GVN.cpp revision b35798347ea87b8b6d36155b211016a7769f01ab
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#define DEBUG_TYPE "gvn" 19#include "llvm/Transforms/Scalar.h" 20#include "llvm/BasicBlock.h" 21#include "llvm/Constants.h" 22#include "llvm/DerivedTypes.h" 23#include "llvm/GlobalVariable.h" 24#include "llvm/Function.h" 25#include "llvm/IntrinsicInst.h" 26#include "llvm/LLVMContext.h" 27#include "llvm/Operator.h" 28#include "llvm/Value.h" 29#include "llvm/ADT/DenseMap.h" 30#include "llvm/ADT/DepthFirstIterator.h" 31#include "llvm/ADT/PostOrderIterator.h" 32#include "llvm/ADT/SmallPtrSet.h" 33#include "llvm/ADT/SmallVector.h" 34#include "llvm/ADT/Statistic.h" 35#include "llvm/Analysis/AliasAnalysis.h" 36#include "llvm/Analysis/ConstantFolding.h" 37#include "llvm/Analysis/Dominators.h" 38#include "llvm/Analysis/MemoryBuiltins.h" 39#include "llvm/Analysis/MemoryDependenceAnalysis.h" 40#include "llvm/Analysis/PHITransAddr.h" 41#include "llvm/Support/CFG.h" 42#include "llvm/Support/CommandLine.h" 43#include "llvm/Support/Debug.h" 44#include "llvm/Support/ErrorHandling.h" 45#include "llvm/Support/GetElementPtrTypeIterator.h" 46#include "llvm/Support/IRBuilder.h" 47#include "llvm/Support/raw_ostream.h" 48#include "llvm/Target/TargetData.h" 49#include "llvm/Transforms/Utils/BasicBlockUtils.h" 50#include "llvm/Transforms/Utils/Local.h" 51#include "llvm/Transforms/Utils/SSAUpdater.h" 52using namespace llvm; 53 54STATISTIC(NumGVNInstr, "Number of instructions deleted"); 55STATISTIC(NumGVNLoad, "Number of loads deleted"); 56STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 57STATISTIC(NumGVNBlocks, "Number of blocks merged"); 58STATISTIC(NumPRELoad, "Number of loads PRE'd"); 59 60static cl::opt<bool> EnablePRE("enable-pre", 61 cl::init(true), cl::Hidden); 62static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 63static cl::opt<bool> EnableFullLoadPRE("enable-full-load-pre", cl::init(false)); 64 65//===----------------------------------------------------------------------===// 66// ValueTable Class 67//===----------------------------------------------------------------------===// 68 69/// This class holds the mapping between values and value numbers. It is used 70/// as an efficient mechanism to determine the expression-wise equivalence of 71/// two values. 72namespace { 73 struct Expression { 74 enum ExpressionOpcode { 75 ADD = Instruction::Add, 76 FADD = Instruction::FAdd, 77 SUB = Instruction::Sub, 78 FSUB = Instruction::FSub, 79 MUL = Instruction::Mul, 80 FMUL = Instruction::FMul, 81 UDIV = Instruction::UDiv, 82 SDIV = Instruction::SDiv, 83 FDIV = Instruction::FDiv, 84 UREM = Instruction::URem, 85 SREM = Instruction::SRem, 86 FREM = Instruction::FRem, 87 SHL = Instruction::Shl, 88 LSHR = Instruction::LShr, 89 ASHR = Instruction::AShr, 90 AND = Instruction::And, 91 OR = Instruction::Or, 92 XOR = Instruction::Xor, 93 TRUNC = Instruction::Trunc, 94 ZEXT = Instruction::ZExt, 95 SEXT = Instruction::SExt, 96 FPTOUI = Instruction::FPToUI, 97 FPTOSI = Instruction::FPToSI, 98 UITOFP = Instruction::UIToFP, 99 SITOFP = Instruction::SIToFP, 100 FPTRUNC = Instruction::FPTrunc, 101 FPEXT = Instruction::FPExt, 102 PTRTOINT = Instruction::PtrToInt, 103 INTTOPTR = Instruction::IntToPtr, 104 BITCAST = Instruction::BitCast, 105 ICMPEQ, ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 106 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 107 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 108 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 109 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 110 SHUFFLE, SELECT, GEP, CALL, CONSTANT, 111 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE }; 112 113 ExpressionOpcode opcode; 114 const Type* type; 115 SmallVector<uint32_t, 4> varargs; 116 Value *function; 117 118 Expression() { } 119 Expression(ExpressionOpcode o) : opcode(o) { } 120 121 bool operator==(const Expression &other) const { 122 if (opcode != other.opcode) 123 return false; 124 else if (opcode == EMPTY || opcode == TOMBSTONE) 125 return true; 126 else if (type != other.type) 127 return false; 128 else if (function != other.function) 129 return false; 130 else { 131 if (varargs.size() != other.varargs.size()) 132 return false; 133 134 for (size_t i = 0; i < varargs.size(); ++i) 135 if (varargs[i] != other.varargs[i]) 136 return false; 137 138 return true; 139 } 140 } 141 142 bool operator!=(const Expression &other) const { 143 return !(*this == other); 144 } 145 }; 146 147 class ValueTable { 148 private: 149 DenseMap<Value*, uint32_t> valueNumbering; 150 DenseMap<Expression, uint32_t> expressionNumbering; 151 AliasAnalysis* AA; 152 MemoryDependenceAnalysis* MD; 153 DominatorTree* DT; 154 155 uint32_t nextValueNumber; 156 157 Expression::ExpressionOpcode getOpcode(CmpInst* C); 158 Expression create_expression(BinaryOperator* BO); 159 Expression create_expression(CmpInst* C); 160 Expression create_expression(ShuffleVectorInst* V); 161 Expression create_expression(ExtractElementInst* C); 162 Expression create_expression(InsertElementInst* V); 163 Expression create_expression(SelectInst* V); 164 Expression create_expression(CastInst* C); 165 Expression create_expression(GetElementPtrInst* G); 166 Expression create_expression(CallInst* C); 167 Expression create_expression(Constant* C); 168 Expression create_expression(ExtractValueInst* C); 169 Expression create_expression(InsertValueInst* C); 170 171 uint32_t lookup_or_add_call(CallInst* C); 172 public: 173 ValueTable() : nextValueNumber(1) { } 174 uint32_t lookup_or_add(Value *V); 175 uint32_t lookup(Value *V) const; 176 void add(Value *V, uint32_t num); 177 void clear(); 178 void erase(Value *v); 179 unsigned size(); 180 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 181 AliasAnalysis *getAliasAnalysis() const { return AA; } 182 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 183 void setDomTree(DominatorTree* D) { DT = D; } 184 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 185 void verifyRemoved(const Value *) const; 186 }; 187} 188 189namespace llvm { 190template <> struct DenseMapInfo<Expression> { 191 static inline Expression getEmptyKey() { 192 return Expression(Expression::EMPTY); 193 } 194 195 static inline Expression getTombstoneKey() { 196 return Expression(Expression::TOMBSTONE); 197 } 198 199 static unsigned getHashValue(const Expression e) { 200 unsigned hash = e.opcode; 201 202 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 203 (unsigned)((uintptr_t)e.type >> 9)); 204 205 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 206 E = e.varargs.end(); I != E; ++I) 207 hash = *I + hash * 37; 208 209 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 210 (unsigned)((uintptr_t)e.function >> 9)) + 211 hash * 37; 212 213 return hash; 214 } 215 static bool isEqual(const Expression &LHS, const Expression &RHS) { 216 return LHS == RHS; 217 } 218}; 219 220template <> 221struct isPodLike<Expression> { static const bool value = true; }; 222 223} 224 225//===----------------------------------------------------------------------===// 226// ValueTable Internal Functions 227//===----------------------------------------------------------------------===// 228 229Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 230 if (isa<ICmpInst>(C)) { 231 switch (C->getPredicate()) { 232 default: // THIS SHOULD NEVER HAPPEN 233 llvm_unreachable("Comparison with unknown predicate?"); 234 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 235 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 236 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 237 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 238 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 239 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 240 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 241 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 242 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 243 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 244 } 245 } else { 246 switch (C->getPredicate()) { 247 default: // THIS SHOULD NEVER HAPPEN 248 llvm_unreachable("Comparison with unknown predicate?"); 249 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 250 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 251 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 252 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 253 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 254 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 255 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 256 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 257 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 258 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 259 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 260 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 261 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 262 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 263 } 264 } 265} 266 267Expression ValueTable::create_expression(CallInst* C) { 268 Expression e; 269 270 e.type = C->getType(); 271 e.function = C->getCalledFunction(); 272 e.opcode = Expression::CALL; 273 274 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 275 I != E; ++I) 276 e.varargs.push_back(lookup_or_add(*I)); 277 278 return e; 279} 280 281Expression ValueTable::create_expression(BinaryOperator* BO) { 282 Expression e; 283 e.varargs.push_back(lookup_or_add(BO->getOperand(0))); 284 e.varargs.push_back(lookup_or_add(BO->getOperand(1))); 285 e.function = 0; 286 e.type = BO->getType(); 287 e.opcode = static_cast<Expression::ExpressionOpcode>(BO->getOpcode()); 288 289 return e; 290} 291 292Expression ValueTable::create_expression(CmpInst* C) { 