GVN.cpp revision 88c3df7afb8e067daab12dbbbc9ce898a52e9624
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/InstructionSimplify.h" 39#include "llvm/Analysis/Loads.h" 40#include "llvm/Analysis/MemoryBuiltins.h" 41#include "llvm/Analysis/MemoryDependenceAnalysis.h" 42#include "llvm/Analysis/PHITransAddr.h" 43#include "llvm/Support/CFG.h" 44#include "llvm/Support/CommandLine.h" 45#include "llvm/Support/Debug.h" 46#include "llvm/Support/ErrorHandling.h" 47#include "llvm/Support/GetElementPtrTypeIterator.h" 48#include "llvm/Support/IRBuilder.h" 49#include "llvm/Support/raw_ostream.h" 50#include "llvm/Target/TargetData.h" 51#include "llvm/Transforms/Utils/BasicBlockUtils.h" 52#include "llvm/Transforms/Utils/Local.h" 53#include "llvm/Transforms/Utils/SSAUpdater.h" 54using namespace llvm; 55 56STATISTIC(NumGVNInstr, "Number of instructions deleted"); 57STATISTIC(NumGVNLoad, "Number of loads deleted"); 58STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 59STATISTIC(NumGVNBlocks, "Number of blocks merged"); 60STATISTIC(NumPRELoad, "Number of loads PRE'd"); 61 62static cl::opt<bool> EnablePRE("enable-pre", 63 cl::init(true), cl::Hidden); 64static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 65 66//===----------------------------------------------------------------------===// 67// ValueTable Class 68//===----------------------------------------------------------------------===// 69 70/// This class holds the mapping between values and value numbers. It is used 71/// as an efficient mechanism to determine the expression-wise equivalence of 72/// two values. 73namespace { 74 struct Expression { 75 enum ExpressionOpcode { 76 ADD = Instruction::Add, 77 FADD = Instruction::FAdd, 78 SUB = Instruction::Sub, 79 FSUB = Instruction::FSub, 80 MUL = Instruction::Mul, 81 FMUL = Instruction::FMul, 82 UDIV = Instruction::UDiv, 83 SDIV = Instruction::SDiv, 84 FDIV = Instruction::FDiv, 85 UREM = Instruction::URem, 86 SREM = Instruction::SRem, 87 FREM = Instruction::FRem, 88 SHL = Instruction::Shl, 89 LSHR = Instruction::LShr, 90 ASHR = Instruction::AShr, 91 AND = Instruction::And, 92 OR = Instruction::Or, 93 XOR = Instruction::Xor, 94 TRUNC = Instruction::Trunc, 95 ZEXT = Instruction::ZExt, 96 SEXT = Instruction::SExt, 97 FPTOUI = Instruction::FPToUI, 98 FPTOSI = Instruction::FPToSI, 99 UITOFP = Instruction::UIToFP, 100 SITOFP = Instruction::SIToFP, 101 FPTRUNC = Instruction::FPTrunc, 102 FPEXT = Instruction::FPExt, 103 PTRTOINT = Instruction::PtrToInt, 104 INTTOPTR = Instruction::IntToPtr, 105 BITCAST = Instruction::BitCast, 106 ICMPEQ, ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 107 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 108 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 109 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 110 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 111 SHUFFLE, SELECT, GEP, CALL, CONSTANT, 112 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE }; 113 114 ExpressionOpcode opcode; 115 const Type* type; 116 SmallVector<uint32_t, 4> varargs; 117 Value *function; 118 119 Expression() { } 120 Expression(ExpressionOpcode o) : opcode(o) { } 121 122 bool operator==(const Expression &other) const { 123 if (opcode != other.opcode) 124 return false; 125 else if (opcode == EMPTY || opcode == TOMBSTONE) 126 return true; 127 else if (type != other.type) 128 return false; 129 else if (function != other.function) 130 return false; 131 else { 132 if (varargs.size() != other.varargs.size()) 133 return false; 134 135 for (size_t i = 0; i < varargs.size(); ++i) 136 if (varargs[i] != other.varargs[i]) 137 return false; 138 139 return true; 140 } 141 } 142 143 /*bool operator!=(const Expression &other) const { 144 return !(*this == other); 145 }*/ 146 }; 147 148 class ValueTable { 149 private: 150 DenseMap<Value*, uint32_t> valueNumbering; 151 DenseMap<Expression, uint32_t> expressionNumbering; 152 AliasAnalysis* AA; 153 MemoryDependenceAnalysis* MD; 154 DominatorTree* DT; 155 156 uint32_t nextValueNumber; 157 158 Expression::ExpressionOpcode getOpcode(CmpInst* C); 159 Expression create_expression(BinaryOperator* BO); 160 Expression create_expression(CmpInst* C); 161 Expression create_expression(ShuffleVectorInst* V); 162 Expression create_expression(ExtractElementInst* C); 163 Expression create_expression(InsertElementInst* V); 164 Expression create_expression(SelectInst* V); 165 Expression create_expression(CastInst* C); 166 Expression create_expression(GetElementPtrInst* G); 167 Expression create_expression(CallInst* 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 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 180 AliasAnalysis *getAliasAnalysis() const { return AA; } 181 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 182 void setDomTree(DominatorTree* D) { DT = D; } 183 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 184 void verifyRemoved(const Value *) const; 185 }; 186} 187 188namespace llvm { 189template <> struct DenseMapInfo<Expression> { 190 static inline Expression getEmptyKey() { 191 return Expression(Expression::EMPTY); 192 } 193 194 static inline Expression getTombstoneKey() { 195 return Expression(Expression::TOMBSTONE); 196 } 197 198 static unsigned getHashValue(const Expression e) { 199 unsigned hash = e.opcode; 200 201 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 202 (unsigned)((uintptr_t)e.type >> 9)); 203 204 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 205 E = e.varargs.end(); I != E; ++I) 206 hash = *I + hash * 37; 207 208 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 209 (unsigned)((uintptr_t)e.function >> 9)) + 210 hash * 37; 211 212 return hash; 213 } 214 static bool isEqual(const Expression &LHS, const Expression &RHS) { 215 return LHS == RHS; 216 } 217}; 218 219template <> 220struct isPodLike<Expression> { static const bool value = true; }; 221 222} 223 224//===----------------------------------------------------------------------===// 225// ValueTable Internal Functions 226//===----------------------------------------------------------------------===// 227 228Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 229 if (isa<ICmpInst>(C)) { 230 switch (C->getPredicate()) { 231 default: // THIS SHOULD NEVER HAPPEN 232 llvm_unreachable("Comparison with unknown predicate?"); 233 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 234 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 235 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 236 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 237 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 238 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 239 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 240 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 241 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 242 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 243 } 244 } else { 245 switch (C->getPredicate()) { 246 default: // THIS SHOULD NEVER HAPPEN 247 llvm_unreachable("Comparison with unknown predicate?"); 248 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 249 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 250 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 251 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 252 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 253 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 254 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 255 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 256 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 257 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 258 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 259 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 260 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 261 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 262 } 263 } 264} 265 266Expression ValueTable::create_expression(CallInst* C) { 267 Expression e; 268 269 e.type = C->getType(); 270 e.function = C->getCalledFunction(); 271 e.opcode = Expression::CALL; 272 273 CallSite CS(C); 274 for (CallInst::op_iterator I = CS.arg_begin(), E = CS.arg_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->getNumArgOperands() != C->getNumArgOperands()) { 451 valueNumbering[C] = nextValueNumber; 452 return nextValueNumber++; 453 } 454 455 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 456 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 457 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(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->getNumArgOperands() != C->getNumArgOperands()) { 508 valueNumbering[C] = nextValueNumber; 509 return nextValueNumber++; 510 } 511 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 512 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 513 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(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 initializeGVNPass(*PassRegistry::getPassRegistry()); 668 } 669 670 private: 671 bool NoLoads; 672 MemoryDependenceAnalysis *MD; 673 DominatorTree *DT; 674 const TargetData* TD; 675 676 ValueTable VN; 677 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 678 679 // List of critical edges to be split between iterations. 