C++ PHINode::getName方法代码示例

/// getInnerResumeDest - Get or create a target for the branch from ResumeInsts.
BasicBlock *InvokeInliningInfo::getInnerResumeDest() {
  if (InnerResumeDest) return InnerResumeDest;

  // Split the landing pad.
  BasicBlock::iterator SplitPoint = CallerLPad; ++SplitPoint;
  InnerResumeDest =
    OuterResumeDest->splitBasicBlock(SplitPoint,
                                     OuterResumeDest->getName() + ".body");

  // The number of incoming edges we expect to the inner landing pad.
  const unsigned PHICapacity = 2;

  // Create corresponding new PHIs for all the PHIs in the outer landing pad.
  BasicBlock::iterator InsertPoint = InnerResumeDest->begin();
  BasicBlock::iterator I = OuterResumeDest->begin();
  for (unsigned i = 0, e = UnwindDestPHIValues.size(); i != e; ++i, ++I) {
    PHINode *OuterPHI = cast<PHINode>(I);
    PHINode *InnerPHI = PHINode::Create(OuterPHI->getType(), PHICapacity,
                                        OuterPHI->getName() + ".lpad-body",
                                        InsertPoint);
    OuterPHI->replaceAllUsesWith(InnerPHI);
    InnerPHI->addIncoming(OuterPHI, OuterResumeDest);
  }

  // Create a PHI for the exception values.
  InnerEHValuesPHI = PHINode::Create(CallerLPad->getType(), PHICapacity,
                                     "eh.lpad-body", InsertPoint);
  CallerLPad->replaceAllUsesWith(InnerEHValuesPHI);
  InnerEHValuesPHI->addIncoming(CallerLPad, OuterResumeDest);

  // All done.
  return InnerResumeDest;
}

/// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming
/// from NewBB. This also updates AliasAnalysis, if available.
static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
                           ArrayRef<BasicBlock*> Preds, BranchInst *BI,
                           Pass *P, bool HasLoopExit) {
  // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
  AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
  for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
    PHINode *PN = cast<PHINode>(I++);

    // Check to see if all of the values coming in are the same.  If so, we
    // don't need to create a new PHI node, unless it's needed for LCSSA.
    Value *InVal = 0;
    if (!HasLoopExit) {
      InVal = PN->getIncomingValueForBlock(Preds[0]);
      for (unsigned i = 1, e = Preds.size(); i != e; ++i)
        if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
          InVal = 0;
          break;
        }
    }

    if (InVal) {
      // If all incoming values for the new PHI would be the same, just don't
      // make a new PHI.  Instead, just remove the incoming values from the old
      // PHI.
      for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
        // Explicitly check the BB index here to handle duplicates in Preds.
        int Idx = PN->getBasicBlockIndex(Preds[i]);
        if (Idx >= 0)
          PN->removeIncomingValue(Idx, false);
      }
    } else {
      // If the values coming into the block are not the same, we need a PHI.
      // Create the new PHI node, insert it into NewBB at the end of the block
      PHINode *NewPHI =
        PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
      if (AA) AA->copyValue(PN, NewPHI);

      // Move all of the PHI values for 'Preds' to the new PHI.
      for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
        Value *V = PN->removeIncomingValue(Preds[i], false);
        NewPHI->addIncoming(V, Preds[i]);
      }

      InVal = NewPHI;
    }

    // Add an incoming value to the PHI node in the loop for the preheader
    // edge.
    PN->addIncoming(InVal, NewBB);
  }
}

bool Scalarizer::visitPHINode(PHINode &PHI) {
  VectorType *VT = dyn_cast<VectorType>(PHI.getType());
  if (!VT)
    return false;

  unsigned NumElems = VT->getNumElements();
  IRBuilder<> Builder(PHI.getParent(), &PHI);
  ValueVector Res;
  Res.resize(NumElems);

  unsigned NumOps = PHI.getNumOperands();
  for (unsigned I = 0; I < NumElems; ++I)
    Res[I] = Builder.CreatePHI(VT->getElementType(), NumOps,
                               PHI.getName() + ".i" + Twine(I));

  for (unsigned I = 0; I < NumOps; ++I) {
    Scatterer Op = scatter(&PHI, PHI.getIncomingValue(I));
    BasicBlock *IncomingBlock = PHI.getIncomingBlock(I);
    for (unsigned J = 0; J < NumElems; ++J)
      cast<PHINode>(Res[J])->addIncoming(Op[J], IncomingBlock);
  }
  gather(&PHI, Res);
  return true;
}

//.........这里部分代码省略.........
  SCEVExpander Expander(*SE, DL, "loop-unroll");
  if (!AllowExpensiveTripCount &&
      Expander.isHighCostExpansion(TripCountSC, L, PreHeaderBR)) {
    DEBUG(dbgs() << "High cost for expanding trip count scev!\n");
    return false;
  }

  // This constraint lets us deal with an overflowing trip count easily; see the
  // comment on ModVal below.
  if (Log2_32(Count) > BEWidth) {
    DEBUG(dbgs()
          << "Count failed constraint on overflow trip count calculation.\n");
    return false;
  }

  // Loop structure is the following:
  //
  // PreHeader
  //   Header
  //   ...
  //   Latch
  // LatchExit

