IfConversion.cpp revision a1a878791b305880c976038b8fcd2697b7799ec1
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the Evan Cheng and is distributed under 6// the University of Illinois Open Source 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/ADT/DepthFirstIterator.h" 25#include "llvm/ADT/Statistic.h" 26#include "llvm/ADT/STLExtras.h" 27using namespace llvm; 28 29namespace { 30 // Hidden options for help debugging. 31 cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); 32 cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); 33 cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); 34 cl::opt<bool> DisableSimple("disable-ifcvt-simple", 35 cl::init(false), cl::Hidden); 36 cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false", 37 cl::init(false), cl::Hidden); 38 cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", 39 cl::init(false), cl::Hidden); 40 cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev", 41 cl::init(false), cl::Hidden); 42 cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false", 43 cl::init(false), cl::Hidden); 44 cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev", 45 cl::init(false), cl::Hidden); 46 cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", 47 cl::init(false), cl::Hidden); 48} 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 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 /// ClobbersPredicate- True if BB would modify the predicate (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 std::vector<MachineOperand> BrCond; 109 std::vector<MachineOperand> 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 /// NeedSubsumsion - 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 NeedSubsumsion; 132 unsigned NumDups; 133 unsigned NumDups2; 134 IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0) 135 : BBI(b), Kind(k), NeedSubsumsion(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 public: 150 static char ID; 151 IfConverter() : MachineFunctionPass((intptr_t)&ID) {} 152 153 virtual bool runOnMachineFunction(MachineFunction &MF); 154 virtual const char *getPassName() const { return "If converter"; } 155 156 private: 157 bool ReverseBranchCondition(BBInfo &BBI); 158 bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const; 159 bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 160 bool FalseBranch, unsigned &Dups) const; 161 bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, 162 unsigned &Dups1, unsigned &Dups2) const; 163 void ScanInstructions(BBInfo &BBI); 164 BBInfo &AnalyzeBlock(MachineBasicBlock *BB, 165 std::vector<IfcvtToken*> &Tokens); 166 bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond, 167 bool isTriangle = false, bool RevBranch = false); 168 bool AnalyzeBlocks(MachineFunction &MF, 169 std::vector<IfcvtToken*> &Tokens); 170 void InvalidatePreds(MachineBasicBlock *BB); 171 void RemoveExtraEdges(BBInfo &BBI); 172 bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind); 173 bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind); 174 bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 175 unsigned NumDups1, unsigned NumDups2); 176 void PredicateBlock(BBInfo &BBI, 177 MachineBasicBlock::iterator E, 178 std::vector<MachineOperand> &Cond); 179 void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 180 std::vector<MachineOperand> &Cond, 181 bool IgnoreBr = false); 182 void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI); 183 184 bool MeetIfcvtSizeLimit(unsigned Size) const { 185 return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit(); 186 } 187 188 // blockAlwaysFallThrough - Block ends without a terminator. 189 bool blockAlwaysFallThrough(BBInfo &BBI) const { 190 return BBI.IsBrAnalyzable && BBI.TrueBB == NULL; 191 } 192 193 // IfcvtTokenCmp - Used to sort if-conversion candidates. 194 static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) { 195 int Incr1 = (C1->Kind == ICDiamond) 196 ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups; 197 int Incr2 = (C2->Kind == ICDiamond) 198 ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups; 199 if (Incr1 > Incr2) 200 return true; 201 else if (Incr1 == Incr2) { 202 // Favors subsumsion. 203 if (C1->NeedSubsumsion == false && C2->NeedSubsumsion == true) 204 return true; 205 else if (C1->NeedSubsumsion == C2->NeedSubsumsion) { 206 // Favors diamond over triangle, etc. 207 if ((unsigned)C1->Kind < (unsigned)C2->Kind) 208 return true; 209 else if (C1->Kind == C2->Kind) 210 return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber(); 211 } 212 } 213 return false; 214 } 215 }; 216 217 char IfConverter::ID = 0; 218} 219 220FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); } 221 222bool IfConverter::runOnMachineFunction(MachineFunction &MF) { 223 TLI = MF.getTarget().getTargetLowering(); 224 TII = MF.getTarget().getInstrInfo(); 225 if (!TII) return false; 226 227 static int FnNum = -1; 228 DOUT << "\nIfcvt: function (" << ++FnNum << ") \'" 229 << MF.getFunction()->getName() << "\'"; 230 231 if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { 232 DOUT << " skipped\n"; 233 return false; 234 } 235 DOUT << "\n"; 236 237 MF.RenumberBlocks(); 238 BBAnalysis.resize(MF.getNumBlockIDs()); 239 240 // Look for root nodes, i.e. blocks without successors. 