lib/CodeGen/IfConversion.cpp

   1 //===-- IfConversion.cpp - Machine code if conversion 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 machine instruction level if-conversion pass.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #define DEBUG_TYPE "ifcvt"
  15 #include "BranchFolding.h"
  16 #include "llvm/Function.h"
  17 #include "llvm/CodeGen/Passes.h"
  18 #include "llvm/CodeGen/MachineModuleInfo.h"
  19 #include "llvm/CodeGen/MachineFunctionPass.h"
  20 #include "llvm/Target/TargetInstrInfo.h"
  21 #include "llvm/Target/TargetLowering.h"
  22 #include "llvm/Target/TargetMachine.h"
  23 #include "llvm/Support/CommandLine.h"
  24 #include "llvm/Support/Debug.h"
  25 #include "llvm/Support/ErrorHandling.h"
  26 #include "llvm/Support/raw_ostream.h"
  27 #include "llvm/ADT/DepthFirstIterator.h"
  28 #include "llvm/ADT/Statistic.h"
  29 #include "llvm/ADT/STLExtras.h"
  30 using namespace llvm;
  31
  32 // Hidden options for help debugging.
  33 static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
  34 static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
  35 static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
  36 static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
  37                                    cl::init(false), cl::Hidden);
  38 static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
  39                                     cl::init(false), cl::Hidden);
  40 static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
  41                                      cl::init(false), cl::Hidden);
  42 static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
  43                                       cl::init(false), cl::Hidden);
  44 static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
  45                                       cl::init(false), cl::Hidden);
  46 static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
  47                                        cl::init(false), cl::Hidden);
  48 static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
  49                                     cl::init(false), cl::Hidden);
  50
  51 STATISTIC(NumSimple,       "Number of simple if-conversions performed");
  52 STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
  53 STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
  54 STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
  55 STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
  56 STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
  57 STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
  58 STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
  59 STATISTIC(NumDupBBs,       "Number of duplicated blocks");
  60
  61 namespace {
  62   class VISIBILITY_HIDDEN IfConverter : public MachineFunctionPass {
  63     enum IfcvtKind {
  64       ICNotClassfied,  // BB data valid, but not classified.
  65       ICSimpleFalse,   // Same as ICSimple, but on the false path.
  66       ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
  67       ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
  68       ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
  69       ICTriangleFalse, // Same as ICTriangle, but on the false path.
  70       ICTriangle,      // BB is entry of a triangle sub-CFG.
  71       ICDiamond        // BB is entry of a diamond sub-CFG.
  72     };
  73
  74     /// BBInfo - One per MachineBasicBlock, this is used to cache the result
  75     /// if-conversion feasibility analysis. This includes results from
  76     /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
  77     /// classification, and common tail block of its successors (if it's a
  78     /// diamond shape), its size, whether it's predicable, and whether any
  79     /// instruction can clobber the 'would-be' predicate.
  80     ///
  81     /// IsDone          - True if BB is not to be considered for ifcvt.
  82     /// IsBeingAnalyzed - True if BB is currently being analyzed.
  83     /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
  84     /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
  85     /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
  86     /// HasFallThrough  - True if BB may fallthrough to the following BB.
  87     /// IsUnpredicable  - True if BB is known to be unpredicable.
  88     /// ClobbersPred    - True if BB could modify predicates (e.g. has
  89     ///                   cmp, call, etc.)
  90     /// NonPredSize     - Number of non-predicated instructions.
  91     /// BB              - Corresponding MachineBasicBlock.
  92     /// TrueBB / FalseBB- See AnalyzeBranch().
  93     /// BrCond          - Conditions for end of block conditional branches.
  94     /// Predicate       - Predicate used in the BB.
  95     struct BBInfo {
  96       bool IsDone          : 1;
  97       bool IsBeingAnalyzed : 1;
  98       bool IsAnalyzed      : 1;
  99       bool IsEnqueued      : 1;
 100       bool IsBrAnalyzable  : 1;
 101       bool HasFallThrough  : 1;
 102       bool IsUnpredicable  : 1;
 103       bool CannotBeCopied  : 1;
 104       bool ClobbersPred    : 1;
 105       unsigned NonPredSize;
 106       MachineBasicBlock *BB;
 107       MachineBasicBlock *TrueBB;
 108       MachineBasicBlock *FalseBB;
 109       SmallVector<MachineOperand, 4> BrCond;
 110       SmallVector<MachineOperand, 4> Predicate;
 111       BBInfo() : IsDone(false), IsBeingAnalyzed(false),
 112                  IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
 113                  HasFallThrough(false), IsUnpredicable(false),
 114                  CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
 115                  BB(0), TrueBB(0), FalseBB(0) {}
 116     };
 117
 118     /// IfcvtToken - Record information about pending if-conversions to attemp:
 119     /// BBI             - Corresponding BBInfo.
 120     /// Kind            - Type of block. See IfcvtKind.
 121     /// NeedSubsumption - True if the to-be-predicated BB has already been
 122     ///                   predicated.
 123     /// NumDups      - Number of instructions that would be duplicated due
 124     ///                   to this if-conversion. (For diamonds, the number of
 125     ///                   identical instructions at the beginnings of both
 126     ///                   paths).
