1 //===- IfConversion.cpp - Machine code if conversion pass -----------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements the machine instruction level if-conversion pass, which 10 // tries to convert conditional branches into predicated instructions. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "BranchFolding.h" 15 #include "llvm/ADT/STLExtras.h" 16 #include "llvm/ADT/ScopeExit.h" 17 #include "llvm/ADT/SmallSet.h" 18 #include "llvm/ADT/SmallVector.h" 19 #include "llvm/ADT/SparseSet.h" 20 #include "llvm/ADT/Statistic.h" 21 #include "llvm/ADT/iterator_range.h" 22 #include "llvm/Analysis/ProfileSummaryInfo.h" 23 #include "llvm/CodeGen/LivePhysRegs.h" 24 #include "llvm/CodeGen/MBFIWrapper.h" 25 #include "llvm/CodeGen/MachineBasicBlock.h" 26 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 27 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h" 28 #include "llvm/CodeGen/MachineFunction.h" 29 #include "llvm/CodeGen/MachineFunctionPass.h" 30 #include "llvm/CodeGen/MachineInstr.h" 31 #include "llvm/CodeGen/MachineInstrBuilder.h" 32 #include "llvm/CodeGen/MachineOperand.h" 33 #include "llvm/CodeGen/MachineRegisterInfo.h" 34 #include "llvm/CodeGen/TargetInstrInfo.h" 35 #include "llvm/CodeGen/TargetLowering.h" 36 #include "llvm/CodeGen/TargetRegisterInfo.h" 37 #include "llvm/CodeGen/TargetSchedule.h" 38 #include "llvm/CodeGen/TargetSubtargetInfo.h" 39 #include "llvm/IR/DebugLoc.h" 40 #include "llvm/InitializePasses.h" 41 #include "llvm/MC/MCRegisterInfo.h" 42 #include "llvm/Pass.h" 43 #include "llvm/Support/BranchProbability.h" 44 #include "llvm/Support/CommandLine.h" 45 #include "llvm/Support/Debug.h" 46 #include "llvm/Support/ErrorHandling.h" 47 #include "llvm/Support/raw_ostream.h" 48 #include <algorithm> 49 #include <cassert> 50 #include <functional> 51 #include <iterator> 52 #include <memory> 53 #include <utility> 54 #include <vector> 55 56 using namespace llvm; 57 58 #define DEBUG_TYPE "if-converter" 59 60 // Hidden options for help debugging. 61 static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); 62 static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); 63 static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); 64 static cl::opt<bool> DisableSimple("disable-ifcvt-simple", 65 cl::init(false), cl::Hidden); 66 static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false", 67 cl::init(false), cl::Hidden); 68 static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", 69 cl::init(false), cl::Hidden); 70 static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev", 71 cl::init(false), cl::Hidden); 72 static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false", 73 cl::init(false), cl::Hidden); 74 static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", 75 cl::init(false), cl::Hidden); 76 static cl::opt<bool> DisableForkedDiamond("disable-ifcvt-forked-diamond", 77 cl::init(false), cl::Hidden); 78 static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold", 79 cl::init(true), cl::Hidden); 80 81 STATISTIC(NumSimple, "Number of simple if-conversions performed"); 82 STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed"); 83 STATISTIC(NumTriangle, "Number of triangle if-conversions performed"); 84 STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed"); 85 STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed"); 86 STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed"); 87 STATISTIC(NumDiamonds, "Number of diamond if-conversions performed"); 88 STATISTIC(NumForkedDiamonds, "Number of forked-diamond if-conversions performed"); 89 STATISTIC(NumIfConvBBs, "Number of if-converted blocks"); 90 STATISTIC(NumDupBBs, "Number of duplicated blocks"); 91 STATISTIC(NumUnpred, "Number of true blocks of diamonds unpredicated"); 92 93 namespace { 94 95 class IfConverter : public MachineFunctionPass { 96 enum IfcvtKind { 97 ICNotClassfied, // BB data valid, but not classified. 98 ICSimpleFalse, // Same as ICSimple, but on the false path. 99 ICSimple, // BB is entry of an one split, no rejoin sub-CFG. 100 ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition. 101 ICTriangleRev, // Same as ICTriangle, but true path rev condition. 102 ICTriangleFalse, // Same as ICTriangle, but on the false path. 103 ICTriangle, // BB is entry of a triangle sub-CFG. 104 ICDiamond, // BB is entry of a diamond sub-CFG. 105 ICForkedDiamond // BB is entry of an almost diamond sub-CFG, with a 106 // common tail that can be shared. 107 }; 108 109 /// One per MachineBasicBlock, this is used to cache the result 110 /// if-conversion feasibility analysis. This includes results from 111 /// TargetInstrInfo::analyzeBranch() (i.e. TBB, FBB, and Cond), and its 112 /// classification, and common tail block of its successors (if it's a 113 /// diamond shape), its size, whether it's predicable, and whether any 114 /// instruction can clobber the 'would-be' predicate. 115 /// 116 /// IsDone - True if BB is not to be considered for ifcvt. 117 /// IsBeingAnalyzed - True if BB is currently being analyzed. 118 /// IsAnalyzed - True if BB has been analyzed (info is still valid). 119 /// IsEnqueued - True if BB has been enqueued to be ifcvt'ed. 120 /// IsBrAnalyzable - True if analyzeBranch() returns false. 121 /// HasFallThrough - True if BB may fallthrough to the following BB. 122 /// IsUnpredicable - True if BB is known to be unpredicable. 123 /// ClobbersPred - True if BB could modify predicates (e.g. has 124 /// cmp, call, etc.) 125 /// NonPredSize - Number of non-predicated instructions. 126 /// ExtraCost - Extra cost for multi-cycle instructions. 127 /// ExtraCost2 - Some instructions are slower when predicated 128 /// BB - Corresponding MachineBasicBlock. 129 /// TrueBB / FalseBB- See analyzeBranch(). 130 /// BrCond - Conditions for end of block conditional branches. 131 /// Predicate - Predicate used in the BB. 132 struct BBInfo { 133 bool IsDone : 1; 134 bool IsBeingAnalyzed : 1; 135 bool IsAnalyzed : 1; 136 bool IsEnqueued : 1; 137 bool IsBrAnalyzable : 1; 138 bool IsBrReversible : 1; 139 bool HasFallThrough : 1; 140 bool IsUnpredicable : 1; 141 bool CannotBeCopied : 1; 142 bool ClobbersPred : 1; 143 unsigned NonPredSize = 0; 144 unsigned ExtraCost = 0; 145 unsigned ExtraCost2 = 0; 146 MachineBasicBlock *BB = nullptr; 147 MachineBasicBlock *TrueBB = nullptr; 148 MachineBasicBlock *FalseBB = nullptr; 149 SmallVector<MachineOperand, 4> BrCond; 150 SmallVector<MachineOperand, 4> Predicate; 151 152 BBInfo() : IsDone(false), IsBeingAnalyzed(false), 153 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false), 154 IsBrReversible(false), HasFallThrough(false), 155 IsUnpredicable(false), CannotBeCopied(false), 156 ClobbersPred(false) {} 157 }; 158 159 /// Record information about pending if-conversions to attempt: 160 /// BBI - Corresponding BBInfo. 161 /// Kind - Type of block. See IfcvtKind. 162 /// NeedSubsumption - True if the to-be-predicated BB has already been 163 /// predicated. 164 /// NumDups - Number of instructions that would be duplicated due 165 /// to this if-conversion. (For diamonds, the number of 166 /// identical instructions at the beginnings of both 167 /// paths). 168 /// NumDups2 - For diamonds, the number of identical instructions 169 /// at the ends of both paths. 170 struct IfcvtToken { 171 BBInfo &BBI; 172 IfcvtKind Kind; 173 unsigned NumDups; 174 unsigned NumDups2; 175 bool NeedSubsumption : 1; 176 bool TClobbersPred : 1; 177 bool FClobbersPred : 1; 178 179 IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0, 180 bool tc = false, bool fc = false) 181 : BBI(b), Kind(k), NumDups(d), NumDups2(d2), NeedSubsumption(s), 182 TClobbersPred(tc), FClobbersPred(fc) {} 183 }; 184 185 /// Results of if-conversion feasibility analysis indexed by basic block 186 /// number. 187 std::vector<BBInfo> BBAnalysis; 188 TargetSchedModel SchedModel; 189 190 const TargetLoweringBase *TLI = nullptr; 191 const TargetInstrInfo *TII = nullptr; 192 const TargetRegisterInfo *TRI = nullptr; 193 const MachineBranchProbabilityInfo *MBPI = nullptr; 194 MachineRegisterInfo *MRI = nullptr; 195 196 LivePhysRegs Redefs; 197 198 bool PreRegAlloc = true; 199 bool MadeChange = false; 200 int FnNum = -1; 201 std::function<bool(const MachineFunction &)> PredicateFtor; 202 203 public: 204 static char ID; 205 206 IfConverter(std::function<bool(const MachineFunction &)> Ftor = nullptr) 207 : MachineFunctionPass(ID), PredicateFtor(std::move(Ftor)) { 208 initializeIfConverterPass(*PassRegistry::getPassRegistry()); 209 } 210 211 void getAnalysisUsage(AnalysisUsage &AU) const override { 212 AU.addRequired<MachineBlockFrequencyInfo>(); 213 AU.addRequired<MachineBranchProbabilityInfo>(); 214 AU.addRequired<ProfileSummaryInfoWrapperPass>(); 215 MachineFunctionPass::getAnalysisUsage(AU); 216 } 217 218 bool runOnMachineFunction(MachineFunction &MF) override; 219 220 MachineFunctionProperties getRequiredProperties() const override { 221 return MachineFunctionProperties().set( 222 MachineFunctionProperties::Property::NoVRegs); 223 } 224 225 private: 226 bool reverseBranchCondition(BBInfo &BBI) const; 227 bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups, 228 BranchProbability Prediction) const; 229 bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 230 bool FalseBranch, unsigned &Dups, 231 BranchProbability Prediction) const; 232 bool CountDuplicatedInstructions( 233 MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB, 234 MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE, 235 unsigned &Dups1, unsigned &Dups2, 236 MachineBasicBlock &TBB, MachineBasicBlock &FBB, 237 bool SkipUnconditionalBranches) const; 238 bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, 239 unsigned &Dups1, unsigned &Dups2, 240 BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const; 241 bool ValidForkedDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, 242 unsigned &Dups1, unsigned &Dups2, 243 BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const; 244 void AnalyzeBranches(BBInfo &BBI); 245 void ScanInstructions(BBInfo &BBI, 246 MachineBasicBlock::iterator &Begin, 247 MachineBasicBlock::iterator &End, 248 bool BranchUnpredicable = false) const; 249 bool RescanInstructions( 250 MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB, 251 MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE, 252 BBInfo &TrueBBI, BBInfo &FalseBBI) const; 253 void AnalyzeBlock(MachineBasicBlock &MBB, 254 std::vector<std::unique_ptr<IfcvtToken>> &Tokens); 255 bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Pred, 256 bool isTriangle = false, bool RevBranch = false, 257 bool hasCommonTail = false); 258 void AnalyzeBlocks(MachineFunction &MF, 259 std::vector<std::unique_ptr<IfcvtToken>> &Tokens); 260 void InvalidatePreds(MachineBasicBlock &MBB); 261 bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind); 262 bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind); 263 bool IfConvertDiamondCommon(BBInfo &BBI, BBInfo &TrueBBI, BBInfo &FalseBBI, 264 unsigned NumDups1, unsigned NumDups2, 265 bool TClobbersPred, bool FClobbersPred, 266 bool RemoveBranch, bool MergeAddEdges); 267 bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 268 unsigned NumDups1, unsigned NumDups2, 269 bool TClobbers, bool FClobbers); 270 bool IfConvertForkedDiamond(BBInfo &BBI, IfcvtKind Kind, 271 unsigned NumDups1, unsigned NumDups2, 272 bool TClobbers, bool FClobbers); 273 void PredicateBlock(BBInfo &BBI, 274 MachineBasicBlock::iterator E, 275 SmallVectorImpl<MachineOperand> &Cond, 276 SmallSet<MCPhysReg, 4> *LaterRedefs = nullptr); 277 void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 278 SmallVectorImpl<MachineOperand> &Cond, 279 bool IgnoreBr = false); 280 void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true); 281 282 bool MeetIfcvtSizeLimit(MachineBasicBlock &BB, 283 unsigned Cycle, unsigned Extra, 284 BranchProbability Prediction) const { 285 return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra, 286 Prediction); 287 } 288 289 bool MeetIfcvtSizeLimit(BBInfo &TBBInfo, BBInfo &FBBInfo, 290 MachineBasicBlock &CommBB, unsigned Dups, 291 BranchProbability Prediction, bool Forked) const { 292 const MachineFunction &MF = *TBBInfo.BB->getParent(); 293 if (MF.getFunction().hasMinSize()) { 294 MachineBasicBlock::iterator TIB = TBBInfo.BB->begin(); 295 MachineBasicBlock::iterator FIB = FBBInfo.BB->begin(); 296 MachineBasicBlock::iterator TIE = TBBInfo.BB->end(); 297 MachineBasicBlock::iterator FIE = FBBInfo.BB->end(); 298 299 unsigned Dups1 = 0, Dups2 = 0; 300 if (!