Eliminate LegalizeOps' LegalizedNodes map and have it just call RAUW

on every node as it legalizes them. This makes it easier to use
hasOneUse() heuristics, since unneeded nodes can be removed from the
DAG earlier.

Make LegalizeOps visit the DAG in an operands-last order. It previously
used operands-first, because LegalizeTypes has to go operands-first, and
LegalizeTypes used to be part of LegalizeOps, but they're now split.
The operands-last order is more natural for several legalization tasks.
For example, it allows lowering code for nodes with floating-point or
vector constants to see those constants directly instead of seeing the
lowered form (often constant-pool loads). This makes some things
somewhat more complicated today, though it ought to allow things to be
simpler in the future. It also fixes some bugs exposed by Legalizing
using RAUW aggressively.

Remove the part of LegalizeOps that attempted to patch up invalid chain
operands on libcalls generated by LegalizeTypes, since it doesn't work
with the new LegalizeOps traversal order. Instead, define what
LegalizeTypes is doing to be correct, and transfer the responsibility
of keeping calls from having overlapping calling sequences into the
scheduler.

Teach the scheduler to model callseq_begin/end pairs as having a
physical register definition/use to prevent calls from having
overlapping calling sequences. This is also somewhat complicated, though
there are ways it might be simplified in the future.

This addresses rdar://9816668, rdar://10043614, rdar://8434668, and others.
Please direct high-level questions about this patch to management.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143177 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 423 insertions, 515 deletions

diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index a8bccda291..263333de4c 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -46,37 +46,18 @@ using namespace llvm;
 /// will attempt merge setcc and brc instructions into brcc's.
 ///
 namespace {
-class SelectionDAGLegalize {
+class SelectionDAGLegalize : public SelectionDAG::DAGUpdateListener {
   const TargetMachine &TM;
   const TargetLowering &TLI;
   SelectionDAG &DAG;
 
-  // Libcall insertion helpers.
-
-  /// LastCALLSEQ_END - This keeps track of the CALLSEQ_END node that has been
-  /// legalized.  We use this to ensure that calls are properly serialized
-  /// against each other, including inserted libcalls.
-  SDValue LastCALLSEQ_END;
-
-  /// IsLegalizingCall - This member is used *only* for purposes of providing
-  /// helpful assertions that a libcall isn't created while another call is
-  /// being legalized (which could lead to non-serialized call sequences).
-  bool IsLegalizingCall;
+  /// LegalizePosition - The iterator for walking through the node list.
+  SelectionDAG::allnodes_iterator LegalizePosition;
 
-  /// LegalizedNodes - For nodes that are of legal width, and that have more
-  /// than one use, this map indicates what regularized operand to use.  This
-  /// allows us to avoid legalizing the same thing more than once.
-  DenseMap<SDValue, SDValue> LegalizedNodes;
+  /// LegalizedNodes - The set of nodes which have already been legalized.
+  SmallPtrSet<SDNode *, 16> LegalizedNodes;
 
-  void AddLegalizedOperand(SDValue From, SDValue To) {
-    LegalizedNodes.insert(std::make_pair(From, To));
-    // If someone requests legalization of the new node, return itself.
-    if (From != To)
-      LegalizedNodes.insert(std::make_pair(To, To));
-
-    // Transfer SDDbgValues.
-    DAG.TransferDbgValues(From, To);
-  }
+  // Libcall insertion helpers.
 
 public:
   explicit SelectionDAGLegalize(SelectionDAG &DAG);
@@ -84,9 +65,8 @@ public:
   void LegalizeDAG();
 
 private:
-  /// LegalizeOp - Return a legal replacement for the given operation, with
-  /// all legal operands.
-  SDValue LegalizeOp(SDValue O);
+  /// LegalizeOp - Legalizes the given operation.
+  void LegalizeOp(SDNode *Node);
 
   SDValue OptimizeFloatStore(StoreSDNode *ST);
 
@@ -107,9 +87,6 @@ private:
                                      SDValue N1, SDValue N2,
                                      SmallVectorImpl<int> &Mask) const;
 
-  bool LegalizeAllNodesNotLeadingTo(SDNode *N, SDNode *Dest,
-                                    SmallPtrSet<SDNode*, 32> &NodesLeadingTo);
-
   void LegalizeSetCCCondCode(EVT VT, SDValue &LHS, SDValue &RHS, SDValue &CC,
                              DebugLoc dl);
 
@@ -150,10 +127,21 @@ private:
   SDValue ExpandInsertToVectorThroughStack(SDValue Op);
   SDValue ExpandVectorBuildThroughStack(SDNode* Node);
 
+  SDValue ExpandConstantFP(ConstantFPSDNode *CFP, bool UseCP);
+
   std::pair<SDValue, SDValue> ExpandAtomic(SDNode *Node);
 
-  void ExpandNode(SDNode *Node, SmallVectorImpl<SDValue> &Results);
-  void PromoteNode(SDNode *Node, SmallVectorImpl<SDValue> &Results);
+  void ExpandNode(SDNode *Node);
+  void PromoteNode(SDNode *Node);
+
+  // DAGUpdateListener implementation.
+  virtual void NodeDeleted(SDNode *N, SDNode *E) {
+    LegalizedNodes.erase(N);
+    if (LegalizePosition == SelectionDAG::allnodes_iterator(N))
+      ++LegalizePosition;
+  }
+
+  virtual void NodeUpdated(SDNode *N) {}
 };
 }
 
@@ -195,145 +183,54 @@ SelectionDAGLegalize::SelectionDAGLegalize(SelectionDAG &dag)
 }
 
 void SelectionDAGLegalize::LegalizeDAG() {
-  LastCALLSEQ_END = DAG.getEntryNode();
-  IsLegalizingCall = false;
-
-  // The legalize process is inherently a bottom-up recursive process (users
-  // legalize their uses before themselves).  Given infinite stack space, we
-  // could just start legalizing on the root and traverse the whole graph.  In
-  // practice however, this causes us to run out of stack space on large basic
-  // blocks.  To avoid this problem, compute an ordering of the nodes where each
-  // node is only legalized after all of its operands are legalized.
   DAG.AssignTopologicalOrder();
-  for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
-       E = prior(DAG.allnodes_end()); I != llvm::next(E); ++I)
-    LegalizeOp(SDValue(I, 0));
-
-  // Finally, it's possible the root changed.  Get the new root.
-  SDValue OldRoot = DAG.getRoot();
-  assert(LegalizedNodes.count(OldRoot) && "Root didn't get legalized?");
-  DAG.setRoot(LegalizedNodes[OldRoot]);
-
-  LegalizedNodes.clear();
-
-  // Remove dead nodes now.
-  DAG.RemoveDeadNodes();
-}
 
-
-/// FindCallEndFromCallStart - Given a chained node that is part of a call
-/// sequence, find the CALLSEQ_END node that terminates the call sequence.
-static SDNode *FindCallEndFromCallStart(SDNode *Node, int depth = 0) {
-  // Nested CALLSEQ_START/END constructs aren't yet legal,
-  // but we can DTRT and handle them correctly here.
-  if (Node->getOpcode() == ISD::CALLSEQ_START)
-    depth++;
-  else if (Node->getOpcode() == ISD::CALLSEQ_END) {
-    depth--;
-    if (depth == 0)
-      return Node;
-  }
-  if (Node->use_empty())
-    return 0;   // No CallSeqEnd
-
-  // The chain is usually at the end.
-  SDValue TheChain(Node, Node->getNumValues()-1);
-  if (TheChain.getValueType() != MVT::Other) {
-    // Sometimes it's at the beginning.
-    TheChain = SDValue(Node, 0);
-    if (TheChain.getValueType() != MVT::Other) {
-      // Otherwise, hunt for it.
-      for (unsigned i = 1, e = Node->getNumValues(); i != e; ++i)
-        if (Node->getValueType(i) == MVT::Other) {
-          TheChain = SDValue(Node, i);
-          break;
-        }
-
-      // Otherwise, we walked into a node without a chain.
-      if (TheChain.getValueType() != MVT::Other)
-        return 0;
-    }
-  }
-
-  for (SDNode::use_iterator UI = Node->use_begin(),
-       E = Node->use_end(); UI != E; ++UI) {
-
-    // Make sure to only follow users of our token chain.
-    SDNode *User = *UI;
-    for (unsigned i = 0, e = User->getNumOperands(); i != e; ++i)
-      if (User->getOperand(i) == TheChain)
-        if (SDNode *Result = FindCallEndFromCallStart(User, depth))
-          return Result;
+#if 0
+  SDValue LastChain = DAG.getEntryNode();
+  for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
+       E = DAG.allnodes_end(); I != E; ++I) {
+    SDNode *N = I;
+    if (N->getOpcode() == ISD::CALLSEQ_START) {
+      SmallVector<SDValue, 4> Ops(N->op_begin(), N->op_end());
+      Ops[0] = LastChain;
+      SDNode *New = DAG.UpdateNodeOperands(N, Ops.data(), Ops.size());
+      assert(New == N && "CALLSEQ_START got CSE'd!");
+    }
+    for (unsigned i = 0, e = N->getNumValues(); i != e; ++i)
+      if (N->getValueType(i) == MVT::Other)
+        LastChain = SDValue(N, i);
   }
-  return 0;
-}
+#endif
 
