1 //===- GVN.cpp - Eliminate redundant values and loads ---------------------===// 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 pass performs global value numbering to eliminate fully redundant 11 // instructions. It also performs simple dead load elimination. 12 // 13 // Note that this pass does the value numbering itself; it does not use the 14 // ValueNumbering analysis passes. 15 // 16 //===----------------------------------------------------------------------===// 17 18 #include "llvm/Transforms/Scalar.h" 19 #include "llvm/ADT/DenseMap.h" 20 #include "llvm/ADT/DepthFirstIterator.h" 21 #include "llvm/ADT/Hashing.h" 22 #include "llvm/ADT/MapVector.h" 23 #include "llvm/ADT/PostOrderIterator.h" 24 #include "llvm/ADT/SetVector.h" 25 #include "llvm/ADT/SmallPtrSet.h" 26 #include "llvm/ADT/Statistic.h" 27 #include "llvm/Analysis/AliasAnalysis.h" 28 #include "llvm/Analysis/AssumptionCache.h" 29 #include "llvm/Analysis/CFG.h" 30 #include "llvm/Analysis/ConstantFolding.h" 31 #include "llvm/Analysis/GlobalsModRef.h" 32 #include "llvm/Analysis/InstructionSimplify.h" 33 #include "llvm/Analysis/Loads.h" 34 #include "llvm/Analysis/MemoryBuiltins.h" 35 #include "llvm/Analysis/MemoryDependenceAnalysis.h" 36 #include "llvm/Analysis/PHITransAddr.h" 37 #include "llvm/Analysis/TargetLibraryInfo.h" 38 #include "llvm/Analysis/ValueTracking.h" 39 #include "llvm/IR/DataLayout.h" 40 #include "llvm/IR/Dominators.h" 41 #include "llvm/IR/GlobalVariable.h" 42 #include "llvm/IR/IRBuilder.h" 43 #include "llvm/IR/IntrinsicInst.h" 44 #include "llvm/IR/LLVMContext.h" 45 #include "llvm/IR/Metadata.h" 46 #include "llvm/IR/PatternMatch.h" 47 #include "llvm/Support/Allocator.h" 48 #include "llvm/Support/CommandLine.h" 49 #include "llvm/Support/Debug.h" 50 #include "llvm/Support/raw_ostream.h" 51 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 52 #include "llvm/Transforms/Utils/Local.h" 53 #include "llvm/Transforms/Utils/SSAUpdater.h" 54 #include <vector> 55 using namespace llvm; 56 using namespace PatternMatch; 57 58 #define DEBUG_TYPE "gvn" 59 60 STATISTIC(NumGVNInstr, "Number of instructions deleted"); 61 STATISTIC(NumGVNLoad, "Number of loads deleted"); 62 STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 63 STATISTIC(NumGVNBlocks, "Number of blocks merged"); 64 STATISTIC(NumGVNSimpl, "Number of instructions simplified"); 65 STATISTIC(NumGVNEqProp, "Number of equalities propagated"); 66 STATISTIC(NumPRELoad, "Number of loads PRE'd"); 67 68 static cl::opt<bool> EnablePRE("enable-pre", 69 cl::init(true), cl::Hidden); 70 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 71 72 // Maximum allowed recursion depth. 73 static cl::opt<uint32_t> 74 MaxRecurseDepth("max-recurse-depth", cl::Hidden, cl::init(1000), cl::ZeroOrMore, 75 cl::desc("Max recurse depth (default = 1000)")); 76 77 //===----------------------------------------------------------------------===// 78 // ValueTable Class 79 //===----------------------------------------------------------------------===// 80 81 /// This class holds the mapping between values and value numbers. It is used 82 /// as an efficient mechanism to determine the expression-wise equivalence of 83 /// two values. 84 namespace { 85 struct Expression { 86 uint32_t opcode; 87 Type *type; 88 SmallVector<uint32_t, 4> varargs; 89 90 Expression(uint32_t o = ~2U) : opcode(o) { } 91 92 bool operator==(const Expression &other) const { 93 if (opcode != other.opcode) 94 return false; 95 if (opcode == ~0U || opcode == ~1U) 96 return true; 97 if (type != other.type) 98 return false; 99 if (varargs != other.varargs) 100 return false; 101 return true; 102 } 103 104 friend hash_code hash_value(const Expression &Value) { 105 return hash_combine(Value.opcode, Value.type, 106 hash_combine_range(Value.varargs.begin(), 107 Value.varargs.end())); 108 } 109 }; 110 111 class ValueTable { 112 DenseMap<Value*, uint32_t> valueNumbering; 113 DenseMap<Expression, uint32_t> expressionNumbering; 114 AliasAnalysis *AA; 115 MemoryDependenceAnalysis *MD; 116 DominatorTree *DT; 117 118 uint32_t nextValueNumber; 119 120 Expression create_expression(Instruction* I); 121 Expression create_cmp_expression(unsigned Opcode, 122 CmpInst::Predicate Predicate, 123 Value *LHS, Value *RHS); 124 Expression create_extractvalue_expression(ExtractValueInst* EI); 125 uint32_t lookup_or_add_call(CallInst* C); 126 public: 127 ValueTable() : nextValueNumber(1) { } 128 uint32_t lookup_or_add(Value *V); 129 uint32_t lookup(Value *V) const; 130 uint32_t lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Pred, 131 Value *LHS, Value *RHS); 132 bool exists(Value *V) const; 133 void add(Value *V, uint32_t num); 134 void clear(); 135 void erase(Value *v); 136 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 137 AliasAnalysis *getAliasAnalysis() const { return AA; } 138 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 139 void setDomTree(DominatorTree* D) { DT = D; } 140 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 141 void verifyRemoved(const Value *) const; 142 }; 143 } 144 145 namespace llvm { 146 template <> struct DenseMapInfo<Expression> { 147 static inline Expression getEmptyKey() { 148 return ~0U; 149 } 150 151 static inline Expression getTombstoneKey() { 152 return ~1U; 153 } 154 155 static unsigned getHashValue(const Expression e) { 156 using llvm::hash_value; 157 return static_cast<unsigned>(hash_value(e)); 158 } 159 static bool isEqual(const Expression &LHS, const Expression &RHS) { 160 return LHS == RHS; 161 } 162 }; 163 164 } 165 166 //===----------------------------------------------------------------------===// 167 // ValueTable Internal Functions 168 //===----------------------------------------------------------------------===// 169 170 Expression ValueTable::create_expression(Instruction *I) { 171 Expression e; 172 e.type = I->getType(); 173 e.opcode = I->getOpcode(); 174 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 175 OI != OE; ++OI) 176 e.varargs.push_back(lookup_or_add(*OI)); 177 if (I->isCommutative()) { 178 // Ensure that commutative instructions that only differ by a permutation 179 // of their operands get the same value number by sorting the operand value 180 // numbers. Since all commutative instructions have two operands it is more 181 // efficient to sort by hand rather than using, say, std::sort. 182 assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!"); 183 if (e.varargs[0] > e.varargs[1]) 184 std::swap(e.varargs[0], e.varargs[1]); 185 } 186 187 if (CmpInst *C = dyn_cast<CmpInst>(I)) { 188 // Sort the operand value numbers so x<y and y>x get the same value number. 189 CmpInst::Predicate Predicate = C->getPredicate(); 190 if (e.varargs[0] > e.varargs[1]) { 191 std::swap(e.varargs[0], e.varargs[1]); 192 Predicate = CmpInst::getSwappedPredicate(Predicate); 193 } 194 e.opcode = (C->getOpcode() << 8) | Predicate; 195 } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) { 196 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 197 II != IE; ++II) 198 e.varargs.push_back(*II); 199 } 200 201 return e; 202 } 203 204 Expression ValueTable::create_cmp_expression(unsigned Opcode, 205 CmpInst::Predicate Predicate, 206 Value *LHS, Value *RHS) { 207 assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) && 208 "Not a comparison!"); 209 Expression e; 210 e.type = CmpInst::makeCmpResultType(LHS->getType()); 211 e.varargs.push_back(lookup_or_add(LHS)); 212 e.varargs.push_back(lookup_or_add(RHS)); 213 214 // Sort the operand value numbers so x<y and y>x get the same value number. 215 if (e.varargs[0] > e.varargs[1]) { 216 std::swap(e.varargs[0], e.varargs[1]); 217 Predicate = CmpInst::getSwappedPredicate(Predicate); 218 } 219 e.opcode = (Opcode << 8) | Predicate; 220 return e; 221 } 222 223 Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) { 224 assert(EI && "Not an ExtractValueInst?"); 225 Expression e; 226 e.type = EI->getType(); 227 e.opcode = 0; 228 229 IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand()); 230 if (I != nullptr && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) { 231 // EI might be an extract from one of our recognised intrinsics. If it 232 // is we'll synthesize a semantically equivalent expression instead on 233 // an extract value expression. 234 switch (I->getIntrinsicID()) { 235 case Intrinsic::sadd_with_overflow: 236 case Intrinsic::uadd_with_overflow: 237 e.opcode = Instruction::Add; 238 break; 239 case Intrinsic::ssub_with_overflow: 240 case Intrinsic::usub_with_overflow: 241 e.opcode = Instruction::Sub; 242 break; 243 case Intrinsic::smul_with_overflow: 244 case Intrinsic::umul_with_overflow: 245 e.opcode = Instruction::Mul; 246 break; 247 default: 248 break; 249 } 250 251 if (e.opcode != 0) { 252 // Intrinsic recognized. Grab its args to finish building the expression. 253 assert(I->getNumArgOperands() == 2 && 254 "Expect two args for recognised intrinsics."); 255 e.varargs.push_back(lookup_or_add(I->getArgOperand(0))); 256 e.varargs.push_back(lookup_or_add(I->getArgOperand(1))); 257 return e; 258 } 259 } 260 261 // Not a recognised intrinsic. Fall back to producing an extract value 262 // expression. 263 e.opcode = EI->getOpcode(); 264 for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end(); 265 OI != OE; ++OI) 266 e.varargs.push_back(lookup_or_add(*OI)); 267 268 for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end(); 269 II != IE; ++II) 270 e.varargs.push_back(*II); 271 272 return e; 273 } 274 275 //===----------------------------------------------------------------------===// 276 // ValueTable External Functions 277 //===----------------------------------------------------------------------===// 278 279 /// add - Insert a value into the table with a specified value number. 280 void ValueTable::add(Value *V, uint32_t num) { 281 valueNumbering.insert(std::make_pair(V, num)); 282 } 283 284 uint32_t ValueTable::lookup_or_add_call(CallInst *C) { 285 if (AA->doesNotAccessMemory(C)) { 286 Expression exp = create_expression(C); 287 uint32_t &e = expressionNumbering[exp]; 288 if (!e) e = nextValueNumber++; 289 valueNumbering[C] = e; 290 return e; 291 } else if (AA->onlyReadsMemory(C)) { 292 Expression exp = create_expression(C); 293 uint32_t &e = expressionNumbering[exp]; 294 if (!e) { 295 e = nextValueNumber++; 296 valueNumbering[C] = e; 297 return e; 298 } 299 if (!MD) { 300 e = nextValueNumber++; 301 valueNumbering[C] = e; 302 return e; 303 } 304 305 MemDepResult local_dep = MD->getDependency(C); 306 307 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 308 valueNumbering[C] = nextValueNumber; 309 return nextValueNumber++; 310 } 311 312 if (local_dep.isDef()) { 313 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 314 315 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { 316 valueNumbering[C] = nextValueNumber; 317 return nextValueNumber++; 318 } 319 320 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 321 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 322 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i)); 323 if (c_vn != cd_vn) { 324 valueNumbering[C] = nextValueNumber; 325 return nextValueNumber++; 326 } 327 } 328 329 uint32_t v = lookup_or_add(local_cdep); 330 valueNumbering[C] = v; 331 return v; 332 } 333 334 // Non-local case. 335 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 336 MD->getNonLocalCallDependency(CallSite(C)); 337 // FIXME: Move the checking logic to MemDep! 338 CallInst* cdep = nullptr; 339 340 // Check to see if we have a single dominating call instruction that is 341 // identical to C. 342 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 343 const NonLocalDepEntry *I = &deps[i]; 344 if (I->getResult().isNonLocal()) 345 continue; 346 347 // We don't handle non-definitions. If we already have a call, reject 348 // instruction dependencies. 349 if (!I->getResult().isDef() || cdep != nullptr) { 350 cdep = nullptr; 351 break; 352 } 353 354 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); 355 // FIXME: All duplicated with non-local case. 356 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ 357 cdep = NonLocalDepCall; 358 continue; 359 } 360 361 cdep = nullptr; 362 break; 363 } 364 365 if (!cdep) { 366 valueNumbering[C] = nextValueNumber; 367 return nextValueNumber++; 368 } 369 370 if (cdep->getNumArgOperands() != C->getNumArgOperands()) { 371 valueNumbering[C] = nextValueNumber; 372 return nextValueNumber++; 373 } 374 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 375 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 376 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i)); 377 if (c_vn != cd_vn) { 378 valueNumbering[C] = nextValueNumber; 379 return nextValueNumber++; 380 } 381 } 382 383 uint32_t v = lookup_or_add(cdep); 384 valueNumbering[C] = v; 385 return v; 386 387 } else { 388 valueNumbering[C] = nextValueNumber; 389 return nextValueNumber++; 390 } 391 } 392 393 /// Returns true if a value number exists for the specified value. 394 bool ValueTable::exists(Value *V) const { return valueNumbering.count(V) != 0; } 395 396 /// lookup_or_add - Returns the value number for the specified value, assigning 397 /// it a new number if it did not have one before. 