1 //===- LazyValueInfo.cpp - Value constraint analysis ----------------------===// 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 file defines the interface for lazy computation of value constraint 11 // information. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #define DEBUG_TYPE "lazy-value-info" 16 #include "llvm/Analysis/LazyValueInfo.h" 17 #include "llvm/Analysis/ValueTracking.h" 18 #include "llvm/Constants.h" 19 #include "llvm/Instructions.h" 20 #include "llvm/IntrinsicInst.h" 21 #include "llvm/Analysis/ConstantFolding.h" 22 #include "llvm/Target/TargetData.h" 23 #include "llvm/Target/TargetLibraryInfo.h" 24 #include "llvm/Support/CFG.h" 25 #include "llvm/Support/ConstantRange.h" 26 #include "llvm/Support/Debug.h" 27 #include "llvm/Support/PatternMatch.h" 28 #include "llvm/Support/raw_ostream.h" 29 #include "llvm/Support/ValueHandle.h" 30 #include "llvm/ADT/DenseSet.h" 31 #include "llvm/ADT/STLExtras.h" 32 #include <map> 33 #include <stack> 34 using namespace llvm; 35 using namespace PatternMatch; 36 37 char LazyValueInfo::ID = 0; 38 INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info", 39 "Lazy Value Information Analysis", false, true) 40 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 41 INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info", 42 "Lazy Value Information Analysis", false, true) 43 44 namespace llvm { 45 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); } 46 } 47 48 49 //===----------------------------------------------------------------------===// 50 // LVILatticeVal 51 //===----------------------------------------------------------------------===// 52 53 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each 54 /// value. 55 /// 56 /// FIXME: This is basically just for bringup, this can be made a lot more rich 57 /// in the future. 58 /// 59 namespace { 60 class LVILatticeVal { 61 enum LatticeValueTy { 62 /// undefined - This Value has no known value yet. 63 undefined, 64 65 /// constant - This Value has a specific constant value. 66 constant, 67 /// notconstant - This Value is known to not have the specified value. 68 notconstant, 69 70 /// constantrange - The Value falls within this range. 71 constantrange, 72 73 /// overdefined - This value is not known to be constant, and we know that 74 /// it has a value. 75 overdefined 76 }; 77 78 /// Val: This stores the current lattice value along with the Constant* for 79 /// the constant if this is a 'constant' or 'notconstant' value. 80 LatticeValueTy Tag; 81 Constant *Val; 82 ConstantRange Range; 83 84 public: 85 LVILatticeVal() : Tag(undefined), Val(0), Range(1, true) {} 86 87 static LVILatticeVal get(Constant *C) { 88 LVILatticeVal Res; 89 if (!isa<UndefValue>(C)) 90 Res.markConstant(C); 91 return Res; 92 } 93 static LVILatticeVal getNot(Constant *C) { 94 LVILatticeVal Res; 95 if (!isa<UndefValue>(C)) 96 Res.markNotConstant(C); 97 return Res; 98 } 99 static LVILatticeVal getRange(ConstantRange CR) { 100 LVILatticeVal Res; 101 Res.markConstantRange(CR); 102 return Res; 103 } 104 105 bool isUndefined() const { return Tag == undefined; } 106 bool isConstant() const { return Tag == constant; } 107 bool isNotConstant() const { return Tag == notconstant; } 108 bool isConstantRange() const { return Tag == constantrange; } 109 bool isOverdefined() const { return Tag == overdefined; } 110 111 Constant *getConstant() const { 112 assert(isConstant() && "Cannot get the constant of a non-constant!"); 113 return Val; 114 } 115 116 Constant *getNotConstant() const { 117 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!"); 118 return Val; 119 } 120 121 ConstantRange getConstantRange() const { 122 assert(isConstantRange() && 123 "Cannot get the constant-range of a non-constant-range!"); 124 return Range; 125 } 126 127 /// markOverdefined - Return true if this is a change in status. 128 bool markOverdefined() { 129 if (isOverdefined()) 130 return false; 131 Tag = overdefined; 132 return true; 133 } 134 135 /// markConstant - Return true if this is a change in status. 136 bool markConstant(Constant *V) { 137 assert(V && "Marking constant with NULL"); 138 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) 139 return markConstantRange(ConstantRange(CI->getValue())); 140 if (isa<UndefValue>(V)) 141 return false; 142 143 assert((!isConstant() || getConstant() == V) && 144 "Marking constant with different value"); 145 assert(isUndefined()); 146 Tag = constant; 147 Val = V; 148 return true; 149 } 150 151 /// markNotConstant - Return true if this is a change in status. 