GVN.cpp revision 42c3f554f4d5e505c3e43cdcf722ec82a7a3f6a5
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/Value.h" 26#include "llvm/ADT/DenseMap.h" 27#include "llvm/ADT/DepthFirstIterator.h" 28#include "llvm/ADT/PostOrderIterator.h" 29#include "llvm/ADT/SmallPtrSet.h" 30#include "llvm/ADT/SmallVector.h" 31#include "llvm/ADT/Statistic.h" 32#include "llvm/Analysis/Dominators.h" 33#include "llvm/Analysis/AliasAnalysis.h" 34#include "llvm/Analysis/MemoryDependenceAnalysis.h" 35#include "llvm/Support/CFG.h" 36#include "llvm/Support/CommandLine.h" 37#include "llvm/Support/Compiler.h" 38#include "llvm/Support/Debug.h" 39#include "llvm/Transforms/Utils/BasicBlockUtils.h" 40#include "llvm/Transforms/Utils/Local.h" 41#include <cstdio> 42using namespace llvm; 43 44STATISTIC(NumGVNInstr, "Number of instructions deleted"); 45STATISTIC(NumGVNLoad, "Number of loads deleted"); 46STATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 47STATISTIC(NumGVNBlocks, "Number of blocks merged"); 48STATISTIC(NumPRELoad, "Number of loads PRE'd"); 49 50static cl::opt<bool> EnablePRE("enable-pre", 51 cl::init(true), cl::Hidden); 52static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 53 54//===----------------------------------------------------------------------===// 55// ValueTable Class 56//===----------------------------------------------------------------------===// 57 58/// This class holds the mapping between values and value numbers. It is used 59/// as an efficient mechanism to determine the expression-wise equivalence of 60/// two values. 61namespace { 62 struct VISIBILITY_HIDDEN Expression { 63 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL, 64 UDIV, SDIV, FDIV, UREM, SREM, 65 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ, 66 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE, 67 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ, 68 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE, 69 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE, 70 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT, 71 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI, 72 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT, 73 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT, 74 EMPTY, TOMBSTONE }; 75 76 ExpressionOpcode opcode; 77 const Type* type; 78 uint32_t firstVN; 79 uint32_t secondVN; 80 uint32_t thirdVN; 81 SmallVector<uint32_t, 4> varargs; 82 Value* function; 83 84 Expression() { } 85 Expression(ExpressionOpcode o) : opcode(o) { } 86 87 bool operator==(const Expression &other) const { 88 if (opcode != other.opcode) 89 return false; 90 else if (opcode == EMPTY || opcode == TOMBSTONE) 91 return true; 92 else if (type != other.type) 93 return false; 94 else if (function != other.function) 95 return false; 96 else if (firstVN != other.firstVN) 97 return false; 98 else if (secondVN != other.secondVN) 99 return false; 100 else if (thirdVN != other.thirdVN) 101 return false; 102 else { 103 if (varargs.size() != other.varargs.size()) 104 return false; 105 106 for (size_t i = 0; i < varargs.size(); ++i) 107 if (varargs[i] != other.varargs[i]) 108 return false; 109 110 return true; 111 } 112 } 113 114 bool operator!=(const Expression &other) const { 115 return !(*this == other); 116 } 117 }; 118 119 class VISIBILITY_HIDDEN ValueTable { 120 private: 121 DenseMap<Value*, uint32_t> valueNumbering; 122 DenseMap<Expression, uint32_t> expressionNumbering; 123 AliasAnalysis* AA; 124 MemoryDependenceAnalysis* MD; 125 DominatorTree* DT; 126 127 uint32_t nextValueNumber; 128 129 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO); 130 Expression::ExpressionOpcode getOpcode(CmpInst* C); 131 Expression::ExpressionOpcode getOpcode(CastInst* C); 132 Expression create_expression(BinaryOperator* BO); 133 Expression create_expression(CmpInst* C); 134 Expression create_expression(ShuffleVectorInst* V); 135 Expression create_expression(ExtractElementInst* C); 136 Expression create_expression(InsertElementInst* V); 137 Expression create_expression(SelectInst* V); 138 Expression create_expression(CastInst* C); 139 Expression create_expression(GetElementPtrInst* G); 140 Expression create_expression(CallInst* C); 141 Expression create_expression(Constant* C); 142 public: 143 ValueTable() : nextValueNumber(1) { } 144 uint32_t lookup_or_add(Value* V); 145 uint32_t lookup(Value* V) const; 146 void add(Value* V, uint32_t num); 147 void clear(); 148 void erase(Value* v); 149 unsigned size(); 150 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 151 AliasAnalysis *getAliasAnalysis() const { return AA; } 152 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 153 void setDomTree(DominatorTree* D) { DT = D; } 154 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 155 void verifyRemoved(const Value *) const; 156 }; 157} 158 159namespace llvm { 160template <> struct DenseMapInfo<Expression> { 161 static inline Expression getEmptyKey() { 162 return Expression(Expression::EMPTY); 163 } 164 165 static inline Expression getTombstoneKey() { 166 return Expression(Expression::TOMBSTONE); 167 } 168 169 static unsigned getHashValue(const Expression e) { 170 unsigned hash = e.opcode; 171 172 hash = e.firstVN + hash * 37; 173 hash = e.secondVN + hash * 37; 174 hash = e.thirdVN + hash * 37; 175 176 hash = ((unsigned)((uintptr_t)e.type >> 4) ^ 177 (unsigned)((uintptr_t)e.type >> 9)) + 178 hash * 37; 179 180 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(), 181 E = e.varargs.end(); I != E; ++I) 182 hash = *I + hash * 37; 183 184 hash = ((unsigned)((uintptr_t)e.function >> 4) ^ 185 (unsigned)((uintptr_t)e.function >> 9)) + 186 hash * 37; 187 188 return hash; 189 } 190 static bool isEqual(const Expression &LHS, const Expression &RHS) { 191 return LHS == RHS; 192 } 193 static bool isPod() { return true; } 194}; 195} 196 197//===----------------------------------------------------------------------===// 198// ValueTable Internal Functions 199//===----------------------------------------------------------------------===// 200Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) { 201 switch(BO->getOpcode()) { 202 default: // THIS SHOULD NEVER HAPPEN 203 assert(0 && "Binary operator with unknown opcode?"); 204 case Instruction::Add: return Expression::ADD; 205 case Instruction::FAdd: return Expression::FADD; 206 case Instruction::Sub: return Expression::SUB; 207 case Instruction::FSub: return Expression::FSUB; 208 case Instruction::Mul: return Expression::MUL; 209 case Instruction::FMul: return Expression::FMUL; 210 case Instruction::UDiv: return Expression::UDIV; 211 case Instruction::SDiv: return Expression::SDIV; 212 case Instruction::FDiv: return Expression::FDIV; 213 case Instruction::URem: return Expression::UREM; 214 case Instruction::SRem: return Expression::SREM; 215 case Instruction::FRem: return Expression::FREM; 216 case Instruction::Shl: return Expression::SHL; 217 case Instruction::LShr: return Expression::LSHR; 218 case Instruction::AShr: return Expression::ASHR; 219 case Instruction::And: return Expression::AND; 220 case Instruction::Or: return Expression::OR; 221 case Instruction::Xor: return Expression::XOR; 222 } 223} 224 225Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) { 226 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) { 227 switch (C->getPredicate()) { 228 default: // THIS SHOULD NEVER HAPPEN 229 assert(0 && "Comparison with unknown predicate?"); 230 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ; 