398 uint32_t ValueTable::lookup_or_add(Value *V) { 399 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 400 if (VI != valueNumbering.end()) 401 return VI->second; 402 403 if (!isa<Instruction>(V)) { 404 valueNumbering[V] = nextValueNumber; 405 return nextValueNumber++; 406 } 407 408 Instruction* I = cast<Instruction>(V); 409 Expression exp; 410 switch (I->getOpcode()) { 411 case Instruction::Call: 412 return lookup_or_add_call(cast<CallInst>(I)); 413 case Instruction::Add: 414 case Instruction::FAdd: 415 case Instruction::Sub: 416 case Instruction::FSub: 417 case Instruction::Mul: 418 case Instruction::FMul: 419 case Instruction::UDiv: 420 case Instruction::SDiv: 421 case Instruction::FDiv: 422 case Instruction::URem: 423 case Instruction::SRem: 424 case Instruction::FRem: 425 case Instruction::Shl: 426 case Instruction::LShr: 427 case Instruction::AShr: 428 case Instruction::And: 429 case Instruction::Or: 430 case Instruction::Xor: 431 case Instruction::ICmp: 432 case Instruction::FCmp: 433 case Instruction::Trunc: 434 case Instruction::ZExt: 435 case Instruction::SExt: 436 case Instruction::FPToUI: 437 case Instruction::FPToSI: 438 case Instruction::UIToFP: 439 case Instruction::SIToFP: 440 case Instruction::FPTrunc: 441 case Instruction::FPExt: 442 case Instruction::PtrToInt: 443 case Instruction::IntToPtr: 444 case Instruction::BitCast: 445 case Instruction::Select: 446 case Instruction::ExtractElement: 447 case Instruction::InsertElement: 448 case Instruction::ShuffleVector: 449 case Instruction::InsertValue: 450 case Instruction::GetElementPtr: 451 exp = create_expression(I); 452 break; 453 case Instruction::ExtractValue: 454 exp = create_extractvalue_expression(cast<ExtractValueInst>(I)); 455 break; 456 default: 457 valueNumbering[V] = nextValueNumber; 458 return nextValueNumber++; 459 } 460 461 uint32_t& e = expressionNumbering[exp]; 462 if (!e) e = nextValueNumber++; 463 valueNumbering[V] = e; 464 return e; 465 } 466 467 /// Returns the value number of the specified value. Fails if 468 /// the value has not yet been numbered. 469 uint32_t ValueTable::lookup(Value *V) const { 470 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); 471 assert(VI != valueNumbering.end() && "Value not numbered?"); 472 return VI->second; 473 } 474 475 /// Returns the value number of the given comparison, 476 /// assigning it a new number if it did not have one before. Useful when 477 /// we deduced the result of a comparison, but don't immediately have an 478 /// instruction realizing that comparison to hand. 479 uint32_t ValueTable::lookup_or_add_cmp(unsigned Opcode, 480 CmpInst::Predicate Predicate, 481 Value *LHS, Value *RHS) { 482 Expression exp = create_cmp_expression(Opcode, Predicate, LHS, RHS); 483 uint32_t& e = expressionNumbering[exp]; 484 if (!e) e = nextValueNumber++; 485 return e; 486 } 487 488 /// Remove all entries from the ValueTable. 489 void ValueTable::clear() { 490 valueNumbering.clear(); 491 expressionNumbering.clear(); 492 nextValueNumber = 1; 493 } 494 495 /// Remove a value from the value numbering. 496 void ValueTable::erase(Value *V) { 497 valueNumbering.erase(V); 498 } 499 500 /// verifyRemoved - Verify that the value is removed from all internal data 501 /// structures. 502 void ValueTable::verifyRemoved(const Value *V) const { 503 for (DenseMap<Value*, uint32_t>::const_iterator 504 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 505 assert(I->first != V && "Inst still occurs in value numbering map!"); 506 } 507 } 508 509 //===----------------------------------------------------------------------===// 510 // GVN Pass 511 //===----------------------------------------------------------------------===// 512 513 namespace { 514 class GVN; 515 struct AvailableValueInBlock { 516 /// BB - The basic block in question. 517 BasicBlock *BB; 518 enum ValType { 519 SimpleVal, // A simple offsetted value that is accessed. 520 LoadVal, // A value produced by a load. 521 MemIntrin, // A memory intrinsic which is loaded from. 522 UndefVal // A UndefValue representing a value from dead block (which 523 // is not yet physically removed from the CFG). 524 }; 525 526 /// V - The value that is live out of the block. 527 PointerIntPair<Value *, 2, ValType> Val; 528 529 /// Offset - The byte offset in Val that is interesting for the load query. 530 unsigned Offset; 531 532 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 533 unsigned Offset = 0) { 534 AvailableValueInBlock Res; 535 Res.BB = BB; 536 Res.Val.setPointer(V); 537 Res.Val.setInt(SimpleVal); 538 Res.Offset = Offset; 539 return Res; 540 } 541 542 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 543 unsigned Offset = 0) { 544 AvailableValueInBlock Res; 545 Res.BB = BB; 546 Res.Val.setPointer(MI); 547 Res.Val.setInt(MemIntrin); 548 Res.Offset = Offset; 549 return Res; 550 } 551 552 static AvailableValueInBlock getLoad(BasicBlock *BB, LoadInst *LI, 553 unsigned Offset = 0) { 554 AvailableValueInBlock Res; 555 Res.BB = BB; 556 Res.Val.setPointer(LI); 557 Res.Val.setInt(LoadVal); 558 Res.Offset = Offset; 559 return Res; 560 } 561 562 static AvailableValueInBlock getUndef(BasicBlock *BB) { 563 AvailableValueInBlock Res; 564 Res.BB = BB; 565 Res.Val.setPointer(nullptr); 566 Res.Val.setInt(UndefVal); 567 Res.Offset = 0; 568 return Res; 569 } 570 571 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 572 bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; } 573 bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; } 574 bool isUndefValue() const { return Val.getInt() == UndefVal; } 575 576 Value *getSimpleValue() const { 577 assert(isSimpleValue() && "Wrong accessor"); 578 return Val.getPointer(); 579 } 580 581 LoadInst *getCoercedLoadValue() const { 582 assert(isCoercedLoadValue() && "Wrong accessor"); 583 return cast<LoadInst>(Val.getPointer()); 584 } 585 586 MemIntrinsic *getMemIntrinValue() const { 587 assert(isMemIntrinValue() && "Wrong accessor"); 588 return cast<MemIntrinsic>(Val.getPointer()); 589 } 590 591 /// Emit code into this block to adjust the value defined here to the 592 /// specified type. This handles various coercion cases. 593 Value *MaterializeAdjustedValue(LoadInst *LI, GVN &gvn) const; 594 }; 595 596 class GVN : public FunctionPass { 597 bool NoLoads; 598 MemoryDependenceAnalysis *MD; 599 DominatorTree *DT; 600 const TargetLibraryInfo *TLI; 601 AssumptionCache *AC; 602 SetVector<BasicBlock *> DeadBlocks; 603 604 ValueTable VN; 605 606 /// A mapping from value numbers to lists of Value*'s that 607 /// have that value number. Use findLeader to query it. 608 struct LeaderTableEntry { 609 Value *Val; 610 const BasicBlock *BB; 611 LeaderTableEntry *Next; 612 }; 613 DenseMap<uint32_t, LeaderTableEntry> LeaderTable; 614 BumpPtrAllocator TableAllocator; 615 616 // Block-local map of equivalent values to their leader, does not 617 // propagate to any successors. Entries added mid-block are applied 618 // to the remaining instructions in the block. 619 SmallMapVector<llvm::Value *, llvm::Constant *, 4> ReplaceWithConstMap; 620 SmallVector<Instruction*, 8> InstrsToErase; 621 622 typedef SmallVector<NonLocalDepResult, 64> LoadDepVect; 623 typedef SmallVector<AvailableValueInBlock, 64> AvailValInBlkVect; 624 typedef SmallVector<BasicBlock*, 64> UnavailBlkVect; 625 626 public: 627 static char ID; // Pass identification, replacement for typeid 628 explicit GVN(bool noloads = false) 629 : FunctionPass(ID), NoLoads(noloads), MD(nullptr) { 630 initializeGVNPass(*PassRegistry::getPassRegistry()); 631 } 632 633 bool runOnFunction(Function &F) override; 634 635 /// This removes the specified instruction from 636 /// our various maps and marks it for deletion. 637 void markInstructionForDeletion(Instruction *I) { 638 VN.erase(I); 639 InstrsToErase.push_back(I); 640 } 641 642 DominatorTree &getDominatorTree() const { return *DT; } 643 AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); } 644 MemoryDependenceAnalysis &getMemDep() const { return *MD; } 645 private: 646 /// Push a new Value to the LeaderTable onto the list for its value number. 647 void addToLeaderTable(uint32_t N, Value *V, const BasicBlock *BB) { 648 LeaderTableEntry &Curr = LeaderTable[N]; 649 if (!Curr.Val) { 650 Curr.Val = V; 651 Curr.BB = BB; 652 return; 653 } 654 655 LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>(); 656 Node->Val = V; 657 Node->BB = BB; 658 Node->Next = Curr.Next; 659 Curr.Next = Node; 660 } 661 662 /// Scan the list of values corresponding to a given 663 /// value number, and remove the given instruction if encountered. 664 void removeFromLeaderTable(uint32_t N, Instruction *I, BasicBlock *BB) { 665 LeaderTableEntry* Prev = nullptr; 666 LeaderTableEntry* Curr = &LeaderTable[N]; 667 668 while (Curr && (Curr->Val != I || Curr->BB != BB)) { 669 Prev = Curr; 670 Curr = Curr->Next; 671 } 672 673 if (!Curr) 674 return; 675 676 if (Prev) { 677 Prev->Next = Curr->Next; 678 } else { 679 if (!Curr->Next) { 680 Curr->Val = nullptr; 681 Curr->BB = nullptr; 682 } else { 683 LeaderTableEntry* Next = Curr->Next; 684 Curr->Val = Next->Val; 685 Curr->BB = Next->BB; 686 Curr->Next = Next->Next; 687 } 688 } 689 } 690 691 // List of critical edges to be split between iterations. 692 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 693 694 // This transformation requires dominator postdominator info 695 void getAnalysisUsage(AnalysisUsage &AU) const override { 696 AU.addRequired<AssumptionCacheTracker>(); 697 AU.addRequired<DominatorTreeWrapperPass>(); 698 AU.addRequired<TargetLibraryInfoWrapperPass>(); 699 if (!NoLoads) 700 AU.addRequired<MemoryDependenceAnalysis>(); 701 AU.addRequired<AAResultsWrapperPass>(); 702 703 AU.addPreserved<DominatorTreeWrapperPass>(); 704 AU.addPreserved<GlobalsAAWrapperPass>(); 705 } 706 707 708 // Helper functions of redundant load elimination 709 bool processLoad(LoadInst *L); 710 bool processNonLocalLoad(LoadInst *L); 711 bool processAssumeIntrinsic(IntrinsicInst *II); 712 void AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, 713 AvailValInBlkVect &ValuesPerBlock, 714 UnavailBlkVect &UnavailableBlocks); 715 bool PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock, 716 UnavailBlkVect &UnavailableBlocks); 717 718 // Other helper routines 719 bool processInstruction(Instruction *I); 720 bool processBlock(BasicBlock *BB); 721 void dump(DenseMap<uint32_t, Value*> &d); 722 bool iterateOnFunction(Function &F); 723 bool performPRE(Function &F); 724 bool performScalarPRE(Instruction *I); 725 bool performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred, 726 unsigned int ValNo); 727 Value *findLeader(const BasicBlock *BB, uint32_t num); 728 void cleanupGlobalSets(); 729 void verifyRemoved(const Instruction *I) const; 730 bool splitCriticalEdges(); 731 BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ); 732 bool replaceOperandsWithConsts(Instruction *I) const; 733 bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root, 734 bool DominatesByEdge); 735 bool processFoldableCondBr(BranchInst *BI); 736 void addDeadBlock(BasicBlock *BB); 737 void assignValNumForDeadCode(); 738 }; 739 740 char GVN::ID = 0; 741 } 742 743 // The public interface to this file... 744 FunctionPass *llvm::createGVNPass(bool NoLoads) { 745 return new GVN(NoLoads); 746 } 747 748 INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) 749 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 750 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) 751 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 752 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 753 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) 754 INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass) 755 INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) 756 757 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 758 void GVN::dump(DenseMap<uint32_t, Value*>& d) { 759 errs() << "{\n"; 760 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 761 E = d.end(); I != E; ++I) { 762 errs() << I->first << "\n"; 763 I->second->dump(); 764 } 765 errs() << "}\n"; 766 } 767 #endif 768 769 /// Return true if we can prove that the value 770 /// we're analyzing is fully available in the specified block. As we go, keep 771 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This 772 /// map is actually a tri-state map with the following values: 773 /// 0) we know the block *is not* fully available. 774 /// 1) we know the block *is* fully available. 775 /// 2) we do not know whether the block is fully available or not, but we are 776 /// currently speculating that it will be. 777 /// 3) we are speculating for this block and have used that to speculate for 778 /// other blocks. 779 static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 780 DenseMap<BasicBlock*, char> &FullyAvailableBlocks, 781 uint32_t RecurseDepth) { 782 if (RecurseDepth > MaxRecurseDepth) 783 return false; 784 785 // Optimistically assume that the block is fully available and check to see 786 // if we already know about this block in one lookup. 787 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 788 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 789 790 // If the entry already existed for this block, return the precomputed value. 791 if (!IV.second) { 792 // If this is a speculative "available" value, mark it as being used for 793 // speculation of other blocks. 794 if (IV.first->second == 2) 795 IV.first->second = 3; 796 return IV.first->second != 0; 797 } 798 799 // Otherwise, see if it is fully available in all predecessors. 