diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 14bfe0d17ac..10b5c74e378 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -6402,9 +6402,8 @@ PushLoopPHIs(const Loop *L, SmallVectorImpl<Instruction *> &Worklist) {
   BasicBlock *Header = L->getHeader();
 
   // Push all Loop-header PHIs onto the Worklist stack.
-  for (BasicBlock::iterator I = Header->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I)
-    Worklist.push_back(PN);
+  for (PHINode &PN : Header->phis())
+    Worklist.push_back(&PN);
 }
 
 const ScalarEvolution::BackedgeTakenInfo &
@@ -7638,12 +7637,9 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
   if (!Latch)
     return nullptr;
 
-  for (auto &I : *Header) {
-    PHINode *PHI = dyn_cast<PHINode>(&I);
-    if (!PHI) break;
-    auto *StartCST = getOtherIncomingValue(PHI, Latch);
-    if (!StartCST) continue;
-    CurrentIterVals[PHI] = StartCST;
+  for (PHINode &PHI : Header->phis()) {
+    if (auto *StartCST = getOtherIncomingValue(&PHI, Latch))
+      CurrentIterVals[&PHI] = StartCST;
   }
   if (!CurrentIterVals.count(PN))
     return RetVal = nullptr;
@@ -7720,13 +7716,9 @@ const SCEV *ScalarEvolution::computeExitCountExhaustively(const Loop *L,
   BasicBlock *Latch = L->getLoopLatch();
   assert(Latch && "Should follow from NumIncomingValues == 2!");
 
-  for (auto &I : *Header) {
-    PHINode *PHI = dyn_cast<PHINode>(&I);
-    if (!PHI)
-      break;
-    auto *StartCST = getOtherIncomingValue(PHI, Latch);
-    if (!StartCST) continue;
-    CurrentIterVals[PHI] = StartCST;
+  for (PHINode &PHI : Header->phis()) {
+    if (auto *StartCST = getOtherIncomingValue(&PHI, Latch))
+      CurrentIterVals[&PHI] = StartCST;
   }
   if (!CurrentIterVals.count(PN))
     return getCouldNotCompute();
diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp
index 3ceda677ba6..53ce33bacbe 100644
--- a/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1154,16 +1154,11 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
         IVIncInsertLoop &&
         SE.DT.properlyDominates(LatchBlock, IVIncInsertLoop->getHeader());
 
-    for (auto &I : *L->getHeader()) {
-      auto *PN = dyn_cast<PHINode>(&I);
-      // Found first non-phi, the rest of instructions are also not Phis.
-      if (!PN)
-        break;
-
-      if (!SE.isSCEVable(PN->getType()))
+    for (PHINode &PN : L->getHeader()->phis()) {
+      if (!SE.isSCEVable(PN.getType()))
         continue;
 
-      const SCEVAddRecExpr *PhiSCEV = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(PN));
+      const SCEVAddRecExpr *PhiSCEV = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(&PN));
       if (!PhiSCEV)
         continue;
 
@@ -1175,16 +1170,16 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
           continue;
 
       Instruction *TempIncV =
-          cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock));
+          cast<Instruction>(PN.getIncomingValueForBlock(LatchBlock));
 
       // Check whether we can reuse this PHI node.
       if (LSRMode) {
-        if (!isExpandedAddRecExprPHI(PN, TempIncV, L))
+        if (!isExpandedAddRecExprPHI(&PN, TempIncV, L))
           continue;
         if (L == IVIncInsertLoop && !hoistIVInc(TempIncV, IVIncInsertPos))
           continue;
       } else {
-        if (!isNormalAddRecExprPHI(PN, TempIncV, L))
+        if (!isNormalAddRecExprPHI(&PN, TempIncV, L))
           continue;
       }
 
@@ -1193,7 +1188,7 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
         IncV = TempIncV;
         TruncTy = nullptr;
         InvertStep = false;
-        AddRecPhiMatch = PN;
+        AddRecPhiMatch = &PN;
         break;
       }
 
@@ -1203,7 +1198,7 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
           canBeCheaplyTransformed(SE, PhiSCEV, Normalized, InvertStep)) {
         // Record the phi node. But don't stop we might find an exact match
         // later.
-        AddRecPhiMatch = PN;
+        AddRecPhiMatch = &PN;
         IncV = TempIncV;
         TruncTy = SE.getEffectiveSCEVType(Normalized->getType());
       }
@@ -1863,12 +1858,8 @@ SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
                                   const TargetTransformInfo *TTI) {
   // Find integer phis in order of increasing width.
   SmallVector<PHINode*, 8> Phis;
-  for (auto &I : *L->getHeader()) {
-    if (auto *PN = dyn_cast<PHINode>(&I))
-      Phis.push_back(PN);
-    else
-      break;
-  }
+  for (PHINode &PN : L->getHeader()->phis())
+    Phis.push_back(&PN);
 
   if (TTI)
     std::sort(Phis.begin(), Phis.end(), [](Value *LHS, Value *RHS) {
diff --git a/lib/CodeGen/CodeGenPrepare.cpp b/lib/CodeGen/CodeGenPrepare.cpp
index d6f55bba716..9dc1ab4e6bb 100644
--- a/lib/CodeGen/CodeGenPrepare.cpp
+++ b/lib/CodeGen/CodeGenPrepare.cpp
@@ -633,16 +633,10 @@ bool CodeGenPrepare::isMergingEmptyBlockProfitable(BasicBlock *BB,
     if (DestBBPred == BB)
       continue;
 
-    bool HasAllSameValue = true;
-    BasicBlock::const_iterator DestBBI = DestBB->begin();
-    while (const PHINode *DestPN = dyn_cast<PHINode>(DestBBI++)) {
-      if (DestPN->getIncomingValueForBlock(BB) !=
-          DestPN->getIncomingValueForBlock(DestBBPred)) {
-        HasAllSameValue = false;
-        break;
-      }
-    }
-    if (HasAllSameValue)
+    if (llvm::all_of(DestBB->phis(), [&](const PHINode &DestPN) {
+          return DestPN.getIncomingValueForBlock(BB) ==
+                 DestPN.getIncomingValueForBlock(DestBBPred);
+        }))
       SameIncomingValueBBs.insert(DestBBPred);
   }
 
@@ -672,9 +666,8 @@ bool CodeGenPrepare::canMergeBlocks(const BasicBlock *BB,
   // We only want to eliminate blocks whose phi nodes are used by phi nodes in
   // the successor.  If there are more complex condition (e.g. preheaders),
   // don't mess around with them.
-  BasicBlock::const_iterator BBI = BB->begin();
-  while (const PHINode *PN = dyn_cast<PHINode>(BBI++)) {
-    for (const User *U : PN->users()) {
+  for (const PHINode &PN : BB->phis()) {
+    for (const User *U : PN.users()) {
       const Instruction *UI = cast<Instruction>(U);
       if (UI->getParent() != DestBB || !isa<PHINode>(UI))
         return false;
@@ -713,10 +706,9 @@ bool CodeGenPrepare::canMergeBlocks(const BasicBlock *BB,
   for (unsigned i = 0, e = DestBBPN->getNumIncomingValues(); i != e; ++i) {
     BasicBlock *Pred = DestBBPN->getIncomingBlock(i);
     if (BBPreds.count(Pred)) {   // Common predecessor?
-      BBI = DestBB->begin();
-      while (const PHINode *PN = dyn_cast<PHINode>(BBI++)) {
-        const Value *V1 = PN->getIncomingValueForBlock(Pred);
-        const Value *V2 = PN->getIncomingValueForBlock(BB);
+      for (const PHINode &PN : DestBB->phis()) {
+        const Value *V1 = PN.getIncomingValueForBlock(Pred);
+        const Value *V2 = PN.getIncomingValueForBlock(BB);
 
         // If V2 is a phi node in BB, look up what the mapped value will be.
         if (const PHINode *V2PN = dyn_cast<PHINode>(V2))
@@ -759,11 +751,9 @@ void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
 
   // Otherwise, we have multiple predecessors of BB.  Update the PHIs in DestBB
   // to handle the new incoming edges it is about to have.
-  PHINode *PN;
-  for (BasicBlock::iterator BBI = DestBB->begin();
-       (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
+  for (PHINode &PN : DestBB->phis()) {
     // Remove the incoming value for BB, and remember it.
-    Value *InVal = PN->removeIncomingValue(BB, false);
+    Value *InVal = PN.removeIncomingValue(BB, false);
 
     // Two options: either the InVal is a phi node defined in BB or it is some
     // value that dominates BB.
@@ -771,17 +761,17 @@ void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
     if (InValPhi && InValPhi->getParent() == BB) {
       // Add all of the input values of the input PHI as inputs of this phi.
       for (unsigned i = 0, e = InValPhi->getNumIncomingValues(); i != e; ++i)
-        PN->addIncoming(InValPhi->getIncomingValue(i),
-                        InValPhi->getIncomingBlock(i));
+        PN.addIncoming(InValPhi->getIncomingValue(i),
+                       InValPhi->getIncomingBlock(i));
     } else {
       // Otherwise, add one instance of the dominating value for each edge that
       // we will be adding.
       if (PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) {
         for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i)
-          PN->addIncoming(InVal, BBPN->getIncomingBlock(i));
+          PN.addIncoming(InVal, BBPN->getIncomingBlock(i));
       } else {
         for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
-          PN->addIncoming(InVal, *PI);
+          PN.addIncoming(InVal, *PI);
       }
     }
   }
@@ -6497,22 +6487,16 @@ bool CodeGenPrepare::splitBranchCondition(Function &F) {
       std::swap(TBB, FBB);
 
     // Replace the old BB with the new BB.
-    for (auto &I : *TBB) {
-      PHINode *PN = dyn_cast<PHINode>(&I);
-      if (!PN)
-        break;
+    for (PHINode &PN : TBB->phis()) {
       int i;
-      while ((i = PN->getBasicBlockIndex(&BB)) >= 0)
-        PN->setIncomingBlock(i, TmpBB);
+      while ((i = PN.getBasicBlockIndex(&BB)) >= 0)
+        PN.setIncomingBlock(i, TmpBB);
     }
 