241 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) 242 if (I->succ_size() == 0) 243 Roots.push_back(I); 244 245 std::vector<IfcvtToken*> Tokens; 246 MadeChange = false; 247 unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + 248 NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds; 249 while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) { 250 // Do an intial analysis for each basic block and finding all the potential 251 // candidates to perform if-convesion. 252 bool Change = AnalyzeBlocks(MF, Tokens); 253 while (!Tokens.empty()) { 254 IfcvtToken *Token = Tokens.back(); 255 Tokens.pop_back(); 256 BBInfo &BBI = Token->BBI; 257 IfcvtKind Kind = Token->Kind; 258 259 // If the block has been evicted out of the queue or it has already been 260 // marked dead (due to it being predicated), then skip it. 261 if (BBI.IsDone) 262 BBI.IsEnqueued = false; 263 if (!BBI.IsEnqueued) 264 continue; 265 266 BBI.IsEnqueued = false; 267 268 bool RetVal = false; 269 switch (Kind) { 270 default: assert(false && "Unexpected!"); 271 break; 272 case ICSimple: 273 case ICSimpleFalse: { 274 bool isFalse = Kind == ICSimpleFalse; 275 if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break; 276 DOUT << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"") 277 << "): BB#" << BBI.BB->getNumber() << " (" 278 << ((Kind == ICSimpleFalse) 279 ? BBI.FalseBB->getNumber() 280 : BBI.TrueBB->getNumber()) << ") "; 281 RetVal = IfConvertSimple(BBI, Kind); 282 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n"; 283 if (RetVal) 284 if (isFalse) NumSimpleFalse++; 285 else NumSimple++; 286 break; 287 } 288 case ICTriangle: 289 case ICTriangleRev: 290 case ICTriangleFalse: 291 case ICTriangleFRev: { 292 bool isFalse = Kind == ICTriangleFalse; 293 bool isRev = (Kind == ICTriangleRev || Kind == ICTriangleFRev); 294 if (DisableTriangle && !isFalse && !isRev) break; 295 if (DisableTriangleR && !isFalse && isRev) break; 296 if (DisableTriangleF && isFalse && !isRev) break; 297 if (DisableTriangleFR && isFalse && isRev) break; 298 DOUT << "Ifcvt (Triangle"; 299 if (isFalse) 300 DOUT << " false"; 301 if (isRev) 302 DOUT << " rev"; 303 DOUT << "): BB#" << BBI.BB->getNumber() << " (T:" 304 << BBI.TrueBB->getNumber() << ",F:" 305 << BBI.FalseBB->getNumber() << ") "; 306 RetVal = IfConvertTriangle(BBI, Kind); 307 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n"; 308 if (RetVal) { 309 if (isFalse) { 310 if (isRev) NumTriangleFRev++; 311 else NumTriangleFalse++; 312 } else { 313 if (isRev) NumTriangleRev++; 314 else NumTriangle++; 315 } 316 } 317 break; 318 } 319 case ICDiamond: { 320 if (DisableDiamond) break; 321 DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:" 322 << BBI.TrueBB->getNumber() << ",F:" 323 << BBI.FalseBB->getNumber() << ") "; 324 RetVal = IfConvertDiamond(BBI, Kind, Token->NumDups, Token->NumDups2); 325 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n"; 326 if (RetVal) NumDiamonds++; 327 break; 328 } 329 } 330 331 Change |= RetVal; 332 333 NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev + 334 NumTriangleFalse + NumTriangleFRev + NumDiamonds; 335 if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit) 336 break; 337 } 338 339 if (!Change) 340 break; 341 MadeChange |= Change; 342 } 343 344 // Delete tokens in case of early exit. 345 while (!Tokens.empty()) { 346 IfcvtToken *Token = Tokens.back(); 347 Tokens.pop_back(); 348 delete Token; 349 } 350 351 Tokens.clear(); 352 Roots.clear(); 353 BBAnalysis.clear(); 354 355 return MadeChange; 356} 357 358/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given 359/// its 'true' successor. 360static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, 361 MachineBasicBlock *TrueBB) { 362 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), 363 E = BB->succ_end(); SI != E; ++SI) { 364 MachineBasicBlock *SuccBB = *SI; 365 if (SuccBB != TrueBB) 366 return SuccBB; 367 } 368 return NULL; 369} 370 371/// ReverseBranchCondition - Reverse the condition of the end of the block 372/// branchs. Swap block's 'true' and 'false' successors. 