IfConversion.cpp revision 030a0a0cdb38924e55773a8e0b5fe7347aa664aa
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" 30using namespace llvm; 31 32// Hidden options for help debugging. 33static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); 34static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); 35static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); 36static cl::opt<bool> DisableSimple("disable-ifcvt-simple", 37 cl::init(false), cl::Hidden); 38static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false", 39 cl::init(false), cl::Hidden); 40static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", 41 cl::init(false), cl::Hidden); 42static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev", 43 cl::init(false), cl::Hidden); 44static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false", 45 cl::init(false), cl::Hidden); 46static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev", 47 cl::init(false), cl::Hidden); 48static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", 49 cl::init(false), cl::Hidden); 50 51STATISTIC(NumSimple, "Number of simple if-conversions performed"); 52STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed"); 53STATISTIC(NumTriangle, "Number of triangle if-conversions performed"); 54STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed"); 55STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed"); 56STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed"); 57STATISTIC(NumDiamonds, "Number of diamond if-conversions performed"); 58STATISTIC(NumIfConvBBs, "Number of if-converted blocks"); 59STATISTIC(NumDupBBs, "Number of duplicated blocks"); 60 61namespace { 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 222static RegisterPass<IfConverter> 223X("if-converter", "If Converter"); 224 225FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); } 226 227bool 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. 376static 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. 389bool 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. 401static 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. 413bool 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'. 437bool 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 475static 476MachineBasicBlock::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. 489bool 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. 543void 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. 620bool 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. 654IfConverter::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. 790bool 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). 811static 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! 824void 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/// 837static 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. 845void 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/// 854bool 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/// 920bool 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/// 1025bool 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. 1136void 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. 1160void 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/// 1211void 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} 1255