-/// FindCallStartFromCallEnd - Given a chained node that is part of a call
-/// sequence, find the CALLSEQ_START node that initiates the call sequence.
-static SDNode *FindCallStartFromCallEnd(SDNode *Node) {
-  int nested = 0;
-  assert(Node && "Didn't find callseq_start for a call??");
-  while (Node->getOpcode() != ISD::CALLSEQ_START || nested) {
-    Node = Node->getOperand(0).getNode();
-    assert(Node->getOperand(0).getValueType() == MVT::Other &&
-           "Node doesn't have a token chain argument!");
-    switch (Node->getOpcode()) {
-    default:
-      break;
-    case ISD::CALLSEQ_START:
-      if (!nested)
-        return Node;
-      nested--;
-      break;
-    case ISD::CALLSEQ_END:
-      nested++;
-      break;
+  // Visit all the nodes. We start in topological order, so that we see
+  // nodes with their original operands intact. Legalization can produce
+  // new nodes which may themselves need to be legalized. Iterate until all
+  // nodes have been legalized.
+  for (;;) {
+    bool AnyLegalized = false;
+    for (LegalizePosition = DAG.allnodes_end();
+         LegalizePosition != DAG.allnodes_begin(); ) {
+      --LegalizePosition;
+
+      SDNode *N = LegalizePosition;
+      if (LegalizedNodes.insert(N)) {
+        AnyLegalized = true;
+        LegalizeOp(N);
+      }
     }
-  }
-  return 0;
-}
-
-/// LegalizeAllNodesNotLeadingTo - Recursively walk the uses of N, looking to
-/// see if any uses can reach Dest.  If no dest operands can get to dest,
-/// legalize them, legalize ourself, and return false, otherwise, return true.
-///
-/// Keep track of the nodes we fine that actually do lead to Dest in
-/// NodesLeadingTo.  This avoids retraversing them exponential number of times.
-///
-bool SelectionDAGLegalize::LegalizeAllNodesNotLeadingTo(SDNode *N, SDNode *Dest,
-                                     SmallPtrSet<SDNode*, 32> &NodesLeadingTo) {
-  if (N == Dest) return true;  // N certainly leads to Dest :)
-
-  // If we've already processed this node and it does lead to Dest, there is no
-  // need to reprocess it.
-  if (NodesLeadingTo.count(N)) return true;
-
-  // If the first result of this node has been already legalized, then it cannot
-  // reach N.
-  if (LegalizedNodes.count(SDValue(N, 0))) return false;
-
-  // Okay, this node has not already been legalized.  Check and legalize all
-  // operands.  If none lead to Dest, then we can legalize this node.
-  bool OperandsLeadToDest = false;
-  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
-    OperandsLeadToDest |=     // If an operand leads to Dest, so do we.
-      LegalizeAllNodesNotLeadingTo(N->getOperand(i).getNode(), Dest,
-                                   NodesLeadingTo);
+    if (!AnyLegalized)
+      break;
 
-  if (OperandsLeadToDest) {
-    NodesLeadingTo.insert(N);
-    return true;
   }
 
-  // Okay, this node looks safe, legalize it and return false.
-  LegalizeOp(SDValue(N, 0));
-  return false;
+  // Remove dead nodes now.
+  DAG.RemoveDeadNodes();
 }
 
 /// ExpandConstantFP - Expands the ConstantFP node to an integer constant or
 /// a load from the constant pool.
-static SDValue ExpandConstantFP(ConstantFPSDNode *CFP, bool UseCP,
-                                SelectionDAG &DAG, const TargetLowering &TLI) {
+SDValue
+SelectionDAGLegalize::ExpandConstantFP(ConstantFPSDNode *CFP, bool UseCP) {
   bool Extend = false;
   DebugLoc dl = CFP->getDebugLoc();
 
@@ -369,20 +266,25 @@ static SDValue ExpandConstantFP(ConstantFPSDNode *CFP, bool UseCP,
 
   SDValue CPIdx = DAG.getConstantPool(LLVMC, TLI.getPointerTy());
   unsigned Alignment = cast<ConstantPoolSDNode>(CPIdx)->getAlignment();
-  if (Extend)
-    return DAG.getExtLoad(ISD::EXTLOAD, dl, OrigVT,
-                          DAG.getEntryNode(),
-                          CPIdx, MachinePointerInfo::getConstantPool(),
-                          VT, false, false, Alignment);
-  return DAG.getLoad(OrigVT, dl, DAG.getEntryNode(), CPIdx,
-                     MachinePointerInfo::getConstantPool(), false, false,
-                     Alignment);
+  if (Extend) {
+    SDValue Result =
+      DAG.getExtLoad(ISD::EXTLOAD, dl, OrigVT,
+                     DAG.getEntryNode(),
+                     CPIdx, MachinePointerInfo::getConstantPool(),
+                     VT, false, false, Alignment);
+    return Result;
+  }
+  SDValue Result =
+    DAG.getLoad(OrigVT, dl, DAG.getEntryNode(), CPIdx,
+                MachinePointerInfo::getConstantPool(), false, false,
+                Alignment);
+  return Result;
 }
 
 /// ExpandUnalignedStore - Expands an unaligned store to 2 half-size stores.
-static
-SDValue ExpandUnalignedStore(StoreSDNode *ST, SelectionDAG &DAG,
-                             const TargetLowering &TLI) {
+static void ExpandUnalignedStore(StoreSDNode *ST, SelectionDAG &DAG,
+                                 const TargetLowering &TLI,
+                                 SelectionDAG::DAGUpdateListener *DUL) {
   SDValue Chain = ST->getChain();
   SDValue Ptr = ST->getBasePtr();
   SDValue Val = ST->getValue();
@@ -397,8 +299,10 @@ SDValue ExpandUnalignedStore(StoreSDNode *ST, SelectionDAG &DAG,
       // same size, then a (misaligned) int store.
       // FIXME: Does not handle truncating floating point stores!
       SDValue Result = DAG.getNode(ISD::BITCAST, dl, intVT, Val);
-      return DAG.getStore(Chain, dl, Result, Ptr, ST->getPointerInfo(),
-                          ST->isVolatile(), ST->isNonTemporal(), Alignment);
+      Result = DAG.getStore(Chain, dl, Result, Ptr, ST->getPointerInfo(),
+                           ST->isVolatile(), ST->isNonTemporal(), Alignment);
+      DAG.ReplaceAllUsesWith(SDValue(ST, 0), Result, DUL);
+      return;
     }
     // Do a (aligned) store to a stack slot, then copy from the stack slot
     // to the final destination using (unaligned) integer loads and stores.
@@ -458,8 +362,11 @@ SDValue ExpandUnalignedStore(StoreSDNode *ST, SelectionDAG &DAG,
                                        ST->isNonTemporal(),
                                        MinAlign(ST->getAlignment(), Offset)));
     // The order of the stores doesn't matter - say it with a TokenFactor.
-    return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, &Stores[0],
-                       Stores.size());
+    SDValue Result =
+      DAG.getNode(ISD::TokenFactor, dl, MVT::Other, &Stores[0],
+                  Stores.size());
+    DAG.ReplaceAllUsesWith(SDValue(ST, 0), Result, DUL);
+    return;
   }
   assert(ST->getMemoryVT().isInteger() &&
          !ST->getMemoryVT().isVector() &&
@@ -488,13 +395,16 @@ SDValue ExpandUnalignedStore(StoreSDNode *ST, SelectionDAG &DAG,
                              NewStoredVT, ST->isVolatile(), ST->isNonTemporal(),
                              Alignment);
 
-  return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Store1, Store2);
+  SDValue Result =
+    DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Store1, Store2);
+  DAG.ReplaceAllUsesWith(SDValue(ST, 0), Result, DUL);
 }
 
 /// ExpandUnalignedLoad - Expands an unaligned load to 2 half-size loads.
-static
-SDValue ExpandUnalignedLoad(LoadSDNode *LD, SelectionDAG &DAG,
-                            const TargetLowering &TLI) {
+static void
+ExpandUnalignedLoad(LoadSDNode *LD, SelectionDAG &DAG,
+                    const TargetLowering &TLI,
+                    SDValue &ValResult, SDValue &ChainResult) {
   SDValue Chain = LD->getChain();
   SDValue Ptr = LD->getBasePtr();
   EVT VT = LD->getValueType(0);
@@ -512,8 +422,9 @@ SDValue ExpandUnalignedLoad(LoadSDNode *LD, SelectionDAG &DAG,
       if (VT.isFloatingPoint() && LoadedVT != VT)
         Result = DAG.getNode(ISD::FP_EXTEND, dl, VT, Result);
 
