IfConversion.cpp revision 327952
1//===- IfConversion.cpp - Machine code if conversion pass -----------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements the machine instruction level if-conversion pass, which 11// tries to convert conditional branches into predicated instructions. 12// 13//===----------------------------------------------------------------------===// 14 15#include "BranchFolding.h" 16#include "llvm/ADT/STLExtras.h" 17#include "llvm/ADT/ScopeExit.h" 18#include "llvm/ADT/SmallSet.h" 19#include "llvm/ADT/SmallVector.h" 20#include "llvm/ADT/SparseSet.h" 21#include "llvm/ADT/Statistic.h" 22#include "llvm/ADT/iterator_range.h" 23#include "llvm/CodeGen/LivePhysRegs.h" 24#include "llvm/CodeGen/MachineBasicBlock.h" 25#include "llvm/CodeGen/MachineBlockFrequencyInfo.h" 26#include "llvm/CodeGen/MachineBranchProbabilityInfo.h" 27#include "llvm/CodeGen/MachineFunction.h" 28#include "llvm/CodeGen/MachineFunctionPass.h" 29#include "llvm/CodeGen/MachineInstr.h" 30#include "llvm/CodeGen/MachineInstrBuilder.h" 31#include "llvm/CodeGen/MachineModuleInfo.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/MC/MCRegisterInfo.h" 41#include "llvm/Pass.h" 42#include "llvm/Support/BranchProbability.h" 43#include "llvm/Support/CommandLine.h" 44#include "llvm/Support/Debug.h" 45#include "llvm/Support/ErrorHandling.h" 46#include "llvm/Support/raw_ostream.h" 47#include <algorithm> 48#include <cassert> 49#include <functional> 50#include <iterator> 51#include <memory> 52#include <utility> 53#include <vector> 54 55using namespace llvm; 56 57#define DEBUG_TYPE "if-converter" 58 59// Hidden options for help debugging. 60static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); 61static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); 62static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); 63static cl::opt<bool> DisableSimple("disable-ifcvt-simple", 64 cl::init(false), cl::Hidden); 65static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false", 66 cl::init(false), cl::Hidden); 67static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", 68 cl::init(false), cl::Hidden); 69static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev", 70 cl::init(false), cl::Hidden); 71static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false", 72 cl::init(false), cl::Hidden); 73static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev", 74 cl::init(false), cl::Hidden); 75static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", 76 cl::init(false), cl::Hidden); 77static cl::opt<bool> DisableForkedDiamond("disable-ifcvt-forked-diamond", 78 cl::init(false), cl::Hidden); 79static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold", 80 cl::init(true), cl::Hidden); 81 82STATISTIC(NumSimple, "Number of simple if-conversions performed"); 83STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed"); 84STATISTIC(NumTriangle, "Number of triangle if-conversions performed"); 85STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed"); 86STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed"); 87STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed"); 88STATISTIC(NumDiamonds, "Number of diamond if-conversions performed"); 89STATISTIC(NumForkedDiamonds, "Number of forked-diamond if-conversions performed"); 90STATISTIC(NumIfConvBBs, "Number of if-converted blocks"); 91STATISTIC(NumDupBBs, "Number of duplicated blocks"); 92STATISTIC(NumUnpred, "Number of true blocks of diamonds unpredicated"); 93 94namespace { 95 96 class IfConverter : public MachineFunctionPass { 97 enum IfcvtKind { 98 ICNotClassfied, // BB data valid, but not classified. 99 ICSimpleFalse, // Same as ICSimple, but on the false path. 100 ICSimple, // BB is entry of an one split, no rejoin sub-CFG. 101 ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition. 102 ICTriangleRev, // Same as ICTriangle, but true path rev condition. 103 ICTriangleFalse, // Same as ICTriangle, but on the false path. 104 ICTriangle, // BB is entry of a triangle sub-CFG. 105 ICDiamond, // BB is entry of a diamond sub-CFG. 106 ICForkedDiamond // BB is entry of an almost diamond sub-CFG, with a 107 // common tail that can be shared. 108 }; 109 110 /// One per MachineBasicBlock, this is used to cache the result 111 /// if-conversion feasibility analysis. This includes results from 112 /// TargetInstrInfo::analyzeBranch() (i.e. TBB, FBB, and Cond), and its 113 /// classification, and common tail block of its successors (if it's a 114 /// diamond shape), its size, whether it's predicable, and whether any 115 /// instruction can clobber the 'would-be' predicate. 116 /// 117 /// IsDone - True if BB is not to be considered for ifcvt. 118 /// IsBeingAnalyzed - True if BB is currently being analyzed. 119 /// IsAnalyzed - True if BB has been analyzed (info is still valid). 120 /// IsEnqueued - True if BB has been enqueued to be ifcvt'ed. 121 /// IsBrAnalyzable - True if analyzeBranch() returns false. 122 /// HasFallThrough - True if BB may fallthrough to the following BB. 123 /// IsUnpredicable - True if BB is known to be unpredicable. 124 /// ClobbersPred - True if BB could modify predicates (e.g. has 125 /// cmp, call, etc.) 126 /// NonPredSize - Number of non-predicated instructions. 127 /// ExtraCost - Extra cost for multi-cycle instructions. 128 /// ExtraCost2 - Some instructions are slower when predicated 129 /// BB - Corresponding MachineBasicBlock. 130 /// TrueBB / FalseBB- See analyzeBranch(). 131 /// BrCond - Conditions for end of block conditional branches. 132 /// Predicate - Predicate used in the BB. 133 struct BBInfo { 134 bool IsDone : 1; 135 bool IsBeingAnalyzed : 1; 136 bool IsAnalyzed : 1; 137 bool IsEnqueued : 1; 138 bool IsBrAnalyzable : 1; 139 bool IsBrReversible : 1; 140 bool HasFallThrough : 1; 141 bool IsUnpredicable : 1; 142 bool CannotBeCopied : 1; 143 bool ClobbersPred : 1; 144 unsigned NonPredSize = 0; 145 unsigned ExtraCost = 0; 146 unsigned ExtraCost2 = 0; 147 MachineBasicBlock *BB = nullptr; 148 MachineBasicBlock *TrueBB = nullptr; 149 MachineBasicBlock *FalseBB = nullptr; 150 SmallVector<MachineOperand, 4> BrCond; 151 SmallVector<MachineOperand, 4> Predicate; 152 153 BBInfo() : IsDone(false), IsBeingAnalyzed(false), 154 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false), 155 IsBrReversible(false), HasFallThrough(false), 156 IsUnpredicable(false), CannotBeCopied(false), 157 ClobbersPred(false) {} 158 }; 159 160 /// Record information about pending if-conversions to attempt: 161 /// BBI - Corresponding BBInfo. 162 /// Kind - Type of block. See IfcvtKind. 163 /// NeedSubsumption - True if the to-be-predicated BB has already been 164 /// predicated. 165 /// NumDups - Number of instructions that would be duplicated due 166 /// to this if-conversion. (For diamonds, the number of 167 /// identical instructions at the beginnings of both 168 /// paths). 169 /// NumDups2 - For diamonds, the number of identical instructions 170 /// at the ends of both paths. 171 struct IfcvtToken { 172 BBInfo &BBI; 173 IfcvtKind Kind; 174 unsigned NumDups; 175 unsigned NumDups2; 176 bool NeedSubsumption : 1; 177 bool TClobbersPred : 1; 178 bool FClobbersPred : 1; 179 180 IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0, 181 bool tc = false, bool fc = false) 182 : BBI(b), Kind(k), NumDups(d), NumDups2(d2), NeedSubsumption(s), 183 TClobbersPred(tc), FClobbersPred(fc) {} 184 }; 185 186 /// Results of if-conversion feasibility analysis indexed by basic block 187 /// number. 188 std::vector<BBInfo> BBAnalysis; 189 TargetSchedModel SchedModel; 190 191 const TargetLoweringBase *TLI; 192 const TargetInstrInfo *TII; 193 const TargetRegisterInfo *TRI; 194 const MachineBranchProbabilityInfo *MBPI; 195 MachineRegisterInfo *MRI; 196 197 LivePhysRegs Redefs; 198 199 bool PreRegAlloc; 200 bool MadeChange; 201 int FnNum = -1; 202 std::function<bool(const MachineFunction &)> PredicateFtor; 203 204 public: 205 static char ID; 206 207 IfConverter(std::function<bool(const MachineFunction &)> Ftor = nullptr) 208 : MachineFunctionPass(ID), PredicateFtor(std::move(Ftor)) { 209 initializeIfConverterPass(*PassRegistry::getPassRegistry()); 210 } 211 212 void getAnalysisUsage(AnalysisUsage &AU) const override { 213 AU.addRequired<MachineBlockFrequencyInfo>(); 214 AU.addRequired<MachineBranchProbabilityInfo>(); 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> &Cond, 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<unsigned, 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(MachineBasicBlock &TBB, 290 unsigned TCycle, unsigned TExtra, 291 MachineBasicBlock &FBB, 292 unsigned FCycle, unsigned FExtra, 293 BranchProbability Prediction) const { 294 return TCycle > 0 && FCycle > 0 && 295 TII->isProfitableToIfCvt(TBB, TCycle, TExtra, FBB, FCycle, FExtra, 296 Prediction); 297 } 298 299 /// Returns true if Block ends without a terminator. 300 bool blockAlwaysFallThrough(BBInfo &BBI) const { 301 return BBI.IsBrAnalyzable && BBI.TrueBB == nullptr; 302 } 303 304 /// Used to sort if-conversion candidates. 305 static bool IfcvtTokenCmp(const std::unique_ptr<IfcvtToken> &C1, 306 const std::unique_ptr<IfcvtToken> &C2) { 307 int Incr1 = (C1->Kind == ICDiamond) 308 ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups; 309 int Incr2 = (C2->Kind == ICDiamond) 310 ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups; 311 if (Incr1 > Incr2) 312 return true; 313 else if (Incr1 == Incr2) { 314 // Favors subsumption. 