IfConversion.cpp revision 2acdbcccd8043d3a91430fdfcef6ba0760c1cc05
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the Evan Cheng and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements the machine instruction level if-conversion pass. 11// 12//===----------------------------------------------------------------------===// 13 14#define DEBUG_TYPE "ifcvt" 15#include "llvm/Function.h" 16#include "llvm/CodeGen/Passes.h" 17#include "llvm/CodeGen/MachineModuleInfo.h" 18#include "llvm/CodeGen/MachineFunctionPass.h" 19#include "llvm/Target/TargetInstrInfo.h" 20#include "llvm/Target/TargetLowering.h" 21#include "llvm/Target/TargetMachine.h" 22#include "llvm/Support/CommandLine.h" 23#include "llvm/Support/Debug.h" 24#include "llvm/ADT/DepthFirstIterator.h" 25#include "llvm/ADT/Statistic.h" 26using namespace llvm; 27 28namespace { 29 // Hidden options for help debugging. 30 cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); 31 cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); 32 cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); 33 cl::opt<bool> DisableSimple("disable-ifcvt-simple", 34 cl::init(false), cl::Hidden); 35 cl::opt<bool> DisableSimpleFalse("disable-ifcvt-simple-false", 36 cl::init(false), cl::Hidden); 37 cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", 38 cl::init(false), cl::Hidden); 39 cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", 40 cl::init(false), cl::Hidden); 41} 42 43STATISTIC(NumSimple, "Number of simple if-conversions performed"); 44STATISTIC(NumSimpleRev, "Number of simple (reversed) if-conversions performed"); 45STATISTIC(NumTriangle, "Number of triangle if-conversions performed"); 46STATISTIC(NumDiamonds, "Number of diamond if-conversions performed"); 47STATISTIC(NumIfConvBBs, "Number of if-converted blocks"); 48 49namespace { 50 class IfConverter : public MachineFunctionPass { 51 enum BBICKind { 52 ICNotAnalyzed, // BB has not been analyzed. 53 ICReAnalyze, // BB must be re-analyzed. 54 ICNotClassfied, // BB data valid, but not classified. 55 ICSimple, // BB is entry of an one split, no rejoin sub-CFG. 56 ICSimpleFalse, // Same as ICSimple, but on the false path. 57 ICTriangle, // BB is entry of a triangle sub-CFG. 58 ICDiamond, // BB is entry of a diamond sub-CFG. 59 ICChild, // BB is part of the sub-CFG that'll be predicated. 60 ICDead // BB cannot be if-converted again. 61 }; 62 63 /// BBInfo - One per MachineBasicBlock, this is used to cache the result 64 /// if-conversion feasibility analysis. This includes results from 65 /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its 66 /// classification, and common tail block of its successors (if it's a 67 /// diamond shape), its size, whether it's predicable, and whether any 68 /// instruction can clobber the 'would-be' predicate. 69 /// 70 /// Kind - Type of block. See BBICKind. 71 /// NonPredSize - Number of non-predicated instructions. 72 /// IsAnalyzable - True if AnalyzeBranch() returns false. 73 /// ModifyPredicate - True if BB would modify the predicate (e.g. has 74 /// cmp, call, etc.) 75 /// BB - Corresponding MachineBasicBlock. 76 /// TrueBB / FalseBB- See AnalyzeBranch(). 77 /// BrCond - Conditions for end of block conditional branches. 78 /// Predicate - Predicate used in the BB. 79 struct BBInfo { 80 BBICKind Kind; 81 unsigned NonPredSize; 82 bool IsAnalyzable; 83 bool hasFallThrough; 84 bool ModifyPredicate; 85 MachineBasicBlock *BB; 86 MachineBasicBlock *TrueBB; 87 MachineBasicBlock *FalseBB; 88 MachineBasicBlock *TailBB; 89 std::vector<MachineOperand> BrCond; 90 std::vector<MachineOperand> Predicate; 91 BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0), 92 IsAnalyzable(false), hasFallThrough(false), 93 ModifyPredicate(false), 94 BB(0), TrueBB(0), FalseBB(0), TailBB(0) {} 95 }; 96 97 /// Roots - Basic blocks that do not have successors. These are the starting 98 /// points of Graph traversal. 