 127     /// NumDups2     - For diamonds, the number of identical instructions
 128     ///                   at the ends of both paths.
 129     struct IfcvtToken {
 130       BBInfo &BBI;
 131       IfcvtKind Kind;
 132       bool NeedSubsumption;
 133       unsigned NumDups;
 134       unsigned NumDups2;
 135       IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
 136         : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
 137     };
 138
 139     /// Roots - Basic blocks that do not have successors. These are the starting
 140     /// points of Graph traversal.
 141     std::vector<MachineBasicBlock*> Roots;
 142
 143     /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
 144     /// basic block number.
 145     std::vector<BBInfo> BBAnalysis;
 146
 147     const TargetLowering *TLI;
 148     const TargetInstrInfo *TII;
 149     bool MadeChange;
 150     int FnNum;
 151   public:
 152     static char ID;
 153     IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {}
 154
 155     virtual bool runOnMachineFunction(MachineFunction &MF);
 156     virtual const char *getPassName() const { return "If Converter"; }
 157
 158   private:
 159     bool ReverseBranchCondition(BBInfo &BBI);
 160     bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
 161     bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
 162                        bool FalseBranch, unsigned &Dups) const;
 163     bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
 164                       unsigned &Dups1, unsigned &Dups2) const;
 165     void ScanInstructions(BBInfo &BBI);
 166     BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
 167                          std::vector<IfcvtToken*> &Tokens);
 168     bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
 169                              bool isTriangle = false, bool RevBranch = false);
 170     bool AnalyzeBlocks(MachineFunction &MF,
 171                        std::vector<IfcvtToken*> &Tokens);
 172     void InvalidatePreds(MachineBasicBlock *BB);
 173     void RemoveExtraEdges(BBInfo &BBI);
 174     bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
 175     bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
 176     bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
 177                           unsigned NumDups1, unsigned NumDups2);
 178     void PredicateBlock(BBInfo &BBI,
 179                         MachineBasicBlock::iterator E,
 180                         SmallVectorImpl<MachineOperand> &Cond);
 181     void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
 182                                SmallVectorImpl<MachineOperand> &Cond,
 183                                bool IgnoreBr = false);
 184     void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
 185
 186     bool MeetIfcvtSizeLimit(unsigned Size) const {
 187       return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
 188     }
 189
 190     // blockAlwaysFallThrough - Block ends without a terminator.
 191     bool blockAlwaysFallThrough(BBInfo &BBI) const {
 192       return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
 193     }
 194
 195     // IfcvtTokenCmp - Used to sort if-conversion candidates.
 196     static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
 197       int Incr1 = (C1->Kind == ICDiamond)
 198         ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
 199       int Incr2 = (C2->Kind == ICDiamond)
 200         ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
 201       if (Incr1 > Incr2)
 202         return true;
 203       else if (Incr1 == Incr2) {
 204         // Favors subsumption.
 205         if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
 206           return true;
 207         else if (C1->NeedSubsumption == C2->NeedSubsumption) {
 208           // Favors diamond over triangle, etc.
 209           if ((unsigned)C1->Kind < (unsigned)C2->Kind)
 210             return true;
 211           else if (C1->Kind == C2->Kind)
 212             return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
 213         }
 214       }
 215       return false;
 216     }
 217   };
 218
 219   char IfConverter::ID = 0;
 220 }
 221
 222 static RegisterPass<IfConverter>
 223 X("if-converter", "If Converter");
 224
 225 FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
 226
 227 bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
 228   TLI = MF.getTarget().getTargetLowering();
 229   TII = MF.getTarget().getInstrInfo();
 230   if (!TII) return false;
 231
 232   DEBUG(errs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
 233                << MF.getFunction()->getName() << "\'");
 234
 235   if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
 236     DEBUG(errs() << " skipped\n");
 237     return false;
 238   }
 239   DEBUG(errs() << "\n");
 240
 241   MF.RenumberBlocks();
 242   BBAnalysis.resize(MF.getNumBlockIDs());
 243
 244   // Look for root nodes, i.e. blocks without successors.
 245   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
 246     if (I->succ_empty())
 247       Roots.push_back(I);
 248
 249   std::vector<IfcvtToken*> Tokens;
 250   MadeChange = false;
 251   unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
 252     NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
 253   while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
 254     // Do an initial analysis for each basic block and find all the potential
 255     // candidates to perform if-conversion.
 256     bool Change = AnalyzeBlocks(MF, Tokens);
 257     while (!Tokens.empty()) {
 258       IfcvtToken *Token = Tokens.back();
 259       Tokens.pop_back();
 260       BBInfo &BBI = Token->BBI;
 261       IfcvtKind Kind = Token->Kind;
 262       unsigned NumDups = Token->NumDups;
 263       unsigned NumDups2 = Token->NumDups2;
 264
 265       delete Token;
 266
 267       // If the block has been evicted out of the queue or it has already been
 268       // marked dead (due to it being predicated), then skip it.
