GVN.cpp revision 9674d15120d657c9a9e681a7dc668349fa3a8de0
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/MallocHelper.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/raw_ostream.h" 44#include "llvm/Target/TargetData.h" 45#include "llvm/Transforms/Utils/BasicBlockUtils.h" 46#include "llvm/Transforms/Utils/Local.h" 47#include "llvm/Transforms/Utils/SSAUpdater.h" 48#include <cstdio> 49using namespace llvm; 50 51STATISTIC(NumGVNInstr, "Number of instructions deleted"); 52STATISTIC(NumGVNLoad, "Number of loads deleted"); 53STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 54STATISTIC(NumGVNBlocks, "Number of blocks merged"); 55STATISTIC(NumPRELoad, "Number of loads PRE'd"); 56 57static cl::opt<bool> EnablePRE("enable-pre", 58 cl::init(true), cl::Hidden); 59static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 60 61//===----------------------------------------------------------------------===// 62// ValueTable Class 63//===----------------------------------------------------------------------===// 64 65/// This class holds the mapping between values and value numbers. It is used 66/// as an efficient mechanism to determine the expression-wise equivalence of 67/// two values. 68namespace { 69 struct Expression { 70 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL, 71 UDIV, SDIV, FDIV, UREM, SREM, 72 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 73 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 74 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 75 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 76 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 77 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 78 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 79 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 80 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 81 EMPTY, TOMBSTONE }; 82 83 ExpressionOpcode opcode; 84 const Type* type; 85 uint32_t firstVN; 86 uint32_t secondVN; 87 uint32_t thirdVN; 88 SmallVector<uint32_t, 4> varargs; 89 Value *function; 90 91 Expression() { } 92 Expression(ExpressionOpcode o) : opcode(o) { } 93 94 bool operator==(const Expression &other) const { 95 if (opcode != other.opcode) 96 return false; 97 else if (opcode == EMPTY || opcode == TOMBSTONE) 98 return true; 99 else if (type != other.type) 100 return false; 101 else if (function != other.function) 102 return false; 103 else if (firstVN != other.firstVN) 104 return false; 105 else if (secondVN != other.secondVN) 106 return false; 107 else if (thirdVN != other.thirdVN) 108 return false; 109 else { 110 if (varargs.size() != other.varargs.size()) 111 return false; 112 113 for (size_t i = 0; i < varargs.size(); ++i) 114 if (varargs[i] != other.varargs[i]) 115 return false; 116 117 return true; 118 } 119 } 120 121 bool operator!=(const Expression &other) const { 122 return !(*this == other); 123 } 124 }; 125 126 class ValueTable { 127 private: 128 DenseMap<Value*, uint32_t> valueNumbering; 129 DenseMap<Expression, uint32_t> expressionNumbering; 130 AliasAnalysis* AA; 131 MemoryDependenceAnalysis* MD; 132 DominatorTree* DT; 133 134 uint32_t nextValueNumber; 135 136 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 137 Expression::ExpressionOpcode getOpcode(CmpInst* C); 138 Expression::ExpressionOpcode getOpcode(CastInst* C); 139 Expression create_expression(BinaryOperator* BO); 140 Expression create_expression(CmpInst* C); 141 Expression create_expression(ShuffleVectorInst* V); 142 Expression create_expression(ExtractElementInst* C); 143 Expression create_expression(InsertElementInst* V); 144 Expression create_expression(SelectInst* V); 145 Expression create_expression(CastInst* C); 146 Expression create_expression(GetElementPtrInst* G); 147 Expression create_expression(CallInst* C); 148 Expression create_expression(Constant* C); 149 public: 150 ValueTable() : nextValueNumber(1) { } 151 uint32_t lookup_or_add(Value *V); 152 uint32_t lookup(Value *V) const; 153 void add(Value *V, uint32_t num); 154 void clear(); 155 void erase(Value *v); 156 unsigned size(); 157 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 158 AliasAnalysis *getAliasAnalysis() const { return AA; } 159 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 160 void setDomTree(DominatorTree* D) { DT = D; } 161 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 162 void verifyRemoved(const Value *) const; 163 }; 164} 165 166namespace llvm { 167template <> struct DenseMapInfo<Expression> { 168 static inline Expression getEmptyKey() { 169 return Expression(Expression::EMPTY); 170 } 171 172 static inline Expression getTombstoneKey() { 173 return Expression(Expression::TOMBSTONE); 174 } 175 176 static unsigned getHashValue(const Expression e) { 177 unsigned hash = e.opcode; 178 179 hash = e.firstVN + hash * 37; 180 hash = e.secondVN + hash * 37; 181 hash = e.thirdVN + hash * 37; 182 183 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 184 (unsigned)((uintptr_t)e.type >> 9)) + 185 hash * 37; 186 187 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 188 E = e.varargs.end(); I != E; ++I) 189 hash = *I + hash * 37; 190 191 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 192 (unsigned)((uintptr_t)e.function >> 9)) + 193 hash * 37; 194 195 return hash; 196 } 197 static bool isEqual(const Expression &LHS, const Expression &RHS) { 198 return LHS == RHS; 199 } 200 static bool isPod() { return true; } 201}; 202} 203 204//===----------------------------------------------------------------------===// 205// ValueTable Internal Functions 206//===----------------------------------------------------------------------===// 207Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 208 switch(BO->getOpcode()) { 209 default: // THIS SHOULD NEVER HAPPEN 210 llvm_unreachable("Binary operator with unknown opcode?"); 211 case Instruction::Add: return Expression::ADD; 212 case Instruction::FAdd: return Expression::FADD; 213 case Instruction::Sub: return Expression::SUB; 214 case Instruction::FSub: return Expression::FSUB; 215 case Instruction::Mul: return Expression::MUL; 216 case Instruction::FMul: return Expression::FMUL; 217 case Instruction::UDiv: return Expression::UDIV; 218 case Instruction::SDiv: return Expression::SDIV; 219 case Instruction::FDiv: return Expression::FDIV; 220 case Instruction::URem: return Expression::UREM; 221 case Instruction::SRem: return Expression::SREM; 222 case Instruction::FRem: return Expression::FREM; 223 case Instruction::Shl: return Expression::SHL; 224 case Instruction::LShr: return Expression::LSHR; 225 case Instruction::AShr: return Expression::ASHR; 226 case Instruction::And: return Expression::AND; 227 case Instruction::Or: return Expression::OR; 228 case Instruction::Xor: return Expression::XOR; 229 } 230} 231 232Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 233 if (isa<ICmpInst>(C)) { 234 switch (C->getPredicate()) { 235 default: // THIS SHOULD NEVER HAPPEN 236 llvm_unreachable("Comparison with unknown predicate?"); 237 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 238 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 239 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 240 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 241 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 242 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 243 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 244 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 245 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 246 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 247 } 248 } else { 249 switch (C->getPredicate()) { 250 default: // THIS SHOULD NEVER HAPPEN 251 llvm_unreachable("Comparison with unknown predicate?"); 252 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 253 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 254 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 255 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 256 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 257 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 258 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 259 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 260 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 261 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 262 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 