-      SDValue Ops[] = { Result, Chain };
-      return DAG.getMergeValues(Ops, 2, dl);
+      ValResult = Result;
+      ChainResult = Chain;
+      return;
     }
 
     // Copy the value to a (aligned) stack slot using (unaligned) integer
@@ -572,8 +483,9 @@ SDValue ExpandUnalignedLoad(LoadSDNode *LD, SelectionDAG &DAG,
                           MachinePointerInfo(), LoadedVT, false, false, 0);
 
     // Callers expect a MERGE_VALUES node.
-    SDValue Ops[] = { Load, TF };
-    return DAG.getMergeValues(Ops, 2, dl);
+    ValResult = Load;
+    ChainResult = TF;
+    return;
   }
   assert(LoadedVT.isInteger() && !LoadedVT.isVector() &&
          "Unaligned load of unsupported type.");
@@ -626,8 +538,8 @@ SDValue ExpandUnalignedLoad(LoadSDNode *LD, SelectionDAG &DAG,
   SDValue TF = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Lo.getValue(1),
                              Hi.getValue(1));
 
-  SDValue Ops[] = { Result, TF };
-  return DAG.getMergeValues(Ops, 2, dl);
+  ValResult = Result;
+  ChainResult = TF;
 }
 
 /// PerformInsertVectorEltInMemory - Some target cannot handle a variable
@@ -763,11 +675,10 @@ SDValue SelectionDAGLegalize::OptimizeFloatStore(StoreSDNode* ST) {
 
 /// LegalizeOp - Return a legal replacement for the given operation, with
 /// all legal operands.
-SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
-  if (Op.getOpcode() == ISD::TargetConstant) // Allow illegal target nodes.
-    return Op;
+void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
+  if (Node->getOpcode() == ISD::TargetConstant) // Allow illegal target nodes.
+    return;
 
-  SDNode *Node = Op.getNode();
   DebugLoc dl = Node->getDebugLoc();
 
   for (unsigned i = 0, e = Node->getNumValues(); i != e; ++i)
@@ -782,13 +693,7 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
             Node->getOperand(i).getOpcode() == ISD::TargetConstant) &&
            "Unexpected illegal type!");
 
-  // Note that LegalizeOp may be reentered even from single-use nodes, which
-  // means that we always must cache transformed nodes.
-  DenseMap<SDValue, SDValue>::iterator I = LegalizedNodes.find(Op);
-  if (I != LegalizedNodes.end()) return I->second;
-
   SDValue Tmp1, Tmp2, Tmp3, Tmp4;
-  SDValue Result = Op;
   bool isCustom = false;
 
   // Figure out the correct action; the way to query this varies by opcode
@@ -882,17 +787,6 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
     if (Action == TargetLowering::Legal)
       Action = TargetLowering::Custom;
     break;
-  case ISD::BUILD_VECTOR:
-    // A weird case: legalization for BUILD_VECTOR never legalizes the
-    // operands!
-    // FIXME: This really sucks... changing it isn't semantically incorrect,
-    // but it massively pessimizes the code for floating-point BUILD_VECTORs
-    // because ConstantFP operands get legalized into constant pool loads
-    // before the BUILD_VECTOR code can see them.  It doesn't usually bite,
-    // though, because BUILD_VECTORS usually get lowered into other nodes
-    // which get legalized properly.
-    SimpleFinishLegalizing = false;
-    break;
   default:
     if (Node->getOpcode() >= ISD::BUILTIN_OP_END) {
       Action = TargetLowering::Legal;
@@ -903,22 +797,11 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
   }
 
   if (SimpleFinishLegalizing) {
-    SmallVector<SDValue, 8> Ops, ResultVals;
+    SmallVector<SDValue, 8> Ops;
     for (unsigned i = 0, e = Node->getNumOperands(); i != e; ++i)
-      Ops.push_back(LegalizeOp(Node->getOperand(i)));
+      Ops.push_back(Node->getOperand(i));
     switch (Node->getOpcode()) {
     default: break;
-    case ISD::BR:
-    case ISD::BRIND:
-    case ISD::BR_JT:
-    case ISD::BR_CC:
-    case ISD::BRCOND:
-      // Branches tweak the chain to include LastCALLSEQ_END
-      Ops[0] = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Ops[0],
-                           LastCALLSEQ_END);
-      Ops[0] = LegalizeOp(Ops[0]);
-      LastCALLSEQ_END = DAG.getEntryNode();
-      break;
     case ISD::SHL:
     case ISD::SRL:
     case ISD::SRA:
@@ -926,57 +809,66 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
     case ISD::ROTR:
       // Legalizing shifts/rotates requires adjusting the shift amount
       // to the appropriate width.
-      if (!Ops[1].getValueType().isVector())
-        Ops[1] = LegalizeOp(DAG.getShiftAmountOperand(Ops[0].getValueType(),
-                                                      Ops[1]));
+      if (!Ops[1].getValueType().isVector()) {
+        SDValue SAO = DAG.getShiftAmountOperand(Ops[0].getValueType(), Ops[1]);
+        HandleSDNode Handle(SAO);
+        LegalizeOp(SAO.getNode());
+        Ops[1] = Handle.getValue();
+      }
       break;
     case ISD::SRL_PARTS:
     case ISD::SRA_PARTS:
     case ISD::SHL_PARTS:
       // Legalizing shifts/rotates requires adjusting the shift amount
       // to the appropriate width.
-      if (!Ops[2].getValueType().isVector())
-        Ops[2] = LegalizeOp(DAG.getShiftAmountOperand(Ops[0].getValueType(),
-                                                      Ops[2]));
+      if (!Ops[2].getValueType().isVector()) {
+        SDValue SAO = DAG.getShiftAmountOperand(Ops[0].getValueType(), Ops[2]);
+        HandleSDNode Handle(SAO);
+        LegalizeOp(SAO.getNode());
+        Ops[2] = Handle.getValue();
+      }
       break;
     }
 
-    Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(), Ops.data(),
-                                            Ops.size()), 0);
+    SDNode *NewNode = DAG.UpdateNodeOperands(Node, Ops.data(), Ops.size());
+    if (NewNode != Node) {
+      DAG.ReplaceAllUsesWith(Node, NewNode, this);
+      for (unsigned i = 0, e = Node->getNumValues(); i != e; ++i)
+        DAG.TransferDbgValues(SDValue(Node, i), SDValue(NewNode, i));
+      DAG.RemoveDeadNode(Node, this);
+      Node = NewNode;
+    }
     switch (Action) {
     case TargetLowering::Legal:
-      for (unsigned i = 0, e = Node->getNumValues(); i != e; ++i)
-        ResultVals.push_back(Result.getValue(i));
-      break;
+      return;
     case TargetLowering::Custom:
       // FIXME: The handling for custom lowering with multiple results is
       // a complete mess.
-      Tmp1 = TLI.LowerOperation(Result, DAG);
+      Tmp1 = TLI.LowerOperation(SDValue(Node, 0), DAG);
       if (Tmp1.getNode()) {
+        SmallVector<SDValue, 8> ResultVals;
         for (unsigned i = 0, e = Node->getNumValues(); i != e; ++i) {
           if (e == 1)
             ResultVals.push_back(Tmp1);
           else
             ResultVals.push_back(Tmp1.getValue(i));
         }
-        break;
+        if (Tmp1.getNode() != Node || Tmp1.getResNo() != 0) {
+          DAG.ReplaceAllUsesWith(Node, ResultVals.data(), this);
+          for (unsigned i = 0, e = Node->getNumValues(); i != e; ++i)
+            DAG.TransferDbgValues(SDValue(Node, i), ResultVals[i]);
+          DAG.RemoveDeadNode(Node, this);
+        }
+        return;
       }
 
       // FALL THROUGH
     case TargetLowering::Expand:
-      ExpandNode(Result.getNode(), ResultVals);
-      break;
+      ExpandNode(Node);
+      return;
     case TargetLowering::Promote:
-      PromoteNode(Result.getNode(), ResultVals);
-      break;
-    }
-    if (!ResultVals.empty()) {
-      for (unsigned i = 0, e = ResultVals.size(); i != e; ++i) {
-        if (ResultVals[i] != SDValue(Node, i))
-          ResultVals[i] = LegalizeOp(ResultVals[i]);
-        AddLegalizedOperand(SDValue(Node, i), ResultVals[i]);
-      }
-      return ResultVals[Op.getResNo()];
+      PromoteNode(Node);
+      return;
     }
   }
 
@@ -989,155 +881,20 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
 #endif
     assert(0 && "Do not know how to legalize this operator!");
 
