IfConversion.cpp revision 89b9c321592b13b84c4da082a66399caf7c46697
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 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 attempt: 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 void AnalyzeBlocks(MachineFunction &MF, std::vector<IfcvtToken*> &Tokens); 171 void InvalidatePreds(MachineBasicBlock *BB); 172 void RemoveExtraEdges(BBInfo &BBI); 173 bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind); 174 bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind); 175 bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 176 unsigned NumDups1, unsigned NumDups2); 177 void PredicateBlock(BBInfo &BBI, 178 MachineBasicBlock::iterator E, 179 SmallVectorImpl<MachineOperand> &Cond); 180 void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 181 SmallVectorImpl<MachineOperand> &Cond, 182 bool IgnoreBr = false); 183 void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI); 184 185 bool MeetIfcvtSizeLimit(unsigned Size) const { 186 return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit(); 187 } 188 189 // blockAlwaysFallThrough - Block ends without a terminator. 190 bool blockAlwaysFallThrough(BBInfo &BBI) const { 191 return BBI.IsBrAnalyzable && BBI.TrueBB == NULL; 192 } 193 194 // IfcvtTokenCmp - Used to sort if-conversion candidates. 195 static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) { 196 int Incr1 = (C1->Kind == ICDiamond) 197 ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups; 198 int Incr2 = (C2->Kind == ICDiamond) 199 ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups; 200 if (Incr1 > Incr2) 201 return true; 202 else if (Incr1 == Incr2) { 203 // Favors subsumption. 204 if (C1->NeedSubsumption == false && C2->NeedSubsumption == true) 205 return true; 206 else if (C1->NeedSubsumption == C2->NeedSubsumption) { 207 // Favors diamond over triangle, etc. 208 if ((unsigned)C1->Kind < (unsigned)C2->Kind) 209 return true; 210 else if (C1->Kind == C2->Kind) 211 return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber(); 212 } 213 } 214 return false; 215 } 216 }; 217 218 char IfConverter::ID = 0; 219} 220 221static RegisterPass<IfConverter> 222X("if-converter", "If Converter"); 223 224FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); } 225 226bool IfConverter::runOnMachineFunction(MachineFunction &MF) { 227 TLI = MF.getTarget().getTargetLowering(); 228 TII = MF.getTarget().getInstrInfo(); 229 if (!TII) return false; 230 231 DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum << ") \'" 232 << MF.getFunction()->getName() << "\'"); 233 234 if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { 235 DEBUG(dbgs() << " skipped\n"); 236 return false; 237 } 238 DEBUG(dbgs() << "\n"); 239 240 MF.RenumberBlocks(); 241 BBAnalysis.resize(MF.getNumBlockIDs()); 242 243 // Look for root nodes, i.e. blocks without successors. 244 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) 245 if (I->succ_empty()) 246 Roots.push_back(I); 247 248 std::vector<IfcvtToken*> Tokens; 249 MadeChange = false; 250 unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + 251 NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds; 252 while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) { 253 // Do an initial analysis for each basic block and find all the potential 254 // candidates to perform if-conversion. 255 bool Change = false; 256 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(dbgs() << "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(dbgs() << (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(dbgs() << "Ifcvt (Triangle"); 308 if (isFalse) 309 DEBUG(dbgs() << " false"); 310 if (isRev) 311 DEBUG(dbgs() << " rev"); 312 DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:" 313 << BBI.TrueBB->getNumber() << ",F:" 314 << BBI.FalseBB->getNumber() << ") "); 315 RetVal = IfConvertTriangle(BBI, Kind); 316 DEBUG(dbgs() << (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(dbgs() << "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(dbgs() << (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 MachineBasicBlock::iterator TIE = TrueBBI.BB->end(); 518 MachineBasicBlock::iterator FIE = FalseBBI.BB->end(); 519 // Skip dbg_value instructions 520 while (TI != TIE && TI->isDebugValue()) 