lib/Transforms/IPO/ArgumentPromotion.cpp - llvm - Git at Google

 //===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file was developed by the LLVM research group and is distributed under
 // the University of Illinois Open Source License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This pass promotes "by reference" arguments to be "by value" arguments.  In
 // practice, this means looking for internal functions that have pointer
 // arguments.  If we can prove, through the use of alias analysis, that an
 // argument is *only* loaded, then we can pass the value into the function
 // instead of the address of the value.  This can cause recursive simplification
 // of code and lead to the elimination of allocas (especially in C++ template
 // code like the STL).
 //
 // This pass also handles aggregate arguments that are passed into a function,
 // scalarizing them if the elements of the aggregate are only loaded.  Note that
 // we refuse to scalarize aggregates which would require passing in more than
 // three operands to the function, because we don't want to pass thousands of
 // operands for a large array or structure!
 //
 // Note that this transformation could also be done for arguments that are only
 // stored to (returning the value instead), but we do not currently handle that
 // case.  This case would be best handled when and if we start supporting
 // multiple return values from functions.
 //
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "argpromotion"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Constants.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Module.h"
 #include "llvm/CallGraphSCCPass.h"
 #include "llvm/Instructions.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/CallGraph.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Support/CallSite.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
 #include <set>
 using namespace llvm;

 namespace {
   Statistic<> NumArgumentsPromoted("argpromotion",
                                    "Number of pointer arguments promoted");
   Statistic<> NumAggregatesPromoted("argpromotion",
                                     "Number of aggregate arguments promoted");
   Statistic<> NumArgumentsDead("argpromotion",
                                "Number of dead pointer args eliminated");

   /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
   ///
   struct ArgPromotion : public CallGraphSCCPass {
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.addRequired<AliasAnalysis>();
       AU.addRequired<TargetData>();
       CallGraphSCCPass::getAnalysisUsage(AU);
     }

     virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
   private:
     bool PromoteArguments(CallGraphNode *CGN);
     bool isSafeToPromoteArgument(Argument *Arg) const;
     Function *DoPromotion(Function *F, std::vector<Argument*> &ArgsToPromote);
   };

   RegisterOpt<ArgPromotion> X("argpromotion",
                               "Promote 'by reference' arguments to scalars");
 }

 ModulePass *llvm::createArgumentPromotionPass() {
   return new ArgPromotion();
 }

 bool ArgPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
   bool Changed = false, LocalChange;

   do {  // Iterate until we stop promoting from this SCC.
     LocalChange = false;
     // Attempt to promote arguments from all functions in this SCC.
     for (unsigned i = 0, e = SCC.size(); i != e; ++i)
       LocalChange |= PromoteArguments(SCC[i]);
     Changed |= LocalChange;               // Remember that we changed something.
   } while (LocalChange);

   return Changed;
 }

 /// PromoteArguments - This method checks the specified function to see if there
 /// are any promotable arguments and if it is safe to promote the function (for
 /// example, all callers are direct).  If safe to promote some arguments, it
 /// calls the DoPromotion method.
 ///
 bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
   Function *F = CGN->getFunction();

   // Make sure that it is local to this module.
   if (!F || !F->hasInternalLinkage()) return false;

   // First check: see if there are any pointer arguments!  If not, quick exit.
   std::vector<Argument*> PointerArgs;
   for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
     if (isa<PointerType>(I->getType()))
       PointerArgs.push_back(I);
   if (PointerArgs.empty()) return false;

   // Second check: make sure that all callers are direct callers.  We can't
   // transform functions that have indirect callers.
   for (Value::use_iterator UI = F->use_begin(), E = F->use_end();
        UI != E; ++UI) {
     CallSite CS = CallSite::get(*UI);
     if (!CS.getInstruction())       // "Taking the address" of the function
       return false;

     // Ensure that this call site is CALLING the function, not passing it as
     // an argument.
     for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
          AI != E; ++AI)
       if (*AI == F) return false;   // Passing the function address in!
   }

   // Check to see which arguments are promotable.  If an argument is not
   // promotable, remove it from the PointerArgs vector.
   for (unsigned i = 0; i != PointerArgs.size(); ++i)
     if (!isSafeToPromoteArgument(PointerArgs[i])) {
       std::swap(PointerArgs[i--], PointerArgs.back());
       PointerArgs.pop_back();
     }

   // No promotable pointer arguments.
   if (PointerArgs.empty()) return false;

   // Okay, promote all of the arguments are rewrite the callees!
   Function *NewF = DoPromotion(F, PointerArgs);

   // Update the call graph to know that the old function is gone.
   getAnalysis<CallGraph>().changeFunction(F, NewF);
   return true;
 }

