LLVM  4.0.0
PromoteMemoryToRegister.cpp
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1 //===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
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 // This file promotes memory references to be register references. It promotes
11 // alloca instructions which only have loads and stores as uses. An alloca is
12 // transformed by using iterated dominator frontiers to place PHI nodes, then
13 // traversing the function in depth-first order to rewrite loads and stores as
14 // appropriate.
15 //
16 //===----------------------------------------------------------------------===//
17 
19 #include "llvm/ADT/ArrayRef.h"
20 #include "llvm/ADT/DenseMap.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/ADT/SmallPtrSet.h"
23 #include "llvm/ADT/SmallVector.h"
24 #include "llvm/ADT/Statistic.h"
29 #include "llvm/IR/CFG.h"
30 #include "llvm/IR/Constants.h"
31 #include "llvm/IR/DIBuilder.h"
32 #include "llvm/IR/DebugInfo.h"
33 #include "llvm/IR/DerivedTypes.h"
34 #include "llvm/IR/Dominators.h"
35 #include "llvm/IR/Function.h"
36 #include "llvm/IR/Instructions.h"
37 #include "llvm/IR/IntrinsicInst.h"
38 #include "llvm/IR/Metadata.h"
39 #include "llvm/IR/Module.h"
41 #include <algorithm>
42 using namespace llvm;
43 
44 #define DEBUG_TYPE "mem2reg"
45 
46 STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block");
47 STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store");
48 STATISTIC(NumDeadAlloca, "Number of dead alloca's removed");
49 STATISTIC(NumPHIInsert, "Number of PHI nodes inserted");
50 
52  // FIXME: If the memory unit is of pointer or integer type, we can permit
53  // assignments to subsections of the memory unit.
54  unsigned AS = AI->getType()->getAddressSpace();
55 
56  // Only allow direct and non-volatile loads and stores...
57  for (const User *U : AI->users()) {
58  if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
59  // Note that atomic loads can be transformed; atomic semantics do
60  // not have any meaning for a local alloca.
61  if (LI->isVolatile())
62  return false;
63  } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
64  if (SI->getOperand(0) == AI)
65  return false; // Don't allow a store OF the AI, only INTO the AI.
66  // Note that atomic stores can be transformed; atomic semantics do
67  // not have any meaning for a local alloca.
68  if (SI->isVolatile())
69  return false;
70  } else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
71  if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
72  II->getIntrinsicID() != Intrinsic::lifetime_end)
73  return false;
74  } else if (const BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
75  if (BCI->getType() != Type::getInt8PtrTy(U->getContext(), AS))
76  return false;
77  if (!onlyUsedByLifetimeMarkers(BCI))
78  return false;
79  } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
80  if (GEPI->getType() != Type::getInt8PtrTy(U->getContext(), AS))
81  return false;
82  if (!GEPI->hasAllZeroIndices())
83  return false;
84  if (!onlyUsedByLifetimeMarkers(GEPI))
85  return false;
86  } else {
87  return false;
88  }
89  }
90 
91  return true;
92 }
93 
94 namespace {
95 
96 struct AllocaInfo {
97  SmallVector<BasicBlock *, 32> DefiningBlocks;
99 
100  StoreInst *OnlyStore;
101  BasicBlock *OnlyBlock;
102  bool OnlyUsedInOneBlock;
103 
104  Value *AllocaPointerVal;
105  DbgDeclareInst *DbgDeclare;
106 
107  void clear() {
108  DefiningBlocks.clear();
109  UsingBlocks.clear();
110  OnlyStore = nullptr;
111  OnlyBlock = nullptr;
112  OnlyUsedInOneBlock = true;
113  AllocaPointerVal = nullptr;
114  DbgDeclare = nullptr;
115  }
116 
117  /// Scan the uses of the specified alloca, filling in the AllocaInfo used
118  /// by the rest of the pass to reason about the uses of this alloca.
119  void AnalyzeAlloca(AllocaInst *AI) {
120  clear();
121 
122  // As we scan the uses of the alloca instruction, keep track of stores,
123  // and decide whether all of the loads and stores to the alloca are within
124  // the same basic block.
125  for (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) {
126  Instruction *User = cast<Instruction>(*UI++);
127 
128  if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
129  // Remember the basic blocks which define new values for the alloca
130  DefiningBlocks.push_back(SI->getParent());
131  AllocaPointerVal = SI->getOperand(0);
132  OnlyStore = SI;
133  } else {
134  LoadInst *LI = cast<LoadInst>(User);
135  // Otherwise it must be a load instruction, keep track of variable
136  // reads.
137  UsingBlocks.push_back(LI->getParent());
138  AllocaPointerVal = LI;
139  }
140 
141  if (OnlyUsedInOneBlock) {
142  if (!OnlyBlock)
143  OnlyBlock = User->getParent();
144  else if (OnlyBlock != User->getParent())
145  OnlyUsedInOneBlock = false;
146  }
147  }
148 
149  DbgDeclare = FindAllocaDbgDeclare(AI);
150  }
151 };
152 
153 // Data package used by RenamePass()
154 class RenamePassData {
155 public:
156  typedef std::vector<Value *> ValVector;
157 
158  RenamePassData() : BB(nullptr), Pred(nullptr), Values() {}
159  RenamePassData(BasicBlock *B, BasicBlock *P, const ValVector &V)
160  : BB(B), Pred(P), Values(V) {}
161  BasicBlock *BB;
162  BasicBlock *Pred;
163  ValVector Values;
164 
165  void swap(RenamePassData &RHS) {
166  std::swap(BB, RHS.BB);
167  std::swap(Pred, RHS.Pred);
168  Values.swap(RHS.Values);
169  }
170 };
171 
172 /// \brief This assigns and keeps a per-bb relative ordering of load/store
173 /// instructions in the block that directly load or store an alloca.
