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ArgumentPromotion.cpp

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00001 //===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
00002 // 
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 // 
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This pass promotes "by reference" arguments to be "by value" arguments.  In
00011 // practice, this means looking for internal functions that have pointer
00012 // arguments.  If we can prove, through the use of alias analysis, that an
00013 // argument is *only* loaded, then we can pass the value into the function
00014 // instead of the address of the value.  This can cause recursive simplification
00015 // of code and lead to the elimination of allocas (especially in C++ template
00016 // code like the STL).
00017 //
00018 // This pass also handles aggregate arguments that are passed into a function,
00019 // scalarizing them if the elements of the aggregate are only loaded.  Note that
00020 // we refuse to scalarize aggregates which would require passing in more than
00021 // three operands to the function, because we don't want to pass thousands of
00022 // operands for a large array or structure!
00023 //
00024 // Note that this transformation could also be done for arguments that are only
00025 // stored to (returning the value instead), but we do not currently handle that
00026 // case.  This case would be best handled when and if we start supporting
00027 // multiple return values from functions.
00028 //
00029 //===----------------------------------------------------------------------===//
00030 
00031 #define DEBUG_TYPE "argpromotion"
00032 #include "llvm/Transforms/IPO.h"
00033 #include "llvm/Constants.h"
00034 #include "llvm/DerivedTypes.h"
00035 #include "llvm/Module.h"
00036 #include "llvm/CallGraphSCCPass.h"
00037 #include "llvm/Instructions.h"
00038 #include "llvm/Analysis/AliasAnalysis.h"
00039 #include "llvm/Analysis/CallGraph.h"
00040 #include "llvm/Target/TargetData.h"
00041 #include "llvm/Support/CallSite.h"
00042 #include "llvm/Support/CFG.h"
00043 #include "llvm/Support/Debug.h"
00044 #include "llvm/ADT/DepthFirstIterator.h"
00045 #include "llvm/ADT/Statistic.h"
00046 #include "llvm/ADT/StringExtras.h"
00047 #include <set>
00048 using namespace llvm;
00049 
00050 namespace {
00051   Statistic<> NumArgumentsPromoted("argpromotion",
00052                                    "Number of pointer arguments promoted");
00053   Statistic<> NumAggregatesPromoted("argpromotion",
00054                                     "Number of aggregate arguments promoted");
00055   Statistic<> NumArgumentsDead("argpromotion",
00056                                "Number of dead pointer args eliminated");
00057 
00058   /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
00059   ///
00060   struct ArgPromotion : public CallGraphSCCPass {
00061     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00062       AU.addRequired<AliasAnalysis>();
00063       AU.addRequired<TargetData>();
00064       CallGraphSCCPass::getAnalysisUsage(AU);
00065     }
00066 
00067     virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
00068   private:
00069     bool PromoteArguments(CallGraphNode *CGN);
00070     bool isSafeToPromoteArgument(Argument *Arg) const;  
00071     Function *DoPromotion(Function *F, std::vector<Argument*> &ArgsToPromote);
00072   };
00073 
00074   RegisterOpt<ArgPromotion> X("argpromotion",
00075                               "Promote 'by reference' arguments to scalars");
00076 }
00077 
00078 ModulePass *llvm::createArgumentPromotionPass() {
00079   return new ArgPromotion();
00080 }
00081 
00082 bool ArgPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
00083   bool Changed = false, LocalChange;
00084 
00085   do {  // Iterate until we stop promoting from this SCC.
00086     LocalChange = false;
00087     // Attempt to promote arguments from all functions in this SCC.
00088     for (unsigned i = 0, e = SCC.size(); i != e; ++i)
00089       LocalChange |= PromoteArguments(SCC[i]);
00090     Changed |= LocalChange;               // Remember that we changed something.
00091   } while (LocalChange);
00092   
00093   return Changed;
00094 }
00095 
00096 /// PromoteArguments - This method checks the specified function to see if there
00097 /// are any promotable arguments and if it is safe to promote the function (for
00098 /// example, all callers are direct).  If safe to promote some arguments, it
00099 /// calls the DoPromotion method.
00100 ///
00101 bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
00102   Function *F = CGN->getFunction();
00103 
00104   // Make sure that it is local to this module.
00105   if (!F || !F->hasInternalLinkage()) return false;
00106 
00107   // First check: see if there are any pointer arguments!  If not, quick exit.
00108   std::vector<Argument*> PointerArgs;
00109   for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
00110     if (isa<PointerType>(I->getType()))
00111       PointerArgs.push_back(I);
00112   if (PointerArgs.empty()) return false;
00113 
00114   // Second check: make sure that all callers are direct callers.  We can't
00115   // transform functions that have indirect callers.
