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      1 //===-- Globals.cpp - Implement the GlobalValue & GlobalVariable 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 GlobalValue & GlobalVariable classes for the IR
     11 // library.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "llvm/IR/GlobalValue.h"
     16 #include "llvm/ADT/SmallPtrSet.h"
     17 #include "llvm/IR/Constants.h"
     18 #include "llvm/IR/DerivedTypes.h"
     19 #include "llvm/IR/GlobalAlias.h"
     20 #include "llvm/IR/GlobalVariable.h"
     21 #include "llvm/IR/Module.h"
     22 #include "llvm/Support/ErrorHandling.h"
     23 #include "llvm/Support/LeakDetector.h"
     24 using namespace llvm;
     25 
     26 //===----------------------------------------------------------------------===//
     27 //                            GlobalValue Class
     28 //===----------------------------------------------------------------------===//
     29 
     30 bool GlobalValue::isMaterializable() const {
     31   return getParent() && getParent()->isMaterializable(this);
     32 }
     33 bool GlobalValue::isDematerializable() const {
     34   return getParent() && getParent()->isDematerializable(this);
     35 }
     36 bool GlobalValue::Materialize(std::string *ErrInfo) {
     37   return getParent()->Materialize(this, ErrInfo);
     38 }
     39 void GlobalValue::Dematerialize() {
     40   getParent()->Dematerialize(this);
     41 }
     42 
     43 /// Override destroyConstant to make sure it doesn't get called on
     44 /// GlobalValue's because they shouldn't be treated like other constants.
     45 void GlobalValue::destroyConstant() {
     46   llvm_unreachable("You can't GV->destroyConstant()!");
     47 }
     48 
     49 /// copyAttributesFrom - copy all additional attributes (those not needed to
     50 /// create a GlobalValue) from the GlobalValue Src to this one.
     51 void GlobalValue::copyAttributesFrom(const GlobalValue *Src) {
     52   setAlignment(Src->getAlignment());
     53   setSection(Src->getSection());
     54   setVisibility(Src->getVisibility());
     55   setUnnamedAddr(Src->hasUnnamedAddr());
     56 }
     57 
     58 void GlobalValue::setAlignment(unsigned Align) {
     59   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
     60   assert(Align <= MaximumAlignment &&
     61          "Alignment is greater than MaximumAlignment!");
     62   Alignment = Log2_32(Align) + 1;
     63   assert(getAlignment() == Align && "Alignment representation error!");
     64 }
     65 
     66 bool GlobalValue::isDeclaration() const {
     67   // Globals are definitions if they have an initializer.
     68   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(this))
     69     return GV->getNumOperands() == 0;
     70 
     71   // Functions are definitions if they have a body.
     72   if (const Function *F = dyn_cast<Function>(this))
     73     return F->empty();
     74 
     75   // Aliases are always definitions.
     76   assert(isa<GlobalAlias>(this));
     77   return false;
     78 }
     79 
     80 //===----------------------------------------------------------------------===//
     81 // GlobalVariable Implementation
     82 //===----------------------------------------------------------------------===//
     83 
     84 GlobalVariable::GlobalVariable(Type *Ty, bool constant, LinkageTypes Link,
     85                                Constant *InitVal,
     86                                const Twine &Name, ThreadLocalMode TLMode,
     87                                unsigned AddressSpace,
     88                                bool isExternallyInitialized)
     89   : GlobalValue(PointerType::get(Ty, AddressSpace),
     90                 Value::GlobalVariableVal,
     91                 OperandTraits<GlobalVariable>::op_begin(this),
     92                 InitVal != 0, Link, Name),
     93     isConstantGlobal(constant), threadLocalMode(TLMode),
     94     isExternallyInitializedConstant(isExternallyInitialized) {
     95   if (InitVal) {
     96     assert(InitVal->getType() == Ty &&
     97            "Initializer should be the same type as the GlobalVariable!");
     98     Op<0>() = InitVal;
     99   }
    100 
    101   LeakDetector::addGarbageObject(this);
    102 }
    103 
    104 GlobalVariable::GlobalVariable(Module &M, Type *Ty, bool constant,
    105                                LinkageTypes Link, Constant *InitVal,
    106                                const Twine &Name,
    107                                GlobalVariable *Before, ThreadLocalMode TLMode,
    108                                unsigned AddressSpace,
    109                                bool isExternallyInitialized)
    110   : GlobalValue(PointerType::get(Ty, AddressSpace),
    111                 Value::GlobalVariableVal,
    112                 OperandTraits<GlobalVariable>::op_begin(this),
    113                 InitVal != 0, Link, Name),
    114     isConstantGlobal(constant), threadLocalMode(TLMode),
    115     isExternallyInitializedConstant(isExternallyInitialized) {
    116   if (InitVal) {
    117     assert(InitVal->getType() == Ty &&
    118            "Initializer should be the same type as the GlobalVariable!");
    119     Op<0>() = InitVal;
    120   }
    121 
    122   LeakDetector::addGarbageObject(this);
    123 
    124   if (Before)
    125     Before->getParent()->getGlobalList().insert(Before, this);
    126   else
    127     M.getGlobalList().push_back(this);
    128 }
    129 
    130 void GlobalVariable::setParent(Module *parent) {
    131   if (getParent())
    132     LeakDetector::addGarbageObject(this);
    133   Parent = parent;
    134   if (getParent())
    135     LeakDetector::removeGarbageObject(this);
    136 }
    137 
    138 void GlobalVariable::removeFromParent() {
    139   getParent()->getGlobalList().remove(this);
    140 }
    141 
    142 void GlobalVariable::eraseFromParent() {
    143   getParent()->getGlobalList().erase(this);
    144 }
    145 
    146 void GlobalVariable::replaceUsesOfWithOnConstant(Value *From, Value *To,
    147                                                  Use *U) {
    148   // If you call this, then you better know this GVar has a constant
    149   // initializer worth replacing. Enforce that here.
