lib/VMCore/Globals.cpp

   1 //===-- Globals.cpp - Implement the GlobalValue & GlobalVariable class ----===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file was developed by the LLVM research group and is distributed under
   6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the GlobalValue & GlobalVariable classes for the VMCore
  11 // library.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/GlobalVariable.h"
  16 #include "llvm/DerivedTypes.h"
  17 #include "llvm/Module.h"
  18 #include "llvm/SymbolTable.h"
  19 #include "llvm/Support/LeakDetector.h"
  20 using namespace llvm;
  21
  22 //===----------------------------------------------------------------------===//
  23 //                            GlobalValue Class
  24 //===----------------------------------------------------------------------===//
  25
  26 /// This could be named "SafeToDestroyGlobalValue". It just makes sure that
  27 /// there are no non-constant uses of this GlobalValue. If there aren't then
  28 /// this and the transitive closure of the constants can be deleted. See the
  29 /// destructor for details.
  30 static bool removeDeadConstantUsers(Constant* C) {
  31   if (isa<GlobalValue>(C)) return false; // Cannot remove this
  32
  33   while (!C->use_empty())
  34     if (Constant *User = dyn_cast<Constant>(C->use_back())) {
  35       if (!removeDeadConstantUsers(User))
  36         return false; // Constant wasn't dead
  37     } else {
  38       return false; // Non-constant usage;
  39     }
  40
  41   C->destroyConstant();
  42   return true;
  43 }
  44
  45 /// removeDeadConstantUsers - If there are any dead constant users dangling
  46 /// off of this global value, remove them.  This method is useful for clients
  47 /// that want to check to see if a global is unused, but don't want to deal
  48 /// with potentially dead constants hanging off of the globals.
  49 ///
  50 /// This function returns true if the global value is now dead.  If all
  51 /// users of this global are not dead, this method may return false and
  52 /// leave some of them around.
  53 void GlobalValue::removeDeadConstantUsers() {
  54   while(!use_empty()) {
  55     if (Constant* User = dyn_cast<Constant>(use_back())) {
  56       if (!::removeDeadConstantUsers(User))
  57         return; // Constant wasn't dead
  58     } else {
  59       return; // Non-constant usage;
  60     }
  61   }
  62 }
  63
  64 /// Override destroyConstant to make sure it doesn't get called on
  65 /// GlobalValue's because they shouldn't be treated like other constants.
  66 void GlobalValue::destroyConstant() {
  67   assert(0 && "You can't GV->destroyConstant()!");
  68   abort();
  69 }
  70 //===----------------------------------------------------------------------===//
  71 // GlobalVariable Implementation
  72 //===----------------------------------------------------------------------===//
  73
  74 GlobalVariable::GlobalVariable(const Type *Ty, bool constant, LinkageTypes Link,
  75                                Constant *InitVal,
  76                                const std::string &Name, Module *ParentModule)
  77   : GlobalValue(PointerType::get(Ty), Value::GlobalVariableVal,
  78                 &Initializer, InitVal != 0, Link, Name),
  79     isConstantGlobal(constant) {
  80   if (InitVal) {
  81     assert(InitVal->getType() == Ty &&
  82            "Initializer should be the same type as the GlobalVariable!");
  83     Initializer.init(InitVal, this);
  84   } else {
  85     Initializer.init(0, this);
  86   }
  87
  88   LeakDetector::addGarbageObject(this);
  89
  90   if (ParentModule)
  91     ParentModule->getGlobalList().push_back(this);
  92 }
  93
  94 void GlobalVariable::setParent(Module *parent) {
  95   if (getParent())
  96     LeakDetector::addGarbageObject(this);
  97   Parent = parent;
  98   if (getParent())
  99     LeakDetector::removeGarbageObject(this);
 100 }
 101
 102 void GlobalVariable::removeFromParent() {
 103   getParent()->getGlobalList().remove(this);
 104 }
 105
 106 void GlobalVariable::eraseFromParent() {
 107   getParent()->getGlobalList().erase(this);
 108 }
 109
 110 void GlobalVariable::replaceUsesOfWithOnConstant(Value *From, Value *To,
 111                                                  Use *U) {
 112   // If you call this, then you better know this GVar has a constant
 113   // initializer worth replacing. Enforce that here.
 114   assert(getNumOperands() == 1 &&
 115          "Attempt to replace uses of Constants on a GVar with no initializer");
 116
 117   // And, since you know it has an initializer, the From value better be
 118   // the initializer :)
 119   assert(getOperand(0) == From &&
 120          "Attempt to replace wrong constant initializer in GVar");
 121
 122   // And, you better have a constant for the replacement value
 123   assert(isa<Constant>(To) &&
 124          "Attempt to replace GVar initializer with non-constant");
 125
 126   // Okay, preconditions out of the way, replace the constant initializer.
 127   this->setOperand(0, cast<Constant>(To));
 128 }