293 Expression e; 294 295 e.varargs.push_back(lookup_or_add(C->getOperand(0))); 296 e.varargs.push_back(lookup_or_add(C->getOperand(1))); 297 e.function = 0; 298 e.type = C->getType(); 299 e.opcode = getOpcode(C); 300 301 return e; 302} 303 304Expression ValueTable::create_expression(CastInst* C) { 305 Expression e; 306 307 e.varargs.push_back(lookup_or_add(C->getOperand(0))); 308 e.function = 0; 309 e.type = C->getType(); 310 e.opcode = static_cast<Expression::ExpressionOpcode>(C->getOpcode()); 311 312 return e; 313} 314 315Expression ValueTable::create_expression(ShuffleVectorInst* S) { 316 Expression e; 317 318 e.varargs.push_back(lookup_or_add(S->getOperand(0))); 319 e.varargs.push_back(lookup_or_add(S->getOperand(1))); 320 e.varargs.push_back(lookup_or_add(S->getOperand(2))); 321 e.function = 0; 322 e.type = S->getType(); 323 e.opcode = Expression::SHUFFLE; 324 325 return e; 326} 327 328Expression ValueTable::create_expression(ExtractElementInst* E) { 329 Expression e; 330 331 e.varargs.push_back(lookup_or_add(E->getOperand(0))); 332 e.varargs.push_back(lookup_or_add(E->getOperand(1))); 333 e.function = 0; 334 e.type = E->getType(); 335 e.opcode = Expression::EXTRACT; 336 337 return e; 338} 339 340Expression ValueTable::create_expression(InsertElementInst* I) { 341 Expression e; 342 343 e.varargs.push_back(lookup_or_add(I->getOperand(0))); 344 e.varargs.push_back(lookup_or_add(I->getOperand(1))); 345 e.varargs.push_back(lookup_or_add(I->getOperand(2))); 346 e.function = 0; 347 e.type = I->getType(); 348 e.opcode = Expression::INSERT; 349 350 return e; 351} 352 353Expression ValueTable::create_expression(SelectInst* I) { 354 Expression e; 355 356 e.varargs.push_back(lookup_or_add(I->getCondition())); 357 e.varargs.push_back(lookup_or_add(I->getTrueValue())); 358 e.varargs.push_back(lookup_or_add(I->getFalseValue())); 359 e.function = 0; 360 e.type = I->getType(); 361 e.opcode = Expression::SELECT; 362 363 return e; 364} 365 366Expression ValueTable::create_expression(GetElementPtrInst* G) { 367 Expression e; 368 369 e.varargs.push_back(lookup_or_add(G->getPointerOperand())); 370 e.function = 0; 371 e.type = G->getType(); 372 e.opcode = Expression::GEP; 373 374 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 375 I != E; ++I) 376 e.varargs.push_back(lookup_or_add(*I)); 377 378 return e; 379} 380 381Expression ValueTable::create_expression(ExtractValueInst* E) { 382 Expression e; 383 384 e.varargs.push_back(lookup_or_add(E->getAggregateOperand())); 385 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 386 II != IE; ++II) 387 e.varargs.push_back(*II); 388 e.function = 0; 389 e.type = E->getType(); 390 e.opcode = Expression::EXTRACTVALUE; 391 392 return e; 393} 394 395Expression ValueTable::create_expression(InsertValueInst* E) { 396 Expression e; 397 398 e.varargs.push_back(lookup_or_add(E->getAggregateOperand())); 399 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand())); 400 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 401 II != IE; ++II) 402 e.varargs.push_back(*II); 403 e.function = 0; 404 e.type = E->getType(); 405 e.opcode = Expression::INSERTVALUE; 406 407 return e; 408} 409 410//===----------------------------------------------------------------------===// 411// ValueTable External Functions 412//===----------------------------------------------------------------------===// 413 414/// add - Insert a value into the table with a specified value number. 415void ValueTable::add(Value *V, uint32_t num) { 416 valueNumbering.insert(std::make_pair(V, num)); 417} 418 419uint32_t ValueTable::lookup_or_add_call(CallInst* C) { 420 if (AA->doesNotAccessMemory(C)) { 421 Expression exp = create_expression(C); 422 uint32_t& e = expressionNumbering[exp]; 423 if (!e) e = nextValueNumber++; 424 valueNumbering[C] = e; 425 return e; 426 } else if (AA->onlyReadsMemory(C)) { 427 Expression exp = create_expression(C); 428 uint32_t& e = expressionNumbering[exp]; 429 if (!e) { 430 e = nextValueNumber++; 431 valueNumbering[C] = e; 432 return e; 433 } 434 if (!MD) { 435 e = nextValueNumber++; 436 valueNumbering[C] = e; 437 return e; 438 } 439 440 MemDepResult local_dep = MD->getDependency(C); 441 442 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 443 valueNumbering[C] = nextValueNumber; 444 return nextValueNumber++; 445 } 446 447 if (local_dep.isDef()) { 448 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 449 450 if (local_cdep->getNumOperands() != C->getNumOperands()) { 451 valueNumbering[C] = nextValueNumber; 452 return nextValueNumber++; 453 } 454 455 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 456 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 457 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 458 if (c_vn != cd_vn) { 459 valueNumbering[C] = nextValueNumber; 460 return nextValueNumber++; 461 } 462 } 463 464 uint32_t v = lookup_or_add(local_cdep); 465 valueNumbering[C] = v; 466 return v; 467 } 468 469 // Non-local case. 470 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 471 MD->getNonLocalCallDependency(CallSite(C)); 472 // FIXME: call/call dependencies for readonly calls should return def, not 473 // clobber! Move the checking logic to MemDep! 474 CallInst* cdep = 0; 475 476 // Check to see if we have a single dominating call instruction that is 477 // identical to C. 478 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 479 const NonLocalDepEntry *I = &deps[i]; 480 // Ignore non-local dependencies. 481 if (I->getResult().isNonLocal()) 482 continue; 483 484 // We don't handle non-depedencies. If we already have a call, reject 485 // instruction dependencies. 486 if (I->getResult().isClobber() || cdep != 0) { 487 cdep = 0; 488 break; 489 } 490 491 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); 492 // FIXME: All duplicated with non-local case. 493 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ 494 cdep = NonLocalDepCall; 495 continue; 496 } 497 498 cdep = 0; 499 break; 500 } 501 502 if (!cdep) { 503 valueNumbering[C] = nextValueNumber; 504 return nextValueNumber++; 505 } 506 507 if (cdep->getNumOperands() != C->getNumOperands()) { 508 valueNumbering[C] = nextValueNumber; 509 return nextValueNumber++; 510 } 511 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 512 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 513 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 514 if (c_vn != cd_vn) { 515 valueNumbering[C] = nextValueNumber; 516 return nextValueNumber++; 517 } 518 } 519 520 uint32_t v = lookup_or_add(cdep); 521 valueNumbering[C] = v; 522 return v; 523 524 } else { 525 valueNumbering[C] = nextValueNumber; 526 return nextValueNumber++; 527 } 528} 529 530/// lookup_or_add - Returns the value number for the specified value, assigning 531/// it a new number if it did not have one before. 532uint32_t ValueTable::lookup_or_add(Value *V) { 533 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 534 if (VI != valueNumbering.end()) 535 return VI->second; 536 537 if (!isa<Instruction>(V)) { 538 valueNumbering[V] = nextValueNumber; 539 return nextValueNumber++; 540 } 541 542 Instruction* I = cast<Instruction>(V); 543 Expression exp; 544 switch (I->getOpcode()) { 545 case Instruction::Call: 546 return lookup_or_add_call(cast<CallInst>(I)); 547 case Instruction::Add: 548 case Instruction::FAdd: 549 case Instruction::Sub: 550 case Instruction::FSub: 551 case Instruction::Mul: 552 case Instruction::FMul: 553 case Instruction::UDiv: 554 case Instruction::SDiv: 555 case Instruction::FDiv: 556 case Instruction::URem: 557 case Instruction::SRem: 558 case Instruction::FRem: 559 case Instruction::Shl: 560 case Instruction::LShr: 561 case Instruction::AShr: 562 case Instruction::And: 563 case Instruction::Or : 564 case Instruction::Xor: 565 exp = create_expression(cast<BinaryOperator>(I)); 566 break; 567 case Instruction::ICmp: 568 case Instruction::FCmp: 569 exp = create_expression(cast<CmpInst>(I)); 570 break; 571 case Instruction::Trunc: 572 case Instruction::ZExt: 573 case Instruction::SExt: 574 case Instruction::FPToUI: 575 case Instruction::FPToSI: 576 case Instruction::UIToFP: 577 case Instruction::SIToFP: 578 case Instruction::FPTrunc: 579 case Instruction::FPExt: 580 case Instruction::PtrToInt: 581 case Instruction::IntToPtr: 582 case Instruction::BitCast: 583 exp = create_expression(cast<CastInst>(I)); 584 break; 585 case Instruction::Select: 586 exp = create_expression(cast<SelectInst>(I)); 587 break; 588 case Instruction::ExtractElement: 589 exp = create_expression(cast<ExtractElementInst>(I)); 590 break; 591 case Instruction::InsertElement: 592 exp = create_expression(cast<InsertElementInst>(I)); 593 break; 594 case Instruction::ShuffleVector: 595 exp = create_expression(cast<ShuffleVectorInst>(I)); 596 break; 597 case Instruction::ExtractValue: 598 exp = create_expression(cast<ExtractValueInst>(I)); 599 break; 600 case Instruction::InsertValue: 601 exp = create_expression(cast<InsertValueInst>(I)); 602 break; 603 case Instruction::GetElementPtr: 604 exp = create_expression(cast<GetElementPtrInst>(I)); 605 break; 606 default: 607 valueNumbering[V] = nextValueNumber; 608 return nextValueNumber++; 609 } 610 611 uint32_t& e = expressionNumbering[exp]; 612 if (!e) e = nextValueNumber++; 613 valueNumbering[V] = e; 614 return e; 615} 616 617/// lookup - Returns the value number of the specified value. Fails if 618/// the value has not yet been numbered. 