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+//===-- Value.cpp - Implement the Value class -----------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Value, ValueHandle, and User classes.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/Value.h"
+#include "LLVMContextImpl.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/IR/ValueSymbolTable.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Support/LeakDetector.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/ValueHandle.h"
+#include <algorithm>
+using namespace llvm;
+
+//===----------------------------------------------------------------------===//
+// Value Class
+//===----------------------------------------------------------------------===//
+
+static inline Type *checkType(Type *Ty) {
+ assert(Ty && "Value defined with a null type: Error!");
+ return const_cast<Type*>(Ty);
+}
+
+Value::Value(Type *ty, unsigned scid)
+ : SubclassID(scid), HasValueHandle(0),
+ SubclassOptionalData(0), SubclassData(0), VTy((Type*)checkType(ty)),
+ UseList(0), Name(0) {
+ // FIXME: Why isn't this in the subclass gunk??
+ // Note, we cannot call isa<CallInst> before the CallInst has been
+ // constructed.
+ if (SubclassID == Instruction::Call || SubclassID == Instruction::Invoke)
+ assert((VTy->isFirstClassType() || VTy->isVoidTy() || VTy->isStructTy()) &&
+ "invalid CallInst type!");
+ else if (SubclassID != BasicBlockVal &&
+ (SubclassID < ConstantFirstVal || SubclassID > ConstantLastVal))
+ assert((VTy->isFirstClassType() || VTy->isVoidTy()) &&
+ "Cannot create non-first-class values except for constants!");
+}
+
+Value::~Value() {
+ // Notify all ValueHandles (if present) that this value is going away.
+ if (HasValueHandle)
+ ValueHandleBase::ValueIsDeleted(this);
+
+#ifndef NDEBUG // Only in -g mode...
+ // Check to make sure that there are no uses of this value that are still
+ // around when the value is destroyed. If there are, then we have a dangling
+ // reference and something is wrong. This code is here to print out what is
+ // still being referenced. The value in question should be printed as
+ // a <badref>
+ //
+ if (!use_empty()) {
+ dbgs() << "While deleting: " << *VTy << " %" << getName() << "\n";
+ for (use_iterator I = use_begin(), E = use_end(); I != E; ++I)
+ dbgs() << "Use still stuck around after Def is destroyed:"
+ << **I << "\n";
+ }
+#endif
+ assert(use_empty() && "Uses remain when a value is destroyed!");
+
+ // If this value is named, destroy the name. This should not be in a symtab
+ // at this point.
+ if (Name && SubclassID != MDStringVal)
+ Name->Destroy();
+
+ // There should be no uses of this object anymore, remove it.
+ LeakDetector::removeGarbageObject(this);
+}
+
+/// hasNUses - Return true if this Value has exactly N users.
+///
+bool Value::hasNUses(unsigned N) const {
+ const_use_iterator UI = use_begin(), E = use_end();
+
+ for (; N; --N, ++UI)
+ if (UI == E) return false; // Too few.
+ return UI == E;
+}
+
+/// hasNUsesOrMore - Return true if this value has N users or more. This is
+/// logically equivalent to getNumUses() >= N.
+///
+bool Value::hasNUsesOrMore(unsigned N) const {
+ const_use_iterator UI = use_begin(), E = use_end();
+
+ for (; N; --N, ++UI)
+ if (UI == E) return false; // Too few.
+
+ return true;
+}
+
+/// isUsedInBasicBlock - Return true if this value is used in the specified
+/// basic block.
+bool Value::isUsedInBasicBlock(const BasicBlock *BB) const {
+ // Start by scanning over the instructions looking for a use before we start
+ // the expensive use iteration.
+ unsigned MaxBlockSize = 3;
+ for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+ if (std::find(I->op_begin(), I->op_end(), this) != I->op_end())
+ return true;
+ if (MaxBlockSize-- == 0) // If the block is larger fall back to use_iterator
+ break;
+ }
+
+ if (MaxBlockSize != 0) // We scanned the entire block and found no use.