263 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 264 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 265 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 266 } 267 } 268} 269 270Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 271 switch(C->getOpcode()) { 272 default: // THIS SHOULD NEVER HAPPEN 273 llvm_unreachable("Cast operator with unknown opcode?"); 274 case Instruction::Trunc: return Expression::TRUNC; 275 case Instruction::ZExt: return Expression::ZEXT; 276 case Instruction::SExt: return Expression::SEXT; 277 case Instruction::FPToUI: return Expression::FPTOUI; 278 case Instruction::FPToSI: return Expression::FPTOSI; 279 case Instruction::UIToFP: return Expression::UITOFP; 280 case Instruction::SIToFP: return Expression::SITOFP; 281 case Instruction::FPTrunc: return Expression::FPTRUNC; 282 case Instruction::FPExt: return Expression::FPEXT; 283 case Instruction::PtrToInt: return Expression::PTRTOINT; 284 case Instruction::IntToPtr: return Expression::INTTOPTR; 285 case Instruction::BitCast: return Expression::BITCAST; 286 } 287} 288 289Expression ValueTable::create_expression(CallInst* C) { 290 Expression e; 291 292 e.type = C->getType(); 293 e.firstVN = 0; 294 e.secondVN = 0; 295 e.thirdVN = 0; 296 e.function = C->getCalledFunction(); 297 e.opcode = Expression::CALL; 298 299 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 300 I != E; ++I) 301 e.varargs.push_back(lookup_or_add(*I)); 302 303 return e; 304} 305 306Expression ValueTable::create_expression(BinaryOperator* BO) { 307 Expression e; 308 309 e.firstVN = lookup_or_add(BO->getOperand(0)); 310 e.secondVN = lookup_or_add(BO->getOperand(1)); 311 e.thirdVN = 0; 312 e.function = 0; 313 e.type = BO->getType(); 314 e.opcode = getOpcode(BO); 315 316 return e; 317} 318 319Expression ValueTable::create_expression(CmpInst* C) { 320 Expression e; 321 322 e.firstVN = lookup_or_add(C->getOperand(0)); 323 e.secondVN = lookup_or_add(C->getOperand(1)); 324 e.thirdVN = 0; 325 e.function = 0; 326 e.type = C->getType(); 327 e.opcode = getOpcode(C); 328 329 return e; 330} 331 332Expression ValueTable::create_expression(CastInst* C) { 333 Expression e; 334 335 e.firstVN = lookup_or_add(C->getOperand(0)); 336 e.secondVN = 0; 337 e.thirdVN = 0; 338 e.function = 0; 339 e.type = C->getType(); 340 e.opcode = getOpcode(C); 341 342 return e; 343} 344 345Expression ValueTable::create_expression(ShuffleVectorInst* S) { 346 Expression e; 347 348 e.firstVN = lookup_or_add(S->getOperand(0)); 349 e.secondVN = lookup_or_add(S->getOperand(1)); 350 e.thirdVN = lookup_or_add(S->getOperand(2)); 351 e.function = 0; 352 e.type = S->getType(); 353 e.opcode = Expression::SHUFFLE; 354 355 return e; 356} 357 358Expression ValueTable::create_expression(ExtractElementInst* E) { 359 Expression e; 360 361 e.firstVN = lookup_or_add(E->getOperand(0)); 362 e.secondVN = lookup_or_add(E->getOperand(1)); 363 e.thirdVN = 0; 364 e.function = 0; 365 e.type = E->getType(); 366 e.opcode = Expression::EXTRACT; 367 368 return e; 369} 370 371Expression ValueTable::create_expression(InsertElementInst* I) { 372 Expression e; 373 374 e.firstVN = lookup_or_add(I->getOperand(0)); 375 e.secondVN = lookup_or_add(I->getOperand(1)); 376 e.thirdVN = lookup_or_add(I->getOperand(2)); 377 e.function = 0; 378 e.type = I->getType(); 379 e.opcode = Expression::INSERT; 380 381 return e; 382} 383 384Expression ValueTable::create_expression(SelectInst* I) { 385 Expression e; 386 387 e.firstVN = lookup_or_add(I->getCondition()); 388 e.secondVN = lookup_or_add(I->getTrueValue()); 389 e.thirdVN = lookup_or_add(I->getFalseValue()); 390 e.function = 0; 391 e.type = I->getType(); 392 e.opcode = Expression::SELECT; 393 394 return e; 395} 396 397Expression ValueTable::create_expression(GetElementPtrInst* G) { 398 Expression e; 399 400 e.firstVN = lookup_or_add(G->getPointerOperand()); 401 e.secondVN = 0; 402 e.thirdVN = 0; 403 e.function = 0; 404 e.type = G->getType(); 405 e.opcode = Expression::GEP; 406 407 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 408 I != E; ++I) 409 e.varargs.push_back(lookup_or_add(*I)); 410 411 return e; 412} 413 414//===----------------------------------------------------------------------===// 415// ValueTable External Functions 416//===----------------------------------------------------------------------===// 417 418/// add - Insert a value into the table with a specified value number. 419void ValueTable::add(Value *V, uint32_t num) { 420 valueNumbering.insert(std::make_pair(V, num)); 421} 422 423/// lookup_or_add - Returns the value number for the specified value, assigning 424/// it a new number if it did not have one before. 425uint32_t ValueTable::lookup_or_add(Value *V) { 426 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 427 if (VI != valueNumbering.end()) 428 return VI->second; 429 430 if (CallInst* C = dyn_cast<CallInst>(V)) { 431 if (AA->doesNotAccessMemory(C)) { 432 Expression e = create_expression(C); 433 434 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 435 if (EI != expressionNumbering.end()) { 436 valueNumbering.insert(std::make_pair(V, EI->second)); 437 return EI->second; 438 } else { 439 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 440 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 441 442 return nextValueNumber++; 443 } 444 } else if (AA->onlyReadsMemory(C)) { 445 Expression e = create_expression(C); 446 447 if (expressionNumbering.find(e) == expressionNumbering.end()) { 448 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 449 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 450 return nextValueNumber++; 451 } 452 453 MemDepResult local_dep = MD->getDependency(C); 454 455 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 456 valueNumbering.insert(std::make_pair(V, 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.insert(std::make_pair(V, 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.insert(std::make_pair(V, nextValueNumber)); 473 return nextValueNumber++; 474 } 475 } 476 477 uint32_t v = lookup_or_add(local_cdep); 478 valueNumbering.insert(std::make_pair(V, 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.insert(std::make_pair(V, nextValueNumber)); 517 return nextValueNumber++; 518 } 519 520 if (cdep->getNumOperands() != C->getNumOperands()) { 521 valueNumbering.insert(std::make_pair(V, 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.insert(std::make_pair(V, nextValueNumber)); 529 return nextValueNumber++; 530 } 531 } 532 533 uint32_t v = lookup_or_add(cdep); 534 valueNumbering.insert(std::make_pair(V, v)); 535 return v; 536 537 } else { 538 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 539 return nextValueNumber++; 540 } 541 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 542 Expression e = create_expression(BO); 543 544 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 545 if (EI != expressionNumbering.end()) { 546 valueNumbering.insert(std::make_pair(V, EI->second)); 547 return EI->second; 548 } else { 549 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 550 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 551 552 return nextValueNumber++; 553 } 554 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 555 Expression e = create_expression(C); 556 557 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 558 if (EI != expressionNumbering.end()) { 559 valueNumbering.insert(std::make_pair(V, EI->second)); 560 return EI->second; 561 } else { 562 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 563 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 564 565 return nextValueNumber++; 566 } 567 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 568 Expression e = create_expression(U); 569 570 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 571 if (EI != expressionNumbering.end()) { 572 valueNumbering.insert(std::make_pair(V, EI->second)); 573 return EI->second; 574 } else { 575 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 576 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 577 578 return nextValueNumber++; 579 } 580 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 581 Expression e = create_expression(U); 582 583 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 584 if (EI != expressionNumbering.end()) { 585 valueNumbering.insert(std::make_pair(V, EI->second)); 586 return EI->second; 587 } else { 588 