619uint32_t ValueTable::lookup(Value *V) const { 620 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); 621 assert(VI != valueNumbering.end() && "Value not numbered?"); 622 return VI->second; 623} 624 625/// clear - Remove all entries from the ValueTable 626void ValueTable::clear() { 627 valueNumbering.clear(); 628 expressionNumbering.clear(); 629 nextValueNumber = 1; 630} 631 632/// erase - Remove a value from the value numbering 633void ValueTable::erase(Value *V) { 634 valueNumbering.erase(V); 635} 636 637/// verifyRemoved - Verify that the value is removed from all internal data 638/// structures. 639void ValueTable::verifyRemoved(const Value *V) const { 640 for (DenseMap<Value*, uint32_t>::const_iterator 641 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 642 assert(I->first != V && "Inst still occurs in value numbering map!"); 643 } 644} 645 646//===----------------------------------------------------------------------===// 647// GVN Pass 648//===----------------------------------------------------------------------===// 649 650namespace { 651 struct ValueNumberScope { 652 ValueNumberScope* parent; 653 DenseMap<uint32_t, Value*> table; 654 655 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 656 }; 657} 658 659namespace { 660 661 class GVN : public FunctionPass { 662 bool runOnFunction(Function &F); 663 public: 664 static char ID; // Pass identification, replacement for typeid 665 explicit GVN(bool noloads = false) 666 : FunctionPass(&ID), NoLoads(noloads), MD(0) { } 667 668 private: 669 bool NoLoads; 670 MemoryDependenceAnalysis *MD; 671 DominatorTree *DT; 672 673 ValueTable VN; 674 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 675 676 // List of critical edges to be split between iterations. 677 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 678 679 // This transformation requires dominator postdominator info 680 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 681 AU.addRequired<DominatorTree>(); 682 if (!NoLoads) 683 AU.addRequired<MemoryDependenceAnalysis>(); 684 AU.addRequired<AliasAnalysis>(); 685 686 AU.addPreserved<DominatorTree>(); 687 AU.addPreserved<AliasAnalysis>(); 688 } 689 690 // Helper fuctions 691 // FIXME: eliminate or document these better 692 bool processLoad(LoadInst* L, 693 SmallVectorImpl<Instruction*> &toErase); 694 bool processInstruction(Instruction *I, 695 SmallVectorImpl<Instruction*> &toErase); 696 bool processNonLocalLoad(LoadInst* L, 697 SmallVectorImpl<Instruction*> &toErase); 698 bool processBlock(BasicBlock *BB); 699 void dump(DenseMap<uint32_t, Value*>& d); 700 bool iterateOnFunction(Function &F); 701 Value *CollapsePhi(PHINode* p); 702 bool performPRE(Function& F); 703 Value *lookupNumber(BasicBlock *BB, uint32_t num); 704 void cleanupGlobalSets(); 705 void verifyRemoved(const Instruction *I) const; 706 bool splitCriticalEdges(); 707 }; 708 709 char GVN::ID = 0; 710} 711 712// createGVNPass - The public interface to this file... 713FunctionPass *llvm::createGVNPass(bool NoLoads) { 714 return new GVN(NoLoads); 715} 716 717static RegisterPass<GVN> X("gvn", 718 "Global Value Numbering"); 719 720void GVN::dump(DenseMap<uint32_t, Value*>& d) { 721 errs() << "{\n"; 722 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 723 E = d.end(); I != E; ++I) { 724 errs() << I->first << "\n"; 725 I->second->dump(); 726 } 727 errs() << "}\n"; 728} 729 730static bool isSafeReplacement(PHINode* p, Instruction *inst) { 731 if (!isa<PHINode>(inst)) 732 return true; 733 734 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 735 UI != E; ++UI) 736 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 737 if (use_phi->getParent() == inst->getParent()) 738 return false; 739 740 return true; 741} 742 743Value *GVN::CollapsePhi(PHINode *PN) { 744 Value *ConstVal = PN->hasConstantValue(DT); 745 if (!ConstVal) return 0; 746 747 Instruction *Inst = dyn_cast<Instruction>(ConstVal); 748 if (!Inst) 749 return ConstVal; 750 751 if (DT->dominates(Inst, PN)) 752 if (isSafeReplacement(PN, Inst)) 753 return Inst; 754 return 0; 755} 756 757/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 758/// we're analyzing is fully available in the specified block. As we go, keep 759/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 760/// map is actually a tri-state map with the following values: 761/// 0) we know the block *is not* fully available. 762/// 1) we know the block *is* fully available. 763/// 2) we do not know whether the block is fully available or not, but we are 764/// currently speculating that it will be. 765/// 3) we are speculating for this block and have used that to speculate for 766/// other blocks. 767static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 768 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 769 // Optimistically assume that the block is fully available and check to see 770 // if we already know about this block in one lookup. 771 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 772 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 773 774 // If the entry already existed for this block, return the precomputed value. 775 if (!IV.second) { 776 // If this is a speculative "available" value, mark it as being used for 777 // speculation of other blocks. 778 if (IV.first->second == 2) 779 IV.first->second = 3; 780 return IV.first->second != 0; 781 } 782 783 // Otherwise, see if it is fully available in all predecessors. 784 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 785 786 // If this block has no predecessors, it isn't live-in here. 787 if (PI == PE) 788 goto SpeculationFailure; 789 790 for (; PI != PE; ++PI) 791 // If the value isn't fully available in one of our predecessors, then it 792 // isn't fully available in this block either. Undo our previous 793 // optimistic assumption and bail out. 794 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 795 goto SpeculationFailure; 796 797 return true; 798 799// SpeculationFailure - If we get here, we found out that this is not, after 800// all, a fully-available block. We have a problem if we speculated on this and 801// used the speculation to mark other blocks as available. 802SpeculationFailure: 803 char &BBVal = FullyAvailableBlocks[BB]; 804 805 // If we didn't speculate on this, just return with it set to false. 806 if (BBVal == 2) { 807 BBVal = 0; 808 return false; 809 } 810 811 // If we did speculate on this value, we could have blocks set to 1 that are 812 // incorrect. Walk the (transitive) successors of this block and mark them as 813 // 0 if set to one. 814 SmallVector<BasicBlock*, 32> BBWorklist; 815 BBWorklist.push_back(BB); 816 817 do { 818 BasicBlock *Entry = BBWorklist.pop_back_val(); 819 // Note that this sets blocks to 0 (unavailable) if they happen to not 820 // already be in FullyAvailableBlocks. This is safe. 821 char &EntryVal = FullyAvailableBlocks[Entry]; 822 if (EntryVal == 0) continue; // Already unavailable. 823 824 // Mark as unavailable. 825 EntryVal = 0; 826 827 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 828 BBWorklist.push_back(*I); 829 } while (!BBWorklist.empty()); 830 831 return false; 832} 833 834 835/// CanCoerceMustAliasedValueToLoad - Return true if 836/// CoerceAvailableValueToLoadType will succeed. 837static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 838 const Type *LoadTy, 839 const TargetData &TD) { 840 // If the loaded or stored value is an first class array or struct, don't try 841 // to transform them. We need to be able to bitcast to integer. 842 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 843 StoredVal->getType()->isStructTy() || 844 StoredVal->getType()->isArrayTy()) 845 return false; 846 847 // The store has to be at least as big as the load. 848 if (TD.getTypeSizeInBits(StoredVal->getType()) < 849 TD.getTypeSizeInBits(LoadTy)) 850 return false; 851 852 return true; 853} 854 855 856/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 857/// then a load from a must-aliased pointer of a different type, try to coerce 858/// the stored value. LoadedTy is the type of the load we want to replace and 859/// InsertPt is the place to insert new instructions. 860/// 861/// If we can't do it, return null. 862static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 863 const Type *LoadedTy, 864 Instruction *InsertPt, 865 const TargetData &TD) { 866 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 867 return 0; 868 869 const Type *StoredValTy = StoredVal->getType(); 870 871 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 872 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 873 874 // If the store and reload are the same size, we can always reuse it. 875 if (StoreSize == LoadSize) { 876 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) { 877 // Pointer to Pointer -> use bitcast. 878 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 879 } 880 881 // Convert source pointers to integers, which can be bitcast. 882 if (StoredValTy->isPointerTy()) { 883 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 884 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 885 } 886 887 const Type *TypeToCastTo = LoadedTy; 888 if (TypeToCastTo->isPointerTy()) 889 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 890 891 if (StoredValTy != TypeToCastTo) 892 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 893 894 // Cast to pointer if the load needs a pointer type. 895 if (LoadedTy->isPointerTy()) 896 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 897 898 return StoredVal; 899 } 900 901 // If the loaded value is smaller than the available value, then we can 902 // extract out a piece from it. If the available value is too small, then we 903 // can't do anything. 904 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 905 906 // Convert source pointers to integers, which can be manipulated. 907 if (StoredValTy->isPointerTy()) { 908 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 909 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 910 } 911 912 // Convert vectors and fp to integer, which can be manipulated. 