GVN.cpp revision 484d4a30c055eef3101d01a7a468db3413dd20d3
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 nopre = false, bool noloads = false) 666 : FunctionPass(&ID), NoPRE(nopre), NoLoads(noloads), MD(0) { } 667 668 private: 669 bool NoPRE; 670 bool NoLoads; 671 MemoryDependenceAnalysis *MD; 672 DominatorTree *DT; 673 674 ValueTable VN; 675 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 676 677 // List of critical edges to be split between iterations. 678 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 679 680 // This transformation requires dominator postdominator info 681 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 682 AU.addRequired<DominatorTree>(); 683 if (!NoLoads) 684 AU.addRequired<MemoryDependenceAnalysis>(); 685 AU.addRequired<AliasAnalysis>(); 686 687 AU.addPreserved<DominatorTree>(); 688 AU.addPreserved<AliasAnalysis>(); 689 } 690 691 // Helper fuctions 692 // FIXME: eliminate or document these better 693 bool processLoad(LoadInst* L, 694 SmallVectorImpl<Instruction*> &toErase); 695 bool processInstruction(Instruction *I, 696 SmallVectorImpl<Instruction*> &toErase); 697 bool processNonLocalLoad(LoadInst* L, 698 SmallVectorImpl<Instruction*> &toErase); 699 bool processBlock(BasicBlock *BB); 700 void dump(DenseMap<uint32_t, Value*>& d); 701 bool iterateOnFunction(Function &F); 702 Value *CollapsePhi(PHINode* p); 703 bool performPRE(Function& F); 704 Value *lookupNumber(BasicBlock *BB, uint32_t num); 705 void cleanupGlobalSets(); 706 void verifyRemoved(const Instruction *I) const; 707 bool splitCriticalEdges(); 708 }; 709 710 char GVN::ID = 0; 711} 712 713// createGVNPass - The public interface to this file... 714FunctionPass *llvm::createGVNPass(bool NoPRE, bool NoLoads) { 715 return new GVN(NoPRE, NoLoads); 716} 717 718static RegisterPass<GVN> X("gvn", 719 "Global Value Numbering"); 720 721void GVN::dump(DenseMap<uint32_t, Value*>& d) { 722 errs() << "{\n"; 723 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 724 E = d.end(); I != E; ++I) { 725 errs() << I->first << "\n"; 726 I->second->dump(); 727 } 728 errs() << "}\n"; 729} 730 731static bool isSafeReplacement(PHINode* p, Instruction *inst) { 732 if (!isa<PHINode>(inst)) 733 return true; 734 735 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 736 UI != E; ++UI) 737 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 738 if (use_phi->getParent() == inst->getParent()) 739 return false; 740 741 return true; 742} 743 744Value *GVN::CollapsePhi(PHINode *PN) { 745 Value *ConstVal = PN->hasConstantValue(DT); 746 if (!ConstVal) return 0; 747 748 Instruction *Inst = dyn_cast<Instruction>(ConstVal); 749 if (!Inst) 750 return ConstVal; 751 752 if (DT->dominates(Inst, PN)) 753 if (isSafeReplacement(PN, Inst)) 754 return Inst; 755 return 0; 756} 757 758/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 759/// we're analyzing is fully available in the specified block. As we go, keep 760/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 761/// map is actually a tri-state map with the following values: 762/// 0) we know the block *is not* fully available. 763/// 1) we know the block *is* fully available. 764/// 2) we do not know whether the block is fully available or not, but we are 765/// currently speculating that it will be. 766/// 3) we are speculating for this block and have used that to speculate for 767/// other blocks. 768static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 769 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 770 // Optimistically assume that the block is fully available and check to see 771 // if we already know about this block in one lookup. 772 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 773 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 774 775 // If the entry already existed for this block, return the precomputed value. 776 if (!IV.second) { 777 // If this is a speculative "available" value, mark it as being used for 778 // speculation of other blocks. 779 if (IV.first->second == 2) 780 IV.first->second = 3; 781 return IV.first->second != 0; 782 } 783 784 // Otherwise, see if it is fully available in all predecessors. 785 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 786 787 // If this block has no predecessors, it isn't live-in here. 788 if (PI == PE) 789 goto SpeculationFailure; 790 791 for (; PI != PE; ++PI) 792 // If the value isn't fully available in one of our predecessors, then it 793 // isn't fully available in this block either. Undo our previous 794 // optimistic assumption and bail out. 795 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 796 goto SpeculationFailure; 797 798 return true; 799 800// SpeculationFailure - If we get here, we found out that this is not, after 801// all, a fully-available block. We have a problem if we speculated on this and 802// used the speculation to mark other blocks as available. 803SpeculationFailure: 804 char &BBVal = FullyAvailableBlocks[BB]; 805 806 // If we didn't speculate on this, just return with it set to false. 807 if (BBVal == 2) { 808 BBVal = 0; 809 return false; 810 } 811 812 // If we did speculate on this value, we could have blocks set to 1 that are 813 // incorrect. Walk the (transitive) successors of this block and mark them as 814 // 0 if set to one. 815 SmallVector<BasicBlock*, 32> BBWorklist; 816 BBWorklist.push_back(BB); 817 818 do { 819 BasicBlock *Entry = BBWorklist.pop_back_val(); 820 // Note that this sets blocks to 0 (unavailable) if they happen to not 821 // already be in FullyAvailableBlocks. This is safe. 822 char &EntryVal = FullyAvailableBlocks[Entry]; 823 if (EntryVal == 0) continue; // Already unavailable. 824 825 // Mark as unavailable. 826 EntryVal = 0; 827 828 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 829 BBWorklist.push_back(*I); 830 } while (!BBWorklist.empty()); 831 832 return false; 833} 834 835 836/// CanCoerceMustAliasedValueToLoad - Return true if 837/// CoerceAvailableValueToLoadType will succeed. 838static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 839 const Type *LoadTy, 840 const TargetData &TD) { 841 // If the loaded or stored value is an first class array or struct, don't try 842 // to transform them. We need to be able to bitcast to integer. 843 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 844 StoredVal->getType()->isStructTy() || 845 StoredVal->getType()->isArrayTy()) 846 return false; 847 848 // The store has to be at least as big as the load. 849 if (TD.getTypeSizeInBits(StoredVal->getType()) < 850 TD.getTypeSizeInBits(LoadTy)) 851 return false; 852 853 return true; 854} 855 856 857/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 858/// then a load from a must-aliased pointer of a different type, try to coerce 859/// the stored value. LoadedTy is the type of the load we want to replace and 860/// InsertPt is the place to insert new instructions. 