99 std::vector<MachineBasicBlock*> Roots; 100 101 /// BBAnalysis - Results of if-conversion feasibility analysis indexed by 102 /// basic block number. 103 std::vector<BBInfo> BBAnalysis; 104 105 const TargetLowering *TLI; 106 const TargetInstrInfo *TII; 107 bool MadeChange; 108 public: 109 static char ID; 110 IfConverter() : MachineFunctionPass((intptr_t)&ID) {} 111 112 virtual bool runOnMachineFunction(MachineFunction &MF); 113 virtual const char *getPassName() const { return "If converter"; } 114 115 private: 116 bool ReverseBranchCondition(BBInfo &BBI); 117 bool ValidSimple(BBInfo &TrueBBI) const; 118 bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 119 bool FalseBranch = false) const; 120 bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const; 121 void ScanInstructions(BBInfo &BBI); 122 void AnalyzeBlock(MachineBasicBlock *BB); 123 bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond, 124 bool isTriangle = false, bool RevBranch = false); 125 bool AttemptRestructuring(BBInfo &BBI); 126 bool AnalyzeBlocks(MachineFunction &MF, 127 std::vector<BBInfo*> &Candidates); 128 void ReTryPreds(MachineBasicBlock *BB); 129 bool IfConvertSimple(BBInfo &BBI); 130 bool IfConvertTriangle(BBInfo &BBI); 131 bool IfConvertDiamond(BBInfo &BBI); 132 void PredicateBlock(BBInfo &BBI, 133 std::vector<MachineOperand> &Cond, 134 bool IgnoreTerm = false); 135 void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI); 136 137 // blockAlwaysFallThrough - Block ends without a terminator. 138 bool blockAlwaysFallThrough(BBInfo &BBI) const { 139 return BBI.IsAnalyzable && BBI.TrueBB == NULL; 140 } 141 142 // IfcvtCandidateCmp - Used to sort if-conversion candidates. 143 static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){ 144 // Favor diamond over triangle, etc. 145 return (unsigned)C1->Kind < (unsigned)C2->Kind; 146 } 147 }; 148 char IfConverter::ID = 0; 149} 150 151FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); } 152 153bool IfConverter::runOnMachineFunction(MachineFunction &MF) { 154 TLI = MF.getTarget().getTargetLowering(); 155 TII = MF.getTarget().getInstrInfo(); 156 if (!TII) return false; 157 158 static int FnNum = -1; 159 DOUT << "\nIfcvt: function (" << ++FnNum << ") \'" 160 << MF.getFunction()->getName() << "\'"; 161 162 if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { 163 DOUT << " skipped\n"; 164 return false; 165 } 166 DOUT << "\n"; 167 168 MF.RenumberBlocks(); 169 BBAnalysis.resize(MF.getNumBlockIDs()); 170 171 // Look for root nodes, i.e. blocks without successors. 172 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) 173 if (I->succ_size() == 0) 174 Roots.push_back(I); 175 176 std::vector<BBInfo*> Candidates; 177 MadeChange = false; 178 while (IfCvtLimit == -1 || (int)NumIfConvBBs < IfCvtLimit) { 179 // Do an intial analysis for each basic block and finding all the potential 180 // candidates to perform if-convesion. 181 bool Change = AnalyzeBlocks(MF, Candidates); 182 while (!Candidates.empty()) { 183 BBInfo &BBI = *Candidates.back(); 184 Candidates.pop_back(); 185 186 bool RetVal = false; 187 switch (BBI.Kind) { 188 default: assert(false && "Unexpected!"); 189 break; 190 case ICReAnalyze: 191 // One or more of 'children' have been modified, abort! 192 case ICDead: 193 // Block has been already been if-converted, abort! 