231 case ICmpInst::ICMP_NE: return Expression::ICMPNE; 232 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT; 233 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE; 234 case ICmpInst::ICMP_ULT: return Expression::ICMPULT; 235 case ICmpInst::ICMP_ULE: return Expression::ICMPULE; 236 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT; 237 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE; 238 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT; 239 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE; 240 } 241 } 242 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare"); 243 switch (C->getPredicate()) { 244 default: // THIS SHOULD NEVER HAPPEN 245 assert(0 && "Comparison with unknown predicate?"); 246 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ; 247 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT; 248 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE; 249 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT; 250 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE; 251 case FCmpInst::FCMP_ONE: return Expression::FCMPONE; 252 case FCmpInst::FCMP_ORD: return Expression::FCMPORD; 253 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO; 254 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ; 255 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT; 256 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE; 257 case FCmpInst::FCMP_ULT: return Expression::FCMPULT; 258 case FCmpInst::FCMP_ULE: return Expression::FCMPULE; 259 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE; 260 } 261} 262 263Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) { 264 switch(C->getOpcode()) { 265 default: // THIS SHOULD NEVER HAPPEN 266 assert(0 && "Cast operator with unknown opcode?"); 267 case Instruction::Trunc: return Expression::TRUNC; 268 case Instruction::ZExt: return Expression::ZEXT; 269 case Instruction::SExt: return Expression::SEXT; 270 case Instruction::FPToUI: return Expression::FPTOUI; 271 case Instruction::FPToSI: return Expression::FPTOSI; 272 case Instruction::UIToFP: return Expression::UITOFP; 273 case Instruction::SIToFP: return Expression::SITOFP; 274 case Instruction::FPTrunc: return Expression::FPTRUNC; 275 case Instruction::FPExt: return Expression::FPEXT; 276 case Instruction::PtrToInt: return Expression::PTRTOINT; 277 case Instruction::IntToPtr: return Expression::INTTOPTR; 278 case Instruction::BitCast: return Expression::BITCAST; 279 } 280} 281 282Expression ValueTable::create_expression(CallInst* C) { 283 Expression e; 284 285 e.type = C->getType(); 286 e.firstVN = 0; 287 e.secondVN = 0; 288 e.thirdVN = 0; 289 e.function = C->getCalledFunction(); 290 e.opcode = Expression::CALL; 291 292 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end(); 293 I != E; ++I) 294 e.varargs.push_back(lookup_or_add(*I)); 295 296 return e; 297} 298 299Expression ValueTable::create_expression(BinaryOperator* BO) { 300 Expression e; 301 302 e.firstVN = lookup_or_add(BO->getOperand(0)); 303 e.secondVN = lookup_or_add(BO->getOperand(1)); 304 e.thirdVN = 0; 305 e.function = 0; 306 e.type = BO->getType(); 307 e.opcode = getOpcode(BO); 308 309 return e; 310} 311 312Expression ValueTable::create_expression(CmpInst* C) { 313 Expression e; 314 315 e.firstVN = lookup_or_add(C->getOperand(0)); 316 e.secondVN = lookup_or_add(C->getOperand(1)); 317 e.thirdVN = 0; 318 e.function = 0; 319 e.type = C->getType(); 320 e.opcode = getOpcode(C); 321 322 return e; 323} 324 325Expression ValueTable::create_expression(CastInst* C) { 326 Expression e; 327 328 e.firstVN = lookup_or_add(C->getOperand(0)); 329 e.secondVN = 0; 330 e.thirdVN = 0; 331 e.function = 0; 332 e.type = C->getType(); 333 e.opcode = getOpcode(C); 334 335 return e; 336} 337 338Expression ValueTable::create_expression(ShuffleVectorInst* S) { 339 Expression e; 340 341 e.firstVN = lookup_or_add(S->getOperand(0)); 342 e.secondVN = lookup_or_add(S->getOperand(1)); 343 e.thirdVN = lookup_or_add(S->getOperand(2)); 344 e.function = 0; 345 e.type = S->getType(); 346 e.opcode = Expression::SHUFFLE; 347 348 return e; 349} 350 351Expression ValueTable::create_expression(ExtractElementInst* E) { 352 Expression e; 353 354 e.firstVN = lookup_or_add(E->getOperand(0)); 355 e.secondVN = lookup_or_add(E->getOperand(1)); 356 e.thirdVN = 0; 357 e.function = 0; 358 e.type = E->getType(); 359 e.opcode = Expression::EXTRACT; 360 361 return e; 362} 363 364Expression ValueTable::create_expression(InsertElementInst* I) { 365 Expression e; 366 367 e.firstVN = lookup_or_add(I->getOperand(0)); 368 e.secondVN = lookup_or_add(I->getOperand(1)); 369 e.thirdVN = lookup_or_add(I->getOperand(2)); 370 e.function = 0; 371 e.type = I->getType(); 372 e.opcode = Expression::INSERT; 373 374 return e; 375} 376 377Expression ValueTable::create_expression(SelectInst* I) { 378 Expression e; 379 380 e.firstVN = lookup_or_add(I->getCondition()); 381 e.secondVN = lookup_or_add(I->getTrueValue()); 382 e.thirdVN = lookup_or_add(I->getFalseValue()); 383 e.function = 0; 384 e.type = I->getType(); 385 e.opcode = Expression::SELECT; 386 387 return e; 388} 389 390Expression ValueTable::create_expression(GetElementPtrInst* G) { 391 Expression e; 392 393 e.firstVN = lookup_or_add(G->getPointerOperand()); 394 e.secondVN = 0; 395 e.thirdVN = 0; 396 e.function = 0; 397 e.type = G->getType(); 398 e.opcode = Expression::GEP; 399 400 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end(); 401 I != E; ++I) 402 e.varargs.push_back(lookup_or_add(*I)); 403 404 return e; 405} 406 407//===----------------------------------------------------------------------===// 408// ValueTable External Functions 409//===----------------------------------------------------------------------===// 410 411/// add - Insert a value into the table with a specified value number. 412void ValueTable::add(Value* V, uint32_t num) { 413 valueNumbering.insert(std::make_pair(V, num)); 414} 415 416/// lookup_or_add - Returns the value number for the specified value, assigning 417/// it a new number if it did not have one before. 418uint32_t ValueTable::lookup_or_add(Value* V) { 419 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 420 if (VI != valueNumbering.end()) 421 return VI->second; 422 423 if (CallInst* C = dyn_cast<CallInst>(V)) { 424 if (AA->doesNotAccessMemory(C)) { 425 Expression e = create_expression(C); 426 427 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 428 if (EI != expressionNumbering.end()) { 429 valueNumbering.insert(std::make_pair(V, EI->second)); 430 return EI->second; 431 } else { 432 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 433 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 434 435 return nextValueNumber++; 436 } 437 } else if (AA->onlyReadsMemory(C)) { 438 Expression e = create_expression(C); 439 440 if (expressionNumbering.find(e) == expressionNumbering.end()) { 441 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 442 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 443 return nextValueNumber++; 444 } 445 446 MemDepResult local_dep = MD->getDependency(C); 447 448 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 449 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 450 return nextValueNumber++; 451 } 452 453 if (local_dep.isDef()) { 454 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 455 456 if (local_cdep->getNumOperands() != C->getNumOperands()) { 457 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 458 return nextValueNumber++; 459 } 460 461 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 462 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 463 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i)); 464 if (c_vn != cd_vn) { 465 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 466 return nextValueNumber++; 467 } 468 } 469 470 uint32_t v = lookup_or_add(local_cdep); 471 valueNumbering.insert(std::make_pair(V, v)); 472 return v; 473 } 474 475 // Non-local case. 476 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 477 MD->getNonLocalCallDependency(CallSite(C)); 478 // FIXME: call/call dependencies for readonly calls should return def, not 479 // clobber! Move the checking logic to MemDep! 