  BasicBlock *NewPreHeader;
  BasicBlock *NewExit = nullptr;
  BasicBlock *PrologExit = nullptr;
  BasicBlock *EpilogPreHeader = nullptr;
  BasicBlock *PrologPreHeader = nullptr;

  if (UseEpilogRemainder) {
    // If epilog remainder
    // Split PreHeader to insert a branch around loop for unrolling.
    NewPreHeader = SplitBlock(PreHeader, PreHeader->getTerminator(), DT, LI);
    NewPreHeader->setName(PreHeader->getName() + ".new");
    // Split LatchExit to create phi nodes from branch above.
    SmallVector<BasicBlock*, 4> Preds(predecessors(LatchExit));
    NewExit = SplitBlockPredecessors(LatchExit, Preds, ".unr-lcssa",
                                     DT, LI, PreserveLCSSA);
    // Split NewExit to insert epilog remainder loop.
    EpilogPreHeader = SplitBlock(NewExit, NewExit->getTerminator(), DT, LI);
    EpilogPreHeader->setName(Header->getName() + ".epil.preheader");
  } else {
    // If prolog remainder
    // Split the original preheader twice to insert prolog remainder loop
    PrologPreHeader = SplitEdge(PreHeader, Header, DT, LI);
    PrologPreHeader->setName(Header->getName() + ".prol.preheader");
    PrologExit = SplitBlock(PrologPreHeader, PrologPreHeader->getTerminator(),
                            DT, LI);
    PrologExit->setName(Header->getName() + ".prol.loopexit");
    // Split PrologExit to get NewPreHeader.
    NewPreHeader = SplitBlock(PrologExit, PrologExit->getTerminator(), DT, LI);
    NewPreHeader->setName(PreHeader->getName() + ".new");
  }
  // Loop structure should be the following:
  //  Epilog             Prolog
  //
  // PreHeader         PreHeader
  // *NewPreHeader     *PrologPreHeader
  //   Header          *PrologExit
  //   ...             *NewPreHeader
  //   Latch             Header
  // *NewExit            ...
  // *EpilogPreHeader    Latch
  // LatchExit              LatchExit

  // Calculate conditions for branch around loop for unrolling

/// Update the PHI nodes in OrigBB to include the values coming from NewBB.
/// This also updates AliasAnalysis, if available.
static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
                           ArrayRef<BasicBlock *> Preds, BranchInst *BI,
                           bool HasLoopExit) {
  // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
  SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
  for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
    PHINode *PN = cast<PHINode>(I++);

    // Check to see if all of the values coming in are the same.  If so, we
    // don't need to create a new PHI node, unless it's needed for LCSSA.
    Value *InVal = nullptr;
    if (!HasLoopExit) {
      InVal = PN->getIncomingValueForBlock(Preds[0]);
      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
        if (!PredSet.count(PN->getIncomingBlock(i)))
          continue;
        if (!InVal)
          InVal = PN->getIncomingValue(i);
        else if (InVal != PN->getIncomingValue(i)) {
          InVal = nullptr;
          break;
        }
      }
    }

    if (InVal) {
      // If all incoming values for the new PHI would be the same, just don't
      // make a new PHI.  Instead, just remove the incoming values from the old
      // PHI.

      // NOTE! This loop walks backwards for a reason! First off, this minimizes
      // the cost of removal if we end up removing a large number of values, and
      // second off, this ensures that the indices for the incoming values
      // aren't invalidated when we remove one.
      for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
        if (PredSet.count(PN->getIncomingBlock(i)))
          PN->removeIncomingValue(i, false);

      // Add an incoming value to the PHI node in the loop for the preheader
      // edge.
      PN->addIncoming(InVal, NewBB);
      continue;
    }

    // If the values coming into the block are not the same, we need a new
    // PHI.
    // Create the new PHI node, insert it into NewBB at the end of the block
    PHINode *NewPHI =
        PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);

    // NOTE! This loop walks backwards for a reason! First off, this minimizes
    // the cost of removal if we end up removing a large number of values, and
    // second off, this ensures that the indices for the incoming values aren't
    // invalidated when we remove one.
    for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
      BasicBlock *IncomingBB = PN->getIncomingBlock(i);
      if (PredSet.count(IncomingBB)) {
        Value *V = PN->removeIncomingValue(i, false);
        NewPHI->addIncoming(V, IncomingBB);
      }
    }

    PN->addIncoming(NewPHI, NewBB);
  }
}

/// severSplitPHINodes - If a PHI node has multiple inputs from outside of the
/// region, we need to split the entry block of the region so that the PHI node
/// is easier to deal with.
void CodeExtractor::severSplitPHINodes(BasicBlock *&Header) {
  unsigned NumPredsFromRegion = 0;
  unsigned NumPredsOutsideRegion = 0;

  if (Header != &Header->getParent()->getEntryBlock()) {
    PHINode *PN = dyn_cast<PHINode>(Header->begin());
    if (!PN) return;  // No PHI nodes.

    // If the header node contains any PHI nodes, check to see if there is more
    // than one entry from outside the region.  If so, we need to sever the
    // header block into two.
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
      if (Blocks.count(PN->getIncomingBlock(i)))
        ++NumPredsFromRegion;
      else
        ++NumPredsOutsideRegion;

    // If there is one (or fewer) predecessor from outside the region, we don't
    // need to do anything special.
    if (NumPredsOutsideRegion <= 1) return;
  }

  // Otherwise, we need to split the header block into two pieces: one
  // containing PHI nodes merging values from outside of the region, and a
  // second that contains all of the code for the block and merges back any
  // incoming values from inside of the region.
  BasicBlock *NewBB = llvm::SplitBlock(Header, Header->getFirstNonPHI(), DT);

  // We only want to code extract the second block now, and it becomes the new
  // header of the region.
  BasicBlock *OldPred = Header;
  Blocks.remove(OldPred);
  Blocks.insert(NewBB);
  Header = NewBB;

  // Okay, now we need to adjust the PHI nodes and any branches from within the
  // region to go to the new header block instead of the old header block.
  if (NumPredsFromRegion) {
    PHINode *PN = cast<PHINode>(OldPred->begin());
    // Loop over all of the predecessors of OldPred that are in the region,
    // changing them to branch to NewBB instead.
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
      if (Blocks.count(PN->getIncomingBlock(i))) {
        TerminatorInst *TI = PN->getIncomingBlock(i)->getTerminator();
        TI->replaceUsesOfWith(OldPred, NewBB);
      }

    // Okay, everything within the region is now branching to the right block, we
    // just have to update the PHI nodes now, inserting PHI nodes into NewBB.
    BasicBlock::iterator AfterPHIs;
    for (AfterPHIs = OldPred->begin(); isa<PHINode>(AfterPHIs); ++AfterPHIs) {
      PHINode *PN = cast<PHINode>(AfterPHIs);
      // Create a new PHI node in the new region, which has an incoming value
      // from OldPred of PN.
      PHINode *NewPN = PHINode::Create(PN->getType(), 1 + NumPredsFromRegion,
                                       PN->getName() + ".ce", &NewBB->front());
      PN->replaceAllUsesWith(NewPN);
      NewPN->addIncoming(PN, OldPred);