861/// 862/// If we can't do it, return null. 863static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 864 const Type *LoadedTy, 865 Instruction *InsertPt, 866 const TargetData &TD) { 867 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 868 return 0; 869 870 const Type *StoredValTy = StoredVal->getType(); 871 872 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 873 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 874 875 // If the store and reload are the same size, we can always reuse it. 876 if (StoreSize == LoadSize) { 877 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) { 878 // Pointer to Pointer -> use bitcast. 879 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 880 } 881 882 // Convert source pointers to integers, which can be bitcast. 883 if (StoredValTy->isPointerTy()) { 884 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 885 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 886 } 887 888 const Type *TypeToCastTo = LoadedTy; 889 if (TypeToCastTo->isPointerTy()) 890 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 891 892 if (StoredValTy != TypeToCastTo) 893 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 894 895 // Cast to pointer if the load needs a pointer type. 896 if (LoadedTy->isPointerTy()) 897 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 898 899 return StoredVal; 900 } 901 902 // If the loaded value is smaller than the available value, then we can 903 // extract out a piece from it. If the available value is too small, then we 904 // can't do anything. 905 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 906 907 // Convert source pointers to integers, which can be manipulated. 908 if (StoredValTy->isPointerTy()) { 909 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 910 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 911 } 912 913 // Convert vectors and fp to integer, which can be manipulated. 914 if (!StoredValTy->isIntegerTy()) { 915 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 916 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 917 } 918 919 // If this is a big-endian system, we need to shift the value down to the low 920 // bits so that a truncate will work. 921 if (TD.isBigEndian()) { 922 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 923 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 924 } 925 926 // Truncate the integer to the right size now. 927 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 928 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 929 930 if (LoadedTy == NewIntTy) 931 return StoredVal; 932 933 // If the result is a pointer, inttoptr. 934 if (LoadedTy->isPointerTy()) 935 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 936 937 // Otherwise, bitcast. 938 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 939} 940 941/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 942/// be expressed as a base pointer plus a constant offset. Return the base and 943/// offset to the caller. 944static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 945 const TargetData &TD) { 946 Operator *PtrOp = dyn_cast<Operator>(Ptr); 947 if (PtrOp == 0) return Ptr; 948 949 // Just look through bitcasts. 950 if (PtrOp->getOpcode() == Instruction::BitCast) 951 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 952 953 // If this is a GEP with constant indices, we can look through it. 954 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 955 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 956 957 gep_type_iterator GTI = gep_type_begin(GEP); 958 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 959 ++I, ++GTI) { 960 ConstantInt *OpC = cast<ConstantInt>(*I); 961 if (OpC->isZero()) continue; 962 963 // Handle a struct and array indices which add their offset to the pointer. 964 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 965 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 966 } else { 967 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 968 Offset += OpC->getSExtValue()*Size; 969 } 970 } 971 972 // Re-sign extend from the pointer size if needed to get overflow edge cases 973 // right. 974 unsigned PtrSize = TD.getPointerSizeInBits(); 975 if (PtrSize < 64) 976 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 977 978 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 979} 980 981 982/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 983/// memdep query of a load that ends up being a clobbering memory write (store, 984/// memset, memcpy, memmove). This means that the write *may* provide bits used 985/// by the load but we can't be sure because the pointers don't mustalias. 986/// 987/// Check this case to see if there is anything more we can do before we give 988/// up. This returns -1 if we have to give up, or a byte number in the stored 989/// value of the piece that feeds the load. 990static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr, 991 Value *WritePtr, 992 uint64_t WriteSizeInBits, 993 const TargetData &TD) { 994 // If the loaded or stored value is an first class array or struct, don't try 995 // to transform them. We need to be able to bitcast to integer. 996 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 997 return -1; 998 999 int64_t StoreOffset = 0, LoadOffset = 0; 1000 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD); 1001 Value *LoadBase = 1002 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD); 1003 if (StoreBase != LoadBase) 1004 return -1; 1005 1006 // If the load and store are to the exact same address, they should have been 1007 // a must alias. AA must have gotten confused. 1008 // FIXME: Study to see if/when this happens. 1009 if (LoadOffset == StoreOffset) { 1010#if 0 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#endif 1018 return -1; 1019 } 1020 1021 // If the load and store don't overlap at all, the store doesn't provide 1022 // anything to the load. In this case, they really don't alias at all, AA 1023 // must have gotten confused. 1024 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1025 // remove this check, as it is duplicated with what we have below. 1026 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); 1027 1028 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 1029 return -1; 1030 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 1031 LoadSize >>= 3; 1032 1033 1034 bool isAAFailure = false; 1035 if (StoreOffset < LoadOffset) { 1036 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1037 } else { 1038 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1039 } 1040 if (isAAFailure) { 1041#if 0 1042 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1043 << "Base = " << *StoreBase << "\n" 1044 << "Store Ptr = " << *WritePtr << "\n" 1045 << "Store Offs = " << StoreOffset << "\n" 1046 << "Load Ptr = " << *LoadPtr << "\n"; 1047 abort(); 1048#endif 1049 return -1; 1050 } 1051 1052 // If the Load isn't completely contained within the stored bits, we don't 1053 // have all the bits to feed it. We could do something crazy in the future 1054 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1055 // valuable. 