 /// IsAlwaysValidPointer - Return true if the specified pointer is always legal
 /// to load.
 static bool IsAlwaysValidPointer(Value *V) {
   if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true;
   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V))
     return IsAlwaysValidPointer(GEP->getOperand(0));
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
     if (CE->getOpcode() == Instruction::GetElementPtr)
       return IsAlwaysValidPointer(CE->getOperand(0));

   return false;
 }

 /// AllCalleesPassInValidPointerForArgument - Return true if we can prove that
 /// all callees pass in a valid pointer for the specified function argument.
 static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
   Function *Callee = Arg->getParent();

   unsigned ArgNo = std::distance(Callee->arg_begin(), Function::arg_iterator(Arg));

   // Look at all call sites of the function.  At this pointer we know we only
   // have direct callees.
   for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end();
        UI != E; ++UI) {
     CallSite CS = CallSite::get(*UI);
     assert(CS.getInstruction() && "Should only have direct calls!");

     if (!IsAlwaysValidPointer(CS.getArgument(ArgNo)))
       return false;
   }
   return true;
 }


 /// isSafeToPromoteArgument - As you might guess from the name of this method,
 /// it checks to see if it is both safe and useful to promote the argument.
 /// This method limits promotion of aggregates to only promote up to three
 /// elements of the aggregate in order to avoid exploding the number of
 /// arguments passed in.
 bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
   // We can only promote this argument if all of the uses are loads, or are GEP
   // instructions (with constant indices) that are subsequently loaded.
   bool HasLoadInEntryBlock = false;
   BasicBlock *EntryBlock = Arg->getParent()->begin();
   std::vector<LoadInst*> Loads;
   std::vector<std::vector<ConstantInt*> > GEPIndices;
   for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end();
        UI != E; ++UI)
     if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
       if (LI->isVolatile()) return false;  // Don't hack volatile loads
       Loads.push_back(LI);
       HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
     } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
       if (GEP->use_empty()) {
         // Dead GEP's cause trouble later.  Just remove them if we run into
         // them.
         getAnalysis<AliasAnalysis>().deleteValue(GEP);
         GEP->getParent()->getInstList().erase(GEP);
         return isSafeToPromoteArgument(Arg);
       }
       // Ensure that all of the indices are constants.
       std::vector<ConstantInt*> Operands;
       for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
         if (ConstantInt *C = dyn_cast<ConstantInt>(GEP->getOperand(i)))
           Operands.push_back(C);
         else
           return false;  // Not a constant operand GEP!

       // Ensure that the only users of the GEP are load instructions.
       for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end();
            UI != E; ++UI)
         if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
           if (LI->isVolatile()) return false;  // Don't hack volatile loads
           Loads.push_back(LI);
           HasLoadInEntryBlock |= LI->getParent() == EntryBlock;
         } else {
           return false;
         }

       // See if there is already a GEP with these indices.  If not, check to
       // make sure that we aren't promoting too many elements.  If so, nothing
       // to do.
       if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) ==
           GEPIndices.end()) {
         if (GEPIndices.size() == 3) {
           DEBUG(std::cerr << "argpromotion disable promoting argument '"
                 << Arg->getName() << "' because it would require adding more "
                 << "than 3 arguments to the function.\n");
           // We limit aggregate promotion to only promoting up to three elements
           // of the aggregate.
           return false;
         }
         GEPIndices.push_back(Operands);
       }
     } else {
       return false;  // Not a load or a GEP.
     }

   if (Loads.empty()) return true;  // No users, this is a dead argument.

   // If we decide that we want to promote this argument, the value is going to
   // be unconditionally loaded in all callees.  This is only safe to do if the
   // pointer was going to be unconditionally loaded anyway (i.e. there is a load
   // of the pointer in the entry block of the function) or if we can prove that
   // all pointers passed in are always to legal locations (for example, no null
   // pointers are passed in, no pointers to free'd memory, etc).
   if (!HasLoadInEntryBlock && !AllCalleesPassInValidPointerForArgument(Arg))
     return false;   // Cannot prove that this is safe!!

   // Okay, now we know that the argument is only used by load instructions and
   // it is safe to unconditionally load the pointer.  Use alias analysis to
   // check to see if the pointer is guaranteed to not be modified from entry of
   // the function to each of the load instructions.
   Function &F = *Arg->getParent();

   // Because there could be several/many load instructions, remember which
   // blocks we know to be transparent to the load.
   std::set<BasicBlock*> TranspBlocks;

   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
   TargetData &TD = getAnalysis<TargetData>();

   for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
     // Check to see if the load is invalidated from the start of the block to
     // the load itself.
     LoadInst *Load = Loads[i];
     BasicBlock *BB = Load->getParent();

     const PointerType *LoadTy =
       cast<PointerType>(Load->getOperand(0)->getType());
     unsigned LoadSize = (unsigned)TD.getTypeSize(LoadTy->getElementType());

     if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize))
       return false;  // Pointer is invalidated!

