lib/Transforms/IPO/StructRetPromotion.cpp - platform/external/llvm - Gitiles

 //===-- StructRetPromotion.cpp - Promote sret arguments -000000------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // TODO : Describe this pass.
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "sretpromotion"
 #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/CallGraph.h"
 #include "llvm/Support/CallSite.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Support/Compiler.h"
 using namespace llvm;

 STATISTIC(NumRejectedSRETUses , "Number of sret rejected due to unexpected uses");
 STATISTIC(NumSRET , "Number of sret promoted");
 namespace {
   /// SRETPromotion - This pass removes sret parameter and updates
   /// function to use multiple return value.
   ///
   struct VISIBILITY_HIDDEN SRETPromotion : public CallGraphSCCPass {
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       CallGraphSCCPass::getAnalysisUsage(AU);
     }

     virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
     static char ID; // Pass identification, replacement for typeid
     SRETPromotion() : CallGraphSCCPass((intptr_t)&ID) {}

   private:
     bool PromoteReturn(CallGraphNode *CGN);
     bool isSafeToUpdateAllCallers(Function *F);
     Function *cloneFunctionBody(Function *F, const StructType *STy);
     void updateCallSites(Function *F, Function *NF);
     bool nestedStructType(const StructType *STy);
   };

   char SRETPromotion::ID = 0;
   RegisterPass<SRETPromotion> X("sretpromotion",
                                "Promote sret arguments to multiple ret values");
 }

 Pass *llvm::createStructRetPromotionPass() {
   return new SRETPromotion();
 }

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

   for (unsigned i = 0, e = SCC.size(); i != e; ++i)
     Changed |= PromoteReturn(SCC[i]);

   return Changed;
 }

 /// PromoteReturn - This method promotes function that uses StructRet paramater
 /// into a function that uses mulitple return value.
 bool SRETPromotion::PromoteReturn(CallGraphNode *CGN) {
   Function *F = CGN->getFunction();

   if (!F || F->isDeclaration())
     return false;

   // Make sure that function returns struct.
   if (F->arg_size() == 0 || !F->hasStructRetAttr() || F->doesNotReturn())
     return false;

   assert (F->getReturnType() == Type::VoidTy && "Invalid function return type");
   Function::arg_iterator AI = F->arg_begin();
   const llvm::PointerType *FArgType = dyn_cast<PointerType>(AI->getType());
   assert (FArgType && "Invalid sret paramater type");
   const llvm::StructType *STy =
     dyn_cast<StructType>(FArgType->getElementType());
   assert (STy && "Invalid sret parameter element type");

   if (nestedStructType(STy))
     return false;

   // Check if it is ok to perform this promotion.
   if (isSafeToUpdateAllCallers(F) == false) {
     NumRejectedSRETUses++;
     return false;
   }

   NumSRET++;
   // [1] Replace use of sret parameter
   AllocaInst *TheAlloca = new AllocaInst (STy, NULL, "mrv",
                                           F->getEntryBlock().begin());
   Value *NFirstArg = F->arg_begin();
   NFirstArg->replaceAllUsesWith(TheAlloca);

   // [2] Find and replace ret instructions
   SmallVector<Value *,4> RetVals;
   for (Function::iterator FI = F->begin(), FE = F->end();  FI != FE; ++FI)
     for(BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
       Instruction *I = BI;
       ++BI;
       if (isa<ReturnInst>(I)) {
         RetVals.clear();
         for (unsigned idx = 0; idx < STy->getNumElements(); ++idx) {
           SmallVector<Value*, 2> GEPIdx;
           GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, 0));
           GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, idx));
           Value *NGEPI = GetElementPtrInst::Create(TheAlloca, GEPIdx.begin(),
                                                    GEPIdx.end(),
                                                    "mrv.gep", I);
           Value *NV = new LoadInst(NGEPI, "mrv.ld", I);
           RetVals.push_back(NV);
         }

         ReturnInst *NR = ReturnInst::Create(&RetVals[0], RetVals.size(), I);
         I->replaceAllUsesWith(NR);
         I->eraseFromParent();
       }
     }

   // [3] Create the new function body and insert it into the module.
   Function *NF = cloneFunctionBody(F, STy);

   // [4] Update all call sites to use new function
   updateCallSites(F, NF);

   F->eraseFromParent();
   getAnalysis<CallGraph>().changeFunction(F, NF);
   return true;
 }

   // Check if it is ok to perform this promotion.
 bool SRETPromotion::isSafeToUpdateAllCallers(Function *F) {

   if (F->use_empty())
     // No users. OK to modify signature.
     return true;

   for (Value::use_iterator FnUseI = F->use_begin(), FnUseE = F->use_end();
        FnUseI != FnUseE; ++FnUseI) {

