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1 //===-- Value.cpp - Implement the Value class -----------------------------===//
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 implements the Value, ValueHandle, and User classes.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/IR/Value.h"
15 #include "LLVMContextImpl.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/IR/Constant.h"
19 #include "llvm/IR/Constants.h"
20 #include "llvm/IR/DerivedTypes.h"
21 #include "llvm/IR/InstrTypes.h"
22 #include "llvm/IR/Instructions.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/IR/Operator.h"
25 #include "llvm/IR/ValueSymbolTable.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Support/GetElementPtrTypeIterator.h"
29 #include "llvm/Support/LeakDetector.h"
30 #include "llvm/Support/ManagedStatic.h"
31 #include "llvm/Support/ValueHandle.h"
32 #include <algorithm>
33 using namespace llvm;
34 
35 //===----------------------------------------------------------------------===//
36 //                                Value Class
37 //===----------------------------------------------------------------------===//
38 
checkType(Type * Ty)39 static inline Type *checkType(Type *Ty) {
40   assert(Ty && "Value defined with a null type: Error!");
41   return const_cast<Type*>(Ty);
42 }
43 
Value(Type * ty,unsigned scid)44 Value::Value(Type *ty, unsigned scid)
45   : SubclassID(scid), HasValueHandle(0),
46     SubclassOptionalData(0), SubclassData(0), VTy((Type*)checkType(ty)),
47     UseList(0), Name(0) {
48   // FIXME: Why isn't this in the subclass gunk??
49   // Note, we cannot call isa<CallInst> before the CallInst has been
50   // constructed.
51   if (SubclassID == Instruction::Call || SubclassID == Instruction::Invoke)
52     assert((VTy->isFirstClassType() || VTy->isVoidTy() || VTy->isStructTy()) &&
53            "invalid CallInst type!");
54   else if (SubclassID != BasicBlockVal &&
55            (SubclassID < ConstantFirstVal || SubclassID > ConstantLastVal))
56     assert((VTy->isFirstClassType() || VTy->isVoidTy()) &&
57            "Cannot create non-first-class values except for constants!");
58 }
59 
~Value()60 Value::~Value() {
61   // Notify all ValueHandles (if present) that this value is going away.
62   if (HasValueHandle)
63     ValueHandleBase::ValueIsDeleted(this);
64 
65 #ifndef NDEBUG      // Only in -g mode...
66   // Check to make sure that there are no uses of this value that are still
67   // around when the value is destroyed.  If there are, then we have a dangling
68   // reference and something is wrong.  This code is here to print out what is
69   // still being referenced.  The value in question should be printed as
70   // a <badref>
71   //
72   if (!use_empty()) {
73     dbgs() << "While deleting: " << *VTy << " %" << getName() << "\n";
74     for (use_iterator I = use_begin(), E = use_end(); I != E; ++I)
75       dbgs() << "Use still stuck around after Def is destroyed:"
76            << **I << "\n";
77   }
78 #endif
79   assert(use_empty() && "Uses remain when a value is destroyed!");
80 
81   // If this value is named, destroy the name.  This should not be in a symtab
82   // at this point.
83   if (Name && SubclassID != MDStringVal)
84     Name->Destroy();
85 
86   // There should be no uses of this object anymore, remove it.
87   LeakDetector::removeGarbageObject(this);
88 }
89 
90 /// hasNUses - Return true if this Value has exactly N users.
91 ///
hasNUses(unsigned N) const92 bool Value::hasNUses(unsigned N) const {
93   const_use_iterator UI = use_begin(), E = use_end();
94 
95   for (; N; --N, ++UI)
96     if (UI == E) return false;  // Too few.
97   return UI == E;
98 }
99 
100 /// hasNUsesOrMore - Return true if this value has N users or more.  This is
101 /// logically equivalent to getNumUses() >= N.
102 ///
hasNUsesOrMore(unsigned N) const103 bool Value::hasNUsesOrMore(unsigned N) const {
104   const_use_iterator UI = use_begin(), E = use_end();
105 
106   for (; N; --N, ++UI)
107     if (UI == E) return false;  // Too few.
108 
109   return true;
110 }
111 
112 /// isUsedInBasicBlock - Return true if this value is used in the specified
113 /// basic block.
isUsedInBasicBlock(const BasicBlock * BB) const114 bool Value::isUsedInBasicBlock(const BasicBlock *BB) const {
115   // Start by scanning over the instructions looking for a use before we start
116   // the expensive use iteration.