     // Now check every path from the entry block to the load for transparency.
     // To do this, we perform a depth first search on the inverse CFG from the
     // loading block.
     for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
       for (idf_ext_iterator<BasicBlock*> I = idf_ext_begin(*PI, TranspBlocks),
              E = idf_ext_end(*PI, TranspBlocks); I != E; ++I)
         if (AA.canBasicBlockModify(**I, Arg, LoadSize))
           return false;
   }

   // If the path from the entry of the function to each load is free of
   // instructions that potentially invalidate the load, we can make the
   // transformation!
   return true;
 }

 namespace {
   /// GEPIdxComparator - Provide a strong ordering for GEP indices.  All Value*
   /// elements are instances of ConstantInt.
   ///
   struct GEPIdxComparator {
     bool operator()(const std::vector<Value*> &LHS,
                     const std::vector<Value*> &RHS) const {
       unsigned idx = 0;
       for (; idx < LHS.size() && idx < RHS.size(); ++idx) {
         if (LHS[idx] != RHS[idx]) {
           return cast<ConstantInt>(LHS[idx])->getRawValue() <
                  cast<ConstantInt>(RHS[idx])->getRawValue();
         }
       }

       // Return less than if we ran out of stuff in LHS and we didn't run out of
       // stuff in RHS.
       return idx == LHS.size() && idx != RHS.size();
     }
   };
 }


 /// DoPromotion - This method actually performs the promotion of the specified
 /// arguments, and returns the new function.  At this point, we know that it's
 /// safe to do so.
 Function *ArgPromotion::DoPromotion(Function *F,
                                     std::vector<Argument*> &Args2Prom) {
   std::set<Argument*> ArgsToPromote(Args2Prom.begin(), Args2Prom.end());

   // Start by computing a new prototype for the function, which is the same as
   // the old function, but has modified arguments.
   const FunctionType *FTy = F->getFunctionType();
   std::vector<const Type*> Params;

   typedef std::set<std::vector<Value*>, GEPIdxComparator> ScalarizeTable;

   // ScalarizedElements - If we are promoting a pointer that has elements
   // accessed out of it, keep track of which elements are accessed so that we
   // can add one argument for each.
   //
   // Arguments that are directly loaded will have a zero element value here, to
   // handle cases where there are both a direct load and GEP accesses.
   //
   std::map<Argument*, ScalarizeTable> ScalarizedElements;

   // OriginalLoads - Keep track of a representative load instruction from the
   // original function so that we can tell the alias analysis implementation
   // what the new GEP/Load instructions we are inserting look like.
   std::map<std::vector<Value*>, LoadInst*> OriginalLoads;

   for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
     if (!ArgsToPromote.count(I)) {
       Params.push_back(I->getType());
     } else if (I->use_empty()) {
       ++NumArgumentsDead;
     } else {
       // Okay, this is being promoted.  Check to see if there are any GEP uses
       // of the argument.
       ScalarizeTable &ArgIndices = ScalarizedElements[I];
       for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
            ++UI) {
         Instruction *User = cast<Instruction>(*UI);
         assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User));
         std::vector<Value*> Indices(User->op_begin()+1, User->op_end());
         ArgIndices.insert(Indices);
         LoadInst *OrigLoad;
         if (LoadInst *L = dyn_cast<LoadInst>(User))
           OrigLoad = L;
         else
           OrigLoad = cast<LoadInst>(User->use_back());
         OriginalLoads[Indices] = OrigLoad;
       }

       // Add a parameter to the function for each element passed in.
       for (ScalarizeTable::iterator SI = ArgIndices.begin(),
              E = ArgIndices.end(); SI != E; ++SI)
         Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));

       if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
         ++NumArgumentsPromoted;
       else
         ++NumAggregatesPromoted;
     }

   const Type *RetTy = FTy->getReturnType();

   // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
   // have zero fixed arguments.
   bool ExtraArgHack = false;
   if (Params.empty() && FTy->isVarArg()) {
     ExtraArgHack = true;
     Params.push_back(Type::IntTy);
   }
   FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());

    // Create the new function body and insert it into the module...
   Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
   NF->setCallingConv(F->getCallingConv());
   F->getParent()->getFunctionList().insert(F, NF);

   // Get the alias analysis information that we need to update to reflect our
   // changes.
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();

   // Loop over all of the callers of the function, transforming the call sites
   // to pass in the loaded pointers.
   //
   std::vector<Value*> Args;
   while (!F->use_empty()) {
     CallSite CS = CallSite::get(F->use_back());
     Instruction *Call = CS.getInstruction();

     // Loop over the operands, inserting GEP and loads in the caller as
     // appropriate.
     CallSite::arg_iterator AI = CS.arg_begin();
     for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
          I != E; ++I, ++AI)
       if (!ArgsToPromote.count(I))
         Args.push_back(*AI);          // Unmodified argument
       else if (!I->use_empty()) {
         // Non-dead argument: insert GEPs and loads as appropriate.
         ScalarizeTable &ArgIndices = ScalarizedElements[I];
         for (ScalarizeTable::iterator SI = ArgIndices.begin(),
                E = ArgIndices.end(); SI != E; ++SI) {
           Value *V = *AI;
           LoadInst *OrigLoad = OriginalLoads[*SI];
           if (!SI->empty()) {
             V = new GetElementPtrInst(V, *SI, V->getName()+".idx", Call);
             AA.copyValue(OrigLoad->getOperand(0), V);
           }
           Args.push_back(new LoadInst(V, V->getName()+".val", Call));
           AA.copyValue(OrigLoad, Args.back());
         }
       }

     if (ExtraArgHack)
       Args.push_back(Constant::getNullValue(Type::IntTy));

