X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FVMCore%2FValue.cpp;h=2fa5f08a3e7f05b3b99f74fb1ab3f5a60531c9fa;hb=e22b321d2276b634519165b101b02d92c2fcf5c7;hp=8710b9461e89f43755ae5a80a4aa1c0fbf3a8d80;hpb=0a0193edf9152bdc47a49a1a513d6e9cbf723131;p=oota-llvm.git diff --git a/lib/VMCore/Value.cpp b/lib/VMCore/Value.cpp index 8710b9461e8..2fa5f08a3e7 100644 --- a/lib/VMCore/Value.cpp +++ b/lib/VMCore/Value.cpp @@ -11,6 +11,7 @@ // //===----------------------------------------------------------------------===// +#include "LLVMContextImpl.h" #include "llvm/Constant.h" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" @@ -18,17 +19,14 @@ #include "llvm/Instructions.h" #include "llvm/Operator.h" #include "llvm/Module.h" -#include "llvm/Metadata.h" #include "llvm/ValueSymbolTable.h" #include "llvm/ADT/SmallString.h" #include "llvm/Support/Debug.h" +#include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/LeakDetector.h" #include "llvm/Support/ManagedStatic.h" #include "llvm/Support/ValueHandle.h" -#include "llvm/Support/raw_ostream.h" -#include "llvm/System/RWMutex.h" -#include "llvm/System/Threading.h" #include "llvm/ADT/DenseMap.h" #include using namespace llvm; @@ -37,38 +35,29 @@ using namespace llvm; // Value Class //===----------------------------------------------------------------------===// -static inline const Type *checkType(const Type *Ty) { +static inline Type *checkType(Type *Ty) { assert(Ty && "Value defined with a null type: Error!"); - return Ty; + return const_cast(Ty); } -Value::Value(const Type *ty, unsigned scid) - : SubclassID(scid), HasValueHandle(0), SubclassOptionalData(0), - SubclassData(0), VTy(checkType(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?? if (isa(this) || isa(this)) - assert((VTy->isFirstClassType() || VTy == Type::VoidTy || - isa(ty) || VTy->getTypeID() == Type::StructTyID) && - "invalid CallInst type!"); + assert((VTy->isFirstClassType() || VTy->isVoidTy() || VTy->isStructTy()) && + "invalid CallInst type!"); else if (!isa(this) && !isa(this)) - assert((VTy->isFirstClassType() || VTy == Type::VoidTy || - isa(ty)) && + assert((VTy->isFirstClassType() || VTy->isVoidTy()) && "Cannot create non-first-class values except for constants!"); } Value::~Value() { - // If this value is named, destroy the name. This should not be in a symtab - // at this point. - if (Name) - Name->Destroy(); - - // There should be no uses of this object anymore, remove it. - LeakDetector::removeGarbageObject(this); - // 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 @@ -77,19 +66,27 @@ Value::~Value() { // a // if (!use_empty()) { - errs() << "While deleting: " << *VTy << " %" << getNameStr() << "\n"; + dbgs() << "While deleting: " << *VTy << " %" << getNameStr() << "\n"; for (use_iterator I = use_begin(), E = use_end(); I != E; ++I) - errs() << "Use still stuck around after Def is destroyed:" + 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) + 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 { - use_const_iterator UI = use_begin(), E = use_end(); + const_use_iterator UI = use_begin(), E = use_end(); for (; N; --N, ++UI) if (UI == E) return false; // Too few. @@ -100,7 +97,7 @@ bool Value::hasNUses(unsigned N) const { /// logically equivalent to getNumUses() >= N. /// bool Value::hasNUsesOrMore(unsigned N) const { - use_const_iterator UI = use_begin(), E = use_end(); + const_use_iterator UI = use_begin(), E = use_end(); for (; N; --N, ++UI) if (UI == E) return false; // Too few. @@ -111,7 +108,7 @@ bool Value::hasNUsesOrMore(unsigned N) const { /// isUsedInBasicBlock - Return true if this value is used in the specified /// basic block. bool Value::isUsedInBasicBlock(const BasicBlock *BB) const { - for (use_const_iterator I = use_begin(), E = use_end(); I != E; ++I) { + for (const_use_iterator I = use_begin(), E = use_end(); I != E; ++I) { const Instruction *User = dyn_cast(*I); if (User && User->getParent() == BB) return true; @@ -134,18 +131,14 @@ static bool getSymTab(Value *V, ValueSymbolTable *&ST) { if (Function *PP = P->getParent()) ST = &PP->getValueSymbolTable(); } else if (BasicBlock *BB = dyn_cast(V)) { - if (Function *P = BB->getParent()) + if (Function *P = BB->getParent()) ST = &P->getValueSymbolTable(); } else if (GlobalValue *GV = dyn_cast(V)) { - if (Module *P = GV->getParent()) + if (Module *P = GV->getParent()) ST = &P->getValueSymbolTable(); } else if (Argument *A = dyn_cast(V)) { - if (Function *P = A->getParent()) + if (Function *P = A->getParent()) ST = &P->getValueSymbolTable(); - } else if (NamedMDNode *N = dyn_cast(V)) { - if (Module *P = N->getParent()) { - ST = &P->getValueSymbolTable(); - } } else if (isa(V)) return true; else { @@ -168,43 +161,44 @@ std::string Value::getNameStr() const { } void Value::setName(const Twine &NewName) { - SmallString<32> NameData; - NewName.toVector(NameData); + // Fast path for common IRBuilder case of setName("") when there is no name. + if (NewName.isTriviallyEmpty() && !hasName()) + return; - const char *NameStr = NameData.data(); - unsigned NameLen = NameData.size(); + SmallString<256> NameData; + StringRef NameRef = NewName.toStringRef(NameData); // Name isn't changing? - if (getName() == StringRef(NameStr, NameLen)) + if (getName() == NameRef) return; - assert(getType() != Type::VoidTy && "Cannot assign a name to void values!"); - + 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 (!ST) { // No symbol table to update? Just do the change. - if (NameLen == 0) { + 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(NameStr, NameStr+NameLen); + 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()) { @@ -213,17 +207,17 @@ void Value::setName(const Twine &NewName) { Name->Destroy(); Name = 0; - if (NameLen == 0) + if (NameRef.empty()) return; } // Name is changing to something new. - Name = ST->createValueName(StringRef(NameStr, NameLen), this); + 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). +/// empty. It is an error to call V->takeName(V). void Value::takeName(Value *V) { ValueSymbolTable *ST = 0; // If this value has a name, drop it. @@ -235,19 +229,19 @@ void Value::takeName(Value *V) { 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)) { @@ -256,12 +250,12 @@ void Value::takeName(Value *V) { 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!"); Failure=Failure; - + 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) { @@ -271,32 +265,31 @@ void Value::takeName(Value *V) { 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); } -// uncheckedReplaceAllUsesWith - This is exactly the same as replaceAllUsesWith, -// except that it doesn't have all of the asserts. The asserts fail because we -// are half-way done resolving types, which causes some types to exist as two -// different Type*'s at the same time. This is a sledgehammer to work around -// this problem. -// -void Value::uncheckedReplaceAllUsesWith(Value *New) { +void Value::replaceAllUsesWith(Value *New) { + assert(New && "Value::replaceAllUsesWith() 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 @@ -310,21 +303,21 @@ void Value::uncheckedReplaceAllUsesWith(Value *New) { U.set(New); } -} - -void Value::replaceAllUsesWith(Value *New) { - assert(New && "Value::replaceAllUsesWith() is invalid!"); - assert(New != this && "this->replaceAllUsesWith(this) is NOT valid!"); - assert(New->getType() == getType() && - "replaceAllUses of value with new value of different type!"); - - uncheckedReplaceAllUsesWith(New); + + if (BasicBlock *BB = dyn_cast(this)) + BB->replaceSuccessorsPhiUsesWith(cast(New)); } Value *Value::stripPointerCasts() { - if (!isa(getType())) + if (!getType()->isPointerTy()) return this; + + // 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 Visited; + Value *V = this; + Visited.insert(V); do { if (GEPOperator *GEP = dyn_cast(V)) { if (!GEP->hasAllZeroIndices()) @@ -332,36 +325,82 @@ Value *Value::stripPointerCasts() { V = GEP->getPointerOperand(); } else if (Operator::getOpcode(V) == Instruction::BitCast) { V = cast(V)->getOperand(0); + } else if (GlobalAlias *GA = dyn_cast(V)) { + if (GA->mayBeOverridden()) + return V; + V = GA->getAliasee(); } else { return V; } - assert(isa(V->getType()) && "Unexpected operand type!"); - } while (1); + assert(V->getType()->isPointerTy() && "Unexpected operand type!"); + } while (Visited.insert(V)); + + return V; } -Value *Value::getUnderlyingObject() { - if (!isa(getType())) - return this; - Value *V = this; - unsigned MaxLookup = 6; - do { - if (GEPOperator *GEP = dyn_cast(V)) { - V = GEP->getPointerOperand(); - } else if (Operator::getOpcode(V) == Instruction::BitCast) { - V = cast(V)->getOperand(0); - } else { - return V; +/// 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 { + // 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 TargetData to check sizes and alignments though. + + // These are obviously ok. + if (isa(this)) return true; + + // Global variables which can't collapse to null are ok. + if (const GlobalVariable *GV = dyn_cast(this)) + return !GV->hasExternalWeakLinkage(); + + // byval arguments are ok. + if (const Argument *A = dyn_cast(this)) + return A->hasByValAttr(); + + // For GEPs, determine if the indexing lands within the allocated object. + if (const GEPOperator *GEP = dyn_cast(this)) { + // Conservatively require that the base pointer be fully dereferenceable. + if (!GEP->getOperand(0)->isDereferenceablePointer()) + 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(Ty)) + continue; + ConstantInt *CI = dyn_cast(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(Ty); + if (!ATy) + return false; + if (CI->getValue().getActiveBits() > 64) + return false; + if (CI->getZExtValue() >= ATy->getNumElements()) + return false; } - assert(isa(V->getType()) && "Unexpected operand type!"); - } while (--MaxLookup); - return V; + // Indices check out; this is dereferenceable. + return true; + } + + // If we don't know, assume the worst. + return false; } /// 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, +Value *Value::DoPHITranslation(const BasicBlock *CurBB, const BasicBlock *PredBB) { PHINode *PN = dyn_cast(this); if (PN && PN->getParent() == CurBB) @@ -375,18 +414,11 @@ LLVMContext &Value::getContext() const { return VTy->getContext(); } // ValueHandleBase Class //===----------------------------------------------------------------------===// -/// ValueHandles - This map keeps track of all of the value handles that are -/// watching a Value*. The Value::HasValueHandle bit is used to know whether or -/// not a value has an entry in this map. -typedef DenseMap ValueHandlesTy; -static ManagedStatic ValueHandles; -static ManagedStatic > ValueHandlesLock; - /// 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; @@ -397,43 +429,54 @@ void ValueHandleBase::AddToExistingUseList(ValueHandleBase **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 && "Null pointer doesn't have a use list!"); + + LLVMContextImpl *pImpl = VP->getContext().pImpl; + if (VP->HasValueHandle) { // If this value already has a ValueHandle, then it must be in the // ValueHandles map already. - sys::SmartScopedReader Reader(*ValueHandlesLock); - ValueHandleBase *&Entry = (*ValueHandles)[VP]; + ValueHandleBase *&Entry = pImpl->ValueHandles[VP]; 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. - sys::SmartScopedWriter Writer(*ValueHandlesLock); - ValueHandlesTy &Handles = *ValueHandles; + DenseMap &Handles = pImpl->ValueHandles; const void *OldBucketPtr = Handles.getPointerIntoBucketsArray(); - + ValueHandleBase *&Entry = Handles[VP]; assert(Entry == 0 && "Value really did already have handles?"); AddToExistingUseList(&Entry); VP->HasValueHandle = true; - + // If reallocation didn't happen or if this was the first insertion, don't // walk the table. - if (Handles.isPointerIntoBucketsArray(OldBucketPtr) || + if (Handles.isPointerIntoBucketsArray(OldBucketPtr) || Handles.size() == 1) { return; } - + // Okay, reallocation did happen. Fix the Prev Pointers. - for (ValueHandlesTy::iterator I = Handles.begin(), E = Handles.end(); - I != E; ++I) { + for (DenseMap::iterator I = Handles.begin(), + E = Handles.end(); I != E; ++I) { assert(I->second && I->first == I->second->VP && "List invariant broken!"); I->second->setPrevPtr(&I->second); } @@ -446,19 +489,19 @@ void ValueHandleBase::RemoveFromUseList() { // 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. - sys::SmartScopedWriter Writer(*ValueHandlesLock); - ValueHandlesTy &Handles = *ValueHandles; + LLVMContextImpl *pImpl = VP->getContext().pImpl; + DenseMap &Handles = pImpl->ValueHandles; if (Handles.isPointerIntoBucketsArray(PrevPtr)) { Handles.erase(VP); VP->HasValueHandle = false; @@ -471,95 +514,119 @@ void ValueHandleBase::ValueIsDeleted(Value *V) { // Get the linked list base, which is guaranteed to exist since the // HasValueHandle flag is set. - ValueHandlesLock->reader_acquire(); - ValueHandleBase *Entry = (*ValueHandles)[V]; - ValueHandlesLock->reader_release(); + LLVMContextImpl *pImpl = V->getContext().pImpl; + ValueHandleBase *Entry = pImpl->ValueHandles[V]; assert(Entry && "Value bit set but no entries exist"); - - while (Entry) { - // Advance pointer to avoid invalidation. - ValueHandleBase *ThisNode = Entry; - Entry = Entry->Next; - - switch (ThisNode->getKind()) { + + // 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: -#ifndef NDEBUG // Only in -g mode... - errs() << "While deleting: " << *V->getType() << " %" << V->getNameStr() - << "\n"; -#endif - llvm_unreachable("An asserting value handle still pointed to this" - " value!"); + break; + case Tracking: + // Mark that this value has been deleted by setting it to an invalid Value + // pointer. + Entry->operator=(DenseMapInfo::getTombstoneKey()); + break; case Weak: // Weak just goes to null, which will unlink it from the list. - ThisNode->operator=(0); + Entry->operator=(0); break; case Callback: // Forward to the subclass's implementation. - static_cast(ThisNode)->deleted(); + static_cast(Entry)->deleted(); break; } } - - // All callbacks and weak references should be dropped by now. - assert(!V->HasValueHandle && "All references to V were not removed?"); + + // 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->getNameStr() + << "\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. - ValueHandlesLock->reader_acquire(); - ValueHandleBase *Entry = (*ValueHandles)[Old]; - ValueHandlesLock->reader_release(); + LLVMContextImpl *pImpl = Old->getContext().pImpl; + ValueHandleBase *Entry = pImpl->ValueHandles[Old]; + assert(Entry && "Value bit set but no entries exist"); - - while (Entry) { - // Advance pointer to avoid invalidation. - ValueHandleBase *ThisNode = Entry; - Entry = Entry->Next; - - switch (ThisNode->getKind()) { + + // 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. - ThisNode->operator=(New); + Entry->operator=(New); break; case Callback: // Forward to the subclass's implementation. - static_cast(ThisNode)->allUsesReplacedWith(New); + static_cast(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->getNameStr() << " to " << *New->getType() << " %" + << New->getNameStr() << "\n"; + llvm_unreachable("A tracking or weak value handle still pointed to the" + " old value!\n"); + default: + break; + } +#endif } /// ~CallbackVH. Empty, but defined here to avoid emitting the vtable /// more than once. CallbackVH::~CallbackVH() {} - - -//===----------------------------------------------------------------------===// -// User Class -//===----------------------------------------------------------------------===// - -// replaceUsesOfWith - Replaces all references to the "From" definition with -// references to the "To" definition. -// -void User::replaceUsesOfWith(Value *From, Value *To) { - if (From == To) return; // Duh what? - - assert((!isa(this) || isa(this)) && - "Cannot call User::replaceUsesofWith on a constant!"); - - for (unsigned i = 0, E = getNumOperands(); i != E; ++i) - if (getOperand(i) == From) { // Is This operand is pointing to oldval? - // The side effects of this setOperand call include linking to - // "To", adding "this" to the uses list of To, and - // most importantly, removing "this" from the use list of "From". - setOperand(i, To); // Fix it now... - } -}