llvm/lib/Transforms/Utils/SSAUpdater.cpp - toolchain/llvm-project - Gitiles

 //===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the SSAUpdater class.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Transforms/Utils/SSAUpdater.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Use.h"
 #include "llvm/IR/Value.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
 #include <cassert>
 #include <utility>

 using namespace llvm;

 #define DEBUG_TYPE "ssaupdater"

 using AvailableValsTy = DenseMap<BasicBlock *, Value *>;

 static AvailableValsTy &getAvailableVals(void *AV) {
   return *static_cast<AvailableValsTy*>(AV);
 }

 SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode *> *NewPHI)
   : InsertedPHIs(NewPHI) {}

 SSAUpdater::~SSAUpdater() {
   delete static_cast<AvailableValsTy*>(AV);
 }

 void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
   if (!AV)
     AV = new AvailableValsTy();
   else
     getAvailableVals(AV).clear();
   ProtoType = Ty;
   ProtoName = Name;
 }

 bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
   return getAvailableVals(AV).count(BB);
 }

 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
   assert(ProtoType && "Need to initialize SSAUpdater");
   assert(ProtoType == V->getType() &&
          "All rewritten values must have the same type");
   getAvailableVals(AV)[BB] = V;
 }

 static bool IsEquivalentPHI(PHINode *PHI,
                         SmallDenseMap<BasicBlock *, Value *, 8> &ValueMapping) {
   unsigned PHINumValues = PHI->getNumIncomingValues();
   if (PHINumValues != ValueMapping.size())
     return false;

   // Scan the phi to see if it matches.
   for (unsigned i = 0, e = PHINumValues; i != e; ++i)
     if (ValueMapping[PHI->getIncomingBlock(i)] !=
         PHI->getIncomingValue(i)) {
       return false;
     }

   return true;
 }

 Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
   Value *Res = GetValueAtEndOfBlockInternal(BB);
   return Res;
 }

 Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
   // If there is no definition of the renamed variable in this block, just use
   // GetValueAtEndOfBlock to do our work.
   if (!HasValueForBlock(BB))
     return GetValueAtEndOfBlock(BB);

   // Otherwise, we have the hard case.  Get the live-in values for each
   // predecessor.
   SmallVector<std::pair<BasicBlock *, Value *>, 8> PredValues;
   Value *SingularValue = nullptr;

   // We can get our predecessor info by walking the pred_iterator list, but it
   // is relatively slow.  If we already have PHI nodes in this block, walk one
   // of them to get the predecessor list instead.
   if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
     for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
       BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
       Value *PredVal = GetValueAtEndOfBlock(PredBB);
       PredValues.push_back(std::make_pair(PredBB, PredVal));

       // Compute SingularValue.
       if (i == 0)
         SingularValue = PredVal;
       else if (PredVal != SingularValue)
         SingularValue = nullptr;
     }
   } else {
     bool isFirstPred = true;
     for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
       BasicBlock *PredBB = *PI;
       Value *PredVal = GetValueAtEndOfBlock(PredBB);
       PredValues.push_back(std::make_pair(PredBB, PredVal));

       // Compute SingularValue.
       if (isFirstPred) {
         SingularValue = PredVal;
         isFirstPred = false;
       } else if (PredVal != SingularValue)
         SingularValue = nullptr;
     }
   }

   // If there are no predecessors, just return undef.
   if (PredValues.empty())
     return UndefValue::get(ProtoType);

   // Otherwise, if all the merged values are the same, just use it.
   if (SingularValue)
     return SingularValue;

   // Otherwise, we do need a PHI: check to see if we already have one available
   // in this block that produces the right value.
   if (isa<PHINode>(BB->begin())) {
     SmallDenseMap<BasicBlock *, Value *, 8> ValueMapping(PredValues.begin(),
                                                          PredValues.end());
     for (PHINode &SomePHI : BB->phis()) {
       if (IsEquivalentPHI(&SomePHI, ValueMapping))
         return &SomePHI;
     }
   }

