IfConversion.cpp revision 705e07f578e2b3af47ddab610feb4e7f2d3063a5
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 "llvm/Function.h" 16#include "llvm/CodeGen/Passes.h" 17#include "llvm/CodeGen/MachineModuleInfo.h" 18#include "llvm/CodeGen/MachineFunctionPass.h" 19#include "llvm/Target/TargetInstrInfo.h" 20#include "llvm/Target/TargetLowering.h" 21#include "llvm/Target/TargetMachine.h" 22#include "llvm/Support/CommandLine.h" 23#include "llvm/Support/Debug.h" 24#include "llvm/Support/ErrorHandling.h" 25#include "llvm/Support/raw_ostream.h" 26#include "llvm/ADT/DepthFirstIterator.h" 27#include "llvm/ADT/Statistic.h" 28#include "llvm/ADT/STLExtras.h" 29using namespace llvm; 30 31// Hidden options for help debugging. 32static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); 33static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); 34static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); 35static cl::opt<bool> DisableSimple("disable-ifcvt-simple", 36 cl::init(false), cl::Hidden); 37static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false", 38 cl::init(false), cl::Hidden); 39static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", 40 cl::init(false), cl::Hidden); 41static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev", 42 cl::init(false), cl::Hidden); 43static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false", 44 cl::init(false), cl::Hidden); 45static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev", 46 cl::init(false), cl::Hidden); 47static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", 48 cl::init(false), cl::Hidden); 49 50STATISTIC(NumSimple, "Number of simple if-conversions performed"); 51STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed"); 52STATISTIC(NumTriangle, "Number of triangle if-conversions performed"); 53STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed"); 54STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed"); 55STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed"); 56STATISTIC(NumDiamonds, "Number of diamond if-conversions performed"); 57STATISTIC(NumIfConvBBs, "Number of if-converted blocks"); 58STATISTIC(NumDupBBs, "Number of duplicated blocks"); 59 60namespace { 61 class VISIBILITY_HIDDEN IfConverter : public MachineFunctionPass { 62 enum IfcvtKind { 63 ICNotClassfied, // BB data valid, but not classified. 64 ICSimpleFalse, // Same as ICSimple, but on the false path. 65 ICSimple, // BB is entry of an one split, no rejoin sub-CFG. 66 ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition. 67 ICTriangleRev, // Same as ICTriangle, but true path rev condition. 68 ICTriangleFalse, // Same as ICTriangle, but on the false path. 69 ICTriangle, // BB is entry of a triangle sub-CFG. 70 ICDiamond // BB is entry of a diamond sub-CFG. 71 }; 72 73 /// BBInfo - One per MachineBasicBlock, this is used to cache the result 74 /// if-conversion feasibility analysis. This includes results from 75 /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its 76 /// classification, and common tail block of its successors (if it's a 77 /// diamond shape), its size, whether it's predicable, and whether any 78 /// instruction can clobber the 'would-be' predicate. 79 /// 80 /// IsDone - True if BB is not to be considered for ifcvt. 81 /// IsBeingAnalyzed - True if BB is currently being analyzed. 82 /// IsAnalyzed - True if BB has been analyzed (info is still valid). 83 /// IsEnqueued - True if BB has been enqueued to be ifcvt'ed. 84 /// IsBrAnalyzable - True if AnalyzeBranch() returns false. 85 /// HasFallThrough - True if BB may fallthrough to the following BB. 86 /// IsUnpredicable - True if BB is known to be unpredicable. 87 /// ClobbersPred - True if BB could modify predicates (e.g. has 88 /// cmp, call, etc.) 89 /// NonPredSize - Number of non-predicated instructions. 90 /// BB - Corresponding MachineBasicBlock. 91 /// TrueBB / FalseBB- See AnalyzeBranch(). 92 /// BrCond - Conditions for end of block conditional branches. 93 /// Predicate - Predicate used in the BB. 94 struct BBInfo { 95 bool IsDone : 1; 96 bool IsBeingAnalyzed : 1; 97 bool IsAnalyzed : 1; 98 bool IsEnqueued : 1; 99 bool IsBrAnalyzable : 1; 100 bool HasFallThrough : 1; 101 bool IsUnpredicable : 1; 102 bool CannotBeCopied : 1; 103 bool ClobbersPred : 1; 104 unsigned NonPredSize; 105 MachineBasicBlock *BB; 106 MachineBasicBlock *TrueBB; 107 MachineBasicBlock *FalseBB; 108 SmallVector<MachineOperand, 4> BrCond; 109 SmallVector<MachineOperand, 4> Predicate; 110 BBInfo() : IsDone(false), IsBeingAnalyzed(false), 111 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false), 112 HasFallThrough(false), IsUnpredicable(false), 113 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0), 114 BB(0), TrueBB(0), FalseBB(0) {} 115 }; 116 117 /// IfcvtToken - Record information about pending if-conversions to attemp: 118 /// BBI - Corresponding BBInfo. 119 /// Kind - Type of block. See IfcvtKind. 