174 ///
175 /// This functionality is important because it avoids scanning large basic
176 /// blocks multiple times when promoting many allocas in the same block.
177 class LargeBlockInfo {
178  /// \brief For each instruction that we track, keep the index of the
179  /// instruction.
180  ///
181  /// The index starts out as the number of the instruction from the start of
182  /// the block.
184 
185 public:
186 
187  /// This code only looks at accesses to allocas.
188  static bool isInterestingInstruction(const Instruction *I) {
189  return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) ||
190  (isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1)));
191  }
192 
193  /// Get or calculate the index of the specified instruction.
194  unsigned getInstructionIndex(const Instruction *I) {
195  assert(isInterestingInstruction(I) &&
196  "Not a load/store to/from an alloca?");
197 
198  // If we already have this instruction number, return it.
200  if (It != InstNumbers.end())
201  return It->second;
202 
203  // Scan the whole block to get the instruction. This accumulates
204  // information for every interesting instruction in the block, in order to
205  // avoid gratuitus rescans.
206  const BasicBlock *BB = I->getParent();
207  unsigned InstNo = 0;
208  for (const Instruction &BBI : *BB)
209  if (isInterestingInstruction(&BBI))
210  InstNumbers[&BBI] = InstNo++;
211  It = InstNumbers.find(I);
212 
213  assert(It != InstNumbers.end() && "Didn't insert instruction?");
214  return It->second;
215  }
216 
217  void deleteValue(const Instruction *I) { InstNumbers.erase(I); }
218 
219  void clear() { InstNumbers.clear(); }
220 };
221 
222 struct PromoteMem2Reg {
223  /// The alloca instructions being promoted.
224  std::vector<AllocaInst *> Allocas;
225  DominatorTree &DT;
226  DIBuilder DIB;
227 
228  /// An AliasSetTracker object to update. If null, don't update it.
229  AliasSetTracker *AST;
230 
231  /// A cache of @llvm.assume intrinsics used by SimplifyInstruction.
232  AssumptionCache *AC;
233 
234  /// Reverse mapping of Allocas.
236 
237  /// \brief The PhiNodes we're adding.
238  ///
239  /// That map is used to simplify some Phi nodes as we iterate over it, so
240  /// it should have deterministic iterators. We could use a MapVector, but
241  /// since we already maintain a map from BasicBlock* to a stable numbering
242  /// (BBNumbers), the DenseMap is more efficient (also supports removal).
244 
245  /// For each PHI node, keep track of which entry in Allocas it corresponds
246  /// to.
247  DenseMap<PHINode *, unsigned> PhiToAllocaMap;
248 
249  /// If we are updating an AliasSetTracker, then for each alloca that is of
250  /// pointer type, we keep track of what to copyValue to the inserted PHI
251  /// nodes here.
252  std::vector<Value *> PointerAllocaValues;
253 
254  /// For each alloca, we keep track of the dbg.declare intrinsic that
255  /// describes it, if any, so that we can convert it to a dbg.value
256  /// intrinsic if the alloca gets promoted.
257  SmallVector<DbgDeclareInst *, 8> AllocaDbgDeclares;
258 
259  /// The set of basic blocks the renamer has already visited.
260  ///
262 
263  /// Contains a stable numbering of basic blocks to avoid non-determinstic
264  /// behavior.
266 
267  /// Lazily compute the number of predecessors a block has.
269 
270 public:
271  PromoteMem2Reg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
273  : Allocas(Allocas.begin(), Allocas.end()), DT(DT),
274  DIB(*DT.getRoot()->getParent()->getParent(), /*AllowUnresolved*/ false),
275  AST(AST), AC(AC) {}
276 
277  void run();
278 
279 private:
280  void RemoveFromAllocasList(unsigned &AllocaIdx) {
281  Allocas[AllocaIdx] = Allocas.back();
282  Allocas.pop_back();
283  --AllocaIdx;
284  }
285 
286  unsigned getNumPreds(const BasicBlock *BB) {
287  unsigned &NP = BBNumPreds[BB];
288  if (NP == 0)
289  NP = std::distance(pred_begin(BB), pred_end(BB)) + 1;
290  return NP - 1;
291  }
292 
293  void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info,
294  const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
295  SmallPtrSetImpl<BasicBlock *> &LiveInBlocks);
296  void RenamePass(BasicBlock *BB, BasicBlock *Pred,
297  RenamePassData::ValVector &IncVals,
298  std::vector<RenamePassData> &Worklist);
299  bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version);
300 };
301 
302 } // end of anonymous namespace
303 
305  // Knowing that this alloca is promotable, we know that it's safe to kill all
306  // instructions except for load and store.
307 
308  for (auto UI = AI->user_begin(), UE = AI->user_end(); UI != UE;) {
309  Instruction *I = cast<Instruction>(*UI);
310  ++UI;
311  if (isa<LoadInst>(I) || isa<StoreInst>(I))
312  continue;
313 
314  if (!I->getType()->isVoidTy()) {
315  // The only users of this bitcast/GEP instruction are lifetime intrinsics.