-  case ISD::SRA:
-  case ISD::SRL:
-  case ISD::SHL: {
-    // Scalarize vector SRA/SRL/SHL.
-    EVT VT = Node->getValueType(0);
-    assert(VT.isVector() && "Unable to legalize non-vector shift");
-    assert(TLI.isTypeLegal(VT.getScalarType())&& "Element type must be legal");
-    unsigned NumElem = VT.getVectorNumElements();
-
-    SmallVector<SDValue, 8> Scalars;
-    for (unsigned Idx = 0; Idx < NumElem; Idx++) {
-      SDValue Ex = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl,
-                               VT.getScalarType(),
-                               Node->getOperand(0), DAG.getIntPtrConstant(Idx));
-      SDValue Sh = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl,
-                               VT.getScalarType(),
-                               Node->getOperand(1), DAG.getIntPtrConstant(Idx));
-      Scalars.push_back(DAG.getNode(Node->getOpcode(), dl,
-                                    VT.getScalarType(), Ex, Sh));
-    }
-    Result = DAG.getNode(ISD::BUILD_VECTOR, dl, Node->getValueType(0),
-                         &Scalars[0], Scalars.size());
-    break;
-  }
-
-  case ISD::BUILD_VECTOR:
-    switch (TLI.getOperationAction(ISD::BUILD_VECTOR, Node->getValueType(0))) {
-    default: assert(0 && "This action is not supported yet!");
-    case TargetLowering::Custom:
-      Tmp3 = TLI.LowerOperation(Result, DAG);
-      if (Tmp3.getNode()) {
-        Result = Tmp3;
-        break;
-      }
-      // FALLTHROUGH
-    case TargetLowering::Expand:
-      Result = ExpandBUILD_VECTOR(Result.getNode());
-      break;
-    }
-    break;
-  case ISD::CALLSEQ_START: {
-    SDNode *CallEnd = FindCallEndFromCallStart(Node);
-
-    // Recursively Legalize all of the inputs of the call end that do not lead
-    // to this call start.  This ensures that any libcalls that need be inserted
-    // are inserted *before* the CALLSEQ_START.
-    {SmallPtrSet<SDNode*, 32> NodesLeadingTo;
-    for (unsigned i = 0, e = CallEnd->getNumOperands(); i != e; ++i)
-      LegalizeAllNodesNotLeadingTo(CallEnd->getOperand(i).getNode(), Node,
-                                   NodesLeadingTo);
-    }
-
-    // Now that we have legalized all of the inputs (which may have inserted
-    // libcalls), create the new CALLSEQ_START node.
-    Tmp1 = LegalizeOp(Node->getOperand(0));  // Legalize the chain.
-
-    // Merge in the last call to ensure that this call starts after the last
-    // call ended.
-    if (LastCALLSEQ_END.getOpcode() != ISD::EntryToken) {
-      Tmp1 = DAG.getNode(ISD::TokenFactor, dl, MVT::Other,
-                         Tmp1, LastCALLSEQ_END);
-      Tmp1 = LegalizeOp(Tmp1);
-    }
-
-    // Do not try to legalize the target-specific arguments (#1+).
-    if (Tmp1 != Node->getOperand(0)) {
-      SmallVector<SDValue, 8> Ops(Node->op_begin(), Node->op_end());
-      Ops[0] = Tmp1;
-      Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(), &Ops[0],
-                                              Ops.size()), Result.getResNo());
-    }
-
-    // Remember that the CALLSEQ_START is legalized.
-    AddLegalizedOperand(Op.getValue(0), Result);
-    if (Node->getNumValues() == 2)    // If this has a flag result, remember it.
-      AddLegalizedOperand(Op.getValue(1), Result.getValue(1));
-
-    // Now that the callseq_start and all of the non-call nodes above this call
-    // sequence have been legalized, legalize the call itself.  During this
-    // process, no libcalls can/will be inserted, guaranteeing that no calls
-    // can overlap.
-    assert(!IsLegalizingCall && "Inconsistent sequentialization of calls!");
-    // Note that we are selecting this call!
-    LastCALLSEQ_END = SDValue(CallEnd, 0);
-    IsLegalizingCall = true;
-
-    // Legalize the call, starting from the CALLSEQ_END.
-    LegalizeOp(LastCALLSEQ_END);
-    assert(!IsLegalizingCall && "CALLSEQ_END should have cleared this!");
-    return Result;
-  }
+  case ISD::CALLSEQ_START:
   case ISD::CALLSEQ_END:
-    // If the CALLSEQ_START node hasn't been legalized first, legalize it.  This
-    // will cause this node to be legalized as well as handling libcalls right.
-    if (LastCALLSEQ_END.getNode() != Node) {
-      LegalizeOp(SDValue(FindCallStartFromCallEnd(Node), 0));
-      DenseMap<SDValue, SDValue>::iterator I = LegalizedNodes.find(Op);
-      assert(I != LegalizedNodes.end() &&
-             "Legalizing the call start should have legalized this node!");
-      return I->second;
-    }
-
-    // Otherwise, the call start has been legalized and everything is going
-    // according to plan.  Just legalize ourselves normally here.
-    Tmp1 = LegalizeOp(Node->getOperand(0));  // Legalize the chain.
-    // Do not try to legalize the target-specific arguments (#1+), except for
-    // an optional flag input.
-    if (Node->getOperand(Node->getNumOperands()-1).getValueType() != MVT::Glue){
-      if (Tmp1 != Node->getOperand(0)) {
-        SmallVector<SDValue, 8> Ops(Node->op_begin(), Node->op_end());
-        Ops[0] = Tmp1;
-        Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(),
-                                                &Ops[0], Ops.size()),
-                         Result.getResNo());
-      }
-    } else {
-      Tmp2 = LegalizeOp(Node->getOperand(Node->getNumOperands()-1));
-      if (Tmp1 != Node->getOperand(0) ||
-          Tmp2 != Node->getOperand(Node->getNumOperands()-1)) {
-        SmallVector<SDValue, 8> Ops(Node->op_begin(), Node->op_end());
-        Ops[0] = Tmp1;
-        Ops.back() = Tmp2;
-        Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(),
-                                                &Ops[0], Ops.size()),
-                         Result.getResNo());
-      }
-    }
-    assert(IsLegalizingCall && "Call sequence imbalance between start/end?");
-    // This finishes up call legalization.
-    IsLegalizingCall = false;
-
-    // If the CALLSEQ_END node has a flag, remember that we legalized it.
-    AddLegalizedOperand(SDValue(Node, 0), Result.getValue(0));
-    if (Node->getNumValues() == 2)
-      AddLegalizedOperand(SDValue(Node, 1), Result.getValue(1));
-    return Result.getValue(Op.getResNo());
+    break;
   case ISD::LOAD: {
     LoadSDNode *LD = cast<LoadSDNode>(Node);
-    Tmp1 = LegalizeOp(LD->getChain());   // Legalize the chain.
-    Tmp2 = LegalizeOp(LD->getBasePtr()); // Legalize the base pointer.
+    Tmp1 = LD->getChain();   // Legalize the chain.
+    Tmp2 = LD->getBasePtr(); // Legalize the base pointer.
 
     ISD::LoadExtType ExtType = LD->getExtensionType();
     if (ExtType == ISD::NON_EXTLOAD) {
       EVT VT = Node->getValueType(0);
-      Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(),
-                                              Tmp1, Tmp2, LD->getOffset()),
-                       Result.getResNo());
-      Tmp3 = Result.getValue(0);
-      Tmp4 = Result.getValue(1);
+      Node = DAG.UpdateNodeOperands(Node, Tmp1, Tmp2, LD->getOffset());
+      Tmp3 = SDValue(Node, 0);
+      Tmp4 = SDValue(Node, 1);
 
       switch (TLI.getOperationAction(Node->getOpcode(), VT)) {
       default: assert(0 && "This action is not supported yet!");
@@ -1148,20 +905,16 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
           Type *Ty = LD->getMemoryVT().getTypeForEVT(*DAG.getContext());
           unsigned ABIAlignment = TLI.getTargetData()->getABITypeAlignment(Ty);
           if (LD->getAlignment() < ABIAlignment){
-            Result = ExpandUnalignedLoad(cast<LoadSDNode>(Result.getNode()),
-                                         DAG, TLI);
-            Tmp3 = Result.getOperand(0);
-            Tmp4 = Result.getOperand(1);
-            Tmp3 = LegalizeOp(Tmp3);
-            Tmp4 = LegalizeOp(Tmp4);
+            ExpandUnalignedLoad(cast<LoadSDNode>(Node),
+                                DAG, TLI, Tmp3, Tmp4);
           }
         }
         break;
       case TargetLowering::Custom:
         Tmp1 = TLI.LowerOperation(Tmp3, DAG);
         if (Tmp1.getNode()) {
-          Tmp3 = LegalizeOp(Tmp1);
-          Tmp4 = LegalizeOp(Tmp1.getValue(1));
+          Tmp3 = Tmp1;
+          Tmp4 = Tmp1.getValue(1);
         }
         break;
       case TargetLowering::Promote: {
@@ -1173,16 +926,16 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
         Tmp1 = DAG.getLoad(NVT, dl, Tmp1, Tmp2, LD->getPointerInfo(),
                            LD->isVolatile(), LD->isNonTemporal(),
                            LD->getAlignment());
-        Tmp3 = LegalizeOp(DAG.getNode(ISD::BITCAST, dl, VT, Tmp1));
-        Tmp4 = LegalizeOp(Tmp1.getValue(1));
+        Tmp3 = DAG.getNode(ISD::BITCAST, dl, VT, Tmp1);
+        Tmp4 = Tmp1.getValue(1);
         break;
       }
       }
       // Since loads produce two values, make sure to remember that we
       // legalized both of them.
-      AddLegalizedOperand(SDValue(Node, 0), Tmp3);
-      AddLegalizedOperand(SDValue(Node, 1), Tmp4);
-      return Op.getResNo() ? Tmp4 : Tmp3;
+      DAG.ReplaceAllUsesOfValueWith(SDValue(Node, 0), Tmp3);
+      DAG.ReplaceAllUsesOfValueWith(SDValue(Node, 1), Tmp4);
+      return;
     }
 