117   unsigned MaxBlockSize = 3;
118   for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
119     if (std::find(I->op_begin(), I->op_end(), this) != I->op_end())
120       return true;
121     if (MaxBlockSize-- == 0) // If the block is larger fall back to use_iterator
122       break;
123   }
124 
125   if (MaxBlockSize != 0) // We scanned the entire block and found no use.
126     return false;
127 
128   for (const_use_iterator I = use_begin(), E = use_end(); I != E; ++I) {
129     const Instruction *User = dyn_cast<Instruction>(*I);
130     if (User && User->getParent() == BB)
131       return true;
132   }
133   return false;
134 }
135 
136 
137 /// getNumUses - This method computes the number of uses of this Value.  This
138 /// is a linear time operation.  Use hasOneUse or hasNUses to check for specific
139 /// values.
getNumUses() const140 unsigned Value::getNumUses() const {
141   return (unsigned)std::distance(use_begin(), use_end());
142 }
143 
getSymTab(Value * V,ValueSymbolTable * & ST)144 static bool getSymTab(Value *V, ValueSymbolTable *&ST) {
145   ST = 0;
146   if (Instruction *I = dyn_cast<Instruction>(V)) {
147     if (BasicBlock *P = I->getParent())
148       if (Function *PP = P->getParent())
149         ST = &PP->getValueSymbolTable();
150   } else if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
151     if (Function *P = BB->getParent())
152       ST = &P->getValueSymbolTable();
153   } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
154     if (Module *P = GV->getParent())
155       ST = &P->getValueSymbolTable();
156   } else if (Argument *A = dyn_cast<Argument>(V)) {
157     if (Function *P = A->getParent())
158       ST = &P->getValueSymbolTable();
159   } else if (isa<MDString>(V))
160     return true;
161   else {
162     assert(isa<Constant>(V) && "Unknown value type!");
163     return true;  // no name is setable for this.
164   }
165   return false;
166 }
167 
getName() const168 StringRef Value::getName() const {
169   // Make sure the empty string is still a C string. For historical reasons,
170   // some clients want to call .data() on the result and expect it to be null
171   // terminated.
172   if (!Name) return StringRef("", 0);
173   return Name->getKey();
174 }
175 
setName(const Twine & NewName)176 void Value::setName(const Twine &NewName) {
177   assert(SubclassID != MDStringVal &&
178          "Cannot set the name of MDString with this method!");
179 
180   // Fast path for common IRBuilder case of setName("") when there is no name.
181   if (NewName.isTriviallyEmpty() && !hasName())
182     return;
183 
184   SmallString<256> NameData;
185   StringRef NameRef = NewName.toStringRef(NameData);
186 
187   // Name isn't changing?
188   if (getName() == NameRef)
189     return;
190 
191   assert(!getType()->isVoidTy() && "Cannot assign a name to void values!");
192 
193   // Get the symbol table to update for this object.
194   ValueSymbolTable *ST;
195   if (getSymTab(this, ST))
196     return;  // Cannot set a name on this value (e.g. constant).
197 
198   if (Function *F = dyn_cast<Function>(this))
199     getContext().pImpl->IntrinsicIDCache.erase(F);
200 
201   if (!ST) { // No symbol table to update?  Just do the change.
202     if (NameRef.empty()) {
203       // Free the name for this value.
204       Name->Destroy();
205       Name = 0;
206       return;
207     }
208 
209     if (Name)
210       Name->Destroy();
211 
212     // NOTE: Could optimize for the case the name is shrinking to not deallocate
213     // then reallocated.
214 
215     // Create the new name.
216     Name = ValueName::Create(NameRef.begin(), NameRef.end());
217     Name->setValue(this);
218     return;
219   }
220 
221   // NOTE: Could optimize for the case the name is shrinking to not deallocate
222   // then reallocated.
223   if (hasName()) {
224     // Remove old name.
225     ST->removeValueName(Name);
226     Name->Destroy();
227     Name = 0;
228 
229     if (NameRef.empty())
230       return;
231   }
232 
233   // Name is changing to something new.
234   Name = ST->createValueName(NameRef, this);
235 }
236 
237 
238 /// takeName - transfer the name from V to this value, setting V's name to
239 /// empty.  It is an error to call V->takeName(V).
takeName(Value * V)240 void Value::takeName(Value *V) {
241   assert(SubclassID != MDStringVal && "Cannot take the name of an MDString!");
242 
243   ValueSymbolTable *ST = 0;
244   // If this value has a name, drop it.
