GVN.cpp revision aad94aa4375d5ed43be728e03d91751c102ff958
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/Constants.h" 21#include "llvm/DerivedTypes.h" 22#include "llvm/GlobalVariable.h" 23#include "llvm/Function.h" 24#include "llvm/IntrinsicInst.h" 25#include "llvm/LLVMContext.h" 26#include "llvm/Operator.h" 27#include "llvm/Analysis/AliasAnalysis.h" 28#include "llvm/Analysis/ConstantFolding.h" 29#include "llvm/Analysis/Dominators.h" 30#include "llvm/Analysis/InstructionSimplify.h" 31#include "llvm/Analysis/Loads.h" 32#include "llvm/Analysis/MemoryBuiltins.h" 33#include "llvm/Analysis/MemoryDependenceAnalysis.h" 34#include "llvm/Analysis/PHITransAddr.h" 35#include "llvm/Analysis/ValueTracking.h" 36#include "llvm/Target/TargetData.h" 37#include "llvm/Transforms/Utils/BasicBlockUtils.h" 38#include "llvm/Transforms/Utils/Local.h" 39#include "llvm/Transforms/Utils/SSAUpdater.h" 40#include "llvm/ADT/DenseMap.h" 41#include "llvm/ADT/DepthFirstIterator.h" 42#include "llvm/ADT/PostOrderIterator.h" 43#include "llvm/ADT/SmallPtrSet.h" 44#include "llvm/ADT/Statistic.h" 45#include "llvm/Support/Allocator.h" 46#include "llvm/Support/CFG.h" 47#include "llvm/Support/CommandLine.h" 48#include "llvm/Support/Debug.h" 49#include "llvm/Support/ErrorHandling.h" 50#include "llvm/Support/GetElementPtrTypeIterator.h" 51#include "llvm/Support/IRBuilder.h" 52#include <list> 53using namespace llvm; 54 55STATISTIC(NumGVNInstr, "Number of instructions deleted"); 56STATISTIC(NumGVNLoad, "Number of loads deleted"); 57STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 58STATISTIC(NumGVNBlocks, "Number of blocks merged"); 59STATISTIC(NumPRELoad, "Number of loads PRE'd"); 60 61static cl::opt<bool> EnablePRE("enable-pre", 62 cl::init(true), cl::Hidden); 63static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 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 if (varargs != other.varargs) 131 return false; 132 return true; 133 } 134 135 /*bool operator!=(const Expression &other) const { 136 return !(*this == other); 137 }*/ 138 }; 139 140 class ValueTable { 141 private: 142 DenseMap<Value*, uint32_t> valueNumbering; 143 DenseMap<Expression, uint32_t> expressionNumbering; 144 AliasAnalysis* AA; 145 MemoryDependenceAnalysis* MD; 146 DominatorTree* DT; 147 148 uint32_t nextValueNumber; 149 150 Expression::ExpressionOpcode getOpcode(CmpInst* C); 151 Expression create_expression(BinaryOperator* BO); 152 Expression create_expression(CmpInst* C); 153 Expression create_expression(ShuffleVectorInst* V); 154 Expression create_expression(ExtractElementInst* C); 155 Expression create_expression(InsertElementInst* V); 156 Expression create_expression(SelectInst* V); 157 Expression create_expression(CastInst* C); 158 Expression create_expression(GetElementPtrInst* G); 159 Expression create_expression(CallInst* C); 160 Expression create_expression(ExtractValueInst* C); 161 Expression create_expression(InsertValueInst* C); 162 163 uint32_t lookup_or_add_call(CallInst* C); 164 public: 165 ValueTable() : nextValueNumber(1) { } 166 uint32_t lookup_or_add(Value *V); 167 uint32_t lookup(Value *V) const; 168 void add(Value *V, uint32_t num); 169 void clear(); 170 void erase(Value *v); 171 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 172 AliasAnalysis *getAliasAnalysis() const { return AA; } 173 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 174 void setDomTree(DominatorTree* D) { DT = D; } 175 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 176 void verifyRemoved(const Value *) const; 177 }; 178} 179 180namespace llvm { 181template <> struct DenseMapInfo<Expression> { 182 static inline Expression getEmptyKey() { 183 return Expression(Expression::EMPTY); 184 } 185 186 static inline Expression getTombstoneKey() { 187 return Expression(Expression::TOMBSTONE); 188 } 189 190 static unsigned getHashValue(const Expression e) { 191 unsigned hash = e.opcode; 192 193 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 194 (unsigned)((uintptr_t)e.type >> 9)); 195 196 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 197 E = e.varargs.end(); I != E; ++I) 198 hash = *I + hash * 37; 199 200 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 201 (unsigned)((uintptr_t)e.function >> 9)) + 202 hash * 37; 203 204 return hash; 205 } 206 static bool isEqual(const Expression &LHS, const Expression &RHS) { 207 return LHS == RHS; 208 } 209}; 210 211} 212 213//===----------------------------------------------------------------------===// 214// ValueTable Internal Functions 215//===----------------------------------------------------------------------===// 216 217Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 218 if (isa<ICmpInst>(C)) { 219 switch (C->getPredicate()) { 220 default: // THIS SHOULD NEVER HAPPEN 221 llvm_unreachable("Comparison with unknown predicate?"); 222 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 223 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 224 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 225 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 226 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 227 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 228 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 229 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 230 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 231 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 232 } 233 } else { 234 switch (C->getPredicate()) { 235 default: // THIS SHOULD NEVER HAPPEN 236 llvm_unreachable("Comparison with unknown predicate?"); 237 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 238 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 239 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 240 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 241 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 242 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 243 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 244 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 245 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 246 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 247 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 248 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 249 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 250 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 251 } 252 } 253} 254 255Expression ValueTable::create_expression(CallInst* C) { 256 Expression e; 257 258 e.type = C->getType(); 259 e.function = C->getCalledFunction(); 260 e.opcode = Expression::CALL; 261 262 CallSite CS(C); 263 for (CallInst::op_iterator I = CS.arg_begin(), E = CS.arg_end(); 264 I != E; ++I) 265 e.varargs.push_back(lookup_or_add(*I)); 266 267 return e; 268} 269 270Expression ValueTable::create_expression(BinaryOperator* BO) { 271 Expression e; 272 e.varargs.push_back(lookup_or_add(BO->getOperand(0))); 273 e.varargs.push_back(lookup_or_add(BO->getOperand(1))); 274 e.function = 0; 275 e.type = BO->getType(); 276 e.opcode = static_cast<Expression::ExpressionOpcode>(BO->getOpcode()); 277 278 return e; 279} 280 281Expression ValueTable::create_expression(CmpInst* C) { 282 Expression e; 283 284 e.varargs.push_back(lookup_or_add(C->getOperand(0))); 285 e.varargs.push_back(lookup_or_add(C->getOperand(1))); 286 e.function = 0; 287 e.type = C->getType(); 288 e.opcode = getOpcode(C); 289 290 return e; 291} 292 293Expression ValueTable::create_expression(CastInst* C) { 294 Expression e; 295 296 e.varargs.push_back(lookup_or_add(C->getOperand(0))); 297 e.function = 0; 298 e.type = C->getType(); 299 e.opcode = static_cast<Expression::ExpressionOpcode>(C->getOpcode()); 300 301 return e; 302} 303 304Expression ValueTable::create_expression(ShuffleVectorInst* S) { 305 Expression e; 306 307 e.varargs.push_back(lookup_or_add(S->getOperand(0))); 308 e.varargs.push_back(lookup_or_add(S->getOperand(1))); 309 e.varargs.push_back(lookup_or_add(S->getOperand(2))); 310 e.function = 0; 311 e.type = S->getType(); 312 e.opcode = Expression::SHUFFLE; 313 314 return e; 315} 316 317Expression ValueTable::create_expression(ExtractElementInst* E) { 318 Expression e; 319 320 e.varargs.push_back(lookup_or_add(E->getOperand(0))); 321 e.varargs.push_back(lookup_or_add(E->getOperand(1))); 322 e.function = 0; 323 e.type = E->getType(); 324 e.opcode = Expression::EXTRACT; 325 326 return e; 327} 328 329Expression ValueTable::create_expression(InsertElementInst* I) { 330 Expression e; 331 332 e.varargs.push_back(lookup_or_add(I->getOperand(0))); 333 e.varargs.push_back(lookup_or_add(I->getOperand(1))); 334 e.varargs.push_back(lookup_or_add(I->getOperand(2))); 335 e.function = 0; 336 e.type = I->getType(); 337 e.opcode = Expression::INSERT; 338 339 return e; 340} 341 342Expression ValueTable::create_expression(SelectInst* I) { 343 Expression e; 344 345 e.varargs.push_back(lookup_or_add(I->getCondition())); 346 e.varargs.push_back(lookup_or_add(I->getTrueValue())); 347 e.varargs.push_back(lookup_or_add(I->getFalseValue())); 348 e.function = 0; 349 e.type = I->getType(); 350 e.opcode = Expression::SELECT; 351 352 return e; 353} 354 355Expression ValueTable::create_expression(GetElementPtrInst* G) { 356 Expression e; 357 358 e.varargs.push_back(lookup_or_add(G->getPointerOperand())); 359 e.function = 0; 360 e.type = G->getType(); 361 e.opcode = Expression::GEP; 362 363 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 364 I != E; ++I) 365 e.varargs.push_back(lookup_or_add(*I)); 366 367 return e; 368} 369 370Expression ValueTable::create_expression(ExtractValueInst* E) { 371 Expression e; 372 373 e.varargs.push_back(lookup_or_add(E->getAggregateOperand())); 374 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 375 II != IE; ++II) 376 e.varargs.push_back(*II); 377 e.function = 0; 378 e.type = E->getType(); 379 e.opcode = Expression::EXTRACTVALUE; 380 381 return e; 382} 383 384Expression ValueTable::create_expression(InsertValueInst* E) { 385 Expression e; 386 387 e.varargs.push_back(lookup_or_add(E->getAggregateOperand())); 388 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand())); 389 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 390 II != IE; ++II) 391 e.varargs.push_back(*II); 392 e.function = 0; 393 e.type = E->getType(); 394 e.opcode = Expression::INSERTVALUE; 395 396 return e; 397} 398 399//===----------------------------------------------------------------------===// 400// ValueTable External Functions 401//===----------------------------------------------------------------------===// 402 403/// add - Insert a value into the table with a specified value number. 