 269       if (BBI.IsDone)
 270         BBI.IsEnqueued = false;
 271       if (!BBI.IsEnqueued)
 272         continue;
 273
 274       BBI.IsEnqueued = false;
 275
 276       bool RetVal = false;
 277       switch (Kind) {
 278       default: assert(false && "Unexpected!");
 279         break;
 280       case ICSimple:
 281       case ICSimpleFalse: {
 282         bool isFalse = Kind == ICSimpleFalse;
 283         if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
 284         DEBUG(errs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
 285                      << "): BB#" << BBI.BB->getNumber() << " ("
 286                      << ((Kind == ICSimpleFalse)
 287                          ? BBI.FalseBB->getNumber()
 288                          : BBI.TrueBB->getNumber()) << ") ");
 289         RetVal = IfConvertSimple(BBI, Kind);
 290         DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
 291         if (RetVal) {
 292           if (isFalse) NumSimpleFalse++;
 293           else         NumSimple++;
 294         }
 295        break;
 296       }
 297       case ICTriangle:
 298       case ICTriangleRev:
 299       case ICTriangleFalse:
 300       case ICTriangleFRev: {
 301         bool isFalse = Kind == ICTriangleFalse;
 302         bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
 303         if (DisableTriangle && !isFalse && !isRev) break;
 304         if (DisableTriangleR && !isFalse && isRev) break;
 305         if (DisableTriangleF && isFalse && !isRev) break;
 306         if (DisableTriangleFR && isFalse && isRev) break;
 307         DEBUG(errs() << "Ifcvt (Triangle");
 308         if (isFalse)
 309           DEBUG(errs() << " false");
 310         if (isRev)
 311           DEBUG(errs() << " rev");
 312         DEBUG(errs() << "): BB#" << BBI.BB->getNumber() << " (T:"
 313                      << BBI.TrueBB->getNumber() << ",F:"
 314                      << BBI.FalseBB->getNumber() << ") ");
 315         RetVal = IfConvertTriangle(BBI, Kind);
 316         DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
 317         if (RetVal) {
 318           if (isFalse) {
 319             if (isRev) NumTriangleFRev++;
 320             else       NumTriangleFalse++;
 321           } else {
 322             if (isRev) NumTriangleRev++;
 323             else       NumTriangle++;
 324           }
 325         }
 326         break;
 327       }
 328       case ICDiamond: {
 329         if (DisableDiamond) break;
 330         DEBUG(errs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
 331                      << BBI.TrueBB->getNumber() << ",F:"
 332                      << BBI.FalseBB->getNumber() << ") ");
 333         RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
 334         DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
 335         if (RetVal) NumDiamonds++;
 336         break;
 337       }
 338       }
 339
 340       Change |= RetVal;
 341
 342       NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
 343         NumTriangleFalse + NumTriangleFRev + NumDiamonds;
 344       if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
 345         break;
 346     }
 347
 348     if (!Change)
 349       break;
 350     MadeChange |= Change;
 351   }
 352
 353   // Delete tokens in case of early exit.
 354   while (!Tokens.empty()) {
 355     IfcvtToken *Token = Tokens.back();
 356     Tokens.pop_back();
 357     delete Token;
 358   }
 359
 360   Tokens.clear();
 361   Roots.clear();
 362   BBAnalysis.clear();
 363
 364   if (MadeChange) {
 365     BranchFolder BF(false);
 366     BF.OptimizeFunction(MF, TII,
 367                         MF.getTarget().getRegisterInfo(),
 368                         getAnalysisIfAvailable<MachineModuleInfo>());
 369   }
 370
 371   return MadeChange;
 372 }
 373
 374 /// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
 375 /// its 'true' successor.
 376 static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
 377                                          MachineBasicBlock *TrueBB) {
 378   for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
 379          E = BB->succ_end(); SI != E; ++SI) {
 380     MachineBasicBlock *SuccBB = *SI;
 381     if (SuccBB != TrueBB)
 382       return SuccBB;
 383   }
 384   return NULL;
 385 }
 386
 387 /// ReverseBranchCondition - Reverse the condition of the end of the block
 388 /// branch. Swap block's 'true' and 'false' successors.
 389 bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
 390   if (!TII->ReverseBranchCondition(BBI.BrCond)) {
 391     TII->RemoveBranch(*BBI.BB);
 392     TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
 393     std::swap(BBI.TrueBB, BBI.FalseBB);
 394     return true;
 395   }
 396   return false;
 397 }
 398
 399 /// getNextBlock - Returns the next block in the function blocks ordering. If
 400 /// it is the end, returns NULL.
 401 static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
 402   MachineFunction::iterator I = BB;
 403   MachineFunction::iterator E = BB->getParent()->end();
 404   if (++I == E)
 405     return NULL;
 406   return I;
 407 }
 408
 409 /// ValidSimple - Returns true if the 'true' block (along with its
 410 /// predecessor) forms a valid simple shape for ifcvt. It also returns the
 411 /// number of instructions that the ifcvt would need to duplicate if performed
 412 /// in Dups.
 413 bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
 414   Dups = 0;
 415   if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
 416     return false;
 417
 418   if (TrueBBI.IsBrAnalyzable)
 419     return false;
 420
 421   if (TrueBBI.BB->pred_size() > 1) {
 422     if (TrueBBI.CannotBeCopied ||
 423         TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
 424       return false;
 425     Dups = TrueBBI.NonPredSize;
 426   }
 427
 428   return true;
 429 }
 430
 431 /// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
 432 /// with their common predecessor) forms a valid triangle shape for ifcvt.