680 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 681 682 // This transformation requires dominator postdominator info 683 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 684 AU.addRequired<DominatorTree>(); 685 if (!NoLoads) 686 AU.addRequired<MemoryDependenceAnalysis>(); 687 AU.addRequired<AliasAnalysis>(); 688 689 AU.addPreserved<DominatorTree>(); 690 AU.addPreserved<AliasAnalysis>(); 691 } 692 693 // Helper fuctions 694 // FIXME: eliminate or document these better 695 bool processLoad(LoadInst* L, 696 SmallVectorImpl<Instruction*> &toErase); 697 bool processInstruction(Instruction *I, 698 SmallVectorImpl<Instruction*> &toErase); 699 bool processNonLocalLoad(LoadInst* L, 700 SmallVectorImpl<Instruction*> &toErase); 701 bool processBlock(BasicBlock *BB); 702 void dump(DenseMap<uint32_t, Value*>& d); 703 bool iterateOnFunction(Function &F); 704 Value *CollapsePhi(PHINode* p); 705 bool performPRE(Function& F); 706 Value *lookupNumber(BasicBlock *BB, uint32_t num); 707 void cleanupGlobalSets(); 708 void verifyRemoved(const Instruction *I) const; 709 bool splitCriticalEdges(); 710 }; 711 712 char GVN::ID = 0; 713} 714 715// createGVNPass - The public interface to this file... 716FunctionPass *llvm::createGVNPass(bool NoLoads) { 717 return new GVN(NoLoads); 718} 719 720INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) 721INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) 722INITIALIZE_PASS_DEPENDENCY(DominatorTree) 723INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 724INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) 725 726void GVN::dump(DenseMap<uint32_t, Value*>& d) { 727 errs() << "{\n"; 728 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 729 E = d.end(); I != E; ++I) { 730 errs() << I->first << "\n"; 731 I->second->dump(); 732 } 733 errs() << "}\n"; 734} 735 736static bool isSafeReplacement(PHINode* p, Instruction *inst) { 737 if (!isa<PHINode>(inst)) 738 return true; 739 740 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 741 UI != E; ++UI) 742 if (PHINode* use_phi = dyn_cast<PHINode>(*UI)) 743 if (use_phi->getParent() == inst->getParent()) 744 return false; 745 746 return true; 747} 748 749Value *GVN::CollapsePhi(PHINode *PN) { 750 Value *ConstVal = PN->hasConstantValue(DT); 751 if (!ConstVal) return 0; 752 753 Instruction *Inst = dyn_cast<Instruction>(ConstVal); 754 if (!Inst) 755 return ConstVal; 756 757 if (DT->dominates(Inst, PN)) 758 if (isSafeReplacement(PN, Inst)) 759 return Inst; 760 return 0; 761} 762 763/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 764/// we're analyzing is fully available in the specified block. As we go, keep 765/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 766/// map is actually a tri-state map with the following values: 767/// 0) we know the block *is not* fully available. 768/// 1) we know the block *is* fully available. 769/// 2) we do not know whether the block is fully available or not, but we are 770/// currently speculating that it will be. 771/// 3) we are speculating for this block and have used that to speculate for 772/// other blocks. 773static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 774 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 775 // Optimistically assume that the block is fully available and check to see 776 // if we already know about this block in one lookup. 777 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 778 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 779 780 // If the entry already existed for this block, return the precomputed value. 781 if (!IV.second) { 782 // If this is a speculative "available" value, mark it as being used for 783 // speculation of other blocks. 784 if (IV.first->second == 2) 785 IV.first->second = 3; 786 return IV.first->second != 0; 787 } 788 789 // Otherwise, see if it is fully available in all predecessors. 790 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 791 792 // If this block has no predecessors, it isn't live-in here. 793 if (PI == PE) 794 goto SpeculationFailure; 795 796 for (; PI != PE; ++PI) 797 // If the value isn't fully available in one of our predecessors, then it 798 // isn't fully available in this block either. Undo our previous 799 // optimistic assumption and bail out. 800 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 801 goto SpeculationFailure; 802 803 return true; 804 805// SpeculationFailure - If we get here, we found out that this is not, after 806// all, a fully-available block. We have a problem if we speculated on this and 807// used the speculation to mark other blocks as available. 808SpeculationFailure: 809 char &BBVal = FullyAvailableBlocks[BB]; 810 811 // If we didn't speculate on this, just return with it set to false. 812 if (BBVal == 2) { 813 BBVal = 0; 814 return false; 815 } 816 817 // If we did speculate on this value, we could have blocks set to 1 that are 818 // incorrect. Walk the (transitive) successors of this block and mark them as 819 // 0 if set to one. 820 SmallVector<BasicBlock*, 32> BBWorklist; 821 BBWorklist.push_back(BB); 822 823 do { 824 BasicBlock *Entry = BBWorklist.pop_back_val(); 825 // Note that this sets blocks to 0 (unavailable) if they happen to not 826 // already be in FullyAvailableBlocks. This is safe. 827 char &EntryVal = FullyAvailableBlocks[Entry]; 828 if (EntryVal == 0) continue; // Already unavailable. 829 830 // Mark as unavailable. 831 EntryVal = 0; 832 833 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 834 BBWorklist.push_back(*I); 835 } while (!BBWorklist.empty()); 836 837 return false; 838} 839 840 841/// CanCoerceMustAliasedValueToLoad - Return true if 842/// CoerceAvailableValueToLoadType will succeed. 843static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 844 const Type *LoadTy, 845 const TargetData &TD) { 846 // If the loaded or stored value is an first class array or struct, don't try 847 // to transform them. We need to be able to bitcast to integer. 848 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 849 StoredVal->getType()->isStructTy() || 850 StoredVal->getType()->isArrayTy()) 851 return false; 852 853 // The store has to be at least as big as the load. 854 if (TD.getTypeSizeInBits(StoredVal->getType()) < 855 TD.getTypeSizeInBits(LoadTy)) 856 return false; 857 858 return true; 859} 860 861 862/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 863/// then a load from a must-aliased pointer of a different type, try to coerce 864/// the stored value. LoadedTy is the type of the load we want to replace and 865/// InsertPt is the place to insert new instructions. 866/// 867/// If we can't do it, return null. 868static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 869 const Type *LoadedTy, 870 Instruction *InsertPt, 871 const TargetData &TD) { 872 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 873 return 0; 874 875 const Type *StoredValTy = StoredVal->getType(); 876 877 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy); 878 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 879 880 // If the store and reload are the same size, we can always reuse it. 881 if (StoreSize == LoadSize) { 882 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) { 883 // Pointer to Pointer -> use bitcast. 