521 ++TI; 522 while (FI != FIE && FI->isDebugValue()) 523 ++FI; 524 while (TI != TIE && FI != FIE) { 525 if (!TI->isIdenticalTo(FI)) 526 break; 527 ++Dups1; 528 ++TI; 529 ++FI; 530 } 531 532 TI = firstNonBranchInst(TrueBBI.BB, TII); 533 FI = firstNonBranchInst(FalseBBI.BB, TII); 534 MachineBasicBlock::iterator TIB = TrueBBI.BB->begin(); 535 MachineBasicBlock::iterator FIB = FalseBBI.BB->begin(); 536 // Skip dbg_value instructions 537 while (TI != TIB && TI->isDebugValue()) 538 --TI; 539 while (FI != FIB && FI->isDebugValue()) 540 --FI; 541 while (TI != TIB && FI != FIB) { 542 if (!TI->isIdenticalTo(FI)) 543 break; 544 ++Dups2; 545 --TI; 546 --FI; 547 } 548 549 return true; 550} 551 552/// ScanInstructions - Scan all the instructions in the block to determine if 553/// the block is predicable. In most cases, that means all the instructions 554/// in the block are isPredicable(). Also checks if the block contains any 555/// instruction which can clobber a predicate (e.g. condition code register). 556/// If so, the block is not predicable unless it's the last instruction. 557void IfConverter::ScanInstructions(BBInfo &BBI) { 558 if (BBI.IsDone) 559 return; 560 561 bool AlreadyPredicated = BBI.Predicate.size() > 0; 562 // First analyze the end of BB branches. 563 BBI.TrueBB = BBI.FalseBB = NULL; 564 BBI.BrCond.clear(); 565 BBI.IsBrAnalyzable = 566 !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); 567 BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL; 568 569 if (BBI.BrCond.size()) { 570 // No false branch. This BB must end with a conditional branch and a 571 // fallthrough. 572 if (!BBI.FalseBB) 573 BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB); 574 if (!BBI.FalseBB) { 575 // Malformed bcc? True and false blocks are the same? 576 BBI.IsUnpredicable = true; 577 return; 578 } 579 } 580 581 // Then scan all the instructions. 582 BBI.NonPredSize = 0; 583 BBI.ClobbersPred = false; 584 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end(); 585 I != E; ++I) { 586 if (I->isDebugValue()) 587 continue; 588 589 const TargetInstrDesc &TID = I->getDesc(); 590 if (TID.isNotDuplicable()) 591 BBI.CannotBeCopied = true; 592 593 bool isPredicated = TII->isPredicated(I); 594 bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch(); 595 596 if (!isCondBr) { 597 if (!isPredicated) 598 BBI.NonPredSize++; 599 else if (!AlreadyPredicated) { 600 // FIXME: This instruction is already predicated before the 601 // if-conversion pass. It's probably something like a conditional move. 602 // Mark this block unpredicable for now. 603 BBI.IsUnpredicable = true; 604 return; 605 } 606 } 607 608 if (BBI.ClobbersPred && !isPredicated) { 609 // Predicate modification instruction should end the block (except for 610 // already predicated instructions and end of block branches). 611 if (isCondBr) { 612 // A conditional branch is not predicable, but it may be eliminated. 613 continue; 614 } 615 616 // Predicate may have been modified, the subsequent (currently) 617 // unpredicated instructions cannot be correctly predicated. 618 BBI.IsUnpredicable = true; 619 return; 620 } 621 622 // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are 623 // still potentially predicable. 624 std::vector<MachineOperand> PredDefs; 625 if (TII->DefinesPredicate(I, PredDefs)) 626 BBI.ClobbersPred = true; 627 628 if (!TII->isPredicable(I)) { 629 BBI.IsUnpredicable = true; 630 return; 631 } 632 } 633} 634 635/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be 636/// predicated by the specified predicate. 637bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, 638 SmallVectorImpl<MachineOperand> &Pred, 639 bool isTriangle, bool RevBranch) { 640 // If the block is dead or unpredicable, then it cannot be predicated. 641 if (BBI.IsDone || BBI.IsUnpredicable) 642 return false; 643 644 // If it is already predicated, check if its predicate subsumes the new 645 // predicate. 646 if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred)) 647 return false; 648 649 if (BBI.BrCond.size()) { 650 if (!isTriangle) 651 return false; 652 653 // Test predicate subsumption. 