diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
new file mode 100644
index 0000000..f794525
--- /dev/null
+++ b/src/compiler/simplified-lowering.cc
@@ -0,0 +1,945 @@
+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/compiler/simplified-lowering.h"
+
+#include "src/base/bits.h"
+#include "src/code-factory.h"
+#include "src/compiler/common-operator.h"
+#include "src/compiler/graph-inl.h"
+#include "src/compiler/node-properties-inl.h"
+#include "src/compiler/representation-change.h"
+#include "src/compiler/simplified-lowering.h"
+#include "src/compiler/simplified-operator.h"
+#include "src/objects.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Macro for outputting trace information from representation inference.
+#define TRACE(x) \
+  if (FLAG_trace_representation) PrintF x
+
+// Representation selection and lowering of {Simplified} operators to machine
+// operators are interwined. We use a fixpoint calculation to compute both the
+// output representation and the best possible lowering for {Simplified} nodes.
+// Representation change insertion ensures that all values are in the correct
+// machine representation after this phase, as dictated by the machine
+// operators themselves.
+enum Phase {
+  // 1.) PROPAGATE: Traverse the graph from the end, pushing usage information
+  //     backwards from uses to definitions, around cycles in phis, according
+  //     to local rules for each operator.
+  //     During this phase, the usage information for a node determines the best
+  //     possible lowering for each operator so far, and that in turn determines
+  //     the output representation.
+  //     Therefore, to be correct, this phase must iterate to a fixpoint before
+  //     the next phase can begin.
+  PROPAGATE,
+
+  // 2.) LOWER: perform lowering for all {Simplified} nodes by replacing some
+  //     operators for some nodes, expanding some nodes to multiple nodes, or
+  //     removing some (redundant) nodes.
+  //     During this phase, use the {RepresentationChanger} to insert
+  //     representation changes between uses that demand a particular
+  //     representation and nodes that produce a different representation.
+  LOWER
+};
+
+
+class RepresentationSelector {
+ public:
+  // Information for each node tracked during the fixpoint.
+  struct NodeInfo {
+    MachineTypeUnion use : 15;     // Union of all usages for the node.
+    bool queued : 1;           // Bookkeeping for the traversal.
+    bool visited : 1;          // Bookkeeping for the traversal.
+    MachineTypeUnion output : 15;  // Output type of the node.
+  };
+
+  RepresentationSelector(JSGraph* jsgraph, Zone* zone,
+                         RepresentationChanger* changer)
+      : jsgraph_(jsgraph),
+        count_(jsgraph->graph()->NodeCount()),
+        info_(zone->NewArray<NodeInfo>(count_)),
+        nodes_(zone),
+        replacements_(zone),
+        contains_js_nodes_(false),
+        phase_(PROPAGATE),
+        changer_(changer),
+        queue_(zone) {
+    memset(info_, 0, sizeof(NodeInfo) * count_);
+  }
+
+  void Run(SimplifiedLowering* lowering) {
+    // Run propagation phase to a fixpoint.
+    TRACE(("--{Propagation phase}--\n"));
+    phase_ = PROPAGATE;
+    Enqueue(jsgraph_->graph()->end());
+    // Process nodes from the queue until it is empty.
+    while (!queue_.empty()) {
+      Node* node = queue_.front();
+      NodeInfo* info = GetInfo(node);
+      queue_.pop();
+      info->queued = false;
+      TRACE((" visit #%d: %s\n", node->id(), node->op()->mnemonic()));
+      VisitNode(node, info->use, NULL);
+      TRACE(("  ==> output "));
+      PrintInfo(info->output);
+      TRACE(("\n"));
+    }
+
+    // Run lowering and change insertion phase.
+    TRACE(("--{Simplified lowering phase}--\n"));
+    phase_ = LOWER;
+    // Process nodes from the collected {nodes_} vector.
+    for (NodeVector::iterator i = nodes_.begin(); i != nodes_.end(); ++i) {
+      Node* node = *i;
+      TRACE((" visit #%d: %s\n", node->id(), node->op()->mnemonic()));
+      // Reuse {VisitNode()} so the representation rules are in one place.
+      VisitNode(node, GetUseInfo(node), lowering);
+    }
+
+    // Perform the final replacements.
+    for (NodeVector::iterator i = replacements_.begin();
+         i != replacements_.end(); ++i) {
+      Node* node = *i;
+      Node* replacement = *(++i);
+      node->ReplaceUses(replacement);
+    }
+  }
+
+  // Enqueue {node} if the {use} contains new information for that node.
+  // Add {node} to {nodes_} if this is the first time it's been visited.
+  void Enqueue(Node* node, MachineTypeUnion use = 0) {
+    if (phase_ != PROPAGATE) return;
+    NodeInfo* info = GetInfo(node);
+    if (!info->visited) {
+      // First visit of this node.
+      info->visited = true;
+      info->queued = true;
+      nodes_.push_back(node);
+      queue_.push(node);
+      TRACE(("  initial: "));
+      info->use |= use;
+      PrintUseInfo(node);
+      return;
+    }
+    TRACE(("   queue?: "));
+    PrintUseInfo(node);
+    if ((info->use & use) != use) {
+      // New usage information for the node is available.