315 if (!C1->NeedSubsumption && C2->NeedSubsumption) 316 return true; 317 else if (C1->NeedSubsumption == C2->NeedSubsumption) { 318 // Favors diamond over triangle, etc. 319 if ((unsigned)C1->Kind < (unsigned)C2->Kind) 320 return true; 321 else if (C1->Kind == C2->Kind) 322 return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber(); 323 } 324 } 325 return false; 326 } 327 }; 328 329} // end anonymous namespace 330 331char IfConverter::ID = 0; 332 333char &llvm::IfConverterID = IfConverter::ID; 334 335INITIALIZE_PASS_BEGIN(IfConverter, DEBUG_TYPE, "If Converter", false, false) 336INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo) 337INITIALIZE_PASS_END(IfConverter, DEBUG_TYPE, "If Converter", false, false) 338 339bool IfConverter::runOnMachineFunction(MachineFunction &MF) { 340 if (skipFunction(MF.getFunction()) || (PredicateFtor && !PredicateFtor(MF))) 341 return false; 342 343 const TargetSubtargetInfo &ST = MF.getSubtarget(); 344 TLI = ST.getTargetLowering(); 345 TII = ST.getInstrInfo(); 346 TRI = ST.getRegisterInfo(); 347 BranchFolder::MBFIWrapper MBFI(getAnalysis<MachineBlockFrequencyInfo>()); 348 MBPI = &getAnalysis<MachineBranchProbabilityInfo>(); 349 MRI = &MF.getRegInfo(); 350 SchedModel.init(ST.getSchedModel(), &ST, TII); 351 352 if (!TII) return false; 353 354 PreRegAlloc = MRI->isSSA(); 355 356 bool BFChange = false; 357 if (!PreRegAlloc) { 358 // Tail merge tend to expose more if-conversion opportunities. 359 BranchFolder BF(true, false, MBFI, *MBPI); 360 BFChange = BF.OptimizeFunction(MF, TII, ST.getRegisterInfo(), 361 getAnalysisIfAvailable<MachineModuleInfo>()); 362 } 363 364 DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum << ") \'" 365 << MF.getName() << "\'"); 366 367 if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { 368 DEBUG(dbgs() << " skipped\n"); 369 return false; 370 } 371 DEBUG(dbgs() << "\n"); 372 373 MF.RenumberBlocks(); 374 BBAnalysis.resize(MF.getNumBlockIDs()); 375 376 std::vector<std::unique_ptr<IfcvtToken>> Tokens; 377 MadeChange = false; 378 unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + 379 NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds; 380 while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) { 381 // Do an initial analysis for each basic block and find all the potential 382 // candidates to perform if-conversion. 383 bool Change = false; 384 AnalyzeBlocks(MF, Tokens); 385 while (!Tokens.empty()) { 386 std::unique_ptr<IfcvtToken> Token = std::move(Tokens.back()); 387 Tokens.pop_back(); 388 BBInfo &BBI = Token->BBI; 389 IfcvtKind Kind = Token->Kind; 390 unsigned NumDups = Token->NumDups; 391 unsigned NumDups2 = Token->NumDups2; 392 393 // If the block has been evicted out of the queue or it has already been 394 // marked dead (due to it being predicated), then skip it. 395 if (BBI.IsDone) 396 BBI.IsEnqueued = false; 397 if (!BBI.IsEnqueued) 398 continue; 399 400 BBI.IsEnqueued = false; 401 402 bool RetVal = false; 403 switch (Kind) { 404 default: llvm_unreachable("Unexpected!"); 405 case ICSimple: 406 case ICSimpleFalse: { 407 bool isFalse = Kind == ICSimpleFalse; 408 if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break; 409 DEBUG(dbgs() << "Ifcvt (Simple" 410 << (Kind == ICSimpleFalse ? " false" : "") 411 << "): " << printMBBReference(*BBI.BB) << " (" 412 << ((Kind == ICSimpleFalse) ? BBI.FalseBB->getNumber() 413 : BBI.TrueBB->getNumber()) 414 << ") "); 415 RetVal = IfConvertSimple(BBI, Kind); 416 DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 417 if (RetVal) { 418 if (isFalse) ++NumSimpleFalse; 419 else ++NumSimple; 420 } 421 break; 422 } 423 case ICTriangle: 424 case ICTriangleRev: 425 case ICTriangleFalse: 426 case ICTriangleFRev: { 427 bool isFalse = Kind == ICTriangleFalse; 428 bool isRev = (Kind == ICTriangleRev || Kind == ICTriangleFRev); 429 if (DisableTriangle && !isFalse && !isRev) break; 430 if (DisableTriangleR && !isFalse && isRev) break; 431 if (DisableTriangleF && isFalse && !isRev) break; 432 if (DisableTriangleFR && isFalse && isRev) break; 433 DEBUG(dbgs() << "Ifcvt (Triangle"); 434 if (isFalse) 435 DEBUG(dbgs() << " false"); 436 if (isRev) 437 DEBUG(dbgs() << " rev"); 438 DEBUG(dbgs() << "): " << printMBBReference(*BBI.BB) 439 << " (T:" << BBI.TrueBB->getNumber() 440 << ",F:" << BBI.FalseBB->getNumber() << ") "); 441 RetVal = IfConvertTriangle(BBI, Kind); 442 DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 443 if (RetVal) { 444 if (isFalse) { 445 if (isRev) ++NumTriangleFRev; 446 else ++NumTriangleFalse; 447 } else { 448 if (isRev) ++NumTriangleRev; 449 else ++NumTriangle; 450 } 451 } 452 break; 453 } 454 case ICDiamond: 455 if (DisableDiamond) break; 456 DEBUG(dbgs() << "Ifcvt (Diamond): " << printMBBReference(*BBI.BB) 457 << " (T:" << BBI.TrueBB->getNumber() 458 << ",F:" << BBI.FalseBB->getNumber() << ") "); 459 RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2, 460 Token->TClobbersPred, 461 Token->FClobbersPred); 462 DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 463 if (RetVal) ++NumDiamonds; 464 break; 465 case ICForkedDiamond: 466 if (DisableForkedDiamond) break; 467 DEBUG(dbgs() << "Ifcvt (Forked Diamond): " << printMBBReference(*BBI.BB) 468 << " (T:" << BBI.TrueBB->getNumber() 469 << ",F:" << BBI.FalseBB->getNumber() << ") "); 470 RetVal = IfConvertForkedDiamond(BBI, Kind, NumDups, NumDups2, 471 Token->TClobbersPred, 472 Token->FClobbersPred); 473 DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); 474 if (RetVal) ++NumForkedDiamonds; 475 break; 476 } 477 478 if (RetVal && MRI->tracksLiveness()) 479 recomputeLivenessFlags(*BBI.BB); 480 481 Change |= RetVal; 482 483 NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev + 484 NumTriangleFalse + NumTriangleFRev + NumDiamonds; 485 if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit) 486 break; 487 } 488 489 if (!Change) 490 break; 491 MadeChange |= Change; 492 } 493 494 Tokens.clear(); 495 BBAnalysis.clear(); 496 497 if (MadeChange && IfCvtBranchFold) { 498 BranchFolder BF(false, false, MBFI, *MBPI); 499 BF.OptimizeFunction(MF, TII, MF.getSubtarget().getRegisterInfo(), 500 getAnalysisIfAvailable<MachineModuleInfo>()); 501 } 502 503 MadeChange |= BFChange; 504 return MadeChange; 505} 506 507/// BB has a fallthrough. Find its 'false' successor given its 'true' successor. 508static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, 509 MachineBasicBlock *TrueBB) { 510 for (MachineBasicBlock *SuccBB : BB->successors()) { 511 if (SuccBB != TrueBB) 512 return SuccBB; 513 } 514 return nullptr; 515} 516 517/// Reverse the condition of the end of the block branch. Swap block's 'true' 518/// and 'false' successors. 519bool IfConverter::reverseBranchCondition(BBInfo &BBI) const { 520 DebugLoc dl; // FIXME: this is nowhere 521 if (!TII->reverseBranchCondition(BBI.BrCond)) { 522 TII->removeBranch(*BBI.BB); 523 TII->insertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl); 524 std::swap(BBI.TrueBB, BBI.FalseBB); 525 return true; 526 } 527 return false; 528} 529 530/// Returns the next block in the function blocks ordering. If it is the end, 531/// returns NULL. 532static inline MachineBasicBlock *getNextBlock(MachineBasicBlock &MBB) { 533 MachineFunction::iterator I = MBB.getIterator(); 534 MachineFunction::iterator E = MBB.getParent()->end(); 535 if (++I == E) 536 return nullptr; 537 return &*I; 538} 539 540/// Returns true if the 'true' block (along with its predecessor) forms a valid 541/// simple shape for ifcvt. It also returns the number of instructions that the 542/// ifcvt would need to duplicate if performed in Dups. 543bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups, 544 BranchProbability Prediction) const { 545 Dups = 0; 546 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 547 return false; 548 549 if (TrueBBI.IsBrAnalyzable) 550 return false; 551 552 if (TrueBBI.BB->pred_size() > 1) { 553 if (TrueBBI.CannotBeCopied || 554 !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize, 555 Prediction)) 556 return false; 557 Dups = TrueBBI.NonPredSize; 558 } 559 560 return true; 561} 562 563/// Returns true if the 'true' and 'false' blocks (along with their common 564/// predecessor) forms a valid triangle shape for ifcvt. If 'FalseBranch' is 565/// true, it checks if 'true' block's false branch branches to the 'false' block 566/// rather than the other way around. It also returns the number of instructions 567/// that the ifcvt would need to duplicate if performed in 'Dups'. 568bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 569 bool FalseBranch, unsigned &Dups, 570 BranchProbability Prediction) const { 571 Dups = 0; 572 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) 573 return false; 574 575 if (TrueBBI.BB->pred_size() > 1) { 576 if (TrueBBI.CannotBeCopied) 577 return false; 578 579 unsigned Size = TrueBBI.NonPredSize; 580 if (TrueBBI.IsBrAnalyzable) { 581 if (TrueBBI.TrueBB && TrueBBI.BrCond.empty()) 582 // Ends with an unconditional branch. It will be removed. 583 --Size; 584 else { 585 MachineBasicBlock *FExit = FalseBranch 586 ? TrueBBI.TrueBB : TrueBBI.FalseBB; 587 if (FExit) 588 // Require a conditional branch 589 ++Size; 590 } 591 } 592 if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, Prediction)) 593 return false; 594 Dups = Size; 595 } 596 597 MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB; 598 if (!TExit && blockAlwaysFallThrough(TrueBBI)) { 599 MachineFunction::iterator I = TrueBBI.BB->getIterator(); 600 if (++I == TrueBBI.BB->getParent()->end()) 601 return false; 602 TExit = &*I; 603 } 604 return TExit && TExit == FalseBBI.BB; 605} 606 607/// Count duplicated instructions and move the iterators to show where they 608/// are. 609/// @param TIB True Iterator Begin 610/// @param FIB False Iterator Begin 611/// These two iterators initially point to the first instruction of the two 612/// blocks, and finally point to the first non-shared instruction. 613/// @param TIE True Iterator End 614/// @param FIE False Iterator End 615/// These two iterators initially point to End() for the two blocks() and 616/// finally point to the first shared instruction in the tail. 617/// Upon return [TIB, TIE), and [FIB, FIE) mark the un-duplicated portions of 618/// two blocks. 