654 SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end()); 655 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 656 if (RevBranch) { 657 if (TII->ReverseBranchCondition(Cond)) 658 return false; 659 } 660 if (TII->ReverseBranchCondition(RevPred) || 661 !TII->SubsumesPredicate(Cond, RevPred)) 662 return false; 663 } 664 665 return true; 666} 667 668/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from 669/// the specified block. Record its successors and whether it looks like an 670/// if-conversion candidate. 671IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB, 672 std::vector<IfcvtToken*> &Tokens) { 673 BBInfo &BBI = BBAnalysis[BB->getNumber()]; 674 675 if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed) 676 return BBI; 677 678 BBI.BB = BB; 679 BBI.IsBeingAnalyzed = true; 680 681 ScanInstructions(BBI); 682 683 // Unanalyzable or ends with fallthrough or unconditional branch. 684 if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) { 685 BBI.IsBeingAnalyzed = false; 686 BBI.IsAnalyzed = true; 687 return BBI; 688 } 689 690 // Do not ifcvt if either path is a back edge to the entry block. 691 if (BBI.TrueBB == BB || BBI.FalseBB == BB) { 692 BBI.IsBeingAnalyzed = false; 693 BBI.IsAnalyzed = true; 694 return BBI; 695 } 696 697 // Do not ifcvt if true and false fallthrough blocks are the same. 698 if (!BBI.FalseBB) { 699 BBI.IsBeingAnalyzed = false; 700 BBI.IsAnalyzed = true; 701 return BBI; 702 } 703 704 BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB, Tokens); 705 BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens); 706 707 if (TrueBBI.IsDone && FalseBBI.IsDone) { 708 BBI.IsBeingAnalyzed = false; 709 BBI.IsAnalyzed = true; 710 return BBI; 711 } 712 713 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 714 bool CanRevCond = !TII->ReverseBranchCondition(RevCond); 715 716 unsigned Dups = 0; 717 unsigned Dups2 = 0; 718 bool TNeedSub = TrueBBI.Predicate.size() > 0; 719 bool FNeedSub = FalseBBI.Predicate.size() > 0; 720 bool Enqueued = false; 721 if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) && 722 MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) && 723 MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) && 724 FeasibilityAnalysis(TrueBBI, BBI.BrCond) && 725 FeasibilityAnalysis(FalseBBI, RevCond)) { 726 // Diamond: 727 // EBB 728 // / \_ 729 // | | 730 // TBB FBB 731 // \ / 732 // TailBB 733 // Note TailBB can be empty. 734 Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups, 735 Dups2)); 736 Enqueued = true; 737 } 738 739 if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) && 740 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 741 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { 742 // Triangle: 743 // EBB 744 // | \_ 745 // | | 746 // | TBB 747 // | / 748 // FBB 749 Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups)); 750 Enqueued = true; 751 } 752 753 if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) && 754 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 755 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) { 756 Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups)); 757 Enqueued = true; 758 } 759 760 if (ValidSimple(TrueBBI, Dups) && 761 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 762 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { 763 // Simple (split, no rejoin): 764 // EBB 765 // | \_ 766 // | | 767 // | TBB---> exit 768 // | 769 // FBB 770 Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups)); 771 Enqueued = true; 772 } 773 774 if (CanRevCond) { 775 // Try the other path... 776 if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) && 777 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 778 FeasibilityAnalysis(FalseBBI, RevCond, true)) { 779 Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups)); 780 Enqueued = true; 781 } 782 783 if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) && 784 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 785 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { 786 Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups)); 787 Enqueued = true; 788 } 789 790 if (ValidSimple(FalseBBI, Dups) && 791 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 792 FeasibilityAnalysis(FalseBBI, RevCond)) { 793 Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups)); 794 Enqueued = true; 795 } 796 } 797 798 BBI.IsEnqueued = Enqueued; 799 BBI.IsBeingAnalyzed = false; 800 BBI.IsAnalyzed = true; 801 return BBI; 802} 803 804/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion 805/// candidates. 