     // Push any varargs arguments on the list
     for (; AI != CS.arg_end(); ++AI)
       Args.push_back(*AI);

     Instruction *New;
     if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
       New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
                            Args, "", Call);
       cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
     } else {
       New = new CallInst(NF, Args, "", Call);
       cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
       if (cast<CallInst>(Call)->isTailCall())
         cast<CallInst>(New)->setTailCall();
     }
     Args.clear();

     // Update the alias analysis implementation to know that we are replacing
     // the old call with a new one.
     AA.replaceWithNewValue(Call, New);

     if (!Call->use_empty()) {
       Call->replaceAllUsesWith(New);
       std::string Name = Call->getName();
       Call->setName("");
       New->setName(Name);
     }

     // Finally, remove the old call from the program, reducing the use-count of
     // F.
     Call->getParent()->getInstList().erase(Call);
   }

   // Since we have now created the new function, splice the body of the old
   // function right into the new function, leaving the old rotting hulk of the
   // function empty.
   NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());

   // Loop over the argument list, transfering uses of the old arguments over to
   // the new arguments, also transfering over the names as well.
   //
   for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), I2 = NF->arg_begin();
        I != E; ++I)
     if (!ArgsToPromote.count(I)) {
       // If this is an unmodified argument, move the name and users over to the
       // new version.
       I->replaceAllUsesWith(I2);
       I2->setName(I->getName());
       AA.replaceWithNewValue(I, I2);
       ++I2;
     } else if (I->use_empty()) {
       AA.deleteValue(I);
     } else {
       // Otherwise, if we promoted this argument, then all users are load
       // instructions, and all loads should be using the new argument that we
       // added.
       ScalarizeTable &ArgIndices = ScalarizedElements[I];

       while (!I->use_empty()) {
         if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) {
           assert(ArgIndices.begin()->empty() &&
                  "Load element should sort to front!");
           I2->setName(I->getName()+".val");
           LI->replaceAllUsesWith(I2);
           AA.replaceWithNewValue(LI, I2);
           LI->getParent()->getInstList().erase(LI);
           DEBUG(std::cerr << "*** Promoted load of argument '" << I->getName()
                           << "' in function '" << F->getName() << "'\n");
         } else {
           GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
           std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end());

           unsigned ArgNo = 0;
           Function::arg_iterator TheArg = I2;
           for (ScalarizeTable::iterator It = ArgIndices.begin();
                *It != Operands; ++It, ++TheArg) {
             assert(It != ArgIndices.end() && "GEP not handled??");
           }

           std::string NewName = I->getName();
           for (unsigned i = 0, e = Operands.size(); i != e; ++i)
             if (ConstantInt *CI = dyn_cast<ConstantInt>(Operands[i]))
               NewName += "."+itostr((int64_t)CI->getRawValue());
             else
               NewName += ".x";
           TheArg->setName(NewName+".val");

           DEBUG(std::cerr << "*** Promoted agg argument '" << TheArg->getName()
                           << "' of function '" << F->getName() << "'\n");

           // All of the uses must be load instructions.  Replace them all with
           // the argument specified by ArgNo.
           while (!GEP->use_empty()) {
             LoadInst *L = cast<LoadInst>(GEP->use_back());
             L->replaceAllUsesWith(TheArg);
             AA.replaceWithNewValue(L, TheArg);
             L->getParent()->getInstList().erase(L);
           }
           AA.deleteValue(GEP);
           GEP->getParent()->getInstList().erase(GEP);
         }
       }

       // Increment I2 past all of the arguments added for this promoted pointer.
       for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i)
         ++I2;
     }

   // Notify the alias analysis implementation that we inserted a new argument.
   if (ExtraArgHack)
     AA.copyValue(Constant::getNullValue(Type::IntTy), NF->arg_begin());


   // Tell the alias analysis that the old function is about to disappear.
   AA.replaceWithNewValue(F, NF);