      // Loop over all of the incoming value in PN, moving them to NewPN if they
      // are from the extracted region.
      for (unsigned i = 0; i != PN->getNumIncomingValues(); ++i) {
        if (Blocks.count(PN->getIncomingBlock(i))) {
          NewPN->addIncoming(PN->getIncomingValue(i), PN->getIncomingBlock(i));
          PN->removeIncomingValue(i);
          --i;
        }
      }
    }
  }
}

/// NormalizeLandingPads - Normalize and discover landing pads, noting them
/// in the LandingPads set.  A landing pad is normal if the only CFG edges
/// that end at it are unwind edges from invoke instructions. If we inlined
/// through an invoke we could have a normal branch from the previous
/// unwind block through to the landing pad for the original invoke.
/// Abnormal landing pads are fixed up by redirecting all unwind edges to
/// a new basic block which falls through to the original.
bool DwarfEHPrepare::NormalizeLandingPads() {
  bool Changed = false;

  for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
    TerminatorInst *TI = I->getTerminator();
    if (!isa<InvokeInst>(TI))
      continue;
    BasicBlock *LPad = TI->getSuccessor(1);
    // Skip landing pads that have already been normalized.
    if (LandingPads.count(LPad))
      continue;

    // Check that only invoke unwind edges end at the landing pad.
    bool OnlyUnwoundTo = true;
    for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad);
         PI != PE; ++PI) {
      TerminatorInst *PT = (*PI)->getTerminator();
      if (!isa<InvokeInst>(PT) || LPad == PT->getSuccessor(0)) {
        OnlyUnwoundTo = false;
        break;
      }
    }

    if (OnlyUnwoundTo) {
      // Only unwind edges lead to the landing pad.  Remember the landing pad.
      LandingPads.insert(LPad);
      continue;
    }

    // At least one normal edge ends at the landing pad.  Redirect the unwind
    // edges to a new basic block which falls through into this one.

    // Create the new basic block.
    BasicBlock *NewBB = BasicBlock::Create(F->getContext(),
                                           LPad->getName() + "_unwind_edge");

    // Insert it into the function right before the original landing pad.
    LPad->getParent()->getBasicBlockList().insert(LPad, NewBB);

    // Redirect unwind edges from the original landing pad to NewBB.
    for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ) {
      TerminatorInst *PT = (*PI++)->getTerminator();
      if (isa<InvokeInst>(PT) && PT->getSuccessor(1) == LPad)
        // Unwind to the new block.
        PT->setSuccessor(1, NewBB);
    }

    // If there are any PHI nodes in LPad, we need to update them so that they
    // merge incoming values from NewBB instead.
    for (BasicBlock::iterator II = LPad->begin(); isa<PHINode>(II); ++II) {
      PHINode *PN = cast<PHINode>(II);
      pred_iterator PB = pred_begin(NewBB), PE = pred_end(NewBB);

      // Check to see if all of the values coming in via unwind edges are the
      // same.  If so, we don't need to create a new PHI node.
      Value *InVal = PN->getIncomingValueForBlock(*PB);
      for (pred_iterator PI = PB; PI != PE; ++PI) {
        if (PI != PB && InVal != PN->getIncomingValueForBlock(*PI)) {
          InVal = 0;
          break;
        }
      }

      if (InVal == 0) {
        // Different unwind edges have different values.  Create a new PHI node
        // in NewBB.
        PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".unwind",
                                         NewBB);
        // Add an entry for each unwind edge, using the value from the old PHI.
        for (pred_iterator PI = PB; PI != PE; ++PI)
          NewPN->addIncoming(PN->getIncomingValueForBlock(*PI), *PI);

        // Now use this new PHI as the common incoming value for NewBB in PN.
        InVal = NewPN;
      }

      // Revector exactly one entry in the PHI node to come from NewBB
      // and delete all other entries that come from unwind edges.  If
      // there are both normal and unwind edges from the same predecessor,
      // this leaves an entry for the normal edge.
      for (pred_iterator PI = PB; PI != PE; ++PI)
        PN->removeIncomingValue(*PI);
      PN->addIncoming(InVal, NewBB);
    }

    // Add a fallthrough from NewBB to the original landing pad.
    BranchInst::Create(LPad, NewBB);

    // Now update DominatorTree and DominanceFrontier analysis information.
    if (DT)
      DT->splitBlock(NewBB);
    if (DF)
      DF->splitBlock(NewBB);
//.........这里部分代码省略.........

/*
 * Renaming uses of V to uses of vSSA_PHI
 * The rule of renaming is:
 *   - All uses of V in the dominator tree of vSSA_PHI are renamed
 *   - Uses of V in the same basicblock of vSSA_PHI are only renamed if they are not in PHI functions
 *   - Uses of V in the dominance frontier follow the same rules of sigma renaming
 */
void vSSA::renameUsesToPhi(Value *V, PHINode *phi)
{
	// This vector of Instruction* points to the uses of operand.
	// This auxiliary vector of pointers is used because the use_iterators are invalidated when we do the renaming
	SmallVector<Instruction*, 25> usepointers;
	unsigned i = 0, n = V->getNumUses();
	 
	usepointers.resize(n);
	
	// This vector contains pointers to all sigmas that have its operand renamed to vSSA_phi
	// For them, we need to try to create phi functions again
	SmallVector<PHINode*, 25> sigmasRenamed;
	
	BasicBlock *BB_next = phi->getParent();
	
	// Get the dominance frontier of the successor
	DominanceFrontier::iterator DF_BB = DF_->find(BB_next);
	
	for (Value::use_iterator uit = V->use_begin(), uend = V->use_end(); uit != uend; ++uit, ++i)
		usepointers[i] = dyn_cast<Instruction>(*uit);
	