1056 if (StoreOffset > LoadOffset || 1057 StoreOffset+StoreSize < LoadOffset+LoadSize) 1058 return -1; 1059 1060 // Okay, we can do this transformation. Return the number of bytes into the 1061 // store that the load is. 1062 return LoadOffset-StoreOffset; 1063} 1064 1065/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1066/// memdep query of a load that ends up being a clobbering store. 1067static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr, 1068 StoreInst *DepSI, 1069 const TargetData &TD) { 1070 // Cannot handle reading from store of first-class aggregate yet. 1071 if (DepSI->getOperand(0)->getType()->isStructTy() || 1072 DepSI->getOperand(0)->getType()->isArrayTy()) 1073 return -1; 1074 1075 Value *StorePtr = DepSI->getPointerOperand(); 1076 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType()); 1077 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1078 StorePtr, StoreSize, TD); 1079} 1080 1081static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr, 1082 MemIntrinsic *MI, 1083 const TargetData &TD) { 1084 // If the mem operation is a non-constant size, we can't handle it. 1085 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 1086 if (SizeCst == 0) return -1; 1087 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 1088 1089 // If this is memset, we just need to see if the offset is valid in the size 1090 // of the memset.. 1091 if (MI->getIntrinsicID() == Intrinsic::memset) 1092 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 1093 MemSizeInBits, TD); 1094 1095 // If we have a memcpy/memmove, the only case we can handle is if this is a 1096 // copy from constant memory. In that case, we can read directly from the 1097 // constant memory. 1098 MemTransferInst *MTI = cast<MemTransferInst>(MI); 1099 1100 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 1101 if (Src == 0) return -1; 1102 1103 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject()); 1104 if (GV == 0 || !GV->isConstant()) return -1; 1105 1106 // See if the access is within the bounds of the transfer. 1107 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1108 MI->getDest(), MemSizeInBits, TD); 1109 if (Offset == -1) 1110 return Offset; 1111 1112 // Otherwise, see if we can constant fold a load from the constant with the 1113 // offset applied as appropriate. 1114 Src = ConstantExpr::getBitCast(Src, 1115 llvm::Type::getInt8PtrTy(Src->getContext())); 1116 Constant *OffsetCst = 1117 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1118 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1119 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1120 if (ConstantFoldLoadFromConstPtr(Src, &TD)) 1121 return Offset; 1122 return -1; 1123} 1124 1125 1126/// GetStoreValueForLoad - 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 *may* provide bits used by the load but we can't be sure 1129/// because the pointers don't mustalias. Check this case to see if there is 1130/// anything more we can do before we give up. 1131static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1132 const Type *LoadTy, 1133 Instruction *InsertPt, const TargetData &TD){ 1134 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1135 1136 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8; 1137 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1138 1139 IRBuilder<> Builder(InsertPt->getParent(), 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()->isPointerTy()) 1144 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp"); 1145 if (!SrcVal->getType()->isIntegerTy()) 1146 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1147 "tmp"); 1148 1149 // Shift the bits to the least significant depending on endianness. 1150 unsigned ShiftAmt; 1151 if (TD.isLittleEndian()) 1152 ShiftAmt = Offset*8; 1153 else 1154 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1155 1156 if (ShiftAmt) 1157 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp"); 1158 1159 if (LoadSize != StoreSize) 1160 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1161 "tmp"); 1162 1163 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1164} 1165 1166/// GetMemInstValueForLoad - This function is called when we have a 1167/// memdep query of a load that ends up being a clobbering mem intrinsic. 1168static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1169 const Type *LoadTy, Instruction *InsertPt, 1170 const TargetData &TD){ 1171 LLVMContext &Ctx = LoadTy->getContext(); 1172 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1173 1174 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1175 1176 // We know that this method is only called when the mem transfer fully 1177 // provides the bits for the load. 1178 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1179 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1180 // independently of what the offset is. 1181 Value *Val = MSI->getValue(); 1182 if (LoadSize != 1) 1183 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1184 1185 Value *OneElt = Val; 1186 1187 // Splat the value out to the right number of bits. 1188 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1189 // If we can double the number of bytes set, do it. 1190 if (NumBytesSet*2 <= LoadSize) { 1191 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1192 Val = Builder.CreateOr(Val, ShVal); 1193 NumBytesSet <<= 1; 1194 continue; 1195 } 1196 1197 // Otherwise insert one byte at a time. 1198 Value *ShVal = Builder.CreateShl(Val, 1*8); 1199 Val = Builder.CreateOr(OneElt, ShVal); 1200 ++NumBytesSet; 1201 } 1202 1203 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 1204 } 1205 1206 // Otherwise, this is a memcpy/memmove from a constant global. 1207 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 1208 Constant *Src = cast<Constant>(MTI->getSource()); 1209 1210 // Otherwise, see if we can constant fold a load from the constant with the 1211 // offset applied as appropriate. 1212 Src = ConstantExpr::getBitCast(Src, 1213 llvm::Type::getInt8PtrTy(Src->getContext())); 1214 Constant *OffsetCst = 1215 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1216 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1217 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1218 return ConstantFoldLoadFromConstPtr(Src, &TD); 1219} 1220 1221 1222 1223struct AvailableValueInBlock { 1224 /// BB - The basic block in question. 1225 BasicBlock *BB; 1226 enum ValType { 1227 SimpleVal, // A simple offsetted value that is accessed. 1228 MemIntrin // A memory intrinsic which is loaded from. 1229 }; 1230 1231 /// V - The value that is live out of the block. 1232 PointerIntPair<Value *, 1, ValType> Val; 1233 1234 /// Offset - The byte offset in Val that is interesting for the load query. 