New files

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5260 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/FloatingPoint.cpp

@@ -0,0 +1,587 @@
+//===-- FloatingPoint.cpp - Floating point Reg -> Stack converter ---------===//
+//
+// This file defines the pass which converts floating point instructions from
+// virtual registers into register stack instructions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "X86InstrInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/LiveVariables.h"
+#include "llvm/Target/MachineInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "Support/Statistic.h"
+#include <algorithm>
+#include <iostream>
+
+namespace {
+  Statistic<> NumFXCH("x86-codegen", "Number of fxch instructions inserted");
+  Statistic<> NumFP  ("x86-codegen", "Number of floating point instructions");
+
+  struct FPS : public MachineFunctionPass {
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+
+    virtual const char *getPassName() const { return "X86 FP Stackifier"; }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addRequired<LiveVariables>();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+  private:
+    LiveVariables     *LV;    // Live variable info for current function...
+    MachineBasicBlock *MBB;   // Current basic block
+    unsigned Stack[8];        // FP<n> Registers in each stack slot...
+    unsigned RegMap[8];       // Track which stack slot contains each register
+    unsigned StackTop;        // The current top of the FP stack.
+
+    void dumpStack() const {
+      std::cerr << "Stack contents:";
+      for (unsigned i = 0; i != StackTop; ++i) {
+	std::cerr << " FP" << Stack[i];
+	assert(RegMap[Stack[i]] == i && "Stack[] doesn't match RegMap[]!"); 
+      }
+      std::cerr << "\n";
+    }
+  private:
+    // getSlot - Return the stack slot number a particular register number is
+    // in...
+    unsigned getSlot(unsigned RegNo) const {
+      assert(RegNo < 8 && "Regno out of range!");
+      return RegMap[RegNo];
+    }
+
+    // getStackEntry - Return the X86::FP<n> register in register ST(i)
+    unsigned getStackEntry(unsigned STi) const {
+      assert(STi < StackTop && "Access past stack top!");
+      return Stack[StackTop-1-STi];
+    }
+
+    // getSTReg - Return the X86::ST(i) register which contains the specified
+    // FP<RegNo> register
+    unsigned getSTReg(unsigned RegNo) const {
+      return StackTop - 1 - getSlot(RegNo) + X86::ST0;
+    }
+
+    // pushReg - Push the specifiex FP<n> register onto the stack
+    void pushReg(unsigned Reg) {
+      assert(Reg < 8 && "Register number out of range!");
+      assert(StackTop < 8 && "Stack overflow!");
+      Stack[StackTop] = Reg;
+      RegMap[Reg] = StackTop++;
+    }
+
+    bool isAtTop(unsigned RegNo) const { return getSlot(RegNo) == StackTop-1; }
+    void moveToTop(unsigned RegNo, MachineBasicBlock::iterator &I) {
+      if (!isAtTop(RegNo)) {
+	unsigned Slot = getSlot(RegNo);
+	unsigned STReg = getSTReg(RegNo);
+	unsigned RegOnTop = getStackEntry(0);
+
+	// Swap the slots the regs are in
+	std::swap(RegMap[RegNo], RegMap[RegOnTop]);
+
+	// Swap stack slot contents
+	assert(RegMap[RegOnTop] < StackTop);
+	std::swap(Stack[RegMap[RegOnTop]], Stack[StackTop-1]);
+
+	// Emit an fxch to update the runtime processors version of the state
+	MachineInstr *MI = BuildMI(X86::FXCH, 1).addReg(STReg);
+	I = 1+MBB->insert(I, MI);
+	NumFXCH++;
+      }
+    }
+
+    void duplicateToTop(unsigned RegNo, unsigned AsReg,
+			MachineBasicBlock::iterator &I) {
+      unsigned STReg = getSTReg(RegNo);
+      pushReg(AsReg);   // New register on top of stack
+
+      MachineInstr *MI = BuildMI(X86::FLDrr, 1).addReg(STReg);
+      I = 1+MBB->insert(I, MI);
+    }
+
+    // popStackAfter - Pop the current value off of the top of the FP stack
+    // after the specified instruction.
+    void popStackAfter(MachineBasicBlock::iterator &I);
+
+    bool processBasicBlock(MachineFunction &MF, MachineBasicBlock &MBB);
+
+    void handleZeroArgFP(MachineBasicBlock::iterator &I);
+    void handleOneArgFP(MachineBasicBlock::iterator &I);
+    void handleTwoArgFP(MachineBasicBlock::iterator &I);
+    void handleSpecialFP(MachineBasicBlock::iterator &I);
+  };
+}
+
+Pass *createX86FloatingPointStackifierPass() { return new FPS(); }
+
+/// runOnMachineFunction - Loop over all of the basic blocks, transforming FP
+/// register references into FP stack references.
+///
+bool FPS::runOnMachineFunction(MachineFunction &MF) {
+  LV = &getAnalysis<LiveVariables>();
+  StackTop = 0;
+
+  bool Changed = false;
+  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
+    Changed |= processBasicBlock(MF, *I);
+  return Changed;
+}
+
+/// processBasicBlock - Loop over all of the instructions in the basic block,
+/// transforming FP instructions into their stack form.
+///
+bool FPS::processBasicBlock(MachineFunction &MF, MachineBasicBlock &BB) {
+  const TargetInstrInfo &TII = MF.getTarget().getInstrInfo();
+  bool Changed = false;
+  MBB = &BB;
+  
+  for (MachineBasicBlock::iterator I = BB.begin(); I != BB.end(); ++I) {
+    MachineInstr *MI = *I;
+    MachineInstr *PrevMI = I == BB.begin() ? 0 : *(I-1);
+    unsigned Flags = TII.get(MI->getOpcode()).TSFlags;
+
+    if ((Flags & X86II::FPTypeMask) == 0) continue;  // Ignore non-fp insts!
+
+    ++NumFP;  // Keep track of # of pseudo instrs
+    DEBUG(std::cerr << "\nFPInst:\t";
+	  MI->print(std::cerr, MF.getTarget()));
+
+    // Get dead variables list now because the MI pointer may be deleted as part
+    // of processing!
+    LiveVariables::killed_iterator IB = LV->dead_begin(MI);
+    LiveVariables::killed_iterator IE = LV->dead_end(MI);
+
+    DEBUG(const MRegisterInfo *MRI = MF.getTarget().getRegisterInfo();
+	  LiveVariables::killed_iterator I = LV->killed_begin(MI);
+	  LiveVariables::killed_iterator E = LV->killed_end(MI);
+	  if (I != E) {
+	    std::cerr << "Killed Operands:";
+	    for (; I != E; ++I)
+	      std::cerr << " %" << MRI->getName(I->second);
+	    std::cerr << "\n";
+	  });
+
+    switch (Flags & X86II::FPTypeMask) {
+    case X86II::ZeroArgFP: handleZeroArgFP(I); break;
+    case X86II::OneArgFP:  handleOneArgFP(I);  break;
+
+    case X86II::OneArgFPRW:   // ST(0) = fsqrt(ST(0))
+      assert(0 && "FP instr type not handled yet!");
+
+    case X86II::TwoArgFP:  handleTwoArgFP(I);  break;
+    case X86II::SpecialFP: handleSpecialFP(I); break;
+    default: assert(0 && "Unknown FP Type!");
+    }
+
+    // Check to see if any of the values defined by this instruction are dead
+    // after definition.  If so, pop them.