+ return false;
+
+ for (const_use_iterator I = use_begin(), E = use_end(); I != E; ++I) {
+ const Instruction *User = dyn_cast<Instruction>(*I);
+ if (User && User->getParent() == BB)
+ return true;
+ }
+ return false;
+}
+
+
+/// getNumUses - This method computes the number of uses of this Value. This
+/// is a linear time operation. Use hasOneUse or hasNUses to check for specific
+/// values.
+unsigned Value::getNumUses() const {
+ return (unsigned)std::distance(use_begin(), use_end());
+}
+
+static bool getSymTab(Value *V, ValueSymbolTable *&ST) {
+ ST = 0;
+ if (Instruction *I = dyn_cast<Instruction>(V)) {
+ if (BasicBlock *P = I->getParent())
+ if (Function *PP = P->getParent())
+ ST = &PP->getValueSymbolTable();
+ } else if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
+ if (Function *P = BB->getParent())
+ ST = &P->getValueSymbolTable();
+ } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
+ if (Module *P = GV->getParent())
+ ST = &P->getValueSymbolTable();
+ } else if (Argument *A = dyn_cast<Argument>(V)) {
+ if (Function *P = A->getParent())
+ ST = &P->getValueSymbolTable();
+ } else if (isa<MDString>(V))
+ return true;
+ else {
+ assert(isa<Constant>(V) && "Unknown value type!");
+ return true; // no name is setable for this.
+ }
+ return false;
+}
+
+StringRef Value::getName() const {
+ // Make sure the empty string is still a C string. For historical reasons,
+ // some clients want to call .data() on the result and expect it to be null
+ // terminated.
+ if (!Name) return StringRef("", 0);
+ return Name->getKey();
+}
+
+void Value::setName(const Twine &NewName) {
+ assert(SubclassID != MDStringVal &&
+ "Cannot set the name of MDString with this method!");
+
+ // Fast path for common IRBuilder case of setName("") when there is no name.
+ if (NewName.isTriviallyEmpty() && !hasName())
+ return;
+
+ SmallString<256> NameData;
+ StringRef NameRef = NewName.toStringRef(NameData);
+
+ // Name isn't changing?
+ if (getName() == NameRef)
+ return;
+
+ assert(!getType()->isVoidTy() && "Cannot assign a name to void values!");
+
+ // Get the symbol table to update for this object.
+ ValueSymbolTable *ST;
+ if (getSymTab(this, ST))
+ return; // Cannot set a name on this value (e.g. constant).
+
+ if (Function *F = dyn_cast<Function>(this))
+ getContext().pImpl->IntrinsicIDCache.erase(F);
+
+ if (!ST) { // No symbol table to update? Just do the change.
+ if (NameRef.empty()) {
+ // Free the name for this value.
+ Name->Destroy();
+ Name = 0;
+ return;
+ }
+
+ if (Name)
+ Name->Destroy();
+
+ // NOTE: Could optimize for the case the name is shrinking to not deallocate
+ // then reallocated.
+
+ // Create the new name.
+ Name = ValueName::Create(NameRef.begin(), NameRef.end());
+ Name->setValue(this);
+ return;
+ }
+
+ // NOTE: Could optimize for the case the name is shrinking to not deallocate
+ // then reallocated.
+ if (hasName()) {
+ // Remove old name.
+ ST->removeValueName(Name);
+ Name->Destroy();
+ Name = 0;
+
+ if (NameRef.empty())
+ return;
+ }
+
+ // Name is changing to something new.
+ Name = ST->createValueName(NameRef, this);
+}
+
+
+/// takeName - transfer the name from V to this value, setting V's name to
+/// empty. It is an error to call V->takeName(V).
+void Value::takeName(Value *V) {
+ assert(SubclassID != MDStringVal && "Cannot take the name of an MDString!");
+
+ ValueSymbolTable *ST = 0;
+ // If this value has a name, drop it.
+ if (hasName()) {
+ // Get the symtab this is in.
+ if (getSymTab(this, ST)) {
+ // We can't set a name on this value, but we need to clear V's name if
+ // it has one.
+ if (V->hasName()) V->setName("");
+ return; // Cannot set a name on this value (e.g. constant).
+ }
+
+ // Remove old name.
