lib/CodeGen/StackSlotColoring.cpp

   1 //===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the stack slot coloring pass.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #define DEBUG_TYPE "stackcoloring"
  15 #include "VirtRegMap.h"
  16 #include "llvm/CodeGen/Passes.h"
  17 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
  18 #include "llvm/CodeGen/LiveStackAnalysis.h"
  19 #include "llvm/CodeGen/MachineFrameInfo.h"
  20 #include "llvm/CodeGen/MachineLoopInfo.h"
  21 #include "llvm/CodeGen/MachineRegisterInfo.h"
  22 #include "llvm/CodeGen/PseudoSourceValue.h"
  23 #include "llvm/Support/CommandLine.h"
  24 #include "llvm/Support/Compiler.h"
  25 #include "llvm/Support/Debug.h"
  26 #include "llvm/Target/TargetInstrInfo.h"
  27 #include "llvm/Target/TargetMachine.h"
  28 #include "llvm/ADT/BitVector.h"
  29 #include "llvm/ADT/SmallVector.h"
  30 #include "llvm/ADT/Statistic.h"
  31 #include <vector>
  32 using namespace llvm;
  33
  34 static cl::opt<bool>
  35 DisableSharing("no-stack-slot-sharing",
  36              cl::init(false), cl::Hidden,
  37              cl::desc("Suppress slot sharing during stack coloring"));
  38
  39 static cl::opt<bool>
  40 ColorWithRegs("-color-ss-with-regs",
  41              cl::init(false), cl::Hidden,
  42              cl::desc("Color stack slots with free registers"));
  43
  44
  45 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
  46
  47 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
  48 STATISTIC(NumDead,       "Number of trivially dead stack accesses eliminated");
  49 STATISTIC(NumRegRepl,    "Number of stack slot refs replaced with reg refs");
  50
  51 namespace {
  52   class VISIBILITY_HIDDEN StackSlotColoring : public MachineFunctionPass {
  53     LiveStacks* LS;
  54     VirtRegMap* VRM;
  55     MachineFrameInfo *MFI;
  56     MachineRegisterInfo *MRI;
  57     const TargetInstrInfo  *TII;
  58     const TargetRegisterInfo *TRI;
  59     const MachineLoopInfo *loopInfo;
  60
  61     // SSIntervals - Spill slot intervals.
  62     std::vector<LiveInterval*> SSIntervals;
  63
  64     // SSRefs - Keep a list of frame index references for each spill slot.
  65     SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
  66
  67     // OrigAlignments - Alignments of stack objects before coloring.
  68     SmallVector<unsigned, 16> OrigAlignments;
  69
  70     // OrigSizes - Sizess of stack objects before coloring.
  71     SmallVector<unsigned, 16> OrigSizes;
  72
  73     // AllColors - If index is set, it's a spill slot, i.e. color.
  74     // FIXME: This assumes PEI locate spill slot with smaller indices
  75     // closest to stack pointer / frame pointer. Therefore, smaller
  76     // index == better color.
  77     BitVector AllColors;
  78
  79     // NextColor - Next "color" that's not yet used.
  80     int NextColor;
  81
  82     // UsedColors - "Colors" that have been assigned.
  83     BitVector UsedColors;
  84
  85     // Assignments - Color to intervals mapping.