+    for (; IB != IE; ++IB) {
+      unsigned Reg = IB->second;
+      if (Reg >= X86::FP0 && Reg <= X86::FP6) {
+	DEBUG(std::cerr << "Register FP#" << Reg-X86::FP0 << " is dead!\n");
+	++I;                         // Insert fxch AFTER the instruction
+	moveToTop(Reg-X86::FP0, I);  // Insert fxch if neccesary
+	--I;                         // Move to fxch or old instruction
+	popStackAfter(I);            // Pop the top of the stack, killing value
+      }
+    }
+    
+    // Print out all of the instructions expanded to if -debug
+    DEBUG(if (*I == PrevMI) {
+            std::cerr<< "Just deleted pseudo instruction\n";
+          } else {
+	    MachineBasicBlock::iterator Start = I;
+	    // Rewind to first instruction newly inserted.
+	    while (Start != BB.begin() && *(Start-1) != PrevMI) --Start;
+	    std::cerr << "Inserted instructions:\n";
+	    do TII.print(*Start, std::cerr << "\t", MF.getTarget());
+	    while (++Start != I+1);
+	  }
+	  dumpStack();
+	  );
+
+    Changed = true;
+  }
+
+  assert(StackTop == 0 && "Stack not empty at end of basic block?");
+  return Changed;
+}
+
+//===----------------------------------------------------------------------===//
+// Efficient Lookup Table Support
+//===----------------------------------------------------------------------===//
+
+struct TableEntry {
+  unsigned from;
+  unsigned to;
+  bool operator<(const TableEntry &TE) const { return from < TE.from; }
+  bool operator<(unsigned V) const { return from < V; }
+};
+
+static bool TableIsSorted(const TableEntry *Table, unsigned NumEntries) {
+  for (unsigned i = 0; i != NumEntries-1; ++i)
+    if (!(Table[i] < Table[i+1])) return false;
+  return true;
+}
+
+static int Lookup(const TableEntry *Table, unsigned N, unsigned Opcode) {
+  const TableEntry *I = std::lower_bound(Table, Table+N, Opcode);
+  if (I != Table+N && I->from == Opcode)
+    return I->to;
+  return -1;
+}
+
+#define ARRAY_SIZE(TABLE)  \
+   (sizeof(TABLE)/sizeof(TABLE[0]))
+
+#ifdef NDEBUG
+#define ASSERT_SORTED(TABLE)
+#else
+#define ASSERT_SORTED(TABLE)                                              \
+  { static bool TABLE##Checked = false;                                   \
+    if (!TABLE##Checked)                                                  \
+       assert(TableIsSorted(TABLE, ARRAY_SIZE(TABLE)) &&                  \
+              "All lookup tables must be sorted for efficient access!");  \
+  }
+#endif
+
+
+//===----------------------------------------------------------------------===//
+// Helper Methods
+//===----------------------------------------------------------------------===//
+
+// PopTable - Sorted map of instructions to their popping version.  The first
+// element is an instruction, the second is the version which pops.
+//
+static const TableEntry PopTable[] = {
+  { X86::FSTr32   , X86::FSTPr32    },
+  { X86::FSTr64   , X86::FSTPr64    },
+  { X86::FSTrr    , X86::FSTPrr     },
+  { X86::FISTr16  , X86::FISTPr16   },
+  { X86::FISTr32  , X86::FISTPr32   },
+
+  { X86::FADDrST0 , X86::FADDPrST0  },
+  { X86::FSUBrST0 , X86::FSUBPrST0  },
+  { X86::FSUBRrST0, X86::FSUBRPrST0 },
+  { X86::FMULrST0 , X86::FMULPrST0  },
+  { X86::FDIVrST0 , X86::FDIVPrST0  },
+  { X86::FDIVRrST0, X86::FDIVRPrST0 },
+
+  { X86::FUCOMr   , X86::FUCOMPr    },
+  { X86::FUCOMPr  , X86::FUCOMPPr   },
+};
+
+/// popStackAfter - Pop the current value off of the top of the FP stack after
+/// the specified instruction.  This attempts to be sneaky and combine the pop
+/// into the instruction itself if possible.  The iterator is left pointing to
+/// the last instruction, be it a new pop instruction inserted, or the old
+/// instruction if it was modified in place.
+///
+void FPS::popStackAfter(MachineBasicBlock::iterator &I) {
+  ASSERT_SORTED(PopTable);
+  assert(StackTop > 0 && "Cannot pop empty stack!");
+  RegMap[Stack[--StackTop]] = ~0;     // Update state
+
+  // Check to see if there is a popping version of this instruction...
+  int Opcode = Lookup(PopTable, ARRAY_SIZE(PopTable), (*I)->getOpcode());
+  if (Opcode != -1) {
+    (*I)->setOpcode(Opcode);
+    if (Opcode == X86::FUCOMPPr)
+      (*I)->RemoveOperand(0);
+
+  } else {    // Insert an explicit pop
+    MachineInstr *MI = BuildMI(X86::FSTPrr, 1).addReg(X86::ST0);
+    I = MBB->insert(I+1, MI);
+  }
+}
+
+static unsigned getFPReg(const MachineOperand &MO) {
+  assert(MO.isPhysicalRegister() && "Expected an FP register!");
+  unsigned Reg = MO.getReg();
+  assert(Reg >= X86::FP0 && Reg <= X86::FP6 && "Expected FP register!");
+  return Reg - X86::FP0;
+}
+
+
+//===----------------------------------------------------------------------===//
+// Instruction transformation implementation
+//===----------------------------------------------------------------------===//
+
+/// handleZeroArgFP - ST(0) = fld0    ST(0) = flds <mem>
+//
+void FPS::handleZeroArgFP(MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  unsigned DestReg = getFPReg(MI->getOperand(0));
+  MI->RemoveOperand(0);   // Remove the explicit ST(0) operand
+
+  // Result gets pushed on the stack...
+  pushReg(DestReg);
+}
+
+/// handleOneArgFP - fst ST(0), <mem>
+//
+void FPS::handleOneArgFP(MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  assert(MI->getNumOperands() == 5 && "Can only handle fst* instructions!");
+
+  unsigned Reg = getFPReg(MI->getOperand(4));
+  bool KillsSrc = false;
+  for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
+	 E = LV->killed_end(MI); KI != E; ++KI)
+    KillsSrc |= KI->second == X86::FP0+Reg;
+
+  // FSTPr80 and FISTPr64 are strange because there are no non-popping versions.
+  // If we have one _and_ we don't want to pop the operand, duplicate the value
+  // on the stack instead of moving it.  This ensure that popping the value is
+  // always ok.