	BasicBlock *BB_parent = phi->getParent();
	 
	for (i = 0; i < n; ++i) {
		// Check if the use is in the dominator tree of vSSA_PHI
		if (DT_->dominates(BB_parent, usepointers[i]->getParent())) {
			if (BB_parent != usepointers[i]->getParent()) {
				usepointers[i]->replaceUsesOfWith(V, phi);
				
				// If this use is in a sigma, we need to check whether phis creation are needed again for this sigma
				if (PHINode *sigma = dyn_cast<PHINode>(usepointers[i])) {
					if (sigma->getName().startswith(vSSA_SIG)) {
						sigmasRenamed.push_back(sigma);
					}
				}
			}
			else if (!isa<PHINode>(usepointers[i]))
				usepointers[i]->replaceUsesOfWith(V, phi);
		}
		// Check if the use is in the dominance frontier of phi
	 	else if (DF_BB->second.find(usepointers[i]->getParent()) != DF_BB->second.end()) {
	 		// Check if the user is a PHI node (it has to be, but only for precaution)
	 		if (PHINode *phiuser = dyn_cast<PHINode>(usepointers[i])) {
	 			for (unsigned i = 0, e = phiuser->getNumIncomingValues(); i < e; ++i) {
	 				Value *operand = phiuser->getIncomingValue(i);
	 				
	 				if (operand != V)
	 					continue;
	 				
	 				if (DT_->dominates(BB_next, phiuser->getIncomingBlock(i))) {
	 					phiuser->setIncomingValue(i, phi);
	 				}
	 			}
	 		}
	 	}
	}
	
	for (unsigned k = 0, f = phi->getNumIncomingValues(); k < f; ++k) {
		PHINode *p = dyn_cast<PHINode>(phi->getIncomingValue(k));
		
		if (!p || !p->getName().startswith(vSSA_SIG))
			continue;
		
		Value *V = p->getIncomingValue(0);
		
		n = V->getNumUses();
		usepointers.resize(n);
		
		unsigned i = 0;
		
		for (Value::use_iterator uit = V->use_begin(), uend = V->use_end(); uit != uend; ++uit, ++i)
			usepointers[i] = dyn_cast<Instruction>(*uit);
		 
		for (i = 0; i < n; ++i) {
			// Check if the use is in the dominator tree of vSSA_PHI
			if (DT_->dominates(BB_parent, usepointers[i]->getParent())) {
				if (BB_parent != usepointers[i]->getParent()) {
					usepointers[i]->replaceUsesOfWith(V, phi);
				
					// If this use is in a sigma, we need to check whether phis creation are needed again for this sigma
					if (PHINode *sigma = dyn_cast<PHINode>(usepointers[i])) {
						if (sigma->getName().startswith(vSSA_SIG)) {
							sigmasRenamed.push_back(sigma);
						}
					}
				}
				else if (!isa<PHINode>(usepointers[i]))
					usepointers[i]->replaceUsesOfWith(V, phi);
			}
			// Check if the use is in the dominance frontier of phi
		 	else if (DF_BB->second.find(usepointers[i]->getParent()) != DF_BB->second.end()) {
		 		// Check if the user is a PHI node (it has to be, but only for precaution)
		 		if (PHINode *phiuser = dyn_cast<PHINode>(usepointers[i])) {
//.........这里部分代码省略.........

/// Create a clone of the blocks in a loop and connect them together.
/// If CreateRemainderLoop is false, loop structure will not be cloned,
/// otherwise a new loop will be created including all cloned blocks, and the
/// iterator of it switches to count NewIter down to 0.
/// The cloned blocks should be inserted between InsertTop and InsertBot.
/// If loop structure is cloned InsertTop should be new preheader, InsertBot
/// new loop exit.
/// Return the new cloned loop that is created when CreateRemainderLoop is true.
static Loop *
CloneLoopBlocks(Loop *L, Value *NewIter, const bool CreateRemainderLoop,
                const bool UseEpilogRemainder, const bool UnrollRemainder,
                BasicBlock *InsertTop,
                BasicBlock *InsertBot, BasicBlock *Preheader,
                std::vector<BasicBlock *> &NewBlocks, LoopBlocksDFS &LoopBlocks,
                ValueToValueMapTy &VMap, DominatorTree *DT, LoopInfo *LI) {
  StringRef suffix = UseEpilogRemainder ? "epil" : "prol";
  BasicBlock *Header = L->getHeader();
  BasicBlock *Latch = L->getLoopLatch();
  Function *F = Header->getParent();
  LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
  LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
  Loop *ParentLoop = L->getParentLoop();
  NewLoopsMap NewLoops;
  NewLoops[ParentLoop] = ParentLoop;
  if (!CreateRemainderLoop)
    NewLoops[L] = ParentLoop;

  // For each block in the original loop, create a new copy,
  // and update the value map with the newly created values.
  for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
    BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, "." + suffix, F);
    NewBlocks.push_back(NewBB);

    // If we're unrolling the outermost loop, there's no remainder loop,
    // and this block isn't in a nested loop, then the new block is not
    // in any loop. Otherwise, add it to loopinfo.
    if (CreateRemainderLoop || LI->getLoopFor(*BB) != L || ParentLoop)
      addClonedBlockToLoopInfo(*BB, NewBB, LI, NewLoops);

    VMap[*BB] = NewBB;
    if (Header == *BB) {
      // For the first block, add a CFG connection to this newly
      // created block.
      InsertTop->getTerminator()->setSuccessor(0, NewBB);
    }

    if (DT) {
      if (Header == *BB) {
        // The header is dominated by the preheader.
        DT->addNewBlock(NewBB, InsertTop);
      } else {
        // Copy information from original loop to unrolled loop.
        BasicBlock *IDomBB = DT->getNode(*BB)->getIDom()->getBlock();
        DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDomBB]));
      }
    }

    if (Latch == *BB) {
      // For the last block, if CreateRemainderLoop is false, create a direct
      // jump to InsertBot. If not, create a loop back to cloned head.
      VMap.erase((*BB)->getTerminator());
      BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]);
      BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator());
      IRBuilder<> Builder(LatchBR);
      if (!CreateRemainderLoop) {
        Builder.CreateBr(InsertBot);
      } else {
        PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2,
                                          suffix + ".iter",
                                          FirstLoopBB->getFirstNonPHI());
        Value *IdxSub =
            Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
                              NewIdx->getName() + ".sub");
        Value *IdxCmp =
            Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp");
        Builder.CreateCondBr(IdxCmp, FirstLoopBB, InsertBot);
        NewIdx->addIncoming(NewIter, InsertTop);
        NewIdx->addIncoming(IdxSub, NewBB);
      }
      LatchBR->eraseFromParent();
    }
  }