152 bool markNotConstant(Constant *V) { 153 assert(V && "Marking constant with NULL"); 154 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) 155 return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue())); 156 if (isa<UndefValue>(V)) 157 return false; 158 159 assert((!isConstant() || getConstant() != V) && 160 "Marking constant !constant with same value"); 161 assert((!isNotConstant() || getNotConstant() == V) && 162 "Marking !constant with different value"); 163 assert(isUndefined() || isConstant()); 164 Tag = notconstant; 165 Val = V; 166 return true; 167 } 168 169 /// markConstantRange - Return true if this is a change in status. 170 bool markConstantRange(const ConstantRange NewR) { 171 if (isConstantRange()) { 172 if (NewR.isEmptySet()) 173 return markOverdefined(); 174 175 bool changed = Range == NewR; 176 Range = NewR; 177 return changed; 178 } 179 180 assert(isUndefined()); 181 if (NewR.isEmptySet()) 182 return markOverdefined(); 183 184 Tag = constantrange; 185 Range = NewR; 186 return true; 187 } 188 189 /// mergeIn - Merge the specified lattice value into this one, updating this 190 /// one and returning true if anything changed. 191 bool mergeIn(const LVILatticeVal &RHS) { 192 if (RHS.isUndefined() || isOverdefined()) return false; 193 if (RHS.isOverdefined()) return markOverdefined(); 194 195 if (isUndefined()) { 196 Tag = RHS.Tag; 197 Val = RHS.Val; 198 Range = RHS.Range; 199 return true; 200 } 201 202 if (isConstant()) { 203 if (RHS.isConstant()) { 204 if (Val == RHS.Val) 205 return false; 206 return markOverdefined(); 207 } 208 209 if (RHS.isNotConstant()) { 210 if (Val == RHS.Val) 211 return markOverdefined(); 212 213 // Unless we can prove that the two Constants are different, we must 214 // move to overdefined. 215 // FIXME: use TargetData/TargetLibraryInfo for smarter constant folding. 216 if (ConstantInt *Res = dyn_cast<ConstantInt>( 217 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE, 218 getConstant(), 219 RHS.getNotConstant()))) 220 if (Res->isOne()) 221 return markNotConstant(RHS.getNotConstant()); 222 223 return markOverdefined(); 224 } 225 226 // RHS is a ConstantRange, LHS is a non-integer Constant. 227 228 // FIXME: consider the case where RHS is a range [1, 0) and LHS is 229 // a function. The correct result is to pick up RHS. 230 231 return markOverdefined(); 232 } 233 234 if (isNotConstant()) { 235 if (RHS.isConstant()) { 236 if (Val == RHS.Val) 237 return markOverdefined(); 238 239 // Unless we can prove that the two Constants are different, we must 240 // move to overdefined. 241 // FIXME: use TargetData/TargetLibraryInfo for smarter constant folding. 242 if (ConstantInt *Res = dyn_cast<ConstantInt>( 243 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE, 244 getNotConstant(), 245 RHS.getConstant()))) 246 if (Res->isOne()) 247 return false; 248 249 return markOverdefined(); 250 } 251 252 if (RHS.isNotConstant()) { 253 if (Val == RHS.Val) 254 return false; 255 return markOverdefined(); 256 } 257 258 return markOverdefined(); 259 } 260 261 assert(isConstantRange() && "New LVILattice type?"); 262 if (!RHS.isConstantRange()) 263 return markOverdefined(); 264 265 ConstantRange NewR = Range.unionWith(RHS.getConstantRange()); 266 if (NewR.isFullSet()) 267 return markOverdefined(); 268 return markConstantRange(NewR); 269 } 270 }; 271 272 } // end anonymous namespace. 273 274 namespace llvm { 275 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) 276 LLVM_ATTRIBUTE_USED; 277 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) { 278 if (Val.isUndefined()) 279 return OS << "undefined"; 280 if (Val.isOverdefined()) 281 return OS << "overdefined"; 282 283 if (Val.isNotConstant()) 284 return OS << "notconstant<" << *Val.getNotConstant() << '>'; 285 else if (Val.isConstantRange()) 286 return OS << "constantrange<" << Val.getConstantRange().getLower() << ", " 287 << Val.getConstantRange().getUpper() << '>'; 288 return OS << "constant<" << *Val.getConstant() << '>'; 289 } 290 } 291 292 //===----------------------------------------------------------------------===// 293 // LazyValueInfoCache Decl 294 //===----------------------------------------------------------------------===// 295 296 namespace { 297 /// LVIValueHandle - A callback value handle update the cache when 298 /// values are erased. 299 class LazyValueInfoCache; 300 struct LVIValueHandle : public CallbackVH { 301 LazyValueInfoCache *Parent; 302 303 LVIValueHandle(Value *V, LazyValueInfoCache *P) 304 : CallbackVH(V), Parent(P) { } 305 306 void deleted(); 307 void allUsesReplacedWith(Value *V) { 308 deleted(); 309 } 310 }; 311 } 312 313 namespace { 314 /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which 315 /// maintains information about queries across the clients' queries. 