+  //
+  if ((MI->getOpcode() == X86::FSTPr80 ||
+       MI->getOpcode() == X86::FISTPr64) && !KillsSrc) {
+    duplicateToTop(Reg, 7 /*temp register*/, I);
+  } else {
+    moveToTop(Reg, I);            // Move to the top of the stack...
+  }
+  MI->RemoveOperand(4);           // Remove explicit ST(0) operand
+  
+  if (MI->getOpcode() == X86::FSTPr80 || MI->getOpcode() == X86::FISTPr64) {
+    assert(StackTop > 0 && "Stack empty??");
+    --StackTop;
+  } else if (KillsSrc) { // Last use of operand?
+    popStackAfter(I);
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// Define tables of various ways to map pseudo instructions
+//
+
+// ForwardST0Table - Map: A = B op C  into: ST(0) = ST(0) op ST(i)
+static const TableEntry ForwardST0Table[] = {
+  { X86::FpADD,  X86::FADDST0r  },
+  { X86::FpSUB,  X86::FSUBST0r  },
+  { X86::FpMUL,  X86::FMULST0r  },
+  { X86::FpDIV,  X86::FDIVST0r  },
+  { X86::FpUCOM, X86::FUCOMr    },
+};
+
+// ReverseST0Table - Map: A = B op C  into: ST(0) = ST(i) op ST(0)
+static const TableEntry ReverseST0Table[] = {
+  { X86::FpADD,  X86::FADDST0r  },   // commutative
+  { X86::FpSUB,  X86::FSUBRST0r },
+  { X86::FpMUL,  X86::FMULST0r  },   // commutative
+  { X86::FpDIV,  X86::FDIVRST0r },
+  { X86::FpUCOM, ~0             },
+};
+
+// ForwardSTiTable - Map: A = B op C  into: ST(i) = ST(0) op ST(i)
+static const TableEntry ForwardSTiTable[] = {
+  { X86::FpADD,  X86::FADDrST0  },   // commutative
+  { X86::FpSUB,  X86::FSUBRrST0 },
+  { X86::FpMUL,  X86::FMULrST0  },   // commutative
+  { X86::FpDIV,  X86::FDIVRrST0 },
+  { X86::FpUCOM, X86::FUCOMr    },
+};
+
+// ReverseSTiTable - Map: A = B op C  into: ST(i) = ST(i) op ST(0)
+static const TableEntry ReverseSTiTable[] = {
+  { X86::FpADD,  X86::FADDrST0 },
+  { X86::FpSUB,  X86::FSUBrST0 },
+  { X86::FpMUL,  X86::FMULrST0 },
+  { X86::FpDIV,  X86::FDIVrST0 },
+  { X86::FpUCOM, ~0            },
+};
+
+
+/// handleTwoArgFP - Handle instructions like FADD and friends which are virtual
+/// instructions which need to be simplified and possibly transformed.
+///
+/// Result: ST(0) = fsub  ST(0), ST(i)
+///         ST(i) = fsub  ST(0), ST(i)
+///         ST(0) = fsubr ST(0), ST(i)
+///         ST(i) = fsubr ST(0), ST(i)
+///
+/// In addition to three address instructions, this also handles the FpUCOM
+/// instruction which only has two operands, but no destination.  This
+/// instruction is also annoying because there is no "reverse" form of it
+/// available.
+/// 
+void FPS::handleTwoArgFP(MachineBasicBlock::iterator &I) {
+  ASSERT_SORTED(ForwardST0Table); ASSERT_SORTED(ReverseST0Table);
+  ASSERT_SORTED(ForwardSTiTable); ASSERT_SORTED(ReverseSTiTable);
+  MachineInstr *MI = *I;
+
+  unsigned NumOperands = MI->getNumOperands();
+  assert(NumOperands == 3 ||
+	 (NumOperands == 2 && MI->getOpcode() == X86::FpUCOM) &&
+	 "Illegal TwoArgFP instruction!");
+  unsigned Dest = getFPReg(MI->getOperand(0));
+  unsigned Op0 = getFPReg(MI->getOperand(NumOperands-2));
+  unsigned Op1 = getFPReg(MI->getOperand(NumOperands-1));
+  bool KillsOp0 = false, KillsOp1 = false;
+
+  for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
+	 E = LV->killed_end(MI); KI != E; ++KI) {
+    KillsOp0 |= (KI->second == X86::FP0+Op0);
+    KillsOp1 |= (KI->second == X86::FP0+Op1);
+  }
+
+  // If this is an FpUCOM instruction, we must make sure the first operand is on
+  // the top of stack, the other one can be anywhere...
+  if (MI->getOpcode() == X86::FpUCOM)
+    moveToTop(Op0, I);
+
+  unsigned TOS = getStackEntry(0);
+
+  // One of our operands must be on the top of the stack.  If neither is yet, we
+  // need to move one.
+  if (Op0 != TOS && Op1 != TOS) {   // No operand at TOS?
+    // We can choose to move either operand to the top of the stack.  If one of
+    // the operands is killed by this instruction, we want that one so that we
+    // can update right on top of the old version.
+    if (KillsOp0) {
+      moveToTop(Op0, I);         // Move dead operand to TOS.
+      TOS = Op0;
+    } else if (KillsOp1) {
+      moveToTop(Op1, I);
+      TOS = Op1;
+    } else {
+      // All of the operands are live after this instruction executes, so we
+      // cannot update on top of any operand.  Because of this, we must
+      // duplicate one of the stack elements to the top.  It doesn't matter
+      // which one we pick.
+      //
+      duplicateToTop(Op0, Dest, I);
+      Op0 = TOS = Dest;
+      KillsOp0 = true;
+    }
+  } else if (!KillsOp0 && !KillsOp1 && MI->getOpcode() != X86::FpUCOM)  {
+    // If we DO have one of our operands at the top of the stack, but we don't
+    // have a dead operand, we must duplicate one of the operands to a new slot
+    // on the stack.
+    duplicateToTop(Op0, Dest, I);
+    Op0 = TOS = Dest;
+    KillsOp0 = true;
+  }
+
+  // Now we know that one of our operands is on the top of the stack, and at
+  // least one of our operands is killed by this instruction.
+  assert((TOS == Op0 || TOS == Op1) &&
+	 (KillsOp0 || KillsOp1 || MI->getOpcode() == X86::FpUCOM) &&
+	 "Stack conditions not set up right!");
+
+  // We decide which form to use based on what is on the top of the stack, and
+  // which operand is killed by this instruction.
+  const TableEntry *InstTable;
+  bool isForward = TOS == Op0;
+  bool updateST0 = (TOS == Op0 && !KillsOp1) || (TOS == Op1 && !KillsOp0);
+  if (updateST0) {
+    if (isForward)
+      InstTable = ForwardST0Table;
+    else
+      InstTable = ReverseST0Table;
+  } else {
+    if (isForward)
+      InstTable = ForwardSTiTable;
+    else
+      InstTable = ReverseSTiTable;
+  }
+  
+  int Opcode = Lookup(InstTable, ARRAY_SIZE(ForwardST0Table), MI->getOpcode());
+  assert(Opcode != -1 && "Unknown TwoArgFP pseudo instruction!");
+
+  // NotTOS - The register which is not on the top of stack...
