GVN.cpp revision 2d7f1d24bf32418de4ff817284eb5222726c2c62
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 <cstdio> 48using namespace llvm; 49 50STATISTIC(NumGVNInstr, "Number of instructions deleted"); 51STATISTIC(NumGVNLoad, "Number of loads deleted"); 52STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 53STATISTIC(NumGVNBlocks, "Number of blocks merged"); 54STATISTIC(NumPRELoad, "Number of loads PRE'd"); 55 56static cl::opt<bool> EnablePRE("enable-pre", 57 cl::init(true), cl::Hidden); 58static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 59 60//===----------------------------------------------------------------------===// 61// ValueTable Class 62//===----------------------------------------------------------------------===// 63 64/// This class holds the mapping between values and value numbers. It is used 65/// as an efficient mechanism to determine the expression-wise equivalence of 66/// two values. 67namespace { 68 struct Expression { 69 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL, 70 UDIV, SDIV, FDIV, UREM, SREM, 71 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 72 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 73 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 74 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 75 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 76 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 77 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 78 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 79 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 80 EMPTY, TOMBSTONE }; 81 82 ExpressionOpcode opcode; 83 const Type* type; 84 uint32_t firstVN; 85 uint32_t secondVN; 86 uint32_t thirdVN; 87 SmallVector<uint32_t, 4> varargs; 88 Value *function; 89 90 Expression() { } 91 Expression(ExpressionOpcode o) : opcode(o) { } 92 93 bool operator==(const Expression &other) const { 94 if (opcode != other.opcode) 95 return false; 96 else if (opcode == EMPTY || opcode == TOMBSTONE) 97 return true; 98 else if (type != other.type) 99 return false; 100 else if (function != other.function) 101 return false; 102 else if (firstVN != other.firstVN) 103 return false; 104 else if (secondVN != other.secondVN) 105 return false; 106 else if (thirdVN != other.thirdVN) 107 return false; 108 else { 109 if (varargs.size() != other.varargs.size()) 110 return false; 111 112 for (size_t i = 0; i < varargs.size(); ++i) 113 if (varargs[i] != other.varargs[i]) 114 return false; 115 116 return true; 117 } 118 } 119 120 bool operator!=(const Expression &other) const { 121 return !(*this == other); 122 } 123 }; 124 125 class ValueTable { 126 private: 127 DenseMap<Value*, uint32_t> valueNumbering; 128 DenseMap<Expression, uint32_t> expressionNumbering; 129 AliasAnalysis* AA; 130 MemoryDependenceAnalysis* MD; 131 DominatorTree* DT; 132 133 uint32_t nextValueNumber; 134 135 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 136 Expression::ExpressionOpcode getOpcode(CmpInst* C); 137 Expression::ExpressionOpcode getOpcode(CastInst* C); 138 Expression create_expression(BinaryOperator* BO); 139 Expression create_expression(CmpInst* C); 140 Expression create_expression(ShuffleVectorInst* V); 141 Expression create_expression(ExtractElementInst* C); 142 Expression create_expression(InsertElementInst* V); 143 Expression create_expression(SelectInst* V); 144 Expression create_expression(CastInst* C); 145 Expression create_expression(GetElementPtrInst* G); 146 Expression create_expression(CallInst* C); 147 Expression create_expression(Constant* C); 148 public: 149 ValueTable() : nextValueNumber(1) { } 150 uint32_t lookup_or_add(Value *V); 151 uint32_t lookup(Value *V) const; 152 void add(Value *V, uint32_t num); 153 void clear(); 154 void erase(Value *v); 155 unsigned size(); 156 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 157 AliasAnalysis *getAliasAnalysis() const { return AA; } 158 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 159 void setDomTree(DominatorTree* D) { DT = D; } 160 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 161 void verifyRemoved(const Value *) const; 162 }; 163} 164 165namespace llvm { 166template <> struct DenseMapInfo<Expression> { 167 static inline Expression getEmptyKey() { 168 return Expression(Expression::EMPTY); 169 } 170 171 static inline Expression getTombstoneKey() { 172 return Expression(Expression::TOMBSTONE); 173 } 174 175 static unsigned getHashValue(const Expression e) { 176 unsigned hash = e.opcode; 177 178 hash = e.firstVN + hash * 37; 179 hash = e.secondVN + hash * 37; 180 hash = e.thirdVN + hash * 37; 181 182 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 183 (unsigned)((uintptr_t)e.type >> 9)) + 184 hash * 37; 185 186 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 187 E = e.varargs.end(); I != E; ++I) 188 hash = *I + hash * 37; 189 190 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 191 (unsigned)((uintptr_t)e.function >> 9)) + 192 hash * 37; 193 194 return hash; 195 } 196 static bool isEqual(const Expression &LHS, const Expression &RHS) { 197 return LHS == RHS; 198 } 199 static bool isPod() { return true; } 200}; 201} 202 203//===----------------------------------------------------------------------===// 204// ValueTable Internal Functions 205//===----------------------------------------------------------------------===// 206Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 207 switch(BO->getOpcode()) { 208 default: // THIS SHOULD NEVER HAPPEN 209 llvm_unreachable("Binary operator with unknown opcode?"); 210 case Instruction::Add: return Expression::ADD; 211 case Instruction::FAdd: return Expression::FADD; 212 case Instruction::Sub: return Expression::SUB; 213 case Instruction::FSub: return Expression::FSUB; 214 case Instruction::Mul: return Expression::MUL; 215 case Instruction::FMul: return Expression::FMUL; 216 case Instruction::UDiv: return Expression::UDIV; 217 case Instruction::SDiv: return Expression::SDIV; 218 case Instruction::FDiv: return Expression::FDIV; 219 case Instruction::URem: return Expression::UREM; 220 case Instruction::SRem: return Expression::SREM; 221 case Instruction::FRem: return Expression::FREM; 222 case Instruction::Shl: return Expression::SHL; 223 case Instruction::LShr: return Expression::LSHR; 224 case Instruction::AShr: return Expression::ASHR; 225 case Instruction::And: return Expression::AND; 226 case Instruction::Or: return Expression::OR; 227 case Instruction::Xor: return Expression::XOR; 228 } 229} 230 231Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 232 if (isa<ICmpInst>(C)) { 233 switch (C->getPredicate()) { 234 default: // THIS SHOULD NEVER HAPPEN 235 llvm_unreachable("Comparison with unknown predicate?"); 236 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 237 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 238 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 239 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 240 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 241 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 242 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 243 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 244 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 245 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 246 } 247 } else { 248 switch (C->getPredicate()) { 249 default: // THIS SHOULD NEVER HAPPEN 250 llvm_unreachable("Comparison with unknown predicate?"); 251 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 252 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 253 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 254 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 255 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 256 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 257 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 258 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 259 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 260 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 261 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 262 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 263 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 264 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 265 } 266 } 267} 268 269Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 270 switch(C->getOpcode()) { 271 default: // THIS SHOULD NEVER HAPPEN 272 llvm_unreachable("Cast operator with unknown opcode?"); 273 case Instruction::Trunc: return Expression::TRUNC; 274 case Instruction::ZExt: return Expression::ZEXT; 275 case Instruction::SExt: return Expression::SEXT; 276 case Instruction::FPToUI: return Expression::FPTOUI; 277 case Instruction::FPToSI: return Expression::FPTOSI; 278 case Instruction::UIToFP: return Expression::UITOFP; 279 case Instruction::SIToFP: return Expression::SITOFP; 280 case Instruction::FPTrunc: return Expression::FPTRUNC; 281 case Instruction::FPExt: return Expression::FPEXT; 282 case Instruction::PtrToInt: return Expression::PTRTOINT; 283 case Instruction::IntToPtr: return Expression::INTTOPTR; 284 case Instruction::BitCast: return Expression::BITCAST; 285 } 286} 287 288Expression ValueTable::create_expression(CallInst* C) { 289 Expression e; 290 291 e.type = C->getType(); 292 e.firstVN = 0; 293 e.secondVN = 0; 294 e.thirdVN = 0; 295 e.function = C->getCalledFunction(); 296 e.opcode = Expression::CALL; 297 298 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 299 I != E; ++I) 300 e.varargs.push_back(lookup_or_add(*I)); 301 302 return e; 303} 304 305Expression ValueTable::create_expression(BinaryOperator* BO) { 306 Expression e; 307 308 e.firstVN = lookup_or_add(BO->getOperand(0)); 309 e.secondVN = lookup_or_add(BO->getOperand(1)); 310 e.thirdVN = 0; 311 e.function = 0; 312 e.type = BO->getType(); 313 e.opcode = getOpcode(BO); 314 315 return e; 316} 317 318Expression ValueTable::create_expression(CmpInst* C) { 319 Expression e; 320 321 e.firstVN = lookup_or_add(C->getOperand(0)); 322 e.secondVN = lookup_or_add(C->getOperand(1)); 323 e.thirdVN = 0; 324 e.function = 0; 325 e.type = C->getType(); 326 e.opcode = getOpcode(C); 327 328 return e; 329} 330 331Expression ValueTable::create_expression(CastInst* C) { 332 Expression e; 333 334 e.firstVN = lookup_or_add(C->getOperand(0)); 335 e.secondVN = 0; 336 e.thirdVN = 0; 337 e.function = 0; 338 e.type = C->getType(); 339 e.opcode = getOpcode(C); 340 341 return e; 342} 343 344Expression ValueTable::create_expression(ShuffleVectorInst* S) { 345 Expression e; 346 347 e.firstVN = lookup_or_add(S->getOperand(0)); 348 e.secondVN = lookup_or_add(S->getOperand(1)); 349 e.thirdVN = lookup_or_add(S->getOperand(2)); 350 e.function = 0; 351 e.type = S->getType(); 352 e.opcode = Expression::SHUFFLE; 353 354 return e; 355} 356 357Expression ValueTable::create_expression(ExtractElementInst* E) { 358 Expression e; 359 360 e.firstVN = lookup_or_add(E->getOperand(0)); 361 e.secondVN = lookup_or_add(E->getOperand(1)); 362 e.thirdVN = 0; 363 e.function = 0; 364 e.type = E->getType(); 365 e.opcode = Expression::EXTRACT; 366 367 return e; 368} 369 370Expression ValueTable::create_expression(InsertElementInst* I) { 371 Expression e; 372 373 e.firstVN = lookup_or_add(I->getOperand(0)); 374 e.secondVN = lookup_or_add(I->getOperand(1)); 375 e.thirdVN = lookup_or_add(I->getOperand(2)); 376 e.function = 0; 377 e.type = I->getType(); 378 e.opcode = Expression::INSERT; 379 380 return e; 381} 382 383Expression ValueTable::create_expression(SelectInst* I) { 384 Expression e; 385 386 e.firstVN = lookup_or_add(I->getCondition()); 387 e.secondVN = lookup_or_add(I->getTrueValue()); 388 e.thirdVN = lookup_or_add(I->getFalseValue()); 389 e.function = 0; 390 e.type = I->getType(); 391 e.opcode = Expression::SELECT; 392 393 return e; 394} 395 396Expression ValueTable::create_expression(GetElementPtrInst* G) { 397 Expression e; 398 399 e.firstVN = lookup_or_add(G->getPointerOperand()); 400 e.secondVN = 0; 401 e.thirdVN = 0; 402 e.function = 0; 403 e.type = G->getType(); 404 e.opcode = Expression::GEP; 405 406 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 407 I != E; ++I) 408 e.varargs.push_back(lookup_or_add(*I)); 409 410 return e; 411} 412 413//===----------------------------------------------------------------------===// 414// ValueTable External Functions 415//===----------------------------------------------------------------------===// 416 417/// add - Insert a value into the table with a specified value number. 418void ValueTable::add(Value *V, uint32_t num) { 419 valueNumbering.insert(std::make_pair(V, num)); 420} 421 422/// lookup_or_add - Returns the value number for the specified value, assigning 423/// it a new number if it did not have one before. 424uint32_t ValueTable::lookup_or_add(Value *V) { 425 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 426 if (VI != valueNumbering.end()) 427 return VI->second; 428 429 if (CallInst* C = dyn_cast<CallInst>(V)) { 430 if (AA->doesNotAccessMemory(C)) { 431 Expression e = create_expression(C); 432 433 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 434 if (EI != expressionNumbering.end()) { 435 valueNumbering.insert(std::make_pair(V, EI->second)); 436 return EI->second; 437 } else { 438 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 439 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 440 441 return nextValueNumber++; 442 } 443 } else if (AA->onlyReadsMemory(C)) { 444 Expression e = create_expression(C); 445 446 if (expressionNumbering.find(e) == expressionNumbering.end()) { 447 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 448 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 449 return nextValueNumber++; 450 } 451 452 MemDepResult local_dep = MD->getDependency(C); 453 454 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 455 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 456 return nextValueNumber++; 457 } 458 459 if (local_dep.isDef()) { 460 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 461 462 if (local_cdep->getNumOperands() != C->getNumOperands()) { 463 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 464 return nextValueNumber++; 465 } 466 467 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 468 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 469 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 470 if (c_vn != cd_vn) { 471 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 472 return nextValueNumber++; 473 } 474 } 475 476 uint32_t v = lookup_or_add(local_cdep); 477 valueNumbering.insert(std::make_pair(V, v)); 478 return v; 479 } 480 481 // Non-local case. 482 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 483 MD->getNonLocalCallDependency(CallSite(C)); 484 // FIXME: call/call dependencies for readonly calls should return def, not 485 // clobber! Move the checking logic to MemDep! 486 CallInst* cdep = 0; 487 488 // Check to see if we have a single dominating call instruction that is 489 // identical to C. 490 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 491 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i]; 492 // Ignore non-local dependencies. 493 if (I->second.isNonLocal()) 494 continue; 495 496 // We don't handle non-depedencies. If we already have a call, reject 497 // instruction dependencies. 498 if (I->second.isClobber() || cdep != 0) { 499 cdep = 0; 500 break; 501 } 502 503 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst()); 504 // FIXME: All duplicated with non-local case. 505 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){ 506 cdep = NonLocalDepCall; 507 continue; 508 } 509 510 cdep = 0; 511 break; 512 } 513 514 if (!cdep) { 515 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 516 return nextValueNumber++; 517 } 518 519 if (cdep->getNumOperands() != C->getNumOperands()) { 520 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 521 return nextValueNumber++; 522 } 523 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 524 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 525 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 526 if (c_vn != cd_vn) { 527 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 528 return nextValueNumber++; 529 } 530 } 531 532 uint32_t v = lookup_or_add(cdep); 533 valueNumbering.insert(std::make_pair(V, v)); 534 return v; 535 536 } else { 537 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 538 return nextValueNumber++; 539 } 540 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 541 Expression e = create_expression(BO); 542 543 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 544 if (EI != expressionNumbering.end()) { 545 valueNumbering.insert(std::make_pair(V, EI->second)); 546 return EI->second; 547 } else { 548 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 549 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 550 551 return nextValueNumber++; 552 } 553 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 554 Expression e = create_expression(C); 555 556 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 557 if (EI != expressionNumbering.end()) { 558 valueNumbering.insert(std::make_pair(V, EI->second)); 559 return EI->second; 560 } else { 561 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 562 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 563 564 return nextValueNumber++; 565 } 566 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 567 Expression e = create_expression(U); 568 569 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 570 if (EI != expressionNumbering.end()) { 571 valueNumbering.insert(std::make_pair(V, EI->second)); 572 return EI->second; 573 } else { 574 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 575 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 576 577 return nextValueNumber++; 578 } 579 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 580 Expression e = create_expression(U); 581 582 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 583 if (EI != expressionNumbering.end()) { 584 valueNumbering.insert(std::make_pair(V, EI->second)); 585 return EI->second; 586 } else { 587 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 588 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 589 590 return nextValueNumber++; 591 } 592 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 593 Expression e = create_expression(U); 594 595 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 596 if (EI != expressionNumbering.end()) { 597 valueNumbering.insert(std::make_pair(V, EI->second)); 598 return EI->second; 599 } else { 600 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 601 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 602 603 return nextValueNumber++; 604 } 605 