913 if (!StoredValTy->isIntegerTy()) { 914 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 915 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 916 } 917 918 // If this is a big-endian system, we need to shift the value down to the low 919 // bits so that a truncate will work. 920 if (TD.isBigEndian()) { 921 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 922 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 923 } 924 925 // Truncate the integer to the right size now. 926 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 927 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 928 929 if (LoadedTy == NewIntTy) 930 return StoredVal; 931 932 // If the result is a pointer, inttoptr. 933 if (LoadedTy->isPointerTy()) 934 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 935 936 // Otherwise, bitcast. 937 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 938} 939 940/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 941/// be expressed as a base pointer plus a constant offset. Return the base and 942/// offset to the caller. 943static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 944 const TargetData &TD) { 945 Operator *PtrOp = dyn_cast<Operator>(Ptr); 946 if (PtrOp == 0) return Ptr; 947 948 // Just look through bitcasts. 949 if (PtrOp->getOpcode() == Instruction::BitCast) 950 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 951 952 // If this is a GEP with constant indices, we can look through it. 953 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 954 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 955 956 gep_type_iterator GTI = gep_type_begin(GEP); 957 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 958 ++I, ++GTI) { 959 ConstantInt *OpC = cast<ConstantInt>(*I); 960 if (OpC->isZero()) continue; 961 962 // Handle a struct and array indices which add their offset to the pointer. 963 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 964 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 965 } else { 966 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 967 Offset += OpC->getSExtValue()*Size; 968 } 969 } 970 971 // Re-sign extend from the pointer size if needed to get overflow edge cases 972 // right. 973 unsigned PtrSize = TD.getPointerSizeInBits(); 974 if (PtrSize < 64) 975 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 976 977 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 978} 979 980 981/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 982/// memdep query of a load that ends up being a clobbering memory write (store, 983/// memset, memcpy, memmove). This means that the write *may* provide bits used 984/// by the load but we can't be sure because the pointers don't mustalias. 985/// 986/// Check this case to see if there is anything more we can do before we give 987/// up. This returns -1 if we have to give up, or a byte number in the stored 988/// value of the piece that feeds the load. 989static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr, 990 Value *WritePtr, 991 uint64_t WriteSizeInBits, 992 const TargetData &TD) { 993 // If the loaded or stored value is an first class array or struct, don't try 994 // to transform them. We need to be able to bitcast to integer. 995 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 996 return -1; 997 998 int64_t StoreOffset = 0, LoadOffset = 0; 999 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD); 1000 Value *LoadBase = 1001 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD); 1002 if (StoreBase != LoadBase) 1003 return -1; 1004 1005 // If the load and store are to the exact same address, they should have been 1006 // a must alias. AA must have gotten confused. 1007 // FIXME: Study to see if/when this happens. One case is forwarding a memset 1008 // to a load from the base of the memset. 1009#if 0 1010 if (LoadOffset == StoreOffset) { 1011 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 1012 << "Base = " << *StoreBase << "\n" 1013 << "Store Ptr = " << *WritePtr << "\n" 1014 << "Store Offs = " << StoreOffset << "\n" 1015 << "Load Ptr = " << *LoadPtr << "\n"; 1016 abort(); 1017 } 1018#endif 1019 1020 // If the load and store don't overlap at all, the store doesn't provide 1021 // anything to the load. In this case, they really don't alias at all, AA 1022 // must have gotten confused. 1023 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1024 // remove this check, as it is duplicated with what we have below. 1025 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); 1026 1027 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 1028 return -1; 1029 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 1030 LoadSize >>= 3; 1031 1032 1033 bool isAAFailure = false; 1034 if (StoreOffset < LoadOffset) 1035 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1036 else 1037 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1038 1039 if (isAAFailure) { 1040#if 0 1041 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1042 << "Base = " << *StoreBase << "\n" 1043 << "Store Ptr = " << *WritePtr << "\n" 1044 << "Store Offs = " << StoreOffset << "\n" 1045 << "Load Ptr = " << *LoadPtr << "\n"; 1046 abort(); 1047#endif 1048 return -1; 1049 } 1050 1051 // If the Load isn't completely contained within the stored bits, we don't 1052 // have all the bits to feed it. We could do something crazy in the future 1053 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1054 // valuable. 1055 if (StoreOffset > LoadOffset || 1056 StoreOffset+StoreSize < LoadOffset+LoadSize) 1057 return -1; 1058 1059 // Okay, we can do this transformation. Return the number of bytes into the 1060 // store that the load is. 1061 return LoadOffset-StoreOffset; 1062} 1063 1064/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1065/// memdep query of a load that ends up being a clobbering store. 1066static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr, 1067 StoreInst *DepSI, 1068 const TargetData &TD) { 1069 // Cannot handle reading from store of first-class aggregate yet. 1070 if (DepSI->getOperand(0)->getType()->isStructTy() || 1071 DepSI->getOperand(0)->getType()->isArrayTy()) 1072 return -1; 1073 1074 Value *StorePtr = DepSI->getPointerOperand(); 1075 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType()); 1076 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1077 StorePtr, StoreSize, TD); 1078} 1079 1080static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr, 1081 MemIntrinsic *MI, 1082 const TargetData &TD) { 1083 // If the mem operation is a non-constant size, we can't handle it. 1084 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 1085 if (SizeCst == 0) return -1; 1086 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 1087 1088 // If this is memset, we just need to see if the offset is valid in the size 1089 // of the memset.. 1090 if (MI->getIntrinsicID() == Intrinsic::memset) 1091 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 1092 MemSizeInBits, TD); 1093 1094 // If we have a memcpy/memmove, the only case we can handle is if this is a 1095 // copy from constant memory. In that case, we can read directly from the 1096 // constant memory. 1097 MemTransferInst *MTI = cast<MemTransferInst>(MI); 1098 1099 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 1100 if (Src == 0) return -1; 1101 1102 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject()); 1103 if (GV == 0 || !GV->isConstant()) return -1; 1104 1105 // See if the access is within the bounds of the transfer. 1106 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1107 MI->getDest(), MemSizeInBits, TD); 1108 if (Offset == -1) 1109 return Offset; 1110 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 llvm::Type::getInt8PtrTy(Src->getContext())); 1115 Constant *OffsetCst = 1116 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1117 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1118 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1119 if (ConstantFoldLoadFromConstPtr(Src, &TD)) 1120 return Offset; 1121 return -1; 1122} 1123 1124 1125/// GetStoreValueForLoad - This function is called when we have a 1126/// memdep query of a load that ends up being a clobbering store. This means 1127/// that the store *may* provide bits used by the load but we can't be sure 1128/// because the pointers don't mustalias. Check this case to see if there is 1129/// anything more we can do before we give up. 1130static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1131 const Type *LoadTy, 1132 Instruction *InsertPt, const TargetData &TD){ 1133 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1134 1135 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8; 1136 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1137 1138 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1139 1140 // Compute which bits of the stored value are being used by the load. Convert 1141 // to an integer type to start with. 1142 if (SrcVal->getType()->isPointerTy()) 1143 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp"); 1144 if (!SrcVal->getType()->isIntegerTy()) 1145 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1146 "tmp"); 1147 1148 // Shift the bits to the least significant depending on endianness. 1149 unsigned ShiftAmt; 1150 if (TD.isLittleEndian()) 1151 ShiftAmt = Offset*8; 1152 else 1153 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1154 1155 if (ShiftAmt) 1156 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp"); 1157 1158 if (LoadSize != StoreSize) 1159 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1160 "tmp"); 1161 1162 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1163} 1164 1165/// GetMemInstValueForLoad - This function is called when we have a 1166/// memdep query of a load that ends up being a clobbering mem intrinsic. 