     // Add another incoming edge form the new BB.
-    for (auto &I : *FBB) {
-      PHINode *PN = dyn_cast<PHINode>(&I);
-      if (!PN)
-        break;
-      auto *Val = PN->getIncomingValueForBlock(&BB);
-      PN->addIncoming(Val, TmpBB);
+    for (PHINode &PN : FBB->phis()) {
+      auto *Val = PN.getIncomingValueForBlock(&BB);
+      PN.addIncoming(Val, TmpBB);
     }
 
     // Update the branch weights (from SelectionDAGBuilder::
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index d3c94b5f9e6..3c856914053 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -2051,11 +2051,9 @@ bool FastISel::handlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
     // At this point we know that there is a 1-1 correspondence between LLVM PHI
     // nodes and Machine PHI nodes, but the incoming operands have not been
     // emitted yet.
-    for (BasicBlock::const_iterator I = SuccBB->begin();
-         const auto *PN = dyn_cast<PHINode>(I); ++I) {
-
+    for (const PHINode &PN : SuccBB->phis()) {
       // Ignore dead phi's.
-      if (PN->use_empty())
+      if (PN.use_empty())
         continue;
 
       // Only handle legal types. Two interesting things to note here. First,
@@ -2064,7 +2062,7 @@ bool FastISel::handlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
       // own moves. Second, this check is necessary because FastISel doesn't
       // use CreateRegs to create registers, so it always creates
       // exactly one register for each non-void instruction.
-      EVT VT = TLI.getValueType(DL, PN->getType(), /*AllowUnknown=*/true);
+      EVT VT = TLI.getValueType(DL, PN.getType(), /*AllowUnknown=*/true);
       if (VT == MVT::Other || !TLI.isTypeLegal(VT)) {
         // Handle integer promotions, though, because they're common and easy.
         if (!(VT == MVT::i1 || VT == MVT::i8 || VT == MVT::i16)) {
@@ -2073,11 +2071,11 @@ bool FastISel::handlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
         }
       }
 
-      const Value *PHIOp = PN->getIncomingValueForBlock(LLVMBB);
+      const Value *PHIOp = PN.getIncomingValueForBlock(LLVMBB);
 
       // Set the DebugLoc for the copy. Prefer the location of the operand
       // if there is one; use the location of the PHI otherwise.
-      DbgLoc = PN->getDebugLoc();
+      DbgLoc = PN.getDebugLoc();
       if (const auto *Inst = dyn_cast<Instruction>(PHIOp))
         DbgLoc = Inst->getDebugLoc();
 
diff --git a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index c7cdb49203b..81347fa4bd4 100644
--- a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -257,20 +257,20 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
 
     // Create Machine PHI nodes for LLVM PHI nodes, lowering them as
     // appropriate.
-    for (BasicBlock::const_iterator I = BB.begin();
-         const PHINode *PN = dyn_cast<PHINode>(I); ++I) {
-      if (PN->use_empty()) continue;
-
-      // Skip empty types
-      if (PN->getType()->isEmptyTy())
+    for (const PHINode &PN : BB.phis()) {
+      if (PN.use_empty())
         continue;
 
-      DebugLoc DL = PN->getDebugLoc();
-      unsigned PHIReg = ValueMap[PN];
+      // Skip empty types
+      if (PN.getType()->isEmptyTy())
+        continue;
+
+      DebugLoc DL = PN.getDebugLoc();
+      unsigned PHIReg = ValueMap[&PN];
       assert(PHIReg && "PHI node does not have an assigned virtual register!");
 
       SmallVector<EVT, 4> ValueVTs;
-      ComputeValueVTs(*TLI, MF->getDataLayout(), PN->getType(), ValueVTs);
+      ComputeValueVTs(*TLI, MF->getDataLayout(), PN.getType(), ValueVTs);
       for (EVT VT : ValueVTs) {
         unsigned NumRegisters = TLI->getNumRegisters(Fn->getContext(), VT);
         const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 71cb8cb78f6..68bbd62e132 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -8940,17 +8940,17 @@ SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
     // At this point we know that there is a 1-1 correspondence between LLVM PHI
     // nodes and Machine PHI nodes, but the incoming operands have not been
     // emitted yet.
-    for (BasicBlock::const_iterator I = SuccBB->begin();
-         const PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+    for (const PHINode &PN : SuccBB->phis()) {
       // Ignore dead phi's.
-      if (PN->use_empty()) continue;
+      if (PN.use_empty())
+        continue;
 
       // Skip empty types
-      if (PN->getType()->isEmptyTy())
+      if (PN.getType()->isEmptyTy())
         continue;
 
       unsigned Reg;
-      const Value *PHIOp = PN->getIncomingValueForBlock(LLVMBB);
+      const Value *PHIOp = PN.getIncomingValueForBlock(LLVMBB);
 
       if (const Constant *C = dyn_cast<Constant>(PHIOp)) {
         unsigned &RegOut = ConstantsOut[C];
@@ -8977,7 +8977,7 @@ SelectionDAGBuilder::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
       // the input for this MBB.
       SmallVector<EVT, 4> ValueVTs;
       const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-      ComputeValueVTs(TLI, DAG.getDataLayout(), PN->getType(), ValueVTs);
+      ComputeValueVTs(TLI, DAG.getDataLayout(), PN.getType(), ValueVTs);
       for (unsigned vti = 0, vte = ValueVTs.size(); vti != vte; ++vti) {
         EVT VT = ValueVTs[vti];
         unsigned NumRegisters = TLI.getNumRegisters(*DAG.getContext(), VT);
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index d13ccc26371..befd797e75b 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1445,13 +1445,11 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
       }
 
       if (AllPredsVisited) {
-        for (BasicBlock::const_iterator I = LLVMBB->begin();
-             const PHINode *PN = dyn_cast<PHINode>(I); ++I)
-          FuncInfo->ComputePHILiveOutRegInfo(PN);
+        for (const PHINode &PN : LLVMBB->phis())
+          FuncInfo->ComputePHILiveOutRegInfo(&PN);
       } else {
-        for (BasicBlock::const_iterator I = LLVMBB->begin();
-             const PHINode *PN = dyn_cast<PHINode>(I); ++I)
-          FuncInfo->InvalidatePHILiveOutRegInfo(PN);
+        for (const PHINode &PN : LLVMBB->phis())
+          FuncInfo->InvalidatePHILiveOutRegInfo(&PN);
       }
 
       FuncInfo->VisitedBBs.insert(LLVMBB);
diff --git a/lib/CodeGen/WinEHPrepare.cpp b/lib/CodeGen/WinEHPrepare.cpp
index 7ad84734203..0b16a113640 100644
--- a/lib/CodeGen/WinEHPrepare.cpp
+++ b/lib/CodeGen/WinEHPrepare.cpp
@@ -838,17 +838,11 @@ void WinEHPrepare::cloneCommonBlocks(Function &F) {
     for (auto &BBMapping : Orig2Clone) {
       BasicBlock *OldBlock = BBMapping.first;
       BasicBlock *NewBlock = BBMapping.second;
-      for (Instruction &OldI : *OldBlock) {
-        auto *OldPN = dyn_cast<PHINode>(&OldI);
-        if (!OldPN)
-          break;
-        UpdatePHIOnClonedBlock(OldPN, /*IsForOldBlock=*/true);
+      for (PHINode &OldPN : OldBlock->phis()) {
+        UpdatePHIOnClonedBlock(&OldPN, /*IsForOldBlock=*/true);
       }
-      for (Instruction &NewI : *NewBlock) {
-        auto *NewPN = dyn_cast<PHINode>(&NewI);
-        if (!NewPN)
-          break;
-        UpdatePHIOnClonedBlock(NewPN, /*IsForOldBlock=*/false);
+      for (PHINode &NewPN : NewBlock->phis()) {
+        UpdatePHIOnClonedBlock(&NewPN, /*IsForOldBlock=*/false);
       }
     }
 
@@ -858,17 +852,13 @@ void WinEHPrepare::cloneCommonBlocks(Function &F) {
       BasicBlock *OldBlock = BBMapping.first;
       BasicBlock *NewBlock = BBMapping.second;
       for (BasicBlock *SuccBB : successors(NewBlock)) {
-        for (Instruction &SuccI : *SuccBB) {
-          auto *SuccPN = dyn_cast<PHINode>(&SuccI);
-          if (!SuccPN)
-            break;
-
+        for (PHINode &SuccPN : SuccBB->phis()) {
           // Ok, we have a PHI node.  Figure out what the incoming value was for
           // the OldBlock.
-          int OldBlockIdx = SuccPN->getBasicBlockIndex(OldBlock);
+          int OldBlockIdx = SuccPN.getBasicBlockIndex(OldBlock);
           if (OldBlockIdx == -1)
             break;
-          Value *IV = SuccPN->getIncomingValue(OldBlockIdx);
+          Value *IV = SuccPN.getIncomingValue(OldBlockIdx);
 
           // Remap the value if necessary.
           if (auto *Inst = dyn_cast<Instruction>(IV)) {
@@ -877,7 +867,7 @@ void WinEHPrepare::cloneCommonBlocks(Function &F) {
               IV = I->second;
           }
 