     CallSite CS = CallSite::get(*FnUseI);
     Instruction *Call = CS.getInstruction();
     CallSite::arg_iterator AI = CS.arg_begin();
     Value *FirstArg = *AI;

     if (!isa<AllocaInst>(FirstArg))
       return false;

     // Check FirstArg's users.
     for (Value::use_iterator ArgI = FirstArg->use_begin(),
            ArgE = FirstArg->use_end(); ArgI != ArgE; ++ArgI) {

       // If FirstArg user is a CallInst that does not correspond to current
       // call site then this function F is not suitable for sret promotion.
       if (CallInst *CI = dyn_cast<CallInst>(ArgI)) {
         if (CI != Call)
           return false;
       }
       // If FirstArg user is a GEP whose all users are not LoadInst then
       // this function F is not suitable for sret promotion.
       else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(ArgI)) {
         // TODO : Use dom info and insert PHINodes to collect get results
         // from multiple call sites for this GEP.
         if (GEP->getParent() != Call->getParent())
           return false;
         for (Value::use_iterator GEPI = GEP->use_begin(), GEPE = GEP->use_end();
              GEPI != GEPE; ++GEPI)
           if (!isa<LoadInst>(GEPI))
             return false;
       }
       // Any other FirstArg users make this function unsuitable for sret
       // promotion.
       else
         return false;
     }
   }

   return true;
 }

 /// cloneFunctionBody - Create a new function based on F and
 /// insert it into module. Remove first argument. Use STy as
 /// the return type for new function.
 Function *SRETPromotion::cloneFunctionBody(Function *F,
                                            const StructType *STy) {

   const FunctionType *FTy = F->getFunctionType();
   std::vector<const Type*> Params;

   // ParamAttrs - Keep track of the parameter attributes for the arguments.
   SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
   const PAListPtr &PAL = F->getParamAttrs();

   // Add any return attributes.
   if (ParameterAttributes attrs = PAL.getParamAttrs(0))
     ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));

   // Skip first argument.
   Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
   ++I;
   // 0th parameter attribute is reserved for return type.
   // 1th parameter attribute is for first 1st sret argument.
   unsigned ParamIndex = 2;
   while (I != E) {
     Params.push_back(I->getType());
     if (ParameterAttributes Attrs = PAL.getParamAttrs(ParamIndex))
       ParamAttrsVec.push_back(ParamAttrsWithIndex::get(ParamIndex - 1, Attrs));
     ++I;
     ++ParamIndex;
   }

   FunctionType *NFTy = FunctionType::get(STy, Params, FTy->isVarArg());
   Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
   NF->setCallingConv(F->getCallingConv());
   NF->setParamAttrs(PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()));
   F->getParent()->getFunctionList().insert(F, NF);
   NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());

   // Replace arguments
   I = F->arg_begin();
   E = F->arg_end();
   Function::arg_iterator NI = NF->arg_begin();
   ++I;
   while (I != E) {
       I->replaceAllUsesWith(NI);
       NI->takeName(I);
       ++I;
       ++NI;
   }

   return NF;
 }

 /// updateCallSites - Update all sites that call F to use NF.
 void SRETPromotion::updateCallSites(Function *F, Function *NF) {

   SmallVector<Value*, 16> Args;

   // ParamAttrs - Keep track of the parameter attributes for the arguments.
   SmallVector<ParamAttrsWithIndex, 8> ArgAttrsVec;

   for (Value::use_iterator FUI = F->use_begin(), FUE = F->use_end();
        FUI != FUE;) {
     CallSite CS = CallSite::get(*FUI);
     ++FUI;
     Instruction *Call = CS.getInstruction();

     const PAListPtr &PAL = F->getParamAttrs();
     // Add any return attributes.
     if (ParameterAttributes attrs = PAL.getParamAttrs(0))
       ArgAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));

     // Copy arguments, however skip first one.
     CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
     Value *FirstCArg = *AI;
     ++AI;
     // 0th parameter attribute is reserved for return type.
     // 1th parameter attribute is for first 1st sret argument.
     unsigned ParamIndex = 2;
     while (AI != AE) {
       Args.push_back(*AI);
       if (ParameterAttributes Attrs = PAL.getParamAttrs(ParamIndex))
         ArgAttrsVec.push_back(ParamAttrsWithIndex::get(ParamIndex - 1, Attrs));
       ++ParamIndex;
       ++AI;
     }


     PAListPtr NewPAL = PAListPtr::get(ArgAttrsVec.begin(), ArgAttrsVec.end());