+  unsigned NotTOS = (TOS == Op0) ? Op1 : Op0;
+
+  // Replace the old instruction with a new instruction
+  *I = BuildMI(Opcode, 1).addReg(getSTReg(NotTOS));
+
+  // If both operands are killed, pop one off of the stack in addition to
+  // overwriting the other one.
+  if (KillsOp0 && KillsOp1 && Op0 != Op1) {
+    assert(!updateST0 && "Should have updated other operand!");
+    popStackAfter(I);   // Pop the top of stack
+  }
+
+  // Insert an explicit pop of the "updated" operand for FUCOM 
+  if (MI->getOpcode() == X86::FpUCOM) {
+    if (KillsOp0 && !KillsOp1)
+      popStackAfter(I);   // If we kill the first operand, pop it!
+    else if (KillsOp1 && Op0 != Op1) {
+      if (getStackEntry(0) == Op1) {
+	popStackAfter(I);     // If it's right at the top of stack, just pop it
+      } else {
+	// Otherwise, move the top of stack into the dead slot, killing the
+	// operand without having to add in an explicit xchg then pop.
+	//
+	unsigned STReg    = getSTReg(Op1);
+	unsigned OldSlot  = getSlot(Op1);
+	unsigned TopReg   = Stack[StackTop-1];
+	Stack[OldSlot]    = TopReg;
+	RegMap[TopReg]    = OldSlot;
+	RegMap[Op1]       = ~0;
+	Stack[--StackTop] = ~0;
+	
+	MachineInstr *MI = BuildMI(X86::FSTPrr, 1).addReg(STReg);
+	I = MBB->insert(I+1, MI);
+      }
+    }
+  }
+      
+  // Update stack information so that we know the destination register is now on
+  // the stack.
+  if (MI->getOpcode() != X86::FpUCOM) {  
+    unsigned UpdatedSlot = getSlot(updateST0 ? TOS : NotTOS);
+    assert(UpdatedSlot < StackTop && Dest < 7);
+    Stack[UpdatedSlot]   = Dest;
+    RegMap[Dest]         = UpdatedSlot;
+  }
+  delete MI;   // Remove the old instruction
+}
+
+
+/// handleSpecialFP - Handle special instructions which behave unlike other
+/// floating point instructions.  This is primarily inteaded for use by pseudo
+/// instructions.
+///
+void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  switch (MI->getOpcode()) {
+  default: assert(0 && "Unknown SpecialFP instruction!");
+  case X86::FpGETRESULT:  // Appears immediately after a call returning FP type!
+    assert(StackTop == 0 && "Stack should be empty after a call!");
+    pushReg(getFPReg(MI->getOperand(0)));
+    break;
+  case X86::FpSETRESULT:
+    assert(StackTop == 1 && "Stack should have one element on it to return!");
+    --StackTop;   // "Forget" we have something on the top of stack!
+    break;
+  case X86::FpMOV: {
+    unsigned SrcReg = getFPReg(MI->getOperand(1));
+    unsigned DestReg = getFPReg(MI->getOperand(0));
+    bool KillsSrc = false;
+    for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
+	   E = LV->killed_end(MI); KI != E; ++KI)
+      KillsSrc |= KI->second == X86::FP0+SrcReg;
+
+    if (KillsSrc) {
+      // If the input operand is killed, we can just change the owner of the
+      // incoming stack slot into the result.
+      unsigned Slot = getSlot(SrcReg);
+      assert(Slot < 7 && DestReg < 7 && "FpMOV operands invalid!");
+      Stack[Slot] = DestReg;
+      RegMap[DestReg] = Slot;
+
+    } else {
+      // For FMOV we just duplicate the specified value to a new stack slot.
+      // This could be made better, but would require substantial changes.
+      duplicateToTop(SrcReg, DestReg, I);
+    }
+    break;
+  }
+  }
+
+  I = MBB->erase(I)-1;  // Remove the pseudo instruction
+}

lib/Target/X86/PeepholeOptimizer.cpp

@@ -0,0 +1,86 @@
+//===-- PeepholeOptimizer.cpp - X86 Peephole Optimizer --------------------===//
+//
+// This file contains a peephole optimizer for the X86.
+//
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+
+namespace {
+  struct PH : public MachineFunctionPass {
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+
+    bool PeepholeOptimize(MachineBasicBlock &MBB,
+			  MachineBasicBlock::iterator &I);
+
+    virtual const char *getPassName() const { return "X86 Peephole Optimizer"; }
+  };
+}
+
+Pass *createX86PeepholeOptimizerPass() { return new PH(); }
+
+bool PH::runOnMachineFunction(MachineFunction &MF) {
+  bool Changed = false;
+
+  for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI)
+    for (MachineBasicBlock::iterator I = BI->begin(), E = BI->end(); I != E; )
+      if (PeepholeOptimize(*BI, I))
+	Changed = true;
+      else
+	++I;
+
+  return Changed;
+}
+
+
+bool PH::PeepholeOptimize(MachineBasicBlock &MBB,
+			  MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  MachineInstr *Next = (I+1 != MBB.end()) ? *(I+1) : 0;
+  unsigned Size = 0;
+  switch (MI->getOpcode()) {
+  case X86::MOVrr8:
+  case X86::MOVrr16:
+  case X86::MOVrr32:   // Destroy X = X copies...
+    if (MI->getOperand(0).getReg() == MI->getOperand(1).getReg()) {
+      I = MBB.erase(I);
+      delete MI;
+      return true;
+    }
+    return false;
+
+#if 0
+  case X86::MOVir32: Size++;
+  case X86::MOVir16: Size++;
+  case X86::MOVir8:
+    // FIXME: We can only do this transformation if we know that flags are not
+    // used here, because XOR clobbers the flags!
+    if (MI->getOperand(1).isImmediate()) {         // avoid mov EAX, <value>
+      int Val = MI->getOperand(1).getImmedValue();
+      if (Val == 0) {                              // mov EAX, 0 -> xor EAX, EAX
+	static const unsigned Opcode[] ={X86::XORrr8,X86::XORrr16,X86::XORrr32};
+	unsigned Reg = MI->getOperand(0).getReg();
+	*I = BuildMI(Opcode[Size], 2, Reg).addReg(Reg).addReg(Reg);
+	delete MI;
+	return true;
+      } else if (Val == -1) {                     // mov EAX, -1 -> or EAX, -1
+	// TODO: 'or Reg, -1' has a smaller encoding than 'mov Reg, -1'
+      }
+    }
+    return false;
+#endif
+  case X86::BSWAPr32:        // Change bswap EAX, bswap EAX into nothing
+    if (Next->getOpcode() == X86::BSWAPr32 &&
+	MI->getOperand(0).getReg() == Next->getOperand(0).getReg()) {
+      I = MBB.erase(MBB.erase(I));
+      delete MI;
+      delete Next;
+      return true;
+    }
+    return false;
+  default:
+    return false;
+  }
+}

lib/Target/X86/X86FloatingPoint.cpp

@@ -0,0 +1,587 @@
+//===-- FloatingPoint.cpp - Floating point Reg -> Stack converter ---------===//
+//
+// This file defines the pass which converts floating point instructions from
+// virtual registers into register stack instructions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "X86InstrInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/LiveVariables.h"
+#include "llvm/Target/MachineInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "Support/Statistic.h"
+#include <algorithm>
+#include <iostream>
+
+namespace {
+  Statistic<> NumFXCH("x86-codegen", "Number of fxch instructions inserted");
+  Statistic<> NumFP  ("x86-codegen", "Number of floating point instructions");
+
+  struct FPS : public MachineFunctionPass {
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+
+    virtual const char *getPassName() const { return "X86 FP Stackifier"; }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addRequired<LiveVariables>();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+  private:
+    LiveVariables     *LV;    // Live variable info for current function...