1235 unsigned Offset; 1236 1237 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1238 unsigned Offset = 0) { 1239 AvailableValueInBlock Res; 1240 Res.BB = BB; 1241 Res.Val.setPointer(V); 1242 Res.Val.setInt(SimpleVal); 1243 Res.Offset = Offset; 1244 return Res; 1245 } 1246 1247 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 1248 unsigned Offset = 0) { 1249 AvailableValueInBlock Res; 1250 Res.BB = BB; 1251 Res.Val.setPointer(MI); 1252 Res.Val.setInt(MemIntrin); 1253 Res.Offset = Offset; 1254 return Res; 1255 } 1256 1257 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 1258 Value *getSimpleValue() const { 1259 assert(isSimpleValue() && "Wrong accessor"); 1260 return Val.getPointer(); 1261 } 1262 1263 MemIntrinsic *getMemIntrinValue() const { 1264 assert(!isSimpleValue() && "Wrong accessor"); 1265 return cast<MemIntrinsic>(Val.getPointer()); 1266 } 1267 1268 /// MaterializeAdjustedValue - Emit code into this block to adjust the value 1269 /// defined here to the specified type. This handles various coercion cases. 1270 Value *MaterializeAdjustedValue(const Type *LoadTy, 1271 const TargetData *TD) const { 1272 Value *Res; 1273 if (isSimpleValue()) { 1274 Res = getSimpleValue(); 1275 if (Res->getType() != LoadTy) { 1276 assert(TD && "Need target data to handle type mismatch case"); 1277 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), 1278 *TD); 1279 1280 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1281 << *getSimpleValue() << '\n' 1282 << *Res << '\n' << "\n\n\n"); 1283 } 1284 } else { 1285 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, 1286 LoadTy, BB->getTerminator(), *TD); 1287 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1288 << " " << *getMemIntrinValue() << '\n' 1289 << *Res << '\n' << "\n\n\n"); 1290 } 1291 return Res; 1292 } 1293}; 1294 1295/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1296/// construct SSA form, allowing us to eliminate LI. This returns the value 1297/// that should be used at LI's definition site. 1298static Value *ConstructSSAForLoadSet(LoadInst *LI, 1299 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1300 const TargetData *TD, 1301 const DominatorTree &DT, 1302 AliasAnalysis *AA) { 1303 // Check for the fully redundant, dominating load case. In this case, we can 1304 // just use the dominating value directly. 1305 if (ValuesPerBlock.size() == 1 && 1306 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent())) 1307 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD); 1308 1309 // Otherwise, we have to construct SSA form. 1310 SmallVector<PHINode*, 8> NewPHIs; 1311 SSAUpdater SSAUpdate(&NewPHIs); 1312 SSAUpdate.Initialize(LI); 1313 1314 const Type *LoadTy = LI->getType(); 1315 1316 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1317 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1318 BasicBlock *BB = AV.BB; 1319 1320 if (SSAUpdate.HasValueForBlock(BB)) 1321 continue; 1322 1323 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD)); 1324 } 1325 1326 // Perform PHI construction. 1327 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1328 1329 // If new PHI nodes were created, notify alias analysis. 1330 if (V->getType()->isPointerTy()) 1331 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1332 AA->copyValue(LI, NewPHIs[i]); 1333 1334 return V; 1335} 1336 1337static bool isLifetimeStart(Instruction *Inst) { 1338 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1339 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1340 return false; 1341} 1342 1343/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1344/// non-local by performing PHI construction. 1345bool GVN::processNonLocalLoad(LoadInst *LI, 1346 SmallVectorImpl<Instruction*> &toErase) { 1347 // Find the non-local dependencies of the load. 1348 SmallVector<NonLocalDepResult, 64> Deps; 1349 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 1350 Deps); 1351 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: " 1352 // << Deps.size() << *LI << '\n'); 1353 1354 // If we had to process more than one hundred blocks to find the 1355 // dependencies, this load isn't worth worrying about. Optimizing 1356 // it will be too expensive. 1357 if (Deps.size() > 100) 1358 return false; 1359 1360 // If we had a phi translation failure, we'll have a single entry which is a 1361 // clobber in the current block. Reject this early. 1362 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) { 1363 DEBUG( 1364 dbgs() << "GVN: non-local load "; 1365 WriteAsOperand(dbgs(), LI); 1366 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n'; 1367 ); 1368 return false; 1369 } 1370 1371 // Filter out useless results (non-locals, etc). Keep track of the blocks 1372 // where we have a value available in repl, also keep track of whether we see 1373 // dependencies that produce an unknown value for the load (such as a call 1374 // that could potentially clobber the load). 1375 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1376 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1377 1378 const TargetData *TD = 0; 1379 1380 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1381 BasicBlock *DepBB = Deps[i].getBB(); 1382 MemDepResult DepInfo = Deps[i].getResult(); 1383 1384 if (DepInfo.isClobber()) { 1385 // The address being loaded in this non-local block may not be the same as 1386 // the pointer operand of the load if PHI translation occurs. Make sure 1387 // to consider the right address. 1388 Value *Address = Deps[i].getAddress(); 1389 1390 // If the dependence is to a store that writes to a superset of the bits 1391 // read by the load, we can extract the bits we need for the load from the 1392 // stored value. 1393 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1394 if (TD == 0) 1395 TD = getAnalysisIfAvailable<TargetData>(); 1396 if (TD && Address) { 1397 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, 1398 DepSI, *TD); 1399 if (Offset != -1) { 1400 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1401 DepSI->getOperand(0), 1402 Offset)); 1403 continue; 1404 } 1405 } 1406 } 1407 1408 // If the clobbering value is a memset/memcpy/memmove, see if we can 1409 // forward a value on from it. 1410 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1411 if (TD == 0) 1412 TD = getAnalysisIfAvailable<TargetData>(); 1413 if (TD && Address) { 1414 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, 1415 DepMI, *TD); 1416 if (Offset != -1) { 1417 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1418 Offset)); 1419 continue; 1420 } 1421 } 1422 } 1423 1424 UnavailableBlocks.push_back(DepBB); 1425 continue; 1426 } 1427 1428 Instruction *DepInst = DepInfo.getInst(); 1429 1430 // Loading the allocation -> undef. 1431 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) || 1432 // Loading immediately after lifetime begin -> undef. 