  // Change the incoming values to the ones defined in the preheader or
  // cloned loop.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
    if (!CreateRemainderLoop) {
      if (UseEpilogRemainder) {
        unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
        NewPHI->setIncomingBlock(idx, InsertTop);
        NewPHI->removeIncomingValue(Latch, false);
      } else {
        VMap[&*I] = NewPHI->getIncomingValueForBlock(Preheader);
        cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
      }
    } else {
      unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
      NewPHI->setIncomingBlock(idx, InsertTop);
      BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
//.........这里部分代码省略.........

/// Create a clone of the blocks in a loop and connect them together.
/// If UnrollProlog is true, loop structure will not be cloned, otherwise a new
/// loop will be created including all cloned blocks, and the iterator of it
/// switches to count NewIter down to 0.
///
static void CloneLoopBlocks(Loop *L, Value *NewIter, const bool UnrollProlog,
                            BasicBlock *InsertTop, BasicBlock *InsertBot,
                            std::vector<BasicBlock *> &NewBlocks,
                            LoopBlocksDFS &LoopBlocks, ValueToValueMapTy &VMap,
                            LoopInfo *LI) {
    BasicBlock *Preheader = L->getLoopPreheader();
    BasicBlock *Header = L->getHeader();
    BasicBlock *Latch = L->getLoopLatch();
    Function *F = Header->getParent();
    LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
    LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
    Loop *NewLoop = 0;
    Loop *ParentLoop = L->getParentLoop();
    if (!UnrollProlog) {
        NewLoop = new Loop();
        if (ParentLoop)
            ParentLoop->addChildLoop(NewLoop);
        else
            LI->addTopLevelLoop(NewLoop);
    }

    // For each block in the original loop, create a new copy,
    // and update the value map with the newly created values.
    for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
        BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, ".prol", F);
        NewBlocks.push_back(NewBB);

        if (NewLoop)
            NewLoop->addBasicBlockToLoop(NewBB, *LI);
        else if (ParentLoop)
            ParentLoop->addBasicBlockToLoop(NewBB, *LI);

        VMap[*BB] = NewBB;
        if (Header == *BB) {
            // For the first block, add a CFG connection to this newly
            // created block.
            InsertTop->getTerminator()->setSuccessor(0, NewBB);

        }
        if (Latch == *BB) {
            // For the last block, if UnrollProlog is true, create a direct jump to
            // InsertBot. If not, create a loop back to cloned head.
            VMap.erase((*BB)->getTerminator());
            BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]);
            BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator());
            IRBuilder<> Builder(LatchBR);
            if (UnrollProlog) {
                Builder.CreateBr(InsertBot);
            } else {
                PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2, "prol.iter",
                                                  FirstLoopBB->getFirstNonPHI());
                Value *IdxSub =
                    Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
                                      NewIdx->getName() + ".sub");
                Value *IdxCmp =
                    Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp");
                Builder.CreateCondBr(IdxCmp, FirstLoopBB, InsertBot);
                NewIdx->addIncoming(NewIter, InsertTop);
                NewIdx->addIncoming(IdxSub, NewBB);
            }
            LatchBR->eraseFromParent();
        }
    }

    // Change the incoming values to the ones defined in the preheader or
    // cloned loop.
    for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
        PHINode *NewPHI = cast<PHINode>(VMap[I]);
        if (UnrollProlog) {
            VMap[I] = NewPHI->getIncomingValueForBlock(Preheader);
            cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
        } else {
            unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
            NewPHI->setIncomingBlock(idx, InsertTop);
            BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
            idx = NewPHI->getBasicBlockIndex(Latch);
            Value *InVal = NewPHI->getIncomingValue(idx);
            NewPHI->setIncomingBlock(idx, NewLatch);
            if (VMap[InVal])
                NewPHI->setIncomingValue(idx, VMap[InVal]);
        }
    }
    if (NewLoop) {
        // Add unroll disable metadata to disable future unrolling for this loop.
        SmallVector<Metadata *, 4> MDs;
        // Reserve first location for self reference to the LoopID metadata node.
        MDs.push_back(nullptr);
        MDNode *LoopID = NewLoop->getLoopID();
        if (LoopID) {
            // First remove any existing loop unrolling metadata.
            for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
                bool IsUnrollMetadata = false;
                MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
                if (MD) {
                    const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
//.........这里部分代码省略.........

/// Create a clone of the blocks in a loop and connect them together.
/// If CreateRemainderLoop is false, loop structure will not be cloned,
/// otherwise a new loop will be created including all cloned blocks, and the
/// iterator of it switches to count NewIter down to 0.
/// The cloned blocks should be inserted between InsertTop and InsertBot.
/// If loop structure is cloned InsertTop should be new preheader, InsertBot
/// new loop exit.
/// Return the new cloned loop that is created when CreateRemainderLoop is true.
static Loop *
CloneLoopBlocks(Loop *L, Value *NewIter, const bool CreateRemainderLoop,
                const bool UseEpilogRemainder, const bool UnrollRemainder,
                BasicBlock *InsertTop,
                BasicBlock *InsertBot, BasicBlock *Preheader,
                std::vector<BasicBlock *> &NewBlocks, LoopBlocksDFS &LoopBlocks,
                ValueToValueMapTy &VMap, DominatorTree *DT, LoopInfo *LI) {
  StringRef suffix = UseEpilogRemainder ? "epil" : "prol";
  BasicBlock *Header = L->getHeader();
  BasicBlock *Latch = L->getLoopLatch();
  Function *F = Header->getParent();
  LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
  LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
  Loop *ParentLoop = L->getParentLoop();
  NewLoopsMap NewLoops;
  NewLoops[ParentLoop] = ParentLoop;
  if (!CreateRemainderLoop)
    NewLoops[L] = ParentLoop;