480 CallInst* cdep = 0; 481 482 // Check to see if we have a single dominating call instruction that is 483 // identical to C. 484 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 485 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i]; 486 // Ignore non-local dependencies. 487 if (I->second.isNonLocal()) 488 continue; 489 490 // We don't handle non-depedencies. If we already have a call, reject 491 // instruction dependencies. 492 if (I->second.isClobber() || cdep != 0) { 493 cdep = 0; 494 break; 495 } 496 497 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst()); 498 // FIXME: All duplicated with non-local case. 499 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){ 500 cdep = NonLocalDepCall; 501 continue; 502 } 503 504 cdep = 0; 505 break; 506 } 507 508 if (!cdep) { 509 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 510 return nextValueNumber++; 511 } 512 513 if (cdep->getNumOperands() != C->getNumOperands()) { 514 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 515 return nextValueNumber++; 516 } 517 for (unsigned i = 1; i < C->getNumOperands(); ++i) { 518 uint32_t c_vn = lookup_or_add(C->getOperand(i)); 519 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i)); 520 if (c_vn != cd_vn) { 521 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 522 return nextValueNumber++; 523 } 524 } 525 526 uint32_t v = lookup_or_add(cdep); 527 valueNumbering.insert(std::make_pair(V, v)); 528 return v; 529 530 } else { 531 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 532 return nextValueNumber++; 533 } 534 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) { 535 Expression e = create_expression(BO); 536 537 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 538 if (EI != expressionNumbering.end()) { 539 valueNumbering.insert(std::make_pair(V, EI->second)); 540 return EI->second; 541 } else { 542 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 543 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 544 545 return nextValueNumber++; 546 } 547 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) { 548 Expression e = create_expression(C); 549 550 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 551 if (EI != expressionNumbering.end()) { 552 valueNumbering.insert(std::make_pair(V, EI->second)); 553 return EI->second; 554 } else { 555 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 556 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 557 558 return nextValueNumber++; 559 } 560 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) { 561 Expression e = create_expression(U); 562 563 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 564 if (EI != expressionNumbering.end()) { 565 valueNumbering.insert(std::make_pair(V, EI->second)); 566 return EI->second; 567 } else { 568 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 569 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 570 571 return nextValueNumber++; 572 } 573 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) { 574 Expression e = create_expression(U); 575 576 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 577 if (EI != expressionNumbering.end()) { 578 valueNumbering.insert(std::make_pair(V, EI->second)); 579 return EI->second; 580 } else { 581 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 582 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 583 584 return nextValueNumber++; 585 } 586 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) { 587 Expression e = create_expression(U); 588 589 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 590 if (EI != expressionNumbering.end()) { 591 valueNumbering.insert(std::make_pair(V, EI->second)); 592 return EI->second; 593 } else { 594 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 595 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 596 597 return nextValueNumber++; 598 } 599 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) { 600 Expression e = create_expression(U); 601 602 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 603 if (EI != expressionNumbering.end()) { 604 valueNumbering.insert(std::make_pair(V, EI->second)); 605 return EI->second; 606 } else { 607 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 608 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 609 610 return nextValueNumber++; 611 } 612 } else if (CastInst* U = dyn_cast<CastInst>(V)) { 613 Expression e = create_expression(U); 614 615 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 616 if (EI != expressionNumbering.end()) { 617 valueNumbering.insert(std::make_pair(V, EI->second)); 618 return EI->second; 619 } else { 620 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 621 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 622 623 return nextValueNumber++; 624 } 625 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) { 626 Expression e = create_expression(U); 627 628 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e); 629 if (EI != expressionNumbering.end()) { 630 valueNumbering.insert(std::make_pair(V, EI->second)); 631 return EI->second; 632 } else { 633 expressionNumbering.insert(std::make_pair(e, nextValueNumber)); 634 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 635 636 return nextValueNumber++; 637 } 638 } else { 639 valueNumbering.insert(std::make_pair(V, nextValueNumber)); 640 return nextValueNumber++; 641 } 642} 643 644/// lookup - Returns the value number of the specified value. Fails if 645/// the value has not yet been numbered. 646uint32_t ValueTable::lookup(Value* V) const { 647 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 648 assert(VI != valueNumbering.end() && "Value not numbered?"); 649 return VI->second; 650} 651 652/// clear - Remove all entries from the ValueTable 653void ValueTable::clear() { 654 valueNumbering.clear(); 655 expressionNumbering.clear(); 656 nextValueNumber = 1; 657} 658 659/// erase - Remove a value from the value numbering 660void ValueTable::erase(Value* V) { 661 valueNumbering.erase(V); 662} 663 664/// verifyRemoved - Verify that the value is removed from all internal data 665/// structures. 