1433 isLifetimeStart(DepInst)) { 1434 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1435 UndefValue::get(LI->getType()))); 1436 continue; 1437 } 1438 1439 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1440 // Reject loads and stores that are to the same address but are of 1441 // different types if we have to. 1442 if (S->getOperand(0)->getType() != LI->getType()) { 1443 if (TD == 0) 1444 TD = getAnalysisIfAvailable<TargetData>(); 1445 1446 // If the stored value is larger or equal to the loaded value, we can 1447 // reuse it. 1448 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0), 1449 LI->getType(), *TD)) { 1450 UnavailableBlocks.push_back(DepBB); 1451 continue; 1452 } 1453 } 1454 1455 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1456 S->getOperand(0))); 1457 continue; 1458 } 1459 1460 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1461 // If the types mismatch and we can't handle it, reject reuse of the load. 1462 if (LD->getType() != LI->getType()) { 1463 if (TD == 0) 1464 TD = getAnalysisIfAvailable<TargetData>(); 1465 1466 // If the stored value is larger or equal to the loaded value, we can 1467 // reuse it. 1468 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1469 UnavailableBlocks.push_back(DepBB); 1470 continue; 1471 } 1472 } 1473 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1474 continue; 1475 } 1476 1477 UnavailableBlocks.push_back(DepBB); 1478 continue; 1479 } 1480 1481 // If we have no predecessors that produce a known value for this load, exit 1482 // early. 1483 if (ValuesPerBlock.empty()) return false; 1484 1485 // If all of the instructions we depend on produce a known value for this 1486 // load, then it is fully redundant and we can use PHI insertion to compute 1487 // its value. Insert PHIs and remove the fully redundant value now. 1488 if (UnavailableBlocks.empty()) { 1489 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1490 1491 // Perform PHI construction. 1492 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1493 VN.getAliasAnalysis()); 1494 LI->replaceAllUsesWith(V); 1495 1496 if (isa<PHINode>(V)) 1497 V->takeName(LI); 1498 if (V->getType()->isPointerTy()) 1499 MD->invalidateCachedPointerInfo(V); 1500 toErase.push_back(LI); 1501 NumGVNLoad++; 1502 return true; 1503 } 1504 1505 if (!EnablePRE || !EnableLoadPRE) 1506 return false; 1507 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; 1517 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1518 Blockers.insert(UnavailableBlocks[i]); 1519 1520 // Lets find first basic block with more than one predecessor. Walk backwards 1521 // through predecessors if needed. 1522 BasicBlock *LoadBB = LI->getParent(); 1523 BasicBlock *TmpBB = LoadBB; 1524 1525 bool isSinglePred = false; 1526 bool allSingleSucc = true; 1527 while (TmpBB->getSinglePredecessor()) { 1528 isSinglePred = true; 1529 TmpBB = TmpBB->getSinglePredecessor(); 1530 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1531 return false; 1532 if (Blockers.count(TmpBB)) 1533 return false; 1534 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1535 allSingleSucc = false; 1536 } 1537 1538 assert(TmpBB); 1539 LoadBB = TmpBB; 1540 1541 // If we have a repl set with LI itself in it, this means we have a loop where 1542 // at least one of the values is LI. Since this means that we won't be able 1543 // to eliminate LI even if we insert uses in the other predecessors, we will 1544 // end up increasing code size. Reject this by scanning for LI. 1545 if (!EnableFullLoadPRE) { 1546 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1547 if (ValuesPerBlock[i].isSimpleValue() && 1548 ValuesPerBlock[i].getSimpleValue() == LI) 1549 return false; 1550 } 1551 1552 // FIXME: It is extremely unclear what this loop is doing, other than 1553 // artificially restricting loadpre. 1554 if (isSinglePred) { 1555 bool isHot = false; 1556 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1557 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1558 if (AV.isSimpleValue()) 1559 // "Hot" Instruction is in some loop (because it dominates its dep. 1560 // instruction). 1561 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) 1562 if (DT->dominates(LI, I)) { 1563 isHot = true; 1564 break; 1565 } 1566 } 1567 1568 // We are interested only in "hot" instructions. We don't want to do any 1569 // mis-optimizations here. 1570 if (!isHot) 1571 return false; 1572 } 1573 1574 // Check to see how many predecessors have the loaded value fully 1575 // available. 1576 DenseMap<BasicBlock*, Value*> PredLoads; 1577 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1578 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1579 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1580 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1581 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1582 1583 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1584 PI != E; ++PI) { 1585 BasicBlock *Pred = *PI; 1586 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { 1587 continue; 1588 } 1589 PredLoads[Pred] = 0; 1590 1591 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1592 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1593 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1594 << Pred->getName() << "': " << *LI << '\n'); 1595 return false; 1596 } 1597 unsigned SuccNum = SuccessorNumber(Pred, LoadBB); 1598 toSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum)); 1599 return false; 1600 } 1601 } 1602 1603 // Decide whether PRE is profitable for this load. 1604 unsigned NumUnavailablePreds = PredLoads.size(); 1605 assert(NumUnavailablePreds != 0 && 1606 "Fully available value should be eliminated above!"); 1607 if (!EnableFullLoadPRE) { 1608 // If this load is unavailable in multiple predecessors, reject it. 1609 // FIXME: If we could restructure the CFG, we could make a common pred with 1610 // all the preds that don't have an available LI and insert a new load into 1611 // that one block. 1612 if (NumUnavailablePreds != 1) 1613 return false; 1614 } 1615 1616 // Check if the load can safely be moved to all the unavailable predecessors. 1617 bool CanDoPRE = true; 1618 SmallVector<Instruction*, 8> NewInsts; 1619 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1620 E = PredLoads.end(); I != E; ++I) { 1621 BasicBlock *UnavailablePred = I->first; 1622 1623 // Do PHI translation to get its value in the predecessor if necessary. The 1624 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1625 1626 // If all preds have a single successor, then we know it is safe to insert 1627 // the load on the pred (?!?), so we can insert code to materialize the 1628 // pointer if it is not available. 1629 PHITransAddr Address(LI->getOperand(0), TD); 1630 Value *LoadPtr = 0; 1631 if (allSingleSucc) { 1632 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1633 *DT, NewInsts); 1634 } else { 1635 Address.PHITranslateValue(LoadBB, UnavailablePred); 1636 LoadPtr = Address.getAddr(); 1637 1638 // Make sure the value is live in the predecessor. 1639 if (Instruction *Inst = dyn_cast_or_null<Instruction>(LoadPtr)) 1640 if (!DT->dominates(Inst->getParent(), UnavailablePred)) 1641 LoadPtr = 0; 1642 } 1643 1644 // If we couldn't find or insert a computation of this phi translated value, 1645 // we fail PRE. 1646 if (LoadPtr == 0) { 1647 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1648 << *LI->getOperand(0) << "\n"); 1649 CanDoPRE = false; 1650 break; 1651 } 1652 1653 // Make sure it is valid to move this load here. We have to watch out for: 1654 // @1 = getelementptr (i8* p, ... 