404void ValueTable::add(Value *V, uint32_t num) { 405 valueNumbering.insert(std::make_pair(V, num)); 406} 407 408uint32_t ValueTable::lookup_or_add_call(CallInst* C) { 409 if (AA->doesNotAccessMemory(C)) { 410 Expression exp = create_expression(C); 411 uint32_t& e = expressionNumbering[exp]; 412 if (!e) e = nextValueNumber++; 413 valueNumbering[C] = e; 414 return e; 415 } else if (AA->onlyReadsMemory(C)) { 416 Expression exp = create_expression(C); 417 uint32_t& e = expressionNumbering[exp]; 418 if (!e) { 419 e = nextValueNumber++; 420 valueNumbering[C] = e; 421 return e; 422 } 423 if (!MD) { 424 e = nextValueNumber++; 425 valueNumbering[C] = e; 426 return e; 427 } 428 429 MemDepResult local_dep = MD->getDependency(C); 430 431 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 432 valueNumbering[C] = nextValueNumber; 433 return nextValueNumber++; 434 } 435 436 if (local_dep.isDef()) { 437 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 438 439 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { 440 valueNumbering[C] = nextValueNumber; 441 return nextValueNumber++; 442 } 443 444 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 445 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 446 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i)); 447 if (c_vn != cd_vn) { 448 valueNumbering[C] = nextValueNumber; 449 return nextValueNumber++; 450 } 451 } 452 453 uint32_t v = lookup_or_add(local_cdep); 454 valueNumbering[C] = v; 455 return v; 456 } 457 458 // Non-local case. 459 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 460 MD->getNonLocalCallDependency(CallSite(C)); 461 // FIXME: call/call dependencies for readonly calls should return def, not 462 // clobber! Move the checking logic to MemDep! 463 CallInst* cdep = 0; 464 465 // Check to see if we have a single dominating call instruction that is 466 // identical to C. 467 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 468 const NonLocalDepEntry *I = &deps[i]; 469 // Ignore non-local dependencies. 470 if (I->getResult().isNonLocal()) 471 continue; 472 473 // We don't handle non-depedencies. If we already have a call, reject 474 // instruction dependencies. 475 if (I->getResult().isClobber() || cdep != 0) { 476 cdep = 0; 477 break; 478 } 479 480 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); 481 // FIXME: All duplicated with non-local case. 482 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ 483 cdep = NonLocalDepCall; 484 continue; 485 } 486 487 cdep = 0; 488 break; 489 } 490 491 if (!cdep) { 492 valueNumbering[C] = nextValueNumber; 493 return nextValueNumber++; 494 } 495 496 if (cdep->getNumArgOperands() != C->getNumArgOperands()) { 497 valueNumbering[C] = nextValueNumber; 498 return nextValueNumber++; 499 } 500 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 501 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 502 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i)); 503 if (c_vn != cd_vn) { 504 valueNumbering[C] = nextValueNumber; 505 return nextValueNumber++; 506 } 507 } 508 509 uint32_t v = lookup_or_add(cdep); 510 valueNumbering[C] = v; 511 return v; 512 513 } else { 514 valueNumbering[C] = nextValueNumber; 515 return nextValueNumber++; 516 } 517} 518 519/// lookup_or_add - Returns the value number for the specified value, assigning 520/// it a new number if it did not have one before. 521uint32_t ValueTable::lookup_or_add(Value *V) { 522 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 523 if (VI != valueNumbering.end()) 524 return VI->second; 525 526 if (!isa<Instruction>(V)) { 527 valueNumbering[V] = nextValueNumber; 528 return nextValueNumber++; 529 } 530 531 Instruction* I = cast<Instruction>(V); 532 Expression exp; 533 switch (I->getOpcode()) { 534 case Instruction::Call: 535 return lookup_or_add_call(cast<CallInst>(I)); 536 case Instruction::Add: 537 case Instruction::FAdd: 538 case Instruction::Sub: 539 case Instruction::FSub: 540 case Instruction::Mul: 541 case Instruction::FMul: 542 case Instruction::UDiv: 543 case Instruction::SDiv: 544 case Instruction::FDiv: 545 case Instruction::URem: 546 case Instruction::SRem: 547 case Instruction::FRem: 548 case Instruction::Shl: 549 case Instruction::LShr: 550 case Instruction::AShr: 551 case Instruction::And: 552 case Instruction::Or : 553 case Instruction::Xor: 554 exp = create_expression(cast<BinaryOperator>(I)); 555 break; 556 case Instruction::ICmp: 557 case Instruction::FCmp: 558 exp = create_expression(cast<CmpInst>(I)); 559 break; 560 case Instruction::Trunc: 561 case Instruction::ZExt: 562 case Instruction::SExt: 563 case Instruction::FPToUI: 564 case Instruction::FPToSI: 565 case Instruction::UIToFP: 566 case Instruction::SIToFP: 567 case Instruction::FPTrunc: 568 case Instruction::FPExt: 569 case Instruction::PtrToInt: 570 case Instruction::IntToPtr: 571 case Instruction::BitCast: 572 exp = create_expression(cast<CastInst>(I)); 573 break; 574 case Instruction::Select: 575 exp = create_expression(cast<SelectInst>(I)); 576 break; 577 case Instruction::ExtractElement: 578 exp = create_expression(cast<ExtractElementInst>(I)); 579 break; 580 case Instruction::InsertElement: 581 exp = create_expression(cast<InsertElementInst>(I)); 582 break; 583 case Instruction::ShuffleVector: 584 exp = create_expression(cast<ShuffleVectorInst>(I)); 585 break; 586 case Instruction::ExtractValue: 587 exp = create_expression(cast<ExtractValueInst>(I)); 588 break; 589 case Instruction::InsertValue: 590 exp = create_expression(cast<InsertValueInst>(I)); 591 break; 592 case Instruction::GetElementPtr: 593 exp = create_expression(cast<GetElementPtrInst>(I)); 594 break; 595 default: 596 valueNumbering[V] = nextValueNumber; 597 return nextValueNumber++; 598 } 599 600 uint32_t& e = expressionNumbering[exp]; 601 if (!e) e = nextValueNumber++; 602 valueNumbering[V] = e; 603 return e; 604} 605 606/// lookup - Returns the value number of the specified value. Fails if 607/// the value has not yet been numbered. 608uint32_t ValueTable::lookup(Value *V) const { 609 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); 610 assert(VI != valueNumbering.end() && "Value not numbered?"); 611 return VI->second; 612} 613 614/// clear - Remove all entries from the ValueTable 615void ValueTable::clear() { 616 valueNumbering.clear(); 617 expressionNumbering.clear(); 618 nextValueNumber = 1; 619} 620 621/// erase - Remove a value from the value numbering 622void ValueTable::erase(Value *V) { 623 valueNumbering.erase(V); 624} 625 626/// verifyRemoved - Verify that the value is removed from all internal data 627/// structures. 628void ValueTable::verifyRemoved(const Value *V) const { 629 for (DenseMap<Value*, uint32_t>::const_iterator 630 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 631 assert(I->first != V && "Inst still occurs in value numbering map!"); 632 } 633} 634 635//===----------------------------------------------------------------------===// 636// GVN Pass 637//===----------------------------------------------------------------------===// 638 639namespace { 640 struct ValueNumberScope { 641 ValueNumberScope* parent; 642 DenseMap<uint32_t, Value*> table; 643 644 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 645 }; 646} 647 648namespace { 649 650 class GVN : public FunctionPass { 651 bool runOnFunction(Function &F); 652 public: 653 static char ID; // Pass identification, replacement for typeid 654 explicit GVN(bool noloads = false) 655 : FunctionPass(ID), NoLoads(noloads), MD(0) { 656 initializeGVNPass(*PassRegistry::getPassRegistry()); 657 } 658 659 private: 660 bool NoLoads; 661 MemoryDependenceAnalysis *MD; 662 DominatorTree *DT; 663 const TargetData* TD; 664 665 ValueTable VN; 666 667 /// NumberTable - A mapping from value numers to lists of Value*'s that 668 /// have that value number. Use lookupNumber to query it. 669 DenseMap<uint32_t, std::pair<Value*, void*> > NumberTable; 670 BumpPtrAllocator TableAllocator; 671 672 /// insert_table - Push a new Value to the NumberTable onto the list for 673 /// its value number. 