GVN.cpp revision cb9cbc494975dc827465af32d806e7b9ae17090c
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/Function.h" 24#include "llvm/IntrinsicInst.h" 25#include "llvm/LLVMContext.h" 26#include "llvm/Operator.h" 27#include "llvm/Value.h" 28#include "llvm/ADT/DenseMap.h" 29#include "llvm/ADT/DepthFirstIterator.h" 30#include "llvm/ADT/PostOrderIterator.h" 31#include "llvm/ADT/SmallPtrSet.h" 32#include "llvm/ADT/SmallVector.h" 33#include "llvm/ADT/Statistic.h" 34#include "llvm/Analysis/Dominators.h" 35#include "llvm/Analysis/AliasAnalysis.h" 36#include "llvm/Analysis/MemoryBuiltins.h" 37#include "llvm/Analysis/MemoryDependenceAnalysis.h" 38#include "llvm/Support/CFG.h" 39#include "llvm/Support/CommandLine.h" 40#include "llvm/Support/Debug.h" 41#include "llvm/Support/ErrorHandling.h" 42#include "llvm/Support/GetElementPtrTypeIterator.h" 43#include "llvm/Support/IRBuilder.h" 44#include "llvm/Support/raw_ostream.h" 45#include "llvm/Target/TargetData.h" 46#include "llvm/Transforms/Utils/BasicBlockUtils.h" 47#include "llvm/Transforms/Utils/Local.h" 48#include "llvm/Transforms/Utils/SSAUpdater.h" 49#include <cstdio> 50using namespace llvm; 51 52STATISTIC(NumGVNInstr, "Number of instructions deleted"); 53STATISTIC(NumGVNLoad, "Number of loads deleted"); 54STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 55STATISTIC(NumGVNBlocks, "Number of blocks merged"); 56STATISTIC(NumPRELoad, "Number of loads PRE'd"); 57 58static cl::opt<bool> EnablePRE("enable-pre", 59 cl::init(true), cl::Hidden); 60static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 61 62//===----------------------------------------------------------------------===// 63// ValueTable Class 64//===----------------------------------------------------------------------===// 65 66/// This class holds the mapping between values and value numbers. It is used 67/// as an efficient mechanism to determine the expression-wise equivalence of 68/// two values. 69namespace { 70 struct Expression { 71 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL, 72 UDIV, SDIV, FDIV, UREM, SREM, 73 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 74 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 75 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 76 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 77 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 78 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 79 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 80 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 81 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 82 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE }; 83 84 ExpressionOpcode opcode; 85 const Type* type; 86 SmallVector<uint32_t, 4> varargs; 87 Value *function; 88 89 Expression() { } 90 Expression(ExpressionOpcode o) : opcode(o) { } 91 92 bool operator==(const Expression &other) const { 93 if (opcode != other.opcode) 94 return false; 95 else if (opcode == EMPTY || opcode == TOMBSTONE) 96 return true; 97 else if (type != other.type) 98 return false; 99 else if (function != other.function) 100 return false; 101 else { 102 if (varargs.size() != other.varargs.size()) 103 return false; 104 105 for (size_t i = 0; i < varargs.size(); ++i) 106 if (varargs[i] != other.varargs[i]) 107 return false; 108 109 return true; 110 } 111 } 112 113 bool operator!=(const Expression &other) const { 114 return !(*this == other); 115 } 116 }; 117 118 class ValueTable { 119 private: 120 DenseMap<Value*, uint32_t> valueNumbering; 121 DenseMap<Expression, uint32_t> expressionNumbering; 122 AliasAnalysis* AA; 123 MemoryDependenceAnalysis* MD; 124 DominatorTree* DT; 125 126 uint32_t nextValueNumber; 127 128 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 129 Expression::ExpressionOpcode getOpcode(CmpInst* C); 130 Expression::ExpressionOpcode getOpcode(CastInst* C); 131 Expression create_expression(BinaryOperator* BO); 132 Expression create_expression(CmpInst* C); 133 Expression create_expression(ShuffleVectorInst* V); 134 Expression create_expression(ExtractElementInst* C); 135 Expression create_expression(InsertElementInst* V); 136 Expression create_expression(SelectInst* V); 137 Expression create_expression(CastInst* C); 138 Expression create_expression(GetElementPtrInst* G); 139 Expression create_expression(CallInst* C); 140 Expression create_expression(Constant* C); 141 Expression create_expression(ExtractValueInst* C); 142 Expression create_expression(InsertValueInst* C); 143 144 uint32_t lookup_or_add_call(CallInst* C); 145 public: 146 ValueTable() : nextValueNumber(1) { } 147 uint32_t lookup_or_add(Value *V); 148 uint32_t lookup(Value *V) const; 149 void add(Value *V, uint32_t num); 150 void clear(); 151 void erase(Value *v); 152 unsigned size(); 153 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 154 AliasAnalysis *getAliasAnalysis() const { return AA; } 155 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 156 void setDomTree(DominatorTree* D) { DT = D; } 157 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 158 void verifyRemoved(const Value *) const; 159 }; 160} 161 162namespace llvm { 163template <> struct DenseMapInfo<Expression> { 164 static inline Expression getEmptyKey() { 165 return Expression(Expression::EMPTY); 166 } 167 168 static inline Expression getTombstoneKey() { 169 return Expression(Expression::TOMBSTONE); 170 } 171 172 static unsigned getHashValue(const Expression e) { 173 unsigned hash = e.opcode; 174 175 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 176 (unsigned)((uintptr_t)e.type >> 9)); 177 178 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 179 E = e.varargs.end(); I != E; ++I) 180 hash = *I + hash * 37; 181 182 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 183 (unsigned)((uintptr_t)e.function >> 9)) + 184 hash * 37; 185 186 return hash; 187 } 188 static bool isEqual(const Expression &LHS, const Expression &RHS) { 189 return LHS == RHS; 190 } 191 static bool isPod() { return true; } 192}; 193} 194 195//===----------------------------------------------------------------------===// 196// ValueTable Internal Functions 197//===----------------------------------------------------------------------===// 198Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 199 switch(BO->getOpcode()) { 200 default: // THIS SHOULD NEVER HAPPEN 201 llvm_unreachable("Binary operator with unknown opcode?"); 202 case Instruction::Add: return Expression::ADD; 203 case Instruction::FAdd: return Expression::FADD; 204 case Instruction::Sub: return Expression::SUB; 205 case Instruction::FSub: return Expression::FSUB; 206 case Instruction::Mul: return Expression::MUL; 207 case Instruction::FMul: return Expression::FMUL; 208 case Instruction::UDiv: return Expression::UDIV; 209 case Instruction::SDiv: return Expression::SDIV; 210 case Instruction::FDiv: return Expression::FDIV; 211 case Instruction::URem: return Expression::UREM; 212 case Instruction::SRem: return Expression::SREM; 213 case Instruction::FRem: return Expression::FREM; 214 case Instruction::Shl: return Expression::SHL; 215 case Instruction::LShr: return Expression::LSHR; 216 case Instruction::AShr: return Expression::ASHR; 217 case Instruction::And: return Expression::AND; 218 case Instruction::Or: return Expression::OR; 219 case Instruction::Xor: return Expression::XOR; 220 } 221} 222 223Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 224 if (isa<ICmpInst>(C)) { 225 switch (C->getPredicate()) { 226 default: // THIS SHOULD NEVER HAPPEN 227 llvm_unreachable("Comparison with unknown predicate?"); 228 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 229 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 230 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 231 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 232 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 233 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 234 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 235 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 236 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 237 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 238 } 239 } else { 240 switch (C->getPredicate()) { 241 default: // THIS SHOULD NEVER HAPPEN 242 llvm_unreachable("Comparison with unknown predicate?"); 243 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 244 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 245 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 246 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 247 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 248 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 249 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 250 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 251 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 252 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 253 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 254 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 255 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 256 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 257 } 258 } 259} 260 261Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 262 switch(C->getOpcode()) { 263 default: // THIS SHOULD NEVER HAPPEN 264 llvm_unreachable("Cast operator with unknown opcode?"); 265 