316 class LazyValueInfoCache { 317 /// ValueCacheEntryTy - This is all of the cached block information for 318 /// exactly one Value*. The entries are sorted by the BasicBlock* of the 319 /// entries, allowing us to do a lookup with a binary search. 320 typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy; 321 322 /// ValueCache - This is all of the cached information for all values, 323 /// mapped from Value* to key information. 324 std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache; 325 326 /// OverDefinedCache - This tracks, on a per-block basis, the set of 327 /// values that are over-defined at the end of that block. This is required 328 /// for cache updating. 329 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy; 330 DenseSet<OverDefinedPairTy> OverDefinedCache; 331 332 /// SeenBlocks - Keep track of all blocks that we have ever seen, so we 333 /// don't spend time removing unused blocks from our caches. 334 DenseSet<AssertingVH<BasicBlock> > SeenBlocks; 335 336 /// BlockValueStack - This stack holds the state of the value solver 337 /// during a query. It basically emulates the callstack of the naive 338 /// recursive value lookup process. 339 std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack; 340 341 friend struct LVIValueHandle; 342 343 /// OverDefinedCacheUpdater - A helper object that ensures that the 344 /// OverDefinedCache is updated whenever solveBlockValue returns. 345 struct OverDefinedCacheUpdater { 346 LazyValueInfoCache *Parent; 347 Value *Val; 348 BasicBlock *BB; 349 LVILatticeVal &BBLV; 350 351 OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV, 352 LazyValueInfoCache *P) 353 : Parent(P), Val(V), BB(B), BBLV(LV) { } 354 355 bool markResult(bool changed) { 356 if (changed && BBLV.isOverdefined()) 357 Parent->OverDefinedCache.insert(std::make_pair(BB, Val)); 358 return changed; 359 } 360 }; 361 362 363 364 LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB); 365 bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T, 366 LVILatticeVal &Result); 367 bool hasBlockValue(Value *Val, BasicBlock *BB); 368 369 // These methods process one work item and may add more. A false value 370 // returned means that the work item was not completely processed and must 371 // be revisited after going through the new items. 372 bool solveBlockValue(Value *Val, BasicBlock *BB); 373 bool solveBlockValueNonLocal(LVILatticeVal &BBLV, 374 Value *Val, BasicBlock *BB); 375 bool solveBlockValuePHINode(LVILatticeVal &BBLV, 376 PHINode *PN, BasicBlock *BB); 377 bool solveBlockValueConstantRange(LVILatticeVal &BBLV, 378 Instruction *BBI, BasicBlock *BB); 379 380 void solve(); 381 382 ValueCacheEntryTy &lookup(Value *V) { 383 return ValueCache[LVIValueHandle(V, this)]; 384 } 385 386 public: 387 /// getValueInBlock - This is the query interface to determine the lattice 388 /// value for the specified Value* at the end of the specified block. 389 LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB); 390 391 /// getValueOnEdge - This is the query interface to determine the lattice 392 /// value for the specified Value* that is true on the specified edge. 393 LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB); 394 395 /// threadEdge - This is the update interface to inform the cache that an 396 /// edge from PredBB to OldSucc has been threaded to be from PredBB to 397 /// NewSucc. 398 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc); 399 400 /// eraseBlock - This is part of the update interface to inform the cache 401 /// that a block has been deleted. 402 void eraseBlock(BasicBlock *BB); 403 404 /// clear - Empty the cache. 405 void clear() { 406 SeenBlocks.clear(); 407 ValueCache.clear(); 408 OverDefinedCache.clear(); 409 } 410 }; 411 } // end anonymous namespace 412 413 void LVIValueHandle::deleted() { 414 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy; 415 416 SmallVector<OverDefinedPairTy, 4> ToErase; 417 for (DenseSet<OverDefinedPairTy>::iterator 418 I = Parent->OverDefinedCache.begin(), 419 E = Parent->OverDefinedCache.end(); 420 I != E; ++I) { 421 if (I->second == getValPtr()) 422 ToErase.push_back(*I); 423 } 424 425 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(), 426 E = ToErase.end(); I != E; ++I) 427 Parent->OverDefinedCache.erase(*I); 428 429 // This erasure deallocates *this, so it MUST happen after we're done 430 // using any and all members of *this. 431 Parent->ValueCache.erase(*this); 432 } 433 434 void LazyValueInfoCache::eraseBlock(BasicBlock *BB) { 435 // Shortcut if we have never seen this block. 