   // Ok, we have no way out, insert a new one now.
   PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
                                          ProtoName, &BB->front());

   // Fill in all the predecessors of the PHI.
   for (const auto &PredValue : PredValues)
     InsertedPHI->addIncoming(PredValue.second, PredValue.first);

   // See if the PHI node can be merged to a single value.  This can happen in
   // loop cases when we get a PHI of itself and one other value.
   if (Value *V =
           SimplifyInstruction(InsertedPHI, BB->getModule()->getDataLayout())) {
     InsertedPHI->eraseFromParent();
     return V;
   }

   // Set the DebugLoc of the inserted PHI, if available.
   DebugLoc DL;
   if (const Instruction *I = BB->getFirstNonPHI())
       DL = I->getDebugLoc();
   InsertedPHI->setDebugLoc(DL);

   // If the client wants to know about all new instructions, tell it.
   if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);

   LLVM_DEBUG(dbgs() << "  Inserted PHI: " << *InsertedPHI << "\n");
   return InsertedPHI;
 }

 void SSAUpdater::RewriteUse(Use &U) {
   Instruction *User = cast<Instruction>(U.getUser());

   Value *V;
   if (PHINode *UserPN = dyn_cast<PHINode>(User))
     V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
   else
     V = GetValueInMiddleOfBlock(User->getParent());

   // Notify that users of the existing value that it is being replaced.
   Value *OldVal = U.get();
   if (OldVal != V && OldVal->hasValueHandle())
     ValueHandleBase::ValueIsRAUWd(OldVal, V);

   U.set(V);
 }

 void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
   Instruction *User = cast<Instruction>(U.getUser());

   Value *V;
   if (PHINode *UserPN = dyn_cast<PHINode>(User))
     V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
   else
     V = GetValueAtEndOfBlock(User->getParent());

   U.set(V);
 }

 namespace llvm {

 template<>
 class SSAUpdaterTraits<SSAUpdater> {
 public:
   using BlkT = BasicBlock;
   using ValT = Value *;
   using PhiT = PHINode;
   using BlkSucc_iterator = succ_iterator;

   static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
   static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }

   class PHI_iterator {
   private:
     PHINode *PHI;
     unsigned idx;

   public:
     explicit PHI_iterator(PHINode *P) // begin iterator
       : PHI(P), idx(0) {}
     PHI_iterator(PHINode *P, bool) // end iterator
       : PHI(P), idx(PHI->getNumIncomingValues()) {}

     PHI_iterator &operator++() { ++idx; return *this; }
     bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
     bool operator!=(const PHI_iterator& x) const { return !operator==(x); }

     Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
     BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
   };

   static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
   static PHI_iterator PHI_end(PhiT *PHI) {
     return PHI_iterator(PHI, true);
   }

   /// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
   /// vector, set Info->NumPreds, and allocate space in Info->Preds.
   static void FindPredecessorBlocks(BasicBlock *BB,
                                     SmallVectorImpl<BasicBlock *> *Preds) {
     // We can get our predecessor info by walking the pred_iterator list,
     // but it is relatively slow.  If we already have PHI nodes in this
     // block, walk one of them to get the predecessor list instead.
     if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
       Preds->append(SomePhi->block_begin(), SomePhi->block_end());
     } else {
       for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
         Preds->push_back(*PI);
     }
   }

   /// GetUndefVal - Get an undefined value of the same type as the value
   /// being handled.
   static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
     return UndefValue::get(Updater->ProtoType);
   }

   /// CreateEmptyPHI - Create a new PHI instruction in the specified block.
   /// Reserve space for the operands but do not fill them in yet.
   static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
                                SSAUpdater *Updater) {
     PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
                                    Updater->ProtoName, &BB->front());
     return PHI;
   }