373bool IfConverter::ReverseBranchCondition(BBInfo &BBI) { 374 if (!TII->ReverseBranchCondition(BBI.BrCond)) { 375 TII->RemoveBranch(*BBI.BB); 376 TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond); 377 std::swap(BBI.TrueBB, BBI.FalseBB); 378 return true; 379 } 380 return false; 381} 382 383/// getNextBlock - Returns the next block in the function blocks ordering. If 384/// it is the end, returns NULL. 385static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) { 386 MachineFunction::iterator I = BB; 387 MachineFunction::iterator E = BB->getParent()->end(); 388 if (++I == E) 389 return NULL; 390 return I; 391} 392 393/// ValidSimple - Returns true if the 'true' block (along with its 394/// predecessor) forms a valid simple shape for ifcvt. It also returns the 395/// number of instructions that the ifcvt would need to duplicate if performed 396/// in Dups. 397bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const { 398 Dups = 0; 399 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 400 return false; 401 402 if (TrueBBI.BB->pred_size() > 1) { 403 if (TrueBBI.CannotBeCopied || 404 TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit()) 405 return false; 406 Dups = TrueBBI.NonPredSize; 407 } 408 409 return !blockAlwaysFallThrough(TrueBBI) && TrueBBI.BrCond.size() == 0; 410} 411 412/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along 413/// with their common predecessor) forms a valid triangle shape for ifcvt. 414/// If 'FalseBranch' is true, it checks if 'true' block's false branch 415/// branches to the false branch rather than the other way around. It also 416/// returns the number of instructions that the ifcvt would need to duplicate 417/// if performed in 'Dups'. 418bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 419 bool FalseBranch, unsigned &Dups) const { 420 Dups = 0; 421 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 422 return false; 423 424 if (TrueBBI.BB->pred_size() > 1) { 425 if (TrueBBI.CannotBeCopied) 426 return false; 427 428 unsigned Size = TrueBBI.NonPredSize; 429 if (TrueBBI.IsBrAnalyzable) { 430 if (TrueBBI.TrueBB && TrueBBI.BrCond.size() == 0) 431 // End with an unconditional branch. It will be removed. 432 --Size; 433 else { 434 MachineBasicBlock *FExit = FalseBranch 435 ? TrueBBI.TrueBB : TrueBBI.FalseBB; 436 if (FExit) 437 // Require a conditional branch 438 ++Size; 439 } 440 } 441 if (Size > TLI->getIfCvtDupBlockSizeLimit()) 442 return false; 443 Dups = Size; 444 } 445 446 MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB; 447 if (!TExit && blockAlwaysFallThrough(TrueBBI)) { 448 MachineFunction::iterator I = TrueBBI.BB; 449 if (++I == TrueBBI.BB->getParent()->end()) 450 return false; 451 TExit = I; 452 } 453 return TExit && TExit == FalseBBI.BB; 454} 455 456static 457MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB, 458 const TargetInstrInfo *TII) { 459 MachineBasicBlock::iterator I = BB->end(); 460 while (I != BB->begin()) { 461 --I; 462 const TargetInstrDescriptor *TID = I->getInstrDescriptor(); 463 if ((TID->Flags & M_BRANCH_FLAG) == 0) 464 break; 465 } 466 return I; 467} 468 469/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along 470/// with their common predecessor) forms a valid diamond shape for ifcvt. 471bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, 472 unsigned &Dups1, unsigned &Dups2) const { 473 Dups1 = Dups2 = 0; 474 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || 475 FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) 476 return false; 477 478 MachineBasicBlock *TT = TrueBBI.TrueBB; 479 MachineBasicBlock *FT = FalseBBI.TrueBB; 480 481 if (!TT && blockAlwaysFallThrough(TrueBBI)) 482 TT = getNextBlock(TrueBBI.BB); 483 if (!FT && blockAlwaysFallThrough(FalseBBI)) 484 FT = getNextBlock(FalseBBI.BB); 485 if (TT != FT) 486 return false; 487 if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable)) 488 return false; 489 // FIXME: Allow false block to have an early exit? 490 if (TrueBBI.BB->pred_size() > 1 || 491 FalseBBI.BB->pred_size() > 1 || 492 TrueBBI.FalseBB || FalseBBI.FalseBB || 493 (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred)) 494 return false; 495 496 MachineBasicBlock::iterator TI = TrueBBI.BB->begin(); 497 MachineBasicBlock::iterator FI = FalseBBI.BB->begin(); 498 while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) { 499 if (!TI->isIdenticalTo(FI)) 500 break; 501 ++Dups1; 502 ++TI; 503 ++FI; 504 } 505 506 TI = firstNonBranchInst(TrueBBI.BB, TII); 507 FI = firstNonBranchInst(FalseBBI.BB, TII); 508 while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) { 509 if (!TI->isIdenticalTo(FI)) 510 break; 511 ++Dups2; 512 --TI; 513 --FI; 514 } 515 516 return true; 517} 518 519/// ScanInstructions - Scan all the instructions in the block to determine if 520/// the block is predicable. In most cases, that means all the instructions 521/// in the block has M_PREDICABLE flag. Also checks if the block contains any 522/// instruction which can clobber a predicate (e.g. condition code register). 523/// If so, the block is not predicable unless it's the last instruction. 