120 /// NeedSubsumption - True if the to-be-predicated BB has already been 121 /// predicated. 122 /// NumDups - Number of instructions that would be duplicated due 123 /// to this if-conversion. (For diamonds, the number of 124 /// identical instructions at the beginnings of both 125 /// paths). 126 /// NumDups2 - For diamonds, the number of identical instructions 127 /// at the ends of both paths. 128 struct IfcvtToken { 129 BBInfo &BBI; 130 IfcvtKind Kind; 131 bool NeedSubsumption; 132 unsigned NumDups; 133 unsigned NumDups2; 134 IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0) 135 : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {} 136 }; 137 138 /// Roots - Basic blocks that do not have successors. These are the starting 139 /// points of Graph traversal. 140 std::vector<MachineBasicBlock*> Roots; 141 142 /// BBAnalysis - Results of if-conversion feasibility analysis indexed by 143 /// basic block number. 144 std::vector<BBInfo> BBAnalysis; 145 146 const TargetLowering *TLI; 147 const TargetInstrInfo *TII; 148 bool MadeChange; 149 int FnNum; 150 public: 151 static char ID; 152 IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {} 153 154 virtual bool runOnMachineFunction(MachineFunction &MF); 155 virtual const char *getPassName() const { return "If Converter"; } 156 157 private: 158 bool ReverseBranchCondition(BBInfo &BBI); 159 bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const; 160 bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 161 bool FalseBranch, unsigned &Dups) const; 162 bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, 163 unsigned &Dups1, unsigned &Dups2) const; 164 void ScanInstructions(BBInfo &BBI); 165 BBInfo &AnalyzeBlock(MachineBasicBlock *BB, 166 std::vector<IfcvtToken*> &Tokens); 167 bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond, 168 bool isTriangle = false, bool RevBranch = false); 169 bool AnalyzeBlocks(MachineFunction &MF, 170 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(errs() << "\nIfcvt: function (" << ++FnNum << ") \'" 232 << MF.getFunction()->getName() << "\'"); 233 234 if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { 235 DEBUG(errs() << " skipped\n"); 236 return false; 237 } 238 DEBUG(errs() << "\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 = AnalyzeBlocks(MF, Tokens); 256 while (!Tokens.empty()) { 257 IfcvtToken *Token = Tokens.back(); 258 Tokens.pop_back(); 259 BBInfo &BBI = Token->BBI; 260 IfcvtKind Kind = Token->Kind; 261 unsigned NumDups = Token->NumDups; 262 unsigned NumDups2 = Token->NumDups2; 263 264 delete Token; 265 266 // If the block has been evicted out of the queue or it has already been 267 // marked dead (due to it being predicated), then skip it. 268 if (BBI.IsDone) 269 BBI.IsEnqueued = false; 270 if (!BBI.IsEnqueued) 271 continue; 272 273 BBI.IsEnqueued = false; 274 275 bool RetVal = false; 276 switch (Kind) { 277 default: assert(false && "Unexpected!"); 278 break; 279 case ICSimple: 280 case ICSimpleFalse: { 281 bool isFalse = Kind == ICSimpleFalse; 282 if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break; 283 DEBUG(errs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"") 284 << "): BB#" << BBI.BB->getNumber() << " (" 285 << ((Kind == ICSimpleFalse) 286 ? BBI.FalseBB->getNumber() 287 : BBI.TrueBB->getNumber()) << ") "); 288 RetVal = IfConvertSimple(BBI, Kind); 289 DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 290 if (RetVal) { 291 if (isFalse) NumSimpleFalse++; 292 else NumSimple++; 293 } 294 break; 295 } 296 case ICTriangle: 297 case ICTriangleRev: 298 case ICTriangleFalse: 299 case ICTriangleFRev: { 300 bool isFalse = Kind == ICTriangleFalse; 301 bool isRev = (Kind == ICTriangleRev || Kind == ICTriangleFRev); 302 if (DisableTriangle && !isFalse && !isRev) break; 303 if (DisableTriangleR && !isFalse && isRev) break; 304 if (DisableTriangleF && isFalse && !isRev) break; 305 if (DisableTriangleFR && isFalse && isRev) break; 306 DEBUG(errs() << "Ifcvt (Triangle"); 307 if (isFalse) 308 DEBUG(errs() << " false"); 309 if (isRev) 310 DEBUG(errs() << " rev"); 311 DEBUG(errs() << "): BB#" << BBI.BB->getNumber() << " (T:" 312 << BBI.TrueBB->getNumber() << ",F:" 313 << BBI.FalseBB->getNumber() << ") "); 314 RetVal = IfConvertTriangle(BBI, Kind); 315 DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 316 if (RetVal) { 317 if (isFalse) { 318 if (isRev) NumTriangleFRev++; 319 else NumTriangleFalse++; 320 } else { 321 if (isRev) NumTriangleRev++; 322 else NumTriangle++; 323 } 324 } 325 break; 326 } 327 case ICDiamond: { 328 if (DisableDiamond) break; 329 DEBUG(errs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:" 330 << BBI.TrueBB->getNumber() << ",F:" 331 << BBI.FalseBB->getNumber() << ") "); 332 RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2); 333 DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 334 if (RetVal) NumDiamonds++; 335 break; 336 } 337 } 338 339 Change |= RetVal; 340 341 NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev + 342 NumTriangleFalse + NumTriangleFRev + NumDiamonds; 343 if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit) 344 break; 345 } 346 347 if (!Change) 348 break; 349 MadeChange |= Change; 350 } 351 352 // Delete tokens in case of early exit. 353 while (!Tokens.empty()) { 354 IfcvtToken *Token = Tokens.back(); 355 Tokens.pop_back(); 356 delete Token; 357 } 358 359 Tokens.clear(); 360 Roots.clear(); 361 BBAnalysis.clear(); 362 363 return MadeChange; 364} 365 366/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given 367/// its 'true' successor. 