619/// @param Dups1 count of duplicated instructions at the beginning of the 2 620/// blocks. 621/// @param Dups2 count of duplicated instructions at the end of the 2 blocks. 622/// @param SkipUnconditionalBranches if true, Don't make sure that 623/// unconditional branches at the end of the blocks are the same. True is 624/// passed when the blocks are analyzable to allow for fallthrough to be 625/// handled. 626/// @return false if the shared portion prevents if conversion. 627bool IfConverter::CountDuplicatedInstructions( 628 MachineBasicBlock::iterator &TIB, 629 MachineBasicBlock::iterator &FIB, 630 MachineBasicBlock::iterator &TIE, 631 MachineBasicBlock::iterator &FIE, 632 unsigned &Dups1, unsigned &Dups2, 633 MachineBasicBlock &TBB, MachineBasicBlock &FBB, 634 bool SkipUnconditionalBranches) const { 635 while (TIB != TIE && FIB != FIE) { 636 // Skip dbg_value instructions. These do not count. 637 TIB = skipDebugInstructionsForward(TIB, TIE); 638 FIB = skipDebugInstructionsForward(FIB, FIE); 639 if (TIB == TIE || FIB == FIE) 640 break; 641 if (!TIB->isIdenticalTo(*FIB)) 642 break; 643 // A pred-clobbering instruction in the shared portion prevents 644 // if-conversion. 645 std::vector<MachineOperand> PredDefs; 646 if (TII->DefinesPredicate(*TIB, PredDefs)) 647 return false; 648 // If we get all the way to the branch instructions, don't count them. 649 if (!TIB->isBranch()) 650 ++Dups1; 651 ++TIB; 652 ++FIB; 653 } 654 655 // Check for already containing all of the block. 656 if (TIB == TIE || FIB == FIE) 657 return true; 658 // Now, in preparation for counting duplicate instructions at the ends of the 659 // blocks, switch to reverse_iterators. Note that getReverse() returns an 660 // iterator that points to the same instruction, unlike std::reverse_iterator. 661 // We have to do our own shifting so that we get the same range. 662 MachineBasicBlock::reverse_iterator RTIE = std::next(TIE.getReverse()); 663 MachineBasicBlock::reverse_iterator RFIE = std::next(FIE.getReverse()); 664 const MachineBasicBlock::reverse_iterator RTIB = std::next(TIB.getReverse()); 665 const MachineBasicBlock::reverse_iterator RFIB = std::next(FIB.getReverse()); 666 667 if (!TBB.succ_empty() || !FBB.succ_empty()) { 668 if (SkipUnconditionalBranches) { 669 while (RTIE != RTIB && RTIE->isUnconditionalBranch()) 670 ++RTIE; 671 while (RFIE != RFIB && RFIE->isUnconditionalBranch()) 672 ++RFIE; 673 } 674 } 675 676 // Count duplicate instructions at the ends of the blocks. 677 while (RTIE != RTIB && RFIE != RFIB) { 678 // Skip dbg_value instructions. These do not count. 679 // Note that these are reverse iterators going forward. 680 RTIE = skipDebugInstructionsForward(RTIE, RTIB); 681 RFIE = skipDebugInstructionsForward(RFIE, RFIB); 682 if (RTIE == RTIB || RFIE == RFIB) 683 break; 684 if (!RTIE->isIdenticalTo(*RFIE)) 685 break; 686 // We have to verify that any branch instructions are the same, and then we 687 // don't count them toward the # of duplicate instructions. 688 if (!RTIE->isBranch()) 689 ++Dups2; 690 ++RTIE; 691 ++RFIE; 692 } 693 TIE = std::next(RTIE.getReverse()); 694 FIE = std::next(RFIE.getReverse()); 695 return true; 696} 697 698/// RescanInstructions - Run ScanInstructions on a pair of blocks. 699/// @param TIB - True Iterator Begin, points to first non-shared instruction 700/// @param FIB - False Iterator Begin, points to first non-shared instruction 701/// @param TIE - True Iterator End, points past last non-shared instruction 702/// @param FIE - False Iterator End, points past last non-shared instruction 703/// @param TrueBBI - BBInfo to update for the true block. 704/// @param FalseBBI - BBInfo to update for the false block. 705/// @returns - false if either block cannot be predicated or if both blocks end 706/// with a predicate-clobbering instruction. 707bool IfConverter::RescanInstructions( 708 MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB, 709 MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE, 710 BBInfo &TrueBBI, BBInfo &FalseBBI) const { 711 bool BranchUnpredicable = true; 712 TrueBBI.IsUnpredicable = FalseBBI.IsUnpredicable = false; 713 ScanInstructions(TrueBBI, TIB, TIE, BranchUnpredicable); 714 if (TrueBBI.IsUnpredicable) 715 return false; 716 ScanInstructions(FalseBBI, FIB, FIE, BranchUnpredicable); 717 if (FalseBBI.IsUnpredicable) 718 return false; 719 if (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) 720 return false; 721 return true; 722} 723 724#ifndef NDEBUG 725static void verifySameBranchInstructions( 726 MachineBasicBlock *MBB1, 727 MachineBasicBlock *MBB2) { 728 const MachineBasicBlock::reverse_iterator B1 = MBB1->rend(); 729 const MachineBasicBlock::reverse_iterator B2 = MBB2->rend(); 730 MachineBasicBlock::reverse_iterator E1 = MBB1->rbegin(); 731 MachineBasicBlock::reverse_iterator E2 = MBB2->rbegin(); 732 while (E1 != B1 && E2 != B2) { 733 skipDebugInstructionsForward(E1, B1); 734 skipDebugInstructionsForward(E2, B2); 735 if (E1 == B1 && E2 == B2) 736 break; 737 738 if (E1 == B1) { 739 assert(!E2->isBranch() && "Branch mis-match, one block is empty."); 740 break; 741 } 742 if (E2 == B2) { 743 assert(!E1->isBranch() && "Branch mis-match, one block is empty."); 744 break; 745 } 746 747 if (E1->isBranch() || E2->isBranch()) 748 assert(E1->isIdenticalTo(*E2) && 749 "Branch mis-match, branch instructions don't match."); 750 else 751 break; 752 ++E1; 753 ++E2; 754 } 755} 756#endif 757 758/// ValidForkedDiamond - Returns true if the 'true' and 'false' blocks (along 759/// with their common predecessor) form a diamond if a common tail block is 760/// extracted. 761/// While not strictly a diamond, this pattern would form a diamond if 762/// tail-merging had merged the shared tails. 763/// EBB 764/// _/ \_ 765/// | | 766/// TBB FBB 767/// / \ / \ 768/// FalseBB TrueBB FalseBB 769/// Currently only handles analyzable branches. 770/// Specifically excludes actual diamonds to avoid overlap. 771bool IfConverter::ValidForkedDiamond( 772 BBInfo &TrueBBI, BBInfo &FalseBBI, 773 unsigned &Dups1, unsigned &Dups2, 774 BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const { 775 Dups1 = Dups2 = 0; 776 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || 777 FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) 778 return false; 779 780 if (!TrueBBI.IsBrAnalyzable || !FalseBBI.IsBrAnalyzable) 781 return false; 782 // Don't IfConvert blocks that can't be folded into their predecessor. 783 if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) 784 return false; 785 786 // This function is specifically looking for conditional tails, as 787 // unconditional tails are already handled by the standard diamond case. 788 if (TrueBBI.BrCond.size() == 0 || 789 FalseBBI.BrCond.size() == 0) 790 return false; 791 792 MachineBasicBlock *TT = TrueBBI.TrueBB; 793 MachineBasicBlock *TF = TrueBBI.FalseBB; 794 MachineBasicBlock *FT = FalseBBI.TrueBB; 795 MachineBasicBlock *FF = FalseBBI.FalseBB; 796 797 if (!TT) 798 TT = getNextBlock(*TrueBBI.BB); 799 if (!TF) 800 TF = getNextBlock(*TrueBBI.BB); 801 if (!FT) 802 FT = getNextBlock(*FalseBBI.BB); 803 if (!FF) 804 FF = getNextBlock(*FalseBBI.BB); 805 806 if (!TT || !TF) 807 return false; 808 809 // Check successors. If they don't match, bail. 810 if (!((TT == FT && TF == FF) || (TF == FT && TT == FF))) 811 return false; 812 813 bool FalseReversed = false; 814 if (TF == FT && TT == FF) { 815 // If the branches are opposing, but we can't reverse, don't do it. 816 if (!FalseBBI.IsBrReversible) 817 return false; 818 FalseReversed = true; 819 reverseBranchCondition(FalseBBI); 820 } 821 auto UnReverseOnExit = make_scope_exit([&]() { 822 if (FalseReversed) 823 reverseBranchCondition(FalseBBI); 824 }); 825 826 // Count duplicate instructions at the beginning of the true and false blocks. 827 MachineBasicBlock::iterator TIB = TrueBBI.BB->begin(); 828 MachineBasicBlock::iterator FIB = FalseBBI.BB->begin(); 829 MachineBasicBlock::iterator TIE = TrueBBI.BB->end(); 830 MachineBasicBlock::iterator FIE = FalseBBI.BB->end(); 831 if(!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, 832 *TrueBBI.BB, *FalseBBI.BB, 833 /* SkipUnconditionalBranches */ true)) 834 return false; 835 836 TrueBBICalc.BB = TrueBBI.BB; 837 FalseBBICalc.BB = FalseBBI.BB; 838 if (!RescanInstructions(TIB, FIB, TIE, FIE, TrueBBICalc, FalseBBICalc)) 839 return false; 840 841 // The size is used to decide whether to if-convert, and the shared portions 842 // are subtracted off. Because of the subtraction, we just use the size that 843 // was calculated by the original ScanInstructions, as it is correct. 844 TrueBBICalc.NonPredSize = TrueBBI.NonPredSize; 845 FalseBBICalc.NonPredSize = FalseBBI.NonPredSize; 846 return true; 847} 848 849/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along 850/// with their common predecessor) forms a valid diamond shape for ifcvt. 851bool IfConverter::ValidDiamond( 852 BBInfo &TrueBBI, BBInfo &FalseBBI, 853 unsigned &Dups1, unsigned &Dups2, 854 BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const { 855 Dups1 = Dups2 = 0; 856 if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || 857 FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) 858 return false; 859 860 MachineBasicBlock *TT = TrueBBI.TrueBB; 861 MachineBasicBlock *FT = FalseBBI.TrueBB; 862 863 if (!TT && blockAlwaysFallThrough(TrueBBI)) 864 TT = getNextBlock(*TrueBBI.BB); 865 if (!FT && blockAlwaysFallThrough(FalseBBI)) 866 FT = getNextBlock(*FalseBBI.BB); 867 if (TT != FT) 868 return false; 869 if (!TT && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable)) 870 return false; 871 if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) 872 return false; 873 874 // FIXME: Allow true block to have an early exit? 875 if (TrueBBI.FalseBB || FalseBBI.FalseBB) 876 return false; 877 878 // Count duplicate instructions at the beginning and end of the true and 879 // false blocks. 