436 DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB); 437 if (I == SeenBlocks.end()) 438 return; 439 SeenBlocks.erase(I); 440 441 SmallVector<OverDefinedPairTy, 4> ToErase; 442 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(), 443 E = OverDefinedCache.end(); I != E; ++I) { 444 if (I->first == BB) 445 ToErase.push_back(*I); 446 } 447 448 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(), 449 E = ToErase.end(); I != E; ++I) 450 OverDefinedCache.erase(*I); 451 452 for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator 453 I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I) 454 I->second.erase(BB); 455 } 456 457 void LazyValueInfoCache::solve() { 458 while (!BlockValueStack.empty()) { 459 std::pair<BasicBlock*, Value*> &e = BlockValueStack.top(); 460 if (solveBlockValue(e.second, e.first)) 461 BlockValueStack.pop(); 462 } 463 } 464 465 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) { 466 // If already a constant, there is nothing to compute. 467 if (isa<Constant>(Val)) 468 return true; 469 470 LVIValueHandle ValHandle(Val, this); 471 if (!ValueCache.count(ValHandle)) return false; 472 return ValueCache[ValHandle].count(BB); 473 } 474 475 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) { 476 // If already a constant, there is nothing to compute. 477 if (Constant *VC = dyn_cast<Constant>(Val)) 478 return LVILatticeVal::get(VC); 479 480 SeenBlocks.insert(BB); 481 return lookup(Val)[BB]; 482 } 483 484 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) { 485 if (isa<Constant>(Val)) 486 return true; 487 488 ValueCacheEntryTy &Cache = lookup(Val); 489 SeenBlocks.insert(BB); 490 LVILatticeVal &BBLV = Cache[BB]; 491 492 // OverDefinedCacheUpdater is a helper object that will update 493 // the OverDefinedCache for us when this method exits. Make sure to 494 // call markResult on it as we exist, passing a bool to indicate if the 495 // cache needs updating, i.e. if we have solve a new value or not. 496 OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this); 497 498 // If we've already computed this block's value, return it. 499 if (!BBLV.isUndefined()) { 500 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n'); 501 502 // Since we're reusing a cached value here, we don't need to update the 503 // OverDefinedCahce. The cache will have been properly updated 504 // whenever the cached value was inserted. 505 ODCacheUpdater.markResult(false); 506 return true; 507 } 508 509 // Otherwise, this is the first time we're seeing this block. Reset the 510 // lattice value to overdefined, so that cycles will terminate and be 511 // conservatively correct. 512 BBLV.markOverdefined(); 513 514 Instruction *BBI = dyn_cast<Instruction>(Val); 515 if (BBI == 0 || BBI->getParent() != BB) { 516 return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB)); 517 } 518 519 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 520 return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB)); 521 } 522 523 if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) { 524 BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType())); 525 return ODCacheUpdater.markResult(true); 526 } 527 528 // We can only analyze the definitions of certain classes of instructions 529 // (integral binops and casts at the moment), so bail if this isn't one. 530 LVILatticeVal Result; 531 if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) || 532 !BBI->getType()->isIntegerTy()) { 533 DEBUG(dbgs() << " compute BB '" << BB->getName() 534 << "' - overdefined because inst def found.\n"); 535 BBLV.markOverdefined(); 536 return ODCacheUpdater.markResult(true); 537 } 538 539 // FIXME: We're currently limited to binops with a constant RHS. This should 540 // be improved. 541 BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI); 542 if (BO && !isa<ConstantInt>(BO->getOperand(1))) { 543 DEBUG(dbgs() << " compute BB '" << BB->getName() 544 << "' - overdefined because inst def found.