524void IfConverter::ScanInstructions(BBInfo &BBI) { 525 if (BBI.IsDone) 526 return; 527 528 // First analyze the end of BB branches. 529 BBI.TrueBB = BBI.FalseBB = NULL; 530 BBI.BrCond.clear(); 531 BBI.IsBrAnalyzable = 532 !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); 533 BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL; 534 535 if (BBI.BrCond.size()) { 536 // No false branch. This BB must end with a conditional branch and a 537 // fallthrough. 538 if (!BBI.FalseBB) 539 BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB); 540 assert(BBI.FalseBB && "Expected to find the fallthrough block!"); 541 } 542 543 // Then scan all the instructions. 544 BBI.NonPredSize = 0; 545 BBI.ClobbersPred = false; 546 bool SeenCondBr = false; 547 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end(); 548 I != E; ++I) { 549 if (!BBI.CannotBeCopied && !TII->CanBeDuplicated(I)) 550 BBI.CannotBeCopied = true; 551 552 const TargetInstrDescriptor *TID = I->getInstrDescriptor(); 553 bool isPredicated = TII->isPredicated(I); 554 bool isCondBr = BBI.IsBrAnalyzable && 555 (TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0; 556 557 if (!isPredicated && !isCondBr) 558 BBI.NonPredSize++; 559 560 if (BBI.ClobbersPred && !isPredicated) { 561 // Predicate modification instruction should end the block (except for 562 // already predicated instructions and end of block branches). 563 if (isCondBr) { 564 SeenCondBr = true; 565 566 // Conditional branches is not predicable. But it may be eliminated. 567 continue; 568 } 569 570 // Predicate may have been modified, the subsequent (currently) 571 // unpredocated instructions cannot be correctly predicated. 572 BBI.IsUnpredicable = true; 573 return; 574 } 575 576 if (TID->Flags & M_CLOBBERS_PRED) 577 BBI.ClobbersPred = true; 578 579 if ((TID->Flags & M_PREDICABLE) == 0) { 580 BBI.IsUnpredicable = true; 581 return; 582 } 583 } 584} 585 586/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be 587/// predicated by the specified predicate. 588bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, 589 std::vector<MachineOperand> &Pred, 590 bool isTriangle, bool RevBranch) { 591 // If the block is dead or unpredicable, then it cannot be predicated. 592 if (BBI.IsDone || BBI.IsUnpredicable) 593 return false; 594 595 // If it is already predicated, check if its predicate subsumes the new 596 // predicate. 597 if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred)) 598 return false; 599 600 if (BBI.BrCond.size()) { 601 if (!isTriangle) 602 return false; 603 604 // Test predicate subsumsion. 605 std::vector<MachineOperand> RevPred(Pred); 606 std::vector<MachineOperand> Cond(BBI.BrCond); 607 if (RevBranch) { 608 if (TII->ReverseBranchCondition(Cond)) 609 return false; 610 } 611 if (TII->ReverseBranchCondition(RevPred) || 612 !TII->SubsumesPredicate(Cond, RevPred)) 613 return false; 614 } 615 616 return true; 617} 618 619/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from 620/// the specified block. Record its successors and whether it looks like an 621/// if-conversion candidate. 622IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB, 623 std::vector<IfcvtToken*> &Tokens) { 624 BBInfo &BBI = BBAnalysis[BB->getNumber()]; 625 626 if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed) 627 return BBI; 628 629 BBI.BB = BB; 630 BBI.IsBeingAnalyzed = true; 631 632 ScanInstructions(BBI); 633 634 // Unanalyable or ends with fallthrough or unconditional branch. 635 if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) { 636 BBI.IsBeingAnalyzed = false; 637 BBI.IsAnalyzed = true; 638 return BBI; 639 } 640 641 // Do not ifcvt if either path is a back edge to the entry block. 642 if (BBI.TrueBB == BB || BBI.FalseBB == BB) { 643 BBI.IsBeingAnalyzed = false; 644 BBI.IsAnalyzed = true; 645 return BBI; 646 } 647 648 BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB, Tokens); 649 BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens); 650 651 if (TrueBBI.IsDone && FalseBBI.IsDone) { 652 BBI.IsBeingAnalyzed = false; 653 BBI.IsAnalyzed = true; 654 return BBI; 655 } 656 657 std::vector<MachineOperand> RevCond(BBI.BrCond); 658 bool CanRevCond = !TII->ReverseBranchCondition(RevCond); 659 660 unsigned Dups = 0; 661 unsigned Dups2 = 0; 662 bool TNeedSub = TrueBBI.Predicate.size() > 0; 663 bool FNeedSub = FalseBBI.Predicate.size() > 0; 664 bool Enqueued = false; 665 if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) && 666 MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) && 667 MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) && 668 FeasibilityAnalysis(TrueBBI, BBI.BrCond) && 669 FeasibilityAnalysis(FalseBBI, RevCond)) { 670 // Diamond: 671 // EBB 672 // / \_ 673 // | | 674 // TBB FBB 675 // \ / 676 // TailBB 677 // Note TailBB can be empty. 