666void ValueTable::verifyRemoved(const Value *V) const { 667 for (DenseMap<Value*, uint32_t>::iterator 668 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 669 assert(I->first != V && "Inst still occurs in value numbering map!"); 670 } 671} 672 673//===----------------------------------------------------------------------===// 674// GVN Pass 675//===----------------------------------------------------------------------===// 676 677namespace { 678 struct VISIBILITY_HIDDEN ValueNumberScope { 679 ValueNumberScope* parent; 680 DenseMap<uint32_t, Value*> table; 681 682 ValueNumberScope(ValueNumberScope* p) : parent(p) { } 683 }; 684} 685 686namespace { 687 688 class VISIBILITY_HIDDEN GVN : public FunctionPass { 689 bool runOnFunction(Function &F); 690 public: 691 static char ID; // Pass identification, replacement for typeid 692 GVN() : FunctionPass(&ID) { } 693 694 private: 695 MemoryDependenceAnalysis *MD; 696 DominatorTree *DT; 697 698 ValueTable VN; 699 DenseMap<BasicBlock*, ValueNumberScope*> localAvail; 700 701 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType; 702 PhiMapType phiMap; 703 704 705 // This transformation requires dominator postdominator info 706 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 707 AU.addRequired<DominatorTree>(); 708 AU.addRequired<MemoryDependenceAnalysis>(); 709 AU.addRequired<AliasAnalysis>(); 710 711 AU.addPreserved<DominatorTree>(); 712 AU.addPreserved<AliasAnalysis>(); 713 } 714 715 // Helper fuctions 716 // FIXME: eliminate or document these better 717 bool processLoad(LoadInst* L, 718 SmallVectorImpl<Instruction*> &toErase); 719 bool processInstruction(Instruction* I, 720 SmallVectorImpl<Instruction*> &toErase); 721 bool processNonLocalLoad(LoadInst* L, 722 SmallVectorImpl<Instruction*> &toErase); 723 bool processBlock(BasicBlock* BB); 724 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig, 725 DenseMap<BasicBlock*, Value*> &Phis, 726 bool top_level = false); 727 void dump(DenseMap<uint32_t, Value*>& d); 728 bool iterateOnFunction(Function &F); 729 Value* CollapsePhi(PHINode* p); 730 bool isSafeReplacement(PHINode* p, Instruction* inst); 731 bool performPRE(Function& F); 732 Value* lookupNumber(BasicBlock* BB, uint32_t num); 733 bool mergeBlockIntoPredecessor(BasicBlock* BB); 734 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno); 735 void cleanupGlobalSets(); 736 void verifyRemoved(const Instruction *I) const; 737 }; 738 739 char GVN::ID = 0; 740} 741 742// createGVNPass - The public interface to this file... 743FunctionPass *llvm::createGVNPass() { return new GVN(); } 744 745static RegisterPass<GVN> X("gvn", 746 "Global Value Numbering"); 747 748void GVN::dump(DenseMap<uint32_t, Value*>& d) { 749 printf("{\n"); 750 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 751 E = d.end(); I != E; ++I) { 752 printf("%d\n", I->first); 753 I->second->dump(); 754 } 755 printf("}\n"); 756} 757 758Value* GVN::CollapsePhi(PHINode* p) { 759 Value* constVal = p->hasConstantValue(); 760 if (!constVal) return 0; 761 762 Instruction* inst = dyn_cast<Instruction>(constVal); 763 if (!inst) 764 return constVal; 765 766 if (DT->dominates(inst, p)) 767 if (isSafeReplacement(p, inst)) 768 return inst; 769 return 0; 770} 771 772bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) { 773 if (!isa<PHINode>(inst)) 774 return true; 775 776 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 777 UI != E; ++UI) 778 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 779 if (use_phi->getParent() == inst->getParent()) 780 return false; 781 782 return true; 783} 784 785/// GetValueForBlock - Get the value to use within the specified basic block. 786/// available values are in Phis. 787Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig, 788 DenseMap<BasicBlock*, Value*> &Phis, 789 bool top_level) { 790 791 // If we have already computed this value, return the previously computed val. 792 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 793 if (V != Phis.end() && !top_level) return V->second; 794 795 // If the block is unreachable, just return undef, since this path 796 // can't actually occur at runtime. 797 if (!DT->isReachableFromEntry(BB)) 798 return Phis[BB] = UndefValue::get(orig->getType()); 799 800 if (BasicBlock *Pred = BB->getSinglePredecessor()) { 801 Value *ret = GetValueForBlock(Pred, orig, Phis); 802 Phis[BB] = ret; 803 return ret; 804 } 805 806 // Get the number of predecessors of this block so we can reserve space later. 807 // If there is already a PHI in it, use the #preds from it, otherwise count. 808 // Getting it from the PHI is constant time. 809 unsigned NumPreds; 810 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin())) 811 NumPreds = ExistingPN->getNumIncomingValues(); 812 else 813 NumPreds = std::distance(pred_begin(BB), pred_end(BB)); 814 815 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so 816 // now, then get values to fill in the incoming values for the PHI. 817 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle", 818 BB->begin()); 819 PN->reserveOperandSpace(NumPreds); 820 821 Phis.insert(std::make_pair(BB, PN)); 822 823 // Fill in the incoming values for the block. 824 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 825 Value* val = GetValueForBlock(*PI, orig, Phis); 826 PN->addIncoming(val, *PI); 827 } 828 829 VN.getAliasAnalysis()->copyValue(orig, PN); 830 831 // Attempt to collapse PHI nodes that are trivially redundant 832 Value* v = CollapsePhi(PN); 833 if (!v) { 834 // Cache our phi construction results 835 if (LoadInst* L = dyn_cast<LoadInst>(orig)) 836 phiMap[L->getPointerOperand()].insert(PN); 837 else 838 phiMap[orig].insert(PN); 839 840 return PN; 841 } 842 843 PN->replaceAllUsesWith(v); 844 if (isa<PointerType>(v->getType())) 845 MD->invalidateCachedPointerInfo(v); 846 847 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 848 E = Phis.end(); I != E; ++I) 849 if (I->second == PN) 850 I->second = v; 851 852 DEBUG(cerr << "GVN removed: " << *PN); 853 MD->removeInstruction(PN); 854 PN->eraseFromParent(); 855 DEBUG(verifyRemoved(PN)); 856 857 Phis[BB] = v; 858 return v; 859} 860 861/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 862/// we're analyzing is fully available in the specified block. As we go, keep 863/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 864/// map is actually a tri-state map with the following values: 865/// 0) we know the block *is not* fully available. 866/// 1) we know the block *is* fully available. 867/// 2) we do not know whether the block is fully available or not, but we are 868/// currently speculating that it will be. 869/// 3) we are speculating for this block and have used that to speculate for 870/// other blocks. 871static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 872 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 873 // Optimistically assume that the block is fully available and check to see 874 // if we already know about this block in one lookup. 875 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 876 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 877 878 // If the entry already existed for this block, return the precomputed value. 879 if (!IV.second) { 880 // If this is a speculative "available" value, mark it as being used for 881 // speculation of other blocks. 882 if (IV.first->second == 2) 883 IV.first->second = 3; 884 return IV.first->second != 0; 885 } 886 887 // Otherwise, see if it is fully available in all predecessors. 888 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 889 890 // If this block has no predecessors, it isn't live-in here. 891 if (PI == PE) 892 goto SpeculationFailure; 893 894 for (; PI != PE; ++PI) 895 // If the value isn't fully available in one of our predecessors, then it 896 // isn't fully available in this block either. Undo our previous 897 // optimistic assumption and bail out. 898 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 899 goto SpeculationFailure; 900 901 return true; 902 903// SpeculationFailure - If we get here, we found out that this is not, after 904// all, a fully-available block. We have a problem if we speculated on this and 905// used the speculation to mark other blocks as available. 