GVN.cpp revision 19ad784dacc10247d47d0928f6222390c60fbb4b
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, the idom is the loop, so we need to insert a PHI node. Do so 820 // now, then get values to fill in the incoming values for the PHI. 821 PHINode *PN = PHINode::Create(Orig->getType(), Orig->getName()+".rle", 822 BB->begin()); 823 PN->reserveOperandSpace(NumPreds); 824 825 Phis.insert(std::make_pair(BB, PN)); 826 827 // Fill in the incoming values for the block. 828 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 829 Value *val = GetValueForBlock(*PI, Orig, Phis); 830 PN->addIncoming(val, *PI); 831 } 832 833 VN.getAliasAnalysis()->copyValue(Orig, PN); 834 835 // Attempt to collapse PHI nodes that are trivially redundant 836 Value *v = CollapsePhi(PN); 837 if (!v) { 838 // Cache our phi construction results 839 if (LoadInst* L = dyn_cast<LoadInst>(Orig)) 840 phiMap[L->getPointerOperand()].insert(PN); 841 else 842 phiMap[Orig].insert(PN); 843 844 return PN; 845 } 846 847 PN->replaceAllUsesWith(v); 848 if (isa<PointerType>(v->getType())) 849 MD->invalidateCachedPointerInfo(v); 850 851 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 852 E = Phis.end(); I != E; ++I) 853 if (I->second == PN) 854 I->second = v; 855 856 DEBUG(errs() << "GVN removed: " << *PN << '\n'); 857 MD->removeInstruction(PN); 858 PN->eraseFromParent(); 859 DEBUG(verifyRemoved(PN)); 860 861 Phis[BB] = v; 862 return v; 863} 864 865/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 866/// we're analyzing is fully available in the specified block. As we go, keep 867/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 868/// map is actually a tri-state map with the following values: 869/// 0) we know the block *is not* fully available. 870/// 1) we know the block *is* fully available. 871/// 2) we do not know whether the block is fully available or not, but we are 872/// currently speculating that it will be. 873/// 3) we are speculating for this block and have used that to speculate for 874/// other blocks. 875static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 876 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 877 // Optimistically assume that the block is fully available and check to see 878 // if we already know about this block in one lookup. 879 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 880 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 881 882 // If the entry already existed for this block, return the precomputed value. 883 if (!IV.second) { 884 // If this is a speculative "available" value, mark it as being used for 885 // speculation of other blocks. 886 if (IV.first->second == 2) 887 IV.first->second = 3; 888 return IV.first->second != 0; 889 } 890 891 // Otherwise, see if it is fully available in all predecessors. 892 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 893 894 // If this block has no predecessors, it isn't live-in here. 895 if (PI == PE) 896 goto SpeculationFailure; 897 898 for (; PI != PE; ++PI) 899 // If the value isn't fully available in one of our predecessors, then it 900 // isn't fully available in this block either. Undo our previous 901 // optimistic assumption and bail out. 902 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 903 goto SpeculationFailure; 904 905 return true; 906 907// SpeculationFailure - If we get here, we found out that this is not, after 908// all, a fully-available block. We have a problem if we speculated on this and 909// used the speculation to mark other blocks as available. 910SpeculationFailure: 911 char &BBVal = FullyAvailableBlocks[BB]; 912 913 // If we didn't speculate on this, just return with it set to false. 914 if (BBVal == 2) { 915 BBVal = 0; 916 return false; 917 } 918 919 // If we did speculate on this value, we could have blocks set to 1 that are 920 // incorrect. Walk the (transitive) successors of this block and mark them as 921 // 0 if set to one. 922 SmallVector<BasicBlock*, 32> BBWorklist; 923 BBWorklist.push_back(BB); 924 925 while (!BBWorklist.empty()) { 926 BasicBlock *Entry = BBWorklist.pop_back_val(); 927 // Note that this sets blocks to 0 (unavailable) if they happen to not 928 // already be in FullyAvailableBlocks. This is safe. 929 char &EntryVal = FullyAvailableBlocks[Entry]; 930 if (EntryVal == 0) continue; // Already unavailable. 931 932 // Mark as unavailable. 933 EntryVal = 0; 934 935 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 936 BBWorklist.push_back(*I); 937 } 938 939 return false; 940} 941 942 943/// CanCoerceMustAliasedValueToLoad - Return true if 944/// CoerceAvailableValueToLoadType will succeed. 945static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 946 const Type *LoadTy, 947 const TargetData &TD) { 948 // If the loaded or stored value is an first class array or struct, don't try 949 // to transform them. We need to be able to bitcast to integer. 950 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy) || 951 isa<StructType>(StoredVal->getType()) || 952 isa<ArrayType>(StoredVal->getType())) 953 return false; 954 955 // The store has to be at least as big as the load. 956 if (TD.getTypeSizeInBits(StoredVal->getType()) < 957 TD.getTypeSizeInBits(LoadTy)) 958 return false; 959 960 return true; 961} 962 963 964/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 965/// then a load from a must-aliased pointer of a different type, try to coerce 966/// the stored value. LoadedTy is the type of the load we want to replace and 967/// InsertPt is the place to insert new instructions. 968/// 969/// If we can't do it, return null. 970static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 971 const Type *LoadedTy, 972 Instruction *InsertPt, 973 const TargetData &TD) { 974 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 975 return 0; 976 977 const Type *StoredValTy = StoredVal->getType(); 978 979 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 980 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 981 982 // If the store and reload are the same size, we can always reuse it. 983 if (StoreSize == LoadSize) { 984 if (isa<PointerType>(StoredValTy) && isa<PointerType>(LoadedTy)) { 985 // Pointer to Pointer -> use bitcast. 