884 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 885 } 886 887 // Convert source pointers to integers, which can be bitcast. 888 if (StoredValTy->isPointerTy()) { 889 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 890 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 891 } 892 893 const Type *TypeToCastTo = LoadedTy; 894 if (TypeToCastTo->isPointerTy()) 895 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 896 897 if (StoredValTy != TypeToCastTo) 898 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 899 900 // Cast to pointer if the load needs a pointer type. 901 if (LoadedTy->isPointerTy()) 902 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 903 904 return StoredVal; 905 } 906 907 // If the loaded value is smaller than the available value, then we can 908 // extract out a piece from it. If the available value is too small, then we 909 // can't do anything. 910 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 911 912 // Convert source pointers to integers, which can be manipulated. 913 if (StoredValTy->isPointerTy()) { 914 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 915 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 916 } 917 918 // Convert vectors and fp to integer, which can be manipulated. 919 if (!StoredValTy->isIntegerTy()) { 920 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 921 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 922 } 923 924 // If this is a big-endian system, we need to shift the value down to the low 925 // bits so that a truncate will work. 926 if (TD.isBigEndian()) { 927 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 928 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 929 } 930 931 // Truncate the integer to the right size now. 932 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 933 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 934 935 if (LoadedTy == NewIntTy) 936 return StoredVal; 937 938 // If the result is a pointer, inttoptr. 939 if (LoadedTy->isPointerTy()) 940 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 941 942 // Otherwise, bitcast. 943 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 944} 945 946/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 947/// be expressed as a base pointer plus a constant offset. Return the base and 948/// offset to the caller. 949static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 950 const TargetData &TD) { 951 Operator *PtrOp = dyn_cast<Operator>(Ptr); 952 if (PtrOp == 0) return Ptr; 953 954 // Just look through bitcasts. 955 if (PtrOp->getOpcode() == Instruction::BitCast) 956 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 957 958 // If this is a GEP with constant indices, we can look through it. 959 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 960 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 961 962 gep_type_iterator GTI = gep_type_begin(GEP); 963 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 964 ++I, ++GTI) { 965 ConstantInt *OpC = cast<ConstantInt>(*I); 966 if (OpC->isZero()) continue; 967 968 // Handle a struct and array indices which add their offset to the pointer. 969 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 970 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 971 } else { 972 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 973 Offset += OpC->getSExtValue()*Size; 974 } 975 } 976 977 // Re-sign extend from the pointer size if needed to get overflow edge cases 978 // right. 979 unsigned PtrSize = TD.getPointerSizeInBits(); 980 if (PtrSize < 64) 981 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 982 983 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 984} 985 986 987/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 988/// memdep query of a load that ends up being a clobbering memory write (store, 989/// memset, memcpy, memmove). This means that the write *may* provide bits used 990/// by the load but we can't be sure because the pointers don't mustalias. 991/// 992/// Check this case to see if there is anything more we can do before we give 993/// up. This returns -1 if we have to give up, or a byte number in the stored 994/// value of the piece that feeds the load. 995static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr, 996 Value *WritePtr, 997 uint64_t WriteSizeInBits, 998 const TargetData &TD) { 999 // If the loaded or stored value is an first class array or struct, don't try 1000 // to transform them. We need to be able to bitcast to integer. 1001 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 1002 return -1; 1003 1004 int64_t StoreOffset = 0, LoadOffset = 0; 1005 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD); 1006 Value *LoadBase = 1007 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD); 1008 if (StoreBase != LoadBase) 1009 return -1; 1010 1011 // If the load and store are to the exact same address, they should have been 1012 // a must alias. AA must have gotten confused. 1013 // FIXME: Study to see if/when this happens. One case is forwarding a memset 1014 // to a load from the base of the memset. 1015#if 0 1016 if (LoadOffset == StoreOffset) { 1017 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 1018 << "Base = " << *StoreBase << "\n" 1019 << "Store Ptr = " << *WritePtr << "\n" 1020 << "Store Offs = " << StoreOffset << "\n" 1021 << "Load Ptr = " << *LoadPtr << "\n"; 1022 abort(); 1023 } 1024#endif 1025 1026 // If the load and store don't overlap at all, the store doesn't provide 1027 // anything to the load. In this case, they really don't alias at all, AA 1028 // must have gotten confused. 1029 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1030 // remove this check, as it is duplicated with what we have below. 1031 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); 1032 1033 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 1034 return -1; 1035 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 1036 LoadSize >>= 3; 1037 1038 1039 bool isAAFailure = false; 1040 if (StoreOffset < LoadOffset) 1041 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1042 else 1043 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1044 1045 if (isAAFailure) { 1046#if 0 1047 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1048 << "Base = " << *StoreBase << "\n" 1049 << "Store Ptr = " << *WritePtr << "\n" 1050 << "Store Offs = " << StoreOffset << "\n" 1051 << "Load Ptr = " << *LoadPtr << "\n"; 1052 abort(); 1053#endif 1054 return -1; 1055 } 1056 1057 // If the Load isn't completely contained within the stored bits, we don't 1058 // have all the bits to feed it. We could do something crazy in the future 1059 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1060 // valuable. 1061 if (StoreOffset > LoadOffset || 1062 StoreOffset+StoreSize < LoadOffset+LoadSize) 1063 return -1; 1064 1065 // Okay, we can do this transformation. Return the number of bytes into the 1066 // store that the load is. 1067 return LoadOffset-StoreOffset; 1068} 1069 1070/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1071/// memdep query of a load that ends up being a clobbering store. 1072static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr, 1073 StoreInst *DepSI, 1074 const TargetData &TD) { 1075 // Cannot handle reading from store of first-class aggregate yet. 1076 if (DepSI->getValueOperand()->getType()->isStructTy() || 1077 DepSI->getValueOperand()->getType()->isArrayTy()) 1078 return -1; 1079 1080 Value *StorePtr = DepSI->getPointerOperand(); 1081 uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType()); 1082 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1083 StorePtr, StoreSize, TD); 1084} 1085 1086static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr, 1087 MemIntrinsic *MI, 1088 const TargetData &TD) { 1089 // If the mem operation is a non-constant size, we can't handle it. 1090 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 1091 if (SizeCst == 0) return -1; 1092 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 1093 1094 // If this is memset, we just need to see if the offset is valid in the size 1095 // of the memset.. 