+      if (!info->queued) {
+        queue_.push(node);
+        info->queued = true;
+        TRACE(("   added: "));
+      } else {
+        TRACE((" inqueue: "));
+      }
+      info->use |= use;
+      PrintUseInfo(node);
+    }
+  }
+
+  bool lower() { return phase_ == LOWER; }
+
+  void Enqueue(Node* node, MachineType use) {
+    Enqueue(node, static_cast<MachineTypeUnion>(use));
+  }
+
+  void SetOutput(Node* node, MachineTypeUnion output) {
+    // Every node should have at most one output representation. Note that
+    // phis can have 0, if they have not been used in a representation-inducing
+    // instruction.
+    DCHECK((output & kRepMask) == 0 ||
+           base::bits::IsPowerOfTwo32(output & kRepMask));
+    GetInfo(node)->output = output;
+  }
+
+  bool BothInputsAre(Node* node, Type* type) {
+    DCHECK_EQ(2, node->InputCount());
+    return NodeProperties::GetBounds(node->InputAt(0)).upper->Is(type) &&
+           NodeProperties::GetBounds(node->InputAt(1)).upper->Is(type);
+  }
+
+  void ProcessInput(Node* node, int index, MachineTypeUnion use) {
+    Node* input = node->InputAt(index);
+    if (phase_ == PROPAGATE) {
+      // In the propagate phase, propagate the usage information backward.
+      Enqueue(input, use);
+    } else {
+      // In the change phase, insert a change before the use if necessary.
+      if ((use & kRepMask) == 0) return;  // No input requirement on the use.
+      MachineTypeUnion output = GetInfo(input)->output;
+      if ((output & kRepMask & use) == 0) {
+        // Output representation doesn't match usage.
+        TRACE(("  change: #%d:%s(@%d #%d:%s) ", node->id(),
+               node->op()->mnemonic(), index, input->id(),
+               input->op()->mnemonic()));
+        TRACE((" from "));
+        PrintInfo(output);
+        TRACE((" to "));
+        PrintInfo(use);
+        TRACE(("\n"));
+        Node* n = changer_->GetRepresentationFor(input, output, use);
+        node->ReplaceInput(index, n);
+      }
+    }
+  }
+
+  void ProcessRemainingInputs(Node* node, int index) {
+    DCHECK_GE(index, NodeProperties::PastValueIndex(node));
+    DCHECK_GE(index, NodeProperties::PastContextIndex(node));
+    for (int i = std::max(index, NodeProperties::FirstEffectIndex(node));
+         i < NodeProperties::PastEffectIndex(node); ++i) {
+      Enqueue(node->InputAt(i));  // Effect inputs: just visit
+    }
+    for (int i = std::max(index, NodeProperties::FirstControlIndex(node));
+         i < NodeProperties::PastControlIndex(node); ++i) {
+      Enqueue(node->InputAt(i));  // Control inputs: just visit
+    }
+  }
+
+  // The default, most general visitation case. For {node}, process all value,
+  // context, effect, and control inputs, assuming that value inputs should have
+  // {kRepTagged} representation and can observe all output values {kTypeAny}.
+  void VisitInputs(Node* node) {
+    InputIter i = node->inputs().begin();
+    for (int j = OperatorProperties::GetValueInputCount(node->op()); j > 0;
+         ++i, j--) {
+      ProcessInput(node, i.index(), kMachAnyTagged);  // Value inputs
+    }
+    for (int j = OperatorProperties::GetContextInputCount(node->op()); j > 0;
+         ++i, j--) {
+      ProcessInput(node, i.index(), kMachAnyTagged);  // Context inputs
+    }
+    for (int j = OperatorProperties::GetEffectInputCount(node->op()); j > 0;
+         ++i, j--) {
+      Enqueue(*i);  // Effect inputs: just visit
+    }
+    for (int j = OperatorProperties::GetControlInputCount(node->op()); j > 0;
+         ++i, j--) {
+      Enqueue(*i);  // Control inputs: just visit
+    }
+    SetOutput(node, kMachAnyTagged);
+  }
+
+  // Helper for binops of the I x I -> O variety.
+  void VisitBinop(Node* node, MachineTypeUnion input_use,
+                  MachineTypeUnion output) {
+    DCHECK_EQ(2, node->InputCount());
+    ProcessInput(node, 0, input_use);
+    ProcessInput(node, 1, input_use);
+    SetOutput(node, output);
+  }
+
+  // Helper for unops of the I -> O variety.
+  void VisitUnop(Node* node, MachineTypeUnion input_use,
+                 MachineTypeUnion output) {
+    DCHECK_EQ(1, node->InputCount());
+    ProcessInput(node, 0, input_use);
+    SetOutput(node, output);
+  }
+
+  // Helper for leaf nodes.
+  void VisitLeaf(Node* node, MachineTypeUnion output) {
+    DCHECK_EQ(0, node->InputCount());
+    SetOutput(node, output);
+  }
+
+  // Helpers for specific types of binops.