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 606 Expression e = create_expression(U); 607 608 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 609 if (EI != expressionNumbering.end()) { 610 valueNumbering.insert(std::make_pair(V, EI->second)); 611 return EI->second; 612 } else { 613 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 614 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 615 616 return nextValueNumber++; 617 } 618 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 619 Expression e = create_expression(U); 620 621 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 622 if (EI != expressionNumbering.end()) { 623 valueNumbering.insert(std::make_pair(V, EI->second)); 624 return EI->second; 625 } else { 626 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 627 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 628 629 return nextValueNumber++; 630 } 631 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 632 Expression e = create_expression(U); 633 634 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 635 if (EI != expressionNumbering.end()) { 636 valueNumbering.insert(std::make_pair(V, EI->second)); 637 return EI->second; 638 } else { 639 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 640 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 641 642 return nextValueNumber++; 643 } 644 } else { 645 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 646 return nextValueNumber++; 647 } 648} 649 650/// lookup - Returns the value number of the specified value. Fails if 651/// the value has not yet been numbered. 652uint32_t ValueTable::lookup(Value *V) const { 653 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 654 assert(VI != valueNumbering.end() && "Value not numbered?"); 655 return VI->second; 656} 657 658/// clear - Remove all entries from the ValueTable 659void ValueTable::clear() { 660 valueNumbering.clear(); 661 expressionNumbering.clear(); 662 nextValueNumber = 1; 663} 664 665/// erase - Remove a value from the value numbering 666void ValueTable::erase(Value *V) { 667 valueNumbering.erase(V); 668} 669 670/// verifyRemoved - Verify that the value is removed from all internal data 671/// structures. 672void ValueTable::verifyRemoved(const Value *V) const { 673 for (DenseMap<Value*, uint32_t>::iterator 674 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 675 assert(I->first != V && "Inst still occurs in value numbering map!"); 676 } 677} 678 679//===----------------------------------------------------------------------===// 680// GVN Pass 681//===----------------------------------------------------------------------===// 682 683namespace { 684 struct ValueNumberScope { 685 ValueNumberScope* parent; 686 DenseMap<uint32_t, Value*> table; 687 688 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 689 }; 690} 691 692namespace { 693 694 class GVN : public FunctionPass { 695 bool runOnFunction(Function &F); 696 public: 697 static char ID; // Pass identification, replacement for typeid 698 GVN() : FunctionPass(&ID) { } 699 700 private: 701 MemoryDependenceAnalysis *MD; 702 DominatorTree *DT; 703 704 ValueTable VN; 705 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 706 707 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 708 PhiMapType phiMap; 709 710 711 // This transformation requires dominator postdominator info 712 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 713 AU.addRequired<DominatorTree>(); 714 AU.addRequired<MemoryDependenceAnalysis>(); 715 AU.addRequired<AliasAnalysis>(); 716 717 AU.addPreserved<DominatorTree>(); 718 AU.addPreserved<AliasAnalysis>(); 719 } 720 721 // Helper fuctions 722 // FIXME: eliminate or document these better 723 bool processLoad(LoadInst* L, 724 SmallVectorImpl<Instruction*> &toErase); 725 bool processInstruction(Instruction *I, 726 SmallVectorImpl<Instruction*> &toErase); 727 bool processNonLocalLoad(LoadInst* L, 728 SmallVectorImpl<Instruction*> &toErase); 729 bool processBlock(BasicBlock *BB); 730 Value *GetValueForBlock(BasicBlock *BB, Instruction *orig, 731 DenseMap<BasicBlock*, Value*> &Phis, 732 bool top_level = false); 733 void dump(DenseMap<uint32_t, Value*>& d); 734 bool iterateOnFunction(Function &F); 735 Value *CollapsePhi(PHINode* p); 736 bool performPRE(Function& F); 737 Value *lookupNumber(BasicBlock *BB, uint32_t num); 738 Value *AttemptRedundancyElimination(Instruction *orig, unsigned valno); 739 void cleanupGlobalSets(); 740 void verifyRemoved(const Instruction *I) const; 741 }; 742 743 char GVN::ID = 0; 744} 745 746// createGVNPass - The public interface to this file... 747FunctionPass *llvm::createGVNPass() { return new GVN(); } 748 749static RegisterPass<GVN> X("gvn", 750 "Global Value Numbering"); 751 752void GVN::dump(DenseMap<uint32_t, Value*>& d) { 753 printf("{\n"); 754 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 755 E = d.end(); I != E; ++I) { 756 printf("%d\n", I->first); 757 I->second->dump(); 758 } 759 printf("}\n"); 760} 761 762static bool isSafeReplacement(PHINode* p, Instruction *inst) { 763 if (!isa<PHINode>(inst)) 764 return true; 765 766 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 767 UI != E; ++UI) 768 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 769 if (use_phi->getParent() == inst->getParent()) 770 return false; 771 772 return true; 773} 774 775Value *GVN::CollapsePhi(PHINode *PN) { 776 Value *ConstVal = PN->hasConstantValue(DT); 777 if (!ConstVal) return 0; 778 779 Instruction *Inst = dyn_cast<Instruction>(ConstVal); 780 if (!Inst) 781 return ConstVal; 782 783 if (DT->dominates(Inst, PN)) 784 if (isSafeReplacement(PN, Inst)) 785 return Inst; 786 return 0; 787} 788 789/// GetValueForBlock - Get the value to use within the specified basic block. 790/// available values are in Phis. 791Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction *Orig, 792 DenseMap<BasicBlock*, Value*> &Phis, 793 bool TopLevel) { 794 795 // If we have already computed this value, return the previously computed val. 796 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 797 if (V != Phis.end() && !TopLevel) return V->second; 798 799 // If the block is unreachable, just return undef, since this path 800 // can't actually occur at runtime. 801 if (!DT->isReachableFromEntry(BB)) 802 return Phis[BB] = UndefValue::get(Orig->getType()); 803 804 if (BasicBlock *Pred = BB->getSinglePredecessor()) { 805 Value *ret = GetValueForBlock(Pred, Orig, Phis); 806 Phis[BB] = ret; 807 return ret; 808 } 809 810 // Get the number of predecessors of this block so we can reserve space later. 811 // If there is already a PHI in it, use the #preds from it, otherwise count. 812 // Getting it from the PHI is constant time. 813 unsigned NumPreds; 814 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin())) 815 NumPreds = ExistingPN->getNumIncomingValues(); 816 else 817 NumPreds = std::distance(pred_begin(BB), pred_end(BB)); 818 819 // Otherwise, we may need to insert a PHI node. Do so now, then get values to 820 // fill in the incoming values for the PHI. If the PHI ends up not being 821 // needed, we can always remove it later. 822 PHINode *PN = PHINode::Create(Orig->getType(), Orig->getName()+".rle", 823 BB->begin()); 824 PN->reserveOperandSpace(NumPreds); 825 826 Phis.insert(std::make_pair(BB, PN)); 827 828 // Fill in the incoming values for the block. 829 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 830 Value *val = GetValueForBlock(*PI, Orig, Phis); 831 PN->addIncoming(val, *PI); 832 } 833 834 VN.getAliasAnalysis()->copyValue(Orig, PN); 835 836 // Attempt to collapse PHI nodes that are trivially redundant. This happens 837 // when we construct a PHI that ends up not being needed. 838 Value *v = CollapsePhi(PN); 839 if (!v) { 840 // Cache our phi construction results 841 if (LoadInst* L = dyn_cast<LoadInst>(Orig)) 842 phiMap[L->getPointerOperand()].insert(PN); 843 else 844 phiMap[Orig].insert(PN); 845 846 return PN; 847 } 848 849 PN->replaceAllUsesWith(v); 850 if (isa<PointerType>(v->getType())) 851 MD->invalidateCachedPointerInfo(v); 852 853 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 854 E = Phis.end(); I != E; ++I) 855 if (I->second == PN) 856 I->second = v; 857 858 DEBUG(errs() << "GVN removed: " << *PN << '\n'); 859 MD->removeInstruction(PN); 860 PN->eraseFromParent(); 861 DEBUG(verifyRemoved(PN)); 862 863 Phis[BB] = v; 864 return v; 865} 866 867/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 868/// we're analyzing is fully available in the specified block. As we go, keep 869/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 870/// map is actually a tri-state map with the following values: 871/// 0) we know the block *is not* fully available. 872/// 1) we know the block *is* fully available. 873/// 2) we do not know whether the block is fully available or not, but we are 874/// currently speculating that it will be. 875/// 3) we are speculating for this block and have used that to speculate for 876/// other blocks. 877static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 878 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 879 // Optimistically assume that the block is fully available and check to see 880 // if we already know about this block in one lookup. 881 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 882 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 883 884 // If the entry already existed for this block, return the precomputed value. 