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 589 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 590 591 return nextValueNumber++; 592 } 593 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 594 Expression e = create_expression(U); 595 596 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 597 if (EI != expressionNumbering.end()) { 598 valueNumbering.insert(std::make_pair(V, EI->second)); 599 return EI->second; 600 } else { 601 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 602 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 603 604 return nextValueNumber++; 605 } 606 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 607 Expression e = create_expression(U); 608 609 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 610 if (EI != expressionNumbering.end()) { 611 valueNumbering.insert(std::make_pair(V, EI->second)); 612 return EI->second; 613 } else { 614 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 615 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 616 617 return nextValueNumber++; 618 } 619 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 620 Expression e = create_expression(U); 621 622 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 623 if (EI != expressionNumbering.end()) { 624 valueNumbering.insert(std::make_pair(V, EI->second)); 625 return EI->second; 626 } else { 627 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 628 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 629 630 return nextValueNumber++; 631 } 632 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 633 Expression e = create_expression(U); 634 635 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 636 if (EI != expressionNumbering.end()) { 637 valueNumbering.insert(std::make_pair(V, EI->second)); 638 return EI->second; 639 } else { 640 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 641 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 642 643 return nextValueNumber++; 644 } 645 } else { 646 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 647 return nextValueNumber++; 648 } 649} 650 651/// lookup - Returns the value number of the specified value. Fails if 652/// the value has not yet been numbered. 653uint32_t ValueTable::lookup(Value *V) const { 654 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 655 assert(VI != valueNumbering.end() && "Value not numbered?"); 656 return VI->second; 657} 658 659/// clear - Remove all entries from the ValueTable 660void ValueTable::clear() { 661 valueNumbering.clear(); 662 expressionNumbering.clear(); 663 nextValueNumber = 1; 664} 665 666/// erase - Remove a value from the value numbering 667void ValueTable::erase(Value *V) { 668 valueNumbering.erase(V); 669} 670 671/// verifyRemoved - Verify that the value is removed from all internal data 672/// structures. 673void ValueTable::verifyRemoved(const Value *V) const { 674 for (DenseMap<Value*, uint32_t>::iterator 675 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 676 assert(I->first != V && "Inst still occurs in value numbering map!"); 677 } 678} 679 680//===----------------------------------------------------------------------===// 681// GVN Pass 682//===----------------------------------------------------------------------===// 683 684namespace { 685 struct ValueNumberScope { 686 ValueNumberScope* parent; 687 DenseMap<uint32_t, Value*> table; 688 689 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 690 }; 691} 692 693namespace { 694 695 class GVN : public FunctionPass { 696 bool runOnFunction(Function &F); 697 public: 698 static char ID; // Pass identification, replacement for typeid 699 GVN() : FunctionPass(&ID) { } 700 701 private: 702 MemoryDependenceAnalysis *MD; 703 DominatorTree *DT; 704 705 ValueTable VN; 706 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 707 708 // This transformation requires dominator postdominator info 709 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 710 AU.addRequired<DominatorTree>(); 711 AU.addRequired<MemoryDependenceAnalysis>(); 712 AU.addRequired<AliasAnalysis>(); 713 714 AU.addPreserved<DominatorTree>(); 715 AU.addPreserved<AliasAnalysis>(); 716 } 717 718 // Helper fuctions 719 // FIXME: eliminate or document these better 720 bool processLoad(LoadInst* L, 721 SmallVectorImpl<Instruction*> &toErase); 722 bool processInstruction(Instruction *I, 723 SmallVectorImpl<Instruction*> &toErase); 724 bool processNonLocalLoad(LoadInst* L, 725 SmallVectorImpl<Instruction*> &toErase); 726 bool processBlock(BasicBlock *BB); 727 void dump(DenseMap<uint32_t, Value*>& d); 728 bool iterateOnFunction(Function &F); 729 Value *CollapsePhi(PHINode* p); 730 bool performPRE(Function& F); 731 Value *lookupNumber(BasicBlock *BB, uint32_t num); 732 void cleanupGlobalSets(); 733 void verifyRemoved(const Instruction *I) const; 734 }; 735 736 char GVN::ID = 0; 737} 738 739// createGVNPass - The public interface to this file... 740FunctionPass *llvm::createGVNPass() { return new GVN(); } 741 742static RegisterPass<GVN> X("gvn", 743 "Global Value Numbering"); 744 745void GVN::dump(DenseMap<uint32_t, Value*>& d) { 746 printf("{\n"); 747 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 748 E = d.end(); I != E; ++I) { 749 printf("%d\n", I->first); 750 I->second->dump(); 751 } 752 printf("}\n"); 753} 754 755static bool isSafeReplacement(PHINode* p, Instruction *inst) { 756 if (!isa<PHINode>(inst)) 757 return true; 758 759 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 760 UI != E; ++UI) 761 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 762 if (use_phi->getParent() == inst->getParent()) 763 return false; 764 765 return true; 766} 767 768Value *GVN::CollapsePhi(PHINode *PN) { 769 Value *ConstVal = PN->hasConstantValue(DT); 770 if (!ConstVal) return 0; 771 772 Instruction *Inst = dyn_cast<Instruction>(ConstVal); 773 if (!Inst) 774 return ConstVal; 775 776 if (DT->dominates(Inst, PN)) 777 if (isSafeReplacement(PN, Inst)) 778 return Inst; 779 return 0; 780} 781 782/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 783/// we're analyzing is fully available in the specified block. As we go, keep 784/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 785/// map is actually a tri-state map with the following values: 786/// 0) we know the block *is not* fully available. 787/// 1) we know the block *is* fully available. 788/// 2) we do not know whether the block is fully available or not, but we are 789/// currently speculating that it will be. 790/// 3) we are speculating for this block and have used that to speculate for 791/// other blocks. 792static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 793 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 794 // Optimistically assume that the block is fully available and check to see 795 // if we already know about this block in one lookup. 796 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 797 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 798 799 // If the entry already existed for this block, return the precomputed value. 800 if (!IV.second) { 801 // If this is a speculative "available" value, mark it as being used for 802 // speculation of other blocks. 803 if (IV.first->second == 2) 804 IV.first->second = 3; 805 return IV.first->second != 0; 806 } 807 808 // Otherwise, see if it is fully available in all predecessors. 809 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 810 811 // If this block has no predecessors, it isn't live-in here. 812 if (PI == PE) 813 goto SpeculationFailure; 814 815 for (; PI != PE; ++PI) 816 // If the value isn't fully available in one of our predecessors, then it 817 // isn't fully available in this block either. Undo our previous 818 // optimistic assumption and bail out. 819 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 820 goto SpeculationFailure; 821 822 return true; 823 824// SpeculationFailure - If we get here, we found out that this is not, after 825// all, a fully-available block. We have a problem if we speculated on this and 826// used the speculation to mark other blocks as available. 827SpeculationFailure: 828 char &BBVal = FullyAvailableBlocks[BB]; 829 830 // If we didn't speculate on this, just return with it set to false. 