316  // Follow the use/def chain to erase them now instead of leaving it for
317  // dead code elimination later.
318  for (auto UUI = I->user_begin(), UUE = I->user_end(); UUI != UUE;) {
319  Instruction *Inst = cast<Instruction>(*UUI);
320  ++UUI;
321  Inst->eraseFromParent();
322  }
323  }
324  I->eraseFromParent();
325  }
326 }
327 
328 /// \brief Rewrite as many loads as possible given a single store.
329 ///
330 /// When there is only a single store, we can use the domtree to trivially
331 /// replace all of the dominated loads with the stored value. Do so, and return
332 /// true if this has successfully promoted the alloca entirely. If this returns
333 /// false there were some loads which were not dominated by the single store
334 /// and thus must be phi-ed with undef. We fall back to the standard alloca
335 /// promotion algorithm in that case.
336 static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
337  LargeBlockInfo &LBI,
338  DominatorTree &DT,
339  AliasSetTracker *AST) {
340  StoreInst *OnlyStore = Info.OnlyStore;
341  bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0));
342  BasicBlock *StoreBB = OnlyStore->getParent();
343  int StoreIndex = -1;
344 
345  // Clear out UsingBlocks. We will reconstruct it here if needed.
346  Info.UsingBlocks.clear();
347 
348  for (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) {
349  Instruction *UserInst = cast<Instruction>(*UI++);
350  if (!isa<LoadInst>(UserInst)) {
351  assert(UserInst == OnlyStore && "Should only have load/stores");
352  continue;
353  }
354  LoadInst *LI = cast<LoadInst>(UserInst);
355 
356  // Okay, if we have a load from the alloca, we want to replace it with the
357  // only value stored to the alloca. We can do this if the value is
358  // dominated by the store. If not, we use the rest of the mem2reg machinery
359  // to insert the phi nodes as needed.
360  if (!StoringGlobalVal) { // Non-instructions are always dominated.
361  if (LI->getParent() == StoreBB) {
362  // If we have a use that is in the same block as the store, compare the
363  // indices of the two instructions to see which one came first. If the
364  // load came before the store, we can't handle it.
365  if (StoreIndex == -1)
366  StoreIndex = LBI.getInstructionIndex(OnlyStore);
367 
368  if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) {
369  // Can't handle this load, bail out.
370  Info.UsingBlocks.push_back(StoreBB);
371  continue;
372  }
373 
374  } else if (LI->getParent() != StoreBB &&
375  !DT.dominates(StoreBB, LI->getParent())) {
376  // If the load and store are in different blocks, use BB dominance to
377  // check their relationships. If the store doesn't dom the use, bail
378  // out.
379  Info.UsingBlocks.push_back(LI->getParent());
380  continue;
381  }
382  }
383 
384  // Otherwise, we *can* safely rewrite this load.
385  Value *ReplVal = OnlyStore->getOperand(0);
386  // If the replacement value is the load, this must occur in unreachable
387  // code.
388  if (ReplVal == LI)
389  ReplVal = UndefValue::get(LI->getType());
390  LI->replaceAllUsesWith(ReplVal);
391  if (AST && LI->getType()->isPointerTy())
392  AST->deleteValue(LI);
393  LI->eraseFromParent();
394  LBI.deleteValue(LI);
395  }
396 
397  // Finally, after the scan, check to see if the store is all that is left.
398  if (!Info.UsingBlocks.empty())
399  return false; // If not, we'll have to fall back for the remainder.
400 
401  // Record debuginfo for the store and remove the declaration's
402  // debuginfo.
403  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
404  DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
405  ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB);
406  DDI->eraseFromParent();
407  LBI.deleteValue(DDI);
408  }
409  // Remove the (now dead) store and alloca.
410  Info.OnlyStore->eraseFromParent();
411  LBI.deleteValue(Info.OnlyStore);
412 
413  if (AST)
414  AST->deleteValue(AI);
415  AI->eraseFromParent();
416  LBI.deleteValue(AI);
417  return true;
418 }
419 
420 /// Many allocas are only used within a single basic block. If this is the
421 /// case, avoid traversing the CFG and inserting a lot of potentially useless
422 /// PHI nodes by just performing a single linear pass over the basic block
423 /// using the Alloca.
424 ///
425 /// If we cannot promote this alloca (because it is read before it is written),
426 /// return false. This is necessary in cases where, due to control flow, the
427 /// alloca is undefined only on some control flow paths. e.g. code like
428 /// this is correct in LLVM IR:
429 /// // A is an alloca with no stores so far
430 /// for (...) {
431 /// int t = *A;
432 /// if (!first_iteration)
433 /// use(t);
434 /// *A = 42;
435 /// }
436 static bool promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info,
437  LargeBlockInfo &LBI,
438  AliasSetTracker *AST) {
439  // The trickiest case to handle is when we have large blocks. Because of this,
440  // this code is optimized assuming that large blocks happen. This does not
441  // significantly pessimize the small block case. This uses LargeBlockInfo to
442  // make it efficient to get the index of various operations in the block.
443 
444  // Walk the use-def list of the alloca, getting the locations of all stores.
445  typedef SmallVector<std::pair<unsigned, StoreInst *>, 64> StoresByIndexTy;
446  StoresByIndexTy StoresByIndex;
447 
448  for (User *U : AI->users())
449  if (StoreInst *SI = dyn_cast<StoreInst>(U))
450  StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI));
451 
452  // Sort the stores by their index, making it efficient to do a lookup with a
453  // binary search.