   /// AddPHIOperand - Add the specified value as an operand of the PHI for
   /// the specified predecessor block.
   static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
     PHI->addIncoming(Val, Pred);
   }

   /// InstrIsPHI - Check if an instruction is a PHI.
   ///
   static PHINode *InstrIsPHI(Instruction *I) {
     return dyn_cast<PHINode>(I);
   }

   /// ValueIsPHI - Check if a value is a PHI.
   static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
     return dyn_cast<PHINode>(Val);
   }

   /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
   /// operands, i.e., it was just added.
   static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
     PHINode *PHI = ValueIsPHI(Val, Updater);
     if (PHI && PHI->getNumIncomingValues() == 0)
       return PHI;
     return nullptr;
   }

   /// GetPHIValue - For the specified PHI instruction, return the value
   /// that it defines.
   static Value *GetPHIValue(PHINode *PHI) {
     return PHI;
   }
 };

 } // end namespace llvm

 /// Check to see if AvailableVals has an entry for the specified BB and if so,
 /// return it.  If not, construct SSA form by first calculating the required
 /// placement of PHIs and then inserting new PHIs where needed.
 Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
   AvailableValsTy &AvailableVals = getAvailableVals(AV);
   if (Value *V = AvailableVals[BB])
     return V;

   SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
   return Impl.GetValue(BB);
 }

 //===----------------------------------------------------------------------===//
 // LoadAndStorePromoter Implementation
 //===----------------------------------------------------------------------===//

 LoadAndStorePromoter::
 LoadAndStorePromoter(ArrayRef<const Instruction *> Insts,
                      SSAUpdater &S, StringRef BaseName) : SSA(S) {
   if (Insts.empty()) return;

   const Value *SomeVal;
   if (const LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
     SomeVal = LI;
   else
     SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);

   if (BaseName.empty())
     BaseName = SomeVal->getName();
   SSA.Initialize(SomeVal->getType(), BaseName);
 }

 void LoadAndStorePromoter::
 run(const SmallVectorImpl<Instruction *> &Insts) const {
   // First step: bucket up uses of the alloca by the block they occur in.
   // This is important because we have to handle multiple defs/uses in a block
   // ourselves: SSAUpdater is purely for cross-block references.
   DenseMap<BasicBlock *, TinyPtrVector<Instruction *>> UsesByBlock;

   for (Instruction *User : Insts)
     UsesByBlock[User->getParent()].push_back(User);

   // Okay, now we can iterate over all the blocks in the function with uses,
   // processing them.  Keep track of which loads are loading a live-in value.
   // Walk the uses in the use-list order to be determinstic.
   SmallVector<LoadInst *, 32> LiveInLoads;
   DenseMap<Value *, Value *> ReplacedLoads;

   for (Instruction *User : Insts) {
     BasicBlock *BB = User->getParent();
     TinyPtrVector<Instruction *> &BlockUses = UsesByBlock[BB];

     // If this block has already been processed, ignore this repeat use.
     if (BlockUses.empty()) continue;

     // Okay, this is the first use in the block.  If this block just has a
     // single user in it, we can rewrite it trivially.
     if (BlockUses.size() == 1) {
       // If it is a store, it is a trivial def of the value in the block.
       if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
         updateDebugInfo(SI);
         SSA.AddAvailableValue(BB, SI->getOperand(0));
       } else
         // Otherwise it is a load, queue it to rewrite as a live-in load.
         LiveInLoads.push_back(cast<LoadInst>(User));
       BlockUses.clear();
       continue;
     }

     // Otherwise, check to see if this block is all loads.
     bool HasStore = false;
     for (Instruction *I : BlockUses) {
       if (isa<StoreInst>(I)) {
         HasStore = true;
         break;
       }
     }

     // If so, we can queue them all as live in loads.  We don't have an
     // efficient way to tell which on is first in the block and don't want to
     // scan large blocks, so just add all loads as live ins.
     if (!HasStore) {
       for (Instruction *I : BlockUses)
         LiveInLoads.push_back(cast<LoadInst>(I));
       BlockUses.clear();
       continue;
     }