     // Build new call instruction.
     Instruction *New;
     if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
       New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
                                Args.begin(), Args.end(), "", Call);
       cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
       cast<InvokeInst>(New)->setParamAttrs(NewPAL);
     } else {
       New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
       cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
       cast<CallInst>(New)->setParamAttrs(NewPAL);
       if (cast<CallInst>(Call)->isTailCall())
         cast<CallInst>(New)->setTailCall();
     }
     Args.clear();
     ArgAttrsVec.clear();
     New->takeName(Call);

     // Update all users of sret parameter to extract value using getresult.
     for (Value::use_iterator UI = FirstCArg->use_begin(),
            UE = FirstCArg->use_end(); UI != UE; ) {
       User *U2 = *UI++;
       CallInst *C2 = dyn_cast<CallInst>(U2);
       if (C2 && (C2 == Call))
         continue;
       else if (GetElementPtrInst *UGEP = dyn_cast<GetElementPtrInst>(U2)) {
         ConstantInt *Idx = dyn_cast<ConstantInt>(UGEP->getOperand(2));
         assert (Idx && "Unexpected getelementptr index!");
         Value *GR = new GetResultInst(New, Idx->getZExtValue(), "gr", UGEP);
         for (Value::use_iterator GI = UGEP->use_begin(),
                GE = UGEP->use_end(); GI != GE; ++GI) {
           if (LoadInst *L = dyn_cast<LoadInst>(*GI)) {
             L->replaceAllUsesWith(GR);
             L->eraseFromParent();
           }
         }
         UGEP->eraseFromParent();
       }
       else assert( 0 && "Unexpected sret parameter use");
     }
     Call->eraseFromParent();
   }
 }

 /// nestedStructType - Return true if STy includes any
 /// other aggregate types
 bool SRETPromotion::nestedStructType(const StructType *STy) {
   unsigned Num = STy->getNumElements();
   for (unsigned i = 0; i < Num; i++) {
     const Type *Ty = STy->getElementType(i);
     if (!Ty->isFirstClassType() && Ty != Type::VoidTy)
       return true;
   }
   return false;
 }
	//===-- StructRetPromotion.cpp - Promote sret arguments -000000------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// TODO : Describe this pass.
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "sretpromotion"
	#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/CallGraph.h"
	#include "llvm/Support/CallSite.h"
	#include "llvm/Support/CFG.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/ADT/SmallVector.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/Support/Compiler.h"
	using namespace llvm;

	STATISTIC(NumRejectedSRETUses , "Number of sret rejected due to unexpected uses");
	STATISTIC(NumSRET , "Number of sret promoted");
	namespace {
	/// SRETPromotion - This pass removes sret parameter and updates
	/// function to use multiple return value.
	///
	struct VISIBILITY_HIDDEN SRETPromotion : public CallGraphSCCPass {
	virtual void getAnalysisUsage(AnalysisUsage &AU) const {
	CallGraphSCCPass::getAnalysisUsage(AU);
	}

	virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
	static char ID; // Pass identification, replacement for typeid
	SRETPromotion() : CallGraphSCCPass((intptr_t)&ID) {}

	private:
	bool PromoteReturn(CallGraphNode *CGN);
	bool isSafeToUpdateAllCallers(Function *F);
	Function cloneFunctionBody(Function F, const StructType *STy);
	void updateCallSites(Function F, Function NF);
	bool nestedStructType(const StructType *STy);
	};

	char SRETPromotion::ID = 0;
	RegisterPass<SRETPromotion> X("sretpromotion",
	"Promote sret arguments to multiple ret values");
	}

	Pass *llvm::createStructRetPromotionPass() {
	return new SRETPromotion();
	}

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

	for (unsigned i = 0, e = SCC.size(); i != e; ++i)
	Changed \|= PromoteReturn(SCC[i]);

	return Changed;
	}

	/// PromoteReturn - This method promotes function that uses StructRet paramater
	/// into a function that uses mulitple return value.
	bool SRETPromotion::PromoteReturn(CallGraphNode *CGN) {
	Function *F = CGN->getFunction();

	if (!F \|\| F->isDeclaration())
	return false;

	// Make sure that function returns struct.
	if (F->arg_size() == 0 \|\| !F->hasStructRetAttr() \|\| F->doesNotReturn())
	return false;

	assert (F->getReturnType() == Type::VoidTy && "Invalid function return type");
	Function::arg_iterator AI = F->arg_begin();
	const llvm::PointerType *FArgType = dyn_cast<PointerType>(AI->getType());
	assert (FArgType && "Invalid sret paramater type");
	const llvm::StructType *STy =
	dyn_cast<StructType>(FArgType->getElementType());
	assert (STy && "Invalid sret parameter element type");

	if (nestedStructType(STy))
	return false;