 433 /// If 'FalseBranch' is true, it checks if 'true' block's false branch
 434 /// branches to the false branch rather than the other way around. It also
 435 /// returns the number of instructions that the ifcvt would need to duplicate
 436 /// if performed in 'Dups'.
 437 bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
 438                                 bool FalseBranch, unsigned &Dups) const {
 439   Dups = 0;
 440   if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
 441     return false;
 442
 443   if (TrueBBI.BB->pred_size() > 1) {
 444     if (TrueBBI.CannotBeCopied)
 445       return false;
 446
 447     unsigned Size = TrueBBI.NonPredSize;
 448     if (TrueBBI.IsBrAnalyzable) {
 449       if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
 450         // Ends with an unconditional branch. It will be removed.
 451         --Size;
 452       else {
 453         MachineBasicBlock *FExit = FalseBranch
 454           ? TrueBBI.TrueBB : TrueBBI.FalseBB;
 455         if (FExit)
 456           // Require a conditional branch
 457           ++Size;
 458       }
 459     }
 460     if (Size > TLI->getIfCvtDupBlockSizeLimit())
 461       return false;
 462     Dups = Size;
 463   }
 464
 465   MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
 466   if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
 467     MachineFunction::iterator I = TrueBBI.BB;
 468     if (++I == TrueBBI.BB->getParent()->end())
 469       return false;
 470     TExit = I;
 471   }
 472   return TExit && TExit == FalseBBI.BB;
 473 }
 474
 475 static
 476 MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
 477                                                const TargetInstrInfo *TII) {
 478   MachineBasicBlock::iterator I = BB->end();
 479   while (I != BB->begin()) {
 480     --I;
 481     if (!I->getDesc().isBranch())
 482       break;
 483   }
 484   return I;
 485 }
 486
 487 /// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
 488 /// with their common predecessor) forms a valid diamond shape for ifcvt.
 489 bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
 490                                unsigned &Dups1, unsigned &Dups2) const {
 491   Dups1 = Dups2 = 0;
 492   if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
 493       FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
 494     return false;
 495
 496   MachineBasicBlock *TT = TrueBBI.TrueBB;
 497   MachineBasicBlock *FT = FalseBBI.TrueBB;
 498
 499   if (!TT && blockAlwaysFallThrough(TrueBBI))
 500     TT = getNextBlock(TrueBBI.BB);
 501   if (!FT && blockAlwaysFallThrough(FalseBBI))
 502     FT = getNextBlock(FalseBBI.BB);
 503   if (TT != FT)
 504     return false;
 505   if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
 506     return false;
 507   if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
 508     return false;
 509
 510   // FIXME: Allow true block to have an early exit?
 511   if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
 512       (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
 513     return false;
 514
 515   MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
 516   MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
 517   while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) {
 518     if (!TI->isIdenticalTo(FI))
 519       break;
 520     ++Dups1;
 521     ++TI;
 522     ++FI;
 523   }
 524
 525   TI = firstNonBranchInst(TrueBBI.BB, TII);
 526   FI = firstNonBranchInst(FalseBBI.BB, TII);
 527   while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) {
 528     if (!TI->isIdenticalTo(FI))
 529       break;
 530     ++Dups2;
 531     --TI;
 532     --FI;
 533   }
 534
 535   return true;
 536 }
 537
 538 /// ScanInstructions - Scan all the instructions in the block to determine if
 539 /// the block is predicable. In most cases, that means all the instructions
 540 /// in the block are isPredicable(). Also checks if the block contains any
 541 /// instruction which can clobber a predicate (e.g. condition code register).
 542 /// If so, the block is not predicable unless it's the last instruction.
 543 void IfConverter::ScanInstructions(BBInfo &BBI) {
 544   if (BBI.IsDone)
 545     return;
 546
 547   bool AlreadyPredicated = BBI.Predicate.size() > 0;
 548   // First analyze the end of BB branches.
 549   BBI.TrueBB = BBI.FalseBB = NULL;
 550   BBI.BrCond.clear();
 551   BBI.IsBrAnalyzable =
 552     !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
 553   BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
 554
 555   if (BBI.BrCond.size()) {
 556     // No false branch. This BB must end with a conditional branch and a
 557     // fallthrough.
 558     if (!BBI.FalseBB)
 559       BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
 560     if (!BBI.FalseBB) {
 561       // Malformed bcc? True and false blocks are the same?
 562       BBI.IsUnpredicable = true;
 563       return;
 564     }
 565   }
 566
 567   // Then scan all the instructions.
 568   BBI.NonPredSize = 0;
 569   BBI.ClobbersPred = false;
 570   for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
 571        I != E; ++I) {
 572     const TargetInstrDesc &TID = I->getDesc();
 573     if (TID.isNotDuplicable())
 574       BBI.CannotBeCopied = true;
 575
 576     bool isPredicated = TII->isPredicated(I);
 577     bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
 578
 579     if (!isCondBr) {
 580       if (!isPredicated)
 581         BBI.NonPredSize++;
 582       else if (!AlreadyPredicated) {
 583         // FIXME: This instruction is already predicated before the
 584         // if-conversion pass. It's probably something like a conditional move.
 585         // Mark this block unpredicable for now.