885 if (!IV.second) { 886 // If this is a speculative "available" value, mark it as being used for 887 // speculation of other blocks. 888 if (IV.first->second == 2) 889 IV.first->second = 3; 890 return IV.first->second != 0; 891 } 892 893 // Otherwise, see if it is fully available in all predecessors. 894 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 895 896 // If this block has no predecessors, it isn't live-in here. 897 if (PI == PE) 898 goto SpeculationFailure; 899 900 for (; PI != PE; ++PI) 901 // If the value isn't fully available in one of our predecessors, then it 902 // isn't fully available in this block either. Undo our previous 903 // optimistic assumption and bail out. 904 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 905 goto SpeculationFailure; 906 907 return true; 908 909// SpeculationFailure - If we get here, we found out that this is not, after 910// all, a fully-available block. We have a problem if we speculated on this and 911// used the speculation to mark other blocks as available. 912SpeculationFailure: 913 char &BBVal = FullyAvailableBlocks[BB]; 914 915 // If we didn't speculate on this, just return with it set to false. 916 if (BBVal == 2) { 917 BBVal = 0; 918 return false; 919 } 920 921 // If we did speculate on this value, we could have blocks set to 1 that are 922 // incorrect. Walk the (transitive) successors of this block and mark them as 923 // 0 if set to one. 924 SmallVector<BasicBlock*, 32> BBWorklist; 925 BBWorklist.push_back(BB); 926 927 while (!BBWorklist.empty()) { 928 BasicBlock *Entry = BBWorklist.pop_back_val(); 929 // Note that this sets blocks to 0 (unavailable) if they happen to not 930 // already be in FullyAvailableBlocks. This is safe. 931 char &EntryVal = FullyAvailableBlocks[Entry]; 932 if (EntryVal == 0) continue; // Already unavailable. 933 934 // Mark as unavailable. 935 EntryVal = 0; 936 937 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 938 BBWorklist.push_back(*I); 939 } 940 941 return false; 942} 943 944 945/// CanCoerceMustAliasedValueToLoad - Return true if 946/// CoerceAvailableValueToLoadType will succeed. 947static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 948 const Type *LoadTy, 949 const TargetData &TD) { 950 // If the loaded or stored value is an first class array or struct, don't try 951 // to transform them. We need to be able to bitcast to integer. 952 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy) || 953 isa<StructType>(StoredVal->getType()) || 954 isa<ArrayType>(StoredVal->getType())) 955 return false; 956 957 // The store has to be at least as big as the load. 958 if (TD.getTypeSizeInBits(StoredVal->getType()) < 959 TD.getTypeSizeInBits(LoadTy)) 960 return false; 961 962 return true; 963} 964 965 966/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 967/// then a load from a must-aliased pointer of a different type, try to coerce 968/// the stored value. LoadedTy is the type of the load we want to replace and 969/// InsertPt is the place to insert new instructions. 970/// 971/// If we can't do it, return null. 972static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 973 const Type *LoadedTy, 974 Instruction *InsertPt, 975 const TargetData &TD) { 976 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 977 return 0; 978 979 const Type *StoredValTy = StoredVal->getType(); 980 981 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 982 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 983 984 // If the store and reload are the same size, we can always reuse it. 985 if (StoreSize == LoadSize) { 986 if (isa<PointerType>(StoredValTy) && isa<PointerType>(LoadedTy)) { 987 // Pointer to Pointer -> use bitcast. 988 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 989 } 990 991 // Convert source pointers to integers, which can be bitcast. 992 if (isa<PointerType>(StoredValTy)) { 993 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 994 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 995 } 996 997 const Type *TypeToCastTo = LoadedTy; 998 if (isa<PointerType>(TypeToCastTo)) 999 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 1000 1001 if (StoredValTy != TypeToCastTo) 1002 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 1003 1004 // Cast to pointer if the load needs a pointer type. 1005 if (isa<PointerType>(LoadedTy)) 1006 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 1007 1008 return StoredVal; 1009 } 1010 1011 // If the loaded value is smaller than the available value, then we can 1012 // extract out a piece from it. If the available value is too small, then we 1013 // can't do anything. 1014 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 1015 1016 // Convert source pointers to integers, which can be manipulated. 1017 if (isa<PointerType>(StoredValTy)) { 1018 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 1019 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 1020 } 1021 1022 // Convert vectors and fp to integer, which can be manipulated. 1023 if (!isa<IntegerType>(StoredValTy)) { 1024 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 1025 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 1026 } 1027 1028 // If this is a big-endian system, we need to shift the value down to the low 1029 // bits so that a truncate will work. 1030 if (TD.isBigEndian()) { 1031 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 1032 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 1033 } 1034 1035 // Truncate the integer to the right size now. 1036 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 1037 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 1038 1039 if (LoadedTy == NewIntTy) 1040 return StoredVal; 1041 1042 // If the result is a pointer, inttoptr. 1043 if (isa<PointerType>(LoadedTy)) 1044 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 1045 1046 // Otherwise, bitcast. 1047 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 1048} 1049 1050/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 1051/// be expressed as a base pointer plus a constant offset. Return the base and 1052/// offset to the caller. 1053static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 1054 const TargetData &TD) { 1055 Operator *PtrOp = dyn_cast<Operator>(Ptr); 1056 if (PtrOp == 0) return Ptr; 1057 1058 // Just look through bitcasts. 1059 if (PtrOp->getOpcode() == Instruction::BitCast) 1060 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 1061 1062 // If this is a GEP with constant indices, we can look through it. 1063 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 1064 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 1065 1066 gep_type_iterator GTI = gep_type_begin(GEP); 1067 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 1068 ++I, ++GTI) { 1069 ConstantInt *OpC = cast<ConstantInt>(*I); 1070 if (OpC->isZero()) continue; 1071 1072 // Handle a struct and array indices which add their offset to the pointer. 1073 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 1074 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 1075 } else { 1076 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 1077 Offset += OpC->getSExtValue()*Size; 1078 } 1079 } 1080 1081 // Re-sign extend from the pointer size if needed to get overflow edge cases 1082 // right. 1083 unsigned PtrSize = TD.getPointerSizeInBits(); 1084 if (PtrSize < 64) 1085 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 1086 1087 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 1088} 1089 1090 1091/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1092/// memdep query of a load that ends up being a clobbering store. This means 1093/// that the store *may* provide bits used by the load but we can't be sure 1094/// because the pointers don't mustalias. Check this case to see if there is 1095/// anything more we can do before we give up. This returns -1 if we have to 1096/// give up, or a byte number in the stored value of the piece that feeds the 1097/// load. 1098static int AnalyzeLoadFromClobberingStore(LoadInst *L, StoreInst *DepSI, 1099 const TargetData &TD) { 1100 // If the loaded or stored value is an first class array or struct, don't try 1101 // to transform them. We need to be able to bitcast to integer. 1102 if (isa<StructType>(L->getType()) || isa<ArrayType>(L->getType()) || 1103 isa<StructType>(DepSI->getOperand(0)->getType()) || 1104 isa<ArrayType>(DepSI->getOperand(0)->getType())) 1105 return -1; 1106 1107 int64_t StoreOffset = 0, LoadOffset = 0; 1108 Value *StoreBase = 1109 GetBaseWithConstantOffset(DepSI->getPointerOperand(), StoreOffset, TD); 1110 Value *LoadBase = 1111 GetBaseWithConstantOffset(L->getPointerOperand(), LoadOffset, TD); 1112 if (StoreBase != LoadBase) 1113 return -1; 1114 1115 // If the load and store are to the exact same address, they should have been 1116 // a must alias. AA must have gotten confused. 1117 // FIXME: Study to see if/when this happens. 1118 if (LoadOffset == StoreOffset) { 1119#if 0 1120 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 1121 << "Base = " << *StoreBase << "\n" 1122 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1123 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1124 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1125 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1126 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1127 << *L->getParent(); 1128#endif 1129 return -1; 1130 } 1131 1132 // If the load and store don't overlap at all, the store doesn't provide 1133 // anything to the load. In this case, they really don't alias at all, AA 1134 // must have gotten confused. 