     // Otherwise, we have mixed loads and stores (or just a bunch of stores).
     // Since SSAUpdater is purely for cross-block values, we need to determine
     // the order of these instructions in the block.  If the first use in the
     // block is a load, then it uses the live in value.  The last store defines
     // the live out value.  We handle this by doing a linear scan of the block.
     Value *StoredValue = nullptr;
     for (Instruction &I : *BB) {
       if (LoadInst *L = dyn_cast<LoadInst>(&I)) {
         // If this is a load from an unrelated pointer, ignore it.
         if (!isInstInList(L, Insts)) continue;

         // If we haven't seen a store yet, this is a live in use, otherwise
         // use the stored value.
         if (StoredValue) {
           replaceLoadWithValue(L, StoredValue);
           L->replaceAllUsesWith(StoredValue);
           ReplacedLoads[L] = StoredValue;
         } else {
           LiveInLoads.push_back(L);
         }
         continue;
       }

       if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
         // If this is a store to an unrelated pointer, ignore it.
         if (!isInstInList(SI, Insts)) continue;
         updateDebugInfo(SI);

         // Remember that this is the active value in the block.
         StoredValue = SI->getOperand(0);
       }
     }

     // The last stored value that happened is the live-out for the block.
     assert(StoredValue && "Already checked that there is a store in block");
     SSA.AddAvailableValue(BB, StoredValue);
     BlockUses.clear();
   }

   // Okay, now we rewrite all loads that use live-in values in the loop,
   // inserting PHI nodes as necessary.
   for (LoadInst *ALoad : LiveInLoads) {
     Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
     replaceLoadWithValue(ALoad, NewVal);

     // Avoid assertions in unreachable code.
     if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
     ALoad->replaceAllUsesWith(NewVal);
     ReplacedLoads[ALoad] = NewVal;
   }

   // Allow the client to do stuff before we start nuking things.
   doExtraRewritesBeforeFinalDeletion();

   // Now that everything is rewritten, delete the old instructions from the
   // function.  They should all be dead now.
   for (Instruction *User : Insts) {
     // If this is a load that still has uses, then the load must have been added
     // as a live value in the SSAUpdate data structure for a block (e.g. because
     // the loaded value was stored later).  In this case, we need to recursively
     // propagate the updates until we get to the real value.
     if (!User->use_empty()) {
       Value *NewVal = ReplacedLoads[User];
       assert(NewVal && "not a replaced load?");

       // Propagate down to the ultimate replacee.  The intermediately loads
       // could theoretically already have been deleted, so we don't want to
       // dereference the Value*'s.
       DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
       while (RLI != ReplacedLoads.end()) {
         NewVal = RLI->second;
         RLI = ReplacedLoads.find(NewVal);
       }

       replaceLoadWithValue(cast<LoadInst>(User), NewVal);
       User->replaceAllUsesWith(NewVal);
     }

     instructionDeleted(User);
     User->eraseFromParent();
   }
 }

 bool
 LoadAndStorePromoter::isInstInList(Instruction *I,
                                    const SmallVectorImpl<Instruction *> &Insts)
                                    const {
   return is_contained(Insts, I);
 }
	//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements the SSAUpdater class.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Transforms/Utils/SSAUpdater.h"
	#include "llvm/ADT/DenseMap.h"
	#include "llvm/ADT/STLExtras.h"
	#include "llvm/ADT/SmallVector.h"
	#include "llvm/ADT/TinyPtrVector.h"
	#include "llvm/Analysis/InstructionSimplify.h"
	#include "llvm/IR/BasicBlock.h"
	#include "llvm/IR/CFG.h"
	#include "llvm/IR/Constants.h"
	#include "llvm/IR/DebugLoc.h"
	#include "llvm/IR/Instruction.h"
	#include "llvm/IR/Instructions.h"
	#include "llvm/IR/Module.h"
	#include "llvm/IR/Use.h"
	#include "llvm/IR/Value.h"
	#include "llvm/IR/ValueHandle.h"
	#include "llvm/Support/Casting.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/raw_ostream.h"
	#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
	#include <cassert>
	#include <utility>

	using namespace llvm;