986 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 987 } 988 989 // Convert source pointers to integers, which can be bitcast. 990 if (isa<PointerType>(StoredValTy)) { 991 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 992 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 993 } 994 995 const Type *TypeToCastTo = LoadedTy; 996 if (isa<PointerType>(TypeToCastTo)) 997 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 998 999 if (StoredValTy != TypeToCastTo) 1000 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 1001 1002 // Cast to pointer if the load needs a pointer type. 1003 if (isa<PointerType>(LoadedTy)) 1004 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 1005 1006 return StoredVal; 1007 } 1008 1009 // If the loaded value is smaller than the available value, then we can 1010 // extract out a piece from it. If the available value is too small, then we 1011 // can't do anything. 1012 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 1013 1014 // Convert source pointers to integers, which can be manipulated. 1015 if (isa<PointerType>(StoredValTy)) { 1016 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 1017 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 1018 } 1019 1020 // Convert vectors and fp to integer, which can be manipulated. 1021 if (!isa<IntegerType>(StoredValTy)) { 1022 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 1023 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 1024 } 1025 1026 // If this is a big-endian system, we need to shift the value down to the low 1027 // bits so that a truncate will work. 1028 if (TD.isBigEndian()) { 1029 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 1030 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 1031 } 1032 1033 // Truncate the integer to the right size now. 1034 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 1035 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 1036 1037 if (LoadedTy == NewIntTy) 1038 return StoredVal; 1039 1040 // If the result is a pointer, inttoptr. 1041 if (isa<PointerType>(LoadedTy)) 1042 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 1043 1044 // Otherwise, bitcast. 1045 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 1046} 1047 1048/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 1049/// be expressed as a base pointer plus a constant offset. Return the base and 1050/// offset to the caller. 1051static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 1052 const TargetData &TD) { 1053 Operator *PtrOp = dyn_cast<Operator>(Ptr); 1054 if (PtrOp == 0) return Ptr; 1055 1056 // Just look through bitcasts. 1057 if (PtrOp->getOpcode() == Instruction::BitCast) 1058 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 1059 1060 // If this is a GEP with constant indices, we can look through it. 1061 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 1062 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 1063 1064 gep_type_iterator GTI = gep_type_begin(GEP); 1065 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 1066 ++I, ++GTI) { 1067 ConstantInt *OpC = cast<ConstantInt>(*I); 1068 if (OpC->isZero()) continue; 1069 1070 // Handle a struct and array indices which add their offset to the pointer. 1071 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 1072 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 1073 } else { 1074 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 1075 Offset += OpC->getSExtValue()*Size; 1076 } 1077 } 1078 1079 // Re-sign extend from the pointer size if needed to get overflow edge cases 1080 // right. 1081 unsigned PtrSize = TD.getPointerSizeInBits(); 1082 if (PtrSize < 64) 1083 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 1084 1085 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 1086} 1087 1088 1089/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1090/// memdep query of a load that ends up being a clobbering store. This means 1091/// that the store *may* provide bits used by the load but we can't be sure 1092/// because the pointers don't mustalias. Check this case to see if there is 1093/// anything more we can do before we give up. This returns -1 if we have to 1094/// give up, or a byte number in the stored value of the piece that feeds the 1095/// load. 1096static int AnalyzeLoadFromClobberingStore(LoadInst *L, StoreInst *DepSI, 1097 const TargetData &TD) { 1098 // If the loaded or stored value is an first class array or struct, don't try 1099 // to transform them. We need to be able to bitcast to integer. 1100 if (isa<StructType>(L->getType()) || isa<ArrayType>(L->getType()) || 1101 isa<StructType>(DepSI->getOperand(0)->getType()) || 1102 isa<ArrayType>(DepSI->getOperand(0)->getType())) 1103 return -1; 1104 1105 int64_t StoreOffset = 0, LoadOffset = 0; 1106 Value *StoreBase = 1107 GetBaseWithConstantOffset(DepSI->getPointerOperand(), StoreOffset, TD); 1108 Value *LoadBase = 1109 GetBaseWithConstantOffset(L->getPointerOperand(), LoadOffset, TD); 1110 if (StoreBase != LoadBase) 1111 return -1; 1112 1113 // If the load and store are to the exact same address, they should have been 1114 // a must alias. AA must have gotten confused. 1115 // FIXME: Study to see if/when this happens. 1116 if (LoadOffset == StoreOffset) { 1117#if 0 1118 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 1119 << "Base = " << *StoreBase << "\n" 1120 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1121 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1122 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1123 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1124 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1125 << *L->getParent(); 1126#endif 1127 return -1; 1128 } 1129 1130 // If the load and store don't overlap at all, the store doesn't provide 1131 // anything to the load. In this case, they really don't alias at all, AA 1132 // must have gotten confused. 1133 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1134 // remove this check, as it is duplicated with what we have below. 1135 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType()); 1136 uint64_t LoadSize = TD.getTypeSizeInBits(L->getType()); 1137 1138 if ((StoreSize & 7) | (LoadSize & 7)) 1139 return -1; 1140 StoreSize >>= 3; // Convert to bytes. 