1096 if (MI->getIntrinsicID() == Intrinsic::memset) 1097 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 1098 MemSizeInBits, TD); 1099 1100 // If we have a memcpy/memmove, the only case we can handle is if this is a 1101 // copy from constant memory. In that case, we can read directly from the 1102 // constant memory. 1103 MemTransferInst *MTI = cast<MemTransferInst>(MI); 1104 1105 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 1106 if (Src == 0) return -1; 1107 1108 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject()); 1109 if (GV == 0 || !GV->isConstant()) return -1; 1110 1111 // See if the access is within the bounds of the transfer. 1112 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1113 MI->getDest(), MemSizeInBits, TD); 1114 if (Offset == -1) 1115 return Offset; 1116 1117 // Otherwise, see if we can constant fold a load from the constant with the 1118 // offset applied as appropriate. 1119 Src = ConstantExpr::getBitCast(Src, 1120 llvm::Type::getInt8PtrTy(Src->getContext())); 1121 Constant *OffsetCst = 1122 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1123 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1124 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1125 if (ConstantFoldLoadFromConstPtr(Src, &TD)) 1126 return Offset; 1127 return -1; 1128} 1129 1130 1131/// GetStoreValueForLoad - This function is called when we have a 1132/// memdep query of a load that ends up being a clobbering store. This means 1133/// that the store *may* provide bits used by the load but we can't be sure 1134/// because the pointers don't mustalias. Check this case to see if there is 1135/// anything more we can do before we give up. 1136static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1137 const Type *LoadTy, 1138 Instruction *InsertPt, const TargetData &TD){ 1139 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1140 1141 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; 1142 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8; 1143 1144 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1145 1146 // Compute which bits of the stored value are being used by the load. Convert 1147 // to an integer type to start with. 1148 if (SrcVal->getType()->isPointerTy()) 1149 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp"); 1150 if (!SrcVal->getType()->isIntegerTy()) 1151 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1152 "tmp"); 1153 1154 // Shift the bits to the least significant depending on endianness. 1155 unsigned ShiftAmt; 1156 if (TD.isLittleEndian()) 1157 ShiftAmt = Offset*8; 1158 else 1159 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1160 1161 if (ShiftAmt) 1162 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp"); 1163 1164 if (LoadSize != StoreSize) 1165 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1166 "tmp"); 1167 1168 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1169} 1170 1171/// GetMemInstValueForLoad - This function is called when we have a 1172/// memdep query of a load that ends up being a clobbering mem intrinsic. 1173static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1174 const Type *LoadTy, Instruction *InsertPt, 1175 const TargetData &TD){ 1176 LLVMContext &Ctx = LoadTy->getContext(); 1177 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1178 1179 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1180 1181 // We know that this method is only called when the mem transfer fully 1182 // provides the bits for the load. 1183 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1184 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1185 // independently of what the offset is. 1186 Value *Val = MSI->getValue(); 1187 if (LoadSize != 1) 1188 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1189 1190 Value *OneElt = Val; 1191 1192 // Splat the value out to the right number of bits. 1193 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1194 // If we can double the number of bytes set, do it. 1195 if (NumBytesSet*2 <= LoadSize) { 1196 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1197 Val = Builder.CreateOr(Val, ShVal); 1198 NumBytesSet <<= 1; 1199 continue; 1200 } 1201 1202 // Otherwise insert one byte at a time. 1203 Value *ShVal = Builder.CreateShl(Val, 1*8); 1204 Val = Builder.CreateOr(OneElt, ShVal); 1205 ++NumBytesSet; 1206 } 1207 1208 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 1209 } 1210 1211 // Otherwise, this is a memcpy/memmove from a constant global. 1212 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 1213 Constant *Src = cast<Constant>(MTI->getSource()); 1214 1215 // Otherwise, see if we can constant fold a load from the constant with the 1216 // offset applied as appropriate. 1217 Src = ConstantExpr::getBitCast(Src, 1218 llvm::Type::getInt8PtrTy(Src->getContext())); 1219 Constant *OffsetCst = 1220 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1221 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1222 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1223 return ConstantFoldLoadFromConstPtr(Src, &TD); 1224} 1225 1226namespace { 1227 1228struct AvailableValueInBlock { 1229 /// BB - The basic block in question. 1230 BasicBlock *BB; 1231 enum ValType { 1232 SimpleVal, // A simple offsetted value that is accessed. 1233 MemIntrin // A memory intrinsic which is loaded from. 1234 }; 1235 1236 /// V - The value that is live out of the block. 1237 PointerIntPair<Value *, 1, ValType> Val; 1238 1239 /// Offset - The byte offset in Val that is interesting for the load query. 1240 unsigned Offset; 1241 1242 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1243 unsigned Offset = 0) { 1244 AvailableValueInBlock Res; 1245 Res.BB = BB; 1246 Res.Val.setPointer(V); 1247 Res.Val.setInt(SimpleVal); 1248 Res.Offset = Offset; 1249 return Res; 1250 } 1251 1252 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 1253 unsigned Offset = 0) { 1254 AvailableValueInBlock Res; 1255 Res.BB = BB; 1256 Res.Val.setPointer(MI); 1257 Res.Val.setInt(MemIntrin); 1258 Res.Offset = Offset; 1259 return Res; 1260 } 1261 1262 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 1263 Value *getSimpleValue() const { 1264 assert(isSimpleValue() && "Wrong accessor"); 1265 return Val.getPointer(); 1266 } 1267 1268 MemIntrinsic *getMemIntrinValue() const { 1269 assert(!isSimpleValue() && "Wrong accessor"); 1270 return cast<MemIntrinsic>(Val.getPointer()); 1271 } 1272 1273 /// MaterializeAdjustedValue - Emit code into this block to adjust the value 1274 /// defined here to the specified type. This handles various coercion cases. 1275 Value *MaterializeAdjustedValue(const Type *LoadTy, 1276 const TargetData *TD) const { 1277 Value *Res; 1278 if (isSimpleValue()) { 1279 Res = getSimpleValue(); 1280 if (Res->getType() != LoadTy) { 1281 assert(TD && "Need target data to handle type mismatch case"); 1282 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), 1283 *TD); 1284 1285 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1286 << *getSimpleValue() << '\n' 1287 << *Res << '\n' << "\n\n\n"); 1288 } 1289 } else { 1290 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, 1291 LoadTy, BB->getTerminator(), *TD); 1292 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1293 << " " << *getMemIntrinValue() << '\n' 1294 << *Res << '\n' << "\n\n\n"); 1295 } 1296 return Res; 1297 } 1298}; 1299 1300} 1301 1302/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1303/// construct SSA form, allowing us to eliminate LI. This returns the value 1304/// that should be used at LI's definition site. 1305static Value *ConstructSSAForLoadSet(LoadInst *LI, 1306 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1307 const TargetData *TD, 1308 const DominatorTree &DT, 1309 AliasAnalysis *AA) { 1310 // Check for the fully redundant, dominating load case. In this case, we can 1311 // just use the dominating value directly. 