906SpeculationFailure: 907 char &BBVal = FullyAvailableBlocks[BB]; 908 909 // If we didn't speculate on this, just return with it set to false. 910 if (BBVal == 2) { 911 BBVal = 0; 912 return false; 913 } 914 915 // If we did speculate on this value, we could have blocks set to 1 that are 916 // incorrect. Walk the (transitive) successors of this block and mark them as 917 // 0 if set to one. 918 SmallVector<BasicBlock*, 32> BBWorklist; 919 BBWorklist.push_back(BB); 920 921 while (!BBWorklist.empty()) { 922 BasicBlock *Entry = BBWorklist.pop_back_val(); 923 // Note that this sets blocks to 0 (unavailable) if they happen to not 924 // already be in FullyAvailableBlocks. This is safe. 925 char &EntryVal = FullyAvailableBlocks[Entry]; 926 if (EntryVal == 0) continue; // Already unavailable. 927 928 // Mark as unavailable. 929 EntryVal = 0; 930 931 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 932 BBWorklist.push_back(*I); 933 } 934 935 return false; 936} 937 938/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 939/// non-local by performing PHI construction. 940bool GVN::processNonLocalLoad(LoadInst *LI, 941 SmallVectorImpl<Instruction*> &toErase) { 942 // Find the non-local dependencies of the load. 943 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 944 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 945 Deps); 946 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI); 947 948 // If we had to process more than one hundred blocks to find the 949 // dependencies, this load isn't worth worrying about. Optimizing 950 // it will be too expensive. 951 if (Deps.size() > 100) 952 return false; 953 954 // If we had a phi translation failure, we'll have a single entry which is a 955 // clobber in the current block. Reject this early. 956 if (Deps.size() == 1 && Deps[0].second.isClobber()) { 957 DEBUG( 958 DOUT << "GVN: non-local load "; 959 WriteAsOperand(*DOUT.stream(), LI); 960 DOUT << " is clobbered by " << *Deps[0].second.getInst(); 961 ); 962 return false; 963 } 964 965 // Filter out useless results (non-locals, etc). Keep track of the blocks 966 // where we have a value available in repl, also keep track of whether we see 967 // dependencies that produce an unknown value for the load (such as a call 968 // that could potentially clobber the load). 969 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock; 970 SmallVector<BasicBlock*, 16> UnavailableBlocks; 971 972 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 973 BasicBlock *DepBB = Deps[i].first; 974 MemDepResult DepInfo = Deps[i].second; 975 976 if (DepInfo.isClobber()) { 977 UnavailableBlocks.push_back(DepBB); 978 continue; 979 } 980 981 Instruction *DepInst = DepInfo.getInst(); 982 983 // Loading the allocation -> undef. 984 if (isa<AllocationInst>(DepInst)) { 985 ValuesPerBlock.push_back(std::make_pair(DepBB, 986 UndefValue::get(LI->getType()))); 987 continue; 988 } 989 990 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) { 991 // Reject loads and stores that are to the same address but are of 992 // different types. 993 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because 994 // of bitfield access, it would be interesting to optimize for it at some 995 // point. 996 if (S->getOperand(0)->getType() != LI->getType()) { 997 UnavailableBlocks.push_back(DepBB); 998 continue; 999 } 1000 1001 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0))); 1002 1003 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) { 1004 if (LD->getType() != LI->getType()) { 1005 UnavailableBlocks.push_back(DepBB); 1006 continue; 1007 } 1008 ValuesPerBlock.push_back(std::make_pair(DepBB, LD)); 1009 } else { 1010 UnavailableBlocks.push_back(DepBB); 1011 continue; 1012 } 1013 } 1014 1015 // If we have no predecessors that produce a known value for this load, exit 1016 // early. 1017 if (ValuesPerBlock.empty()) return false; 1018 1019 // If all of the instructions we depend on produce a known value for this 1020 // load, then it is fully redundant and we can use PHI insertion to compute 1021 // its value. Insert PHIs and remove the fully redundant value now. 1022 if (UnavailableBlocks.empty()) { 1023 // Use cached PHI construction information from previous runs 1024 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1025 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated? 1026 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1027 I != E; ++I) { 1028 if ((*I)->getParent() == LI->getParent()) { 1029 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI); 1030 LI->replaceAllUsesWith(*I); 1031 if (isa<PointerType>((*I)->getType())) 1032 MD->invalidateCachedPointerInfo(*I); 1033 toErase.push_back(LI); 1034 NumGVNLoad++; 1035 return true; 1036 } 1037 1038 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I)); 1039 } 1040 1041 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI); 1042 1043 DenseMap<BasicBlock*, Value*> BlockReplValues; 1044 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); 1045 // Perform PHI construction. 1046 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1047 LI->replaceAllUsesWith(v); 1048 1049 if (isa<PHINode>(v)) 1050 v->takeName(LI); 1051 if (isa<PointerType>(v->getType())) 1052 MD->invalidateCachedPointerInfo(v); 1053 toErase.push_back(LI); 1054 NumGVNLoad++; 1055 return true; 1056 } 1057 1058 if (!EnablePRE || !EnableLoadPRE) 1059 return false; 1060 1061 // Okay, we have *some* definitions of the value. This means that the value 1062 // is available in some of our (transitive) predecessors. Lets think about 1063 // doing PRE of this load. This will involve inserting a new load into the 1064 // predecessor when it's not available. We could do this in general, but 1065 // prefer to not increase code size. As such, we only do this when we know 1066 // that we only have to insert *one* load (which means we're basically moving 1067 // the load, not inserting a new one). 1068 1069 SmallPtrSet<BasicBlock *, 4> Blockers; 1070 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1071 Blockers.insert(UnavailableBlocks[i]); 1072 1073 // Lets find first basic block with more than one predecessor. Walk backwards 1074 // through predecessors if needed. 1075 BasicBlock *LoadBB = LI->getParent(); 1076 BasicBlock *TmpBB = LoadBB; 1077 1078 bool isSinglePred = false; 1079 bool allSingleSucc = true; 1080 while (TmpBB->getSinglePredecessor()) { 1081 isSinglePred = true; 1082 TmpBB = TmpBB->getSinglePredecessor(); 1083 if (!TmpBB) // If haven't found any, bail now. 1084 return false; 1085 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1086 return false; 1087 if (Blockers.count(TmpBB)) 1088 return false; 1089 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1090 allSingleSucc = false; 1091 } 1092 1093 assert(TmpBB); 1094 LoadBB = TmpBB; 1095 1096 // If we have a repl set with LI itself in it, this means we have a loop where 1097 // at least one of the values is LI. Since this means that we won't be able 1098 // to eliminate LI even if we insert uses in the other predecessors, we will 1099 // end up increasing code size. Reject this by scanning for LI. 1100 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1101 if (ValuesPerBlock[i].second == LI) 1102 return false; 1103 1104 if (isSinglePred) { 1105 bool isHot = false; 1106 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1107 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second)) 1108 // "Hot" Instruction is in some loop (because it dominates its dep. 1109 // instruction). 