674 void insert_table(uint32_t N, Value *V) { 675 std::pair<Value*, void*>& Curr = NumberTable[N]; 676 if (!Curr.first) { 677 Curr.first = V; 678 return; 679 } 680 681 std::pair<Value*, void*>* Node = 682 TableAllocator.Allocate<std::pair<Value*, void*> >(); 683 Node->first = V; 684 Node->second = Curr.second; 685 Curr.second = Node; 686 } 687 688 /// erase_table - Scan the list of values corresponding to a given value 689 /// number, and remove the given value if encountered. 690 void erase_table(uint32_t N, Value *V) { 691 std::pair<Value*, void*>* Prev = 0; 692 std::pair<Value*, void*>* Curr = &NumberTable[N]; 693 694 while (Curr->first != V) { 695 Prev = Curr; 696 Curr = static_cast<std::pair<Value*, void*>*>(Curr->second); 697 } 698 699 if (Prev) { 700 Prev->second = Curr->second; 701 } else { 702 if (!Curr->second) { 703 Curr->first = 0; 704 } else { 705 std::pair<Value*, void*>* Next = 706 static_cast<std::pair<Value*, void*>*>(Curr->second); 707 Curr->first = Next->first; 708 Curr->second = Next->second; 709 } 710 } 711 } 712 713 // List of critical edges to be split between iterations. 714 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 715 716 // This transformation requires dominator postdominator info 717 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 718 AU.addRequired<DominatorTree>(); 719 if (!NoLoads) 720 AU.addRequired<MemoryDependenceAnalysis>(); 721 AU.addRequired<AliasAnalysis>(); 722 723 AU.addPreserved<DominatorTree>(); 724 AU.addPreserved<AliasAnalysis>(); 725 } 726 727 // Helper fuctions 728 // FIXME: eliminate or document these better 729 bool processLoad(LoadInst* L, 730 SmallVectorImpl<Instruction*> &toErase); 731 bool processInstruction(Instruction *I, 732 SmallVectorImpl<Instruction*> &toErase); 733 bool processNonLocalLoad(LoadInst* L, 734 SmallVectorImpl<Instruction*> &toErase); 735 bool processBlock(BasicBlock *BB); 736 void dump(DenseMap<uint32_t, Value*>& d); 737 bool iterateOnFunction(Function &F); 738 bool performPRE(Function& F); 739 Value *lookupNumber(BasicBlock *BB, uint32_t num); 740 void cleanupGlobalSets(); 741 void verifyRemoved(const Instruction *I) const; 742 bool splitCriticalEdges(); 743 }; 744 745 char GVN::ID = 0; 746} 747 748// createGVNPass - The public interface to this file... 749FunctionPass *llvm::createGVNPass(bool NoLoads) { 750 return new GVN(NoLoads); 751} 752 753INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) 754INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) 755INITIALIZE_PASS_DEPENDENCY(DominatorTree) 756INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 757INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) 758 759void GVN::dump(DenseMap<uint32_t, Value*>& d) { 760 errs() << "{\n"; 761 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 762 E = d.end(); I != E; ++I) { 763 errs() << I->first << "\n"; 764 I->second->dump(); 765 } 766 errs() << "}\n"; 767} 768 769/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 770/// we're analyzing is fully available in the specified block. As we go, keep 771/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 772/// map is actually a tri-state map with the following values: 773/// 0) we know the block *is not* fully available. 774/// 1) we know the block *is* fully available. 775/// 2) we do not know whether the block is fully available or not, but we are 776/// currently speculating that it will be. 777/// 3) we are speculating for this block and have used that to speculate for 778/// other blocks. 779static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 780 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 781 // Optimistically assume that the block is fully available and check to see 782 // if we already know about this block in one lookup. 783 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 784 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 785 786 // If the entry already existed for this block, return the precomputed value. 787 if (!IV.second) { 788 // If this is a speculative "available" value, mark it as being used for 789 // speculation of other blocks. 790 if (IV.first->second == 2) 791 IV.first->second = 3; 792 return IV.first->second != 0; 793 } 794 795 // Otherwise, see if it is fully available in all predecessors. 796 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 797 798 // If this block has no predecessors, it isn't live-in here. 799 if (PI == PE) 800 goto SpeculationFailure; 801 802 for (; PI != PE; ++PI) 803 // If the value isn't fully available in one of our predecessors, then it 804 // isn't fully available in this block either. Undo our previous 805 // optimistic assumption and bail out. 806 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 807 goto SpeculationFailure; 808 809 return true; 810 811// SpeculationFailure - If we get here, we found out that this is not, after 812// all, a fully-available block. We have a problem if we speculated on this and 813// used the speculation to mark other blocks as available. 814SpeculationFailure: 815 char &BBVal = FullyAvailableBlocks[BB]; 816 817 // If we didn't speculate on this, just return with it set to false. 818 if (BBVal == 2) { 819 BBVal = 0; 820 return false; 821 } 822 823 // If we did speculate on this value, we could have blocks set to 1 that are 824 // incorrect. Walk the (transitive) successors of this block and mark them as 825 // 0 if set to one. 826 SmallVector<BasicBlock*, 32> BBWorklist; 827 BBWorklist.push_back(BB); 828 829 do { 830 BasicBlock *Entry = BBWorklist.pop_back_val(); 831 // Note that this sets blocks to 0 (unavailable) if they happen to not 832 // already be in FullyAvailableBlocks. This is safe. 833 char &EntryVal = FullyAvailableBlocks[Entry]; 834 if (EntryVal == 0) continue; // Already unavailable. 835 836 // Mark as unavailable. 837 EntryVal = 0; 838 839 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 840 BBWorklist.push_back(*I); 841 } while (!BBWorklist.empty()); 842 843 return false; 844} 845 846 847/// CanCoerceMustAliasedValueToLoad - Return true if 848/// CoerceAvailableValueToLoadType will succeed. 849static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 850 const Type *LoadTy, 851 const TargetData &TD) { 852 // If the loaded or stored value is an first class array or struct, don't try 853 // to transform them. We need to be able to bitcast to integer. 854 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 855 StoredVal->getType()->isStructTy() || 856 StoredVal->getType()->isArrayTy()) 857 return false; 858 859 // The store has to be at least as big as the load. 860 if (TD.getTypeSizeInBits(StoredVal->getType()) < 861 TD.getTypeSizeInBits(LoadTy)) 862 return false; 863 864 return true; 865} 866 867 868/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 869/// then a load from a must-aliased pointer of a different type, try to coerce 870/// the stored value. LoadedTy is the type of the load we want to replace and 871/// InsertPt is the place to insert new instructions. 872/// 873/// If we can't do it, return null. 874static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 875 const Type *LoadedTy, 876 Instruction *InsertPt, 877 const TargetData &TD) { 878 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 879 return 0; 880 881 const Type *StoredValTy = StoredVal->getType(); 882 883 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy); 884 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 885 886 // If the store and reload are the same size, we can always reuse it. 887 if (StoreSize == LoadSize) { 888 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) { 889 // Pointer to Pointer -> use bitcast. 890 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 891 } 892 893 // Convert source pointers to integers, which can be bitcast. 894 if (StoredValTy->isPointerTy()) { 895 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 896 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 897 } 898 899 const Type *TypeToCastTo = LoadedTy; 900 if (TypeToCastTo->isPointerTy()) 901 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 902 903 if (StoredValTy != TypeToCastTo) 904 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 905 906 // Cast to pointer if the load needs a pointer type. 907 if (LoadedTy->isPointerTy()) 908 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 909 910 return StoredVal; 911 } 912 913 // If the loaded value is smaller than the available value, then we can 914 // extract out a piece from it. If the available value is too small, then we 915 // can't do anything. 916 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 917 918 // Convert source pointers to integers, which can be manipulated. 919 if (StoredValTy->isPointerTy()) { 920 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 921 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 922 } 923 924 // Convert vectors and fp to integer, which can be manipulated. 