1312 if (ValuesPerBlock.size() == 1 && 1313 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent())) 1314 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD); 1315 1316 // Otherwise, we have to construct SSA form. 1317 SmallVector<PHINode*, 8> NewPHIs; 1318 SSAUpdater SSAUpdate(&NewPHIs); 1319 SSAUpdate.Initialize(LI->getType(), LI->getName()); 1320 1321 const Type *LoadTy = LI->getType(); 1322 1323 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1324 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1325 BasicBlock *BB = AV.BB; 1326 1327 if (SSAUpdate.HasValueForBlock(BB)) 1328 continue; 1329 1330 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD)); 1331 } 1332 1333 // Perform PHI construction. 1334 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1335 1336 // If new PHI nodes were created, notify alias analysis. 1337 if (V->getType()->isPointerTy()) 1338 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1339 AA->copyValue(LI, NewPHIs[i]); 1340 1341 return V; 1342} 1343 1344static bool isLifetimeStart(const Instruction *Inst) { 1345 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1346 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1347 return false; 1348} 1349 1350/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1351/// non-local by performing PHI construction. 1352bool GVN::processNonLocalLoad(LoadInst *LI, 1353 SmallVectorImpl<Instruction*> &toErase) { 1354 // Find the non-local dependencies of the load. 1355 SmallVector<NonLocalDepResult, 64> Deps; 1356 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI); 1357 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps); 1358 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: " 1359 // << Deps.size() << *LI << '\n'); 1360 1361 // If we had to process more than one hundred blocks to find the 1362 // dependencies, this load isn't worth worrying about. Optimizing 1363 // it will be too expensive. 1364 if (Deps.size() > 100) 1365 return false; 1366 1367 // If we had a phi translation failure, we'll have a single entry which is a 1368 // clobber in the current block. Reject this early. 1369 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) { 1370 DEBUG( 1371 dbgs() << "GVN: non-local load "; 1372 WriteAsOperand(dbgs(), LI); 1373 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n'; 1374 ); 1375 return false; 1376 } 1377 1378 // Filter out useless results (non-locals, etc). Keep track of the blocks 1379 // where we have a value available in repl, also keep track of whether we see 1380 // dependencies that produce an unknown value for the load (such as a call 1381 // that could potentially clobber the load). 1382 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1383 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1384 1385 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1386 BasicBlock *DepBB = Deps[i].getBB(); 1387 MemDepResult DepInfo = Deps[i].getResult(); 1388 1389 if (DepInfo.isClobber()) { 1390 // The address being loaded in this non-local block may not be the same as 1391 // the pointer operand of the load if PHI translation occurs. Make sure 1392 // to consider the right address. 1393 Value *Address = Deps[i].getAddress(); 1394 1395 // If the dependence is to a store that writes to a superset of the bits 1396 // read by the load, we can extract the bits we need for the load from the 1397 // stored value. 1398 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1399 if (TD && Address) { 1400 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, 1401 DepSI, *TD); 1402 if (Offset != -1) { 1403 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1404 DepSI->getValueOperand(), 1405 Offset)); 1406 continue; 1407 } 1408 } 1409 } 1410 1411 // If the clobbering value is a memset/memcpy/memmove, see if we can 1412 // forward a value on from it. 1413 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 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->getValueOperand()->getType() != LI->getType()) { 1444 // If the stored value is larger or equal to the loaded value, we can 1445 // reuse it. 1446 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(), 1447 LI->getType(), *TD)) { 1448 UnavailableBlocks.push_back(DepBB); 1449 continue; 1450 } 1451 } 1452 1453 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1454 S->getValueOperand())); 1455 continue; 1456 } 1457 1458 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1459 // If the types mismatch and we can't handle it, reject reuse of the load. 1460 if (LD->getType() != LI->getType()) { 1461 // If the stored value is larger or equal to the loaded value, we can 1462 // reuse it. 1463 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1464 UnavailableBlocks.push_back(DepBB); 1465 continue; 1466 } 1467 } 1468 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1469 continue; 1470 } 1471 1472 UnavailableBlocks.push_back(DepBB); 1473 continue; 1474 } 1475 1476 // If we have no predecessors that produce a known value for this load, exit 1477 // early. 1478 if (ValuesPerBlock.empty()) return false; 1479 1480 // If all of the instructions we depend on produce a known value for this 1481 // load, then it is fully redundant and we can use PHI insertion to compute 1482 // its value. Insert PHIs and remove the fully redundant value now. 1483 if (UnavailableBlocks.empty()) { 1484 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1485 1486 // Perform PHI construction. 1487 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1488 VN.getAliasAnalysis()); 1489 LI->replaceAllUsesWith(V); 1490 1491 if (isa<PHINode>(V)) 1492 V->takeName(LI); 1493 if (V->getType()->isPointerTy()) 1494 MD->invalidateCachedPointerInfo(V); 1495 VN.erase(LI); 1496 toErase.push_back(LI); 1497 ++NumGVNLoad; 1498 return true; 1499 } 1500 1501 if (!EnablePRE || !EnableLoadPRE) 1502 return false; 1503 1504 // Okay, we have *some* definitions of the value. This means that the value 1505 // is available in some of our (transitive) predecessors. Lets think about 1506 // doing PRE of this load. This will involve inserting a new load into the 1507 // predecessor when it's not available. We could do this in general, but 1508 // prefer to not increase code size. As such, we only do this when we know 1509 // that we only have to insert *one* load (which means we're basically moving 1510 // the load, not inserting a new one). 1511 1512 SmallPtrSet<BasicBlock *, 4> Blockers; 1513 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1514 Blockers.insert(UnavailableBlocks[i]); 1515 1516 // Lets find first basic block with more than one predecessor. Walk backwards 1517 // through predecessors if needed. 1518 BasicBlock *LoadBB = LI->getParent(); 1519 BasicBlock *TmpBB = LoadBB; 1520 1521 bool isSinglePred = false; 1522 bool allSingleSucc = true; 1523 while (TmpBB->getSinglePredecessor()) { 1524 isSinglePred = true; 1525 TmpBB = TmpBB->getSinglePredecessor(); 1526 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1527 return false; 1528 if (Blockers.count(TmpBB)) 1529 return false; 1530 1531 // If any of these blocks has more than one successor (i.e. if the edge we 1532 // just traversed was critical), then there are other paths through this 1533 // block along which the load may not be anticipated. Hoisting the load 1534 // above this block would be adding the load to execution paths along 1535 // which it was not previously executed. 1536 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1537 return false; 1538 } 1539 1540 assert(TmpBB); 1541 LoadBB = TmpBB; 1542 1543 // FIXME: It is extremely unclear what this loop is doing, other than 1544 // artificially restricting loadpre. 1545 if (isSinglePred) { 1546 bool isHot = false; 1547 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1548 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1549 if (AV.isSimpleValue()) 1550 // "Hot" Instruction is in some loop (because it dominates its dep. 1551 // instruction). 1552 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) 1553 if (DT->dominates(LI, I)) { 1554 isHot = true; 1555 break; 1556 } 1557 } 1558 1559 // We are interested only in "hot" instructions. We don't want to do any 1560 // mis-optimizations here. 1561 if (!isHot) 1562 return false; 1563 } 1564 1565 // Check to see how many predecessors have the loaded value fully 1566 // available. 