1110 if (DT->dominates(LI, I)) { 1111 isHot = true; 1112 break; 1113 } 1114 1115 // We are interested only in "hot" instructions. We don't want to do any 1116 // mis-optimizations here. 1117 if (!isHot) 1118 return false; 1119 } 1120 1121 // Okay, we have some hope :). Check to see if the loaded value is fully 1122 // available in all but one predecessor. 1123 // FIXME: If we could restructure the CFG, we could make a common pred with 1124 // all the preds that don't have an available LI and insert a new load into 1125 // that one block. 1126 BasicBlock *UnavailablePred = 0; 1127 1128 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1129 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1130 FullyAvailableBlocks[ValuesPerBlock[i].first] = true; 1131 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1132 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1133 1134 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1135 PI != E; ++PI) { 1136 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1137 continue; 1138 1139 // If this load is not available in multiple predecessors, reject it. 1140 if (UnavailablePred && UnavailablePred != *PI) 1141 return false; 1142 UnavailablePred = *PI; 1143 } 1144 1145 assert(UnavailablePred != 0 && 1146 "Fully available value should be eliminated above!"); 1147 1148 // If the loaded pointer is PHI node defined in this block, do PHI translation 1149 // to get its value in the predecessor. 1150 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); 1151 1152 // Make sure the value is live in the predecessor. If it was defined by a 1153 // non-PHI instruction in this block, we don't know how to recompute it above. 1154 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) 1155 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { 1156 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " 1157 << *LPInst << *LI << "\n"); 1158 return false; 1159 } 1160 1161 // We don't currently handle critical edges :( 1162 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1163 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1164 << UnavailablePred->getName() << "': " << *LI); 1165 return false; 1166 } 1167 1168 // Make sure it is valid to move this load here. We have to watch out for: 1169 // @1 = getelementptr (i8* p, ... 1170 // test p and branch if == 0 1171 // load @1 1172 // It is valid to have the getelementptr before the test, even if p can be 0, 1173 // as getelementptr only does address arithmetic. 1174 // If we are not pushing the value through any multiple-successor blocks 1175 // we do not have this case. Otherwise, check that the load is safe to 1176 // put anywhere; this can be improved, but should be conservatively safe. 1177 if (!allSingleSucc && 1178 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) 1179 return false; 1180 1181 // Okay, we can eliminate this load by inserting a reload in the predecessor 1182 // and using PHI construction to get the value in the other predecessors, do 1183 // it. 1184 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI); 1185 1186 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1187 LI->getAlignment(), 1188 UnavailablePred->getTerminator()); 1189 1190 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1191 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1192 I != E; ++I) 1193 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I)); 1194 1195 DenseMap<BasicBlock*, Value*> BlockReplValues; 1196 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end()); 1197 BlockReplValues[UnavailablePred] = NewLoad; 1198 1199 // Perform PHI construction. 1200 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1201 LI->replaceAllUsesWith(v); 1202 if (isa<PHINode>(v)) 1203 v->takeName(LI); 1204 if (isa<PointerType>(v->getType())) 1205 MD->invalidateCachedPointerInfo(v); 1206 toErase.push_back(LI); 1207 NumPRELoad++; 1208 return true; 1209} 1210 1211/// processLoad - Attempt to eliminate a load, first by eliminating it 1212/// locally, and then attempting non-local elimination if that fails. 1213bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1214 if (L->isVolatile()) 1215 return false; 1216 1217 Value* pointer = L->getPointerOperand(); 1218 1219 // ... to a pointer that has been loaded from before... 1220 MemDepResult dep = MD->getDependency(L); 1221 1222 // If the value isn't available, don't do anything! 1223 if (dep.isClobber()) { 1224 DEBUG( 1225 // fast print dep, using operator<< on instruction would be too slow 1226 DOUT << "GVN: load "; 1227 WriteAsOperand(*DOUT.stream(), L); 1228 Instruction *I = dep.getInst(); 1229 DOUT << " is clobbered by " << *I; 1230 ); 1231 return false; 1232 } 1233 1234 // If it is defined in another block, try harder. 1235 if (dep.isNonLocal()) 1236 return processNonLocalLoad(L, toErase); 1237 1238 Instruction *DepInst = dep.getInst(); 1239 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1240 // Only forward substitute stores to loads of the same type. 1241 // FIXME: Could do better! 1242 if (DepSI->getPointerOperand()->getType() != pointer->getType()) 1243 return false; 1244 1245 // Remove it! 1246 L->replaceAllUsesWith(DepSI->getOperand(0)); 1247 if (isa<PointerType>(DepSI->getOperand(0)->getType())) 1248 MD->invalidateCachedPointerInfo(DepSI->getOperand(0)); 1249 toErase.push_back(L); 1250 NumGVNLoad++; 1251 return true; 1252 } 1253 1254 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1255 // Only forward substitute stores to loads of the same type. 1256 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian. 1257 if (DepLI->getType() != L->getType()) 1258 return false; 1259 1260 // Remove it! 1261 L->replaceAllUsesWith(DepLI); 1262 if (isa<PointerType>(DepLI->getType())) 1263 MD->invalidateCachedPointerInfo(DepLI); 1264 toErase.push_back(L); 1265 NumGVNLoad++; 1266 return true; 1267 } 1268 1269 // If this load really doesn't depend on anything, then we must be loading an 1270 // undef value. This can happen when loading for a fresh allocation with no 1271 // intervening stores, for example. 1272 if (isa<AllocationInst>(DepInst)) { 1273 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1274 toErase.push_back(L); 1275 NumGVNLoad++; 1276 return true; 1277 } 1278 1279 return false; 1280} 1281 1282Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) { 1283 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1284 if (I == localAvail.end()) 1285 return 0; 1286 1287 ValueNumberScope* locals = I->second; 1288 1289 while (locals) { 1290 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num); 1291 if (I != locals->table.end()) 1292 return I->second; 1293 else 1294 locals = locals->parent; 1295 } 1296 1297 return 0; 1298} 1299 1300/// AttemptRedundancyElimination - If the "fast path" of redundancy elimination 1301/// by inheritance from the dominator fails, see if we can perform phi 1302/// construction to eliminate the redundancy. 1303Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) { 1304 BasicBlock* BaseBlock = orig->getParent(); 1305 1306 SmallPtrSet<BasicBlock*, 4> Visited; 1307 SmallVector<BasicBlock*, 8> Stack; 1308 Stack.push_back(BaseBlock); 1309 1310 DenseMap<BasicBlock*, Value*> Results; 1311 1312 // Walk backwards through our predecessors, looking for instances of the 1313 // value number we're looking for. Instances are recorded in the Results 1314 // map, which is then used to perform phi construction. 