GVN.cpp revision 813dbd59127973b1cba17933ca368d3d734121d6
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 void cleanupGlobalSets(); 739 void verifyRemoved(const Instruction *I) const; 740 }; 741 742 char GVN::ID = 0; 743} 744 745// createGVNPass - The public interface to this file... 746FunctionPass *llvm::createGVNPass() { return new GVN(); } 747 748static RegisterPass<GVN> X("gvn", 749 "Global Value Numbering"); 750 751void GVN::dump(DenseMap<uint32_t, Value*>& d) { 752 printf("{\n"); 753 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 754 E = d.end(); I != E; ++I) { 755 printf("%d\n", I->first); 756 I->second->dump(); 757 } 758 printf("}\n"); 759} 760 761static bool isSafeReplacement(PHINode* p, Instruction *inst) { 762 if (!isa<PHINode>(inst)) 763 return true; 764 765 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end(); 766 UI != E; ++UI) 767 if (PHINode* use_phi = dyn_cast<PHINode>(UI)) 768 if (use_phi->getParent() == inst->getParent()) 769 return false; 770 771 return true; 772} 773 774Value *GVN::CollapsePhi(PHINode *PN) { 775 Value *ConstVal = PN->hasConstantValue(DT); 776 if (!ConstVal) return 0; 777 778 Instruction *Inst = dyn_cast<Instruction>(ConstVal); 779 if (!Inst) 780 return ConstVal; 781 782 if (DT->dominates(Inst, PN)) 783 if (isSafeReplacement(PN, Inst)) 784 return Inst; 785 return 0; 786} 787 788/// GetValueForBlock - Get the value to use within the specified basic block. 789/// available values are in Phis. 790Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction *Orig, 791 DenseMap<BasicBlock*, Value*> &Phis, 792 bool TopLevel) { 793 794 // If we have already computed this value, return the previously computed val. 795 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB); 796 if (V != Phis.end() && !TopLevel) return V->second; 797 798 // If the block is unreachable, just return undef, since this path 799 // can't actually occur at runtime. 800 if (!DT->isReachableFromEntry(BB)) 801 return Phis[BB] = UndefValue::get(Orig->getType()); 802 803 if (BasicBlock *Pred = BB->getSinglePredecessor()) { 804 Value *ret = GetValueForBlock(Pred, Orig, Phis); 805 Phis[BB] = ret; 806 return ret; 807 } 808 809 // Get the number of predecessors of this block so we can reserve space later. 810 // If there is already a PHI in it, use the #preds from it, otherwise count. 811 // Getting it from the PHI is constant time. 812 unsigned NumPreds; 813 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin())) 814 NumPreds = ExistingPN->getNumIncomingValues(); 815 else 816 NumPreds = std::distance(pred_begin(BB), pred_end(BB)); 817 818 // Otherwise, we may need to insert a PHI node. Do so now, then get values to 819 // fill in the incoming values for the PHI. If the PHI ends up not being 820 // needed, we can always remove it later. 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. This happens 836 // when we construct a PHI that ends up not being needed. 837 Value *v = CollapsePhi(PN); 838 if (!v) { 839 // Cache our phi construction results 840 if (LoadInst* L = dyn_cast<LoadInst>(Orig)) 841 phiMap[L->getPointerOperand()].insert(PN); 842 else 843 phiMap[Orig].insert(PN); 844 845 return PN; 846 } 847 848 PN->replaceAllUsesWith(v); 849 if (isa<PointerType>(v->getType())) 850 MD->invalidateCachedPointerInfo(v); 851 852 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(), 853 E = Phis.end(); I != E; ++I) 854 if (I->second == PN) 855 I->second = v; 856 857 DEBUG(errs() << "GVN removed: " << *PN << '\n'); 858 MD->removeInstruction(PN); 859 PN->eraseFromParent(); 860 DEBUG(verifyRemoved(PN)); 861 862 Phis[BB] = v; 863 return v; 864} 865 866/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 867/// we're analyzing is fully available in the specified block. As we go, keep 868/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 869/// map is actually a tri-state map with the following values: 870/// 0) we know the block *is not* fully available. 871/// 1) we know the block *is* fully available. 872/// 2) we do not know whether the block is fully available or not, but we are 873/// currently speculating that it will be. 874/// 3) we are speculating for this block and have used that to speculate for 875/// other blocks. 876static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 877 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) { 878 // Optimistically assume that the block is fully available and check to see 879 // if we already know about this block in one lookup. 880 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 881 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 882 883 // If the entry already existed for this block, return the precomputed value. 884 if (!IV.second) { 885 // If this is a speculative "available" value, mark it as being used for 886 // speculation of other blocks. 887 if (IV.first->second == 2) 888 IV.first->second = 3; 889 return IV.first->second != 0; 890 } 891 892 // Otherwise, see if it is fully available in all predecessors. 893 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 894 895 // If this block has no predecessors, it isn't live-in here. 896 if (PI == PE) 897 goto SpeculationFailure; 898 899 for (; PI != PE; ++PI) 900 // If the value isn't fully available in one of our predecessors, then it 901 // isn't fully available in this block either. Undo our previous 902 // optimistic assumption and bail out. 903 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 904 goto SpeculationFailure; 905 906 return true; 907 908// SpeculationFailure - If we get here, we found out that this is not, after 909// all, a fully-available block. We have a problem if we speculated on this and 910// used the speculation to mark other blocks as available. 911SpeculationFailure: 912 char &BBVal = FullyAvailableBlocks[BB]; 913 914 // If we didn't speculate on this, just return with it set to false. 