-          SuccPN->addIncoming(IV, NewBlock);
+          SuccPN.addIncoming(IV, NewBlock);
         }
       }
     }
diff --git a/lib/IR/Verifier.cpp b/lib/IR/Verifier.cpp
index 534104686d8..1754f7d4501 100644
--- a/lib/IR/Verifier.cpp
+++ b/lib/IR/Verifier.cpp
@@ -2210,24 +2210,23 @@ void Verifier::visitBasicBlock(BasicBlock &BB) {
     SmallVector<BasicBlock*, 8> Preds(pred_begin(&BB), pred_end(&BB));
     SmallVector<std::pair<BasicBlock*, Value*>, 8> Values;
     std::sort(Preds.begin(), Preds.end());
-    PHINode *PN;
-    for (BasicBlock::iterator I = BB.begin(); (PN = dyn_cast<PHINode>(I));++I) {
+    for (const PHINode &PN : BB.phis()) {
       // Ensure that PHI nodes have at least one entry!
-      Assert(PN->getNumIncomingValues() != 0,
+      Assert(PN.getNumIncomingValues() != 0,
              "PHI nodes must have at least one entry.  If the block is dead, "
              "the PHI should be removed!",
-             PN);
-      Assert(PN->getNumIncomingValues() == Preds.size(),
+             &PN);
+      Assert(PN.getNumIncomingValues() == Preds.size(),
              "PHINode should have one entry for each predecessor of its "
              "parent basic block!",
-             PN);
+             &PN);
 
       // Get and sort all incoming values in the PHI node...
       Values.clear();
-      Values.reserve(PN->getNumIncomingValues());
-      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
-        Values.push_back(std::make_pair(PN->getIncomingBlock(i),
-                                        PN->getIncomingValue(i)));
+      Values.reserve(PN.getNumIncomingValues());
+      for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
+        Values.push_back(
+            std::make_pair(PN.getIncomingBlock(i), PN.getIncomingValue(i)));
       std::sort(Values.begin(), Values.end());
 
       for (unsigned i = 0, e = Values.size(); i != e; ++i) {
@@ -2239,12 +2238,12 @@ void Verifier::visitBasicBlock(BasicBlock &BB) {
                    Values[i].second == Values[i - 1].second,
                "PHI node has multiple entries for the same basic block with "
                "different incoming values!",
-               PN, Values[i].first, Values[i].second, Values[i - 1].second);
+               &PN, Values[i].first, Values[i].second, Values[i - 1].second);
 
         // Check to make sure that the predecessors and PHI node entries are
         // matched up.
         Assert(Values[i].first == Preds[i],
-               "PHI node entries do not match predecessors!", PN,
+               "PHI node entries do not match predecessors!", &PN,
                Values[i].first, Preds[i]);
       }
     }
diff --git a/lib/Target/Hexagon/HexagonLoopIdiomRecognition.cpp b/lib/Target/Hexagon/HexagonLoopIdiomRecognition.cpp
index fd602257934..2646d0bcbf4 100644
--- a/lib/Target/Hexagon/HexagonLoopIdiomRecognition.cpp
+++ b/lib/Target/Hexagon/HexagonLoopIdiomRecognition.cpp
@@ -1050,14 +1050,11 @@ bool PolynomialMultiplyRecognize::promoteTypes(BasicBlock *LoopB,
   // Check if the exit values have types that are no wider than the type
   // that we want to promote to.
   unsigned DestBW = DestTy->getBitWidth();
-  for (Instruction &In : *ExitB) {
-    PHINode *P = dyn_cast<PHINode>(&In);
-    if (!P)
-      break;
-    if (P->getNumIncomingValues() != 1)
+  for (PHINode &P : ExitB->phis()) {
+    if (P.getNumIncomingValues() != 1)
       return false;
-    assert(P->getIncomingBlock(0) == LoopB);
-    IntegerType *T = dyn_cast<IntegerType>(P->getType());
+    assert(P.getIncomingBlock(0) == LoopB);
+    IntegerType *T = dyn_cast<IntegerType>(P.getType());
     if (!T || T->getBitWidth() > DestBW)
       return false;
   }
diff --git a/lib/Transforms/Coroutines/CoroSplit.cpp b/lib/Transforms/Coroutines/CoroSplit.cpp
index 8712ca4823c..122f51a0d21 100644
--- a/lib/Transforms/Coroutines/CoroSplit.cpp
+++ b/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -440,16 +440,14 @@ static void
 scanPHIsAndUpdateValueMap(Instruction *Prev, BasicBlock *NewBlock,
                           DenseMap<Value *, Value *> &ResolvedValues) {
   auto *PrevBB = Prev->getParent();
-  auto *I = &*NewBlock->begin();
-  while (auto PN = dyn_cast<PHINode>(I)) {
-    auto V = PN->getIncomingValueForBlock(PrevBB);
+  for (PHINode &PN : NewBlock->phis()) {
+    auto V = PN.getIncomingValueForBlock(PrevBB);
     // See if we already resolved it.
     auto VI = ResolvedValues.find(V);
     if (VI != ResolvedValues.end())
       V = VI->second;
     // Remember the value.
-    ResolvedValues[PN] = V;
-    I = I->getNextNode();
+    ResolvedValues[&PN] = V;
   }
 }
 
diff --git a/lib/Transforms/Scalar/CallSiteSplitting.cpp b/lib/Transforms/Scalar/CallSiteSplitting.cpp
index 207243231aa..caa73b2ff01 100644
--- a/lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ b/lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -265,15 +265,12 @@ static void splitCallSite(CallSite CS, BasicBlock *PredBB1, BasicBlock *PredBB2,
   CallSite CS2(CallInst2);
 
   // Handle PHIs used as arguments in the call-site.
-  for (auto &PI : *TailBB) {
-    PHINode *PN = dyn_cast<PHINode>(&PI);
-    if (!PN)
-      break;
+  for (PHINode &PN : TailBB->phis()) {
     unsigned ArgNo = 0;
     for (auto &CI : CS.args()) {
-      if (&*CI == PN) {
-        CS1.setArgument(ArgNo, PN->getIncomingValueForBlock(SplitBlock1));
-        CS2.setArgument(ArgNo, PN->getIncomingValueForBlock(SplitBlock2));
+      if (&*CI == &PN) {
+        CS1.setArgument(ArgNo, PN.getIncomingValueForBlock(SplitBlock1));
+        CS2.setArgument(ArgNo, PN.getIncomingValueForBlock(SplitBlock2));
       }
       ++ArgNo;
     }
diff --git a/lib/Transforms/Scalar/GVNSink.cpp b/lib/Transforms/Scalar/GVNSink.cpp
index bf92e43c471..5594c29bbd9 100644
--- a/lib/Transforms/Scalar/GVNSink.cpp
+++ b/lib/Transforms/Scalar/GVNSink.cpp
@@ -592,12 +592,8 @@ private:
   /// Create a ModelledPHI for each PHI in BB, adding to PHIs.
   void analyzeInitialPHIs(BasicBlock *BB, ModelledPHISet &PHIs,
                           SmallPtrSetImpl<Value *> &PHIContents) {
-    for (auto &I : *BB) {
-      auto *PN = dyn_cast<PHINode>(&I);
-      if (!PN)
-        return;
-
-      auto MPHI = ModelledPHI(PN);
+    for (PHINode &PN : BB->phis()) {
+      auto MPHI = ModelledPHI(&PN);
       PHIs.insert(MPHI);
       for (auto *V : MPHI.getValues())
         PHIContents.insert(V);
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 74d6014d3e3..221fe57581c 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -485,9 +485,8 @@ void IndVarSimplify::rewriteNonIntegerIVs(Loop *L) {
   BasicBlock *Header = L->getHeader();
 
   SmallVector<WeakTrackingVH, 8> PHIs;
-  for (BasicBlock::iterator I = Header->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I)
-    PHIs.push_back(PN);
+  for (PHINode &PN : Header->phis())
+    PHIs.push_back(&PN);
 
   for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
     if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
@@ -724,13 +723,12 @@ void IndVarSimplify::rewriteFirstIterationLoopExitValues(Loop *L) {
   assert(LoopHeader && "Invalid loop");
 
   for (auto *ExitBB : ExitBlocks) {
-    BasicBlock::iterator BBI = ExitBB->begin();
     // If there are no more PHI nodes in this exit block, then no more
     // values defined inside the loop are used on this path.
-    while (auto *PN = dyn_cast<PHINode>(BBI++)) {
-      for (unsigned IncomingValIdx = 0, E = PN->getNumIncomingValues();
-          IncomingValIdx != E; ++IncomingValIdx) {
-        auto *IncomingBB = PN->getIncomingBlock(IncomingValIdx);
+    for (PHINode &PN : ExitBB->phis()) {
+      for (unsigned IncomingValIdx = 0, E = PN.getNumIncomingValues();
+           IncomingValIdx != E; ++IncomingValIdx) {
+        auto *IncomingBB = PN.getIncomingBlock(IncomingValIdx);
 
         // We currently only support loop exits from loop header. If the
         // incoming block is not loop header, we need to recursively check
@@ -755,8 +753,7 @@ void IndVarSimplify::rewriteFirstIterationLoopExitValues(Loop *L) {
         if (!L->isLoopInvariant(Cond))
           continue;
 
-        auto *ExitVal =
-            dyn_cast<PHINode>(PN->getIncomingValue(IncomingValIdx));
+        auto *ExitVal = dyn_cast<PHINode>(PN.getIncomingValue(IncomingValIdx));
 
         // Only deal with PHIs.
         if (!ExitVal)
@@ -771,8 +768,8 @@ void IndVarSimplify::rewriteFirstIterationLoopExitValues(Loop *L) {
         if (PreheaderIdx != -1) {
           assert(ExitVal->getParent() == LoopHeader &&
                  "ExitVal must be in loop header");
-          PN->setIncomingValue(IncomingValIdx,
-              ExitVal->getIncomingValue(PreheaderIdx));
+          PN.setIncomingValue(IncomingValIdx,
+                              ExitVal->getIncomingValue(PreheaderIdx));
         }
       }
     }
diff --git a/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index 5c4d55bfbb2..cf98088111b 100644
--- a/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -1174,13 +1174,9 @@ void LoopConstrainer::cloneLoop(LoopConstrainer::ClonedLoop &Result,
       if (OriginalLoop.contains(SBB))
         continue; // not an exit block
 
