diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
new file mode 100644
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--- /dev/null
+++ b/src/IceTargetLowering.h
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+//===- subzero/src/IceTargetLowering.h - Lowering interface -----*- C++ -*-===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the TargetLowering and LoweringContext
+// classes.  TargetLowering is an abstract class used to drive the
+// translation/lowering process.  LoweringContext maintains a
+// context for lowering each instruction, offering conveniences such
+// as iterating over non-deleted instructions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SUBZERO_SRC_ICETARGETLOWERING_H
+#define SUBZERO_SRC_ICETARGETLOWERING_H
+
+#include "IceDefs.h"
+#include "IceTypes.h"
+
+#include "IceInst.h" // for the names of the Inst subtypes
+
+namespace Ice {
+
+// LoweringContext makes it easy to iterate through non-deleted
+// instructions in a node, and insert new (lowered) instructions at
+// the current point.  Along with the instruction list container and
+// associated iterators, it holds the current node, which is needed
+// when inserting new instructions in order to track whether variables
+// are used as single-block or multi-block.
+class LoweringContext {
+public:
+  LoweringContext() : Node(NULL) {}
+  ~LoweringContext() {}
+  void init(CfgNode *Node);
+  Inst *getNextInst() const {
+    if (Next == End)
+      return NULL;
+    return *Next;
+  }
+  CfgNode *getNode() const { return Node; }
+  bool atEnd() const { return Cur == End; }
+  InstList::iterator getCur() const { return Cur; }
+  InstList::iterator getEnd() const { return End; }
+  void insert(Inst *Inst);
+  void advanceCur() { Cur = Next; }
+  void advanceNext() { advance(Next); }
+  void setInsertPoint(const InstList::iterator &Position) { Next = Position; }
+
+private:
+  // Node is the argument to Inst::updateVars().
+  CfgNode *Node;
+  // Cur points to the current instruction being considered.  It is
+  // guaranteed to point to a non-deleted instruction, or to be End.
+  InstList::iterator Cur;
+  // Next doubles as a pointer to the next valid instruction (if any),
+  // and the new-instruction insertion point.  It is also updated for
+  // the caller in case the lowering consumes more than one high-level
+  // instruction.  It is guaranteed to point to a non-deleted
+  // instruction after Cur, or to be End.  TODO: Consider separating
+  // the notion of "next valid instruction" and "new instruction
+  // insertion point", to avoid confusion when previously-deleted
+  // instructions come between the two points.
+  InstList::iterator Next;
+  // End is a copy of Insts.end(), used if Next needs to be advanced.
+  InstList::iterator End;
+
+  void skipDeleted(InstList::iterator &I);
+  void advance(InstList::iterator &I);
+  LoweringContext(const LoweringContext &) LLVM_DELETED_FUNCTION;
+  LoweringContext &operator=(const LoweringContext &) LLVM_DELETED_FUNCTION;
+};
+
+class TargetLowering {
+public:
+  static TargetLowering *createLowering(TargetArch Target, Cfg *Func);
+  void translate() {
+    switch (Ctx->getOptLevel()) {
+    case Opt_m1:
+      translateOm1();
+      break;
+    case Opt_0:
+      translateO0();
+      break;
+    case Opt_1:
+      translateO1();
+      break;
+    case Opt_2:
+      translateO2();
+      break;
+    default:
+      Func->setError("Target doesn't specify lowering steps.");
+      break;
+    }
+  }
+  virtual void translateOm1() {
+    Func->setError("Target doesn't specify Om1 lowering steps.");
+  }
+  virtual void translateO0() {
+    Func->setError("Target doesn't specify O0 lowering steps.");
+  }
+  virtual void translateO1() {
+    Func->setError("Target doesn't specify O1 lowering steps.");
+  }
+  virtual void translateO2() {
+    Func->setError("Target doesn't specify O2 lowering steps.");
+  }
+
+  // Lowers a single instruction.
+  void lower();
+
+  // Returns a variable pre-colored to the specified physical
+  // register.  This is generally used to get very direct access to
+  // the register such as in the prolog or epilog or for marking
+  // scratch registers as killed by a call.