245   if (hasName()) {
246     // Get the symtab this is in.
247     if (getSymTab(this, ST)) {
248       // We can't set a name on this value, but we need to clear V's name if
249       // it has one.
250       if (V->hasName()) V->setName("");
251       return;  // Cannot set a name on this value (e.g. constant).
252     }
253 
254     // Remove old name.
255     if (ST)
256       ST->removeValueName(Name);
257     Name->Destroy();
258     Name = 0;
259   }
260 
261   // Now we know that this has no name.
262 
263   // If V has no name either, we're done.
264   if (!V->hasName()) return;
265 
266   // Get this's symtab if we didn't before.
267   if (!ST) {
268     if (getSymTab(this, ST)) {
269       // Clear V's name.
270       V->setName("");
271       return;  // Cannot set a name on this value (e.g. constant).
272     }
273   }
274 
275   // Get V's ST, this should always succed, because V has a name.
276   ValueSymbolTable *VST;
277   bool Failure = getSymTab(V, VST);
278   assert(!Failure && "V has a name, so it should have a ST!"); (void)Failure;
279 
280   // If these values are both in the same symtab, we can do this very fast.
281   // This works even if both values have no symtab yet.
282   if (ST == VST) {
283     // Take the name!
284     Name = V->Name;
285     V->Name = 0;
286     Name->setValue(this);
287     return;
288   }
289 
290   // Otherwise, things are slightly more complex.  Remove V's name from VST and
291   // then reinsert it into ST.
292 
293   if (VST)
294     VST->removeValueName(V->Name);
295   Name = V->Name;
296   V->Name = 0;
297   Name->setValue(this);
298 
299   if (ST)
300     ST->reinsertValue(this);
301 }
302 
303 
replaceAllUsesWith(Value * New)304 void Value::replaceAllUsesWith(Value *New) {
305   assert(New && "Value::replaceAllUsesWith(<null>) is invalid!");
306   assert(New != this && "this->replaceAllUsesWith(this) is NOT valid!");
307   assert(New->getType() == getType() &&
308          "replaceAllUses of value with new value of different type!");
309 
310   // Notify all ValueHandles (if present) that this value is going away.
311   if (HasValueHandle)
312     ValueHandleBase::ValueIsRAUWd(this, New);
313 
314   while (!use_empty()) {
315     Use &U = *UseList;
316     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
317     // constant because they are uniqued.
318     if (Constant *C = dyn_cast<Constant>(U.getUser())) {
319       if (!isa<GlobalValue>(C)) {
320         C->replaceUsesOfWithOnConstant(this, New, &U);
321         continue;
322       }
323     }
324 
325     U.set(New);
326   }
327 
328   if (BasicBlock *BB = dyn_cast<BasicBlock>(this))
329     BB->replaceSuccessorsPhiUsesWith(cast<BasicBlock>(New));
330 }
331 
332 namespace {
333 // Various metrics for how much to strip off of pointers.
334 enum PointerStripKind {
335   PSK_ZeroIndices,
336   PSK_InBoundsConstantIndices,
337   PSK_InBounds
338 };
339 
340 template <PointerStripKind StripKind>
stripPointerCastsAndOffsets(Value * V)341 static Value *stripPointerCastsAndOffsets(Value *V) {
342   if (!V->getType()->isPointerTy())
343     return V;
344 
345   // Even though we don't look through PHI nodes, we could be called on an
346   // instruction in an unreachable block, which may be on a cycle.
347   SmallPtrSet<Value *, 4> Visited;
348 
349   Visited.insert(V);
350   do {
351     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
352       switch (StripKind) {
353       case PSK_ZeroIndices:
354         if (!GEP->hasAllZeroIndices())
355           return V;
356         break;
357       case PSK_InBoundsConstantIndices:
358         if (!GEP->hasAllConstantIndices())
359           return V;
360         // fallthrough
361       case PSK_InBounds:
362         if (!GEP->isInBounds())
363           return V;
364         break;
365       }
366       V = GEP->getPointerOperand();
367     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
368       V = cast<Operator>(V)->getOperand(0);
369     } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
370       if (GA->mayBeOverridden())
371         return V;
372       V = GA->getAliasee();
373     } else {
374       return V;
375     }
376     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
377   } while (Visited.insert(V));
378 
379   return V;
380 }
381 } // namespace
382 
stripPointerCasts()383 Value *Value::stripPointerCasts() {
384   return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
385 }
386 
stripInBoundsConstantOffsets()387 Value *Value::stripInBoundsConstantOffsets() {
388   return stripPointerCastsAndOffsets<PSK_InBoundsConstantIndices>(this);
389 }
390 
stripInBoundsOffsets()391 Value *Value::stripInBoundsOffsets() {
392   return stripPointerCastsAndOffsets<PSK_InBounds>(this);
393 }
394 
395 /// isDereferenceablePointer - Test if this value is always a pointer to
396 /// allocated and suitably aligned memory for a simple load or store.