368static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, 369 MachineBasicBlock *TrueBB) { 370 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), 371 E = BB->succ_end(); SI != E; ++SI) { 372 MachineBasicBlock *SuccBB = *SI; 373 if (SuccBB != TrueBB) 374 return SuccBB; 375 } 376 return NULL; 377} 378 379/// ReverseBranchCondition - Reverse the condition of the end of the block 380/// branch. Swap block's 'true' and 'false' successors. 381bool IfConverter::ReverseBranchCondition(BBInfo &BBI) { 382 if (!TII->ReverseBranchCondition(BBI.BrCond)) { 383 TII->RemoveBranch(*BBI.BB); 384 TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond); 385 std::swap(BBI.TrueBB, BBI.FalseBB); 386 return true; 387 } 388 return false; 389} 390 391/// getNextBlock - Returns the next block in the function blocks ordering. If 392/// it is the end, returns NULL. 393static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) { 394 MachineFunction::iterator I = BB; 395 MachineFunction::iterator E = BB->getParent()->end(); 396 if (++I == E) 397 return NULL; 398 return I; 399} 400 401/// ValidSimple - Returns true if the 'true' block (along with its 402/// predecessor) forms a valid simple shape for ifcvt. It also returns the 403/// number of instructions that the ifcvt would need to duplicate if performed 404/// in Dups. 405bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const { 406 Dups = 0; 407 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 408 return false; 409 410 if (TrueBBI.IsBrAnalyzable) 411 return false; 412 413 if (TrueBBI.BB->pred_size() > 1) { 414 if (TrueBBI.CannotBeCopied || 415 TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit()) 416 return false; 417 Dups = TrueBBI.NonPredSize; 418 } 419 420 return true; 421} 422 423/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along 424/// with their common predecessor) forms a valid triangle shape for ifcvt. 425/// If 'FalseBranch' is true, it checks if 'true' block's false branch 426/// branches to the false branch rather than the other way around. It also 427/// returns the number of instructions that the ifcvt would need to duplicate 428/// if performed in 'Dups'. 429bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 430 bool FalseBranch, unsigned &Dups) const { 431 Dups = 0; 432 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 433 return false; 434 435 if (TrueBBI.BB->pred_size() > 1) { 436 if (TrueBBI.CannotBeCopied) 437 return false; 438 439 unsigned Size = TrueBBI.NonPredSize; 440 if (TrueBBI.IsBrAnalyzable) { 441 if (TrueBBI.TrueBB && TrueBBI.BrCond.empty()) 442 // Ends with an unconditional branch. It will be removed. 443 --Size; 444 else { 445 MachineBasicBlock *FExit = FalseBranch 446 ? TrueBBI.TrueBB : TrueBBI.FalseBB; 447 if (FExit) 448 // Require a conditional branch 449 ++Size; 450 } 451 } 452 if (Size > TLI->getIfCvtDupBlockSizeLimit()) 453 return false; 454 Dups = Size; 455 } 456 457 MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB; 458 if (!TExit && blockAlwaysFallThrough(TrueBBI)) { 459 MachineFunction::iterator I = TrueBBI.BB; 460 if (++I == TrueBBI.BB->getParent()->end()) 461 return false; 462 TExit = I; 463 } 464 return TExit && TExit == FalseBBI.BB; 465} 466 467static 468MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB, 469 const TargetInstrInfo *TII) { 470 MachineBasicBlock::iterator I = BB->end(); 471 while (I != BB->begin()) { 472 --I; 473 if (!I->getDesc().isBranch()) 474 break; 475 } 476 return I; 477} 478 479/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along 480/// with their common predecessor) forms a valid diamond shape for ifcvt. 481bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, 482 unsigned &Dups1, unsigned &Dups2) const { 483 Dups1 = Dups2 = 0; 484 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || 485 FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) 486 return false; 487 488 MachineBasicBlock *TT = TrueBBI.TrueBB; 489 MachineBasicBlock *FT = FalseBBI.TrueBB; 490 491 if (!TT && blockAlwaysFallThrough(TrueBBI)) 492 TT = getNextBlock(TrueBBI.BB); 493 if (!FT && blockAlwaysFallThrough(FalseBBI)) 494 FT = getNextBlock(FalseBBI.BB); 495 if (TT != FT) 496 return false; 497 if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable)) 498 return false; 499 if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) 500 return false; 501 502 // FIXME: Allow true block to have an early exit? 503 if (TrueBBI.FalseBB || FalseBBI.FalseBB || 504 (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred)) 505 return false; 506 507 MachineBasicBlock::iterator TI = TrueBBI.BB->begin(); 508 MachineBasicBlock::iterator FI = FalseBBI.BB->begin(); 509 while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) { 510 if (!TI->isIdenticalTo(FI)) 511 break; 512 ++Dups1; 513 ++TI; 514 ++FI; 515 } 516 517 TI = firstNonBranchInst(TrueBBI.BB, TII); 518 FI = firstNonBranchInst(FalseBBI.BB, TII); 519 while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) { 520 if (!TI->isIdenticalTo(FI)) 521 break; 522 ++Dups2; 523 --TI; 524 --FI; 525 } 526 527 return true; 528} 529 530/// ScanInstructions - Scan all the instructions in the block to determine if 531/// the block is predicable. In most cases, that means all the instructions 532/// in the block are isPredicable(). Also checks if the block contains any 533/// instruction which can clobber a predicate (e.g. condition code register). 534/// If so, the block is not predicable unless it's the last instruction. 535void IfConverter::ScanInstructions(BBInfo &BBI) { 536 if (BBI.IsDone) 537 return; 538 539 bool AlreadyPredicated = BBI.Predicate.size() > 0; 540 // First analyze the end of BB branches. 541 BBI.TrueBB = BBI.FalseBB = NULL; 542 BBI.BrCond.clear(); 543 BBI.IsBrAnalyzable = 544 !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); 545 BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL; 546 547 if (BBI.BrCond.size()) { 548 // No false branch. This BB must end with a conditional branch and a 549 // fallthrough. 550 if (!BBI.FalseBB) 551 BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB); 552 if (!BBI.FalseBB) { 553 // Malformed bcc? True and false blocks are the same? 554 BBI.IsUnpredicable = true; 555 return; 556 } 557 } 558 559 // Then scan all the instructions. 560 BBI.NonPredSize = 0; 561 BBI.ClobbersPred = false; 562 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end(); 563 I != E; ++I) { 564 const TargetInstrDesc &TID = I->getDesc(); 565 if (TID.isNotDuplicable()) 566 BBI.CannotBeCopied = true; 567 568 bool isPredicated = TII->isPredicated(I); 569 bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch(); 570 571 if (!isCondBr) { 572 if (!isPredicated) 573 BBI.NonPredSize++; 574 else if (!AlreadyPredicated) { 575 // FIXME: This instruction is already predicated before the 576 // if-conversion pass. It's probably something like a conditional move. 577 // Mark this block unpredicable for now. 578 BBI.IsUnpredicable = true; 579 return; 580 } 581 } 582 583 if (BBI.ClobbersPred && !isPredicated) { 584 // Predicate modification instruction should end the block (except for 585 // already predicated instructions and end of block branches). 586 if (isCondBr) { 587 // A conditional branch is not predicable, but it may be eliminated. 588 continue; 589 } 590 591 // Predicate may have been modified, the subsequent (currently) 592 // unpredicated instructions cannot be correctly predicated. 593 BBI.IsUnpredicable = true; 594 return; 595 } 596 597 // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are 598 // still potentially predicable. 599 std::vector<MachineOperand> PredDefs; 600 if (TII->DefinesPredicate(I, PredDefs)) 601 BBI.ClobbersPred = true; 602 603 if (!TID.isPredicable()) { 604 BBI.IsUnpredicable = true; 605 return; 606 } 607 } 608} 609 610/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be 611/// predicated by the specified predicate. 612bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, 613 SmallVectorImpl<MachineOperand> &Pred, 614 bool isTriangle, bool RevBranch) { 615 // If the block is dead or unpredicable, then it cannot be predicated. 616 if (BBI.IsDone || BBI.IsUnpredicable) 617 return false; 618 619 // If it is already predicated, check if its predicate subsumes the new 620 // predicate. 621 if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred)) 622 return false; 623 624 if (BBI.BrCond.size()) { 625 if (!isTriangle) 626 return false; 627 628 // Test predicate subsumption. 629 SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end()); 630 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 631 if (RevBranch) { 632 if (TII->ReverseBranchCondition(Cond)) 633 return false; 634 } 635 if (TII->ReverseBranchCondition(RevPred) || 636 !TII->SubsumesPredicate(Cond, RevPred)) 637 return false; 638 } 639 640 return true; 641} 642 643/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from 644/// the specified block. Record its successors and whether it looks like an 645/// if-conversion candidate. 646IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB, 647 std::vector<IfcvtToken*> &Tokens) { 648 BBInfo &BBI = BBAnalysis[BB->getNumber()]; 649 650 if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed) 651 return BBI; 652 653 BBI.BB = BB; 654 BBI.IsBeingAnalyzed = true; 655 656 ScanInstructions(BBI); 657 658 // Unanalyzable or ends with fallthrough or unconditional branch. 