1567 DenseMap<BasicBlock*, Value*> PredLoads; 1568 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1569 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1570 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1571 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1572 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1573 1574 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit; 1575 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1576 PI != E; ++PI) { 1577 BasicBlock *Pred = *PI; 1578 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { 1579 continue; 1580 } 1581 PredLoads[Pred] = 0; 1582 1583 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1584 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1585 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1586 << Pred->getName() << "': " << *LI << '\n'); 1587 return false; 1588 } 1589 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB); 1590 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum)); 1591 } 1592 } 1593 if (!NeedToSplit.empty()) { 1594 toSplit.append(NeedToSplit.begin(), NeedToSplit.end()); 1595 return false; 1596 } 1597 1598 // Decide whether PRE is profitable for this load. 1599 unsigned NumUnavailablePreds = PredLoads.size(); 1600 assert(NumUnavailablePreds != 0 && 1601 "Fully available value should be eliminated above!"); 1602 1603 // If this load is unavailable in multiple predecessors, reject it. 1604 // FIXME: If we could restructure the CFG, we could make a common pred with 1605 // all the preds that don't have an available LI and insert a new load into 1606 // that one block. 1607 if (NumUnavailablePreds != 1) 1608 return false; 1609 1610 // Check if the load can safely be moved to all the unavailable predecessors. 1611 bool CanDoPRE = true; 1612 SmallVector<Instruction*, 8> NewInsts; 1613 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1614 E = PredLoads.end(); I != E; ++I) { 1615 BasicBlock *UnavailablePred = I->first; 1616 1617 // Do PHI translation to get its value in the predecessor if necessary. The 1618 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1619 1620 // If all preds have a single successor, then we know it is safe to insert 1621 // the load on the pred (?!?), so we can insert code to materialize the 1622 // pointer if it is not available. 1623 PHITransAddr Address(LI->getPointerOperand(), TD); 1624 Value *LoadPtr = 0; 1625 if (allSingleSucc) { 1626 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1627 *DT, NewInsts); 1628 } else { 1629 Address.PHITranslateValue(LoadBB, UnavailablePred, DT); 1630 LoadPtr = Address.getAddr(); 1631 } 1632 1633 // If we couldn't find or insert a computation of this phi translated value, 1634 // we fail PRE. 1635 if (LoadPtr == 0) { 1636 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1637 << *LI->getPointerOperand() << "\n"); 1638 CanDoPRE = false; 1639 break; 1640 } 1641 1642 // Make sure it is valid to move this load here. We have to watch out for: 1643 // @1 = getelementptr (i8* p, ... 1644 // test p and branch if == 0 1645 // load @1 1646 // It is valid to have the getelementptr before the test, even if p can be 0, 1647 // as getelementptr only does address arithmetic. 1648 // If we are not pushing the value through any multiple-successor blocks 1649 // we do not have this case. Otherwise, check that the load is safe to 1650 // put anywhere; this can be improved, but should be conservatively safe. 1651 if (!allSingleSucc && 1652 // FIXME: REEVALUTE THIS. 1653 !isSafeToLoadUnconditionally(LoadPtr, 1654 UnavailablePred->getTerminator(), 1655 LI->getAlignment(), TD)) { 1656 CanDoPRE = false; 1657 break; 1658 } 1659 1660 I->second = LoadPtr; 1661 } 1662 1663 if (!CanDoPRE) { 1664 while (!NewInsts.empty()) 1665 NewInsts.pop_back_val()->eraseFromParent(); 1666 return false; 1667 } 1668 1669 // Okay, we can eliminate this load by inserting a reload in the predecessor 1670 // and using PHI construction to get the value in the other predecessors, do 1671 // it. 1672 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1673 DEBUG(if (!NewInsts.empty()) 1674 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1675 << *NewInsts.back() << '\n'); 1676 1677 // Assign value numbers to the new instructions. 1678 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { 1679 // FIXME: We really _ought_ to insert these value numbers into their 1680 // parent's availability map. However, in doing so, we risk getting into 1681 // ordering issues. If a block hasn't been processed yet, we would be 1682 // marking a value as AVAIL-IN, which isn't what we intend. 1683 VN.lookup_or_add(NewInsts[i]); 1684 } 1685 1686 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1687 E = PredLoads.end(); I != E; ++I) { 1688 BasicBlock *UnavailablePred = I->first; 1689 Value *LoadPtr = I->second; 1690 1691 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1692 LI->getAlignment(), 1693 UnavailablePred->getTerminator()); 1694 1695 // Add the newly created load. 1696 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1697 NewLoad)); 1698 MD->invalidateCachedPointerInfo(LoadPtr); 1699 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); 1700 } 1701 1702 // Perform PHI construction. 1703 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1704 VN.getAliasAnalysis()); 1705 LI->replaceAllUsesWith(V); 1706 if (isa<PHINode>(V)) 1707 V->takeName(LI); 1708 if (V->getType()->isPointerTy()) 1709 MD->invalidateCachedPointerInfo(V); 1710 VN.erase(LI); 1711 toErase.push_back(LI); 1712 ++NumPRELoad; 1713 return true; 1714} 1715 1716/// processLoad - Attempt to eliminate a load, first by eliminating it 1717/// locally, and then attempting non-local elimination if that fails. 1718bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1719 if (!MD) 1720 return false; 1721 1722 if (L->isVolatile()) 1723 return false; 1724 1725 // ... to a pointer that has been loaded from before... 1726 MemDepResult Dep = MD->getDependency(L); 1727 1728 // If the value isn't available, don't do anything! 1729 if (Dep.isClobber()) { 1730 // Check to see if we have something like this: 1731 // store i32 123, i32* %P 1732 // %A = bitcast i32* %P to i8* 1733 // %B = gep i8* %A, i32 1 1734 // %C = load i8* %B 1735 // 1736 // We could do that by recognizing if the clobber instructions are obviously 1737 // a common base + constant offset, and if the previous store (or memset) 1738 // completely covers this load. This sort of thing can happen in bitfield 1739 // access code. 1740 Value *AvailVal = 0; 1741 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1742 if (TD) { 1743 int Offset = AnalyzeLoadFromClobberingStore(L->getType(), 1744 L->getPointerOperand(), 1745 DepSI, *TD); 1746 if (Offset != -1) 1747 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, 1748 L->getType(), L, *TD); 1749 } 1750 1751 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1752 // a value on from it. 1753 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1754 if (TD) { 1755 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), 1756 L->getPointerOperand(), 1757 DepMI, *TD); 1758 if (Offset != -1) 1759 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD); 1760 } 1761 } 1762 1763 if (AvailVal) { 1764 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1765 << *AvailVal << '\n' << *L << "\n\n\n"); 1766 1767 // Replace the load! 1768 L->replaceAllUsesWith(AvailVal); 1769 if (AvailVal->getType()->isPointerTy()) 1770 MD->invalidateCachedPointerInfo(AvailVal); 1771 VN.erase(L); 1772 toErase.push_back(L); 1773 ++NumGVNLoad; 1774 return true; 1775 } 1776 1777 DEBUG( 1778 // fast print dep, using operator<< on instruction would be too slow 1779 dbgs() << "GVN: load "; 1780 WriteAsOperand(dbgs(), L); 1781 Instruction *I = Dep.getInst(); 1782 dbgs() << " is clobbered by " << *I << '\n'; 1783 ); 1784 return false; 1785 } 1786 1787 // If it is defined in another block, try harder. 1788 if (Dep.isNonLocal()) 1789 return processNonLocalLoad(L, toErase); 1790 1791 Instruction *DepInst = Dep.getInst(); 1792 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1793 Value *StoredVal = DepSI->getValueOperand(); 1794 1795 // The store and load are to a must-aliased pointer, but they may not 1796 // actually have the same type. See if we know how to reuse the stored 1797 // value (depending on its type). 