	#define DEBUG_TYPE "ssaupdater"

	using AvailableValsTy = DenseMap<BasicBlock , Value >;

	static AvailableValsTy &getAvailableVals(void *AV) {
	return static_cast<AvailableValsTy>(AV);
	}

	SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode > NewPHI)
	: InsertedPHIs(NewPHI) {}

	SSAUpdater::~SSAUpdater() {
	delete static_cast<AvailableValsTy*>(AV);
	}

	void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
	if (!AV)
	AV = new AvailableValsTy();
	else
	getAvailableVals(AV).clear();
	ProtoType = Ty;
	ProtoName = Name;
	}

	bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
	return getAvailableVals(AV).count(BB);
	}

	void SSAUpdater::AddAvailableValue(BasicBlock BB, Value V) {
	assert(ProtoType && "Need to initialize SSAUpdater");
	assert(ProtoType == V->getType() &&
	"All rewritten values must have the same type");
	getAvailableVals(AV)[BB] = V;
	}

	static bool IsEquivalentPHI(PHINode *PHI,
	SmallDenseMap<BasicBlock , Value , 8> &ValueMapping) {
	unsigned PHINumValues = PHI->getNumIncomingValues();
	if (PHINumValues != ValueMapping.size())
	return false;

	// Scan the phi to see if it matches.
	for (unsigned i = 0, e = PHINumValues; i != e; ++i)
	if (ValueMapping[PHI->getIncomingBlock(i)] !=
	PHI->getIncomingValue(i)) {
	return false;
	}

	return true;
	}

	Value SSAUpdater::GetValueAtEndOfBlock(BasicBlock BB) {
	Value *Res = GetValueAtEndOfBlockInternal(BB);
	return Res;
	}

	Value SSAUpdater::GetValueInMiddleOfBlock(BasicBlock BB) {
	// If there is no definition of the renamed variable in this block, just use
	// GetValueAtEndOfBlock to do our work.
	if (!HasValueForBlock(BB))
	return GetValueAtEndOfBlock(BB);

	// Otherwise, we have the hard case. Get the live-in values for each
	// predecessor.
	SmallVector<std::pair<BasicBlock , Value >, 8> PredValues;
	Value *SingularValue = nullptr;

	// We can get our predecessor info by walking the pred_iterator list, but it
	// is relatively slow. If we already have PHI nodes in this block, walk one
	// of them to get the predecessor list instead.
	if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
	for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
	BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
	Value *PredVal = GetValueAtEndOfBlock(PredBB);
	PredValues.push_back(std::make_pair(PredBB, PredVal));

	// Compute SingularValue.
	if (i == 0)
	SingularValue = PredVal;
	else if (PredVal != SingularValue)
	SingularValue = nullptr;
	}
	} else {
	bool isFirstPred = true;
	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
	BasicBlock PredBB = PI;
	Value *PredVal = GetValueAtEndOfBlock(PredBB);
	PredValues.push_back(std::make_pair(PredBB, PredVal));

	// Compute SingularValue.
	if (isFirstPred) {
	SingularValue = PredVal;
	isFirstPred = false;
	} else if (PredVal != SingularValue)
	SingularValue = nullptr;
	}
	}

	// If there are no predecessors, just return undef.
	if (PredValues.empty())
	return UndefValue::get(ProtoType);

	// Otherwise, if all the merged values are the same, just use it.
	if (SingularValue)
	return SingularValue;