     EVT SrcVT = LD->getMemoryVT();
@@ -1213,9 +966,10 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
       ISD::LoadExtType NewExtType =
         ExtType == ISD::ZEXTLOAD ? ISD::ZEXTLOAD : ISD::EXTLOAD;
 
-      Result = DAG.getExtLoad(NewExtType, dl, Node->getValueType(0),
-                              Tmp1, Tmp2, LD->getPointerInfo(),
-                              NVT, isVolatile, isNonTemporal, Alignment);
+      SDValue Result =
+        DAG.getExtLoad(NewExtType, dl, Node->getValueType(0),
+                       Tmp1, Tmp2, LD->getPointerInfo(),
+                       NVT, isVolatile, isNonTemporal, Alignment);
 
       Ch = Result.getValue(1); // The chain.
 
@@ -1230,8 +984,8 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
                              Result.getValueType(), Result,
                              DAG.getValueType(SrcVT));
 
-      Tmp1 = LegalizeOp(Result);
-      Tmp2 = LegalizeOp(Ch);
+      Tmp1 = Result;
+      Tmp2 = Ch;
     } else if (SrcWidth & (SrcWidth - 1)) {
       // If not loading a power-of-2 number of bits, expand as two loads.
       assert(!SrcVT.isVector() && "Unsupported extload!");
@@ -1274,7 +1028,7 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
                                       TLI.getShiftAmountTy(Hi.getValueType())));
 
         // Join the hi and lo parts.
-        Result = DAG.getNode(ISD::OR, dl, Node->getValueType(0), Lo, Hi);
+        Tmp1 = DAG.getNode(ISD::OR, dl, Node->getValueType(0), Lo, Hi);
       } else {
         // Big endian - avoid unaligned loads.
         // EXTLOAD:i24 -> (shl EXTLOAD:i16, 8) | ZEXTLOAD@+2:i8
@@ -1304,11 +1058,10 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
                                       TLI.getShiftAmountTy(Hi.getValueType())));
 
         // Join the hi and lo parts.
-        Result = DAG.getNode(ISD::OR, dl, Node->getValueType(0), Lo, Hi);
+        Tmp1 = DAG.getNode(ISD::OR, dl, Node->getValueType(0), Lo, Hi);
       }
 
-      Tmp1 = LegalizeOp(Result);
-      Tmp2 = LegalizeOp(Ch);
+      Tmp2 = Ch;
     } else {
       switch (TLI.getLoadExtAction(ExtType, SrcVT)) {
       default: assert(0 && "This action is not supported yet!");
@@ -1316,17 +1069,16 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
         isCustom = true;
         // FALLTHROUGH
       case TargetLowering::Legal:
-        Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(),
-                                                Tmp1, Tmp2, LD->getOffset()),
-                         Result.getResNo());
-        Tmp1 = Result.getValue(0);
-        Tmp2 = Result.getValue(1);
+        Node = DAG.UpdateNodeOperands(Node,
+                                      Tmp1, Tmp2, LD->getOffset());
+        Tmp1 = SDValue(Node, 0);
+        Tmp2 = SDValue(Node, 1);
 
         if (isCustom) {
-          Tmp3 = TLI.LowerOperation(Result, DAG);
+          Tmp3 = TLI.LowerOperation(SDValue(Node, 0), DAG);
           if (Tmp3.getNode()) {
-            Tmp1 = LegalizeOp(Tmp3);
-            Tmp2 = LegalizeOp(Tmp3.getValue(1));
+            Tmp1 = Tmp3;
+            Tmp2 = Tmp3.getValue(1);
           }
         } else {
           // If this is an unaligned load and the target doesn't support it,
@@ -1337,12 +1089,8 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
             unsigned ABIAlignment =
               TLI.getTargetData()->getABITypeAlignment(Ty);
             if (LD->getAlignment() < ABIAlignment){
-              Result = ExpandUnalignedLoad(cast<LoadSDNode>(Result.getNode()),
-                                           DAG, TLI);
-              Tmp1 = Result.getOperand(0);
-              Tmp2 = Result.getOperand(1);
-              Tmp1 = LegalizeOp(Tmp1);
-              Tmp2 = LegalizeOp(Tmp2);
+              ExpandUnalignedLoad(cast<LoadSDNode>(Node),
+                                  DAG, TLI, Tmp1, Tmp2);
             }
           }
         }
@@ -1363,9 +1111,8 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
           case ISD::ZEXTLOAD: ExtendOp = ISD::ZERO_EXTEND; break;
           default: llvm_unreachable("Unexpected extend load type!");
           }
-          Result = DAG.getNode(ExtendOp, dl, Node->getValueType(0), Load);
-          Tmp1 = LegalizeOp(Result);  // Relegalize new nodes.
-          Tmp2 = LegalizeOp(Load.getValue(1));
+          Tmp1 = DAG.getNode(ExtendOp, dl, Node->getValueType(0), Load);
+          Tmp2 = Load.getValue(1);
           break;
         }
 
@@ -1380,10 +1127,10 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
                "EXTLOAD should always be supported!");
         // Turn the unsupported load into an EXTLOAD followed by an explicit
         // zero/sign extend inreg.
-        Result = DAG.getExtLoad(ISD::EXTLOAD, dl, Node->getValueType(0),
-                                Tmp1, Tmp2, LD->getPointerInfo(), SrcVT,
-                                LD->isVolatile(), LD->isNonTemporal(),
-                                LD->getAlignment());
+        SDValue Result = DAG.getExtLoad(ISD::EXTLOAD, dl, Node->getValueType(0),
+                                        Tmp1, Tmp2, LD->getPointerInfo(), SrcVT,
+                                        LD->isVolatile(), LD->isNonTemporal(),
+                                        LD->getAlignment());
         SDValue ValRes;
         if (ExtType == ISD::SEXTLOAD)
           ValRes = DAG.getNode(ISD::SIGN_EXTEND_INREG, dl,
@@ -1391,38 +1138,37 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
                                Result, DAG.getValueType(SrcVT));
         else
           ValRes = DAG.getZeroExtendInReg(Result, dl, SrcVT.getScalarType());
-        Tmp1 = LegalizeOp(ValRes);  // Relegalize new nodes.
-        Tmp2 = LegalizeOp(Result.getValue(1));  // Relegalize new nodes.
+        Tmp1 = ValRes;
+        Tmp2 = Result.getValue(1);
         break;
       }
     }
 
     // Since loads produce two values, make sure to remember that we legalized
     // both of them.
-    AddLegalizedOperand(SDValue(Node, 0), Tmp1);
-    AddLegalizedOperand(SDValue(Node, 1), Tmp2);
-    return Op.getResNo() ? Tmp2 : Tmp1;
+    DAG.ReplaceAllUsesOfValueWith(SDValue(Node, 0), Tmp1);
+    DAG.ReplaceAllUsesOfValueWith(SDValue(Node, 1), Tmp2);
+    break;
   }
   case ISD::STORE: {
     StoreSDNode *ST = cast<StoreSDNode>(Node);
-    Tmp1 = LegalizeOp(ST->getChain());    // Legalize the chain.
-    Tmp2 = LegalizeOp(ST->getBasePtr());  // Legalize the pointer.
+    Tmp1 = ST->getChain();
+    Tmp2 = ST->getBasePtr();
     unsigned Alignment = ST->getAlignment();
     bool isVolatile = ST->isVolatile();
     bool isNonTemporal = ST->isNonTemporal();
 
     if (!ST->isTruncatingStore()) {
       if (SDNode *OptStore = OptimizeFloatStore(ST).getNode()) {
-        Result = SDValue(OptStore, 0);
+        DAG.ReplaceAllUsesWith(ST, OptStore, this);
         break;
       }
 
       {
-        Tmp3 = LegalizeOp(ST->getValue());
-        Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(),
-                                                Tmp1, Tmp3, Tmp2,
-                                                ST->getOffset()),
-                         Result.getResNo());
+        Tmp3 = ST->getValue();
+        Node = DAG.UpdateNodeOperands(Node,
+                                      Tmp1, Tmp3, Tmp2,
+                                      ST->getOffset());
 