915 if (BBVal == 2) { 916 BBVal = 0; 917 return false; 918 } 919 920 // If we did speculate on this value, we could have blocks set to 1 that are 921 // incorrect. Walk the (transitive) successors of this block and mark them as 922 // 0 if set to one. 923 SmallVector<BasicBlock*, 32> BBWorklist; 924 BBWorklist.push_back(BB); 925 926 while (!BBWorklist.empty()) { 927 BasicBlock *Entry = BBWorklist.pop_back_val(); 928 // Note that this sets blocks to 0 (unavailable) if they happen to not 929 // already be in FullyAvailableBlocks. This is safe. 930 char &EntryVal = FullyAvailableBlocks[Entry]; 931 if (EntryVal == 0) continue; // Already unavailable. 932 933 // Mark as unavailable. 934 EntryVal = 0; 935 936 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 937 BBWorklist.push_back(*I); 938 } 939 940 return false; 941} 942 943 944/// CanCoerceMustAliasedValueToLoad - Return true if 945/// CoerceAvailableValueToLoadType will succeed. 946static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 947 const Type *LoadTy, 948 const TargetData &TD) { 949 // If the loaded or stored value is an first class array or struct, don't try 950 // to transform them. We need to be able to bitcast to integer. 951 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy) || 952 isa<StructType>(StoredVal->getType()) || 953 isa<ArrayType>(StoredVal->getType())) 954 return false; 955 956 // The store has to be at least as big as the load. 957 if (TD.getTypeSizeInBits(StoredVal->getType()) < 958 TD.getTypeSizeInBits(LoadTy)) 959 return false; 960 961 return true; 962} 963 964 965/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 966/// then a load from a must-aliased pointer of a different type, try to coerce 967/// the stored value. LoadedTy is the type of the load we want to replace and 968/// InsertPt is the place to insert new instructions. 969/// 970/// If we can't do it, return null. 971static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 972 const Type *LoadedTy, 973 Instruction *InsertPt, 974 const TargetData &TD) { 975 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 976 return 0; 977 978 const Type *StoredValTy = StoredVal->getType(); 979 980 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 981 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 982 983 // If the store and reload are the same size, we can always reuse it. 984 if (StoreSize == LoadSize) { 985 if (isa<PointerType>(StoredValTy) && isa<PointerType>(LoadedTy)) { 986 // Pointer to Pointer -> use bitcast. 987 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 988 } 989 990 // Convert source pointers to integers, which can be bitcast. 991 if (isa<PointerType>(StoredValTy)) { 992 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 993 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 994 } 995 996 const Type *TypeToCastTo = LoadedTy; 997 if (isa<PointerType>(TypeToCastTo)) 998 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext()); 999 1000 if (StoredValTy != TypeToCastTo) 1001 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 1002 1003 // Cast to pointer if the load needs a pointer type. 1004 if (isa<PointerType>(LoadedTy)) 1005 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 1006 1007 return StoredVal; 1008 } 1009 1010 // If the loaded value is smaller than the available value, then we can 1011 // extract out a piece from it. If the available value is too small, then we 1012 // can't do anything. 1013 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 1014 1015 // Convert source pointers to integers, which can be manipulated. 1016 if (isa<PointerType>(StoredValTy)) { 1017 StoredValTy = TD.getIntPtrType(StoredValTy->getContext()); 1018 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 1019 } 1020 1021 // Convert vectors and fp to integer, which can be manipulated. 1022 if (!isa<IntegerType>(StoredValTy)) { 1023 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 1024 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 1025 } 1026 1027 // If this is a big-endian system, we need to shift the value down to the low 1028 // bits so that a truncate will work. 1029 if (TD.isBigEndian()) { 1030 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 1031 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 1032 } 1033 1034 // Truncate the integer to the right size now. 1035 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 1036 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 1037 1038 if (LoadedTy == NewIntTy) 1039 return StoredVal; 1040 1041 // If the result is a pointer, inttoptr. 1042 if (isa<PointerType>(LoadedTy)) 1043 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 1044 1045 // Otherwise, bitcast. 1046 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 1047} 1048 1049/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can 1050/// be expressed as a base pointer plus a constant offset. Return the base and 1051/// offset to the caller. 1052static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 1053 const TargetData &TD) { 1054 Operator *PtrOp = dyn_cast<Operator>(Ptr); 1055 if (PtrOp == 0) return Ptr; 1056 1057 // Just look through bitcasts. 1058 if (PtrOp->getOpcode() == Instruction::BitCast) 1059 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD); 1060 1061 // If this is a GEP with constant indices, we can look through it. 1062 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp); 1063 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr; 1064 1065 gep_type_iterator GTI = gep_type_begin(GEP); 1066 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E; 1067 ++I, ++GTI) { 1068 ConstantInt *OpC = cast<ConstantInt>(*I); 1069 if (OpC->isZero()) continue; 1070 1071 // Handle a struct and array indices which add their offset to the pointer. 1072 if (const StructType *STy = dyn_cast<StructType>(*GTI)) { 1073 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); 1074 } else { 1075 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()); 1076 Offset += OpC->getSExtValue()*Size; 1077 } 1078 } 1079 1080 // Re-sign extend from the pointer size if needed to get overflow edge cases 1081 // right. 