880 // Skip unconditional branches only if we are considering an analyzable 881 // diamond. Otherwise the branches must be the same. 882 bool SkipUnconditionalBranches = 883 TrueBBI.IsBrAnalyzable && FalseBBI.IsBrAnalyzable; 884 MachineBasicBlock::iterator TIB = TrueBBI.BB->begin(); 885 MachineBasicBlock::iterator FIB = FalseBBI.BB->begin(); 886 MachineBasicBlock::iterator TIE = TrueBBI.BB->end(); 887 MachineBasicBlock::iterator FIE = FalseBBI.BB->end(); 888 if(!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, 889 *TrueBBI.BB, *FalseBBI.BB, 890 SkipUnconditionalBranches)) 891 return false; 892 893 TrueBBICalc.BB = TrueBBI.BB; 894 FalseBBICalc.BB = FalseBBI.BB; 895 if (!RescanInstructions(TIB, FIB, TIE, FIE, TrueBBICalc, FalseBBICalc)) 896 return false; 897 // The size is used to decide whether to if-convert, and the shared portions 898 // are subtracted off. Because of the subtraction, we just use the size that 899 // was calculated by the original ScanInstructions, as it is correct. 900 TrueBBICalc.NonPredSize = TrueBBI.NonPredSize; 901 FalseBBICalc.NonPredSize = FalseBBI.NonPredSize; 902 return true; 903} 904 905/// AnalyzeBranches - Look at the branches at the end of a block to determine if 906/// the block is predicable. 907void IfConverter::AnalyzeBranches(BBInfo &BBI) { 908 if (BBI.IsDone) 909 return; 910 911 BBI.TrueBB = BBI.FalseBB = nullptr; 912 BBI.BrCond.clear(); 913 BBI.IsBrAnalyzable = 914 !TII->analyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); 915 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 916 BBI.IsBrReversible = (RevCond.size() == 0) || 917 !TII->reverseBranchCondition(RevCond); 918 BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == nullptr; 919 920 if (BBI.BrCond.size()) { 921 // No false branch. This BB must end with a conditional branch and a 922 // fallthrough. 923 if (!BBI.FalseBB) 924 BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB); 925 if (!BBI.FalseBB) { 926 // Malformed bcc? True and false blocks are the same? 927 BBI.IsUnpredicable = true; 928 } 929 } 930} 931 932/// ScanInstructions - Scan all the instructions in the block to determine if 933/// the block is predicable. In most cases, that means all the instructions 934/// in the block are isPredicable(). Also checks if the block contains any 935/// instruction which can clobber a predicate (e.g. condition code register). 936/// If so, the block is not predicable unless it's the last instruction. 937void IfConverter::ScanInstructions(BBInfo &BBI, 938 MachineBasicBlock::iterator &Begin, 939 MachineBasicBlock::iterator &End, 940 bool BranchUnpredicable) const { 941 if (BBI.IsDone || BBI.IsUnpredicable) 942 return; 943 944 bool AlreadyPredicated = !BBI.Predicate.empty(); 945 946 BBI.NonPredSize = 0; 947 BBI.ExtraCost = 0; 948 BBI.ExtraCost2 = 0; 949 BBI.ClobbersPred = false; 950 for (MachineInstr &MI : make_range(Begin, End)) { 951 if (MI.isDebugValue()) 952 continue; 953 954 // It's unsafe to duplicate convergent instructions in this context, so set 955 // BBI.CannotBeCopied to true if MI is convergent. To see why, consider the 956 // following CFG, which is subject to our "simple" transformation. 957 // 958 // BB0 // if (c1) goto BB1; else goto BB2; 959 // / \ 960 // BB1 | 961 // | BB2 // if (c2) goto TBB; else goto FBB; 962 // | / | 963 // | / | 964 // TBB | 965 // | | 966 // | FBB 967 // | 968 // exit 969 // 970 // Suppose we want to move TBB's contents up into BB1 and BB2 (in BB1 they'd 971 // be unconditional, and in BB2, they'd be predicated upon c2), and suppose 972 // TBB contains a convergent instruction. This is safe iff doing so does 973 // not add a control-flow dependency to the convergent instruction -- i.e., 974 // it's safe iff the set of control flows that leads us to the convergent 975 // instruction does not get smaller after the transformation. 976 // 977 // Originally we executed TBB if c1 || c2. After the transformation, there 978 // are two copies of TBB's instructions. We get to the first if c1, and we 979 // get to the second if !c1 && c2. 980 // 981 // There are clearly fewer ways to satisfy the condition "c1" than 982 // "c1 || c2". Since we've shrunk the set of control flows which lead to 983 // our convergent instruction, the transformation is unsafe. 984 if (MI.isNotDuplicable() || MI.isConvergent()) 985 BBI.CannotBeCopied = true; 986 987 bool isPredicated = TII->isPredicated(MI); 988 bool isCondBr = BBI.IsBrAnalyzable && MI.isConditionalBranch(); 989 990 if (BranchUnpredicable && MI.isBranch()) { 991 BBI.IsUnpredicable = true; 992 return; 993 } 994 995 // A conditional branch is not predicable, but it may be eliminated. 996 if (isCondBr) 997 continue; 998 999 if (!isPredicated) { 1000 BBI.NonPredSize++; 1001 unsigned ExtraPredCost = TII->getPredicationCost(MI); 1002 unsigned NumCycles = SchedModel.computeInstrLatency(&MI, false); 1003 if (NumCycles > 1) 1004 BBI.ExtraCost += NumCycles-1; 1005 BBI.ExtraCost2 += ExtraPredCost; 1006 } else if (!AlreadyPredicated) { 1007 // FIXME: This instruction is already predicated before the 1008 // if-conversion pass. It's probably something like a conditional move. 1009 // Mark this block unpredicable for now. 1010 BBI.IsUnpredicable = true; 1011 return; 1012 } 1013 1014 if (BBI.ClobbersPred && !isPredicated) { 1015 // Predicate modification instruction should end the block (except for 1016 // already predicated instructions and end of block branches). 1017 // Predicate may have been modified, the subsequent (currently) 1018 // unpredicated instructions cannot be correctly predicated. 1019 BBI.IsUnpredicable = true; 1020 return; 1021 } 1022 1023 // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are 1024 // still potentially predicable. 1025 std::vector<MachineOperand> PredDefs; 1026 if (TII->DefinesPredicate(MI, PredDefs)) 1027 BBI.ClobbersPred = true; 1028 1029 if (!TII->isPredicable(MI)) { 1030 BBI.IsUnpredicable = true; 1031 return; 1032 } 1033 } 1034} 1035 1036/// Determine if the block is a suitable candidate to be predicated by the 1037/// specified predicate. 1038/// @param BBI BBInfo for the block to check 1039/// @param Pred Predicate array for the branch that leads to BBI 1040/// @param isTriangle true if the Analysis is for a triangle 1041/// @param RevBranch true if Reverse(Pred) leads to BBI (e.g. BBI is the false 1042/// case 1043/// @param hasCommonTail true if BBI shares a tail with a sibling block that 1044/// contains any instruction that would make the block unpredicable. 1045bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, 1046 SmallVectorImpl<MachineOperand> &Pred, 1047 bool isTriangle, bool RevBranch, 1048 bool hasCommonTail) { 1049 // If the block is dead or unpredicable, then it cannot be predicated. 1050 // Two blocks may share a common unpredicable tail, but this doesn't prevent 1051 // them from being if-converted. The non-shared portion is assumed to have 1052 // been checked 1053 if (BBI.IsDone || (BBI.IsUnpredicable && !hasCommonTail)) 1054 return false; 1055 1056 // If it is already predicated but we couldn't analyze its terminator, the 1057 // latter might fallthrough, but we can't determine where to. 1058 // Conservatively avoid if-converting again. 1059 if (BBI.Predicate.size() && !BBI.IsBrAnalyzable) 1060 return false; 1061 1062 // If it is already predicated, check if the new predicate subsumes 1063 // its predicate. 1064 if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate)) 1065 return false; 1066 1067 if (!hasCommonTail && BBI.BrCond.size()) { 1068 if (!isTriangle) 1069 return false; 1070 1071 // Test predicate subsumption. 1072 SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end()); 1073 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 1074 if (RevBranch) { 1075 if (TII->reverseBranchCondition(Cond)) 1076 return false; 1077 } 1078 if (TII->reverseBranchCondition(RevPred) || 1079 !TII->SubsumesPredicate(Cond, RevPred)) 1080 return false; 1081 } 1082 1083 return true; 1084} 1085 1086/// Analyze the structure of the sub-CFG starting from the specified block. 1087/// Record its successors and whether it looks like an if-conversion candidate. 1088void IfConverter::AnalyzeBlock( 1089 MachineBasicBlock &MBB, std::vector<std::unique_ptr<IfcvtToken>> &Tokens) { 1090 struct BBState { 1091 BBState(MachineBasicBlock &MBB) : MBB(&MBB), SuccsAnalyzed(false) {} 1092 MachineBasicBlock *MBB; 1093 1094 /// This flag is true if MBB's successors have been analyzed. 1095 bool SuccsAnalyzed; 1096 }; 1097 1098 // Push MBB to the stack. 1099 SmallVector<BBState, 16> BBStack(1, MBB); 1100 1101 while (!BBStack.empty()) { 1102 BBState &State = BBStack.back(); 1103 MachineBasicBlock *BB = State.MBB; 1104 BBInfo &BBI = BBAnalysis[BB->getNumber()]; 1105 1106 if (!State.SuccsAnalyzed) { 1107 if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed) { 1108 BBStack.pop_back(); 1109 continue; 1110 } 1111 1112 BBI.BB = BB; 1113 BBI.IsBeingAnalyzed = true; 1114 1115 AnalyzeBranches(BBI); 1116 MachineBasicBlock::iterator Begin = BBI.BB->begin(); 1117 MachineBasicBlock::iterator End = BBI.BB->end(); 1118 ScanInstructions(BBI, Begin, End); 1119 1120 // Unanalyzable or ends with fallthrough or unconditional branch, or if is 1121 // not considered for ifcvt anymore. 1122 if (!BBI.IsBrAnalyzable || BBI.BrCond.empty() || BBI.IsDone) { 1123 BBI.IsBeingAnalyzed = false; 1124 BBI.IsAnalyzed = true; 1125 BBStack.pop_back(); 1126 continue; 1127 } 1128 1129 // Do not ifcvt if either path is a back edge to the entry block. 1130 if (BBI.TrueBB == BB || BBI.FalseBB == BB) { 1131 BBI.IsBeingAnalyzed = false; 1132 BBI.IsAnalyzed = true; 1133 BBStack.pop_back(); 1134 continue; 1135 } 1136 1137 // Do not ifcvt if true and false fallthrough blocks are the same. 1138 if (!BBI.FalseBB) { 1139 BBI.IsBeingAnalyzed = false; 1140 BBI.IsAnalyzed = true; 1141 BBStack.pop_back(); 1142 continue; 1143 } 1144 1145 // Push the False and True blocks to the stack. 