1315 while (!Stack.empty()) { 1316 BasicBlock* Current = Stack.back(); 1317 Stack.pop_back(); 1318 1319 // If we've walked all the way to a proper dominator, then give up. Cases 1320 // where the instance is in the dominator will have been caught by the fast 1321 // path, and any cases that require phi construction further than this are 1322 // probably not worth it anyways. Note that this is a SIGNIFICANT compile 1323 // time improvement. 1324 if (DT->properlyDominates(Current, orig->getParent())) return 0; 1325 1326 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA = 1327 localAvail.find(Current); 1328 if (LA == localAvail.end()) return 0; 1329 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno); 1330 1331 if (V != LA->second->table.end()) { 1332 // Found an instance, record it. 1333 Results.insert(std::make_pair(Current, V->second)); 1334 continue; 1335 } 1336 1337 // If we reach the beginning of the function, then give up. 1338 if (pred_begin(Current) == pred_end(Current)) 1339 return 0; 1340 1341 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current); 1342 PI != PE; ++PI) 1343 if (Visited.insert(*PI)) 1344 Stack.push_back(*PI); 1345 } 1346 1347 // If we didn't find instances, give up. Otherwise, perform phi construction. 1348 if (Results.size() == 0) 1349 return 0; 1350 else 1351 return GetValueForBlock(BaseBlock, orig, Results, true); 1352} 1353 1354/// processInstruction - When calculating availability, handle an instruction 1355/// by inserting it into the appropriate sets 1356bool GVN::processInstruction(Instruction *I, 1357 SmallVectorImpl<Instruction*> &toErase) { 1358 if (LoadInst* L = dyn_cast<LoadInst>(I)) { 1359 bool changed = processLoad(L, toErase); 1360 1361 if (!changed) { 1362 unsigned num = VN.lookup_or_add(L); 1363 localAvail[I->getParent()]->table.insert(std::make_pair(num, L)); 1364 } 1365 1366 return changed; 1367 } 1368 1369 uint32_t nextNum = VN.getNextUnusedValueNumber(); 1370 unsigned num = VN.lookup_or_add(I); 1371 1372 if (BranchInst* BI = dyn_cast<BranchInst>(I)) { 1373 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1374 1375 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1376 return false; 1377 1378 Value* branchCond = BI->getCondition(); 1379 uint32_t condVN = VN.lookup_or_add(branchCond); 1380 1381 BasicBlock* trueSucc = BI->getSuccessor(0); 1382 BasicBlock* falseSucc = BI->getSuccessor(1); 1383 1384 if (trueSucc->getSinglePredecessor()) 1385 localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue(); 1386 if (falseSucc->getSinglePredecessor()) 1387 localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse(); 1388 1389 return false; 1390 1391 // Allocations are always uniquely numbered, so we can save time and memory 1392 // by fast failing them. 1393 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1394 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1395 return false; 1396 } 1397 1398 // Collapse PHI nodes 1399 if (PHINode* p = dyn_cast<PHINode>(I)) { 1400 Value* constVal = CollapsePhi(p); 1401 1402 if (constVal) { 1403 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1404 PI != PE; ++PI) 1405 PI->second.erase(p); 1406 1407 p->replaceAllUsesWith(constVal); 1408 if (isa<PointerType>(constVal->getType())) 1409 MD->invalidateCachedPointerInfo(constVal); 1410 VN.erase(p); 1411 1412 toErase.push_back(p); 1413 } else { 1414 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1415 } 1416 1417 // If the number we were assigned was a brand new VN, then we don't 1418 // need to do a lookup to see if the number already exists 1419 // somewhere in the domtree: it can't! 1420 } else if (num == nextNum) { 1421 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1422 1423 // Perform fast-path value-number based elimination of values inherited from 1424 // dominators. 1425 } else if (Value* repl = lookupNumber(I->getParent(), num)) { 1426 // Remove it! 1427 VN.erase(I); 1428 I->replaceAllUsesWith(repl); 1429 if (isa<PointerType>(repl->getType())) 1430 MD->invalidateCachedPointerInfo(repl); 1431 toErase.push_back(I); 1432 return true; 1433 1434#if 0 1435 // Perform slow-pathvalue-number based elimination with phi construction. 1436 } else if (Value* repl = AttemptRedundancyElimination(I, num)) { 1437 // Remove it! 1438 VN.erase(I); 1439 I->replaceAllUsesWith(repl); 1440 if (isa<PointerType>(repl->getType())) 1441 MD->invalidateCachedPointerInfo(repl); 1442 toErase.push_back(I); 1443 return true; 1444#endif 1445 } else { 1446 localAvail[I->getParent()]->table.insert(std::make_pair(num, I)); 1447 } 1448 1449 return false; 1450} 1451 1452/// runOnFunction - This is the main transformation entry point for a function. 1453bool GVN::runOnFunction(Function& F) { 1454 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1455 DT = &getAnalysis<DominatorTree>(); 1456 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1457 VN.setMemDep(MD); 1458 VN.setDomTree(DT); 1459 1460 bool changed = false; 1461 bool shouldContinue = true; 1462 1463 // Merge unconditional branches, allowing PRE to catch more 1464 // optimization opportunities. 1465 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1466 BasicBlock* BB = FI; 1467 ++FI; 1468 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1469 if (removedBlock) NumGVNBlocks++; 1470 1471 changed |= removedBlock; 1472 } 1473 1474 unsigned Iteration = 0; 1475 1476 while (shouldContinue) { 1477 DEBUG(cerr << "GVN iteration: " << Iteration << "\n"); 1478 shouldContinue = iterateOnFunction(F); 1479 changed |= shouldContinue; 1480 ++Iteration; 1481 } 1482 1483 if (EnablePRE) { 1484 bool PREChanged = true; 1485 while (PREChanged) { 1486 PREChanged = performPRE(F); 1487 changed |= PREChanged; 1488 } 1489 } 1490 // FIXME: Should perform GVN again after PRE does something. PRE can move 1491 // computations into blocks where they become fully redundant. Note that 1492 // we can't do this until PRE's critical edge splitting updates memdep. 1493 // Actually, when this happens, we should just fully integrate PRE into GVN. 1494 1495 cleanupGlobalSets(); 1496 1497 return changed; 1498} 1499 1500 1501bool GVN::processBlock(BasicBlock* BB) { 1502 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1503 // incrementing BI before processing an instruction). 1504 SmallVector<Instruction*, 8> toErase; 1505 bool changed_function = false; 1506 1507 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1508 BI != BE;) { 1509 changed_function |= processInstruction(BI, toErase); 1510 if (toErase.empty()) { 1511 ++BI; 1512 continue; 1513 } 1514 1515 // If we need some instructions deleted, do it now. 1516 NumGVNInstr += toErase.size(); 1517 1518 // Avoid iterator invalidation. 1519 bool AtStart = BI == BB->begin(); 1520 if (!AtStart) 1521 --BI; 1522 1523 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1524 E = toErase.end(); I != E; ++I) { 1525 DEBUG(cerr << "GVN removed: " << **I); 1526 MD->removeInstruction(*I); 1527 (*I)->eraseFromParent(); 1528 DEBUG(verifyRemoved(*I)); 1529 } 1530 toErase.clear(); 1531 1532 if (AtStart) 1533 BI = BB->begin(); 1534 else 1535 ++BI; 1536 } 1537 1538 return changed_function; 1539} 1540 1541/// performPRE - Perform a purely local form of PRE that looks for diamond 1542/// control flow patterns and attempts to perform simple PRE at the join point. 