831 if (BBVal == 2) { 832 BBVal = 0; 833 return false; 834 } 835 836 // If we did speculate on this value, we could have blocks set to 1 that are 837 // incorrect. Walk the (transitive) successors of this block and mark them as 838 // 0 if set to one. 839 SmallVector<BasicBlock*, 32> BBWorklist; 840 BBWorklist.push_back(BB); 841 842 while (!BBWorklist.empty()) { 843 BasicBlock *Entry = BBWorklist.pop_back_val(); 844 // Note that this sets blocks to 0 (unavailable) if they happen to not 845 // already be in FullyAvailableBlocks. This is safe. 846 char &EntryVal = FullyAvailableBlocks[Entry]; 847 if (EntryVal == 0) continue; // Already unavailable. 848 849 // Mark as unavailable. 850 EntryVal = 0; 851 852 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 853 BBWorklist.push_back(*I); 854 } 855 856 return false; 857} 858 859 860/// CanCoerceMustAliasedValueToLoad - Return true if 861/// CoerceAvailableValueToLoadType will succeed. 862static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 863 const Type *LoadTy, 864 const TargetData &TD) { 865 // If the loaded or stored value is an first class array or struct, don't try 866 // to transform them. We need to be able to bitcast to integer. 867 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy) || 868 isa<StructType>(StoredVal->getType()) || 869 isa<ArrayType>(StoredVal->getType())) 870 return false; 871 872 // The store has to be at least as big as the load. 873 if (TD.getTypeSizeInBits(StoredVal->getType()) < 874 TD.getTypeSizeInBits(LoadTy)) 875 return false; 876 877 return true; 878} 879 880 881/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 882/// then a load from a must-aliased pointer of a different type, try to coerce 883/// the stored value. LoadedTy is the type of the load we want to replace and 884/// InsertPt is the place to insert new instructions. 885/// 886/// If we can't do it, return null. 887static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 888 const Type *LoadedTy, 889 Instruction *InsertPt, 890 const TargetData &TD) { 891 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 892 return 0; 893 894 const Type *StoredValTy = StoredVal->getType(); 895 896 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 897 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 898 899 // If the store and reload are the same size, we can always reuse it. 900 if (StoreSize == LoadSize) { 901 if (isa<PointerType>(StoredValTy) && isa<PointerType>(LoadedTy)) { 902 // Pointer to Pointer -> use bitcast. 903 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 904 } 905 906 // Convert source pointers to integers, which can be bitcast. 907 if (isa<PointerType>(StoredValTy)) { 908 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 909 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 910 } 911 912 const Type *TypeToCastTo = LoadedTy; 913 if (isa<PointerType>(TypeToCastTo)) 914 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 915 916 if (StoredValTy != TypeToCastTo) 917 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 918 919 // Cast to pointer if the load needs a pointer type. 920 if (isa<PointerType>(LoadedTy)) 921 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 922 923 return StoredVal; 924 } 925 926 // If the loaded value is smaller than the available value, then we can 927 // extract out a piece from it. If the available value is too small, then we 928 // can't do anything. 929 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 930 931 // Convert source pointers to integers, which can be manipulated. 932 if (isa<PointerType>(StoredValTy)) { 933 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 934 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 935 } 936 937 // Convert vectors and fp to integer, which can be manipulated. 938 if (!isa<IntegerType>(StoredValTy)) { 939 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 940 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 941 } 942 943 // If this is a big-endian system, we need to shift the value down to the low 944 // bits so that a truncate will work. 945 if (TD.isBigEndian()) { 946 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 947 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 948 } 949 950 // Truncate the integer to the right size now. 951 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 952 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 953 954 if (LoadedTy == NewIntTy) 955 return StoredVal; 956 957 // If the result is a pointer, inttoptr. 958 if (isa<PointerType>(LoadedTy)) 959 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 960 961 // Otherwise, bitcast. 962 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 963} 964 965/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 966/// be expressed as a base pointer plus a constant offset. Return the base and 967/// offset to the caller. 968static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 969 const TargetData &TD) { 970 Operator *PtrOp = dyn_cast<Operator>(Ptr); 971 if (PtrOp == 0) return Ptr; 972 973 // Just look through bitcasts. 974 if (PtrOp->getOpcode() == Instruction::BitCast) 975 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 976 977 // If this is a GEP with constant indices, we can look through it. 978 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 979 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 980 981 gep_type_iterator GTI = gep_type_begin(GEP); 982 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 983 ++I, ++GTI) { 984 ConstantInt *OpC = cast<ConstantInt>(*I); 985 if (OpC->isZero()) continue; 986 987 // Handle a struct and array indices which add their offset to the pointer. 988 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 989 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 990 } else { 991 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 992 Offset += OpC->getSExtValue()*Size; 993 } 994 } 995 996 // Re-sign extend from the pointer size if needed to get overflow edge cases 997 // right. 998 unsigned PtrSize = TD.getPointerSizeInBits(); 999 if (PtrSize < 64) 1000 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 1001 1002 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 1003} 1004 1005 1006/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1007/// memdep query of a load that ends up being a clobbering store. This means 1008/// that the store *may* provide bits used by the load but we can't be sure 1009/// because the pointers don't mustalias. Check this case to see if there is 1010/// anything more we can do before we give up. This returns -1 if we have to 1011/// give up, or a byte number in the stored value of the piece that feeds the 1012/// load. 1013static int AnalyzeLoadFromClobberingStore(LoadInst *L, StoreInst *DepSI, 1014 const TargetData &TD) { 1015 // If the loaded or stored value is an first class array or struct, don't try 1016 // to transform them. We need to be able to bitcast to integer. 1017 if (isa<StructType>(L->getType()) || isa<ArrayType>(L->getType()) || 1018 isa<StructType>(DepSI->getOperand(0)->getType()) || 1019 isa<ArrayType>(DepSI->getOperand(0)->getType())) 1020 return -1; 1021 1022 int64_t StoreOffset = 0, LoadOffset = 0; 1023 Value *StoreBase = 1024 GetBaseWithConstantOffset(DepSI->getPointerOperand(), StoreOffset, TD); 1025 Value *LoadBase = 1026 GetBaseWithConstantOffset(L->getPointerOperand(), LoadOffset, TD); 1027 if (StoreBase != LoadBase) 1028 return -1; 1029 1030 // If the load and store are to the exact same address, they should have been 1031 // a must alias. AA must have gotten confused. 1032 // FIXME: Study to see if/when this happens. 1033 if (LoadOffset == StoreOffset) { 1034#if 0 1035 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 1036 << "Base = " << *StoreBase << "\n" 1037 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1038 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1039 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1040 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1041 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1042 << *L->getParent(); 1043#endif 1044 return -1; 1045 } 1046 1047 // If the load and store don't overlap at all, the store doesn't provide 1048 // anything to the load. In this case, they really don't alias at all, AA 1049 // must have gotten confused. 1050 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1051 // remove this check, as it is duplicated with what we have below. 