  // For each block in the original loop, create a new copy,
  // and update the value map with the newly created values.
  for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
    BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, "." + suffix, F);
    NewBlocks.push_back(NewBB);

    // If we're unrolling the outermost loop, there's no remainder loop,
    // and this block isn't in a nested loop, then the new block is not
    // in any loop. Otherwise, add it to loopinfo.
    if (CreateRemainderLoop || LI->getLoopFor(*BB) != L || ParentLoop)
      addClonedBlockToLoopInfo(*BB, NewBB, LI, NewLoops);

    VMap[*BB] = NewBB;
    if (Header == *BB) {
      // For the first block, add a CFG connection to this newly
      // created block.
      InsertTop->getTerminator()->setSuccessor(0, NewBB);
    }

    if (DT) {
      if (Header == *BB) {
        // The header is dominated by the preheader.
        DT->addNewBlock(NewBB, InsertTop);
      } else {
        // Copy information from original loop to unrolled loop.
        BasicBlock *IDomBB = DT->getNode(*BB)->getIDom()->getBlock();
        DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDomBB]));
      }
    }

    if (Latch == *BB) {
      // For the last block, if CreateRemainderLoop is false, create a direct
      // jump to InsertBot. If not, create a loop back to cloned head.
      VMap.erase((*BB)->getTerminator());
      BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]);
      BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator());
      IRBuilder<> Builder(LatchBR);
      if (!CreateRemainderLoop) {
        Builder.CreateBr(InsertBot);
      } else {
        PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2,
                                          suffix + ".iter",
                                          FirstLoopBB->getFirstNonPHI());
        Value *IdxSub =
            Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
                              NewIdx->getName() + ".sub");
        Value *IdxCmp =
            Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp");
        Builder.CreateCondBr(IdxCmp, FirstLoopBB, InsertBot);
        NewIdx->addIncoming(NewIter, InsertTop);
        NewIdx->addIncoming(IdxSub, NewBB);
      }
      LatchBR->eraseFromParent();
    }
  }

  // Change the incoming values to the ones defined in the preheader or
  // cloned loop.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
    if (!CreateRemainderLoop) {
      if (UseEpilogRemainder) {
        unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
        NewPHI->setIncomingBlock(idx, InsertTop);
        NewPHI->removeIncomingValue(Latch, false);
      } else {
        VMap[&*I] = NewPHI->getIncomingValueForBlock(Preheader);
        cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
      }
    } else {
      unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
      NewPHI->setIncomingBlock(idx, InsertTop);
      BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
//.........这里部分代码省略.........

/// \brief This method is called when the specified loop has more than one
/// backedge in it.
///
/// If this occurs, revector all of these backedges to target a new basic block
/// and have that block branch to the loop header.  This ensures that loops
/// have exactly one backedge.
static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
                                             DominatorTree *DT, LoopInfo *LI) {
  assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");

  // Get information about the loop
  BasicBlock *Header = L->getHeader();
  Function *F = Header->getParent();

  // Unique backedge insertion currently depends on having a preheader.
  if (!Preheader)
    return nullptr;

  // The header is not a landing pad; preheader insertion should ensure this.
  assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");

  // Figure out which basic blocks contain back-edges to the loop header.
  std::vector<BasicBlock*> BackedgeBlocks;
  for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I){
    BasicBlock *P = *I;

    // Indirectbr edges cannot be split, so we must fail if we find one.
    if (isa<IndirectBrInst>(P->getTerminator()))
      return nullptr;

    if (P != Preheader) BackedgeBlocks.push_back(P);
  }

  // Create and insert the new backedge block...
  BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
                                           Header->getName() + ".backedge", F);
  BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
  BETerminator->setDebugLoc(Header->getFirstNonPHI()->getDebugLoc());

  DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
               << BEBlock->getName() << "\n");

  // Move the new backedge block to right after the last backedge block.
  Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
  F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);

  // Now that the block has been inserted into the function, create PHI nodes in
  // the backedge block which correspond to any PHI nodes in the header block.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PN = cast<PHINode>(I);
    PHINode *NewPN = PHINode::Create(PN->getType(), BackedgeBlocks.size(),
                                     PN->getName()+".be", BETerminator);

    // Loop over the PHI node, moving all entries except the one for the
    // preheader over to the new PHI node.
    unsigned PreheaderIdx = ~0U;
    bool HasUniqueIncomingValue = true;
    Value *UniqueValue = nullptr;
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *IBB = PN->getIncomingBlock(i);
      Value *IV = PN->getIncomingValue(i);
      if (IBB == Preheader) {
        PreheaderIdx = i;
      } else {
        NewPN->addIncoming(IV, IBB);
        if (HasUniqueIncomingValue) {
          if (!UniqueValue)
            UniqueValue = IV;
          else if (UniqueValue != IV)
            HasUniqueIncomingValue = false;
        }
      }
    }

    // Delete all of the incoming values from the old PN except the preheader's
    assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
    if (PreheaderIdx != 0) {
      PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
      PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
    }
    // Nuke all entries except the zero'th.
    for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
      PN->removeIncomingValue(e-i, false);

    // Finally, add the newly constructed PHI node as the entry for the BEBlock.
    PN->addIncoming(NewPN, BEBlock);

    // As an optimization, if all incoming values in the new PhiNode (which is a
    // subset of the incoming values of the old PHI node) have the same value,
    // eliminate the PHI Node.
    if (HasUniqueIncomingValue) {
      NewPN->replaceAllUsesWith(UniqueValue);
      BEBlock->getInstList().erase(NewPN);
    }
  }

  // Now that all of the PHI nodes have been inserted and adjusted, modify the
  // backedge blocks to just to the BEBlock instead of the header.
  for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
    TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
//.........这里部分代码省略.........