454  std::sort(StoresByIndex.begin(), StoresByIndex.end(), less_first());
455 
456  // Walk all of the loads from this alloca, replacing them with the nearest
457  // store above them, if any.
458  for (auto UI = AI->user_begin(), E = AI->user_end(); UI != E;) {
459  LoadInst *LI = dyn_cast<LoadInst>(*UI++);
460  if (!LI)
461  continue;
462 
463  unsigned LoadIdx = LBI.getInstructionIndex(LI);
464 
465  // Find the nearest store that has a lower index than this load.
466  StoresByIndexTy::iterator I =
467  std::lower_bound(StoresByIndex.begin(), StoresByIndex.end(),
468  std::make_pair(LoadIdx,
469  static_cast<StoreInst *>(nullptr)),
470  less_first());
471  if (I == StoresByIndex.begin()) {
472  if (StoresByIndex.empty())
473  // If there are no stores, the load takes the undef value.
475  else
476  // There is no store before this load, bail out (load may be affected
477  // by the following stores - see main comment).
478  return false;
479  }
480  else
481  // Otherwise, there was a store before this load, the load takes its value.
482  LI->replaceAllUsesWith(std::prev(I)->second->getOperand(0));
483 
484  if (AST && LI->getType()->isPointerTy())
485  AST->deleteValue(LI);
486  LI->eraseFromParent();
487  LBI.deleteValue(LI);
488  }
489 
490  // Remove the (now dead) stores and alloca.
491  while (!AI->use_empty()) {
492  StoreInst *SI = cast<StoreInst>(AI->user_back());
493  // Record debuginfo for the store before removing it.
494  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
495  DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
496  ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
497  }
498  SI->eraseFromParent();
499  LBI.deleteValue(SI);
500  }
501 
502  if (AST)
503  AST->deleteValue(AI);
504  AI->eraseFromParent();
505  LBI.deleteValue(AI);
506 
507  // The alloca's debuginfo can be removed as well.
508  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
509  DDI->eraseFromParent();
510  LBI.deleteValue(DDI);
511  }
512 
513  ++NumLocalPromoted;
514  return true;
515 }
516 
517 void PromoteMem2Reg::run() {
518  Function &F = *DT.getRoot()->getParent();
519 
520  if (AST)
521  PointerAllocaValues.resize(Allocas.size());
522  AllocaDbgDeclares.resize(Allocas.size());
523 
524  AllocaInfo Info;
525  LargeBlockInfo LBI;
526  ForwardIDFCalculator IDF(DT);
527 
528  for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
529  AllocaInst *AI = Allocas[AllocaNum];
530 
531  assert(isAllocaPromotable(AI) && "Cannot promote non-promotable alloca!");
532  assert(AI->getParent()->getParent() == &F &&
533  "All allocas should be in the same function, which is same as DF!");
534 
536 
537  if (AI->use_empty()) {
538  // If there are no uses of the alloca, just delete it now.
539  if (AST)
540  AST->deleteValue(AI);
541  AI->eraseFromParent();
542 
543  // Remove the alloca from the Allocas list, since it has been processed
544  RemoveFromAllocasList(AllocaNum);
545  ++NumDeadAlloca;
546  continue;
547  }
548 
549  // Calculate the set of read and write-locations for each alloca. This is
550  // analogous to finding the 'uses' and 'definitions' of each variable.
551  Info.AnalyzeAlloca(AI);
552 
553  // If there is only a single store to this value, replace any loads of
554  // it that are directly dominated by the definition with the value stored.
555  if (Info.DefiningBlocks.size() == 1) {
556  if (rewriteSingleStoreAlloca(AI, Info, LBI, DT, AST)) {
557  // The alloca has been processed, move on.
558  RemoveFromAllocasList(AllocaNum);
559  ++NumSingleStore;
560  continue;
561  }
562  }
563 
564  // If the alloca is only read and written in one basic block, just perform a
565  // linear sweep over the block to eliminate it.
566  if (Info.OnlyUsedInOneBlock &&
567  promoteSingleBlockAlloca(AI, Info, LBI, AST)) {
568  // The alloca has been processed, move on.
569  RemoveFromAllocasList(AllocaNum);
570  continue;
571  }
572 
573  // If we haven't computed a numbering for the BB's in the function, do so
574  // now.
575  if (BBNumbers.empty()) {
576  unsigned ID = 0;
577  for (auto &BB : F)
578  BBNumbers[&BB] = ID++;
579  }
580 
581  // If we have an AST to keep updated, remember some pointer value that is
582  // stored into the alloca.
583  if (AST)
584  PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
585 
586  // Remember the dbg.declare intrinsic describing this alloca, if any.
587  if (Info.DbgDeclare)
588  AllocaDbgDeclares[AllocaNum] = Info.DbgDeclare;
589 
590  // Keep the reverse mapping of the 'Allocas' array for the rename pass.
591  AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
592 
593  // At this point, we're committed to promoting the alloca using IDF's, and
594  // the standard SSA construction algorithm. Determine which blocks need PHI
595  // nodes and see if we can optimize out some work by avoiding insertion of
596  // dead phi nodes.
597 
598 
599  // Unique the set of defining blocks for efficient lookup.
601  DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end());
602 
603  // Determine which blocks the value is live in. These are blocks which lead
604  // to uses.
605  SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
606  ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);
607 
608  // At this point, we're committed to promoting the alloca using IDF's, and
609  // the standard SSA construction algorithm. Determine which blocks need phi
610  // nodes and see if we can optimize out some work by avoiding insertion of
611  // dead phi nodes.