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, 301 *TBBInfo.BB, *FBBInfo.BB, 302 /*SkipUnconditionalBranches*/ true)) 303 llvm_unreachable("should already have been checked by ValidDiamond"); 304 305 unsigned BranchBytes = 0; 306 unsigned CommonBytes = 0; 307 308 // Count common instructions at the start of the true and false blocks. 309 for (auto &I : make_range(TBBInfo.BB->begin(), TIB)) { 310 LLVM_DEBUG(dbgs() << "Common inst: " << I); 311 CommonBytes += TII->getInstSizeInBytes(I); 312 } 313 for (auto &I : make_range(FBBInfo.BB->begin(), FIB)) { 314 LLVM_DEBUG(dbgs() << "Common inst: " << I); 315 CommonBytes += TII->getInstSizeInBytes(I); 316 } 317 318 // Count instructions at the end of the true and false blocks, after 319 // the ones we plan to predicate. Analyzable branches will be removed 320 // (unless this is a forked diamond), and all other instructions are 321 // common between the two blocks. 322 for (auto &I : make_range(TIE, TBBInfo.BB->end())) { 323 if (I.isBranch() && TBBInfo.IsBrAnalyzable && !Forked) { 324 LLVM_DEBUG(dbgs() << "Saving branch: " << I); 325 BranchBytes += TII->predictBranchSizeForIfCvt(I); 326 } else { 327 LLVM_DEBUG(dbgs() << "Common inst: " << I); 328 CommonBytes += TII->getInstSizeInBytes(I); 329 } 330 } 331 for (auto &I : make_range(FIE, FBBInfo.BB->end())) { 332 if (I.isBranch() && FBBInfo.IsBrAnalyzable && !Forked) { 333 LLVM_DEBUG(dbgs() << "Saving branch: " << I); 334 BranchBytes += TII->predictBranchSizeForIfCvt(I); 335 } else { 336 LLVM_DEBUG(dbgs() << "Common inst: " << I); 337 CommonBytes += TII->getInstSizeInBytes(I); 338 } 339 } 340 for (auto &I : CommBB.terminators()) { 341 if (I.isBranch()) { 342 LLVM_DEBUG(dbgs() << "Saving branch: " << I); 343 BranchBytes += TII->predictBranchSizeForIfCvt(I); 344 } 345 } 346 347 // The common instructions in one branch will be eliminated, halving 348 // their code size. 349 CommonBytes /= 2; 350 351 // Count the instructions which we need to predicate. 352 unsigned NumPredicatedInstructions = 0; 353 for (auto &I : make_range(TIB, TIE)) { 354 if (!I.isDebugInstr()) { 355 LLVM_DEBUG(dbgs() << "Predicating: " << I); 356 NumPredicatedInstructions++; 357 } 358 } 359 for (auto &I : make_range(FIB, FIE)) { 360 if (!I.isDebugInstr()) { 361 LLVM_DEBUG(dbgs() << "Predicating: " << I); 362 NumPredicatedInstructions++; 363 } 364 } 365 366 // Even though we're optimising for size at the expense of performance, 367 // avoid creating really long predicated blocks. 368 if (NumPredicatedInstructions > 15) 369 return false; 370 371 // Some targets (e.g. Thumb2) need to insert extra instructions to 372 // start predicated blocks. 373 unsigned ExtraPredicateBytes = TII->extraSizeToPredicateInstructions( 374 MF, NumPredicatedInstructions); 375 376 LLVM_DEBUG(dbgs() << "MeetIfcvtSizeLimit(BranchBytes=" << BranchBytes 377 << ", CommonBytes=" << CommonBytes 378 << ", NumPredicatedInstructions=" 379 << NumPredicatedInstructions 380 << ", ExtraPredicateBytes=" << ExtraPredicateBytes 381 << ")\n"); 382 return (BranchBytes + CommonBytes) > ExtraPredicateBytes; 383 } else { 384 unsigned TCycle = TBBInfo.NonPredSize + TBBInfo.ExtraCost - Dups; 385 unsigned FCycle = FBBInfo.NonPredSize + FBBInfo.ExtraCost - Dups; 386 bool Res = TCycle > 0 && FCycle > 0 && 387 TII->isProfitableToIfCvt( 388 *TBBInfo.BB, TCycle, TBBInfo.ExtraCost2, *FBBInfo.BB, 389 FCycle, FBBInfo.ExtraCost2, Prediction); 390 LLVM_DEBUG(dbgs() << "MeetIfcvtSizeLimit(TCycle=" << TCycle 391 << ", FCycle=" << FCycle 392 << ", TExtra=" << TBBInfo.ExtraCost2 << ", FExtra=" 393 << FBBInfo.ExtraCost2 << ") = " << Res << "\n"); 394 return Res; 395 } 396 } 397 398 /// Returns true if Block ends without a terminator. 399 bool blockAlwaysFallThrough(BBInfo &BBI) const { 400 return BBI.IsBrAnalyzable && BBI.TrueBB == nullptr; 401 } 402 403 /// Used to sort if-conversion candidates. 404 static bool IfcvtTokenCmp(const std::unique_ptr<IfcvtToken> &C1, 405 const std::unique_ptr<IfcvtToken> &C2) { 406 int Incr1 = (C1->Kind == ICDiamond) 407 ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups; 408 int Incr2 = (C2->Kind == ICDiamond) 409 ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups; 410 if (Incr1 > Incr2) 411 return true; 412 else if (Incr1 == Incr2) { 413 // Favors subsumption. 414 if (!C1->NeedSubsumption && C2->NeedSubsumption) 415 return true; 416 else if (C1->NeedSubsumption == C2->NeedSubsumption) { 417 // Favors diamond over triangle, etc. 418 if ((unsigned)C1->Kind < (unsigned)C2->Kind) 419 return true; 420 else if (C1->Kind == C2->Kind) 421 return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber(); 422 } 423 } 424 return false; 425 } 426 }; 427 428 } // end anonymous namespace 429 430 char IfConverter::ID = 0; 431 432 char &llvm::IfConverterID = IfConverter::ID; 433 434 INITIALIZE_PASS_BEGIN(IfConverter, DEBUG_TYPE, "If Converter", false, false) 435 INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo) 436 INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass) 437 INITIALIZE_PASS_END(IfConverter, DEBUG_TYPE, "If Converter", false, false) 438 439 bool IfConverter::runOnMachineFunction(MachineFunction &MF) { 440 if (skipFunction(MF.getFunction()) || (PredicateFtor && !PredicateFtor(MF))) 441 return false; 442 443 const TargetSubtargetInfo &ST = MF.getSubtarget(); 444 TLI = ST.getTargetLowering(); 445 TII = ST.getInstrInfo(); 446 TRI = ST.getRegisterInfo(); 447 MBFIWrapper MBFI(getAnalysis<MachineBlockFrequencyInfo>()); 448 MBPI = &getAnalysis<MachineBranchProbabilityInfo>(); 449 ProfileSummaryInfo *PSI = 450 &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI(); 451 MRI = &MF.getRegInfo(); 452 SchedModel.init(&ST); 453 454 if (!TII) return false; 455 456 PreRegAlloc = MRI->isSSA(); 457 458 bool BFChange = false; 459 if (!PreRegAlloc) { 460 // Tail merge tend to expose more if-conversion opportunities. 461 BranchFolder BF(true, false, MBFI, *MBPI, PSI); 462 BFChange = BF.OptimizeFunction(MF, TII, ST.getRegisterInfo()); 463 } 464 465 LLVM_DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum << ") \'" 466 << MF.getName() << "\'"); 467 468 if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { 469 LLVM_DEBUG(dbgs() << " skipped\n"); 470 return false; 471 } 472 LLVM_DEBUG(dbgs() << "\n"); 473 474 MF.RenumberBlocks(); 475 BBAnalysis.resize(MF.getNumBlockIDs()); 476 477 std::vector<std::unique_ptr<IfcvtToken>> Tokens; 478 MadeChange = false; 479 unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + 480 NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds; 481 while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) { 482 // Do an initial analysis for each basic block and find all the potential 483 // candidates to perform if-conversion. 484 bool Change = false; 485 AnalyzeBlocks(MF, Tokens); 486 while (!Tokens.empty()) { 487 std::unique_ptr<IfcvtToken> Token = std::move(Tokens.back()); 488 Tokens.pop_back(); 489 BBInfo &BBI = Token->BBI; 490 IfcvtKind Kind = Token->Kind; 491 unsigned NumDups = Token->NumDups; 492 unsigned NumDups2 = Token->NumDups2; 493 494 // If the block has been evicted out of the queue or it has already been 495 // marked dead (due to it being predicated), then skip it. 496 if (BBI.IsDone) 497 BBI.IsEnqueued = false; 498 if (!BBI.IsEnqueued) 499 continue; 500 501 BBI.IsEnqueued = false; 502 503 bool RetVal = false; 504 switch (Kind) { 505 default: llvm_unreachable("Unexpected!"); 506 case ICSimple: 507 case ICSimpleFalse: { 508 bool isFalse = Kind == ICSimpleFalse; 509 if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break; 510 LLVM_DEBUG(dbgs() << "Ifcvt (Simple" 511 << (Kind == ICSimpleFalse ? " false" : "") 512 << "): " << printMBBReference(*BBI.BB) << " (" 513 << ((Kind == ICSimpleFalse) ? BBI.FalseBB->getNumber() 514 : BBI.TrueBB->getNumber()) 515 << ") "); 516 RetVal = IfConvertSimple(BBI, Kind); 517 LLVM_DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 518 if (RetVal) { 519 if (isFalse) ++NumSimpleFalse; 520 else ++NumSimple; 521 } 522 break; 523 } 524 case ICTriangle: 525 case ICTriangleRev: 526 case ICTriangleFalse: 527 case ICTriangleFRev: { 528 bool isFalse = Kind == ICTriangleFalse; 529 bool isRev = (Kind == ICTriangleRev || Kind == ICTriangleFRev); 530 if (DisableTriangle && !isFalse && !isRev) break; 531 if (DisableTriangleR && !isFalse && isRev) break; 532 if (DisableTriangleF && isFalse && !isRev) break; 533 LLVM_DEBUG(dbgs() << "Ifcvt (Triangle"); 534 if (isFalse) 535 LLVM_DEBUG(dbgs() << " false"); 536 if (isRev) 537 LLVM_DEBUG(dbgs() << " rev"); 538 LLVM_DEBUG(dbgs() << "): " << printMBBReference(*BBI.BB) 539 << " (T:" << BBI.TrueBB->getNumber() 540 << ",F:" << BBI.FalseBB->getNumber() << ") "); 541 RetVal = IfConvertTriangle(BBI, Kind); 542 LLVM_DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 543 if (RetVal) { 544 if (isFalse) 545 ++NumTriangleFalse; 546 else if (isRev) 547 ++NumTriangleRev; 548 else 549 ++NumTriangle; 550 } 551 break; 552 } 553 case ICDiamond: 554 if (DisableDiamond) break; 555 LLVM_DEBUG(dbgs() << "Ifcvt (Diamond): " << printMBBReference(*BBI.BB) 556 << " (T:" << BBI.TrueBB->getNumber() 557 << ",F:" << BBI.FalseBB->getNumber() << ") "); 558 RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2, 559 Token->TClobbersPred, 560 Token->FClobbersPred); 561 LLVM_DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 562 if (RetVal) ++NumDiamonds; 563 break; 564 case ICForkedDiamond: 565 if (DisableForkedDiamond) break; 566 LLVM_DEBUG(dbgs() << "Ifcvt (Forked Diamond): " 567 << printMBBReference(*BBI.BB) 568 << " (T:" << BBI.TrueBB->getNumber() 569 << ",F:" << BBI.FalseBB->getNumber() << ") "); 570 RetVal = IfConvertForkedDiamond(BBI, Kind, NumDups, NumDups2, 571 Token->TClobbersPred, 572 Token->FClobbersPred); 573 LLVM_DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 574 if (RetVal) ++NumForkedDiamonds; 575 break; 576 } 577 578 if (RetVal && MRI->tracksLiveness()) 579 recomputeLivenessFlags(*BBI.BB); 580 581 Change |= RetVal; 582 583 NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev + 584 NumTriangleFalse + NumTriangleFRev + NumDiamonds; 585 if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit) 586 break; 587 } 588 589 if (!Change) 590 break; 591 MadeChange |= Change; 592 } 593 594 Tokens.clear(); 595 BBAnalysis.clear(); 596 597 if (MadeChange && IfCvtBranchFold) { 598 BranchFolder BF(false, false, MBFI, *MBPI, PSI); 599 BF.OptimizeFunction(MF, TII, MF.getSubtarget().getRegisterInfo()); 600 } 601 602 MadeChange |= BFChange; 603 return MadeChange; 604 } 605 606 /// BB has a fallthrough. Find its 'false' successor given its 'true' successor. 