+    MachineBasicBlock *MBB;   // Current basic block
+    unsigned Stack[8];        // FP<n> Registers in each stack slot...
+    unsigned RegMap[8];       // Track which stack slot contains each register
+    unsigned StackTop;        // The current top of the FP stack.
+
+    void dumpStack() const {
+      std::cerr << "Stack contents:";
+      for (unsigned i = 0; i != StackTop; ++i) {
+	std::cerr << " FP" << Stack[i];
+	assert(RegMap[Stack[i]] == i && "Stack[] doesn't match RegMap[]!"); 
+      }
+      std::cerr << "\n";
+    }
+  private:
+    // getSlot - Return the stack slot number a particular register number is
+    // in...
+    unsigned getSlot(unsigned RegNo) const {
+      assert(RegNo < 8 && "Regno out of range!");
+      return RegMap[RegNo];
+    }
+
+    // getStackEntry - Return the X86::FP<n> register in register ST(i)
+    unsigned getStackEntry(unsigned STi) const {
+      assert(STi < StackTop && "Access past stack top!");
+      return Stack[StackTop-1-STi];
+    }
+
+    // getSTReg - Return the X86::ST(i) register which contains the specified
+    // FP<RegNo> register
+    unsigned getSTReg(unsigned RegNo) const {
+      return StackTop - 1 - getSlot(RegNo) + X86::ST0;
+    }
+
+    // pushReg - Push the specifiex FP<n> register onto the stack
+    void pushReg(unsigned Reg) {
+      assert(Reg < 8 && "Register number out of range!");
+      assert(StackTop < 8 && "Stack overflow!");
+      Stack[StackTop] = Reg;
+      RegMap[Reg] = StackTop++;
+    }
+
+    bool isAtTop(unsigned RegNo) const { return getSlot(RegNo) == StackTop-1; }
+    void moveToTop(unsigned RegNo, MachineBasicBlock::iterator &I) {
+      if (!isAtTop(RegNo)) {
+	unsigned Slot = getSlot(RegNo);
+	unsigned STReg = getSTReg(RegNo);
+	unsigned RegOnTop = getStackEntry(0);
+
+	// Swap the slots the regs are in
+	std::swap(RegMap[RegNo], RegMap[RegOnTop]);
+
+	// Swap stack slot contents
+	assert(RegMap[RegOnTop] < StackTop);
+	std::swap(Stack[RegMap[RegOnTop]], Stack[StackTop-1]);
+
+	// Emit an fxch to update the runtime processors version of the state
+	MachineInstr *MI = BuildMI(X86::FXCH, 1).addReg(STReg);
+	I = 1+MBB->insert(I, MI);
+	NumFXCH++;
+      }
+    }
+
+    void duplicateToTop(unsigned RegNo, unsigned AsReg,
+			MachineBasicBlock::iterator &I) {
+      unsigned STReg = getSTReg(RegNo);
+      pushReg(AsReg);   // New register on top of stack
+
+      MachineInstr *MI = BuildMI(X86::FLDrr, 1).addReg(STReg);
+      I = 1+MBB->insert(I, MI);
+    }
+
+    // popStackAfter - Pop the current value off of the top of the FP stack
+    // after the specified instruction.
+    void popStackAfter(MachineBasicBlock::iterator &I);
+
+    bool processBasicBlock(MachineFunction &MF, MachineBasicBlock &MBB);
+
+    void handleZeroArgFP(MachineBasicBlock::iterator &I);
+    void handleOneArgFP(MachineBasicBlock::iterator &I);
+    void handleTwoArgFP(MachineBasicBlock::iterator &I);
+    void handleSpecialFP(MachineBasicBlock::iterator &I);
+  };
+}
+
+Pass *createX86FloatingPointStackifierPass() { return new FPS(); }
+
+/// runOnMachineFunction - Loop over all of the basic blocks, transforming FP
+/// register references into FP stack references.
+///
+bool FPS::runOnMachineFunction(MachineFunction &MF) {
+  LV = &getAnalysis<LiveVariables>();
+  StackTop = 0;
+
+  bool Changed = false;
+  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
+    Changed |= processBasicBlock(MF, *I);
+  return Changed;
+}
+
+/// processBasicBlock - Loop over all of the instructions in the basic block,
+/// transforming FP instructions into their stack form.
+///
+bool FPS::processBasicBlock(MachineFunction &MF, MachineBasicBlock &BB) {
+  const TargetInstrInfo &TII = MF.getTarget().getInstrInfo();
+  bool Changed = false;
+  MBB = &BB;
+  
+  for (MachineBasicBlock::iterator I = BB.begin(); I != BB.end(); ++I) {
+    MachineInstr *MI = *I;
+    MachineInstr *PrevMI = I == BB.begin() ? 0 : *(I-1);
+    unsigned Flags = TII.get(MI->getOpcode()).TSFlags;
+
+    if ((Flags & X86II::FPTypeMask) == 0) continue;  // Ignore non-fp insts!
+
+    ++NumFP;  // Keep track of # of pseudo instrs
+    DEBUG(std::cerr << "\nFPInst:\t";
+	  MI->print(std::cerr, MF.getTarget()));
+
+    // Get dead variables list now because the MI pointer may be deleted as part
+    // of processing!
+    LiveVariables::killed_iterator IB = LV->dead_begin(MI);
+    LiveVariables::killed_iterator IE = LV->dead_end(MI);
+
+    DEBUG(const MRegisterInfo *MRI = MF.getTarget().getRegisterInfo();
+	  LiveVariables::killed_iterator I = LV->killed_begin(MI);
+	  LiveVariables::killed_iterator E = LV->killed_end(MI);
+	  if (I != E) {
+	    std::cerr << "Killed Operands:";
+	    for (; I != E; ++I)
+	      std::cerr << " %" << MRI->getName(I->second);
+	    std::cerr << "\n";
+	  });
+
+    switch (Flags & X86II::FPTypeMask) {
+    case X86II::ZeroArgFP: handleZeroArgFP(I); break;
+    case X86II::OneArgFP:  handleOneArgFP(I);  break;
+
+    case X86II::OneArgFPRW:   // ST(0) = fsqrt(ST(0))
+      assert(0 && "FP instr type not handled yet!");
+
+    case X86II::TwoArgFP:  handleTwoArgFP(I);  break;
+    case X86II::SpecialFP: handleSpecialFP(I); break;
+    default: assert(0 && "Unknown FP Type!");
+    }
+
+    // Check to see if any of the values defined by this instruction are dead
+    // after definition.  If so, pop them.