800 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 801 802 // If this block has no predecessors, it isn't live-in here. 803 if (PI == PE) 804 goto SpeculationFailure; 805 806 for (; PI != PE; ++PI) 807 // If the value isn't fully available in one of our predecessors, then it 808 // isn't fully available in this block either. Undo our previous 809 // optimistic assumption and bail out. 810 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks,RecurseDepth+1)) 811 goto SpeculationFailure; 812 813 return true; 814 815 // If we get here, we found out that this is not, after 816 // all, a fully-available block. We have a problem if we speculated on this and 817 // used the speculation to mark other blocks as available. 818 SpeculationFailure: 819 char &BBVal = FullyAvailableBlocks[BB]; 820 821 // If we didn't speculate on this, just return with it set to false. 822 if (BBVal == 2) { 823 BBVal = 0; 824 return false; 825 } 826 827 // If we did speculate on this value, we could have blocks set to 1 that are 828 // incorrect. Walk the (transitive) successors of this block and mark them as 829 // 0 if set to one. 830 SmallVector<BasicBlock*, 32> BBWorklist; 831 BBWorklist.push_back(BB); 832 833 do { 834 BasicBlock *Entry = BBWorklist.pop_back_val(); 835 // Note that this sets blocks to 0 (unavailable) if they happen to not 836 // already be in FullyAvailableBlocks. This is safe. 837 char &EntryVal = FullyAvailableBlocks[Entry]; 838 if (EntryVal == 0) continue; // Already unavailable. 839 840 // Mark as unavailable. 841 EntryVal = 0; 842 843 BBWorklist.append(succ_begin(Entry), succ_end(Entry)); 844 } while (!BBWorklist.empty()); 845 846 return false; 847 } 848 849 850 /// Return true if CoerceAvailableValueToLoadType will succeed. 851 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 852 Type *LoadTy, 853 const DataLayout &DL) { 854 // If the loaded or stored value is an first class array or struct, don't try 855 // to transform them. We need to be able to bitcast to integer. 856 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 857 StoredVal->getType()->isStructTy() || 858 StoredVal->getType()->isArrayTy()) 859 return false; 860 861 // The store has to be at least as big as the load. 862 if (DL.getTypeSizeInBits(StoredVal->getType()) < 863 DL.getTypeSizeInBits(LoadTy)) 864 return false; 865 866 return true; 867 } 868 869 /// If we saw a store of a value to memory, and 870 /// then a load from a must-aliased pointer of a different type, try to coerce 871 /// the stored value. LoadedTy is the type of the load we want to replace. 872 /// IRB is IRBuilder used to insert new instructions. 873 /// 874 /// If we can't do it, return null. 875 static Value *CoerceAvailableValueToLoadType(Value *StoredVal, Type *LoadedTy, 876 IRBuilder<> &IRB, 877 const DataLayout &DL) { 878 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, DL)) 879 return nullptr; 880 881 // If this is already the right type, just return it. 882 Type *StoredValTy = StoredVal->getType(); 883 884 uint64_t StoreSize = DL.getTypeSizeInBits(StoredValTy); 885 uint64_t LoadSize = DL.getTypeSizeInBits(LoadedTy); 886 887 // If the store and reload are the same size, we can always reuse it. 888 if (StoreSize == LoadSize) { 889 // Pointer to Pointer -> use bitcast. 890 if (StoredValTy->getScalarType()->isPointerTy() && 891 LoadedTy->getScalarType()->isPointerTy()) 892 return IRB.CreateBitCast(StoredVal, LoadedTy); 893 894 // Convert source pointers to integers, which can be bitcast. 895 if (StoredValTy->getScalarType()->isPointerTy()) { 896 StoredValTy = DL.getIntPtrType(StoredValTy); 897 StoredVal = IRB.CreatePtrToInt(StoredVal, StoredValTy); 898 } 899 900 Type *TypeToCastTo = LoadedTy; 901 if (TypeToCastTo->getScalarType()->isPointerTy()) 902 TypeToCastTo = DL.getIntPtrType(TypeToCastTo); 903 904 if (StoredValTy != TypeToCastTo) 905 StoredVal = IRB.CreateBitCast(StoredVal, TypeToCastTo); 906 907 // Cast to pointer if the load needs a pointer type. 908 if (LoadedTy->getScalarType()->isPointerTy()) 909 StoredVal = IRB.CreateIntToPtr(StoredVal, LoadedTy); 910 911 return StoredVal; 912 } 913 914 // If the loaded value is smaller than the available value, then we can 915 // extract out a piece from it. If the available value is too small, then we 916 // can't do anything. 917 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 918 919 // Convert source pointers to integers, which can be manipulated. 920 if (StoredValTy->getScalarType()->isPointerTy()) { 921 StoredValTy = DL.getIntPtrType(StoredValTy); 922 StoredVal = IRB.CreatePtrToInt(StoredVal, StoredValTy); 923 } 924 925 // Convert vectors and fp to integer, which can be manipulated. 926 if (!StoredValTy->isIntegerTy()) { 927 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 928 StoredVal = IRB.CreateBitCast(StoredVal, StoredValTy); 929 } 930 931 // If this is a big-endian system, we need to shift the value down to the low 932 // bits so that a truncate will work. 933 if (DL.isBigEndian()) { 934 StoredVal = IRB.CreateLShr(StoredVal, StoreSize - LoadSize, "tmp"); 935 } 936 937 // Truncate the integer to the right size now. 938 Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 939 StoredVal = IRB.CreateTrunc(StoredVal, NewIntTy, "trunc"); 940 941 if (LoadedTy == NewIntTy) 942 return StoredVal; 943 944 // If the result is a pointer, inttoptr. 945 if (LoadedTy->getScalarType()->isPointerTy()) 946 return IRB.CreateIntToPtr(StoredVal, LoadedTy, "inttoptr"); 947 948 // Otherwise, bitcast. 949 return IRB.CreateBitCast(StoredVal, LoadedTy, "bitcast"); 950 } 951 952 /// This function is called when we have a 953 /// memdep query of a load that ends up being a clobbering memory write (store, 954 /// memset, memcpy, memmove). This means that the write *may* provide bits used 955 /// by the load but we can't be sure because the pointers don't mustalias. 956 /// 957 /// Check this case to see if there is anything more we can do before we give 958 /// up. This returns -1 if we have to give up, or a byte number in the stored 959 /// value of the piece that feeds the load. 960 static int AnalyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr, 961 Value *WritePtr, 962 uint64_t WriteSizeInBits, 963 const DataLayout &DL) { 964 // If the loaded or stored value is a first class array or struct, don't try 965 // to transform them. We need to be able to bitcast to integer. 966 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 967 return -1; 968 969 int64_t StoreOffset = 0, LoadOffset = 0; 970 Value *StoreBase = 971 GetPointerBaseWithConstantOffset(WritePtr, StoreOffset, DL); 972 Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, DL); 973 if (StoreBase != LoadBase) 974 return -1; 975 976 // If the load and store are to the exact same address, they should have been 977 // a must alias. AA must have gotten confused. 978 // FIXME: Study to see if/when this happens. One case is forwarding a memset 979 // to a load from the base of the memset. 980 #if 0 981 if (LoadOffset == StoreOffset) { 982 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 983 << "Base = " << *StoreBase << "\n" 984 << "Store Ptr = " << *WritePtr << "\n" 985 << "Store Offs = " << StoreOffset << "\n" 986 << "Load Ptr = " << *LoadPtr << "\n"; 987 abort(); 988 } 989 #endif 990 991 // If the load and store don't overlap at all, the store doesn't provide 992 // anything to the load. In this case, they really don't alias at all, AA 993 // must have gotten confused. 994 uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy); 995 996 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 997 return -1; 998 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 999 LoadSize >>= 3; 1000 1001 1002 bool isAAFailure = false; 1003 if (StoreOffset < LoadOffset) 1004 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1005 else 1006 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1007 1008 if (isAAFailure) { 1009 #if 0 1010 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1011 << "Base = " << *StoreBase << "\n" 1012 << "Store Ptr = " << *WritePtr << "\n" 1013 << "Store Offs = " << StoreOffset << "\n" 1014 << "Load Ptr = " << *LoadPtr << "\n"; 1015 abort(); 1016 #endif 1017 return -1; 1018 } 1019 1020 // If the Load isn't completely contained within the stored bits, we don't 1021 // have all the bits to feed it. We could do something crazy in the future 1022 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1023 // valuable. 1024 if (StoreOffset > LoadOffset || 1025 StoreOffset+StoreSize < LoadOffset+LoadSize) 1026 return -1; 1027 1028 // Okay, we can do this transformation. Return the number of bytes into the 1029 // store that the load is. 1030 return LoadOffset-StoreOffset; 1031 } 1032 1033 /// This function is called when we have a 1034 /// memdep query of a load that ends up being a clobbering store. 1035 static int AnalyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr, 1036 StoreInst *DepSI) { 1037 // Cannot handle reading from store of first-class aggregate yet. 1038 if (DepSI->getValueOperand()->getType()->isStructTy() || 1039 DepSI->getValueOperand()->getType()->isArrayTy()) 1040 return -1; 1041 1042 const DataLayout &DL = DepSI->getModule()->getDataLayout(); 1043 Value *StorePtr = DepSI->getPointerOperand(); 1044 uint64_t StoreSize =DL.getTypeSizeInBits(DepSI->getValueOperand()->getType()); 1045 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1046 StorePtr, StoreSize, DL); 1047 } 1048 1049 /// This function is called when we have a 1050 /// memdep query of a load that ends up being clobbered by another load. See if 1051 /// the other load can feed into the second load. 1052 static int AnalyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr, 1053 LoadInst *DepLI, const DataLayout &DL){ 1054 // Cannot handle reading from store of first-class aggregate yet. 1055 if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy()) 1056 return -1; 1057 1058 Value *DepPtr = DepLI->getPointerOperand(); 1059 uint64_t DepSize = DL.getTypeSizeInBits(DepLI->getType()); 1060 int R = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, DL); 1061 if (R != -1) return R; 1062 1063 // If we have a load/load clobber an DepLI can be widened to cover this load, 1064 // then we should widen it! 1065 int64_t LoadOffs = 0; 1066 const Value *LoadBase = 1067 GetPointerBaseWithConstantOffset(LoadPtr, LoadOffs, DL); 1068 unsigned LoadSize = DL.getTypeStoreSize(LoadTy); 1069 1070 unsigned Size = MemoryDependenceAnalysis::getLoadLoadClobberFullWidthSize( 1071 LoadBase, LoadOffs, LoadSize, DepLI); 1072 if (Size == 0) return -1; 1073 1074 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, Size*8, DL); 1075 } 1076 1077 1078 1079 static int AnalyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr, 1080 MemIntrinsic *MI, 1081 const DataLayout &DL) { 1082 // If the mem operation is a non-constant size, we can't handle it. 1083 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 1084 if (!SizeCst) return -1; 1085 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 1086 1087 // If this is memset, we just need to see if the offset is valid in the size 1088 // of the memset.. 1089 if (MI->getIntrinsicID() == Intrinsic::memset) 1090 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 1091 MemSizeInBits, DL); 1092 1093 // If we have a memcpy/memmove, the only case we can handle is if this is a 1094 // copy from constant memory. In that case, we can read directly from the 1095 // constant memory. 1096 MemTransferInst *MTI = cast<MemTransferInst>(MI); 1097 1098 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 1099 if (!Src) return -1; 1100 1101 GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, DL)); 1102 if (!GV || !GV->isConstant()) return -1; 1103 1104 // See if the access is within the bounds of the transfer. 1105 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1106 MI->getDest(), MemSizeInBits, DL); 1107 if (Offset == -1) 1108 return Offset; 1109 1110 unsigned AS = Src->getType()->getPointerAddressSpace(); 1111 // Otherwise, see if we can constant fold a load from the constant with the 1112 // offset applied as appropriate. 1113 Src = ConstantExpr::getBitCast(Src, 1114 Type::getInt8PtrTy(Src->getContext(), AS)); 1115 Constant *OffsetCst = 1116 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1117 Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()), Src, 1118 OffsetCst); 1119 Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS)); 1120 if (ConstantFoldLoadFromConstPtr(Src, DL)) 1121 return Offset; 1122 return -1; 1123 } 1124 1125 1126 /// This function is called when we have a 1127 /// memdep query of a load that ends up being a clobbering store. This means 1128 /// that the store provides bits used by the load but we the pointers don't 1129 /// mustalias. Check this case to see if there is anything more we can do 1130 /// before we give up. 1131 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1132 Type *LoadTy, 1133 Instruction *InsertPt, const DataLayout &DL){ 1134 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1135 1136 uint64_t StoreSize = (DL.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; 1137 uint64_t LoadSize = (DL.getTypeSizeInBits(LoadTy) + 7) / 8; 1138 1139 IRBuilder<> Builder(InsertPt); 1140 1141 // Compute which bits of the stored value are being used by the load. Convert 1142 // to an integer type to start with. 1143 if (SrcVal->getType()->getScalarType()->isPointerTy()) 1144 SrcVal = Builder.CreatePtrToInt(SrcVal, 1145 DL.getIntPtrType(SrcVal->getType())); 1146 if (!SrcVal->getType()->isIntegerTy()) 1147 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8)); 1148 1149 // Shift the bits to the least significant depending on endianness. 