	// Otherwise, we do need a PHI: check to see if we already have one available
	// in this block that produces the right value.
	if (isa<PHINode>(BB->begin())) {
	SmallDenseMap<BasicBlock , Value , 8> ValueMapping(PredValues.begin(),
	PredValues.end());
	for (PHINode &SomePHI : BB->phis()) {
	if (IsEquivalentPHI(&SomePHI, ValueMapping))
	return &SomePHI;
	}
	}

	// Ok, we have no way out, insert a new one now.
	PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
	ProtoName, &BB->front());

	// Fill in all the predecessors of the PHI.
	for (const auto &PredValue : PredValues)
	InsertedPHI->addIncoming(PredValue.second, PredValue.first);

	// See if the PHI node can be merged to a single value. This can happen in
	// loop cases when we get a PHI of itself and one other value.
	if (Value *V =
	SimplifyInstruction(InsertedPHI, BB->getModule()->getDataLayout())) {
	InsertedPHI->eraseFromParent();
	return V;
	}

	// Set the DebugLoc of the inserted PHI, if available.
	DebugLoc DL;
	if (const Instruction *I = BB->getFirstNonPHI())
	DL = I->getDebugLoc();
	InsertedPHI->setDebugLoc(DL);

	// If the client wants to know about all new instructions, tell it.
	if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);

	LLVM_DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
	return InsertedPHI;
	}

	void SSAUpdater::RewriteUse(Use &U) {
	Instruction *User = cast<Instruction>(U.getUser());

	Value *V;
	if (PHINode *UserPN = dyn_cast<PHINode>(User))
	V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
	else
	V = GetValueInMiddleOfBlock(User->getParent());

	// Notify that users of the existing value that it is being replaced.
	Value *OldVal = U.get();
	if (OldVal != V && OldVal->hasValueHandle())
	ValueHandleBase::ValueIsRAUWd(OldVal, V);

	U.set(V);
	}

	void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
	Instruction *User = cast<Instruction>(U.getUser());

	Value *V;
	if (PHINode *UserPN = dyn_cast<PHINode>(User))
	V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
	else
	V = GetValueAtEndOfBlock(User->getParent());

	U.set(V);
	}

	namespace llvm {

	template<>
	class SSAUpdaterTraits<SSAUpdater> {
	public:
	using BlkT = BasicBlock;
	using ValT = Value *;
	using PhiT = PHINode;
	using BlkSucc_iterator = succ_iterator;

	static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
	static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }

	class PHI_iterator {
	private:
	PHINode *PHI;
	unsigned idx;

	public:
	explicit PHI_iterator(PHINode *P) // begin iterator
	: PHI(P), idx(0) {}
	PHI_iterator(PHINode *P, bool) // end iterator
	: PHI(P), idx(PHI->getNumIncomingValues()) {}

	PHI_iterator &operator++() { ++idx; return *this; }
	bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
	bool operator!=(const PHI_iterator& x) const { return !operator==(x); }

	Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
	BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
	};

	static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
	static PHI_iterator PHI_end(PhiT *PHI) {
	return PHI_iterator(PHI, true);
	}

	/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
	/// vector, set Info->NumPreds, and allocate space in Info->Preds.
	static void FindPredecessorBlocks(BasicBlock *BB,
	SmallVectorImpl<BasicBlock > Preds) {
	// We can get our predecessor info by walking the pred_iterator list,
	// but it is relatively slow. If we already have PHI nodes in this
	// block, walk one of them to get the predecessor list instead.
	if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
	Preds->append(SomePhi->block_begin(), SomePhi->block_end());
	} else {
	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
	Preds->push_back(*PI);
	}
	}

	/// GetUndefVal - Get an undefined value of the same type as the value
	/// being handled.
	static Value GetUndefVal(BasicBlock BB, SSAUpdater *Updater) {
	return UndefValue::get(Updater->ProtoType);
	}