-      for (Instruction &I : *SBB) {
-        auto *PN = dyn_cast<PHINode>(&I);
-        if (!PN)
-          break;
-
-        Value *OldIncoming = PN->getIncomingValueForBlock(OriginalBB);
-        PN->addIncoming(GetClonedValue(OldIncoming), ClonedBB);
+      for (PHINode &PN : SBB->phis()) {
+        Value *OldIncoming = PN.getIncomingValueForBlock(OriginalBB);
+        PN.addIncoming(GetClonedValue(OldIncoming), ClonedBB);
       }
     }
   }
@@ -1327,16 +1323,12 @@ LoopConstrainer::RewrittenRangeInfo LoopConstrainer::changeIterationSpaceEnd(
   // We emit PHI nodes into `RRI.PseudoExit' that compute the "latest" value of
   // each of the PHI nodes in the loop header.  This feeds into the initial
   // value of the same PHI nodes if/when we continue execution.
-  for (Instruction &I : *LS.Header) {
-    auto *PN = dyn_cast<PHINode>(&I);
-    if (!PN)
-      break;
-
-    PHINode *NewPHI = PHINode::Create(PN->getType(), 2, PN->getName() + ".copy",
+  for (PHINode &PN : LS.Header->phis()) {
+    PHINode *NewPHI = PHINode::Create(PN.getType(), 2, PN.getName() + ".copy",
                                       BranchToContinuation);
 
-    NewPHI->addIncoming(PN->getIncomingValueForBlock(Preheader), Preheader);
-    NewPHI->addIncoming(PN->getIncomingValueForBlock(LS.Latch),
+    NewPHI->addIncoming(PN.getIncomingValueForBlock(Preheader), Preheader);
+    NewPHI->addIncoming(PN.getIncomingValueForBlock(LS.Latch),
                         RRI.ExitSelector);
     RRI.PHIValuesAtPseudoExit.push_back(NewPHI);
   }
@@ -1348,12 +1340,8 @@ LoopConstrainer::RewrittenRangeInfo LoopConstrainer::changeIterationSpaceEnd(
 
   // The latch exit now has a branch from `RRI.ExitSelector' instead of
   // `LS.Latch'.  The PHI nodes need to be updated to reflect that.
-  for (Instruction &I : *LS.LatchExit) {
-    if (PHINode *PN = dyn_cast<PHINode>(&I))
-      replacePHIBlock(PN, LS.Latch, RRI.ExitSelector);
-    else
-      break;
-  }
+  for (PHINode &PN : LS.LatchExit->phis())
+    replacePHIBlock(&PN, LS.Latch, RRI.ExitSelector);
 
   return RRI;
 }
@@ -1362,15 +1350,10 @@ void LoopConstrainer::rewriteIncomingValuesForPHIs(
     LoopStructure &LS, BasicBlock *ContinuationBlock,
     const LoopConstrainer::RewrittenRangeInfo &RRI) const {
   unsigned PHIIndex = 0;
-  for (Instruction &I : *LS.Header) {
-    auto *PN = dyn_cast<PHINode>(&I);
-    if (!PN)
-      break;
-
-    for (unsigned i = 0, e = PN->getNumIncomingValues(); i < e; ++i)
-      if (PN->getIncomingBlock(i) == ContinuationBlock)
-        PN->setIncomingValue(i, RRI.PHIValuesAtPseudoExit[PHIIndex++]);
-  }
+  for (PHINode &PN : LS.Header->phis())
+    for (unsigned i = 0, e = PN.getNumIncomingValues(); i < e; ++i)
+      if (PN.getIncomingBlock(i) == ContinuationBlock)
+        PN.setIncomingValue(i, RRI.PHIValuesAtPseudoExit[PHIIndex++]);
 
   LS.IndVarStart = RRI.IndVarEnd;
 }
@@ -1381,14 +1364,9 @@ BasicBlock *LoopConstrainer::createPreheader(const LoopStructure &LS,
   BasicBlock *Preheader = BasicBlock::Create(Ctx, Tag, &F, LS.Header);
   BranchInst::Create(LS.Header, Preheader);
 
-  for (Instruction &I : *LS.Header) {
-    auto *PN = dyn_cast<PHINode>(&I);
-    if (!PN)
-      break;
-
-    for (unsigned i = 0, e = PN->getNumIncomingValues(); i < e; ++i)
-      replacePHIBlock(PN, OldPreheader, Preheader);
-  }
+  for (PHINode &PN : LS.Header->phis())
+    for (unsigned i = 0, e = PN.getNumIncomingValues(); i < e; ++i)
+      replacePHIBlock(&PN, OldPreheader, Preheader);
 
   return Preheader;
 }
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 1476f7850cf..141c9938bf8 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1800,11 +1800,10 @@ static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
                                             BasicBlock *OldPred,
                                             BasicBlock *NewPred,
                                      DenseMap<Instruction*, Value*> &ValueMap) {
-  for (BasicBlock::iterator PNI = PHIBB->begin();
-       PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
+  for (PHINode &PN : PHIBB->phis()) {
     // Ok, we have a PHI node.  Figure out what the incoming value was for the
     // DestBlock.
-    Value *IV = PN->getIncomingValueForBlock(OldPred);
+    Value *IV = PN.getIncomingValueForBlock(OldPred);
 
     // Remap the value if necessary.
     if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
@@ -1813,7 +1812,7 @@ static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
         IV = I->second;
     }
 
-    PN->addIncoming(IV, NewPred);
+    PN.addIncoming(IV, NewPred);
   }
 }
 
diff --git a/lib/Transforms/Scalar/LoopDeletion.cpp b/lib/Transforms/Scalar/LoopDeletion.cpp
index 82604a8842b..15cd1086f20 100644
--- a/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -49,11 +49,10 @@ static bool isLoopDead(Loop *L, ScalarEvolution &SE,
   // must pass through a PHI in the exit block, meaning that this check is
   // sufficient to guarantee that no loop-variant values are used outside
   // of the loop.
-  BasicBlock::iterator BI = ExitBlock->begin();
   bool AllEntriesInvariant = true;
   bool AllOutgoingValuesSame = true;
-  while (PHINode *P = dyn_cast<PHINode>(BI)) {
-    Value *incoming = P->getIncomingValueForBlock(ExitingBlocks[0]);
+  for (PHINode &P : ExitBlock->phis()) {
+    Value *incoming = P.getIncomingValueForBlock(ExitingBlocks[0]);
 
     // Make sure all exiting blocks produce the same incoming value for the exit
     // block.  If there are different incoming values for different exiting
@@ -61,7 +60,7 @@ static bool isLoopDead(Loop *L, ScalarEvolution &SE,
     // be used.
     AllOutgoingValuesSame =
         all_of(makeArrayRef(ExitingBlocks).slice(1), [&](BasicBlock *BB) {
-          return incoming == P->getIncomingValueForBlock(BB);
+          return incoming == P.getIncomingValueForBlock(BB);
         });
 
     if (!AllOutgoingValuesSame)
@@ -72,8 +71,6 @@ static bool isLoopDead(Loop *L, ScalarEvolution &SE,
         AllEntriesInvariant = false;
         break;
       }
-
-    ++BI;
   }
 
   if (Changed)
@@ -162,11 +159,9 @@ static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
   if (ExitBlock && isLoopNeverExecuted(L)) {
     DEBUG(dbgs() << "Loop is proven to never execute, delete it!");
     // Set incoming value to undef for phi nodes in the exit block.
-    BasicBlock::iterator BI = ExitBlock->begin();
-    while (PHINode *P = dyn_cast<PHINode>(BI)) {
-      for (unsigned i = 0; i < P->getNumIncomingValues(); i++)
-        P->setIncomingValue(i, UndefValue::get(P->getType()));
-      BI++;
+    for (PHINode &P : ExitBlock->phis()) {
+      std::fill(P.incoming_values().begin(), P.incoming_values().end(),
+                UndefValue::get(P.getType()));
     }
     deleteDeadLoop(L, &DT, &SE, &LI);
     ++NumDeleted;
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 953854c8b7b..ff3e9eef16d 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -857,12 +857,11 @@ static MemAccessTy getAccessType(const TargetTransformInfo &TTI,
 
 /// Return true if this AddRec is already a phi in its loop.
 static bool isExistingPhi(const SCEVAddRecExpr *AR, ScalarEvolution &SE) {
-  for (BasicBlock::iterator I = AR->getLoop()->getHeader()->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I) {
-    if (SE.isSCEVable(PN->getType()) &&
-        (SE.getEffectiveSCEVType(PN->getType()) ==
+  for (PHINode &PN : AR->getLoop()->getHeader()->phis()) {
+    if (SE.isSCEVable(PN.getType()) &&
+        (SE.getEffectiveSCEVType(PN.getType()) ==
          SE.getEffectiveSCEVType(AR->getType())) &&
-        SE.getSCEV(PN) == AR)
+        SE.getSCEV(&PN) == AR)
       return true;
   }
   return false;
@@ -3013,15 +3012,14 @@ void LSRInstance::CollectChains() {
     } // Continue walking down the instructions.
   } // Continue walking down the domtree.
   // Visit phi backedges to determine if the chain can generate the IV postinc.
-  for (BasicBlock::iterator I = L->getHeader()->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I) {
-    if (!SE.isSCEVable(PN->getType()))
+  for (PHINode &PN : L->getHeader()->phis()) {
+    if (!SE.isSCEVable(PN.getType()))
       continue;
 