1135 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1136 // remove this check, as it is duplicated with what we have below. 1137 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType()); 1138 uint64_t LoadSize = TD.getTypeSizeInBits(L->getType()); 1139 1140 if ((StoreSize & 7) | (LoadSize & 7)) 1141 return -1; 1142 StoreSize >>= 3; // Convert to bytes. 1143 LoadSize >>= 3; 1144 1145 1146 bool isAAFailure = false; 1147 if (StoreOffset < LoadOffset) { 1148 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1149 } else { 1150 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1151 } 1152 if (isAAFailure) { 1153#if 0 1154 errs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1155 << "Base = " << *StoreBase << "\n" 1156 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1157 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1158 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1159 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1160 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1161 << *L->getParent(); 1162#endif 1163 return -1; 1164 } 1165 1166 // If the Load isn't completely contained within the stored bits, we don't 1167 // have all the bits to feed it. We could do something crazy in the future 1168 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1169 // valuable. 1170 if (StoreOffset > LoadOffset || 1171 StoreOffset+StoreSize < LoadOffset+LoadSize) 1172 return -1; 1173 1174 // Okay, we can do this transformation. Return the number of bytes into the 1175 // store that the load is. 1176 return LoadOffset-StoreOffset; 1177} 1178 1179 1180/// GetStoreValueForLoad - This function is called when we have a 1181/// memdep query of a load that ends up being a clobbering store. This means 1182/// that the store *may* provide bits used by the load but we can't be sure 1183/// because the pointers don't mustalias. Check this case to see if there is 1184/// anything more we can do before we give up. 1185static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1186 const Type *LoadTy, 1187 Instruction *InsertPt, const TargetData &TD){ 1188 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1189 1190 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8; 1191 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1192 1193 1194 // Compute which bits of the stored value are being used by the load. Convert 1195 // to an integer type to start with. 1196 if (isa<PointerType>(SrcVal->getType())) 1197 SrcVal = new PtrToIntInst(SrcVal, TD.getIntPtrType(Ctx), "tmp", InsertPt); 1198 if (!isa<IntegerType>(SrcVal->getType())) 1199 SrcVal = new BitCastInst(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1200 "tmp", InsertPt); 1201 1202 // Shift the bits to the least significant depending on endianness. 1203 unsigned ShiftAmt; 1204 if (TD.isLittleEndian()) { 1205 ShiftAmt = Offset*8; 1206 } else { 1207 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1208 } 1209 1210 if (ShiftAmt) 1211 SrcVal = BinaryOperator::CreateLShr(SrcVal, 1212 ConstantInt::get(SrcVal->getType(), ShiftAmt), "tmp", InsertPt); 1213 1214 if (LoadSize != StoreSize) 1215 SrcVal = new TruncInst(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1216 "tmp", InsertPt); 1217 1218 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1219} 1220 1221struct AvailableValueInBlock { 1222 /// BB - The basic block in question. 1223 BasicBlock *BB; 1224 /// V - The value that is live out of the block. 1225 Value *V; 1226 /// Offset - The byte offset in V that is interesting for the load query. 1227 unsigned Offset; 1228 1229 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1230 unsigned Offset = 0) { 1231 AvailableValueInBlock Res; 1232 Res.BB = BB; 1233 Res.V = V; 1234 Res.Offset = Offset; 1235 return Res; 1236 } 1237}; 1238 1239/// GetAvailableBlockValues - Given the ValuesPerBlock list, convert all of the 1240/// available values to values of the expected LoadTy in their blocks and insert 1241/// the new values into BlockReplValues. 1242static void 1243GetAvailableBlockValues(DenseMap<BasicBlock*, Value*> &BlockReplValues, 1244 const SmallVector<AvailableValueInBlock, 16> &ValuesPerBlock, 1245 const Type *LoadTy, 1246 const TargetData *TD) { 1247 1248 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1249 BasicBlock *BB = ValuesPerBlock[i].BB; 1250 Value *AvailableVal = ValuesPerBlock[i].V; 1251 unsigned Offset = ValuesPerBlock[i].Offset; 1252 1253 Value *&BlockEntry = BlockReplValues[BB]; 1254 if (BlockEntry) continue; 1255 1256 if (AvailableVal->getType() != LoadTy) { 1257 assert(TD && "Need target data to handle type mismatch case"); 1258 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy, 1259 BB->getTerminator(), *TD); 1260 1261 if (Offset) { 1262 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1263 << *ValuesPerBlock[i].V << '\n' 1264 << *AvailableVal << '\n' << "\n\n\n"); 1265 } 1266 1267 1268 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1269 << *ValuesPerBlock[i].V << '\n' 1270 << *AvailableVal << '\n' << "\n\n\n"); 1271 } 1272 BlockEntry = AvailableVal; 1273 } 1274} 1275 1276/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1277/// non-local by performing PHI construction. 1278bool GVN::processNonLocalLoad(LoadInst *LI, 1279 SmallVectorImpl<Instruction*> &toErase) { 1280 // Find the non-local dependencies of the load. 1281 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 1282 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 1283 Deps); 1284 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: " 1285 // << Deps.size() << *LI << '\n'); 1286 1287 // If we had to process more than one hundred blocks to find the 1288 // dependencies, this load isn't worth worrying about. Optimizing 1289 // it will be too expensive. 1290 if (Deps.size() > 100) 1291 return false; 1292 1293 // If we had a phi translation failure, we'll have a single entry which is a 1294 // clobber in the current block. Reject this early. 1295 if (Deps.size() == 1 && Deps[0].second.isClobber()) { 1296 DEBUG( 1297 errs() << "GVN: non-local load "; 1298 WriteAsOperand(errs(), LI); 1299 errs() << " is clobbered by " << *Deps[0].second.getInst() << '\n'; 1300 ); 1301 return false; 1302 } 1303 1304 // Filter out useless results (non-locals, etc). Keep track of the blocks 1305 // where we have a value available in repl, also keep track of whether we see 1306 // dependencies that produce an unknown value for the load (such as a call 1307 // that could potentially clobber the load). 1308 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1309 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1310 1311 const TargetData *TD = 0; 1312 1313 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1314 BasicBlock *DepBB = Deps[i].first; 1315 MemDepResult DepInfo = Deps[i].second; 1316 1317 if (DepInfo.isClobber()) { 1318 // If the dependence is to a store that writes to a superset of the bits 1319 // read by the load, we can extract the bits we need for the load from the 1320 // stored value. 1321 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1322 if (TD == 0) 1323 TD = getAnalysisIfAvailable<TargetData>(); 1324 if (TD) { 1325 int Offset = AnalyzeLoadFromClobberingStore(LI, DepSI, *TD); 1326 if (Offset != -1) { 1327 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1328 DepSI->getOperand(0), 1329 Offset)); 1330 continue; 1331 } 1332 } 1333 } 1334 1335 // FIXME: Handle memset/memcpy. 1336 UnavailableBlocks.push_back(DepBB); 1337 continue; 1338 } 1339 1340 Instruction *DepInst = DepInfo.getInst(); 1341 1342 // Loading the allocation -> undef. 1343 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1344 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1345 UndefValue::get(LI->getType()))); 1346 continue; 1347 } 1348 1349 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1350 // Reject loads and stores that are to the same address but are of 1351 // different types if we have to. 1352 if (S->getOperand(0)->getType() != LI->getType()) { 1353 if (TD == 0) 1354 TD = getAnalysisIfAvailable<TargetData>(); 1355 1356 // If the stored value is larger or equal to the loaded value, we can 1357 // reuse it. 1358 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0), 1359 LI->getType(), *TD)) { 1360 UnavailableBlocks.push_back(DepBB); 1361 continue; 1362 } 1363 } 1364 1365 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1366 S->getOperand(0))); 1367 continue; 1368 } 1369 1370 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1371 // If the types mismatch and we can't handle it, reject reuse of the load. 1372 if (LD->getType() != LI->getType()) { 1373 if (TD == 0) 1374 TD = getAnalysisIfAvailable<TargetData>(); 1375 1376 // If the stored value is larger or equal to the loaded value, we can 1377 // reuse it. 1378 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1379 UnavailableBlocks.push_back(DepBB); 1380 continue; 1381 } 1382 } 1383 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1384 continue; 1385 } 1386 1387 UnavailableBlocks.push_back(DepBB); 1388 continue; 1389 } 1390 1391 // If we have no predecessors that produce a known value for this load, exit 1392 // early. 