612  IDF.setLiveInBlocks(LiveInBlocks);
613  IDF.setDefiningBlocks(DefBlocks);
615  IDF.calculate(PHIBlocks);
616  if (PHIBlocks.size() > 1)
617  std::sort(PHIBlocks.begin(), PHIBlocks.end(),
618  [this](BasicBlock *A, BasicBlock *B) {
619  return BBNumbers.lookup(A) < BBNumbers.lookup(B);
620  });
621 
622  unsigned CurrentVersion = 0;
623  for (unsigned i = 0, e = PHIBlocks.size(); i != e; ++i)
624  QueuePhiNode(PHIBlocks[i], AllocaNum, CurrentVersion);
625  }
626 
627  if (Allocas.empty())
628  return; // All of the allocas must have been trivial!
629 
630  LBI.clear();
631 
632  // Set the incoming values for the basic block to be null values for all of
633  // the alloca's. We do this in case there is a load of a value that has not
634  // been stored yet. In this case, it will get this null value.
635  //
636  RenamePassData::ValVector Values(Allocas.size());
637  for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
638  Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
639 
640  // Walks all basic blocks in the function performing the SSA rename algorithm
641  // and inserting the phi nodes we marked as necessary
642  //
643  std::vector<RenamePassData> RenamePassWorkList;
644  RenamePassWorkList.emplace_back(&F.front(), nullptr, std::move(Values));
645  do {
646  RenamePassData RPD;
647  RPD.swap(RenamePassWorkList.back());
648  RenamePassWorkList.pop_back();
649  // RenamePass may add new worklist entries.
650  RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList);
651  } while (!RenamePassWorkList.empty());
652 
653  // The renamer uses the Visited set to avoid infinite loops. Clear it now.
654  Visited.clear();
655 
656  // Remove the allocas themselves from the function.
657  for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
658  Instruction *A = Allocas[i];
659 
660  // If there are any uses of the alloca instructions left, they must be in
661  // unreachable basic blocks that were not processed by walking the dominator
662  // tree. Just delete the users now.
663  if (!A->use_empty())
665  if (AST)
666  AST->deleteValue(A);
667  A->eraseFromParent();
668  }
669 
670  const DataLayout &DL = F.getParent()->getDataLayout();
671 
672  // Remove alloca's dbg.declare instrinsics from the function.
673  for (unsigned i = 0, e = AllocaDbgDeclares.size(); i != e; ++i)
674  if (DbgDeclareInst *DDI = AllocaDbgDeclares[i])
675  DDI->eraseFromParent();
676 
677  // Loop over all of the PHI nodes and see if there are any that we can get
678  // rid of because they merge all of the same incoming values. This can
679  // happen due to undef values coming into the PHI nodes. This process is
680  // iterative, because eliminating one PHI node can cause others to be removed.
681  bool EliminatedAPHI = true;
682  while (EliminatedAPHI) {
683  EliminatedAPHI = false;
684 
685  // Iterating over NewPhiNodes is deterministic, so it is safe to try to
686  // simplify and RAUW them as we go. If it was not, we could add uses to
687  // the values we replace with in a non-deterministic order, thus creating
688  // non-deterministic def->use chains.
689  for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
690  I = NewPhiNodes.begin(),
691  E = NewPhiNodes.end();
692  I != E;) {
693  PHINode *PN = I->second;
694 
695  // If this PHI node merges one value and/or undefs, get the value.
696  if (Value *V = SimplifyInstruction(PN, DL, nullptr, &DT, AC)) {
697  if (AST && PN->getType()->isPointerTy())
698  AST->deleteValue(PN);
699  PN->replaceAllUsesWith(V);
700  PN->eraseFromParent();
701  NewPhiNodes.erase(I++);
702  EliminatedAPHI = true;
703  continue;
704  }
705  ++I;
706  }
707  }
708 
709  // At this point, the renamer has added entries to PHI nodes for all reachable
710  // code. Unfortunately, there may be unreachable blocks which the renamer
711  // hasn't traversed. If this is the case, the PHI nodes may not
712  // have incoming values for all predecessors. Loop over all PHI nodes we have
713  // created, inserting undef values if they are missing any incoming values.
714  //
715  for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
716  I = NewPhiNodes.begin(),
717  E = NewPhiNodes.end();
718  I != E; ++I) {
719  // We want to do this once per basic block. As such, only process a block
720  // when we find the PHI that is the first entry in the block.
721  PHINode *SomePHI = I->second;
722  BasicBlock *BB = SomePHI->getParent();
723  if (&BB->front() != SomePHI)
724  continue;
725 
726  // Only do work here if there the PHI nodes are missing incoming values. We
727  // know that all PHI nodes that were inserted in a block will have the same
728  // number of incoming values, so we can just check any of them.
729  if (SomePHI->getNumIncomingValues() == getNumPreds(BB))
730  continue;
731 
732  // Get the preds for BB.
734 
735  // Ok, now we know that all of the PHI nodes are missing entries for some
736  // basic blocks. Start by sorting the incoming predecessors for efficient
737  // access.
738  std::sort(Preds.begin(), Preds.end());
739 
740  // Now we loop through all BB's which have entries in SomePHI and remove
741  // them from the Preds list.
742  for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
743  // Do a log(n) search of the Preds list for the entry we want.