+  void VisitFloat64Binop(Node* node) {
+    VisitBinop(node, kMachFloat64, kMachFloat64);
+  }
+  void VisitInt32Binop(Node* node) { VisitBinop(node, kMachInt32, kMachInt32); }
+  void VisitUint32Binop(Node* node) {
+    VisitBinop(node, kMachUint32, kMachUint32);
+  }
+  void VisitInt64Binop(Node* node) { VisitBinop(node, kMachInt64, kMachInt64); }
+  void VisitUint64Binop(Node* node) {
+    VisitBinop(node, kMachUint64, kMachUint64);
+  }
+  void VisitFloat64Cmp(Node* node) { VisitBinop(node, kMachFloat64, kRepBit); }
+  void VisitInt32Cmp(Node* node) { VisitBinop(node, kMachInt32, kRepBit); }
+  void VisitUint32Cmp(Node* node) { VisitBinop(node, kMachUint32, kRepBit); }
+  void VisitInt64Cmp(Node* node) { VisitBinop(node, kMachInt64, kRepBit); }
+  void VisitUint64Cmp(Node* node) { VisitBinop(node, kMachUint64, kRepBit); }
+
+  // Helper for handling phis.
+  void VisitPhi(Node* node, MachineTypeUnion use,
+                SimplifiedLowering* lowering) {
+    // First, propagate the usage information to inputs of the phi.
+    if (!lower()) {
+      int values = OperatorProperties::GetValueInputCount(node->op());
+      // Propagate {use} of the phi to value inputs, and 0 to control.
+      Node::Inputs inputs = node->inputs();
+      for (Node::Inputs::iterator iter(inputs.begin()); iter != inputs.end();
+           ++iter, --values) {
+        // TODO(titzer): it'd be nice to have distinguished edge kinds here.
+        ProcessInput(node, iter.index(), values > 0 ? use : 0);
+      }
+    }
+    // Phis adapt to whatever output representation their uses demand,
+    // pushing representation changes to their inputs.
+    MachineTypeUnion use_rep = GetUseInfo(node) & kRepMask;
+    MachineTypeUnion use_type = GetUseInfo(node) & kTypeMask;
+    MachineTypeUnion rep = 0;
+    if (use_rep & kRepTagged) {
+      rep = kRepTagged;  // Tagged overrides everything.
+    } else if (use_rep & kRepFloat64) {
+      rep = kRepFloat64;
+    } else if (use_rep & kRepWord64) {
+      rep = kRepWord64;
+    } else if (use_rep & kRepWord32) {
+      rep = kRepWord32;
+    } else if (use_rep & kRepBit) {
+      rep = kRepBit;
+    } else {
+      // There was no representation associated with any of the uses.
+      // TODO(titzer): Select the best rep using phi's type, not the usage type?
+      if (use_type & kTypeAny) {
+        rep = kRepTagged;
+      } else if (use_type & kTypeNumber) {
+        rep = kRepFloat64;
+      } else if (use_type & kTypeInt64 || use_type & kTypeUint64) {
+        rep = kRepWord64;
+      } else if (use_type & kTypeInt32 || use_type & kTypeUint32) {
+        rep = kRepWord32;
+      } else if (use_type & kTypeBool) {
+        rep = kRepBit;
+      } else {
+        UNREACHABLE();  // should have at least a usage type!
+      }
+    }
+    // Preserve the usage type, but set the representation.
+    Type* upper = NodeProperties::GetBounds(node).upper;
+    MachineTypeUnion output_type = rep | changer_->TypeFromUpperBound(upper);
+    SetOutput(node, output_type);
+
+    if (lower()) {
+      int values = OperatorProperties::GetValueInputCount(node->op());
+
+      // Update the phi operator.
+      MachineType type = static_cast<MachineType>(output_type);
+      if (type != OpParameter<MachineType>(node)) {
+        node->set_op(lowering->common()->Phi(type, values));
+      }
+
+      // Convert inputs to the output representation of this phi.
+      Node::Inputs inputs = node->inputs();
+      for (Node::Inputs::iterator iter(inputs.begin()); iter != inputs.end();
+           ++iter, --values) {
+        // TODO(titzer): it'd be nice to have distinguished edge kinds here.
+        ProcessInput(node, iter.index(), values > 0 ? output_type : 0);
+      }
+    }
+  }
+
+  const Operator* Int32Op(Node* node) {
+    return changer_->Int32OperatorFor(node->opcode());
+  }
+
+  const Operator* Uint32Op(Node* node) {
+    return changer_->Uint32OperatorFor(node->opcode());
+  }
+
+  const Operator* Float64Op(Node* node) {
+    return changer_->Float64OperatorFor(node->opcode());
+  }
+
+  static MachineType AssumeImplicitFloat32Change(MachineType type) {
+    // TODO(titzer): Assume loads of float32 change representation to float64.
+    // Fix this with full support for float32 representations.
+    if (type & kRepFloat32) {
+      return static_cast<MachineType>((type & ~kRepFloat32) | kRepFloat64);
+    }
+    return type;
+  }
+
+  // Dispatching routine for visiting the node {node} with the usage {use}.
+  // Depending on the operator, propagate new usage info to the inputs.
+  void VisitNode(Node* node, MachineTypeUnion use,
+                 SimplifiedLowering* lowering) {
+    switch (node->opcode()) {
+      //------------------------------------------------------------------
+      // Common operators.