1150 unsigned ShiftAmt; 1151 if (DL.isLittleEndian()) 1152 ShiftAmt = Offset*8; 1153 else 1154 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1155 1156 if (ShiftAmt) 1157 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt); 1158 1159 if (LoadSize != StoreSize) 1160 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8)); 1161 1162 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, Builder, DL); 1163 } 1164 1165 /// This function is called when we have a 1166 /// memdep query of a load that ends up being a clobbering load. This means 1167 /// that the load *may* provide bits used by the load but we can't be sure 1168 /// because the pointers don't mustalias. Check this case to see if there is 1169 /// anything more we can do before we give up. 1170 static Value *GetLoadValueForLoad(LoadInst *SrcVal, unsigned Offset, 1171 Type *LoadTy, Instruction *InsertPt, 1172 GVN &gvn) { 1173 const DataLayout &DL = SrcVal->getModule()->getDataLayout(); 1174 // If Offset+LoadTy exceeds the size of SrcVal, then we must be wanting to 1175 // widen SrcVal out to a larger load. 1176 unsigned SrcValSize = DL.getTypeStoreSize(SrcVal->getType()); 1177 unsigned LoadSize = DL.getTypeStoreSize(LoadTy); 1178 if (Offset+LoadSize > SrcValSize) { 1179 assert(SrcVal->isSimple() && "Cannot widen volatile/atomic load!"); 1180 assert(SrcVal->getType()->isIntegerTy() && "Can't widen non-integer load"); 1181 // If we have a load/load clobber an DepLI can be widened to cover this 1182 // load, then we should widen it to the next power of 2 size big enough! 1183 unsigned NewLoadSize = Offset+LoadSize; 1184 if (!isPowerOf2_32(NewLoadSize)) 1185 NewLoadSize = NextPowerOf2(NewLoadSize); 1186 1187 Value *PtrVal = SrcVal->getPointerOperand(); 1188 1189 // Insert the new load after the old load. This ensures that subsequent 1190 // memdep queries will find the new load. We can't easily remove the old 1191 // load completely because it is already in the value numbering table. 1192 IRBuilder<> Builder(SrcVal->getParent(), ++BasicBlock::iterator(SrcVal)); 1193 Type *DestPTy = 1194 IntegerType::get(LoadTy->getContext(), NewLoadSize*8); 1195 DestPTy = PointerType::get(DestPTy, 1196 PtrVal->getType()->getPointerAddressSpace()); 1197 Builder.SetCurrentDebugLocation(SrcVal->getDebugLoc()); 1198 PtrVal = Builder.CreateBitCast(PtrVal, DestPTy); 1199 LoadInst *NewLoad = Builder.CreateLoad(PtrVal); 1200 NewLoad->takeName(SrcVal); 1201 NewLoad->setAlignment(SrcVal->getAlignment()); 1202 1203 DEBUG(dbgs() << "GVN WIDENED LOAD: " << *SrcVal << "\n"); 1204 DEBUG(dbgs() << "TO: " << *NewLoad << "\n"); 1205 1206 // Replace uses of the original load with the wider load. On a big endian 1207 // system, we need to shift down to get the relevant bits. 1208 Value *RV = NewLoad; 1209 if (DL.isBigEndian()) 1210 RV = Builder.CreateLShr(RV, 1211 NewLoadSize*8-SrcVal->getType()->getPrimitiveSizeInBits()); 1212 RV = Builder.CreateTrunc(RV, SrcVal->getType()); 1213 SrcVal->replaceAllUsesWith(RV); 1214 1215 // We would like to use gvn.markInstructionForDeletion here, but we can't 1216 // because the load is already memoized into the leader map table that GVN 1217 // tracks. It is potentially possible to remove the load from the table, 1218 // but then there all of the operations based on it would need to be 1219 // rehashed. Just leave the dead load around. 1220 gvn.getMemDep().removeInstruction(SrcVal); 1221 SrcVal = NewLoad; 1222 } 1223 1224 return GetStoreValueForLoad(SrcVal, Offset, LoadTy, InsertPt, DL); 1225 } 1226 1227 1228 /// This function is called when we have a 1229 /// memdep query of a load that ends up being a clobbering mem intrinsic. 1230 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1231 Type *LoadTy, Instruction *InsertPt, 1232 const DataLayout &DL){ 1233 LLVMContext &Ctx = LoadTy->getContext(); 1234 uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy)/8; 1235 1236 IRBuilder<> Builder(InsertPt); 1237 1238 // We know that this method is only called when the mem transfer fully 1239 // provides the bits for the load. 1240 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1241 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1242 // independently of what the offset is. 1243 Value *Val = MSI->getValue(); 1244 if (LoadSize != 1) 1245 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1246 1247 Value *OneElt = Val; 1248 1249 // Splat the value out to the right number of bits. 1250 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1251 // If we can double the number of bytes set, do it. 1252 if (NumBytesSet*2 <= LoadSize) { 1253 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1254 Val = Builder.CreateOr(Val, ShVal); 1255 NumBytesSet <<= 1; 1256 continue; 1257 } 1258 1259 // Otherwise insert one byte at a time. 1260 Value *ShVal = Builder.CreateShl(Val, 1*8); 1261 Val = Builder.CreateOr(OneElt, ShVal); 1262 ++NumBytesSet; 1263 } 1264 1265 return CoerceAvailableValueToLoadType(Val, LoadTy, Builder, DL); 1266 } 1267 1268 // Otherwise, this is a memcpy/memmove from a constant global. 1269 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 1270 Constant *Src = cast<Constant>(MTI->getSource()); 1271 unsigned AS = Src->getType()->getPointerAddressSpace(); 1272 1273 // Otherwise, see if we can constant fold a load from the constant with the 1274 // offset applied as appropriate. 1275 Src = ConstantExpr::getBitCast(Src, 1276 Type::getInt8PtrTy(Src->getContext(), AS)); 1277 Constant *OffsetCst = 1278 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1279 Src = ConstantExpr::getGetElementPtr(Type::getInt8Ty(Src->getContext()), Src, 1280 OffsetCst); 1281 Src = ConstantExpr::getBitCast(Src, PointerType::get(LoadTy, AS)); 1282 return ConstantFoldLoadFromConstPtr(Src, DL); 1283 } 1284 1285 1286 /// Given a set of loads specified by ValuesPerBlock, 1287 /// construct SSA form, allowing us to eliminate LI. This returns the value 1288 /// that should be used at LI's definition site. 1289 static Value *ConstructSSAForLoadSet(LoadInst *LI, 1290 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1291 GVN &gvn) { 1292 // Check for the fully redundant, dominating load case. In this case, we can 1293 // just use the dominating value directly. 1294 if (ValuesPerBlock.size() == 1 && 1295 gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB, 1296 LI->getParent())) { 1297 assert(!ValuesPerBlock[0].isUndefValue() && "Dead BB dominate this block"); 1298 return ValuesPerBlock[0].MaterializeAdjustedValue(LI, gvn); 1299 } 1300 1301 // Otherwise, we have to construct SSA form. 1302 SmallVector<PHINode*, 8> NewPHIs; 1303 SSAUpdater SSAUpdate(&NewPHIs); 1304 SSAUpdate.Initialize(LI->getType(), LI->getName()); 1305 1306 for (const AvailableValueInBlock &AV : ValuesPerBlock) { 1307 BasicBlock *BB = AV.BB; 1308 1309 if (SSAUpdate.HasValueForBlock(BB)) 1310 continue; 1311 1312 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LI, gvn)); 1313 } 1314 1315 // Perform PHI construction. 1316 return SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1317 } 1318 1319 Value *AvailableValueInBlock::MaterializeAdjustedValue(LoadInst *LI, 1320 GVN &gvn) const { 1321 Value *Res; 1322 Type *LoadTy = LI->getType(); 1323 const DataLayout &DL = LI->getModule()->getDataLayout(); 1324 if (isSimpleValue()) { 1325 Res = getSimpleValue(); 1326 if (Res->getType() != LoadTy) { 1327 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), DL); 1328 1329 DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1330 << *getSimpleValue() << '\n' 1331 << *Res << '\n' << "\n\n\n"); 1332 } 1333 } else if (isCoercedLoadValue()) { 1334 LoadInst *Load = getCoercedLoadValue(); 1335 if (Load->getType() == LoadTy && Offset == 0) { 1336 Res = Load; 1337 } else { 1338 Res = GetLoadValueForLoad(Load, Offset, LoadTy, BB->getTerminator(), 1339 gvn); 1340 1341 DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " " 1342 << *getCoercedLoadValue() << '\n' 1343 << *Res << '\n' << "\n\n\n"); 1344 } 1345 } else if (isMemIntrinValue()) { 1346 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, LoadTy, 1347 BB->getTerminator(), DL); 1348 DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1349 << " " << *getMemIntrinValue() << '\n' 1350 << *Res << '\n' << "\n\n\n"); 1351 } else { 1352 assert(isUndefValue() && "Should be UndefVal"); 1353 DEBUG(dbgs() << "GVN COERCED NONLOCAL Undef:\n";); 1354 return UndefValue::get(LoadTy); 1355 } 1356 return Res; 1357 } 1358 1359 static bool isLifetimeStart(const Instruction *Inst) { 1360 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1361 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1362 return false; 1363 } 1364 1365 void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, 1366 AvailValInBlkVect &ValuesPerBlock, 1367 UnavailBlkVect &UnavailableBlocks) { 1368 1369 // Filter out useless results (non-locals, etc). Keep track of the blocks 1370 // where we have a value available in repl, also keep track of whether we see 1371 // dependencies that produce an unknown value for the load (such as a call 1372 // that could potentially clobber the load). 1373 unsigned NumDeps = Deps.size(); 1374 const DataLayout &DL = LI->getModule()->getDataLayout(); 1375 for (unsigned i = 0, e = NumDeps; i != e; ++i) { 1376 BasicBlock *DepBB = Deps[i].getBB(); 1377 MemDepResult DepInfo = Deps[i].getResult(); 1378 1379 if (DeadBlocks.count(DepBB)) { 1380 // Dead dependent mem-op disguise as a load evaluating the same value 1381 // as the load in question. 1382 ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB)); 1383 continue; 1384 } 1385 1386 if (!DepInfo.isDef() && !DepInfo.isClobber()) { 1387 UnavailableBlocks.push_back(DepBB); 1388 continue; 1389 } 1390 1391 if (DepInfo.isClobber()) { 1392 // The address being loaded in this non-local block may not be the same as 1393 // the pointer operand of the load if PHI translation occurs. Make sure 1394 // to consider the right address. 1395 Value *Address = Deps[i].getAddress(); 1396 1397 // If the dependence is to a store that writes to a superset of the bits 1398 // read by the load, we can extract the bits we need for the load from the 1399 // stored value. 1400 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1401 if (Address) { 1402 int Offset = 1403 AnalyzeLoadFromClobberingStore(LI->getType(), Address, DepSI); 1404 if (Offset != -1) { 1405 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1406 DepSI->getValueOperand(), 1407 Offset)); 1408 continue; 1409 } 1410 } 1411 } 1412 1413 // Check to see if we have something like this: 1414 // load i32* P 1415 // load i8* (P+1) 1416 // if we have this, replace the later with an extraction from the former. 1417 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) { 1418 // If this is a clobber and L is the first instruction in its block, then 1419 // we have the first instruction in the entry block. 1420 if (DepLI != LI && Address) { 1421 int Offset = 1422 AnalyzeLoadFromClobberingLoad(LI->getType(), Address, DepLI, DL); 1423 1424 if (Offset != -1) { 1425 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB,DepLI, 1426 Offset)); 1427 continue; 1428 } 1429 } 1430 } 1431 1432 // If the clobbering value is a memset/memcpy/memmove, see if we can 1433 // forward a value on from it. 1434 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1435 if (Address) { 1436 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, 1437 DepMI, DL); 1438 if (Offset != -1) { 1439 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1440 Offset)); 1441 continue; 1442 } 1443 } 1444 } 1445 1446 UnavailableBlocks.push_back(DepBB); 1447 continue; 1448 } 1449 1450 // DepInfo.isDef() here 1451 1452 Instruction *DepInst = DepInfo.getInst(); 1453 1454 // Loading the allocation -> undef. 1455 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) || 1456 // Loading immediately after lifetime begin -> undef. 1457 isLifetimeStart(DepInst)) { 1458 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1459 UndefValue::get(LI->getType()))); 1460 continue; 1461 } 1462 1463 // Loading from calloc (which zero initializes memory) -> zero 1464 if (isCallocLikeFn(DepInst, TLI)) { 1465 ValuesPerBlock.push_back(AvailableValueInBlock::get( 1466 DepBB, Constant::getNullValue(LI->getType()))); 1467 continue; 1468 } 1469 1470 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1471 // Reject loads and stores that are to the same address but are of 1472 // different types if we have to. 1473 if (S->getValueOperand()->getType() != LI->getType()) { 1474 // If the stored value is larger or equal to the loaded value, we can 1475 // reuse it. 1476 if (!CanCoerceMustAliasedValueToLoad(S->getValueOperand(), 1477 LI->getType(), DL)) { 1478 UnavailableBlocks.push_back(DepBB); 1479 continue; 1480 } 1481 } 1482 1483 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1484 S->getValueOperand())); 1485 continue; 1486 } 1487 1488 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1489 // If the types mismatch and we can't handle it, reject reuse of the load. 1490 if (LD->getType() != LI->getType()) { 1491 // If the stored value is larger or equal to the loaded value, we can 1492 // reuse it. 1493 if (!CanCoerceMustAliasedValueToLoad(LD, LI->getType(), DL)) { 1494 UnavailableBlocks.push_back(DepBB); 1495 continue; 1496 } 1497 } 1498 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB, LD)); 1499 continue; 1500 } 1501 1502 UnavailableBlocks.push_back(DepBB); 1503 } 1504 } 1505 1506 bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock, 1507 UnavailBlkVect &UnavailableBlocks) { 1508 // Okay, we have *some* definitions of the value. This means that the value 1509 // is available in some of our (transitive) predecessors. Lets think about 1510 // doing PRE of this load. This will involve inserting a new load into the 1511 // predecessor when it's not available. We could do this in general, but 1512 // prefer to not increase code size. As such, we only do this when we know 1513 // that we only have to insert *one* load (which means we're basically moving 1514 // the load, not inserting a new one). 