00116   for (Value::use_iterator UI = F->use_begin(), E = F->use_end();
00117        UI != E; ++UI) {
00118     CallSite CS = CallSite::get(*UI);
00119     if (!CS.getInstruction())       // "Taking the address" of the function
00120       return false;
00121 
00122     // Ensure that this call site is CALLING the function, not passing it as
00123     // an argument.
00124     for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
00125          AI != E; ++AI)
00126       if (*AI == F) return false;   // Passing the function address in!
00127   }
00128 
00129   // Check to see which arguments are promotable.  If an argument is not
00130   // promotable, remove it from the PointerArgs vector.
00131   for (unsigned i = 0; i != PointerArgs.size(); ++i)
00132     if (!isSafeToPromoteArgument(PointerArgs[i])) {
00133       std::swap(PointerArgs[i--], PointerArgs.back());
00134       PointerArgs.pop_back();
00135     }
00136 
00137   // No promotable pointer arguments.
00138   if (PointerArgs.empty()) return false;
00139 
00140   // Okay, promote all of the arguments are rewrite the callees!
00141   Function *NewF = DoPromotion(F, PointerArgs);
00142 
00143   // Update the call graph to know that the old function is gone.
00144   getAnalysis<CallGraph>().changeFunction(F, NewF);
00145   return true;
00146 }
00147 
00148 /// IsAlwaysValidPointer - Return true if the specified pointer is always legal
00149 /// to load.
00150 static bool IsAlwaysValidPointer(Value *V) {
00151   if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true;
00152   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V))
00153     return IsAlwaysValidPointer(GEP->getOperand(0));
00154   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
00155     if (CE->getOpcode() == Instruction::GetElementPtr)
00156       return IsAlwaysValidPointer(CE->getOperand(0));
00157 
00158   return false;
00159 }
00160 
00161 /// AllCalleesPassInValidPointerForArgument - Return true if we can prove that
00162 /// all callees pass in a valid pointer for the specified function argument.
00163 static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
00164   Function *Callee = Arg->getParent();
00165 
00166   unsigned ArgNo = std::distance(Callee->abegin(), Function::aiterator(Arg));
00167 
00168   // Look at all call sites of the function.  At this pointer we know we only
00169   // have direct callees.
00170   for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end();
00171        UI != E; ++UI) {
00172     CallSite CS = CallSite::get(*UI);
00173     assert(CS.getInstruction() && "Should only have direct calls!");
00174 
00175     if (!IsAlwaysValidPointer(CS.getArgument(ArgNo)))
00176       return false;
00177   }
00178   return true;
00179 }
00180 
00181 
00182 /// isSafeToPromoteArgument - As you might guess from the name of this method,
00183 /// it checks to see if it is both safe and useful to promote the argument.
00184 /// This method limits promotion of aggregates to only promote up to three
00185 /// elements of the aggregate in order to avoid exploding the number of
00186 /// arguments passed in.
00187 bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
00188   // We can only promote this argument if all of the uses are loads, or are GEP
00189   // instructions (with constant indices) that are subsequently loaded.
00190   bool HasLoadInEntryBlock = false;
00191   BasicBlock *EntryBlock = Arg->getParent()->begin();
00192   std::vector<LoadInst*> Loads;
00193   std::vector<std::vector<ConstantInt*> > GEPIndices;
00194   for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end();
00195        UI != E; ++UI)
00196     if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
00197       if (LI->isVolatile()) return false;  // Don't hack volatile loads
00198       Loads.push_back(LI);
00199       HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
00200     } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
00201       if (GEP->use_empty()) {
00202         // Dead GEP's cause trouble later.  Just remove them if we run into
00203         // them.
00204         getAnalysis<AliasAnalysis>().deleteValue(GEP);
00205         GEP->getParent()->getInstList().erase(GEP);
00206         return isSafeToPromoteArgument(Arg);
00207       }
00208       // Ensure that all of the indices are constants.
00209       std::vector<ConstantInt*> Operands;
00210       for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
00211         if (ConstantInt *C = dyn_cast<ConstantInt>(GEP->getOperand(i)))
00212           Operands.push_back(C);
00213         else
00214           return false;  // Not a constant operand GEP!
00215 
00216       // Ensure that the only users of the GEP are load instructions.