	// Check if it is ok to perform this promotion.
	if (isSafeToUpdateAllCallers(F) == false) {
	NumRejectedSRETUses++;
	return false;
	}

	NumSRET++;
	// [1] Replace use of sret parameter
	AllocaInst *TheAlloca = new AllocaInst (STy, NULL, "mrv",
	F->getEntryBlock().begin());
	Value *NFirstArg = F->arg_begin();
	NFirstArg->replaceAllUsesWith(TheAlloca);

	// [2] Find and replace ret instructions
	SmallVector<Value *,4> RetVals;
	for (Function::iterator FI = F->begin(), FE = F->end(); FI != FE; ++FI)
	for(BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
	Instruction *I = BI;
	++BI;
	if (isa<ReturnInst>(I)) {
	RetVals.clear();
	for (unsigned idx = 0; idx < STy->getNumElements(); ++idx) {
	SmallVector<Value*, 2> GEPIdx;
	GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, 0));
	GEPIdx.push_back(ConstantInt::get(Type::Int32Ty, idx));
	Value *NGEPI = GetElementPtrInst::Create(TheAlloca, GEPIdx.begin(),
	GEPIdx.end(),
	"mrv.gep", I);
	Value *NV = new LoadInst(NGEPI, "mrv.ld", I);
	RetVals.push_back(NV);
	}

	ReturnInst *NR = ReturnInst::Create(&RetVals[0], RetVals.size(), I);
	I->replaceAllUsesWith(NR);
	I->eraseFromParent();
	}
	}

	// [3] Create the new function body and insert it into the module.
	Function *NF = cloneFunctionBody(F, STy);

	// [4] Update all call sites to use new function
	updateCallSites(F, NF);

	F->eraseFromParent();
	getAnalysis<CallGraph>().changeFunction(F, NF);
	return true;
	}

	// Check if it is ok to perform this promotion.
	bool SRETPromotion::isSafeToUpdateAllCallers(Function *F) {

	if (F->use_empty())
	// No users. OK to modify signature.
	return true;

	for (Value::use_iterator FnUseI = F->use_begin(), FnUseE = F->use_end();
	FnUseI != FnUseE; ++FnUseI) {

	CallSite CS = CallSite::get(*FnUseI);
	Instruction *Call = CS.getInstruction();
	CallSite::arg_iterator AI = CS.arg_begin();
	Value FirstArg = AI;

	if (!isa<AllocaInst>(FirstArg))
	return false;

	// Check FirstArg's users.
	for (Value::use_iterator ArgI = FirstArg->use_begin(),
	ArgE = FirstArg->use_end(); ArgI != ArgE; ++ArgI) {

	// If FirstArg user is a CallInst that does not correspond to current
	// call site then this function F is not suitable for sret promotion.
	if (CallInst *CI = dyn_cast<CallInst>(ArgI)) {
	if (CI != Call)
	return false;
	}
	// If FirstArg user is a GEP whose all users are not LoadInst then
	// this function F is not suitable for sret promotion.
	else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(ArgI)) {
	// TODO : Use dom info and insert PHINodes to collect get results
	// from multiple call sites for this GEP.
	if (GEP->getParent() != Call->getParent())
	return false;
	for (Value::use_iterator GEPI = GEP->use_begin(), GEPE = GEP->use_end();
	GEPI != GEPE; ++GEPI)
	if (!isa<LoadInst>(GEPI))
	return false;
	}
	// Any other FirstArg users make this function unsuitable for sret
	// promotion.
	else
	return false;
	}
	}

	return true;
	}

	/// cloneFunctionBody - Create a new function based on F and
	/// insert it into module. Remove first argument. Use STy as
	/// the return type for new function.
	Function SRETPromotion::cloneFunctionBody(Function F,
	const StructType *STy) {

	const FunctionType *FTy = F->getFunctionType();
	std::vector<const Type*> Params;

	// ParamAttrs - Keep track of the parameter attributes for the arguments.
	SmallVector<ParamAttrsWithIndex, 8> ParamAttrsVec;
	const PAListPtr &PAL = F->getParamAttrs();

	// Add any return attributes.
	if (ParameterAttributes attrs = PAL.getParamAttrs(0))
	ParamAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));