925 if (!StoredValTy->isIntegerTy()) { 926 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 927 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 928 } 929 930 // If this is a big-endian system, we need to shift the value down to the low 931 // bits so that a truncate will work. 932 if (TD.isBigEndian()) { 933 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 934 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 935 } 936 937 // Truncate the integer to the right size now. 938 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 939 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 940 941 if (LoadedTy == NewIntTy) 942 return StoredVal; 943 944 // If the result is a pointer, inttoptr. 945 if (LoadedTy->isPointerTy()) 946 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 947 948 // Otherwise, bitcast. 949 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 950} 951 952/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 953/// memdep query of a load that ends up being a clobbering memory write (store, 954/// memset, memcpy, memmove). This means that the write *may* provide bits used 955/// by the load but we can't be sure because the pointers don't mustalias. 956/// 957/// Check this case to see if there is anything more we can do before we give 958/// up. This returns -1 if we have to give up, or a byte number in the stored 959/// value of the piece that feeds the load. 960static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr, 961 Value *WritePtr, 962 uint64_t WriteSizeInBits, 963 const TargetData &TD) { 964 // If the loaded or stored value is an first class array or struct, don't try 965 // to transform them. We need to be able to bitcast to integer. 966 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 967 return -1; 968 969 int64_t StoreOffset = 0, LoadOffset = 0; 970 Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr, StoreOffset,TD); 971 Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, TD); 972 if (StoreBase != LoadBase) 973 return -1; 974 975 // If the load and store are to the exact same address, they should have been 976 // a must alias. AA must have gotten confused. 977 // FIXME: Study to see if/when this happens. One case is forwarding a memset 978 // to a load from the base of the memset. 979#if 0 980 if (LoadOffset == StoreOffset) { 981 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 982 << "Base = " << *StoreBase << "\n" 983 << "Store Ptr = " << *WritePtr << "\n" 984 << "Store Offs = " << StoreOffset << "\n" 985 << "Load Ptr = " << *LoadPtr << "\n"; 986 abort(); 987 } 988#endif 989 990 // If the load and store don't overlap at all, the store doesn't provide 991 // anything to the load. In this case, they really don't alias at all, AA 992 // must have gotten confused. 993 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); 994 995 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 996 return -1; 997 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 998 LoadSize >>= 3; 999 1000 1001 bool isAAFailure = false; 1002 if (StoreOffset < LoadOffset) 1003 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1004 else 1005 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1006 1007 if (isAAFailure) { 1008#if 0 1009 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1010 << "Base = " << *StoreBase << "\n" 1011 << "Store Ptr = " << *WritePtr << "\n" 1012 << "Store Offs = " << StoreOffset << "\n" 1013 << "Load Ptr = " << *LoadPtr << "\n"; 1014 abort(); 1015#endif 1016 return -1; 1017 } 1018 1019 // If the Load isn't completely contained within the stored bits, we don't 1020 // have all the bits to feed it. We could do something crazy in the future 1021 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1022 // valuable. 1023 if (StoreOffset > LoadOffset || 1024 StoreOffset+StoreSize < LoadOffset+LoadSize) 1025 return -1; 1026 1027 // Okay, we can do this transformation. Return the number of bytes into the 1028 // store that the load is. 1029 return LoadOffset-StoreOffset; 1030} 1031 1032/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1033/// memdep query of a load that ends up being a clobbering store. 1034static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr, 1035 StoreInst *DepSI, 1036 const TargetData &TD) { 1037 // Cannot handle reading from store of first-class aggregate yet. 1038 if (DepSI->getValueOperand()->getType()->isStructTy() || 1039 DepSI->getValueOperand()->getType()->isArrayTy()) 1040 return -1; 1041 1042 Value *StorePtr = DepSI->getPointerOperand(); 1043 uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType()); 1044 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1045 StorePtr, StoreSize, TD); 1046} 1047 1048static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr, 1049 MemIntrinsic *MI, 1050 const TargetData &TD) { 1051 // If the mem operation is a non-constant size, we can't handle it. 1052 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 1053 if (SizeCst == 0) return -1; 1054 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 1055 1056 // If this is memset, we just need to see if the offset is valid in the size 1057 // of the memset.. 1058 if (MI->getIntrinsicID() == Intrinsic::memset) 1059 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 1060 MemSizeInBits, TD); 1061 1062 // If we have a memcpy/memmove, the only case we can handle is if this is a 1063 // copy from constant memory. In that case, we can read directly from the 1064 // constant memory. 1065 MemTransferInst *MTI = cast<MemTransferInst>(MI); 1066 1067 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 1068 if (Src == 0) return -1; 1069 1070 GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src)); 1071 if (GV == 0 || !GV->isConstant()) return -1; 1072 1073 // See if the access is within the bounds of the transfer. 1074 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1075 MI->getDest(), MemSizeInBits, TD); 1076 if (Offset == -1) 1077 return Offset; 1078 1079 // Otherwise, see if we can constant fold a load from the constant with the 1080 // offset applied as appropriate. 1081 Src = ConstantExpr::getBitCast(Src, 1082 llvm::Type::getInt8PtrTy(Src->getContext())); 1083 Constant *OffsetCst = 1084 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1085 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1086 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1087 if (ConstantFoldLoadFromConstPtr(Src, &TD)) 1088 return Offset; 1089 return -1; 1090} 1091 1092 1093/// GetStoreValueForLoad - This function is called when we have a 1094/// memdep query of a load that ends up being a clobbering store. This means 1095/// that the store *may* provide bits used by the load but we can't be sure 1096/// because the pointers don't mustalias. Check this case to see if there is 1097/// anything more we can do before we give up. 1098static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1099 const Type *LoadTy, 1100 Instruction *InsertPt, const TargetData &TD){ 1101 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1102 1103 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; 1104 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8; 1105 1106 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1107 1108 // Compute which bits of the stored value are being used by the load. Convert 1109 // to an integer type to start with. 1110 if (SrcVal->getType()->isPointerTy()) 1111 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp"); 1112 if (!SrcVal->getType()->isIntegerTy()) 1113 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1114 "tmp"); 1115 1116 // Shift the bits to the least significant depending on endianness. 1117 unsigned ShiftAmt; 1118 if (TD.isLittleEndian()) 1119 ShiftAmt = Offset*8; 1120 else 1121 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1122 1123 if (ShiftAmt) 1124 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp"); 1125 1126 if (LoadSize != StoreSize) 1127 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1128 "tmp"); 1129 1130 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1131} 1132 1133/// GetMemInstValueForLoad - This function is called when we have a 1134/// memdep query of a load that ends up being a clobbering mem intrinsic. 1135static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1136 const Type *LoadTy, Instruction *InsertPt, 1137 const TargetData &TD){ 1138 LLVMContext &Ctx = LoadTy->getContext(); 1139 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1140 1141 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1142 1143 // We know that this method is only called when the mem transfer fully 1144 // provides the bits for the load. 1145 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1146 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1147 // independently of what the offset is. 1148 Value *Val = MSI->getValue(); 1149 if (LoadSize != 1) 1150 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1151 1152 Value *OneElt = Val; 1153 1154 // Splat the value out to the right number of bits. 1155 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1156 // If we can double the number of bytes set, do it. 1157 if (NumBytesSet*2 <= LoadSize) { 1158 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1159 Val = Builder.CreateOr(Val, ShVal); 1160 NumBytesSet <<= 1; 1161 continue; 1162 } 1163 1164 // Otherwise insert one byte at a time. 1165 Value *ShVal = Builder.CreateShl(Val, 1*8); 1166 Val = Builder.CreateOr(OneElt, ShVal); 1167 ++NumBytesSet; 1168 } 1169 1170 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 1171 } 1172 1173 // Otherwise, this is a memcpy/memmove from a constant global. 