00217       for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end();
00218            UI != E; ++UI)
00219         if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
00220           if (LI->isVolatile()) return false;  // Don't hack volatile loads
00221           Loads.push_back(LI);
00222           HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
00223         } else {
00224           return false;
00225         }
00226 
00227       // See if there is already a GEP with these indices.  If not, check to
00228       // make sure that we aren't promoting too many elements.  If so, nothing
00229       // to do.
00230       if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) ==
00231           GEPIndices.end()) {
00232         if (GEPIndices.size() == 3) {
00233           DEBUG(std::cerr << "argpromotion disable promoting argument '"
00234                 << Arg->getName() << "' because it would require adding more "
00235                 << "than 3 arguments to the function.\n");
00236           // We limit aggregate promotion to only promoting up to three elements
00237           // of the aggregate.
00238           return false;
00239         }
00240         GEPIndices.push_back(Operands);
00241       }
00242     } else {
00243       return false;  // Not a load or a GEP.
00244     }
00245 
00246   if (Loads.empty()) return true;  // No users, this is a dead argument.
00247 
00248   // If we decide that we want to promote this argument, the value is going to
00249   // be unconditionally loaded in all callees.  This is only safe to do if the
00250   // pointer was going to be unconditionally loaded anyway (i.e. there is a load
00251   // of the pointer in the entry block of the function) or if we can prove that
00252   // all pointers passed in are always to legal locations (for example, no null
00253   // pointers are passed in, no pointers to free'd memory, etc).
00254   if (!HasLoadInEntryBlock && !AllCalleesPassInValidPointerForArgument(Arg))
00255     return false;   // Cannot prove that this is safe!!
00256 
00257   // Okay, now we know that the argument is only used by load instructions and
00258   // it is safe to unconditionally load the pointer.  Use alias analysis to
00259   // check to see if the pointer is guaranteed to not be modified from entry of
00260   // the function to each of the load instructions.
00261   Function &F = *Arg->getParent();
00262 
00263   // Because there could be several/many load instructions, remember which
00264   // blocks we know to be transparent to the load.
00265   std::set<BasicBlock*> TranspBlocks;
00266 
00267   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
00268   TargetData &TD = getAnalysis<TargetData>();
00269 
00270   for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
00271     // Check to see if the load is invalidated from the start of the block to
00272     // the load itself.
00273     LoadInst *Load = Loads[i];
00274     BasicBlock *BB = Load->getParent();
00275 
00276     const PointerType *LoadTy =
00277       cast<PointerType>(Load->getOperand(0)->getType());
00278     unsigned LoadSize = TD.getTypeSize(LoadTy->getElementType());
00279 
00280     if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize))
00281       return false;  // Pointer is invalidated!
00282 
00283     // Now check every path from the entry block to the load for transparency.
00284     // To do this, we perform a depth first search on the inverse CFG from the
00285     // loading block.
00286     for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
00287       for (idf_ext_iterator<BasicBlock*> I = idf_ext_begin(*PI, TranspBlocks),
00288              E = idf_ext_end(*PI, TranspBlocks); I != E; ++I)
00289         if (AA.canBasicBlockModify(**I, Arg, LoadSize))
00290           return false;
00291   }
00292 
00293   // If the path from the entry of the function to each load is free of
00294   // instructions that potentially invalidate the load, we can make the
00295   // transformation!
00296   return true;
00297 }
00298 
00299 namespace {
00300   /// GEPIdxComparator - Provide a strong ordering for GEP indices.  All Value*
00301   /// elements are instances of ConstantInt.
00302   ///
00303   struct GEPIdxComparator {
00304     bool operator()(const std::vector<Value*> &LHS,
00305                     const std::vector<Value*> &RHS) const {
00306       unsigned idx = 0;
00307       for (; idx < LHS.size() && idx < RHS.size(); ++idx) {
00308         if (LHS[idx] != RHS[idx]) {
00309           return cast<ConstantInt>(LHS[idx])->getRawValue() < 
00310                  cast<ConstantInt>(RHS[idx])->getRawValue();
00311         }
00312       }
00313 
00314       // Return less than if we ran out of stuff in LHS and we didn't run out of
00315       // stuff in RHS.
00316       return idx == LHS.size() && idx != RHS.size();
00317     }
00318   };
00319 }
00320 
00321 
00322 /// DoPromotion - This method actually performs the promotion of the specified
00323 /// arguments, and returns the new function.  At this point, we know that it's
00324 /// safe to do so.
00325 Function *ArgPromotion::DoPromotion(Function *F,
00326                                     std::vector<Argument*> &Args2Prom) {
00327   std::set<Argument*> ArgsToPromote(Args2Prom.begin(), Args2Prom.end());
00328   
00329   // Start by computing a new prototype for the function, which is the same as
00330   // the old function, but has modified arguments.