isDereferenceablePointer(const Value * V,SmallPtrSet<const Value *,32> & Visited)397 static bool isDereferenceablePointer(const Value *V,
398                                      SmallPtrSet<const Value *, 32> &Visited) {
399   // Note that it is not safe to speculate into a malloc'd region because
400   // malloc may return null.
401   // It's also not always safe to follow a bitcast, for example:
402   //   bitcast i8* (alloca i8) to i32*
403   // would result in a 4-byte load from a 1-byte alloca. Some cases could
404   // be handled using DataLayout to check sizes and alignments though.
405 
406   // These are obviously ok.
407   if (isa<AllocaInst>(V)) return true;
408 
409   // Global variables which can't collapse to null are ok.
410   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
411     return !GV->hasExternalWeakLinkage();
412 
413   // byval arguments are ok.
414   if (const Argument *A = dyn_cast<Argument>(V))
415     return A->hasByValAttr();
416 
417   // For GEPs, determine if the indexing lands within the allocated object.
418   if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
419     // Conservatively require that the base pointer be fully dereferenceable.
420     if (!Visited.insert(GEP->getOperand(0)))
421       return false;
422     if (!isDereferenceablePointer(GEP->getOperand(0), Visited))
423       return false;
424     // Check the indices.
425     gep_type_iterator GTI = gep_type_begin(GEP);
426     for (User::const_op_iterator I = GEP->op_begin()+1,
427          E = GEP->op_end(); I != E; ++I) {
428       Value *Index = *I;
429       Type *Ty = *GTI++;
430       // Struct indices can't be out of bounds.
431       if (isa<StructType>(Ty))
432         continue;
433       ConstantInt *CI = dyn_cast<ConstantInt>(Index);
434       if (!CI)
435         return false;
436       // Zero is always ok.
437       if (CI->isZero())
438         continue;
439       // Check to see that it's within the bounds of an array.
440       ArrayType *ATy = dyn_cast<ArrayType>(Ty);
441       if (!ATy)
442         return false;
443       if (CI->getValue().getActiveBits() > 64)
444         return false;
445       if (CI->getZExtValue() >= ATy->getNumElements())
446         return false;
447     }
448     // Indices check out; this is dereferenceable.
449     return true;
450   }
451 
452   // If we don't know, assume the worst.
453   return false;
454 }
455 
456 /// isDereferenceablePointer - Test if this value is always a pointer to
457 /// allocated and suitably aligned memory for a simple load or store.
isDereferenceablePointer() const458 bool Value::isDereferenceablePointer() const {
459   SmallPtrSet<const Value *, 32> Visited;
460   return ::isDereferenceablePointer(this, Visited);
461 }
462 
463 /// DoPHITranslation - If this value is a PHI node with CurBB as its parent,
464 /// return the value in the PHI node corresponding to PredBB.  If not, return
465 /// ourself.  This is useful if you want to know the value something has in a
466 /// predecessor block.
DoPHITranslation(const BasicBlock * CurBB,const BasicBlock * PredBB)467 Value *Value::DoPHITranslation(const BasicBlock *CurBB,
468                                const BasicBlock *PredBB) {
469   PHINode *PN = dyn_cast<PHINode>(this);
470   if (PN && PN->getParent() == CurBB)
471     return PN->getIncomingValueForBlock(PredBB);
472   return this;
473 }
474 
getContext() const475 LLVMContext &Value::getContext() const { return VTy->getContext(); }
476 
477 //===----------------------------------------------------------------------===//
478 //                             ValueHandleBase Class
479 //===----------------------------------------------------------------------===//
480 
481 /// AddToExistingUseList - Add this ValueHandle to the use list for VP, where
482 /// List is known to point into the existing use list.
AddToExistingUseList(ValueHandleBase ** List)483 void ValueHandleBase::AddToExistingUseList(ValueHandleBase **List) {
484   assert(List && "Handle list is null?");
485 
486   // Splice ourselves into the list.