194 break; 195 case ICSimple: 196 case ICSimpleFalse: { 197 bool isRev = BBI.Kind == ICSimpleFalse; 198 if ((isRev && DisableSimpleFalse) || (!isRev && DisableSimple)) break; 199 DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "") 200 << "): BB#" << BBI.BB->getNumber() << " (" 201 << ((BBI.Kind == ICSimpleFalse) 202 ? BBI.FalseBB->getNumber() : BBI.TrueBB->getNumber()) << ") "; 203 RetVal = IfConvertSimple(BBI); 204 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n"; 205 if (RetVal) 206 if (isRev) NumSimpleRev++; 207 else NumSimple++; 208 break; 209 } 210 case ICTriangle: 211 if (DisableTriangle) break; 212 DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << " (T:" 213 << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber() 214 << ") "; 215 RetVal = IfConvertTriangle(BBI); 216 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n"; 217 if (RetVal) NumTriangle++; 218 break; 219 case ICDiamond: 220 if (DisableDiamond) break; 221 DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:" 222 << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber(); 223 if (BBI.TailBB) 224 DOUT << "," << BBI.TailBB->getNumber() ; 225 DOUT << ") "; 226 RetVal = IfConvertDiamond(BBI); 227 DOUT << (RetVal ? "succeeded!" : "failed!") << "\n"; 228 if (RetVal) NumDiamonds++; 229 break; 230 } 231 Change |= RetVal; 232 233 if (IfCvtLimit != -1 && (int)NumIfConvBBs > IfCvtLimit) 234 break; 235 } 236 237 if (!Change) 238 break; 239 MadeChange |= Change; 240 } 241 242 Roots.clear(); 243 BBAnalysis.clear(); 244 245 return MadeChange; 246} 247 248static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, 249 MachineBasicBlock *TrueBB) { 250 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), 251 E = BB->succ_end(); SI != E; ++SI) { 252 MachineBasicBlock *SuccBB = *SI; 253 if (SuccBB != TrueBB) 254 return SuccBB; 255 } 256 return NULL; 257} 258 259bool IfConverter::ReverseBranchCondition(BBInfo &BBI) { 260 if (!TII->ReverseBranchCondition(BBI.BrCond)) { 261 TII->RemoveBranch(*BBI.BB); 262 TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond); 263 std::swap(BBI.TrueBB, BBI.FalseBB); 264 return true; 265 } 266 return false; 267} 268 269/// ValidSimple - Returns true if the 'true' block (along with its 270/// predecessor) forms a valid simple shape for ifcvt. 271bool IfConverter::ValidSimple(BBInfo &TrueBBI) const { 272 return !blockAlwaysFallThrough(TrueBBI) && 273 TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1; 274} 275 276/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along 277/// with their common predecessor) forms a valid triangle shape for ifcvt. 278bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, 279 bool FalseBranch) const { 280 if (TrueBBI.BB->pred_size() != 1) 281 return false; 282 283 MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB; 284 if (!TExit && blockAlwaysFallThrough(TrueBBI)) { 285 MachineFunction::iterator I = TrueBBI.BB; 286 if (++I == TrueBBI.BB->getParent()->end()) 287 return false; 288 TExit = I; 289 } 290 return TExit && TExit == FalseBBI.BB; 291} 292 293/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along 294/// with their common predecessor) forms a valid diamond shape for ifcvt. 295bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const { 296 // FIXME: Also look for fallthrough 297 return (TrueBBI.TrueBB == FalseBBI.TrueBB && 298 TrueBBI.BB->pred_size() == 1 && 299 FalseBBI.BB->pred_size() == 1 && 300 !TrueBBI.FalseBB && !FalseBBI.FalseBB); 301} 302 303/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from 304/// the specified block. Record its successors and whether it looks like an 305/// if-conversion candidate. 306void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) { 307 BBInfo &BBI = BBAnalysis[BB->getNumber()]; 308 309 if (BBI.Kind == ICReAnalyze) { 310 BBI.BrCond.clear(); 311 BBI.TrueBB = BBI.FalseBB = NULL; 312 } else { 313 if (BBI.Kind != ICNotAnalyzed) 314 return; // Already analyzed. 