00331   const FunctionType *FTy = F->getFunctionType();
00332   std::vector<const Type*> Params;
00333 
00334   typedef std::set<std::vector<Value*>, GEPIdxComparator> ScalarizeTable;
00335 
00336   // ScalarizedElements - If we are promoting a pointer that has elements
00337   // accessed out of it, keep track of which elements are accessed so that we
00338   // can add one argument for each.
00339   //
00340   // Arguments that are directly loaded will have a zero element value here, to
00341   // handle cases where there are both a direct load and GEP accesses.
00342   //
00343   std::map<Argument*, ScalarizeTable> ScalarizedElements;
00344 
00345   // OriginalLoads - Keep track of a representative load instruction from the
00346   // original function so that we can tell the alias analysis implementation
00347   // what the new GEP/Load instructions we are inserting look like.
00348   std::map<std::vector<Value*>, LoadInst*> OriginalLoads;
00349 
00350   for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
00351     if (!ArgsToPromote.count(I)) {
00352       Params.push_back(I->getType());
00353     } else if (I->use_empty()) {
00354       ++NumArgumentsDead;
00355     } else {
00356       // Okay, this is being promoted.  Check to see if there are any GEP uses
00357       // of the argument.
00358       ScalarizeTable &ArgIndices = ScalarizedElements[I];
00359       for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
00360            ++UI) {
00361         Instruction *User = cast<Instruction>(*UI);
00362         assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User));
00363         std::vector<Value*> Indices(User->op_begin()+1, User->op_end());
00364         ArgIndices.insert(Indices);
00365         LoadInst *OrigLoad;
00366         if (LoadInst *L = dyn_cast<LoadInst>(User))
00367           OrigLoad = L;
00368         else
00369           OrigLoad = cast<LoadInst>(User->use_back());
00370         OriginalLoads[Indices] = OrigLoad;
00371       }
00372 
00373       // Add a parameter to the function for each element passed in.
00374       for (ScalarizeTable::iterator SI = ArgIndices.begin(),
00375              E = ArgIndices.end(); SI != E; ++SI)
00376         Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));
00377 
00378       if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
00379         ++NumArgumentsPromoted;
00380       else
00381         ++NumAggregatesPromoted;
00382     }
00383 
00384   const Type *RetTy = FTy->getReturnType();
00385 
00386   // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
00387   // have zero fixed arguments.
00388   bool ExtraArgHack = false;
00389   if (Params.empty() && FTy->isVarArg()) {
00390     ExtraArgHack = true;
00391     Params.push_back(Type::IntTy);
00392   }
00393   FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
00394   
00395    // Create the new function body and insert it into the module...
00396   Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
00397   F->getParent()->getFunctionList().insert(F, NF);
00398 
00399   // Get the alias analysis information that we need to update to reflect our
00400   // changes.
00401   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
00402 
00403   // Loop over all of the callers of the function, transforming the call sites
00404   // to pass in the loaded pointers.
00405   //
00406   std::vector<Value*> Args;
00407   while (!F->use_empty()) {
00408     CallSite CS = CallSite::get(F->use_back());
00409     Instruction *Call = CS.getInstruction();
00410 
00411     // Loop over the operands, inserting GEP and loads in the caller as
00412     // appropriate.
00413     CallSite::arg_iterator AI = CS.arg_begin();
00414     for (Function::aiterator I = F->abegin(), E = F->aend(); I != E; ++I, ++AI)
00415       if (!ArgsToPromote.count(I))
00416         Args.push_back(*AI);          // Unmodified argument
00417       else if (!I->use_empty()) {
00418         // Non-dead argument: insert GEPs and loads as appropriate.
00419         ScalarizeTable &ArgIndices = ScalarizedElements[I];
00420         for (ScalarizeTable::iterator SI = ArgIndices.begin(),
00421                E = ArgIndices.end(); SI != E; ++SI) {
00422           Value *V = *AI;
00423           LoadInst *OrigLoad = OriginalLoads[*SI];
00424           if (!SI->empty()) {
00425             V = new GetElementPtrInst(V, *SI, V->getName()+".idx", Call);
00426             AA.copyValue(OrigLoad->getOperand(0), V);
00427           }
00428           Args.push_back(new LoadInst(V, V->getName()+".val", Call));
00429           AA.copyValue(OrigLoad, Args.back());
00430         }
00431       }
00432 
00433     if (ExtraArgHack)
00434       Args.push_back(Constant::getNullValue(Type::IntTy));
00435 
00436     // Push any varargs arguments on the list
00437     for (; AI != CS.arg_end(); ++AI)
00438       Args.push_back(*AI);
00439 
00440     Instruction *New;
00441     if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
00442       New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
00443                            Args, "", Call);
00444     } else {
00445       New = new CallInst(NF, Args, "", Call);
00446     }
00447     Args.clear();
00448 
00449     // Update the alias analysis implementation to know that we are replacing
00450     // the old call with a new one.