607 static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, 608 MachineBasicBlock *TrueBB) { 609 for (MachineBasicBlock *SuccBB : BB->successors()) { 610 if (SuccBB != TrueBB) 611 return SuccBB; 612 } 613 return nullptr; 614 } 615 616 /// Reverse the condition of the end of the block branch. Swap block's 'true' 617 /// and 'false' successors. 618 bool IfConverter::reverseBranchCondition(BBInfo &BBI) const { 619 DebugLoc dl; // FIXME: this is nowhere 620 if (!TII->reverseBranchCondition(BBI.BrCond)) { 621 TII->removeBranch(*BBI.BB); 622 TII->insertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl); 623 std::swap(BBI.TrueBB, BBI.FalseBB); 624 return true; 625 } 626 return false; 627 } 628 629 /// Returns the next block in the function blocks ordering. If it is the end, 630 /// returns NULL. 631 static inline MachineBasicBlock *getNextBlock(MachineBasicBlock &MBB) { 632 MachineFunction::iterator I = MBB.getIterator(); 633 MachineFunction::iterator E = MBB.getParent()->end(); 634 if (++I == E) 635 return nullptr; 636 return &*I; 637 } 638 639 /// Returns true if the 'true' block (along with its predecessor) forms a valid 640 /// simple shape for ifcvt. It also returns the number of instructions that the 641 /// ifcvt would need to duplicate if performed in Dups. 642 bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups, 643 BranchProbability Prediction) const { 644 Dups = 0; 645 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 646 return false; 647 648 if (TrueBBI.IsBrAnalyzable) 649 return false; 650 651 if (TrueBBI.BB->pred_size() > 1) { 652 if (TrueBBI.CannotBeCopied || 653 !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize, 654 Prediction)) 655 return false; 656 Dups = TrueBBI.NonPredSize; 657 } 658 659 return true; 660 } 661 662 /// Returns true if the 'true' and 'false' blocks (along with their common 663 /// predecessor) forms a valid triangle shape for ifcvt. If 'FalseBranch' is 664 /// true, it checks if 'true' block's false branch branches to the 'false' block 665 /// rather than the other way around. It also returns the number of instructions 666 /// that the ifcvt would need to duplicate if performed in 'Dups'. 667 bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 668 bool FalseBranch, unsigned &Dups, 669 BranchProbability Prediction) const { 670 Dups = 0; 671 if (TrueBBI.BB == FalseBBI.BB) 672 return false; 673 674 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 675 return false; 676 677 if (TrueBBI.BB->pred_size() > 1) { 678 if (TrueBBI.CannotBeCopied) 679 return false; 680 681 unsigned Size = TrueBBI.NonPredSize; 682 if (TrueBBI.IsBrAnalyzable) { 683 if (TrueBBI.TrueBB && TrueBBI.BrCond.empty()) 684 // Ends with an unconditional branch. It will be removed. 685 --Size; 686 else { 687 MachineBasicBlock *FExit = FalseBranch 688 ? TrueBBI.TrueBB : TrueBBI.FalseBB; 689 if (FExit) 690 // Require a conditional branch 691 ++Size; 692 } 693 } 694 if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, Prediction)) 695 return false; 696 Dups = Size; 697 } 698 699 MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB; 700 if (!TExit && blockAlwaysFallThrough(TrueBBI)) { 701 MachineFunction::iterator I = TrueBBI.BB->getIterator(); 702 if (++I == TrueBBI.BB->getParent()->end()) 703 return false; 704 TExit = &*I; 705 } 706 return TExit && TExit == FalseBBI.BB; 707 } 708 709 /// Count duplicated instructions and move the iterators to show where they 710 /// are. 711 /// @param TIB True Iterator Begin 712 /// @param FIB False Iterator Begin 713 /// These two iterators initially point to the first instruction of the two 714 /// blocks, and finally point to the first non-shared instruction. 715 /// @param TIE True Iterator End 716 /// @param FIE False Iterator End 717 /// These two iterators initially point to End() for the two blocks() and 718 /// finally point to the first shared instruction in the tail. 719 /// Upon return [TIB, TIE), and [FIB, FIE) mark the un-duplicated portions of 720 /// two blocks. 721 /// @param Dups1 count of duplicated instructions at the beginning of the 2 722 /// blocks. 723 /// @param Dups2 count of duplicated instructions at the end of the 2 blocks. 724 /// @param SkipUnconditionalBranches if true, Don't make sure that 725 /// unconditional branches at the end of the blocks are the same. True is 726 /// passed when the blocks are analyzable to allow for fallthrough to be 727 /// handled. 728 /// @return false if the shared portion prevents if conversion. 729 bool IfConverter::CountDuplicatedInstructions( 730 MachineBasicBlock::iterator &TIB, 731 MachineBasicBlock::iterator &FIB, 732 MachineBasicBlock::iterator &TIE, 733 MachineBasicBlock::iterator &FIE, 734 unsigned &Dups1, unsigned &Dups2, 735 MachineBasicBlock &TBB, MachineBasicBlock &FBB, 736 bool SkipUnconditionalBranches) const { 737 while (TIB != TIE && FIB != FIE) { 738 // Skip dbg_value instructions. These do not count. 739 TIB = skipDebugInstructionsForward(TIB, TIE, false); 740 FIB = skipDebugInstructionsForward(FIB, FIE, false); 741 if (TIB == TIE || FIB == FIE) 742 break; 743 if (!TIB->isIdenticalTo(*FIB)) 744 break; 745 // A pred-clobbering instruction in the shared portion prevents 746 // if-conversion. 747 std::vector<MachineOperand> PredDefs; 748 if (TII->ClobbersPredicate(*TIB, PredDefs, false)) 749 return false; 750 // If we get all the way to the branch instructions, don't count them. 751 if (!TIB->isBranch()) 752 ++Dups1; 753 ++TIB; 754 ++FIB; 755 } 756 757 // Check for already containing all of the block. 758 if (TIB == TIE || FIB == FIE) 759 return true; 760 // Now, in preparation for counting duplicate instructions at the ends of the 761 // blocks, switch to reverse_iterators. Note that getReverse() returns an 762 // iterator that points to the same instruction, unlike std::reverse_iterator. 763 // We have to do our own shifting so that we get the same range. 764 MachineBasicBlock::reverse_iterator RTIE = std::next(TIE.getReverse()); 765 MachineBasicBlock::reverse_iterator RFIE = std::next(FIE.getReverse()); 766 const MachineBasicBlock::reverse_iterator RTIB = std::next(TIB.getReverse()); 767 const MachineBasicBlock::reverse_iterator RFIB = std::next(FIB.getReverse()); 768 769 if (!TBB.succ_empty() || !FBB.succ_empty()) { 770 if (SkipUnconditionalBranches) { 771 while (RTIE != RTIB && RTIE->isUnconditionalBranch()) 772 ++RTIE; 773 while (RFIE != RFIB && RFIE->isUnconditionalBranch()) 774 ++RFIE; 775 } 776 } 777 778 // Count duplicate instructions at the ends of the blocks. 779 while (RTIE != RTIB && RFIE != RFIB) { 780 // Skip dbg_value instructions. These do not count. 781 // Note that these are reverse iterators going forward. 782 RTIE = skipDebugInstructionsForward(RTIE, RTIB, false); 783 RFIE = skipDebugInstructionsForward(RFIE, RFIB, false); 784 if (RTIE == RTIB || RFIE == RFIB) 785 break; 786 if (!RTIE->isIdenticalTo(*RFIE)) 787 break; 788 // We have to verify that any branch instructions are the same, and then we 789 // don't count them toward the # of duplicate instructions. 790 if (!RTIE->isBranch()) 791 ++Dups2; 792 ++RTIE; 793 ++RFIE; 794 } 795 TIE = std::next(RTIE.getReverse()); 796 FIE = std::next(RFIE.getReverse()); 797 return true; 798 } 799 800 /// RescanInstructions - Run ScanInstructions on a pair of blocks. 801 /// @param TIB - True Iterator Begin, points to first non-shared instruction 802 /// @param FIB - False Iterator Begin, points to first non-shared instruction 803 /// @param TIE - True Iterator End, points past last non-shared instruction 804 /// @param FIE - False Iterator End, points past last non-shared instruction 805 /// @param TrueBBI - BBInfo to update for the true block. 806 /// @param FalseBBI - BBInfo to update for the false block. 807 /// @returns - false if either block cannot be predicated or if both blocks end 808 /// with a predicate-clobbering instruction. 809 bool IfConverter::RescanInstructions( 810 MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB, 811 MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE, 812 BBInfo &TrueBBI, BBInfo &FalseBBI) const { 813 bool BranchUnpredicable = true; 814 TrueBBI.IsUnpredicable = FalseBBI.IsUnpredicable = false; 815 ScanInstructions(TrueBBI, TIB, TIE, BranchUnpredicable); 816 if (TrueBBI.IsUnpredicable) 817 return false; 818 ScanInstructions(FalseBBI, FIB, FIE, BranchUnpredicable); 819 if (FalseBBI.IsUnpredicable) 820 return false; 821 if (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) 822 return false; 823 return true; 824 } 825 826 #ifndef NDEBUG 827 static void verifySameBranchInstructions( 828 MachineBasicBlock *MBB1, 829 MachineBasicBlock *MBB2) { 830 const MachineBasicBlock::reverse_iterator B1 = MBB1->rend(); 831 const MachineBasicBlock::reverse_iterator B2 = MBB2->rend(); 832 MachineBasicBlock::reverse_iterator E1 = MBB1->rbegin(); 833 MachineBasicBlock::reverse_iterator E2 = MBB2->rbegin(); 834 while (E1 != B1 && E2 != B2) { 835 skipDebugInstructionsForward(E1, B1, false); 836 skipDebugInstructionsForward(E2, B2, false); 837 if (E1 == B1 && E2 == B2) 838 break; 839 840 if (E1 == B1) { 841 assert(!E2->isBranch() && "Branch mis-match, one block is empty."); 842 break; 843 } 844 if (E2 == B2) { 845 assert(!E1->isBranch() && "Branch mis-match, one block is empty."); 846 break; 847 } 848 849 if (E1->isBranch() || E2->isBranch()) 850 assert(E1->isIdenticalTo(*E2) && 851 "Branch mis-match, branch instructions don't match."); 852 else 853 break; 854 ++E1; 855 ++E2; 856 } 857 } 858 #endif 859 860 /// ValidForkedDiamond - Returns true if the 'true' and 'false' blocks (along 861 /// with their common predecessor) form a diamond if a common tail block is 862 /// extracted. 863 /// While not strictly a diamond, this pattern would form a diamond if 864 /// tail-merging had merged the shared tails. 865 /// EBB 866 /// _/ \_ 867 /// | | 868 /// TBB FBB 869 /// / \ / \ 870 /// FalseBB TrueBB FalseBB 871 /// Currently only handles analyzable branches. 872 /// Specifically excludes actual diamonds to avoid overlap. 