1798 if (StoredVal->getType() != L->getType()) { 1799 if (TD) { 1800 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1801 L, *TD); 1802 if (StoredVal == 0) 1803 return false; 1804 1805 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1806 << '\n' << *L << "\n\n\n"); 1807 } 1808 else 1809 return false; 1810 } 1811 1812 // Remove it! 1813 L->replaceAllUsesWith(StoredVal); 1814 if (StoredVal->getType()->isPointerTy()) 1815 MD->invalidateCachedPointerInfo(StoredVal); 1816 VN.erase(L); 1817 toErase.push_back(L); 1818 ++NumGVNLoad; 1819 return true; 1820 } 1821 1822 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1823 Value *AvailableVal = DepLI; 1824 1825 // The loads are of a must-aliased pointer, but they may not actually have 1826 // the same type. See if we know how to reuse the previously loaded value 1827 // (depending on its type). 1828 if (DepLI->getType() != L->getType()) { 1829 if (TD) { 1830 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1831 if (AvailableVal == 0) 1832 return false; 1833 1834 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1835 << "\n" << *L << "\n\n\n"); 1836 } 1837 else 1838 return false; 1839 } 1840 1841 // Remove it! 1842 L->replaceAllUsesWith(AvailableVal); 1843 if (DepLI->getType()->isPointerTy()) 1844 MD->invalidateCachedPointerInfo(DepLI); 1845 VN.erase(L); 1846 toErase.push_back(L); 1847 ++NumGVNLoad; 1848 return true; 1849 } 1850 1851 // If this load really doesn't depend on anything, then we must be loading an 1852 // undef value. This can happen when loading for a fresh allocation with no 1853 // intervening stores, for example. 1854 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { 1855 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1856 VN.erase(L); 1857 toErase.push_back(L); 1858 ++NumGVNLoad; 1859 return true; 1860 } 1861 1862 // If this load occurs either right after a lifetime begin, 1863 // then the loaded value is undefined. 1864 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) { 1865 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1866 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1867 VN.erase(L); 1868 toErase.push_back(L); 1869 ++NumGVNLoad; 1870 return true; 1871 } 1872 } 1873 1874 return false; 1875} 1876 1877Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1878 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1879 if (I == localAvail.end()) 1880 return 0; 1881 1882 ValueNumberScope *Locals = I->second; 1883 while (Locals) { 1884 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1885 if (I != Locals->table.end()) 1886 return I->second; 1887 Locals = Locals->parent; 1888 } 1889 1890 return 0; 1891} 1892 1893 1894/// processInstruction - When calculating availability, handle an instruction 1895/// by inserting it into the appropriate sets 1896bool GVN::processInstruction(Instruction *I, 1897 SmallVectorImpl<Instruction*> &toErase) { 1898 // Ignore dbg info intrinsics. 1899 if (isa<DbgInfoIntrinsic>(I)) 1900 return false; 1901 1902 // If the instruction can be easily simplified then do so now in preference 1903 // to value numbering it. Value numbering often exposes redundancies, for 1904 // example if it determines that %y is equal to %x then the instruction 1905 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. 1906 if (Value *V = SimplifyInstruction(I, TD)) { 1907 I->replaceAllUsesWith(V); 1908 if (MD && V->getType()->isPointerTy()) 1909 MD->invalidateCachedPointerInfo(V); 1910 VN.erase(I); 1911 toErase.push_back(I); 1912 return true; 1913 } 1914 1915 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1916 bool Changed = processLoad(LI, toErase); 1917 1918 if (!Changed) { 1919 unsigned Num = VN.lookup_or_add(LI); 1920 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1921 } 1922 1923 return Changed; 1924 } 1925 1926 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1927 unsigned Num = VN.lookup_or_add(I); 1928 1929 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1930 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1931 1932 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1933 return false; 1934 1935 Value *BranchCond = BI->getCondition(); 1936 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1937 1938 BasicBlock *TrueSucc = BI->getSuccessor(0); 1939 BasicBlock *FalseSucc = BI->getSuccessor(1); 1940 1941 if (TrueSucc->getSinglePredecessor()) 1942 localAvail[TrueSucc]->table[CondVN] = 1943 ConstantInt::getTrue(TrueSucc->getContext()); 1944 if (FalseSucc->getSinglePredecessor()) 1945 localAvail[FalseSucc]->table[CondVN] = 1946 ConstantInt::getFalse(TrueSucc->getContext()); 1947 1948 return false; 1949 1950 // Allocations are always uniquely numbered, so we can save time and memory 1951 // by fast failing them. 1952 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) { 1953 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1954 return false; 1955 } 1956 1957 // Collapse PHI nodes 1958 if (PHINode* p = dyn_cast<PHINode>(I)) { 1959 Value *constVal = CollapsePhi(p); 1960 1961 if (constVal) { 1962 p->replaceAllUsesWith(constVal); 1963 if (MD && constVal->getType()->isPointerTy()) 1964 MD->invalidateCachedPointerInfo(constVal); 1965 VN.erase(p); 1966 1967 toErase.push_back(p); 1968 } else { 1969 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1970 } 1971 1972 // If the number we were assigned was a brand new VN, then we don't 1973 // need to do a lookup to see if the number already exists 1974 // somewhere in the domtree: it can't! 1975 } else if (Num == NextNum) { 1976 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1977 1978 // Perform fast-path value-number based elimination of values inherited from 1979 // dominators. 1980 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1981 // Remove it! 1982 VN.erase(I); 1983 I->replaceAllUsesWith(repl); 1984 if (MD && repl->getType()->isPointerTy()) 1985 MD->invalidateCachedPointerInfo(repl); 1986 toErase.push_back(I); 1987 return true; 1988 1989 } else { 1990 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1991 } 1992 1993 return false; 1994} 1995 1996/// runOnFunction - This is the main transformation entry point for a function. 1997bool GVN::runOnFunction(Function& F) { 1998 if (!NoLoads) 1999 MD = &getAnalysis<MemoryDependenceAnalysis>(); 2000 DT = &getAnalysis<DominatorTree>(); 2001 TD = getAnalysisIfAvailable<TargetData>(); 2002 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 2003 VN.setMemDep(MD); 2004 VN.setDomTree(DT); 2005 2006 bool Changed = false; 2007 bool ShouldContinue = true; 2008 2009 // Merge unconditional branches, allowing PRE to catch more 2010 // optimization opportunities. 2011 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 2012 BasicBlock *BB = FI; 2013 ++FI; 2014 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 2015 if (removedBlock) ++NumGVNBlocks; 2016 2017 Changed |= removedBlock; 2018 } 2019 2020 unsigned Iteration = 0; 2021 2022 while (ShouldContinue) { 2023 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 2024 ShouldContinue = iterateOnFunction(F); 2025 if (splitCriticalEdges()) 2026 ShouldContinue = true; 2027 Changed |= ShouldContinue; 2028 ++Iteration; 2029 } 2030 2031 if (EnablePRE) { 2032 bool PREChanged = true; 2033 while (PREChanged) { 2034 PREChanged = performPRE(F); 2035 Changed |= PREChanged; 2036 } 2037 } 2038 // FIXME: Should perform GVN again after PRE does something. PRE can move 2039 // computations into blocks where they become fully redundant. Note that 2040 // we can't do this until PRE's critical edge splitting updates memdep. 2041 // Actually, when this happens, we should just fully integrate PRE into GVN. 2042 2043 cleanupGlobalSets(); 2044 2045 return Changed; 2046} 2047 2048 2049bool GVN::processBlock(BasicBlock *BB) { 2050 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 2051 // incrementing BI before processing an instruction). 2052 SmallVector<Instruction*, 8> toErase; 2053 bool ChangedFunction = false; 2054 2055 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 2056 BI != BE;) { 2057 ChangedFunction |= processInstruction(BI, toErase); 2058 if (toErase.empty()) { 2059 ++BI; 2060 continue; 2061 } 2062 2063 // If we need some instructions deleted, do it now. 2064 NumGVNInstr += toErase.size(); 2065 2066 // Avoid iterator invalidation. 