         EVT VT = Tmp3.getValueType();
         switch (TLI.getOperationAction(ISD::STORE, VT)) {
@@ -1434,27 +1180,31 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
             Type *Ty = ST->getMemoryVT().getTypeForEVT(*DAG.getContext());
             unsigned ABIAlignment= TLI.getTargetData()->getABITypeAlignment(Ty);
             if (ST->getAlignment() < ABIAlignment)
-              Result = ExpandUnalignedStore(cast<StoreSDNode>(Result.getNode()),
-                                            DAG, TLI);
+              ExpandUnalignedStore(cast<StoreSDNode>(Node),
+                                   DAG, TLI, this);
           }
           break;
         case TargetLowering::Custom:
-          Tmp1 = TLI.LowerOperation(Result, DAG);
-          if (Tmp1.getNode()) Result = Tmp1;
+          Tmp1 = TLI.LowerOperation(SDValue(Node, 0), DAG);
+          if (Tmp1.getNode())
+            DAG.ReplaceAllUsesWith(SDValue(Node, 0), Tmp1, this);
           break;
-        case TargetLowering::Promote:
+        case TargetLowering::Promote: {
           assert(VT.isVector() && "Unknown legal promote case!");
           Tmp3 = DAG.getNode(ISD::BITCAST, dl,
                              TLI.getTypeToPromoteTo(ISD::STORE, VT), Tmp3);
-          Result = DAG.getStore(Tmp1, dl, Tmp3, Tmp2,
-                                ST->getPointerInfo(), isVolatile,
-                                isNonTemporal, Alignment);
+          SDValue Result =
+            DAG.getStore(Tmp1, dl, Tmp3, Tmp2,
+                         ST->getPointerInfo(), isVolatile,
+                         isNonTemporal, Alignment);
+          DAG.ReplaceAllUsesWith(SDValue(Node, 0), Result, this);
           break;
         }
+        }
         break;
       }
     } else {
-      Tmp3 = LegalizeOp(ST->getValue());
+      Tmp3 = ST->getValue();
 
       EVT StVT = ST->getMemoryVT();
       unsigned StWidth = StVT.getSizeInBits();
@@ -1466,8 +1216,10 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
         EVT NVT = EVT::getIntegerVT(*DAG.getContext(),
                                     StVT.getStoreSizeInBits());
         Tmp3 = DAG.getZeroExtendInReg(Tmp3, dl, StVT);
-        Result = DAG.getTruncStore(Tmp1, dl, Tmp3, Tmp2, ST->getPointerInfo(),
-                                   NVT, isVolatile, isNonTemporal, Alignment);
+        SDValue Result =
+          DAG.getTruncStore(Tmp1, dl, Tmp3, Tmp2, ST->getPointerInfo(),
+                            NVT, isVolatile, isNonTemporal, Alignment);
+        DAG.ReplaceAllUsesWith(SDValue(Node, 0), Result, this);
       } else if (StWidth & (StWidth - 1)) {
         // If not storing a power-of-2 number of bits, expand as two stores.
         assert(!StVT.isVector() && "Unsupported truncstore!");
@@ -1521,14 +1273,13 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
         }
 
         // The order of the stores doesn't matter.
-        Result = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Lo, Hi);
+        SDValue Result = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Lo, Hi);
+        DAG.ReplaceAllUsesWith(SDValue(Node, 0), Result, this);
       } else {
         if (Tmp1 != ST->getChain() || Tmp3 != ST->getValue() ||
             Tmp2 != ST->getBasePtr())
-          Result = SDValue(DAG.UpdateNodeOperands(Result.getNode(),
-                                                  Tmp1, Tmp3, Tmp2,
-                                                  ST->getOffset()),
-                           Result.getResNo());
+          Node = DAG.UpdateNodeOperands(Node, Tmp1, Tmp3, Tmp2,
+                                        ST->getOffset());
 
         switch (TLI.getTruncStoreAction(ST->getValue().getValueType(), StVT)) {
         default: assert(0 && "This action is not supported yet!");
@@ -1539,12 +1290,13 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
             Type *Ty = ST->getMemoryVT().getTypeForEVT(*DAG.getContext());
             unsigned ABIAlignment= TLI.getTargetData()->getABITypeAlignment(Ty);
             if (ST->getAlignment() < ABIAlignment)
-              Result = ExpandUnalignedStore(cast<StoreSDNode>(Result.getNode()),
-                                            DAG, TLI);
+              ExpandUnalignedStore(cast<StoreSDNode>(Node), DAG, TLI, this);
           }
           break;
         case TargetLowering::Custom:
-          Result = TLI.LowerOperation(Result, DAG);
+          DAG.ReplaceAllUsesWith(SDValue(Node, 0),
+                                 TLI.LowerOperation(SDValue(Node, 0), DAG),
+                                 this);
           break;
         case TargetLowering::Expand:
           assert(!StVT.isVector() &&
@@ -1553,8 +1305,10 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
           // TRUNCSTORE:i16 i32 -> STORE i16
           assert(TLI.isTypeLegal(StVT) && "Do not know how to expand this store!");
           Tmp3 = DAG.getNode(ISD::TRUNCATE, dl, StVT, Tmp3);
-          Result = DAG.getStore(Tmp1, dl, Tmp3, Tmp2, ST->getPointerInfo(),
-                                isVolatile, isNonTemporal, Alignment);
+          SDValue Result =
+            DAG.getStore(Tmp1, dl, Tmp3, Tmp2, ST->getPointerInfo(),
+                         isVolatile, isNonTemporal, Alignment);
+          DAG.ReplaceAllUsesWith(SDValue(Node, 0), Result, this);
           break;
         }
       }
@@ -1562,17 +1316,6 @@ SDValue SelectionDAGLegalize::LegalizeOp(SDValue Op) {
     break;
   }
   }
-  assert(Result.getValueType() == Op.getValueType() &&
-         "Bad legalization!");
-
-  // Make sure that the generated code is itself legal.
-  if (Result != Op)
-    Result = LegalizeOp(Result);
-
-  // Note that LegalizeOp may be reentered even from single-use nodes, which
-  // means that we always must cache transformed nodes.
-  AddLegalizedOperand(Op, Result);
-  return Result;
 }
 
 SDValue SelectionDAGLegalize::ExpandExtractFromVectorThroughStack(SDValue Op) {
@@ -2011,7 +1754,6 @@ SDValue SelectionDAGLegalize::ExpandBUILD_VECTOR(SDNode *Node) {
 // and leave the Hi part unset.
 SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, SDNode *Node,
                                             bool isSigned) {
-  assert(!IsLegalizingCall && "Cannot overlap legalization of calls!");
   // The input chain to this libcall is the entry node of the function.
   // Legalizing the call will automatically add the previous call to the
   // dependence.
@@ -2030,7 +1772,6 @@ SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, SDNode *Node,
   SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(LC),
                                          TLI.getPointerTy());
 
-  // Splice the libcall in wherever FindInputOutputChains tells us to.
   Type *RetTy = Node->getValueType(0).getTypeForEVT(*DAG.getContext());
 
   // isTailCall may be true since the callee does not reference caller stack
@@ -2046,10 +1787,6 @@ SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, SDNode *Node,
     // It's a tailcall, return the chain (which is the DAG root).
     return DAG.getRoot();
 
-  // Legalize the call sequence, starting with the chain.  This will advance
-  // the LastCALLSEQ_END to the legalized version of the CALLSEQ_END node that
-  // was added by LowerCallTo (guaranteeing proper serialization of calls).
-  LegalizeOp(CallInfo.second);
   return CallInfo.first;
 }
 
@@ -2079,11 +1816,6 @@ SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, EVT RetVT,
                   /*isReturnValueUsed=*/true,
                   Callee, Args, DAG, dl);
 
-  // Legalize the call sequence, starting with the chain.  This will advance
-  // the LastCALLSEQ_END to the legalized version of the CALLSEQ_END node that
-  // was added by LowerCallTo (guaranteeing proper serialization of calls).
-  LegalizeOp(CallInfo.second);
-
   return CallInfo.first;
 }
 
@@ -2093,7 +1825,6 @@ std::pair<SDValue, SDValue>
 SelectionDAGLegalize::ExpandChainLibCall(RTLIB::Libcall LC,
                                          SDNode *Node,
                                          bool isSigned) {
-  assert(!IsLegalizingCall && "Cannot overlap legalization of calls!");
   SDValue InChain = Node->getOperand(0);
 
   TargetLowering::ArgListTy Args;
@@ -2110,7 +1841,6 @@ SelectionDAGLegalize::ExpandChainLibCall(RTLIB::Libcall LC,
   SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(LC),
                                          TLI.getPointerTy());
 