873 bool IfConverter::ValidForkedDiamond( 874 BBInfo &TrueBBI, BBInfo &FalseBBI, 875 unsigned &Dups1, unsigned &Dups2, 876 BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const { 877 Dups1 = Dups2 = 0; 878 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || 879 FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) 880 return false; 881 882 if (!TrueBBI.IsBrAnalyzable || !FalseBBI.IsBrAnalyzable) 883 return false; 884 // Don't IfConvert blocks that can't be folded into their predecessor. 885 if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) 886 return false; 887 888 // This function is specifically looking for conditional tails, as 889 // unconditional tails are already handled by the standard diamond case. 890 if (TrueBBI.BrCond.size() == 0 || 891 FalseBBI.BrCond.size() == 0) 892 return false; 893 894 MachineBasicBlock *TT = TrueBBI.TrueBB; 895 MachineBasicBlock *TF = TrueBBI.FalseBB; 896 MachineBasicBlock *FT = FalseBBI.TrueBB; 897 MachineBasicBlock *FF = FalseBBI.FalseBB; 898 899 if (!TT) 900 TT = getNextBlock(*TrueBBI.BB); 901 if (!TF) 902 TF = getNextBlock(*TrueBBI.BB); 903 if (!FT) 904 FT = getNextBlock(*FalseBBI.BB); 905 if (!FF) 906 FF = getNextBlock(*FalseBBI.BB); 907 908 if (!TT || !TF) 909 return false; 910 911 // Check successors. If they don't match, bail. 912 if (!((TT == FT && TF == FF) || (TF == FT && TT == FF))) 913 return false; 914 915 bool FalseReversed = false; 916 if (TF == FT && TT == FF) { 917 // If the branches are opposing, but we can't reverse, don't do it. 918 if (!FalseBBI.IsBrReversible) 919 return false; 920 FalseReversed = true; 921 reverseBranchCondition(FalseBBI); 922 } 923 auto UnReverseOnExit = make_scope_exit([&]() { 924 if (FalseReversed) 925 reverseBranchCondition(FalseBBI); 926 }); 927 928 // Count duplicate instructions at the beginning of the true and false blocks. 929 MachineBasicBlock::iterator TIB = TrueBBI.BB->begin(); 930 MachineBasicBlock::iterator FIB = FalseBBI.BB->begin(); 931 MachineBasicBlock::iterator TIE = TrueBBI.BB->end(); 932 MachineBasicBlock::iterator FIE = FalseBBI.BB->end(); 933 if(!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, 934 *TrueBBI.BB, *FalseBBI.BB, 935 /* SkipUnconditionalBranches */ true)) 936 return false; 937 938 TrueBBICalc.BB = TrueBBI.BB; 939 FalseBBICalc.BB = FalseBBI.BB; 940 TrueBBICalc.IsBrAnalyzable = TrueBBI.IsBrAnalyzable; 941 FalseBBICalc.IsBrAnalyzable = FalseBBI.IsBrAnalyzable; 942 if (!RescanInstructions(TIB, FIB, TIE, FIE, TrueBBICalc, FalseBBICalc)) 943 return false; 944 945 // The size is used to decide whether to if-convert, and the shared portions 946 // are subtracted off. Because of the subtraction, we just use the size that 947 // was calculated by the original ScanInstructions, as it is correct. 948 TrueBBICalc.NonPredSize = TrueBBI.NonPredSize; 949 FalseBBICalc.NonPredSize = FalseBBI.NonPredSize; 950 return true; 951 } 952 953 /// ValidDiamond - Returns true if the 'true' and 'false' blocks (along 954 /// with their common predecessor) forms a valid diamond shape for ifcvt. 955 bool IfConverter::ValidDiamond( 956 BBInfo &TrueBBI, BBInfo &FalseBBI, 957 unsigned &Dups1, unsigned &Dups2, 958 BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const { 959 Dups1 = Dups2 = 0; 960 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || 961 FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) 962 return false; 963 964 // If the True and False BBs are equal we're dealing with a degenerate case 965 // that we don't treat as a diamond. 966 if (TrueBBI.BB == FalseBBI.BB) 967 return false; 968 969 MachineBasicBlock *TT = TrueBBI.TrueBB; 970 MachineBasicBlock *FT = FalseBBI.TrueBB; 971 972 if (!TT && blockAlwaysFallThrough(TrueBBI)) 973 TT = getNextBlock(*TrueBBI.BB); 974 if (!FT && blockAlwaysFallThrough(FalseBBI)) 975 FT = getNextBlock(*FalseBBI.BB); 976 if (TT != FT) 977 return false; 978 if (!TT && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable)) 979 return false; 980 if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) 981 return false; 982 983 // FIXME: Allow true block to have an early exit? 984 if (TrueBBI.FalseBB || FalseBBI.FalseBB) 985 return false; 986 987 // Count duplicate instructions at the beginning and end of the true and 988 // false blocks. 989 // Skip unconditional branches only if we are considering an analyzable 990 // diamond. Otherwise the branches must be the same. 991 bool SkipUnconditionalBranches = 992 TrueBBI.IsBrAnalyzable && FalseBBI.IsBrAnalyzable; 993 MachineBasicBlock::iterator TIB = TrueBBI.BB->begin(); 994 MachineBasicBlock::iterator FIB = FalseBBI.BB->begin(); 995 MachineBasicBlock::iterator TIE = TrueBBI.BB->end(); 996 MachineBasicBlock::iterator FIE = FalseBBI.BB->end(); 997 if(!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, 998 *TrueBBI.BB, *FalseBBI.BB, 999 SkipUnconditionalBranches)) 1000 return false; 1001 1002 TrueBBICalc.BB = TrueBBI.BB; 1003 FalseBBICalc.BB = FalseBBI.BB; 1004 TrueBBICalc.IsBrAnalyzable = TrueBBI.IsBrAnalyzable; 1005 FalseBBICalc.IsBrAnalyzable = FalseBBI.IsBrAnalyzable; 1006 if (!RescanInstructions(TIB, FIB, TIE, FIE, TrueBBICalc, FalseBBICalc)) 1007 return false; 1008 // The size is used to decide whether to if-convert, and the shared portions 1009 // are subtracted off. Because of the subtraction, we just use the size that 1010 // was calculated by the original ScanInstructions, as it is correct. 1011 TrueBBICalc.NonPredSize = TrueBBI.NonPredSize; 1012 FalseBBICalc.NonPredSize = FalseBBI.NonPredSize; 1013 return true; 1014 } 1015 1016 /// AnalyzeBranches - Look at the branches at the end of a block to determine if 1017 /// the block is predicable. 1018 void IfConverter::AnalyzeBranches(BBInfo &BBI) { 1019 if (BBI.IsDone) 1020 return; 1021 1022 BBI.TrueBB = BBI.FalseBB = nullptr; 1023 BBI.BrCond.clear(); 1024 BBI.IsBrAnalyzable = 1025 !TII->analyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); 1026 if (!BBI.IsBrAnalyzable) { 1027 BBI.TrueBB = nullptr; 1028 BBI.FalseBB = nullptr; 1029 BBI.BrCond.clear(); 1030 } 1031 1032 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 1033 BBI.IsBrReversible = (RevCond.size() == 0) || 1034 !TII->reverseBranchCondition(RevCond); 1035 BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == nullptr; 1036 1037 if (BBI.BrCond.size()) { 1038 // No false branch. This BB must end with a conditional branch and a 1039 // fallthrough. 1040 if (!BBI.FalseBB) 1041 BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB); 1042 if (!BBI.FalseBB) { 1043 // Malformed bcc? True and false blocks are the same? 1044 BBI.IsUnpredicable = true; 1045 } 1046 } 1047 } 1048 1049 /// ScanInstructions - Scan all the instructions in the block to determine if 1050 /// the block is predicable. In most cases, that means all the instructions 1051 /// in the block are isPredicable(). Also checks if the block contains any 1052 /// instruction which can clobber a predicate (e.g. condition code register). 1053 /// If so, the block is not predicable unless it's the last instruction. 1054 void IfConverter::ScanInstructions(BBInfo &BBI, 1055 MachineBasicBlock::iterator &Begin, 1056 MachineBasicBlock::iterator &End, 1057 bool BranchUnpredicable) const { 1058 if (BBI.IsDone || BBI.IsUnpredicable) 1059 return; 1060 1061 bool AlreadyPredicated = !BBI.Predicate.empty(); 1062 1063 BBI.NonPredSize = 0; 1064 BBI.ExtraCost = 0; 1065 BBI.ExtraCost2 = 0; 1066 BBI.ClobbersPred = false; 1067 for (MachineInstr &MI : make_range(Begin, End)) { 1068 if (MI.isDebugInstr()) 1069 continue; 1070 1071 // It's unsafe to duplicate convergent instructions in this context, so set 1072 // BBI.CannotBeCopied to true if MI is convergent. To see why, consider the 1073 // following CFG, which is subject to our "simple" transformation. 1074 // 1075 // BB0 // if (c1) goto BB1; else goto BB2; 1076 // / \ 1077 // BB1 | 1078 // | BB2 // if (c2) goto TBB; else goto FBB; 1079 // | / | 1080 // | / | 1081 // TBB | 1082 // | | 1083 // | FBB 1084 // | 1085 // exit 1086 // 1087 // Suppose we want to move TBB's contents up into BB1 and BB2 (in BB1 they'd 1088 // be unconditional, and in BB2, they'd be predicated upon c2), and suppose 1089 // TBB contains a convergent instruction. This is safe iff doing so does 1090 // not add a control-flow dependency to the convergent instruction -- i.e., 1091 // it's safe iff the set of control flows that leads us to the convergent 1092 // instruction does not get smaller after the transformation. 1093 // 1094 // Originally we executed TBB if c1 || c2. After the transformation, there 1095 // are two copies of TBB's instructions. We get to the first if c1, and we 1096 // get to the second if !c1 && c2. 1097 // 1098 // There are clearly fewer ways to satisfy the condition "c1" than 1099 // "c1 || c2". Since we've shrunk the set of control flows which lead to 1100 // our convergent instruction, the transformation is unsafe. 1101 if (MI.isNotDuplicable() || MI.isConvergent()) 1102 BBI.CannotBeCopied = true; 1103 1104 bool isPredicated = TII->isPredicated(MI); 1105 bool isCondBr = BBI.IsBrAnalyzable && MI.isConditionalBranch(); 1106 1107 if (BranchUnpredicable && MI.isBranch()) { 1108 BBI.IsUnpredicable = true; 1109 return; 1110 } 1111 1112 // A conditional branch is not predicable, but it may be eliminated. 1113 if (isCondBr) 1114 continue; 1115 1116 if (!isPredicated) { 1117 BBI.NonPredSize++; 1118 unsigned ExtraPredCost = TII->getPredicationCost(MI); 1119 unsigned NumCycles = SchedModel.computeInstrLatency(&MI, false); 1120 if (NumCycles > 1) 1121 BBI.ExtraCost += NumCycles-1; 1122 BBI.ExtraCost2 += ExtraPredCost; 1123 } else if (!AlreadyPredicated) { 1124 // FIXME: This instruction is already predicated before the 1125 // if-conversion pass. It's probably something like a conditional move. 1126 // Mark this block unpredicable for now. 1127 BBI.IsUnpredicable = true; 1128 return; 1129 } 1130 1131 if (BBI.ClobbersPred && !isPredicated) { 1132 // Predicate modification instruction should end the block (except for 1133 // already predicated instructions and end of block branches). 1134 // Predicate may have been modified, the subsequent (currently) 1135 // unpredicated instructions cannot be correctly predicated. 1136 BBI.IsUnpredicable = true; 1137 return; 1138 } 1139 1140 // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are 1141 // still potentially predicable. 1142 std::vector<MachineOperand> PredDefs; 1143 if (TII->ClobbersPredicate(MI, PredDefs, true)) 1144 BBI.ClobbersPred = true; 1145 1146 if (!TII->isPredicable(MI)) { 1147 BBI.IsUnpredicable = true; 1148 return; 1149 } 1150 } 1151 } 1152 1153 /// Determine if the block is a suitable candidate to be predicated by the 1154 /// specified predicate. 1155 /// @param BBI BBInfo for the block to check 1156 /// @param Pred Predicate array for the branch that leads to BBI 1157 /// @param isTriangle true if the Analysis is for a triangle 1158 /// @param RevBranch true if Reverse(Pred) leads to BBI (e.g. BBI is the false 1159 /// case 1160 /// @param hasCommonTail true if BBI shares a tail with a sibling block that 1161 /// contains any instruction that would make the block unpredicable. 