659 if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) { 660 BBI.IsBeingAnalyzed = false; 661 BBI.IsAnalyzed = true; 662 return BBI; 663 } 664 665 // Do not ifcvt if either path is a back edge to the entry block. 666 if (BBI.TrueBB == BB || BBI.FalseBB == BB) { 667 BBI.IsBeingAnalyzed = false; 668 BBI.IsAnalyzed = true; 669 return BBI; 670 } 671 672 // Do not ifcvt if true and false fallthrough blocks are the same. 673 if (!BBI.FalseBB) { 674 BBI.IsBeingAnalyzed = false; 675 BBI.IsAnalyzed = true; 676 return BBI; 677 } 678 679 BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB, Tokens); 680 BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens); 681 682 if (TrueBBI.IsDone && FalseBBI.IsDone) { 683 BBI.IsBeingAnalyzed = false; 684 BBI.IsAnalyzed = true; 685 return BBI; 686 } 687 688 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 689 bool CanRevCond = !TII->ReverseBranchCondition(RevCond); 690 691 unsigned Dups = 0; 692 unsigned Dups2 = 0; 693 bool TNeedSub = TrueBBI.Predicate.size() > 0; 694 bool FNeedSub = FalseBBI.Predicate.size() > 0; 695 bool Enqueued = false; 696 if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) && 697 MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) && 698 MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) && 699 FeasibilityAnalysis(TrueBBI, BBI.BrCond) && 700 FeasibilityAnalysis(FalseBBI, RevCond)) { 701 // Diamond: 702 // EBB 703 // / \_ 704 // | | 705 // TBB FBB 706 // \ / 707 // TailBB 708 // Note TailBB can be empty. 709 Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups, 710 Dups2)); 711 Enqueued = true; 712 } 713 714 if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) && 715 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 716 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { 717 // Triangle: 718 // EBB 719 // | \_ 720 // | | 721 // | TBB 722 // | / 723 // FBB 724 Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups)); 725 Enqueued = true; 726 } 727 728 if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) && 729 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 730 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) { 731 Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups)); 732 Enqueued = true; 733 } 734 735 if (ValidSimple(TrueBBI, Dups) && 736 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 737 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { 738 // Simple (split, no rejoin): 739 // EBB 740 // | \_ 741 // | | 742 // | TBB---> exit 743 // | 744 // FBB 745 Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups)); 746 Enqueued = true; 747 } 748 749 if (CanRevCond) { 750 // Try the other path... 751 if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) && 752 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 753 FeasibilityAnalysis(FalseBBI, RevCond, true)) { 754 Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups)); 755 Enqueued = true; 756 } 757 758 if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) && 759 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 760 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { 761 Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups)); 762 Enqueued = true; 763 } 764 765 if (ValidSimple(FalseBBI, Dups) && 766 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 767 FeasibilityAnalysis(FalseBBI, RevCond)) { 768 Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups)); 769 Enqueued = true; 770 } 771 } 772 773 BBI.IsEnqueued = Enqueued; 774 BBI.IsBeingAnalyzed = false; 775 BBI.IsAnalyzed = true; 776 return BBI; 777} 778 779/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion 780/// candidates. It returns true if any CFG restructuring is done to expose more 781/// if-conversion opportunities. 782bool IfConverter::AnalyzeBlocks(MachineFunction &MF, 783 std::vector<IfcvtToken*> &Tokens) { 784 bool Change = false; 785 std::set<MachineBasicBlock*> Visited; 786 for (unsigned i = 0, e = Roots.size(); i != e; ++i) { 787 for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited), 788 E = idf_ext_end(Roots[i], Visited); I != E; ++I) { 789 MachineBasicBlock *BB = *I; 790 AnalyzeBlock(BB, Tokens); 791 } 792 } 793 794 // Sort to favor more complex ifcvt scheme. 795 std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp); 796 797 return Change; 798} 799 800/// canFallThroughTo - Returns true either if ToBB is the next block after BB or 801/// that all the intervening blocks are empty (given BB can fall through to its 802/// next block). 