+      //------------------------------------------------------------------
+      case IrOpcode::kStart:
+      case IrOpcode::kDead:
+        return VisitLeaf(node, 0);
+      case IrOpcode::kParameter: {
+        // TODO(titzer): use representation from linkage.
+        Type* upper = NodeProperties::GetBounds(node).upper;
+        ProcessInput(node, 0, 0);
+        SetOutput(node, kRepTagged | changer_->TypeFromUpperBound(upper));
+        return;
+      }
+      case IrOpcode::kInt32Constant:
+        return VisitLeaf(node, kRepWord32);
+      case IrOpcode::kInt64Constant:
+        return VisitLeaf(node, kRepWord64);
+      case IrOpcode::kFloat64Constant:
+        return VisitLeaf(node, kRepFloat64);
+      case IrOpcode::kExternalConstant:
+        return VisitLeaf(node, kMachPtr);
+      case IrOpcode::kNumberConstant:
+        return VisitLeaf(node, kRepTagged);
+      case IrOpcode::kHeapConstant:
+        return VisitLeaf(node, kRepTagged);
+
+      case IrOpcode::kEnd:
+      case IrOpcode::kIfTrue:
+      case IrOpcode::kIfFalse:
+      case IrOpcode::kReturn:
+      case IrOpcode::kMerge:
+      case IrOpcode::kThrow:
+        return VisitInputs(node);  // default visit for all node inputs.
+
+      case IrOpcode::kBranch:
+        ProcessInput(node, 0, kRepBit);
+        Enqueue(NodeProperties::GetControlInput(node, 0));
+        break;
+      case IrOpcode::kPhi:
+        return VisitPhi(node, use, lowering);
+
+//------------------------------------------------------------------
+// JavaScript operators.
+//------------------------------------------------------------------
+// For now, we assume that all JS operators were too complex to lower
+// to Simplified and that they will always require tagged value inputs
+// and produce tagged value outputs.
+// TODO(turbofan): it might be possible to lower some JSOperators here,
+// but that responsibility really lies in the typed lowering phase.
+#define DEFINE_JS_CASE(x) case IrOpcode::k##x:
+        JS_OP_LIST(DEFINE_JS_CASE)
+#undef DEFINE_JS_CASE
+        contains_js_nodes_ = true;
+        VisitInputs(node);
+        return SetOutput(node, kRepTagged);
+
+      //------------------------------------------------------------------
+      // Simplified operators.
+      //------------------------------------------------------------------
+      case IrOpcode::kBooleanNot: {
+        if (lower()) {
+          MachineTypeUnion input = GetInfo(node->InputAt(0))->output;
+          if (input & kRepBit) {
+            // BooleanNot(x: kRepBit) => WordEqual(x, #0)
+            node->set_op(lowering->machine()->WordEqual());
+            node->AppendInput(jsgraph_->zone(), jsgraph_->Int32Constant(0));
+          } else {
+            // BooleanNot(x: kRepTagged) => WordEqual(x, #false)
+            node->set_op(lowering->machine()->WordEqual());
+            node->AppendInput(jsgraph_->zone(), jsgraph_->FalseConstant());
+          }
+        } else {
+          // No input representation requirement; adapt during lowering.
+          ProcessInput(node, 0, kTypeBool);
+          SetOutput(node, kRepBit);
+        }
+        break;
+      }
+      case IrOpcode::kBooleanToNumber: {
+        if (lower()) {
+          MachineTypeUnion input = GetInfo(node->InputAt(0))->output;
+          if (input & kRepBit) {
+            // BooleanToNumber(x: kRepBit) => x
+            DeferReplacement(node, node->InputAt(0));
+          } else {
+            // BooleanToNumber(x: kRepTagged) => WordEqual(x, #true)
+            node->set_op(lowering->machine()->WordEqual());
+            node->AppendInput(jsgraph_->zone(), jsgraph_->TrueConstant());
+          }
+        } else {
+          // No input representation requirement; adapt during lowering.
+          ProcessInput(node, 0, kTypeBool);
+          SetOutput(node, kMachInt32);
+        }
+        break;
+      }
+      case IrOpcode::kNumberEqual:
+      case IrOpcode::kNumberLessThan:
+      case IrOpcode::kNumberLessThanOrEqual: {
+        // Number comparisons reduce to integer comparisons for integer inputs.
+        if (BothInputsAre(node, Type::Signed32())) {
+          // => signed Int32Cmp
+          VisitInt32Cmp(node);
+          if (lower()) node->set_op(Int32Op(node));
+        } else if (BothInputsAre(node, Type::Unsigned32())) {
+          // => unsigned Int32Cmp
+          VisitUint32Cmp(node);
+          if (lower()) node->set_op(Uint32Op(node));
+        } else {
+          // => Float64Cmp
+          VisitFloat64Cmp(node);
+          if (lower()) node->set_op(Float64Op(node));
+        }
+        break;
+      }
+      case IrOpcode::kNumberAdd:
+      case IrOpcode::kNumberSubtract: {
+        // Add and subtract reduce to Int32Add/Sub if the inputs
+        // are already integers and all uses are truncating.