/// Connect the unrolling epilog code to the original loop.
/// The unrolling epilog code contains code to execute the
/// 'extra' iterations if the run-time trip count modulo the
/// unroll count is non-zero.
///
/// This function performs the following:
/// - Update PHI nodes at the unrolling loop exit and epilog loop exit
/// - Create PHI nodes at the unrolling loop exit to combine
///   values that exit the unrolling loop code and jump around it.
/// - Update PHI operands in the epilog loop by the new PHI nodes
/// - Branch around the epilog loop if extra iters (ModVal) is zero.
///
static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
                          BasicBlock *Exit, BasicBlock *PreHeader,
                          BasicBlock *EpilogPreHeader, BasicBlock *NewPreHeader,
                          ValueToValueMapTy &VMap, DominatorTree *DT,
                          LoopInfo *LI, bool PreserveLCSSA)  {
  BasicBlock *Latch = L->getLoopLatch();
  assert(Latch && "Loop must have a latch");
  BasicBlock *EpilogLatch = cast<BasicBlock>(VMap[Latch]);

  // Loop structure should be the following:
  //
  // PreHeader
  // NewPreHeader
  //   Header
  //   ...
  //   Latch
  // NewExit (PN)
  // EpilogPreHeader
  //   EpilogHeader
  //   ...
  //   EpilogLatch
  // Exit (EpilogPN)

  // Update PHI nodes at NewExit and Exit.
  for (Instruction &BBI : *NewExit) {
    PHINode *PN = dyn_cast<PHINode>(&BBI);
    // Exit when we passed all PHI nodes.
    if (!PN)
      break;
    // PN should be used in another PHI located in Exit block as
    // Exit was split by SplitBlockPredecessors into Exit and NewExit
    // Basicaly it should look like:
    // NewExit:
    //   PN = PHI [I, Latch]
    // ...
    // Exit:
    //   EpilogPN = PHI [PN, EpilogPreHeader]
    //
    // There is EpilogPreHeader incoming block instead of NewExit as
    // NewExit was spilt 1 more time to get EpilogPreHeader.
    assert(PN->hasOneUse() && "The phi should have 1 use");
    PHINode *EpilogPN = cast<PHINode> (PN->use_begin()->getUser());
    assert(EpilogPN->getParent() == Exit && "EpilogPN should be in Exit block");

    // Add incoming PreHeader from branch around the Loop
    PN->addIncoming(UndefValue::get(PN->getType()), PreHeader);

    Value *V = PN->getIncomingValueForBlock(Latch);
    Instruction *I = dyn_cast<Instruction>(V);
    if (I && L->contains(I))
      // If value comes from an instruction in the loop add VMap value.
      V = VMap.lookup(I);
    // For the instruction out of the loop, constant or undefined value
    // insert value itself.
    EpilogPN->addIncoming(V, EpilogLatch);

    assert(EpilogPN->getBasicBlockIndex(EpilogPreHeader) >= 0 &&
          "EpilogPN should have EpilogPreHeader incoming block");
    // Change EpilogPreHeader incoming block to NewExit.
    EpilogPN->setIncomingBlock(EpilogPN->getBasicBlockIndex(EpilogPreHeader),
                               NewExit);
    // Now PHIs should look like:
    // NewExit:
    //   PN = PHI [I, Latch], [undef, PreHeader]
    // ...
    // Exit:
    //   EpilogPN = PHI [PN, NewExit], [VMap[I], EpilogLatch]
  }

  // Create PHI nodes at NewExit (from the unrolling loop Latch and PreHeader).
  // Update corresponding PHI nodes in epilog loop.
  for (BasicBlock *Succ : successors(Latch)) {
    // Skip this as we already updated phis in exit blocks.
    if (!L->contains(Succ))
      continue;
    for (Instruction &BBI : *Succ) {
      PHINode *PN = dyn_cast<PHINode>(&BBI);
      // Exit when we passed all PHI nodes.
      if (!PN)
        break;
      // Add new PHI nodes to the loop exit block and update epilog
      // PHIs with the new PHI values.
      PHINode *NewPN = PHINode::Create(PN->getType(), 2, PN->getName() + ".unr",
                                       NewExit->getFirstNonPHI());
      // Adding a value to the new PHI node from the unrolling loop preheader.
      NewPN->addIncoming(PN->getIncomingValueForBlock(NewPreHeader), PreHeader);
      // Adding a value to the new PHI node from the unrolling loop latch.
      NewPN->addIncoming(PN->getIncomingValueForBlock(Latch), Latch);
//.........这里部分代码省略.........

bool llvm::UnrollRuntimeLoopRemainder(Loop *L, unsigned Count,
                                      bool AllowExpensiveTripCount,
                                      bool UseEpilogRemainder,
                                      LoopInfo *LI, ScalarEvolution *SE,
                                      DominatorTree *DT, bool PreserveLCSSA) {
  // for now, only unroll loops that contain a single exit
  if (!L->getExitingBlock())
    return false;

  // Make sure the loop is in canonical form, and there is a single
  // exit block only.
  if (!L->isLoopSimplifyForm())
    return false;
  BasicBlock *Exit = L->getUniqueExitBlock(); // successor out of loop
  if (!Exit)
    return false;

  // Use Scalar Evolution to compute the trip count. This allows more loops to
  // be unrolled than relying on induction var simplification.
  if (!SE)
    return false;

  // Only unroll loops with a computable trip count, and the trip count needs
  // to be an int value (allowing a pointer type is a TODO item).
  const SCEV *BECountSC = SE->getBackedgeTakenCount(L);
  if (isa<SCEVCouldNotCompute>(BECountSC) ||
      !BECountSC->getType()->isIntegerTy())
    return false;

  unsigned BEWidth = cast<IntegerType>(BECountSC->getType())->getBitWidth();

  // Add 1 since the backedge count doesn't include the first loop iteration.
  const SCEV *TripCountSC =
      SE->getAddExpr(BECountSC, SE->getConstant(BECountSC->getType(), 1));
  if (isa<SCEVCouldNotCompute>(TripCountSC))
    return false;