1167static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1168 const Type *LoadTy, Instruction *InsertPt, 1169 const TargetData &TD){ 1170 LLVMContext &Ctx = LoadTy->getContext(); 1171 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1172 1173 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1174 1175 // We know that this method is only called when the mem transfer fully 1176 // provides the bits for the load. 1177 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1178 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1179 // independently of what the offset is. 1180 Value *Val = MSI->getValue(); 1181 if (LoadSize != 1) 1182 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1183 1184 Value *OneElt = Val; 1185 1186 // Splat the value out to the right number of bits. 1187 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1188 // If we can double the number of bytes set, do it. 1189 if (NumBytesSet*2 <= LoadSize) { 1190 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1191 Val = Builder.CreateOr(Val, ShVal); 1192 NumBytesSet <<= 1; 1193 continue; 1194 } 1195 1196 // Otherwise insert one byte at a time. 1197 Value *ShVal = Builder.CreateShl(Val, 1*8); 1198 Val = Builder.CreateOr(OneElt, ShVal); 1199 ++NumBytesSet; 1200 } 1201 1202 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 1203 } 1204 1205 // Otherwise, this is a memcpy/memmove from a constant global. 1206 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 1207 Constant *Src = cast<Constant>(MTI->getSource()); 1208 1209 // Otherwise, see if we can constant fold a load from the constant with the 1210 // offset applied as appropriate. 1211 Src = ConstantExpr::getBitCast(Src, 1212 llvm::Type::getInt8PtrTy(Src->getContext())); 1213 Constant *OffsetCst = 1214 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1215 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1216 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1217 return ConstantFoldLoadFromConstPtr(Src, &TD); 1218} 1219 1220namespace { 1221 1222struct AvailableValueInBlock { 1223 /// BB - The basic block in question. 1224 BasicBlock *BB; 1225 enum ValType { 1226 SimpleVal, // A simple offsetted value that is accessed. 1227 MemIntrin // A memory intrinsic which is loaded from. 1228 }; 1229 1230 /// V - The value that is live out of the block. 1231 PointerIntPair<Value *, 1, ValType> Val; 1232 1233 /// Offset - The byte offset in Val that is interesting for the load query. 1234 unsigned Offset; 1235 1236 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1237 unsigned Offset = 0) { 1238 AvailableValueInBlock Res; 1239 Res.BB = BB; 1240 Res.Val.setPointer(V); 1241 Res.Val.setInt(SimpleVal); 1242 Res.Offset = Offset; 1243 return Res; 1244 } 1245 1246 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 1247 unsigned Offset = 0) { 1248 AvailableValueInBlock Res; 1249 Res.BB = BB; 1250 Res.Val.setPointer(MI); 1251 Res.Val.setInt(MemIntrin); 1252 Res.Offset = Offset; 1253 return Res; 1254 } 1255 1256 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 1257 Value *getSimpleValue() const { 1258 assert(isSimpleValue() && "Wrong accessor"); 1259 return Val.getPointer(); 1260 } 1261 1262 MemIntrinsic *getMemIntrinValue() const { 1263 assert(!isSimpleValue() && "Wrong accessor"); 1264 return cast<MemIntrinsic>(Val.getPointer()); 1265 } 1266 1267 /// MaterializeAdjustedValue - Emit code into this block to adjust the value 1268 /// defined here to the specified type. This handles various coercion cases. 1269 Value *MaterializeAdjustedValue(const Type *LoadTy, 1270 const TargetData *TD) const { 1271 Value *Res; 1272 if (isSimpleValue()) { 1273 Res = getSimpleValue(); 1274 if (Res->getType() != LoadTy) { 1275 assert(TD && "Need target data to handle type mismatch case"); 1276 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), 1277 *TD); 1278 1279 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1280 << *getSimpleValue() << '\n' 1281 << *Res << '\n' << "\n\n\n"); 1282 } 1283 } else { 1284 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, 1285 LoadTy, BB->getTerminator(), *TD); 1286 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1287 << " " << *getMemIntrinValue() << '\n' 1288 << *Res << '\n' << "\n\n\n"); 1289 } 1290 return Res; 1291 } 1292}; 1293 1294} 1295 1296/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1297/// construct SSA form, allowing us to eliminate LI. This returns the value 1298/// that should be used at LI's definition site. 1299static Value *ConstructSSAForLoadSet(LoadInst *LI, 1300 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1301 const TargetData *TD, 1302 const DominatorTree &DT, 1303 AliasAnalysis *AA) { 1304 // Check for the fully redundant, dominating load case. In this case, we can 1305 // just use the dominating value directly. 1306 if (ValuesPerBlock.size() == 1 && 1307 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent())) 1308 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD); 1309 1310 // Otherwise, we have to construct SSA form. 1311 SmallVector<PHINode*, 8> NewPHIs; 1312 SSAUpdater SSAUpdate(&NewPHIs); 1313 SSAUpdate.Initialize(LI); 1314 1315 const Type *LoadTy = LI->getType(); 1316 1317 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1318 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1319 BasicBlock *BB = AV.BB; 1320 1321 if (SSAUpdate.HasValueForBlock(BB)) 1322 continue; 1323 1324 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD)); 1325 } 1326 1327 // Perform PHI construction. 1328 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1329 1330 // If new PHI nodes were created, notify alias analysis. 1331 if (V->getType()->isPointerTy()) 1332 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1333 AA->copyValue(LI, NewPHIs[i]); 1334 1335 return V; 1336} 1337 1338static bool isLifetimeStart(const Instruction *Inst) { 1339 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1340 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1341 return false; 1342} 1343 1344/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1345/// non-local by performing PHI construction. 1346bool GVN::processNonLocalLoad(LoadInst *LI, 1347 SmallVectorImpl<Instruction*> &toErase) { 1348 // Find the non-local dependencies of the load. 1349 SmallVector<NonLocalDepResult, 64> Deps; 1350 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 1351 Deps); 1352 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: " 1353 // << Deps.size() << *LI << '\n'); 1354 1355 // If we had to process more than one hundred blocks to find the 1356 // dependencies, this load isn't worth worrying about. Optimizing 1357 // it will be too expensive. 1358 if (Deps.size() > 100) 1359 return false; 1360 1361 // If we had a phi translation failure, we'll have a single entry which is a 1362 // clobber in the current block. Reject this early. 1363 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) { 1364 DEBUG( 1365 dbgs() << "GVN: non-local load "; 1366 WriteAsOperand(dbgs(), LI); 1367 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n'; 1368 ); 1369 return false; 1370 } 1371 1372 // Filter out useless results (non-locals, etc). Keep track of the blocks 1373 // where we have a value available in repl, also keep track of whether we see 1374 // dependencies that produce an unknown value for the load (such as a call 1375 // that could potentially clobber the load). 1376 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1377 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1378 1379 const TargetData *TD = 0; 1380 1381 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1382 BasicBlock *DepBB = Deps[i].getBB(); 1383 MemDepResult DepInfo = Deps[i].getResult(); 1384 1385 if (DepInfo.isClobber()) { 1386 // The address being loaded in this non-local block may not be the same as 1387 // the pointer operand of the load if PHI translation occurs. Make sure 1388 // to consider the right address. 1389 Value *Address = Deps[i].getAddress(); 1390 1391 // If the dependence is to a store that writes to a superset of the bits 1392 // read by the load, we can extract the bits we need for the load from the 1393 // stored value. 1394 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1395 if (TD == 0) 1396 TD = getAnalysisIfAvailable<TargetData>(); 1397 if (TD && Address) { 1398 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, 1399 DepSI, *TD); 1400 if (Offset != -1) { 1401 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1402 DepSI->getOperand(0), 1403 Offset)); 1404 continue; 1405 } 1406 } 1407 } 1408 1409 // If the clobbering value is a memset/memcpy/memmove, see if we can 1410 // forward a value on from it. 1411 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1412 if (TD == 0) 1413 TD = getAnalysisIfAvailable<TargetData>(); 1414 if (TD && Address) { 1415 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, 1416 DepMI, *TD); 1417 if (Offset != -1) { 1418 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1419 Offset)); 1420 continue; 1421 } 1422 } 1423 } 1424 1425 UnavailableBlocks.push_back(DepBB); 1426 continue; 1427 } 1428 1429 Instruction *DepInst = DepInfo.getInst(); 1430 1431 // Loading the allocation -> undef. 1432 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) || 1433 // Loading immediately after lifetime begin -> undef. 