case Instruction::Trunc: return Expression::TRUNC; 266 case Instruction::ZExt: return Expression::ZEXT; 267 case Instruction::SExt: return Expression::SEXT; 268 case Instruction::FPToUI: return Expression::FPTOUI; 269 case Instruction::FPToSI: return Expression::FPTOSI; 270 case Instruction::UIToFP: return Expression::UITOFP; 271 case Instruction::SIToFP: return Expression::SITOFP; 272 case Instruction::FPTrunc: return Expression::FPTRUNC; 273 case Instruction::FPExt: return Expression::FPEXT; 274 case Instruction::PtrToInt: return Expression::PTRTOINT; 275 case Instruction::IntToPtr: return Expression::INTTOPTR; 276 case Instruction::BitCast: return Expression::BITCAST; 277 } 278} 279 280Expression ValueTable::create_expression(CallInst* C) { 281 Expression e; 282 283 e.type = C->getType(); 284 e.function = C->getCalledFunction(); 285 e.opcode = Expression::CALL; 286 287 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 288 I != E; ++I) 289 e.varargs.push_back(lookup_or_add(*I)); 290 291 return e; 292} 293 294Expression ValueTable::create_expression(BinaryOperator* BO) { 295 Expression e; 296 e.varargs.push_back(lookup_or_add(BO->getOperand(0))); 297 e.varargs.push_back(lookup_or_add(BO->getOperand(1))); 298 e.function = 0; 299 e.type = BO->getType(); 300 e.opcode = getOpcode(BO); 301 302 return e; 303} 304 305Expression ValueTable::create_expression(CmpInst* C) { 306 Expression e; 307 308 e.varargs.push_back(lookup_or_add(C->getOperand(0))); 309 e.varargs.push_back(lookup_or_add(C->getOperand(1))); 310 e.function = 0; 311 e.type = C->getType(); 312 e.opcode = getOpcode(C); 313 314 return e; 315} 316 317Expression ValueTable::create_expression(CastInst* C) { 318 Expression e; 319 320 e.varargs.push_back(lookup_or_add(C->getOperand(0))); 321 e.function = 0; 322 e.type = C->getType(); 323 e.opcode = getOpcode(C); 324 325 return e; 326} 327 328Expression ValueTable::create_expression(ShuffleVectorInst* S) { 329 Expression e; 330 331 e.varargs.push_back(lookup_or_add(S->getOperand(0))); 332 e.varargs.push_back(lookup_or_add(S->getOperand(1))); 333 e.varargs.push_back(lookup_or_add(S->getOperand(2))); 334 e.function = 0; 335 e.type = S->getType(); 336 e.opcode = Expression::SHUFFLE; 337 338 return e; 339} 340 341Expression ValueTable::create_expression(ExtractElementInst* E) { 342 Expression e; 343 344 e.varargs.push_back(lookup_or_add(E->getOperand(0))); 345 e.varargs.push_back(lookup_or_add(E->getOperand(1))); 346 e.function = 0; 347 e.type = E->getType(); 348 e.opcode = Expression::EXTRACT; 349 350 return e; 351} 352 353Expression ValueTable::create_expression(InsertElementInst* I) { 354 Expression e; 355 356 e.varargs.push_back(lookup_or_add(I->getOperand(0))); 357 e.varargs.push_back(lookup_or_add(I->getOperand(1))); 358 e.varargs.push_back(lookup_or_add(I->getOperand(2))); 359 e.function = 0; 360 e.type = I->getType(); 361 e.opcode = Expression::INSERT; 362 363 return e; 364} 365 366Expression ValueTable::create_expression(SelectInst* I) { 367 Expression e; 368 369 e.varargs.push_back(lookup_or_add(I->getCondition())); 370 e.varargs.push_back(lookup_or_add(I->getTrueValue())); 371 e.varargs.push_back(lookup_or_add(I->getFalseValue())); 372 e.function = 0; 373 e.type = I->getType(); 374 e.opcode = Expression::SELECT; 375 376 return e; 377} 378 379Expression ValueTable::create_expression(GetElementPtrInst* G) { 380 Expression e; 381 382 e.varargs.push_back(lookup_or_add(G->getPointerOperand())); 383 e.function = 0; 384 e.type = G->getType(); 385 e.opcode = Expression::GEP; 386 387 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 388 I != E; ++I) 389 e.varargs.push_back(lookup_or_add(*I)); 390 391 return e; 392} 393 394Expression ValueTable::create_expression(ExtractValueInst* E) { 395 Expression e; 396 397 e.varargs.push_back(lookup_or_add(E->getAggregateOperand())); 398 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 399 II != IE; ++II) 400 e.varargs.push_back(*II); 401 e.function = 0; 402 e.type = E->getType(); 403 e.opcode = Expression::EXTRACTVALUE; 404 405 return e; 406} 407 408Expression ValueTable::create_expression(InsertValueInst* E) { 409 Expression e; 410 411 e.varargs.push_back(lookup_or_add(E->getAggregateOperand())); 412 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand())); 413 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 414 II != IE; ++II) 415 e.varargs.push_back(*II); 416 e.function = 0; 417 e.type = E->getType(); 418 e.opcode = Expression::INSERTVALUE; 419 420 return e; 421} 422 423//===----------------------------------------------------------------------===// 424// ValueTable External Functions 425//===----------------------------------------------------------------------===// 426 427/// add - Insert a value into the table with a specified value number. 428void ValueTable::add(Value *V, uint32_t num) { 429 valueNumbering.insert(std::make_pair(V, num)); 430} 431 432uint32_t ValueTable::lookup_or_add_call(CallInst* C) { 433 if (AA->doesNotAccessMemory(C)) { 434 Expression exp = create_expression(C); 435 uint32_t& e = expressionNumbering[exp]; 436 if (!e) e = nextValueNumber++; 437 valueNumbering[C] = e; 438 return e; 439 } else if (AA->onlyReadsMemory(C)) { 440 Expression exp = create_expression(C); 441 uint32_t& e = expressionNumbering[exp]; 442 if (!e) { 443 e = nextValueNumber++; 444 valueNumbering[C] = e; 445 return e; 446 } 447 if (!MD) { 448 e = nextValueNumber++; 449 valueNumbering[C] = e; 450 return e; 451 } 452 453 MemDepResult local_dep = MD->getDependency(C); 454 455 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 456 valueNumbering[C] = nextValueNumber; 457 return nextValueNumber++; 458 } 459 460 if (local_dep.isDef()) { 461 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 462 463 if (local_cdep->getNumOperands() != C->getNumOperands()) { 464 valueNumbering[C] = nextValueNumber; 465 return nextValueNumber++; 466 } 467 468 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 469 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 470 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 471 if (c_vn != cd_vn) { 472 valueNumbering[C] = nextValueNumber; 473 return nextValueNumber++; 474 } 475 } 476 477 uint32_t v = lookup_or_add(local_cdep); 478 valueNumbering[C] = v; 479 return v; 480 } 481 482 // Non-local case. 483 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 484 MD->getNonLocalCallDependency(CallSite(C)); 485 // FIXME: call/call dependencies for readonly calls should return def, not 486 // clobber! Move the checking logic to MemDep! 487 CallInst* cdep = 0; 488 489 // Check to see if we have a single dominating call instruction that is 490 // identical to C. 491 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 492 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i]; 493 // Ignore non-local dependencies. 494 if (I->second.isNonLocal()) 495 continue; 496 497 // We don't handle non-depedencies. If we already have a call, reject 498 // instruction dependencies. 499 if (I->second.isClobber() || cdep != 0) { 500 cdep = 0; 501 break; 502 } 503 504 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst()); 505 // FIXME: All duplicated with non-local case. 506 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){ 507 cdep = NonLocalDepCall; 508 continue; 509 } 510 511 cdep = 0; 512 break; 513 } 514 515 if (!cdep) { 516 valueNumbering[C] = nextValueNumber; 517 return nextValueNumber++; 518 } 519 520 if (cdep->getNumOperands() != C->getNumOperands()) { 521 valueNumbering[C] = nextValueNumber; 522 return nextValueNumber++; 523 } 524 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 525 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 526 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 527 if (c_vn != cd_vn) { 528 valueNumbering[C] = nextValueNumber; 529 return nextValueNumber++; 530 } 531 } 532 533 uint32_t v = lookup_or_add(cdep); 534 valueNumbering[C] = v; 535 return v; 536 537 } else { 538 valueNumbering[C] = nextValueNumber; 539 return nextValueNumber++; 540 } 541} 542 543/// lookup_or_add - Returns the value number for the specified value, assigning 544/// it a new number if it did not have one before. 