1082 unsigned PtrSize = TD.getPointerSizeInBits(); 1083 if (PtrSize < 64) 1084 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize); 1085 1086 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD); 1087} 1088 1089 1090/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1091/// memdep query of a load that ends up being a clobbering store. This means 1092/// that the store *may* provide bits used by the load but we can't be sure 1093/// because the pointers don't mustalias. Check this case to see if there is 1094/// anything more we can do before we give up. This returns -1 if we have to 1095/// give up, or a byte number in the stored value of the piece that feeds the 1096/// load. 1097static int AnalyzeLoadFromClobberingStore(LoadInst *L, StoreInst *DepSI, 1098 const TargetData &TD) { 1099 // If the loaded or stored value is an first class array or struct, don't try 1100 // to transform them. We need to be able to bitcast to integer. 1101 if (isa<StructType>(L->getType()) || isa<ArrayType>(L->getType()) || 1102 isa<StructType>(DepSI->getOperand(0)->getType()) || 1103 isa<ArrayType>(DepSI->getOperand(0)->getType())) 1104 return -1; 1105 1106 int64_t StoreOffset = 0, LoadOffset = 0; 1107 Value *StoreBase = 1108 GetBaseWithConstantOffset(DepSI->getPointerOperand(), StoreOffset, TD); 1109 Value *LoadBase = 1110 GetBaseWithConstantOffset(L->getPointerOperand(), LoadOffset, TD); 1111 if (StoreBase != LoadBase) 1112 return -1; 1113 1114 // If the load and store are to the exact same address, they should have been 1115 // a must alias. AA must have gotten confused. 1116 // FIXME: Study to see if/when this happens. 1117 if (LoadOffset == StoreOffset) { 1118#if 0 1119 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 1120 << "Base = " << *StoreBase << "\n" 1121 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1122 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1123 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1124 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1125 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1126 << *L->getParent(); 1127#endif 1128 return -1; 1129 } 1130 1131 // If the load and store don't overlap at all, the store doesn't provide 1132 // anything to the load. In this case, they really don't alias at all, AA 1133 // must have gotten confused. 1134 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then 1135 // remove this check, as it is duplicated with what we have below. 1136 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType()); 1137 uint64_t LoadSize = TD.getTypeSizeInBits(L->getType()); 1138 1139 if ((StoreSize & 7) | (LoadSize & 7)) 1140 return -1; 1141 StoreSize >>= 3; // Convert to bytes. 1142 LoadSize >>= 3; 1143 1144 1145 bool isAAFailure = false; 1146 if (StoreOffset < LoadOffset) { 1147 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 1148 } else { 1149 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 1150 } 1151 if (isAAFailure) { 1152#if 0 1153 errs() << "STORE LOAD DEP WITH COMMON BASE:\n" 1154 << "Base = " << *StoreBase << "\n" 1155 << "Store Ptr = " << *DepSI->getPointerOperand() << "\n" 1156 << "Store Offs = " << StoreOffset << " - " << *DepSI << "\n" 1157 << "Load Ptr = " << *L->getPointerOperand() << "\n" 1158 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n"; 1159 errs() << "'" << L->getParent()->getParent()->getName() << "'" 1160 << *L->getParent(); 1161#endif 1162 return -1; 1163 } 1164 1165 // If the Load isn't completely contained within the stored bits, we don't 1166 // have all the bits to feed it. We could do something crazy in the future 1167 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1168 // valuable. 1169 if (StoreOffset > LoadOffset || 1170 StoreOffset+StoreSize < LoadOffset+LoadSize) 1171 return -1; 1172 1173 // Okay, we can do this transformation. Return the number of bytes into the 1174 // store that the load is. 1175 return LoadOffset-StoreOffset; 1176} 1177 1178 1179/// GetStoreValueForLoad - This function is called when we have a 1180/// memdep query of a load that ends up being a clobbering store. This means 1181/// that the store *may* provide bits used by the load but we can't be sure 1182/// because the pointers don't mustalias. Check this case to see if there is 1183/// anything more we can do before we give up. 1184static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1185 const Type *LoadTy, 1186 Instruction *InsertPt, const TargetData &TD){ 1187 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1188 1189 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8; 1190 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1191 1192 1193 // Compute which bits of the stored value are being used by the load. Convert 1194 // to an integer type to start with. 1195 if (isa<PointerType>(SrcVal->getType())) 1196 SrcVal = new PtrToIntInst(SrcVal, TD.getIntPtrType(Ctx), "tmp", InsertPt); 1197 if (!isa<IntegerType>(SrcVal->getType())) 1198 SrcVal = new BitCastInst(SrcVal, IntegerType::get(Ctx, StoreSize*8), 1199 "tmp", InsertPt); 1200 1201 // Shift the bits to the least significant depending on endianness. 1202 unsigned ShiftAmt; 1203 if (TD.isLittleEndian()) { 1204 ShiftAmt = Offset*8; 1205 } else { 1206 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1207 } 1208 1209 if (ShiftAmt) 1210 SrcVal = BinaryOperator::CreateLShr(SrcVal, 1211 ConstantInt::get(SrcVal->getType(), ShiftAmt), "tmp", InsertPt); 1212 1213 if (LoadSize != StoreSize) 1214 SrcVal = new TruncInst(SrcVal, IntegerType::get(Ctx, LoadSize*8), 1215 "tmp", InsertPt); 1216 1217 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1218} 1219 1220struct AvailableValueInBlock { 1221 /// BB - The basic block in question. 1222 BasicBlock *BB; 1223 /// V - The value that is live out of the block. 1224 Value *V; 1225 /// Offset - The byte offset in V that is interesting for the load query. 1226 unsigned Offset; 1227 1228 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 1229 unsigned Offset = 0) { 1230 AvailableValueInBlock Res; 1231 Res.BB = BB; 1232 Res.V = V; 1233 Res.Offset = Offset; 1234 return Res; 1235 } 1236}; 1237 1238/// GetAvailableBlockValues - Given the ValuesPerBlock list, convert all of the 1239/// available values to values of the expected LoadTy in their blocks and insert 1240/// the new values into BlockReplValues. 