315 BBI.BB = BB; 316 BBI.NonPredSize = std::distance(BB->begin(), BB->end()); 317 } 318 319 // Look for 'root' of a simple (non-nested) triangle or diamond. 320 BBI.Kind = ICNotClassfied; 321 BBI.IsAnalyzable = 322 !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); 323 BBI.hasFallThrough = BBI.IsAnalyzable && BBI.FalseBB == NULL; 324 // Unanalyable or ends with fallthrough or unconditional branch. 325 if (!BBI.IsAnalyzable || BBI.BrCond.size() == 0) 326 return; 327 // Do not ifcvt if either path is a back edge to the entry block. 328 if (BBI.TrueBB == BB || BBI.FalseBB == BB) 329 return; 330 331 AnalyzeBlock(BBI.TrueBB); 332 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 333 334 // No false branch. This BB must end with a conditional branch and a 335 // fallthrough. 336 if (!BBI.FalseBB) 337 BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB); 338 assert(BBI.FalseBB && "Expected to find the fallthrough block!"); 339 340 AnalyzeBlock(BBI.FalseBB); 341 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 342 343 // If both paths are dead, then forget about it. 344 if (TrueBBI.Kind == ICDead && FalseBBI.Kind == ICDead) { 345 BBI.Kind = ICDead; 346 return; 347 } 348 349 // Look for more opportunities to if-convert a triangle. Try to restructure 350 // the CFG to form a triangle with the 'false' path. 351 std::vector<MachineOperand> RevCond(BBI.BrCond); 352 bool CanRevCond = !TII->ReverseBranchCondition(RevCond); 353 354 if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) && 355 !(TrueBBI.ModifyPredicate && FalseBBI.ModifyPredicate) && 356 FeasibilityAnalysis(TrueBBI, BBI.BrCond) && 357 FeasibilityAnalysis(FalseBBI, RevCond)) { 358 // Diamond: 359 // EBB 360 // / \_ 361 // | | 362 // TBB FBB 363 // \ / 364 // TailBB 365 // Note TailBB can be empty. 366 BBI.Kind = ICDiamond; 367 TrueBBI.Kind = FalseBBI.Kind = ICChild; 368 BBI.TailBB = TrueBBI.TrueBB; 369 } else { 370 // FIXME: Consider duplicating if BB is small. 371 if (ValidTriangle(TrueBBI, FalseBBI) && 372 FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { 373 // Triangle: 374 // EBB 375 // | \_ 376 // | | 377 // | TBB 378 // | / 379 // FBB 380 BBI.Kind = ICTriangle; 381 TrueBBI.Kind = ICChild; 382 } else if (ValidSimple(TrueBBI) && 383 FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { 384 // Simple (split, no rejoin): 385 // EBB 386 // | \_ 387 // | | 388 // | TBB---> exit 389 // | 390 // FBB 391 BBI.Kind = ICSimple; 392 TrueBBI.Kind = ICChild; 393 } else if (CanRevCond) { 394 // Try the other path... 395 if (ValidTriangle(FalseBBI, TrueBBI) && 396 FeasibilityAnalysis(FalseBBI, RevCond, true)) { 397 // Reverse 'true' and 'false' paths. 398 ReverseBranchCondition(BBI); 399 BBI.Kind = ICTriangle; 400 FalseBBI.Kind = ICChild; 401 } else if (ValidTriangle(FalseBBI, TrueBBI, true) && 402 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { 403 ReverseBranchCondition(FalseBBI); 404 ReverseBranchCondition(BBI); 405 BBI.Kind = ICTriangle; 406 FalseBBI.Kind = ICChild; 407 } else if (ValidSimple(FalseBBI) && 408 FeasibilityAnalysis(FalseBBI, RevCond)) { 409 BBI.Kind = ICSimpleFalse; 410 FalseBBI.Kind = ICChild; 411 } 412 } 413 } 414 return; 415} 416 417/// FeasibilityAnalysis - Determine if the block is predicable. In most 418/// cases, that means all the instructions in the block has M_PREDICABLE flag. 419/// Also checks if the block contains any instruction which can clobber a 420/// predicate (e.g. condition code register). If so, the block is not 421/// predicable unless it's the last instruction. 422bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, 423 std::vector<MachineOperand> &Pred, 424 bool isTriangle, bool RevBranch) { 425 // If the block is dead, or it is going to be the entry block of a sub-CFG 426 // that will be if-converted, then it cannot be predicated. 