1141 LoadSize >>= 3; 1142 1143 1144 bool isAAFailure = false; 1145 if (StoreOffset < LoadOffset) { 1146 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1147 } else { 1148 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1149 } 1150 if (isAAFailure) { 1151#if 0 1152 errs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1153 << "Base = " << *StoreBase << "\n" 1154 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1155 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1156 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1157 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1158 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1159 << *L->getParent(); 1160#endif 1161 return -1; 1162 } 1163 1164 // If the Load isn't completely contained within the stored bits, we don't 1165 // have all the bits to feed it. We could do something crazy in the future 1166 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1167 // valuable. 1168 if (StoreOffset > LoadOffset || 1169 StoreOffset+StoreSize < LoadOffset+LoadSize) 1170 return -1; 1171 1172 // Okay, we can do this transformation. Return the number of bytes into the 1173 // store that the load is. 1174 return LoadOffset-StoreOffset; 1175} 1176 1177 1178/// GetStoreValueForLoad - This function is called when we have a 1179/// memdep query of a load that ends up being a clobbering store. This means 1180/// that the store *may* provide bits used by the load but we can't be sure 1181/// because the pointers don't mustalias. Check this case to see if there is 1182/// anything more we can do before we give up. 1183static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1184 const Type *LoadTy, 1185 Instruction *InsertPt, const TargetData &TD){ 1186 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1187 1188 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8; 1189 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1190 1191 1192 // Compute which bits of the stored value are being used by the load. Convert 1193 // to an integer type to start with. 1194 if (isa<PointerType>(SrcVal->getType())) 1195 SrcVal = new PtrToIntInst(SrcVal, TD.getIntPtrType(Ctx), "tmp", InsertPt); 1196 if (!isa<IntegerType>(SrcVal->getType())) 1197 SrcVal = new BitCastInst(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1198 "tmp", InsertPt); 1199 1200 // Shift the bits to the least significant depending on endianness. 1201 unsigned ShiftAmt; 1202 if (TD.isLittleEndian()) { 1203 ShiftAmt = Offset*8; 1204 } else { 1205 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1206 } 1207 1208 if (ShiftAmt) 1209 SrcVal = BinaryOperator::CreateLShr(SrcVal, 1210 ConstantInt::get(SrcVal->getType(), ShiftAmt), "tmp", InsertPt); 1211 1212 if (LoadSize != StoreSize) 1213 SrcVal = new TruncInst(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1214 "tmp", InsertPt); 1215 1216 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1217} 1218 1219struct AvailableValueInBlock { 1220 /// BB - The basic block in question. 1221 BasicBlock *BB; 1222 /// V - The value that is live out of the block. 1223 Value *V; 1224 /// Offset - The byte offset in V that is interesting for the load query. 1225 unsigned Offset; 1226 1227 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1228 unsigned Offset = 0) { 1229 AvailableValueInBlock Res; 1230 Res.BB = BB; 1231 Res.V = V; 1232 Res.Offset = Offset; 1233 return Res; 1234 } 1235}; 1236 1237/// GetAvailableBlockValues - Given the ValuesPerBlock list, convert all of the 1238/// available values to values of the expected LoadTy in their blocks and insert 1239/// the new values into BlockReplValues. 1240static void 1241GetAvailableBlockValues(DenseMap<BasicBlock*, Value*> &BlockReplValues, 1242 const SmallVector<AvailableValueInBlock, 16> &ValuesPerBlock, 1243 const Type *LoadTy, 1244 const TargetData *TD) { 1245 1246 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1247 BasicBlock *BB = ValuesPerBlock[i].BB; 1248 Value *AvailableVal = ValuesPerBlock[i].V; 1249 unsigned Offset = ValuesPerBlock[i].Offset; 1250 1251 Value *&BlockEntry = BlockReplValues[BB]; 1252 if (BlockEntry) continue; 1253 1254 if (AvailableVal->getType() != LoadTy) { 1255 assert(TD && "Need target data to handle type mismatch case"); 1256 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy, 1257 BB->getTerminator(), *TD); 1258 1259 if (Offset) { 1260 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1261 << *ValuesPerBlock[i].V << '\n' 1262 << *AvailableVal << '\n' << "\n\n\n"); 1263 } 1264 1265 1266 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1267 << *ValuesPerBlock[i].V << '\n' 1268 << *AvailableVal << '\n' << "\n\n\n"); 1269 } 1270 BlockEntry = AvailableVal; 1271 } 1272} 1273 1274/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1275/// non-local by performing PHI construction. 1276bool GVN::processNonLocalLoad(LoadInst *LI, 1277 SmallVectorImpl<Instruction*> &toErase) { 1278 // Find the non-local dependencies of the load. 1279 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 1280 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 1281 Deps); 1282 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: " 1283 // << Deps.size() << *LI << '\n'); 1284 1285 // If we had to process more than one hundred blocks to find the 1286 // dependencies, this load isn't worth worrying about. Optimizing 1287 // it will be too expensive. 1288 if (Deps.size() > 100) 1289 return false; 1290 1291 // If we had a phi translation failure, we'll have a single entry which is a 1292 // clobber in the current block. Reject this early. 1293 if (Deps.size() == 1 && Deps[0].second.isClobber()) { 1294 DEBUG( 1295 errs() << "GVN: non-local load "; 1296 WriteAsOperand(errs(), LI); 1297 errs() << " is clobbered by " << *Deps[0].second.getInst() << '\n'; 1298 ); 1299 return false; 1300 } 1301 1302 // Filter out useless results (non-locals, etc). Keep track of the blocks 1303 // where we have a value available in repl, also keep track of whether we see 1304 // dependencies that produce an unknown value for the load (such as a call 1305 // that could potentially clobber the load). 