803static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) { 804 MachineFunction::iterator I = BB; 805 MachineFunction::iterator TI = ToBB; 806 MachineFunction::iterator E = BB->getParent()->end(); 807 while (++I != TI) 808 if (I == E || !I->empty()) 809 return false; 810 return true; 811} 812 813/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed 814/// to determine if it can be if-converted. If predecessor is already enqueued, 815/// dequeue it! 816void IfConverter::InvalidatePreds(MachineBasicBlock *BB) { 817 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(), 818 E = BB->pred_end(); PI != E; ++PI) { 819 BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()]; 820 if (PBBI.IsDone || PBBI.BB == BB) 821 continue; 822 PBBI.IsAnalyzed = false; 823 PBBI.IsEnqueued = false; 824 } 825} 826 827/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB. 828/// 829static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB, 830 const TargetInstrInfo *TII) { 831 SmallVector<MachineOperand, 0> NoCond; 832 TII->InsertBranch(*BB, ToBB, NULL, NoCond); 833} 834 835/// RemoveExtraEdges - Remove true / false edges if either / both are no longer 836/// successors. 837void IfConverter::RemoveExtraEdges(BBInfo &BBI) { 838 MachineBasicBlock *TBB = NULL, *FBB = NULL; 839 SmallVector<MachineOperand, 4> Cond; 840 if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond)) 841 BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty()); 842} 843 844/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG. 845/// 846bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) { 847 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 848 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 849 BBInfo *CvtBBI = &TrueBBI; 850 BBInfo *NextBBI = &FalseBBI; 851 852 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 853 if (Kind == ICSimpleFalse) 854 std::swap(CvtBBI, NextBBI); 855 856 if (CvtBBI->IsDone || 857 (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { 858 // Something has changed. It's no longer safe to predicate this block. 859 BBI.IsAnalyzed = false; 860 CvtBBI->IsAnalyzed = false; 861 return false; 862 } 863 864 if (Kind == ICSimpleFalse) 865 if (TII->ReverseBranchCondition(Cond)) 866 assert(false && "Unable to reverse branch condition!"); 867 868 if (CvtBBI->BB->pred_size() > 1) { 869 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 870 // Copy instructions in the true block, predicate them, and add them to 871 // the entry block. 872 CopyAndPredicateBlock(BBI, *CvtBBI, Cond); 873 } else { 874 PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); 875 876 // Merge converted block into entry block. 877 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 878 MergeBlocks(BBI, *CvtBBI); 879 } 880 881 bool IterIfcvt = true; 882 if (!canFallThroughTo(BBI.BB, NextBBI->BB)) { 883 InsertUncondBranch(BBI.BB, NextBBI->BB, TII); 884 BBI.HasFallThrough = false; 885 // Now ifcvt'd block will look like this: 886 // BB: 887 // ... 888 // t, f = cmp 889 // if t op 890 // b BBf 891 // 892 // We cannot further ifcvt this block because the unconditional branch 893 // will have to be predicated on the new condition, that will not be 894 // available if cmp executes. 895 IterIfcvt = false; 896 } 897 898 RemoveExtraEdges(BBI); 899 900 // Update block info. BB can be iteratively if-converted. 901 if (!IterIfcvt) 902 BBI.IsDone = true; 903 InvalidatePreds(BBI.BB); 904 CvtBBI->IsDone = true; 905 906 // FIXME: Must maintain LiveIns. 907 return true; 908} 909 910/// IfConvertTriangle - If convert a triangle sub-CFG. 911/// 912bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) { 913 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 914 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 915 BBInfo *CvtBBI = &TrueBBI; 916 BBInfo *NextBBI = &FalseBBI; 917 918 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 919 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 920 std::swap(CvtBBI, NextBBI); 921 922 if (CvtBBI->IsDone || 923 (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { 924 // Something has changed. It's no longer safe to predicate this block. 925 BBI.IsAnalyzed = false; 926 CvtBBI->IsAnalyzed = false; 927 return false; 928 } 929 930 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 931 if (TII->ReverseBranchCondition(Cond)) 932 assert(false && "Unable to reverse branch condition!"); 933 934 if (Kind == ICTriangleRev || Kind == ICTriangleFRev) { 935 if (ReverseBranchCondition(*CvtBBI)) { 936 // BB has been changed, modify its predecessors (except for this 937 // one) so they don't get ifcvt'ed based on bad intel. 938 for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(), 939 E = CvtBBI->BB->pred_end(); PI != E; ++PI) { 940 MachineBasicBlock *PBB = *PI; 941 if (PBB == BBI.BB) 942 continue; 943 BBInfo &PBBI = BBAnalysis[PBB->getNumber()]; 944 if (PBBI.IsEnqueued) { 945 PBBI.IsAnalyzed = false; 946 PBBI.IsEnqueued = false; 947 } 948 } 949 } 950 } 951 952 bool HasEarlyExit = CvtBBI->FalseBB != NULL; 953 bool DupBB = CvtBBI->BB->pred_size() > 1; 954 if (DupBB) { 955 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 956 // Copy instructions in the true block, predicate them, and add them to 957 // the entry block. 958 CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true); 959 } else { 960 // Predicate the 'true' block after removing its branch. 