427 if (BBI.Kind != ICNotAnalyzed && 428 BBI.Kind != ICNotClassfied && 429 BBI.Kind != ICChild) 430 return false; 431 432 // Check predication threshold. 433 if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit()) 434 return false; 435 436 // If it is already predicated, check if its predicate subsumes the new 437 // predicate. 438 if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred)) 439 return false; 440 441 bool SeenPredMod = false; 442 bool SeenCondBr = false; 443 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end(); 444 I != E; ++I) { 445 const TargetInstrDescriptor *TID = I->getInstrDescriptor(); 446 if (SeenPredMod) { 447 // Predicate modification instruction should end the block (except for 448 // already predicated instructions and end of block branches). 449 if (!TII->isPredicated(I)) { 450 // This is the 'true' block of a triangle, i.e. its 'true' block is 451 // the same as the 'false' block of the entry. So false positive 452 // is ok. 453 if (isTriangle && !SeenCondBr && BBI.IsAnalyzable && 454 (TID->Flags & M_BRANCH_FLAG) != 0 && 455 (TID->Flags & M_BARRIER_FLAG) == 0) { 456 // This is the first conditional branch, test predicate subsumsion. 457 std::vector<MachineOperand> RevPred(Pred); 458 std::vector<MachineOperand> Cond(BBI.BrCond); 459 if (RevBranch) { 460 if (TII->ReverseBranchCondition(Cond)) 461 return false; 462 } 463 if (TII->ReverseBranchCondition(RevPred) || 464 !TII->SubsumesPredicate(Cond, RevPred)) 465 return false; 466 SeenCondBr = true; 467 continue; // Conditional branches is not predicable. 468 } 469 return false; 470 } 471 } 472 473 if (TID->Flags & M_CLOBBERS_PRED) { 474 BBI.ModifyPredicate = true; 475 SeenPredMod = true; 476 } 477 478 if (!I->isPredicable()) 479 return false; 480 } 481 482 return true; 483} 484 485/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to 486/// expose more if-conversion opportunities. e.g. 487/// 488/// cmp 489/// b le BB1 490/// / \____ 491/// / | 492/// cmp | 493/// b eq BB1 | 494/// / \____ | 495/// / \ | 496/// BB1 497/// ==> 498/// 499/// cmp 500/// b eq BB1 501/// / \____ 502/// / | 503/// cmp | 504/// b le BB1 | 505/// / \____ | 506/// / \ | 507/// BB1 508bool IfConverter::AttemptRestructuring(BBInfo &BBI) { 509 return false; 510} 511 512/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion 513/// candidates. It returns true if any CFG restructuring is done to expose more 514/// if-conversion opportunities. 515bool IfConverter::AnalyzeBlocks(MachineFunction &MF, 516 std::vector<BBInfo*> &Candidates) { 517 bool Change = false; 518 std::set<MachineBasicBlock*> Visited; 519 for (unsigned i = 0, e = Roots.size(); i != e; ++i) { 520 for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited), 521 E = idf_ext_end(Roots[i], Visited); I != E; ++I) { 522 MachineBasicBlock *BB = *I; 523 AnalyzeBlock(BB); 524 BBInfo &BBI = BBAnalysis[BB->getNumber()]; 525 switch (BBI.Kind) { 526 case ICSimple: 527 case ICSimpleFalse: 528 case ICTriangle: 529 case ICDiamond: 530 Candidates.push_back(&BBI); 531 break; 532 default: 533 Change |= AttemptRestructuring(BBI); 534 break; 535 } 536 } 537 } 538 539 // Sort to favor more complex ifcvt scheme. 540 std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp); 541 542 return Change; 543} 544 545/// isNextBlock - Returns true either if ToBB the next block after BB or 546/// that all the intervening blocks are empty. 547static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) { 548 MachineFunction::iterator I = BB; 549 MachineFunction::iterator TI = ToBB; 550 MachineFunction::iterator E = BB->getParent()->end(); 551 while (++I != TI) 552 if (I == E || !I->empty()) 553 return false; 554 return true; 555} 556 557/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed 558/// to determine if it can be if-converted. 