1146 State.SuccsAnalyzed = true; 1147 BBStack.push_back(*BBI.FalseBB); 1148 BBStack.push_back(*BBI.TrueBB); 1149 continue; 1150 } 1151 1152 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1153 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1154 1155 if (TrueBBI.IsDone && FalseBBI.IsDone) { 1156 BBI.IsBeingAnalyzed = false; 1157 BBI.IsAnalyzed = true; 1158 BBStack.pop_back(); 1159 continue; 1160 } 1161 1162 SmallVector<MachineOperand, 4> 1163 RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 1164 bool CanRevCond = !TII->reverseBranchCondition(RevCond); 1165 1166 unsigned Dups = 0; 1167 unsigned Dups2 = 0; 1168 bool TNeedSub = !TrueBBI.Predicate.empty(); 1169 bool FNeedSub = !FalseBBI.Predicate.empty(); 1170 bool Enqueued = false; 1171 1172 BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB); 1173 1174 if (CanRevCond) { 1175 BBInfo TrueBBICalc, FalseBBICalc; 1176 auto feasibleDiamond = [&]() { 1177 bool MeetsSize = MeetIfcvtSizeLimit( 1178 *TrueBBI.BB, (TrueBBICalc.NonPredSize - (Dups + Dups2) + 1179 TrueBBICalc.ExtraCost), TrueBBICalc.ExtraCost2, 1180 *FalseBBI.BB, (FalseBBICalc.NonPredSize - (Dups + Dups2) + 1181 FalseBBICalc.ExtraCost), FalseBBICalc.ExtraCost2, 1182 Prediction); 1183 bool TrueFeasible = FeasibilityAnalysis(TrueBBI, BBI.BrCond, 1184 /* IsTriangle */ false, /* RevCond */ false, 1185 /* hasCommonTail */ true); 1186 bool FalseFeasible = FeasibilityAnalysis(FalseBBI, RevCond, 1187 /* IsTriangle */ false, /* RevCond */ false, 1188 /* hasCommonTail */ true); 1189 return MeetsSize && TrueFeasible && FalseFeasible; 1190 }; 1191 1192 if (ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2, 1193 TrueBBICalc, FalseBBICalc)) { 1194 if (feasibleDiamond()) { 1195 // Diamond: 1196 // EBB 1197 // / \_ 1198 // | | 1199 // TBB FBB 1200 // \ / 1201 // TailBB 1202 // Note TailBB can be empty. 1203 Tokens.push_back(llvm::make_unique<IfcvtToken>( 1204 BBI, ICDiamond, TNeedSub | FNeedSub, Dups, Dups2, 1205 (bool) TrueBBICalc.ClobbersPred, (bool) FalseBBICalc.ClobbersPred)); 1206 Enqueued = true; 1207 } 1208 } else if (ValidForkedDiamond(TrueBBI, FalseBBI, Dups, Dups2, 1209 TrueBBICalc, FalseBBICalc)) { 1210 if (feasibleDiamond()) { 1211 // ForkedDiamond: 1212 // if TBB and FBB have a common tail that includes their conditional 1213 // branch instructions, then we can If Convert this pattern. 1214 // EBB 1215 // _/ \_ 1216 // | | 1217 // TBB FBB 1218 // / \ / \ 1219 // FalseBB TrueBB FalseBB 1220 // 1221 Tokens.push_back(llvm::make_unique<IfcvtToken>( 1222 BBI, ICForkedDiamond, TNeedSub | FNeedSub, Dups, Dups2, 1223 (bool) TrueBBICalc.ClobbersPred, (bool) FalseBBICalc.ClobbersPred)); 1224 Enqueued = true; 1225 } 1226 } 1227 } 1228 1229 if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) && 1230 MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, 1231 TrueBBI.ExtraCost2, Prediction) && 1232 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { 1233 // Triangle: 1234 // EBB 1235 // | \_ 1236 // | | 1237 // | TBB 1238 // | / 1239 // FBB 1240 Tokens.push_back( 1241 llvm::make_unique<IfcvtToken>(BBI, ICTriangle, TNeedSub, Dups)); 1242 Enqueued = true; 1243 } 1244 1245 if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction) && 1246 MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, 1247 TrueBBI.ExtraCost2, Prediction) && 1248 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) { 1249 Tokens.push_back( 1250 llvm::make_unique<IfcvtToken>(BBI, ICTriangleRev, TNeedSub, Dups)); 1251 Enqueued = true; 1252 } 1253 1254 if (ValidSimple(TrueBBI, Dups, Prediction) && 1255 MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, 1256 TrueBBI.ExtraCost2, Prediction) && 1257 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { 1258 // Simple (split, no rejoin): 1259 // EBB 1260 // | \_ 1261 // | | 1262 // | TBB---> exit 1263 // | 1264 // FBB 1265 Tokens.push_back( 1266 llvm::make_unique<IfcvtToken>(BBI, ICSimple, TNeedSub, Dups)); 1267 Enqueued = true; 1268 } 1269 1270 if (CanRevCond) { 1271 // Try the other path... 1272 if (ValidTriangle(FalseBBI, TrueBBI, false, Dups, 1273 Prediction.getCompl()) && 1274 MeetIfcvtSizeLimit(*FalseBBI.BB, 1275 FalseBBI.NonPredSize + FalseBBI.ExtraCost, 1276 FalseBBI.ExtraCost2, Prediction.getCompl()) && 1277 FeasibilityAnalysis(FalseBBI, RevCond, true)) { 1278 Tokens.push_back(llvm::make_unique<IfcvtToken>(BBI, ICTriangleFalse, 1279 FNeedSub, Dups)); 1280 Enqueued = true; 1281 } 1282 1283 if (ValidTriangle(FalseBBI, TrueBBI, true, Dups, 1284 Prediction.getCompl()) && 1285 MeetIfcvtSizeLimit(*FalseBBI.BB, 1286 FalseBBI.NonPredSize + FalseBBI.ExtraCost, 1287 FalseBBI.ExtraCost2, Prediction.getCompl()) && 1288 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { 1289 Tokens.push_back( 1290 llvm::make_unique<IfcvtToken>(BBI, ICTriangleFRev, FNeedSub, Dups)); 1291 Enqueued = true; 1292 } 1293 1294 if (ValidSimple(FalseBBI, Dups, Prediction.getCompl()) && 1295 MeetIfcvtSizeLimit(*FalseBBI.BB, 1296 FalseBBI.NonPredSize + FalseBBI.ExtraCost, 1297 FalseBBI.ExtraCost2, Prediction.getCompl()) && 1298 FeasibilityAnalysis(FalseBBI, RevCond)) { 1299 Tokens.push_back( 1300 llvm::make_unique<IfcvtToken>(BBI, ICSimpleFalse, FNeedSub, Dups)); 1301 Enqueued = true; 1302 } 1303 } 1304 1305 BBI.IsEnqueued = Enqueued; 1306 BBI.IsBeingAnalyzed = false; 1307 BBI.IsAnalyzed = true; 1308 BBStack.pop_back(); 1309 } 1310} 1311 1312/// Analyze all blocks and find entries for all if-conversion candidates. 1313void IfConverter::AnalyzeBlocks( 1314 MachineFunction &MF, std::vector<std::unique_ptr<IfcvtToken>> &Tokens) { 1315 for (MachineBasicBlock &MBB : MF) 1316 AnalyzeBlock(MBB, Tokens); 1317 1318 // Sort to favor more complex ifcvt scheme. 1319 std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp); 1320} 1321 1322/// Returns true either if ToMBB is the next block after MBB or that all the 1323/// intervening blocks are empty (given MBB can fall through to its next block). 1324static bool canFallThroughTo(MachineBasicBlock &MBB, MachineBasicBlock &ToMBB) { 1325 MachineFunction::iterator PI = MBB.getIterator(); 1326 MachineFunction::iterator I = std::next(PI); 1327 MachineFunction::iterator TI = ToMBB.getIterator(); 1328 MachineFunction::iterator E = MBB.getParent()->end(); 1329 while (I != TI) { 1330 // Check isSuccessor to avoid case where the next block is empty, but 1331 // it's not a successor. 1332 if (I == E || !I->empty() || !PI->isSuccessor(&*I)) 1333 return false; 1334 PI = I++; 1335 } 1336 // Finally see if the last I is indeed a successor to PI. 1337 return PI->isSuccessor(&*I); 1338} 1339 1340/// Invalidate predecessor BB info so it would be re-analyzed to determine if it 1341/// can be if-converted. If predecessor is already enqueued, dequeue it! 1342void IfConverter::InvalidatePreds(MachineBasicBlock &MBB) { 1343 for (const MachineBasicBlock *Predecessor : MBB.predecessors()) { 1344 BBInfo &PBBI = BBAnalysis[Predecessor->getNumber()]; 1345 if (PBBI.IsDone || PBBI.BB == &MBB) 1346 continue; 1347 PBBI.IsAnalyzed = false; 1348 PBBI.IsEnqueued = false; 1349 } 1350} 1351 1352/// Inserts an unconditional branch from \p MBB to \p ToMBB. 1353static void InsertUncondBranch(MachineBasicBlock &MBB, MachineBasicBlock &ToMBB, 1354 const TargetInstrInfo *TII) { 1355 DebugLoc dl; // FIXME: this is nowhere 1356 SmallVector<MachineOperand, 0> NoCond; 1357 TII->insertBranch(MBB, &ToMBB, nullptr, NoCond, dl); 1358} 1359 1360/// Behaves like LiveRegUnits::StepForward() but also adds implicit uses to all 1361/// values defined in MI which are also live/used by MI. 1362static void UpdatePredRedefs(MachineInstr &MI, LivePhysRegs &Redefs) { 1363 const TargetRegisterInfo *TRI = MI.getMF()->getSubtarget().getRegisterInfo(); 1364 1365 // Before stepping forward past MI, remember which regs were live 1366 // before MI. This is needed to set the Undef flag only when reg is 1367 // dead. 1368 SparseSet<unsigned> LiveBeforeMI; 1369 LiveBeforeMI.setUniverse(TRI->getNumRegs()); 1370 for (unsigned Reg : Redefs) 1371 LiveBeforeMI.insert(Reg); 1372 1373 SmallVector<std::pair<unsigned, const MachineOperand*>, 4> Clobbers; 1374 Redefs.stepForward(MI, Clobbers); 1375 1376 // Now add the implicit uses for each of the clobbered values. 1377 for (auto Clobber : Clobbers) { 1378 // FIXME: Const cast here is nasty, but better than making StepForward 1379 // take a mutable instruction instead of const. 1380 unsigned Reg = Clobber.first; 1381 MachineOperand &Op = const_cast<MachineOperand&>(*Clobber.second); 1382 MachineInstr *OpMI = Op.getParent(); 1383 MachineInstrBuilder MIB(*OpMI->getMF(), OpMI); 1384 if (Op.isRegMask()) { 1385 // First handle regmasks. They clobber any entries in the mask which 1386 // means that we need a def for those registers. 1387 if (LiveBeforeMI.count(Reg)) 1388 MIB.addReg(Reg, RegState::Implicit); 1389 1390 // We also need to add an implicit def of this register for the later 1391 // use to read from. 1392 // For the register allocator to have allocated a register clobbered 1393 // by the call which is used later, it must be the case that 1394 // the call doesn't return. 1395 MIB.addReg(Reg, RegState::Implicit | RegState::Define); 1396 continue; 1397 } 1398 if (LiveBeforeMI.count(Reg)) 1399 MIB.addReg(Reg, RegState::Implicit); 1400 else { 1401 bool HasLiveSubReg = false; 1402 for (MCSubRegIterator S(Reg, TRI); S.isValid(); ++S) { 1403 if (!LiveBeforeMI.count(*S)) 1404 continue; 1405 HasLiveSubReg = true; 1406 break; 1407 } 1408 if (HasLiveSubReg) 1409 MIB.addReg(Reg, RegState::Implicit); 1410 } 1411 } 1412} 1413 1414/// If convert a simple (split, no rejoin) sub-CFG. 1415bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) { 1416 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1417 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1418 BBInfo *CvtBBI = &TrueBBI; 1419 BBInfo *NextBBI = &FalseBBI; 1420 1421 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 1422 if (Kind == ICSimpleFalse) 1423 std::swap(CvtBBI, NextBBI); 1424 1425 MachineBasicBlock &CvtMBB = *CvtBBI->BB; 1426 MachineBasicBlock &NextMBB = *NextBBI->BB; 1427 if (CvtBBI->IsDone || 1428 (CvtBBI->CannotBeCopied && CvtMBB.pred_size() > 1)) { 1429 // Something has changed. It's no longer safe to predicate this block. 