   // Now that the old function is dead, delete it.
   F->getParent()->getFunctionList().erase(F);
   return NF;
 }
	//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file was developed by the LLVM research group and is distributed under
	// the University of Illinois Open Source License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This pass promotes "by reference" arguments to be "by value" arguments. In
	// practice, this means looking for internal functions that have pointer
	// arguments. If we can prove, through the use of alias analysis, that an
	// argument is only loaded, then we can pass the value into the function
	// instead of the address of the value. This can cause recursive simplification
	// of code and lead to the elimination of allocas (especially in C++ template
	// code like the STL).
	//
	// This pass also handles aggregate arguments that are passed into a function,
	// scalarizing them if the elements of the aggregate are only loaded. Note that
	// we refuse to scalarize aggregates which would require passing in more than
	// three operands to the function, because we don't want to pass thousands of
	// operands for a large array or structure!
	//
	// Note that this transformation could also be done for arguments that are only
	// stored to (returning the value instead), but we do not currently handle that
	// case. This case would be best handled when and if we start supporting
	// multiple return values from functions.
	//
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "argpromotion"
	#include "llvm/Transforms/IPO.h"
	#include "llvm/Constants.h"
	#include "llvm/DerivedTypes.h"
	#include "llvm/Module.h"
	#include "llvm/CallGraphSCCPass.h"
	#include "llvm/Instructions.h"
	#include "llvm/Analysis/AliasAnalysis.h"
	#include "llvm/Analysis/CallGraph.h"
	#include "llvm/Target/TargetData.h"
	#include "llvm/Support/CallSite.h"
	#include "llvm/Support/CFG.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/ADT/DepthFirstIterator.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/ADT/StringExtras.h"
	#include <set>
	using namespace llvm;

	namespace {
	Statistic<> NumArgumentsPromoted("argpromotion",
	"Number of pointer arguments promoted");
	Statistic<> NumAggregatesPromoted("argpromotion",
	"Number of aggregate arguments promoted");
	Statistic<> NumArgumentsDead("argpromotion",
	"Number of dead pointer args eliminated");

	/// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
	///
	struct ArgPromotion : public CallGraphSCCPass {
	virtual void getAnalysisUsage(AnalysisUsage &AU) const {
	AU.addRequired<AliasAnalysis>();
	AU.addRequired<TargetData>();
	CallGraphSCCPass::getAnalysisUsage(AU);
	}

	virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
	private:
	bool PromoteArguments(CallGraphNode *CGN);
	bool isSafeToPromoteArgument(Argument *Arg) const;
	Function DoPromotion(Function F, std::vector<Argument*> &ArgsToPromote);
	};

	RegisterOpt<ArgPromotion> X("argpromotion",
	"Promote 'by reference' arguments to scalars");
	}

	ModulePass *llvm::createArgumentPromotionPass() {
	return new ArgPromotion();
	}

	bool ArgPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
	bool Changed = false, LocalChange;

	do { // Iterate until we stop promoting from this SCC.
	LocalChange = false;
	// Attempt to promote arguments from all functions in this SCC.
	for (unsigned i = 0, e = SCC.size(); i != e; ++i)
	LocalChange \|= PromoteArguments(SCC[i]);
	Changed \|= LocalChange; // Remember that we changed something.
	} while (LocalChange);

	return Changed;
	}

	/// PromoteArguments - This method checks the specified function to see if there
	/// are any promotable arguments and if it is safe to promote the function (for
	/// example, all callers are direct). If safe to promote some arguments, it
	/// calls the DoPromotion method.
	///
	bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
	Function *F = CGN->getFunction();

	// Make sure that it is local to this module.
	if (!F \|\| !F->hasInternalLinkage()) return false;

	// First check: see if there are any pointer arguments! If not, quick exit.
	std::vector<Argument*> PointerArgs;
	for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
	if (isa<PointerType>(I->getType()))
	PointerArgs.push_back(I);
	if (PointerArgs.empty()) return false;

	// Second check: make sure that all callers are direct callers. We can't
	// transform functions that have indirect callers.
	for (Value::use_iterator UI = F->use_begin(), E = F->use_end();
	UI != E; ++UI) {
	CallSite CS = CallSite::get(*UI);
	if (!CS.getInstruction()) // "Taking the address" of the function
	return false;

	// Ensure that this call site is CALLING the function, not passing it as
	// an argument.
	for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
	AI != E; ++AI)
	if (*AI == F) return false; // Passing the function address in!
	}

	// Check to see which arguments are promotable. If an argument is not
	// promotable, remove it from the PointerArgs vector.
	for (unsigned i = 0; i != PointerArgs.size(); ++i)
	if (!isSafeToPromoteArgument(PointerArgs[i])) {
	std::swap(PointerArgs[i--], PointerArgs.back());
	PointerArgs.pop_back();
	}

	// No promotable pointer arguments.
	if (PointerArgs.empty()) return false;

	// Okay, promote all of the arguments are rewrite the callees!
	Function *NewF = DoPromotion(F, PointerArgs);

	// Update the call graph to know that the old function is gone.
	getAnalysis<CallGraph>().changeFunction(F, NewF);
	return true;
	}