 586         BBI.IsUnpredicable = true;
 587         return;
 588       }
 589     }
 590
 591     if (BBI.ClobbersPred && !isPredicated) {
 592       // Predicate modification instruction should end the block (except for
 593       // already predicated instructions and end of block branches).
 594       if (isCondBr) {
 595         // A conditional branch is not predicable, but it may be eliminated.
 596         continue;
 597       }
 598
 599       // Predicate may have been modified, the subsequent (currently)
 600       // unpredicated instructions cannot be correctly predicated.
 601       BBI.IsUnpredicable = true;
 602       return;
 603     }
 604
 605     // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
 606     // still potentially predicable.
 607     std::vector<MachineOperand> PredDefs;
 608     if (TII->DefinesPredicate(I, PredDefs))
 609       BBI.ClobbersPred = true;
 610
 611     if (!TID.isPredicable()) {
 612       BBI.IsUnpredicable = true;
 613       return;
 614     }
 615   }
 616 }
 617
 618 /// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
 619 /// predicated by the specified predicate.
 620 bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
 621                                       SmallVectorImpl<MachineOperand> &Pred,
 622                                       bool isTriangle, bool RevBranch) {
 623   // If the block is dead or unpredicable, then it cannot be predicated.
 624   if (BBI.IsDone || BBI.IsUnpredicable)
 625     return false;
 626
 627   // If it is already predicated, check if its predicate subsumes the new
 628   // predicate.
 629   if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
 630     return false;
 631
 632   if (BBI.BrCond.size()) {
 633     if (!isTriangle)
 634       return false;
 635
 636     // Test predicate subsumption.
 637     SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
 638     SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
 639     if (RevBranch) {
 640       if (TII->ReverseBranchCondition(Cond))
 641         return false;
 642     }
 643     if (TII->ReverseBranchCondition(RevPred) ||
 644         !TII->SubsumesPredicate(Cond, RevPred))
 645       return false;
 646   }
 647
 648   return true;
 649 }
 650
 651 /// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
 652 /// the specified block. Record its successors and whether it looks like an
 653 /// if-conversion candidate.
 654 IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
 655                                              std::vector<IfcvtToken*> &Tokens) {
 656   BBInfo &BBI = BBAnalysis[BB->getNumber()];
 657
 658   if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
 659     return BBI;
 660
 661   BBI.BB = BB;
 662   BBI.IsBeingAnalyzed = true;
 663
 664   ScanInstructions(BBI);
 665
 666   // Unanalyzable or ends with fallthrough or unconditional branch.
 667   if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
 668     BBI.IsBeingAnalyzed = false;
 669     BBI.IsAnalyzed = true;
 670     return BBI;
 671   }
 672
 673   // Do not ifcvt if either path is a back edge to the entry block.
 674   if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
 675     BBI.IsBeingAnalyzed = false;
 676     BBI.IsAnalyzed = true;
 677     return BBI;
 678   }
 679
 680   // Do not ifcvt if true and false fallthrough blocks are the same.
 681   if (!BBI.FalseBB) {
 682     BBI.IsBeingAnalyzed = false;
 683     BBI.IsAnalyzed = true;
 684     return BBI;
 685   }
 686
 687   BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
 688   BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
 689
 690   if (TrueBBI.IsDone && FalseBBI.IsDone) {
 691     BBI.IsBeingAnalyzed = false;
 692     BBI.IsAnalyzed = true;
 693     return BBI;
 694   }
 695
 696   SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
 697   bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
 698
 699   unsigned Dups = 0;
 700   unsigned Dups2 = 0;
 701   bool TNeedSub = TrueBBI.Predicate.size() > 0;
 702   bool FNeedSub = FalseBBI.Predicate.size() > 0;
 703   bool Enqueued = false;
 704   if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
 705       MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
 706       MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
 707       FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
 708       FeasibilityAnalysis(FalseBBI, RevCond)) {
 709     // Diamond:
 710     //   EBB
 711     //   / \_
 712     //  |   |
 713     // TBB FBB
 714     //   \ /
 715     //  TailBB
 716     // Note TailBB can be empty.
 717     Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
 718                                     Dups2));
 719     Enqueued = true;
 720   }
 721
 722   if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
 723       MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
 724       FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
 725     // Triangle:
 726     //   EBB
 727     //   | \_
 728     //   |  |
 729     //   | TBB
 730     //   |  /
 731     //   FBB
 732     Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
 733     Enqueued = true;
 734   }
 735
 736   if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
 737       MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
 738       FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
 739     Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
 740     Enqueued = true;
 741   }
 742
 743   if (ValidSimple(TrueBBI, Dups) &&
 744       MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
 745       FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
 746     // Simple (split, no rejoin):
 747     //   EBB
 748     //   | \_
 749     //   |  |
 750     //   | TBB---> exit
 751     //   |
 752     //   FBB
 753     Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
 754     Enqueued = true;
 755   }
 756
 757   if (CanRevCond) {
 758     // Try the other path...