+    for (; IB != IE; ++IB) {
+      unsigned Reg = IB->second;
+      if (Reg >= X86::FP0 && Reg <= X86::FP6) {
+	DEBUG(std::cerr << "Register FP#" << Reg-X86::FP0 << " is dead!\n");
+	++I;                         // Insert fxch AFTER the instruction
+	moveToTop(Reg-X86::FP0, I);  // Insert fxch if neccesary
+	--I;                         // Move to fxch or old instruction
+	popStackAfter(I);            // Pop the top of the stack, killing value
+      }
+    }
+    
+    // Print out all of the instructions expanded to if -debug
+    DEBUG(if (*I == PrevMI) {
+            std::cerr<< "Just deleted pseudo instruction\n";
+          } else {
+	    MachineBasicBlock::iterator Start = I;
+	    // Rewind to first instruction newly inserted.
+	    while (Start != BB.begin() && *(Start-1) != PrevMI) --Start;
+	    std::cerr << "Inserted instructions:\n";
+	    do TII.print(*Start, std::cerr << "\t", MF.getTarget());
+	    while (++Start != I+1);
+	  }
+	  dumpStack();
+	  );
+
+    Changed = true;
+  }
+
+  assert(StackTop == 0 && "Stack not empty at end of basic block?");
+  return Changed;
+}
+
+//===----------------------------------------------------------------------===//
+// Efficient Lookup Table Support
+//===----------------------------------------------------------------------===//
+
+struct TableEntry {
+  unsigned from;
+  unsigned to;
+  bool operator<(const TableEntry &TE) const { return from < TE.from; }
+  bool operator<(unsigned V) const { return from < V; }
+};
+
+static bool TableIsSorted(const TableEntry *Table, unsigned NumEntries) {
+  for (unsigned i = 0; i != NumEntries-1; ++i)
+    if (!(Table[i] < Table[i+1])) return false;
+  return true;
+}
+
+static int Lookup(const TableEntry *Table, unsigned N, unsigned Opcode) {
+  const TableEntry *I = std::lower_bound(Table, Table+N, Opcode);
+  if (I != Table+N && I->from == Opcode)
+    return I->to;
+  return -1;
+}
+
+#define ARRAY_SIZE(TABLE)  \
+   (sizeof(TABLE)/sizeof(TABLE[0]))
+
+#ifdef NDEBUG
+#define ASSERT_SORTED(TABLE)
+#else
+#define ASSERT_SORTED(TABLE)                                              \
+  { static bool TABLE##Checked = false;                                   \
+    if (!TABLE##Checked)                                                  \
+       assert(TableIsSorted(TABLE, ARRAY_SIZE(TABLE)) &&                  \
+              "All lookup tables must be sorted for efficient access!");  \
+  }
+#endif
+
+
+//===----------------------------------------------------------------------===//
+// Helper Methods
+//===----------------------------------------------------------------------===//
+
+// PopTable - Sorted map of instructions to their popping version.  The first
+// element is an instruction, the second is the version which pops.
+//
+static const TableEntry PopTable[] = {
+  { X86::FSTr32   , X86::FSTPr32    },
+  { X86::FSTr64   , X86::FSTPr64    },
+  { X86::FSTrr    , X86::FSTPrr     },
+  { X86::FISTr16  , X86::FISTPr16   },
+  { X86::FISTr32  , X86::FISTPr32   },
+
+  { X86::FADDrST0 , X86::FADDPrST0  },
+  { X86::FSUBrST0 , X86::FSUBPrST0  },
+  { X86::FSUBRrST0, X86::FSUBRPrST0 },
+  { X86::FMULrST0 , X86::FMULPrST0  },
+  { X86::FDIVrST0 , X86::FDIVPrST0  },
+  { X86::FDIVRrST0, X86::FDIVRPrST0 },
+
+  { X86::FUCOMr   , X86::FUCOMPr    },
+  { X86::FUCOMPr  , X86::FUCOMPPr   },
+};
+
+/// popStackAfter - Pop the current value off of the top of the FP stack after
+/// the specified instruction.  This attempts to be sneaky and combine the pop
+/// into the instruction itself if possible.  The iterator is left pointing to
+/// the last instruction, be it a new pop instruction inserted, or the old
+/// instruction if it was modified in place.
+///
+void FPS::popStackAfter(MachineBasicBlock::iterator &I) {
+  ASSERT_SORTED(PopTable);
+  assert(StackTop > 0 && "Cannot pop empty stack!");
+  RegMap[Stack[--StackTop]] = ~0;     // Update state
+
+  // Check to see if there is a popping version of this instruction...
+  int Opcode = Lookup(PopTable, ARRAY_SIZE(PopTable), (*I)->getOpcode());
+  if (Opcode != -1) {
+    (*I)->setOpcode(Opcode);
+    if (Opcode == X86::FUCOMPPr)
+      (*I)->RemoveOperand(0);
+
+  } else {    // Insert an explicit pop
+    MachineInstr *MI = BuildMI(X86::FSTPrr, 1).addReg(X86::ST0);
+    I = MBB->insert(I+1, MI);
+  }
+}
+
+static unsigned getFPReg(const MachineOperand &MO) {
+  assert(MO.isPhysicalRegister() && "Expected an FP register!");
+  unsigned Reg = MO.getReg();
+  assert(Reg >= X86::FP0 && Reg <= X86::FP6 && "Expected FP register!");
+  return Reg - X86::FP0;
+}
+
+
+//===----------------------------------------------------------------------===//
+// Instruction transformation implementation
+//===----------------------------------------------------------------------===//
+
+/// handleZeroArgFP - ST(0) = fld0    ST(0) = flds <mem>
+//
+void FPS::handleZeroArgFP(MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  unsigned DestReg = getFPReg(MI->getOperand(0));
+  MI->RemoveOperand(0);   // Remove the explicit ST(0) operand
+
+  // Result gets pushed on the stack...
+  pushReg(DestReg);
+}
+
+/// handleOneArgFP - fst ST(0), <mem>
+//
+void FPS::handleOneArgFP(MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  assert(MI->getNumOperands() == 5 && "Can only handle fst* instructions!");
+
+  unsigned Reg = getFPReg(MI->getOperand(4));
+  bool KillsSrc = false;
+  for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
+	 E = LV->killed_end(MI); KI != E; ++KI)
+    KillsSrc |= KI->second == X86::FP0+Reg;
+
+  // FSTPr80 and FISTPr64 are strange because there are no non-popping versions.
+  // If we have one _and_ we don't want to pop the operand, duplicate the value
+  // on the stack instead of moving it.  This ensure that popping the value is
+  // always ok.
+  //
+  if ((MI->getOpcode() == X86::FSTPr80 ||
+       MI->getOpcode() == X86::FISTPr64) && !KillsSrc) {
+    duplicateToTop(Reg, 7 /*temp register*/, I);
+  } else {
+    moveToTop(Reg, I);            // Move to the top of the stack...
