMotion::removeInstruction(Instruction *Inst) {
143   // Notify the memory dependence analysis.
144   if (MD) {
145     MD->removeInstruction(Inst);
146     if (auto *LI = dyn_cast<LoadInst>(Inst))
147       MD->invalidateCachedPointerInfo(LI->getPointerOperand());
148     if (Inst->getType()->isPtrOrPtrVectorTy()) {
149       MD->invalidateCachedPointerInfo(Inst);
150     }
151   }
152   Inst->eraseFromParent();
153 }
154 
155 ///
156 /// \brief Return tail block of a diamond.
157 ///
158 BasicBlock *MergedLoadStoreMotion::getDiamondTail(BasicBlock *BB) {
159   assert(isDiamondHead(BB) && "Basic block is not head of a diamond");
160   return BB->getTerminator()->getSuccessor(0)->getSingleSuccessor();
161 }
162 
163 ///
164 /// \brief True when BB is the head of a diamond (hammock)
165 ///
166 bool MergedLoadStoreMotion::isDiamondHead(BasicBlock *BB) {
167   if (!BB)
168     return false;
169   auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
170   if (!BI || !BI->isConditional())
171     return false;
172 
173   BasicBlock *Succ0 = BI->getSuccessor(0);
174   BasicBlock *Succ1 = BI->getSuccessor(1);
175 
176   if (!Succ0->getSinglePredecessor())
177     return false;
178   if (!Succ1->getSinglePredecessor())
179     return false;
180 
181   BasicBlock *Succ0Succ = Succ0->getSingleSuccessor();
182   BasicBlock *Succ1Succ = Succ1->getSingleSuccessor();
183   // Ignore triangles.
184   if (!Succ0Succ || !Succ1Succ || Succ0Succ != Succ1Succ)
185     return false;
186   return true;
187 }
188 
189 ///
190 /// \brief True when instruction is a hoist barrier for a load
191 ///
192 /// Whenever an instruction could possibly modify the value
193 /// being loaded or protect against the load from happening
194 /// it is considered a hoist barrier.
195 ///
196 bool MergedLoadStoreMotion::isLoadHoistBarrierInRange(
197     const Instruction &Start, const Instruction &End, LoadInst *LI,
198     bool SafeToLoadUnconditionally) {
199   if (!SafeToLoadUnconditionally)
200     for (const Instruction &Inst :
201          make_range(Start.getIterator(), End.getIterator()))
202       if (!isGuaranteedToTransferExecutionToSuccessor(&Inst))
203         return true;
204   MemoryLocation Loc = MemoryLocation::get(LI);
205   return AA->canInstructionRangeModRef(Start, End, Loc, MRI_Mod);
206 }
207 
208 ///
209 /// \brief Decide if a load can be hoisted
210 ///
211 /// When there is a load in \p BB to the same address as \p LI
212 /// and it can be hoisted from \p BB, return that load.
213 /// Otherwise return Null.