	/// IsAlwaysValidPointer - Return true if the specified pointer is always legal
	/// to load.
	static bool IsAlwaysValidPointer(Value *V) {
	if (isa<AllocaInst>(V) \|\| isa<GlobalVariable>(V)) return true;
	if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V))
	return IsAlwaysValidPointer(GEP->getOperand(0));
	if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
	if (CE->getOpcode() == Instruction::GetElementPtr)
	return IsAlwaysValidPointer(CE->getOperand(0));

	return false;
	}

	/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that
	/// all callees pass in a valid pointer for the specified function argument.
	static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
	Function *Callee = Arg->getParent();

	unsigned ArgNo = std::distance(Callee->arg_begin(), Function::arg_iterator(Arg));

	// Look at all call sites of the function. At this pointer we know we only
	// have direct callees.
	for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end();
	UI != E; ++UI) {
	CallSite CS = CallSite::get(*UI);
	assert(CS.getInstruction() && "Should only have direct calls!");

	if (!IsAlwaysValidPointer(CS.getArgument(ArgNo)))
	return false;
	}
	return true;
	}


	/// isSafeToPromoteArgument - As you might guess from the name of this method,
	/// it checks to see if it is both safe and useful to promote the argument.
	/// This method limits promotion of aggregates to only promote up to three
	/// elements of the aggregate in order to avoid exploding the number of
	/// arguments passed in.
	bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
	// We can only promote this argument if all of the uses are loads, or are GEP
	// instructions (with constant indices) that are subsequently loaded.
	bool HasLoadInEntryBlock = false;
	BasicBlock *EntryBlock = Arg->getParent()->begin();
	std::vector<LoadInst*> Loads;
	std::vector<std::vector<ConstantInt*> > GEPIndices;
	for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end();
	UI != E; ++UI)
	if (LoadInst LI = dyn_cast<LoadInst>(UI)) {
	if (LI->isVolatile()) return false; // Don't hack volatile loads
	Loads.push_back(LI);
	HasLoadInEntryBlock \|= LI->getParent() == EntryBlock;
	} else if (GetElementPtrInst GEP = dyn_cast<GetElementPtrInst>(UI)) {
	if (GEP->use_empty()) {
	// Dead GEP's cause trouble later. Just remove them if we run into
	// them.
	getAnalysis<AliasAnalysis>().deleteValue(GEP);
	GEP->getParent()->getInstList().erase(GEP);
	return isSafeToPromoteArgument(Arg);
	}
	// Ensure that all of the indices are constants.
	std::vector<ConstantInt*> Operands;
	for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
	if (ConstantInt *C = dyn_cast<ConstantInt>(GEP->getOperand(i)))
	Operands.push_back(C);
	else
	return false; // Not a constant operand GEP!

	// Ensure that the only users of the GEP are load instructions.
	for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end();
	UI != E; ++UI)
	if (LoadInst LI = dyn_cast<LoadInst>(UI)) {
	if (LI->isVolatile()) return false; // Don't hack volatile loads
	Loads.push_back(LI);
	HasLoadInEntryBlock \|= LI->getParent() == EntryBlock;
	} else {
	return false;
	}

	// See if there is already a GEP with these indices. If not, check to
	// make sure that we aren't promoting too many elements. If so, nothing
	// to do.
	if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) ==
	GEPIndices.end()) {
	if (GEPIndices.size() == 3) {
	DEBUG(std::cerr << "argpromotion disable promoting argument '"
	<< Arg->getName() << "' because it would require adding more "
	<< "than 3 arguments to the function.\n");
	// We limit aggregate promotion to only promoting up to three elements
	// of the aggregate.
	return false;
	}
	GEPIndices.push_back(Operands);
	}
	} else {
	return false; // Not a load or a GEP.
	}

	if (Loads.empty()) return true; // No users, this is a dead argument.

	// If we decide that we want to promote this argument, the value is going to
	// be unconditionally loaded in all callees. This is only safe to do if the
	// pointer was going to be unconditionally loaded anyway (i.e. there is a load
	// of the pointer in the entry block of the function) or if we can prove that
	// all pointers passed in are always to legal locations (for example, no null
	// pointers are passed in, no pointers to free'd memory, etc).
	if (!HasLoadInEntryBlock && !AllCalleesPassInValidPointerForArgument(Arg))
	return false; // Cannot prove that this is safe!!

	// Okay, now we know that the argument is only used by load instructions and
	// it is safe to unconditionally load the pointer. Use alias analysis to
	// check to see if the pointer is guaranteed to not be modified from entry of
	// the function to each of the load instructions.
	Function &F = *Arg->getParent();

	// Because there could be several/many load instructions, remember which
	// blocks we know to be transparent to the load.
	std::set<BasicBlock*> TranspBlocks;

	AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
	TargetData &TD = getAnalysis<TargetData>();

	for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
	// Check to see if the load is invalidated from the start of the block to
	// the load itself.
	LoadInst *Load = Loads[i];
	BasicBlock *BB = Load->getParent();

	const PointerType *LoadTy =
	cast<PointerType>(Load->getOperand(0)->getType());
	unsigned LoadSize = (unsigned)TD.getTypeSize(LoadTy->getElementType());

	if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize))
	return false; // Pointer is invalidated!