+        if (BothInputsAre(node, Type::Signed32()) &&
+            (use & (kTypeUint32 | kTypeNumber | kTypeAny)) == 0) {
+          // => signed Int32Add/Sub
+          VisitInt32Binop(node);
+          if (lower()) node->set_op(Int32Op(node));
+        } else if (BothInputsAre(node, Type::Unsigned32()) &&
+                   (use & (kTypeInt32 | kTypeNumber | kTypeAny)) == 0) {
+          // => unsigned Int32Add/Sub
+          VisitUint32Binop(node);
+          if (lower()) node->set_op(Uint32Op(node));
+        } else {
+          // => Float64Add/Sub
+          VisitFloat64Binop(node);
+          if (lower()) node->set_op(Float64Op(node));
+        }
+        break;
+      }
+      case IrOpcode::kNumberMultiply:
+      case IrOpcode::kNumberDivide:
+      case IrOpcode::kNumberModulus: {
+        // Float64Mul/Div/Mod
+        VisitFloat64Binop(node);
+        if (lower()) node->set_op(Float64Op(node));
+        break;
+      }
+      case IrOpcode::kNumberToInt32: {
+        MachineTypeUnion use_rep = use & kRepMask;
+        if (lower()) {
+          MachineTypeUnion in = GetInfo(node->InputAt(0))->output;
+          if ((in & kTypeMask) == kTypeInt32 || (in & kRepMask) == kRepWord32) {
+            // If the input has type int32, or is already a word32, just change
+            // representation if necessary.
+            VisitUnop(node, kTypeInt32 | use_rep, kTypeInt32 | use_rep);
+            DeferReplacement(node, node->InputAt(0));
+          } else {
+            // Require the input in float64 format and perform truncation.
+            // TODO(turbofan): avoid a truncation with a smi check.
+            VisitUnop(node, kTypeInt32 | kRepFloat64, kTypeInt32 | kRepWord32);
+            node->set_op(lowering->machine()->TruncateFloat64ToInt32());
+          }
+        } else {
+          // Propagate a type to the input, but pass through representation.
+          VisitUnop(node, kTypeInt32, kTypeInt32 | use_rep);
+        }
+        break;
+      }
+      case IrOpcode::kNumberToUint32: {
+        MachineTypeUnion use_rep = use & kRepMask;
+        if (lower()) {
+          MachineTypeUnion in = GetInfo(node->InputAt(0))->output;
+          if ((in & kTypeMask) == kTypeUint32 ||
+              (in & kRepMask) == kRepWord32) {
+            // The input has type int32, just change representation.
+            VisitUnop(node, kTypeUint32 | use_rep, kTypeUint32 | use_rep);
+            DeferReplacement(node, node->InputAt(0));
+          } else {
+            // Require the input in float64 format to perform truncation.
+            // TODO(turbofan): avoid the truncation with a smi check.
+            VisitUnop(node, kTypeUint32 | kRepFloat64,
+                      kTypeUint32 | kRepWord32);
+            node->set_op(lowering->machine()->TruncateFloat64ToInt32());
+          }
+        } else {
+          // Propagate a type to the input, but pass through representation.
+          VisitUnop(node, kTypeUint32, kTypeUint32 | use_rep);
+        }
+        break;
+      }
+      case IrOpcode::kReferenceEqual: {
+        VisitBinop(node, kMachAnyTagged, kRepBit);
+        if (lower()) node->set_op(lowering->machine()->WordEqual());
+        break;
+      }
+      case IrOpcode::kStringEqual: {
+        VisitBinop(node, kMachAnyTagged, kRepBit);
+        if (lower()) lowering->DoStringEqual(node);
+        break;
+      }
+      case IrOpcode::kStringLessThan: {
+        VisitBinop(node, kMachAnyTagged, kRepBit);
+        if (lower()) lowering->DoStringLessThan(node);
+        break;
+      }
+      case IrOpcode::kStringLessThanOrEqual: {
+        VisitBinop(node, kMachAnyTagged, kRepBit);
+        if (lower()) lowering->DoStringLessThanOrEqual(node);
+        break;
+      }
+      case IrOpcode::kStringAdd: {
+        VisitBinop(node, kMachAnyTagged, kMachAnyTagged);
+        if (lower()) lowering->DoStringAdd(node);
+        break;
+      }
+      case IrOpcode::kLoadField: {
+        FieldAccess access = FieldAccessOf(node->op());
+        ProcessInput(node, 0, changer_->TypeForBasePointer(access));
+        ProcessRemainingInputs(node, 1);
+        SetOutput(node, AssumeImplicitFloat32Change(access.machine_type));
+        if (lower()) lowering->DoLoadField(node);
+        break;
+      }
+      case IrOpcode::kStoreField: {
+        FieldAccess access = FieldAccessOf(node->op());
+        ProcessInput(node, 0, changer_->TypeForBasePointer(access));
+        ProcessInput(node, 1, AssumeImplicitFloat32Change(access.machine_type));
+        ProcessRemainingInputs(node, 2);
+        SetOutput(node, 0);
+        if (lower()) lowering->DoStoreField(node);
+        break;
+      }
+      case IrOpcode::kLoadElement: {
+        ElementAccess access = ElementAccessOf(node->op());
+        ProcessInput(node, 0, changer_->TypeForBasePointer(access));
+        ProcessInput(node, 1, kMachInt32);  // element index
+        ProcessInput(node, 2, kMachInt32);  // length
+        ProcessRemainingInputs(node, 3);
+        SetOutput(node, AssumeImplicitFloat32Change(access.machine_type));
+        if (lower()) lowering->DoLoadElement(node);
+        break;
+      }
+      case IrOpcode::kStoreElement: {
+        ElementAccess access = ElementAccessOf(node->op());
+        ProcessInput(node, 0, changer_->TypeForBasePointer(access));
+        ProcessInput(node, 1, kMachInt32);  // element index
+        ProcessInput(node, 2, kMachInt32);  // length
+        ProcessInput(node, 3, AssumeImplicitFloat32Change(access.machine_type));
+        ProcessRemainingInputs(node, 4);
+        SetOutput(node, 0);
+        if (lower()) lowering->DoStoreElement(node);
+        break;
+      }
+
+      //------------------------------------------------------------------
+      // Machine-level operators.