  BasicBlock *Header = L->getHeader();
  BasicBlock *PreHeader = L->getLoopPreheader();
  BranchInst *PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator());
  const DataLayout &DL = Header->getModule()->getDataLayout();
  SCEVExpander Expander(*SE, DL, "loop-unroll");
  if (!AllowExpensiveTripCount &&
      Expander.isHighCostExpansion(TripCountSC, L, PreHeaderBR))
    return false;

  // This constraint lets us deal with an overflowing trip count easily; see the
  // comment on ModVal below.
  if (Log2_32(Count) > BEWidth)
    return false;

  BasicBlock *Latch = L->getLoopLatch();

  // Loop structure is the following:
  //
  // PreHeader
  //   Header
  //   ...
  //   Latch
  // Exit

  BasicBlock *NewPreHeader;
  BasicBlock *NewExit = nullptr;
  BasicBlock *PrologExit = nullptr;
  BasicBlock *EpilogPreHeader = nullptr;
  BasicBlock *PrologPreHeader = nullptr;

  if (UseEpilogRemainder) {
    // If epilog remainder
    // Split PreHeader to insert a branch around loop for unrolling.
    NewPreHeader = SplitBlock(PreHeader, PreHeader->getTerminator(), DT, LI);
    NewPreHeader->setName(PreHeader->getName() + ".new");
    // Split Exit to create phi nodes from branch above.
    SmallVector<BasicBlock*, 4> Preds(predecessors(Exit));
    NewExit = SplitBlockPredecessors(Exit, Preds, ".unr-lcssa",
                                     DT, LI, PreserveLCSSA);
    // Split NewExit to insert epilog remainder loop.
    EpilogPreHeader = SplitBlock(NewExit, NewExit->getTerminator(), DT, LI);
    EpilogPreHeader->setName(Header->getName() + ".epil.preheader");
  } else {
    // If prolog remainder
    // Split the original preheader twice to insert prolog remainder loop
    PrologPreHeader = SplitEdge(PreHeader, Header, DT, LI);
    PrologPreHeader->setName(Header->getName() + ".prol.preheader");
    PrologExit = SplitBlock(PrologPreHeader, PrologPreHeader->getTerminator(),
                            DT, LI);
    PrologExit->setName(Header->getName() + ".prol.loopexit");
    // Split PrologExit to get NewPreHeader.
    NewPreHeader = SplitBlock(PrologExit, PrologExit->getTerminator(), DT, LI);
    NewPreHeader->setName(PreHeader->getName() + ".new");
  }
  // Loop structure should be the following:
  //  Epilog             Prolog
  //
  // PreHeader         PreHeader
  // *NewPreHeader     *PrologPreHeader
  //   Header          *PrologExit
  //   ...             *NewPreHeader
  //   Latch             Header
  // *NewExit            ...
//.........这里部分代码省略.........

/// SplitBlockPredecessors - This method transforms BB by introducing a new
/// basic block into the function, and moving some of the predecessors of BB to
/// be predecessors of the new block.  The new predecessors are indicated by the
/// Preds array, which has NumPreds elements in it.  The new block is given a
/// suffix of 'Suffix'.
///
/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and
/// DominanceFrontier, but no other analyses.
BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, 
                                         BasicBlock *const *Preds,
                                         unsigned NumPreds, const char *Suffix,
                                         Pass *P) {
  // Create new basic block, insert right before the original block.
  BasicBlock *NewBB =
    BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB);
  
  // The new block unconditionally branches to the old block.
  BranchInst *BI = BranchInst::Create(BB, NewBB);
  
  // Move the edges from Preds to point to NewBB instead of BB.
  for (unsigned i = 0; i != NumPreds; ++i)
    Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
  
  // Update dominator tree and dominator frontier if available.
  DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0;
  if (DT)
    DT->splitBlock(NewBB);
  if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0)
    DF->splitBlock(NewBB);
  AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
  
  
  // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
  // node becomes an incoming value for BB's phi node.  However, if the Preds
  // list is empty, we need to insert dummy entries into the PHI nodes in BB to
  // account for the newly created predecessor.
  if (NumPreds == 0) {
    // Insert dummy values as the incoming value.
    for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
      cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
    return NewBB;
  }
  
  // Otherwise, create a new PHI node in NewBB for each PHI node in BB.
  for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
    PHINode *PN = cast<PHINode>(I++);
    
    // Check to see if all of the values coming in are the same.  If so, we
    // don't need to create a new PHI node.
    Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
    for (unsigned i = 1; i != NumPreds; ++i)
      if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
        InVal = 0;
        break;
      }
    
    if (InVal) {
      // If all incoming values for the new PHI would be the same, just don't
      // make a new PHI.  Instead, just remove the incoming values from the old
      // PHI.
      for (unsigned i = 0; i != NumPreds; ++i)
        PN->removeIncomingValue(Preds[i], false);
    } else {
      // If the values coming into the block are not the same, we need a PHI.
      // Create the new PHI node, insert it into NewBB at the end of the block
      PHINode *NewPHI =
        PHINode::Create(PN->getType(), PN->getName()+".ph", BI);
      if (AA) AA->copyValue(PN, NewPHI);
      
      // Move all of the PHI values for 'Preds' to the new PHI.
      for (unsigned i = 0; i != NumPreds; ++i) {
        Value *V = PN->removeIncomingValue(Preds[i], false);
        NewPHI->addIncoming(V, Preds[i]);
      }
      InVal = NewPHI;
    }
    
    // Add an incoming value to the PHI node in the loop for the preheader
    // edge.
    PN->addIncoming(InVal, NewBB);
    
    // Check to see if we can eliminate this phi node.
    if (Value *V = PN->hasConstantValue(DT != 0)) {
      Instruction *I = dyn_cast<Instruction>(V);
      if (!I || DT == 0 || DT->dominates(I, PN)) {
        PN->replaceAllUsesWith(V);
        if (AA) AA->deleteValue(PN);
        PN->eraseFromParent();
      }
    }
  }
  
  return NewBB;
}