     Instruction *IncV =
-      dyn_cast<Instruction>(PN->getIncomingValueForBlock(L->getLoopLatch()));
+        dyn_cast<Instruction>(PN.getIncomingValueForBlock(L->getLoopLatch()));
     if (IncV)
-      ChainInstruction(PN, IncV, ChainUsersVec);
+      ChainInstruction(&PN, IncV, ChainUsersVec);
   }
   // Remove any unprofitable chains.
   unsigned ChainIdx = 0;
@@ -3152,12 +3150,11 @@ void LSRInstance::GenerateIVChain(const IVChain &Chain, SCEVExpander &Rewriter,
   // If LSR created a new, wider phi, we may also replace its postinc. We only
   // do this if we also found a wide value for the head of the chain.
   if (isa<PHINode>(Chain.tailUserInst())) {
-    for (BasicBlock::iterator I = L->getHeader()->begin();
-         PHINode *Phi = dyn_cast<PHINode>(I); ++I) {
-      if (!isCompatibleIVType(Phi, IVSrc))
+    for (PHINode &Phi : L->getHeader()->phis()) {
+      if (!isCompatibleIVType(&Phi, IVSrc))
         continue;
       Instruction *PostIncV = dyn_cast<Instruction>(
-        Phi->getIncomingValueForBlock(L->getLoopLatch()));
+          Phi.getIncomingValueForBlock(L->getLoopLatch()));
       if (!PostIncV || (SE.getSCEV(PostIncV) != SE.getSCEV(IVSrc)))
         continue;
       Value *IVOper = IVSrc;
@@ -3168,7 +3165,7 @@ void LSRInstance::GenerateIVChain(const IVChain &Chain, SCEVExpander &Rewriter,
         Builder.SetCurrentDebugLocation(PostIncV->getDebugLoc());
         IVOper = Builder.CreatePointerCast(IVSrc, PostIncTy, "lsr.chain");
       }
-      Phi->replaceUsesOfWith(PostIncV, IVOper);
+      Phi.replaceUsesOfWith(PostIncV, IVOper);
       DeadInsts.emplace_back(PostIncV);
     }
   }
diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp
index bd468338a1d..f2405d9b0c0 100644
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -1274,12 +1274,11 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
 
     // If the successor of the exit block had PHI nodes, add an entry for
     // NewExit.
-    for (BasicBlock::iterator I = ExitSucc->begin();
-         PHINode *PN = dyn_cast<PHINode>(I); ++I) {
-      Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
+    for (PHINode &PN : ExitSucc->phis()) {
+      Value *V = PN.getIncomingValueForBlock(ExitBlocks[i]);
       ValueToValueMapTy::iterator It = VMap.find(V);
       if (It != VMap.end()) V = It->second;
-      PN->addIncoming(V, NewExit);
+      PN.addIncoming(V, NewExit);
     }
 
     if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
@@ -1496,10 +1495,9 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
     BranchInst::Create(Abort, OldSISucc,
                        ConstantInt::getTrue(Context), NewSISucc);
     // Release the PHI operands for this edge.
-    for (BasicBlock::iterator II = NewSISucc->begin();
-         PHINode *PN = dyn_cast<PHINode>(II); ++II)
-      PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
-                           UndefValue::get(PN->getType()));
+    for (PHINode &PN : NewSISucc->phis())
+      PN.setIncomingValue(PN.getBasicBlockIndex(Switch),
+                          UndefValue::get(PN.getType()));
     // Tell the domtree about the new block. We don't fully update the
     // domtree here -- instead we force it to do a full recomputation
     // after the pass is complete -- but we do need to inform it of
diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 66608ec631f..9dc550ceaec 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -523,10 +523,8 @@ private:
       DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
             << " -> " << Dest->getName() << '\n');
 
-      PHINode *PN;
-      for (BasicBlock::iterator I = Dest->begin();
-           (PN = dyn_cast<PHINode>(I)); ++I)
-        visitPHINode(*PN);
+      for (PHINode &PN : Dest->phis())
+        visitPHINode(PN);
     }
   }
 
diff --git a/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 3d0fca0bc3a..aba732bc413 100644
--- a/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -271,19 +271,14 @@ static bool areLoopExitPHIsLoopInvariant(Loop &L, BasicBlock &ExitingBB,
 static void rewritePHINodesForUnswitchedExitBlock(BasicBlock &UnswitchedBB,
                                                   BasicBlock &OldExitingBB,
                                                   BasicBlock &OldPH) {
-  for (Instruction &I : UnswitchedBB) {
-    auto *PN = dyn_cast<PHINode>(&I);
-    if (!PN)
-      // No more PHIs to check.
-      break;
-
+  for (PHINode &PN : UnswitchedBB.phis()) {
     // When the loop exit is directly unswitched we just need to update the
     // incoming basic block. We loop to handle weird cases with repeated
     // incoming blocks, but expect to typically only have one operand here.
-    for (auto i : seq<int>(0, PN->getNumOperands())) {
-      assert(PN->getIncomingBlock(i) == &OldExitingBB &&
+    for (auto i : seq<int>(0, PN.getNumOperands())) {
+      assert(PN.getIncomingBlock(i) == &OldExitingBB &&
              "Found incoming block different from unique predecessor!");
-      PN->setIncomingBlock(i, &OldPH);
+      PN.setIncomingBlock(i, &OldPH);
     }
   }
 }
@@ -302,14 +297,9 @@ static void rewritePHINodesForExitAndUnswitchedBlocks(BasicBlock &ExitBB,
   assert(&ExitBB != &UnswitchedBB &&
          "Must have different loop exit and unswitched blocks!");
   Instruction *InsertPt = &*UnswitchedBB.begin();
-  for (Instruction &I : ExitBB) {
-    auto *PN = dyn_cast<PHINode>(&I);
-    if (!PN)
-      // No more PHIs to check.
-      break;
-
-    auto *NewPN = PHINode::Create(PN->getType(), /*NumReservedValues*/ 2,
-                                  PN->getName() + ".split", InsertPt);
+  for (PHINode &PN : ExitBB.phis()) {
+    auto *NewPN = PHINode::Create(PN.getType(), /*NumReservedValues*/ 2,
+                                  PN.getName() + ".split", InsertPt);
 
     // Walk backwards over the old PHI node's inputs to minimize the cost of
     // removing each one. We have to do this weird loop manually so that we
@@ -320,18 +310,18 @@ static void rewritePHINodesForExitAndUnswitchedBlocks(BasicBlock &ExitBB,
     // allowed us to create a single entry for a predecessor block without
     // having separate entries for each "edge" even though these edges are
     // required to produce identical results.
-    for (int i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
-      if (PN->getIncomingBlock(i) != &OldExitingBB)
+    for (int i = PN.getNumIncomingValues() - 1; i >= 0; --i) {
+      if (PN.getIncomingBlock(i) != &OldExitingBB)
         continue;
 
-      Value *Incoming = PN->removeIncomingValue(i);
+      Value *Incoming = PN.removeIncomingValue(i);
       NewPN->addIncoming(Incoming, &OldPH);
     }
 
     // Now replace the old PHI with the new one and wire the old one in as an
     // input to the new one.
-    PN->replaceAllUsesWith(NewPN);
-    NewPN->addIncoming(PN, &ExitBB);
+    PN.replaceAllUsesWith(NewPN);
+    NewPN->addIncoming(&PN, &ExitBB);
   }
 }
 
diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 606bd8bacca..5f04f14518d 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -94,9 +94,8 @@ bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
   // Recursively deleting a PHI may cause multiple PHIs to be deleted
   // or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
   SmallVector<WeakTrackingVH, 8> PHIs;
-  for (BasicBlock::iterator I = BB->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I)
-    PHIs.push_back(PN);
+  for (PHINode &PN : BB->phis())
+    PHIs.push_back(&PN);
 
   bool Changed = false;
   for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
@@ -134,24 +133,17 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
   if (!OnlySucc) return false;
 
   // Can't merge if there is PHI loop.
-  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
-    if (PHINode *PN = dyn_cast<PHINode>(BI)) {
-      for (Value *IncValue : PN->incoming_values())
-        if (IncValue == PN)
-          return false;
-    } else
-      break;
-  }
+  for (PHINode &PN : BB->phis())
+    for (Value *IncValue : PN.incoming_values())
+      if (IncValue == &PN)
+        return false;
 
   // Begin by getting rid of unneeded PHIs.
   SmallVector<Value *, 4> IncomingValues;
   if (isa<PHINode>(BB->front())) {
-    for (auto &I : *BB)
-      if (PHINode *PN = dyn_cast<PHINode>(&I)) {
-        if (PN->getIncomingValue(0) != PN)
-          IncomingValues.push_back(PN->getIncomingValue(0));
-      } else
-        break;
+    for (PHINode &PN : BB->phis())
+      if (PN.getIncomingValue(0) != &PN)
+        IncomingValues.push_back(PN.getIncomingValue(0));
     FoldSingleEntryPHINodes(BB, MemDep);
   }
 
diff --git a/lib/Transforms/Utils/BreakCriticalEdges.cpp b/lib/Transforms/Utils/BreakCriticalEdges.cpp
index 3653c307619..464d1a34f51 100644
--- a/lib/Transforms/Utils/BreakCriticalEdges.cpp
+++ b/lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -106,10 +106,9 @@ static void createPHIsForSplitLoopExit(ArrayRef<BasicBlock *> Preds,
           SplitBB->isLandingPad()) && "SplitBB has non-PHI nodes!");
 
   // For each PHI in the destination block.
-  for (BasicBlock::iterator I = DestBB->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I) {
-    unsigned Idx = PN->getBasicBlockIndex(SplitBB);
-    Value *V = PN->getIncomingValue(Idx);
+  for (PHINode &PN : DestBB->phis()) {
+    unsigned Idx = PN.getBasicBlockIndex(SplitBB);
+    Value *V = PN.getIncomingValue(Idx);
 
     // If the input is a PHI which already satisfies LCSSA, don't create
     // a new one.
@@ -119,13 +118,13 @@ static void createPHIsForSplitLoopExit(ArrayRef<BasicBlock *> Preds,
 