1306 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1307 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1308 1309 const TargetData *TD = 0; 1310 1311 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1312 BasicBlock *DepBB = Deps[i].first; 1313 MemDepResult DepInfo = Deps[i].second; 1314 1315 if (DepInfo.isClobber()) { 1316 // If the dependence is to a store that writes to a superset of the bits 1317 // read by the load, we can extract the bits we need for the load from the 1318 // stored value. 1319 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1320 if (TD == 0) 1321 TD = getAnalysisIfAvailable<TargetData>(); 1322 if (TD) { 1323 int Offset = AnalyzeLoadFromClobberingStore(LI, DepSI, *TD); 1324 if (Offset != -1) { 1325 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1326 DepSI->getOperand(0), 1327 Offset)); 1328 continue; 1329 } 1330 } 1331 } 1332 1333 // FIXME: Handle memset/memcpy. 1334 UnavailableBlocks.push_back(DepBB); 1335 continue; 1336 } 1337 1338 Instruction *DepInst = DepInfo.getInst(); 1339 1340 // Loading the allocation -> undef. 1341 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1342 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1343 UndefValue::get(LI->getType()))); 1344 continue; 1345 } 1346 1347 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1348 // Reject loads and stores that are to the same address but are of 1349 // different types if we have to. 1350 if (S->getOperand(0)->getType() != LI->getType()) { 1351 if (TD == 0) 1352 TD = getAnalysisIfAvailable<TargetData>(); 1353 1354 // If the stored value is larger or equal to the loaded value, we can 1355 // reuse it. 1356 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0), 1357 LI->getType(), *TD)) { 1358 UnavailableBlocks.push_back(DepBB); 1359 continue; 1360 } 1361 } 1362 1363 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1364 S->getOperand(0))); 1365 continue; 1366 } 1367 1368 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1369 // If the types mismatch and we can't handle it, reject reuse of the load. 1370 if (LD->getType() != LI->getType()) { 1371 if (TD == 0) 1372 TD = getAnalysisIfAvailable<TargetData>(); 1373 1374 // If the stored value is larger or equal to the loaded value, we can 1375 // reuse it. 1376 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1377 UnavailableBlocks.push_back(DepBB); 1378 continue; 1379 } 1380 } 1381 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1382 continue; 1383 } 1384 1385 UnavailableBlocks.push_back(DepBB); 1386 continue; 1387 } 1388 1389 // If we have no predecessors that produce a known value for this load, exit 1390 // early. 1391 if (ValuesPerBlock.empty()) return false; 1392 1393 // If all of the instructions we depend on produce a known value for this 1394 // load, then it is fully redundant and we can use PHI insertion to compute 1395 // its value. Insert PHIs and remove the fully redundant value now. 1396 if (UnavailableBlocks.empty()) { 1397 // Use cached PHI construction information from previous runs 1398 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1399 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated? 1400 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1401 I != E; ++I) { 1402 if ((*I)->getParent() == LI->getParent()) { 1403 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD #1: " << *LI << '\n'); 1404 LI->replaceAllUsesWith(*I); 1405 if (isa<PointerType>((*I)->getType())) 1406 MD->invalidateCachedPointerInfo(*I); 1407 toErase.push_back(LI); 1408 NumGVNLoad++; 1409 return true; 1410 } 1411 1412 ValuesPerBlock.push_back(AvailableValueInBlock::get((*I)->getParent(), 1413 *I)); 1414 } 1415 1416 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1417 1418 // Convert the block information to a map, and insert coersions as needed. 1419 DenseMap<BasicBlock*, Value*> BlockReplValues; 1420 GetAvailableBlockValues(BlockReplValues, ValuesPerBlock, LI->getType(), TD); 1421 1422 // Perform PHI construction. 1423 Value *V = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1424 LI->replaceAllUsesWith(V); 1425 1426 if (isa<PHINode>(V)) 1427 V->takeName(LI); 1428 if (isa<PointerType>(V->getType())) 1429 MD->invalidateCachedPointerInfo(V); 1430 toErase.push_back(LI); 1431 NumGVNLoad++; 1432 return true; 1433 } 1434 1435 if (!EnablePRE || !EnableLoadPRE) 1436 return false; 1437 1438 // Okay, we have *some* definitions of the value. This means that the value 1439 // is available in some of our (transitive) predecessors. Lets think about 1440 // doing PRE of this load. This will involve inserting a new load into the 1441 // predecessor when it's not available. We could do this in general, but 1442 // prefer to not increase code size. As such, we only do this when we know 1443 // that we only have to insert *one* load (which means we're basically moving 1444 // the load, not inserting a new one). 1445 1446 SmallPtrSet<BasicBlock *, 4> Blockers; 1447 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1448 Blockers.insert(UnavailableBlocks[i]); 1449 1450 // Lets find first basic block with more than one predecessor. Walk backwards 1451 // through predecessors if needed. 1452 BasicBlock *LoadBB = LI->getParent(); 1453 BasicBlock *TmpBB = LoadBB; 1454 1455 bool isSinglePred = false; 1456 bool allSingleSucc = true; 1457 while (TmpBB->getSinglePredecessor()) { 1458 isSinglePred = true; 1459 TmpBB = TmpBB->getSinglePredecessor(); 1460 if (!TmpBB) // If haven't found any, bail now. 1461 return false; 1462 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1463 return false; 1464 if (Blockers.count(TmpBB)) 1465 return false; 1466 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1467 allSingleSucc = false; 1468 } 1469 1470 assert(TmpBB); 1471 LoadBB = TmpBB; 1472 1473 // If we have a repl set with LI itself in it, this means we have a loop where 1474 // at least one of the values is LI. Since this means that we won't be able 1475 // to eliminate LI even if we insert uses in the other predecessors, we will 1476 // end up increasing code size. Reject this by scanning for LI. 1477 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1478 if (ValuesPerBlock[i].V == LI) 1479 return false; 1480 1481 if (isSinglePred) { 1482 bool isHot = false; 1483 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1484 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].V)) 1485 // "Hot" Instruction is in some loop (because it dominates its dep. 1486 // instruction). 