806void IfConverter::AnalyzeBlocks(MachineFunction &MF, 807 std::vector<IfcvtToken*> &Tokens) { 808 std::set<MachineBasicBlock*> Visited; 809 for (unsigned i = 0, e = Roots.size(); i != e; ++i) { 810 for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited), 811 E = idf_ext_end(Roots[i], Visited); I != E; ++I) { 812 MachineBasicBlock *BB = *I; 813 AnalyzeBlock(BB, Tokens); 814 } 815 } 816 817 // Sort to favor more complex ifcvt scheme. 818 std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp); 819} 820 821/// canFallThroughTo - Returns true either if ToBB is the next block after BB or 822/// that all the intervening blocks are empty (given BB can fall through to its 823/// next block). 824static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) { 825 MachineFunction::iterator I = BB; 826 MachineFunction::iterator TI = ToBB; 827 MachineFunction::iterator E = BB->getParent()->end(); 828 while (++I != TI) 829 if (I == E || !I->empty()) 830 return false; 831 return true; 832} 833 834/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed 835/// to determine if it can be if-converted. If predecessor is already enqueued, 836/// dequeue it! 837void IfConverter::InvalidatePreds(MachineBasicBlock *BB) { 838 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(), 839 E = BB->pred_end(); PI != E; ++PI) { 840 BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()]; 841 if (PBBI.IsDone || PBBI.BB == BB) 842 continue; 843 PBBI.IsAnalyzed = false; 844 PBBI.IsEnqueued = false; 845 } 846} 847 848/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB. 849/// 850static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB, 851 const TargetInstrInfo *TII) { 852 SmallVector<MachineOperand, 0> NoCond; 853 TII->InsertBranch(*BB, ToBB, NULL, NoCond); 854} 855 856/// RemoveExtraEdges - Remove true / false edges if either / both are no longer 857/// successors. 858void IfConverter::RemoveExtraEdges(BBInfo &BBI) { 859 MachineBasicBlock *TBB = NULL, *FBB = NULL; 860 SmallVector<MachineOperand, 4> Cond; 861 if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond)) 862 BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty()); 863} 864 865/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG. 866/// 867bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) { 868 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 869 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 870 BBInfo *CvtBBI = &TrueBBI; 871 BBInfo *NextBBI = &FalseBBI; 872 873 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 874 if (Kind == ICSimpleFalse) 875 std::swap(CvtBBI, NextBBI); 876 877 if (CvtBBI->IsDone || 878 (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { 879 // Something has changed. It's no longer safe to predicate this block. 880 BBI.IsAnalyzed = false; 881 CvtBBI->IsAnalyzed = false; 882 return false; 883 } 884 885 if (Kind == ICSimpleFalse) 886 if (TII->ReverseBranchCondition(Cond)) 887 assert(false && "Unable to reverse branch condition!"); 888 889 if (CvtBBI->BB->pred_size() > 1) { 890 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 891 // Copy instructions in the true block, predicate them, and add them to 892 // the entry block. 893 CopyAndPredicateBlock(BBI, *CvtBBI, Cond); 894 } else { 895 PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); 896 897 // Merge converted block into entry block. 898 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 899 MergeBlocks(BBI, *CvtBBI); 900 } 901 902 bool IterIfcvt = true; 903 if (!canFallThroughTo(BBI.BB, NextBBI->BB)) { 904 InsertUncondBranch(BBI.BB, NextBBI->BB, TII); 905 BBI.HasFallThrough = false; 906 // Now ifcvt'd block will look like this: 907 // BB: 908 // ... 909 // t, f = cmp 910 // if t op 911 // b BBf 912 // 913 // We cannot further ifcvt this block because the unconditional branch 914 // will have to be predicated on the new condition, that will not be 915 // available if cmp executes. 916 IterIfcvt = false; 917 } 918 919 RemoveExtraEdges(BBI); 920 921 // Update block info. BB can be iteratively if-converted. 