     // Otherwise a new PHI is needed. Create one and populate it.
     PHINode *NewPN = PHINode::Create(
-        PN->getType(), Preds.size(), "split",
+        PN.getType(), Preds.size(), "split",
         SplitBB->isLandingPad() ? &SplitBB->front() : SplitBB->getTerminator());
     for (unsigned i = 0, e = Preds.size(); i != e; ++i)
       NewPN->addIncoming(V, Preds[i]);
 
     // Update the original PHI.
-    PN->setIncomingValue(Idx, NewPN);
+    PN.setIncomingValue(Idx, NewPN);
   }
 }
 
diff --git a/lib/Transforms/Utils/CallPromotionUtils.cpp b/lib/Transforms/Utils/CallPromotionUtils.cpp
index 8825f77555e..5dc6068d4a0 100644
--- a/lib/Transforms/Utils/CallPromotionUtils.cpp
+++ b/lib/Transforms/Utils/CallPromotionUtils.cpp
@@ -47,14 +47,11 @@ using namespace llvm;
 ///
 static void fixupPHINodeForNormalDest(InvokeInst *Invoke, BasicBlock *OrigBlock,
                                       BasicBlock *MergeBlock) {
-  for (auto &I : *Invoke->getNormalDest()) {
-    auto *Phi = dyn_cast<PHINode>(&I);
-    if (!Phi)
-      break;
-    int Idx = Phi->getBasicBlockIndex(OrigBlock);
+  for (PHINode &Phi : Invoke->getNormalDest()->phis()) {
+    int Idx = Phi.getBasicBlockIndex(OrigBlock);
     if (Idx == -1)
       continue;
-    Phi->setIncomingBlock(Idx, MergeBlock);
+    Phi.setIncomingBlock(Idx, MergeBlock);
   }
 }
 
@@ -82,16 +79,13 @@ static void fixupPHINodeForNormalDest(InvokeInst *Invoke, BasicBlock *OrigBlock,
 static void fixupPHINodeForUnwindDest(InvokeInst *Invoke, BasicBlock *OrigBlock,
                                       BasicBlock *ThenBlock,
                                       BasicBlock *ElseBlock) {
-  for (auto &I : *Invoke->getUnwindDest()) {
-    auto *Phi = dyn_cast<PHINode>(&I);
-    if (!Phi)
-      break;
-    int Idx = Phi->getBasicBlockIndex(OrigBlock);
+  for (PHINode &Phi : Invoke->getUnwindDest()->phis()) {
+    int Idx = Phi.getBasicBlockIndex(OrigBlock);
     if (Idx == -1)
       continue;
-    auto *V = Phi->getIncomingValue(Idx);
-    Phi->setIncomingBlock(Idx, ThenBlock);
-    Phi->addIncoming(V, ElseBlock);
+    auto *V = Phi.getIncomingValue(Idx);
+    Phi.setIncomingBlock(Idx, ThenBlock);
+    Phi.addIncoming(V, ElseBlock);
   }
 }
 
diff --git a/lib/Transforms/Utils/CloneFunction.cpp b/lib/Transforms/Utils/CloneFunction.cpp
index 3b19ba1b50f..16af2c7b808 100644
--- a/lib/Transforms/Utils/CloneFunction.cpp
+++ b/lib/Transforms/Utils/CloneFunction.cpp
@@ -493,17 +493,13 @@ void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
 
     // Handle PHI nodes specially, as we have to remove references to dead
     // blocks.
-    for (BasicBlock::const_iterator I = BI.begin(), E = BI.end(); I != E; ++I) {
+    for (const PHINode &PN : BI.phis()) {
       // PHI nodes may have been remapped to non-PHI nodes by the caller or
       // during the cloning process.
-      if (const PHINode *PN = dyn_cast<PHINode>(I)) {
-        if (isa<PHINode>(VMap[PN]))
-          PHIToResolve.push_back(PN);
-        else
-          break;
-      } else {
+      if (isa<PHINode>(VMap[&PN]))
+        PHIToResolve.push_back(&PN);
+      else
         break;
-      }
     }
 
     // Finally, remap the terminator instructions, as those can't be remapped
diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index dc98a39adcc..92dfb1c7204 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -258,11 +258,8 @@ static bool isEpilogProfitable(Loop *L) {
   BasicBlock *PreHeader = L->getLoopPreheader();
   BasicBlock *Header = L->getHeader();
   assert(PreHeader && Header);
-  for (Instruction &BBI : *Header) {
-    PHINode *PN = dyn_cast<PHINode>(&BBI);
-    if (!PN)
-      break;
-    if (isa<ConstantInt>(PN->getIncomingValueForBlock(PreHeader)))
+  for (const PHINode &PN : Header->phis()) {
+    if (isa<ConstantInt>(PN.getIncomingValueForBlock(PreHeader)))
       return true;
   }
   return false;
@@ -611,13 +608,12 @@ LoopUnrollResult llvm::UnrollLoop(
       for (BasicBlock *Succ : successors(*BB)) {
         if (L->contains(Succ))
           continue;
-        for (BasicBlock::iterator BBI = Succ->begin();
-             PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
-          Value *Incoming = phi->getIncomingValueForBlock(*BB);
+        for (PHINode &PHI : Succ->phis()) {
+          Value *Incoming = PHI.getIncomingValueForBlock(*BB);
           ValueToValueMapTy::iterator It = LastValueMap.find(Incoming);
           if (It != LastValueMap.end())
             Incoming = It->second;
-          phi->addIncoming(Incoming, New);
+          PHI.addIncoming(Incoming, New);
         }
       }
       // Keep track of new headers and latches as we create them, so that
@@ -721,10 +717,8 @@ LoopUnrollResult llvm::UnrollLoop(
         for (BasicBlock *Succ: successors(BB)) {
           if (Succ == Headers[i])
             continue;
-          for (BasicBlock::iterator BBI = Succ->begin();
-               PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) {
-            Phi->removeIncomingValue(BB, false);
-          }
+          for (PHINode &Phi : Succ->phis())
+            Phi.removeIncomingValue(BB, false);
         }
       }
       // Replace the conditional branch with an unconditional one.
diff --git a/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/lib/Transforms/Utils/LoopUnrollRuntime.cpp
index e00541d3c81..f79f423ce01 100644
--- a/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ b/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -80,25 +80,21 @@ static void ConnectProlog(Loop *L, Value *BECount, unsigned Count,
   // The new PHI node value is added as an operand of a PHI node in either
   // the loop header or the loop exit block.
   for (BasicBlock *Succ : successors(Latch)) {
-    for (Instruction &BBI : *Succ) {
-      PHINode *PN = dyn_cast<PHINode>(&BBI);
-      // Exit when we passed all PHI nodes.
-      if (!PN)
-        break;
+    for (PHINode &PN : Succ->phis()) {
       // Add a new PHI node to the prolog end block and add the
       // appropriate incoming values.
-      PHINode *NewPN = PHINode::Create(PN->getType(), 2, PN->getName() + ".unr",
+      PHINode *NewPN = PHINode::Create(PN.getType(), 2, PN.getName() + ".unr",
                                        PrologExit->getFirstNonPHI());
       // Adding a value to the new PHI node from the original loop preheader.
       // This is the value that skips all the prolog code.
-      if (L->contains(PN)) {
-        NewPN->addIncoming(PN->getIncomingValueForBlock(NewPreHeader),
+      if (L->contains(&PN)) {
+        NewPN->addIncoming(PN.getIncomingValueForBlock(NewPreHeader),
                            PreHeader);
       } else {
-        NewPN->addIncoming(UndefValue::get(PN->getType()), PreHeader);
+        NewPN->addIncoming(UndefValue::get(PN.getType()), PreHeader);
       }
 
-      Value *V = PN->getIncomingValueForBlock(Latch);
+      Value *V = PN.getIncomingValueForBlock(Latch);
       if (Instruction *I = dyn_cast<Instruction>(V)) {
         if (L->contains(I)) {
           V = VMap.lookup(I);
@@ -111,10 +107,10 @@ static void ConnectProlog(Loop *L, Value *BECount, unsigned Count,
       // Update the existing PHI node operand with the value from the
       // new PHI node.  How this is done depends on if the existing
       // PHI node is in the original loop block, or the exit block.
-      if (L->contains(PN)) {
-        PN->setIncomingValue(PN->getBasicBlockIndex(NewPreHeader), NewPN);
+      if (L->contains(&PN)) {
+        PN.setIncomingValue(PN.getBasicBlockIndex(NewPreHeader), NewPN);
       } else {
-        PN->addIncoming(NewPN, PrologExit);
+        PN.addIncoming(NewPN, PrologExit);
       }
     }
   }
@@ -191,11 +187,7 @@ static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
   // 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;
+  for (PHINode &PN : NewExit->phis()) {
     // 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:
@@ -207,14 +199,14 @@ static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
     //
     // 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(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);
+    PN.addIncoming(UndefValue::get(PN.getType()), PreHeader);
 
-    Value *V = PN->getIncomingValueForBlock(Latch);
+    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.
@@ -242,23 +234,19 @@ static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
     // 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;
+    for (PHINode &PN : Succ->phis()) {
       // 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",
+      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);
+      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);
+      NewPN->addIncoming(PN.getIncomingValueForBlock(Latch), Latch);
 
       // Update the existing PHI node operand with the value from the new PHI
       // node.  Corresponding instruction in epilog loop should be PHI.
-      PHINode *VPN = cast<PHINode>(VMap[&BBI]);
+      PHINode *VPN = cast<PHINode>(VMap[&PN]);
       VPN->setIncomingValue(VPN->getBasicBlockIndex(EpilogPreHeader), NewPN);
     }
   }
diff --git a/lib/Transforms/Utils/LoopUtils.cpp b/lib/Transforms/Utils/LoopUtils.cpp
index fe106e33bca..a5a305ef582 100644
--- a/lib/Transforms/Utils/LoopUtils.cpp
+++ b/lib/Transforms/Utils/LoopUtils.cpp
@@ -1321,13 +1321,12 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT = nullptr,
 