545uint32_t ValueTable::lookup_or_add(Value *V) { 546 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 547 if (VI != valueNumbering.end()) 548 return VI->second; 549 550 if (!isa<Instruction>(V)) { 551 valueNumbering[V] = nextValueNumber; 552 return nextValueNumber++; 553 } 554 555 Instruction* I = cast<Instruction>(V); 556 Expression exp; 557 switch (I->getOpcode()) { 558 case Instruction::Call: 559 return lookup_or_add_call(cast<CallInst>(I)); 560 case Instruction::Add: 561 case Instruction::FAdd: 562 case Instruction::Sub: 563 case Instruction::FSub: 564 case Instruction::Mul: 565 case Instruction::FMul: 566 case Instruction::UDiv: 567 case Instruction::SDiv: 568 case Instruction::FDiv: 569 case Instruction::URem: 570 case Instruction::SRem: 571 case Instruction::FRem: 572 case Instruction::Shl: 573 case Instruction::LShr: 574 case Instruction::AShr: 575 case Instruction::And: 576 case Instruction::Or : 577 case Instruction::Xor: 578 exp = create_expression(cast<BinaryOperator>(I)); 579 break; 580 case Instruction::ICmp: 581 case Instruction::FCmp: 582 exp = create_expression(cast<CmpInst>(I)); 583 break; 584 case Instruction::Trunc: 585 case Instruction::ZExt: 586 case Instruction::SExt: 587 case Instruction::FPToUI: 588 case Instruction::FPToSI: 589 case Instruction::UIToFP: 590 case Instruction::SIToFP: 591 case Instruction::FPTrunc: 592 case Instruction::FPExt: 593 case Instruction::PtrToInt: 594 case Instruction::IntToPtr: 595 case Instruction::BitCast: 596 exp = create_expression(cast<CastInst>(I)); 597 break; 598 case Instruction::Select: 599 exp = create_expression(cast<SelectInst>(I)); 600 break; 601 case Instruction::ExtractElement: 602 exp = create_expression(cast<ExtractElementInst>(I)); 603 break; 604 case Instruction::InsertElement: 605 exp = create_expression(cast<InsertElementInst>(I)); 606 break; 607 case Instruction::ShuffleVector: 608 exp = create_expression(cast<ShuffleVectorInst>(I)); 609 break; 610 case Instruction::ExtractValue: 611 exp = create_expression(cast<ExtractValueInst>(I)); 612 break; 613 case Instruction::InsertValue: 614 exp = create_expression(cast<InsertValueInst>(I)); 615 break; 616 case Instruction::GetElementPtr: 617 exp = create_expression(cast<GetElementPtrInst>(I)); 618 break; 619 default: 620 valueNumbering[V] = nextValueNumber; 621 return nextValueNumber++; 622 } 623 624 uint32_t& e = expressionNumbering[exp]; 625 if (!e) e = nextValueNumber++; 626 valueNumbering[V] = e; 627 return e; 628} 629 630/// lookup - Returns the value number of the specified value. Fails if 631/// the value has not yet been numbered. 632uint32_t ValueTable::lookup(Value *V) const { 633 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); 634 assert(VI != valueNumbering.end() && "Value not numbered?"); 635 return VI->second; 636} 637 638/// clear - Remove all entries from the ValueTable 639void ValueTable::clear() { 640 valueNumbering.clear(); 641 expressionNumbering.clear(); 642 nextValueNumber = 1; 643} 644 645/// erase - Remove a value from the value numbering 646void ValueTable::erase(Value *V) { 647 valueNumbering.erase(V); 648} 649 650/// verifyRemoved - Verify that the value is removed from all internal data 651/// structures. 652void ValueTable::verifyRemoved(const Value *V) const { 653 for (DenseMap<Value*, uint32_t>::const_iterator 654 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 655 assert(I->first != V && "Inst still occurs in value numbering map!"); 656 } 657} 658 659//===----------------------------------------------------------------------===// 660// GVN Pass 661//===----------------------------------------------------------------------===// 662 663namespace { 664 struct ValueNumberScope { 665 ValueNumberScope* parent; 666 DenseMap<uint32_t, Value*> table; 667 668 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 669 }; 670} 671 672namespace { 673 674 class GVN : public FunctionPass { 675 bool runOnFunction(Function &F); 676 public: 677 static char ID; // Pass identification, replacement for typeid 678 explicit GVN(bool nopre = false, bool noloads = false) 679 : FunctionPass(&ID), NoPRE(nopre), NoLoads(noloads), MD(0) { } 680 681 private: 682 bool NoPRE; 683 bool NoLoads; 684 MemoryDependenceAnalysis *MD; 685 DominatorTree *DT; 686 687 ValueTable VN; 688 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 689 690 // This transformation requires dominator postdominator info 691 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 692 AU.addRequired<DominatorTree>(); 693 if (!NoLoads) 694 AU.addRequired<MemoryDependenceAnalysis>(); 695 AU.addRequired<AliasAnalysis>(); 696 697 AU.addPreserved<DominatorTree>(); 698 AU.addPreserved<AliasAnalysis>(); 699 } 700 701 // Helper fuctions 702 // FIXME: eliminate or document these better 703 bool processLoad(LoadInst* L, 704 SmallVectorImpl<Instruction*> &toErase); 705 bool processInstruction(Instruction *I, 706 SmallVectorImpl<Instruction*> &toErase); 707 bool processNonLocalLoad(LoadInst* L, 708 SmallVectorImpl<Instruction*> &toErase); 709 bool processBlock(BasicBlock *BB); 710 void dump(DenseMap<uint32_t, Value*>& d); 711 bool iterateOnFunction(Function &F); 712 Value *CollapsePhi(PHINode* p); 713 bool performPRE(Function& F); 714 Value *lookupNumber(BasicBlock *BB, uint32_t num); 715 void cleanupGlobalSets(); 716 void verifyRemoved(const Instruction *I) const; 717 }; 718 719 char GVN::ID = 0; 720} 721 722// createGVNPass - The public interface to this file... 723FunctionPass *llvm::createGVNPass(bool NoPRE, bool NoLoads) { 724 return new GVN(NoPRE, NoLoads); 725} 726 727static RegisterPass<GVN> X("gvn", 728 "Global Value Numbering"); 729 730void GVN::dump(DenseMap<uint32_t, Value*>& d) { 731 printf("{\n"); 732 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 733 E = d.end(); I != E; ++I) { 734 printf("%d\n", I->first); 735 I->second->dump(); 736 } 737 printf("}\n"); 738} 739 740static bool isSafeReplacement(PHINode* p, Instruction *inst) { 741 if (!isa<PHINode>(inst)) 742 return true; 743 744 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 745 UI != E; ++UI) 746 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 747 if (use_phi->getParent() == inst->getParent()) 748 return false; 749 750 return true; 751} 752 753Value *GVN::CollapsePhi(PHINode *PN) { 754 Value *ConstVal = PN->hasConstantValue(DT); 755 if (!ConstVal) return 0; 756 757 Instruction *Inst = dyn_cast<Instruction>(ConstVal); 758 if (!Inst) 759 return ConstVal; 760 761 if (DT->dominates(Inst, PN)) 762 if (isSafeReplacement(PN, Inst)) 763 return Inst; 764 return 0; 765} 766 767/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 768/// we're analyzing is fully available in the specified block. As we go, keep 769/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 770/// map is actually a tri-state map with the following values: 771/// 0) we know the block *is not* fully available. 772/// 1) we know the block *is* fully available. 773/// 2) we do not know whether the block is fully available or not, but we are 774/// currently speculating that it will be. 775/// 3) we are speculating for this block and have used that to speculate for 776/// other blocks. 777static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 778 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 779 // Optimistically assume that the block is fully available and check to see 780 // if we already know about this block in one lookup. 781 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 782 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 783 784 // If the entry already existed for this block, return the precomputed value. 785 if (!IV.second) { 786 // If this is a speculative "available" value, mark it as being used for 787 // speculation of other blocks. 788 if (IV.first->second == 2) 789 IV.first->second = 3; 790 return IV.first->second != 0; 791 } 792 793 // Otherwise, see if it is fully available in all predecessors. 794 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 795 796 // If this block has no predecessors, it isn't live-in here. 797 if (PI == PE) 798 goto SpeculationFailure; 799 800 for (; PI != PE; ++PI) 801 // If the value isn't fully available in one of our predecessors, then it 802 // isn't fully available in this block either. Undo our previous 803 // optimistic assumption and bail out. 804 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 805 goto SpeculationFailure; 806 807 return true; 808 809// SpeculationFailure - If we get here, we found out that this is not, after 810// all, a fully-available block. We have a problem if we speculated on this and 811// used the speculation to mark other blocks as available. 812SpeculationFailure: 813 char &BBVal = FullyAvailableBlocks[BB]; 814 815 // If we didn't speculate on this, just return with it set to false. 816 if (BBVal == 2) { 817 BBVal = 0; 818 return false; 819 } 820 821 // If we did speculate on this value, we could have blocks set to 1 that are 822 // incorrect. Walk the (transitive) successors of this block and mark them as 823 // 0 if set to one. 824 SmallVector<BasicBlock*, 32> BBWorklist; 825 BBWorklist.push_back(BB); 826 827 while (!BBWorklist.empty()) { 828 BasicBlock *Entry = BBWorklist.pop_back_val(); 829 // Note that this sets blocks to 0 (unavailable) if they happen to not 830 // already be in FullyAvailableBlocks. This is safe. 831 char &EntryVal = FullyAvailableBlocks[Entry]; 832 if (EntryVal == 0) continue; // Already unavailable. 833 834 // Mark as unavailable. 835 EntryVal = 0; 836 837 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 838 BBWorklist.push_back(*I); 839 } 840 841 return false; 842} 843 844 845/// CanCoerceMustAliasedValueToLoad - Return true if 846/// CoerceAvailableValueToLoadType will succeed. 847static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 848 const Type *LoadTy, 849 const TargetData &TD) { 850 // If the loaded or stored value is an first class array or struct, don't try 851 // to transform them. We need to be able to bitcast to integer. 852 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy) || 853 isa<StructType>(StoredVal->getType()) || 854 isa<ArrayType>(StoredVal->getType())) 855 return false; 856 857 // The store has to be at least as big as the load. 858 if (TD.getTypeSizeInBits(StoredVal->getType()) < 859 TD.getTypeSizeInBits(LoadTy)) 860 return false; 861 862 return true; 863} 864 865 866/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 867/// then a load from a must-aliased pointer of a different type, try to coerce 868/// the stored value. LoadedTy is the type of the load we want to replace and 869/// InsertPt is the place to insert new instructions. 