1174 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 1175 Constant *Src = cast<Constant>(MTI->getSource()); 1176 1177 // Otherwise, see if we can constant fold a load from the constant with the 1178 // offset applied as appropriate. 1179 Src = ConstantExpr::getBitCast(Src, 1180 llvm::Type::getInt8PtrTy(Src->getContext())); 1181 Constant *OffsetCst = 1182 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1183 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1); 1184 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1185 return ConstantFoldLoadFromConstPtr(Src, &TD); 1186} 1187 1188namespace { 1189 1190struct AvailableValueInBlock { 1191 /// BB - The basic block in question. 1192 BasicBlock *BB; 1193 enum ValType { 1194 SimpleVal, // A simple offsetted value that is accessed. 1195 MemIntrin // A memory intrinsic which is loaded from. 1196 }; 1197 1198 /// V - The value that is live out of the block. 1199 PointerIntPair<Value *, 1, ValType> Val; 1200 1201 /// Offset - The byte offset in Val that is interesting for the load query. 1202 unsigned Offset; 1203 1204 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1205 unsigned Offset = 0) { 1206 AvailableValueInBlock Res; 1207 Res.BB = BB; 1208 Res.Val.setPointer(V); 1209 Res.Val.setInt(SimpleVal); 1210 Res.Offset = Offset; 1211 return Res; 1212 } 1213 1214 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 1215 unsigned Offset = 0) { 1216 AvailableValueInBlock Res; 1217 Res.BB = BB; 1218 Res.Val.setPointer(MI); 1219 Res.Val.setInt(MemIntrin); 1220 Res.Offset = Offset; 1221 return Res; 1222 } 1223 1224 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 1225 Value *getSimpleValue() const { 1226 assert(isSimpleValue() && "Wrong accessor"); 1227 return Val.getPointer(); 1228 } 1229 1230 MemIntrinsic *getMemIntrinValue() const { 1231 assert(!isSimpleValue() && "Wrong accessor"); 1232 return cast<MemIntrinsic>(Val.getPointer()); 1233 } 1234 1235 /// MaterializeAdjustedValue - Emit code into this block to adjust the value 1236 /// defined here to the specified type. This handles various coercion cases. 1237 Value *MaterializeAdjustedValue(const Type *LoadTy, 1238 const TargetData *TD) const { 1239 Value *Res; 1240 if (isSimpleValue()) { 1241 Res = getSimpleValue(); 1242 if (Res->getType() != LoadTy) { 1243 assert(TD && "Need target data to handle type mismatch case"); 1244 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), 1245 *TD); 1246 1247 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1248 << *getSimpleValue() << '\n' 1249 << *Res << '\n' << "\n\n\n"); 1250 } 1251 } else { 1252 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, 1253 LoadTy, BB->getTerminator(), *TD); 1254 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1255 << " " << *getMemIntrinValue() << '\n' 1256 << *Res << '\n' << "\n\n\n"); 1257 } 1258 return Res; 1259 } 1260}; 1261 1262} 1263 1264/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1265/// construct SSA form, allowing us to eliminate LI. This returns the value 1266/// that should be used at LI's definition site. 1267static Value *ConstructSSAForLoadSet(LoadInst *LI, 1268 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1269 const TargetData *TD, 1270 const DominatorTree &DT, 1271 AliasAnalysis *AA) { 1272 // Check for the fully redundant, dominating load case. In this case, we can 1273 // just use the dominating value directly. 1274 if (ValuesPerBlock.size() == 1 && 1275 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent())) 1276 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD); 1277 1278 // Otherwise, we have to construct SSA form. 1279 SmallVector<PHINode*, 8> NewPHIs; 1280 SSAUpdater SSAUpdate(&NewPHIs); 1281 SSAUpdate.Initialize(LI->getType(), LI->getName()); 1282 1283 const Type *LoadTy = LI->getType(); 1284 1285 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1286 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1287 BasicBlock *BB = AV.BB; 1288 1289 if (SSAUpdate.HasValueForBlock(BB)) 1290 continue; 1291 1292 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD)); 1293 } 1294 1295 // Perform PHI construction. 1296 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1297 1298 // If new PHI nodes were created, notify alias analysis. 1299 if (V->getType()->isPointerTy()) 1300 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1301 AA->copyValue(LI, NewPHIs[i]); 1302 1303 return V; 1304} 1305 1306static bool isLifetimeStart(const Instruction *Inst) { 1307 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1308 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1309 return false; 1310} 1311 1312/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1313/// non-local by performing PHI construction. 1314bool GVN::processNonLocalLoad(LoadInst *LI, 1315 SmallVectorImpl<Instruction*> &toErase) { 1316 // Find the non-local dependencies of the load. 1317 SmallVector<NonLocalDepResult, 64> Deps; 1318 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI); 1319 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps); 1320 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: " 1321 // << Deps.size() << *LI << '\n'); 1322 1323 // If we had to process more than one hundred blocks to find the 1324 // dependencies, this load isn't worth worrying about. Optimizing 1325 // it will be too expensive. 1326 if (Deps.size() > 100) 1327 return false; 1328 1329 // If we had a phi translation failure, we'll have a single entry which is a 1330 // clobber in the current block. Reject this early. 1331 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) { 1332 DEBUG( 1333 dbgs() << "GVN: non-local load "; 1334 WriteAsOperand(dbgs(), LI); 1335 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n'; 1336 ); 1337 return false; 1338 } 1339 1340 // Filter out useless results (non-locals, etc). Keep track of the blocks 1341 // where we have a value available in repl, also keep track of whether we see 1342 // dependencies that produce an unknown value for the load (such as a call 1343 // that could potentially clobber the load). 1344 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1345 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1346 1347 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1348 BasicBlock *DepBB = Deps[i].getBB(); 1349 MemDepResult DepInfo = Deps[i].getResult(); 1350 1351 if (DepInfo.isClobber()) { 1352 // The address being loaded in this non-local block may not be the same as 1353 // the pointer operand of the load if PHI translation occurs. Make sure 1354 // to consider the right address. 1355 Value *Address = Deps[i].getAddress(); 1356 1357 // If the dependence is to a store that writes to a superset of the bits 1358 // read by the load, we can extract the bits we need for the load from the 1359 // stored value. 1360 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1361 if (TD && Address) { 1362 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, 1363 DepSI, *TD); 1364 if (Offset != -1) { 1365 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1366 DepSI->getValueOperand(), 1367 Offset)); 1368 continue; 1369 } 1370 } 1371 } 1372 1373 // If the clobbering value is a memset/memcpy/memmove, see if we can 1374 // forward a value on from it. 1375 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1376 if (TD && Address) { 1377 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, 1378 DepMI, *TD); 1379 if (Offset != -1) { 1380 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1381 Offset)); 1382 continue; 1383 } 1384 } 1385 } 1386 1387 UnavailableBlocks.push_back(DepBB); 1388 continue; 1389 } 1390 1391 Instruction *DepInst = DepInfo.getInst(); 1392 1393 // Loading the allocation -> undef. 1394 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) || 1395 // Loading immediately after lifetime begin -> undef. 1396 isLifetimeStart(DepInst)) { 1397 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1398 UndefValue::get(LI->getType()))); 1399 continue; 1400 } 1401 1402 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1403 // Reject loads and stores that are to the same address but are of 1404 // different types if we have to. 1405 if (S->getValueOperand()->getType() != LI->getType()) { 1406 // If the stored value is larger or equal to the loaded value, we can 1407 // reuse it. 1408 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(), 1409 LI->getType(), *TD)) { 1410 UnavailableBlocks.push_back(DepBB); 1411 continue; 1412 } 1413 } 1414 1415 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1416 S->getValueOperand())); 1417 continue; 1418 } 1419 1420 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1421 // If the types mismatch and we can't handle it, reject reuse of the load. 1422 if (LD->getType() != LI->getType()) { 1423 // If the stored value is larger or equal to the loaded value, we can 1424 // reuse it. 1425 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1426 UnavailableBlocks.push_back(DepBB); 1427 continue; 1428 } 1429 } 1430 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1431 continue; 1432 } 1433 1434 UnavailableBlocks.push_back(DepBB); 1435 continue; 1436 } 1437 1438 // If we have no predecessors that produce a known value for this load, exit 1439 // early. 