678 Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups, 679 Dups2)); 680 Enqueued = true; 681 } 682 683 if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) && 684 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 685 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { 686 // Triangle: 687 // EBB 688 // | \_ 689 // | | 690 // | TBB 691 // | / 692 // FBB 693 Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups)); 694 Enqueued = true; 695 } 696 697 if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) && 698 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 699 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) { 700 Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups)); 701 Enqueued = true; 702 } 703 704 if (ValidSimple(TrueBBI, Dups) && 705 MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && 706 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { 707 // Simple (split, no rejoin): 708 // EBB 709 // | \_ 710 // | | 711 // | TBB---> exit 712 // | 713 // FBB 714 Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups)); 715 Enqueued = true; 716 } 717 718 if (CanRevCond) { 719 // Try the other path... 720 if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) && 721 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 722 FeasibilityAnalysis(FalseBBI, RevCond, true)) { 723 Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups)); 724 Enqueued = true; 725 } 726 727 if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) && 728 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 729 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { 730 Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups)); 731 Enqueued = true; 732 } 733 734 if (ValidSimple(FalseBBI, Dups) && 735 MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && 736 FeasibilityAnalysis(FalseBBI, RevCond)) { 737 Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups)); 738 Enqueued = true; 739 } 740 } 741 742 BBI.IsEnqueued = Enqueued; 743 BBI.IsBeingAnalyzed = false; 744 BBI.IsAnalyzed = true; 745 return BBI; 746} 747 748/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion 749/// candidates. It returns true if any CFG restructuring is done to expose more 750/// if-conversion opportunities. 751bool IfConverter::AnalyzeBlocks(MachineFunction &MF, 752 std::vector<IfcvtToken*> &Tokens) { 753 bool Change = false; 754 std::set<MachineBasicBlock*> Visited; 755 for (unsigned i = 0, e = Roots.size(); i != e; ++i) { 756 for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited), 757 E = idf_ext_end(Roots[i], Visited); I != E; ++I) { 758 MachineBasicBlock *BB = *I; 759 AnalyzeBlock(BB, Tokens); 760 } 761 } 762 763 // Sort to favor more complex ifcvt scheme. 764 std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp); 765 766 return Change; 767} 768 769/// canFallThroughTo - Returns true either if ToBB is the next block after BB or 770/// that all the intervening blocks are empty (given BB can fall through to its 771/// next block). 772static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) { 773 MachineFunction::iterator I = BB; 774 MachineFunction::iterator TI = ToBB; 775 MachineFunction::iterator E = BB->getParent()->end(); 776 while (++I != TI) 777 if (I == E || !I->empty()) 778 return false; 779 return true; 780} 781 782/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed 783/// to determine if it can be if-converted. If predecessor is already enqueued, 784/// dequeue it! 785void IfConverter::InvalidatePreds(MachineBasicBlock *BB) { 786 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(), 787 E = BB->pred_end(); PI != E; ++PI) { 788 BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()]; 789 if (PBBI.IsDone || PBBI.BB == BB) 790 continue; 791 PBBI.IsAnalyzed = false; 792 PBBI.IsEnqueued = false; 793 } 794} 795 796/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB. 797/// 798static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB, 799 const TargetInstrInfo *TII) { 800 std::vector<MachineOperand> NoCond; 801 TII->InsertBranch(*BB, ToBB, NULL, NoCond); 802} 803 804/// RemoveExtraEdges - Remove true / false edges if either / both are no longer 805/// successors. 806void IfConverter::RemoveExtraEdges(BBInfo &BBI) { 807 MachineBasicBlock *TBB = NULL, *FBB = NULL; 808 std::vector<MachineOperand> Cond; 809 bool isAnalyzable = !TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond); 810 bool CanFallthrough = isAnalyzable && (TBB == NULL || FBB == NULL); 811 if (BBI.TrueBB && BBI.BB->isSuccessor(BBI.TrueBB)) 812 if (!(BBI.TrueBB == TBB || BBI.TrueBB == FBB || 813 (CanFallthrough && getNextBlock(BBI.BB) == BBI.TrueBB))) 814 BBI.BB->removeSuccessor(BBI.TrueBB); 815 if (BBI.FalseBB && BBI.BB->isSuccessor(BBI.FalseBB)) 816 if (!