487   Next = *List;
488   *List = this;
489   setPrevPtr(List);
490   if (Next) {
491     Next->setPrevPtr(&Next);
492     assert(VP.getPointer() == Next->VP.getPointer() && "Added to wrong list?");
493   }
494 }
495 
AddToExistingUseListAfter(ValueHandleBase * List)496 void ValueHandleBase::AddToExistingUseListAfter(ValueHandleBase *List) {
497   assert(List && "Must insert after existing node");
498 
499   Next = List->Next;
500   setPrevPtr(&List->Next);
501   List->Next = this;
502   if (Next)
503     Next->setPrevPtr(&Next);
504 }
505 
506 /// AddToUseList - Add this ValueHandle to the use list for VP.
AddToUseList()507 void ValueHandleBase::AddToUseList() {
508   assert(VP.getPointer() && "Null pointer doesn't have a use list!");
509 
510   LLVMContextImpl *pImpl = VP.getPointer()->getContext().pImpl;
511 
512   if (VP.getPointer()->HasValueHandle) {
513     // If this value already has a ValueHandle, then it must be in the
514     // ValueHandles map already.
515     ValueHandleBase *&Entry = pImpl->ValueHandles[VP.getPointer()];
516     assert(Entry != 0 && "Value doesn't have any handles?");
517     AddToExistingUseList(&Entry);
518     return;
519   }
520 
521   // Ok, it doesn't have any handles yet, so we must insert it into the
522   // DenseMap.  However, doing this insertion could cause the DenseMap to
523   // reallocate itself, which would invalidate all of the PrevP pointers that
524   // point into the old table.  Handle this by checking for reallocation and
525   // updating the stale pointers only if needed.
526   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
527   const void *OldBucketPtr = Handles.getPointerIntoBucketsArray();
528 
529   ValueHandleBase *&Entry = Handles[VP.getPointer()];
530   assert(Entry == 0 && "Value really did already have handles?");
531   AddToExistingUseList(&Entry);
532   VP.getPointer()->HasValueHandle = true;
533 
534   // If reallocation didn't happen or if this was the first insertion, don't
535   // walk the table.
536   if (Handles.isPointerIntoBucketsArray(OldBucketPtr) ||
537       Handles.size() == 1) {
538     return;
539   }
540 
541   // Okay, reallocation did happen.  Fix the Prev Pointers.
542   for (DenseMap<Value*, ValueHandleBase*>::iterator I = Handles.begin(),
543        E = Handles.end(); I != E; ++I) {
544     assert(I->second && I->first == I->second->VP.getPointer() &&
545            "List invariant broken!");
546     I->second->setPrevPtr(&I->second);
547   }
548 }
549 
550 /// RemoveFromUseList - Remove this ValueHandle from its current use list.
RemoveFromUseList()551 void ValueHandleBase::RemoveFromUseList() {
552   assert(VP.getPointer() && VP.getPointer()->HasValueHandle &&
553          "Pointer doesn't have a use list!");
554 
555   // Unlink this from its use list.
556   ValueHandleBase **PrevPtr = getPrevPtr();
557   assert(*PrevPtr == this && "List invariant broken");
558 
559   *PrevPtr = Next;
560   if (Next) {
561     assert(Next->getPrevPtr() == &Next && "List invariant broken");
562     Next->setPrevPtr(PrevPtr);
563     return;
564   }
565 
566   // If the Next pointer was null, then it is possible that this was the last
567   // ValueHandle watching VP.  If so, delete its entry from the ValueHandles
568   // map.
569   LLVMContextImpl *pImpl = VP.getPointer()->getContext().pImpl;
570   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
571   if (Handles.isPointerIntoBucketsArray(PrevPtr)) {
572     Handles.erase(VP.getPointer());
573     VP.getPointer()->HasValueHandle = false;
574   }
575 }
576 
577 
ValueIsDeleted(Value * V)578 void ValueHandleBase::ValueIsDeleted(Value *V) {
579   assert(V->HasValueHandle && "Should only be called if ValueHandles present");
580 
581   // Get the linked list base, which is guaranteed to exist since the
582   // HasValueHandle flag is set.
583   LLVMContextImpl *pImpl = V->getContext().pImpl;
584   ValueHandleBase *Entry = pImpl->ValueHandles[V];
585   assert(Entry && "Value bit set but no entries exist");
586 
587   // We use a local ValueHandleBase as an iterator so that ValueHandles can add
588   // and remove themselves from the list without breaking our iteration.  This
589   // is not really an AssertingVH; we just have to give ValueHandleBase a kind.