1543bool GVN::performPRE(Function& F) { 1544 bool Changed = false; 1545 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1546 DenseMap<BasicBlock*, Value*> predMap; 1547 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1548 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1549 BasicBlock* CurrentBlock = *DI; 1550 1551 // Nothing to PRE in the entry block. 1552 if (CurrentBlock == &F.getEntryBlock()) continue; 1553 1554 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1555 BE = CurrentBlock->end(); BI != BE; ) { 1556 Instruction *CurInst = BI++; 1557 1558 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) || 1559 isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) || 1560 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 1561 isa<DbgInfoIntrinsic>(CurInst)) 1562 continue; 1563 1564 uint32_t valno = VN.lookup(CurInst); 1565 1566 // Look for the predecessors for PRE opportunities. We're 1567 // only trying to solve the basic diamond case, where 1568 // a value is computed in the successor and one predecessor, 1569 // but not the other. We also explicitly disallow cases 1570 // where the successor is its own predecessor, because they're 1571 // more complicated to get right. 1572 unsigned numWith = 0; 1573 unsigned numWithout = 0; 1574 BasicBlock* PREPred = 0; 1575 predMap.clear(); 1576 1577 for (pred_iterator PI = pred_begin(CurrentBlock), 1578 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1579 // We're not interested in PRE where the block is its 1580 // own predecessor, on in blocks with predecessors 1581 // that are not reachable. 1582 if (*PI == CurrentBlock) { 1583 numWithout = 2; 1584 break; 1585 } else if (!localAvail.count(*PI)) { 1586 numWithout = 2; 1587 break; 1588 } 1589 1590 DenseMap<uint32_t, Value*>::iterator predV = 1591 localAvail[*PI]->table.find(valno); 1592 if (predV == localAvail[*PI]->table.end()) { 1593 PREPred = *PI; 1594 numWithout++; 1595 } else if (predV->second == CurInst) { 1596 numWithout = 2; 1597 } else { 1598 predMap[*PI] = predV->second; 1599 numWith++; 1600 } 1601 } 1602 1603 // Don't do PRE when it might increase code size, i.e. when 1604 // we would need to insert instructions in more than one pred. 1605 if (numWithout != 1 || numWith == 0) 1606 continue; 1607 1608 // We can't do PRE safely on a critical edge, so instead we schedule 1609 // the edge to be split and perform the PRE the next time we iterate 1610 // on the function. 1611 unsigned succNum = 0; 1612 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1613 i != e; ++i) 1614 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1615 succNum = i; 1616 break; 1617 } 1618 1619 if (isCriticalEdge(PREPred->getTerminator(), succNum)) { 1620 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum)); 1621 continue; 1622 } 1623 1624 // Instantiate the expression the in predecessor that lacked it. 1625 // Because we are going top-down through the block, all value numbers 1626 // will be available in the predecessor by the time we need them. Any 1627 // that weren't original present will have been instantiated earlier 1628 // in this loop. 1629 Instruction* PREInstr = CurInst->clone(); 1630 bool success = true; 1631 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 1632 Value *Op = PREInstr->getOperand(i); 1633 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 1634 continue; 1635 1636 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 1637 PREInstr->setOperand(i, V); 1638 } else { 1639 success = false; 1640 break; 1641 } 1642 } 1643 1644 // Fail out if we encounter an operand that is not available in 1645 // the PRE predecessor. This is typically because of loads which 1646 // are not value numbered precisely. 1647 if (!success) { 1648 delete PREInstr; 1649 DEBUG(verifyRemoved(PREInstr)); 1650 continue; 1651 } 1652 1653 PREInstr->insertBefore(PREPred->getTerminator()); 1654 PREInstr->setName(CurInst->getName() + ".pre"); 1655 predMap[PREPred] = PREInstr; 1656 VN.add(PREInstr, valno); 1657 NumGVNPRE++; 1658 1659 // Update the availability map to include the new instruction. 1660 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr)); 1661 1662 // Create a PHI to make the value available in this block. 1663 PHINode* Phi = PHINode::Create(CurInst->getType(), 1664 CurInst->getName() + ".pre-phi", 1665 CurrentBlock->begin()); 1666 for (pred_iterator PI = pred_begin(CurrentBlock), 1667 PE = pred_end(CurrentBlock); PI != PE; ++PI) 1668 Phi->addIncoming(predMap[*PI], *PI); 1669 1670 VN.add(Phi, valno); 1671 localAvail[CurrentBlock]->table[valno] = Phi; 1672 1673 CurInst->replaceAllUsesWith(Phi); 1674 if (isa<PointerType>(Phi->getType())) 1675 MD->invalidateCachedPointerInfo(Phi); 1676 VN.erase(CurInst); 1677 1678 DEBUG(cerr << "GVN PRE removed: " << *CurInst); 1679 MD->removeInstruction(CurInst); 1680 CurInst->eraseFromParent(); 1681 DEBUG(verifyRemoved(CurInst)); 1682 Changed = true; 1683 } 1684 } 1685 1686 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 1687 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 1688 SplitCriticalEdge(I->first, I->second, this); 1689 1690 return Changed || toSplit.size(); 1691} 1692 1693/// iterateOnFunction - Executes one iteration of GVN 1694bool GVN::iterateOnFunction(Function &F) { 1695 cleanupGlobalSets(); 1696 1697 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1698 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 1699 if (DI->getIDom()) 1700 localAvail[DI->getBlock()] = 1701 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 1702 else 1703 localAvail[DI->getBlock()] = new ValueNumberScope(0); 1704 } 1705 1706 // Top-down walk of the dominator tree 1707 bool changed = false; 1708#if 0 1709 // Needed for value numbering with phi construction to work. 1710 ReversePostOrderTraversal<Function*> RPOT(&F); 1711 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 1712 RE = RPOT.end(); RI != RE; ++RI) 1713 changed |= processBlock(*RI); 1714#else 1715 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 1716 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 1717 changed |= processBlock(DI->getBlock()); 1718#endif 1719 1720 return changed; 1721} 1722 1723void GVN::cleanupGlobalSets() { 1724 VN.clear(); 1725 phiMap.clear(); 1726 1727 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1728 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 1729 delete I->second; 1730 localAvail.clear(); 1731} 1732 1733/// verifyRemoved - Verify that the specified instruction does not occur in our 1734/// internal data structures. 1735void GVN::verifyRemoved(const Instruction *Inst) const { 1736 VN.verifyRemoved(Inst); 1737 1738 // Walk through the PHI map to make sure the instruction isn't hiding in there 1739 // somewhere. 1740 for (PhiMapType::iterator 1741 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) { 1742 assert(I->first != Inst && "Inst is still a key in PHI map!"); 1743 1744 for (SmallPtrSet<Instruction*, 4>::iterator 1745 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) { 1746 assert(*II != Inst && "Inst is still a value in PHI map!"); 1747 } 1748 } 1749 1750 // Walk through the value number scope to make sure the instruction isn't 1751 // ferreted away in it. 1752 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 1753 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 1754 const ValueNumberScope *VNS = I->second; 1755 1756 while (VNS) { 1757 for (DenseMap<uint32_t, Value*>::iterator 1758 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 1759 assert(II->second != Inst && "Inst still in value numbering scope!"); 1760 } 1761 1762 VNS = VNS->parent; 1763 } 1764 } 1765} 1766