1052 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType()); 1053 uint64_t LoadSize = TD.getTypeSizeInBits(L->getType()); 1054 1055 if ((StoreSize & 7) | (LoadSize & 7)) 1056 return -1; 1057 StoreSize >>= 3; // Convert to bytes. 1058 LoadSize >>= 3; 1059 1060 1061 bool isAAFailure = false; 1062 if (StoreOffset < LoadOffset) { 1063 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1064 } else { 1065 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1066 } 1067 if (isAAFailure) { 1068#if 0 1069 errs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1070 << "Base = " << *StoreBase << "\n" 1071 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1072 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1073 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1074 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1075 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1076 << *L->getParent(); 1077#endif 1078 return -1; 1079 } 1080 1081 // If the Load isn't completely contained within the stored bits, we don't 1082 // have all the bits to feed it. We could do something crazy in the future 1083 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1084 // valuable. 1085 if (StoreOffset > LoadOffset || 1086 StoreOffset+StoreSize < LoadOffset+LoadSize) 1087 return -1; 1088 1089 // Okay, we can do this transformation. Return the number of bytes into the 1090 // store that the load is. 1091 return LoadOffset-StoreOffset; 1092} 1093 1094 1095/// GetStoreValueForLoad - This function is called when we have a 1096/// memdep query of a load that ends up being a clobbering store. This means 1097/// that the store *may* provide bits used by the load but we can't be sure 1098/// because the pointers don't mustalias. Check this case to see if there is 1099/// anything more we can do before we give up. 1100static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1101 const Type *LoadTy, 1102 Instruction *InsertPt, const TargetData &TD){ 1103 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1104 1105 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8; 1106 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1107 1108 1109 // Compute which bits of the stored value are being used by the load. Convert 1110 // to an integer type to start with. 1111 if (isa<PointerType>(SrcVal->getType())) 1112 SrcVal = new PtrToIntInst(SrcVal, TD.getIntPtrType(Ctx), "tmp", InsertPt); 1113 if (!isa<IntegerType>(SrcVal->getType())) 1114 SrcVal = new BitCastInst(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1115 "tmp", InsertPt); 1116 1117 // Shift the bits to the least significant depending on endianness. 1118 unsigned ShiftAmt; 1119 if (TD.isLittleEndian()) { 1120 ShiftAmt = Offset*8; 1121 } else { 1122 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1123 } 1124 1125 if (ShiftAmt) 1126 SrcVal = BinaryOperator::CreateLShr(SrcVal, 1127 ConstantInt::get(SrcVal->getType(), ShiftAmt), "tmp", InsertPt); 1128 1129 if (LoadSize != StoreSize) 1130 SrcVal = new TruncInst(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1131 "tmp", InsertPt); 1132 1133 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1134} 1135 1136struct AvailableValueInBlock { 1137 /// BB - The basic block in question. 1138 BasicBlock *BB; 1139 /// V - The value that is live out of the block. 1140 Value *V; 1141 /// Offset - The byte offset in V that is interesting for the load query. 1142 unsigned Offset; 1143 1144 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1145 unsigned Offset = 0) { 1146 AvailableValueInBlock Res; 1147 Res.BB = BB; 1148 Res.V = V; 1149 Res.Offset = Offset; 1150 return Res; 1151 } 1152}; 1153 1154/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1155/// construct SSA form, allowing us to eliminate LI. This returns the value 1156/// that should be used at LI's definition site. 1157static Value *ConstructSSAForLoadSet(LoadInst *LI, 1158 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1159 const TargetData *TD, 1160 AliasAnalysis *AA) { 1161 SmallVector<PHINode*, 8> NewPHIs; 1162 SSAUpdater SSAUpdate(&NewPHIs); 1163 SSAUpdate.Initialize(LI); 1164 1165 const Type *LoadTy = LI->getType(); 1166 1167 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1168 BasicBlock *BB = ValuesPerBlock[i].BB; 1169 Value *AvailableVal = ValuesPerBlock[i].V; 1170 unsigned Offset = ValuesPerBlock[i].Offset; 1171 1172 if (SSAUpdate.HasValueForBlock(BB)) 1173 continue; 1174 1175 if (AvailableVal->getType() != LoadTy) { 1176 assert(TD && "Need target data to handle type mismatch case"); 1177 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy, 1178 BB->getTerminator(), *TD); 1179 1180 if (Offset) { 1181 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1182 << *ValuesPerBlock[i].V << '\n' 1183 << *AvailableVal << '\n' << "\n\n\n"); 1184 } 1185 1186 1187 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1188 << *ValuesPerBlock[i].V << '\n' 1189 << *AvailableVal << '\n' << "\n\n\n"); 1190 } 1191 1192 SSAUpdate.AddAvailableValue(BB, AvailableVal); 1193 } 1194 1195 // Perform PHI construction. 1196 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1197 1198 // If new PHI nodes were created, notify alias analysis. 1199 if (isa<PointerType>(V->getType())) 1200 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1201 AA->copyValue(LI, NewPHIs[i]); 1202 1203 return V; 1204} 1205 1206/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1207/// non-local by performing PHI construction. 1208bool GVN::processNonLocalLoad(LoadInst *LI, 1209 SmallVectorImpl<Instruction*> &toErase) { 1210 // Find the non-local dependencies of the load. 1211 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 1212 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 1213 Deps); 1214 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: " 1215 // << Deps.size() << *LI << '\n'); 1216 1217 // If we had to process more than one hundred blocks to find the 1218 // dependencies, this load isn't worth worrying about. Optimizing 1219 // it will be too expensive. 1220 if (Deps.size() > 100) 1221 return false; 1222 1223 // If we had a phi translation failure, we'll have a single entry which is a 1224 // clobber in the current block. Reject this early. 1225 if (Deps.size() == 1 && Deps[0].second.isClobber()) { 1226 DEBUG( 1227 errs() << "GVN: non-local load "; 1228 WriteAsOperand(errs(), LI); 1229 errs() << " is clobbered by " << *Deps[0].second.getInst() << '\n'; 1230 ); 1231 return false; 1232 } 1233 1234 // Filter out useless results (non-locals, etc). Keep track of the blocks 1235 // where we have a value available in repl, also keep track of whether we see 1236 // dependencies that produce an unknown value for the load (such as a call 1237 // that could potentially clobber the load). 1238 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1239 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1240 1241 const TargetData *TD = 0; 1242 1243 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1244 BasicBlock *DepBB = Deps[i].first; 1245 MemDepResult DepInfo = Deps[i].second; 1246 1247 if (DepInfo.isClobber()) { 1248 // If the dependence is to a store that writes to a superset of the bits 1249 // read by the load, we can extract the bits we need for the load from the 1250 // stored value. 1251 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1252 if (TD == 0) 1253 TD = getAnalysisIfAvailable<TargetData>(); 1254 if (TD) { 1255 int Offset = AnalyzeLoadFromClobberingStore(LI, DepSI, *TD); 1256 if (Offset != -1) { 1257 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1258 DepSI->getOperand(0), 1259 Offset)); 1260 continue; 1261 } 1262 } 1263 } 1264 1265 // FIXME: Handle memset/memcpy. 1266 UnavailableBlocks.push_back(DepBB); 1267 continue; 1268 } 1269 1270 Instruction *DepInst = DepInfo.getInst(); 1271 1272 // Loading the allocation -> undef. 