(BBI.FalseBB == TBB || BBI.FalseBB == FBB || 817 (CanFallthrough && getNextBlock(BBI.BB) == BBI.FalseBB))) 818 BBI.BB->removeSuccessor(BBI.FalseBB); 819} 820 821/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG. 822/// 823bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) { 824 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 825 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 826 BBInfo *CvtBBI = &TrueBBI; 827 BBInfo *NextBBI = &FalseBBI; 828 829 std::vector<MachineOperand> Cond(BBI.BrCond); 830 if (Kind == ICSimpleFalse) 831 std::swap(CvtBBI, NextBBI); 832 833 if (CvtBBI->IsDone || 834 (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { 835 // Something has changed. It's no longer safe to predicate this block. 836 BBI.IsAnalyzed = false; 837 CvtBBI->IsAnalyzed = false; 838 return false; 839 } 840 841 if (Kind == ICSimpleFalse) 842 TII->ReverseBranchCondition(Cond); 843 844 if (CvtBBI->BB->pred_size() > 1) { 845 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 846 // Copy instructions in the true block, predicate them add them to 847 // the entry block. 848 CopyAndPredicateBlock(BBI, *CvtBBI, Cond); 849 } else { 850 PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); 851 852 // Merge converted block into entry block. 853 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 854 MergeBlocks(BBI, *CvtBBI); 855 } 856 857 bool IterIfcvt = true; 858 if (!canFallThroughTo(BBI.BB, NextBBI->BB)) { 859 InsertUncondBranch(BBI.BB, NextBBI->BB, TII); 860 BBI.HasFallThrough = false; 861 // Now ifcvt'd block will look like this: 862 // BB: 863 // ... 864 // t, f = cmp 865 // if t op 866 // b BBf 867 // 868 // We cannot further ifcvt this block because the unconditional branch 869 // will have to be predicated on the new condition, that will not be 870 // available if cmp executes. 871 IterIfcvt = false; 872 } 873 874 RemoveExtraEdges(BBI); 875 876 // Update block info. BB can be iteratively if-converted. 877 if (!IterIfcvt) 878 BBI.IsDone = true; 879 InvalidatePreds(BBI.BB); 880 CvtBBI->IsDone = true; 881 882 // FIXME: Must maintain LiveIns. 883 return true; 884} 885 886/// IfConvertTriangle - If convert a triangle sub-CFG. 887/// 888bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) { 889 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 890 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 891 BBInfo *CvtBBI = &TrueBBI; 892 BBInfo *NextBBI = &FalseBBI; 893 894 std::vector<MachineOperand> Cond(BBI.BrCond); 895 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 896 std::swap(CvtBBI, NextBBI); 897 898 if (CvtBBI->IsDone || 899 (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { 900 // Something has changed. It's no longer safe to predicate this block. 901 BBI.IsAnalyzed = false; 902 CvtBBI->IsAnalyzed = false; 903 return false; 904 } 905 906 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 907 TII->ReverseBranchCondition(Cond); 908 909 if (Kind == ICTriangleRev || Kind == ICTriangleFRev) { 910 ReverseBranchCondition(*CvtBBI); 911 // BB has been changed, modify its predecessors (except for this 912 // one) so they don't get ifcvt'ed based on bad intel. 913 for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(), 914 E = CvtBBI->BB->pred_end(); PI != E; ++PI) { 915 MachineBasicBlock *PBB = *PI; 916 if (PBB == BBI.BB) 917 continue; 918 BBInfo &PBBI = BBAnalysis[PBB->getNumber()]; 919 if (PBBI.IsEnqueued) { 920 PBBI.IsAnalyzed = false; 921 PBBI.IsEnqueued = false; 922 } 923 } 924 } 925 926 bool HasEarlyExit = CvtBBI->FalseBB != NULL; 927 bool DupBB = CvtBBI->BB->pred_size() > 1; 928 if (DupBB) { 929 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 930 // Copy instructions in the true block, predicate them add them to 931 // the entry block. 932 CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true); 933 } else { 934 // Predicate the 'true' block after removing its branch. 935 CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB); 936 PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); 937 } 938 939 // If 'true' block has a 'false' successor, add an exit branch to it. 940 if (HasEarlyExit) { 941 std::vector<MachineOperand> RevCond(CvtBBI->BrCond); 942 if (TII->ReverseBranchCondition(RevCond)) 943 assert(false && "Unable to reverse branch condition!"); 944 if (DupBB) { 945 TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond); 946 BBI.BB->addSuccessor(CvtBBI->FalseBB); 947 } else { 948 TII->InsertBranch(*CvtBBI->BB, CvtBBI->FalseBB, NULL, RevCond); 949 } 950 } 951 952 if (!DupBB) { 953 // Now merge the entry of the triangle with the true block. 954 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 955 MergeBlocks(BBI, *CvtBBI); 956 } 957 958 // Merge in the 'false' block if the 'false' block has no other 959 // predecessors. Otherwise, add a unconditional branch from to 'false'. 960 bool FalseBBDead = false; 961 bool IterIfcvt = true; 962 bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB); 963 if (!isFallThrough) { 964 // Only merge them if the true block does not fallthrough to the false 965 // block. By not merging them, we make it possible to iteratively 966 // ifcvt the blocks. 