\n"); 545 546 BBLV.markOverdefined(); 547 return ODCacheUpdater.markResult(true); 548 } 549 550 return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB)); 551 } 552 553 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) { 554 if (LoadInst *L = dyn_cast<LoadInst>(I)) { 555 return L->getPointerAddressSpace() == 0 && 556 GetUnderlyingObject(L->getPointerOperand()) == 557 GetUnderlyingObject(Ptr); 558 } 559 if (StoreInst *S = dyn_cast<StoreInst>(I)) { 560 return S->getPointerAddressSpace() == 0 && 561 GetUnderlyingObject(S->getPointerOperand()) == 562 GetUnderlyingObject(Ptr); 563 } 564 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) { 565 if (MI->isVolatile()) return false; 566 567 // FIXME: check whether it has a valuerange that excludes zero? 568 ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength()); 569 if (!Len || Len->isZero()) return false; 570 571 if (MI->getDestAddressSpace() == 0) 572 if (MI->getRawDest() == Ptr || MI->getDest() == Ptr) 573 return true; 574 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) 575 if (MTI->getSourceAddressSpace() == 0) 576 if (MTI->getRawSource() == Ptr || MTI->getSource() == Ptr) 577 return true; 578 } 579 return false; 580 } 581 582 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV, 583 Value *Val, BasicBlock *BB) { 584 LVILatticeVal Result; // Start Undefined. 585 586 // If this is a pointer, and there's a load from that pointer in this BB, 587 // then we know that the pointer can't be NULL. 588 bool NotNull = false; 589 if (Val->getType()->isPointerTy()) { 590 if (isa<AllocaInst>(Val)) { 591 NotNull = true; 592 } else { 593 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){ 594 if (InstructionDereferencesPointer(BI, Val)) { 595 NotNull = true; 596 break; 597 } 598 } 599 } 600 } 601 602 // If this is the entry block, we must be asking about an argument. The 603 // value is overdefined. 604 if (BB == &BB->getParent()->getEntryBlock()) { 605 assert(isa<Argument>(Val) && "Unknown live-in to the entry block"); 606 if (NotNull) { 607 PointerType *PTy = cast<PointerType>(Val->getType()); 608 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy)); 609 } else { 610 Result.markOverdefined(); 611 } 612 BBLV = Result; 613 return true; 614 } 615 616 // Loop over all of our predecessors, merging what we know from them into 617 // result. 618 bool EdgesMissing = false; 619 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 620 LVILatticeVal EdgeResult; 621 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult); 622 if (EdgesMissing) 623 continue; 624 625 Result.mergeIn(EdgeResult); 626 627 // If we hit overdefined, exit early. The BlockVals entry is already set 628 // to overdefined. 629 if (Result.isOverdefined()) { 630 DEBUG(dbgs() << " compute BB '" << BB->getName() 631 << "' - overdefined because of pred.\n"); 632 // If we previously determined that this is a pointer that can't be null 633 // then return that rather than giving up entirely. 634 if (NotNull) { 635 PointerType *PTy = cast<PointerType>(Val->getType()); 636 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy)); 637 } 638 639 BBLV = Result; 640 return true; 641 } 642 } 643 if (EdgesMissing) 644 return false; 645 646 // Return the merged value, which is more precise than 'overdefined'. 647 assert(!Result.isOverdefined()); 648 BBLV = Result; 649 return true; 650 } 651 652 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV, 653 PHINode *PN, BasicBlock *BB) { 654 LVILatticeVal Result; // Start Undefined. 655 656 // Loop over all of our predecessors, merging what we know from them into 657 // result. 658 bool EdgesMissing = false; 659 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 660 BasicBlock *PhiBB = PN->getIncomingBlock(i); 661 Value *PhiVal = PN->getIncomingValue(i); 662 LVILatticeVal EdgeResult; 663 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult); 664 if (EdgesMissing) 665 continue; 666 667 Result.mergeIn(EdgeResult); 668 669 // If we hit overdefined, exit early. The BlockVals entry is already set 670 // to overdefined. 671 if (Result.isOverdefined()) { 672 DEBUG(dbgs() << " compute BB '" << BB->getName() 673 << "' - overdefined because of pred.\n"); 674 675 BBLV = Result; 676 return true; 677 } 678 } 679 if (EdgesMissing) 680 return false; 681 682 // Return the merged value, which is more precise than 'overdefined'. 683 assert(!Result.isOverdefined() && "Possible PHI in entry block?"); 684 BBLV = Result; 685 return true; 686 } 687 688 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV, 689 Instruction *BBI, 690 BasicBlock *BB) { 691 // Figure out the range of the LHS. If that fails, bail. 692 if (!hasBlockValue(BBI->getOperand(0), BB)) { 693 BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0))); 694 return false; 695 } 696 697 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB); 698 if (!LHSVal.isConstantRange()) { 699 BBLV.markOverdefined(); 700 return true; 701 } 702 703 ConstantRange LHSRange = LHSVal.getConstantRange(); 704 ConstantRange RHSRange(1); 705 IntegerType *ResultTy = cast<IntegerType>(BBI->getType()); 706 if (isa<BinaryOperator>(BBI)) { 707 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) { 708 RHSRange = ConstantRange(RHS->getValue()); 709 } else { 710 BBLV.markOverdefined(); 711 return true; 712 } 713 } 714 715 // NOTE: We're currently limited by the set of operations that ConstantRange 716 // can evaluate symbolically. Enhancing that set will allows us to analyze 717 // more definitions. 