	// Now check every path from the entry block to the load for transparency.
	// To do this, we perform a depth first search on the inverse CFG from the
	// loading block.
	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
	for (idf_ext_iterator<BasicBlock> I = idf_ext_begin(PI, TranspBlocks),
	E = idf_ext_end(*PI, TranspBlocks); I != E; ++I)
	if (AA.canBasicBlockModify(**I, Arg, LoadSize))
	return false;
	}

	// If the path from the entry of the function to each load is free of
	// instructions that potentially invalidate the load, we can make the
	// transformation!
	return true;
	}

	namespace {
	/// GEPIdxComparator - Provide a strong ordering for GEP indices. All Value*
	/// elements are instances of ConstantInt.
	///
	struct GEPIdxComparator {
	bool operator()(const std::vector<Value*> &LHS,
	const std::vector<Value*> &RHS) const {
	unsigned idx = 0;
	for (; idx < LHS.size() && idx < RHS.size(); ++idx) {
	if (LHS[idx] != RHS[idx]) {
	return cast<ConstantInt>(LHS[idx])->getRawValue() <
	cast<ConstantInt>(RHS[idx])->getRawValue();
	}
	}

	// Return less than if we ran out of stuff in LHS and we didn't run out of
	// stuff in RHS.
	return idx == LHS.size() && idx != RHS.size();
	}
	};
	}


	/// DoPromotion - This method actually performs the promotion of the specified
	/// arguments, and returns the new function. At this point, we know that it's
	/// safe to do so.
	Function ArgPromotion::DoPromotion(Function F,
	std::vector<Argument*> &Args2Prom) {
	std::set<Argument*> ArgsToPromote(Args2Prom.begin(), Args2Prom.end());

	// Start by computing a new prototype for the function, which is the same as
	// the old function, but has modified arguments.
	const FunctionType *FTy = F->getFunctionType();
	std::vector<const Type*> Params;

	typedef std::set<std::vector<Value*>, GEPIdxComparator> ScalarizeTable;

	// ScalarizedElements - If we are promoting a pointer that has elements
	// accessed out of it, keep track of which elements are accessed so that we
	// can add one argument for each.
	//
	// Arguments that are directly loaded will have a zero element value here, to
	// handle cases where there are both a direct load and GEP accesses.
	//
	std::map<Argument*, ScalarizeTable> ScalarizedElements;

	// OriginalLoads - Keep track of a representative load instruction from the
	// original function so that we can tell the alias analysis implementation
	// what the new GEP/Load instructions we are inserting look like.
	std::map<std::vector<Value>, LoadInst> OriginalLoads;

	for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
	if (!ArgsToPromote.count(I)) {
	Params.push_back(I->getType());
	} else if (I->use_empty()) {
	++NumArgumentsDead;
	} else {
	// Okay, this is being promoted. Check to see if there are any GEP uses
	// of the argument.
	ScalarizeTable &ArgIndices = ScalarizedElements[I];
	for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
	++UI) {
	Instruction User = cast<Instruction>(UI);
	assert(isa<LoadInst>(User) \|\| isa<GetElementPtrInst>(User));
	std::vector<Value*> Indices(User->op_begin()+1, User->op_end());
	ArgIndices.insert(Indices);
	LoadInst *OrigLoad;
	if (LoadInst *L = dyn_cast<LoadInst>(User))
	OrigLoad = L;
	else
	OrigLoad = cast<LoadInst>(User->use_back());
	OriginalLoads[Indices] = OrigLoad;
	}

	// Add a parameter to the function for each element passed in.
	for (ScalarizeTable::iterator SI = ArgIndices.begin(),
	E = ArgIndices.end(); SI != E; ++SI)
	Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));

	if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
	++NumArgumentsPromoted;
	else
	++NumAggregatesPromoted;
	}

	const Type *RetTy = FTy->getReturnType();

	// Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
	// have zero fixed arguments.
	bool ExtraArgHack = false;
	if (Params.empty() && FTy->isVarArg()) {
	ExtraArgHack = true;
	Params.push_back(Type::IntTy);
	}
	FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());

	// Create the new function body and insert it into the module...
	Function *NF = new Function(NFTy, F->getLinkage(), F->getName());
	NF->setCallingConv(F->getCallingConv());
	F->getParent()->getFunctionList().insert(F, NF);

	// Get the alias analysis information that we need to update to reflect our
	// changes.
	AliasAnalysis &AA = getAnalysis<AliasAnalysis>();

	// Loop over all of the callers of the function, transforming the call sites
	// to pass in the loaded pointers.
	//
	std::vector<Value*> Args;
	while (!F->use_empty()) {
	CallSite CS = CallSite::get(F->use_back());
	Instruction *Call = CS.getInstruction();