1430 BBI.IsAnalyzed = false; 1431 CvtBBI->IsAnalyzed = false; 1432 return false; 1433 } 1434 1435 if (CvtMBB.hasAddressTaken()) 1436 // Conservatively abort if-conversion if BB's address is taken. 1437 return false; 1438 1439 if (Kind == ICSimpleFalse) 1440 if (TII->reverseBranchCondition(Cond)) 1441 llvm_unreachable("Unable to reverse branch condition!"); 1442 1443 Redefs.init(*TRI); 1444 1445 if (MRI->tracksLiveness()) { 1446 // Initialize liveins to the first BB. These are potentiall redefined by 1447 // predicated instructions. 1448 Redefs.addLiveIns(CvtMBB); 1449 Redefs.addLiveIns(NextMBB); 1450 } 1451 1452 // Remove the branches from the entry so we can add the contents of the true 1453 // block to it. 1454 BBI.NonPredSize -= TII->removeBranch(*BBI.BB); 1455 1456 if (CvtMBB.pred_size() > 1) { 1457 // Copy instructions in the true block, predicate them, and add them to 1458 // the entry block. 1459 CopyAndPredicateBlock(BBI, *CvtBBI, Cond); 1460 1461 // Keep the CFG updated. 1462 BBI.BB->removeSuccessor(&CvtMBB, true); 1463 } else { 1464 // Predicate the instructions in the true block. 1465 PredicateBlock(*CvtBBI, CvtMBB.end(), Cond); 1466 1467 // Merge converted block into entry block. The BB to Cvt edge is removed 1468 // by MergeBlocks. 1469 MergeBlocks(BBI, *CvtBBI); 1470 } 1471 1472 bool IterIfcvt = true; 1473 if (!canFallThroughTo(*BBI.BB, NextMBB)) { 1474 InsertUncondBranch(*BBI.BB, NextMBB, TII); 1475 BBI.HasFallThrough = false; 1476 // Now ifcvt'd block will look like this: 1477 // BB: 1478 // ... 1479 // t, f = cmp 1480 // if t op 1481 // b BBf 1482 // 1483 // We cannot further ifcvt this block because the unconditional branch 1484 // will have to be predicated on the new condition, that will not be 1485 // available if cmp executes. 1486 IterIfcvt = false; 1487 } 1488 1489 // Update block info. BB can be iteratively if-converted. 1490 if (!IterIfcvt) 1491 BBI.IsDone = true; 1492 InvalidatePreds(*BBI.BB); 1493 CvtBBI->IsDone = true; 1494 1495 // FIXME: Must maintain LiveIns. 1496 return true; 1497} 1498 1499/// If convert a triangle sub-CFG. 1500bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) { 1501 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1502 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1503 BBInfo *CvtBBI = &TrueBBI; 1504 BBInfo *NextBBI = &FalseBBI; 1505 DebugLoc dl; // FIXME: this is nowhere 1506 1507 SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); 1508 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 1509 std::swap(CvtBBI, NextBBI); 1510 1511 MachineBasicBlock &CvtMBB = *CvtBBI->BB; 1512 MachineBasicBlock &NextMBB = *NextBBI->BB; 1513 if (CvtBBI->IsDone || 1514 (CvtBBI->CannotBeCopied && CvtMBB.pred_size() > 1)) { 1515 // Something has changed. It's no longer safe to predicate this block. 1516 BBI.IsAnalyzed = false; 1517 CvtBBI->IsAnalyzed = false; 1518 return false; 1519 } 1520 1521 if (CvtMBB.hasAddressTaken()) 1522 // Conservatively abort if-conversion if BB's address is taken. 1523 return false; 1524 1525 if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) 1526 if (TII->reverseBranchCondition(Cond)) 1527 llvm_unreachable("Unable to reverse branch condition!"); 1528 1529 if (Kind == ICTriangleRev || Kind == ICTriangleFRev) { 1530 if (reverseBranchCondition(*CvtBBI)) { 1531 // BB has been changed, modify its predecessors (except for this 1532 // one) so they don't get ifcvt'ed based on bad intel. 1533 for (MachineBasicBlock *PBB : CvtMBB.predecessors()) { 1534 if (PBB == BBI.BB) 1535 continue; 1536 BBInfo &PBBI = BBAnalysis[PBB->getNumber()]; 1537 if (PBBI.IsEnqueued) { 1538 PBBI.IsAnalyzed = false; 1539 PBBI.IsEnqueued = false; 1540 } 1541 } 1542 } 1543 } 1544 1545 // Initialize liveins to the first BB. These are potentially redefined by 1546 // predicated instructions. 1547 Redefs.init(*TRI); 1548 if (MRI->tracksLiveness()) { 1549 Redefs.addLiveIns(CvtMBB); 1550 Redefs.addLiveIns(NextMBB); 1551 } 1552 1553 bool HasEarlyExit = CvtBBI->FalseBB != nullptr; 1554 BranchProbability CvtNext, CvtFalse, BBNext, BBCvt; 1555 1556 if (HasEarlyExit) { 1557 // Get probabilities before modifying CvtMBB and BBI.BB. 1558 CvtNext = MBPI->getEdgeProbability(&CvtMBB, &NextMBB); 1559 CvtFalse = MBPI->getEdgeProbability(&CvtMBB, CvtBBI->FalseBB); 1560 BBNext = MBPI->getEdgeProbability(BBI.BB, &NextMBB); 1561 BBCvt = MBPI->getEdgeProbability(BBI.BB, &CvtMBB); 1562 } 1563 1564 // Remove the branches from the entry so we can add the contents of the true 1565 // block to it. 1566 BBI.NonPredSize -= TII->removeBranch(*BBI.BB); 1567 1568 if (CvtMBB.pred_size() > 1) { 1569 // Copy instructions in the true block, predicate them, and add them to 1570 // the entry block. 1571 CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true); 1572 } else { 1573 // Predicate the 'true' block after removing its branch. 1574 CvtBBI->NonPredSize -= TII->removeBranch(CvtMBB); 1575 PredicateBlock(*CvtBBI, CvtMBB.end(), Cond); 1576 1577 // Now merge the entry of the triangle with the true block. 1578 MergeBlocks(BBI, *CvtBBI, false); 1579 } 1580 1581 // Keep the CFG updated. 1582 BBI.BB->removeSuccessor(&CvtMBB, true); 1583 1584 // If 'true' block has a 'false' successor, add an exit branch to it. 1585 if (HasEarlyExit) { 1586 SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(), 1587 CvtBBI->BrCond.end()); 1588 if (TII->reverseBranchCondition(RevCond)) 1589 llvm_unreachable("Unable to reverse branch condition!"); 1590 1591 // Update the edge probability for both CvtBBI->FalseBB and NextBBI. 1592 // NewNext = New_Prob(BBI.BB, NextMBB) = 1593 // Prob(BBI.BB, NextMBB) + 1594 // Prob(BBI.BB, CvtMBB) * Prob(CvtMBB, NextMBB) 1595 // NewFalse = New_Prob(BBI.BB, CvtBBI->FalseBB) = 1596 // Prob(BBI.BB, CvtMBB) * Prob(CvtMBB, CvtBBI->FalseBB) 1597 auto NewTrueBB = getNextBlock(*BBI.BB); 1598 auto NewNext = BBNext + BBCvt * CvtNext; 1599 auto NewTrueBBIter = find(BBI.BB->successors(), NewTrueBB); 1600 if (NewTrueBBIter != BBI.BB->succ_end()) 1601 BBI.BB->setSuccProbability(NewTrueBBIter, NewNext); 1602 1603 auto NewFalse = BBCvt * CvtFalse; 1604 TII->insertBranch(*BBI.BB, CvtBBI->FalseBB, nullptr, RevCond, dl); 1605 BBI.BB->addSuccessor(CvtBBI->FalseBB, NewFalse); 1606 } 1607 1608 // Merge in the 'false' block if the 'false' block has no other 1609 // predecessors. Otherwise, add an unconditional branch to 'false'. 1610 bool FalseBBDead = false; 1611 bool IterIfcvt = true; 1612 bool isFallThrough = canFallThroughTo(*BBI.BB, NextMBB); 1613 if (!isFallThrough) { 1614 // Only merge them if the true block does not fallthrough to the false 1615 // block. By not merging them, we make it possible to iteratively 1616 // ifcvt the blocks. 1617 if (!HasEarlyExit && 1618 NextMBB.pred_size() == 1 && !NextBBI->HasFallThrough && 1619 !NextMBB.hasAddressTaken()) { 1620 MergeBlocks(BBI, *NextBBI); 1621 FalseBBDead = true; 1622 } else { 1623 InsertUncondBranch(*BBI.BB, NextMBB, TII); 1624 BBI.HasFallThrough = false; 1625 } 1626 // Mixed predicated and unpredicated code. This cannot be iteratively 1627 // predicated. 1628 IterIfcvt = false; 1629 } 1630 1631 // Update block info. BB can be iteratively if-converted. 1632 if (!IterIfcvt) 1633 BBI.IsDone = true; 1634 InvalidatePreds(*BBI.BB); 1635 CvtBBI->IsDone = true; 1636 if (FalseBBDead) 1637 NextBBI->IsDone = true; 1638 1639 // FIXME: Must maintain LiveIns. 1640 return true; 1641} 1642 1643/// Common code shared between diamond conversions. 1644/// \p BBI, \p TrueBBI, and \p FalseBBI form the diamond shape. 1645/// \p NumDups1 - number of shared instructions at the beginning of \p TrueBBI 1646/// and FalseBBI 1647/// \p NumDups2 - number of shared instructions at the end of \p TrueBBI 1648/// and \p FalseBBI 1649/// \p RemoveBranch - Remove the common branch of the two blocks before 1650/// predicating. Only false for unanalyzable fallthrough 1651/// cases. The caller will replace the branch if necessary. 1652/// \p MergeAddEdges - Add successor edges when merging blocks. Only false for 1653/// unanalyzable fallthrough 1654bool IfConverter::IfConvertDiamondCommon( 1655 BBInfo &BBI, BBInfo &TrueBBI, BBInfo &FalseBBI, 1656 unsigned NumDups1, unsigned NumDups2, 1657 bool TClobbersPred, bool FClobbersPred, 1658 bool RemoveBranch, bool MergeAddEdges) { 1659 1660 if (TrueBBI.IsDone || FalseBBI.IsDone || 1661 TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) { 1662 // Something has changed. It's no longer safe to predicate these blocks. 1663 BBI.IsAnalyzed = false; 1664 TrueBBI.IsAnalyzed = false; 1665 FalseBBI.IsAnalyzed = false; 1666 return false; 1667 } 1668 1669 if (TrueBBI.BB->hasAddressTaken() || FalseBBI.BB->hasAddressTaken()) 1670 // Conservatively abort if-conversion if either BB has its address taken. 1671 return false; 1672 1673 // Put the predicated instructions from the 'true' block before the 1674 // instructions from the 'false' block, unless the true block would clobber 1675 // the predicate, in which case, do the opposite. 1676 BBInfo *BBI1 = &TrueBBI; 1677 BBInfo *BBI2 = &FalseBBI; 1678 SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); 1679 if (TII->reverseBranchCondition(RevCond)) 1680 llvm_unreachable("Unable to reverse branch condition!"); 1681 SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond; 1682 SmallVector<MachineOperand, 4> *Cond2 = &RevCond; 1683 1684 // Figure out the more profitable ordering. 