214 ///
215 LoadInst *MergedLoadStoreMotion::canHoistFromBlock(BasicBlock *BB1,
216                                                    LoadInst *Load0) {
217   BasicBlock *BB0 = Load0->getParent();
218   BasicBlock *Head = BB0->getSinglePredecessor();
219   bool SafeToLoadUnconditionally = isSafeToLoadUnconditionally(
220       Load0->getPointerOperand(), Load0->getAlignment(),
221       Load0->getModule()->getDataLayout(),
222       /*ScanFrom=*/Head->getTerminator());
223   for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); BBI != BBE;
224        ++BBI) {
225     Instruction *Inst = &*BBI;
226 
227     // Only merge and hoist loads when their result in used only in BB
228     auto *Load1 = dyn_cast<LoadInst>(Inst);
229     if (!Load1 || Inst->isUsedOutsideOfBlock(BB1))
230       continue;
231 
232     MemoryLocation Loc0 = MemoryLocation::get(Load0);
233     MemoryLocation Loc1 = MemoryLocation::get(Load1);
234     if (Load0->isSameOperationAs(Load1) && AA->isMustAlias(Loc0, Loc1) &&
235         !isLoadHoistBarrierInRange(BB1->front(), *Load1, Load1,
236                                    SafeToLoadUnconditionally) &&
237         !isLoadHoistBarrierInRange(BB0->front(), *Load0, Load0,
238                                    SafeToLoadUnconditionally)) {
239       return Load1;
240     }
241   }
242   return nullptr;
243 }
244 
245 ///
246 /// \brief Merge two equivalent instructions \p HoistCand and \p ElseInst into
247 /// \p BB
248 ///
249 /// BB is the head of a diamond
250 ///
251 void MergedLoadStoreMotion::hoistInstruction(BasicBlock *BB,
252                                              Instruction *HoistCand,
253                                              Instruction *ElseInst) {
254   DEBUG(dbgs() << " Hoist Instruction into BB \n"; BB->dump();
255         dbgs() << "Instruction Left\n"; HoistCand->dump(); dbgs() << "\n";
256         dbgs() << "Instruction Right\n"; ElseInst->dump(); dbgs() << "\n");
257   // Hoist the instruction.
258   assert(HoistCand->getParent() != BB);
259 
260   // Intersect optional metadata.
261   HoistCand->intersectOptionalDataWith(ElseInst);
262   HoistCand->dropUnknownNonDebugMetadata();
263 
264   // Prepend point for instruction insert
265   Instruction *HoistPt = BB->getTerminator();
266 
267   // Merged instruction
268   Instruction *HoistedInst = HoistCand->clone();
269 
270   // Hoist instruction.
271   HoistedInst->insertBefore(HoistPt);
272 
273   HoistCand->replaceAllUsesWith(HoistedInst);
274   removeInstruction(HoistCand);
275   // Replace the else block instruction.
276   ElseInst->replaceAllUsesWith(HoistedInst);
277   removeInstruction(ElseInst);
278 }
279 
280 ///
281 /// \brief Return true if no operand of \p I is defined in I's parent block
282 ///
283 bool MergedLoadStoreMotion::isSafeToHoist(Instruction *I) const {
284   BasicBlock *Parent = I->getParent();
285   for (Use &U : I->operands())
286     if (auto *Instr = dyn_cast<Instruction>(&U))
287       if (Instr->getParent() == Parent)
288         return false;
289   return true;
290 }
291 
292 ///
293 /// \brief Merge two equivalent loads and GEPs and hoist into diamond head
294 ///
295 bool MergedLoadStoreMotion::hoistLoad(BasicBlock *BB, LoadInst *L0,
296                                       LoadInst *L1) {
297   // Only one definition?
298   auto *A0 = dyn_cast<Instruction>(L0->getPointerOperand());
299   auto *A1 = dyn_cast<Instruction>(L1->getPointerOperand());
300   if (A0 && A1 && A0->isIdenticalTo(A1) && isSafeToHoist(A0) &&
301       A0->hasOneUse() && (A0->getParent() == L0->getParent()) &&
302       A1->hasOneUse() && (A1->getParent() == L1->getParent()) &&
303       isa<GetElementPtrInst>(A0)) {
304     DEBUG(dbgs() << "Hoist Instruction into BB \n"; BB->dump();
305           dbgs() << "Instruction Left\n"; L0->dump(); dbgs() << "\n";
306           dbgs() << "Instruction Right\n"; L1->dump(); dbgs() << "\n");
307     hoistInstruction(BB, A0, A1);
308     hoistInstruction(BB, L0, L1);
309     return true;
310   }
311   return false;
312 }
313 
314 ///
315 /// \brief Try to hoist two loads to same address into diamond header
316 ///
317 /// Starting from a diamond head block, iterate over the instructions in one
318 /// successor block and try to match a load in the second successor.