1487 if (DT->dominates(LI, I)) { 1488 isHot = true; 1489 break; 1490 } 1491 1492 // We are interested only in "hot" instructions. We don't want to do any 1493 // mis-optimizations here. 1494 if (!isHot) 1495 return false; 1496 } 1497 1498 // Okay, we have some hope :). Check to see if the loaded value is fully 1499 // available in all but one predecessor. 1500 // FIXME: If we could restructure the CFG, we could make a common pred with 1501 // all the preds that don't have an available LI and insert a new load into 1502 // that one block. 1503 BasicBlock *UnavailablePred = 0; 1504 1505 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1506 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1507 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1508 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1509 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1510 1511 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1512 PI != E; ++PI) { 1513 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1514 continue; 1515 1516 // If this load is not available in multiple predecessors, reject it. 1517 if (UnavailablePred && UnavailablePred != *PI) 1518 return false; 1519 UnavailablePred = *PI; 1520 } 1521 1522 assert(UnavailablePred != 0 && 1523 "Fully available value should be eliminated above!"); 1524 1525 // If the loaded pointer is PHI node defined in this block, do PHI translation 1526 // to get its value in the predecessor. 1527 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); 1528 1529 // Make sure the value is live in the predecessor. If it was defined by a 1530 // non-PHI instruction in this block, we don't know how to recompute it above. 1531 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) 1532 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { 1533 DEBUG(errs() << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " 1534 << *LPInst << '\n' << *LI << "\n"); 1535 return false; 1536 } 1537 1538 // We don't currently handle critical edges :( 1539 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1540 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1541 << UnavailablePred->getName() << "': " << *LI << '\n'); 1542 return false; 1543 } 1544 1545 // Make sure it is valid to move this load here. We have to watch out for: 1546 // @1 = getelementptr (i8* p, ... 1547 // test p and branch if == 0 1548 // load @1 1549 // It is valid to have the getelementptr before the test, even if p can be 0, 1550 // as getelementptr only does address arithmetic. 1551 // If we are not pushing the value through any multiple-successor blocks 1552 // we do not have this case. Otherwise, check that the load is safe to 1553 // put anywhere; this can be improved, but should be conservatively safe. 1554 if (!allSingleSucc && 1555 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) 1556 return false; 1557 1558 // Okay, we can eliminate this load by inserting a reload in the predecessor 1559 // and using PHI construction to get the value in the other predecessors, do 1560 // it. 1561 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1562 1563 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1564 LI->getAlignment(), 1565 UnavailablePred->getTerminator()); 1566 1567 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1568 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1569 I != E; ++I) 1570 ValuesPerBlock.push_back(AvailableValueInBlock::get((*I)->getParent(), *I)); 1571 1572 DenseMap<BasicBlock*, Value*> BlockReplValues; 1573 GetAvailableBlockValues(BlockReplValues, ValuesPerBlock, LI->getType(), TD); 1574 BlockReplValues[UnavailablePred] = NewLoad; 1575 1576 // Perform PHI construction. 1577 Value *V = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1578 LI->replaceAllUsesWith(V); 1579 if (isa<PHINode>(V)) 1580 V->takeName(LI); 1581 if (isa<PointerType>(V->getType())) 1582 MD->invalidateCachedPointerInfo(V); 1583 toErase.push_back(LI); 1584 NumPRELoad++; 1585 return true; 1586} 1587 1588/// processLoad - Attempt to eliminate a load, first by eliminating it 1589/// locally, and then attempting non-local elimination if that fails. 1590bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1591 if (L->isVolatile()) 1592 return false; 1593 1594 // ... to a pointer that has been loaded from before... 1595 MemDepResult Dep = MD->getDependency(L); 1596 1597 // If the value isn't available, don't do anything! 1598 if (Dep.isClobber()) { 1599 // FIXME: We should handle memset/memcpy/memmove as dependent instructions 1600 // to forward the value if available. 1601 //if (isa<MemIntrinsic>(Dep.getInst())) 1602 //errs() << "LOAD DEPENDS ON MEM: " << *L << "\n" << *Dep.getInst()<<"\n\n"; 1603 1604 // Check to see if we have something like this: 1605 // store i32 123, i32* %P 1606 // %A = bitcast i32* %P to i8* 1607 // %B = gep i8* %A, i32 1 1608 // %C = load i8* %B 1609 // 1610 // We could do that by recognizing if the clobber instructions are obviously 1611 // a common base + constant offset, and if the previous store (or memset) 1612 // completely covers this load. This sort of thing can happen in bitfield 1613 // access code. 1614 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1615 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1616 int Offset = AnalyzeLoadFromClobberingStore(L, DepSI, *TD); 1617 if (Offset != -1) { 1618 Value *AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset, 1619 L->getType(), L, *TD); 1620 DEBUG(errs() << "GVN COERCED STORE BITS:\n" << *DepSI << '\n' 1621 << *AvailVal << '\n' << *L << "\n\n\n"); 1622 1623 // Replace the load! 1624 L->replaceAllUsesWith(AvailVal); 1625 if (isa<PointerType>(AvailVal->getType())) 1626 MD->invalidateCachedPointerInfo(AvailVal); 1627 toErase.push_back(L); 1628 NumGVNLoad++; 1629 return true; 1630 } 1631 } 1632 1633 DEBUG( 1634 // fast print dep, using operator<< on instruction would be too slow 1635 errs() << "GVN: load "; 1636 WriteAsOperand(errs(), L); 1637 Instruction *I = Dep.getInst(); 1638 errs() << " is clobbered by " << *I << '\n'; 1639 ); 1640 return false; 1641 } 1642 1643 // If it is defined in another block, try harder. 