718 LVILatticeVal Result; 719 switch (BBI->getOpcode()) { 720 case Instruction::Add: 721 Result.markConstantRange(LHSRange.add(RHSRange)); 722 break; 723 case Instruction::Sub: 724 Result.markConstantRange(LHSRange.sub(RHSRange)); 725 break; 726 case Instruction::Mul: 727 Result.markConstantRange(LHSRange.multiply(RHSRange)); 728 break; 729 case Instruction::UDiv: 730 Result.markConstantRange(LHSRange.udiv(RHSRange)); 731 break; 732 case Instruction::Shl: 733 Result.markConstantRange(LHSRange.shl(RHSRange)); 734 break; 735 case Instruction::LShr: 736 Result.markConstantRange(LHSRange.lshr(RHSRange)); 737 break; 738 case Instruction::Trunc: 739 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth())); 740 break; 741 case Instruction::SExt: 742 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth())); 743 break; 744 case Instruction::ZExt: 745 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth())); 746 break; 747 case Instruction::BitCast: 748 Result.markConstantRange(LHSRange); 749 break; 750 case Instruction::And: 751 Result.markConstantRange(LHSRange.binaryAnd(RHSRange)); 752 break; 753 case Instruction::Or: 754 Result.markConstantRange(LHSRange.binaryOr(RHSRange)); 755 break; 756 757 // Unhandled instructions are overdefined. 758 default: 759 DEBUG(dbgs() << " compute BB '" << BB->getName() 760 << "' - overdefined because inst def found.\n"); 761 Result.markOverdefined(); 762 break; 763 } 764 765 BBLV = Result; 766 return true; 767 } 768 769 /// getEdgeValue - This method attempts to infer more complex 770 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom, 771 BasicBlock *BBTo, LVILatticeVal &Result) { 772 // If already a constant, there is nothing to compute. 773 if (Constant *VC = dyn_cast<Constant>(Val)) { 774 Result = LVILatticeVal::get(VC); 775 return true; 776 } 777 778 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we 779 // know that v != 0. 780 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) { 781 // If this is a conditional branch and only one successor goes to BBTo, then 782 // we maybe able to infer something from the condition. 783 if (BI->isConditional() && 784 BI->getSuccessor(0) != BI->getSuccessor(1)) { 785 bool isTrueDest = BI->getSuccessor(0) == BBTo; 786 assert(BI->getSuccessor(!isTrueDest) == BBTo && 787 "BBTo isn't a successor of BBFrom"); 788 789 // If V is the condition of the branch itself, then we know exactly what 790 // it is. 791 if (BI->getCondition() == Val) { 792 Result = LVILatticeVal::get(ConstantInt::get( 793 Type::getInt1Ty(Val->getContext()), isTrueDest)); 794 return true; 795 } 796 797 // If the condition of the branch is an equality comparison, we may be 798 // able to infer the value. 799 ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()); 800 if (ICI && isa<Constant>(ICI->getOperand(1))) { 801 if (ICI->isEquality() && ICI->getOperand(0) == Val) { 802 // We know that V has the RHS constant if this is a true SETEQ or 803 // false SETNE. 804 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ)) 805 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1))); 806 else 807 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1))); 808 return true; 809 } 810 811 // Recognize the range checking idiom that InstCombine produces. 812 // (X-C1) u< C2 --> [C1, C1+C2) 813 ConstantInt *NegOffset = 0; 814 if (ICI->getPredicate() == ICmpInst::ICMP_ULT) 815 match(ICI->getOperand(0), m_Add(m_Specific(Val), 816 m_ConstantInt(NegOffset))); 817 818 ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1)); 819 if (CI && (ICI->getOperand(0) == Val || NegOffset)) { 820 // Calculate the range of values that would satisfy the comparison. 821 ConstantRange CmpRange(CI->getValue(), CI->getValue()+1); 822 ConstantRange TrueValues = 823 ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange); 824 825 if (NegOffset) // Apply the offset from above. 826 TrueValues = TrueValues.subtract(NegOffset->getValue()); 827 828 // If we're interested in the false dest, invert the condition. 829 if (!isTrueDest) TrueValues = TrueValues.inverse(); 830 831 // Figure out the possible values of the query BEFORE this branch. 832 if (!hasBlockValue(Val, BBFrom)) { 833 BlockValueStack.push(std::make_pair(BBFrom, Val)); 834 return false; 835 } 836 837 LVILatticeVal InBlock = getBlockValue(Val, BBFrom); 838 if (!InBlock.isConstantRange()) { 839 Result = LVILatticeVal::getRange(TrueValues); 840 return true; 841 } 842 843 // Find all potential values that satisfy both the input and output 844 // conditions. 