+ if (ST)
+ ST->removeValueName(Name);
+ Name->Destroy();
+ Name = 0;
+ }
+
+ // Now we know that this has no name.
+
+ // If V has no name either, we're done.
+ if (!V->hasName()) return;
+
+ // Get this's symtab if we didn't before.
+ if (!ST) {
+ if (getSymTab(this, ST)) {
+ // Clear V's name.
+ V->setName("");
+ return; // Cannot set a name on this value (e.g. constant).
+ }
+ }
+
+ // Get V's ST, this should always succed, because V has a name.
+ ValueSymbolTable *VST;
+ bool Failure = getSymTab(V, VST);
+ assert(!Failure && "V has a name, so it should have a ST!"); (void)Failure;
+
+ // If these values are both in the same symtab, we can do this very fast.
+ // This works even if both values have no symtab yet.
+ if (ST == VST) {
+ // Take the name!
+ Name = V->Name;
+ V->Name = 0;
+ Name->setValue(this);
+ return;
+ }
+
+ // Otherwise, things are slightly more complex. Remove V's name from VST and
+ // then reinsert it into ST.
+
+ if (VST)
+ VST->removeValueName(V->Name);
+ Name = V->Name;
+ V->Name = 0;
+ Name->setValue(this);
+
+ if (ST)
+ ST->reinsertValue(this);
+}
+
+
+void Value::replaceAllUsesWith(Value *New) {
+ assert(New && "Value::replaceAllUsesWith(<null>) is invalid!");
+ assert(New != this && "this->replaceAllUsesWith(this) is NOT valid!");
+ assert(New->getType() == getType() &&
+ "replaceAllUses of value with new value of different type!");
+
+ // Notify all ValueHandles (if present) that this value is going away.
+ if (HasValueHandle)
+ ValueHandleBase::ValueIsRAUWd(this, New);
+
+ while (!use_empty()) {
+ Use &U = *UseList;
+ // Must handle Constants specially, we cannot call replaceUsesOfWith on a
+ // constant because they are uniqued.
+ if (Constant *C = dyn_cast<Constant>(U.getUser())) {
+ if (!isa<GlobalValue>(C)) {
+ C->replaceUsesOfWithOnConstant(this, New, &U);
+ continue;
+ }
+ }
+
+ U.set(New);
+ }
+
+ if (BasicBlock *BB = dyn_cast<BasicBlock>(this))
+ BB->replaceSuccessorsPhiUsesWith(cast<BasicBlock>(New));
+}
+
+namespace {
+// Various metrics for how much to strip off of pointers.
+enum PointerStripKind {
+ PSK_ZeroIndices,
+ PSK_InBoundsConstantIndices,
+ PSK_InBounds
+};
+
+template <PointerStripKind StripKind>
+static Value *stripPointerCastsAndOffsets(Value *V) {
+ if (!V->getType()->isPointerTy())
+ return V;
+
+ // Even though we don't look through PHI nodes, we could be called on an
+ // instruction in an unreachable block, which may be on a cycle.
+ SmallPtrSet<Value *, 4> Visited;
+
+ Visited.insert(V);
+ do {
+ if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
+ switch (StripKind) {
+ case PSK_ZeroIndices:
+ if (!GEP->hasAllZeroIndices())
+ return V;
+ break;
+ case PSK_InBoundsConstantIndices:
+ if (!GEP->hasAllConstantIndices())
+ return V;
+ // fallthrough
+ case PSK_InBounds:
+ if (!GEP->isInBounds())
+ return V;
+ break;
+ }
+ V = GEP->getPointerOperand();
+ } else if (Operator::getOpcode(V) == Instruction::BitCast) {
+ V = cast<Operator>(V)->getOperand(0);
+ } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
+ if (GA->mayBeOverridden())
+ return V;
+ V = GA->getAliasee();
+ } else {
+ return V;
+ }
+ assert(V->getType()->isPointerTy() && "Unexpected operand type!");
+ } while (Visited.insert(V));
+
+ return V;
+}
+} // namespace
+
+Value *Value::stripPointerCasts() {
+ return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
+}
+
+Value *Value::stripInBoundsConstantOffsets() {
+ return stripPointerCastsAndOffsets<PSK_InBoundsConstantIndices>(this);
+}
+
+Value *Value::stripInBoundsOffsets() {
+ return stripPointerCastsAndOffsets<PSK_InBounds>(this);
+}
+
+/// isDereferenceablePointer - Test if this value is always a pointer to
+/// allocated and suitably aligned memory for a simple load or store.