961 CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB); 962 PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); 963 964 // Now merge the entry of the triangle with the true block. 965 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 966 MergeBlocks(BBI, *CvtBBI); 967 } 968 969 // If 'true' block has a 'false' successor, add an exit branch to it. 970 if (HasEarlyExit) { 971 SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(), 972 CvtBBI->BrCond.end()); 973 if (TII->ReverseBranchCondition(RevCond)) 974 assert(false && "Unable to reverse branch condition!"); 975 TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond); 976 BBI.BB->addSuccessor(CvtBBI->FalseBB); 977 } 978 979 // Merge in the 'false' block if the 'false' block has no other 980 // predecessors. Otherwise, add an unconditional branch to 'false'. 981 bool FalseBBDead = false; 982 bool IterIfcvt = true; 983 bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB); 984 if (!isFallThrough) { 985 // Only merge them if the true block does not fallthrough to the false 986 // block. By not merging them, we make it possible to iteratively 987 // ifcvt the blocks. 988 if (!HasEarlyExit && 989 NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) { 990 MergeBlocks(BBI, *NextBBI); 991 FalseBBDead = true; 992 } else { 993 InsertUncondBranch(BBI.BB, NextBBI->BB, TII); 994 BBI.HasFallThrough = false; 995 } 996 // Mixed predicated and unpredicated code. This cannot be iteratively 997 // predicated. 998 IterIfcvt = false; 999 } 1000 1001 RemoveExtraEdges(BBI); 1002 1003 // Update block info. BB can be iteratively if-converted. 1004 if (!IterIfcvt) 1005 BBI.IsDone = true; 1006 InvalidatePreds(BBI.BB); 1007 CvtBBI->IsDone = true; 1008 if (FalseBBDead) 1009 NextBBI->IsDone = true; 1010 1011 // FIXME: Must maintain LiveIns. 1012 return true; 1013} 1014 1015/// IfConvertDiamond - If convert a diamond sub-CFG. 1016/// 1017bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 1018 unsigned NumDups1, unsigned NumDups2) { 1019 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1020 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1021 MachineBasicBlock *TailBB = TrueBBI.TrueBB; 1022 // True block must fall through or end with an unanalyzable terminator. 1023 if (!TailBB) { 1024 if (blockAlwaysFallThrough(TrueBBI)) 1025 TailBB = FalseBBI.TrueBB; 1026 assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!"); 1027 } 1028 1029 if (TrueBBI.IsDone || FalseBBI.IsDone || 1030 TrueBBI.BB->pred_size() > 1 || 1031 FalseBBI.BB->pred_size() > 1) { 1032 // Something has changed. It's no longer safe to predicate these blocks. 1033 BBI.IsAnalyzed = false; 1034 TrueBBI.IsAnalyzed = false; 1035 FalseBBI.IsAnalyzed = false; 1036 return false; 1037 } 1038 1039 // Merge the 'true' and 'false' blocks by copying the instructions 1040 // from the 'false' block to the 'true' block. That is, unless the true 1041 // block would clobber the predicate, in that case, do the opposite. 1042 BBInfo *BBI1 = &TrueBBI; 1043 BBInfo *BBI2 = &FalseBBI; 1044 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 1045 if (TII->ReverseBranchCondition(RevCond)) 1046 assert(false && "Unable to reverse branch condition!"); 1047 SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond; 1048 SmallVector<MachineOperand, 4> *Cond2 = &RevCond; 1049 1050 // Figure out the more profitable ordering. 1051 bool DoSwap = false; 1052 if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) 1053 DoSwap = true; 1054 else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) { 1055 if (TrueBBI.NonPredSize > FalseBBI.NonPredSize) 1056 DoSwap = true; 1057 } 1058 if (DoSwap) { 1059 std::swap(BBI1, BBI2); 1060 std::swap(Cond1, Cond2); 1061 } 1062 1063 // Remove the conditional branch from entry to the blocks. 1064 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 1065 1066 // Remove the duplicated instructions at the beginnings of both paths. 1067 MachineBasicBlock::iterator DI1 = BBI1->BB->begin(); 1068 MachineBasicBlock::iterator DI2 = BBI2->BB->begin(); 1069 BBI1->NonPredSize -= NumDups1; 1070 BBI2->NonPredSize -= NumDups1; 1071 while (NumDups1 != 0) { 1072 ++DI1; 1073 ++DI2; 1074 --NumDups1; 1075 } 1076 BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1); 1077 BBI2->BB->erase(BBI2->BB->begin(), DI2); 1078 1079 // Predicate the 'true' block after removing its branch. 1080 BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB); 1081 DI1 = BBI1->BB->end(); 1082 for (unsigned i = 0; i != NumDups2; ++i) 1083 --DI1; 1084 BBI1->BB->erase(DI1, BBI1->BB->end()); 1085 PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1); 1086 1087 // Predicate the 'false' block. 1088 BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB); 1089 DI2 = BBI2->BB->end(); 1090 while (NumDups2 != 0) { 1091 --DI2; 1092 --NumDups2; 1093 } 1094 PredicateBlock(*BBI2, DI2, *Cond2); 1095 1096 // Merge the true block into the entry of the diamond. 