845 ConstantRange PossibleValues = 846 TrueValues.intersectWith(InBlock.getConstantRange()); 847 848 Result = LVILatticeVal::getRange(PossibleValues); 849 return true; 850 } 851 } 852 } 853 } 854 855 // If the edge was formed by a switch on the value, then we may know exactly 856 // what it is. 857 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) { 858 if (SI->getCondition() == Val) { 859 // We don't know anything in the default case. 860 if (SI->getDefaultDest() == BBTo) { 861 Result.markOverdefined(); 862 return true; 863 } 864 865 // We only know something if there is exactly one value that goes from 866 // BBFrom to BBTo. 867 unsigned NumEdges = 0; 868 ConstantInt *EdgeVal = 0; 869 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 870 i != e; ++i) { 871 if (i.getCaseSuccessor() != BBTo) continue; 872 if (NumEdges++) break; 873 EdgeVal = i.getCaseValue(); 874 } 875 assert(EdgeVal && "Missing successor?"); 876 if (NumEdges == 1) { 877 Result = LVILatticeVal::get(EdgeVal); 878 return true; 879 } 880 } 881 } 882 883 // Otherwise see if the value is known in the block. 884 if (hasBlockValue(Val, BBFrom)) { 885 Result = getBlockValue(Val, BBFrom); 886 return true; 887 } 888 BlockValueStack.push(std::make_pair(BBFrom, Val)); 889 return false; 890 } 891 892 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) { 893 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '" 894 << BB->getName() << "'\n"); 895 896 BlockValueStack.push(std::make_pair(BB, V)); 897 solve(); 898 LVILatticeVal Result = getBlockValue(V, BB); 899 900 DEBUG(dbgs() << " Result = " << Result << "\n"); 901 return Result; 902 } 903 904 LVILatticeVal LazyValueInfoCache:: 905 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) { 906 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '" 907 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n"); 908 909 LVILatticeVal Result; 910 if (!getEdgeValue(V, FromBB, ToBB, Result)) { 911 solve(); 912 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result); 913 (void)WasFastQuery; 914 assert(WasFastQuery && "More work to do after problem solved?"); 915 } 916 917 DEBUG(dbgs() << " Result = " << Result << "\n"); 918 return Result; 919 } 920 921 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, 922 BasicBlock *NewSucc) { 923 // When an edge in the graph has been threaded, values that we could not 924 // determine a value for before (i.e. were marked overdefined) may be possible 925 // to solve now. We do NOT try to proactively update these values. Instead, 926 // we clear their entries from the cache, and allow lazy updating to recompute 927 // them when needed. 928 929 // The updating process is fairly simple: we need to dropped cached info 930 // for all values that were marked overdefined in OldSucc, and for those same 931 // values in any successor of OldSucc (except NewSucc) in which they were 932 // also marked overdefined. 933 std::vector<BasicBlock*> worklist; 934 worklist.push_back(OldSucc); 935 936 DenseSet<Value*> ClearSet; 937 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(), 938 E = OverDefinedCache.end(); I != E; ++I) { 939 if (I->first == OldSucc) 940 ClearSet.insert(I->second); 941 } 942 943 // Use a worklist to perform a depth-first search of OldSucc's successors. 944 // NOTE: We do not need a visited list since any blocks we have already 945 // visited will have had their overdefined markers cleared already, and we 946 // thus won't loop to their successors. 947 while (!worklist.empty()) { 948 BasicBlock *ToUpdate = worklist.back(); 949 worklist.pop_back(); 950 951 // Skip blocks only accessible through NewSucc. 952 if (ToUpdate == NewSucc) continue; 953 954 bool changed = false; 955 for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end(); 956 I != E; ++I) { 957 // If a value was marked overdefined in OldSucc, and is here too... 958 DenseSet<OverDefinedPairTy>::iterator OI = 959 OverDefinedCache.find(std::make_pair(ToUpdate, *I)); 960 if (OI == OverDefinedCache.end()) continue; 961 962 // Remove it from the caches. 963 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)]; 964 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate); 965 966 assert(CI != Entry.end() && "Couldn't find entry to update?"); 967 Entry.erase(CI); 968 OverDefinedCache.erase(OI); 969 970 // If we removed anything, then we potentially need to update 971 // blocks successors too. 972 changed = true; 973 } 974 975 if (!changed) continue; 976 977 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate)); 978 } 979 } 980 981 //===----------------------------------------------------------------------===// 982 // LazyValueInfo Impl 983 //===----------------------------------------------------------------------===// 984 985 /// getCache - This lazily constructs the LazyValueInfoCache. 