1162 bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, 1163 SmallVectorImpl<MachineOperand> &Pred, 1164 bool isTriangle, bool RevBranch, 1165 bool hasCommonTail) { 1166 // If the block is dead or unpredicable, then it cannot be predicated. 1167 // Two blocks may share a common unpredicable tail, but this doesn't prevent 1168 // them from being if-converted. The non-shared portion is assumed to have 1169 // been checked 1170 if (BBI.IsDone || (BBI.IsUnpredicable && !hasCommonTail)) 1171 return false; 1172 1173 // If it is already predicated but we couldn't analyze its terminator, the 1174 // latter might fallthrough, but we can't determine where to. 1175 // Conservatively avoid if-converting again. 1176 if (BBI.Predicate.size() && !BBI.IsBrAnalyzable) 1177 return false; 1178 1179 // If it is already predicated, check if the new predicate subsumes 1180 // its predicate. 1181 if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate)) 1182 return false; 1183 1184 if (!hasCommonTail && BBI.BrCond.size()) { 1185 if (!isTriangle) 1186 return false; 1187 1188 // Test predicate subsumption. 1189 SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end()); 1190 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 1191 if (RevBranch) { 1192 if (TII->reverseBranchCondition(Cond)) 1193 return false; 1194 } 1195 if (TII->reverseBranchCondition(RevPred) || 1196 !TII->SubsumesPredicate(Cond, RevPred)) 1197 return false; 1198 } 1199 1200 return true; 1201 } 1202 1203 /// Analyze the structure of the sub-CFG starting from the specified block. 1204 /// Record its successors and whether it looks like an if-conversion candidate. 1205 void IfConverter::AnalyzeBlock( 1206 MachineBasicBlock &MBB, std::vector<std::unique_ptr<IfcvtToken>> &Tokens) { 1207 struct BBState { 1208 BBState(MachineBasicBlock &MBB) : MBB(&MBB) {} 1209 MachineBasicBlock *MBB; 1210 1211 /// This flag is true if MBB's successors have been analyzed. 1212 bool SuccsAnalyzed = false; 1213 }; 1214 1215 // Push MBB to the stack. 1216 SmallVector<BBState, 16> BBStack(1, MBB); 1217 1218 while (!BBStack.empty()) { 1219 BBState &State = BBStack.back(); 1220 MachineBasicBlock *BB = State.MBB; 1221 BBInfo &BBI = BBAnalysis[BB->getNumber()]; 1222 1223 if (!State.SuccsAnalyzed) { 1224 if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed) { 1225 BBStack.pop_back(); 1226 continue; 1227 } 1228 1229 BBI.BB = BB; 1230 BBI.IsBeingAnalyzed = true; 1231 1232 AnalyzeBranches(BBI); 1233 MachineBasicBlock::iterator Begin = BBI.BB->begin(); 1234 MachineBasicBlock::iterator End = BBI.BB->end(); 1235 ScanInstructions(BBI, Begin, End); 1236 1237 // Unanalyzable or ends with fallthrough or unconditional branch, or if is 1238 // not considered for ifcvt anymore. 1239 if (!BBI.IsBrAnalyzable || BBI.BrCond.empty() || BBI.IsDone) { 1240 BBI.IsBeingAnalyzed = false; 1241 BBI.IsAnalyzed = true; 1242 BBStack.pop_back(); 1243 continue; 1244 } 1245 1246 // Do not ifcvt if either path is a back edge to the entry block. 1247 if (BBI.TrueBB == BB || BBI.FalseBB == BB) { 1248 BBI.IsBeingAnalyzed = false; 1249 BBI.IsAnalyzed = true; 1250 BBStack.pop_back(); 1251 continue; 1252 } 1253 1254 // Do not ifcvt if true and false fallthrough blocks are the same. 1255 if (!BBI.FalseBB) { 1256 BBI.IsBeingAnalyzed = false; 1257 BBI.IsAnalyzed = true; 1258 BBStack.pop_back(); 1259 continue; 1260 } 1261 1262 // Push the False and True blocks to the stack. 1263 State.SuccsAnalyzed = true; 1264 BBStack.push_back(*BBI.FalseBB); 1265 BBStack.push_back(*BBI.TrueBB); 1266 continue; 1267 } 1268 1269 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1270 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1271 1272 if (TrueBBI.IsDone && FalseBBI.IsDone) { 1273 BBI.IsBeingAnalyzed = false; 1274 BBI.IsAnalyzed = true; 1275 BBStack.pop_back(); 1276 continue; 1277 } 1278 1279 SmallVector<MachineOperand, 4> 1280 RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 1281 bool CanRevCond = !TII->reverseBranchCondition(RevCond); 1282 1283 unsigned Dups = 0; 1284 unsigned Dups2 = 0; 1285 bool TNeedSub = !TrueBBI.Predicate.empty(); 1286 bool FNeedSub = !FalseBBI.Predicate.empty(); 1287 bool Enqueued = false; 1288 1289 BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB); 1290 1291 if (CanRevCond) { 1292 BBInfo TrueBBICalc, FalseBBICalc; 1293 auto feasibleDiamond = [&](bool Forked) { 1294 bool MeetsSize = MeetIfcvtSizeLimit(TrueBBICalc, FalseBBICalc, *BB, 1295 Dups + Dups2, Prediction, Forked); 1296 bool TrueFeasible = FeasibilityAnalysis(TrueBBI, BBI.BrCond, 1297 /* IsTriangle */ false, /* RevCond */ false, 1298 /* hasCommonTail */ true); 1299 bool FalseFeasible = FeasibilityAnalysis(FalseBBI, RevCond, 1300 /* IsTriangle */ false, /* RevCond */ false, 1301 /* hasCommonTail */ true); 1302 return MeetsSize && TrueFeasible && FalseFeasible; 1303 }; 1304 1305 if (ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2, 1306 TrueBBICalc, FalseBBICalc)) { 1307 if (feasibleDiamond(false)) { 1308 // Diamond: 1309 // EBB 1310 // / \_ 1311 // | | 1312 // TBB FBB 1313 // \ / 1314 // TailBB 1315 // Note TailBB can be empty. 1316 Tokens.push_back(std::make_unique<IfcvtToken>( 1317 BBI, ICDiamond, TNeedSub | FNeedSub, Dups, Dups2, 1318 (bool) TrueBBICalc.ClobbersPred, (bool) FalseBBICalc.ClobbersPred)); 1319 Enqueued = true; 1320 } 1321 } else if (ValidForkedDiamond(TrueBBI, FalseBBI, Dups, Dups2, 1322 TrueBBICalc, FalseBBICalc)) { 1323 if (feasibleDiamond(true)) { 1324 // ForkedDiamond: 1325 // if TBB and FBB have a common tail that includes their conditional 1326 // branch instructions, then we can If Convert this pattern. 1327 // EBB 1328 // _/ \_ 1329 // | | 1330 // TBB FBB 1331 // / \ / \ 1332 // FalseBB TrueBB FalseBB 1333 // 1334 Tokens.push_back(std::make_unique<IfcvtToken>( 1335 BBI, ICForkedDiamond, TNeedSub | FNeedSub, Dups, Dups2, 1336 (bool) TrueBBICalc.ClobbersPred, (bool) FalseBBICalc.ClobbersPred)); 1337 Enqueued = true; 1338 } 1339 } 1340 } 1341 1342 if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) && 1343 MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, 1344 TrueBBI.ExtraCost2, Prediction) && 1345 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { 1346 // Triangle: 1347 // EBB 1348 // | \_ 1349 // | | 1350 // | TBB 1351 // | / 1352 // FBB 1353 Tokens.push_back( 1354 std::make_unique<IfcvtToken>(BBI, ICTriangle, TNeedSub, Dups)); 1355 Enqueued = true; 1356 } 1357 1358 if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction) && 1359 MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, 1360 TrueBBI.ExtraCost2, Prediction) && 1361 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) { 1362 Tokens.push_back( 1363 std::make_unique<IfcvtToken>(BBI, ICTriangleRev, TNeedSub, Dups)); 1364 Enqueued = true; 1365 } 1366 1367 if (ValidSimple(TrueBBI, Dups, Prediction) && 1368 MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, 1369 TrueBBI.ExtraCost2, Prediction) && 1370 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { 1371 // Simple (split, no rejoin): 1372 // EBB 1373 // | \_ 1374 // | | 1375 // | TBB---> exit 1376 // | 1377 // FBB 1378 Tokens.push_back( 1379 std::make_unique<IfcvtToken>(BBI, ICSimple, TNeedSub, Dups)); 1380 Enqueued = true; 1381 } 1382 1383 if (CanRevCond) { 1384 // Try the other path... 1385 if (ValidTriangle(FalseBBI, TrueBBI, false, Dups, 1386 Prediction.getCompl()) && 1387 MeetIfcvtSizeLimit(*FalseBBI.BB, 1388 FalseBBI.NonPredSize + FalseBBI.ExtraCost, 1389 FalseBBI.ExtraCost2, Prediction.getCompl()) && 1390 FeasibilityAnalysis(FalseBBI, RevCond, true)) { 1391 Tokens.push_back(std::make_unique<IfcvtToken>(BBI, ICTriangleFalse, 1392 FNeedSub, Dups)); 1393 Enqueued = true; 1394 } 1395 1396 if (ValidTriangle(FalseBBI, TrueBBI, true, Dups, 1397 Prediction.getCompl()) && 1398 MeetIfcvtSizeLimit(*FalseBBI.BB, 1399 FalseBBI.NonPredSize + FalseBBI.ExtraCost, 1400 FalseBBI.ExtraCost2, Prediction.getCompl()) && 1401 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { 1402 Tokens.push_back( 1403 std::make_unique<IfcvtToken>(BBI, ICTriangleFRev, FNeedSub, Dups)); 1404 Enqueued = true; 1405 } 1406 1407 if (ValidSimple(FalseBBI, Dups, Prediction.getCompl()) && 1408 MeetIfcvtSizeLimit(*FalseBBI.BB, 1409 FalseBBI.NonPredSize + FalseBBI.ExtraCost, 1410 FalseBBI.ExtraCost2, Prediction.getCompl()) && 1411 FeasibilityAnalysis(FalseBBI, RevCond)) { 1412 Tokens.push_back( 1413 std::make_unique<IfcvtToken>(BBI, ICSimpleFalse, FNeedSub, Dups)); 1414 Enqueued = true; 1415 } 1416 } 1417 1418 BBI.IsEnqueued = Enqueued; 1419 BBI.IsBeingAnalyzed = false; 1420 BBI.IsAnalyzed = true; 1421 BBStack.pop_back(); 1422 } 1423 } 1424 1425 /// Analyze all blocks and find entries for all if-conversion candidates. 1426 void IfConverter::AnalyzeBlocks( 1427 MachineFunction &MF, std::vector<std::unique_ptr<IfcvtToken>> &Tokens) { 1428 for (MachineBasicBlock &MBB : MF) 1429 AnalyzeBlock(MBB, Tokens); 1430 1431 // Sort to favor more complex ifcvt scheme. 1432 llvm::stable_sort(Tokens, IfcvtTokenCmp); 1433 } 1434 1435 /// Returns true either if ToMBB is the next block after MBB or that all the 1436 /// intervening blocks are empty (given MBB can fall through to its next block). 1437 static bool canFallThroughTo(MachineBasicBlock &MBB, MachineBasicBlock &ToMBB) { 1438 MachineFunction::iterator PI = MBB.getIterator(); 1439 MachineFunction::iterator I = std::next(PI); 1440 MachineFunction::iterator TI = ToMBB.getIterator(); 1441 MachineFunction::iterator E = MBB.getParent()->end(); 1442 while (I != TI) { 1443 // Check isSuccessor to avoid case where the next block is empty, but 1444 // it's not a successor. 1445 if (I == E || !I->empty() || !PI->isSuccessor(&*I)) 1446 return false; 1447 PI = I++; 1448 } 1449 // Finally see if the last I is indeed a successor to PI. 1450 return PI->isSuccessor(&*I); 1451 } 1452 1453 /// Invalidate predecessor BB info so it would be re-analyzed to determine if it 1454 /// can be if-converted. If predecessor is already enqueued, dequeue it! 1455 void IfConverter::InvalidatePreds(MachineBasicBlock &MBB) { 1456 for (const MachineBasicBlock *Predecessor : MBB.predecessors()) { 1457 BBInfo &PBBI = BBAnalysis[Predecessor->getNumber()]; 1458 if (PBBI.IsDone || PBBI.BB == &MBB) 1459 continue; 1460 PBBI.IsAnalyzed = false; 1461 PBBI.IsEnqueued = false; 1462 } 1463 } 1464 1465 /// Inserts an unconditional branch from \p MBB to \p ToMBB. 1466 static void InsertUncondBranch(MachineBasicBlock &MBB, MachineBasicBlock &ToMBB, 1467 const TargetInstrInfo *TII) { 1468 DebugLoc dl; // FIXME: this is nowhere 1469 SmallVector<MachineOperand, 0> NoCond; 1470 TII->insertBranch(MBB, &ToMBB, nullptr, NoCond, dl); 1471 } 1472 1473 /// Behaves like LiveRegUnits::StepForward() but also adds implicit uses to all 1474 /// values defined in MI which are also live/used by MI. 1475 static void UpdatePredRedefs(MachineInstr &MI, LivePhysRegs &Redefs) { 1476 const TargetRegisterInfo *TRI = MI.getMF()->getSubtarget().getRegisterInfo(); 1477 1478 // Before stepping forward past MI, remember which regs were live 1479 // before MI. This is needed to set the Undef flag only when reg is 1480 // dead. 1481 SparseSet<MCPhysReg, identity<MCPhysReg>> LiveBeforeMI; 1482 LiveBeforeMI.setUniverse(TRI->getNumRegs()); 1483 for (unsigned Reg : Redefs) 1484 LiveBeforeMI.insert(Reg); 1485 1486 SmallVector<std::pair<MCPhysReg, const MachineOperand*>, 4> Clobbers; 1487 Redefs.stepForward(MI, Clobbers); 1488 1489 // Now add the implicit uses for each of the clobbered values. 