+  virtual Variable *getPhysicalRegister(SizeT RegNum) = 0;
+  // Returns a printable name for the register.
+  virtual IceString getRegName(SizeT RegNum, Type Ty) const = 0;
+
+  virtual bool hasFramePointer() const { return false; }
+  virtual SizeT getFrameOrStackReg() const = 0;
+  virtual size_t typeWidthInBytesOnStack(Type Ty) = 0;
+  bool hasComputedFrame() const { return HasComputedFrame; }
+  int32_t getStackAdjustment() const { return StackAdjustment; }
+  void updateStackAdjustment(int32_t Offset) { StackAdjustment += Offset; }
+  void resetStackAdjustment() { StackAdjustment = 0; }
+  LoweringContext &getContext() { return Context; }
+
+  enum RegSet {
+    RegSet_None = 0,
+    RegSet_CallerSave = 1 << 0,
+    RegSet_CalleeSave = 1 << 1,
+    RegSet_StackPointer = 1 << 2,
+    RegSet_FramePointer = 1 << 3,
+    RegSet_All = ~RegSet_None
+  };
+  typedef uint32_t RegSetMask;
+
+  virtual llvm::SmallBitVector getRegisterSet(RegSetMask Include,
+                                              RegSetMask Exclude) const = 0;
+  virtual const llvm::SmallBitVector &getRegisterSetForType(Type Ty) const = 0;
+  void regAlloc();
+
+  virtual void emitVariable(const Variable *Var, const Cfg *Func) const = 0;
+
+  virtual void addProlog(CfgNode *Node) = 0;
+  virtual void addEpilog(CfgNode *Node) = 0;
+
+  virtual ~TargetLowering() {}
+
+protected:
+  TargetLowering(Cfg *Func)
+      : Func(Func), Ctx(Func->getContext()), HasComputedFrame(false),
+        StackAdjustment(0) {}
+  virtual void lowerAlloca(const InstAlloca *Inst) = 0;
+  virtual void lowerArithmetic(const InstArithmetic *Inst) = 0;
+  virtual void lowerAssign(const InstAssign *Inst) = 0;
+  virtual void lowerBr(const InstBr *Inst) = 0;
+  virtual void lowerCall(const InstCall *Inst) = 0;
+  virtual void lowerCast(const InstCast *Inst) = 0;
+  virtual void lowerFcmp(const InstFcmp *Inst) = 0;
+  virtual void lowerIcmp(const InstIcmp *Inst) = 0;
+  virtual void lowerLoad(const InstLoad *Inst) = 0;
+  virtual void lowerPhi(const InstPhi *Inst) = 0;
+  virtual void lowerRet(const InstRet *Inst) = 0;
+  virtual void lowerSelect(const InstSelect *Inst) = 0;
+  virtual void lowerStore(const InstStore *Inst) = 0;
+  virtual void lowerSwitch(const InstSwitch *Inst) = 0;
+  virtual void lowerUnreachable(const InstUnreachable *Inst) = 0;
+
+  // This gives the target an opportunity to post-process the lowered
+  // expansion before returning.  The primary intention is to do some
+  // Register Manager activity as necessary, specifically to eagerly
+  // allocate registers based on affinity and other factors.  The
+  // simplest lowering does nothing here and leaves it all to a
+  // subsequent global register allocation pass.
+  virtual void postLower() {}
+
+  Cfg *Func;
+  GlobalContext *Ctx;
+  bool HasComputedFrame;
+  // StackAdjustment keeps track of the current stack offset from its
+  // natural location, as arguments are pushed for a function call.
+  int32_t StackAdjustment;
+  LoweringContext Context;
+
+private:
+  TargetLowering(const TargetLowering &) LLVM_DELETED_FUNCTION;
+  TargetLowering &operator=(const TargetLowering &) LLVM_DELETED_FUNCTION;
+};
+
+} // end of namespace Ice
+
+#endif // SUBZERO_SRC_ICETARGETLOWERING_H