1655 // test p and branch if == 0 1656 // load @1 1657 // It is valid to have the getelementptr before the test, even if p can be 0, 1658 // as getelementptr only does address arithmetic. 1659 // If we are not pushing the value through any multiple-successor blocks 1660 // we do not have this case. Otherwise, check that the load is safe to 1661 // put anywhere; this can be improved, but should be conservatively safe. 1662 if (!allSingleSucc && 1663 // FIXME: REEVALUTE THIS. 1664 !isSafeToLoadUnconditionally(LoadPtr, 1665 UnavailablePred->getTerminator(), 1666 LI->getAlignment(), TD)) { 1667 CanDoPRE = false; 1668 break; 1669 } 1670 1671 I->second = LoadPtr; 1672 } 1673 1674 if (!CanDoPRE) { 1675 while (!NewInsts.empty()) 1676 NewInsts.pop_back_val()->eraseFromParent(); 1677 return false; 1678 } 1679 1680 // Okay, we can eliminate this load by inserting a reload in the predecessor 1681 // and using PHI construction to get the value in the other predecessors, do 1682 // it. 1683 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1684 DEBUG(if (!NewInsts.empty()) 1685 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1686 << *NewInsts.back() << '\n'); 1687 1688 // Assign value numbers to the new instructions. 1689 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { 1690 // FIXME: We really _ought_ to insert these value numbers into their 1691 // parent's availability map. However, in doing so, we risk getting into 1692 // ordering issues. If a block hasn't been processed yet, we would be 1693 // marking a value as AVAIL-IN, which isn't what we intend. 1694 VN.lookup_or_add(NewInsts[i]); 1695 } 1696 1697 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1698 E = PredLoads.end(); I != E; ++I) { 1699 BasicBlock *UnavailablePred = I->first; 1700 Value *LoadPtr = I->second; 1701 1702 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1703 LI->getAlignment(), 1704 UnavailablePred->getTerminator()); 1705 1706 // Add the newly created load. 1707 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1708 NewLoad)); 1709 } 1710 1711 // Perform PHI construction. 1712 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1713 VN.getAliasAnalysis()); 1714 LI->replaceAllUsesWith(V); 1715 if (isa<PHINode>(V)) 1716 V->takeName(LI); 1717 if (V->getType()->isPointerTy()) 1718 MD->invalidateCachedPointerInfo(V); 1719 toErase.push_back(LI); 1720 NumPRELoad++; 1721 return true; 1722} 1723 1724/// processLoad - Attempt to eliminate a load, first by eliminating it 1725/// locally, and then attempting non-local elimination if that fails. 1726bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1727 if (!MD) 1728 return false; 1729 1730 if (L->isVolatile()) 1731 return false; 1732 1733 // ... to a pointer that has been loaded from before... 1734 MemDepResult Dep = MD->getDependency(L); 1735 1736 // If the value isn't available, don't do anything! 1737 if (Dep.isClobber()) { 1738 // Check to see if we have something like this: 1739 // store i32 123, i32* %P 1740 // %A = bitcast i32* %P to i8* 1741 // %B = gep i8* %A, i32 1 1742 // %C = load i8* %B 1743 // 1744 // We could do that by recognizing if the clobber instructions are obviously 1745 // a common base + constant offset, and if the previous store (or memset) 1746 // completely covers this load. This sort of thing can happen in bitfield 1747 // access code. 1748 Value *AvailVal = 0; 1749 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1750 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1751 int Offset = AnalyzeLoadFromClobberingStore(L->getType(), 1752 L->getPointerOperand(), 1753 DepSI, *TD); 1754 if (Offset != -1) 1755 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset, 1756 L->getType(), L, *TD); 1757 } 1758 1759 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1760 // a value on from it. 1761 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1762 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1763 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), 1764 L->getPointerOperand(), 1765 DepMI, *TD); 1766 if (Offset != -1) 1767 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD); 1768 } 1769 } 1770 1771 if (AvailVal) { 1772 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1773 << *AvailVal << '\n' << *L << "\n\n\n"); 1774 1775 // Replace the load! 1776 L->replaceAllUsesWith(AvailVal); 1777 if (AvailVal->getType()->isPointerTy()) 1778 MD->invalidateCachedPointerInfo(AvailVal); 1779 toErase.push_back(L); 1780 NumGVNLoad++; 1781 return true; 1782 } 1783 1784 DEBUG( 1785 // fast print dep, using operator<< on instruction would be too slow 1786 dbgs() << "GVN: load "; 1787 WriteAsOperand(dbgs(), L); 1788 Instruction *I = Dep.getInst(); 1789 dbgs() << " is clobbered by " << *I << '\n'; 1790 ); 1791 return false; 1792 } 1793 1794 // If it is defined in another block, try harder. 1795 if (Dep.isNonLocal()) 1796 return processNonLocalLoad(L, toErase); 1797 1798 Instruction *DepInst = Dep.getInst(); 1799 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1800 Value *StoredVal = DepSI->getOperand(0); 1801 1802 // The store and load are to a must-aliased pointer, but they may not 1803 // actually have the same type. See if we know how to reuse the stored 1804 // value (depending on its type). 1805 const TargetData *TD = 0; 1806 if (StoredVal->getType() != L->getType()) { 1807 if ((TD = getAnalysisIfAvailable<TargetData>())) { 1808 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1809 L, *TD); 1810 if (StoredVal == 0) 1811 return false; 1812 1813 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1814 << '\n' << *L << "\n\n\n"); 1815 } 1816 else 1817 return false; 1818 } 1819 1820 // Remove it! 1821 L->replaceAllUsesWith(StoredVal); 1822 if (StoredVal->getType()->isPointerTy()) 1823 MD->invalidateCachedPointerInfo(StoredVal); 1824 toErase.push_back(L); 1825 NumGVNLoad++; 1826 return true; 1827 } 1828 1829 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1830 Value *AvailableVal = DepLI; 1831 1832 // The loads are of a must-aliased pointer, but they may not actually have 1833 // the same type. See if we know how to reuse the previously loaded value 1834 // (depending on its type). 1835 const TargetData *TD = 0; 1836 if (DepLI->getType() != L->getType()) { 1837 if ((TD = getAnalysisIfAvailable<TargetData>())) { 1838 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1839 if (AvailableVal == 0) 1840 return false; 1841 1842 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1843 << "\n" << *L << "\n\n\n"); 1844 } 1845 else 1846 return false; 1847 } 1848 1849 // Remove it! 1850 L->replaceAllUsesWith(AvailableVal); 1851 if (DepLI->getType()->isPointerTy()) 1852 MD->invalidateCachedPointerInfo(DepLI); 1853 toErase.push_back(L); 1854 NumGVNLoad++; 1855 return true; 1856 } 1857 1858 // If this load really doesn't depend on anything, then we must be loading an 1859 // undef value. This can happen when loading for a fresh allocation with no 1860 // intervening stores, for example. 