1434 isLifetimeStart(DepInst)) { 1435 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1436 UndefValue::get(LI->getType()))); 1437 continue; 1438 } 1439 1440 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1441 // Reject loads and stores that are to the same address but are of 1442 // different types if we have to. 1443 if (S->getOperand(0)->getType() != LI->getType()) { 1444 if (TD == 0) 1445 TD = getAnalysisIfAvailable<TargetData>(); 1446 1447 // If the stored value is larger or equal to the loaded value, we can 1448 // reuse it. 1449 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0), 1450 LI->getType(), *TD)) { 1451 UnavailableBlocks.push_back(DepBB); 1452 continue; 1453 } 1454 } 1455 1456 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1457 S->getOperand(0))); 1458 continue; 1459 } 1460 1461 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1462 // If the types mismatch and we can't handle it, reject reuse of the load. 1463 if (LD->getType() != LI->getType()) { 1464 if (TD == 0) 1465 TD = getAnalysisIfAvailable<TargetData>(); 1466 1467 // If the stored value is larger or equal to the loaded value, we can 1468 // reuse it. 1469 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1470 UnavailableBlocks.push_back(DepBB); 1471 continue; 1472 } 1473 } 1474 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1475 continue; 1476 } 1477 1478 UnavailableBlocks.push_back(DepBB); 1479 continue; 1480 } 1481 1482 // If we have no predecessors that produce a known value for this load, exit 1483 // early. 1484 if (ValuesPerBlock.empty()) return false; 1485 1486 // If all of the instructions we depend on produce a known value for this 1487 // load, then it is fully redundant and we can use PHI insertion to compute 1488 // its value. Insert PHIs and remove the fully redundant value now. 1489 if (UnavailableBlocks.empty()) { 1490 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1491 1492 // Perform PHI construction. 1493 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1494 VN.getAliasAnalysis()); 1495 LI->replaceAllUsesWith(V); 1496 1497 if (isa<PHINode>(V)) 1498 V->takeName(LI); 1499 if (V->getType()->isPointerTy()) 1500 MD->invalidateCachedPointerInfo(V); 1501 VN.erase(LI); 1502 toErase.push_back(LI); 1503 NumGVNLoad++; 1504 return true; 1505 } 1506 1507 if (!EnablePRE || !EnableLoadPRE) 1508 return false; 1509 1510 // Okay, we have *some* definitions of the value. This means that the value 1511 // is available in some of our (transitive) predecessors. Lets think about 1512 // doing PRE of this load. This will involve inserting a new load into the 1513 // predecessor when it's not available. We could do this in general, but 1514 // prefer to not increase code size. As such, we only do this when we know 1515 // that we only have to insert *one* load (which means we're basically moving 1516 // the load, not inserting a new one). 1517 1518 SmallPtrSet<BasicBlock *, 4> Blockers; 1519 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1520 Blockers.insert(UnavailableBlocks[i]); 1521 1522 // Lets find first basic block with more than one predecessor. Walk backwards 1523 // through predecessors if needed. 1524 BasicBlock *LoadBB = LI->getParent(); 1525 BasicBlock *TmpBB = LoadBB; 1526 1527 bool isSinglePred = false; 1528 bool allSingleSucc = true; 1529 while (TmpBB->getSinglePredecessor()) { 1530 isSinglePred = true; 1531 TmpBB = TmpBB->getSinglePredecessor(); 1532 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1533 return false; 1534 if (Blockers.count(TmpBB)) 1535 return false; 1536 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1537 allSingleSucc = false; 1538 } 1539 1540 assert(TmpBB); 1541 LoadBB = TmpBB; 1542 1543 // If we have a repl set with LI itself in it, this means we have a loop where 1544 // at least one of the values is LI. Since this means that we won't be able 1545 // to eliminate LI even if we insert uses in the other predecessors, we will 1546 // end up increasing code size. Reject this by scanning for LI. 1547 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1548 if (ValuesPerBlock[i].isSimpleValue() && 1549 ValuesPerBlock[i].getSimpleValue() == LI) { 1550 // Skip cases where LI is the only definition, even for EnableFullLoadPRE. 1551 if (!EnableFullLoadPRE || e == 1) 1552 return false; 1553 } 1554 } 1555 1556 // FIXME: It is extremely unclear what this loop is doing, other than 1557 // artificially restricting loadpre. 1558 if (isSinglePred) { 1559 bool isHot = false; 1560 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1561 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1562 if (AV.isSimpleValue()) 1563 // "Hot" Instruction is in some loop (because it dominates its dep. 1564 // instruction). 1565 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) 1566 if (DT->dominates(LI, I)) { 1567 isHot = true; 1568 break; 1569 } 1570 } 1571 1572 // We are interested only in "hot" instructions. We don't want to do any 1573 // mis-optimizations here. 1574 if (!isHot) 1575 return false; 1576 } 1577 1578 // Check to see how many predecessors have the loaded value fully 1579 // available. 1580 DenseMap<BasicBlock*, Value*> PredLoads; 1581 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1582 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1583 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1584 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1585 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1586 1587 bool NeedToSplitEdges = false; 1588 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1589 PI != E; ++PI) { 1590 BasicBlock *Pred = *PI; 1591 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { 1592 continue; 1593 } 1594 PredLoads[Pred] = 0; 1595 1596 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1597 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1598 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1599 << Pred->getName() << "': " << *LI << '\n'); 1600 return false; 1601 } 1602 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB); 1603 toSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum)); 1604 NeedToSplitEdges = true; 1605 } 1606 } 1607 if (NeedToSplitEdges) 1608 return false; 1609 1610 // Decide whether PRE is profitable for this load. 1611 unsigned NumUnavailablePreds = PredLoads.size(); 1612 assert(NumUnavailablePreds != 0 && 1613 "Fully available value should be eliminated above!"); 1614 if (!EnableFullLoadPRE) { 1615 // If this load is unavailable in multiple predecessors, reject it. 1616 // FIXME: If we could restructure the CFG, we could make a common pred with 1617 // all the preds that don't have an available LI and insert a new load into 1618 // that one block. 1619 if (NumUnavailablePreds != 1) 1620 return false; 1621 } 1622 1623 // Check if the load can safely be moved to all the unavailable predecessors. 1624 bool CanDoPRE = true; 1625 SmallVector<Instruction*, 8> NewInsts; 1626 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1627 E = PredLoads.end(); I != E; ++I) { 1628 BasicBlock *UnavailablePred = I->first; 1629 1630 // Do PHI translation to get its value in the predecessor if necessary. The 1631 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1632 1633 // If all preds have a single successor, then we know it is safe to insert 1634 // the load on the pred (?!?), so we can insert code to materialize the 1635 // pointer if it is not available. 1636 PHITransAddr Address(LI->getOperand(0), TD); 1637 Value *LoadPtr = 0; 1638 if (allSingleSucc) { 1639 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1640 *DT, NewInsts); 1641 } else { 1642 Address.PHITranslateValue(LoadBB, UnavailablePred, DT); 1643 LoadPtr = Address.getAddr(); 1644 } 1645 1646 // If we couldn't find or insert a computation of this phi translated value, 1647 // we fail PRE. 1648 if (LoadPtr == 0) { 1649 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1650 << *LI->getOperand(0) << "\n"); 1651 CanDoPRE = false; 1652 break; 1653 } 1654 1655 // Make sure it is valid to move this load here. We have to watch out for: 1656 // @1 = getelementptr (i8* p, ... 1657 // test p and branch if == 0 1658 // load @1 1659 // It is valid to have the getelementptr before the test, even if p can be 0, 1660 // as getelementptr only does address arithmetic. 1661 // If we are not pushing the value through any multiple-successor blocks 1662 // we do not have this case. Otherwise, check that the load is safe to 1663 // put anywhere; this can be improved, but should be conservatively safe. 1664 if (!allSingleSucc && 1665 // FIXME: REEVALUTE THIS. 1666 !isSafeToLoadUnconditionally(LoadPtr, 1667 UnavailablePred->getTerminator(), 1668 LI->getAlignment(), TD)) { 1669 CanDoPRE = false; 1670 break; 1671 } 1672 1673 I->second = LoadPtr; 1674 } 1675 1676 if (!CanDoPRE) { 1677 while (!NewInsts.empty()) 1678 NewInsts.pop_back_val()->eraseFromParent(); 1679 return false; 1680 } 1681 1682 // Okay, we can eliminate this load by inserting a reload in the predecessor 1683 // and using PHI construction to get the value in the other predecessors, do 1684 // it. 1685 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1686 DEBUG(if (!NewInsts.empty()) 1687 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1688 << *NewInsts.back() << '\n'); 1689 1690 // Assign value numbers to the new instructions. 1691 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { 1692 // FIXME: We really _ought_ to insert these value numbers into their 1693 // parent's availability map. However, in doing so, we risk getting into 1694 // ordering issues. If a block hasn't been processed yet, we would be 1695 // marking a value as AVAIL-IN, which isn't what we intend. 