1490 for (auto Clobber : Clobbers) { 1491 // FIXME: Const cast here is nasty, but better than making StepForward 1492 // take a mutable instruction instead of const. 1493 unsigned Reg = Clobber.first; 1494 MachineOperand &Op = const_cast<MachineOperand&>(*Clobber.second); 1495 MachineInstr *OpMI = Op.getParent(); 1496 MachineInstrBuilder MIB(*OpMI->getMF(), OpMI); 1497 if (Op.isRegMask()) { 1498 // First handle regmasks. They clobber any entries in the mask which 1499 // means that we need a def for those registers. 1500 if (LiveBeforeMI.count(Reg)) 1501 MIB.addReg(Reg, RegState::Implicit); 1502 1503 // We also need to add an implicit def of this register for the later 1504 // use to read from. 1505 // For the register allocator to have allocated a register clobbered 1506 // by the call which is used later, it must be the case that 1507 // the call doesn't return. 1508 MIB.addReg(Reg, RegState::Implicit | RegState::Define); 1509 continue; 1510 } 1511 if (any_of(TRI->subregs_inclusive(Reg), 1512 [&](MCPhysReg S) { return LiveBeforeMI.count(S); })) 1513 MIB.addReg(Reg, RegState::Implicit); 1514 } 1515 } 1516 1517 /// If convert a simple (split, no rejoin) sub-CFG. 1518 bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) { 1519 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1520 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1521 BBInfo *CvtBBI = &TrueBBI; 1522 BBInfo *NextBBI = &FalseBBI; 1523 1524 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 1525 if (Kind == ICSimpleFalse) 1526 std::swap(CvtBBI, NextBBI); 1527 1528 MachineBasicBlock &CvtMBB = *CvtBBI->BB; 1529 MachineBasicBlock &NextMBB = *NextBBI->BB; 1530 if (CvtBBI->IsDone || 1531 (CvtBBI->CannotBeCopied && CvtMBB.pred_size() > 1)) { 1532 // Something has changed. It's no longer safe to predicate this block. 1533 BBI.IsAnalyzed = false; 1534 CvtBBI->IsAnalyzed = false; 1535 return false; 1536 } 1537 1538 if (CvtMBB.hasAddressTaken()) 1539 // Conservatively abort if-conversion if BB's address is taken. 1540 return false; 1541 1542 if (Kind == ICSimpleFalse) 1543 if (TII->reverseBranchCondition(Cond)) 1544 llvm_unreachable("Unable to reverse branch condition!"); 1545 1546 Redefs.init(*TRI); 1547 1548 if (MRI->tracksLiveness()) { 1549 // Initialize liveins to the first BB. These are potentially redefined by 1550 // predicated instructions. 1551 Redefs.addLiveInsNoPristines(CvtMBB); 1552 Redefs.addLiveInsNoPristines(NextMBB); 1553 } 1554 1555 // Remove the branches from the entry so we can add the contents of the true 1556 // block to it. 1557 BBI.NonPredSize -= TII->removeBranch(*BBI.BB); 1558 1559 if (CvtMBB.pred_size() > 1) { 1560 // Copy instructions in the true block, predicate them, and add them to 1561 // the entry block. 1562 CopyAndPredicateBlock(BBI, *CvtBBI, Cond); 1563 1564 // Keep the CFG updated. 1565 BBI.BB->removeSuccessor(&CvtMBB, true); 1566 } else { 1567 // Predicate the instructions in the true block. 1568 PredicateBlock(*CvtBBI, CvtMBB.end(), Cond); 1569 1570 // Merge converted block into entry block. The BB to Cvt edge is removed 1571 // by MergeBlocks. 1572 MergeBlocks(BBI, *CvtBBI); 1573 } 1574 1575 bool IterIfcvt = true; 1576 if (!canFallThroughTo(*BBI.BB, NextMBB)) { 1577 InsertUncondBranch(*BBI.BB, NextMBB, TII); 1578 BBI.HasFallThrough = false; 1579 // Now ifcvt'd block will look like this: 1580 // BB: 1581 // ... 1582 // t, f = cmp 1583 // if t op 1584 // b BBf 1585 // 1586 // We cannot further ifcvt this block because the unconditional branch 1587 // will have to be predicated on the new condition, that will not be 1588 // available if cmp executes. 1589 IterIfcvt = false; 1590 } 1591 1592 // Update block info. BB can be iteratively if-converted. 1593 if (!IterIfcvt) 1594 BBI.IsDone = true; 1595 InvalidatePreds(*BBI.BB); 1596 CvtBBI->IsDone = true; 1597 1598 // FIXME: Must maintain LiveIns. 1599 return true; 1600 } 1601 1602 /// If convert a triangle sub-CFG. 1603 bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) { 1604 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1605 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1606 BBInfo *CvtBBI = &TrueBBI; 1607 BBInfo *NextBBI = &FalseBBI; 1608 DebugLoc dl; // FIXME: this is nowhere 1609 1610 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 1611 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 1612 std::swap(CvtBBI, NextBBI); 1613 1614 MachineBasicBlock &CvtMBB = *CvtBBI->BB; 1615 MachineBasicBlock &NextMBB = *NextBBI->BB; 1616 if (CvtBBI->IsDone || 1617 (CvtBBI->CannotBeCopied && CvtMBB.pred_size() > 1)) { 1618 // Something has changed. It's no longer safe to predicate this block. 1619 BBI.IsAnalyzed = false; 1620 CvtBBI->IsAnalyzed = false; 1621 return false; 1622 } 1623 1624 if (CvtMBB.hasAddressTaken()) 1625 // Conservatively abort if-conversion if BB's address is taken. 1626 return false; 1627 1628 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 1629 if (TII->reverseBranchCondition(Cond)) 1630 llvm_unreachable("Unable to reverse branch condition!"); 1631 1632 if (Kind == ICTriangleRev || Kind == ICTriangleFRev) { 1633 if (reverseBranchCondition(*CvtBBI)) { 1634 // BB has been changed, modify its predecessors (except for this 1635 // one) so they don't get ifcvt'ed based on bad intel. 1636 for (MachineBasicBlock *PBB : CvtMBB.predecessors()) { 1637 if (PBB == BBI.BB) 1638 continue; 1639 BBInfo &PBBI = BBAnalysis[PBB->getNumber()]; 1640 if (PBBI.IsEnqueued) { 1641 PBBI.IsAnalyzed = false; 1642 PBBI.IsEnqueued = false; 1643 } 1644 } 1645 } 1646 } 1647 1648 // Initialize liveins to the first BB. These are potentially redefined by 1649 // predicated instructions. 1650 Redefs.init(*TRI); 1651 if (MRI->tracksLiveness()) { 1652 Redefs.addLiveInsNoPristines(CvtMBB); 1653 Redefs.addLiveInsNoPristines(NextMBB); 1654 } 1655 1656 bool HasEarlyExit = CvtBBI->FalseBB != nullptr; 1657 BranchProbability CvtNext, CvtFalse, BBNext, BBCvt; 1658 1659 if (HasEarlyExit) { 1660 // Get probabilities before modifying CvtMBB and BBI.BB. 1661 CvtNext = MBPI->getEdgeProbability(&CvtMBB, &NextMBB); 1662 CvtFalse = MBPI->getEdgeProbability(&CvtMBB, CvtBBI->FalseBB); 1663 BBNext = MBPI->getEdgeProbability(BBI.BB, &NextMBB); 1664 BBCvt = MBPI->getEdgeProbability(BBI.BB, &CvtMBB); 1665 } 1666 1667 // Remove the branches from the entry so we can add the contents of the true 1668 // block to it. 1669 BBI.NonPredSize -= TII->removeBranch(*BBI.BB); 1670 1671 if (CvtMBB.pred_size() > 1) { 1672 // Copy instructions in the true block, predicate them, and add them to 1673 // the entry block. 1674 CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true); 1675 } else { 1676 // Predicate the 'true' block after removing its branch. 1677 CvtBBI->NonPredSize -= TII->removeBranch(CvtMBB); 1678 PredicateBlock(*CvtBBI, CvtMBB.end(), Cond); 1679 1680 // Now merge the entry of the triangle with the true block. 1681 MergeBlocks(BBI, *CvtBBI, false); 1682 } 1683 1684 // Keep the CFG updated. 1685 BBI.BB->removeSuccessor(&CvtMBB, true); 1686 1687 // If 'true' block has a 'false' successor, add an exit branch to it. 1688 if (HasEarlyExit) { 1689 SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(), 1690 CvtBBI->BrCond.end()); 1691 if (TII->reverseBranchCondition(RevCond)) 1692 llvm_unreachable("Unable to reverse branch condition!"); 1693 1694 // Update the edge probability for both CvtBBI->FalseBB and NextBBI. 1695 // NewNext = New_Prob(BBI.BB, NextMBB) = 1696 // Prob(BBI.BB, NextMBB) + 1697 // Prob(BBI.BB, CvtMBB) * Prob(CvtMBB, NextMBB) 1698 // NewFalse = New_Prob(BBI.BB, CvtBBI->FalseBB) = 1699 // Prob(BBI.BB, CvtMBB) * Prob(CvtMBB, CvtBBI->FalseBB) 1700 auto NewTrueBB = getNextBlock(*BBI.BB); 1701 auto NewNext = BBNext + BBCvt * CvtNext; 1702 auto NewTrueBBIter = find(BBI.BB->successors(), NewTrueBB); 1703 if (NewTrueBBIter != BBI.BB->succ_end()) 1704 BBI.BB->setSuccProbability(NewTrueBBIter, NewNext); 1705 1706 auto NewFalse = BBCvt * CvtFalse; 1707 TII->insertBranch(*BBI.BB, CvtBBI->FalseBB, nullptr, RevCond, dl); 1708 BBI.BB->addSuccessor(CvtBBI->FalseBB, NewFalse); 1709 } 1710 1711 // Merge in the 'false' block if the 'false' block has no other 1712 // predecessors. Otherwise, add an unconditional branch to 'false'. 1713 bool FalseBBDead = false; 1714 bool IterIfcvt = true; 1715 bool isFallThrough = canFallThroughTo(*BBI.BB, NextMBB); 1716 if (!isFallThrough) { 1717 // Only merge them if the true block does not fallthrough to the false 1718 // block. By not merging them, we make it possible to iteratively 1719 // ifcvt the blocks. 1720 if (!HasEarlyExit && 1721 NextMBB.pred_size() == 1 && !NextBBI->HasFallThrough && 1722 !NextMBB.hasAddressTaken()) { 1723 MergeBlocks(BBI, *NextBBI); 1724 FalseBBDead = true; 1725 } else { 1726 InsertUncondBranch(*BBI.BB, NextMBB, TII); 1727 BBI.HasFallThrough = false; 1728 } 1729 // Mixed predicated and unpredicated code. This cannot be iteratively 1730 // predicated. 1731 IterIfcvt = false; 1732 } 1733 1734 // Update block info. BB can be iteratively if-converted. 1735 if (!IterIfcvt) 1736 BBI.IsDone = true; 1737 InvalidatePreds(*BBI.BB); 1738 CvtBBI->IsDone = true; 1739 if (FalseBBDead) 1740 NextBBI->IsDone = true; 1741 1742 // FIXME: Must maintain LiveIns. 1743 return true; 1744 } 1745 1746 /// Common code shared between diamond conversions. 1747 /// \p BBI, \p TrueBBI, and \p FalseBBI form the diamond shape. 1748 /// \p NumDups1 - number of shared instructions at the beginning of \p TrueBBI 1749 /// and FalseBBI 1750 /// \p NumDups2 - number of shared instructions at the end of \p TrueBBI 1751 /// and \p FalseBBI 1752 /// \p RemoveBranch - Remove the common branch of the two blocks before 1753 /// predicating. Only false for unanalyzable fallthrough 1754 /// cases. The caller will replace the branch if necessary. 1755 /// \p MergeAddEdges - Add successor edges when merging blocks. Only false for 1756 /// unanalyzable fallthrough 1757 bool IfConverter::IfConvertDiamondCommon( 1758 BBInfo &BBI, BBInfo &TrueBBI, BBInfo &FalseBBI, 1759 unsigned NumDups1, unsigned NumDups2, 1760 bool TClobbersPred, bool FClobbersPred, 1761 bool RemoveBranch, bool MergeAddEdges) { 1762 1763 if (TrueBBI.IsDone || FalseBBI.IsDone || 1764 TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) { 1765 // Something has changed. It's no longer safe to predicate these blocks. 1766 BBI.IsAnalyzed = false; 1767 TrueBBI.IsAnalyzed = false; 1768 FalseBBI.IsAnalyzed = false; 1769 return false; 1770 } 1771 1772 if (TrueBBI.BB->hasAddressTaken() || FalseBBI.BB->hasAddressTaken()) 1773 // Conservatively abort if-conversion if either BB has its address taken. 1774 return false; 1775 1776 // Put the predicated instructions from the 'true' block before the 1777 // instructions from the 'false' block, unless the true block would clobber 1778 // the predicate, in which case, do the opposite. 