319 ///
320 bool MergedLoadStoreMotion::mergeLoads(BasicBlock *BB) {
321   bool MergedLoads = false;
322   assert(isDiamondHead(BB));
323   BranchInst *BI = cast<BranchInst>(BB->getTerminator());
324   BasicBlock *Succ0 = BI->getSuccessor(0);
325   BasicBlock *Succ1 = BI->getSuccessor(1);
326   // #Instructions in Succ1 for Compile Time Control
327   int Size1 = Succ1->size();
328   int NLoads = 0;
329   for (BasicBlock::iterator BBI = Succ0->begin(), BBE = Succ0->end();
330        BBI != BBE;) {
331     Instruction *I = &*BBI;
332     ++BBI;
333 
334     // Don't move non-simple (atomic, volatile) loads.
335     auto *L0 = dyn_cast<LoadInst>(I);
336     if (!L0 || !L0->isSimple() || L0->isUsedOutsideOfBlock(Succ0))
337       continue;
338 
339     ++NLoads;
340     if (NLoads * Size1 >= MagicCompileTimeControl)
341       break;
342     if (LoadInst *L1 = canHoistFromBlock(Succ1, L0)) {
343       bool Res = hoistLoad(BB, L0, L1);
344       MergedLoads |= Res;
345       // Don't attempt to hoist above loads that had not been hoisted.
346       if (!Res)
347         break;
348     }
349   }
350   return MergedLoads;
351 }
352 
353 ///
354 /// \brief True when instruction is a sink barrier for a store
355 /// located in Loc
356 ///
357 /// Whenever an instruction could possibly read or modify the
358 /// value being stored or protect against the store from
359 /// happening it is considered a sink barrier.
360 ///
361 bool MergedLoadStoreMotion::isStoreSinkBarrierInRange(const Instruction &Start,
362                                                       const Instruction &End,
363                                                       MemoryLocation Loc) {
364   for (const Instruction &Inst :
365        make_range(Start.getIterator(), End.getIterator()))
366     if (Inst.mayThrow())
367       return true;
368   return AA->canInstructionRangeModRef(Start, End, Loc, MRI_ModRef);
369 }
370 
371 ///
372 /// \brief Check if \p BB contains a store to the same address as \p SI
373 ///
374 /// \return The store in \p  when it is safe to sink. Otherwise return Null.
375 ///
376 StoreInst *MergedLoadStoreMotion::canSinkFromBlock(BasicBlock *BB1,
377                                                    StoreInst *Store0) {
378   DEBUG(dbgs() << "can Sink? : "; Store0->dump(); dbgs() << "\n");
379   BasicBlock *BB0 = Store0->getParent();
380   for (Instruction &Inst : reverse(*BB1)) {
381     auto *Store1 = dyn_cast<StoreInst>(&Inst);
382     if (!Store1)
383       continue;
384 
385     MemoryLocation Loc0 = MemoryLocation::get(Store0);
386     MemoryLocation Loc1 = MemoryLocation::get(Store1);
387     if (AA->isMustAlias(Loc0, Loc1) && Store0->isSameOperationAs(Store1) &&
388         !isStoreSinkBarrierInRange(*Store1->getNextNode(), BB1->back(), Loc1) &&
389         !isStoreSinkBarrierInRange(*Store0->getNextNode(), BB0->back(), Loc0)) {
390       return Store1;
391     }
392   }
393   return nullptr;
394 }
395 
396 ///
397 /// \brief Create a PHI node in BB for the operands of S0 and S1
398 ///
399 PHINode *MergedLoadStoreMotion::getPHIOperand(BasicBlock *BB, StoreInst *S0,
400                                               StoreInst *S1) {
401   // Create a phi if the values mismatch.
402   Value *Opd1 = S0->getValueOperand();
403   Value *Opd2 = S1->getValueOperand();
404   if (Opd1 == Opd2)
405     return nullptr;
406 
407   auto *NewPN = PHINode::Create(Opd1->getType(), 2, Opd2->getName() + ".sink",
408                                 &BB->front());
409   NewPN->addIncoming(Opd1, S0->getParent());
410   NewPN->addIncoming(Opd2, S1->getParent());
411   if (MD && NewPN->getType()->getScalarType()->isPointerTy())
412     MD->invalidateCachedPointerInfo(NewPN);
413   return NewPN;
414 }
415 
416 ///
417 /// \brief Merge two stores to same address and sink into \p BB
418 ///
419 /// Also sinks GEP instruction computing the store address
420 ///
421 bool MergedLoadStoreMotion::sinkStore(BasicBlock *BB, StoreInst *S0,
422                                       StoreInst *S1) {
423   // Only one definition?