1515 1516 SmallPtrSet<BasicBlock *, 4> Blockers(UnavailableBlocks.begin(), 1517 UnavailableBlocks.end()); 1518 1519 // Let's find the first basic block with more than one predecessor. Walk 1520 // backwards through predecessors if needed. 1521 BasicBlock *LoadBB = LI->getParent(); 1522 BasicBlock *TmpBB = LoadBB; 1523 1524 while (TmpBB->getSinglePredecessor()) { 1525 TmpBB = TmpBB->getSinglePredecessor(); 1526 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1527 return false; 1528 if (Blockers.count(TmpBB)) 1529 return false; 1530 1531 // If any of these blocks has more than one successor (i.e. if the edge we 1532 // just traversed was critical), then there are other paths through this 1533 // block along which the load may not be anticipated. Hoisting the load 1534 // above this block would be adding the load to execution paths along 1535 // which it was not previously executed. 1536 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1537 return false; 1538 } 1539 1540 assert(TmpBB); 1541 LoadBB = TmpBB; 1542 1543 // Check to see how many predecessors have the loaded value fully 1544 // available. 1545 MapVector<BasicBlock *, Value *> PredLoads; 1546 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1547 for (const AvailableValueInBlock &AV : ValuesPerBlock) 1548 FullyAvailableBlocks[AV.BB] = true; 1549 for (BasicBlock *UnavailableBB : UnavailableBlocks) 1550 FullyAvailableBlocks[UnavailableBB] = false; 1551 1552 SmallVector<BasicBlock *, 4> CriticalEdgePred; 1553 for (BasicBlock *Pred : predecessors(LoadBB)) { 1554 // If any predecessor block is an EH pad that does not allow non-PHI 1555 // instructions before the terminator, we can't PRE the load. 1556 if (Pred->getTerminator()->isEHPad()) { 1557 DEBUG(dbgs() 1558 << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD PREDECESSOR '" 1559 << Pred->getName() << "': " << *LI << '\n'); 1560 return false; 1561 } 1562 1563 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks, 0)) { 1564 continue; 1565 } 1566 1567 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1568 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1569 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1570 << Pred->getName() << "': " << *LI << '\n'); 1571 return false; 1572 } 1573 1574 if (LoadBB->isEHPad()) { 1575 DEBUG(dbgs() 1576 << "COULD NOT PRE LOAD BECAUSE OF AN EH PAD CRITICAL EDGE '" 1577 << Pred->getName() << "': " << *LI << '\n'); 1578 return false; 1579 } 1580 1581 CriticalEdgePred.push_back(Pred); 1582 } else { 1583 // Only add the predecessors that will not be split for now. 1584 PredLoads[Pred] = nullptr; 1585 } 1586 } 1587 1588 // Decide whether PRE is profitable for this load. 1589 unsigned NumUnavailablePreds = PredLoads.size() + CriticalEdgePred.size(); 1590 assert(NumUnavailablePreds != 0 && 1591 "Fully available value should already be eliminated!"); 1592 1593 // If this load is unavailable in multiple predecessors, reject it. 1594 // FIXME: If we could restructure the CFG, we could make a common pred with 1595 // all the preds that don't have an available LI and insert a new load into 1596 // that one block. 1597 if (NumUnavailablePreds != 1) 1598 return false; 1599 1600 // Split critical edges, and update the unavailable predecessors accordingly. 1601 for (BasicBlock *OrigPred : CriticalEdgePred) { 1602 BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB); 1603 assert(!PredLoads.count(OrigPred) && "Split edges shouldn't be in map!"); 1604 PredLoads[NewPred] = nullptr; 1605 DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->" 1606 << LoadBB->getName() << '\n'); 1607 } 1608 1609 // Check if the load can safely be moved to all the unavailable predecessors. 1610 bool CanDoPRE = true; 1611 const DataLayout &DL = LI->getModule()->getDataLayout(); 1612 SmallVector<Instruction*, 8> NewInsts; 1613 for (auto &PredLoad : PredLoads) { 1614 BasicBlock *UnavailablePred = PredLoad.first; 1615 1616 // Do PHI translation to get its value in the predecessor if necessary. The 1617 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1618 1619 // If all preds have a single successor, then we know it is safe to insert 1620 // the load on the pred (?!?), so we can insert code to materialize the 1621 // pointer if it is not available. 1622 PHITransAddr Address(LI->getPointerOperand(), DL, AC); 1623 Value *LoadPtr = nullptr; 1624 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1625 *DT, NewInsts); 1626 1627 // If we couldn't find or insert a computation of this phi translated value, 1628 // we fail PRE. 1629 if (!LoadPtr) { 1630 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1631 << *LI->getPointerOperand() << "\n"); 1632 CanDoPRE = false; 1633 break; 1634 } 1635 1636 PredLoad.second = LoadPtr; 1637 } 1638 1639 if (!CanDoPRE) { 1640 while (!NewInsts.empty()) { 1641 Instruction *I = NewInsts.pop_back_val(); 1642 if (MD) MD->removeInstruction(I); 1643 I->eraseFromParent(); 1644 } 1645 // HINT: Don't revert the edge-splitting as following transformation may 1646 // also need to split these critical edges. 1647 return !CriticalEdgePred.empty(); 1648 } 1649 1650 // Okay, we can eliminate this load by inserting a reload in the predecessor 1651 // and using PHI construction to get the value in the other predecessors, do 1652 // it. 1653 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1654 DEBUG(if (!NewInsts.empty()) 1655 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1656 << *NewInsts.back() << '\n'); 1657 1658 // Assign value numbers to the new instructions. 1659 for (Instruction *I : NewInsts) { 1660 // FIXME: We really _ought_ to insert these value numbers into their 1661 // parent's availability map. However, in doing so, we risk getting into 1662 // ordering issues. If a block hasn't been processed yet, we would be 1663 // marking a value as AVAIL-IN, which isn't what we intend. 1664 VN.lookup_or_add(I); 1665 } 1666 1667 for (const auto &PredLoad : PredLoads) { 1668 BasicBlock *UnavailablePred = PredLoad.first; 1669 Value *LoadPtr = PredLoad.second; 1670 1671 Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1672 LI->getAlignment(), 1673 UnavailablePred->getTerminator()); 1674 1675 // Transfer the old load's AA tags to the new load. 1676 AAMDNodes Tags; 1677 LI->getAAMetadata(Tags); 1678 if (Tags) 1679 NewLoad->setAAMetadata(Tags); 1680 1681 if (auto *MD = LI->getMetadata(LLVMContext::MD_invariant_load)) 1682 NewLoad->setMetadata(LLVMContext::MD_invariant_load, MD); 1683 if (auto *InvGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group)) 1684 NewLoad->setMetadata(LLVMContext::MD_invariant_group, InvGroupMD); 1685 1686 // Transfer DebugLoc. 1687 NewLoad->setDebugLoc(LI->getDebugLoc()); 1688 1689 // Add the newly created load. 1690 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1691 NewLoad)); 1692 MD->invalidateCachedPointerInfo(LoadPtr); 1693 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); 1694 } 1695 1696 // Perform PHI construction. 1697 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); 1698 LI->replaceAllUsesWith(V); 1699 if (isa<PHINode>(V)) 1700 V->takeName(LI); 1701 if (Instruction *I = dyn_cast<Instruction>(V)) 1702 I->setDebugLoc(LI->getDebugLoc()); 1703 if (V->getType()->getScalarType()->isPointerTy()) 1704 MD->invalidateCachedPointerInfo(V); 1705 markInstructionForDeletion(LI); 1706 ++NumPRELoad; 1707 return true; 1708 } 1709 1710 /// Attempt to eliminate a load whose dependencies are 1711 /// non-local by performing PHI construction. 1712 bool GVN::processNonLocalLoad(LoadInst *LI) { 1713 // non-local speculations are not allowed under asan. 1714 if (LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeAddress)) 1715 return false; 1716 1717 // Step 1: Find the non-local dependencies of the load. 1718 LoadDepVect Deps; 1719 MD->getNonLocalPointerDependency(LI, Deps); 1720 1721 // If we had to process more than one hundred blocks to find the 1722 // dependencies, this load isn't worth worrying about. Optimizing 1723 // it will be too expensive. 1724 unsigned NumDeps = Deps.size(); 1725 if (NumDeps > 100) 1726 return false; 1727 1728 // If we had a phi translation failure, we'll have a single entry which is a 1729 // clobber in the current block. Reject this early. 1730 if (NumDeps == 1 && 1731 !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) { 1732 DEBUG( 1733 dbgs() << "GVN: non-local load "; 1734 LI->printAsOperand(dbgs()); 1735 dbgs() << " has unknown dependencies\n"; 1736 ); 1737 return false; 1738 } 1739 1740 // If this load follows a GEP, see if we can PRE the indices before analyzing. 1741 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0))) { 1742 for (GetElementPtrInst::op_iterator OI = GEP->idx_begin(), 1743 OE = GEP->idx_end(); 1744 OI != OE; ++OI) 1745 if (Instruction *I = dyn_cast<Instruction>(OI->get())) 1746 performScalarPRE(I); 1747 } 1748 1749 // Step 2: Analyze the availability of the load 1750 AvailValInBlkVect ValuesPerBlock; 1751 UnavailBlkVect UnavailableBlocks; 1752 AnalyzeLoadAvailability(LI, Deps, ValuesPerBlock, UnavailableBlocks); 1753 1754 // If we have no predecessors that produce a known value for this load, exit 1755 // early. 1756 if (ValuesPerBlock.empty()) 1757 return false; 1758 1759 // Step 3: Eliminate fully redundancy. 1760 // 1761 // If all of the instructions we depend on produce a known value for this 1762 // load, then it is fully redundant and we can use PHI insertion to compute 1763 // its value. Insert PHIs and remove the fully redundant value now. 1764 if (UnavailableBlocks.empty()) { 1765 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1766 1767 // Perform PHI construction. 1768 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); 1769 LI->replaceAllUsesWith(V); 1770 1771 if (isa<PHINode>(V)) 1772 V->takeName(LI); 1773 if (Instruction *I = dyn_cast<Instruction>(V)) 1774 if (LI->getDebugLoc()) 1775 I->setDebugLoc(LI->getDebugLoc()); 1776 if (V->getType()->getScalarType()->isPointerTy()) 1777 MD->invalidateCachedPointerInfo(V); 1778 markInstructionForDeletion(LI); 1779 ++NumGVNLoad; 1780 return true; 1781 } 1782 1783 // Step 4: Eliminate partial redundancy. 1784 if (!EnablePRE || !EnableLoadPRE) 1785 return false; 1786 1787 return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks); 1788 } 1789 1790 bool GVN::processAssumeIntrinsic(IntrinsicInst *IntrinsicI) { 1791 assert(IntrinsicI->getIntrinsicID() == Intrinsic::assume && 1792 "This function can only be called with llvm.assume intrinsic"); 1793 Value *V = IntrinsicI->getArgOperand(0); 1794 1795 if (ConstantInt *Cond = dyn_cast<ConstantInt>(V)) { 1796 if (Cond->isZero()) { 1797 Type *Int8Ty = Type::getInt8Ty(V->getContext()); 1798 // Insert a new store to null instruction before the load to indicate that 1799 // this code is not reachable. FIXME: We could insert unreachable 1800 // instruction directly because we can modify the CFG. 1801 new StoreInst(UndefValue::get(Int8Ty), 1802 Constant::getNullValue(Int8Ty->getPointerTo()), 1803 IntrinsicI); 1804 } 1805 markInstructionForDeletion(IntrinsicI); 1806 return false; 1807 } 1808 1809 Constant *True = ConstantInt::getTrue(V->getContext()); 1810 bool Changed = false; 1811 1812 for (BasicBlock *Successor : successors(IntrinsicI->getParent())) { 1813 BasicBlockEdge Edge(IntrinsicI->getParent(), Successor); 1814 1815 // This property is only true in dominated successors, propagateEquality 1816 // will check dominance for us. 1817 Changed |= propagateEquality(V, True, Edge, false); 1818 } 1819 1820 // We can replace assume value with true, which covers cases like this: 1821 // call void @llvm.assume(i1 %cmp) 1822 // br i1 %cmp, label %bb1, label %bb2 ; will change %cmp to true 1823 ReplaceWithConstMap[V] = True; 1824 1825 // If one of *cmp *eq operand is const, adding it to map will cover this: 1826 // %cmp = fcmp oeq float 3.000000e+00, %0 ; const on lhs could happen 1827 // call void @llvm.assume(i1 %cmp) 1828 // ret float %0 ; will change it to ret float 3.000000e+00 1829 if (auto *CmpI = dyn_cast<CmpInst>(V)) { 1830 if (CmpI->getPredicate() == CmpInst::Predicate::ICMP_EQ || 1831 CmpI->getPredicate() == CmpInst::Predicate::FCMP_OEQ || 1832 (CmpI->getPredicate() == CmpInst::Predicate::FCMP_UEQ && 1833 CmpI->getFastMathFlags().noNaNs())) { 1834 Value *CmpLHS = CmpI->getOperand(0); 1835 Value *CmpRHS = CmpI->getOperand(1); 1836 if (isa<Constant>(CmpLHS)) 1837 std::swap(CmpLHS, CmpRHS); 1838 auto *RHSConst = dyn_cast<Constant>(CmpRHS); 1839 1840 // If only one operand is constant. 