 759     if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
 760         MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
 761         FeasibilityAnalysis(FalseBBI, RevCond, true)) {
 762       Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
 763       Enqueued = true;
 764     }
 765
 766     if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
 767         MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
 768         FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
 769       Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
 770       Enqueued = true;
 771     }
 772
 773     if (ValidSimple(FalseBBI, Dups) &&
 774         MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
 775         FeasibilityAnalysis(FalseBBI, RevCond)) {
 776       Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
 777       Enqueued = true;
 778     }
 779   }
 780
 781   BBI.IsEnqueued = Enqueued;
 782   BBI.IsBeingAnalyzed = false;
 783   BBI.IsAnalyzed = true;
 784   return BBI;
 785 }
 786
 787 /// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
 788 /// candidates. It returns true if any CFG restructuring is done to expose more
 789 /// if-conversion opportunities.
 790 bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
 791                                 std::vector<IfcvtToken*> &Tokens) {
 792   bool Change = false;
 793   std::set<MachineBasicBlock*> Visited;
 794   for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
 795     for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
 796            E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
 797       MachineBasicBlock *BB = *I;
 798       AnalyzeBlock(BB, Tokens);
 799     }
 800   }
 801
 802   // Sort to favor more complex ifcvt scheme.
 803   std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
 804
 805   return Change;
 806 }
 807
 808 /// canFallThroughTo - Returns true either if ToBB is the next block after BB or
 809 /// that all the intervening blocks are empty (given BB can fall through to its
 810 /// next block).
 811 static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
 812   MachineFunction::iterator I = BB;
 813   MachineFunction::iterator TI = ToBB;
 814   MachineFunction::iterator E = BB->getParent()->end();
 815   while (++I != TI)
 816     if (I == E || !I->empty())
 817       return false;
 818   return true;
 819 }
 820
 821 /// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
 822 /// to determine if it can be if-converted. If predecessor is already enqueued,
 823 /// dequeue it!
 824 void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
 825   for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
 826          E = BB->pred_end(); PI != E; ++PI) {
 827     BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
 828     if (PBBI.IsDone || PBBI.BB == BB)
 829       continue;
 830     PBBI.IsAnalyzed = false;
 831     PBBI.IsEnqueued = false;
 832   }
 833 }
 834
 835 /// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
 836 ///
 837 static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
 838                                const TargetInstrInfo *TII) {
 839   SmallVector<MachineOperand, 0> NoCond;
 840   TII->InsertBranch(*BB, ToBB, NULL, NoCond);
 841 }
 842
 843 /// RemoveExtraEdges - Remove true / false edges if either / both are no longer
 844 /// successors.
 845 void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
 846   MachineBasicBlock *TBB = NULL, *FBB = NULL;
 847   SmallVector<MachineOperand, 4> Cond;
 848   if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
 849     BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
 850 }
 851
 852 /// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
 853 ///
 854 bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
 855   BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
 856   BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
 857   BBInfo *CvtBBI = &TrueBBI;
 858   BBInfo *NextBBI = &FalseBBI;
 859
 860   SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
 861   if (Kind == ICSimpleFalse)
 862     std::swap(CvtBBI, NextBBI);
 863
 864   if (CvtBBI->IsDone ||
 865       (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
 866     // Something has changed. It's no longer safe to predicate this block.
 867     BBI.IsAnalyzed = false;
 868     CvtBBI->IsAnalyzed = false;
 869     return false;
 870   }
 871
 872   if (Kind == ICSimpleFalse)
 873     if (TII->ReverseBranchCondition(Cond))
 874       assert(false && "Unable to reverse branch condition!");
 875
 876   if (CvtBBI->BB->pred_size() > 1) {
 877     BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
 878     // Copy instructions in the true block, predicate them, and add them to
 879     // the entry block.
 880     CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
 881   } else {
 882     PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
 883
 884     // Merge converted block into entry block.
 885     BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
 886     MergeBlocks(BBI, *CvtBBI);
 887   }
 888
 889   bool IterIfcvt = true;
 890   if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
 891     InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
 892     BBI.HasFallThrough = false;
 893     // Now ifcvt'd block will look like this:
 894     // BB:
 895     // ...
 896     // t, f = cmp
 897     // if t op
 898     // b BBf
 899     //
 900     // We cannot further ifcvt this block because the unconditional branch
 901     // will have to be predicated on the new condition, that will not be
 902     // available if cmp executes.
 903     IterIfcvt = false;
 904   }
 905
 906   RemoveExtraEdges(BBI);
 907
 908   // Update block info. BB can be iteratively if-converted.
 909   if (!IterIfcvt)
 910     BBI.IsDone = true;
 911   InvalidatePreds(BBI.BB);
 912   CvtBBI->IsDone = true;
 913
 914   // FIXME: Must maintain LiveIns.
 915   return true;
 916 }
 917
 918 /// IfConvertTriangle - If convert a triangle sub-CFG.
 919 ///
 920 bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
 921   BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
 922   BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
 923   BBInfo *CvtBBI = &TrueBBI;
 924   BBInfo *NextBBI = &FalseBBI;
 925
 926   SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
 927   if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
 928     std::swap(CvtBBI, NextBBI);
 929
 930   if (CvtBBI->IsDone ||
 931       (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
 932     // Something has changed. It's no longer safe to predicate this block.
 933     BBI.IsAnalyzed = false;
 934     CvtBBI->IsAnalyzed = false;
 935     return false;
 936   }
 937
 938   if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
 939     if (TII->ReverseBranchCondition(Cond))
 940       assert(false && "Unable to reverse branch condition!");
 941
 942   if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
 943     if (ReverseBranchCondition(*CvtBBI)) {
 944       // BB has been changed, modify its predecessors (except for this
 945       // one) so they don't get ifcvt'ed based on bad intel.