1861 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { 1862 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1863 toErase.push_back(L); 1864 NumGVNLoad++; 1865 return true; 1866 } 1867 1868 // If this load occurs either right after a lifetime begin, 1869 // then the loaded value is undefined. 1870 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) { 1871 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1872 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1873 toErase.push_back(L); 1874 NumGVNLoad++; 1875 return true; 1876 } 1877 } 1878 1879 return false; 1880} 1881 1882Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1883 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1884 if (I == localAvail.end()) 1885 return 0; 1886 1887 ValueNumberScope *Locals = I->second; 1888 while (Locals) { 1889 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1890 if (I != Locals->table.end()) 1891 return I->second; 1892 Locals = Locals->parent; 1893 } 1894 1895 return 0; 1896} 1897 1898 1899/// processInstruction - When calculating availability, handle an instruction 1900/// by inserting it into the appropriate sets 1901bool GVN::processInstruction(Instruction *I, 1902 SmallVectorImpl<Instruction*> &toErase) { 1903 // Ignore dbg info intrinsics. 1904 if (isa<DbgInfoIntrinsic>(I)) 1905 return false; 1906 1907 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1908 bool Changed = processLoad(LI, toErase); 1909 1910 if (!Changed) { 1911 unsigned Num = VN.lookup_or_add(LI); 1912 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1913 } 1914 1915 return Changed; 1916 } 1917 1918 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1919 unsigned Num = VN.lookup_or_add(I); 1920 1921 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1922 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1923 1924 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1925 return false; 1926 1927 Value *BranchCond = BI->getCondition(); 1928 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1929 1930 BasicBlock *TrueSucc = BI->getSuccessor(0); 1931 BasicBlock *FalseSucc = BI->getSuccessor(1); 1932 1933 if (TrueSucc->getSinglePredecessor()) 1934 localAvail[TrueSucc]->table[CondVN] = 1935 ConstantInt::getTrue(TrueSucc->getContext()); 1936 if (FalseSucc->getSinglePredecessor()) 1937 localAvail[FalseSucc]->table[CondVN] = 1938 ConstantInt::getFalse(TrueSucc->getContext()); 1939 1940 return false; 1941 1942 // Allocations are always uniquely numbered, so we can save time and memory 1943 // by fast failing them. 1944 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) { 1945 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1946 return false; 1947 } 1948 1949 // Collapse PHI nodes 1950 if (PHINode* p = dyn_cast<PHINode>(I)) { 1951 Value *constVal = CollapsePhi(p); 1952 1953 if (constVal) { 1954 p->replaceAllUsesWith(constVal); 1955 if (MD && constVal->getType()->isPointerTy()) 1956 MD->invalidateCachedPointerInfo(constVal); 1957 VN.erase(p); 1958 1959 toErase.push_back(p); 1960 } else { 1961 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1962 } 1963 1964 // If the number we were assigned was a brand new VN, then we don't 1965 // need to do a lookup to see if the number already exists 1966 // somewhere in the domtree: it can't! 1967 } else if (Num == NextNum) { 1968 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1969 1970 // Perform fast-path value-number based elimination of values inherited from 1971 // dominators. 1972 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1973 // Remove it! 1974 VN.erase(I); 1975 I->replaceAllUsesWith(repl); 1976 if (MD && repl->getType()->isPointerTy()) 1977 MD->invalidateCachedPointerInfo(repl); 1978 toErase.push_back(I); 1979 return true; 1980 1981 } else { 1982 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1983 } 1984 1985 return false; 1986} 1987 1988/// runOnFunction - This is the main transformation entry point for a function. 1989bool GVN::runOnFunction(Function& F) { 1990 if (!NoLoads) 1991 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1992 DT = &getAnalysis<DominatorTree>(); 1993 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1994 VN.setMemDep(MD); 1995 VN.setDomTree(DT); 1996 1997 bool Changed = false; 1998 bool ShouldContinue = true; 1999 2000 // Merge unconditional branches, allowing PRE to catch more 2001 // optimization opportunities. 2002 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 2003 BasicBlock *BB = FI; 2004 ++FI; 2005 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 2006 if (removedBlock) NumGVNBlocks++; 2007 2008 Changed |= removedBlock; 2009 } 2010 2011 unsigned Iteration = 0; 2012 2013 while (ShouldContinue) { 2014 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 2015 ShouldContinue = iterateOnFunction(F); 2016 if (splitCriticalEdges()) 2017 ShouldContinue = true; 2018 Changed |= ShouldContinue; 2019 ++Iteration; 2020 } 2021 2022 if (EnablePRE) { 2023 bool PREChanged = true; 2024 while (PREChanged) { 2025 PREChanged = performPRE(F); 2026 Changed |= PREChanged; 2027 } 2028 } 2029 // FIXME: Should perform GVN again after PRE does something. PRE can move 2030 // computations into blocks where they become fully redundant. Note that 2031 // we can't do this until PRE's critical edge splitting updates memdep. 2032 // Actually, when this happens, we should just fully integrate PRE into GVN. 2033 2034 cleanupGlobalSets(); 2035 2036 return Changed; 2037} 2038 2039 2040bool GVN::processBlock(BasicBlock *BB) { 2041 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 2042 // incrementing BI before processing an instruction). 2043 SmallVector<Instruction*, 8> toErase; 2044 bool ChangedFunction = false; 2045 2046 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 2047 BI != BE;) { 2048 ChangedFunction |= processInstruction(BI, toErase); 2049 if (toErase.empty()) { 2050 ++BI; 2051 continue; 2052 } 2053 2054 // If we need some instructions deleted, do it now. 2055 NumGVNInstr += toErase.size(); 2056 2057 // Avoid iterator invalidation. 2058 bool AtStart = BI == BB->begin(); 2059 if (!AtStart) 2060 --BI; 2061 2062 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 2063 E = toErase.end(); I != E; ++I) { 2064 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 2065 if (MD) MD->removeInstruction(*I); 2066 (*I)->eraseFromParent(); 2067 DEBUG(verifyRemoved(*I)); 2068 } 2069 toErase.clear(); 2070 2071 if (AtStart) 2072 BI = BB->begin(); 2073 else 2074 ++BI; 2075 } 2076 2077 return ChangedFunction; 2078} 2079 2080/// performPRE - Perform a purely local form of PRE that looks for diamond 2081/// control flow patterns and attempts to perform simple PRE at the join point. 2082bool GVN::performPRE(Function &F) { 2083 bool Changed = false; 2084 DenseMap<BasicBlock*, Value*> predMap; 2085 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 2086 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 2087 BasicBlock *CurrentBlock = *DI; 2088 2089 // Nothing to PRE in the entry block. 