+  }
+  MI->RemoveOperand(4);           // Remove explicit ST(0) operand
+  
+  if (MI->getOpcode() == X86::FSTPr80 || MI->getOpcode() == X86::FISTPr64) {
+    assert(StackTop > 0 && "Stack empty??");
+    --StackTop;
+  } else if (KillsSrc) { // Last use of operand?
+    popStackAfter(I);
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// Define tables of various ways to map pseudo instructions
+//
+
+// ForwardST0Table - Map: A = B op C  into: ST(0) = ST(0) op ST(i)
+static const TableEntry ForwardST0Table[] = {
+  { X86::FpADD,  X86::FADDST0r  },
+  { X86::FpSUB,  X86::FSUBST0r  },
+  { X86::FpMUL,  X86::FMULST0r  },
+  { X86::FpDIV,  X86::FDIVST0r  },
+  { X86::FpUCOM, X86::FUCOMr    },
+};
+
+// ReverseST0Table - Map: A = B op C  into: ST(0) = ST(i) op ST(0)
+static const TableEntry ReverseST0Table[] = {
+  { X86::FpADD,  X86::FADDST0r  },   // commutative
+  { X86::FpSUB,  X86::FSUBRST0r },
+  { X86::FpMUL,  X86::FMULST0r  },   // commutative
+  { X86::FpDIV,  X86::FDIVRST0r },
+  { X86::FpUCOM, ~0             },
+};
+
+// ForwardSTiTable - Map: A = B op C  into: ST(i) = ST(0) op ST(i)
+static const TableEntry ForwardSTiTable[] = {
+  { X86::FpADD,  X86::FADDrST0  },   // commutative
+  { X86::FpSUB,  X86::FSUBRrST0 },
+  { X86::FpMUL,  X86::FMULrST0  },   // commutative
+  { X86::FpDIV,  X86::FDIVRrST0 },
+  { X86::FpUCOM, X86::FUCOMr    },
+};
+
+// ReverseSTiTable - Map: A = B op C  into: ST(i) = ST(i) op ST(0)
+static const TableEntry ReverseSTiTable[] = {
+  { X86::FpADD,  X86::FADDrST0 },
+  { X86::FpSUB,  X86::FSUBrST0 },
+  { X86::FpMUL,  X86::FMULrST0 },
+  { X86::FpDIV,  X86::FDIVrST0 },
+  { X86::FpUCOM, ~0            },
+};
+
+
+/// handleTwoArgFP - Handle instructions like FADD and friends which are virtual
+/// instructions which need to be simplified and possibly transformed.
+///
+/// Result: ST(0) = fsub  ST(0), ST(i)
+///         ST(i) = fsub  ST(0), ST(i)
+///         ST(0) = fsubr ST(0), ST(i)
+///         ST(i) = fsubr ST(0), ST(i)
+///
+/// In addition to three address instructions, this also handles the FpUCOM
+/// instruction which only has two operands, but no destination.  This
+/// instruction is also annoying because there is no "reverse" form of it
+/// available.
+/// 
+void FPS::handleTwoArgFP(MachineBasicBlock::iterator &I) {
+  ASSERT_SORTED(ForwardST0Table); ASSERT_SORTED(ReverseST0Table);
+  ASSERT_SORTED(ForwardSTiTable); ASSERT_SORTED(ReverseSTiTable);
+  MachineInstr *MI = *I;
+
+  unsigned NumOperands = MI->getNumOperands();
+  assert(NumOperands == 3 ||
+	 (NumOperands == 2 && MI->getOpcode() == X86::FpUCOM) &&
+	 "Illegal TwoArgFP instruction!");
+  unsigned Dest = getFPReg(MI->getOperand(0));
+  unsigned Op0 = getFPReg(MI->getOperand(NumOperands-2));
+  unsigned Op1 = getFPReg(MI->getOperand(NumOperands-1));
+  bool KillsOp0 = false, KillsOp1 = false;
+
+  for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
+	 E = LV->killed_end(MI); KI != E; ++KI) {
+    KillsOp0 |= (KI->second == X86::FP0+Op0);
+    KillsOp1 |= (KI->second == X86::FP0+Op1);
+  }
+
+  // If this is an FpUCOM instruction, we must make sure the first operand is on
+  // the top of stack, the other one can be anywhere...
+  if (MI->getOpcode() == X86::FpUCOM)
+    moveToTop(Op0, I);
+
+  unsigned TOS = getStackEntry(0);
+
+  // One of our operands must be on the top of the stack.  If neither is yet, we
+  // need to move one.
+  if (Op0 != TOS && Op1 != TOS) {   // No operand at TOS?
+    // We can choose to move either operand to the top of the stack.  If one of
+    // the operands is killed by this instruction, we want that one so that we
+    // can update right on top of the old version.
+    if (KillsOp0) {
+      moveToTop(Op0, I);         // Move dead operand to TOS.
+      TOS = Op0;
+    } else if (KillsOp1) {
+      moveToTop(Op1, I);
+      TOS = Op1;
+    } else {
+      // All of the operands are live after this instruction executes, so we
+      // cannot update on top of any operand.  Because of this, we must
+      // duplicate one of the stack elements to the top.  It doesn't matter
+      // which one we pick.
+      //
+      duplicateToTop(Op0, Dest, I);
+      Op0 = TOS = Dest;
+      KillsOp0 = true;
+    }
+  } else if (!KillsOp0 && !KillsOp1 && MI->getOpcode() != X86::FpUCOM)  {
+    // If we DO have one of our operands at the top of the stack, but we don't
+    // have a dead operand, we must duplicate one of the operands to a new slot
+    // on the stack.
+    duplicateToTop(Op0, Dest, I);
+    Op0 = TOS = Dest;
+    KillsOp0 = true;
+  }
+
+  // Now we know that one of our operands is on the top of the stack, and at
+  // least one of our operands is killed by this instruction.
+  assert((TOS == Op0 || TOS == Op1) &&
+	 (KillsOp0 || KillsOp1 || MI->getOpcode() == X86::FpUCOM) &&
+	 "Stack conditions not set up right!");
+
+  // We decide which form to use based on what is on the top of the stack, and
+  // which operand is killed by this instruction.
+  const TableEntry *InstTable;
+  bool isForward = TOS == Op0;
+  bool updateST0 = (TOS == Op0 && !KillsOp1) || (TOS == Op1 && !KillsOp0);
+  if (updateST0) {
+    if (isForward)
+      InstTable = ForwardST0Table;
+    else
+      InstTable = ReverseST0Table;
+  } else {
+    if (isForward)
+      InstTable = ForwardSTiTable;
+    else
+      InstTable = ReverseSTiTable;
+  }
+  
+  int Opcode = Lookup(InstTable, ARRAY_SIZE(ForwardST0Table), MI->getOpcode());
+  assert(Opcode != -1 && "Unknown TwoArgFP pseudo instruction!");
+
+  // NotTOS - The register which is not on the top of stack...