870/// 871/// If we can't do it, return null. 872static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 873 const Type *LoadedTy, 874 Instruction *InsertPt, 875 const TargetData &TD) { 876 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 877 return 0; 878 879 const Type *StoredValTy = StoredVal->getType(); 880 881 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 882 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 883 884 // If the store and reload are the same size, we can always reuse it. 885 if (StoreSize == LoadSize) { 886 if (isa<PointerType>(StoredValTy) && isa<PointerType>(LoadedTy)) { 887 // Pointer to Pointer -> use bitcast. 888 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 889 } 890 891 // Convert source pointers to integers, which can be bitcast. 892 if (isa<PointerType>(StoredValTy)) { 893 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 894 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 895 } 896 897 const Type *TypeToCastTo = LoadedTy; 898 if (isa<PointerType>(TypeToCastTo)) 899 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 900 901 if (StoredValTy != TypeToCastTo) 902 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 903 904 // Cast to pointer if the load needs a pointer type. 905 if (isa<PointerType>(LoadedTy)) 906 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 907 908 return StoredVal; 909 } 910 911 // If the loaded value is smaller than the available value, then we can 912 // extract out a piece from it. If the available value is too small, then we 913 // can't do anything. 914 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 915 916 // Convert source pointers to integers, which can be manipulated. 917 if (isa<PointerType>(StoredValTy)) { 918 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 919 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 920 } 921 922 // Convert vectors and fp to integer, which can be manipulated. 923 if (!isa<IntegerType>(StoredValTy)) { 924 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 925 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 926 } 927 928 // If this is a big-endian system, we need to shift the value down to the low 929 // bits so that a truncate will work. 930 if (TD.isBigEndian()) { 931 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 932 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 933 } 934 935 // Truncate the integer to the right size now. 936 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 937 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 938 939 if (LoadedTy == NewIntTy) 940 return StoredVal; 941 942 // If the result is a pointer, inttoptr. 943 if (isa<PointerType>(LoadedTy)) 944 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 945 946 // Otherwise, bitcast. 947 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 948} 949 950/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 951/// be expressed as a base pointer plus a constant offset. Return the base and 952/// offset to the caller. 953static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 954 const TargetData &TD) { 955 Operator *PtrOp = dyn_cast<Operator>(Ptr); 956 if (PtrOp == 0) return Ptr; 957 958 // Just look through bitcasts. 959 if (PtrOp->getOpcode() == Instruction::BitCast) 960 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 961 962 // If this is a GEP with constant indices, we can look through it. 963 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 964 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 965 966 gep_type_iterator GTI = gep_type_begin(GEP); 967 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 968 ++I, ++GTI) { 969 ConstantInt *OpC = cast<ConstantInt>(*I); 970 if (OpC->isZero()) continue; 971 972 // Handle a struct and array indices which add their offset to the pointer. 973 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 974 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 975 } else { 976 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 977 Offset += OpC->getSExtValue()*Size; 978 } 979 } 980 981 // Re-sign extend from the pointer size if needed to get overflow edge cases 982 // right. 983 unsigned PtrSize = TD.getPointerSizeInBits(); 984 if (PtrSize < 64) 985 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 986 987 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 988} 989 990 991/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 992/// memdep query of a load that ends up being a clobbering memory write (store, 993/// memset, memcpy, memmove). This means that the write *may* provide bits used 994/// by the load but we can't be sure because the pointers don't mustalias. 995/// 996/// Check this case to see if there is anything more we can do before we give 997/// up. This returns -1 if we have to give up, or a byte number in the stored 998/// value of the piece that feeds the load. 999static int AnalyzeLoadFromClobberingWrite(LoadInst *L, Value *WritePtr, 1000 uint64_t WriteSizeInBits, 1001 const TargetData &TD) { 1002 // If the loaded or stored value is an first class array or struct, don't try 1003 // to transform them. We need to be able to bitcast to integer. 1004 if (isa<StructType>(L->getType()) || isa<ArrayType>(L->getType())) 1005 return -1; 1006 1007 int64_t StoreOffset = 0, LoadOffset = 0; 1008 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD); 1009 Value *LoadBase = 1010 GetBaseWithConstantOffset(L->getPointerOperand(), LoadOffset, TD); 1011 if (StoreBase != LoadBase) 1012 return -1; 1013 1014 // If the load and store are to the exact same address, they should have been 1015 // a must alias. AA must have gotten confused. 1016 // FIXME: Study to see if/when this happens. 1017 if (LoadOffset == StoreOffset) { 1018#if 0 1019 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 1020 << "Base = " << *StoreBase << "\n" 1021 << "Store Ptr = " << *WritePtr << "\n" 1022 << "Store Offs = " << StoreOffset << "\n" 1023 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1024 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1025 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1026 << *L->getParent(); 1027#endif 1028 return -1; 1029 } 1030 1031 // If the load and store don't overlap at all, the store doesn't provide 1032 // anything to the load. In this case, they really don't alias at all, AA 1033 // must have gotten confused. 1034 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1035 // remove this check, as it is duplicated with what we have below. 1036 uint64_t LoadSize = TD.getTypeSizeInBits(L->getType()); 1037 1038 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 1039 return -1; 1040 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 1041 LoadSize >>= 3; 1042 1043 1044 bool isAAFailure = false; 1045 if (StoreOffset < LoadOffset) { 1046 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1047 } else { 1048 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1049 } 1050 if (isAAFailure) { 1051#if 0 1052 errs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1053 << "Base = " << *StoreBase << "\n" 1054 << "Store Ptr = " << *WritePtr << "\n" 1055 << "Store Offs = " << StoreOffset << "\n" 1056 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1057 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1058 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1059 << *L->getParent(); 1060#endif 1061 return -1; 1062 } 1063 1064 // If the Load isn't completely contained within the stored bits, we don't 1065 // have all the bits to feed it. We could do something crazy in the future 1066 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1067 // valuable. 1068 if (StoreOffset > LoadOffset || 1069 StoreOffset+StoreSize < LoadOffset+LoadSize) 1070 return -1; 1071 1072 // Okay, we can do this transformation. Return the number of bytes into the 1073 // store that the load is. 1074 return LoadOffset-StoreOffset; 1075} 1076 1077/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1078/// memdep query of a load that ends up being a clobbering store. 1079static int AnalyzeLoadFromClobberingStore(LoadInst *L, StoreInst *DepSI, 1080 const TargetData &TD) { 1081 // Cannot handle reading from store of first-class aggregate yet. 1082 if (isa<StructType>(DepSI->getOperand(0)->getType()) || 1083 isa<ArrayType>(DepSI->getOperand(0)->getType())) 1084 return -1; 1085 1086 Value *StorePtr = DepSI->getPointerOperand(); 1087 uint64_t StoreSize = TD.getTypeSizeInBits(StorePtr->getType()); 1088 return AnalyzeLoadFromClobberingWrite(L, StorePtr, StoreSize, TD); 1089} 1090 1091static int AnalyzeLoadFromClobberingMemInst(LoadInst *L, MemIntrinsic *MI, 1092 const TargetData &TD) { 1093 // If the mem operation is a non-constant size, we can't handle it. 1094 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 1095 if (SizeCst == 0) return -1; 1096 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 1097 1098 if (MI->getIntrinsicID() == Intrinsic::memset) 1099 return AnalyzeLoadFromClobberingWrite(L, MI->getDest(), MemSizeInBits, TD); 1100 1101 // Unhandled memcpy/memmove. 