1696 VN.lookup_or_add(NewInsts[i]); 1697 } 1698 1699 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1700 E = PredLoads.end(); I != E; ++I) { 1701 BasicBlock *UnavailablePred = I->first; 1702 Value *LoadPtr = I->second; 1703 1704 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1705 LI->getAlignment(), 1706 UnavailablePred->getTerminator()); 1707 1708 // Add the newly created load. 1709 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1710 NewLoad)); 1711 MD->invalidateCachedPointerInfo(LoadPtr); 1712 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); 1713 } 1714 1715 // Perform PHI construction. 1716 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1717 VN.getAliasAnalysis()); 1718 LI->replaceAllUsesWith(V); 1719 if (isa<PHINode>(V)) 1720 V->takeName(LI); 1721 if (V->getType()->isPointerTy()) 1722 MD->invalidateCachedPointerInfo(V); 1723 VN.erase(LI); 1724 toErase.push_back(LI); 1725 NumPRELoad++; 1726 return true; 1727} 1728 1729/// processLoad - Attempt to eliminate a load, first by eliminating it 1730/// locally, and then attempting non-local elimination if that fails. 1731bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1732 if (!MD) 1733 return false; 1734 1735 if (L->isVolatile()) 1736 return false; 1737 1738 // ... to a pointer that has been loaded from before... 1739 MemDepResult Dep = MD->getDependency(L); 1740 1741 // If the value isn't available, don't do anything! 1742 if (Dep.isClobber()) { 1743 // Check to see if we have something like this: 1744 // store i32 123, i32* %P 1745 // %A = bitcast i32* %P to i8* 1746 // %B = gep i8* %A, i32 1 1747 // %C = load i8* %B 1748 // 1749 // We could do that by recognizing if the clobber instructions are obviously 1750 // a common base + constant offset, and if the previous store (or memset) 1751 // completely covers this load. This sort of thing can happen in bitfield 1752 // access code. 1753 Value *AvailVal = 0; 1754 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1755 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1756 int Offset = AnalyzeLoadFromClobberingStore(L->getType(), 1757 L->getPointerOperand(), 1758 DepSI, *TD); 1759 if (Offset != -1) 1760 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset, 1761 L->getType(), L, *TD); 1762 } 1763 1764 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1765 // a value on from it. 1766 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1767 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1768 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), 1769 L->getPointerOperand(), 1770 DepMI, *TD); 1771 if (Offset != -1) 1772 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD); 1773 } 1774 } 1775 1776 if (AvailVal) { 1777 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1778 << *AvailVal << '\n' << *L << "\n\n\n"); 1779 1780 // Replace the load! 1781 L->replaceAllUsesWith(AvailVal); 1782 if (AvailVal->getType()->isPointerTy()) 1783 MD->invalidateCachedPointerInfo(AvailVal); 1784 VN.erase(L); 1785 toErase.push_back(L); 1786 NumGVNLoad++; 1787 return true; 1788 } 1789 1790 DEBUG( 1791 // fast print dep, using operator<< on instruction would be too slow 1792 dbgs() << "GVN: load "; 1793 WriteAsOperand(dbgs(), L); 1794 Instruction *I = Dep.getInst(); 1795 dbgs() << " is clobbered by " << *I << '\n'; 1796 ); 1797 return false; 1798 } 1799 1800 // If it is defined in another block, try harder. 1801 if (Dep.isNonLocal()) 1802 return processNonLocalLoad(L, toErase); 1803 1804 Instruction *DepInst = Dep.getInst(); 1805 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1806 Value *StoredVal = DepSI->getOperand(0); 1807 1808 // The store and load are to a must-aliased pointer, but they may not 1809 // actually have the same type. See if we know how to reuse the stored 1810 // value (depending on its type). 1811 const TargetData *TD = 0; 1812 if (StoredVal->getType() != L->getType()) { 1813 if ((TD = getAnalysisIfAvailable<TargetData>())) { 1814 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1815 L, *TD); 1816 if (StoredVal == 0) 1817 return false; 1818 1819 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1820 << '\n' << *L << "\n\n\n"); 1821 } 1822 else 1823 return false; 1824 } 1825 1826 // Remove it! 1827 L->replaceAllUsesWith(StoredVal); 1828 if (StoredVal->getType()->isPointerTy()) 1829 MD->invalidateCachedPointerInfo(StoredVal); 1830 VN.erase(L); 1831 toErase.push_back(L); 1832 NumGVNLoad++; 1833 return true; 1834 } 1835 1836 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1837 Value *AvailableVal = DepLI; 1838 1839 // The loads are of a must-aliased pointer, but they may not actually have 1840 // the same type. See if we know how to reuse the previously loaded value 1841 // (depending on its type). 1842 const TargetData *TD = 0; 1843 if (DepLI->getType() != L->getType()) { 1844 if ((TD = getAnalysisIfAvailable<TargetData>())) { 1845 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1846 if (AvailableVal == 0) 1847 return false; 1848 1849 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1850 << "\n" << *L << "\n\n\n"); 1851 } 1852 else 1853 return false; 1854 } 1855 1856 // Remove it! 1857 L->replaceAllUsesWith(AvailableVal); 1858 if (DepLI->getType()->isPointerTy()) 1859 MD->invalidateCachedPointerInfo(DepLI); 1860 VN.erase(L); 1861 toErase.push_back(L); 1862 NumGVNLoad++; 1863 return true; 1864 } 1865 1866 // If this load really doesn't depend on anything, then we must be loading an 1867 // undef value. This can happen when loading for a fresh allocation with no 1868 // intervening stores, for example. 1869 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { 1870 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1871 VN.erase(L); 1872 toErase.push_back(L); 1873 NumGVNLoad++; 1874 return true; 1875 } 1876 1877 // If this load occurs either right after a lifetime begin, 1878 // then the loaded value is undefined. 1879 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) { 1880 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1881 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1882 VN.erase(L); 1883 toErase.push_back(L); 1884 NumGVNLoad++; 1885 return true; 1886 } 1887 } 1888 1889 return false; 1890} 1891 1892Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1893 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1894 if (I == localAvail.end()) 1895 return 0; 1896 1897 ValueNumberScope *Locals = I->second; 1898 while (Locals) { 1899 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1900 if (I != Locals->table.end()) 1901 return I->second; 1902 Locals = Locals->parent; 1903 } 1904 1905 return 0; 1906} 1907 1908 1909/// processInstruction - When calculating availability, handle an instruction 1910/// by inserting it into the appropriate sets 1911bool GVN::processInstruction(Instruction *I, 1912 SmallVectorImpl<Instruction*> &toErase) { 1913 // Ignore dbg info intrinsics. 1914 if (isa<DbgInfoIntrinsic>(I)) 1915 return false; 1916 1917 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1918 bool Changed = processLoad(LI, toErase); 1919 1920 if (!Changed) { 1921 unsigned Num = VN.lookup_or_add(LI); 1922 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1923 } 1924 1925 return Changed; 1926 } 1927 1928 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1929 unsigned Num = VN.lookup_or_add(I); 1930 1931 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1932 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1933 1934 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1935 return false; 1936 1937 Value *BranchCond = BI->getCondition(); 1938 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1939 1940 BasicBlock *TrueSucc = BI->getSuccessor(0); 1941 BasicBlock *FalseSucc = BI->getSuccessor(1); 1942 1943 if (TrueSucc->getSinglePredecessor()) 1944 localAvail[TrueSucc]->table[CondVN] = 1945 ConstantInt::getTrue(TrueSucc->getContext()); 1946 if (FalseSucc->getSinglePredecessor()) 1947 localAvail[FalseSucc]->table[CondVN] = 1948 ConstantInt::getFalse(TrueSucc->getContext()); 1949 1950 return false; 1951 1952 // Allocations are always uniquely numbered, so we can save time and memory 1953 // by fast failing them. 1954 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) { 1955 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1956 return false; 1957 } 1958 1959 // Collapse PHI nodes 1960 if (PHINode* p = dyn_cast<PHINode>(I)) { 1961 Value *constVal = CollapsePhi(p); 1962 1963 if (constVal) { 1964 p->replaceAllUsesWith(constVal); 1965 if (MD && constVal->getType()->isPointerTy()) 1966 MD->invalidateCachedPointerInfo(constVal); 1967 VN.erase(p); 1968 1969 toErase.push_back(p); 1970 } else { 1971 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1972 } 1973 1974 // If the number we were assigned was a brand new VN, then we don't 1975 // need to do a lookup to see if the number already exists 1976 // somewhere in the domtree: it can't! 1977 } else if (Num == NextNum) { 1978 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1979 1980 // Perform fast-path value-number based elimination of values inherited from 1981 // dominators. 1982 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1983 // Remove it! 1984 VN.erase(I); 1985 I->replaceAllUsesWith(repl); 1986 if (MD && repl->getType()->isPointerTy()) 1987 MD->invalidateCachedPointerInfo(repl); 1988 toErase.push_back(I); 1989 return true; 1990 1991 } else { 1992 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1993 } 1994 1995 return false; 1996} 1997 1998/// runOnFunction - This is the main transformation entry point for a function. 1999bool GVN::runOnFunction(Function& F) { 2000 if (!NoLoads) 2001 MD = &getAnalysis<MemoryDependenceAnalysis>(); 2002 DT = &getAnalysis<DominatorTree>(); 2003 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 2004 VN.setMemDep(MD); 2005 VN.setDomTree(DT); 2006 2007 bool Changed = false; 2008 bool ShouldContinue = true; 2009 2010 // Merge unconditional branches, allowing PRE to catch more 2011 // optimization opportunities. 