1440 if (ValuesPerBlock.empty()) return false; 1441 1442 // If all of the instructions we depend on produce a known value for this 1443 // load, then it is fully redundant and we can use PHI insertion to compute 1444 // its value. Insert PHIs and remove the fully redundant value now. 1445 if (UnavailableBlocks.empty()) { 1446 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1447 1448 // Perform PHI construction. 1449 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1450 VN.getAliasAnalysis()); 1451 LI->replaceAllUsesWith(V); 1452 1453 if (isa<PHINode>(V)) 1454 V->takeName(LI); 1455 if (V->getType()->isPointerTy()) 1456 MD->invalidateCachedPointerInfo(V); 1457 VN.erase(LI); 1458 toErase.push_back(LI); 1459 ++NumGVNLoad; 1460 return true; 1461 } 1462 1463 if (!EnablePRE || !EnableLoadPRE) 1464 return false; 1465 1466 // Okay, we have *some* definitions of the value. This means that the value 1467 // is available in some of our (transitive) predecessors. Lets think about 1468 // doing PRE of this load. This will involve inserting a new load into the 1469 // predecessor when it's not available. We could do this in general, but 1470 // prefer to not increase code size. As such, we only do this when we know 1471 // that we only have to insert *one* load (which means we're basically moving 1472 // the load, not inserting a new one). 1473 1474 SmallPtrSet<BasicBlock *, 4> Blockers; 1475 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1476 Blockers.insert(UnavailableBlocks[i]); 1477 1478 // Lets find first basic block with more than one predecessor. Walk backwards 1479 // through predecessors if needed. 1480 BasicBlock *LoadBB = LI->getParent(); 1481 BasicBlock *TmpBB = LoadBB; 1482 1483 bool isSinglePred = false; 1484 bool allSingleSucc = true; 1485 while (TmpBB->getSinglePredecessor()) { 1486 isSinglePred = true; 1487 TmpBB = TmpBB->getSinglePredecessor(); 1488 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1489 return false; 1490 if (Blockers.count(TmpBB)) 1491 return false; 1492 1493 // If any of these blocks has more than one successor (i.e. if the edge we 1494 // just traversed was critical), then there are other paths through this 1495 // block along which the load may not be anticipated. Hoisting the load 1496 // above this block would be adding the load to execution paths along 1497 // which it was not previously executed. 1498 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1499 return false; 1500 } 1501 1502 assert(TmpBB); 1503 LoadBB = TmpBB; 1504 1505 // FIXME: It is extremely unclear what this loop is doing, other than 1506 // artificially restricting loadpre. 1507 if (isSinglePred) { 1508 bool isHot = false; 1509 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1510 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1511 if (AV.isSimpleValue()) 1512 // "Hot" Instruction is in some loop (because it dominates its dep. 1513 // instruction). 1514 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) 1515 if (DT->dominates(LI, I)) { 1516 isHot = true; 1517 break; 1518 } 1519 } 1520 1521 // We are interested only in "hot" instructions. We don't want to do any 1522 // mis-optimizations here. 1523 if (!isHot) 1524 return false; 1525 } 1526 1527 // Check to see how many predecessors have the loaded value fully 1528 // available. 1529 DenseMap<BasicBlock*, Value*> PredLoads; 1530 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1531 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1532 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1533 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1534 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1535 1536 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit; 1537 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1538 PI != E; ++PI) { 1539 BasicBlock *Pred = *PI; 1540 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) { 1541 continue; 1542 } 1543 PredLoads[Pred] = 0; 1544 1545 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1546 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1547 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1548 << Pred->getName() << "': " << *LI << '\n'); 1549 return false; 1550 } 1551 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB); 1552 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum)); 1553 } 1554 } 1555 if (!NeedToSplit.empty()) { 1556 toSplit.append(NeedToSplit.begin(), NeedToSplit.end()); 1557 return false; 1558 } 1559 1560 // Decide whether PRE is profitable for this load. 1561 unsigned NumUnavailablePreds = PredLoads.size(); 1562 assert(NumUnavailablePreds != 0 && 1563 "Fully available value should be eliminated above!"); 1564 1565 // If this load is unavailable in multiple predecessors, reject it. 1566 // FIXME: If we could restructure the CFG, we could make a common pred with 1567 // all the preds that don't have an available LI and insert a new load into 1568 // that one block. 1569 if (NumUnavailablePreds != 1) 1570 return false; 1571 1572 // Check if the load can safely be moved to all the unavailable predecessors. 1573 bool CanDoPRE = true; 1574 SmallVector<Instruction*, 8> NewInsts; 1575 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1576 E = PredLoads.end(); I != E; ++I) { 1577 BasicBlock *UnavailablePred = I->first; 1578 1579 // Do PHI translation to get its value in the predecessor if necessary. The 1580 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1581 1582 // If all preds have a single successor, then we know it is safe to insert 1583 // the load on the pred (?!?), so we can insert code to materialize the 1584 // pointer if it is not available. 1585 PHITransAddr Address(LI->getPointerOperand(), TD); 1586 Value *LoadPtr = 0; 1587 if (allSingleSucc) { 1588 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1589 *DT, NewInsts); 1590 } else { 1591 Address.PHITranslateValue(LoadBB, UnavailablePred, DT); 1592 LoadPtr = Address.getAddr(); 1593 } 1594 1595 // If we couldn't find or insert a computation of this phi translated value, 1596 // we fail PRE. 1597 if (LoadPtr == 0) { 1598 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1599 << *LI->getPointerOperand() << "\n"); 1600 CanDoPRE = false; 1601 break; 1602 } 1603 1604 // Make sure it is valid to move this load here. We have to watch out for: 1605 // @1 = getelementptr (i8* p, ... 1606 // test p and branch if == 0 1607 // load @1 1608 // It is valid to have the getelementptr before the test, even if p can be 0, 1609 // as getelementptr only does address arithmetic. 1610 // If we are not pushing the value through any multiple-successor blocks 1611 // we do not have this case. Otherwise, check that the load is safe to 1612 // put anywhere; this can be improved, but should be conservatively safe. 1613 if (!allSingleSucc && 1614 // FIXME: REEVALUTE THIS. 1615 !isSafeToLoadUnconditionally(LoadPtr, 1616 UnavailablePred->getTerminator(), 1617 LI->getAlignment(), TD)) { 1618 CanDoPRE = false; 1619 break; 1620 } 1621 1622 I->second = LoadPtr; 1623 } 1624 1625 if (!CanDoPRE) { 1626 while (!NewInsts.empty()) 1627 NewInsts.pop_back_val()->eraseFromParent(); 1628 return false; 1629 } 1630 1631 // Okay, we can eliminate this load by inserting a reload in the predecessor 1632 // and using PHI construction to get the value in the other predecessors, do 1633 // it. 1634 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1635 DEBUG(if (!NewInsts.empty()) 1636 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1637 << *NewInsts.back() << '\n'); 1638 1639 // Assign value numbers to the new instructions. 1640 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { 1641 // FIXME: We really _ought_ to insert these value numbers into their 1642 // parent's availability map. However, in doing so, we risk getting into 1643 // ordering issues. If a block hasn't been processed yet, we would be 1644 // marking a value as AVAIL-IN, which isn't what we intend. 1645 VN.lookup_or_add(NewInsts[i]); 1646 } 1647 1648 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1649 E = PredLoads.end(); I != E; ++I) { 1650 BasicBlock *UnavailablePred = I->first; 1651 Value *LoadPtr = I->second; 1652 1653 Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1654 LI->getAlignment(), 1655 UnavailablePred->getTerminator()); 1656 1657 // Transfer the old load's TBAA tag to the new load. 1658 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) 1659 NewLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1660 1661 // Add the newly created load. 1662 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1663 NewLoad)); 1664 MD->invalidateCachedPointerInfo(LoadPtr); 1665 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); 1666 } 1667 1668 // Perform PHI construction. 1669 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT, 1670 VN.getAliasAnalysis()); 1671 LI->replaceAllUsesWith(V); 1672 if (isa<PHINode>(V)) 1673 V->takeName(LI); 1674 if (V->getType()->isPointerTy()) 1675 MD->invalidateCachedPointerInfo(V); 1676 VN.erase(LI); 1677 toErase.push_back(LI); 1678 ++NumPRELoad; 1679 return true; 1680} 1681 1682/// processLoad - Attempt to eliminate a load, first by eliminating it 1683/// locally, and then attempting non-local elimination if that fails. 