1102 return -1; 1103} 1104 1105 1106/// GetStoreValueForLoad - This function is called when we have a 1107/// memdep query of a load that ends up being a clobbering store. This means 1108/// that the store *may* provide bits used by the load but we can't be sure 1109/// because the pointers don't mustalias. Check this case to see if there is 1110/// anything more we can do before we give up. 1111static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1112 const Type *LoadTy, 1113 Instruction *InsertPt, const TargetData &TD){ 1114 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1115 1116 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8; 1117 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1118 1119 1120 // Compute which bits of the stored value are being used by the load. Convert 1121 // to an integer type to start with. 1122 if (isa<PointerType>(SrcVal->getType())) 1123 SrcVal = new PtrToIntInst(SrcVal, TD.getIntPtrType(Ctx), "tmp", InsertPt); 1124 if (!isa<IntegerType>(SrcVal->getType())) 1125 SrcVal = new BitCastInst(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1126 "tmp", InsertPt); 1127 1128 // Shift the bits to the least significant depending on endianness. 1129 unsigned ShiftAmt; 1130 if (TD.isLittleEndian()) 1131 ShiftAmt = Offset*8; 1132 else 1133 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1134 1135 if (ShiftAmt) 1136 SrcVal = BinaryOperator::CreateLShr(SrcVal, 1137 ConstantInt::get(SrcVal->getType(), ShiftAmt), "tmp", InsertPt); 1138 1139 if (LoadSize != StoreSize) 1140 SrcVal = new TruncInst(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1141 "tmp", InsertPt); 1142 1143 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1144} 1145 1146/// GetMemInstValueForLoad - This function is called when we have a 1147/// memdep query of a load that ends up being a clobbering mem intrinsic. 1148static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1149 const Type *LoadTy, Instruction *InsertPt, 1150 const TargetData &TD){ 1151 LLVMContext &Ctx = LoadTy->getContext(); 1152 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1153 1154 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1155 1156 // We know that this method is only called when the mem transfer fully 1157 // provides the bits for the load. 1158 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1159 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1160 // independently of what the offset is. 1161 Value *Val = MSI->getValue(); 1162 if (LoadSize != 1) 1163 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1164 1165 Value *OneElt = Val; 1166 1167 // Splat the value out to the right number of bits. 1168 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1169 // If we can double the number of bytes set, do it. 1170 if (NumBytesSet*2 <= LoadSize) { 1171 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1172 Val = Builder.CreateOr(Val, ShVal); 1173 NumBytesSet <<= 1; 1174 continue; 1175 } 1176 1177 // Otherwise insert one byte at a time. 1178 Value *ShVal = Builder.CreateShl(Val, 1*8); 1179 Val = Builder.CreateOr(OneElt, ShVal); 1180 ++NumBytesSet; 1181 } 1182 1183 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 1184 } 1185 1186 // ABORT; 1187 return 0; 1188} 1189 1190 1191 1192struct AvailableValueInBlock { 1193 /// BB - The basic block in question. 1194 BasicBlock *BB; 1195 enum ValType { 1196 SimpleVal, // A simple offsetted value that is accessed. 1197 MemIntrin // A memory intrinsic which is loaded from. 1198 }; 1199 1200 /// V - The value that is live out of the block. 1201 PointerIntPair<Value *, 1, ValType> Val; 1202 1203 /// Offset - The byte offset in Val that is interesting for the load query. 1204 unsigned Offset; 1205 1206 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1207 unsigned Offset = 0) { 1208 AvailableValueInBlock Res; 1209 Res.BB = BB; 1210 Res.Val.setPointer(V); 1211 Res.Val.setInt(SimpleVal); 1212 Res.Offset = Offset; 1213 return Res; 1214 } 1215 1216 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 1217 unsigned Offset = 0) { 1218 AvailableValueInBlock Res; 1219 Res.BB = BB; 1220 Res.Val.setPointer(MI); 1221 Res.Val.setInt(MemIntrin); 1222 Res.Offset = Offset; 1223 return Res; 1224 } 1225 1226 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 1227 Value *getSimpleValue() const { 1228 assert(isSimpleValue() && "Wrong accessor"); 1229 return Val.getPointer(); 1230 } 1231 1232 MemIntrinsic *getMemIntrinValue() const { 1233 assert(!isSimpleValue() && "Wrong accessor"); 1234 return cast<MemIntrinsic>(Val.getPointer()); 1235 } 1236}; 1237 1238/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1239/// construct SSA form, allowing us to eliminate LI. This returns the value 1240/// that should be used at LI's definition site. 1241static Value *ConstructSSAForLoadSet(LoadInst *LI, 1242 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1243 const TargetData *TD, 1244 AliasAnalysis *AA) { 1245 SmallVector<PHINode*, 8> NewPHIs; 1246 SSAUpdater SSAUpdate(&NewPHIs); 1247 SSAUpdate.Initialize(LI); 1248 1249 const Type *LoadTy = LI->getType(); 1250 1251 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1252 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1253 BasicBlock *BB = AV.BB; 1254 1255 if (SSAUpdate.HasValueForBlock(BB)) 1256 continue; 1257 1258 unsigned Offset = AV.Offset; 1259 1260 Value *AvailableVal; 1261 if (AV.isSimpleValue()) { 1262 AvailableVal = AV.getSimpleValue(); 1263 if (AvailableVal->getType() != LoadTy) { 1264 assert(TD && "Need target data to handle type mismatch case"); 1265 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy, 1266 BB->getTerminator(), *TD); 1267 1268 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1269 << *AV.getSimpleValue() << '\n' 1270 << *AvailableVal << '\n' << "\n\n\n"); 1271 } 1272 } else { 1273 AvailableVal = GetMemInstValueForLoad(AV.getMemIntrinValue(), Offset, 1274 LoadTy, BB->getTerminator(), *TD); 1275 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1276 << " " << *AV.getMemIntrinValue() << '\n' 1277 << *AvailableVal << '\n' << "\n\n\n"); 1278 } 1279 SSAUpdate.AddAvailableValue(BB, AvailableVal); 1280 } 1281 1282 // Perform PHI construction. 1283 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1284 1285 // If new PHI nodes were created, notify alias analysis. 1286 if (isa<PointerType>(V->getType())) 1287 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1288 AA->copyValue(LI, NewPHIs[i]); 1289 1290 return V; 1291} 1292 1293static bool isLifetimeStart(Instruction *Inst) { 1294 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1295 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1296 return false; 1297} 1298 1299/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1300/// non-local by performing PHI construction. 1301bool GVN::processNonLocalLoad(LoadInst *LI, 1302 SmallVectorImpl<Instruction*> &toErase) { 1303 // Find the non-local dependencies of the load. 1304 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 1305 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 1306 Deps); 1307 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: " 1308 // << Deps.size() << *LI << '\n'); 1309 1310 // If we had to process more than one hundred blocks to find the 1311 // dependencies, this load isn't worth worrying about. Optimizing 1312 // it will be too expensive. 1313 if (Deps.size() > 100) 1314 return false; 1315 1316 // If we had a phi translation failure, we'll have a single entry which is a 1317 // clobber in the current block. Reject this early. 1318 if (Deps.size() == 1 && Deps[0].second.isClobber()) { 1319 DEBUG( 1320 errs() << "GVN: non-local load "; 1321 WriteAsOperand(errs(), LI); 1322 errs() << " is clobbered by " << *Deps[0].second.getInst() << '\n'; 1323 ); 1324 return false; 1325 } 1326 1327 // Filter out useless results (non-locals, etc). Keep track of the blocks 1328 // where we have a value available in repl, also keep track of whether we see 1329 // dependencies that produce an unknown value for the load (such as a call 1330 // that could potentially clobber the load). 1331 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1332 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1333 1334 const TargetData *TD = 0; 1335 1336 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1337 BasicBlock *DepBB = Deps[i].first; 1338 MemDepResult DepInfo = Deps[i].second; 1339 1340 if (DepInfo.isClobber()) { 1341 // If the dependence is to a store that writes to a superset of the bits 1342 // read by the load, we can extract the bits we need for the load from the 1343 // stored value. 1344 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1345 if (TD == 0) 1346 TD = getAnalysisIfAvailable<TargetData>(); 1347 if (TD) { 1348 int Offset = AnalyzeLoadFromClobberingStore(LI, DepSI, *TD); 1349 if (Offset != -1) { 1350 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1351 DepSI->getOperand(0), 1352 Offset)); 1353 continue; 1354 } 1355 } 1356 } 1357 1358 // If the clobbering value is a memset/memcpy/memmove, see if we can 1359 // forward a value on from it. 1360 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1361 if (TD == 0) 1362 TD = getAnalysisIfAvailable<TargetData>(); 1363 if (TD) { 1364 int Offset = AnalyzeLoadFromClobberingMemInst(LI, DepMI, *TD); 1365 if (Offset != -1) { 1366 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1367 Offset)); 1368 continue; 1369 } 1370 } 1371 } 1372 1373 UnavailableBlocks.push_back(DepBB); 1374 continue; 1375 } 1376 1377 Instruction *DepInst = DepInfo.getInst(); 1378 1379 // Loading the allocation -> undef. 