   // Rewrite phis in the exit block to get their inputs from the Preheader
   // instead of the exiting block.
-  BasicBlock::iterator BI = ExitBlock->begin();
-  while (PHINode *P = dyn_cast<PHINode>(BI)) {
+  for (PHINode &P : ExitBlock->phis()) {
     // Set the zero'th element of Phi to be from the preheader and remove all
     // other incoming values. Given the loop has dedicated exits, all other
     // incoming values must be from the exiting blocks.
     int PredIndex = 0;
-    P->setIncomingBlock(PredIndex, Preheader);
+    P.setIncomingBlock(PredIndex, Preheader);
     // Removes all incoming values from all other exiting blocks (including
     // duplicate values from an exiting block).
     // Nuke all entries except the zero'th entry which is the preheader entry.
@@ -1335,13 +1334,12 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT = nullptr,
     // below, to keep the indices valid for deletion (removeIncomingValues
     // updates getNumIncomingValues and shifts all values down into the operand
     // being deleted).
-    for (unsigned i = 0, e = P->getNumIncomingValues() - 1; i != e; ++i)
-      P->removeIncomingValue(e - i, false);
+    for (unsigned i = 0, e = P.getNumIncomingValues() - 1; i != e; ++i)
+      P.removeIncomingValue(e - i, false);
 
-    assert((P->getNumIncomingValues() == 1 &&
-            P->getIncomingBlock(PredIndex) == Preheader) &&
+    assert((P.getNumIncomingValues() == 1 &&
+            P.getIncomingBlock(PredIndex) == Preheader) &&
            "Should have exactly one value and that's from the preheader!");
-    ++BI;
   }
 
   // Disconnect the loop body by branching directly to its exit.
diff --git a/lib/Transforms/Utils/SSAUpdater.cpp b/lib/Transforms/Utils/SSAUpdater.cpp
index e4b20b0faa1..b2231d68a30 100644
--- a/lib/Transforms/Utils/SSAUpdater.cpp
+++ b/lib/Transforms/Utils/SSAUpdater.cpp
@@ -147,11 +147,9 @@ Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
   if (isa<PHINode>(BB->begin())) {
     SmallDenseMap<BasicBlock *, Value *, 8> ValueMapping(PredValues.begin(),
                                                          PredValues.end());
-    PHINode *SomePHI;
-    for (BasicBlock::iterator It = BB->begin();
-         (SomePHI = dyn_cast<PHINode>(It)); ++It) {
-      if (IsEquivalentPHI(SomePHI, ValueMapping))
-        return SomePHI;
+    for (PHINode &SomePHI : BB->phis()) {
+      if (IsEquivalentPHI(&SomePHI, ValueMapping))
+        return &SomePHI;
     }
   }
 
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index e7358dbcb62..58f1e8008ea 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -283,12 +283,8 @@ isProfitableToFoldUnconditional(BranchInst *SI1, BranchInst *SI2,
 /// of Succ.
 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
                                   BasicBlock *ExistPred) {
-  if (!isa<PHINode>(Succ->begin()))
-    return; // Quick exit if nothing to do
-
-  PHINode *PN;
-  for (BasicBlock::iterator I = Succ->begin(); (PN = dyn_cast<PHINode>(I)); ++I)
-    PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
+  for (PHINode &PN : Succ->phis())
+    PN.addIncoming(PN.getIncomingValueForBlock(ExistPred), NewPred);
 }
 
 /// Compute an abstract "cost" of speculating the given instruction,
@@ -1228,11 +1224,9 @@ bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
                                 Instruction *I1, Instruction *I2) {
   for (BasicBlock *Succ : successors(BB1)) {
-    PHINode *PN;
-    for (BasicBlock::iterator BBI = Succ->begin();
-         (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
-      Value *BB1V = PN->getIncomingValueForBlock(BB1);
-      Value *BB2V = PN->getIncomingValueForBlock(BB2);
+    for (const PHINode &PN : Succ->phis()) {
+      Value *BB1V = PN.getIncomingValueForBlock(BB1);
+      Value *BB2V = PN.getIncomingValueForBlock(BB2);
       if (BB1V != BB2V && (BB1V == I1 || BB2V == I2)) {
         return false;
       }
@@ -1332,18 +1326,16 @@ HoistTerminator:
     return Changed;
 
   for (BasicBlock *Succ : successors(BB1)) {
-    PHINode *PN;
-    for (BasicBlock::iterator BBI = Succ->begin();
-         (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
-      Value *BB1V = PN->getIncomingValueForBlock(BB1);
-      Value *BB2V = PN->getIncomingValueForBlock(BB2);
+    for (PHINode &PN : Succ->phis()) {
+      Value *BB1V = PN.getIncomingValueForBlock(BB1);
+      Value *BB2V = PN.getIncomingValueForBlock(BB2);
       if (BB1V == BB2V)
         continue;
 
       // Check for passingValueIsAlwaysUndefined here because we would rather
       // eliminate undefined control flow then converting it to a select.
-      if (passingValueIsAlwaysUndefined(BB1V, PN) ||
-          passingValueIsAlwaysUndefined(BB2V, PN))
+      if (passingValueIsAlwaysUndefined(BB1V, &PN) ||
+          passingValueIsAlwaysUndefined(BB2V, &PN))
         return Changed;
 
       if (isa<ConstantExpr>(BB1V) && !isSafeToSpeculativelyExecute(BB1V))
@@ -1369,11 +1361,9 @@ HoistTerminator:
   // nodes, so we insert select instruction to compute the final result.
   std::map<std::pair<Value *, Value *>, SelectInst *> InsertedSelects;
   for (BasicBlock *Succ : successors(BB1)) {
-    PHINode *PN;
-    for (BasicBlock::iterator BBI = Succ->begin();
-         (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
-      Value *BB1V = PN->getIncomingValueForBlock(BB1);
-      Value *BB2V = PN->getIncomingValueForBlock(BB2);
+    for (PHINode &PN : Succ->phis()) {
+      Value *BB1V = PN.getIncomingValueForBlock(BB1);
+      Value *BB2V = PN.getIncomingValueForBlock(BB2);
       if (BB1V == BB2V)
         continue;
 
@@ -1386,9 +1376,9 @@ HoistTerminator:
                                  BB1V->getName() + "." + BB2V->getName(), BI));
 
       // Make the PHI node use the select for all incoming values for BB1/BB2
-      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
-        if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
-          PN->setIncomingValue(i, SI);
+      for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
+        if (PN.getIncomingBlock(i) == BB1 || PN.getIncomingBlock(i) == BB2)
+          PN.setIncomingValue(i, SI);
     }
   }
 
@@ -1999,10 +1989,9 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
 
   // Check that the PHI nodes can be converted to selects.
   bool HaveRewritablePHIs = false;
-  for (BasicBlock::iterator I = EndBB->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I) {
-    Value *OrigV = PN->getIncomingValueForBlock(BB);
-    Value *ThenV = PN->getIncomingValueForBlock(ThenBB);
+  for (PHINode &PN : EndBB->phis()) {
+    Value *OrigV = PN.getIncomingValueForBlock(BB);
+    Value *ThenV = PN.getIncomingValueForBlock(ThenBB);
 
     // FIXME: Try to remove some of the duplication with HoistThenElseCodeToIf.
     // Skip PHIs which are trivial.
@@ -2010,8 +1999,8 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
       continue;
 
     // Don't convert to selects if we could remove undefined behavior instead.
-    if (passingValueIsAlwaysUndefined(OrigV, PN) ||
-        passingValueIsAlwaysUndefined(ThenV, PN))
+    if (passingValueIsAlwaysUndefined(OrigV, &PN) ||
+        passingValueIsAlwaysUndefined(ThenV, &PN))
       return false;
 
     HaveRewritablePHIs = true;
@@ -2072,12 +2061,11 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
 
   // Insert selects and rewrite the PHI operands.
   IRBuilder<NoFolder> Builder(BI);
-  for (BasicBlock::iterator I = EndBB->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I) {
-    unsigned OrigI = PN->getBasicBlockIndex(BB);
-    unsigned ThenI = PN->getBasicBlockIndex(ThenBB);
-    Value *OrigV = PN->getIncomingValue(OrigI);
-    Value *ThenV = PN->getIncomingValue(ThenI);
+  for (PHINode &PN : EndBB->phis()) {
+    unsigned OrigI = PN.getBasicBlockIndex(BB);
+    unsigned ThenI = PN.getBasicBlockIndex(ThenBB);
+    Value *OrigV = PN.getIncomingValue(OrigI);
+    Value *ThenV = PN.getIncomingValue(ThenI);
 
     // Skip PHIs which are trivial.
     if (OrigV == ThenV)
@@ -2091,8 +2079,8 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
       std::swap(TrueV, FalseV);
     Value *V = Builder.CreateSelect(
         BrCond, TrueV, FalseV, "spec.select", BI);
-    PN->setIncomingValue(OrigI, V);
-    PN->setIncomingValue(ThenI, V);
+    PN.setIncomingValue(OrigI, V);
+    PN.setIncomingValue(ThenI, V);
   }
 
   // Remove speculated dbg intrinsics.
@@ -3335,17 +3323,15 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
   // it.  If it has PHIs though, the PHIs may have different
   // entries for BB and PBI's BB.  If so, insert a select to make
   // them agree.
-  PHINode *PN;
-  for (BasicBlock::iterator II = CommonDest->begin();
-       (PN = dyn_cast<PHINode>(II)); ++II) {
-    Value *BIV = PN->getIncomingValueForBlock(BB);
-    unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
-    Value *PBIV = PN->getIncomingValue(PBBIdx);
+  for (PHINode &PN : CommonDest->phis()) {
+    Value *BIV = PN.getIncomingValueForBlock(BB);
+    unsigned PBBIdx = PN.getBasicBlockIndex(PBI->getParent());
+    Value *PBIV = PN.getIncomingValue(PBBIdx);
     if (BIV != PBIV) {
       // Insert a select in PBI to pick the right value.
       SelectInst *NV = cast<SelectInst>(
           Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux"));
-      PN->setIncomingValue(PBBIdx, NV);
+      PN.setIncomingValue(PBBIdx, NV);
       // Although the select has the same condition as PBI, the original branch
       // weights for PBI do not apply to the new select because the select's
       // 'logical' edges are incoming edges of the phi that is eliminated, not
@@ -4451,17 +4437,16 @@ static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
 
   BasicBlock *Succ = Branch->getSuccessor(0);
 
-  BasicBlock::iterator I = Succ->begin();
-  while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
-    int Idx = PHI->getBasicBlockIndex(BB);
+  for (PHINode &PHI : Succ->phis()) {
+    int Idx = PHI.getBasicBlockIndex(BB);
     assert(Idx >= 0 && "PHI has no entry for predecessor?");
 
-    Value *InValue = PHI->getIncomingValue(Idx);
+    Value *InValue = PHI.getIncomingValue(Idx);
     if (InValue != CaseValue)
       continue;
 
     *PhiIndex = Idx;
-    return PHI;
+    return &PHI;
   }
 
   return nullptr;
@@ -4491,19 +4476,16 @@ static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
     // -->
     //     %r = phi i32 ... [ %x, %switchbb ] ...
 