1273 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1274 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1275 UndefValue::get(LI->getType()))); 1276 continue; 1277 } 1278 1279 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1280 // Reject loads and stores that are to the same address but are of 1281 // different types if we have to. 1282 if (S->getOperand(0)->getType() != LI->getType()) { 1283 if (TD == 0) 1284 TD = getAnalysisIfAvailable<TargetData>(); 1285 1286 // If the stored value is larger or equal to the loaded value, we can 1287 // reuse it. 1288 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0), 1289 LI->getType(), *TD)) { 1290 UnavailableBlocks.push_back(DepBB); 1291 continue; 1292 } 1293 } 1294 1295 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1296 S->getOperand(0))); 1297 continue; 1298 } 1299 1300 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1301 // If the types mismatch and we can't handle it, reject reuse of the load. 1302 if (LD->getType() != LI->getType()) { 1303 if (TD == 0) 1304 TD = getAnalysisIfAvailable<TargetData>(); 1305 1306 // If the stored value is larger or equal to the loaded value, we can 1307 // reuse it. 1308 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1309 UnavailableBlocks.push_back(DepBB); 1310 continue; 1311 } 1312 } 1313 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1314 continue; 1315 } 1316 1317 UnavailableBlocks.push_back(DepBB); 1318 continue; 1319 } 1320 1321 // If we have no predecessors that produce a known value for this load, exit 1322 // early. 1323 if (ValuesPerBlock.empty()) return false; 1324 1325 // If all of the instructions we depend on produce a known value for this 1326 // load, then it is fully redundant and we can use PHI insertion to compute 1327 // its value. Insert PHIs and remove the fully redundant value now. 1328 if (UnavailableBlocks.empty()) { 1329 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1330 1331 // Perform PHI construction. 1332 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, 1333 VN.getAliasAnalysis()); 1334 LI->replaceAllUsesWith(V); 1335 1336 if (isa<PHINode>(V)) 1337 V->takeName(LI); 1338 if (isa<PointerType>(V->getType())) 1339 MD->invalidateCachedPointerInfo(V); 1340 toErase.push_back(LI); 1341 NumGVNLoad++; 1342 return true; 1343 } 1344 1345 if (!EnablePRE || !EnableLoadPRE) 1346 return false; 1347 1348 // Okay, we have *some* definitions of the value. This means that the value 1349 // is available in some of our (transitive) predecessors. Lets think about 1350 // doing PRE of this load. This will involve inserting a new load into the 1351 // predecessor when it's not available. We could do this in general, but 1352 // prefer to not increase code size. As such, we only do this when we know 1353 // that we only have to insert *one* load (which means we're basically moving 1354 // the load, not inserting a new one). 1355 1356 SmallPtrSet<BasicBlock *, 4> Blockers; 1357 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1358 Blockers.insert(UnavailableBlocks[i]); 1359 1360 // Lets find first basic block with more than one predecessor. Walk backwards 1361 // through predecessors if needed. 1362 BasicBlock *LoadBB = LI->getParent(); 1363 BasicBlock *TmpBB = LoadBB; 1364 1365 bool isSinglePred = false; 1366 bool allSingleSucc = true; 1367 while (TmpBB->getSinglePredecessor()) { 1368 isSinglePred = true; 1369 TmpBB = TmpBB->getSinglePredecessor(); 1370 if (!TmpBB) // If haven't found any, bail now. 1371 return false; 1372 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1373 return false; 1374 if (Blockers.count(TmpBB)) 1375 return false; 1376 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1377 allSingleSucc = false; 1378 } 1379 1380 assert(TmpBB); 1381 LoadBB = TmpBB; 1382 1383 // If we have a repl set with LI itself in it, this means we have a loop where 1384 // at least one of the values is LI. Since this means that we won't be able 1385 // to eliminate LI even if we insert uses in the other predecessors, we will 1386 // end up increasing code size. Reject this by scanning for LI. 1387 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1388 if (ValuesPerBlock[i].V == LI) 1389 return false; 1390 1391 if (isSinglePred) { 1392 bool isHot = false; 1393 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1394 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].V)) 1395 // "Hot" Instruction is in some loop (because it dominates its dep. 1396 // instruction). 1397 if (DT->dominates(LI, I)) { 1398 isHot = true; 1399 break; 1400 } 1401 1402 // We are interested only in "hot" instructions. We don't want to do any 1403 // mis-optimizations here. 1404 if (!isHot) 1405 return false; 1406 } 1407 1408 // Okay, we have some hope :). Check to see if the loaded value is fully 1409 // available in all but one predecessor. 1410 // FIXME: If we could restructure the CFG, we could make a common pred with 1411 // all the preds that don't have an available LI and insert a new load into 1412 // that one block. 1413 BasicBlock *UnavailablePred = 0; 1414 1415 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1416 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1417 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1418 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1419 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1420 1421 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1422 PI != E; ++PI) { 1423 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1424 continue; 1425 1426 // If this load is not available in multiple predecessors, reject it. 1427 if (UnavailablePred && UnavailablePred != *PI) 1428 return false; 1429 UnavailablePred = *PI; 1430 } 1431 1432 assert(UnavailablePred != 0 && 1433 "Fully available value should be eliminated above!"); 1434 1435 // If the loaded pointer is PHI node defined in this block, do PHI translation 1436 // to get its value in the predecessor. 1437 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); 1438 1439 // Make sure the value is live in the predecessor. If it was defined by a 1440 // non-PHI instruction in this block, we don't know how to recompute it above. 1441 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) 1442 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { 1443 DEBUG(errs() << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " 1444 << *LPInst << '\n' << *LI << "\n"); 1445 return false; 1446 } 1447 1448 // We don't currently handle critical edges :( 1449 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1450 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1451 << UnavailablePred->getName() << "': " << *LI << '\n'); 1452 return false; 1453 } 1454 1455 // Make sure it is valid to move this load here. We have to watch out for: 1456 // @1 = getelementptr (i8* p, ... 1457 // test p and branch if == 0 1458 // load @1 1459 // It is valid to have the getelementptr before the test, even if p can be 0, 1460 // as getelementptr only does address arithmetic. 1461 // If we are not pushing the value through any multiple-successor blocks 1462 // we do not have this case. Otherwise, check that the load is safe to 1463 // put anywhere; this can be improved, but should be conservatively safe. 1464 if (!allSingleSucc && 1465 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) 1466 return false; 1467 1468 // Okay, we can eliminate this load by inserting a reload in the predecessor 1469 // and using PHI construction to get the value in the other predecessors, do 1470 // it. 1471 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1472 1473 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1474 LI->getAlignment(), 1475 UnavailablePred->getTerminator()); 1476 1477 // Add the newly created load. 1478 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,NewLoad)); 1479 1480 // Perform PHI construction. 1481 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, 1482 VN.getAliasAnalysis()); 1483 LI->replaceAllUsesWith(V); 1484 if (isa<PHINode>(V)) 1485 V->takeName(LI); 1486 if (isa<PointerType>(V->getType())) 1487 MD->invalidateCachedPointerInfo(V); 1488 toErase.push_back(LI); 1489 NumPRELoad++; 1490 return true; 1491} 1492 1493/// processLoad - Attempt to eliminate a load, first by eliminating it 1494/// locally, and then attempting non-local elimination if that fails. 1495bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1496 if (L->isVolatile()) 1497 return false; 1498 1499 // ... to a pointer that has been loaded from before... 1500 MemDepResult Dep = MD->getDependency(L); 1501 1502 // If the value isn't available, don't do anything! 1503 if (Dep.isClobber()) { 1504 // FIXME: We should handle memset/memcpy/memmove as dependent instructions 1505 // to forward the value if available. 