1380 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) || 1381 // Loading immediately after lifetime begin -> undef. 1382 isLifetimeStart(DepInst)) { 1383 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1384 UndefValue::get(LI->getType()))); 1385 continue; 1386 } 1387 1388 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1389 // Reject loads and stores that are to the same address but are of 1390 // different types if we have to. 1391 if (S->getOperand(0)->getType() != LI->getType()) { 1392 if (TD == 0) 1393 TD = getAnalysisIfAvailable<TargetData>(); 1394 1395 // If the stored value is larger or equal to the loaded value, we can 1396 // reuse it. 1397 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0), 1398 LI->getType(), *TD)) { 1399 UnavailableBlocks.push_back(DepBB); 1400 continue; 1401 } 1402 } 1403 1404 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1405 S->getOperand(0))); 1406 continue; 1407 } 1408 1409 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1410 // If the types mismatch and we can't handle it, reject reuse of the load. 1411 if (LD->getType() != LI->getType()) { 1412 if (TD == 0) 1413 TD = getAnalysisIfAvailable<TargetData>(); 1414 1415 // If the stored value is larger or equal to the loaded value, we can 1416 // reuse it. 1417 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1418 UnavailableBlocks.push_back(DepBB); 1419 continue; 1420 } 1421 } 1422 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1423 continue; 1424 } 1425 1426 UnavailableBlocks.push_back(DepBB); 1427 continue; 1428 } 1429 1430 // If we have no predecessors that produce a known value for this load, exit 1431 // early. 1432 if (ValuesPerBlock.empty()) return false; 1433 1434 // If all of the instructions we depend on produce a known value for this 1435 // load, then it is fully redundant and we can use PHI insertion to compute 1436 // its value. Insert PHIs and remove the fully redundant value now. 1437 if (UnavailableBlocks.empty()) { 1438 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1439 1440 // Perform PHI construction. 1441 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, 1442 VN.getAliasAnalysis()); 1443 LI->replaceAllUsesWith(V); 1444 1445 if (isa<PHINode>(V)) 1446 V->takeName(LI); 1447 if (isa<PointerType>(V->getType())) 1448 MD->invalidateCachedPointerInfo(V); 1449 toErase.push_back(LI); 1450 NumGVNLoad++; 1451 return true; 1452 } 1453 1454 if (!EnablePRE || !EnableLoadPRE) 1455 return false; 1456 1457 // Okay, we have *some* definitions of the value. This means that the value 1458 // is available in some of our (transitive) predecessors. Lets think about 1459 // doing PRE of this load. This will involve inserting a new load into the 1460 // predecessor when it's not available. We could do this in general, but 1461 // prefer to not increase code size. As such, we only do this when we know 1462 // that we only have to insert *one* load (which means we're basically moving 1463 // the load, not inserting a new one). 1464 1465 SmallPtrSet<BasicBlock *, 4> Blockers; 1466 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1467 Blockers.insert(UnavailableBlocks[i]); 1468 1469 // Lets find first basic block with more than one predecessor. Walk backwards 1470 // through predecessors if needed. 1471 BasicBlock *LoadBB = LI->getParent(); 1472 BasicBlock *TmpBB = LoadBB; 1473 1474 bool isSinglePred = false; 1475 bool allSingleSucc = true; 1476 while (TmpBB->getSinglePredecessor()) { 1477 isSinglePred = true; 1478 TmpBB = TmpBB->getSinglePredecessor(); 1479 if (!TmpBB) // If haven't found any, bail now. 1480 return false; 1481 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1482 return false; 1483 if (Blockers.count(TmpBB)) 1484 return false; 1485 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1486 allSingleSucc = false; 1487 } 1488 1489 assert(TmpBB); 1490 LoadBB = TmpBB; 1491 1492 // If we have a repl set with LI itself in it, this means we have a loop where 1493 // at least one of the values is LI. Since this means that we won't be able 1494 // to eliminate LI even if we insert uses in the other predecessors, we will 1495 // end up increasing code size. Reject this by scanning for LI. 1496 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1497 if (ValuesPerBlock[i].isSimpleValue() && 1498 ValuesPerBlock[i].getSimpleValue() == LI) 1499 return false; 1500 1501 // FIXME: It is extremely unclear what this loop is doing, other than 1502 // artificially restricting loadpre. 1503 if (isSinglePred) { 1504 bool isHot = false; 1505 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1506 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1507 if (AV.isSimpleValue()) 1508 // "Hot" Instruction is in some loop (because it dominates its dep. 1509 // instruction). 1510 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue())) 1511 if (DT->dominates(LI, I)) { 1512 isHot = true; 1513 break; 1514 } 1515 } 1516 1517 // We are interested only in "hot" instructions. We don't want to do any 1518 // mis-optimizations here. 1519 if (!isHot) 1520 return false; 1521 } 1522 1523 // Okay, we have some hope :). Check to see if the loaded value is fully 1524 // available in all but one predecessor. 1525 // FIXME: If we could restructure the CFG, we could make a common pred with 1526 // all the preds that don't have an available LI and insert a new load into 1527 // that one block. 1528 BasicBlock *UnavailablePred = 0; 1529 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 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1537 PI != E; ++PI) { 1538 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1539 continue; 1540 1541 // If this load is not available in multiple predecessors, reject it. 1542 if (UnavailablePred && UnavailablePred != *PI) 1543 return false; 1544 UnavailablePred = *PI; 1545 } 1546 1547 assert(UnavailablePred != 0 && 1548 "Fully available value should be eliminated above!"); 1549 1550 // We don't currently handle critical edges :( 1551 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1552 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1553 << UnavailablePred->getName() << "': " << *LI << '\n'); 1554 return false; 1555 } 1556 1557 // Do PHI translation to get its value in the predecessor if necessary. The 1558 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1559 // 1560 // FIXME: This may insert a computation, but we don't tell scalar GVN 1561 // optimization stuff about it. How do we do this? 1562 SmallVector<Instruction*, 8> NewInsts; 1563 Value *LoadPtr = 0; 1564 1565 // If all preds have a single successor, then we know it is safe to insert the 1566 // load on the pred (?!?), so we can insert code to materialize the pointer if 1567 // it is not available. 1568 if (allSingleSucc) { 1569 LoadPtr = MD->InsertPHITranslatedPointer(LI->getOperand(0), LoadBB, 1570 UnavailablePred, TD, *DT,NewInsts); 1571 } else { 1572 LoadPtr = MD->GetAvailablePHITranslatedValue(LI->getOperand(0), LoadBB, 1573 UnavailablePred, TD, *DT); 1574 } 1575 1576 // Assign value numbers to these new instructions. 1577 for (SmallVector<Instruction*, 8>::iterator NI = NewInsts.begin(), 1578 NE = NewInsts.end(); NI != NE; ++NI) { 1579 // FIXME: We really _ought_ to insert these value numbers into their 1580 // parent's availability map. However, in doing so, we risk getting into 1581 // ordering issues. If a block hasn't been processed yet, we would be 1582 // marking a value as AVAIL-IN, which isn't what we intend. 1583 VN.lookup_or_add(*NI); 1584 } 1585 1586 // If we couldn't find or insert a computation of this phi translated value, 1587 // we fail PRE. 1588 if (LoadPtr == 0) { 1589 DEBUG(errs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1590 << *LI->getOperand(0) << "\n"); 1591 return false; 1592 } 1593 1594 // Make sure it is valid to move this load here. We have to watch out for: 1595 // @1 = getelementptr (i8* p, ... 1596 // test p and branch if == 0 1597 // load @1 1598 // It is valid to have the getelementptr before the test, even if p can be 0, 1599 // as getelementptr only does address arithmetic. 1600 // If we are not pushing the value through any multiple-successor blocks 1601 // we do not have this case. Otherwise, check that the load is safe to 1602 // put anywhere; this can be improved, but should be conservatively safe. 1603 if (!allSingleSucc && 1604 // FIXME: REEVALUTE THIS. 1605 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) { 1606 assert(NewInsts.empty() && "Should not have inserted instructions"); 1607 return false; 1608 } 1609 1610 // Okay, we can eliminate this load by inserting a reload in the predecessor 1611 // and using PHI construction to get the value in the other predecessors, do 1612 // it. 1613 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1614 DEBUG(if (!NewInsts.empty()) 1615 errs() << "INSERTED " << NewInsts.size() << " INSTS: " 1616 << *NewInsts.back() << '\n'); 1617 1618 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1619 LI->getAlignment(), 1620 UnavailablePred->getTerminator()); 1621 1622 // Add the newly created load. 1623 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,NewLoad)); 1624 1625 // Perform PHI construction. 