-    for (Instruction &InstInCaseDest : *CaseDest) {
-      auto *Phi = dyn_cast<PHINode>(&InstInCaseDest);
-      if (!Phi) break;
-
+    for (PHINode &Phi : CaseDest->phis()) {
       // This only works if there is exactly 1 incoming edge from the switch to
       // a phi. If there is >1, that means multiple cases of the switch map to 1
       // value in the phi, and that phi value is not the switch condition. Thus,
       // this transform would not make sense (the phi would be invalid because
       // a phi can't have different incoming values from the same block).
-      int SwitchBBIdx = Phi->getBasicBlockIndex(SwitchBlock);
-      if (Phi->getIncomingValue(SwitchBBIdx) == CaseValue &&
-          count(Phi->blocks(), SwitchBlock) == 1) {
-        Phi->setIncomingValue(SwitchBBIdx, SI->getCondition());
+      int SwitchBBIdx = Phi.getBasicBlockIndex(SwitchBlock);
+      if (Phi.getIncomingValue(SwitchBBIdx) == CaseValue &&
+          count(Phi.blocks(), SwitchBlock) == 1) {
+        Phi.setIncomingValue(SwitchBBIdx, SI->getCondition());
         Changed = true;
       }
     }
@@ -4656,14 +4638,13 @@ GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
     return false;
 
   // Get the values for this case from phi nodes in the destination block.
-  BasicBlock::iterator I = (*CommonDest)->begin();
-  while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
-    int Idx = PHI->getBasicBlockIndex(Pred);
+  for (PHINode &PHI : (*CommonDest)->phis()) {
+    int Idx = PHI.getBasicBlockIndex(Pred);
     if (Idx == -1)
       continue;
 
     Constant *ConstVal =
-        LookupConstant(PHI->getIncomingValue(Idx), ConstantPool);
+        LookupConstant(PHI.getIncomingValue(Idx), ConstantPool);
     if (!ConstVal)
       return false;
 
@@ -4671,7 +4652,7 @@ GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
     if (!ValidLookupTableConstant(ConstVal, TTI))
       return false;
 
-    Res.push_back(std::make_pair(PHI, ConstVal));
+    Res.push_back(std::make_pair(&PHI, ConstVal));
   }
 
   return Res.size() > 0;
@@ -5946,14 +5927,13 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
 /// If BB has an incoming value that will always trigger undefined behavior
 /// (eg. null pointer dereference), remove the branch leading here.
 static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
-  for (BasicBlock::iterator i = BB->begin();
-       PHINode *PHI = dyn_cast<PHINode>(i); ++i)
-    for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
-      if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
-        TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
+  for (PHINode &PHI : BB->phis())
+    for (unsigned i = 0, e = PHI.getNumIncomingValues(); i != e; ++i)
+      if (passingValueIsAlwaysUndefined(PHI.getIncomingValue(i), &PHI)) {
+        TerminatorInst *T = PHI.getIncomingBlock(i)->getTerminator();
         IRBuilder<> Builder(T);
         if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
-          BB->removePredecessor(PHI->getIncomingBlock(i));
+          BB->removePredecessor(PHI.getIncomingBlock(i));
           // Turn uncoditional branches into unreachables and remove the dead
           // destination from conditional branches.
           if (BI->isUnconditional())
diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index 52f32cda260..6ef54385c45 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4164,15 +4164,12 @@ void InnerLoopVectorizer::fixCrossIterationPHIs() {
   // the currently empty PHI nodes. At this point every instruction in the
   // original loop is widened to a vector form so we can use them to construct
   // the incoming edges.
-  for (Instruction &I : *OrigLoop->getHeader()) {
-    PHINode *Phi = dyn_cast<PHINode>(&I);
-    if (!Phi)
-      break;
+  for (PHINode &Phi : OrigLoop->getHeader()->phis()) {
     // Handle first-order recurrences and reductions that need to be fixed.
-    if (Legal->isFirstOrderRecurrence(Phi))
-      fixFirstOrderRecurrence(Phi);
-    else if (Legal->isReductionVariable(Phi))
-      fixReduction(Phi);
+    if (Legal->isFirstOrderRecurrence(&Phi))
+      fixFirstOrderRecurrence(&Phi);
+    else if (Legal->isReductionVariable(&Phi))
+      fixReduction(&Phi);
   }
 }
 
@@ -4337,12 +4334,9 @@ void InnerLoopVectorizer::fixFirstOrderRecurrence(PHINode *Phi) {
   // vector recurrence we extracted in the middle block. Since the loop is in
   // LCSSA form, we just need to find the phi node for the original scalar
   // recurrence in the exit block, and then add an edge for the middle block.
-  for (auto &I : *LoopExitBlock) {
-    auto *LCSSAPhi = dyn_cast<PHINode>(&I);
-    if (!LCSSAPhi)
-      break;
-    if (LCSSAPhi->getIncomingValue(0) == Phi) {
-      LCSSAPhi->addIncoming(ExtractForPhiUsedOutsideLoop, LoopMiddleBlock);
+  for (PHINode &LCSSAPhi : LoopExitBlock->phis()) {
+    if (LCSSAPhi.getIncomingValue(0) == Phi) {
+      LCSSAPhi.addIncoming(ExtractForPhiUsedOutsideLoop, LoopMiddleBlock);
       break;
     }
   }
@@ -4499,21 +4493,15 @@ void InnerLoopVectorizer::fixReduction(PHINode *Phi) {
   // inside and outside of the scalar remainder loop.
   // We know that the loop is in LCSSA form. We need to update the
   // PHI nodes in the exit blocks.
-  for (BasicBlock::iterator LEI = LoopExitBlock->begin(),
-         LEE = LoopExitBlock->end();
-       LEI != LEE; ++LEI) {
-    PHINode *LCSSAPhi = dyn_cast<PHINode>(LEI);
-    if (!LCSSAPhi)
-      break;
-
+  for (PHINode &LCSSAPhi : LoopExitBlock->phis()) {
     // All PHINodes need to have a single entry edge, or two if
     // we already fixed them.
-    assert(LCSSAPhi->getNumIncomingValues() < 3 && "Invalid LCSSA PHI");
+    assert(LCSSAPhi.getNumIncomingValues() < 3 && "Invalid LCSSA PHI");
 
     // We found a reduction value exit-PHI. Update it with the
     // incoming bypass edge.
-    if (LCSSAPhi->getIncomingValue(0) == LoopExitInst)
-      LCSSAPhi->addIncoming(ReducedPartRdx, LoopMiddleBlock);
+    if (LCSSAPhi.getIncomingValue(0) == LoopExitInst)
+      LCSSAPhi.addIncoming(ReducedPartRdx, LoopMiddleBlock);
   } // end of the LCSSA phi scan.
 
     // Fix the scalar loop reduction variable with the incoming reduction sum
@@ -4528,14 +4516,11 @@ void InnerLoopVectorizer::fixReduction(PHINode *Phi) {
 }
 
 void InnerLoopVectorizer::fixLCSSAPHIs() {
-  for (Instruction &LEI : *LoopExitBlock) {
-    auto *LCSSAPhi = dyn_cast<PHINode>(&LEI);
-    if (!LCSSAPhi)
-      break;
-    if (LCSSAPhi->getNumIncomingValues() == 1) {
-      assert(OrigLoop->isLoopInvariant(LCSSAPhi->getIncomingValue(0)) &&
+  for (PHINode &LCSSAPhi : LoopExitBlock->phis()) {
+    if (LCSSAPhi.getNumIncomingValues() == 1) {
+      assert(OrigLoop->isLoopInvariant(LCSSAPhi.getIncomingValue(0)) &&
              "Incoming value isn't loop invariant");
-      LCSSAPhi->addIncoming(LCSSAPhi->getIncomingValue(0), LoopMiddleBlock);
+      LCSSAPhi.addIncoming(LCSSAPhi.getIncomingValue(0), LoopMiddleBlock);
     }
   }
 }
@@ -4981,11 +4966,8 @@ void InnerLoopVectorizer::updateAnalysis() {
 /// Phi nodes with constant expressions that can trap are not safe to if
 /// convert.
 static bool canIfConvertPHINodes(BasicBlock *BB) {
-  for (Instruction &I : *BB) {
-    auto *Phi = dyn_cast<PHINode>(&I);
-    if (!Phi)
-      return true;
-    for (Value *V : Phi->incoming_values())
+  for (PHINode &Phi : BB->phis()) {
+    for (Value *V : Phi.incoming_values())
       if (auto *C = dyn_cast<Constant>(V))
         if (C->canTrap())
           return false;