-  // Splice the libcall in wherever FindInputOutputChains tells us to.
   Type *RetTy = Node->getValueType(0).getTypeForEVT(*DAG.getContext());
   std::pair<SDValue, SDValue> CallInfo =
     TLI.LowerCallTo(InChain, RetTy, isSigned, !isSigned, false, false,
@@ -2118,10 +1848,6 @@ SelectionDAGLegalize::ExpandChainLibCall(RTLIB::Libcall LC,
                     /*isReturnValueUsed=*/true,
                     Callee, Args, DAG, Node->getDebugLoc());
 
-  // Legalize the call sequence, starting with the chain.  This will advance
-  // the LastCALLSEQ_END to the legalized version of the CALLSEQ_END node that
-  // was added by LowerCallTo (guaranteeing proper serialization of calls).
-  LegalizeOp(CallInfo.second);
   return CallInfo;
 }
 
@@ -2247,20 +1973,14 @@ SelectionDAGLegalize::ExpandDivRemLibCall(SDNode *Node,
   SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(LC),
                                          TLI.getPointerTy());
 
-  // Splice the libcall in wherever FindInputOutputChains tells us to.
   DebugLoc dl = Node->getDebugLoc();
   std::pair<SDValue, SDValue> CallInfo =
     TLI.LowerCallTo(InChain, RetTy, isSigned, !isSigned, false, false,
                     0, TLI.getLibcallCallingConv(LC), /*isTailCall=*/false,
                     /*isReturnValueUsed=*/true, Callee, Args, DAG, dl);
 
-  // Legalize the call sequence, starting with the chain.  This will advance
-  // the LastCALLSEQ to the legalized version of the CALLSEQ_END node that
-  // was added by LowerCallTo (guaranteeing proper serialization of calls).
-  LegalizeOp(CallInfo.second);
-
   // Remainder is loaded back from the stack frame.
-  SDValue Rem = DAG.getLoad(RetVT, dl, LastCALLSEQ_END, FIPtr,
+  SDValue Rem = DAG.getLoad(RetVT, dl, CallInfo.second, FIPtr,
                             MachinePointerInfo(), false, false, 0);
   Results.push_back(CallInfo.first);
   Results.push_back(Rem);
@@ -2452,11 +2172,13 @@ SDValue SelectionDAGLegalize::ExpandLegalINT_TO_FP(bool isSigned,
                              MachinePointerInfo::getConstantPool(),
                              false, false, Alignment);
   else {
-    FudgeInReg =
-      LegalizeOp(DAG.getExtLoad(ISD::EXTLOAD, dl, DestVT,
-                                DAG.getEntryNode(), CPIdx,
-                                MachinePointerInfo::getConstantPool(),
-                                MVT::f32, false, false, Alignment));
+    SDValue Load = DAG.getExtLoad(ISD::EXTLOAD, dl, DestVT,
+                                  DAG.getEntryNode(), CPIdx,
+                                  MachinePointerInfo::getConstantPool(),
+                                  MVT::f32, false, false, Alignment);
+    HandleSDNode Handle(Load);
+    LegalizeOp(Load.getNode());
+    FudgeInReg = Handle.getValue();
   }
 
   return DAG.getNode(ISD::FADD, dl, DestVT, Tmp1, FudgeInReg);
@@ -2780,8 +2502,8 @@ std::pair <SDValue, SDValue> SelectionDAGLegalize::ExpandAtomic(SDNode *Node) {
   return ExpandChainLibCall(LC, Node, false);
 }
 
-void SelectionDAGLegalize::ExpandNode(SDNode *Node,
-                                      SmallVectorImpl<SDValue> &Results) {
+void SelectionDAGLegalize::ExpandNode(SDNode *Node) {
+  SmallVector<SDValue, 8> Results;
   DebugLoc dl = Node->getDebugLoc();
   SDValue Tmp1, Tmp2, Tmp3, Tmp4;
   switch (Node->getOpcode()) {
@@ -3229,10 +2951,8 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
     ConstantFPSDNode *CFP = cast<ConstantFPSDNode>(Node);
     // Check to see if this FP immediate is already legal.
     // If this is a legal constant, turn it into a TargetConstantFP node.
-    if (TLI.isFPImmLegal(CFP->getValueAPF(), Node->getValueType(0)))
-      Results.push_back(SDValue(Node, 0));
-    else
-      Results.push_back(ExpandConstantFP(CFP, true, DAG, TLI));
+    if (!TLI.isFPImmLegal(CFP->getValueAPF(), Node->getValueType(0)))
+      Results.push_back(ExpandConstantFP(CFP, true));
     break;
   }
   case ISD::EHSELECTION: {
@@ -3478,6 +3198,10 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
                                DAG.getIntPtrConstant(0));
       TopHalf = DAG.getNode(ISD::EXTRACT_ELEMENT, dl, VT, Ret,
                             DAG.getIntPtrConstant(1));
+      // Ret is a node with an illegal type. Because such things are not
+      // generally permitted during this phase of legalization, delete the
+      // node. The above EXTRACT_ELEMENT nodes should have been folded.
+      DAG.DeleteNode(Ret.getNode());
     }
 
     if (isSigned) {
@@ -3618,7 +3342,6 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
 
     LegalizeSetCCCondCode(TLI.getSetCCResultType(Tmp2.getValueType()),
                           Tmp2, Tmp3, Tmp4, dl);
-    LastCALLSEQ_END = DAG.getEntryNode();
 
     assert(!Tmp3.getNode() && "Can't legalize BR_CC with legal condition!");
     Tmp3 = DAG.getConstant(0, Tmp2.getValueType());
@@ -3628,6 +3351,35 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
     Results.push_back(Tmp1);
     break;
   }
+  case ISD::BUILD_VECTOR:
+    Results.push_back(ExpandBUILD_VECTOR(Node));
+    break;
+  case ISD::SRA:
+  case ISD::SRL:
+  case ISD::SHL: {
+    // Scalarize vector SRA/SRL/SHL.
+    EVT VT = Node->getValueType(0);
+    assert(VT.isVector() && "Unable to legalize non-vector shift");
+    assert(TLI.isTypeLegal(VT.getScalarType())&& "Element type must be legal");
+    unsigned NumElem = VT.getVectorNumElements();
+
+    SmallVector<SDValue, 8> Scalars;
+    for (unsigned Idx = 0; Idx < NumElem; Idx++) {
+      SDValue Ex = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl,
+                               VT.getScalarType(),
+                               Node->getOperand(0), DAG.getIntPtrConstant(Idx));
+      SDValue Sh = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl,
+                               VT.getScalarType(),
+                               Node->getOperand(1), DAG.getIntPtrConstant(Idx));
+      Scalars.push_back(DAG.getNode(Node->getOpcode(), dl,
+                                    VT.getScalarType(), Ex, Sh));
+    }
+    SDValue Result =
+      DAG.getNode(ISD::BUILD_VECTOR, dl, Node->getValueType(0),
+                  &Scalars[0], Scalars.size());
+    DAG.ReplaceAllUsesWith(SDValue(Node, 0), Result, this);
+    break;
+  }
   case ISD::GLOBAL_OFFSET_TABLE:
   case ISD::GlobalAddress:
   case ISD::GlobalTLSAddress:
@@ -3638,13 +3390,16 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
   case ISD::INTRINSIC_WO_CHAIN:
   case ISD::INTRINSIC_VOID:
     // FIXME: Custom lowering for these operations shouldn't return null!
-    for (unsigned i = 0, e = Node->getNumValues(); i != e; ++i)
-      Results.push_back(SDValue(Node, i));
     break;
   }
+
+  // Replace the original node with the legalized result.
+  if (!Results.empty())
+    DAG.ReplaceAllUsesWith(Node, Results.data(), this);
 }
-void SelectionDAGLegalize::PromoteNode(SDNode *Node,
-                                       SmallVectorImpl<SDValue> &Results) {
+
+void SelectionDAGLegalize::PromoteNode(SDNode *Node) {
+  SmallVector<SDValue, 8> Results;
   EVT OVT = Node->getValueType(0);
   if (Node->getOpcode() == ISD::UINT_TO_FP ||
       Node->getOpcode() == ISD::SINT_TO_FP ||
@@ -3772,6 +3527,10 @@ void SelectionDAGLegalize::PromoteNode(SDNode *Node,
     break;
   }
   }
+
+  // Replace the original node with the legalized result.
+  if (!Results.empty())
+    DAG.ReplaceAllUsesWith(Node, Results.data(), this);
 }
 
 // SelectionDAG::Legalize - This is the entry point for the file.
diff --git a/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp b/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
index a4bb577433..7ed1b98f10 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeTypes.cpp
@@ -1084,7 +1084,6 @@ DAGTypeLegalizer::ExpandChainLibCall(RTLIB::Libcall LC,
   SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(LC),
                                          TLI.getPointerTy());
 