  86     SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
  87
  88   public:
  89     static char ID; // Pass identification
  90     StackSlotColoring() : MachineFunctionPass(&ID), NextColor(-1) {}
  91
  92     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  93       AU.addRequired<LiveStacks>();
  94       AU.addRequired<VirtRegMap>();
  95       AU.addPreserved<VirtRegMap>();
  96       AU.addRequired<MachineLoopInfo>();
  97       AU.addPreserved<MachineLoopInfo>();
  98       AU.addPreservedID(MachineDominatorsID);
  99       MachineFunctionPass::getAnalysisUsage(AU);
 100     }
 101
 102     virtual bool runOnMachineFunction(MachineFunction &MF);
 103     virtual const char* getPassName() const {
 104       return "Stack Slot Coloring";
 105     }
 106
 107   private:
 108     void InitializeSlots();
 109     void ScanForSpillSlotRefs(MachineFunction &MF);
 110     bool OverlapWithAssignments(LiveInterval *li, int Color) const;
 111     int ColorSlot(LiveInterval *li);
 112     bool ColorSlots(MachineFunction &MF);
 113     bool ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
 114                                 SmallVector<SmallVector<int, 4>, 16> &RevMap,
 115                                 BitVector &SlotIsReg);
 116     void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
 117                             MachineFunction &MF);
 118     void UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
 119                                      unsigned Reg, MachineFunction &MF);
 120     bool AllMemRefsCanBeUnfolded(int SS);
 121     bool RemoveDeadStores(MachineBasicBlock* MBB);
 122   };
 123 } // end anonymous namespace
 124
 125 char StackSlotColoring::ID = 0;
 126
 127 static RegisterPass<StackSlotColoring>
 128 X("stack-slot-coloring", "Stack Slot Coloring");
 129
 130 FunctionPass *llvm::createStackSlotColoringPass() {
 131   return new StackSlotColoring();
 132 }
 133
 134 namespace {
 135   // IntervalSorter - Comparison predicate that sort live intervals by
 136   // their weight.
 137   struct IntervalSorter {
 138     bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
 139       return LHS->weight > RHS->weight;
 140     }
 141   };
 142 }
 143
 144 /// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
 145 /// references and update spill slot weights.
 146 void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
 147   SSRefs.resize(MFI->getObjectIndexEnd());
 148
 149   // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
 150   for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
 151        MBBI != E; ++MBBI) {
 152     MachineBasicBlock *MBB = &*MBBI;
 153     unsigned loopDepth = loopInfo->getLoopDepth(MBB);
 154     for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
 155          MII != EE; ++MII) {
 156       MachineInstr *MI = &*MII;
 157       for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
 158         MachineOperand &MO = MI->getOperand(i);
 159         if (!MO.isFI())
 160           continue;
 161         int FI = MO.getIndex();
 162         if (FI < 0)
 163           continue;
 164         if (!LS->hasInterval(FI))
 165           continue;
 166         LiveInterval &li = LS->getInterval(FI);
 167         li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
 168         SSRefs[FI].push_back(MI);
 169       }
 170     }
 171   }
 172 }
 173
 174 /// InitializeSlots - Process all spill stack slot liveintervals and add them
 175 /// to a sorted (by weight) list.
 176 void StackSlotColoring::InitializeSlots() {
 177   int LastFI = MFI->getObjectIndexEnd();
 178   OrigAlignments.resize(LastFI);
 179   OrigSizes.resize(LastFI);
 180   AllColors.resize(LastFI);
 181   UsedColors.resize(LastFI);
 182   Assignments.resize(LastFI);
 183
 184   // Gather all spill slots into a list.
 185   DOUT << "Spill slot intervals:\n";
 186   for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
 187     LiveInterval &li = i->second;
 188     DEBUG(li.dump());
 189     int FI = li.getStackSlotIndex();
 190     if (MFI->isDeadObjectIndex(FI))
 191       continue;
 192     SSIntervals.push_back(&li);
 193     OrigAlignments[FI] = MFI->getObjectAlignment(FI);
 194     OrigSizes[FI]      = MFI->getObjectSize(FI);
 195     AllColors.set(FI);
 196   }
 197   DOUT << '\n';
 198
 199   // Sort them by weight.
 200   std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
 201
 202   // Get first "color".
 203   NextColor = AllColors.find_first();
 204 }
 205
 206 /// OverlapWithAssignments - Return true if LiveInterval overlaps with any
 207 /// LiveIntervals that have already been assigned to the specified color.
 208 bool
 209 StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
 210   const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
 211   for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
 212     LiveInterval *OtherLI = OtherLIs[i];
 213     if (OtherLI->overlaps(*li))
 214       return true;
 215   }
 216   return false;
 217 }
 218
 219 /// ColorSlotsWithFreeRegs - If there are any free registers available, try
 220 /// replacing spill slots references with registers instead.