2012 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 2013 BasicBlock *BB = FI; 2014 ++FI; 2015 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 2016 if (removedBlock) NumGVNBlocks++; 2017 2018 Changed |= removedBlock; 2019 } 2020 2021 unsigned Iteration = 0; 2022 2023 while (ShouldContinue) { 2024 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 2025 ShouldContinue = iterateOnFunction(F); 2026 if (splitCriticalEdges()) 2027 ShouldContinue = true; 2028 Changed |= ShouldContinue; 2029 ++Iteration; 2030 } 2031 2032 if (EnablePRE) { 2033 bool PREChanged = true; 2034 while (PREChanged) { 2035 PREChanged = performPRE(F); 2036 Changed |= PREChanged; 2037 } 2038 } 2039 // FIXME: Should perform GVN again after PRE does something. PRE can move 2040 // computations into blocks where they become fully redundant. Note that 2041 // we can't do this until PRE's critical edge splitting updates memdep. 2042 // Actually, when this happens, we should just fully integrate PRE into GVN. 2043 2044 cleanupGlobalSets(); 2045 2046 return Changed; 2047} 2048 2049 2050bool GVN::processBlock(BasicBlock *BB) { 2051 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 2052 // incrementing BI before processing an instruction). 2053 SmallVector<Instruction*, 8> toErase; 2054 bool ChangedFunction = false; 2055 2056 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 2057 BI != BE;) { 2058 ChangedFunction |= processInstruction(BI, toErase); 2059 if (toErase.empty()) { 2060 ++BI; 2061 continue; 2062 } 2063 2064 // If we need some instructions deleted, do it now. 2065 NumGVNInstr += toErase.size(); 2066 2067 // Avoid iterator invalidation. 2068 bool AtStart = BI == BB->begin(); 2069 if (!AtStart) 2070 --BI; 2071 2072 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 2073 E = toErase.end(); I != E; ++I) { 2074 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 2075 if (MD) MD->removeInstruction(*I); 2076 (*I)->eraseFromParent(); 2077 DEBUG(verifyRemoved(*I)); 2078 } 2079 toErase.clear(); 2080 2081 if (AtStart) 2082 BI = BB->begin(); 2083 else 2084 ++BI; 2085 } 2086 2087 return ChangedFunction; 2088} 2089 2090/// performPRE - Perform a purely local form of PRE that looks for diamond 2091/// control flow patterns and attempts to perform simple PRE at the join point. 2092bool GVN::performPRE(Function &F) { 2093 bool Changed = false; 2094 DenseMap<BasicBlock*, Value*> predMap; 2095 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 2096 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 2097 BasicBlock *CurrentBlock = *DI; 2098 2099 // Nothing to PRE in the entry block. 2100 if (CurrentBlock == &F.getEntryBlock()) continue; 2101 2102 for (BasicBlock::iterator BI = CurrentBlock->begin(), 2103 BE = CurrentBlock->end(); BI != BE; ) { 2104 Instruction *CurInst = BI++; 2105 2106 if (isa<AllocaInst>(CurInst) || 2107 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 2108 CurInst->getType()->isVoidTy() || 2109 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2110 isa<DbgInfoIntrinsic>(CurInst)) 2111 continue; 2112 2113 uint32_t ValNo = VN.lookup(CurInst); 2114 2115 // Look for the predecessors for PRE opportunities. We're 2116 // only trying to solve the basic diamond case, where 2117 // a value is computed in the successor and one predecessor, 2118 // but not the other. We also explicitly disallow cases 2119 // where the successor is its own predecessor, because they're 2120 // more complicated to get right. 2121 unsigned NumWith = 0; 2122 unsigned NumWithout = 0; 2123 BasicBlock *PREPred = 0; 2124 predMap.clear(); 2125 2126 for (pred_iterator PI = pred_begin(CurrentBlock), 2127 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2128 // We're not interested in PRE where the block is its 2129 // own predecessor, or in blocks with predecessors 2130 // that are not reachable. 2131 if (*PI == CurrentBlock) { 2132 NumWithout = 2; 2133 break; 2134 } else if (!localAvail.count(*PI)) { 2135 NumWithout = 2; 2136 break; 2137 } 2138 2139 DenseMap<uint32_t, Value*>::iterator predV = 2140 localAvail[*PI]->table.find(ValNo); 2141 if (predV == localAvail[*PI]->table.end()) { 2142 PREPred = *PI; 2143 NumWithout++; 2144 } else if (predV->second == CurInst) { 2145 NumWithout = 2; 2146 } else { 2147 predMap[*PI] = predV->second; 2148 NumWith++; 2149 } 2150 } 2151 2152 // Don't do PRE when it might increase code size, i.e. when 2153 // we would need to insert instructions in more than one pred. 2154 if (NumWithout != 1 || NumWith == 0) 2155 continue; 2156 2157 // Don't do PRE across indirect branch. 2158 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2159 continue; 2160 2161 // We can't do PRE safely on a critical edge, so instead we schedule 2162 // the edge to be split and perform the PRE the next time we iterate 2163 // on the function. 2164 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); 2165 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2166 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2167 continue; 2168 } 2169 2170 // Instantiate the expression in the predecessor that lacked it. 2171 // Because we are going top-down through the block, all value numbers 2172 // will be available in the predecessor by the time we need them. Any 2173 // that weren't originally present will have been instantiated earlier 2174 // in this loop. 2175 Instruction *PREInstr = CurInst->clone(); 2176 bool success = true; 2177 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2178 Value *Op = PREInstr->getOperand(i); 2179 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2180 continue; 2181 2182 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2183 PREInstr->setOperand(i, V); 2184 } else { 2185 success = false; 2186 break; 2187 } 2188 } 2189 2190 // Fail out if we encounter an operand that is not available in 2191 // the PRE predecessor. This is typically because of loads which 2192 // are not value numbered precisely. 2193 if (!success) { 2194 delete PREInstr; 2195 DEBUG(verifyRemoved(PREInstr)); 2196 continue; 2197 } 2198 2199 PREInstr->insertBefore(PREPred->getTerminator()); 2200 PREInstr->setName(CurInst->getName() + ".pre"); 2201 predMap[PREPred] = PREInstr; 2202 VN.add(PREInstr, ValNo); 2203 NumGVNPRE++; 2204 2205 // Update the availability map to include the new instruction. 2206 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 2207 2208 // Create a PHI to make the value available in this block. 2209 PHINode* Phi = PHINode::Create(CurInst->getType(), 2210 CurInst->getName() + ".pre-phi", 2211 CurrentBlock->begin()); 2212 for (pred_iterator PI = pred_begin(CurrentBlock), 2213 PE = pred_end(CurrentBlock); PI != PE; ++PI) 2214 Phi->addIncoming(predMap[*PI], *PI); 2215 2216 VN.add(Phi, ValNo); 2217 localAvail[CurrentBlock]->table[ValNo] = Phi; 2218 2219 CurInst->replaceAllUsesWith(Phi); 2220 if (MD && Phi->getType()->isPointerTy()) 2221 MD->invalidateCachedPointerInfo(Phi); 2222 VN.erase(CurInst); 2223 2224 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2225 if (MD) MD->removeInstruction(CurInst); 2226 CurInst->eraseFromParent(); 2227 DEBUG(verifyRemoved(CurInst)); 2228 Changed = true; 2229 } 2230 } 2231 2232 if (splitCriticalEdges()) 2233 Changed = true; 2234 2235 return Changed; 2236} 2237 2238/// splitCriticalEdges - Split critical edges found during the previous 2239/// iteration that may enable further optimization. 2240bool GVN::splitCriticalEdges() { 2241 if (toSplit.empty()) 2242 return false; 2243 do { 2244 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2245 SplitCriticalEdge(Edge.first, Edge.second, this); 2246 } while (!toSplit.empty()); 2247 if (MD) MD->invalidateCachedPredecessors(); 2248 return true; 2249} 2250 2251/// iterateOnFunction - Executes one iteration of GVN 2252bool GVN::iterateOnFunction(Function &F) { 2253 cleanupGlobalSets(); 2254 2255 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2256 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 2257 if (DI->getIDom()) 2258 localAvail[DI->getBlock()] = 2259 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 2260 else 2261 localAvail[DI->getBlock()] = new ValueNumberScope(0); 2262 } 2263 2264 // Top-down walk of the dominator tree 2265 bool Changed = false; 2266#if 0 2267 // Needed for value numbering with phi construction to work. 2268 ReversePostOrderTraversal<Function*> RPOT(&F); 2269 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2270 RE = RPOT.end(); RI != RE; ++RI) 2271 Changed |= processBlock(*RI); 2272#else 2273 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2274 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2275 Changed |= processBlock(DI->getBlock()); 2276#endif 2277 2278 return Changed; 2279} 2280 2281void GVN::cleanupGlobalSets() { 2282 VN.clear(); 2283 2284 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2285 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 2286 delete I->second; 2287 localAvail.clear(); 2288} 2289 2290/// verifyRemoved - Verify that the specified instruction does not occur in our 2291/// internal data structures. 2292void GVN::verifyRemoved(const Instruction *Inst) const { 2293 VN.verifyRemoved(Inst); 2294 2295 // Walk through the value number scope to make sure the instruction isn't 2296 // ferreted away in it. 2297 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator 2298 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 2299 const ValueNumberScope *VNS = I->second; 2300 2301 while (VNS) { 2302 for (DenseMap<uint32_t, Value*>::const_iterator 2303 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 2304 assert(II->second != Inst && "Inst still in value numbering scope!"); 2305 } 2306 2307 VNS = VNS->parent; 2308 } 2309 } 2310} 2311