744  SmallVectorImpl<BasicBlock *>::iterator EntIt = std::lower_bound(
745  Preds.begin(), Preds.end(), SomePHI->getIncomingBlock(i));
746  assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i) &&
747  "PHI node has entry for a block which is not a predecessor!");
748 
749  // Remove the entry
750  Preds.erase(EntIt);
751  }
752 
753  // At this point, the blocks left in the preds list must have dummy
754  // entries inserted into every PHI nodes for the block. Update all the phi
755  // nodes in this block that we are inserting (there could be phis before
756  // mem2reg runs).
757  unsigned NumBadPreds = SomePHI->getNumIncomingValues();
758  BasicBlock::iterator BBI = BB->begin();
759  while ((SomePHI = dyn_cast<PHINode>(BBI++)) &&
760  SomePHI->getNumIncomingValues() == NumBadPreds) {
761  Value *UndefVal = UndefValue::get(SomePHI->getType());
762  for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
763  SomePHI->addIncoming(UndefVal, Preds[pred]);
764  }
765  }
766 
767  NewPhiNodes.clear();
768 }
769 
770 /// \brief Determine which blocks the value is live in.
771 ///
772 /// These are blocks which lead to uses. Knowing this allows us to avoid
773 /// inserting PHI nodes into blocks which don't lead to uses (thus, the
774 /// inserted phi nodes would be dead).
775 void PromoteMem2Reg::ComputeLiveInBlocks(
776  AllocaInst *AI, AllocaInfo &Info,
777  const SmallPtrSetImpl<BasicBlock *> &DefBlocks,
778  SmallPtrSetImpl<BasicBlock *> &LiveInBlocks) {
779 
780  // To determine liveness, we must iterate through the predecessors of blocks
781  // where the def is live. Blocks are added to the worklist if we need to
782  // check their predecessors. Start with all the using blocks.
783  SmallVector<BasicBlock *, 64> LiveInBlockWorklist(Info.UsingBlocks.begin(),
784  Info.UsingBlocks.end());
785 
786  // If any of the using blocks is also a definition block, check to see if the
787  // definition occurs before or after the use. If it happens before the use,
788  // the value isn't really live-in.
789  for (unsigned i = 0, e = LiveInBlockWorklist.size(); i != e; ++i) {
790  BasicBlock *BB = LiveInBlockWorklist[i];
791  if (!DefBlocks.count(BB))
792  continue;
793 
794  // Okay, this is a block that both uses and defines the value. If the first
795  // reference to the alloca is a def (store), then we know it isn't live-in.
796  for (BasicBlock::iterator I = BB->begin();; ++I) {
797  if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
798  if (SI->getOperand(1) != AI)
799  continue;
800 
801  // We found a store to the alloca before a load. The alloca is not
802  // actually live-in here.
803  LiveInBlockWorklist[i] = LiveInBlockWorklist.back();
804  LiveInBlockWorklist.pop_back();
805  --i;
806  --e;
807  break;
808  }
809 
810  if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
811  if (LI->getOperand(0) != AI)
812  continue;
813 
814  // Okay, we found a load before a store to the alloca. It is actually
815  // live into this block.
816  break;
817  }
818  }
819  }
820 
821  // Now that we have a set of blocks where the phi is live-in, recursively add
822  // their predecessors until we find the full region the value is live.
823  while (!LiveInBlockWorklist.empty()) {
824  BasicBlock *BB = LiveInBlockWorklist.pop_back_val();
825 
826  // The block really is live in here, insert it into the set. If already in
827  // the set, then it has already been processed.
828  if (!LiveInBlocks.insert(BB).second)
829  continue;
830 
831  // Since the value is live into BB, it is either defined in a predecessor or
832  // live into it to. Add the preds to the worklist unless they are a
833  // defining block.
834  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
835  BasicBlock *P = *PI;
836 
837  // The value is not live into a predecessor if it defines the value.
838  if (DefBlocks.count(P))
839  continue;
840 
841  // Otherwise it is, add to the worklist.
842  LiveInBlockWorklist.push_back(P);
843  }
844  }
845 }
846 
847 /// \brief Queue a phi-node to be added to a basic-block for a specific Alloca.
848 ///
849 /// Returns true if there wasn't already a phi-node for that variable
850 bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
851  unsigned &Version) {
852  // Look up the basic-block in question.
853  PHINode *&PN = NewPhiNodes[std::make_pair(BBNumbers[BB], AllocaNo)];
854 
855  // If the BB already has a phi node added for the i'th alloca then we're done!
856  if (PN)
857  return false;
858 
859  // Create a PhiNode using the dereferenced type... and add the phi-node to the
860  // BasicBlock.
861  PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(), getNumPreds(BB),
862  Allocas[AllocaNo]->getName() + "." + Twine(Version++),
863  &BB->front());
864  ++NumPHIInsert;
865  PhiToAllocaMap[PN] = AllocaNo;
866 
867  if (AST && PN->getType()->isPointerTy())
868  AST->copyValue(PointerAllocaValues[AllocaNo], PN);
869 
870  return true;
871 }
872 
873 /// \brief Recursively traverse the CFG of the function, renaming loads and
874 /// stores to the allocas which we are promoting.
875 ///
876 /// IncomingVals indicates what value each Alloca contains on exit from the
877 /// predecessor block Pred.
878 void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
879  RenamePassData::ValVector &IncomingVals,
880  std::vector<RenamePassData> &Worklist) {
881 NextIteration:
882  // If we are inserting any phi nodes into this BB, they will already be in the
883  // block.