967 if (!HasEarlyExit && 968 NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) { 969 MergeBlocks(BBI, *NextBBI); 970 FalseBBDead = true; 971 } else { 972 InsertUncondBranch(BBI.BB, NextBBI->BB, TII); 973 BBI.HasFallThrough = false; 974 } 975 // Mixed predicated and unpredicated code. This cannot be iteratively 976 // predicated. 977 IterIfcvt = false; 978 } 979 980 RemoveExtraEdges(BBI); 981 982 // Update block info. BB can be iteratively if-converted. 983 if (!IterIfcvt) 984 BBI.IsDone = true; 985 InvalidatePreds(BBI.BB); 986 CvtBBI->IsDone = true; 987 if (FalseBBDead) 988 NextBBI->IsDone = true; 989 990 // FIXME: Must maintain LiveIns. 991 return true; 992} 993 994/// IfConvertDiamond - If convert a diamond sub-CFG. 995/// 996bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 997 unsigned NumDups1, unsigned NumDups2) { 998 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 999 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1000 MachineBasicBlock *TailBB = TrueBBI.TrueBB; 1001 // True block must fall through or ended with unanalyzable terminator. 1002 if (!TailBB) { 1003 if (blockAlwaysFallThrough(TrueBBI)) 1004 TailBB = FalseBBI.TrueBB; 1005 assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!"); 1006 } 1007 1008 if (TrueBBI.IsDone || FalseBBI.IsDone || 1009 TrueBBI.BB->pred_size() > 1 || 1010 FalseBBI.BB->pred_size() > 1) { 1011 // Something has changed. It's no longer safe to predicate these blocks. 1012 BBI.IsAnalyzed = false; 1013 TrueBBI.IsAnalyzed = false; 1014 FalseBBI.IsAnalyzed = false; 1015 return false; 1016 } 1017 1018 // Merge the 'true' and 'false' blocks by copying the instructions 1019 // from the 'false' block to the 'true' block. That is, unless the true 1020 // block would clobber the predicate, in that case, do the opposite. 1021 BBInfo *BBI1 = &TrueBBI; 1022 BBInfo *BBI2 = &FalseBBI; 1023 std::vector<MachineOperand> RevCond(BBI.BrCond); 1024 TII->ReverseBranchCondition(RevCond); 1025 std::vector<MachineOperand> *Cond1 = &BBI.BrCond; 1026 std::vector<MachineOperand> *Cond2 = &RevCond; 1027 bool NeedBr1 = BBI1->FalseBB != NULL; 1028 bool NeedBr2 = BBI2->FalseBB != NULL; 1029 1030 // Figure out the more profitable ordering. 1031 bool DoSwap = false; 1032 if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) 1033 DoSwap = true; 1034 else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) { 1035 if (!NeedBr1 && NeedBr2) 1036 DoSwap = true; 1037 else if (NeedBr1 == NeedBr2) { 1038 if (TrueBBI.NonPredSize > FalseBBI.NonPredSize) 1039 DoSwap = true; 1040 } 1041 } 1042 if (DoSwap) { 1043 std::swap(BBI1, BBI2); 1044 std::swap(Cond1, Cond2); 1045 std::swap(NeedBr1, NeedBr2); 1046 } 1047 1048 // Remove the conditional branch from entry to the blocks. 1049 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 1050 1051 // Remove the duplicated instructions at the beginnings of both paths. 1052 MachineBasicBlock::iterator DI1 = BBI1->BB->begin(); 1053 MachineBasicBlock::iterator DI2 = BBI2->BB->begin(); 1054 BBI1->NonPredSize -= NumDups1; 1055 BBI2->NonPredSize -= NumDups1; 1056 while (NumDups1 != 0) { 1057 ++DI1; 1058 ++DI2; 1059 --NumDups1; 1060 } 1061 BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1); 1062 BBI2->BB->erase(BBI2->BB->begin(), DI2); 1063 1064 // Predicate the 'true' block after removing its branch. 1065 BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB); 1066 DI1 = BBI1->BB->end(); 1067 for (unsigned i = 0; i != NumDups2; ++i) 1068 --DI1; 1069 BBI1->BB->erase(DI1, BBI1->BB->end()); 1070 PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1); 1071 1072 // Add an early exit branch if needed. 1073 if (NeedBr1) 1074 TII->InsertBranch(*BBI1->BB, BBI1->FalseBB, NULL, *Cond1); 1075 1076 // Predicate the 'false' block. 1077 BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB); 1078 DI2 = BBI2->BB->end(); 1079 while (NumDups2 != 0) { 1080 --DI2; 1081 --NumDups2; 1082 } 1083 PredicateBlock(*BBI2, DI2, *Cond2); 1084 1085 // Add an unconditional branch from 'false' to to 'false' successor if it 1086 // will not be the fallthrough block. 1087 if (NeedBr2 && !NeedBr1) { 1088 // If BBI2 isn't going to be merged in, then the existing fallthrough 1089 // or branch is fine. 1090 if (!canFallThroughTo(BBI.BB, BBI2->FalseBB)) { 1091 InsertUncondBranch(BBI2->BB, BBI2->FalseBB, TII); 1092 BBI2->HasFallThrough = false; 1093 } 1094 } 1095 1096 // Keep them as two separate blocks if there is an early exit. 1097 if (!NeedBr1) 1098 MergeBlocks(*BBI1, *BBI2); 1099 1100 // Merge the combined block into the entry of the diamond. 1101 MergeBlocks(BBI, *BBI1); 1102 1103 // 'True' and 'false' aren't combined, see if we need to add a unconditional 1104 // branch to the 'false' block. 