1626 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, 1627 VN.getAliasAnalysis()); 1628 LI->replaceAllUsesWith(V); 1629 if (isa<PHINode>(V)) 1630 V->takeName(LI); 1631 if (isa<PointerType>(V->getType())) 1632 MD->invalidateCachedPointerInfo(V); 1633 toErase.push_back(LI); 1634 NumPRELoad++; 1635 return true; 1636} 1637 1638/// processLoad - Attempt to eliminate a load, first by eliminating it 1639/// locally, and then attempting non-local elimination if that fails. 1640bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1641 if (!MD) 1642 return false; 1643 1644 if (L->isVolatile()) 1645 return false; 1646 1647 // ... to a pointer that has been loaded from before... 1648 MemDepResult Dep = MD->getDependency(L); 1649 1650 // If the value isn't available, don't do anything! 1651 if (Dep.isClobber()) { 1652 // Check to see if we have something like this: 1653 // store i32 123, i32* %P 1654 // %A = bitcast i32* %P to i8* 1655 // %B = gep i8* %A, i32 1 1656 // %C = load i8* %B 1657 // 1658 // We could do that by recognizing if the clobber instructions are obviously 1659 // a common base + constant offset, and if the previous store (or memset) 1660 // completely covers this load. This sort of thing can happen in bitfield 1661 // access code. 1662 Value *AvailVal = 0; 1663 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1664 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1665 int Offset = AnalyzeLoadFromClobberingStore(L, DepSI, *TD); 1666 if (Offset != -1) 1667 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset, 1668 L->getType(), L, *TD); 1669 } 1670 1671 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1672 // a value on from it. 1673 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1674 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1675 int Offset = AnalyzeLoadFromClobberingMemInst(L, DepMI, *TD); 1676 if (Offset != -1) 1677 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD); 1678 } 1679 } 1680 1681 if (AvailVal) { 1682 DEBUG(errs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1683 << *AvailVal << '\n' << *L << "\n\n\n"); 1684 1685 // Replace the load! 1686 L->replaceAllUsesWith(AvailVal); 1687 if (isa<PointerType>(AvailVal->getType())) 1688 MD->invalidateCachedPointerInfo(AvailVal); 1689 toErase.push_back(L); 1690 NumGVNLoad++; 1691 return true; 1692 } 1693 1694 DEBUG( 1695 // fast print dep, using operator<< on instruction would be too slow 1696 errs() << "GVN: load "; 1697 WriteAsOperand(errs(), L); 1698 Instruction *I = Dep.getInst(); 1699 errs() << " is clobbered by " << *I << '\n'; 1700 ); 1701 return false; 1702 } 1703 1704 // If it is defined in another block, try harder. 1705 if (Dep.isNonLocal()) 1706 return processNonLocalLoad(L, toErase); 1707 1708 Instruction *DepInst = Dep.getInst(); 1709 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1710 Value *StoredVal = DepSI->getOperand(0); 1711 1712 // The store and load are to a must-aliased pointer, but they may not 1713 // actually have the same type. See if we know how to reuse the stored 1714 // value (depending on its type). 1715 const TargetData *TD = 0; 1716 if (StoredVal->getType() != L->getType()) { 1717 if ((TD = getAnalysisIfAvailable<TargetData>())) { 1718 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1719 L, *TD); 1720 if (StoredVal == 0) 1721 return false; 1722 1723 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1724 << '\n' << *L << "\n\n\n"); 1725 } 1726 else 1727 return false; 1728 } 1729 1730 // Remove it! 1731 L->replaceAllUsesWith(StoredVal); 1732 if (isa<PointerType>(StoredVal->getType())) 1733 MD->invalidateCachedPointerInfo(StoredVal); 1734 toErase.push_back(L); 1735 NumGVNLoad++; 1736 return true; 1737 } 1738 1739 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1740 Value *AvailableVal = DepLI; 1741 1742 // The loads are of a must-aliased pointer, but they may not actually have 1743 // the same type. See if we know how to reuse the previously loaded value 1744 // (depending on its type). 1745 const TargetData *TD = 0; 1746 if (DepLI->getType() != L->getType()) { 1747 if ((TD = getAnalysisIfAvailable<TargetData>())) { 1748 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1749 if (AvailableVal == 0) 1750 return false; 1751 1752 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1753 << "\n" << *L << "\n\n\n"); 1754 } 1755 else 1756 return false; 1757 } 1758 1759 // Remove it! 1760 L->replaceAllUsesWith(AvailableVal); 1761 if (isa<PointerType>(DepLI->getType())) 1762 MD->invalidateCachedPointerInfo(DepLI); 1763 toErase.push_back(L); 1764 NumGVNLoad++; 1765 return true; 1766 } 1767 1768 // If this load really doesn't depend on anything, then we must be loading an 1769 // undef value. This can happen when loading for a fresh allocation with no 1770 // intervening stores, for example. 1771 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) { 1772 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1773 toErase.push_back(L); 1774 NumGVNLoad++; 1775 return true; 1776 } 1777 1778 // If this load occurs either right after a lifetime begin, 1779 // then the loaded value is undefined. 1780 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) { 1781 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1782 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1783 toErase.push_back(L); 1784 NumGVNLoad++; 1785 return true; 1786 } 1787 } 1788 1789 return false; 1790} 1791 1792Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1793 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1794 if (I == localAvail.end()) 1795 return 0; 1796 1797 ValueNumberScope *Locals = I->second; 1798 while (Locals) { 1799 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1800 if (I != Locals->table.end()) 1801 return I->second; 1802 Locals = Locals->parent; 1803 } 1804 1805 return 0; 1806} 1807 1808 1809/// processInstruction - When calculating availability, handle an instruction 1810/// by inserting it into the appropriate sets 1811bool GVN::processInstruction(Instruction *I, 1812 SmallVectorImpl<Instruction*> &toErase) { 1813 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1814 bool Changed = processLoad(LI, toErase); 1815 1816 if (!Changed) { 1817 unsigned Num = VN.lookup_or_add(LI); 1818 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1819 } 1820 1821 return Changed; 1822 } 1823 1824 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1825 unsigned Num = VN.lookup_or_add(I); 1826 1827 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1828 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1829 1830 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1831 return false; 1832 1833 Value *BranchCond = BI->getCondition(); 1834 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1835 1836 BasicBlock *TrueSucc = BI->getSuccessor(0); 1837 BasicBlock *FalseSucc = BI->getSuccessor(1); 1838 1839 if (TrueSucc->getSinglePredecessor()) 1840 localAvail[TrueSucc]->table[CondVN] = 1841 ConstantInt::getTrue(TrueSucc->getContext()); 1842 if (FalseSucc->getSinglePredecessor()) 1843 localAvail[FalseSucc]->table[CondVN] = 1844 ConstantInt::getFalse(TrueSucc->getContext()); 1845 1846 return false; 1847 1848 // Allocations are always uniquely numbered, so we can save time and memory 1849 // by fast failing them. 1850 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) { 1851 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1852 return false; 1853 } 1854 1855 // Collapse PHI nodes 1856 if (PHINode* p = dyn_cast<PHINode>(I)) { 1857 Value *constVal = CollapsePhi(p); 1858 1859 if (constVal) { 1860 p->replaceAllUsesWith(constVal); 1861 if (MD && isa<PointerType>(constVal->getType())) 1862 MD->invalidateCachedPointerInfo(constVal); 1863 VN.erase(p); 1864 1865 toErase.push_back(p); 1866 } else { 1867 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1868 } 1869 1870 // If the number we were assigned was a brand new VN, then we don't 1871 // need to do a lookup to see if the number already exists 1872 // somewhere in the domtree: it can't! 1873 } else if (Num == NextNum) { 1874 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1875 1876 // Perform fast-path value-number based elimination of values inherited from 1877 // dominators. 1878 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1879 // Remove it! 1880 VN.erase(I); 1881 I->replaceAllUsesWith(repl); 1882 if (MD && isa<PointerType>(repl->getType())) 1883 MD->invalidateCachedPointerInfo(repl); 1884 toErase.push_back(I); 1885 return true; 1886 1887 } else { 1888 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1889 } 1890 1891 return false; 1892} 1893 1894/// runOnFunction - This is the main transformation entry point for a function. 1895bool GVN::runOnFunction(Function& F) { 1896 if (!NoLoads) 1897 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1898 DT = &getAnalysis<DominatorTree>(); 1899 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1900 VN.setMemDep(MD); 1901 VN.setDomTree(DT); 1902 1903 bool Changed = false; 1904 bool ShouldContinue = true; 1905 1906 // Merge unconditional branches, allowing PRE to catch more 1907 // optimization opportunities. 