424   auto *A0 = dyn_cast<Instruction>(S0->getPointerOperand());
425   auto *A1 = dyn_cast<Instruction>(S1->getPointerOperand());
426   if (A0 && A1 && A0->isIdenticalTo(A1) && A0->hasOneUse() &&
427       (A0->getParent() == S0->getParent()) && A1->hasOneUse() &&
428       (A1->getParent() == S1->getParent()) && isa<GetElementPtrInst>(A0)) {
429     DEBUG(dbgs() << "Sink Instruction into BB \n"; BB->dump();
430           dbgs() << "Instruction Left\n"; S0->dump(); dbgs() << "\n";
431           dbgs() << "Instruction Right\n"; S1->dump(); dbgs() << "\n");
432     // Hoist the instruction.
433     BasicBlock::iterator InsertPt = BB->getFirstInsertionPt();
434     // Intersect optional metadata.
435     S0->intersectOptionalDataWith(S1);
436     S0->dropUnknownNonDebugMetadata();
437 
438     // Create the new store to be inserted at the join point.
439     StoreInst *SNew = cast<StoreInst>(S0->clone());
440     Instruction *ANew = A0->clone();
441     SNew->insertBefore(&*InsertPt);
442     ANew->insertBefore(SNew);
443 
444     assert(S0->getParent() == A0->getParent());
445     assert(S1->getParent() == A1->getParent());
446 
447     // New PHI operand? Use it.
448     if (PHINode *NewPN = getPHIOperand(BB, S0, S1))
449       SNew->setOperand(0, NewPN);
450     removeInstruction(S0);
451     removeInstruction(S1);
452     A0->replaceAllUsesWith(ANew);
453     removeInstruction(A0);
454     A1->replaceAllUsesWith(ANew);
455     removeInstruction(A1);
456     return true;
457   }
458   return false;
459 }
460 
461 ///
462 /// \brief True when two stores are equivalent and can sink into the footer
463 ///
464 /// Starting from a diamond tail block, iterate over the instructions in one
465 /// predecessor block and try to match a store in the second predecessor.
466 ///
467 bool MergedLoadStoreMotion::mergeStores(BasicBlock *T) {
468 
469   bool MergedStores = false;
470   assert(T && "Footer of a diamond cannot be empty");
471 
472   pred_iterator PI = pred_begin(T), E = pred_end(T);
473   assert(PI != E);
474   BasicBlock *Pred0 = *PI;
475   ++PI;
476   BasicBlock *Pred1 = *PI;
477   ++PI;
478   // tail block  of a diamond/hammock?
479   if (Pred0 == Pred1)
480     return false; // No.
481   if (PI != E)
482     return false; // No. More than 2 predecessors.
483 
484   // #Instructions in Succ1 for Compile Time Control
485   int Size1 = Pred1->size();
486   int NStores = 0;
487 
488   for (BasicBlock::reverse_iterator RBI = Pred0->rbegin(), RBE = Pred0->rend();
489        RBI != RBE;) {
490 
491     Instruction *I = &*RBI;
492     ++RBI;
493 
494     // Don't sink non-simple (atomic, volatile) stores.
495     auto *S0 = dyn_cast<StoreInst>(I);
496     if (!S0 || !S0->isSimple())
497       continue;
498 
499     ++NStores;
500     if (NStores * Size1 >= MagicCompileTimeControl)
501       break;
502     if (StoreInst *S1 = canSinkFromBlock(Pred1, S0)) {
503       bool Res = sinkStore(T, S0, S1);
504       MergedStores |= Res;
505       // Don't attempt to sink below stores that had to stick around
506       // But after removal of a store and some of its feeding
507       // instruction search again from the beginning since the iterator
508       // is likely stale at this point.