1841 if (RHSConst != nullptr && !isa<Constant>(CmpLHS)) 1842 ReplaceWithConstMap[CmpLHS] = RHSConst; 1843 } 1844 } 1845 return Changed; 1846 } 1847 1848 static void patchReplacementInstruction(Instruction *I, Value *Repl) { 1849 // Patch the replacement so that it is not more restrictive than the value 1850 // being replaced. 1851 BinaryOperator *Op = dyn_cast<BinaryOperator>(I); 1852 BinaryOperator *ReplOp = dyn_cast<BinaryOperator>(Repl); 1853 if (Op && ReplOp) 1854 ReplOp->andIRFlags(Op); 1855 1856 if (Instruction *ReplInst = dyn_cast<Instruction>(Repl)) { 1857 // FIXME: If both the original and replacement value are part of the 1858 // same control-flow region (meaning that the execution of one 1859 // guarantees the execution of the other), then we can combine the 1860 // noalias scopes here and do better than the general conservative 1861 // answer used in combineMetadata(). 1862 1863 // In general, GVN unifies expressions over different control-flow 1864 // regions, and so we need a conservative combination of the noalias 1865 // scopes. 1866 static const unsigned KnownIDs[] = { 1867 LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope, 1868 LLVMContext::MD_noalias, LLVMContext::MD_range, 1869 LLVMContext::MD_fpmath, LLVMContext::MD_invariant_load, 1870 LLVMContext::MD_invariant_group}; 1871 combineMetadata(ReplInst, I, KnownIDs); 1872 } 1873 } 1874 1875 static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) { 1876 patchReplacementInstruction(I, Repl); 1877 I->replaceAllUsesWith(Repl); 1878 } 1879 1880 /// Attempt to eliminate a load, first by eliminating it 1881 /// locally, and then attempting non-local elimination if that fails. 1882 bool GVN::processLoad(LoadInst *L) { 1883 if (!MD) 1884 return false; 1885 1886 if (!L->isSimple()) 1887 return false; 1888 1889 if (L->use_empty()) { 1890 markInstructionForDeletion(L); 1891 return true; 1892 } 1893 1894 // ... to a pointer that has been loaded from before... 1895 MemDepResult Dep = MD->getDependency(L); 1896 const DataLayout &DL = L->getModule()->getDataLayout(); 1897 1898 // If we have a clobber and target data is around, see if this is a clobber 1899 // that we can fix up through code synthesis. 1900 if (Dep.isClobber()) { 1901 // Check to see if we have something like this: 1902 // store i32 123, i32* %P 1903 // %A = bitcast i32* %P to i8* 1904 // %B = gep i8* %A, i32 1 1905 // %C = load i8* %B 1906 // 1907 // We could do that by recognizing if the clobber instructions are obviously 1908 // a common base + constant offset, and if the previous store (or memset) 1909 // completely covers this load. This sort of thing can happen in bitfield 1910 // access code. 1911 Value *AvailVal = nullptr; 1912 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) { 1913 int Offset = AnalyzeLoadFromClobberingStore( 1914 L->getType(), L->getPointerOperand(), DepSI); 1915 if (Offset != -1) 1916 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, 1917 L->getType(), L, DL); 1918 } 1919 1920 // Check to see if we have something like this: 1921 // load i32* P 1922 // load i8* (P+1) 1923 // if we have this, replace the later with an extraction from the former. 1924 if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) { 1925 // If this is a clobber and L is the first instruction in its block, then 1926 // we have the first instruction in the entry block. 1927 if (DepLI == L) 1928 return false; 1929 1930 int Offset = AnalyzeLoadFromClobberingLoad( 1931 L->getType(), L->getPointerOperand(), DepLI, DL); 1932 if (Offset != -1) 1933 AvailVal = GetLoadValueForLoad(DepLI, Offset, L->getType(), L, *this); 1934 } 1935 1936 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1937 // a value on from it. 1938 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1939 int Offset = AnalyzeLoadFromClobberingMemInst( 1940 L->getType(), L->getPointerOperand(), DepMI, DL); 1941 if (Offset != -1) 1942 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, DL); 1943 } 1944 1945 if (AvailVal) { 1946 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1947 << *AvailVal << '\n' << *L << "\n\n\n"); 1948 1949 // Replace the load! 1950 L->replaceAllUsesWith(AvailVal); 1951 if (AvailVal->getType()->getScalarType()->isPointerTy()) 1952 MD->invalidateCachedPointerInfo(AvailVal); 1953 markInstructionForDeletion(L); 1954 ++NumGVNLoad; 1955 return true; 1956 } 1957 1958 // If the value isn't available, don't do anything! 1959 DEBUG( 1960 // fast print dep, using operator<< on instruction is too slow. 1961 dbgs() << "GVN: load "; 1962 L->printAsOperand(dbgs()); 1963 Instruction *I = Dep.getInst(); 1964 dbgs() << " is clobbered by " << *I << '\n'; 1965 ); 1966 return false; 1967 } 1968 1969 // If it is defined in another block, try harder. 1970 if (Dep.isNonLocal()) 1971 return processNonLocalLoad(L); 1972 1973 if (!Dep.isDef()) { 1974 DEBUG( 1975 // fast print dep, using operator<< on instruction is too slow. 1976 dbgs() << "GVN: load "; 1977 L->printAsOperand(dbgs()); 1978 dbgs() << " has unknown dependence\n"; 1979 ); 1980 return false; 1981 } 1982 1983 Instruction *DepInst = Dep.getInst(); 1984 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1985 Value *StoredVal = DepSI->getValueOperand(); 1986 1987 // The store and load are to a must-aliased pointer, but they may not 1988 // actually have the same type. See if we know how to reuse the stored 1989 // value (depending on its type). 1990 if (StoredVal->getType() != L->getType()) { 1991 IRBuilder<> Builder(L); 1992 StoredVal = 1993 CoerceAvailableValueToLoadType(StoredVal, L->getType(), Builder, DL); 1994 if (!StoredVal) 1995 return false; 1996 1997 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1998 << '\n' << *L << "\n\n\n"); 1999 } 2000 2001 // Remove it! 2002 L->replaceAllUsesWith(StoredVal); 2003 if (StoredVal->getType()->getScalarType()->isPointerTy()) 2004 MD->invalidateCachedPointerInfo(StoredVal); 2005 markInstructionForDeletion(L); 2006 ++NumGVNLoad; 2007 return true; 2008 } 2009 2010 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 2011 Value *AvailableVal = DepLI; 2012 2013 // The loads are of a must-aliased pointer, but they may not actually have 2014 // the same type. See if we know how to reuse the previously loaded value 2015 // (depending on its type). 2016 if (DepLI->getType() != L->getType()) { 2017 IRBuilder<> Builder(L); 2018 AvailableVal = 2019 CoerceAvailableValueToLoadType(DepLI, L->getType(), Builder, DL); 2020 if (!AvailableVal) 2021 return false; 2022 2023 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 2024 << "\n" << *L << "\n\n\n"); 2025 } 2026 2027 // Remove it! 2028 patchAndReplaceAllUsesWith(L, AvailableVal); 2029 if (DepLI->getType()->getScalarType()->isPointerTy()) 2030 MD->invalidateCachedPointerInfo(DepLI); 2031 markInstructionForDeletion(L); 2032 ++NumGVNLoad; 2033 return true; 2034 } 2035 2036 // If this load really doesn't depend on anything, then we must be loading an 2037 // undef value. This can happen when loading for a fresh allocation with no 2038 // intervening stores, for example. 2039 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) { 2040 L->replaceAllUsesWith(UndefValue::get(L->getType())); 2041 markInstructionForDeletion(L); 2042 ++NumGVNLoad; 2043 return true; 2044 } 2045 2046 // If this load occurs either right after a lifetime begin, 2047 // then the loaded value is undefined. 2048 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(DepInst)) { 2049 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 2050 L->replaceAllUsesWith(UndefValue::get(L->getType())); 2051 markInstructionForDeletion(L); 2052 ++NumGVNLoad; 2053 return true; 2054 } 2055 } 2056 2057 // If this load follows a calloc (which zero initializes memory), 2058 // then the loaded value is zero 2059 if (isCallocLikeFn(DepInst, TLI)) { 2060 L->replaceAllUsesWith(Constant::getNullValue(L->getType())); 2061 markInstructionForDeletion(L); 2062 ++NumGVNLoad; 2063 return true; 2064 } 2065 2066 return false; 2067 } 2068 2069 // In order to find a leader for a given value number at a 2070 // specific basic block, we first obtain the list of all Values for that number, 2071 // and then scan the list to find one whose block dominates the block in 2072 // question. This is fast because dominator tree queries consist of only 2073 // a few comparisons of DFS numbers. 2074 Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) { 2075 LeaderTableEntry Vals = LeaderTable[num]; 2076 if (!Vals.Val) return nullptr; 2077 2078 Value *Val = nullptr; 2079 if (DT->dominates(Vals.BB, BB)) { 2080 Val = Vals.Val; 2081 if (isa<Constant>(Val)) return Val; 2082 } 2083 2084 LeaderTableEntry* Next = Vals.Next; 2085 while (Next) { 2086 if (DT->dominates(Next->BB, BB)) { 2087 if (isa<Constant>(Next->Val)) return Next->Val; 2088 if (!Val) Val = Next->Val; 2089 } 2090 2091 Next = Next->Next; 2092 } 2093 2094 return Val; 2095 } 2096 2097 /// There is an edge from 'Src' to 'Dst'. Return 2098 /// true if every path from the entry block to 'Dst' passes via this edge. In 2099 /// particular 'Dst' must not be reachable via another edge from 'Src'. 2100 static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E, 2101 DominatorTree *DT) { 2102 // While in theory it is interesting to consider the case in which Dst has 2103 // more than one predecessor, because Dst might be part of a loop which is 2104 // only reachable from Src, in practice it is pointless since at the time 2105 // GVN runs all such loops have preheaders, which means that Dst will have 2106 // been changed to have only one predecessor, namely Src. 2107 const BasicBlock *Pred = E.getEnd()->getSinglePredecessor(); 2108 const BasicBlock *Src = E.getStart(); 2109 assert((!Pred || Pred == Src) && "No edge between these basic blocks!"); 2110 (void)Src; 2111 return Pred != nullptr; 2112 } 2113 2114 // Tries to replace instruction with const, using information from 2115 // ReplaceWithConstMap. 2116 bool GVN::replaceOperandsWithConsts(Instruction *Instr) const { 2117 bool Changed = false; 2118 for (unsigned OpNum = 0; OpNum < Instr->getNumOperands(); ++OpNum) { 2119 Value *Operand = Instr->getOperand(OpNum); 2120 auto it = ReplaceWithConstMap.find(Operand); 2121 if (it != ReplaceWithConstMap.end()) { 2122 assert(!isa<Constant>(Operand) && 2123 "Replacing constants with constants is invalid"); 2124 DEBUG(dbgs() << "GVN replacing: " << *Operand << " with " << *it->second 2125 << " in instruction " << *Instr << '\n'); 2126 Instr->setOperand(OpNum, it->second); 2127 Changed = true; 2128 } 2129 } 2130 return Changed; 2131 } 2132 2133 /// The given values are known to be equal in every block 2134 /// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with 2135 /// 'RHS' everywhere in the scope. Returns whether a change was made. 2136 /// If DominatesByEdge is false, then it means that it is dominated by Root.End. 2137 bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root, 2138 bool DominatesByEdge) { 2139 SmallVector<std::pair<Value*, Value*>, 4> Worklist; 2140 Worklist.push_back(std::make_pair(LHS, RHS)); 2141 bool Changed = false; 2142 // For speed, compute a conservative fast approximation to 2143 // DT->dominates(Root, Root.getEnd()); 2144 bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT); 2145 2146 while (!Worklist.empty()) { 2147 std::pair<Value*, Value*> Item = Worklist.pop_back_val(); 2148 LHS = Item.first; RHS = Item.second; 2149 2150 if (LHS == RHS) 2151 continue; 2152 assert(LHS->getType() == RHS->getType() && "Equality but unequal types!"); 2153 2154 // Don't try to propagate equalities between constants. 2155 if (isa<Constant>(LHS) && isa<Constant>(RHS)) 2156 continue; 2157 2158 // Prefer a constant on the right-hand side, or an Argument if no constants. 2159 if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS))) 2160 std::swap(LHS, RHS); 2161 assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!"); 2162 2163 // If there is no obvious reason to prefer the left-hand side over the 2164 // right-hand side, ensure the longest lived term is on the right-hand side, 2165 // so the shortest lived term will be replaced by the longest lived. 2166 // This tends to expose more simplifications. 2167 uint32_t LVN = VN.lookup_or_add(LHS); 2168 if ((isa<Argument>(LHS) && isa<Argument>(RHS)) || 2169 (isa<Instruction>(LHS) && isa<Instruction>(RHS))) { 2170 // Move the 'oldest' value to the right-hand side, using the value number 2171 // as a proxy for age. 2172 uint32_t RVN = VN.lookup_or_add(RHS); 2173 if (LVN < RVN) { 2174 std::swap(LHS, RHS); 2175 LVN = RVN; 2176 } 2177 } 2178 2179 // If value numbering later sees that an instruction in the scope is equal 2180 // to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve 2181 // the invariant that instructions only occur in the leader table for their 2182 // own value number (this is used by removeFromLeaderTable), do not do this 2183 // if RHS is an instruction (if an instruction in the scope is morphed into 2184 // LHS then it will be turned into RHS by the next GVN iteration anyway, so 2185 // using the leader table is about compiling faster, not optimizing better). 