884  if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) {
885  // If we have PHI nodes to update, compute the number of edges from Pred to
886  // BB.
887  if (PhiToAllocaMap.count(APN)) {
888  // We want to be able to distinguish between PHI nodes being inserted by
889  // this invocation of mem2reg from those phi nodes that already existed in
890  // the IR before mem2reg was run. We determine that APN is being inserted
891  // because it is missing incoming edges. All other PHI nodes being
892  // inserted by this pass of mem2reg will have the same number of incoming
893  // operands so far. Remember this count.
894  unsigned NewPHINumOperands = APN->getNumOperands();
895 
896  unsigned NumEdges = std::count(succ_begin(Pred), succ_end(Pred), BB);
897  assert(NumEdges && "Must be at least one edge from Pred to BB!");
898 
899  // Add entries for all the phis.
900  BasicBlock::iterator PNI = BB->begin();
901  do {
902  unsigned AllocaNo = PhiToAllocaMap[APN];
903 
904  // Add N incoming values to the PHI node.
905  for (unsigned i = 0; i != NumEdges; ++i)
906  APN->addIncoming(IncomingVals[AllocaNo], Pred);
907 
908  // The currently active variable for this block is now the PHI.
909  IncomingVals[AllocaNo] = APN;
910  if (DbgDeclareInst *DDI = AllocaDbgDeclares[AllocaNo])
911  ConvertDebugDeclareToDebugValue(DDI, APN, DIB);
912 
913  // Get the next phi node.
914  ++PNI;
915  APN = dyn_cast<PHINode>(PNI);
916  if (!APN)
917  break;
918 
919  // Verify that it is missing entries. If not, it is not being inserted
920  // by this mem2reg invocation so we want to ignore it.
921  } while (APN->getNumOperands() == NewPHINumOperands);
922  }
923  }
924 
925  // Don't revisit blocks.
926  if (!Visited.insert(BB).second)
927  return;
928 
929  for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II);) {
930  Instruction *I = &*II++; // get the instruction, increment iterator
931 
932  if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
934  if (!Src)
935  continue;
936 
937  DenseMap<AllocaInst *, unsigned>::iterator AI = AllocaLookup.find(Src);
938  if (AI == AllocaLookup.end())
939  continue;
940 
941  Value *V = IncomingVals[AI->second];
942 
943  // Anything using the load now uses the current value.
944  LI->replaceAllUsesWith(V);
945  if (AST && LI->getType()->isPointerTy())
946  AST->deleteValue(LI);
947  BB->getInstList().erase(LI);
948  } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
949  // Delete this instruction and mark the name as the current holder of the
950  // value
951  AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand());
952  if (!Dest)
953  continue;
954 
955  DenseMap<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
956  if (ai == AllocaLookup.end())
957  continue;
958 
959  // what value were we writing?
960  IncomingVals[ai->second] = SI->getOperand(0);
961  // Record debuginfo for the store before removing it.
962  if (DbgDeclareInst *DDI = AllocaDbgDeclares[ai->second])
963  ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
964  BB->getInstList().erase(SI);
965  }
966  }
967 
968  // 'Recurse' to our successors.
969  succ_iterator I = succ_begin(BB), E = succ_end(BB);
970  if (I == E)
971  return;
972 
973  // Keep track of the successors so we don't visit the same successor twice
974  SmallPtrSet<BasicBlock *, 8> VisitedSuccs;
975 
976  // Handle the first successor without using the worklist.
977  VisitedSuccs.insert(*I);
978  Pred = BB;
979  BB = *I;
980  ++I;
981 
982  for (; I != E; ++I)
983  if (VisitedSuccs.insert(*I).second)
984  Worklist.emplace_back(*I, Pred, IncomingVals);
985 
986  goto NextIteration;
987 }
988 
990  AliasSetTracker *AST, AssumptionCache *AC) {
991  // If there is nothing to do, bail out...
992  if (Allocas.empty())
993  return;
994 
995  PromoteMem2Reg(Allocas, DT, AST, AC).run();
996 }
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:76
void push_back(const T &Elt)
Definition: SmallVector.h:211
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:102
const_iterator end(StringRef path)
Get end iterator over path.
Definition: Path.cpp:241
void addIncoming(Value *V, BasicBlock *BB)
Add an incoming value to the end of the PHI list.
const Instruction & back() const
Definition: BasicBlock.h:242
STATISTIC(NumFunctions,"Total number of functions")
iterator erase(iterator where)
Definition: ilist.h:280
size_t i
DbgDeclareInst * FindAllocaDbgDeclare(Value *V)
Finds the llvm.dbg.declare intrinsic corresponding to an alloca, if any.
Definition: Local.cpp:1234
static void removeLifetimeIntrinsicUsers(AllocaInst *AI)
This file contains the declarations for metadata subclasses.
size_type count(PtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:380
A cache of .assume calls within a function.
const_iterator begin(StringRef path)
Get begin iterator over path.
Definition: Path.cpp:233
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:100
const Instruction & front() const
Definition: BasicBlock.h:240
unsigned getAddressSpace() const
Return the address space of the Pointer type.
Definition: DerivedTypes.h:471
An instruction for reading from memory.
Definition: Instructions.h:164
bool isAllocaPromotable(const AllocaInst *AI)
Return true if this alloca is legal for promotion.
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:345
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:228
Twine - A lightweight data structure for efficiently representing the concatenation of temporary valu...