509       if (!Res)
510         break;
511       RBI = Pred0->rbegin();
512       RBE = Pred0->rend();
513       DEBUG(dbgs() << "Search again\n"; Instruction *I = &*RBI; I->dump());
514     }
515   }
516   return MergedStores;
517 }
518 
519 bool MergedLoadStoreMotion::run(Function &F, MemoryDependenceResults *MD,
520                                 AliasAnalysis &AA) {
521   this->MD = MD;
522   this->AA = &AA;
523 
524   bool Changed = false;
525   DEBUG(dbgs() << "Instruction Merger\n");
526 
527   // Merge unconditional branches, allowing PRE to catch more
528   // optimization opportunities.
529   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE;) {
530     BasicBlock *BB = &*FI++;
531 
532     // Hoist equivalent loads and sink stores
533     // outside diamonds when possible
534     if (isDiamondHead(BB)) {
535       Changed |= mergeLoads(BB);
536       Changed |= mergeStores(getDiamondTail(BB));
537     }
538   }
539   return Changed;
540 }
541 
542 namespace {
543 class MergedLoadStoreMotionLegacyPass : public FunctionPass {
544 public:
545   static char ID; // Pass identification, replacement for typeid
546   MergedLoadStoreMotionLegacyPass() : FunctionPass(ID) {
547     initializeMergedLoadStoreMotionLegacyPassPass(
548         *PassRegistry::getPassRegistry());
549   }
550 
551   ///
552   /// \brief Run the transformation for each function
553   ///
554   bool runOnFunction(Function &F) override {
555     if (skipFunction(F))
556       return false;
557     MergedLoadStoreMotion Impl;
558     auto *MDWP = getAnalysisIfAvailable<MemoryDependenceWrapperPass>();
559     return Impl.run(F, MDWP ? &MDWP->getMemDep() : nullptr,
560                     getAnalysis<AAResultsWrapperPass>().getAAResults());
561   }
562 
563 private:
564   // This transformation requires dominator postdominator info
565   void getAnalysisUsage(AnalysisUsage &AU) const override {
566     AU.setPreservesCFG();
567     AU.addRequired<AAResultsWrapperPass>();
568     AU.addPreserved<GlobalsAAWrapperPass>();
569     AU.addPreserved<MemoryDependenceWrapperPass>();
570   }
571 };
572 
573 char MergedLoadStoreMotionLegacyPass::ID = 0;
574 } // anonymous namespace
575 
576 ///
577 /// \brief createMergedLoadStoreMotionPass - The public interface to this file.
578 ///
579 FunctionPass *llvm::createMergedLoadStoreMotionPass() {
580   return new MergedLoadStoreMotionLegacyPass();
581 }
582 
583 INITIALIZE_PASS_BEGIN(MergedLoadStoreMotionLegacyPass, "mldst-motion",
584                       "MergedLoadStoreMotion", false, false)
585 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
586 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
587 INITIALIZE_PASS_END(MergedLoadStoreMotionLegacyPass, "mldst-motion",
588                     "MergedLoadStoreMotion", false, false)
589 
590 PreservedAnalyses
591 MergedLoadStoreMotionPass::run(Function &F, AnalysisManager<Function> &AM) {
592   MergedLoadStoreMotion Impl;
593   auto *MD = AM.getCachedResult<MemoryDependenceAnalysis>(F);
594   auto &AA = AM.getResult<AAManager>(F);
595   if (!Impl.run(F, MD, AA))
596     return PreservedAnalyses::all();
597 
598   // FIXME: This pass should also 'preserve the CFG'.
599   // The new pass manager has currently no way to do it.
600   PreservedAnalyses PA;
601   PA.preserve<GlobalsAA>();
602   PA.preserve<MemoryDependenceAnalysis>();
603   return PA;
604 }
605