+static bool isDereferenceablePointer(const Value *V,
+ SmallPtrSet<const Value *, 32> &Visited) {
+ // Note that it is not safe to speculate into a malloc'd region because
+ // malloc may return null.
+ // It's also not always safe to follow a bitcast, for example:
+ // bitcast i8* (alloca i8) to i32*
+ // would result in a 4-byte load from a 1-byte alloca. Some cases could
+ // be handled using DataLayout to check sizes and alignments though.
+
+ // These are obviously ok.
+ if (isa<AllocaInst>(V)) return true;
+
+ // Global variables which can't collapse to null are ok.
+ if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
+ return !GV->hasExternalWeakLinkage();
+
+ // byval arguments are ok.
+ if (const Argument *A = dyn_cast<Argument>(V))
+ return A->hasByValAttr();
+
+ // For GEPs, determine if the indexing lands within the allocated object.
+ if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
+ // Conservatively require that the base pointer be fully dereferenceable.
+ if (!Visited.insert(GEP->getOperand(0)))
+ return false;
+ if (!isDereferenceablePointer(GEP->getOperand(0), Visited))
+ return false;
+ // Check the indices.
+ gep_type_iterator GTI = gep_type_begin(GEP);
+ for (User::const_op_iterator I = GEP->op_begin()+1,
+ E = GEP->op_end(); I != E; ++I) {
+ Value *Index = *I;
+ Type *Ty = *GTI++;
+ // Struct indices can't be out of bounds.
+ if (isa<StructType>(Ty))
+ continue;
+ ConstantInt *CI = dyn_cast<ConstantInt>(Index);
+ if (!CI)
+ return false;
+ // Zero is always ok.
+ if (CI->isZero())
+ continue;
+ // Check to see that it's within the bounds of an array.
+ ArrayType *ATy = dyn_cast<ArrayType>(Ty);
+ if (!ATy)
+ return false;
+ if (CI->getValue().getActiveBits() > 64)
+ return false;
+ if (CI->getZExtValue() >= ATy->getNumElements())
+ return false;
+ }
+ // Indices check out; this is dereferenceable.
+ return true;
+ }
+
+ // If we don't know, assume the worst.
+ return false;
+}
+
+/// isDereferenceablePointer - Test if this value is always a pointer to
+/// allocated and suitably aligned memory for a simple load or store.
+bool Value::isDereferenceablePointer() const {
+ SmallPtrSet<const Value *, 32> Visited;
+ return ::isDereferenceablePointer(this, Visited);
+}
+
+/// DoPHITranslation - If this value is a PHI node with CurBB as its parent,
+/// return the value in the PHI node corresponding to PredBB. If not, return
+/// ourself. This is useful if you want to know the value something has in a
+/// predecessor block.
+Value *Value::DoPHITranslation(const BasicBlock *CurBB,
+ const BasicBlock *PredBB) {
+ PHINode *PN = dyn_cast<PHINode>(this);
+ if (PN && PN->getParent() == CurBB)
+ return PN->getIncomingValueForBlock(PredBB);
+ return this;
+}
+
+LLVMContext &Value::getContext() const { return VTy->getContext(); }
+
+//===----------------------------------------------------------------------===//
+// ValueHandleBase Class
+//===----------------------------------------------------------------------===//
+
+/// AddToExistingUseList - Add this ValueHandle to the use list for VP, where
+/// List is known to point into the existing use list.
+void ValueHandleBase::AddToExistingUseList(ValueHandleBase **List) {
+ assert(List && "Handle list is null?");
+
+ // Splice ourselves into the list.