+      //------------------------------------------------------------------
+      case IrOpcode::kLoad: {
+        // TODO(titzer): machine loads/stores need to know BaseTaggedness!?
+        MachineType tBase = kRepTagged;
+        LoadRepresentation rep = OpParameter<LoadRepresentation>(node);
+        ProcessInput(node, 0, tBase);   // pointer or object
+        ProcessInput(node, 1, kMachInt32);  // index
+        ProcessRemainingInputs(node, 2);
+        SetOutput(node, rep);
+        break;
+      }
+      case IrOpcode::kStore: {
+        // TODO(titzer): machine loads/stores need to know BaseTaggedness!?
+        MachineType tBase = kRepTagged;
+        StoreRepresentation rep = OpParameter<StoreRepresentation>(node);
+        ProcessInput(node, 0, tBase);   // pointer or object
+        ProcessInput(node, 1, kMachInt32);  // index
+        ProcessInput(node, 2, rep.machine_type());
+        ProcessRemainingInputs(node, 3);
+        SetOutput(node, 0);
+        break;
+      }
+      case IrOpcode::kWord32Shr:
+        // We output unsigned int32 for shift right because JavaScript.
+        return VisitBinop(node, kRepWord32, kRepWord32 | kTypeUint32);
+      case IrOpcode::kWord32And:
+      case IrOpcode::kWord32Or:
+      case IrOpcode::kWord32Xor:
+      case IrOpcode::kWord32Shl:
+      case IrOpcode::kWord32Sar:
+        // We use signed int32 as the output type for these word32 operations,
+        // though the machine bits are the same for either signed or unsigned,
+        // because JavaScript considers the result from these operations signed.
+        return VisitBinop(node, kRepWord32, kRepWord32 | kTypeInt32);
+      case IrOpcode::kWord32Equal:
+        return VisitBinop(node, kRepWord32, kRepBit);
+
+      case IrOpcode::kInt32Add:
+      case IrOpcode::kInt32Sub:
+      case IrOpcode::kInt32Mul:
+      case IrOpcode::kInt32Div:
+      case IrOpcode::kInt32Mod:
+        return VisitInt32Binop(node);
+      case IrOpcode::kInt32UDiv:
+      case IrOpcode::kInt32UMod:
+        return VisitUint32Binop(node);
+      case IrOpcode::kInt32LessThan:
+      case IrOpcode::kInt32LessThanOrEqual:
+        return VisitInt32Cmp(node);
+
+      case IrOpcode::kUint32LessThan:
+      case IrOpcode::kUint32LessThanOrEqual:
+        return VisitUint32Cmp(node);
+
+      case IrOpcode::kInt64Add:
+      case IrOpcode::kInt64Sub:
+      case IrOpcode::kInt64Mul:
+      case IrOpcode::kInt64Div:
+      case IrOpcode::kInt64Mod:
+        return VisitInt64Binop(node);
+      case IrOpcode::kInt64LessThan:
+      case IrOpcode::kInt64LessThanOrEqual:
+        return VisitInt64Cmp(node);
+
+      case IrOpcode::kInt64UDiv:
+      case IrOpcode::kInt64UMod:
+        return VisitUint64Binop(node);
+
+      case IrOpcode::kWord64And:
+      case IrOpcode::kWord64Or:
+      case IrOpcode::kWord64Xor:
+      case IrOpcode::kWord64Shl:
+      case IrOpcode::kWord64Shr:
+      case IrOpcode::kWord64Sar:
+        return VisitBinop(node, kRepWord64, kRepWord64);
+      case IrOpcode::kWord64Equal:
+        return VisitBinop(node, kRepWord64, kRepBit);
+
+      case IrOpcode::kChangeInt32ToInt64:
+        return VisitUnop(node, kTypeInt32 | kRepWord32,
+                         kTypeInt32 | kRepWord64);
+      case IrOpcode::kChangeUint32ToUint64:
+        return VisitUnop(node, kTypeUint32 | kRepWord32,
+                         kTypeUint32 | kRepWord64);
+      case IrOpcode::kTruncateInt64ToInt32:
+        // TODO(titzer): Is kTypeInt32 correct here?