1685 bool DoSwap = false; 1686 if (TClobbersPred && !FClobbersPred) 1687 DoSwap = true; 1688 else if (!TClobbersPred && !FClobbersPred) { 1689 if (TrueBBI.NonPredSize > FalseBBI.NonPredSize) 1690 DoSwap = true; 1691 } else if (TClobbersPred && FClobbersPred) 1692 llvm_unreachable("Predicate info cannot be clobbered by both sides."); 1693 if (DoSwap) { 1694 std::swap(BBI1, BBI2); 1695 std::swap(Cond1, Cond2); 1696 } 1697 1698 // Remove the conditional branch from entry to the blocks. 1699 BBI.NonPredSize -= TII->removeBranch(*BBI.BB); 1700 1701 MachineBasicBlock &MBB1 = *BBI1->BB; 1702 MachineBasicBlock &MBB2 = *BBI2->BB; 1703 1704 // Initialize the Redefs: 1705 // - BB2 live-in regs need implicit uses before being redefined by BB1 1706 // instructions. 1707 // - BB1 live-out regs need implicit uses before being redefined by BB2 1708 // instructions. We start with BB1 live-ins so we have the live-out regs 1709 // after tracking the BB1 instructions. 1710 Redefs.init(*TRI); 1711 if (MRI->tracksLiveness()) { 1712 Redefs.addLiveIns(MBB1); 1713 Redefs.addLiveIns(MBB2); 1714 } 1715 1716 // Remove the duplicated instructions at the beginnings of both paths. 1717 // Skip dbg_value instructions 1718 MachineBasicBlock::iterator DI1 = MBB1.getFirstNonDebugInstr(); 1719 MachineBasicBlock::iterator DI2 = MBB2.getFirstNonDebugInstr(); 1720 BBI1->NonPredSize -= NumDups1; 1721 BBI2->NonPredSize -= NumDups1; 1722 1723 // Skip past the dups on each side separately since there may be 1724 // differing dbg_value entries. 1725 for (unsigned i = 0; i < NumDups1; ++DI1) { 1726 if (!DI1->isDebugValue()) 1727 ++i; 1728 } 1729 while (NumDups1 != 0) { 1730 ++DI2; 1731 if (!DI2->isDebugValue()) 1732 --NumDups1; 1733 } 1734 1735 if (MRI->tracksLiveness()) { 1736 for (const MachineInstr &MI : make_range(MBB1.begin(), DI1)) { 1737 SmallVector<std::pair<unsigned, const MachineOperand*>, 4> Dummy; 1738 Redefs.stepForward(MI, Dummy); 1739 } 1740 } 1741 BBI.BB->splice(BBI.BB->end(), &MBB1, MBB1.begin(), DI1); 1742 MBB2.erase(MBB2.begin(), DI2); 1743 1744 // The branches have been checked to match, so it is safe to remove the branch 1745 // in BB1 and rely on the copy in BB2 1746#ifndef NDEBUG 1747 // Unanalyzable branches must match exactly. Check that now. 1748 if (!BBI1->IsBrAnalyzable) 1749 verifySameBranchInstructions(&MBB1, &MBB2); 1750#endif 1751 BBI1->NonPredSize -= TII->removeBranch(*BBI1->BB); 1752 // Remove duplicated instructions. 1753 DI1 = MBB1.end(); 1754 for (unsigned i = 0; i != NumDups2; ) { 1755 // NumDups2 only counted non-dbg_value instructions, so this won't 1756 // run off the head of the list. 1757 assert(DI1 != MBB1.begin()); 1758 --DI1; 1759 // skip dbg_value instructions 1760 if (!DI1->isDebugValue()) 1761 ++i; 1762 } 1763 MBB1.erase(DI1, MBB1.end()); 1764 1765 DI2 = BBI2->BB->end(); 1766 // The branches have been checked to match. Skip over the branch in the false 1767 // block so that we don't try to predicate it. 1768 if (RemoveBranch) 1769 BBI2->NonPredSize -= TII->removeBranch(*BBI2->BB); 1770 else { 1771 do { 1772 assert(DI2 != MBB2.begin()); 1773 DI2--; 1774 } while (DI2->isBranch() || DI2->isDebugValue()); 1775 DI2++; 1776 } 1777 while (NumDups2 != 0) { 1778 // NumDups2 only counted non-dbg_value instructions, so this won't 1779 // run off the head of the list. 1780 assert(DI2 != MBB2.begin()); 1781 --DI2; 1782 // skip dbg_value instructions 1783 if (!DI2->isDebugValue()) 1784 --NumDups2; 1785 } 1786 1787 // Remember which registers would later be defined by the false block. 1788 // This allows us not to predicate instructions in the true block that would 1789 // later be re-defined. That is, rather than 1790 // subeq r0, r1, #1 1791 // addne r0, r1, #1 1792 // generate: 1793 // sub r0, r1, #1 1794 // addne r0, r1, #1 1795 SmallSet<unsigned, 4> RedefsByFalse; 1796 SmallSet<unsigned, 4> ExtUses; 1797 if (TII->isProfitableToUnpredicate(MBB1, MBB2)) { 1798 for (const MachineInstr &FI : make_range(MBB2.begin(), DI2)) { 1799 if (FI.isDebugValue()) 1800 continue; 1801 SmallVector<unsigned, 4> Defs; 1802 for (const MachineOperand &MO : FI.operands()) { 1803 if (!MO.isReg()) 1804 continue; 1805 unsigned Reg = MO.getReg(); 1806 if (!Reg) 1807 continue; 1808 if (MO.isDef()) { 1809 Defs.push_back(Reg); 1810 } else if (!RedefsByFalse.count(Reg)) { 1811 // These are defined before ctrl flow reach the 'false' instructions. 1812 // They cannot be modified by the 'true' instructions. 1813 for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true); 1814 SubRegs.isValid(); ++SubRegs) 1815 ExtUses.insert(*SubRegs); 1816 } 1817 } 1818 1819 for (unsigned Reg : Defs) { 1820 if (!ExtUses.count(Reg)) { 1821 for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true); 1822 SubRegs.isValid(); ++SubRegs) 1823 RedefsByFalse.insert(*SubRegs); 1824 } 1825 } 1826 } 1827 } 1828 1829 // Predicate the 'true' block. 1830 PredicateBlock(*BBI1, MBB1.end(), *Cond1, &RedefsByFalse); 1831 1832 // After predicating BBI1, if there is a predicated terminator in BBI1 and 1833 // a non-predicated in BBI2, then we don't want to predicate the one from 1834 // BBI2. The reason is that if we merged these blocks, we would end up with 1835 // two predicated terminators in the same block. 1836 if (!MBB2.empty() && (DI2 == MBB2.end())) { 1837 MachineBasicBlock::iterator BBI1T = MBB1.getFirstTerminator(); 1838 MachineBasicBlock::iterator BBI2T = MBB2.getFirstTerminator(); 1839 if (BBI1T != MBB1.end() && TII->isPredicated(*BBI1T) && 1840 BBI2T != MBB2.end() && !TII->isPredicated(*BBI2T)) 1841 --DI2; 1842 } 1843 1844 // Predicate the 'false' block. 1845 PredicateBlock(*BBI2, DI2, *Cond2); 1846 1847 // Merge the true block into the entry of the diamond. 1848 MergeBlocks(BBI, *BBI1, MergeAddEdges); 1849 MergeBlocks(BBI, *BBI2, MergeAddEdges); 1850 return true; 1851} 1852 1853/// If convert an almost-diamond sub-CFG where the true 1854/// and false blocks share a common tail. 1855bool IfConverter::IfConvertForkedDiamond( 1856 BBInfo &BBI, IfcvtKind Kind, 1857 unsigned NumDups1, unsigned NumDups2, 1858 bool TClobbersPred, bool FClobbersPred) { 1859 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1860 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1861 1862 // Save the debug location for later. 1863 DebugLoc dl; 1864 MachineBasicBlock::iterator TIE = TrueBBI.BB->getFirstTerminator(); 1865 if (TIE != TrueBBI.BB->end()) 1866 dl = TIE->getDebugLoc(); 1867 // Removing branches from both blocks is safe, because we have already 1868 // determined that both blocks have the same branch instructions. The branch 1869 // will be added back at the end, unpredicated. 1870 if (!IfConvertDiamondCommon( 1871 BBI, TrueBBI, FalseBBI, 1872 NumDups1, NumDups2, 1873 TClobbersPred, FClobbersPred, 1874 /* RemoveBranch */ true, /* MergeAddEdges */ true)) 1875 return false; 1876 1877 // Add back the branch. 1878 // Debug location saved above when removing the branch from BBI2 1879 TII->insertBranch(*BBI.BB, TrueBBI.TrueBB, TrueBBI.FalseBB, 1880 TrueBBI.BrCond, dl); 1881 1882 // Update block info. 1883 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; 1884 InvalidatePreds(*BBI.BB); 1885 1886 // FIXME: Must maintain LiveIns. 1887 return true; 1888} 1889 1890/// If convert a diamond sub-CFG. 1891bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, 1892 unsigned NumDups1, unsigned NumDups2, 1893 bool TClobbersPred, bool FClobbersPred) { 1894 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 1895 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 1896 MachineBasicBlock *TailBB = TrueBBI.TrueBB; 1897 1898 // True block must fall through or end with an unanalyzable terminator. 1899 if (!TailBB) { 1900 if (blockAlwaysFallThrough(TrueBBI)) 1901 TailBB = FalseBBI.TrueBB; 1902 assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!"); 1903 } 1904 1905 if (!IfConvertDiamondCommon( 1906 BBI, TrueBBI, FalseBBI, 1907 NumDups1, NumDups2, 1908 TClobbersPred, FClobbersPred, 1909 /* RemoveBranch */ TrueBBI.IsBrAnalyzable, 1910 /* MergeAddEdges */ TailBB == nullptr)) 1911 return false; 1912 1913 // If the if-converted block falls through or unconditionally branches into 1914 // the tail block, and the tail block does not have other predecessors, then 1915 // fold the tail block in as well. Otherwise, unless it falls through to the 1916 // tail, add a unconditional branch to it. 1917 if (TailBB) { 1918 // We need to remove the edges to the true and false blocks manually since 1919 // we didn't let IfConvertDiamondCommon update the CFG. 1920 BBI.BB->removeSuccessor(TrueBBI.BB); 1921 BBI.BB->removeSuccessor(FalseBBI.BB, true); 1922 1923 BBInfo &TailBBI = BBAnalysis[TailBB->getNumber()]; 1924 bool CanMergeTail = !TailBBI.HasFallThrough && 1925 !TailBBI.BB->hasAddressTaken(); 1926 // The if-converted block can still have a predicated terminator 1927 // (e.g. a predicated return). If that is the case, we cannot merge 1928 // it with the tail block. 1929 MachineBasicBlock::const_iterator TI = BBI.BB->getFirstTerminator(); 1930 if (TI != BBI.BB->end() && TII->isPredicated(*TI)) 1931 CanMergeTail = false; 1932 // There may still be a fall-through edge from BBI1 or BBI2 to TailBB; 1933 // check if there are any other predecessors besides those. 1934 unsigned NumPreds = TailBB->pred_size(); 1935 if (NumPreds > 1) 1936 CanMergeTail = false; 1937 else if (NumPreds == 1 && CanMergeTail) { 1938 MachineBasicBlock::pred_iterator PI = TailBB->pred_begin(); 1939 if (*PI != TrueBBI.BB && *PI != FalseBBI.BB) 1940 CanMergeTail = false; 1941 } 1942 if (CanMergeTail) { 1943 MergeBlocks(BBI, TailBBI); 1944 TailBBI.IsDone = true; 1945 } else { 1946 BBI.BB->addSuccessor(TailBB, BranchProbability::getOne()); 1947 InsertUncondBranch(*BBI.BB, *TailBB, TII); 1948 BBI.HasFallThrough = false; 1949 } 1950 } 1951 1952 // Update block info. 1953 BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; 1954 InvalidatePreds(*BBI.BB); 1955 1956 // FIXME: Must maintain LiveIns. 