 946       for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
 947              E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
 948         MachineBasicBlock *PBB = *PI;
 949         if (PBB == BBI.BB)
 950           continue;
 951         BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
 952         if (PBBI.IsEnqueued) {
 953           PBBI.IsAnalyzed = false;
 954           PBBI.IsEnqueued = false;
 955         }
 956       }
 957     }
 958   }
 959
 960   bool HasEarlyExit = CvtBBI->FalseBB != NULL;
 961   bool DupBB = CvtBBI->BB->pred_size() > 1;
 962   if (DupBB) {
 963     BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
 964     // Copy instructions in the true block, predicate them, and add them to
 965     // the entry block.
 966     CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
 967   } else {
 968     // Predicate the 'true' block after removing its branch.
 969     CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
 970     PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
 971
 972     // Now merge the entry of the triangle with the true block.
 973     BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
 974     MergeBlocks(BBI, *CvtBBI);
 975   }
 976
 977   // If 'true' block has a 'false' successor, add an exit branch to it.
 978   if (HasEarlyExit) {
 979     SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
 980                                            CvtBBI->BrCond.end());
 981     if (TII->ReverseBranchCondition(RevCond))
 982       assert(false && "Unable to reverse branch condition!");
 983     TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
 984     BBI.BB->addSuccessor(CvtBBI->FalseBB);
 985   }
 986
 987   // Merge in the 'false' block if the 'false' block has no other
 988   // predecessors. Otherwise, add an unconditional branch to 'false'.
 989   bool FalseBBDead = false;
 990   bool IterIfcvt = true;
 991   bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
 992   if (!isFallThrough) {
 993     // Only merge them if the true block does not fallthrough to the false
 994     // block. By not merging them, we make it possible to iteratively
 995     // ifcvt the blocks.
 996     if (!HasEarlyExit &&
 997         NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
 998       MergeBlocks(BBI, *NextBBI);
 999       FalseBBDead = true;
1000     } else {
1001       InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1002       BBI.HasFallThrough = false;
1003     }
1004     // Mixed predicated and unpredicated code. This cannot be iteratively
1005     // predicated.
1006     IterIfcvt = false;
1007   }
1008
1009   RemoveExtraEdges(BBI);
1010
1011   // Update block info. BB can be iteratively if-converted.
1012   if (!IterIfcvt)
1013     BBI.IsDone = true;
1014   InvalidatePreds(BBI.BB);
1015   CvtBBI->IsDone = true;
1016   if (FalseBBDead)
1017     NextBBI->IsDone = true;
1018
1019   // FIXME: Must maintain LiveIns.
1020   return true;
1021 }
1022
1023 /// IfConvertDiamond - If convert a diamond sub-CFG.
1024 ///
1025 bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1026                                    unsigned NumDups1, unsigned NumDups2) {
1027   BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1028   BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1029   MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1030   // True block must fall through or end with an unanalyzable terminator.
1031   if (!TailBB) {
1032     if (blockAlwaysFallThrough(TrueBBI))
1033       TailBB = FalseBBI.TrueBB;
1034     assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1035   }
1036
1037   if (TrueBBI.IsDone || FalseBBI.IsDone ||
1038       TrueBBI.BB->pred_size() > 1 ||
1039       FalseBBI.BB->pred_size() > 1) {
1040     // Something has changed. It's no longer safe to predicate these blocks.
1041     BBI.IsAnalyzed = false;
1042     TrueBBI.IsAnalyzed = false;
1043     FalseBBI.IsAnalyzed = false;
1044     return false;
1045   }
1046
1047   // Merge the 'true' and 'false' blocks by copying the instructions
1048   // from the 'false' block to the 'true' block. That is, unless the true
1049   // block would clobber the predicate, in that case, do the opposite.
1050   BBInfo *BBI1 = &TrueBBI;
1051   BBInfo *BBI2 = &FalseBBI;
1052   SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1053   if (TII->ReverseBranchCondition(RevCond))
1054     assert(false && "Unable to reverse branch condition!");
1055   SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1056   SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1057
1058   // Figure out the more profitable ordering.
1059   bool DoSwap = false;
1060   if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1061     DoSwap = true;
1062   else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1063     if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1064       DoSwap = true;
1065   }
1066   if (DoSwap) {
1067     std::swap(BBI1, BBI2);
1068     std::swap(Cond1, Cond2);
1069   }
1070
1071   // Remove the conditional branch from entry to the blocks.
1072   BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1073
1074   // Remove the duplicated instructions at the beginnings of both paths.
1075   MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1076   MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1077   BBI1->NonPredSize -= NumDups1;
1078   BBI2->NonPredSize -= NumDups1;
1079   while (NumDups1 != 0) {
1080     ++DI1;
1081     ++DI2;
1082     --NumDups1;
1083   }
1084   BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1085   BBI2->BB->erase(BBI2->BB->begin(), DI2);
1086
1087   // Predicate the 'true' block after removing its branch.
1088   BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1089   DI1 = BBI1->BB->end();
1090   for (unsigned i = 0; i != NumDups2; ++i)
1091     --DI1;
1092   BBI1->BB->erase(DI1, BBI1->BB->end());
1093   PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1094
1095   // Predicate the 'false' block.