1241static void 1242GetAvailableBlockValues(DenseMap<BasicBlock*, Value*> &BlockReplValues, 1243 const SmallVector<AvailableValueInBlock, 16> &ValuesPerBlock, 1244 const Type *LoadTy, 1245 const TargetData *TD) { 1246 1247 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1248 BasicBlock *BB = ValuesPerBlock[i].BB; 1249 Value *AvailableVal = ValuesPerBlock[i].V; 1250 unsigned Offset = ValuesPerBlock[i].Offset; 1251 1252 Value *&BlockEntry = BlockReplValues[BB]; 1253 if (BlockEntry) continue; 1254 1255 if (AvailableVal->getType() != LoadTy) { 1256 assert(TD && "Need target data to handle type mismatch case"); 1257 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy, 1258 BB->getTerminator(), *TD); 1259 1260 if (Offset) { 1261 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1262 << *ValuesPerBlock[i].V << '\n' 1263 << *AvailableVal << '\n' << "\n\n\n"); 1264 } 1265 1266 1267 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\n" 1268 << *ValuesPerBlock[i].V << '\n' 1269 << *AvailableVal << '\n' << "\n\n\n"); 1270 } 1271 BlockEntry = AvailableVal; 1272 } 1273} 1274 1275/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1276/// non-local by performing PHI construction. 1277bool GVN::processNonLocalLoad(LoadInst *LI, 1278 SmallVectorImpl<Instruction*> &toErase) { 1279 // Find the non-local dependencies of the load. 1280 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps; 1281 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(), 1282 Deps); 1283 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: " 1284 // << Deps.size() << *LI << '\n'); 1285 1286 // If we had to process more than one hundred blocks to find the 1287 // dependencies, this load isn't worth worrying about. Optimizing 1288 // it will be too expensive. 1289 if (Deps.size() > 100) 1290 return false; 1291 1292 // If we had a phi translation failure, we'll have a single entry which is a 1293 // clobber in the current block. Reject this early. 1294 if (Deps.size() == 1 && Deps[0].second.isClobber()) { 1295 DEBUG( 1296 errs() << "GVN: non-local load "; 1297 WriteAsOperand(errs(), LI); 1298 errs() << " is clobbered by " << *Deps[0].second.getInst() << '\n'; 1299 ); 1300 return false; 1301 } 1302 1303 // Filter out useless results (non-locals, etc). Keep track of the blocks 1304 // where we have a value available in repl, also keep track of whether we see 1305 // dependencies that produce an unknown value for the load (such as a call 1306 // that could potentially clobber the load). 1307 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock; 1308 SmallVector<BasicBlock*, 16> UnavailableBlocks; 1309 1310 const TargetData *TD = 0; 1311 1312 for (unsigned i = 0, e = Deps.size(); i != e; ++i) { 1313 BasicBlock *DepBB = Deps[i].first; 1314 MemDepResult DepInfo = Deps[i].second; 1315 1316 if (DepInfo.isClobber()) { 1317 // If the dependence is to a store that writes to a superset of the bits 1318 // read by the load, we can extract the bits we need for the load from the 1319 // stored value. 1320 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1321 if (TD == 0) 1322 TD = getAnalysisIfAvailable<TargetData>(); 1323 if (TD) { 1324 int Offset = AnalyzeLoadFromClobberingStore(LI, DepSI, *TD); 1325 if (Offset != -1) { 1326 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1327 DepSI->getOperand(0), 1328 Offset)); 1329 continue; 1330 } 1331 } 1332 } 1333 1334 // FIXME: Handle memset/memcpy. 1335 UnavailableBlocks.push_back(DepBB); 1336 continue; 1337 } 1338 1339 Instruction *DepInst = DepInfo.getInst(); 1340 1341 // Loading the allocation -> undef. 1342 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1343 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1344 UndefValue::get(LI->getType()))); 1345 continue; 1346 } 1347 1348 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1349 // Reject loads and stores that are to the same address but are of 1350 // different types if we have to. 1351 if (S->getOperand(0)->getType() != LI->getType()) { 1352 if (TD == 0) 1353 TD = getAnalysisIfAvailable<TargetData>(); 1354 1355 // If the stored value is larger or equal to the loaded value, we can 1356 // reuse it. 1357 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0), 1358 LI->getType(), *TD)) { 1359 UnavailableBlocks.push_back(DepBB); 1360 continue; 1361 } 1362 } 1363 1364 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1365 S->getOperand(0))); 1366 continue; 1367 } 1368 1369 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1370 // If the types mismatch and we can't handle it, reject reuse of the load. 1371 if (LD->getType() != LI->getType()) { 1372 if (TD == 0) 1373 TD = getAnalysisIfAvailable<TargetData>(); 1374 1375 // If the stored value is larger or equal to the loaded value, we can 1376 // reuse it. 1377 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1378 UnavailableBlocks.push_back(DepBB); 1379 continue; 1380 } 1381 } 1382 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD)); 1383 continue; 1384 } 1385 1386 UnavailableBlocks.push_back(DepBB); 1387 continue; 1388 } 1389 1390 // If we have no predecessors that produce a known value for this load, exit 1391 // early. 1392 if (ValuesPerBlock.empty()) return false; 1393 1394 // If all of the instructions we depend on produce a known value for this 1395 // load, then it is fully redundant and we can use PHI insertion to compute 1396 // its value. Insert PHIs and remove the fully redundant value now. 1397 if (UnavailableBlocks.empty()) { 1398 // Use cached PHI construction information from previous runs 1399 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1400 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated? 1401 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1402 I != E; ++I) { 1403 if ((*I)->getParent() == LI->getParent()) { 1404 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD #1: " << *LI << '\n'); 1405 LI->replaceAllUsesWith(*I); 1406 if (isa<PointerType>((*I)->getType())) 1407 MD->invalidateCachedPointerInfo(*I); 1408 toErase.push_back(LI); 1409 NumGVNLoad++; 1410 return true; 1411 } 1412 1413 ValuesPerBlock.push_back(AvailableValueInBlock::get((*I)->getParent(), 1414 *I)); 1415 } 1416 1417 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1418 1419 // Convert the block information to a map, and insert coersions as needed. 1420 DenseMap<BasicBlock*, Value*> BlockReplValues; 1421 GetAvailableBlockValues(BlockReplValues, ValuesPerBlock, LI->getType(), TD); 1422 1423 // Perform PHI construction. 