1644 if (Dep.isNonLocal()) 1645 return processNonLocalLoad(L, toErase); 1646 1647 Instruction *DepInst = Dep.getInst(); 1648 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1649 Value *StoredVal = DepSI->getOperand(0); 1650 1651 // The store and load are to a must-aliased pointer, but they may not 1652 // actually have the same type. See if we know how to reuse the stored 1653 // value (depending on its type). 1654 const TargetData *TD = 0; 1655 if (StoredVal->getType() != L->getType() && 1656 (TD = getAnalysisIfAvailable<TargetData>())) { 1657 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1658 L, *TD); 1659 if (StoredVal == 0) 1660 return false; 1661 1662 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1663 << '\n' << *L << "\n\n\n"); 1664 } 1665 1666 // Remove it! 1667 L->replaceAllUsesWith(StoredVal); 1668 if (isa<PointerType>(StoredVal->getType())) 1669 MD->invalidateCachedPointerInfo(StoredVal); 1670 toErase.push_back(L); 1671 NumGVNLoad++; 1672 return true; 1673 } 1674 1675 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1676 Value *AvailableVal = DepLI; 1677 1678 // The loads are of a must-aliased pointer, but they may not actually have 1679 // the same type. See if we know how to reuse the previously loaded value 1680 // (depending on its type). 1681 const TargetData *TD = 0; 1682 if (DepLI->getType() != L->getType() && 1683 (TD = getAnalysisIfAvailable<TargetData>())) { 1684 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1685 if (AvailableVal == 0) 1686 return false; 1687 1688 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1689 << "\n" << *L << "\n\n\n"); 1690 } 1691 1692 // Remove it! 1693 L->replaceAllUsesWith(AvailableVal); 1694 if (isa<PointerType>(DepLI->getType())) 1695 MD->invalidateCachedPointerInfo(DepLI); 1696 toErase.push_back(L); 1697 NumGVNLoad++; 1698 return true; 1699 } 1700 1701 // If this load really doesn't depend on anything, then we must be loading an 1702 // undef value. This can happen when loading for a fresh allocation with no 1703 // intervening stores, for example. 1704 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1705 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1706 toErase.push_back(L); 1707 NumGVNLoad++; 1708 return true; 1709 } 1710 1711 return false; 1712} 1713 1714Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1715 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1716 if (I == localAvail.end()) 1717 return 0; 1718 1719 ValueNumberScope *Locals = I->second; 1720 while (Locals) { 1721 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1722 if (I != Locals->table.end()) 1723 return I->second; 1724 Locals = Locals->parent; 1725 } 1726 1727 return 0; 1728} 1729 1730/// AttemptRedundancyElimination - If the "fast path" of redundancy elimination 1731/// by inheritance from the dominator fails, see if we can perform phi 1732/// construction to eliminate the redundancy. 1733Value *GVN::AttemptRedundancyElimination(Instruction *orig, unsigned valno) { 1734 BasicBlock *BaseBlock = orig->getParent(); 1735 1736 SmallPtrSet<BasicBlock*, 4> Visited; 1737 SmallVector<BasicBlock*, 8> Stack; 1738 Stack.push_back(BaseBlock); 1739 1740 DenseMap<BasicBlock*, Value*> Results; 1741 1742 // Walk backwards through our predecessors, looking for instances of the 1743 // value number we're looking for. Instances are recorded in the Results 1744 // map, which is then used to perform phi construction. 1745 while (!Stack.empty()) { 1746 BasicBlock *Current = Stack.back(); 1747 Stack.pop_back(); 1748 1749 // If we've walked all the way to a proper dominator, then give up. Cases 1750 // where the instance is in the dominator will have been caught by the fast 1751 // path, and any cases that require phi construction further than this are 1752 // probably not worth it anyways. Note that this is a SIGNIFICANT compile 1753 // time improvement. 1754 if (DT->properlyDominates(Current, orig->getParent())) return 0; 1755 1756 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA = 1757 localAvail.find(Current); 1758 if (LA == localAvail.end()) return 0; 1759 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno); 1760 1761 if (V != LA->second->table.end()) { 1762 // Found an instance, record it. 1763 Results.insert(std::make_pair(Current, V->second)); 1764 continue; 1765 } 1766 1767 // If we reach the beginning of the function, then give up. 1768 if (pred_begin(Current) == pred_end(Current)) 1769 return 0; 1770 1771 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current); 1772 PI != PE; ++PI) 1773 if (Visited.insert(*PI)) 1774 Stack.push_back(*PI); 1775 } 1776 1777 // If we didn't find instances, give up. Otherwise, perform phi construction. 1778 if (Results.size() == 0) 1779 return 0; 1780 else 1781 return GetValueForBlock(BaseBlock, orig, Results, true); 1782} 1783 1784/// processInstruction - When calculating availability, handle an instruction 1785/// by inserting it into the appropriate sets 1786bool GVN::processInstruction(Instruction *I, 1787 SmallVectorImpl<Instruction*> &toErase) { 1788 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1789 bool Changed = processLoad(LI, toErase); 1790 1791 if (!Changed) { 1792 unsigned Num = VN.lookup_or_add(LI); 1793 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1794 } 1795 1796 return Changed; 1797 } 1798 1799 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1800 unsigned Num = VN.lookup_or_add(I); 1801 1802 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1803 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1804 1805 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1806 return false; 1807 1808 Value *BranchCond = BI->getCondition(); 1809 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1810 1811 BasicBlock *TrueSucc = BI->getSuccessor(0); 1812 BasicBlock *FalseSucc = BI->getSuccessor(1); 1813 1814 if (TrueSucc->getSinglePredecessor()) 1815 localAvail[TrueSucc]->table[CondVN] = 1816 ConstantInt::getTrue(TrueSucc->getContext()); 1817 if (FalseSucc->getSinglePredecessor()) 1818 localAvail[FalseSucc]->table[CondVN] = 