1506 //if (isa<MemIntrinsic>(Dep.getInst())) 1507 //errs() << "LOAD DEPENDS ON MEM: " << *L << "\n" << *Dep.getInst()<<"\n\n"; 1508 1509 // Check to see if we have something like this: 1510 // store i32 123, i32* %P 1511 // %A = bitcast i32* %P to i8* 1512 // %B = gep i8* %A, i32 1 1513 // %C = load i8* %B 1514 // 1515 // We could do that by recognizing if the clobber instructions are obviously 1516 // a common base + constant offset, and if the previous store (or memset) 1517 // completely covers this load. This sort of thing can happen in bitfield 1518 // access code. 1519 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1520 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1521 int Offset = AnalyzeLoadFromClobberingStore(L, DepSI, *TD); 1522 if (Offset != -1) { 1523 Value *AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset, 1524 L->getType(), L, *TD); 1525 DEBUG(errs() << "GVN COERCED STORE BITS:\n" << *DepSI << '\n' 1526 << *AvailVal << '\n' << *L << "\n\n\n"); 1527 1528 // Replace the load! 1529 L->replaceAllUsesWith(AvailVal); 1530 if (isa<PointerType>(AvailVal->getType())) 1531 MD->invalidateCachedPointerInfo(AvailVal); 1532 toErase.push_back(L); 1533 NumGVNLoad++; 1534 return true; 1535 } 1536 } 1537 1538 DEBUG( 1539 // fast print dep, using operator<< on instruction would be too slow 1540 errs() << "GVN: load "; 1541 WriteAsOperand(errs(), L); 1542 Instruction *I = Dep.getInst(); 1543 errs() << " is clobbered by " << *I << '\n'; 1544 ); 1545 return false; 1546 } 1547 1548 // If it is defined in another block, try harder. 1549 if (Dep.isNonLocal()) 1550 return processNonLocalLoad(L, toErase); 1551 1552 Instruction *DepInst = Dep.getInst(); 1553 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1554 Value *StoredVal = DepSI->getOperand(0); 1555 1556 // The store and load are to a must-aliased pointer, but they may not 1557 // actually have the same type. See if we know how to reuse the stored 1558 // value (depending on its type). 1559 const TargetData *TD = 0; 1560 if (StoredVal->getType() != L->getType() && 1561 (TD = getAnalysisIfAvailable<TargetData>())) { 1562 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1563 L, *TD); 1564 if (StoredVal == 0) 1565 return false; 1566 1567 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1568 << '\n' << *L << "\n\n\n"); 1569 } 1570 1571 // Remove it! 1572 L->replaceAllUsesWith(StoredVal); 1573 if (isa<PointerType>(StoredVal->getType())) 1574 MD->invalidateCachedPointerInfo(StoredVal); 1575 toErase.push_back(L); 1576 NumGVNLoad++; 1577 return true; 1578 } 1579 1580 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1581 Value *AvailableVal = DepLI; 1582 1583 // The loads are of a must-aliased pointer, but they may not actually have 1584 // the same type. See if we know how to reuse the previously loaded value 1585 // (depending on its type). 1586 const TargetData *TD = 0; 1587 if (DepLI->getType() != L->getType() && 1588 (TD = getAnalysisIfAvailable<TargetData>())) { 1589 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1590 if (AvailableVal == 0) 1591 return false; 1592 1593 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1594 << "\n" << *L << "\n\n\n"); 1595 } 1596 1597 // Remove it! 1598 L->replaceAllUsesWith(AvailableVal); 1599 if (isa<PointerType>(DepLI->getType())) 1600 MD->invalidateCachedPointerInfo(DepLI); 1601 toErase.push_back(L); 1602 NumGVNLoad++; 1603 return true; 1604 } 1605 1606 // If this load really doesn't depend on anything, then we must be loading an 1607 // undef value. This can happen when loading for a fresh allocation with no 1608 // intervening stores, for example. 1609 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1610 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1611 toErase.push_back(L); 1612 NumGVNLoad++; 1613 return true; 1614 } 1615 1616 return false; 1617} 1618 1619Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1620 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1621 if (I == localAvail.end()) 1622 return 0; 1623 1624 ValueNumberScope *Locals = I->second; 1625 while (Locals) { 1626 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1627 if (I != Locals->table.end()) 1628 return I->second; 1629 Locals = Locals->parent; 1630 } 1631 1632 return 0; 1633} 1634 1635 1636/// processInstruction - When calculating availability, handle an instruction 1637/// by inserting it into the appropriate sets 1638bool GVN::processInstruction(Instruction *I, 1639 SmallVectorImpl<Instruction*> &toErase) { 1640 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1641 bool Changed = processLoad(LI, toErase); 1642 1643 if (!Changed) { 1644 unsigned Num = VN.lookup_or_add(LI); 1645 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1646 } 1647 1648 return Changed; 1649 } 1650 1651 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1652 unsigned Num = VN.lookup_or_add(I); 1653 1654 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1655 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1656 1657 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1658 return false; 1659 1660 Value *BranchCond = BI->getCondition(); 1661 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1662 1663 BasicBlock *TrueSucc = BI->getSuccessor(0); 1664 BasicBlock *FalseSucc = BI->getSuccessor(1); 1665 1666 if (TrueSucc->getSinglePredecessor()) 1667 localAvail[TrueSucc]->table[CondVN] = 1668 ConstantInt::getTrue(TrueSucc->getContext()); 1669 if (FalseSucc->getSinglePredecessor()) 1670 localAvail[FalseSucc]->table[CondVN] = 1671 ConstantInt::getFalse(TrueSucc->getContext()); 1672 1673 return false; 1674 1675 // Allocations are always uniquely numbered, so we can save time and memory 1676 // by fast failing them. 1677 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1678 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1679 return false; 1680 } 1681 1682 // Collapse PHI nodes 1683 if (PHINode* p = dyn_cast<PHINode>(I)) { 1684 Value *constVal = CollapsePhi(p); 1685 1686 if (constVal) { 1687 p->replaceAllUsesWith(constVal); 1688 if (isa<PointerType>(constVal->getType())) 1689 MD->invalidateCachedPointerInfo(constVal); 1690 VN.erase(p); 1691 1692 toErase.push_back(p); 1693 } else { 1694 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1695 } 1696 1697 // If the number we were assigned was a brand new VN, then we don't 1698 // need to do a lookup to see if the number already exists 1699 // somewhere in the domtree: it can't! 1700 } else if (Num == NextNum) { 1701 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1702 1703 // Perform fast-path value-number based elimination of values inherited from 1704 // dominators. 1705 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1706 // Remove it! 1707 VN.erase(I); 1708 I->replaceAllUsesWith(repl); 1709 if (isa<PointerType>(repl->getType())) 1710 MD->invalidateCachedPointerInfo(repl); 1711 toErase.push_back(I); 1712 return true; 1713 1714 } else { 1715 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1716 } 1717 1718 return false; 1719} 1720 1721/// runOnFunction - This is the main transformation entry point for a function. 1722bool GVN::runOnFunction(Function& F) { 1723 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1724 DT = &getAnalysis<DominatorTree>(); 1725 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1726 VN.setMemDep(MD); 1727 VN.setDomTree(DT); 1728 1729 bool Changed = false; 1730 bool ShouldContinue = true; 1731 1732 // Merge unconditional branches, allowing PRE to catch more 1733 // optimization opportunities. 1734 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1735 BasicBlock *BB = FI; 1736 ++FI; 1737 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1738 if (removedBlock) NumGVNBlocks++; 1739 1740 Changed |= removedBlock; 1741 } 1742 1743 unsigned Iteration = 0; 1744 1745 while (ShouldContinue) { 1746 DEBUG(errs() << "GVN iteration: " << Iteration << "\n"); 1747 ShouldContinue = iterateOnFunction(F); 1748 Changed |= ShouldContinue; 1749 ++Iteration; 1750 } 1751 1752 if (EnablePRE) { 1753 bool PREChanged = true; 1754 while (PREChanged) { 1755 PREChanged = performPRE(F); 1756 Changed |= PREChanged; 1757 } 1758 } 1759 // FIXME: Should perform GVN again after PRE does something. PRE can move 1760 // computations into blocks where they become fully redundant. Note that 1761 // we can't do this until PRE's critical edge splitting updates memdep. 