922 if (!IterIfcvt) 923 BBI.IsDone = true; 924 InvalidatePreds(BBI.BB); 925 CvtBBI->IsDone = true; 926 927 // FIXME: Must maintain LiveIns. 928 return true; 929} 930 931/// IfConvertTriangle - If convert a triangle sub-CFG. 932/// 933bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) { 934 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 935 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 936 BBInfo *CvtBBI = &TrueBBI; 937 BBInfo *NextBBI = &FalseBBI; 938 939 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 940 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 941 std::swap(CvtBBI, NextBBI); 942 943 if (CvtBBI->IsDone || 944 (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { 945 // Something has changed. It's no longer safe to predicate this block. 946 BBI.IsAnalyzed = false; 947 CvtBBI->IsAnalyzed = false; 948 return false; 949 } 950 951 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 952 if (TII->ReverseBranchCondition(Cond)) 953 assert(false && "Unable to reverse branch condition!"); 954 955 if (Kind == ICTriangleRev || Kind == ICTriangleFRev) { 956 if (ReverseBranchCondition(*CvtBBI)) { 957 // BB has been changed, modify its predecessors (except for this 958 // one) so they don't get ifcvt'ed based on bad intel. 959 for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(), 960 E = CvtBBI->BB->pred_end(); PI != E; ++PI) { 961 MachineBasicBlock *PBB = *PI; 962 if (PBB == BBI.BB) 963 continue; 964 BBInfo &PBBI = BBAnalysis[PBB->getNumber()]; 965 if (PBBI.IsEnqueued) { 966 PBBI.IsAnalyzed = false; 967 PBBI.IsEnqueued = false; 968 } 969 } 970 } 971 } 972 973 bool HasEarlyExit = CvtBBI->FalseBB != NULL; 974 bool DupBB = CvtBBI->BB->pred_size() > 1; 975 if (DupBB) { 976 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 977 // Copy instructions in the true block, predicate them, and add them to 978 // the entry block. 979 CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true); 980 } else { 981 // Predicate the 'true' block after removing its branch. 982 CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB); 983 PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); 984 985 // Now merge the entry of the triangle with the true block. 986 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 987 MergeBlocks(BBI, *CvtBBI); 988 } 989 990 // If 'true' block has a 'false' successor, add an exit branch to it. 991 if (HasEarlyExit) { 992 SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(), 993 CvtBBI->BrCond.end()); 994 if (TII->ReverseBranchCondition(RevCond)) 995 assert(false && "Unable to reverse branch condition!"); 996 TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond); 997 BBI.BB->addSuccessor(CvtBBI->FalseBB); 998 } 999 1000 // Merge in the 'false' block if the 'false' block has no other 1001 // predecessors. Otherwise, add an unconditional branch to 'false'. 1002 bool FalseBBDead = false; 1003 bool IterIfcvt = true; 1004 bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB); 1005 if (!isFallThrough) { 1006 // Only merge them if the true block does not fallthrough to the false 1007 // block. By not merging them, we make it possible to iteratively 1008 // ifcvt the blocks. 1009 if (!HasEarlyExit && 1010 NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) { 1011 MergeBlocks(BBI, *NextBBI); 1012 FalseBBDead = true; 1013 } else { 1014 InsertUncondBranch(BBI.BB, NextBBI->BB, TII); 1015 BBI.HasFallThrough = false; 1016 } 1017 // Mixed predicated and unpredicated code. This cannot be iteratively 1018 // predicated. 1019 IterIfcvt = false; 1020 } 1021 1022 RemoveExtraEdges(BBI); 1023 1024 // Update block info. BB can be iteratively if-converted. 1025 if (!IterIfcvt) 1026 BBI.IsDone = true; 1027 InvalidatePreds(BBI.BB); 1028 CvtBBI->IsDone = true; 1029 if (FalseBBDead) 1030 NextBBI->IsDone = true; 1031 1032 // FIXME: Must maintain LiveIns. 1033 return true; 1034} 1035 1036/// IfConvertDiamond - If convert a diamond sub-CFG. 1037/// 1038bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 1039 unsigned NumDups1, unsigned NumDups2) { 1040 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1041 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1042 MachineBasicBlock *TailBB = TrueBBI.TrueBB; 1043 // True block must fall through or end with an unanalyzable terminator. 