	// Loop over the operands, inserting GEP and loads in the caller as
	// appropriate.
	CallSite::arg_iterator AI = CS.arg_begin();
	for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
	I != E; ++I, ++AI)
	if (!ArgsToPromote.count(I))
	Args.push_back(*AI); // Unmodified argument
	else if (!I->use_empty()) {
	// Non-dead argument: insert GEPs and loads as appropriate.
	ScalarizeTable &ArgIndices = ScalarizedElements[I];
	for (ScalarizeTable::iterator SI = ArgIndices.begin(),
	E = ArgIndices.end(); SI != E; ++SI) {
	Value V = AI;
	LoadInst OrigLoad = OriginalLoads[SI];
	if (!SI->empty()) {
	V = new GetElementPtrInst(V, *SI, V->getName()+".idx", Call);
	AA.copyValue(OrigLoad->getOperand(0), V);
	}
	Args.push_back(new LoadInst(V, V->getName()+".val", Call));
	AA.copyValue(OrigLoad, Args.back());
	}
	}

	if (ExtraArgHack)
	Args.push_back(Constant::getNullValue(Type::IntTy));

	// Push any varargs arguments on the list
	for (; AI != CS.arg_end(); ++AI)
	Args.push_back(*AI);

	Instruction *New;
	if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
	New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(),
	Args, "", Call);
	cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
	} else {
	New = new CallInst(NF, Args, "", Call);
	cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
	if (cast<CallInst>(Call)->isTailCall())
	cast<CallInst>(New)->setTailCall();
	}
	Args.clear();

	// Update the alias analysis implementation to know that we are replacing
	// the old call with a new one.
	AA.replaceWithNewValue(Call, New);

	if (!Call->use_empty()) {
	Call->replaceAllUsesWith(New);
	std::string Name = Call->getName();
	Call->setName("");
	New->setName(Name);
	}

	// Finally, remove the old call from the program, reducing the use-count of
	// F.
	Call->getParent()->getInstList().erase(Call);
	}

	// Since we have now created the new function, splice the body of the old
	// function right into the new function, leaving the old rotting hulk of the
	// function empty.
	NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());

	// Loop over the argument list, transfering uses of the old arguments over to
	// the new arguments, also transfering over the names as well.
	//
	for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), I2 = NF->arg_begin();
	I != E; ++I)
	if (!ArgsToPromote.count(I)) {
	// If this is an unmodified argument, move the name and users over to the
	// new version.
	I->replaceAllUsesWith(I2);
	I2->setName(I->getName());
	AA.replaceWithNewValue(I, I2);
	++I2;
	} else if (I->use_empty()) {
	AA.deleteValue(I);
	} else {
	// Otherwise, if we promoted this argument, then all users are load
	// instructions, and all loads should be using the new argument that we
	// added.
	ScalarizeTable &ArgIndices = ScalarizedElements[I];

	while (!I->use_empty()) {
	if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) {
	assert(ArgIndices.begin()->empty() &&
	"Load element should sort to front!");
	I2->setName(I->getName()+".val");
	LI->replaceAllUsesWith(I2);
	AA.replaceWithNewValue(LI, I2);
	LI->getParent()->getInstList().erase(LI);
	DEBUG(std::cerr << "*** Promoted load of argument '" << I->getName()
	<< "' in function '" << F->getName() << "'\n");
	} else {
	GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
	std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end());

	unsigned ArgNo = 0;
	Function::arg_iterator TheArg = I2;
	for (ScalarizeTable::iterator It = ArgIndices.begin();
	*It != Operands; ++It, ++TheArg) {
	assert(It != ArgIndices.end() && "GEP not handled??");
	}

	std::string NewName = I->getName();
	for (unsigned i = 0, e = Operands.size(); i != e; ++i)
	if (ConstantInt *CI = dyn_cast<ConstantInt>(Operands[i]))
	NewName += "."+itostr((int64_t)CI->getRawValue());
	else
	NewName += ".x";
	TheArg->setName(NewName+".val");

	DEBUG(std::cerr << "*** Promoted agg argument '" << TheArg->getName()
	<< "' of function '" << F->getName() << "'\n");

	// All of the uses must be load instructions. Replace them all with
	// the argument specified by ArgNo.
	while (!GEP->use_empty()) {
	LoadInst *L = cast<LoadInst>(GEP->use_back());
	L->replaceAllUsesWith(TheArg);
	AA.replaceWithNewValue(L, TheArg);
	L->getParent()->getInstList().erase(L);
	}
	AA.deleteValue(GEP);
	GEP->getParent()->getInstList().erase(GEP);
	}
	}

	// Increment I2 past all of the arguments added for this promoted pointer.
	for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i)
	++I2;
	}

	// Notify the alias analysis implementation that we inserted a new argument.
	if (ExtraArgHack)
	AA.copyValue(Constant::getNullValue(Type::IntTy), NF->arg_begin());


	// Tell the alias analysis that the old function is about to disappear.
	AA.replaceWithNewValue(F, NF);

	// Now that the old function is dead, delete it.
	F->getParent()->getFunctionList().erase(F);
	return NF;
	}