1957 return true; 1958} 1959 1960static bool MaySpeculate(const MachineInstr &MI, 1961 SmallSet<unsigned, 4> &LaterRedefs) { 1962 bool SawStore = true; 1963 if (!MI.isSafeToMove(nullptr, SawStore)) 1964 return false; 1965 1966 for (const MachineOperand &MO : MI.operands()) { 1967 if (!MO.isReg()) 1968 continue; 1969 unsigned Reg = MO.getReg(); 1970 if (!Reg) 1971 continue; 1972 if (MO.isDef() && !LaterRedefs.count(Reg)) 1973 return false; 1974 } 1975 1976 return true; 1977} 1978 1979/// Predicate instructions from the start of the block to the specified end with 1980/// the specified condition. 1981void IfConverter::PredicateBlock(BBInfo &BBI, 1982 MachineBasicBlock::iterator E, 1983 SmallVectorImpl<MachineOperand> &Cond, 1984 SmallSet<unsigned, 4> *LaterRedefs) { 1985 bool AnyUnpred = false; 1986 bool MaySpec = LaterRedefs != nullptr; 1987 for (MachineInstr &I : make_range(BBI.BB->begin(), E)) { 1988 if (I.isDebugValue() || TII->isPredicated(I)) 1989 continue; 1990 // It may be possible not to predicate an instruction if it's the 'true' 1991 // side of a diamond and the 'false' side may re-define the instruction's 1992 // defs. 1993 if (MaySpec && MaySpeculate(I, *LaterRedefs)) { 1994 AnyUnpred = true; 1995 continue; 1996 } 1997 // If any instruction is predicated, then every instruction after it must 1998 // be predicated. 1999 MaySpec = false; 2000 if (!TII->PredicateInstruction(I, Cond)) { 2001#ifndef NDEBUG 2002 dbgs() << "Unable to predicate " << I << "!\n"; 2003#endif 2004 llvm_unreachable(nullptr); 2005 } 2006 2007 // If the predicated instruction now redefines a register as the result of 2008 // if-conversion, add an implicit kill. 2009 UpdatePredRedefs(I, Redefs); 2010 } 2011 2012 BBI.Predicate.append(Cond.begin(), Cond.end()); 2013 2014 BBI.IsAnalyzed = false; 2015 BBI.NonPredSize = 0; 2016 2017 ++NumIfConvBBs; 2018 if (AnyUnpred) 2019 ++NumUnpred; 2020} 2021 2022/// Copy and predicate instructions from source BB to the destination block. 2023/// Skip end of block branches if IgnoreBr is true. 2024void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, 2025 SmallVectorImpl<MachineOperand> &Cond, 2026 bool IgnoreBr) { 2027 MachineFunction &MF = *ToBBI.BB->getParent(); 2028 2029 MachineBasicBlock &FromMBB = *FromBBI.BB; 2030 for (MachineInstr &I : FromMBB) { 2031 // Do not copy the end of the block branches. 2032 if (IgnoreBr && I.isBranch()) 2033 break; 2034 2035 MachineInstr *MI = MF.CloneMachineInstr(&I); 2036 ToBBI.BB->insert(ToBBI.BB->end(), MI); 2037 ToBBI.NonPredSize++; 2038 unsigned ExtraPredCost = TII->getPredicationCost(I); 2039 unsigned NumCycles = SchedModel.computeInstrLatency(&I, false); 2040 if (NumCycles > 1) 2041 ToBBI.ExtraCost += NumCycles-1; 2042 ToBBI.ExtraCost2 += ExtraPredCost; 2043 2044 if (!TII->isPredicated(I) && !MI->isDebugValue()) { 2045 if (!TII->PredicateInstruction(*MI, Cond)) { 2046#ifndef NDEBUG 2047 dbgs() << "Unable to predicate " << I << "!\n"; 2048#endif 2049 llvm_unreachable(nullptr); 2050 } 2051 } 2052 2053 // If the predicated instruction now redefines a register as the result of 2054 // if-conversion, add an implicit kill. 2055 UpdatePredRedefs(*MI, Redefs); 2056 } 2057 2058 if (!IgnoreBr) { 2059 std::vector<MachineBasicBlock *> Succs(FromMBB.succ_begin(), 2060 FromMBB.succ_end()); 2061 MachineBasicBlock *NBB = getNextBlock(FromMBB); 2062 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : nullptr; 2063 2064 for (MachineBasicBlock *Succ : Succs) { 2065 // Fallthrough edge can't be transferred. 2066 if (Succ == FallThrough) 2067 continue; 2068 ToBBI.BB->addSuccessor(Succ); 2069 } 2070 } 2071 2072 ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end()); 2073 ToBBI.Predicate.append(Cond.begin(), Cond.end()); 2074 2075 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 2076 ToBBI.IsAnalyzed = false; 2077 2078 ++NumDupBBs; 2079} 2080 2081/// Move all instructions from FromBB to the end of ToBB. This will leave 2082/// FromBB as an empty block, so remove all of its successor edges except for 2083/// the fall-through edge. If AddEdges is true, i.e., when FromBBI's branch is 2084/// being moved, add those successor edges to ToBBI and remove the old edge 2085/// from ToBBI to FromBBI. 2086void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) { 2087 MachineBasicBlock &FromMBB = *FromBBI.BB; 2088 assert(!FromMBB.hasAddressTaken() && 2089 "Removing a BB whose address is taken!"); 2090 2091 // In case FromMBB contains terminators (e.g. return instruction), 2092 // first move the non-terminator instructions, then the terminators. 2093 MachineBasicBlock::iterator FromTI = FromMBB.getFirstTerminator(); 2094 MachineBasicBlock::iterator ToTI = ToBBI.BB->getFirstTerminator(); 2095 ToBBI.BB->splice(ToTI, &FromMBB, FromMBB.begin(), FromTI); 2096 2097 // If FromBB has non-predicated terminator we should copy it at the end. 2098 if (FromTI != FromMBB.end() && !TII->isPredicated(*FromTI)) 2099 ToTI = ToBBI.BB->end(); 2100 ToBBI.BB->splice(ToTI, &FromMBB, FromTI, FromMBB.end()); 2101 2102 // Force normalizing the successors' probabilities of ToBBI.BB to convert all 2103 // unknown probabilities into known ones. 2104 // FIXME: This usage is too tricky and in the future we would like to 2105 // eliminate all unknown probabilities in MBB. 2106 if (ToBBI.IsBrAnalyzable) 2107 ToBBI.BB->normalizeSuccProbs(); 2108 2109 SmallVector<MachineBasicBlock *, 4> FromSuccs(FromMBB.succ_begin(), 2110 FromMBB.succ_end()); 2111 MachineBasicBlock *NBB = getNextBlock(FromMBB); 2112 MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : nullptr; 2113 // The edge probability from ToBBI.BB to FromMBB, which is only needed when 2114 // AddEdges is true and FromMBB is a successor of ToBBI.BB. 2115 auto To2FromProb = BranchProbability::getZero(); 2116 if (AddEdges && ToBBI.BB->isSuccessor(&FromMBB)) { 2117 // Remove the old edge but remember the edge probability so we can calculate 2118 // the correct weights on the new edges being added further down. 2119 To2FromProb = MBPI->getEdgeProbability(ToBBI.BB, &FromMBB); 2120 ToBBI.BB->removeSuccessor(&FromMBB); 2121 } 2122 2123 for (MachineBasicBlock *Succ : FromSuccs) { 2124 // Fallthrough edge can't be transferred. 2125 if (Succ == FallThrough) 2126 continue; 2127 2128 auto NewProb = BranchProbability::getZero(); 2129 if (AddEdges) { 2130 // Calculate the edge probability for the edge from ToBBI.BB to Succ, 2131 // which is a portion of the edge probability from FromMBB to Succ. The 2132 // portion ratio is the edge probability from ToBBI.BB to FromMBB (if 2133 // FromBBI is a successor of ToBBI.BB. See comment below for excepion). 2134 NewProb = MBPI->getEdgeProbability(&FromMBB, Succ); 2135 2136 // To2FromProb is 0 when FromMBB is not a successor of ToBBI.BB. This 2137 // only happens when if-converting a diamond CFG and FromMBB is the 2138 // tail BB. In this case FromMBB post-dominates ToBBI.BB and hence we 2139 // could just use the probabilities on FromMBB's out-edges when adding 2140 // new successors. 2141 if (!To2FromProb.isZero()) 2142 NewProb *= To2FromProb; 2143 } 2144 2145 FromMBB.removeSuccessor(Succ); 2146 2147 if (AddEdges) { 2148 // If the edge from ToBBI.BB to Succ already exists, update the 2149 // probability of this edge by adding NewProb to it. An example is shown 2150 // below, in which A is ToBBI.BB and B is FromMBB. In this case we 2151 // don't have to set C as A's successor as it already is. We only need to 2152 // update the edge probability on A->C. Note that B will not be 2153 // immediately removed from A's successors. It is possible that B->D is 2154 // not removed either if D is a fallthrough of B. Later the edge A->D 2155 // (generated here) and B->D will be combined into one edge. To maintain 2156 // correct edge probability of this combined edge, we need to set the edge 2157 // probability of A->B to zero, which is already done above. The edge 2158 // probability on A->D is calculated by scaling the original probability 2159 // on A->B by the probability of B->D. 2160 // 2161 // Before ifcvt: After ifcvt (assume B->D is kept): 2162 // 2163 // A A 2164 // /| /|\ 2165 // / B / B| 2166 // | /| | || 2167 // |/ | | |/ 2168 // C D C D 2169 // 2170 if (ToBBI.BB->isSuccessor(Succ)) 2171 ToBBI.BB->setSuccProbability( 2172 find(ToBBI.BB->successors(), Succ), 2173 MBPI->getEdgeProbability(ToBBI.BB, Succ) + NewProb); 2174 else 2175 ToBBI.BB->addSuccessor(Succ, NewProb); 2176 } 2177 } 2178 2179 // Move the now empty FromMBB out of the way to the end of the function so 2180 // it doesn't interfere with fallthrough checks done by canFallThroughTo(). 2181 MachineBasicBlock *Last = &*FromMBB.getParent()->rbegin(); 2182 if (Last != &FromMBB) 2183 FromMBB.moveAfter(Last); 2184 2185 // Normalize the probabilities of ToBBI.BB's successors with all adjustment 2186 // we've done above. 2187 if (ToBBI.IsBrAnalyzable && FromBBI.IsBrAnalyzable) 2188 ToBBI.BB->normalizeSuccProbs(); 2189 2190 ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end()); 2191 FromBBI.Predicate.clear(); 2192 2193 ToBBI.NonPredSize += FromBBI.NonPredSize; 2194 ToBBI.ExtraCost += FromBBI.ExtraCost; 2195 ToBBI.ExtraCost2 += FromBBI.ExtraCost2; 2196 FromBBI.NonPredSize = 0; 2197 FromBBI.ExtraCost = 0; 2198 FromBBI.ExtraCost2 = 0; 2199 2200 ToBBI.ClobbersPred |= FromBBI.ClobbersPred; 2201 ToBBI.HasFallThrough = FromBBI.HasFallThrough; 2202 ToBBI.IsAnalyzed = false; 2203 FromBBI.IsAnalyzed = false; 2204} 2205 2206FunctionPass * 2207llvm::createIfConverter(std::function<bool(const MachineFunction &)> Ftor) { 2208 return new IfConverter(std::move(Ftor)); 2209} 2210