+  unsigned NotTOS = (TOS == Op0) ? Op1 : Op0;
+
+  // Replace the old instruction with a new instruction
+  *I = BuildMI(Opcode, 1).addReg(getSTReg(NotTOS));
+
+  // If both operands are killed, pop one off of the stack in addition to
+  // overwriting the other one.
+  if (KillsOp0 && KillsOp1 && Op0 != Op1) {
+    assert(!updateST0 && "Should have updated other operand!");
+    popStackAfter(I);   // Pop the top of stack
+  }
+
+  // Insert an explicit pop of the "updated" operand for FUCOM 
+  if (MI->getOpcode() == X86::FpUCOM) {
+    if (KillsOp0 && !KillsOp1)
+      popStackAfter(I);   // If we kill the first operand, pop it!
+    else if (KillsOp1 && Op0 != Op1) {
+      if (getStackEntry(0) == Op1) {
+	popStackAfter(I);     // If it's right at the top of stack, just pop it
+      } else {
+	// Otherwise, move the top of stack into the dead slot, killing the
+	// operand without having to add in an explicit xchg then pop.
+	//
+	unsigned STReg    = getSTReg(Op1);
+	unsigned OldSlot  = getSlot(Op1);
+	unsigned TopReg   = Stack[StackTop-1];
+	Stack[OldSlot]    = TopReg;
+	RegMap[TopReg]    = OldSlot;
+	RegMap[Op1]       = ~0;
+	Stack[--StackTop] = ~0;
+	
+	MachineInstr *MI = BuildMI(X86::FSTPrr, 1).addReg(STReg);
+	I = MBB->insert(I+1, MI);
+      }
+    }
+  }
+      
+  // Update stack information so that we know the destination register is now on
+  // the stack.
+  if (MI->getOpcode() != X86::FpUCOM) {  
+    unsigned UpdatedSlot = getSlot(updateST0 ? TOS : NotTOS);
+    assert(UpdatedSlot < StackTop && Dest < 7);
+    Stack[UpdatedSlot]   = Dest;
+    RegMap[Dest]         = UpdatedSlot;
+  }
+  delete MI;   // Remove the old instruction
+}
+
+
+/// handleSpecialFP - Handle special instructions which behave unlike other
+/// floating point instructions.  This is primarily inteaded for use by pseudo
+/// instructions.
+///
+void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  switch (MI->getOpcode()) {
+  default: assert(0 && "Unknown SpecialFP instruction!");
+  case X86::FpGETRESULT:  // Appears immediately after a call returning FP type!
+    assert(StackTop == 0 && "Stack should be empty after a call!");
+    pushReg(getFPReg(MI->getOperand(0)));
+    break;
+  case X86::FpSETRESULT:
+    assert(StackTop == 1 && "Stack should have one element on it to return!");
+    --StackTop;   // "Forget" we have something on the top of stack!
+    break;
+  case X86::FpMOV: {
+    unsigned SrcReg = getFPReg(MI->getOperand(1));
+    unsigned DestReg = getFPReg(MI->getOperand(0));
+    bool KillsSrc = false;
+    for (LiveVariables::killed_iterator KI = LV->killed_begin(MI),
+	   E = LV->killed_end(MI); KI != E; ++KI)
+      KillsSrc |= KI->second == X86::FP0+SrcReg;
+
+    if (KillsSrc) {
+      // If the input operand is killed, we can just change the owner of the
+      // incoming stack slot into the result.
+      unsigned Slot = getSlot(SrcReg);
+      assert(Slot < 7 && DestReg < 7 && "FpMOV operands invalid!");
+      Stack[Slot] = DestReg;
+      RegMap[DestReg] = Slot;
+
+    } else {
+      // For FMOV we just duplicate the specified value to a new stack slot.
+      // This could be made better, but would require substantial changes.
+      duplicateToTop(SrcReg, DestReg, I);
+    }
+    break;
+  }
+  }
+
+  I = MBB->erase(I)-1;  // Remove the pseudo instruction
+}

lib/Target/X86/X86PeepholeOpt.cpp

@@ -0,0 +1,86 @@
+//===-- PeepholeOptimizer.cpp - X86 Peephole Optimizer --------------------===//
+//
+// This file contains a peephole optimizer for the X86.
+//
+//===----------------------------------------------------------------------===//
+
+#include "X86.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+
+namespace {
+  struct PH : public MachineFunctionPass {
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+
+    bool PeepholeOptimize(MachineBasicBlock &MBB,
+			  MachineBasicBlock::iterator &I);
+
+    virtual const char *getPassName() const { return "X86 Peephole Optimizer"; }
+  };
+}
+
+Pass *createX86PeepholeOptimizerPass() { return new PH(); }
+
+bool PH::runOnMachineFunction(MachineFunction &MF) {
+  bool Changed = false;
+
+  for (MachineFunction::iterator BI = MF.begin(), E = MF.end(); BI != E; ++BI)
+    for (MachineBasicBlock::iterator I = BI->begin(), E = BI->end(); I != E; )
+      if (PeepholeOptimize(*BI, I))
+	Changed = true;
+      else
+	++I;
+
+  return Changed;
+}
+
+
+bool PH::PeepholeOptimize(MachineBasicBlock &MBB,
+			  MachineBasicBlock::iterator &I) {
+  MachineInstr *MI = *I;
+  MachineInstr *Next = (I+1 != MBB.end()) ? *(I+1) : 0;
+  unsigned Size = 0;
+  switch (MI->getOpcode()) {
+  case X86::MOVrr8:
+  case X86::MOVrr16:
+  case X86::MOVrr32:   // Destroy X = X copies...
+    if (MI->getOperand(0).getReg() == MI->getOperand(1).getReg()) {
+      I = MBB.erase(I);
+      delete MI;
+      return true;
+    }
+    return false;
+
+#if 0
+  case X86::MOVir32: Size++;
+  case X86::MOVir16: Size++;
+  case X86::MOVir8:
+    // FIXME: We can only do this transformation if we know that flags are not
+    // used here, because XOR clobbers the flags!
+    if (MI->getOperand(1).isImmediate()) {         // avoid mov EAX, <value>
+      int Val = MI->getOperand(1).getImmedValue();
+      if (Val == 0) {                              // mov EAX, 0 -> xor EAX, EAX
+	static const unsigned Opcode[] ={X86::XORrr8,X86::XORrr16,X86::XORrr32};
+	unsigned Reg = MI->getOperand(0).getReg();
+	*I = BuildMI(Opcode[Size], 2, Reg).addReg(Reg).addReg(Reg);
+	delete MI;
+	return true;
+      } else if (Val == -1) {                     // mov EAX, -1 -> or EAX, -1
+	// TODO: 'or Reg, -1' has a smaller encoding than 'mov Reg, -1'
+      }
+    }
+    return false;
+#endif
+  case X86::BSWAPr32:        // Change bswap EAX, bswap EAX into nothing
+    if (Next->getOpcode() == X86::BSWAPr32 &&
+	MI->getOperand(0).getReg() == Next->getOperand(0).getReg()) {
+      I = MBB.erase(MBB.erase(I));
+      delete MI;
+      delete Next;
+      return true;
+    }
+    return false;
+  default:
+    return false;
+  }
+}