2090 if (CurrentBlock == &F.getEntryBlock()) continue; 2091 2092 for (BasicBlock::iterator BI = CurrentBlock->begin(), 2093 BE = CurrentBlock->end(); BI != BE; ) { 2094 Instruction *CurInst = BI++; 2095 2096 if (isa<AllocaInst>(CurInst) || 2097 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 2098 CurInst->getType()->isVoidTy() || 2099 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2100 isa<DbgInfoIntrinsic>(CurInst)) 2101 continue; 2102 2103 uint32_t ValNo = VN.lookup(CurInst); 2104 2105 // Look for the predecessors for PRE opportunities. We're 2106 // only trying to solve the basic diamond case, where 2107 // a value is computed in the successor and one predecessor, 2108 // but not the other. We also explicitly disallow cases 2109 // where the successor is its own predecessor, because they're 2110 // more complicated to get right. 2111 unsigned NumWith = 0; 2112 unsigned NumWithout = 0; 2113 BasicBlock *PREPred = 0; 2114 predMap.clear(); 2115 2116 for (pred_iterator PI = pred_begin(CurrentBlock), 2117 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2118 // We're not interested in PRE where the block is its 2119 // own predecessor, or in blocks with predecessors 2120 // that are not reachable. 2121 if (*PI == CurrentBlock) { 2122 NumWithout = 2; 2123 break; 2124 } else if (!localAvail.count(*PI)) { 2125 NumWithout = 2; 2126 break; 2127 } 2128 2129 DenseMap<uint32_t, Value*>::iterator predV = 2130 localAvail[*PI]->table.find(ValNo); 2131 if (predV == localAvail[*PI]->table.end()) { 2132 PREPred = *PI; 2133 NumWithout++; 2134 } else if (predV->second == CurInst) { 2135 NumWithout = 2; 2136 } else { 2137 predMap[*PI] = predV->second; 2138 NumWith++; 2139 } 2140 } 2141 2142 // Don't do PRE when it might increase code size, i.e. when 2143 // we would need to insert instructions in more than one pred. 2144 if (NumWithout != 1 || NumWith == 0) 2145 continue; 2146 2147 // Don't do PRE across indirect branch. 2148 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2149 continue; 2150 2151 // We can't do PRE safely on a critical edge, so instead we schedule 2152 // the edge to be split and perform the PRE the next time we iterate 2153 // on the function. 2154 unsigned SuccNum = SuccessorNumber(PREPred, CurrentBlock); 2155 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2156 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2157 continue; 2158 } 2159 2160 // Instantiate the expression in the predecessor that lacked it. 2161 // Because we are going top-down through the block, all value numbers 2162 // will be available in the predecessor by the time we need them. Any 2163 // that weren't originally present will have been instantiated earlier 2164 // in this loop. 2165 Instruction *PREInstr = CurInst->clone(); 2166 bool success = true; 2167 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2168 Value *Op = PREInstr->getOperand(i); 2169 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2170 continue; 2171 2172 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2173 PREInstr->setOperand(i, V); 2174 } else { 2175 success = false; 2176 break; 2177 } 2178 } 2179 2180 // Fail out if we encounter an operand that is not available in 2181 // the PRE predecessor. This is typically because of loads which 2182 // are not value numbered precisely. 2183 if (!success) { 2184 delete PREInstr; 2185 DEBUG(verifyRemoved(PREInstr)); 2186 continue; 2187 } 2188 2189 PREInstr->insertBefore(PREPred->getTerminator()); 2190 PREInstr->setName(CurInst->getName() + ".pre"); 2191 predMap[PREPred] = PREInstr; 2192 VN.add(PREInstr, ValNo); 2193 NumGVNPRE++; 2194 2195 // Update the availability map to include the new instruction. 2196 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 2197 2198 // Create a PHI to make the value available in this block. 2199 PHINode* Phi = PHINode::Create(CurInst->getType(), 2200 CurInst->getName() + ".pre-phi", 2201 CurrentBlock->begin()); 2202 for (pred_iterator PI = pred_begin(CurrentBlock), 2203 PE = pred_end(CurrentBlock); PI != PE; ++PI) 2204 Phi->addIncoming(predMap[*PI], *PI); 2205 2206 VN.add(Phi, ValNo); 2207 localAvail[CurrentBlock]->table[ValNo] = Phi; 2208 2209 CurInst->replaceAllUsesWith(Phi); 2210 if (MD && Phi->getType()->isPointerTy()) 2211 MD->invalidateCachedPointerInfo(Phi); 2212 VN.erase(CurInst); 2213 2214 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2215 if (MD) MD->removeInstruction(CurInst); 2216 CurInst->eraseFromParent(); 2217 DEBUG(verifyRemoved(CurInst)); 2218 Changed = true; 2219 } 2220 } 2221 2222 if (splitCriticalEdges()) 2223 Changed = true; 2224 2225 return Changed; 2226} 2227 2228/// splitCriticalEdges - Split critical edges found during the previous 2229/// iteration that may enable further optimization. 2230bool GVN::splitCriticalEdges() { 2231 if (toSplit.empty()) 2232 return false; 2233 do { 2234 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2235 SplitCriticalEdge(Edge.first, Edge.second, this); 2236 } while (!toSplit.empty()); 2237 MD->invalidateCachedPredecessors(); 2238 return true; 2239} 2240 2241/// iterateOnFunction - Executes one iteration of GVN 2242bool GVN::iterateOnFunction(Function &F) { 2243 cleanupGlobalSets(); 2244 2245 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2246 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 2247 if (DI->getIDom()) 2248 localAvail[DI->getBlock()] = 2249 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 2250 else 2251 localAvail[DI->getBlock()] = new ValueNumberScope(0); 2252 } 2253 2254 // Top-down walk of the dominator tree 2255 bool Changed = false; 2256#if 0 2257 // Needed for value numbering with phi construction to work. 2258 ReversePostOrderTraversal<Function*> RPOT(&F); 2259 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2260 RE = RPOT.end(); RI != RE; ++RI) 2261 Changed |= processBlock(*RI); 2262#else 2263 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2264 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2265 Changed |= processBlock(DI->getBlock()); 2266#endif 2267 2268 return Changed; 2269} 2270 2271void GVN::cleanupGlobalSets() { 2272 VN.clear(); 2273 2274 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2275 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 2276 delete I->second; 2277 localAvail.clear(); 2278} 2279 2280/// verifyRemoved - Verify that the specified instruction does not occur in our 2281/// internal data structures. 2282void GVN::verifyRemoved(const Instruction *Inst) const { 2283 VN.verifyRemoved(Inst); 2284 2285 // Walk through the value number scope to make sure the instruction isn't 2286 // ferreted away in it. 2287 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator 2288 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 2289 const ValueNumberScope *VNS = I->second; 2290 2291 while (VNS) { 2292 for (DenseMap<uint32_t, Value*>::const_iterator 2293 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 2294 assert(II->second != Inst && "Inst still in value numbering scope!"); 2295 } 2296 2297 VNS = VNS->parent; 2298 } 2299 } 2300} 2301