1819 ConstantInt::getFalse(TrueSucc->getContext()); 1820 1821 return false; 1822 1823 // Allocations are always uniquely numbered, so we can save time and memory 1824 // by fast failing them. 1825 } else if (isa<AllocationInst>(I) || isMalloc(I) || isa<TerminatorInst>(I)) { 1826 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1827 return false; 1828 } 1829 1830 // Collapse PHI nodes 1831 if (PHINode* p = dyn_cast<PHINode>(I)) { 1832 Value *constVal = CollapsePhi(p); 1833 1834 if (constVal) { 1835 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1836 PI != PE; ++PI) 1837 PI->second.erase(p); 1838 1839 p->replaceAllUsesWith(constVal); 1840 if (isa<PointerType>(constVal->getType())) 1841 MD->invalidateCachedPointerInfo(constVal); 1842 VN.erase(p); 1843 1844 toErase.push_back(p); 1845 } else { 1846 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1847 } 1848 1849 // If the number we were assigned was a brand new VN, then we don't 1850 // need to do a lookup to see if the number already exists 1851 // somewhere in the domtree: it can't! 1852 } else if (Num == NextNum) { 1853 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1854 1855 // Perform fast-path value-number based elimination of values inherited from 1856 // dominators. 1857 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1858 // Remove it! 1859 VN.erase(I); 1860 I->replaceAllUsesWith(repl); 1861 if (isa<PointerType>(repl->getType())) 1862 MD->invalidateCachedPointerInfo(repl); 1863 toErase.push_back(I); 1864 return true; 1865 1866#if 0 1867 // Perform slow-pathvalue-number based elimination with phi construction. 1868 } else if (Value *repl = AttemptRedundancyElimination(I, Num)) { 1869 // Remove it! 1870 VN.erase(I); 1871 I->replaceAllUsesWith(repl); 1872 if (isa<PointerType>(repl->getType())) 1873 MD->invalidateCachedPointerInfo(repl); 1874 toErase.push_back(I); 1875 return true; 1876#endif 1877 } else { 1878 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1879 } 1880 1881 return false; 1882} 1883 1884/// runOnFunction - This is the main transformation entry point for a function. 1885bool GVN::runOnFunction(Function& F) { 1886 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1887 DT = &getAnalysis<DominatorTree>(); 1888 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1889 VN.setMemDep(MD); 1890 VN.setDomTree(DT); 1891 1892 bool Changed = false; 1893 bool ShouldContinue = true; 1894 1895 // Merge unconditional branches, allowing PRE to catch more 1896 // optimization opportunities. 1897 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1898 BasicBlock *BB = FI; 1899 ++FI; 1900 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1901 if (removedBlock) NumGVNBlocks++; 1902 1903 Changed |= removedBlock; 1904 } 1905 1906 unsigned Iteration = 0; 1907 1908 while (ShouldContinue) { 1909 DEBUG(errs() << "GVN iteration: " << Iteration << "\n"); 1910 ShouldContinue = iterateOnFunction(F); 1911 Changed |= ShouldContinue; 1912 ++Iteration; 1913 } 1914 1915 if (EnablePRE) { 1916 bool PREChanged = true; 1917 while (PREChanged) { 1918 PREChanged = performPRE(F); 1919 Changed |= PREChanged; 1920 } 1921 } 1922 // FIXME: Should perform GVN again after PRE does something. PRE can move 1923 // computations into blocks where they become fully redundant. Note that 1924 // we can't do this until PRE's critical edge splitting updates memdep. 1925 // Actually, when this happens, we should just fully integrate PRE into GVN. 1926 1927 cleanupGlobalSets(); 1928 1929 return Changed; 1930} 1931 1932 1933bool GVN::processBlock(BasicBlock *BB) { 1934 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1935 // incrementing BI before processing an instruction). 1936 SmallVector<Instruction*, 8> toErase; 1937 bool ChangedFunction = false; 1938 1939 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1940 BI != BE;) { 1941 ChangedFunction |= processInstruction(BI, toErase); 1942 if (toErase.empty()) { 1943 ++BI; 1944 continue; 1945 } 1946 1947 // If we need some instructions deleted, do it now. 1948 NumGVNInstr += toErase.size(); 1949 1950 // Avoid iterator invalidation. 1951 bool AtStart = BI == BB->begin(); 1952 if (!AtStart) 1953 --BI; 1954 1955 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1956 E = toErase.end(); I != E; ++I) { 1957 DEBUG(errs() << "GVN removed: " << **I << '\n'); 1958 MD->removeInstruction(*I); 1959 (*I)->eraseFromParent(); 1960 DEBUG(verifyRemoved(*I)); 1961 } 1962 toErase.clear(); 1963 1964 if (AtStart) 1965 BI = BB->begin(); 1966 else 1967 ++BI; 1968 } 1969 1970 return ChangedFunction; 1971} 1972 1973/// performPRE - Perform a purely local form of PRE that looks for diamond 1974/// control flow patterns and attempts to perform simple PRE at the join point. 1975bool GVN::performPRE(Function& F) { 1976 bool Changed = false; 1977 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1978 DenseMap<BasicBlock*, Value*> predMap; 1979 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1980 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1981 BasicBlock *CurrentBlock = *DI; 1982 1983 // Nothing to PRE in the entry block. 1984 if (CurrentBlock == &F.getEntryBlock()) continue; 1985 1986 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1987 BE = CurrentBlock->end(); BI != BE; ) { 1988 Instruction *CurInst = BI++; 1989 1990 if (isa<AllocationInst>(CurInst) || isMalloc(CurInst) || 1991 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 1992 (CurInst->getType() == Type::getVoidTy(F.getContext())) || 1993 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 1994 isa<DbgInfoIntrinsic>(CurInst)) 1995 continue; 1996 1997 uint32_t ValNo = VN.lookup(CurInst); 1998 1999 // Look for the predecessors for PRE opportunities. We're 2000 // only trying to solve the basic diamond case, where 2001 // a value is computed in the successor and one predecessor, 2002 // but not the other. We also explicitly disallow cases 2003 // where the successor is its own predecessor, because they're 2004 // more complicated to get right. 2005 unsigned NumWith = 0; 2006 unsigned NumWithout = 0; 2007 BasicBlock *PREPred = 0; 2008 predMap.clear(); 2009 2010 for (pred_iterator PI = pred_begin(CurrentBlock), 2011 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2012 // We're not interested in PRE where the block is its 2013 // own predecessor, on in blocks with predecessors 2014 // that are not reachable. 