	/// CreateEmptyPHI - Create a new PHI instruction in the specified block.
	/// Reserve space for the operands but do not fill them in yet.
	static Value CreateEmptyPHI(BasicBlock BB, unsigned NumPreds,
	SSAUpdater *Updater) {
	PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
	Updater->ProtoName, &BB->front());
	return PHI;
	}

	/// AddPHIOperand - Add the specified value as an operand of the PHI for
	/// the specified predecessor block.
	static void AddPHIOperand(PHINode PHI, Value Val, BasicBlock *Pred) {
	PHI->addIncoming(Val, Pred);
	}

	/// InstrIsPHI - Check if an instruction is a PHI.
	///
	static PHINode InstrIsPHI(Instruction I) {
	return dyn_cast<PHINode>(I);
	}

	/// ValueIsPHI - Check if a value is a PHI.
	static PHINode ValueIsPHI(Value Val, SSAUpdater *Updater) {
	return dyn_cast<PHINode>(Val);
	}

	/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
	/// operands, i.e., it was just added.
	static PHINode ValueIsNewPHI(Value Val, SSAUpdater *Updater) {
	PHINode *PHI = ValueIsPHI(Val, Updater);
	if (PHI && PHI->getNumIncomingValues() == 0)
	return PHI;
	return nullptr;
	}

	/// GetPHIValue - For the specified PHI instruction, return the value
	/// that it defines.
	static Value GetPHIValue(PHINode PHI) {
	return PHI;
	}
	};

	} // end namespace llvm

	/// Check to see if AvailableVals has an entry for the specified BB and if so,
	/// return it. If not, construct SSA form by first calculating the required
	/// placement of PHIs and then inserting new PHIs where needed.
	Value SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock BB) {
	AvailableValsTy &AvailableVals = getAvailableVals(AV);
	if (Value *V = AvailableVals[BB])
	return V;

	SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
	return Impl.GetValue(BB);
	}

	//===----------------------------------------------------------------------===//
	// LoadAndStorePromoter Implementation
	//===----------------------------------------------------------------------===//

	LoadAndStorePromoter::
	LoadAndStorePromoter(ArrayRef<const Instruction *> Insts,
	SSAUpdater &S, StringRef BaseName) : SSA(S) {
	if (Insts.empty()) return;

	const Value *SomeVal;
	if (const LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
	SomeVal = LI;
	else
	SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);

	if (BaseName.empty())
	BaseName = SomeVal->getName();
	SSA.Initialize(SomeVal->getType(), BaseName);
	}

	void LoadAndStorePromoter::
	run(const SmallVectorImpl<Instruction *> &Insts) const {
	// First step: bucket up uses of the alloca by the block they occur in.
	// This is important because we have to handle multiple defs/uses in a block
	// ourselves: SSAUpdater is purely for cross-block references.
	DenseMap<BasicBlock , TinyPtrVector<Instruction >> UsesByBlock;

	for (Instruction *User : Insts)
	UsesByBlock[User->getParent()].push_back(User);

	// Okay, now we can iterate over all the blocks in the function with uses,
	// processing them. Keep track of which loads are loading a live-in value.
	// Walk the uses in the use-list order to be determinstic.
	SmallVector<LoadInst *, 32> LiveInLoads;
	DenseMap<Value , Value > ReplacedLoads;

	for (Instruction *User : Insts) {
	BasicBlock *BB = User->getParent();
	TinyPtrVector<Instruction *> &BlockUses = UsesByBlock[BB];

	// If this block has already been processed, ignore this repeat use.
	if (BlockUses.empty()) continue;

	// Okay, this is the first use in the block. If this block just has a
	// single user in it, we can rewrite it trivially.
	if (BlockUses.size() == 1) {
	// If it is a store, it is a trivial def of the value in the block.
	if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
	updateDebugInfo(SI);
	SSA.AddAvailableValue(BB, SI->getOperand(0));
	} else
	// Otherwise it is a load, queue it to rewrite as a live-in load.
	LiveInLoads.push_back(cast<LoadInst>(User));
	BlockUses.clear();
	continue;
	}