2067 bool AtStart = BI == BB->begin(); 2068 if (!AtStart) 2069 --BI; 2070 2071 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 2072 E = toErase.end(); I != E; ++I) { 2073 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 2074 if (MD) MD->removeInstruction(*I); 2075 (*I)->eraseFromParent(); 2076 DEBUG(verifyRemoved(*I)); 2077 } 2078 toErase.clear(); 2079 2080 if (AtStart) 2081 BI = BB->begin(); 2082 else 2083 ++BI; 2084 } 2085 2086 return ChangedFunction; 2087} 2088 2089/// performPRE - Perform a purely local form of PRE that looks for diamond 2090/// control flow patterns and attempts to perform simple PRE at the join point. 2091bool GVN::performPRE(Function &F) { 2092 bool Changed = false; 2093 DenseMap<BasicBlock*, Value*> predMap; 2094 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 2095 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 2096 BasicBlock *CurrentBlock = *DI; 2097 2098 // Nothing to PRE in the entry block. 2099 if (CurrentBlock == &F.getEntryBlock()) continue; 2100 2101 for (BasicBlock::iterator BI = CurrentBlock->begin(), 2102 BE = CurrentBlock->end(); BI != BE; ) { 2103 Instruction *CurInst = BI++; 2104 2105 if (isa<AllocaInst>(CurInst) || 2106 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 2107 CurInst->getType()->isVoidTy() || 2108 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2109 isa<DbgInfoIntrinsic>(CurInst)) 2110 continue; 2111 2112 // We don't currently value number ANY inline asm calls. 2113 if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) 2114 if (CallI->isInlineAsm()) 2115 continue; 2116 2117 uint32_t ValNo = VN.lookup(CurInst); 2118 2119 // Look for the predecessors for PRE opportunities. We're 2120 // only trying to solve the basic diamond case, where 2121 // a value is computed in the successor and one predecessor, 2122 // but not the other. We also explicitly disallow cases 2123 // where the successor is its own predecessor, because they're 2124 // more complicated to get right. 2125 unsigned NumWith = 0; 2126 unsigned NumWithout = 0; 2127 BasicBlock *PREPred = 0; 2128 predMap.clear(); 2129 2130 for (pred_iterator PI = pred_begin(CurrentBlock), 2131 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2132 BasicBlock *P = *PI; 2133 // We're not interested in PRE where the block is its 2134 // own predecessor, or in blocks with predecessors 2135 // that are not reachable. 2136 if (P == CurrentBlock) { 2137 NumWithout = 2; 2138 break; 2139 } else if (!localAvail.count(P)) { 2140 NumWithout = 2; 2141 break; 2142 } 2143 2144 DenseMap<uint32_t, Value*>::iterator predV = 2145 localAvail[P]->table.find(ValNo); 2146 if (predV == localAvail[P]->table.end()) { 2147 PREPred = P; 2148 ++NumWithout; 2149 } else if (predV->second == CurInst) { 2150 NumWithout = 2; 2151 } else { 2152 predMap[P] = predV->second; 2153 ++NumWith; 2154 } 2155 } 2156 2157 // Don't do PRE when it might increase code size, i.e. when 2158 // we would need to insert instructions in more than one pred. 2159 if (NumWithout != 1 || NumWith == 0) 2160 continue; 2161 2162 // Don't do PRE across indirect branch. 2163 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2164 continue; 2165 2166 // We can't do PRE safely on a critical edge, so instead we schedule 2167 // the edge to be split and perform the PRE the next time we iterate 2168 // on the function. 2169 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); 2170 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2171 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2172 continue; 2173 } 2174 2175 // Instantiate the expression in the predecessor that lacked it. 2176 // Because we are going top-down through the block, all value numbers 2177 // will be available in the predecessor by the time we need them. Any 2178 // that weren't originally present will have been instantiated earlier 2179 // in this loop. 2180 Instruction *PREInstr = CurInst->clone(); 2181 bool success = true; 2182 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2183 Value *Op = PREInstr->getOperand(i); 2184 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2185 continue; 2186 2187 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2188 PREInstr->setOperand(i, V); 2189 } else { 2190 success = false; 2191 break; 2192 } 2193 } 2194 2195 // Fail out if we encounter an operand that is not available in 2196 // the PRE predecessor. This is typically because of loads which 2197 // are not value numbered precisely. 2198 if (!success) { 2199 delete PREInstr; 2200 DEBUG(verifyRemoved(PREInstr)); 2201 continue; 2202 } 2203 2204 PREInstr->insertBefore(PREPred->getTerminator()); 2205 PREInstr->setName(CurInst->getName() + ".pre"); 2206 predMap[PREPred] = PREInstr; 2207 VN.add(PREInstr, ValNo); 2208 ++NumGVNPRE; 2209 2210 // Update the availability map to include the new instruction. 2211 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 2212 2213 // Create a PHI to make the value available in this block. 2214 PHINode* Phi = PHINode::Create(CurInst->getType(), 2215 CurInst->getName() + ".pre-phi", 2216 CurrentBlock->begin()); 2217 for (pred_iterator PI = pred_begin(CurrentBlock), 2218 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2219 BasicBlock *P = *PI; 2220 Phi->addIncoming(predMap[P], P); 2221 } 2222 2223 VN.add(Phi, ValNo); 2224 localAvail[CurrentBlock]->table[ValNo] = Phi; 2225 2226 CurInst->replaceAllUsesWith(Phi); 2227 if (MD && Phi->getType()->isPointerTy()) 2228 MD->invalidateCachedPointerInfo(Phi); 2229 VN.erase(CurInst); 2230 2231 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2232 if (MD) MD->removeInstruction(CurInst); 2233 CurInst->eraseFromParent(); 2234 DEBUG(verifyRemoved(CurInst)); 2235 Changed = true; 2236 } 2237 } 2238 2239 if (splitCriticalEdges()) 2240 Changed = true; 2241 2242 return Changed; 2243} 2244 2245/// splitCriticalEdges - Split critical edges found during the previous 2246/// iteration that may enable further optimization. 2247bool GVN::splitCriticalEdges() { 2248 if (toSplit.empty()) 2249 return false; 2250 do { 2251 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2252 SplitCriticalEdge(Edge.first, Edge.second, this); 2253 } while (!toSplit.empty()); 2254 if (MD) MD->invalidateCachedPredecessors(); 2255 return true; 2256} 2257 2258/// iterateOnFunction - Executes one iteration of GVN 2259bool GVN::iterateOnFunction(Function &F) { 2260 cleanupGlobalSets(); 2261 2262 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2263 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 2264 if (DI->getIDom()) 2265 localAvail[DI->getBlock()] = 2266 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 2267 else 2268 localAvail[DI->getBlock()] = new ValueNumberScope(0); 2269 } 2270 2271 // Top-down walk of the dominator tree 2272 bool Changed = false; 2273#if 0 2274 // Needed for value numbering with phi construction to work. 2275 ReversePostOrderTraversal<Function*> RPOT(&F); 2276 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2277 RE = RPOT.end(); RI != RE; ++RI) 2278 Changed |= processBlock(*RI); 2279#else 2280 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2281 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2282 Changed |= processBlock(DI->getBlock()); 2283#endif 2284 2285 return Changed; 2286} 2287 2288void GVN::cleanupGlobalSets() { 2289 VN.clear(); 2290 2291 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2292 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 2293 delete I->second; 2294 localAvail.clear(); 2295} 2296 2297/// verifyRemoved - Verify that the specified instruction does not occur in our 2298/// internal data structures. 2299void GVN::verifyRemoved(const Instruction *Inst) const { 2300 VN.verifyRemoved(Inst); 2301 2302 // Walk through the value number scope to make sure the instruction isn't 2303 // ferreted away in it. 2304 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator 2305 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 2306 const ValueNumberScope *VNS = I->second; 2307 2308 while (VNS) { 2309 for (DenseMap<uint32_t, Value*>::const_iterator 2310 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 2311 assert(II->second != Inst && "Inst still in value numbering scope!"); 2312 } 2313 2314 VNS = VNS->parent; 2315 } 2316 } 2317} 2318