+        return VisitUnop(node, kTypeInt32 | kRepWord64,
+                         kTypeInt32 | kRepWord32);
+
+      case IrOpcode::kChangeInt32ToFloat64:
+        return VisitUnop(node, kTypeInt32 | kRepWord32,
+                         kTypeInt32 | kRepFloat64);
+      case IrOpcode::kChangeUint32ToFloat64:
+        return VisitUnop(node, kTypeUint32 | kRepWord32,
+                         kTypeUint32 | kRepFloat64);
+      case IrOpcode::kChangeFloat64ToInt32:
+        return VisitUnop(node, kTypeInt32 | kRepFloat64,
+                         kTypeInt32 | kRepWord32);
+      case IrOpcode::kChangeFloat64ToUint32:
+        return VisitUnop(node, kTypeUint32 | kRepFloat64,
+                         kTypeUint32 | kRepWord32);
+
+      case IrOpcode::kFloat64Add:
+      case IrOpcode::kFloat64Sub:
+      case IrOpcode::kFloat64Mul:
+      case IrOpcode::kFloat64Div:
+      case IrOpcode::kFloat64Mod:
+        return VisitFloat64Binop(node);
+      case IrOpcode::kFloat64Sqrt:
+        return VisitUnop(node, kMachFloat64, kMachFloat64);
+      case IrOpcode::kFloat64Equal:
+      case IrOpcode::kFloat64LessThan:
+      case IrOpcode::kFloat64LessThanOrEqual:
+        return VisitFloat64Cmp(node);
+      default:
+        VisitInputs(node);
+        break;
+    }
+  }
+
+  void DeferReplacement(Node* node, Node* replacement) {
+    if (replacement->id() < count_) {
+      // Replace with a previously existing node eagerly.
+      node->ReplaceUses(replacement);
+    } else {
+      // Otherwise, we are replacing a node with a representation change.
+      // Such a substitution must be done after all lowering is done, because
+      // new nodes do not have {NodeInfo} entries, and that would confuse
+      // the representation change insertion for uses of it.
+      replacements_.push_back(node);
+      replacements_.push_back(replacement);
+    }
+    // TODO(titzer) node->RemoveAllInputs();  // Node is now dead.
+  }
+
+  void PrintUseInfo(Node* node) {
+    TRACE(("#%d:%-20s ", node->id(), node->op()->mnemonic()));
+    PrintInfo(GetUseInfo(node));
+    TRACE(("\n"));
+  }
+
+  void PrintInfo(MachineTypeUnion info) {
+    if (FLAG_trace_representation) {
+      OFStream os(stdout);
+      os << static_cast<MachineType>(info);
+    }
+  }
+
+ private:
+  JSGraph* jsgraph_;
+  int count_;                       // number of nodes in the graph
+  NodeInfo* info_;                  // node id -> usage information
+  NodeVector nodes_;                // collected nodes
+  NodeVector replacements_;         // replacements to be done after lowering
+  bool contains_js_nodes_;          // {true} if a JS operator was seen
+  Phase phase_;                     // current phase of algorithm
+  RepresentationChanger* changer_;  // for inserting representation changes
+  ZoneQueue<Node*> queue_;          // queue for traversing the graph
+
+  NodeInfo* GetInfo(Node* node) {
+    DCHECK(node->id() >= 0);
+    DCHECK(node->id() < count_);
+    return &info_[node->id()];
+  }
+
+  MachineTypeUnion GetUseInfo(Node* node) { return GetInfo(node)->use; }
+};
+
+
+Node* SimplifiedLowering::IsTagged(Node* node) {
+  // TODO(titzer): factor this out to a TaggingScheme abstraction.
+  STATIC_ASSERT(kSmiTagMask == 1);  // Only works if tag is the low bit.
+  return graph()->NewNode(machine()->WordAnd(), node,
+                          jsgraph()->Int32Constant(kSmiTagMask));
+}
+
+
+void SimplifiedLowering::LowerAllNodes() {
+  SimplifiedOperatorBuilder simplified(graph()->zone());
+  RepresentationChanger changer(jsgraph(), &simplified,
+                                graph()->zone()->isolate());
+  RepresentationSelector selector(jsgraph(), zone(), &changer);
+  selector.Run(this);
+}
+
+
+Node* SimplifiedLowering::Untag(Node* node) {
+  // TODO(titzer): factor this out to a TaggingScheme abstraction.
+  Node* shift_amount = jsgraph()->Int32Constant(kSmiTagSize + kSmiShiftSize);
+  return graph()->NewNode(machine()->WordSar(), node, shift_amount);
+}
+
+
+Node* SimplifiedLowering::SmiTag(Node* node) {
+  // TODO(titzer): factor this out to a TaggingScheme abstraction.
+  Node* shift_amount = jsgraph()->Int32Constant(kSmiTagSize + kSmiShiftSize);
+  return graph()->NewNode(machine()->WordShl(), node, shift_amount);
+}
+
+
+Node* SimplifiedLowering::OffsetMinusTagConstant(int32_t offset) {
+  return jsgraph()->Int32Constant(offset - kHeapObjectTag);
+}
+
+
+static WriteBarrierKind ComputeWriteBarrierKind(BaseTaggedness base_is_tagged,
+                                                MachineType representation,
+                                                Type* type) {
+  // TODO(turbofan): skip write barriers for Smis, etc.