1097 MergeBlocks(BBI, *BBI1); 1098 MergeBlocks(BBI, *BBI2); 1099 1100 // If the if-converted block falls through or unconditionally branches into 1101 // the tail block, and the tail block does not have other predecessors, then 1102 // fold the tail block in as well. Otherwise, unless it falls through to the 1103 // tail, add a unconditional branch to it. 1104 if (TailBB) { 1105 BBInfo TailBBI = BBAnalysis[TailBB->getNumber()]; 1106 if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) { 1107 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 1108 MergeBlocks(BBI, TailBBI); 1109 TailBBI.IsDone = true; 1110 } else { 1111 InsertUncondBranch(BBI.BB, TailBB, TII); 1112 BBI.HasFallThrough = false; 1113 } 1114 } 1115 1116 RemoveExtraEdges(BBI); 1117 1118 // Update block info. 1119 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; 1120 InvalidatePreds(BBI.BB); 1121 1122 // FIXME: Must maintain LiveIns. 1123 return true; 1124} 1125 1126/// PredicateBlock - Predicate instructions from the start of the block to the 1127/// specified end with the specified condition. 1128void IfConverter::PredicateBlock(BBInfo &BBI, 1129 MachineBasicBlock::iterator E, 1130 SmallVectorImpl<MachineOperand> &Cond) { 1131 for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) { 1132 if (TII->isPredicated(I)) 1133 continue; 1134 if (!TII->PredicateInstruction(I, Cond)) { 1135#ifndef NDEBUG 1136 errs() << "Unable to predicate " << *I << "!\n"; 1137#endif 1138 llvm_unreachable(0); 1139 } 1140 } 1141 1142 std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate)); 1143 1144 BBI.IsAnalyzed = false; 1145 BBI.NonPredSize = 0; 1146 1147 NumIfConvBBs++; 1148} 1149 1150/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to 1151/// the destination block. Skip end of block branches if IgnoreBr is true. 1152void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 1153 SmallVectorImpl<MachineOperand> &Cond, 1154 bool IgnoreBr) { 1155 MachineFunction &MF = *ToBBI.BB->getParent(); 1156 1157 for (MachineBasicBlock::iterator I = FromBBI.BB->begin(), 1158 E = FromBBI.BB->end(); I != E; ++I) { 1159 const TargetInstrDesc &TID = I->getDesc(); 1160 bool isPredicated = TII->isPredicated(I); 1161 // Do not copy the end of the block branches. 1162 if (IgnoreBr && !isPredicated && TID.isBranch()) 1163 break; 1164 1165 MachineInstr *MI = MF.CloneMachineInstr(I); 1166 ToBBI.BB->insert(ToBBI.BB->end(), MI); 1167 ToBBI.NonPredSize++; 1168 1169 if (!isPredicated) 1170 if (!TII->PredicateInstruction(MI, Cond)) { 1171#ifndef NDEBUG 1172 errs() << "Unable to predicate " << *I << "!\n"; 1173#endif 1174 llvm_unreachable(0); 1175 } 1176 } 1177 1178 std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(), 1179 FromBBI.BB->succ_end()); 1180 MachineBasicBlock *NBB = getNextBlock(FromBBI.BB); 1181 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL; 1182 1183 for (unsigned i = 0, e = Succs.size(); i != e; ++i) { 1184 MachineBasicBlock *Succ = Succs[i]; 1185 // Fallthrough edge can't be transferred. 1186 if (Succ == FallThrough) 1187 continue; 1188 ToBBI.BB->addSuccessor(Succ); 1189 } 1190 1191 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), 1192 std::back_inserter(ToBBI.Predicate)); 1193 std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate)); 1194 1195 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 1196 ToBBI.IsAnalyzed = false; 1197 1198 NumDupBBs++; 1199} 1200 1201/// MergeBlocks - Move all instructions from FromBB to the end of ToBB. 1202/// 1203void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) { 1204 ToBBI.BB->splice(ToBBI.BB->end(), 1205 FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end()); 1206 1207 // Redirect all branches to FromBB to ToBB. 1208 std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(), 1209 FromBBI.BB->pred_end()); 1210 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 1211 MachineBasicBlock *Pred = Preds[i]; 1212 if (Pred == ToBBI.BB) 1213 continue; 1214 Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB); 1215 } 1216 1217 std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(), 1218 FromBBI.BB->succ_end()); 1219 MachineBasicBlock *NBB = getNextBlock(FromBBI.BB); 1220 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL; 1221 1222 for (unsigned i = 0, e = Succs.size(); i != e; ++i) { 1223 MachineBasicBlock *Succ = Succs[i]; 1224 // Fallthrough edge can't be transferred. 1225 if (Succ == FallThrough) 1226 continue; 1227 FromBBI.BB->removeSuccessor(Succ); 1228 ToBBI.BB->addSuccessor(Succ); 1229 } 1230 1231 // Now FromBBI always falls through to the next block! 1232 if (NBB && !FromBBI.BB->isSuccessor(NBB)) 1233 FromBBI.BB->addSuccessor(NBB); 1234 1235 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), 1236 std::back_inserter(ToBBI.Predicate)); 1237 FromBBI.Predicate.clear(); 1238 1239 ToBBI.NonPredSize += FromBBI.NonPredSize; 1240 FromBBI.NonPredSize = 0; 1241 1242 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 1243 ToBBI.HasFallThrough = FromBBI.HasFallThrough; 1244 ToBBI.IsAnalyzed = false; 1245 FromBBI.IsAnalyzed = false; 1246} 1247