1684bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1685 if (!MD) 1686 return false; 1687 1688 if (L->isVolatile()) 1689 return false; 1690 1691 // ... to a pointer that has been loaded from before... 1692 MemDepResult Dep = MD->getDependency(L); 1693 1694 // If the value isn't available, don't do anything! 1695 if (Dep.isClobber()) { 1696 // Check to see if we have something like this: 1697 // store i32 123, i32* %P 1698 // %A = bitcast i32* %P to i8* 1699 // %B = gep i8* %A, i32 1 1700 // %C = load i8* %B 1701 // 1702 // We could do that by recognizing if the clobber instructions are obviously 1703 // a common base + constant offset, and if the previous store (or memset) 1704 // completely covers this load. This sort of thing can happen in bitfield 1705 // access code. 1706 Value *AvailVal = 0; 1707 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1708 if (TD) { 1709 int Offset = AnalyzeLoadFromClobberingStore(L->getType(), 1710 L->getPointerOperand(), 1711 DepSI, *TD); 1712 if (Offset != -1) 1713 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, 1714 L->getType(), L, *TD); 1715 } 1716 1717 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1718 // a value on from it. 1719 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1720 if (TD) { 1721 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), 1722 L->getPointerOperand(), 1723 DepMI, *TD); 1724 if (Offset != -1) 1725 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD); 1726 } 1727 } 1728 1729 if (AvailVal) { 1730 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1731 << *AvailVal << '\n' << *L << "\n\n\n"); 1732 1733 // Replace the load! 1734 L->replaceAllUsesWith(AvailVal); 1735 if (AvailVal->getType()->isPointerTy()) 1736 MD->invalidateCachedPointerInfo(AvailVal); 1737 VN.erase(L); 1738 toErase.push_back(L); 1739 ++NumGVNLoad; 1740 return true; 1741 } 1742 1743 DEBUG( 1744 // fast print dep, using operator<< on instruction would be too slow 1745 dbgs() << "GVN: load "; 1746 WriteAsOperand(dbgs(), L); 1747 Instruction *I = Dep.getInst(); 1748 dbgs() << " is clobbered by " << *I << '\n'; 1749 ); 1750 return false; 1751 } 1752 1753 // If it is defined in another block, try harder. 1754 if (Dep.isNonLocal()) 1755 return processNonLocalLoad(L, toErase); 1756 1757 Instruction *DepInst = Dep.getInst(); 1758 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1759 Value *StoredVal = DepSI->getValueOperand(); 1760 1761 // The store and load are to a must-aliased pointer, but they may not 1762 // actually have the same type. See if we know how to reuse the stored 1763 // value (depending on its type). 1764 if (StoredVal->getType() != L->getType()) { 1765 if (TD) { 1766 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1767 L, *TD); 1768 if (StoredVal == 0) 1769 return false; 1770 1771 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1772 << '\n' << *L << "\n\n\n"); 1773 } 1774 else 1775 return false; 1776 } 1777 1778 // Remove it! 1779 L->replaceAllUsesWith(StoredVal); 1780 if (StoredVal->getType()->isPointerTy()) 1781 MD->invalidateCachedPointerInfo(StoredVal); 1782 VN.erase(L); 1783 toErase.push_back(L); 1784 ++NumGVNLoad; 1785 return true; 1786 } 1787 1788 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1789 Value *AvailableVal = DepLI; 1790 1791 // The loads are of a must-aliased pointer, but they may not actually have 1792 // the same type. See if we know how to reuse the previously loaded value 1793 // (depending on its type). 1794 if (DepLI->getType() != L->getType()) { 1795 if (TD) { 1796 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1797 if (AvailableVal == 0) 1798 return false; 1799 1800 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1801 << "\n" << *L << "\n\n\n"); 1802 } 1803 else 1804 return false; 1805 } 1806 1807 // Remove it! 1808 L->replaceAllUsesWith(AvailableVal); 1809 if (DepLI->getType()->isPointerTy()) 1810 MD->invalidateCachedPointerInfo(DepLI); 1811 VN.erase(L); 1812 toErase.push_back(L); 1813 ++NumGVNLoad; 1814 return true; 1815 } 1816 1817 // If this load really doesn't depend on anything, then we must be loading an 1818 // undef value. This can happen when loading for a fresh allocation with no 1819 // intervening stores, for example. 1820 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { 1821 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1822 VN.erase(L); 1823 toErase.push_back(L); 1824 ++NumGVNLoad; 1825 return true; 1826 } 1827 1828 // If this load occurs either right after a lifetime begin, 1829 // then the loaded value is undefined. 1830 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) { 1831 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1832 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1833 VN.erase(L); 1834 toErase.push_back(L); 1835 ++NumGVNLoad; 1836 return true; 1837 } 1838 } 1839 1840 return false; 1841} 1842 1843// lookupNumber - In order to find a leader for a given value number at a 1844// specific basic block, we first obtain the list of all Values for that number, 1845// and then scan the list to find one whose block dominates the block in 1846// question. This is fast because dominator tree queries consist of only 1847// a few comparisons of DFS numbers. 1848Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1849 std::pair<Value*, void*> Vals = NumberTable[num]; 1850 if (!Vals.first) return 0; 1851 Instruction *Inst = dyn_cast<Instruction>(Vals.first); 1852 if (!Inst) return Vals.first; 1853 BasicBlock *Parent = Inst->getParent(); 1854 if (DT->dominates(Parent, BB)) 1855 return Inst; 1856 1857 std::pair<Value*, void*>* Next = 1858 static_cast<std::pair<Value*, void*>*>(Vals.second); 1859 while (Next) { 1860 Instruction *CurrInst = dyn_cast<Instruction>(Next->first); 1861 if (!CurrInst) return Next->first; 1862 1863 BasicBlock *Parent = CurrInst->getParent(); 1864 if (DT->dominates(Parent, BB)) 1865 return CurrInst; 1866 1867 Next = static_cast<std::pair<Value*, void*>*>(Next->second); 1868 } 1869 1870 return 0; 1871} 1872 1873 1874/// processInstruction - When calculating availability, handle an instruction 1875/// by inserting it into the appropriate sets 1876bool GVN::processInstruction(Instruction *I, 1877 SmallVectorImpl<Instruction*> &toErase) { 1878 // Ignore dbg info intrinsics. 1879 if (isa<DbgInfoIntrinsic>(I)) 1880 return false; 1881 1882 // If the instruction can be easily simplified then do so now in preference 1883 // to value numbering it. Value numbering often exposes redundancies, for 1884 // example if it determines that %y is equal to %x then the instruction 1885 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. 1886 if (Value *V = SimplifyInstruction(I, TD, DT)) { 1887 I->replaceAllUsesWith(V); 1888 if (MD && V->getType()->isPointerTy()) 1889 MD->invalidateCachedPointerInfo(V); 1890 VN.erase(I); 1891 toErase.push_back(I); 1892 return true; 1893 } 1894 1895 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1896 bool Changed = processLoad(LI, toErase); 1897 1898 if (!Changed) { 1899 unsigned Num = VN.lookup_or_add(LI); 1900 insert_table(Num, LI); 1901 } 1902 1903 return Changed; 1904 } 1905 1906 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1907 unsigned Num = VN.lookup_or_add(I); 1908 1909 // Allocations are always uniquely numbered, so we can save time and memory 1910 // by fast failing them. 1911 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) { 1912 insert_table(Num, I); 1913 return false; 1914 } 1915 1916 // If the number we were assigned was a brand new VN, then we don't 1917 // need to do a lookup to see if the number already exists 1918 // somewhere in the domtree: it can't! 1919 if (Num == NextNum) { 1920 insert_table(Num, I); 1921 return false; 1922 } 1923 1924 // Perform fast-path value-number based elimination of values inherited from 1925 // dominators. 1926 Value *repl = lookupNumber(I->getParent(), Num); 1927 if (repl == 0) { 1928 // Failure, just remember this instance for future use. 1929 insert_table(Num, I); 1930 return false; 1931 } 1932 1933 // Remove it! 1934 VN.erase(I); 1935 I->replaceAllUsesWith(repl); 1936 if (MD && repl->getType()->isPointerTy()) 1937 MD->invalidateCachedPointerInfo(repl); 1938 toErase.push_back(I); 1939 return true; 1940} 1941 1942/// runOnFunction - This is the main transformation entry point for a function. 1943bool GVN::runOnFunction(Function& F) { 1944 if (!NoLoads) 1945 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1946 DT = &getAnalysis<DominatorTree>(); 1947 TD = getAnalysisIfAvailable<TargetData>(); 1948 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1949 VN.setMemDep(MD); 1950 VN.setDomTree(DT); 1951 1952 bool Changed = false; 1953 bool ShouldContinue = true; 1954 1955 // Merge unconditional branches, allowing PRE to catch more 1956 // optimization opportunities. 