1424 Value *V = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1425 LI->replaceAllUsesWith(V); 1426 1427 if (isa<PHINode>(V)) 1428 V->takeName(LI); 1429 if (isa<PointerType>(V->getType())) 1430 MD->invalidateCachedPointerInfo(V); 1431 toErase.push_back(LI); 1432 NumGVNLoad++; 1433 return true; 1434 } 1435 1436 if (!EnablePRE || !EnableLoadPRE) 1437 return false; 1438 1439 // Okay, we have *some* definitions of the value. This means that the value 1440 // is available in some of our (transitive) predecessors. Lets think about 1441 // doing PRE of this load. This will involve inserting a new load into the 1442 // predecessor when it's not available. We could do this in general, but 1443 // prefer to not increase code size. As such, we only do this when we know 1444 // that we only have to insert *one* load (which means we're basically moving 1445 // the load, not inserting a new one). 1446 1447 SmallPtrSet<BasicBlock *, 4> Blockers; 1448 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1449 Blockers.insert(UnavailableBlocks[i]); 1450 1451 // Lets find first basic block with more than one predecessor. Walk backwards 1452 // through predecessors if needed. 1453 BasicBlock *LoadBB = LI->getParent(); 1454 BasicBlock *TmpBB = LoadBB; 1455 1456 bool isSinglePred = false; 1457 bool allSingleSucc = true; 1458 while (TmpBB->getSinglePredecessor()) { 1459 isSinglePred = true; 1460 TmpBB = TmpBB->getSinglePredecessor(); 1461 if (!TmpBB) // If haven't found any, bail now. 1462 return false; 1463 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1464 return false; 1465 if (Blockers.count(TmpBB)) 1466 return false; 1467 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1468 allSingleSucc = false; 1469 } 1470 1471 assert(TmpBB); 1472 LoadBB = TmpBB; 1473 1474 // If we have a repl set with LI itself in it, this means we have a loop where 1475 // at least one of the values is LI. Since this means that we won't be able 1476 // to eliminate LI even if we insert uses in the other predecessors, we will 1477 // end up increasing code size. Reject this by scanning for LI. 1478 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1479 if (ValuesPerBlock[i].V == LI) 1480 return false; 1481 1482 if (isSinglePred) { 1483 bool isHot = false; 1484 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1485 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].V)) 1486 // "Hot" Instruction is in some loop (because it dominates its dep. 1487 // instruction). 1488 if (DT->dominates(LI, I)) { 1489 isHot = true; 1490 break; 1491 } 1492 1493 // We are interested only in "hot" instructions. We don't want to do any 1494 // mis-optimizations here. 1495 if (!isHot) 1496 return false; 1497 } 1498 1499 // Okay, we have some hope :). Check to see if the loaded value is fully 1500 // available in all but one predecessor. 1501 // FIXME: If we could restructure the CFG, we could make a common pred with 1502 // all the preds that don't have an available LI and insert a new load into 1503 // that one block. 1504 BasicBlock *UnavailablePred = 0; 1505 1506 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1507 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1508 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1509 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1510 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1511 1512 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1513 PI != E; ++PI) { 1514 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks)) 1515 continue; 1516 1517 // If this load is not available in multiple predecessors, reject it. 1518 if (UnavailablePred && UnavailablePred != *PI) 1519 return false; 1520 UnavailablePred = *PI; 1521 } 1522 1523 assert(UnavailablePred != 0 && 1524 "Fully available value should be eliminated above!"); 1525 1526 // If the loaded pointer is PHI node defined in this block, do PHI translation 1527 // to get its value in the predecessor. 1528 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred); 1529 1530 // Make sure the value is live in the predecessor. If it was defined by a 1531 // non-PHI instruction in this block, we don't know how to recompute it above. 1532 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr)) 1533 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) { 1534 DEBUG(errs() << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: " 1535 << *LPInst << '\n' << *LI << "\n"); 1536 return false; 1537 } 1538 1539 // We don't currently handle critical edges :( 1540 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) { 1541 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '" 1542 << UnavailablePred->getName() << "': " << *LI << '\n'); 1543 return false; 1544 } 1545 1546 // Make sure it is valid to move this load here. We have to watch out for: 1547 // @1 = getelementptr (i8* p, ... 1548 // test p and branch if == 0 1549 // load @1 1550 // It is valid to have the getelementptr before the test, even if p can be 0, 1551 // as getelementptr only does address arithmetic. 1552 // If we are not pushing the value through any multiple-successor blocks 1553 // we do not have this case. Otherwise, check that the load is safe to 1554 // put anywhere; this can be improved, but should be conservatively safe. 1555 if (!allSingleSucc && 1556 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) 1557 return false; 1558 1559 // Okay, we can eliminate this load by inserting a reload in the predecessor 1560 // and using PHI construction to get the value in the other predecessors, do 1561 // it. 1562 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1563 1564 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1565 LI->getAlignment(), 1566 UnavailablePred->getTerminator()); 1567 1568 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()]; 1569 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end(); 1570 I != E; ++I) 1571 ValuesPerBlock.push_back(AvailableValueInBlock::get((*I)->getParent(), *I)); 1572 1573 DenseMap<BasicBlock*, Value*> BlockReplValues; 1574 GetAvailableBlockValues(BlockReplValues, ValuesPerBlock, LI->getType(), TD); 1575 BlockReplValues[UnavailablePred] = NewLoad; 1576 1577 // Perform PHI construction. 