00451     AA.replaceWithNewValue(Call, New);
00452 
00453     if (!Call->use_empty()) {
00454       Call->replaceAllUsesWith(New);
00455       std::string Name = Call->getName();
00456       Call->setName("");
00457       New->setName(Name);
00458     }
00459     
00460     // Finally, remove the old call from the program, reducing the use-count of
00461     // F.
00462     Call->getParent()->getInstList().erase(Call);
00463   }
00464 
00465   // Since we have now created the new function, splice the body of the old
00466   // function right into the new function, leaving the old rotting hulk of the
00467   // function empty.
00468   NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
00469 
00470   // Loop over the argument list, transfering uses of the old arguments over to
00471   // the new arguments, also transfering over the names as well.
00472   //
00473   for (Function::aiterator I = F->abegin(), E = F->aend(), I2 = NF->abegin();
00474        I != E; ++I)
00475     if (!ArgsToPromote.count(I)) {
00476       // If this is an unmodified argument, move the name and users over to the
00477       // new version.
00478       I->replaceAllUsesWith(I2);
00479       I2->setName(I->getName());
00480       AA.replaceWithNewValue(I, I2);
00481       ++I2;
00482     } else if (I->use_empty()) {
00483       AA.deleteValue(I);
00484     } else {
00485       // Otherwise, if we promoted this argument, then all users are load
00486       // instructions, and all loads should be using the new argument that we
00487       // added.
00488       ScalarizeTable &ArgIndices = ScalarizedElements[I];
00489 
00490       while (!I->use_empty()) {
00491         if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) {
00492           assert(ArgIndices.begin()->empty() &&
00493                  "Load element should sort to front!");
00494           I2->setName(I->getName()+".val");
00495           LI->replaceAllUsesWith(I2);
00496           AA.replaceWithNewValue(LI, I2);
00497           LI->getParent()->getInstList().erase(LI);
00498           DEBUG(std::cerr << "*** Promoted load of argument '" << I->getName()
00499                           << "' in function '" << F->getName() << "'\n");
00500         } else {
00501           GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
00502           std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end());
00503 
00504           unsigned ArgNo = 0;
00505           Function::aiterator TheArg = I2;
00506           for (ScalarizeTable::iterator It = ArgIndices.begin();
00507                *It != Operands; ++It, ++TheArg) {
00508             assert(It != ArgIndices.end() && "GEP not handled??");
00509           }
00510 
00511           std::string NewName = I->getName();
00512           for (unsigned i = 0, e = Operands.size(); i != e; ++i)
00513             if (ConstantInt *CI = dyn_cast<ConstantInt>(Operands[i]))
00514               NewName += "."+itostr((int64_t)CI->getRawValue());
00515             else
00516               NewName += ".x";
00517           TheArg->setName(NewName+".val");
00518 
00519           DEBUG(std::cerr << "*** Promoted agg argument '" << TheArg->getName()
00520                           << "' of function '" << F->getName() << "'\n");
00521 
00522           // All of the uses must be load instructions.  Replace them all with
00523           // the argument specified by ArgNo.
00524           while (!GEP->use_empty()) {
00525             LoadInst *L = cast<LoadInst>(GEP->use_back());
00526             L->replaceAllUsesWith(TheArg);
00527             AA.replaceWithNewValue(L, TheArg);
00528             L->getParent()->getInstList().erase(L);
00529           }
00530           AA.deleteValue(GEP);
00531           GEP->getParent()->getInstList().erase(GEP);
00532         }
00533       }
00534 
00535       // Increment I2 past all of the arguments added for this promoted pointer.
00536       for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i)
00537         ++I2;
00538     }
00539 
00540   // Notify the alias analysis implementation that we inserted a new argument.
00541   if (ExtraArgHack)
00542     AA.copyValue(Constant::getNullValue(Type::IntTy), NF->abegin());
00543 
00544 
00545   // Tell the alias analysis that the old function is about to disappear.
00546   AA.replaceWithNewValue(F, NF);
00547 
00548   // Now that the old function is dead, delete it.
00549   F->getParent()->getFunctionList().erase(F);
00550   return NF;
00551 }