1044 if (!TailBB) { 1045 if (blockAlwaysFallThrough(TrueBBI)) 1046 TailBB = FalseBBI.TrueBB; 1047 assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!"); 1048 } 1049 1050 if (TrueBBI.IsDone || FalseBBI.IsDone || 1051 TrueBBI.BB->pred_size() > 1 || 1052 FalseBBI.BB->pred_size() > 1) { 1053 // Something has changed. It's no longer safe to predicate these blocks. 1054 BBI.IsAnalyzed = false; 1055 TrueBBI.IsAnalyzed = false; 1056 FalseBBI.IsAnalyzed = false; 1057 return false; 1058 } 1059 1060 // Merge the 'true' and 'false' blocks by copying the instructions 1061 // from the 'false' block to the 'true' block. That is, unless the true 1062 // block would clobber the predicate, in that case, do the opposite. 1063 BBInfo *BBI1 = &TrueBBI; 1064 BBInfo *BBI2 = &FalseBBI; 1065 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 1066 if (TII->ReverseBranchCondition(RevCond)) 1067 assert(false && "Unable to reverse branch condition!"); 1068 SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond; 1069 SmallVector<MachineOperand, 4> *Cond2 = &RevCond; 1070 1071 // Figure out the more profitable ordering. 1072 bool DoSwap = false; 1073 if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) 1074 DoSwap = true; 1075 else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) { 1076 if (TrueBBI.NonPredSize > FalseBBI.NonPredSize) 1077 DoSwap = true; 1078 } 1079 if (DoSwap) { 1080 std::swap(BBI1, BBI2); 1081 std::swap(Cond1, Cond2); 1082 } 1083 1084 // Remove the conditional branch from entry to the blocks. 1085 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 1086 1087 // Remove the duplicated instructions at the beginnings of both paths. 1088 MachineBasicBlock::iterator DI1 = BBI1->BB->begin(); 1089 MachineBasicBlock::iterator DI2 = BBI2->BB->begin(); 1090 MachineBasicBlock::iterator DIE1 = BBI1->BB->end(); 1091 MachineBasicBlock::iterator DIE2 = BBI2->BB->end(); 1092 // Skip dbg_value instructions 1093 while (DI1 != DIE1 && DI1->isDebugValue()) 1094 ++DI1; 1095 while (DI2 != DIE2 && DI2->isDebugValue()) 1096 ++DI2; 1097 BBI1->NonPredSize -= NumDups1; 1098 BBI2->NonPredSize -= NumDups1; 1099 while (NumDups1 != 0) { 1100 ++DI1; 1101 ++DI2; 1102 --NumDups1; 1103 } 1104 BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1); 1105 BBI2->BB->erase(BBI2->BB->begin(), DI2); 1106 1107 // Predicate the 'true' block after removing its branch. 1108 BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB); 1109 DI1 = BBI1->BB->end(); 1110 for (unsigned i = 0; i != NumDups2; ) { 1111 // NumDups2 only counted non-dbg_value instructions, so this won't 1112 // run off the head of the list. 1113 assert (DI1 != BBI1->BB->begin()); 1114 --DI1; 1115 // skip dbg_value instructions 1116 if (!DI1->isDebugValue()) 1117 ++i; 1118 } 1119 BBI1->BB->erase(DI1, BBI1->BB->end()); 1120 PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1); 1121 1122 // Predicate the 'false' block. 1123 BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB); 1124 DI2 = BBI2->BB->end(); 1125 while (NumDups2 != 0) { 1126 // NumDups2 only counted non-dbg_value instructions, so this won't 1127 // run off the head of the list. 1128 assert (DI2 != BBI2->BB->begin()); 1129 --DI2; 1130 // skip dbg_value instructions 1131 if (!DI2->isDebugValue()) 1132 --NumDups2; 1133 } 1134 PredicateBlock(*BBI2, DI2, *Cond2); 1135 1136 // Merge the true block into the entry of the diamond. 1137 MergeBlocks(BBI, *BBI1); 1138 MergeBlocks(BBI, *BBI2); 1139 1140 // If the if-converted block falls through or unconditionally branches into 1141 // the tail block, and the tail block does not have other predecessors, then 1142 // fold the tail block in as well. Otherwise, unless it falls through to the 1143 // tail, add a unconditional branch to it. 1144 if (TailBB) { 1145 BBInfo TailBBI = BBAnalysis[TailBB->getNumber()]; 1146 if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) { 1147 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 1148 MergeBlocks(BBI, TailBBI); 1149 TailBBI.IsDone = true; 1150 } else { 1151 InsertUncondBranch(BBI.BB, TailBB, TII); 1152 BBI.HasFallThrough = false; 1153 } 1154 } 1155 1156 RemoveExtraEdges(BBI); 1157 1158 // Update block info. 1159 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; 1160 InvalidatePreds(BBI.BB); 1161 1162 // FIXME: Must maintain LiveIns. 