 221 bool
 222 StackSlotColoring::ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
 223                                    SmallVector<SmallVector<int, 4>, 16> &RevMap,
 224                                    BitVector &SlotIsReg) {
 225   if (!ColorWithRegs || !VRM->HasUnusedRegisters())
 226     return false;
 227
 228   bool Changed = false;
 229   DOUT << "Assigning unused registers to spill slots:\n";
 230   for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
 231     LiveInterval *li = SSIntervals[i];
 232     int SS = li->getStackSlotIndex();
 233     if (!UsedColors[SS])
 234       continue;
 235     // Get the largest common sub- register class of all the stack slots that
 236     // are colored to this stack slot.
 237     const TargetRegisterClass *RC = 0;
 238     for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
 239       int RSS = RevMap[SS][j];
 240       const TargetRegisterClass *RRC = LS->getIntervalRegClass(RSS);
 241       if (!RC)
 242         RC = RRC;
 243       else
 244         RC = getCommonSubClass(RC, RRC);
 245     }
 246
 247     // If it's not colored to another stack slot, try coloring it
 248     // to a "free" register.
 249     if (!RC)
 250       continue;
 251     unsigned Reg = VRM->getFirstUnusedRegister(RC);
 252     if (!Reg)
 253       continue;
 254     bool IsSafe = true;
 255     for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
 256       int RSS = RevMap[SS][j];
 257       if (!AllMemRefsCanBeUnfolded(RSS)) {
 258         IsSafe = false;
 259         break;
 260       }
 261     }
 262     if (!IsSafe)
 263       // Try color the next spill slot.
 264       continue;
 265
 266     DOUT << "Assigning fi#" << SS << " to " << TRI->getName(Reg)
 267          << ", which in turn means...\n";
 268     // Register and its sub-registers are no longer free.
 269     VRM->setRegisterUsed(Reg);
 270     // If reg is a callee-saved register, it will have to be spilled in
 271     // the prologue.
 272     MRI->setPhysRegUsed(Reg);
 273     for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
 274       VRM->setRegisterUsed(*AS);
 275       MRI->setPhysRegUsed(*AS);
 276     }
 277     // This spill slot is dead after the rewrites
 278     MFI->RemoveStackObject(SS);
 279
 280     // Remember all these FI references will have to be unfolded.
 281     for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
 282       int RSS = RevMap[SS][j];
 283       DOUT << "  Assigning fi#" << RSS << " to " << TRI->getName(Reg) << '\n';
 284       SlotMapping[RSS] = Reg;
 285       SlotIsReg.set(RSS);
 286     }
 287
 288     ++NumEliminated;
 289     Changed = true;
 290   }
 291   DOUT << '\n';
 292
 293   return Changed;
 294 }
 295
 296 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
 297 ///
 298 int StackSlotColoring::ColorSlot(LiveInterval *li) {
 299   int Color = -1;
 300   bool Share = false;
 301   if (!DisableSharing) {
 302     // Check if it's possible to reuse any of the used colors.
 303     Color = UsedColors.find_first();
 304     while (Color != -1) {
 305       if (!OverlapWithAssignments(li, Color)) {
 306         Share = true;
 307         ++NumEliminated;
 308         break;
 309       }
 310       Color = UsedColors.find_next(Color);
 311     }
 312   }
 313
 314   // Assign it to the first available color (assumed to be the best) if it's
 315   // not possible to share a used color with other objects.
 316   if (!Share) {
 317     assert(NextColor != -1 && "No more spill slots?");
 318     Color = NextColor;
 319     UsedColors.set(Color);
 320     NextColor = AllColors.find_next(NextColor);
 321   }
 322
 323   // Record the assignment.
 324   Assignments[Color].push_back(li);
 325   int FI = li->getStackSlotIndex();
 326   DOUT << "Assigning fi#" << FI << " to fi#" << Color << "\n";
 327
 328   // Change size and alignment of the allocated slot. If there are multiple
 329   // objects sharing the same slot, then make sure the size and alignment
 330   // are large enough for all.