1779 BBInfo *BBI1 = &TrueBBI; 1780 BBInfo *BBI2 = &FalseBBI; 1781 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 1782 if (TII->reverseBranchCondition(RevCond)) 1783 llvm_unreachable("Unable to reverse branch condition!"); 1784 SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond; 1785 SmallVector<MachineOperand, 4> *Cond2 = &RevCond; 1786 1787 // Figure out the more profitable ordering. 1788 bool DoSwap = false; 1789 if (TClobbersPred && !FClobbersPred) 1790 DoSwap = true; 1791 else if (!TClobbersPred && !FClobbersPred) { 1792 if (TrueBBI.NonPredSize > FalseBBI.NonPredSize) 1793 DoSwap = true; 1794 } else if (TClobbersPred && FClobbersPred) 1795 llvm_unreachable("Predicate info cannot be clobbered by both sides."); 1796 if (DoSwap) { 1797 std::swap(BBI1, BBI2); 1798 std::swap(Cond1, Cond2); 1799 } 1800 1801 // Remove the conditional branch from entry to the blocks. 1802 BBI.NonPredSize -= TII->removeBranch(*BBI.BB); 1803 1804 MachineBasicBlock &MBB1 = *BBI1->BB; 1805 MachineBasicBlock &MBB2 = *BBI2->BB; 1806 1807 // Initialize the Redefs: 1808 // - BB2 live-in regs need implicit uses before being redefined by BB1 1809 // instructions. 1810 // - BB1 live-out regs need implicit uses before being redefined by BB2 1811 // instructions. We start with BB1 live-ins so we have the live-out regs 1812 // after tracking the BB1 instructions. 1813 Redefs.init(*TRI); 1814 if (MRI->tracksLiveness()) { 1815 Redefs.addLiveInsNoPristines(MBB1); 1816 Redefs.addLiveInsNoPristines(MBB2); 1817 } 1818 1819 // Remove the duplicated instructions at the beginnings of both paths. 1820 // Skip dbg_value instructions. 1821 MachineBasicBlock::iterator DI1 = MBB1.getFirstNonDebugInstr(false); 1822 MachineBasicBlock::iterator DI2 = MBB2.getFirstNonDebugInstr(false); 1823 BBI1->NonPredSize -= NumDups1; 1824 BBI2->NonPredSize -= NumDups1; 1825 1826 // Skip past the dups on each side separately since there may be 1827 // differing dbg_value entries. NumDups1 can include a "return" 1828 // instruction, if it's not marked as "branch". 1829 for (unsigned i = 0; i < NumDups1; ++DI1) { 1830 if (DI1 == MBB1.end()) 1831 break; 1832 if (!DI1->isDebugInstr()) 1833 ++i; 1834 } 1835 while (NumDups1 != 0) { 1836 // Since this instruction is going to be deleted, update call 1837 // site info state if the instruction is call instruction. 1838 if (DI2->shouldUpdateCallSiteInfo()) 1839 MBB2.getParent()->eraseCallSiteInfo(&*DI2); 1840 1841 ++DI2; 1842 if (DI2 == MBB2.end()) 1843 break; 1844 if (!DI2->isDebugInstr()) 1845 --NumDups1; 1846 } 1847 1848 if (MRI->tracksLiveness()) { 1849 for (const MachineInstr &MI : make_range(MBB1.begin(), DI1)) { 1850 SmallVector<std::pair<MCPhysReg, const MachineOperand*>, 4> Dummy; 1851 Redefs.stepForward(MI, Dummy); 1852 } 1853 } 1854 1855 BBI.BB->splice(BBI.BB->end(), &MBB1, MBB1.begin(), DI1); 1856 MBB2.erase(MBB2.begin(), DI2); 1857 1858 // The branches have been checked to match, so it is safe to remove the 1859 // branch in BB1 and rely on the copy in BB2. The complication is that 1860 // the blocks may end with a return instruction, which may or may not 1861 // be marked as "branch". If it's not, then it could be included in 1862 // "dups1", leaving the blocks potentially empty after moving the common 1863 // duplicates. 1864 #ifndef NDEBUG 1865 // Unanalyzable branches must match exactly. Check that now. 1866 if (!BBI1->IsBrAnalyzable) 1867 verifySameBranchInstructions(&MBB1, &MBB2); 1868 #endif 1869 // Remove duplicated instructions from the tail of MBB1: any branch 1870 // instructions, and the common instructions counted by NumDups2. 1871 DI1 = MBB1.end(); 1872 while (DI1 != MBB1.begin()) { 1873 MachineBasicBlock::iterator Prev = std::prev(DI1); 1874 if (!Prev->isBranch() && !Prev->isDebugInstr()) 1875 break; 1876 DI1 = Prev; 1877 } 1878 for (unsigned i = 0; i != NumDups2; ) { 1879 // NumDups2 only counted non-dbg_value instructions, so this won't 1880 // run off the head of the list. 1881 assert(DI1 != MBB1.begin()); 1882 1883 --DI1; 1884 1885 // Since this instruction is going to be deleted, update call 1886 // site info state if the instruction is call instruction. 1887 if (DI1->shouldUpdateCallSiteInfo()) 1888 MBB1.getParent()->eraseCallSiteInfo(&*DI1); 1889 1890 // skip dbg_value instructions 1891 if (!DI1->isDebugInstr()) 1892 ++i; 1893 } 1894 MBB1.erase(DI1, MBB1.end()); 1895 1896 DI2 = BBI2->BB->end(); 1897 // The branches have been checked to match. Skip over the branch in the false 1898 // block so that we don't try to predicate it. 1899 if (RemoveBranch) 1900 BBI2->NonPredSize -= TII->removeBranch(*BBI2->BB); 1901 else { 1902 // Make DI2 point to the end of the range where the common "tail" 1903 // instructions could be found. 1904 while (DI2 != MBB2.begin()) { 1905 MachineBasicBlock::iterator Prev = std::prev(DI2); 1906 if (!Prev->isBranch() && !Prev->isDebugInstr()) 1907 break; 1908 DI2 = Prev; 1909 } 1910 } 1911 while (NumDups2 != 0) { 1912 // NumDups2 only counted non-dbg_value instructions, so this won't 1913 // run off the head of the list. 1914 assert(DI2 != MBB2.begin()); 1915 --DI2; 1916 // skip dbg_value instructions 1917 if (!DI2->isDebugInstr()) 1918 --NumDups2; 1919 } 1920 1921 // Remember which registers would later be defined by the false block. 1922 // This allows us not to predicate instructions in the true block that would 1923 // later be re-defined. That is, rather than 1924 // subeq r0, r1, #1 1925 // addne r0, r1, #1 1926 // generate: 1927 // sub r0, r1, #1 1928 // addne r0, r1, #1 1929 SmallSet<MCPhysReg, 4> RedefsByFalse; 1930 SmallSet<MCPhysReg, 4> ExtUses; 1931 if (TII->isProfitableToUnpredicate(MBB1, MBB2)) { 1932 for (const MachineInstr &FI : make_range(MBB2.begin(), DI2)) { 1933 if (FI.isDebugInstr()) 1934 continue; 1935 SmallVector<MCPhysReg, 4> Defs; 1936 for (const MachineOperand &MO : FI.operands()) { 1937 if (!MO.isReg()) 1938 continue; 1939 Register Reg = MO.getReg(); 1940 if (!Reg) 1941 continue; 1942 if (MO.isDef()) { 1943 Defs.push_back(Reg); 1944 } else if (!RedefsByFalse.count(Reg)) { 1945 // These are defined before ctrl flow reach the 'false' instructions. 1946 // They cannot be modified by the 'true' instructions. 1947 for (MCPhysReg SubReg : TRI->subregs_inclusive(Reg)) 1948 ExtUses.insert(SubReg); 1949 } 1950 } 1951 1952 for (MCPhysReg Reg : Defs) { 1953 if (!ExtUses.count(Reg)) { 1954 for (MCPhysReg SubReg : TRI->subregs_inclusive(Reg)) 1955 RedefsByFalse.insert(SubReg); 1956 } 1957 } 1958 } 1959 } 1960 1961 // Predicate the 'true' block. 1962 PredicateBlock(*BBI1, MBB1.end(), *Cond1, &RedefsByFalse); 1963 1964 // After predicating BBI1, if there is a predicated terminator in BBI1 and 1965 // a non-predicated in BBI2, then we don't want to predicate the one from 1966 // BBI2. The reason is that if we merged these blocks, we would end up with 1967 // two predicated terminators in the same block. 1968 // Also, if the branches in MBB1 and MBB2 were non-analyzable, then don't 1969 // predicate them either. They were checked to be identical, and so the 1970 // same branch would happen regardless of which path was taken. 1971 if (!MBB2.empty() && (DI2 == MBB2.end())) { 1972 MachineBasicBlock::iterator BBI1T = MBB1.getFirstTerminator(); 1973 MachineBasicBlock::iterator BBI2T = MBB2.getFirstTerminator(); 1974 bool BB1Predicated = BBI1T != MBB1.end() && TII->isPredicated(*BBI1T); 1975 bool BB2NonPredicated = BBI2T != MBB2.end() && !TII->isPredicated(*BBI2T); 1976 if (BB2NonPredicated && (BB1Predicated || !BBI2->IsBrAnalyzable)) 1977 --DI2; 1978 } 1979 1980 // Predicate the 'false' block. 1981 PredicateBlock(*BBI2, DI2, *Cond2); 1982 1983 // Merge the true block into the entry of the diamond. 1984 MergeBlocks(BBI, *BBI1, MergeAddEdges); 1985 MergeBlocks(BBI, *BBI2, MergeAddEdges); 1986 return true; 1987 } 1988 1989 /// If convert an almost-diamond sub-CFG where the true 1990 /// and false blocks share a common tail. 1991 bool IfConverter::IfConvertForkedDiamond( 1992 BBInfo &BBI, IfcvtKind Kind, 1993 unsigned NumDups1, unsigned NumDups2, 1994 bool TClobbersPred, bool FClobbersPred) { 1995 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1996 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1997 1998 // Save the debug location for later. 1999 DebugLoc dl; 2000 MachineBasicBlock::iterator TIE = TrueBBI.BB->getFirstTerminator(); 2001 if (TIE != TrueBBI.BB->end()) 2002 dl = TIE->getDebugLoc(); 2003 // Removing branches from both blocks is safe, because we have already 2004 // determined that both blocks have the same branch instructions. The branch 2005 // will be added back at the end, unpredicated. 2006 if (!IfConvertDiamondCommon( 2007 BBI, TrueBBI, FalseBBI, 2008 NumDups1, NumDups2, 2009 TClobbersPred, FClobbersPred, 2010 /* RemoveBranch */ true, /* MergeAddEdges */ true)) 2011 return false; 2012 2013 // Add back the branch. 2014 // Debug location saved above when removing the branch from BBI2 2015 TII->insertBranch(*BBI.BB, TrueBBI.TrueBB, TrueBBI.FalseBB, 2016 TrueBBI.BrCond, dl); 2017 2018 // Update block info. 2019 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; 2020 InvalidatePreds(*BBI.BB); 2021 2022 // FIXME: Must maintain LiveIns. 2023 return true; 2024 } 2025 2026 /// If convert a diamond sub-CFG. 2027 bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 2028 unsigned NumDups1, unsigned NumDups2, 2029 bool TClobbersPred, bool FClobbersPred) { 2030 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 2031 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 2032 MachineBasicBlock *TailBB = TrueBBI.TrueBB; 2033 2034 // True block must fall through or end with an unanalyzable terminator. 2035 if (!TailBB) { 2036 if (blockAlwaysFallThrough(TrueBBI)) 2037 TailBB = FalseBBI.TrueBB; 2038 assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!"); 2039 } 2040 2041 if (!IfConvertDiamondCommon( 2042 BBI, TrueBBI, FalseBBI, 2043 NumDups1, NumDups2, 2044 TClobbersPred, FClobbersPred, 2045 /* RemoveBranch */ TrueBBI.IsBrAnalyzable, 2046 /* MergeAddEdges */ TailBB == nullptr)) 2047 return false; 2048 2049 // If the if-converted block falls through or unconditionally branches into 2050 // the tail block, and the tail block does not have other predecessors, then 2051 // fold the tail block in as well. Otherwise, unless it falls through to the 2052 // tail, add a unconditional branch to it. 2053 if (TailBB) { 2054 // We need to remove the edges to the true and false blocks manually since 2055 // we didn't let IfConvertDiamondCommon update the CFG. 2056 BBI.BB->removeSuccessor(TrueBBI.BB); 2057 BBI.BB->removeSuccessor(FalseBBI.BB, true); 2058 2059 BBInfo &TailBBI = BBAnalysis[TailBB->getNumber()]; 2060 bool CanMergeTail = !TailBBI.HasFallThrough && 2061 !TailBBI.BB->hasAddressTaken(); 2062 // The if-converted block can still have a predicated terminator 2063 // (e.g. a predicated return). If that is the case, we cannot merge 2064 // it with the tail block. 