1578 Value *V = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true); 1579 LI->replaceAllUsesWith(V); 1580 if (isa<PHINode>(V)) 1581 V->takeName(LI); 1582 if (isa<PointerType>(V->getType())) 1583 MD->invalidateCachedPointerInfo(V); 1584 toErase.push_back(LI); 1585 NumPRELoad++; 1586 return true; 1587} 1588 1589/// processLoad - Attempt to eliminate a load, first by eliminating it 1590/// locally, and then attempting non-local elimination if that fails. 1591bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) { 1592 if (L->isVolatile()) 1593 return false; 1594 1595 // ... to a pointer that has been loaded from before... 1596 MemDepResult Dep = MD->getDependency(L); 1597 1598 // If the value isn't available, don't do anything! 1599 if (Dep.isClobber()) { 1600 // FIXME: We should handle memset/memcpy/memmove as dependent instructions 1601 // to forward the value if available. 1602 //if (isa<MemIntrinsic>(Dep.getInst())) 1603 //errs() << "LOAD DEPENDS ON MEM: " << *L << "\n" << *Dep.getInst()<<"\n\n"; 1604 1605 // Check to see if we have something like this: 1606 // store i32 123, i32* %P 1607 // %A = bitcast i32* %P to i8* 1608 // %B = gep i8* %A, i32 1 1609 // %C = load i8* %B 1610 // 1611 // We could do that by recognizing if the clobber instructions are obviously 1612 // a common base + constant offset, and if the previous store (or memset) 1613 // completely covers this load. This sort of thing can happen in bitfield 1614 // access code. 1615 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) 1616 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) { 1617 int Offset = AnalyzeLoadFromClobberingStore(L, DepSI, *TD); 1618 if (Offset != -1) { 1619 Value *AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset, 1620 L->getType(), L, *TD); 1621 DEBUG(errs() << "GVN COERCED STORE BITS:\n" << *DepSI << '\n' 1622 << *AvailVal << '\n' << *L << "\n\n\n"); 1623 1624 // Replace the load! 1625 L->replaceAllUsesWith(AvailVal); 1626 if (isa<PointerType>(AvailVal->getType())) 1627 MD->invalidateCachedPointerInfo(AvailVal); 1628 toErase.push_back(L); 1629 NumGVNLoad++; 1630 return true; 1631 } 1632 } 1633 1634 DEBUG( 1635 // fast print dep, using operator<< on instruction would be too slow 1636 errs() << "GVN: load "; 1637 WriteAsOperand(errs(), L); 1638 Instruction *I = Dep.getInst(); 1639 errs() << " is clobbered by " << *I << '\n'; 1640 ); 1641 return false; 1642 } 1643 1644 // If it is defined in another block, try harder. 1645 if (Dep.isNonLocal()) 1646 return processNonLocalLoad(L, toErase); 1647 1648 Instruction *DepInst = Dep.getInst(); 1649 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1650 Value *StoredVal = DepSI->getOperand(0); 1651 1652 // The store and load are to a must-aliased pointer, but they may not 1653 // actually have the same type. See if we know how to reuse the stored 1654 // value (depending on its type). 1655 const TargetData *TD = 0; 1656 if (StoredVal->getType() != L->getType() && 1657 (TD = getAnalysisIfAvailable<TargetData>())) { 1658 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1659 L, *TD); 1660 if (StoredVal == 0) 1661 return false; 1662 1663 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1664 << '\n' << *L << "\n\n\n"); 1665 } 1666 1667 // Remove it! 1668 L->replaceAllUsesWith(StoredVal); 1669 if (isa<PointerType>(StoredVal->getType())) 1670 MD->invalidateCachedPointerInfo(StoredVal); 1671 toErase.push_back(L); 1672 NumGVNLoad++; 1673 return true; 1674 } 1675 1676 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1677 Value *AvailableVal = DepLI; 1678 1679 // The loads are of a must-aliased pointer, but they may not actually have 1680 // the same type. See if we know how to reuse the previously loaded value 1681 // (depending on its type). 1682 const TargetData *TD = 0; 1683 if (DepLI->getType() != L->getType() && 1684 (TD = getAnalysisIfAvailable<TargetData>())) { 1685 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD); 1686 if (AvailableVal == 0) 1687 return false; 1688 1689 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1690 << "\n" << *L << "\n\n\n"); 1691 } 1692 1693 // Remove it! 1694 L->replaceAllUsesWith(AvailableVal); 1695 if (isa<PointerType>(DepLI->getType())) 1696 MD->invalidateCachedPointerInfo(DepLI); 1697 toErase.push_back(L); 1698 NumGVNLoad++; 1699 return true; 1700 } 1701 1702 // If this load really doesn't depend on anything, then we must be loading an 1703 // undef value. This can happen when loading for a fresh allocation with no 1704 // intervening stores, for example. 1705 if (isa<AllocationInst>(DepInst) || isMalloc(DepInst)) { 1706 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1707 toErase.push_back(L); 1708 NumGVNLoad++; 1709 return true; 1710 } 1711 1712 return false; 1713} 1714 1715Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) { 1716 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB); 1717 if (I == localAvail.end()) 1718 return 0; 1719 1720 ValueNumberScope *Locals = I->second; 1721 while (Locals) { 1722 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num); 1723 if (I != Locals->table.end()) 1724 return I->second; 1725 Locals = Locals->parent; 1726 } 1727 1728 return 0; 1729} 1730 1731 1732/// processInstruction - When calculating availability, handle an instruction 1733/// by inserting it into the appropriate sets 1734bool GVN::processInstruction(Instruction *I, 1735 SmallVectorImpl<Instruction*> &toErase) { 1736 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 1737 bool Changed = processLoad(LI, toErase); 1738 1739 if (!Changed) { 1740 unsigned Num = VN.lookup_or_add(LI); 1741 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI)); 1742 } 1743 1744 return Changed; 1745 } 1746 1747 uint32_t NextNum = VN.getNextUnusedValueNumber(); 1748 unsigned Num = VN.lookup_or_add(I); 1749 1750 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 1751 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1752 1753 if (!BI->isConditional() || isa<Constant>(BI->getCondition())) 1754 return false; 1755 1756 Value *BranchCond = BI->getCondition(); 1757 uint32_t CondVN = VN.lookup_or_add(BranchCond); 