 331   unsigned Align = OrigAlignments[FI];
 332   if (!Share || Align > MFI->getObjectAlignment(Color))
 333     MFI->setObjectAlignment(Color, Align);
 334   int64_t Size = OrigSizes[FI];
 335   if (!Share || Size > MFI->getObjectSize(Color))
 336     MFI->setObjectSize(Color, Size);
 337   return Color;
 338 }
 339
 340 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
 341 /// operands in the function.
 342 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
 343   unsigned NumObjs = MFI->getObjectIndexEnd();
 344   SmallVector<int, 16> SlotMapping(NumObjs, -1);
 345   SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
 346   SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
 347   BitVector SlotIsReg(NumObjs);
 348   BitVector UsedColors(NumObjs);
 349
 350   DOUT << "Color spill slot intervals:\n";
 351   bool Changed = false;
 352   for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
 353     LiveInterval *li = SSIntervals[i];
 354     int SS = li->getStackSlotIndex();
 355     int NewSS = ColorSlot(li);
 356     assert(NewSS >= 0 && "Stack coloring failed?");
 357     SlotMapping[SS] = NewSS;
 358     RevMap[NewSS].push_back(SS);
 359     SlotWeights[NewSS] += li->weight;
 360     UsedColors.set(NewSS);
 361     Changed |= (SS != NewSS);
 362   }
 363
 364   DOUT << "\nSpill slots after coloring:\n";
 365   for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
 366     LiveInterval *li = SSIntervals[i];
 367     int SS = li->getStackSlotIndex();
 368     li->weight = SlotWeights[SS];
 369   }
 370   // Sort them by new weight.
 371   std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
 372
 373 #ifndef NDEBUG
 374   for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
 375     DEBUG(SSIntervals[i]->dump());
 376   DOUT << '\n';
 377 #endif
 378
 379   // Can we "color" a stack slot with a unused register?
 380   Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
 381
 382   if (!Changed)
 383     return false;
 384
 385   // Rewrite all MO_FrameIndex operands.
 386   for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
 387     bool isReg = SlotIsReg[SS];
 388     int NewFI = SlotMapping[SS];
 389     if (NewFI == -1 || (NewFI == (int)SS && !isReg))
 390       continue;
 391
 392     SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
 393     for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
 394       if (isReg)
 395         // Rewrite to use a register instead.
 396         UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, MF);
 397       else
 398         RewriteInstruction(RefMIs[i], SS, NewFI, MF);
 399   }
 400
 401   // Delete unused stack slots.
 402   while (NextColor != -1) {
 403     DOUT << "Removing unused stack object fi#" << NextColor << "\n";
 404     MFI->RemoveStackObject(NextColor);
 405     NextColor = AllColors.find_next(NextColor);
 406   }
 407
 408   return true;
 409 }
 410
 411 /// AllMemRefsCanBeUnfolded - Return true if all references of the specified
 412 /// spill slot index can be unfolded.
 413 bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
 414   SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
 415   for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
 416     MachineInstr *MI = RefMIs[i];
 417     if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
 418       return false;
 419     for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
 420       MachineOperand &MO = MI->getOperand(j);
 421       if (MO.isFI() && MO.getIndex() != SS)
 422         // If it uses another frameindex, we can, currently* unfold it.
 423         return false;
 424     }
 425   }
 426   return true;
 427 }
 428
 429 /// RewriteInstruction - Rewrite specified instruction by replacing references
 430 /// to old frame index with new one.
 431 void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
 432                                            int NewFI, MachineFunction &MF) {
 433   for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
 434     MachineOperand &MO = MI->getOperand(i);
 435     if (!MO.isFI())
 436       continue;
 437     int FI = MO.getIndex();
 438     if (FI != OldFI)
 439       continue;
 440     MO.setIndex(NewFI);
 441   }
 442
 443   // Update the MachineMemOperand for the new memory location.
 444   // FIXME: We need a better method of managing these too.