559void IfConverter::ReTryPreds(MachineBasicBlock *BB) { 560 for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(), 561 E = BB->pred_end(); PI != E; ++PI) { 562 BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()]; 563 PBBI.Kind = ICReAnalyze; 564 } 565} 566 567/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB. 568/// 569static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB, 570 const TargetInstrInfo *TII) { 571 std::vector<MachineOperand> NoCond; 572 TII->InsertBranch(*BB, ToBB, NULL, NoCond); 573} 574 575/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG. 576/// 577bool IfConverter::IfConvertSimple(BBInfo &BBI) { 578 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 579 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 580 BBInfo *CvtBBI = &TrueBBI; 581 BBInfo *NextBBI = &FalseBBI; 582 583 std::vector<MachineOperand> Cond(BBI.BrCond); 584 if (BBI.Kind == ICSimpleFalse) { 585 std::swap(CvtBBI, NextBBI); 586 TII->ReverseBranchCondition(Cond); 587 } 588 589 PredicateBlock(*CvtBBI, Cond); 590 591 // Merge converted block into entry block. Also add an unconditional branch 592 // to the 'false' branch. 593 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 594 MergeBlocks(BBI, *CvtBBI); 595 BBI.BB->removeSuccessor(CvtBBI->BB); 596 597 bool IterIfcvt = true; 598 if (!isNextBlock(BBI.BB, NextBBI->BB)) { 599 InsertUncondBranch(BBI.BB, NextBBI->BB, TII); 600 BBI.hasFallThrough = false; 601 // Now ifcvt'd block will look like this: 602 // BB: 603 // ... 604 // t, f = cmp 605 // if t op 606 // b BBf 607 // 608 // We cannot further ifcvt this block because the unconditional branch 609 // will have to be predicated on the new condition, that will not be 610 // available if cmp executes. 611 IterIfcvt = false; 612 } 613 614 // Update block info. BB can be iteratively if-converted. 615 if (IterIfcvt) 616 BBI.Kind = ICReAnalyze; 617 else 618 BBI.Kind = ICDead; 619 ReTryPreds(BBI.BB); 620 CvtBBI->Kind = ICDead; 621 622 // FIXME: Must maintain LiveIns. 623 return true; 624} 625 626/// IfConvertTriangle - If convert a triangle sub-CFG. 627/// 628bool IfConverter::IfConvertTriangle(BBInfo &BBI) { 629 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 630 631 // Predicate the 'true' block after removing its branch. 632 TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB); 633 PredicateBlock(TrueBBI, BBI.BrCond); 634 635 // If 'true' block has a 'false' successor, add an exit branch to it. 636 bool HasEarlyExit = TrueBBI.FalseBB != NULL; 637 if (HasEarlyExit) { 638 std::vector<MachineOperand> RevCond(TrueBBI.BrCond); 639 if (TII->ReverseBranchCondition(RevCond)) 640 assert(false && "Unable to reverse branch condition!"); 641 TII->InsertBranch(*BBI.TrueBB, TrueBBI.FalseBB, NULL, RevCond); 642 } 643 644 // Now merge the entry of the triangle with the true block. 645 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 646 MergeBlocks(BBI, TrueBBI); 647 648 // Merge in the 'false' block if the 'false' block has no other 649 // predecessors. Otherwise, add a unconditional branch from to 'false'. 650 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 651 bool FalseBBDead = false; 652 bool IterIfcvt = true; 653 bool isFallThrough = isNextBlock(BBI.BB, FalseBBI.BB); 654 if (!isFallThrough) { 655 // Only merge them if the true block does not fallthrough to the false 656 // block. By not merging them, we make it possible to iteratively 657 // ifcvt the blocks. 658 if (!HasEarlyExit && FalseBBI.BB->pred_size() == 1) { 659 MergeBlocks(BBI, FalseBBI); 660 FalseBBDead = true; 661 } else { 662 InsertUncondBranch(BBI.BB, FalseBBI.BB, TII); 663 TrueBBI.hasFallThrough = false; 664 } 665 // Mixed predicated and unpredicated code. This cannot be iteratively 666 // predicated. 