1758 1759 BasicBlock *TrueSucc = BI->getSuccessor(0); 1760 BasicBlock *FalseSucc = BI->getSuccessor(1); 1761 1762 if (TrueSucc->getSinglePredecessor()) 1763 localAvail[TrueSucc]->table[CondVN] = 1764 ConstantInt::getTrue(TrueSucc->getContext()); 1765 if (FalseSucc->getSinglePredecessor()) 1766 localAvail[FalseSucc]->table[CondVN] = 1767 ConstantInt::getFalse(TrueSucc->getContext()); 1768 1769 return false; 1770 1771 // Allocations are always uniquely numbered, so we can save time and memory 1772 // by fast failing them. 1773 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) { 1774 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1775 return false; 1776 } 1777 1778 // Collapse PHI nodes 1779 if (PHINode* p = dyn_cast<PHINode>(I)) { 1780 Value *constVal = CollapsePhi(p); 1781 1782 if (constVal) { 1783 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end(); 1784 PI != PE; ++PI) 1785 PI->second.erase(p); 1786 1787 p->replaceAllUsesWith(constVal); 1788 if (isa<PointerType>(constVal->getType())) 1789 MD->invalidateCachedPointerInfo(constVal); 1790 VN.erase(p); 1791 1792 toErase.push_back(p); 1793 } else { 1794 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1795 } 1796 1797 // If the number we were assigned was a brand new VN, then we don't 1798 // need to do a lookup to see if the number already exists 1799 // somewhere in the domtree: it can't! 1800 } else if (Num == NextNum) { 1801 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1802 1803 // Perform fast-path value-number based elimination of values inherited from 1804 // dominators. 1805 } else if (Value *repl = lookupNumber(I->getParent(), Num)) { 1806 // Remove it! 1807 VN.erase(I); 1808 I->replaceAllUsesWith(repl); 1809 if (isa<PointerType>(repl->getType())) 1810 MD->invalidateCachedPointerInfo(repl); 1811 toErase.push_back(I); 1812 return true; 1813 1814 } else { 1815 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I)); 1816 } 1817 1818 return false; 1819} 1820 1821/// runOnFunction - This is the main transformation entry point for a function. 1822bool GVN::runOnFunction(Function& F) { 1823 MD = &getAnalysis<MemoryDependenceAnalysis>(); 1824 DT = &getAnalysis<DominatorTree>(); 1825 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 1826 VN.setMemDep(MD); 1827 VN.setDomTree(DT); 1828 1829 bool Changed = false; 1830 bool ShouldContinue = true; 1831 1832 // Merge unconditional branches, allowing PRE to catch more 1833 // optimization opportunities. 1834 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 1835 BasicBlock *BB = FI; 1836 ++FI; 1837 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 1838 if (removedBlock) NumGVNBlocks++; 1839 1840 Changed |= removedBlock; 1841 } 1842 1843 unsigned Iteration = 0; 1844 1845 while (ShouldContinue) { 1846 DEBUG(errs() << "GVN iteration: " << Iteration << "\n"); 1847 ShouldContinue = iterateOnFunction(F); 1848 Changed |= ShouldContinue; 1849 ++Iteration; 1850 } 1851 1852 if (EnablePRE) { 1853 bool PREChanged = true; 1854 while (PREChanged) { 1855 PREChanged = performPRE(F); 1856 Changed |= PREChanged; 1857 } 1858 } 1859 // FIXME: Should perform GVN again after PRE does something. PRE can move 1860 // computations into blocks where they become fully redundant. Note that 1861 // we can't do this until PRE's critical edge splitting updates memdep. 1862 // Actually, when this happens, we should just fully integrate PRE into GVN. 1863 1864 cleanupGlobalSets(); 1865 1866 return Changed; 1867} 1868 1869 1870bool GVN::processBlock(BasicBlock *BB) { 1871 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and 1872 // incrementing BI before processing an instruction). 1873 SmallVector<Instruction*, 8> toErase; 1874 bool ChangedFunction = false; 1875 1876 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 1877 BI != BE;) { 1878 ChangedFunction |= processInstruction(BI, toErase); 1879 if (toErase.empty()) { 1880 ++BI; 1881 continue; 1882 } 1883 1884 // If we need some instructions deleted, do it now. 1885 NumGVNInstr += toErase.size(); 1886 1887 // Avoid iterator invalidation. 1888 bool AtStart = BI == BB->begin(); 1889 if (!AtStart) 1890 --BI; 1891 1892 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(), 1893 E = toErase.end(); I != E; ++I) { 1894 DEBUG(errs() << "GVN removed: " << **I << '\n'); 1895 MD->removeInstruction(*I); 1896 (*I)->eraseFromParent(); 1897 DEBUG(verifyRemoved(*I)); 1898 } 1899 toErase.clear(); 1900 1901 if (AtStart) 1902 BI = BB->begin(); 1903 else 1904 ++BI; 1905 } 1906 1907 return ChangedFunction; 1908} 1909 1910/// performPRE - Perform a purely local form of PRE that looks for diamond 1911/// control flow patterns and attempts to perform simple PRE at the join point. 1912bool GVN::performPRE(Function& F) { 1913 bool Changed = false; 1914 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 1915 DenseMap<BasicBlock*, Value*> predMap; 1916 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 1917 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 1918 BasicBlock *CurrentBlock = *DI; 1919 1920 // Nothing to PRE in the entry block. 1921 if (CurrentBlock == &F.getEntryBlock()) continue; 1922 1923 for (BasicBlock::iterator BI = CurrentBlock->begin(), 1924 BE = CurrentBlock->end(); BI != BE; ) { 1925 Instruction *CurInst = BI++; 1926 1927 if (isa<AllocationInst>(CurInst) || 1928 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 1929 (CurInst->getType() == Type::getVoidTy(F.getContext())) || 1930 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 1931 isa<DbgInfoIntrinsic>(CurInst)) 1932 continue; 1933 1934 uint32_t ValNo = VN.lookup(CurInst); 1935 1936 // Look for the predecessors for PRE opportunities. We're 1937 // only trying to solve the basic diamond case, where 1938 // a value is computed in the successor and one predecessor, 1939 // but not the other. We also explicitly disallow cases 1940 // where the successor is its own predecessor, because they're 1941 // more complicated to get right. 1942 unsigned NumWith = 0; 1943 unsigned NumWithout = 0; 1944 BasicBlock *PREPred = 0; 1945 predMap.clear(); 1946 1947 for (pred_iterator PI = pred_begin(CurrentBlock), 1948 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 1949 // We're not interested in PRE where the block is its 1950 // own predecessor, on in blocks with predecessors 1951 // that are not reachable. 