986 static LazyValueInfoCache &getCache(void *&PImpl) { 987 if (!PImpl) 988 PImpl = new LazyValueInfoCache(); 989 return *static_cast<LazyValueInfoCache*>(PImpl); 990 } 991 992 bool LazyValueInfo::runOnFunction(Function &F) { 993 if (PImpl) 994 getCache(PImpl).clear(); 995 996 TD = getAnalysisIfAvailable<TargetData>(); 997 TLI = &getAnalysis<TargetLibraryInfo>(); 998 999 // Fully lazy. 1000 return false; 1001 } 1002 1003 void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const { 1004 AU.setPreservesAll(); 1005 AU.addRequired<TargetLibraryInfo>(); 1006 } 1007 1008 void LazyValueInfo::releaseMemory() { 1009 // If the cache was allocated, free it. 1010 if (PImpl) { 1011 delete &getCache(PImpl); 1012 PImpl = 0; 1013 } 1014 } 1015 1016 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) { 1017 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB); 1018 1019 if (Result.isConstant()) 1020 return Result.getConstant(); 1021 if (Result.isConstantRange()) { 1022 ConstantRange CR = Result.getConstantRange(); 1023 if (const APInt *SingleVal = CR.getSingleElement()) 1024 return ConstantInt::get(V->getContext(), *SingleVal); 1025 } 1026 return 0; 1027 } 1028 1029 /// getConstantOnEdge - Determine whether the specified value is known to be a 1030 /// constant on the specified edge. Return null if not. 1031 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB, 1032 BasicBlock *ToBB) { 1033 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB); 1034 1035 if (Result.isConstant()) 1036 return Result.getConstant(); 1037 if (Result.isConstantRange()) { 1038 ConstantRange CR = Result.getConstantRange(); 1039 if (const APInt *SingleVal = CR.getSingleElement()) 1040 return ConstantInt::get(V->getContext(), *SingleVal); 1041 } 1042 return 0; 1043 } 1044 1045 /// getPredicateOnEdge - Determine whether the specified value comparison 1046 /// with a constant is known to be true or false on the specified CFG edge. 1047 /// Pred is a CmpInst predicate. 1048 LazyValueInfo::Tristate 1049 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C, 1050 BasicBlock *FromBB, BasicBlock *ToBB) { 1051 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB); 1052 1053 // If we know the value is a constant, evaluate the conditional. 1054 Constant *Res = 0; 1055 if (Result.isConstant()) { 1056 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD, 1057 TLI); 1058 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res)) 1059 return ResCI->isZero() ? False : True; 1060 return Unknown; 1061 } 1062 1063 if (Result.isConstantRange()) { 1064 ConstantInt *CI = dyn_cast<ConstantInt>(C); 1065 if (!CI) return Unknown; 1066 1067 ConstantRange CR = Result.getConstantRange(); 1068 if (Pred == ICmpInst::ICMP_EQ) { 1069 if (!CR.contains(CI->getValue())) 1070 return False; 1071 1072 if (CR.isSingleElement() && CR.contains(CI->getValue())) 1073 return True; 1074 } else if (Pred == ICmpInst::ICMP_NE) { 1075 if (!CR.contains(CI->getValue())) 1076 return True; 1077 1078 if (CR.isSingleElement() && CR.contains(CI->getValue())) 1079 return False; 1080 } 1081 1082 // Handle more complex predicates. 1083 ConstantRange TrueValues = 1084 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue()); 1085 if (TrueValues.contains(CR)) 1086 return True; 1087 if (TrueValues.inverse().contains(CR)) 1088 return False; 1089 return Unknown; 1090 } 1091 1092 if (Result.isNotConstant()) { 1093 // If this is an equality comparison, we can try to fold it knowing that 1094 // "V != C1". 1095 if (Pred == ICmpInst::ICMP_EQ) { 1096 // !C1 == C -> false iff C1 == C. 1097 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE, 1098 Result.getNotConstant(), C, TD, 1099 TLI); 1100 if (Res->isNullValue()) 1101 return False; 1102 } else if (Pred == ICmpInst::ICMP_NE) { 1103 // !C1 != C -> true iff C1 == C. 1104 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE, 1105 Result.getNotConstant(), C, TD, 1106 TLI); 1107 if (Res->isNullValue()) 1108 return True; 1109 } 1110 return Unknown; 1111 } 1112 1113 return Unknown; 1114 } 1115 1116 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, 1117 BasicBlock *NewSucc) { 1118 if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc); 1119 } 1120 1121 void LazyValueInfo::eraseBlock(BasicBlock *BB) { 1122 if (PImpl) getCache(PImpl).eraseBlock(BB); 1123 } 1124