667 IterIfcvt = false; 668 } 669 670 // Remove entry to false edge if false block is merged in as well. 671 if (FalseBBDead) 672 BBI.BB->removeSuccessor(FalseBBI.BB); 673 674 // Update block info. BB can be iteratively if-converted. 675 if (IterIfcvt) 676 BBI.Kind = ICReAnalyze; 677 else 678 BBI.Kind = ICDead; 679 ReTryPreds(BBI.BB); 680 TrueBBI.Kind = ICDead; 681 if (FalseBBDead) 682 FalseBBI.Kind = ICDead; 683 684 // FIXME: Must maintain LiveIns. 685 return true; 686} 687 688/// IfConvertDiamond - If convert a diamond sub-CFG. 689/// 690bool IfConverter::IfConvertDiamond(BBInfo &BBI) { 691 BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; 692 BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; 693 694 SmallVector<MachineInstr*, 2> Dups; 695 if (!BBI.TailBB) { 696 // No common merge block. Check if the terminators (e.g. return) are 697 // the same or predicable. 698 MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator(); 699 MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator(); 700 while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) { 701 if (TT->isIdenticalTo(FT)) 702 Dups.push_back(TT); // Will erase these later. 703 else if (!TT->isPredicable() && !FT->isPredicable()) 704 return false; // Can't if-convert. Abort! 705 ++TT; 706 ++FT; 707 } 708 709 // One of the two pathes have more terminators, make sure they are 710 // all predicable. 711 while (TT != BBI.TrueBB->end()) { 712 if (!TT->isPredicable()) { 713 return false; // Can't if-convert. Abort! 714 } 715 ++TT; 716 } 717 while (FT != BBI.FalseBB->end()) { 718 if (!FT->isPredicable()) { 719 return false; // Can't if-convert. Abort! 720 } 721 ++FT; 722 } 723 } 724 725 // Remove the duplicated instructions from the 'true' block. 726 for (unsigned i = 0, e = Dups.size(); i != e; ++i) { 727 Dups[i]->eraseFromParent(); 728 --TrueBBI.NonPredSize; 729 } 730 731 // Merge the 'true' and 'false' blocks by copying the instructions 732 // from the 'false' block to the 'true' block. That is, unless the true 733 // block would clobber the predicate, in that case, do the opposite. 734 BBInfo *BBI1 = &TrueBBI; 735 BBInfo *BBI2 = &FalseBBI; 736 std::vector<MachineOperand> RevCond(BBI.BrCond); 737 TII->ReverseBranchCondition(RevCond); 738 std::vector<MachineOperand> *Cond1 = &BBI.BrCond; 739 std::vector<MachineOperand> *Cond2 = &RevCond; 740 // Check the 'true' and 'false' blocks if either isn't ended with a branch. 741 // Either the block fallthrough to another block or it ends with a 742 // return. If it's the former, add a branch to its successor. 743 bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size(); 744 bool NeedBr2 = !BBI2->TrueBB && BBI2->BB->succ_size(); 745 746 if ((TrueBBI.ModifyPredicate && !FalseBBI.ModifyPredicate) || 747 (!TrueBBI.ModifyPredicate && !FalseBBI.ModifyPredicate && 748 NeedBr1 && !NeedBr2)) { 749 std::swap(BBI1, BBI2); 750 std::swap(Cond1, Cond2); 751 std::swap(NeedBr1, NeedBr2); 752 } 753 754 // Predicate the 'true' block after removing its branch. 755 BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB); 756 PredicateBlock(*BBI1, *Cond1); 757 758 // Add an early exit branch if needed. 759 if (NeedBr1) 760 TII->InsertBranch(*BBI1->BB, *BBI1->BB->succ_begin(), NULL, *Cond1); 761 762 // Predicate the 'false' block. 763 PredicateBlock(*BBI2, *Cond2, true); 764 765 // Add an unconditional branch from 'false' to to 'false' successor if it 766 // will not be the fallthrough block. 