1393 if (ValuesPerBlock.empty()) return false; 1394 1395 // If all of the instructions we depend on produce a known value for this 1396 // load, then it is fully redundant and we can use PHI insertion to compute 1397 // its value. Insert PHIs and remove the fully redundant value now. 1398 if (UnavailableBlocks.empty()) { 1399 // Use cached PHI construction information from previous runs 1400 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1401 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated? 1402 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1403 I != E; ++I) { 1404 if ((*I)->getParent() == LI->getParent()) { 1405 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD #1: " << *LI << '\n'); 1406 LI->replaceAllUsesWith(*I); 1407 if (isa<PointerType>((*I)->getType())) 1408 MD->invalidateCachedPointerInfo(*I); 1409 toErase.push_back(LI); 1410 NumGVNLoad++; 1411 return true; 1412 } 1413 1414 ValuesPerBlock.push_back(AvailableValueInBlock::get((*I)->getParent(), 1415 *I)); 1416 } 1417 1418 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1419 1420 // Convert the block information to a map, and insert coersions as needed. 1421 DenseMap<BasicBlock*, Value*> BlockReplValues; 1422 GetAvailableBlockValues(BlockReplValues, ValuesPerBlock, LI->getType(), TD); 1423 1424 // Perform PHI construction. 1425 Value *V = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1426 LI->replaceAllUsesWith(V); 1427 1428 if (isa<PHINode>(V)) 1429 V->takeName(LI); 1430 if (isa<PointerType>(V->getType())) 1431 MD->invalidateCachedPointerInfo(V); 1432 toErase.push_back(LI); 1433 NumGVNLoad++; 1434 return true; 1435 } 1436 1437 if (!EnablePRE || !EnableLoadPRE) 1438 return false; 1439 1440 // Okay, we have *some* definitions of the value. This means that the value 1441 // is available in some of our (transitive) predecessors. Lets think about 1442 // doing PRE of this load. This will involve inserting a new load into the 1443 // predecessor when it's not available. We could do this in general, but 1444 // prefer to not increase code size. As such, we only do this when we know 1445 // that we only have to insert *one* load (which means we're basically moving 1446 // the load, not inserting a new one). 1447 1448 SmallPtrSet<BasicBlock *, 4> Blockers; 1449 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1450 Blockers.insert(UnavailableBlocks[i]); 1451 1452 // Lets find first basic block with more than one predecessor. Walk backwards 1453 // through predecessors if needed. 1454 BasicBlock *LoadBB = LI->getParent(); 1455 BasicBlock *TmpBB = LoadBB; 1456 1457 bool isSinglePred = false; 1458 bool allSingleSucc = true; 1459 while (TmpBB->getSinglePredecessor()) { 1460 isSinglePred = true; 1461 TmpBB = TmpBB->getSinglePredecessor(); 1462 if (!TmpBB) // If haven't found any, bail now. 1463 return false; 1464 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1465 return false; 1466 if (Blockers.count(TmpBB)) 1467 return false; 1468 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1469 allSingleSucc = false; 1470 } 1471 1472 assert(TmpBB); 1473 LoadBB = TmpBB; 1474 1475 // If we have a repl set with LI itself in it, this means we have a loop where 1476 // at least one of the values is LI. Since this means that we won't be able 1477 // to eliminate LI even if we insert uses in the other predecessors, we will 1478 // end up increasing code size. Reject this by scanning for LI. 1479 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1480 if (ValuesPerBlock[i].V == LI) 1481 return false; 1482 1483 if (isSinglePred) { 1484 bool isHot = false; 1485 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1486 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].V)) 1487 // "Hot" Instruction is in some loop (because it dominates its dep. 1488 // instruction). 1489 if (DT->dominates(LI, I)) { 1490 isHot = true; 1491 break; 1492 } 1493 1494 // We are interested only in "hot" instructions. We don't want to do any 1495 // mis-optimizations here. 1496 if (!isHot) 1497 return false; 1498 } 1499 1500 // Okay, we have some hope :). Check to see if the loaded value is fully 1501 // available in all but one predecessor. 1502 // FIXME: If we could restructure the CFG, we could make a common pred with 1503 // all the preds that don't have an available LI and insert a new load into 1504 // that one block. 1505 BasicBlock *UnavailablePred = 0; 1506 1507 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1508 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1509 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1510 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1511 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1512 1513 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1514 PI != E; ++PI) { 1515 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1516 continue; 1517 1518 // If this load is not available in multiple predecessors, reject it. 1519 if (UnavailablePred && UnavailablePred != *PI) 1520 return false; 1521 UnavailablePred = *PI; 1522 } 1523 1524 assert(UnavailablePred != 0 && 1525 "Fully available value should be eliminated above!"); 1526 1527 // If the loaded pointer is PHI node defined in this block, do PHI translation 1528 // to get its value in the predecessor. 1529 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); 1530 1531 // Make sure the value is live in the predecessor. If it was defined by a 1532 // non-PHI instruction in this block, we don't know how to recompute it above. 1533 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) 1534 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { 1535 DEBUG(errs() << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " 1536 << *LPInst << '\n' << *LI << "\n"); 1537 return false; 1538 } 1539 1540 // We don't currently handle critical edges :( 1541 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1542 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1543 << UnavailablePred->getName() << "': " << *LI << '\n'); 1544 return false; 1545 } 1546 1547 // Make sure it is valid to move this load here. We have to watch out for: 1548 // @1 = getelementptr (i8* p, ... 1549 // test p and branch if == 0 1550 // load @1 1551 // It is valid to have the getelementptr before the test, even if p can be 0, 1552 // as getelementptr only does address arithmetic. 1553 // If we are not pushing the value through any multiple-successor blocks 1554 // we do not have this case. Otherwise, check that the load is safe to 1555 // put anywhere; this can be improved, but should be conservatively safe. 1556 if (!allSingleSucc && 1557 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) 1558 return false; 1559 1560 // Okay, we can eliminate this load by inserting a reload in the predecessor 1561 // and using PHI construction to get the value in the other predecessors, do 1562 // it. 1563 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1564 1565 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1566 LI->getAlignment(), 1567 UnavailablePred->getTerminator()); 1568 1569 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1570 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1571 I != E; ++I) 1572 ValuesPerBlock.push_back(AvailableValueInBlock::get((*I)->getParent(), *I)); 1573 1574 DenseMap<BasicBlock*, Value*> BlockReplValues; 1575 GetAvailableBlockValues(BlockReplValues, ValuesPerBlock, LI->getType(), TD); 1576 BlockReplValues[UnavailablePred] = NewLoad; 1577 1578 // Perform PHI construction. 1579 Value *V = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1580 LI->replaceAllUsesWith(V); 1581 if (isa<PHINode>(V)) 1582 V->takeName(LI); 1583 if (isa<PointerType>(V->getType())) 1584 MD->invalidateCachedPointerInfo(V); 1585 toErase.push_back(LI); 1586 NumPRELoad++; 1587 return true; 1588} 1589 1590/// processLoad - Attempt to eliminate a load, first by eliminating it 1591/// locally, and then attempting non-local elimination if that fails. 1592bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1593 if (L->isVolatile()) 1594 return false; 1595 1596 // ... to a pointer that has been loaded from before... 1597 MemDepResult Dep = MD->getDependency(L); 1598 1599 // If the value isn't available, don't do anything! 1600 if (Dep.isClobber()) { 1601 // FIXME: We should handle memset/memcpy/memmove as dependent instructions 1602 // to forward the value if available. 1603 //if (isa<MemIntrinsic>(Dep.getInst())) 1604 //errs() << "LOAD DEPENDS ON MEM: " << *L << "\n" << *Dep.getInst()<<"\n\n"; 1605 1606 // Check to see if we have something like this: 1607 // store i32 123, i32* %P 1608 // %A = bitcast i32* %P to i8* 1609 // %B = gep i8* %A, i32 1 1610 // %C = load i8* %B 1611 // 1612 // We could do that by recognizing if the clobber instructions are obviously 1613 // a common base + constant offset, and if the previous store (or memset) 1614 // completely covers this load. This sort of thing can happen in bitfield 1615 // access code. 1616 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1617 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1618 int Offset = AnalyzeLoadFromClobberingStore(L, DepSI, *TD); 1619 if (Offset != -1) { 1620 Value *AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset, 1621 L->getType(), L, *TD); 1622 DEBUG(errs() << "GVN COERCED STORE BITS:\n" << *DepSI << '\n' 1623 << *AvailVal << '\n' << *L << "\n\n\n"); 1624 1625 // Replace the load! 1626 L->replaceAllUsesWith(AvailVal); 1627 if (isa<PointerType>(AvailVal->getType())) 1628 MD->invalidateCachedPointerInfo(AvailVal); 1629 toErase.push_back(L); 1630 NumGVNLoad++; 1631 return true; 1632 } 1633 } 1634 1635 DEBUG( 1636 // fast print dep, using operator<< on instruction would be too slow 1637 errs() << "GVN: load "; 1638 WriteAsOperand(errs(), L); 1639 Instruction *I = Dep.getInst(); 1640 errs() << " is clobbered by " << *I << '\n'; 1641 ); 1642 return false; 1643 } 1644 1645 // If it is defined in another block, try harder. 