	// Skip first argument.
	Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
	++I;
	// 0th parameter attribute is reserved for return type.
	// 1th parameter attribute is for first 1st sret argument.
	unsigned ParamIndex = 2;
	while (I != E) {
	Params.push_back(I->getType());
	if (ParameterAttributes Attrs = PAL.getParamAttrs(ParamIndex))
	ParamAttrsVec.push_back(ParamAttrsWithIndex::get(ParamIndex - 1, Attrs));
	++I;
	++ParamIndex;
	}

	FunctionType *NFTy = FunctionType::get(STy, Params, FTy->isVarArg());
	Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
	NF->setCallingConv(F->getCallingConv());
	NF->setParamAttrs(PAListPtr::get(ParamAttrsVec.begin(), ParamAttrsVec.end()));
	F->getParent()->getFunctionList().insert(F, NF);
	NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());

	// Replace arguments
	I = F->arg_begin();
	E = F->arg_end();
	Function::arg_iterator NI = NF->arg_begin();
	++I;
	while (I != E) {
	I->replaceAllUsesWith(NI);
	NI->takeName(I);
	++I;
	++NI;
	}

	return NF;
	}

	/// updateCallSites - Update all sites that call F to use NF.
	void SRETPromotion::updateCallSites(Function F, Function NF) {

	SmallVector<Value*, 16> Args;

	// ParamAttrs - Keep track of the parameter attributes for the arguments.
	SmallVector<ParamAttrsWithIndex, 8> ArgAttrsVec;

	for (Value::use_iterator FUI = F->use_begin(), FUE = F->use_end();
	FUI != FUE;) {
	CallSite CS = CallSite::get(*FUI);
	++FUI;
	Instruction *Call = CS.getInstruction();

	const PAListPtr &PAL = F->getParamAttrs();
	// Add any return attributes.
	if (ParameterAttributes attrs = PAL.getParamAttrs(0))
	ArgAttrsVec.push_back(ParamAttrsWithIndex::get(0, attrs));

	// Copy arguments, however skip first one.
	CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
	Value FirstCArg = AI;
	++AI;
	// 0th parameter attribute is reserved for return type.
	// 1th parameter attribute is for first 1st sret argument.
	unsigned ParamIndex = 2;
	while (AI != AE) {
	Args.push_back(*AI);
	if (ParameterAttributes Attrs = PAL.getParamAttrs(ParamIndex))
	ArgAttrsVec.push_back(ParamAttrsWithIndex::get(ParamIndex - 1, Attrs));
	++ParamIndex;
	++AI;
	}


	PAListPtr NewPAL = PAListPtr::get(ArgAttrsVec.begin(), ArgAttrsVec.end());

	// Build new call instruction.
	Instruction *New;
	if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
	New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
	Args.begin(), Args.end(), "", Call);
	cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
	cast<InvokeInst>(New)->setParamAttrs(NewPAL);
	} else {
	New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call);
	cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
	cast<CallInst>(New)->setParamAttrs(NewPAL);
	if (cast<CallInst>(Call)->isTailCall())
	cast<CallInst>(New)->setTailCall();
	}
	Args.clear();
	ArgAttrsVec.clear();
	New->takeName(Call);

	// Update all users of sret parameter to extract value using getresult.
	for (Value::use_iterator UI = FirstCArg->use_begin(),
	UE = FirstCArg->use_end(); UI != UE; ) {
	User U2 = UI++;
	CallInst *C2 = dyn_cast<CallInst>(U2);
	if (C2 && (C2 == Call))
	continue;
	else if (GetElementPtrInst *UGEP = dyn_cast<GetElementPtrInst>(U2)) {
	ConstantInt *Idx = dyn_cast<ConstantInt>(UGEP->getOperand(2));
	assert (Idx && "Unexpected getelementptr index!");
	Value *GR = new GetResultInst(New, Idx->getZExtValue(), "gr", UGEP);
	for (Value::use_iterator GI = UGEP->use_begin(),
	GE = UGEP->use_end(); GI != GE; ++GI) {
	if (LoadInst L = dyn_cast<LoadInst>(GI)) {
	L->replaceAllUsesWith(GR);
	L->eraseFromParent();
	}
	}
	UGEP->eraseFromParent();
	}
	else assert( 0 && "Unexpected sret parameter use");
	}
	Call->eraseFromParent();
	}
	}

	/// nestedStructType - Return true if STy includes any
	/// other aggregate types
	bool SRETPromotion::nestedStructType(const StructType *STy) {
	unsigned Num = STy->getNumElements();
	for (unsigned i = 0; i < Num; i++) {
	const Type *Ty = STy->getElementType(i);
	if (!Ty->isFirstClassType() && Ty != Type::VoidTy)
	return true;
	}
	return false;
	}