+ Next = *List;
+ *List = this;
+ setPrevPtr(List);
+ if (Next) {
+ Next->setPrevPtr(&Next);
+ assert(VP.getPointer() == Next->VP.getPointer() && "Added to wrong list?");
+ }
+}
+
+void ValueHandleBase::AddToExistingUseListAfter(ValueHandleBase *List) {
+ assert(List && "Must insert after existing node");
+
+ Next = List->Next;
+ setPrevPtr(&List->Next);
+ List->Next = this;
+ if (Next)
+ Next->setPrevPtr(&Next);
+}
+
+/// AddToUseList - Add this ValueHandle to the use list for VP.
+void ValueHandleBase::AddToUseList() {
+ assert(VP.getPointer() && "Null pointer doesn't have a use list!");
+
+ LLVMContextImpl *pImpl = VP.getPointer()->getContext().pImpl;
+
+ if (VP.getPointer()->HasValueHandle) {
+ // If this value already has a ValueHandle, then it must be in the
+ // ValueHandles map already.
+ ValueHandleBase *&Entry = pImpl->ValueHandles[VP.getPointer()];
+ assert(Entry != 0 && "Value doesn't have any handles?");
+ AddToExistingUseList(&Entry);
+ return;
+ }
+
+ // Ok, it doesn't have any handles yet, so we must insert it into the
+ // DenseMap. However, doing this insertion could cause the DenseMap to
+ // reallocate itself, which would invalidate all of the PrevP pointers that
+ // point into the old table. Handle this by checking for reallocation and
+ // updating the stale pointers only if needed.
+ DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
+ const void *OldBucketPtr = Handles.getPointerIntoBucketsArray();
+
+ ValueHandleBase *&Entry = Handles[VP.getPointer()];
+ assert(Entry == 0 && "Value really did already have handles?");
+ AddToExistingUseList(&Entry);
+ VP.getPointer()->HasValueHandle = true;
+
+ // If reallocation didn't happen or if this was the first insertion, don't
+ // walk the table.
+ if (Handles.isPointerIntoBucketsArray(OldBucketPtr) ||
+ Handles.size() == 1) {
+ return;
+ }
+
+ // Okay, reallocation did happen. Fix the Prev Pointers.
+ for (DenseMap<Value*, ValueHandleBase*>::iterator I = Handles.begin(),
+ E = Handles.end(); I != E; ++I) {
+ assert(I->second && I->first == I->second->VP.getPointer() &&
+ "List invariant broken!");
+ I->second->setPrevPtr(&I->second);
+ }
+}
+
+/// RemoveFromUseList - Remove this ValueHandle from its current use list.
+void ValueHandleBase::RemoveFromUseList() {
+ assert(VP.getPointer() && VP.getPointer()->HasValueHandle &&
+ "Pointer doesn't have a use list!");
+
+ // Unlink this from its use list.
+ ValueHandleBase **PrevPtr = getPrevPtr();
+ assert(*PrevPtr == this && "List invariant broken");
+
+ *PrevPtr = Next;
+ if (Next) {
+ assert(Next->getPrevPtr() == &Next && "List invariant broken");
+ Next->setPrevPtr(PrevPtr);
+ return;
+ }
+
+ // If the Next pointer was null, then it is possible that this was the last
+ // ValueHandle watching VP. If so, delete its entry from the ValueHandles
+ // map.
+ LLVMContextImpl *pImpl = VP.getPointer()->getContext().pImpl;
+ DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
+ if (Handles.isPointerIntoBucketsArray(PrevPtr)) {
+ Handles.erase(VP.getPointer());
+ VP.getPointer()->HasValueHandle = false;
+ }
+}
+
+
+void ValueHandleBase::ValueIsDeleted(Value *V) {
+ assert(V->HasValueHandle && "Should only be called if ValueHandles present");
+
+ // Get the linked list base, which is guaranteed to exist since the
+ // HasValueHandle flag is set.
+ LLVMContextImpl *pImpl = V->getContext().pImpl;
+ ValueHandleBase *Entry = pImpl->ValueHandles[V];
+ assert(Entry && "Value bit set but no entries exist");
+
+ // We use a local ValueHandleBase as an iterator so that ValueHandles can add
+ // and remove themselves from the list without breaking our iteration. This
+ // is not really an AssertingVH; we just have to give ValueHandleBase a kind.