1163 return true; 1164} 1165 1166/// PredicateBlock - Predicate instructions from the start of the block to the 1167/// specified end with the specified condition. 1168void IfConverter::PredicateBlock(BBInfo &BBI, 1169 MachineBasicBlock::iterator E, 1170 SmallVectorImpl<MachineOperand> &Cond) { 1171 for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) { 1172 if (I->isDebugValue() || TII->isPredicated(I)) 1173 continue; 1174 if (!TII->PredicateInstruction(I, Cond)) { 1175#ifndef NDEBUG 1176 dbgs() << "Unable to predicate " << *I << "!\n"; 1177#endif 1178 llvm_unreachable(0); 1179 } 1180 } 1181 1182 std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate)); 1183 1184 BBI.IsAnalyzed = false; 1185 BBI.NonPredSize = 0; 1186 1187 NumIfConvBBs++; 1188} 1189 1190/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to 1191/// the destination block. Skip end of block branches if IgnoreBr is true. 1192void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 1193 SmallVectorImpl<MachineOperand> &Cond, 1194 bool IgnoreBr) { 1195 MachineFunction &MF = *ToBBI.BB->getParent(); 1196 1197 for (MachineBasicBlock::iterator I = FromBBI.BB->begin(), 1198 E = FromBBI.BB->end(); I != E; ++I) { 1199 const TargetInstrDesc &TID = I->getDesc(); 1200 bool isPredicated = TII->isPredicated(I); 1201 // Do not copy the end of the block branches. 1202 if (IgnoreBr && !isPredicated && TID.isBranch()) 1203 break; 1204 1205 MachineInstr *MI = MF.CloneMachineInstr(I); 1206 ToBBI.BB->insert(ToBBI.BB->end(), MI); 1207 ToBBI.NonPredSize++; 1208 1209 if (!isPredicated && !MI->isDebugValue()) 1210 if (!TII->PredicateInstruction(MI, Cond)) { 1211#ifndef NDEBUG 1212 dbgs() << "Unable to predicate " << *I << "!\n"; 1213#endif 1214 llvm_unreachable(0); 1215 } 1216 } 1217 1218 std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(), 1219 FromBBI.BB->succ_end()); 1220 MachineBasicBlock *NBB = getNextBlock(FromBBI.BB); 1221 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL; 1222 1223 for (unsigned i = 0, e = Succs.size(); i != e; ++i) { 1224 MachineBasicBlock *Succ = Succs[i]; 1225 // Fallthrough edge can't be transferred. 1226 if (Succ == FallThrough) 1227 continue; 1228 ToBBI.BB->addSuccessor(Succ); 1229 } 1230 1231 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), 1232 std::back_inserter(ToBBI.Predicate)); 1233 std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate)); 1234 1235 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 1236 ToBBI.IsAnalyzed = false; 1237 1238 NumDupBBs++; 1239} 1240 1241/// MergeBlocks - Move all instructions from FromBB to the end of ToBB. 1242/// 1243void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) { 1244 ToBBI.BB->splice(ToBBI.BB->end(), 1245 FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end()); 1246 1247 // Redirect all branches to FromBB to ToBB. 1248 std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(), 1249 FromBBI.BB->pred_end()); 1250 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 1251 MachineBasicBlock *Pred = Preds[i]; 1252 if (Pred == ToBBI.BB) 1253 continue; 1254 Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB); 1255 } 1256 1257 std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(), 1258 FromBBI.BB->succ_end()); 1259 MachineBasicBlock *NBB = getNextBlock(FromBBI.BB); 1260 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL; 1261 1262 for (unsigned i = 0, e = Succs.size(); i != e; ++i) { 1263 MachineBasicBlock *Succ = Succs[i]; 1264 // Fallthrough edge can't be transferred. 1265 if (Succ == FallThrough) 1266 continue; 1267 FromBBI.BB->removeSuccessor(Succ); 1268 ToBBI.BB->addSuccessor(Succ); 1269 } 1270 1271 // Now FromBBI always falls through to the next block! 1272 if (NBB && !FromBBI.BB->isSuccessor(NBB)) 1273 FromBBI.BB->addSuccessor(NBB); 1274 1275 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), 1276 std::back_inserter(ToBBI.Predicate)); 1277 FromBBI.Predicate.clear(); 1278 1279 ToBBI.NonPredSize += FromBBI.NonPredSize; 1280 FromBBI.NonPredSize = 0; 1281 1282 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 1283 ToBBI.HasFallThrough = FromBBI.HasFallThrough; 1284 ToBBI.IsAnalyzed = false; 1285 FromBBI.IsAnalyzed = false; 1286} 1287