    150   assert(getNumOperands() == 1 &&
    151          "Attempt to replace uses of Constants on a GVar with no initializer");
    152 
    153   // And, since you know it has an initializer, the From value better be
    154   // the initializer :)
    155   assert(getOperand(0) == From &&
    156          "Attempt to replace wrong constant initializer in GVar");
    157 
    158   // And, you better have a constant for the replacement value
    159   assert(isa<Constant>(To) &&
    160          "Attempt to replace GVar initializer with non-constant");
    161 
    162   // Okay, preconditions out of the way, replace the constant initializer.
    163   this->setOperand(0, cast<Constant>(To));
    164 }
    165 
    166 void GlobalVariable::setInitializer(Constant *InitVal) {
    167   if (InitVal == 0) {
    168     if (hasInitializer()) {
    169       Op<0>().set(0);
    170       NumOperands = 0;
    171     }
    172   } else {
    173     assert(InitVal->getType() == getType()->getElementType() &&
    174            "Initializer type must match GlobalVariable type");
    175     if (!hasInitializer())
    176       NumOperands = 1;
    177     Op<0>().set(InitVal);
    178   }
    179 }
    180 
    181 /// copyAttributesFrom - copy all additional attributes (those not needed to
    182 /// create a GlobalVariable) from the GlobalVariable Src to this one.
    183 void GlobalVariable::copyAttributesFrom(const GlobalValue *Src) {
    184   assert(isa<GlobalVariable>(Src) && "Expected a GlobalVariable!");
    185   GlobalValue::copyAttributesFrom(Src);
    186   const GlobalVariable *SrcVar = cast<GlobalVariable>(Src);
    187   setThreadLocal(SrcVar->isThreadLocal());
    188 }
    189 
    190 
    191 //===----------------------------------------------------------------------===//
    192 // GlobalAlias Implementation
    193 //===----------------------------------------------------------------------===//
    194 
    195 GlobalAlias::GlobalAlias(Type *Ty, LinkageTypes Link,
    196                          const Twine &Name, Constant* aliasee,
    197                          Module *ParentModule)
    198   : GlobalValue(Ty, Value::GlobalAliasVal, &Op<0>(), 1, Link, Name) {
    199   LeakDetector::addGarbageObject(this);
    200 
    201   if (aliasee)
    202     assert(aliasee->getType() == Ty && "Alias and aliasee types should match!");
    203   Op<0>() = aliasee;
    204 
    205   if (ParentModule)
    206     ParentModule->getAliasList().push_back(this);
    207 }
    208 
    209 void GlobalAlias::setParent(Module *parent) {
    210   if (getParent())
    211     LeakDetector::addGarbageObject(this);
    212   Parent = parent;
    213   if (getParent())
    214     LeakDetector::removeGarbageObject(this);
    215 }
    216 
    217 void GlobalAlias::removeFromParent() {
    218   getParent()->getAliasList().remove(this);
    219 }
    220 
    221 void GlobalAlias::eraseFromParent() {
    222   getParent()->getAliasList().erase(this);
    223 }
    224 
    225 void GlobalAlias::setAliasee(Constant *Aliasee) {
    226   assert((!Aliasee || Aliasee->getType() == getType()) &&
    227          "Alias and aliasee types should match!");
    228 
    229   setOperand(0, Aliasee);
    230 }
    231 
    232 const GlobalValue *GlobalAlias::getAliasedGlobal() const {
    233   const Constant *C = getAliasee();
    234   if (C == 0) return 0;
    235 
    236   if (const GlobalValue *GV = dyn_cast<GlobalValue>(C))
    237     return GV;
    238 
    239   const ConstantExpr *CE = cast<ConstantExpr>(C);
    240   assert((CE->getOpcode() == Instruction::BitCast ||
    241           CE->getOpcode() == Instruction::GetElementPtr) &&
    242          "Unsupported aliasee");
    243 
    244   return cast<GlobalValue>(CE->getOperand(0));
    245 }
    246 
    247 const GlobalValue *GlobalAlias::resolveAliasedGlobal(bool stopOnWeak) const {
    248   SmallPtrSet<const GlobalValue*, 3> Visited;
    249 
    250   // Check if we need to stop early.
    251   if (stopOnWeak && mayBeOverridden())
    252     return this;
    253 
    254   const GlobalValue *GV = getAliasedGlobal();
    255   Visited.insert(GV);
    256 
    257   // Iterate over aliasing chain, stopping on weak alias if necessary.
    258   while (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV)) {
    259     if (stopOnWeak && GA->mayBeOverridden())
    260       break;
    261 
    262     GV = GA->getAliasedGlobal();
    263 
    264     if (!Visited.insert(GV))
    265       return 0;
    266   }
    267 
    268   return GV;
    269 }
    270