2065 MachineBasicBlock::const_iterator TI = BBI.BB->getFirstTerminator(); 2066 if (TI != BBI.BB->end() && TII->isPredicated(*TI)) 2067 CanMergeTail = false; 2068 // There may still be a fall-through edge from BBI1 or BBI2 to TailBB; 2069 // check if there are any other predecessors besides those. 2070 unsigned NumPreds = TailBB->pred_size(); 2071 if (NumPreds > 1) 2072 CanMergeTail = false; 2073 else if (NumPreds == 1 && CanMergeTail) { 2074 MachineBasicBlock::pred_iterator PI = TailBB->pred_begin(); 2075 if (*PI != TrueBBI.BB && *PI != FalseBBI.BB) 2076 CanMergeTail = false; 2077 } 2078 if (CanMergeTail) { 2079 MergeBlocks(BBI, TailBBI); 2080 TailBBI.IsDone = true; 2081 } else { 2082 BBI.BB->addSuccessor(TailBB, BranchProbability::getOne()); 2083 InsertUncondBranch(*BBI.BB, *TailBB, TII); 2084 BBI.HasFallThrough = false; 2085 } 2086 } 2087 2088 // Update block info. 2089 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; 2090 InvalidatePreds(*BBI.BB); 2091 2092 // FIXME: Must maintain LiveIns. 2093 return true; 2094 } 2095 2096 static bool MaySpeculate(const MachineInstr &MI, 2097 SmallSet<MCPhysReg, 4> &LaterRedefs) { 2098 bool SawStore = true; 2099 if (!MI.isSafeToMove(nullptr, SawStore)) 2100 return false; 2101 2102 for (const MachineOperand &MO : MI.operands()) { 2103 if (!MO.isReg()) 2104 continue; 2105 Register Reg = MO.getReg(); 2106 if (!Reg) 2107 continue; 2108 if (MO.isDef() && !LaterRedefs.count(Reg)) 2109 return false; 2110 } 2111 2112 return true; 2113 } 2114 2115 /// Predicate instructions from the start of the block to the specified end with 2116 /// the specified condition. 2117 void IfConverter::PredicateBlock(BBInfo &BBI, 2118 MachineBasicBlock::iterator E, 2119 SmallVectorImpl<MachineOperand> &Cond, 2120 SmallSet<MCPhysReg, 4> *LaterRedefs) { 2121 bool AnyUnpred = false; 2122 bool MaySpec = LaterRedefs != nullptr; 2123 for (MachineInstr &I : make_range(BBI.BB->begin(), E)) { 2124 if (I.isDebugInstr() || TII->isPredicated(I)) 2125 continue; 2126 // It may be possible not to predicate an instruction if it's the 'true' 2127 // side of a diamond and the 'false' side may re-define the instruction's 2128 // defs. 2129 if (MaySpec && MaySpeculate(I, *LaterRedefs)) { 2130 AnyUnpred = true; 2131 continue; 2132 } 2133 // If any instruction is predicated, then every instruction after it must 2134 // be predicated. 2135 MaySpec = false; 2136 if (!TII->PredicateInstruction(I, Cond)) { 2137 #ifndef NDEBUG 2138 dbgs() << "Unable to predicate " << I << "!\n"; 2139 #endif 2140 llvm_unreachable(nullptr); 2141 } 2142 2143 // If the predicated instruction now redefines a register as the result of 2144 // if-conversion, add an implicit kill. 2145 UpdatePredRedefs(I, Redefs); 2146 } 2147 2148 BBI.Predicate.append(Cond.begin(), Cond.end()); 2149 2150 BBI.IsAnalyzed = false; 2151 BBI.NonPredSize = 0; 2152 2153 ++NumIfConvBBs; 2154 if (AnyUnpred) 2155 ++NumUnpred; 2156 } 2157 2158 /// Copy and predicate instructions from source BB to the destination block. 2159 /// Skip end of block branches if IgnoreBr is true. 2160 void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 2161 SmallVectorImpl<MachineOperand> &Cond, 2162 bool IgnoreBr) { 2163 MachineFunction &MF = *ToBBI.BB->getParent(); 2164 2165 MachineBasicBlock &FromMBB = *FromBBI.BB; 2166 for (MachineInstr &I : FromMBB) { 2167 // Do not copy the end of the block branches. 2168 if (IgnoreBr && I.isBranch()) 2169 break; 2170 2171 MachineInstr *MI = MF.CloneMachineInstr(&I); 2172 // Make a copy of the call site info. 2173 if (I.isCandidateForCallSiteEntry()) 2174 MF.copyCallSiteInfo(&I, MI); 2175 2176 ToBBI.BB->insert(ToBBI.BB->end(), MI); 2177 ToBBI.NonPredSize++; 2178 unsigned ExtraPredCost = TII->getPredicationCost(I); 2179 unsigned NumCycles = SchedModel.computeInstrLatency(&I, false); 2180 if (NumCycles > 1) 2181 ToBBI.ExtraCost += NumCycles-1; 2182 ToBBI.ExtraCost2 += ExtraPredCost; 2183 2184 if (!TII->isPredicated(I) && !MI->isDebugInstr()) { 2185 if (!TII->PredicateInstruction(*MI, Cond)) { 2186 #ifndef NDEBUG 2187 dbgs() << "Unable to predicate " << I << "!\n"; 2188 #endif 2189 llvm_unreachable(nullptr); 2190 } 2191 } 2192 2193 // If the predicated instruction now redefines a register as the result of 2194 // if-conversion, add an implicit kill. 2195 UpdatePredRedefs(*MI, Redefs); 2196 } 2197 2198 if (!IgnoreBr) { 2199 std::vector<MachineBasicBlock *> Succs(FromMBB.succ_begin(), 2200 FromMBB.succ_end()); 2201 MachineBasicBlock *NBB = getNextBlock(FromMBB); 2202 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : nullptr; 2203 2204 for (MachineBasicBlock *Succ : Succs) { 2205 // Fallthrough edge can't be transferred. 2206 if (Succ == FallThrough) 2207 continue; 2208 ToBBI.BB->addSuccessor(Succ); 2209 } 2210 } 2211 2212 ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end()); 2213 ToBBI.Predicate.append(Cond.begin(), Cond.end()); 2214 2215 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 2216 ToBBI.IsAnalyzed = false; 2217 2218 ++NumDupBBs; 2219 } 2220 2221 /// Move all instructions from FromBB to the end of ToBB. This will leave 2222 /// FromBB as an empty block, so remove all of its successor edges and move it 2223 /// to the end of the function. If AddEdges is true, i.e., when FromBBI's 2224 /// branch is being moved, add those successor edges to ToBBI and remove the old 2225 /// edge from ToBBI to FromBBI. 2226 void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) { 2227 MachineBasicBlock &FromMBB = *FromBBI.BB; 2228 assert(!FromMBB.hasAddressTaken() && 2229 "Removing a BB whose address is taken!"); 2230 2231 // If we're about to splice an INLINEASM_BR from FromBBI, we need to update 2232 // ToBBI's successor list accordingly. 2233 if (FromMBB.mayHaveInlineAsmBr()) 2234 for (MachineInstr &MI : FromMBB) 2235 if (MI.getOpcode() == TargetOpcode::INLINEASM_BR) 2236 for (MachineOperand &MO : MI.operands()) 2237 if (MO.isMBB() && !ToBBI.BB->isSuccessor(MO.getMBB())) 2238 ToBBI.BB->addSuccessor(MO.getMBB(), BranchProbability::getZero()); 2239 2240 // In case FromMBB contains terminators (e.g. return instruction), 2241 // first move the non-terminator instructions, then the terminators. 2242 MachineBasicBlock::iterator FromTI = FromMBB.getFirstTerminator(); 2243 MachineBasicBlock::iterator ToTI = ToBBI.BB->getFirstTerminator(); 2244 ToBBI.BB->splice(ToTI, &FromMBB, FromMBB.begin(), FromTI); 2245 2246 // If FromBB has non-predicated terminator we should copy it at the end. 2247 if (FromTI != FromMBB.end() && !TII->isPredicated(*FromTI)) 2248 ToTI = ToBBI.BB->end(); 2249 ToBBI.BB->splice(ToTI, &FromMBB, FromTI, FromMBB.end()); 2250 2251 // Force normalizing the successors' probabilities of ToBBI.BB to convert all 2252 // unknown probabilities into known ones. 2253 // FIXME: This usage is too tricky and in the future we would like to 2254 // eliminate all unknown probabilities in MBB. 2255 if (ToBBI.IsBrAnalyzable) 2256 ToBBI.BB->normalizeSuccProbs(); 2257 2258 SmallVector<MachineBasicBlock *, 4> FromSuccs(FromMBB.successors()); 2259 MachineBasicBlock *NBB = getNextBlock(FromMBB); 2260 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : nullptr; 2261 // The edge probability from ToBBI.BB to FromMBB, which is only needed when 2262 // AddEdges is true and FromMBB is a successor of ToBBI.BB. 2263 auto To2FromProb = BranchProbability::getZero(); 2264 if (AddEdges && ToBBI.BB->isSuccessor(&FromMBB)) { 2265 // Remove the old edge but remember the edge probability so we can calculate 2266 // the correct weights on the new edges being added further down. 2267 To2FromProb = MBPI->getEdgeProbability(ToBBI.BB, &FromMBB); 2268 ToBBI.BB->removeSuccessor(&FromMBB); 2269 } 2270 2271 for (MachineBasicBlock *Succ : FromSuccs) { 2272 // Fallthrough edge can't be transferred. 2273 if (Succ == FallThrough) { 2274 FromMBB.removeSuccessor(Succ); 2275 continue; 2276 } 2277 2278 auto NewProb = BranchProbability::getZero(); 2279 if (AddEdges) { 2280 // Calculate the edge probability for the edge from ToBBI.BB to Succ, 2281 // which is a portion of the edge probability from FromMBB to Succ. The 2282 // portion ratio is the edge probability from ToBBI.BB to FromMBB (if 2283 // FromBBI is a successor of ToBBI.BB. See comment below for exception). 2284 NewProb = MBPI->getEdgeProbability(&FromMBB, Succ); 2285 2286 // To2FromProb is 0 when FromMBB is not a successor of ToBBI.BB. This 2287 // only happens when if-converting a diamond CFG and FromMBB is the 2288 // tail BB. In this case FromMBB post-dominates ToBBI.BB and hence we 2289 // could just use the probabilities on FromMBB's out-edges when adding 2290 // new successors. 2291 if (!To2FromProb.isZero()) 2292 NewProb *= To2FromProb; 2293 } 2294 2295 FromMBB.removeSuccessor(Succ); 2296 2297 if (AddEdges) { 2298 // If the edge from ToBBI.BB to Succ already exists, update the 2299 // probability of this edge by adding NewProb to it. An example is shown 2300 // below, in which A is ToBBI.BB and B is FromMBB. In this case we 2301 // don't have to set C as A's successor as it already is. We only need to 2302 // update the edge probability on A->C. Note that B will not be 2303 // immediately removed from A's successors. It is possible that B->D is 2304 // not removed either if D is a fallthrough of B. Later the edge A->D 2305 // (generated here) and B->D will be combined into one edge. To maintain 2306 // correct edge probability of this combined edge, we need to set the edge 2307 // probability of A->B to zero, which is already done above. The edge 2308 // probability on A->D is calculated by scaling the original probability 2309 // on A->B by the probability of B->D. 2310 // 2311 // Before ifcvt: After ifcvt (assume B->D is kept): 2312 // 2313 // A A 2314 // /| /|\ 2315 // / B / B| 2316 // | /| | || 2317 // |/ | | |/ 2318 // C D C D 2319 // 2320 if (ToBBI.BB->isSuccessor(Succ)) 2321 ToBBI.BB->setSuccProbability( 2322 find(ToBBI.BB->successors(), Succ), 2323 MBPI->getEdgeProbability(ToBBI.BB, Succ) + NewProb); 2324 else 2325 ToBBI.BB->addSuccessor(Succ, NewProb); 2326 } 2327 } 2328 2329 // Move the now empty FromMBB out of the way to the end of the function so 2330 // it doesn't interfere with fallthrough checks done by canFallThroughTo(). 2331 MachineBasicBlock *Last = &*FromMBB.getParent()->rbegin(); 2332 if (Last != &FromMBB) 2333 FromMBB.moveAfter(Last); 2334 2335 // Normalize the probabilities of ToBBI.BB's successors with all adjustment 2336 // we've done above. 2337 if (ToBBI.IsBrAnalyzable && FromBBI.IsBrAnalyzable) 2338 ToBBI.BB->normalizeSuccProbs(); 2339 2340 ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end()); 2341 FromBBI.Predicate.clear(); 2342 2343 ToBBI.NonPredSize += FromBBI.NonPredSize; 2344 ToBBI.ExtraCost += FromBBI.ExtraCost; 2345 ToBBI.ExtraCost2 += FromBBI.ExtraCost2; 2346 FromBBI.NonPredSize = 0; 2347 FromBBI.ExtraCost = 0; 2348 FromBBI.ExtraCost2 = 0; 2349 2350 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 2351 ToBBI.HasFallThrough = FromBBI.HasFallThrough; 2352 ToBBI.IsAnalyzed = false; 2353 FromBBI.IsAnalyzed = false; 2354 } 2355 2356 FunctionPass * 2357 llvm::createIfConverter(std::function<bool(const MachineFunction &)> Ftor) { 2358 return new IfConverter(std::move(Ftor)); 2359 } 2360