2186 // The leader table only tracks basic blocks, not edges. Only add to if we 2187 // have the simple case where the edge dominates the end. 2188 if (RootDominatesEnd && !isa<Instruction>(RHS)) 2189 addToLeaderTable(LVN, RHS, Root.getEnd()); 2190 2191 // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As 2192 // LHS always has at least one use that is not dominated by Root, this will 2193 // never do anything if LHS has only one use. 2194 if (!LHS->hasOneUse()) { 2195 unsigned NumReplacements = 2196 DominatesByEdge 2197 ? replaceDominatedUsesWith(LHS, RHS, *DT, Root) 2198 : replaceDominatedUsesWith(LHS, RHS, *DT, Root.getEnd()); 2199 2200 Changed |= NumReplacements > 0; 2201 NumGVNEqProp += NumReplacements; 2202 } 2203 2204 // Now try to deduce additional equalities from this one. For example, if 2205 // the known equality was "(A != B)" == "false" then it follows that A and B 2206 // are equal in the scope. Only boolean equalities with an explicit true or 2207 // false RHS are currently supported. 2208 if (!RHS->getType()->isIntegerTy(1)) 2209 // Not a boolean equality - bail out. 2210 continue; 2211 ConstantInt *CI = dyn_cast<ConstantInt>(RHS); 2212 if (!CI) 2213 // RHS neither 'true' nor 'false' - bail out. 2214 continue; 2215 // Whether RHS equals 'true'. Otherwise it equals 'false'. 2216 bool isKnownTrue = CI->isAllOnesValue(); 2217 bool isKnownFalse = !isKnownTrue; 2218 2219 // If "A && B" is known true then both A and B are known true. If "A || B" 2220 // is known false then both A and B are known false. 2221 Value *A, *B; 2222 if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) || 2223 (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) { 2224 Worklist.push_back(std::make_pair(A, RHS)); 2225 Worklist.push_back(std::make_pair(B, RHS)); 2226 continue; 2227 } 2228 2229 // If we are propagating an equality like "(A == B)" == "true" then also 2230 // propagate the equality A == B. When propagating a comparison such as 2231 // "(A >= B)" == "true", replace all instances of "A < B" with "false". 2232 if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) { 2233 Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1); 2234 2235 // If "A == B" is known true, or "A != B" is known false, then replace 2236 // A with B everywhere in the scope. 2237 if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) || 2238 (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE)) 2239 Worklist.push_back(std::make_pair(Op0, Op1)); 2240 2241 // Handle the floating point versions of equality comparisons too. 2242 if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) || 2243 (isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE)) { 2244 2245 // Floating point -0.0 and 0.0 compare equal, so we can only 2246 // propagate values if we know that we have a constant and that 2247 // its value is non-zero. 2248 2249 // FIXME: We should do this optimization if 'no signed zeros' is 2250 // applicable via an instruction-level fast-math-flag or some other 2251 // indicator that relaxed FP semantics are being used. 2252 2253 if (isa<ConstantFP>(Op1) && !cast<ConstantFP>(Op1)->isZero()) 2254 Worklist.push_back(std::make_pair(Op0, Op1)); 2255 } 2256 2257 // If "A >= B" is known true, replace "A < B" with false everywhere. 2258 CmpInst::Predicate NotPred = Cmp->getInversePredicate(); 2259 Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse); 2260 // Since we don't have the instruction "A < B" immediately to hand, work 2261 // out the value number that it would have and use that to find an 2262 // appropriate instruction (if any). 2263 uint32_t NextNum = VN.getNextUnusedValueNumber(); 2264 uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1); 2265 // If the number we were assigned was brand new then there is no point in 2266 // looking for an instruction realizing it: there cannot be one! 2267 if (Num < NextNum) { 2268 Value *NotCmp = findLeader(Root.getEnd(), Num); 2269 if (NotCmp && isa<Instruction>(NotCmp)) { 2270 unsigned NumReplacements = 2271 DominatesByEdge 2272 ? replaceDominatedUsesWith(NotCmp, NotVal, *DT, Root) 2273 : replaceDominatedUsesWith(NotCmp, NotVal, *DT, 2274 Root.getEnd()); 2275 Changed |= NumReplacements > 0; 2276 NumGVNEqProp += NumReplacements; 2277 } 2278 } 2279 // Ensure that any instruction in scope that gets the "A < B" value number 2280 // is replaced with false. 2281 // The leader table only tracks basic blocks, not edges. Only add to if we 2282 // have the simple case where the edge dominates the end. 2283 if (RootDominatesEnd) 2284 addToLeaderTable(Num, NotVal, Root.getEnd()); 2285 2286 continue; 2287 } 2288 } 2289 2290 return Changed; 2291 } 2292 2293 /// When calculating availability, handle an instruction 2294 /// by inserting it into the appropriate sets 2295 bool GVN::processInstruction(Instruction *I) { 2296 // Ignore dbg info intrinsics. 2297 if (isa<DbgInfoIntrinsic>(I)) 2298 return false; 2299 2300 // If the instruction can be easily simplified then do so now in preference 2301 // to value numbering it. Value numbering often exposes redundancies, for 2302 // example if it determines that %y is equal to %x then the instruction 2303 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. 2304 const DataLayout &DL = I->getModule()->getDataLayout(); 2305 if (Value *V = SimplifyInstruction(I, DL, TLI, DT, AC)) { 2306 I->replaceAllUsesWith(V); 2307 if (MD && V->getType()->getScalarType()->isPointerTy()) 2308 MD->invalidateCachedPointerInfo(V); 2309 markInstructionForDeletion(I); 2310 ++NumGVNSimpl; 2311 return true; 2312 } 2313 2314 if (IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(I)) 2315 if (IntrinsicI->getIntrinsicID() == Intrinsic::assume) 2316 return processAssumeIntrinsic(IntrinsicI); 2317 2318 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 2319 if (processLoad(LI)) 2320 return true; 2321 2322 unsigned Num = VN.lookup_or_add(LI); 2323 addToLeaderTable(Num, LI, LI->getParent()); 2324 return false; 2325 } 2326 2327 // For conditional branches, we can perform simple conditional propagation on 2328 // the condition value itself. 2329 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 2330 if (!BI->isConditional()) 2331 return false; 2332 2333 if (isa<Constant>(BI->getCondition())) 2334 return processFoldableCondBr(BI); 2335 2336 Value *BranchCond = BI->getCondition(); 2337 BasicBlock *TrueSucc = BI->getSuccessor(0); 2338 BasicBlock *FalseSucc = BI->getSuccessor(1); 2339 // Avoid multiple edges early. 2340 if (TrueSucc == FalseSucc) 2341 return false; 2342 2343 BasicBlock *Parent = BI->getParent(); 2344 bool Changed = false; 2345 2346 Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext()); 2347 BasicBlockEdge TrueE(Parent, TrueSucc); 2348 Changed |= propagateEquality(BranchCond, TrueVal, TrueE, true); 2349 2350 Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext()); 2351 BasicBlockEdge FalseE(Parent, FalseSucc); 2352 Changed |= propagateEquality(BranchCond, FalseVal, FalseE, true); 2353 2354 return Changed; 2355 } 2356 2357 // For switches, propagate the case values into the case destinations. 2358 if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { 2359 Value *SwitchCond = SI->getCondition(); 2360 BasicBlock *Parent = SI->getParent(); 2361 bool Changed = false; 2362 2363 // Remember how many outgoing edges there are to every successor. 2364 SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges; 2365 for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i) 2366 ++SwitchEdges[SI->getSuccessor(i)]; 2367 2368 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2369 i != e; ++i) { 2370 BasicBlock *Dst = i.getCaseSuccessor(); 2371 // If there is only a single edge, propagate the case value into it. 2372 if (SwitchEdges.lookup(Dst) == 1) { 2373 BasicBlockEdge E(Parent, Dst); 2374 Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E, true); 2375 } 2376 } 2377 return Changed; 2378 } 2379 2380 // Instructions with void type don't return a value, so there's 2381 // no point in trying to find redundancies in them. 2382 if (I->getType()->isVoidTy()) 2383 return false; 2384 2385 uint32_t NextNum = VN.getNextUnusedValueNumber(); 2386 unsigned Num = VN.lookup_or_add(I); 2387 2388 // Allocations are always uniquely numbered, so we can save time and memory 2389 // by fast failing them. 2390 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) { 2391 addToLeaderTable(Num, I, I->getParent()); 2392 return false; 2393 } 2394 2395 // If the number we were assigned was a brand new VN, then we don't 2396 // need to do a lookup to see if the number already exists 2397 // somewhere in the domtree: it can't! 2398 if (Num >= NextNum) { 2399 addToLeaderTable(Num, I, I->getParent()); 2400 return false; 2401 } 2402 2403 // Perform fast-path value-number based elimination of values inherited from 2404 // dominators. 2405 Value *Repl = findLeader(I->getParent(), Num); 2406 if (!Repl) { 2407 // Failure, just remember this instance for future use. 2408 addToLeaderTable(Num, I, I->getParent()); 2409 return false; 2410 } else if (Repl == I) { 2411 // If I was the result of a shortcut PRE, it might already be in the table 2412 // and the best replacement for itself. Nothing to do. 2413 return false; 2414 } 2415 2416 // Remove it! 2417 patchAndReplaceAllUsesWith(I, Repl); 2418 if (MD && Repl->getType()->getScalarType()->isPointerTy()) 2419 MD->invalidateCachedPointerInfo(Repl); 2420 markInstructionForDeletion(I); 2421 return true; 2422 } 2423 2424 /// runOnFunction - This is the main transformation entry point for a function. 2425 bool GVN::runOnFunction(Function& F) { 2426 if (skipOptnoneFunction(F)) 2427 return false; 2428 2429 if (!NoLoads) 2430 MD = &getAnalysis<MemoryDependenceAnalysis>(); 2431 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 2432 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); 2433 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); 2434 VN.setAliasAnalysis(&getAnalysis<AAResultsWrapperPass>().getAAResults()); 2435 VN.setMemDep(MD); 2436 VN.setDomTree(DT); 2437 2438 bool Changed = false; 2439 bool ShouldContinue = true; 2440 2441 // Merge unconditional branches, allowing PRE to catch more 2442 // optimization opportunities. 2443 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 2444 BasicBlock *BB = &*FI++; 2445 2446 bool removedBlock = 2447 MergeBlockIntoPredecessor(BB, DT, /* LoopInfo */ nullptr, MD); 2448 if (removedBlock) ++NumGVNBlocks; 2449 2450 Changed |= removedBlock; 2451 } 2452 2453 unsigned Iteration = 0; 2454 while (ShouldContinue) { 2455 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 2456 ShouldContinue = iterateOnFunction(F); 2457 Changed |= ShouldContinue; 2458 ++Iteration; 2459 } 2460 2461 if (EnablePRE) { 2462 // Fabricate val-num for dead-code in order to suppress assertion in 2463 // performPRE(). 2464 assignValNumForDeadCode(); 2465 bool PREChanged = true; 2466 while (PREChanged) { 2467 PREChanged = performPRE(F); 2468 Changed |= PREChanged; 2469 } 2470 } 2471 2472 // FIXME: Should perform GVN again after PRE does something. PRE can move 2473 // computations into blocks where they become fully redundant. Note that 2474 // we can't do this until PRE's critical edge splitting updates memdep. 2475 // Actually, when this happens, we should just fully integrate PRE into GVN. 2476 2477 cleanupGlobalSets(); 2478 // Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each 2479 // iteration. 2480 DeadBlocks.clear(); 2481 2482 return Changed; 2483 } 2484 2485 bool GVN::processBlock(BasicBlock *BB) { 2486 // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function 2487 // (and incrementing BI before processing an instruction). 2488 assert(InstrsToErase.empty() && 2489 "We expect InstrsToErase to be empty across iterations"); 2490 if (DeadBlocks.count(BB)) 2491 return false; 2492 2493 // Clearing map before every BB because it can be used only for single BB. 2494 ReplaceWithConstMap.clear(); 2495 bool ChangedFunction = false; 2496 2497 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 2498 BI != BE;) { 2499 if (!ReplaceWithConstMap.empty()) 2500 ChangedFunction |= replaceOperandsWithConsts(&*BI); 2501 ChangedFunction |= processInstruction(&*BI); 2502 2503 if (InstrsToErase.empty()) { 2504 ++BI; 2505 continue; 2506 } 2507 2508 // If we need some instructions deleted, do it now. 2509 NumGVNInstr += InstrsToErase.size(); 2510 2511 // Avoid iterator invalidation. 2512 bool AtStart = BI == BB->begin(); 2513 if (!AtStart) 2514 --BI; 2515 2516 for (SmallVectorImpl<Instruction *>::iterator I = InstrsToErase.begin(), 2517 E = InstrsToErase.end(); I != E; ++I) { 2518 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 2519 if (MD) MD->removeInstruction(*I); 2520 DEBUG(verifyRemoved(*I)); 2521 (*I)->eraseFromParent(); 2522 } 2523 InstrsToErase.clear(); 2524 2525 if (AtStart) 2526 BI = BB->begin(); 2527 else 2528 ++BI; 2529 } 2530 2531 return ChangedFunction; 2532 } 2533 2534 // Instantiate an expression in a predecessor that lacked it. 2535 bool GVN::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred, 2536 unsigned int ValNo) { 2537 // Because we are going top-down through the block, all value numbers 2538 // will be available in the predecessor by the time we need them. Any 2539 // that weren't originally present will have been instantiated earlier 2540 // in this loop. 2541 bool success = true; 2542 for (unsigned i = 0, e = Instr->getNumOperands(); i != e; ++i) { 2543 Value *Op = Instr->getOperand(i); 2544 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2545 continue; 2546 // This could be a newly inserted instruction, in which case, we won't 2547 // find a value number, and should give up before we hurt ourselves. 