1952 if (*PI == CurrentBlock) { 1953 NumWithout = 2; 1954 break; 1955 } else if (!localAvail.count(*PI)) { 1956 NumWithout = 2; 1957 break; 1958 } 1959 1960 DenseMap<uint32_t, Value*>::iterator predV = 1961 localAvail[*PI]->table.find(ValNo); 1962 if (predV == localAvail[*PI]->table.end()) { 1963 PREPred = *PI; 1964 NumWithout++; 1965 } else if (predV->second == CurInst) { 1966 NumWithout = 2; 1967 } else { 1968 predMap[*PI] = predV->second; 1969 NumWith++; 1970 } 1971 } 1972 1973 // Don't do PRE when it might increase code size, i.e. when 1974 // we would need to insert instructions in more than one pred. 1975 if (NumWithout != 1 || NumWith == 0) 1976 continue; 1977 1978 // We can't do PRE safely on a critical edge, so instead we schedule 1979 // the edge to be split and perform the PRE the next time we iterate 1980 // on the function. 1981 unsigned SuccNum = 0; 1982 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors(); 1983 i != e; ++i) 1984 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) { 1985 SuccNum = i; 1986 break; 1987 } 1988 1989 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 1990 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 1991 continue; 1992 } 1993 1994 // Instantiate the expression the in predecessor that lacked it. 1995 // Because we are going top-down through the block, all value numbers 1996 // will be available in the predecessor by the time we need them. Any 1997 // that weren't original present will have been instantiated earlier 1998 // in this loop. 1999 Instruction *PREInstr = CurInst->clone(); 2000 bool success = true; 2001 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2002 Value *Op = PREInstr->getOperand(i); 2003 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2004 continue; 2005 2006 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) { 2007 PREInstr->setOperand(i, V); 2008 } else { 2009 success = false; 2010 break; 2011 } 2012 } 2013 2014 // Fail out if we encounter an operand that is not available in 2015 // the PRE predecessor. This is typically because of loads which 2016 // are not value numbered precisely. 2017 if (!success) { 2018 delete PREInstr; 2019 DEBUG(verifyRemoved(PREInstr)); 2020 continue; 2021 } 2022 2023 PREInstr->insertBefore(PREPred->getTerminator()); 2024 PREInstr->setName(CurInst->getName() + ".pre"); 2025 predMap[PREPred] = PREInstr; 2026 VN.add(PREInstr, ValNo); 2027 NumGVNPRE++; 2028 2029 // Update the availability map to include the new instruction. 2030 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr)); 2031 2032 // Create a PHI to make the value available in this block. 2033 PHINode* Phi = PHINode::Create(CurInst->getType(), 2034 CurInst->getName() + ".pre-phi", 2035 CurrentBlock->begin()); 2036 for (pred_iterator PI = pred_begin(CurrentBlock), 2037 PE = pred_end(CurrentBlock); PI != PE; ++PI) 2038 Phi->addIncoming(predMap[*PI], *PI); 2039 2040 VN.add(Phi, ValNo); 2041 localAvail[CurrentBlock]->table[ValNo] = Phi; 2042 2043 CurInst->replaceAllUsesWith(Phi); 2044 if (isa<PointerType>(Phi->getType())) 2045 MD->invalidateCachedPointerInfo(Phi); 2046 VN.erase(CurInst); 2047 2048 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n'); 2049 MD->removeInstruction(CurInst); 2050 CurInst->eraseFromParent(); 2051 DEBUG(verifyRemoved(CurInst)); 2052 Changed = true; 2053 } 2054 } 2055 2056 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator 2057 I = toSplit.begin(), E = toSplit.end(); I != E; ++I) 2058 SplitCriticalEdge(I->first, I->second, this); 2059 2060 return Changed || toSplit.size(); 2061} 2062 2063/// iterateOnFunction - Executes one iteration of GVN 2064bool GVN::iterateOnFunction(Function &F) { 2065 cleanupGlobalSets(); 2066 2067 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2068 DE = df_end(DT->getRootNode()); DI != DE; ++DI) { 2069 if (DI->getIDom()) 2070 localAvail[DI->getBlock()] = 2071 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]); 2072 else 2073 localAvail[DI->getBlock()] = new ValueNumberScope(0); 2074 } 2075 2076 // Top-down walk of the dominator tree 2077 bool Changed = false; 2078#if 0 2079 // Needed for value numbering with phi construction to work. 2080 ReversePostOrderTraversal<Function*> RPOT(&F); 2081 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2082 RE = RPOT.end(); RI != RE; ++RI) 2083 Changed |= processBlock(*RI); 2084#else 2085 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2086 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2087 Changed |= processBlock(DI->getBlock()); 2088#endif 2089 2090 return Changed; 2091} 2092 2093void GVN::cleanupGlobalSets() { 2094 VN.clear(); 2095 phiMap.clear(); 2096 2097 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2098 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) 2099 delete I->second; 2100 localAvail.clear(); 2101} 2102 2103/// verifyRemoved - Verify that the specified instruction does not occur in our 2104/// internal data structures. 2105void GVN::verifyRemoved(const Instruction *Inst) const { 2106 VN.verifyRemoved(Inst); 2107 2108 // Walk through the PHI map to make sure the instruction isn't hiding in there 2109 // somewhere. 2110 for (PhiMapType::iterator 2111 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) { 2112 assert(I->first != Inst && "Inst is still a key in PHI map!"); 2113 2114 for (SmallPtrSet<Instruction*, 4>::iterator 2115 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) { 2116 assert(*II != Inst && "Inst is still a value in PHI map!"); 2117 } 2118 } 2119 2120 // Walk through the value number scope to make sure the instruction isn't 2121 // ferreted away in it. 2122 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator 2123 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) { 2124 const ValueNumberScope *VNS = I->second; 2125 2126 while (VNS) { 2127 for (DenseMap<uint32_t, Value*>::iterator 2128 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) { 2129 assert(II->second != Inst && "Inst still in value numbering scope!"); 2130 } 2131 2132 VNS = VNS->parent; 2133 } 2134 } 2135} 2136