1762 // Actually, when this happens, we should just fully integrate PRE into GVN. 1763 1764 cleanupGlobalSets(); 1765 1766 return Changed; 1767} 1768 1769 1770bool GVN::processBlock(BasicBlock *BB) { 1771 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1772 // incrementing BI before processing an instruction). 1773 SmallVector<Instruction*, 8> toErase; 1774 bool ChangedFunction = false; 1775 1776 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1777 BI != BE;) { 1778 ChangedFunction |= processInstruction(BI, toErase); 1779 if (toErase.empty()) { 1780 ++BI; 1781 continue; 1782 } 1783 1784 // If we need some instructions deleted, do it now. 1785 NumGVNInstr += toErase.size(); 1786 1787 // Avoid iterator invalidation. 1788 bool AtStart = BI == BB->begin(); 1789 if (!AtStart) 1790 --BI; 1791 1792 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1793 E = toErase.end(); I != E; ++I) { 1794 DEBUG(errs() << "GVN removed: " << **I << '\n'); 1795 MD->removeInstruction(*I); 1796 (*I)->eraseFromParent(); 1797 DEBUG(verifyRemoved(*I)); 1798 } 1799 toErase.clear(); 1800 1801 if (AtStart) 1802 BI = BB->begin(); 1803 else 1804 ++BI; 1805 } 1806 1807 return ChangedFunction; 1808} 1809 1810/// performPRE - Perform a purely local form of PRE that looks for diamond 1811/// control flow patterns and attempts to perform simple PRE at the join point. 1812bool GVN::performPRE(Function& F) { 1813 bool Changed = false; 1814 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1815 DenseMap<BasicBlock*, Value*> predMap; 1816 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1817 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1818 BasicBlock *CurrentBlock = *DI; 1819 1820 // Nothing to PRE in the entry block. 1821 if (CurrentBlock == &F.getEntryBlock()) continue; 1822 1823 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1824 BE = CurrentBlock->end(); BI != BE; ) { 1825 Instruction *CurInst = BI++; 1826 1827 if (isa<AllocationInst>(CurInst) || 1828 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 1829 CurInst->getType()->isVoidTy() || 1830 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 1831 isa<DbgInfoIntrinsic>(CurInst)) 1832 continue; 1833 1834 uint32_t ValNo = VN.lookup(CurInst); 1835 1836 // Look for the predecessors for PRE opportunities. We're 1837 // only trying to solve the basic diamond case, where 1838 // a value is computed in the successor and one predecessor, 1839 // but not the other. We also explicitly disallow cases 1840 // where the successor is its own predecessor, because they're 1841 // more complicated to get right. 1842 unsigned NumWith = 0; 1843 unsigned NumWithout = 0; 1844 BasicBlock *PREPred = 0; 1845 predMap.clear(); 1846 1847 for (pred_iterator PI = pred_begin(CurrentBlock), 1848 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1849 // We're not interested in PRE where the block is its 1850 // own predecessor, on in blocks with predecessors 1851 // that are not reachable. 1852 if (*PI == CurrentBlock) { 1853 NumWithout = 2; 1854 break; 1855 } else if (!localAvail.count(*PI)) { 1856 NumWithout = 2; 1857 break; 1858 } 1859 1860 DenseMap<uint32_t, Value*>::iterator predV = 1861 localAvail[*PI]->table.find(ValNo); 1862 if (predV == localAvail[*PI]->table.end()) { 1863 PREPred = *PI; 1864 NumWithout++; 1865 } else if (predV->second == CurInst) { 1866 NumWithout = 2; 1867 } else { 1868 predMap[*PI] = predV->second; 1869 NumWith++; 1870 } 1871 } 1872 1873 // Don't do PRE when it might increase code size, i.e. when 1874 // we would need to insert instructions in more than one pred. 1875 if (NumWithout != 1 || NumWith == 0) 1876 continue; 1877 1878 // We can't do PRE safely on a critical edge, so instead we schedule 1879 // the edge to be split and perform the PRE the next time we iterate 1880 // on the function. 1881 unsigned SuccNum = 0; 1882 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1883 i != e; ++i) 1884 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1885 SuccNum = i; 1886 break; 1887 } 1888 1889 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 1890 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 1891 continue; 1892 } 1893 1894 // Instantiate the expression the in predecessor that lacked it. 1895 // Because we are going top-down through the block, all value numbers 1896 // will be available in the predecessor by the time we need them. Any 1897 // that weren't original present will have been instantiated earlier 1898 // in this loop. 1899 Instruction *PREInstr = CurInst->clone(); 1900 bool success = true; 1901 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 1902 Value *Op = PREInstr->getOperand(i); 1903 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 1904 continue; 1905 1906 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 1907 PREInstr->setOperand(i, V); 1908 } else { 1909 success = false; 1910 break; 1911 } 1912 } 1913 1914 // Fail out if we encounter an operand that is not available in 1915 // the PRE predecessor. This is typically because of loads which 1916 // are not value numbered precisely. 1917 if (!success) { 1918 delete PREInstr; 1919 DEBUG(verifyRemoved(PREInstr)); 1920 continue; 1921 } 1922 1923 PREInstr->insertBefore(PREPred->getTerminator()); 1924 PREInstr->setName(CurInst->getName() + ".pre"); 1925 predMap[PREPred] = PREInstr; 1926 VN.add(PREInstr, ValNo); 1927 NumGVNPRE++; 1928 1929 // Update the availability map to include the new instruction. 1930 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 1931 1932 // Create a PHI to make the value available in this block. 1933 PHINode* Phi = PHINode::Create(CurInst->getType(), 1934 CurInst->getName() + ".pre-phi", 1935 CurrentBlock->begin()); 1936 for (pred_iterator PI = pred_begin(CurrentBlock), 1937 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1938 Phi->addIncoming(predMap[*PI], *PI); 1939 1940 VN.add(Phi, ValNo); 1941 localAvail[CurrentBlock]->table[ValNo] = Phi; 1942 1943 CurInst->replaceAllUsesWith(Phi); 1944 if (isa<PointerType>(Phi->getType())) 1945 MD->invalidateCachedPointerInfo(Phi); 1946 VN.erase(CurInst); 1947 1948 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n'); 1949 MD->removeInstruction(CurInst); 1950 CurInst->eraseFromParent(); 1951 DEBUG(verifyRemoved(CurInst)); 1952 Changed = true; 1953 } 1954 } 1955 1956 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1957 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1958 SplitCriticalEdge(I->first, I->second, this); 1959 1960 return Changed || toSplit.size(); 1961} 1962 1963/// iterateOnFunction - Executes one iteration of GVN 1964bool GVN::iterateOnFunction(Function &F) { 1965 cleanupGlobalSets(); 1966 1967 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1968 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 1969 if (DI->getIDom()) 1970 localAvail[DI->getBlock()] = 1971 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 1972 else 1973 localAvail[DI->getBlock()] = new ValueNumberScope(0); 1974 } 1975 1976 // Top-down walk of the dominator tree 1977 bool Changed = false; 1978#if 0 1979 // Needed for value numbering with phi construction to work. 1980 ReversePostOrderTraversal<Function*> RPOT(&F); 1981 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 1982 RE = RPOT.end(); RI != RE; ++RI) 1983 Changed |= processBlock(*RI); 1984#else 1985 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1986 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 1987 Changed |= processBlock(DI->getBlock()); 1988#endif 1989 1990 return Changed; 1991} 1992 1993void GVN::cleanupGlobalSets() { 1994 VN.clear(); 1995 1996 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1997 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1998 delete I->second; 1999 localAvail.clear(); 2000} 2001 2002/// verifyRemoved - Verify that the specified instruction does not occur in our 2003/// internal data structures. 2004void GVN::verifyRemoved(const Instruction *Inst) const { 2005 VN.verifyRemoved(Inst); 2006 2007 // Walk through the value number scope to make sure the instruction isn't 2008 // ferreted away in it. 2009 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2010 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 2011 const ValueNumberScope *VNS = I->second; 2012 2013 while (VNS) { 2014 for (DenseMap<uint32_t, Value*>::iterator 2015 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 2016 assert(II->second != Inst && "Inst still in value numbering scope!"); 2017 } 2018 2019 VNS = VNS->parent; 2020 } 2021 } 2022} 2023