-  // Splice the libcall in wherever FindInputOutputChains tells us to.
   Type *RetTy = Node->getValueType(0).getTypeForEVT(*DAG.getContext());
   std::pair<SDValue, SDValue> CallInfo =
     TLI.LowerCallTo(InChain, RetTy, isSigned, !isSigned, false, false,
diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
index a1abdb4d9b..fd768b1dd9 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
@@ -386,6 +386,90 @@ void ScheduleDAGRRList::ReleasePred(SUnit *SU, const SDep *PredEdge) {
   }
 }
 
+/// IsChainDependent - Test if Outer is reachable from Inner through
+/// chain dependencies.
+static bool IsChainDependent(SDNode *Outer, SDNode *Inner) {
+  SDNode *N = Outer;
+  for (;;) {
+    if (N == Inner)
+      return true;
+    if (N->getOpcode() == ISD::TokenFactor) {
+      for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
+        if (IsChainDependent(N->getOperand(i).getNode(), Inner))
+          return true;
+      return false;
+    }
+    for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
+      if (N->getOperand(i).getValueType() == MVT::Other) {
+        N = N->getOperand(i).getNode();
+        goto found_chain_operand;
+      }
+    return false;
+  found_chain_operand:;
+    if (N->getOpcode() == ISD::EntryToken)
+      return false;
+  }
+}
+
+/// FindCallSeqStart - Starting from the (lowered) CALLSEQ_END node, locate
+/// the corresponding (lowered) CALLSEQ_BEGIN node.
+///
+/// NestLevel and MaxNested are used in recursion to indcate the current level
+/// of nesting of CALLSEQ_BEGIN and CALLSEQ_END pairs, as well as the maximum
+/// level seen so far.
+///
+/// TODO: It would be better to give CALLSEQ_END an explicit operand to point
+/// to the corresponding CALLSEQ_BEGIN to avoid needing to search for it.
+static SDNode *
+FindCallSeqStart(SDNode *N, unsigned &NestLevel, unsigned &MaxNest,
+                 const TargetInstrInfo *TII) {
+  for (;;) {
+    // For a TokenFactor, examine each operand. There may be multiple ways
+    // to get to the CALLSEQ_BEGIN, but we need to find the path with the
+    // most nesting in order to ensure that we find the corresponding match.
+    if (N->getOpcode() == ISD::TokenFactor) {
+      SDNode *Best = 0;
+      unsigned BestMaxNest = MaxNest;
+      for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+        unsigned MyNestLevel = NestLevel;
+        unsigned MyMaxNest = MaxNest;
+        if (SDNode *New = FindCallSeqStart(N->getOperand(i).getNode(),
+                                           MyNestLevel, MyMaxNest, TII))
+          if (!Best || (MyMaxNest > BestMaxNest)) {
+            Best = New;
+            BestMaxNest = MyMaxNest;
+          }
+      }
+      assert(Best);
+      MaxNest = BestMaxNest;
+      return Best;
+    }
+    // Check for a lowered CALLSEQ_BEGIN or CALLSEQ_END.
+    if (N->isMachineOpcode()) {
+      if (N->getMachineOpcode() ==
+          (unsigned)TII->getCallFrameDestroyOpcode()) {
+        ++NestLevel;
+        MaxNest = std::max(MaxNest, NestLevel);
+      } else if (N->getMachineOpcode() ==
+                 (unsigned)TII->getCallFrameSetupOpcode()) {
+        --NestLevel;
+        if (NestLevel == 0)
+          return N;
+      }
+    }
+    // Otherwise, find the chain and continue climbing.
+    for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
+      if (N->getOperand(i).getValueType() == MVT::Other) {
+        N = N->getOperand(i).getNode();
+        goto found_chain_operand;
+      }
+    return 0;
+  found_chain_operand:;
+    if (N->getOpcode() == ISD::EntryToken)
+      return 0;
+  }
+}
+
 /// Call ReleasePred for each predecessor, then update register live def/gen.
 /// Always update LiveRegDefs for a register dependence even if the current SU
 /// also defines the register. This effectively create one large live range
@@ -423,6 +507,26 @@ void ScheduleDAGRRList::ReleasePredecessors(SUnit *SU) {
       }
     }
   }
+
+  // If we're scheduling a lowered CALLSEQ_END, find the corresponding CALLSEQ_BEGIN.
+  // Inject an artificial physical register dependence between these nodes, to
+  // prevent other calls from being interscheduled with them.
+  const TargetLowering *TLI = TM.getTargetLowering();
+  unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
+  if (!LiveRegDefs[SP])
+    for (SDNode *Node = SU->getNode(); Node; Node = Node->getGluedNode())
+      if (Node->isMachineOpcode() &&
+          Node->getMachineOpcode() == (unsigned)TII->getCallFrameDestroyOpcode()) {
+        unsigned NestLevel = 0;
+        unsigned MaxNest = 0;
+        SDNode *N = FindCallSeqStart(Node, NestLevel, MaxNest, TII);
+
+        SUnit *Def = &SUnits[N->getNodeId()];
+        ++NumLiveRegs;
+        LiveRegDefs[SP] = Def;
+        LiveRegGens[SP] = SU;
+        break;
+      }
 }
 
 /// Check to see if any of the pending instructions are ready to issue.  If
@@ -605,6 +709,22 @@ void ScheduleDAGRRList::ScheduleNodeBottomUp(SUnit *SU) {
       LiveRegGens[I->getReg()] = NULL;
     }
   }
+  // Release the special call resource dependence, if this is the beginning
+  // of a call.
+  const TargetLowering *TLI = TM.getTargetLowering();
+  unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
+  if (LiveRegDefs[SP] == SU)
+  for (const SDNode *SUNode = SU->getNode(); SUNode;
+       SUNode = SUNode->getGluedNode()) {
+    if (SUNode->isMachineOpcode() &&
+        SUNode->getMachineOpcode() == (unsigned)TII->getCallFrameSetupOpcode() &&
+        LiveRegDefs[SP] == SU) {
+      assert(NumLiveRegs > 0 && "NumLiveRegs is already zero!");
+      --NumLiveRegs;
+      LiveRegDefs[SP] = NULL;
+      LiveRegGens[SP] = NULL;
+    }
+  }
 
   resetVRegCycle(SU);
 
@@ -1083,6 +1203,20 @@ DelayForLiveRegsBottomUp(SUnit *SU, SmallVector<unsigned, 4> &LRegs) {
 
     if (!Node->isMachineOpcode())
       continue;
+    // If we're in the middle of scheduling a call, don't begin scheduling
+    // another call.
+    if (Node->getMachineOpcode() == (unsigned)TII->getCallFrameSetupOpcode() ||
+        Node->getMachineOpcode() == (unsigned)TII->getCallFrameDestroyOpcode()) {
+      for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i)
+        if (LiveRegDefs[i]) {
+          SDNode *Gen = LiveRegGens[i]->getNode();
+          while (SDNode *Glued = Gen->getGluedNode())
+            Gen = Glued;
+          if (!IsChainDependent(Gen, Node) && RegAdded.insert(i))
+            LRegs.push_back(i);
+        }
+      continue;
+    }
     const MCInstrDesc &MCID = TII->get(Node->getMachineOpcode());
     if (!MCID.ImplicitDefs)
       continue;
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 07d2db63fa..010a740dc7 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5290,6 +5290,10 @@ void SelectionDAG::ReplaceAllUsesWith(SDValue FromN, SDValue To,
     // already exists there, recursively merge the results together.
     AddModifiedNodeToCSEMaps(User, &Listener);
   }
+
+  // If we just RAUW'd the root, take note.
+  if (FromN == getRoot())
+    setRoot(To);
 }
 
 /// ReplaceAllUsesWith - Modify anything using 'From' to use 'To' instead.
@@ -5335,6 +5339,10 @@ void SelectionDAG::ReplaceAllUsesWith(SDNode *From, SDNode *To,
     // already exists there, recursively merge the results together.
     AddModifiedNodeToCSEMaps(User, &Listener);
   }
+
+  // If we just RAUW'd the root, take note.
+  if (From == getRoot().getNode())
+    setRoot(SDValue(To, getRoot().getResNo()));
 }
 
 /// ReplaceAllUsesWith - Modify anything using 'From' to use 'To' instead.
@@ -5373,6 +5381,10 @@ void SelectionDAG::ReplaceAllUsesWith(SDNode *From,
     // already exists there, recursively merge the results together.
     AddModifiedNodeToCSEMaps(User, &Listener);
   }
+
+  // If we just RAUW'd the root, take note.
+  if (From == getRoot().getNode())
+    setRoot(SDValue(To[getRoot().getResNo()]));
 }
 
 /// ReplaceAllUsesOfValueWith - Replace any uses of From with To, leaving
@@ -5431,6 +5443,10 @@ void SelectionDAG::ReplaceAllUsesOfValueWith(SDValue From, SDValue To,
     // already exists there, recursively merge the results together.
     AddModifiedNodeToCSEMaps(User, &Listener);
   }
+
+  // If we just RAUW'd the root, take note.
+  if (From == getRoot())
+    setRoot(To);
 }
 
 namespace {