	// Otherwise, check to see if this block is all loads.
	bool HasStore = false;
	for (Instruction *I : BlockUses) {
	if (isa<StoreInst>(I)) {
	HasStore = true;
	break;
	}
	}

	// If so, we can queue them all as live in loads. We don't have an
	// efficient way to tell which on is first in the block and don't want to
	// scan large blocks, so just add all loads as live ins.
	if (!HasStore) {
	for (Instruction *I : BlockUses)
	LiveInLoads.push_back(cast<LoadInst>(I));
	BlockUses.clear();
	continue;
	}

	// Otherwise, we have mixed loads and stores (or just a bunch of stores).
	// Since SSAUpdater is purely for cross-block values, we need to determine
	// the order of these instructions in the block. If the first use in the
	// block is a load, then it uses the live in value. The last store defines
	// the live out value. We handle this by doing a linear scan of the block.
	Value *StoredValue = nullptr;
	for (Instruction &I : *BB) {
	if (LoadInst *L = dyn_cast<LoadInst>(&I)) {
	// If this is a load from an unrelated pointer, ignore it.
	if (!isInstInList(L, Insts)) continue;

	// If we haven't seen a store yet, this is a live in use, otherwise
	// use the stored value.
	if (StoredValue) {
	replaceLoadWithValue(L, StoredValue);
	L->replaceAllUsesWith(StoredValue);
	ReplacedLoads[L] = StoredValue;
	} else {
	LiveInLoads.push_back(L);
	}
	continue;
	}

	if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
	// If this is a store to an unrelated pointer, ignore it.
	if (!isInstInList(SI, Insts)) continue;
	updateDebugInfo(SI);

	// Remember that this is the active value in the block.
	StoredValue = SI->getOperand(0);
	}
	}

	// The last stored value that happened is the live-out for the block.
	assert(StoredValue && "Already checked that there is a store in block");
	SSA.AddAvailableValue(BB, StoredValue);
	BlockUses.clear();
	}

	// Okay, now we rewrite all loads that use live-in values in the loop,
	// inserting PHI nodes as necessary.
	for (LoadInst *ALoad : LiveInLoads) {
	Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
	replaceLoadWithValue(ALoad, NewVal);

	// Avoid assertions in unreachable code.
	if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
	ALoad->replaceAllUsesWith(NewVal);
	ReplacedLoads[ALoad] = NewVal;
	}

	// Allow the client to do stuff before we start nuking things.
	doExtraRewritesBeforeFinalDeletion();

	// Now that everything is rewritten, delete the old instructions from the
	// function. They should all be dead now.
	for (Instruction *User : Insts) {
	// If this is a load that still has uses, then the load must have been added
	// as a live value in the SSAUpdate data structure for a block (e.g. because
	// the loaded value was stored later). In this case, we need to recursively
	// propagate the updates until we get to the real value.
	if (!User->use_empty()) {
	Value *NewVal = ReplacedLoads[User];
	assert(NewVal && "not a replaced load?");

	// Propagate down to the ultimate replacee. The intermediately loads
	// could theoretically already have been deleted, so we don't want to
	// dereference the Value*'s.
	DenseMap<Value, Value>::iterator RLI = ReplacedLoads.find(NewVal);
	while (RLI != ReplacedLoads.end()) {
	NewVal = RLI->second;
	RLI = ReplacedLoads.find(NewVal);
	}

	replaceLoadWithValue(cast<LoadInst>(User), NewVal);
	User->replaceAllUsesWith(NewVal);
	}

	instructionDeleted(User);
	User->eraseFromParent();
	}
	}

	bool
	LoadAndStorePromoter::isInstInList(Instruction *I,
	const SmallVectorImpl<Instruction *> &Insts)
	const {
	return is_contained(Insts, I);
	}