1105 if (NeedBr1 && !canFallThroughTo(BBI.BB, BBI2->BB)) { 1106 InsertUncondBranch(BBI.BB, BBI2->BB, TII); 1107 BBI1->HasFallThrough = false; 1108 } 1109 1110 // If the if-converted block fallthrough or unconditionally branch into the 1111 // tail block, and the tail block does not have other predecessors, then 1112 // fold the tail block in as well. Otherwise, unless it falls through to the 1113 // tail, add a unconditional branch to it. 1114 if (TailBB) { 1115 BBInfo TailBBI = BBAnalysis[TailBB->getNumber()]; 1116 BBInfo *LastBBI = NeedBr1 ? BBI2 : &BBI; 1117 bool HasEarlyExit = NeedBr1 ? NeedBr2 : false; 1118 if (!HasEarlyExit && 1119 TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) { 1120 LastBBI->NonPredSize -= TII->RemoveBranch(*LastBBI->BB); 1121 MergeBlocks(*LastBBI, TailBBI); 1122 TailBBI.IsDone = true; 1123 } else { 1124 bool isFallThrough = canFallThroughTo(LastBBI->BB, TailBB); 1125 if (!isFallThrough) { 1126 InsertUncondBranch(LastBBI->BB, TailBB, TII); 1127 LastBBI->HasFallThrough = false; 1128 } 1129 } 1130 } 1131 1132 RemoveExtraEdges(BBI); 1133 1134 // Update block info. 1135 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; 1136 InvalidatePreds(BBI.BB); 1137 1138 // FIXME: Must maintain LiveIns. 1139 return true; 1140} 1141 1142/// PredicateBlock - Predicate instructions from the start of the block to the 1143/// specified end with the specified condition. 1144void IfConverter::PredicateBlock(BBInfo &BBI, 1145 MachineBasicBlock::iterator E, 1146 std::vector<MachineOperand> &Cond) { 1147 for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) { 1148 if (TII->isPredicated(I)) 1149 continue; 1150 if (!TII->PredicateInstruction(I, Cond)) { 1151 cerr << "Unable to predicate " << *I << "!\n"; 1152 abort(); 1153 } 1154 } 1155 1156 std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate)); 1157 1158 BBI.IsAnalyzed = false; 1159 BBI.NonPredSize = 0; 1160 1161 NumIfConvBBs++; 1162} 1163 1164/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to 1165/// the destination block. Skip end of block branches if IgnoreBr is true. 1166void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 1167 std::vector<MachineOperand> &Cond, 1168 bool IgnoreBr) { 1169 for (MachineBasicBlock::iterator I = FromBBI.BB->begin(), 1170 E = FromBBI.BB->end(); I != E; ++I) { 1171 const TargetInstrDescriptor *TID = I->getInstrDescriptor(); 1172 bool isPredicated = TII->isPredicated(I); 1173 // Do not copy the end of the block branches. 1174 if (IgnoreBr && !isPredicated && (TID->Flags & M_BRANCH_FLAG) != 0) 1175 break; 1176 1177 MachineInstr *MI = I->clone(); 1178 ToBBI.BB->insert(ToBBI.BB->end(), MI); 1179 ToBBI.NonPredSize++; 1180 1181 if (!isPredicated) 1182 if (!TII->PredicateInstruction(MI, Cond)) { 1183 cerr << "Unable to predicate " << *MI << "!\n"; 1184 abort(); 1185 } 1186 } 1187 1188 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), 1189 std::back_inserter(ToBBI.Predicate)); 1190 std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate)); 1191 1192 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 1193 ToBBI.IsAnalyzed = false; 1194 1195 NumDupBBs++; 1196} 1197 1198/// MergeBlocks - Move all instructions from FromBB to the end of ToBB. 1199/// 1200void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) { 1201 ToBBI.BB->splice(ToBBI.BB->end(), 1202 FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end()); 1203 1204 // Redirect all branches to FromBB to ToBB. 1205 std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(), 1206 FromBBI.BB->pred_end()); 1207 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 1208 MachineBasicBlock *Pred = Preds[i]; 1209 if (Pred == ToBBI.BB) 1210 continue; 1211 Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB); 1212 } 1213 1214 std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(), 1215 FromBBI.BB->succ_end()); 1216 MachineBasicBlock *NBB = getNextBlock(FromBBI.BB); 1217 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL; 1218 1219 for (unsigned i = 0, e = Succs.size(); i != e; ++i) { 1220 MachineBasicBlock *Succ = Succs[i]; 1221 // Fallthrough edge can't be transferred. 1222 if (Succ == FallThrough) 1223 continue; 1224 FromBBI.BB->removeSuccessor(Succ); 1225 if (!ToBBI.BB->isSuccessor(Succ)) 1226 ToBBI.BB->addSuccessor(Succ); 1227 } 1228 1229 // Now FromBBI always fall through to the next block! 1230 if (NBB) 1231 FromBBI.BB->addSuccessor(NBB); 1232 1233 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), 1234 std::back_inserter(ToBBI.Predicate)); 1235 FromBBI.Predicate.clear(); 1236 1237 ToBBI.NonPredSize += FromBBI.NonPredSize; 1238 FromBBI.NonPredSize = 0; 1239 1240 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 1241 ToBBI.HasFallThrough = FromBBI.HasFallThrough; 1242 ToBBI.IsAnalyzed = false; 1243 FromBBI.IsAnalyzed = false; 1244} 1245