Definition: Twine.h:81
static StringRef getName(Value *V)
Interval::succ_iterator succ_begin(Interval *I)
succ_begin/succ_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:106
void PromoteMemToReg(ArrayRef< AllocaInst * > Allocas, DominatorTree &DT, AliasSetTracker *AST=nullptr, AssumptionCache *AC=nullptr)
Promote the specified list of alloca instructions into scalar registers, inserting PHI nodes as appro...
#define F(x, y, z)
Definition: MD5.cpp:51
Function Alias Analysis false
This class represents a no-op cast from one type to another.
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: APInt.h:33
static GCRegistry::Add< OcamlGC > B("ocaml","ocaml 3.10-compatible GC")
An instruction for storing to memory.
Definition: Instructions.h:300
auto count(R &&Range, const E &Element) -> typename std::iterator_traits< decltype(std::begin(Range))>::difference_type
Wrapper function around std::count to count the number of times an element Element occurs in the give...
Definition: STLExtras.h:791
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:401
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:96
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
Interval::succ_iterator succ_end(Interval *I)
Definition: Interval.h:109
unsigned getNumIncomingValues() const
Return the number of incoming edges.
an instruction for type-safe pointer arithmetic to access elements of arrays and structs ...
Definition: Instructions.h:830
#define P(N)
LLVM Basic Block Representation.
Definition: BasicBlock.h:51
void ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, StoreInst *SI, DIBuilder &Builder)
===---------------------------------------------------------------——===// Dbg Intrinsic utilities ...
Definition: Local.cpp:1091
PointerType * getType() const
Overload to return most specific pointer type.
Definition: Instructions.h:97
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:115
This file contains the declarations for the subclasses of Constant, which represent the different fla...
bool onlyUsedByLifetimeMarkers(const Value *V)
Return true if the only users of this pointer are lifetime markers.
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:368
Interval::pred_iterator pred_begin(Interval *I)
pred_begin/pred_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:116
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
const InstListType & getInstList() const
Return the underlying instruction list container.
Definition: BasicBlock.h:249
Value * getOperand(unsigned i) const
Definition: User.h:145
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:119
Value * getPointerOperand()
Definition: Instructions.h:270
bool empty() const
empty - Check if the array is empty.
Definition: ArrayRef.h:136
bool isPointerTy() const
True if this is an instance of PointerType.
Definition: Type.h:213
static UndefValue * get(Type *T)
Static factory methods - Return an 'undef' object of the specified type.
Definition: Constants.cpp:1337
static PointerType * getInt8PtrTy(LLVMContext &C, unsigned AS=0)
Definition: Type.cpp:213
hexagon gen pred
bool dominates(const Instruction *Def, const Use &U) const
Return true if Def dominates a use in User.
Definition: Dominators.cpp:218
Iterator for intrusive lists based on ilist_node.
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:425
const Module * getModule() const
Return the module owning the function this instruction belongs to or nullptr it the function does not...
Definition: Instruction.cpp:58
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:843
Module.h This file contains the declarations for the Module class.
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:230
Instruction * user_back()
Specialize the methods defined in Value, as we know that an instruction can only be used by other ins...
Definition: Instruction.h:59
static PHINode * Create(Type *Ty, unsigned NumReservedValues, const Twine &NameStr="", Instruction *InsertBefore=nullptr)
Constructors - NumReservedValues is a hint for the number of incoming edges that this phi node will h...
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
Definition: BitVector.h:586
iterator_range< user_iterator > users()
Definition: Value.h:370
static void clear(coro::Shape &Shape)
Definition: Coroutines.cpp:191
const DataLayout & getDataLayout() const
Get the data layout for the module's target platform.
Definition: Module.cpp:384
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:119
#define I(x, y, z)
Definition: MD5.cpp:54
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:135
iterator find(const KeyT &Val)
Definition: DenseMap.h:127
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:287
static bool promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info, LargeBlockInfo &LBI, AliasSetTracker *AST)
Many allocas are only used within a single basic block.
static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, LargeBlockInfo &LBI, DominatorTree &DT, AliasSetTracker *AST)
Rewrite as many loads as possible given a single store.
Determine the iterated dominance frontier, given a set of defining blocks, and optionally, a set of live-in blocks.
bool use_empty() const
Definition: Value.h:299
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
user_iterator user_begin()
Definition: Value.h:346
const BasicBlock & front() const
Definition: Function.h:542
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:537
LLVM Value Representation.
Definition: Value.h:71
static const Function * getParent(const Value *V)
Value * SimplifyInstruction(Instruction *I, const DataLayout &DL, const TargetLibraryInfo *TLI=nullptr, const DominatorTree *DT=nullptr, AssumptionCache *AC=nullptr)
See if we can compute a simplified version of this instruction.
This represents the llvm.dbg.declare instruction.
Definition: IntrinsicInst.h:89
static GCRegistry::Add< ErlangGC > A("erlang","erlang-compatible garbage collector")
const uint64_t Version
Definition: InstrProf.h:799
Function object to check whether the first component of a std::pair compares less than the first comp...
Definition: STLExtras.h:590
const BasicBlock * getParent() const
Definition: Instruction.h:62
void deleteValue(Value *PtrVal)
This method is used to remove a pointer value from the AliasSetTracker entirely.
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:44
bool isVoidTy() const
Return true if this is 'void'.
Definition: Type.h:139
an instruction to allocate memory on the stack
Definition: Instructions.h:60
user_iterator user_end()
Definition: Value.h:354