1096   BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1097   DI2 = BBI2->BB->end();
1098   while (NumDups2 != 0) {
1099     --DI2;
1100     --NumDups2;
1101   }
1102   PredicateBlock(*BBI2, DI2, *Cond2);
1103
1104   // Merge the true block into the entry of the diamond.
1105   MergeBlocks(BBI, *BBI1);
1106   MergeBlocks(BBI, *BBI2);
1107
1108   // If the if-converted block falls through or unconditionally branches into
1109   // the tail block, and the tail block does not have other predecessors, then
1110   // fold the tail block in as well. Otherwise, unless it falls through to the
1111   // tail, add a unconditional branch to it.
1112   if (TailBB) {
1113     BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1114     if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1115       BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1116       MergeBlocks(BBI, TailBBI);
1117       TailBBI.IsDone = true;
1118     } else {
1119       InsertUncondBranch(BBI.BB, TailBB, TII);
1120       BBI.HasFallThrough = false;
1121     }
1122   }
1123
1124   RemoveExtraEdges(BBI);
1125
1126   // Update block info.
1127   BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1128   InvalidatePreds(BBI.BB);
1129
1130   // FIXME: Must maintain LiveIns.
1131   return true;
1132 }
1133
1134 /// PredicateBlock - Predicate instructions from the start of the block to the
1135 /// specified end with the specified condition.
1136 void IfConverter::PredicateBlock(BBInfo &BBI,
1137                                  MachineBasicBlock::iterator E,
1138                                  SmallVectorImpl<MachineOperand> &Cond) {
1139   for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1140     if (TII->isPredicated(I))
1141       continue;
1142     if (!TII->PredicateInstruction(I, Cond)) {
1143 #ifndef NDEBUG
1144       errs() << "Unable to predicate " << *I << "!\n";
1145 #endif
1146       llvm_unreachable(0);
1147     }
1148   }
1149
1150   std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1151
1152   BBI.IsAnalyzed = false;
1153   BBI.NonPredSize = 0;
1154
1155   NumIfConvBBs++;
1156 }
1157
1158 /// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1159 /// the destination block. Skip end of block branches if IgnoreBr is true.
1160 void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1161                                         SmallVectorImpl<MachineOperand> &Cond,
1162                                         bool IgnoreBr) {
1163   MachineFunction &MF = *ToBBI.BB->getParent();
1164
1165   for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1166          E = FromBBI.BB->end(); I != E; ++I) {
1167     const TargetInstrDesc &TID = I->getDesc();
1168     bool isPredicated = TII->isPredicated(I);
1169     // Do not copy the end of the block branches.
1170     if (IgnoreBr && !isPredicated && TID.isBranch())
1171       break;
1172
1173     MachineInstr *MI = MF.CloneMachineInstr(I);
1174     ToBBI.BB->insert(ToBBI.BB->end(), MI);
1175     ToBBI.NonPredSize++;
1176
1177     if (!isPredicated)
1178       if (!TII->PredicateInstruction(MI, Cond)) {
1179 #ifndef NDEBUG
1180         errs() << "Unable to predicate " << *I << "!\n";
1181 #endif
1182         llvm_unreachable(0);
1183       }
1184   }
1185
1186   std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1187                                          FromBBI.BB->succ_end());
1188   MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1189   MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1190
1191   for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1192     MachineBasicBlock *Succ = Succs[i];
1193     // Fallthrough edge can't be transferred.
1194     if (Succ == FallThrough)
1195       continue;
1196     ToBBI.BB->addSuccessor(Succ);
1197   }
1198
1199   std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1200             std::back_inserter(ToBBI.Predicate));
1201   std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1202
1203   ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1204   ToBBI.IsAnalyzed = false;
1205
1206   NumDupBBs++;
1207 }
1208
1209 /// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1210 ///
1211 void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1212   ToBBI.BB->splice(ToBBI.BB->end(),
1213                    FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1214
1215   // Redirect all branches to FromBB to ToBB.
1216   std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1217                                          FromBBI.BB->pred_end());
1218   for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1219     MachineBasicBlock *Pred = Preds[i];
1220     if (Pred == ToBBI.BB)
1221       continue;
1222     Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1223   }
1224
1225   std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1226                                          FromBBI.BB->succ_end());
1227   MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1228   MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1229
1230   for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1231     MachineBasicBlock *Succ = Succs[i];
1232     // Fallthrough edge can't be transferred.
1233     if (Succ == FallThrough)
1234       continue;
1235     FromBBI.BB->removeSuccessor(Succ);
1236     ToBBI.BB->addSuccessor(Succ);
1237   }
1238
1239   // Now FromBBI always falls through to the next block!
1240   if (NBB && !FromBBI.BB->isSuccessor(NBB))
1241     FromBBI.BB->addSuccessor(NBB);
1242
1243   std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1244             std::back_inserter(ToBBI.Predicate));
1245   FromBBI.Predicate.clear();
1246
1247   ToBBI.NonPredSize += FromBBI.NonPredSize;
1248   FromBBI.NonPredSize = 0;
1249
1250   ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1251   ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1252   ToBBI.IsAnalyzed = false;
1253   FromBBI.IsAnalyzed = false;
1254 }