590   // Note that we deliberately do not the support the case when dropping a value
591   // handle results in a new value handle being permanently added to the list
592   // (as might occur in theory for CallbackVH's): the new value handle will not
593   // be processed and the checking code will mete out righteous punishment if
594   // the handle is still present once we have finished processing all the other
595   // value handles (it is fine to momentarily add then remove a value handle).
596   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
597     Iterator.RemoveFromUseList();
598     Iterator.AddToExistingUseListAfter(Entry);
599     assert(Entry->Next == &Iterator && "Loop invariant broken.");
600 
601     switch (Entry->getKind()) {
602     case Assert:
603       break;
604     case Tracking:
605       // Mark that this value has been deleted by setting it to an invalid Value
606       // pointer.
607       Entry->operator=(DenseMapInfo<Value *>::getTombstoneKey());
608       break;
609     case Weak:
610       // Weak just goes to null, which will unlink it from the list.
611       Entry->operator=(0);
612       break;
613     case Callback:
614       // Forward to the subclass's implementation.
615       static_cast<CallbackVH*>(Entry)->deleted();
616       break;
617     }
618   }
619 
620   // All callbacks, weak references, and assertingVHs should be dropped by now.
621   if (V->HasValueHandle) {
622 #ifndef NDEBUG      // Only in +Asserts mode...
623     dbgs() << "While deleting: " << *V->getType() << " %" << V->getName()
624            << "\n";
625     if (pImpl->ValueHandles[V]->getKind() == Assert)
626       llvm_unreachable("An asserting value handle still pointed to this"
627                        " value!");
628 
629 #endif
630     llvm_unreachable("All references to V were not removed?");
631   }
632 }
633 
634 
ValueIsRAUWd(Value * Old,Value * New)635 void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
636   assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");
637   assert(Old != New && "Changing value into itself!");
638 
639   // Get the linked list base, which is guaranteed to exist since the
640   // HasValueHandle flag is set.
641   LLVMContextImpl *pImpl = Old->getContext().pImpl;
642   ValueHandleBase *Entry = pImpl->ValueHandles[Old];
643 
644   assert(Entry && "Value bit set but no entries exist");
645 
646   // We use a local ValueHandleBase as an iterator so that
647   // ValueHandles can add and remove themselves from the list without
648   // breaking our iteration.  This is not really an AssertingVH; we
649   // just have to give ValueHandleBase some kind.
650   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
651     Iterator.RemoveFromUseList();
652     Iterator.AddToExistingUseListAfter(Entry);
653     assert(Entry->Next == &Iterator && "Loop invariant broken.");
654 
655     switch (Entry->getKind()) {
656     case Assert:
657       // Asserting handle does not follow RAUW implicitly.
658       break;
659     case Tracking:
660       // Tracking goes to new value like a WeakVH. Note that this may make it
661       // something incompatible with its templated type. We don't want to have a
662       // virtual (or inline) interface to handle this though, so instead we make
663       // the TrackingVH accessors guarantee that a client never sees this value.
664 
665       // FALLTHROUGH
666     case Weak:
667       // Weak goes to the new value, which will unlink it from Old's list.
668       Entry->operator=(New);
669       break;
670     case Callback:
671       // Forward to the subclass's implementation.
672       static_cast<CallbackVH*>(Entry)->allUsesReplacedWith(New);
673       break;
674     }
675   }
676 
677 #ifndef NDEBUG
678   // If any new tracking or weak value handles were added while processing the
679   // list, then complain about it now.
680   if (Old->HasValueHandle)
681     for (Entry = pImpl->ValueHandles[Old]; Entry; Entry = Entry->Next)
682       switch (Entry->getKind()) {
683       case Tracking:
684       case Weak:
685         dbgs() << "After RAUW from " << *Old->getType() << " %"
686                << Old->getName() << " to " << *New->getType() << " %"
687                << New->getName() << "\n";
688         llvm_unreachable("A tracking or weak value handle still pointed to the"
689                          " old value!\n");
690       default:
691         break;
692       }
693 #endif
694 }
695 
696 // Default implementation for CallbackVH.
allUsesReplacedWith(Value *)697 void CallbackVH::allUsesReplacedWith(Value *) {}
698 
deleted()699 void CallbackVH::deleted() {
700   setValPtr(NULL);
701 }
702