2548 // FIXME: Rewrite the infrastructure to let it easier to value number 2549 // and process newly inserted instructions. 2550 if (!VN.exists(Op)) { 2551 success = false; 2552 break; 2553 } 2554 if (Value *V = findLeader(Pred, VN.lookup(Op))) { 2555 Instr->setOperand(i, V); 2556 } else { 2557 success = false; 2558 break; 2559 } 2560 } 2561 2562 // Fail out if we encounter an operand that is not available in 2563 // the PRE predecessor. This is typically because of loads which 2564 // are not value numbered precisely. 2565 if (!success) 2566 return false; 2567 2568 Instr->insertBefore(Pred->getTerminator()); 2569 Instr->setName(Instr->getName() + ".pre"); 2570 Instr->setDebugLoc(Instr->getDebugLoc()); 2571 VN.add(Instr, ValNo); 2572 2573 // Update the availability map to include the new instruction. 2574 addToLeaderTable(ValNo, Instr, Pred); 2575 return true; 2576 } 2577 2578 bool GVN::performScalarPRE(Instruction *CurInst) { 2579 SmallVector<std::pair<Value*, BasicBlock*>, 8> predMap; 2580 2581 if (isa<AllocaInst>(CurInst) || isa<TerminatorInst>(CurInst) || 2582 isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() || 2583 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2584 isa<DbgInfoIntrinsic>(CurInst)) 2585 return false; 2586 2587 // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from 2588 // sinking the compare again, and it would force the code generator to 2589 // move the i1 from processor flags or predicate registers into a general 2590 // purpose register. 2591 if (isa<CmpInst>(CurInst)) 2592 return false; 2593 2594 // We don't currently value number ANY inline asm calls. 2595 if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) 2596 if (CallI->isInlineAsm()) 2597 return false; 2598 2599 uint32_t ValNo = VN.lookup(CurInst); 2600 2601 // Look for the predecessors for PRE opportunities. We're 2602 // only trying to solve the basic diamond case, where 2603 // a value is computed in the successor and one predecessor, 2604 // but not the other. We also explicitly disallow cases 2605 // where the successor is its own predecessor, because they're 2606 // more complicated to get right. 2607 unsigned NumWith = 0; 2608 unsigned NumWithout = 0; 2609 BasicBlock *PREPred = nullptr; 2610 BasicBlock *CurrentBlock = CurInst->getParent(); 2611 predMap.clear(); 2612 2613 for (BasicBlock *P : predecessors(CurrentBlock)) { 2614 // We're not interested in PRE where the block is its 2615 // own predecessor, or in blocks with predecessors 2616 // that are not reachable. 2617 if (P == CurrentBlock) { 2618 NumWithout = 2; 2619 break; 2620 } else if (!DT->isReachableFromEntry(P)) { 2621 NumWithout = 2; 2622 break; 2623 } 2624 2625 Value *predV = findLeader(P, ValNo); 2626 if (!predV) { 2627 predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P)); 2628 PREPred = P; 2629 ++NumWithout; 2630 } else if (predV == CurInst) { 2631 /* CurInst dominates this predecessor. */ 2632 NumWithout = 2; 2633 break; 2634 } else { 2635 predMap.push_back(std::make_pair(predV, P)); 2636 ++NumWith; 2637 } 2638 } 2639 2640 // Don't do PRE when it might increase code size, i.e. when 2641 // we would need to insert instructions in more than one pred. 2642 if (NumWithout > 1 || NumWith == 0) 2643 return false; 2644 2645 // We may have a case where all predecessors have the instruction, 2646 // and we just need to insert a phi node. Otherwise, perform 2647 // insertion. 2648 Instruction *PREInstr = nullptr; 2649 2650 if (NumWithout != 0) { 2651 // Don't do PRE across indirect branch. 2652 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2653 return false; 2654 2655 // We can't do PRE safely on a critical edge, so instead we schedule 2656 // the edge to be split and perform the PRE the next time we iterate 2657 // on the function. 2658 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); 2659 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2660 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2661 return false; 2662 } 2663 // We need to insert somewhere, so let's give it a shot 2664 PREInstr = CurInst->clone(); 2665 if (!performScalarPREInsertion(PREInstr, PREPred, ValNo)) { 2666 // If we failed insertion, make sure we remove the instruction. 2667 DEBUG(verifyRemoved(PREInstr)); 2668 delete PREInstr; 2669 return false; 2670 } 2671 } 2672 2673 // Either we should have filled in the PRE instruction, or we should 2674 // not have needed insertions. 2675 assert (PREInstr != nullptr || NumWithout == 0); 2676 2677 ++NumGVNPRE; 2678 2679 // Create a PHI to make the value available in this block. 2680 PHINode *Phi = 2681 PHINode::Create(CurInst->getType(), predMap.size(), 2682 CurInst->getName() + ".pre-phi", &CurrentBlock->front()); 2683 for (unsigned i = 0, e = predMap.size(); i != e; ++i) { 2684 if (Value *V = predMap[i].first) 2685 Phi->addIncoming(V, predMap[i].second); 2686 else 2687 Phi->addIncoming(PREInstr, PREPred); 2688 } 2689 2690 VN.add(Phi, ValNo); 2691 addToLeaderTable(ValNo, Phi, CurrentBlock); 2692 Phi->setDebugLoc(CurInst->getDebugLoc()); 2693 CurInst->replaceAllUsesWith(Phi); 2694 if (MD && Phi->getType()->getScalarType()->isPointerTy()) 2695 MD->invalidateCachedPointerInfo(Phi); 2696 VN.erase(CurInst); 2697 removeFromLeaderTable(ValNo, CurInst, CurrentBlock); 2698 2699 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2700 if (MD) 2701 MD->removeInstruction(CurInst); 2702 DEBUG(verifyRemoved(CurInst)); 2703 CurInst->eraseFromParent(); 2704 ++NumGVNInstr; 2705 2706 return true; 2707 } 2708 2709 /// Perform a purely local form of PRE that looks for diamond 2710 /// control flow patterns and attempts to perform simple PRE at the join point. 2711 bool GVN::performPRE(Function &F) { 2712 bool Changed = false; 2713 for (BasicBlock *CurrentBlock : depth_first(&F.getEntryBlock())) { 2714 // Nothing to PRE in the entry block. 2715 if (CurrentBlock == &F.getEntryBlock()) 2716 continue; 2717 2718 // Don't perform PRE on an EH pad. 2719 if (CurrentBlock->isEHPad()) 2720 continue; 2721 2722 for (BasicBlock::iterator BI = CurrentBlock->begin(), 2723 BE = CurrentBlock->end(); 2724 BI != BE;) { 2725 Instruction *CurInst = &*BI++; 2726 Changed |= performScalarPRE(CurInst); 2727 } 2728 } 2729 2730 if (splitCriticalEdges()) 2731 Changed = true; 2732 2733 return Changed; 2734 } 2735 2736 /// Split the critical edge connecting the given two blocks, and return 2737 /// the block inserted to the critical edge. 2738 BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) { 2739 BasicBlock *BB = 2740 SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT)); 2741 if (MD) 2742 MD->invalidateCachedPredecessors(); 2743 return BB; 2744 } 2745 2746 /// Split critical edges found during the previous 2747 /// iteration that may enable further optimization. 2748 bool GVN::splitCriticalEdges() { 2749 if (toSplit.empty()) 2750 return false; 2751 do { 2752 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2753 SplitCriticalEdge(Edge.first, Edge.second, 2754 CriticalEdgeSplittingOptions(DT)); 2755 } while (!toSplit.empty()); 2756 if (MD) MD->invalidateCachedPredecessors(); 2757 return true; 2758 } 2759 2760 /// Executes one iteration of GVN 2761 bool GVN::iterateOnFunction(Function &F) { 2762 cleanupGlobalSets(); 2763 2764 // Top-down walk of the dominator tree 2765 bool Changed = false; 2766 // Save the blocks this function have before transformation begins. GVN may 2767 // split critical edge, and hence may invalidate the RPO/DT iterator. 2768 // 2769 std::vector<BasicBlock *> BBVect; 2770 BBVect.reserve(256); 2771 // Needed for value numbering with phi construction to work. 2772 ReversePostOrderTraversal<Function *> RPOT(&F); 2773 for (ReversePostOrderTraversal<Function *>::rpo_iterator RI = RPOT.begin(), 2774 RE = RPOT.end(); 2775 RI != RE; ++RI) 2776 BBVect.push_back(*RI); 2777 2778 for (std::vector<BasicBlock *>::iterator I = BBVect.begin(), E = BBVect.end(); 2779 I != E; I++) 2780 Changed |= processBlock(*I); 2781 2782 return Changed; 2783 } 2784 2785 void GVN::cleanupGlobalSets() { 2786 VN.clear(); 2787 LeaderTable.clear(); 2788 TableAllocator.Reset(); 2789 } 2790 2791 /// Verify that the specified instruction does not occur in our 2792 /// internal data structures. 2793 void GVN::verifyRemoved(const Instruction *Inst) const { 2794 VN.verifyRemoved(Inst); 2795 2796 // Walk through the value number scope to make sure the instruction isn't 2797 // ferreted away in it. 2798 for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator 2799 I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) { 2800 const LeaderTableEntry *Node = &I->second; 2801 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2802 2803 while (Node->Next) { 2804 Node = Node->Next; 2805 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2806 } 2807 } 2808 } 2809 2810 /// BB is declared dead, which implied other blocks become dead as well. This 2811 /// function is to add all these blocks to "DeadBlocks". For the dead blocks' 2812 /// live successors, update their phi nodes by replacing the operands 2813 /// corresponding to dead blocks with UndefVal. 2814 void GVN::addDeadBlock(BasicBlock *BB) { 2815 SmallVector<BasicBlock *, 4> NewDead; 2816 SmallSetVector<BasicBlock *, 4> DF; 2817 2818 NewDead.push_back(BB); 2819 while (!NewDead.empty()) { 2820 BasicBlock *D = NewDead.pop_back_val(); 2821 if (DeadBlocks.count(D)) 2822 continue; 2823 2824 // All blocks dominated by D are dead. 2825 SmallVector<BasicBlock *, 8> Dom; 2826 DT->getDescendants(D, Dom); 2827 DeadBlocks.insert(Dom.begin(), Dom.end()); 2828 2829 // Figure out the dominance-frontier(D). 2830 for (BasicBlock *B : Dom) { 2831 for (BasicBlock *S : successors(B)) { 2832 if (DeadBlocks.count(S)) 2833 continue; 2834 2835 bool AllPredDead = true; 2836 for (BasicBlock *P : predecessors(S)) 2837 if (!DeadBlocks.count(P)) { 2838 AllPredDead = false; 2839 break; 2840 } 2841 2842 if (!AllPredDead) { 2843 // S could be proved dead later on. That is why we don't update phi 2844 // operands at this moment. 2845 DF.insert(S); 2846 } else { 2847 // While S is not dominated by D, it is dead by now. This could take 2848 // place if S already have a dead predecessor before D is declared 2849 // dead. 2850 NewDead.push_back(S); 2851 } 2852 } 2853 } 2854 } 2855 2856 // For the dead blocks' live successors, update their phi nodes by replacing 2857 // the operands corresponding to dead blocks with UndefVal. 2858 for(SmallSetVector<BasicBlock *, 4>::iterator I = DF.begin(), E = DF.end(); 2859 I != E; I++) { 2860 BasicBlock *B = *I; 2861 if (DeadBlocks.count(B)) 2862 continue; 2863 2864 SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B)); 2865 for (BasicBlock *P : Preds) { 2866 if (!DeadBlocks.count(P)) 2867 continue; 2868 2869 if (isCriticalEdge(P->getTerminator(), GetSuccessorNumber(P, B))) { 2870 if (BasicBlock *S = splitCriticalEdges(P, B)) 2871 DeadBlocks.insert(P = S); 2872 } 2873 2874 for (BasicBlock::iterator II = B->begin(); isa<PHINode>(II); ++II) { 2875 PHINode &Phi = cast<PHINode>(*II); 2876 Phi.setIncomingValue(Phi.getBasicBlockIndex(P), 2877 UndefValue::get(Phi.getType())); 2878 } 2879 } 2880 } 2881 } 2882 2883 // If the given branch is recognized as a foldable branch (i.e. conditional 2884 // branch with constant condition), it will perform following analyses and 2885 // transformation. 2886 // 1) If the dead out-coming edge is a critical-edge, split it. Let 2887 // R be the target of the dead out-coming edge. 2888 // 1) Identify the set of dead blocks implied by the branch's dead outcoming 2889 // edge. The result of this step will be {X| X is dominated by R} 2890 // 2) Identify those blocks which haves at least one dead predecessor. The 2891 // result of this step will be dominance-frontier(R). 2892 // 3) Update the PHIs in DF(R) by replacing the operands corresponding to 2893 // dead blocks with "UndefVal" in an hope these PHIs will optimized away. 2894 // 2895 // Return true iff *NEW* dead code are found. 2896 bool GVN::processFoldableCondBr(BranchInst *BI) { 2897 if (!BI || BI->isUnconditional()) 2898 return false; 2899 2900 // If a branch has two identical successors, we cannot declare either dead. 2901 if (BI->getSuccessor(0) == BI->getSuccessor(1)) 2902 return false; 2903 2904 ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition()); 2905 if (!Cond) 2906 return false; 2907 2908 BasicBlock *DeadRoot = Cond->getZExtValue() ? 2909 BI->getSuccessor(1) : BI->getSuccessor(0); 2910 if (DeadBlocks.count(DeadRoot)) 2911 return false; 2912 2913 if (!DeadRoot->getSinglePredecessor()) 2914 DeadRoot = splitCriticalEdges(BI->getParent(), DeadRoot); 2915 2916 addDeadBlock(DeadRoot); 2917 return true; 2918 } 2919 2920 // performPRE() will trigger assert if it comes across an instruction without 2921 // associated val-num. As it normally has far more live instructions than dead 2922 // instructions, it makes more sense just to "fabricate" a val-number for the 2923 // dead code than checking if instruction involved is dead or not. 2924 void GVN::assignValNumForDeadCode() { 2925 for (BasicBlock *BB : DeadBlocks) { 2926 for (Instruction &Inst : *BB) { 2927 unsigned ValNum = VN.lookup_or_add(&Inst); 2928 addToLeaderTable(ValNum, &Inst, BB); 2929 } 2930 } 2931 } 2932