1957 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1958 BasicBlock *BB = FI; 1959 ++FI; 1960 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1961 if (removedBlock) ++NumGVNBlocks; 1962 1963 Changed |= removedBlock; 1964 } 1965 1966 unsigned Iteration = 0; 1967 1968 while (ShouldContinue) { 1969 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 1970 ShouldContinue = iterateOnFunction(F); 1971 if (splitCriticalEdges()) 1972 ShouldContinue = true; 1973 Changed |= ShouldContinue; 1974 ++Iteration; 1975 } 1976 1977 if (EnablePRE) { 1978 bool PREChanged = true; 1979 while (PREChanged) { 1980 PREChanged = performPRE(F); 1981 Changed |= PREChanged; 1982 } 1983 } 1984 // FIXME: Should perform GVN again after PRE does something. PRE can move 1985 // computations into blocks where they become fully redundant. Note that 1986 // we can't do this until PRE's critical edge splitting updates memdep. 1987 // Actually, when this happens, we should just fully integrate PRE into GVN. 1988 1989 cleanupGlobalSets(); 1990 1991 return Changed; 1992} 1993 1994 1995bool GVN::processBlock(BasicBlock *BB) { 1996 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1997 // incrementing BI before processing an instruction). 1998 SmallVector<Instruction*, 8> toErase; 1999 bool ChangedFunction = false; 2000 2001 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 2002 BI != BE;) { 2003 ChangedFunction |= processInstruction(BI, toErase); 2004 if (toErase.empty()) { 2005 ++BI; 2006 continue; 2007 } 2008 2009 // If we need some instructions deleted, do it now. 2010 NumGVNInstr += toErase.size(); 2011 2012 // Avoid iterator invalidation. 2013 bool AtStart = BI == BB->begin(); 2014 if (!AtStart) 2015 --BI; 2016 2017 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 2018 E = toErase.end(); I != E; ++I) { 2019 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 2020 if (MD) MD->removeInstruction(*I); 2021 (*I)->eraseFromParent(); 2022 DEBUG(verifyRemoved(*I)); 2023 } 2024 toErase.clear(); 2025 2026 if (AtStart) 2027 BI = BB->begin(); 2028 else 2029 ++BI; 2030 } 2031 2032 return ChangedFunction; 2033} 2034 2035/// performPRE - Perform a purely local form of PRE that looks for diamond 2036/// control flow patterns and attempts to perform simple PRE at the join point. 2037bool GVN::performPRE(Function &F) { 2038 bool Changed = false; 2039 DenseMap<BasicBlock*, Value*> predMap; 2040 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 2041 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 2042 BasicBlock *CurrentBlock = *DI; 2043 2044 // Nothing to PRE in the entry block. 2045 if (CurrentBlock == &F.getEntryBlock()) continue; 2046 2047 for (BasicBlock::iterator BI = CurrentBlock->begin(), 2048 BE = CurrentBlock->end(); BI != BE; ) { 2049 Instruction *CurInst = BI++; 2050 2051 if (isa<AllocaInst>(CurInst) || 2052 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 2053 CurInst->getType()->isVoidTy() || 2054 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2055 isa<DbgInfoIntrinsic>(CurInst)) 2056 continue; 2057 2058 // We don't currently value number ANY inline asm calls. 2059 if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) 2060 if (CallI->isInlineAsm()) 2061 continue; 2062 2063 uint32_t ValNo = VN.lookup(CurInst); 2064 2065 // Look for the predecessors for PRE opportunities. We're 2066 // only trying to solve the basic diamond case, where 2067 // a value is computed in the successor and one predecessor, 2068 // but not the other. We also explicitly disallow cases 2069 // where the successor is its own predecessor, because they're 2070 // more complicated to get right. 2071 unsigned NumWith = 0; 2072 unsigned NumWithout = 0; 2073 BasicBlock *PREPred = 0; 2074 predMap.clear(); 2075 2076 for (pred_iterator PI = pred_begin(CurrentBlock), 2077 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2078 BasicBlock *P = *PI; 2079 // We're not interested in PRE where the block is its 2080 // own predecessor, or in blocks with predecessors 2081 // that are not reachable. 2082 if (P == CurrentBlock) { 2083 NumWithout = 2; 2084 break; 2085 } else if (!DT->dominates(&F.getEntryBlock(), P)) { 2086 NumWithout = 2; 2087 break; 2088 } 2089 2090 Value* predV = lookupNumber(P, ValNo); 2091 if (predV == 0) { 2092 PREPred = P; 2093 ++NumWithout; 2094 } else if (predV == CurInst) { 2095 NumWithout = 2; 2096 } else { 2097 predMap[P] = predV; 2098 ++NumWith; 2099 } 2100 } 2101 2102 // Don't do PRE when it might increase code size, i.e. when 2103 // we would need to insert instructions in more than one pred. 2104 if (NumWithout != 1 || NumWith == 0) 2105 continue; 2106 2107 // Don't do PRE across indirect branch. 2108 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2109 continue; 2110 2111 // We can't do PRE safely on a critical edge, so instead we schedule 2112 // the edge to be split and perform the PRE the next time we iterate 2113 // on the function. 2114 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); 2115 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2116 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2117 continue; 2118 } 2119 2120 // Instantiate the expression in the predecessor that lacked it. 2121 // Because we are going top-down through the block, all value numbers 2122 // will be available in the predecessor by the time we need them. Any 2123 // that weren't originally present will have been instantiated earlier 2124 // in this loop. 2125 Instruction *PREInstr = CurInst->clone(); 2126 bool success = true; 2127 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2128 Value *Op = PREInstr->getOperand(i); 2129 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2130 continue; 2131 2132 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2133 PREInstr->setOperand(i, V); 2134 } else { 2135 success = false; 2136 break; 2137 } 2138 } 2139 2140 // Fail out if we encounter an operand that is not available in 2141 // the PRE predecessor. This is typically because of loads which 2142 // are not value numbered precisely. 2143 if (!success) { 2144 delete PREInstr; 2145 DEBUG(verifyRemoved(PREInstr)); 2146 continue; 2147 } 2148 2149 PREInstr->insertBefore(PREPred->getTerminator()); 2150 PREInstr->setName(CurInst->getName() + ".pre"); 2151 predMap[PREPred] = PREInstr; 2152 VN.add(PREInstr, ValNo); 2153 ++NumGVNPRE; 2154 2155 // Update the availability map to include the new instruction. 2156 insert_table(ValNo, PREInstr); 2157 2158 // Create a PHI to make the value available in this block. 2159 PHINode* Phi = PHINode::Create(CurInst->getType(), 2160 CurInst->getName() + ".pre-phi", 2161 CurrentBlock->begin()); 2162 for (pred_iterator PI = pred_begin(CurrentBlock), 2163 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2164 BasicBlock *P = *PI; 2165 Phi->addIncoming(predMap[P], P); 2166 } 2167 2168 VN.add(Phi, ValNo); 2169 insert_table(ValNo, Phi); 2170 2171 CurInst->replaceAllUsesWith(Phi); 2172 if (MD && Phi->getType()->isPointerTy()) 2173 MD->invalidateCachedPointerInfo(Phi); 2174 VN.erase(CurInst); 2175 erase_table(ValNo, CurInst); 2176 2177 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2178 if (MD) MD->removeInstruction(CurInst); 2179 CurInst->eraseFromParent(); 2180 DEBUG(verifyRemoved(CurInst)); 2181 Changed = true; 2182 } 2183 } 2184 2185 if (splitCriticalEdges()) 2186 Changed = true; 2187 2188 return Changed; 2189} 2190 2191/// splitCriticalEdges - Split critical edges found during the previous 2192/// iteration that may enable further optimization. 2193bool GVN::splitCriticalEdges() { 2194 if (toSplit.empty()) 2195 return false; 2196 do { 2197 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2198 SplitCriticalEdge(Edge.first, Edge.second, this); 2199 } while (!toSplit.empty()); 2200 if (MD) MD->invalidateCachedPredecessors(); 2201 return true; 2202} 2203 2204/// iterateOnFunction - Executes one iteration of GVN 2205bool GVN::iterateOnFunction(Function &F) { 2206 cleanupGlobalSets(); 2207 2208 // Top-down walk of the dominator tree 2209 bool Changed = false; 2210#if 0 2211 // Needed for value numbering with phi construction to work. 2212 ReversePostOrderTraversal<Function*> RPOT(&F); 2213 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2214 RE = RPOT.end(); RI != RE; ++RI) 2215 Changed |= processBlock(*RI); 2216#else 2217 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2218 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2219 Changed |= processBlock(DI->getBlock()); 2220#endif 2221 2222 return Changed; 2223} 2224 2225void GVN::cleanupGlobalSets() { 2226 VN.clear(); 2227 NumberTable.clear(); 2228 TableAllocator.Reset(); 2229} 2230 2231/// verifyRemoved - Verify that the specified instruction does not occur in our 2232/// internal data structures. 2233void GVN::verifyRemoved(const Instruction *Inst) const { 2234 VN.verifyRemoved(Inst); 2235 2236 // Walk through the value number scope to make sure the instruction isn't 2237 // ferreted away in it. 2238 for (DenseMap<uint32_t, std::pair<Value*, void*> >::const_iterator 2239 I = NumberTable.begin(), E = NumberTable.end(); I != E; ++I) { 2240 std::pair<Value*, void*> const * Node = &I->second; 2241 assert(Node->first != Inst && "Inst still in value numbering scope!"); 2242 2243 while (Node->second) { 2244 Node = static_cast<std::pair<Value*, void*>*>(Node->second); 2245 assert(Node->first != Inst && "Inst still in value numbering scope!"); 2246 } 2247 } 2248} 2249