2015 if (*PI == CurrentBlock) { 2016 NumWithout = 2; 2017 break; 2018 } else if (!localAvail.count(*PI)) { 2019 NumWithout = 2; 2020 break; 2021 } 2022 2023 DenseMap<uint32_t, Value*>::iterator predV = 2024 localAvail[*PI]->table.find(ValNo); 2025 if (predV == localAvail[*PI]->table.end()) { 2026 PREPred = *PI; 2027 NumWithout++; 2028 } else if (predV->second == CurInst) { 2029 NumWithout = 2; 2030 } else { 2031 predMap[*PI] = predV->second; 2032 NumWith++; 2033 } 2034 } 2035 2036 // Don't do PRE when it might increase code size, i.e. when 2037 // we would need to insert instructions in more than one pred. 2038 if (NumWithout != 1 || NumWith == 0) 2039 continue; 2040 2041 // We can't do PRE safely on a critical edge, so instead we schedule 2042 // the edge to be split and perform the PRE the next time we iterate 2043 // on the function. 2044 unsigned SuccNum = 0; 2045 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 2046 i != e; ++i) 2047 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 2048 SuccNum = i; 2049 break; 2050 } 2051 2052 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2053 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2054 continue; 2055 } 2056 2057 // Instantiate the expression the in predecessor that lacked it. 2058 // Because we are going top-down through the block, all value numbers 2059 // will be available in the predecessor by the time we need them. Any 2060 // that weren't original present will have been instantiated earlier 2061 // in this loop. 2062 Instruction *PREInstr = CurInst->clone(CurInst->getContext()); 2063 bool success = true; 2064 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2065 Value *Op = PREInstr->getOperand(i); 2066 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2067 continue; 2068 2069 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2070 PREInstr->setOperand(i, V); 2071 } else { 2072 success = false; 2073 break; 2074 } 2075 } 2076 2077 // Fail out if we encounter an operand that is not available in 2078 // the PRE predecessor. This is typically because of loads which 2079 // are not value numbered precisely. 2080 if (!success) { 2081 delete PREInstr; 2082 DEBUG(verifyRemoved(PREInstr)); 2083 continue; 2084 } 2085 2086 PREInstr->insertBefore(PREPred->getTerminator()); 2087 PREInstr->setName(CurInst->getName() + ".pre"); 2088 predMap[PREPred] = PREInstr; 2089 VN.add(PREInstr, ValNo); 2090 NumGVNPRE++; 2091 2092 // Update the availability map to include the new instruction. 2093 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 2094 2095 // Create a PHI to make the value available in this block. 2096 PHINode* Phi = PHINode::Create(CurInst->getType(), 2097 CurInst->getName() + ".pre-phi", 2098 CurrentBlock->begin()); 2099 for (pred_iterator PI = pred_begin(CurrentBlock), 2100 PE = pred_end(CurrentBlock); PI != PE; ++PI) 2101 Phi->addIncoming(predMap[*PI], *PI); 2102 2103 VN.add(Phi, ValNo); 2104 localAvail[CurrentBlock]->table[ValNo] = Phi; 2105 2106 CurInst->replaceAllUsesWith(Phi); 2107 if (isa<PointerType>(Phi->getType())) 2108 MD->invalidateCachedPointerInfo(Phi); 2109 VN.erase(CurInst); 2110 2111 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n'); 2112 MD->removeInstruction(CurInst); 2113 CurInst->eraseFromParent(); 2114 DEBUG(verifyRemoved(CurInst)); 2115 Changed = true; 2116 } 2117 } 2118 2119 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 2120 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 2121 SplitCriticalEdge(I->first, I->second, this); 2122 2123 return Changed || toSplit.size(); 2124} 2125 2126/// iterateOnFunction - Executes one iteration of GVN 2127bool GVN::iterateOnFunction(Function &F) { 2128 cleanupGlobalSets(); 2129 2130 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2131 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 2132 if (DI->getIDom()) 2133 localAvail[DI->getBlock()] = 2134 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 2135 else 2136 localAvail[DI->getBlock()] = new ValueNumberScope(0); 2137 } 2138 2139 // Top-down walk of the dominator tree 2140 bool Changed = false; 2141#if 0 2142 // Needed for value numbering with phi construction to work. 2143 ReversePostOrderTraversal<Function*> RPOT(&F); 2144 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2145 RE = RPOT.end(); RI != RE; ++RI) 2146 Changed |= processBlock(*RI); 2147#else 2148 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2149 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2150 Changed |= processBlock(DI->getBlock()); 2151#endif 2152 2153 return Changed; 2154} 2155 2156void GVN::cleanupGlobalSets() { 2157 VN.clear(); 2158 phiMap.clear(); 2159 2160 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2161 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 2162 delete I->second; 2163 localAvail.clear(); 2164} 2165 2166/// verifyRemoved - Verify that the specified instruction does not occur in our 2167/// internal data structures. 2168void GVN::verifyRemoved(const Instruction *Inst) const { 2169 VN.verifyRemoved(Inst); 2170 2171 // Walk through the PHI map to make sure the instruction isn't hiding in there 2172 // somewhere. 2173 for (PhiMapType::iterator 2174 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) { 2175 assert(I->first != Inst && "Inst is still a key in PHI map!"); 2176 2177 for (SmallPtrSet<Instruction*, 4>::iterator 2178 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) { 2179 assert(*II != Inst && "Inst is still a value in PHI map!"); 2180 } 2181 } 2182 2183 // Walk through the value number scope to make sure the instruction isn't 2184 // ferreted away in it. 2185 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2186 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 2187 const ValueNumberScope *VNS = I->second; 2188 2189 while (VNS) { 2190 for (DenseMap<uint32_t, Value*>::iterator 2191 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 2192 assert(II->second != Inst && "Inst still in value numbering scope!"); 2193 } 2194 2195 VNS = VNS->parent; 2196 } 2197 } 2198} 2199