1646 if (Dep.isNonLocal()) 1647 return processNonLocalLoad(L, toErase); 1648 1649 Instruction *DepInst = Dep.getInst(); 1650 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1651 Value *StoredVal = DepSI->getOperand(0); 1652 1653 // The store and load are to a must-aliased pointer, but they may not 1654 // actually have the same type. See if we know how to reuse the stored 1655 // value (depending on its type). 1656 const TargetData *TD = 0; 1657 if (StoredVal->getType() != L->getType() && 1658 (TD = getAnalysisIfAvailable<TargetData>())) { 1659 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1660 L, *TD); 1661 if (StoredVal == 0) 1662 return false; 1663 1664 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1665 << '\n' << *L << "\n\n\n"); 1666 } 1667 1668 // Remove it! 1669 L->replaceAllUsesWith(StoredVal); 1670 if (isa<PointerType>(StoredVal->getType())) 1671 MD->invalidateCachedPointerInfo(StoredVal); 1672 toErase.push_back(L); 1673 NumGVNLoad++; 1674 return true; 1675 } 1676 1677 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1678 Value *AvailableVal = DepLI; 1679 1680 // The loads are of a must-aliased pointer, but they may not actually have 1681 // the same type. See if we know how to reuse the previously loaded value 1682 // (depending on its type). 1683 const TargetData *TD = 0; 1684 if (DepLI->getType() != L->getType() && 1685 (TD = getAnalysisIfAvailable<TargetData>())) { 1686 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1687 if (AvailableVal == 0) 1688 return false; 1689 1690 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1691 << "\n" << *L << "\n\n\n"); 1692 } 1693 1694 // Remove it! 1695 L->replaceAllUsesWith(AvailableVal); 1696 if (isa<PointerType>(DepLI->getType())) 1697 MD->invalidateCachedPointerInfo(DepLI); 1698 toErase.push_back(L); 1699 NumGVNLoad++; 1700 return true; 1701 } 1702 1703 // If this load really doesn't depend on anything, then we must be loading an 1704 // undef value. This can happen when loading for a fresh allocation with no 1705 // intervening stores, for example. 1706 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1707 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1708 toErase.push_back(L); 1709 NumGVNLoad++; 1710 return true; 1711 } 1712 1713 return false; 1714} 1715 1716Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1717 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1718 if (I == localAvail.end()) 1719 return 0; 1720 1721 ValueNumberScope *Locals = I->second; 1722 while (Locals) { 1723 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1724 if (I != Locals->table.end()) 1725 return I->second; 1726 Locals = Locals->parent; 1727 } 1728 1729 return 0; 1730} 1731 1732/// AttemptRedundancyElimination - If the "fast path" of redundancy elimination 1733/// by inheritance from the dominator fails, see if we can perform phi 1734/// construction to eliminate the redundancy. 1735Value *GVN::AttemptRedundancyElimination(Instruction *orig, unsigned valno) { 1736 BasicBlock *BaseBlock = orig->getParent(); 1737 1738 SmallPtrSet<BasicBlock*, 4> Visited; 1739 SmallVector<BasicBlock*, 8> Stack; 1740 Stack.push_back(BaseBlock); 1741 1742 DenseMap<BasicBlock*, Value*> Results; 1743 1744 // Walk backwards through our predecessors, looking for instances of the 1745 // value number we're looking for. Instances are recorded in the Results 1746 // map, which is then used to perform phi construction. 1747 while (!Stack.empty()) { 1748 BasicBlock *Current = Stack.back(); 1749 Stack.pop_back(); 1750 1751 // If we've walked all the way to a proper dominator, then give up. Cases 1752 // where the instance is in the dominator will have been caught by the fast 1753 // path, and any cases that require phi construction further than this are 1754 // probably not worth it anyways. Note that this is a SIGNIFICANT compile 1755 // time improvement. 1756 if (DT->properlyDominates(Current, orig->getParent())) return 0; 1757 1758 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA = 1759 localAvail.find(Current); 1760 if (LA == localAvail.end()) return 0; 1761 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno); 1762 1763 if (V != LA->second->table.end()) { 1764 // Found an instance, record it. 1765 Results.insert(std::make_pair(Current, V->second)); 1766 continue; 1767 } 1768 1769 // If we reach the beginning of the function, then give up. 1770 if (pred_begin(Current) == pred_end(Current)) 1771 return 0; 1772 1773 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current); 1774 PI != PE; ++PI) 1775 if (Visited.insert(*PI)) 1776 Stack.push_back(*PI); 1777 } 1778 1779 // If we didn't find instances, give up. Otherwise, perform phi construction. 1780 if (Results.size() == 0) 1781 return 0; 1782 1783 return GetValueForBlock(BaseBlock, orig, Results, true); 1784} 1785 1786/// processInstruction - When calculating availability, handle an instruction 1787/// by inserting it into the appropriate sets 1788bool GVN::processInstruction(Instruction *I, 1789 SmallVectorImpl<Instruction*> &toErase) { 1790 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1791 bool Changed = processLoad(LI, toErase); 1792 1793 if (!Changed) { 1794 unsigned Num = VN.lookup_or_add(LI); 1795 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1796 } 1797 1798 return Changed; 1799 } 1800 1801 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1802 unsigned Num = VN.lookup_or_add(I); 1803 1804 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1805 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1806 1807 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1808 return false; 1809 1810 Value *BranchCond = BI->getCondition(); 1811 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1812 1813 BasicBlock *TrueSucc = BI->getSuccessor(0); 1814 BasicBlock *FalseSucc = BI->getSuccessor(1); 1815 1816 if (TrueSucc->getSinglePredecessor()) 1817 localAvail[TrueSucc]->table[CondVN] = 1818 ConstantInt::getTrue(TrueSucc->getContext()); 1819 if (FalseSucc->getSinglePredecessor()) 1820 localAvail[FalseSucc]->table[CondVN] = 1821 ConstantInt::getFalse(TrueSucc->getContext()); 1822 1823 return false; 1824 1825 // Allocations are always uniquely numbered, so we can save time and memory 1826 // by fast failing them. 1827 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1828 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1829 return false; 1830 } 1831 1832 // Collapse PHI nodes 1833 if (PHINode* p = dyn_cast<PHINode>(I)) { 1834 Value *constVal = CollapsePhi(p); 1835 1836 if (constVal) { 1837 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1838 PI != PE; ++PI) 1839 PI->second.erase(p); 1840 1841 p->replaceAllUsesWith(constVal); 1842 if (isa<PointerType>(constVal->getType())) 1843 MD->invalidateCachedPointerInfo(constVal); 1844 VN.erase(p); 1845 1846 toErase.push_back(p); 1847 } else { 1848 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1849 } 1850 1851 // If the number we were assigned was a brand new VN, then we don't 1852 // need to do a lookup to see if the number already exists 1853 // somewhere in the domtree: it can't! 1854 } else if (Num == NextNum) { 1855 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1856 1857 // Perform fast-path value-number based elimination of values inherited from 1858 // dominators. 1859 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1860 // Remove it! 1861 VN.erase(I); 1862 I->replaceAllUsesWith(repl); 1863 if (isa<PointerType>(repl->getType())) 1864 MD->invalidateCachedPointerInfo(repl); 1865 toErase.push_back(I); 1866 return true; 1867 1868#if 0 1869 // Perform slow-pathvalue-number based elimination with phi construction. 1870 } else if (Value *repl = AttemptRedundancyElimination(I, Num)) { 1871 // Remove it! 1872 VN.erase(I); 1873 I->replaceAllUsesWith(repl); 1874 if (isa<PointerType>(repl->getType())) 1875 MD->invalidateCachedPointerInfo(repl); 1876 toErase.push_back(I); 1877 return true; 1878#endif 1879 } else { 1880 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1881 } 1882 1883 return false; 1884} 1885 1886/// runOnFunction - This is the main transformation entry point for a function. 1887bool GVN::runOnFunction(Function& F) { 1888 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1889 DT = &getAnalysis<DominatorTree>(); 1890 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1891 VN.setMemDep(MD); 1892 VN.setDomTree(DT); 1893 1894 bool Changed = false; 1895 bool ShouldContinue = true; 1896 1897 // Merge unconditional branches, allowing PRE to catch more 1898 // optimization opportunities. 