+ // Note that we deliberately do not the support the case when dropping a value
+ // handle results in a new value handle being permanently added to the list
+ // (as might occur in theory for CallbackVH's): the new value handle will not
+ // be processed and the checking code will mete out righteous punishment if
+ // the handle is still present once we have finished processing all the other
+ // value handles (it is fine to momentarily add then remove a value handle).
+ for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
+ Iterator.RemoveFromUseList();
+ Iterator.AddToExistingUseListAfter(Entry);
+ assert(Entry->Next == &Iterator && "Loop invariant broken.");
+
+ switch (Entry->getKind()) {
+ case Assert:
+ break;
+ case Tracking:
+ // Mark that this value has been deleted by setting it to an invalid Value
+ // pointer.
+ Entry->operator=(DenseMapInfo<Value *>::getTombstoneKey());
+ break;
+ case Weak:
+ // Weak just goes to null, which will unlink it from the list.
+ Entry->operator=(0);
+ break;
+ case Callback:
+ // Forward to the subclass's implementation.
+ static_cast<CallbackVH*>(Entry)->deleted();
+ break;
+ }
+ }
+
+ // All callbacks, weak references, and assertingVHs should be dropped by now.
+ if (V->HasValueHandle) {
+#ifndef NDEBUG // Only in +Asserts mode...
+ dbgs() << "While deleting: " << *V->getType() << " %" << V->getName()
+ << "\n";
+ if (pImpl->ValueHandles[V]->getKind() == Assert)
+ llvm_unreachable("An asserting value handle still pointed to this"
+ " value!");
+
+#endif
+ llvm_unreachable("All references to V were not removed?");
+ }
+}
+
+
+void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
+ assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");
+ assert(Old != New && "Changing value into itself!");
+
+ // Get the linked list base, which is guaranteed to exist since the
+ // HasValueHandle flag is set.
+ LLVMContextImpl *pImpl = Old->getContext().pImpl;
+ ValueHandleBase *Entry = pImpl->ValueHandles[Old];
+
+ assert(Entry && "Value bit set but no entries exist");
+
+ // We use a local ValueHandleBase as an iterator so that
+ // ValueHandles can add and remove themselves from the list without
+ // breaking our iteration. This is not really an AssertingVH; we
+ // just have to give ValueHandleBase some kind.
+ for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
+ Iterator.RemoveFromUseList();
+ Iterator.AddToExistingUseListAfter(Entry);
+ assert(Entry->Next == &Iterator && "Loop invariant broken.");
+
+ switch (Entry->getKind()) {
+ case Assert:
+ // Asserting handle does not follow RAUW implicitly.
+ break;
+ case Tracking:
+ // Tracking goes to new value like a WeakVH. Note that this may make it
+ // something incompatible with its templated type. We don't want to have a
+ // virtual (or inline) interface to handle this though, so instead we make
+ // the TrackingVH accessors guarantee that a client never sees this value.
+
+ // FALLTHROUGH
+ case Weak:
+ // Weak goes to the new value, which will unlink it from Old's list.
+ Entry->operator=(New);
+ break;
+ case Callback:
+ // Forward to the subclass's implementation.
+ static_cast<CallbackVH*>(Entry)->allUsesReplacedWith(New);
+ break;
+ }
+ }
+
+#ifndef NDEBUG
+ // If any new tracking or weak value handles were added while processing the
+ // list, then complain about it now.
+ if (Old->HasValueHandle)
+ for (Entry = pImpl->ValueHandles[Old]; Entry; Entry = Entry->Next)
+ switch (Entry->getKind()) {
+ case Tracking:
+ case Weak:
+ dbgs() << "After RAUW from " << *Old->getType() << " %"
+ << Old->getName() << " to " << *New->getType() << " %"
+ << New->getName() << "\n";
+ llvm_unreachable("A tracking or weak value handle still pointed to the"
+ " old value!\n");
+ default:
+ break;
+ }
+#endif
+}
+
+// Default implementation for CallbackVH.
+void CallbackVH::allUsesReplacedWith(Value *) {}
+
+void CallbackVH::deleted() {
+ setValPtr(NULL);
+}
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