 445   SmallVector<MachineMemOperand, 2> MMOs(MI->memoperands_begin(),
 446                                          MI->memoperands_end());
 447   MI->clearMemOperands(MF);
 448   const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
 449   for (unsigned i = 0, ee = MMOs.size(); i != ee; ++i) {
 450     if (MMOs[i].getValue() != OldSV)
 451       MI->addMemOperand(MF, MMOs[i]);
 452     else {
 453       MachineMemOperand MMO(PseudoSourceValue::getFixedStack(NewFI),
 454                             MMOs[i].getFlags(), MMOs[i].getOffset(),
 455                             MMOs[i].getSize(),  MMOs[i].getAlignment());
 456       MI->addMemOperand(MF, MMO);
 457     }
 458   }
 459 }
 460
 461 /// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
 462 /// folded memory references and replacing those references with register
 463 /// references instead.
 464 void StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
 465                                                     unsigned Reg,
 466                                                     MachineFunction &MF) {
 467   MachineBasicBlock *MBB = MI->getParent();
 468   SmallVector<MachineInstr*, 4> NewMIs;
 469   bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
 470   assert(Success && "Failed to unfold!");
 471   MBB->insert(MI, NewMIs[0]);
 472   MBB->erase(MI);
 473   ++NumRegRepl;
 474 }
 475
 476 /// RemoveDeadStores - Scan through a basic block and look for loads followed
 477 /// by stores.  If they're both using the same stack slot, then the store is
 478 /// definitely dead.  This could obviously be much more aggressive (consider
 479 /// pairs with instructions between them), but such extensions might have a
 480 /// considerable compile time impact.
 481 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
 482   // FIXME: This could be much more aggressive, but we need to investigate
 483   // the compile time impact of doing so.
 484   bool changed = false;
 485
 486   SmallVector<MachineInstr*, 4> toErase;
 487
 488   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
 489        I != E; ++I) {
 490     if (DCELimit != -1 && (int)NumDead >= DCELimit)
 491       break;
 492
 493     MachineBasicBlock::iterator NextMI = next(I);
 494     if (NextMI == MBB->end()) continue;
 495
 496     int FirstSS, SecondSS;
 497     unsigned LoadReg = 0;
 498     unsigned StoreReg = 0;
 499     if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
 500     if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
 501     if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
 502
 503     ++NumDead;
 504     changed = true;
 505
 506     if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
 507       ++NumDead;
 508       toErase.push_back(I);
 509     }
 510
 511     toErase.push_back(NextMI);
 512     ++I;
 513   }
 514
 515   for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
 516        E = toErase.end(); I != E; ++I)
 517     (*I)->eraseFromParent();
 518
 519   return changed;
 520 }
 521
 522
 523 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
 524   DOUT << "********** Stack Slot Coloring **********\n";
 525
 526   MFI = MF.getFrameInfo();
 527   MRI = &MF.getRegInfo();
 528   TII = MF.getTarget().getInstrInfo();
 529   TRI = MF.getTarget().getRegisterInfo();
 530   LS = &getAnalysis<LiveStacks>();
 531   VRM = &getAnalysis<VirtRegMap>();
 532   loopInfo = &getAnalysis<MachineLoopInfo>();
 533
 534   bool Changed = false;
 535
 536   unsigned NumSlots = LS->getNumIntervals();
 537   if (NumSlots < 2) {
 538     if (NumSlots == 0 || !VRM->HasUnusedRegisters())
 539       // Nothing to do!
 540       return false;
 541   }
 542
 543   // Gather spill slot references
 544   ScanForSpillSlotRefs(MF);
 545   InitializeSlots();
 546   Changed = ColorSlots(MF);
 547
 548   NextColor = -1;
 549   SSIntervals.clear();
 550   for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
 551     SSRefs[i].clear();
 552   SSRefs.clear();
 553   OrigAlignments.clear();
 554   OrigSizes.clear();
 555   AllColors.clear();
 556   UsedColors.clear();
 557   for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
 558     Assignments[i].clear();
 559   Assignments.clear();
 560
 561   if (Changed) {
 562     for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
 563       Changed |= RemoveDeadStores(I);
 564   }
 565
 566   return Changed;
 567 }