1899 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1900 BasicBlock *BB = FI; 1901 ++FI; 1902 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1903 if (removedBlock) NumGVNBlocks++; 1904 1905 Changed |= removedBlock; 1906 } 1907 1908 unsigned Iteration = 0; 1909 1910 while (ShouldContinue) { 1911 DEBUG(errs() << "GVN iteration: " << Iteration << "\n"); 1912 ShouldContinue = iterateOnFunction(F); 1913 Changed |= ShouldContinue; 1914 ++Iteration; 1915 } 1916 1917 if (EnablePRE) { 1918 bool PREChanged = true; 1919 while (PREChanged) { 1920 PREChanged = performPRE(F); 1921 Changed |= PREChanged; 1922 } 1923 } 1924 // FIXME: Should perform GVN again after PRE does something. PRE can move 1925 // computations into blocks where they become fully redundant. Note that 1926 // we can't do this until PRE's critical edge splitting updates memdep. 1927 // Actually, when this happens, we should just fully integrate PRE into GVN. 1928 1929 cleanupGlobalSets(); 1930 1931 return Changed; 1932} 1933 1934 1935bool GVN::processBlock(BasicBlock *BB) { 1936 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1937 // incrementing BI before processing an instruction). 1938 SmallVector<Instruction*, 8> toErase; 1939 bool ChangedFunction = false; 1940 1941 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1942 BI != BE;) { 1943 ChangedFunction |= processInstruction(BI, toErase); 1944 if (toErase.empty()) { 1945 ++BI; 1946 continue; 1947 } 1948 1949 // If we need some instructions deleted, do it now. 1950 NumGVNInstr += toErase.size(); 1951 1952 // Avoid iterator invalidation. 1953 bool AtStart = BI == BB->begin(); 1954 if (!AtStart) 1955 --BI; 1956 1957 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1958 E = toErase.end(); I != E; ++I) { 1959 DEBUG(errs() << "GVN removed: " << **I << '\n'); 1960 MD->removeInstruction(*I); 1961 (*I)->eraseFromParent(); 1962 DEBUG(verifyRemoved(*I)); 1963 } 1964 toErase.clear(); 1965 1966 if (AtStart) 1967 BI = BB->begin(); 1968 else 1969 ++BI; 1970 } 1971 1972 return ChangedFunction; 1973} 1974 1975/// performPRE - Perform a purely local form of PRE that looks for diamond 1976/// control flow patterns and attempts to perform simple PRE at the join point. 1977bool GVN::performPRE(Function& F) { 1978 bool Changed = false; 1979 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1980 DenseMap<BasicBlock*, Value*> predMap; 1981 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1982 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1983 BasicBlock *CurrentBlock = *DI; 1984 1985 // Nothing to PRE in the entry block. 1986 if (CurrentBlock == &F.getEntryBlock()) continue; 1987 1988 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1989 BE = CurrentBlock->end(); BI != BE; ) { 1990 Instruction *CurInst = BI++; 1991 1992 if (isa<AllocationInst>(CurInst) || 1993 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 1994 (CurInst->getType() == Type::getVoidTy(F.getContext())) || 1995 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 1996 isa<DbgInfoIntrinsic>(CurInst)) 1997 continue; 1998 1999 uint32_t ValNo = VN.lookup(CurInst); 2000 2001 // Look for the predecessors for PRE opportunities. We're 2002 // only trying to solve the basic diamond case, where 2003 // a value is computed in the successor and one predecessor, 2004 // but not the other. We also explicitly disallow cases 2005 // where the successor is its own predecessor, because they're 2006 // more complicated to get right. 2007 unsigned NumWith = 0; 2008 unsigned NumWithout = 0; 2009 BasicBlock *PREPred = 0; 2010 predMap.clear(); 2011 2012 for (pred_iterator PI = pred_begin(CurrentBlock), 2013 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2014 // We're not interested in PRE where the block is its 2015 // own predecessor, on in blocks with predecessors 2016 // that are not reachable. 2017 if (*PI == CurrentBlock) { 2018 NumWithout = 2; 2019 break; 2020 } else if (!localAvail.count(*PI)) { 2021 NumWithout = 2; 2022 break; 2023 } 2024 2025 DenseMap<uint32_t, Value*>::iterator predV = 2026 localAvail[*PI]->table.find(ValNo); 2027 if (predV == localAvail[*PI]->table.end()) { 2028 PREPred = *PI; 2029 NumWithout++; 2030 } else if (predV->second == CurInst) { 2031 NumWithout = 2; 2032 } else { 2033 predMap[*PI] = predV->second; 2034 NumWith++; 2035 } 2036 } 2037 2038 // Don't do PRE when it might increase code size, i.e. when 2039 // we would need to insert instructions in more than one pred. 2040 if (NumWithout != 1 || NumWith == 0) 2041 continue; 2042 2043 // We can't do PRE safely on a critical edge, so instead we schedule 2044 // the edge to be split and perform the PRE the next time we iterate 2045 // on the function. 2046 unsigned SuccNum = 0; 2047 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 2048 i != e; ++i) 2049 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 2050 SuccNum = i; 2051 break; 2052 } 2053 2054 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2055 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2056 continue; 2057 } 2058 2059 // Instantiate the expression the in predecessor that lacked it. 2060 // Because we are going top-down through the block, all value numbers 2061 // will be available in the predecessor by the time we need them. Any 2062 // that weren't original present will have been instantiated earlier 2063 // in this loop. 2064 Instruction *PREInstr = CurInst->clone(); 2065 bool success = true; 2066 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2067 Value *Op = PREInstr->getOperand(i); 2068 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2069 continue; 2070 2071 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2072 PREInstr->setOperand(i, V); 2073 } else { 2074 success = false; 2075 break; 2076 } 2077 } 2078 2079 // Fail out if we encounter an operand that is not available in 2080 // the PRE predecessor. This is typically because of loads which 2081 // are not value numbered precisely. 2082 if (!success) { 2083 delete PREInstr; 2084 DEBUG(verifyRemoved(PREInstr)); 2085 continue; 2086 } 2087 2088 PREInstr->insertBefore(PREPred->getTerminator()); 2089 PREInstr->setName(CurInst->getName() + ".pre"); 2090 predMap[PREPred] = PREInstr; 2091 VN.add(PREInstr, ValNo); 2092 NumGVNPRE++; 2093 2094 // Update the availability map to include the new instruction. 2095 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 2096 2097 // Create a PHI to make the value available in this block. 2098 PHINode* Phi = PHINode::Create(CurInst->getType(), 2099 CurInst->getName() + ".pre-phi", 2100 CurrentBlock->begin()); 2101 for (pred_iterator PI = pred_begin(CurrentBlock), 2102 PE = pred_end(CurrentBlock); PI != PE; ++PI) 2103 Phi->addIncoming(predMap[*PI], *PI); 2104 2105 VN.add(Phi, ValNo); 2106 localAvail[CurrentBlock]->table[ValNo] = Phi; 2107 2108 CurInst->replaceAllUsesWith(Phi); 2109 if (isa<PointerType>(Phi->getType())) 2110 MD->invalidateCachedPointerInfo(Phi); 2111 VN.erase(CurInst); 2112 2113 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n'); 2114 MD->removeInstruction(CurInst); 2115 CurInst->eraseFromParent(); 2116 DEBUG(verifyRemoved(CurInst)); 2117 Changed = true; 2118 } 2119 } 2120 2121 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 2122 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 2123 SplitCriticalEdge(I->first, I->second, this); 2124 2125 return Changed || toSplit.size(); 2126} 2127 2128/// iterateOnFunction - Executes one iteration of GVN 2129bool GVN::iterateOnFunction(Function &F) { 2130 cleanupGlobalSets(); 2131 2132 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2133 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 2134 if (DI->getIDom()) 2135 localAvail[DI->getBlock()] = 2136 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 2137 else 2138 localAvail[DI->getBlock()] = new ValueNumberScope(0); 2139 } 2140 2141 // Top-down walk of the dominator tree 2142 bool Changed = false; 2143#if 0 2144 // Needed for value numbering with phi construction to work. 2145 ReversePostOrderTraversal<Function*> RPOT(&F); 2146 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2147 RE = RPOT.end(); RI != RE; ++RI) 2148 Changed |= processBlock(*RI); 2149#else 2150 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2151 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2152 Changed |= processBlock(DI->getBlock()); 2153#endif 2154 2155 return Changed; 2156} 2157 2158void GVN::cleanupGlobalSets() { 2159 VN.clear(); 2160 phiMap.clear(); 2161 2162 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2163 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 2164 delete I->second; 2165 localAvail.clear(); 2166} 2167 2168/// verifyRemoved - Verify that the specified instruction does not occur in our 2169/// internal data structures. 2170void GVN::verifyRemoved(const Instruction *Inst) const { 2171 VN.verifyRemoved(Inst); 2172 2173 // Walk through the PHI map to make sure the instruction isn't hiding in there 2174 // somewhere. 2175 for (PhiMapType::iterator 2176 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) { 2177 assert(I->first != Inst && "Inst is still a key in PHI map!"); 2178 2179 for (SmallPtrSet<Instruction*, 4>::iterator 2180 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) { 2181 assert(*II != Inst && "Inst is still a value in PHI map!"); 2182 } 2183 } 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*>::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*>::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