+  if (base_is_tagged == kTaggedBase &&
+      RepresentationOf(representation) == kRepTagged) {
+    // Write barriers are only for writes into heap objects (i.e. tagged base).
+    return kFullWriteBarrier;
+  }
+  return kNoWriteBarrier;
+}
+
+
+void SimplifiedLowering::DoLoadField(Node* node) {
+  const FieldAccess& access = FieldAccessOf(node->op());
+  node->set_op(machine()->Load(access.machine_type));
+  Node* offset = jsgraph()->Int32Constant(access.offset - access.tag());
+  node->InsertInput(zone(), 1, offset);
+}
+
+
+void SimplifiedLowering::DoStoreField(Node* node) {
+  const FieldAccess& access = FieldAccessOf(node->op());
+  WriteBarrierKind kind = ComputeWriteBarrierKind(
+      access.base_is_tagged, access.machine_type, access.type);
+  node->set_op(
+      machine()->Store(StoreRepresentation(access.machine_type, kind)));
+  Node* offset = jsgraph()->Int32Constant(access.offset - access.tag());
+  node->InsertInput(zone(), 1, offset);
+}
+
+
+Node* SimplifiedLowering::ComputeIndex(const ElementAccess& access,
+                                       Node* index) {
+  int element_size = ElementSizeOf(access.machine_type);
+  if (element_size != 1) {
+    index = graph()->NewNode(machine()->Int32Mul(),
+                             jsgraph()->Int32Constant(element_size), index);
+  }
+  int fixed_offset = access.header_size - access.tag();
+  if (fixed_offset == 0) return index;
+  return graph()->NewNode(machine()->Int32Add(), index,
+                          jsgraph()->Int32Constant(fixed_offset));
+}
+
+
+void SimplifiedLowering::DoLoadElement(Node* node) {
+  const ElementAccess& access = ElementAccessOf(node->op());
+  node->set_op(machine()->Load(access.machine_type));
+  node->ReplaceInput(1, ComputeIndex(access, node->InputAt(1)));
+  node->RemoveInput(2);
+}
+
+
+void SimplifiedLowering::DoStoreElement(Node* node) {
+  const ElementAccess& access = ElementAccessOf(node->op());
+  WriteBarrierKind kind = ComputeWriteBarrierKind(
+      access.base_is_tagged, access.machine_type, access.type);
+  node->set_op(
+      machine()->Store(StoreRepresentation(access.machine_type, kind)));
+  node->ReplaceInput(1, ComputeIndex(access, node->InputAt(1)));
+  node->RemoveInput(2);
+}
+
+
+void SimplifiedLowering::DoStringAdd(Node* node) {
+  Callable callable = CodeFactory::StringAdd(
+      zone()->isolate(), STRING_ADD_CHECK_NONE, NOT_TENURED);
+  CallDescriptor::Flags flags = CallDescriptor::kNoFlags;
+  CallDescriptor* desc =
+      Linkage::GetStubCallDescriptor(callable.descriptor(), 0, flags, zone());
+  node->set_op(common()->Call(desc));
+  node->InsertInput(zone(), 0, jsgraph()->HeapConstant(callable.code()));
+  node->AppendInput(zone(), jsgraph()->UndefinedConstant());
+  node->AppendInput(zone(), graph()->start());
+  node->AppendInput(zone(), graph()->start());
+}
+
+
+Node* SimplifiedLowering::StringComparison(Node* node, bool requires_ordering) {
+  CEntryStub stub(zone()->isolate(), 1);
+  Runtime::FunctionId f =
+      requires_ordering ? Runtime::kStringCompare : Runtime::kStringEquals;
+  ExternalReference ref(f, zone()->isolate());
+  Operator::Properties props = node->op()->properties();
+  // TODO(mstarzinger): We should call StringCompareStub here instead, once an
+  // interface descriptor is available for it.
+  CallDescriptor* desc = Linkage::GetRuntimeCallDescriptor(f, 2, props, zone());
+  return graph()->NewNode(common()->Call(desc),
+                          jsgraph()->HeapConstant(stub.GetCode()),
+                          NodeProperties::GetValueInput(node, 0),
+                          NodeProperties::GetValueInput(node, 1),
+                          jsgraph()->ExternalConstant(ref),
+                          jsgraph()->Int32Constant(2),
+                          jsgraph()->UndefinedConstant());
+}
+
+
+void SimplifiedLowering::DoStringEqual(Node* node) {
+  node->set_op(machine()->WordEqual());
+  node->ReplaceInput(0, StringComparison(node, false));
+  node->ReplaceInput(1, jsgraph()->SmiConstant(EQUAL));
+}
+
+
+void SimplifiedLowering::DoStringLessThan(Node* node) {
+  node->set_op(machine()->IntLessThan());
+  node->ReplaceInput(0, StringComparison(node, true));
+  node->ReplaceInput(1, jsgraph()->SmiConstant(EQUAL));
+}
+
+
+void SimplifiedLowering::DoStringLessThanOrEqual(Node* node) {
+  node->set_op(machine()->IntLessThanOrEqual());
+  node->ReplaceInput(0, StringComparison(node, true));
+  node->ReplaceInput(1, jsgraph()->SmiConstant(EQUAL));
+}
+
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8