1908 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1909 BasicBlock *BB = FI; 1910 ++FI; 1911 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1912 if (removedBlock) NumGVNBlocks++; 1913 1914 Changed |= removedBlock; 1915 } 1916 1917 unsigned Iteration = 0; 1918 1919 while (ShouldContinue) { 1920 DEBUG(errs() << "GVN iteration: " << Iteration << "\n"); 1921 ShouldContinue = iterateOnFunction(F); 1922 Changed |= ShouldContinue; 1923 ++Iteration; 1924 } 1925 1926 if (EnablePRE) { 1927 bool PREChanged = true; 1928 while (PREChanged) { 1929 PREChanged = performPRE(F); 1930 Changed |= PREChanged; 1931 } 1932 } 1933 // FIXME: Should perform GVN again after PRE does something. PRE can move 1934 // computations into blocks where they become fully redundant. Note that 1935 // we can't do this until PRE's critical edge splitting updates memdep. 1936 // Actually, when this happens, we should just fully integrate PRE into GVN. 1937 1938 cleanupGlobalSets(); 1939 1940 return Changed; 1941} 1942 1943 1944bool GVN::processBlock(BasicBlock *BB) { 1945 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1946 // incrementing BI before processing an instruction). 1947 SmallVector<Instruction*, 8> toErase; 1948 bool ChangedFunction = false; 1949 1950 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1951 BI != BE;) { 1952 ChangedFunction |= processInstruction(BI, toErase); 1953 if (toErase.empty()) { 1954 ++BI; 1955 continue; 1956 } 1957 1958 // If we need some instructions deleted, do it now. 1959 NumGVNInstr += toErase.size(); 1960 1961 // Avoid iterator invalidation. 1962 bool AtStart = BI == BB->begin(); 1963 if (!AtStart) 1964 --BI; 1965 1966 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1967 E = toErase.end(); I != E; ++I) { 1968 DEBUG(errs() << "GVN removed: " << **I << '\n'); 1969 if (MD) MD->removeInstruction(*I); 1970 (*I)->eraseFromParent(); 1971 DEBUG(verifyRemoved(*I)); 1972 } 1973 toErase.clear(); 1974 1975 if (AtStart) 1976 BI = BB->begin(); 1977 else 1978 ++BI; 1979 } 1980 1981 return ChangedFunction; 1982} 1983 1984/// performPRE - Perform a purely local form of PRE that looks for diamond 1985/// control flow patterns and attempts to perform simple PRE at the join point. 1986bool GVN::performPRE(Function &F) { 1987 bool Changed = false; 1988 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1989 DenseMap<BasicBlock*, Value*> predMap; 1990 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1991 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1992 BasicBlock *CurrentBlock = *DI; 1993 1994 // Nothing to PRE in the entry block. 1995 if (CurrentBlock == &F.getEntryBlock()) continue; 1996 1997 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1998 BE = CurrentBlock->end(); BI != BE; ) { 1999 Instruction *CurInst = BI++; 2000 2001 if (isa<AllocaInst>(CurInst) || 2002 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 2003 CurInst->getType()->isVoidTy() || 2004 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2005 isa<DbgInfoIntrinsic>(CurInst)) 2006 continue; 2007 2008 uint32_t ValNo = VN.lookup(CurInst); 2009 2010 // Look for the predecessors for PRE opportunities. We're 2011 // only trying to solve the basic diamond case, where 2012 // a value is computed in the successor and one predecessor, 2013 // but not the other. We also explicitly disallow cases 2014 // where the successor is its own predecessor, because they're 2015 // more complicated to get right. 2016 unsigned NumWith = 0; 2017 unsigned NumWithout = 0; 2018 BasicBlock *PREPred = 0; 2019 predMap.clear(); 2020 2021 for (pred_iterator PI = pred_begin(CurrentBlock), 2022 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2023 // We're not interested in PRE where the block is its 2024 // own predecessor, on in blocks with predecessors 2025 // that are not reachable. 2026 if (*PI == CurrentBlock) { 2027 NumWithout = 2; 2028 break; 2029 } else if (!localAvail.count(*PI)) { 2030 NumWithout = 2; 2031 break; 2032 } 2033 2034 DenseMap<uint32_t, Value*>::iterator predV = 2035 localAvail[*PI]->table.find(ValNo); 2036 if (predV == localAvail[*PI]->table.end()) { 2037 PREPred = *PI; 2038 NumWithout++; 2039 } else if (predV->second == CurInst) { 2040 NumWithout = 2; 2041 } else { 2042 predMap[*PI] = predV->second; 2043 NumWith++; 2044 } 2045 } 2046 2047 // Don't do PRE when it might increase code size, i.e. when 2048 // we would need to insert instructions in more than one pred. 2049 if (NumWithout != 1 || NumWith == 0) 2050 continue; 2051 2052 // Don't do PRE across indirect branch. 2053 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2054 continue; 2055 2056 // We can't do PRE safely on a critical edge, so instead we schedule 2057 // the edge to be split and perform the PRE the next time we iterate 2058 // on the function. 2059 unsigned SuccNum = 0; 2060 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 2061 i != e; ++i) 2062 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 2063 SuccNum = i; 2064 break; 2065 } 2066 2067 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2068 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2069 continue; 2070 } 2071 2072 // Instantiate the expression the in predecessor that lacked it. 2073 // Because we are going top-down through the block, all value numbers 2074 // will be available in the predecessor by the time we need them. Any 2075 // that weren't original present will have been instantiated earlier 2076 // in this loop. 2077 Instruction *PREInstr = CurInst->clone(); 2078 bool success = true; 2079 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2080 Value *Op = PREInstr->getOperand(i); 2081 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2082 continue; 2083 2084 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2085 PREInstr->setOperand(i, V); 2086 } else { 2087 success = false; 2088 break; 2089 } 2090 } 2091 2092 // Fail out if we encounter an operand that is not available in 2093 // the PRE predecessor. This is typically because of loads which 2094 // are not value numbered precisely. 2095 if (!success) { 2096 delete PREInstr; 2097 DEBUG(verifyRemoved(PREInstr)); 2098 continue; 2099 } 2100 2101 PREInstr->insertBefore(PREPred->getTerminator()); 2102 PREInstr->setName(CurInst->getName() + ".pre"); 2103 predMap[PREPred] = PREInstr; 2104 VN.add(PREInstr, ValNo); 2105 NumGVNPRE++; 2106 2107 // Update the availability map to include the new instruction. 2108 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 2109 2110 // Create a PHI to make the value available in this block. 2111 PHINode* Phi = PHINode::Create(CurInst->getType(), 2112 CurInst->getName() + ".pre-phi", 2113 CurrentBlock->begin()); 2114 for (pred_iterator PI = pred_begin(CurrentBlock), 2115 PE = pred_end(CurrentBlock); PI != PE; ++PI) 2116 Phi->addIncoming(predMap[*PI], *PI); 2117 2118 VN.add(Phi, ValNo); 2119 localAvail[CurrentBlock]->table[ValNo] = Phi; 2120 2121 CurInst->replaceAllUsesWith(Phi); 2122 if (MD && isa<PointerType>(Phi->getType())) 2123 MD->invalidateCachedPointerInfo(Phi); 2124 VN.erase(CurInst); 2125 2126 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n'); 2127 if (MD) MD->removeInstruction(CurInst); 2128 CurInst->eraseFromParent(); 2129 DEBUG(verifyRemoved(CurInst)); 2130 Changed = true; 2131 } 2132 } 2133 2134 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 2135 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 2136 SplitCriticalEdge(I->first, I->second, this); 2137 2138 return Changed || toSplit.size(); 2139} 2140 2141/// iterateOnFunction - Executes one iteration of GVN 2142bool GVN::iterateOnFunction(Function &F) { 2143 cleanupGlobalSets(); 2144 2145 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2146 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 2147 if (DI->getIDom()) 2148 localAvail[DI->getBlock()] = 2149 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 2150 else 2151 localAvail[DI->getBlock()] = new ValueNumberScope(0); 2152 } 2153 2154 // Top-down walk of the dominator tree 2155 bool Changed = false; 2156#if 0 2157 // Needed for value numbering with phi construction to work. 2158 ReversePostOrderTraversal<Function*> RPOT(&F); 2159 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2160 RE = RPOT.end(); RI != RE; ++RI) 2161 Changed |= processBlock(*RI); 2162#else 2163 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2164 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2165 Changed |= processBlock(DI->getBlock()); 2166#endif 2167 2168 return Changed; 2169} 2170 2171void GVN::cleanupGlobalSets() { 2172 VN.clear(); 2173 2174 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2175 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 2176 delete I->second; 2177 localAvail.clear(); 2178} 2179 2180/// verifyRemoved - Verify that the specified instruction does not occur in our 2181/// internal data structures. 2182void GVN::verifyRemoved(const Instruction *Inst) const { 2183 VN.verifyRemoved(Inst); 2184 2185 // Walk through the value number scope to make sure the instruction isn't 2186 // ferreted away in it. 2187 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator 2188 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 2189 const ValueNumberScope *VNS = I->second; 2190 2191 while (VNS) { 2192 for (DenseMap<uint32_t, Value*>::const_iterator 2193 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 2194 assert(II->second != Inst && "Inst still in value numbering scope!"); 2195 } 2196 2197 VNS = VNS->parent; 2198 } 2199 } 2200} 2201