767 if (NeedBr2 && !NeedBr1) { 768 // If BBI2 isn't going to be merged in, then the existing fallthrough 769 // or branch is fine. 770 if (!isNextBlock(BBI.BB, *BBI2->BB->succ_begin())) { 771 InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII); 772 BBI2->hasFallThrough = false; 773 } 774 } 775 776 // Keep them as two separate blocks if there is an early exit. 777 if (!NeedBr1) 778 MergeBlocks(*BBI1, *BBI2); 779 780 // Remove the conditional branch from entry to the blocks. 781 BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); 782 783 // Merge the combined block into the entry of the diamond. 784 MergeBlocks(BBI, *BBI1); 785 786 // 'True' and 'false' aren't combined, see if we need to add a unconditional 787 // branch to the 'false' block. 788 if (NeedBr1 && !isNextBlock(BBI.BB, BBI2->BB)) { 789 InsertUncondBranch(BBI.BB, BBI2->BB, TII); 790 BBI1->hasFallThrough = false; 791 } 792 793 // If the if-converted block fallthrough or unconditionally branch into the 794 // tail block, and the tail block does not have other predecessors, then 795 // fold the tail block in as well. 796 BBInfo *CvtBBI = NeedBr1 ? BBI2 : &BBI; 797 if (BBI.TailBB && 798 BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) { 799 CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB); 800 BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()]; 801 MergeBlocks(*CvtBBI, TailBBI); 802 TailBBI.Kind = ICDead; 803 } 804 805 // Update block info. 806 BBI.Kind = ICDead; 807 TrueBBI.Kind = ICDead; 808 FalseBBI.Kind = ICDead; 809 810 // FIXME: Must maintain LiveIns. 811 return true; 812} 813 814/// PredicateBlock - Predicate every instruction in the block with the specified 815/// condition. If IgnoreTerm is true, skip over all terminator instructions. 816void IfConverter::PredicateBlock(BBInfo &BBI, 817 std::vector<MachineOperand> &Cond, 818 bool IgnoreTerm) { 819 for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end(); 820 I != E; ++I) { 821 if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode())) 822 continue; 823 if (TII->isPredicated(I)) 824 continue; 825 if (!TII->PredicateInstruction(I, Cond)) { 826 cerr << "Unable to predicate " << *I << "!\n"; 827 abort(); 828 } 829 } 830 831 BBI.NonPredSize = 0; 832 std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate)); 833 834 NumIfConvBBs++; 835} 836 837static MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) { 838 MachineFunction::iterator I = BB; 839 MachineFunction::iterator E = BB->getParent()->end(); 840 if (++I == E) 841 return NULL; 842 return I; 843} 844 845/// MergeBlocks - Move all instructions from FromBB to the end of ToBB. 846/// 847void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) { 848 ToBBI.BB->splice(ToBBI.BB->end(), 849 FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end()); 850 851 // Redirect all branches to FromBB to ToBB. 852 std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(), 853 FromBBI.BB->pred_end()); 854 for (unsigned i = 0, e = Preds.size(); i != e; ++i) { 855 MachineBasicBlock *Pred = Preds[i]; 856 if (Pred == ToBBI.BB) 857 continue; 858 Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB); 859 } 860 861 std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(), 862 FromBBI.BB->succ_end()); 863 MachineBasicBlock *FallThrough = FromBBI.hasFallThrough 864 ? getNextBlock(FromBBI.BB) : NULL; 865 866 for (unsigned i = 0, e = Succs.size(); i != e; ++i) { 867 MachineBasicBlock *Succ = Succs[i]; 868 if (Succ == FallThrough) 869 continue; 870 FromBBI.BB->removeSuccessor(Succ); 871 if (!ToBBI.BB->isSuccessor(Succ)) 872 ToBBI.BB->addSuccessor(Succ); 873 } 874 875 ToBBI.NonPredSize += FromBBI.NonPredSize; 876 FromBBI.NonPredSize = 0; 877 878 ToBBI.ModifyPredicate |= FromBBI.ModifyPredicate; 879 ToBBI.hasFallThrough = FromBBI.hasFallThrough; 880 881 std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), 882 std::back_inserter(ToBBI.Predicate)); 883 FromBBI.Predicate.clear(); 884} 885