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/ADT/DenseSet.h" 18 #include "llvm/ADT/STLExtras.h" 19 #include "llvm/Analysis/ConstantFolding.h" 20 #include "llvm/Analysis/ValueTracking.h" 21 #include "llvm/IR/Constants.h" 22 #include "llvm/IR/DataLayout.h" 23 #include "llvm/IR/Instructions.h" 24 #include "llvm/IR/IntrinsicInst.h" 25 #include "llvm/Support/CFG.h" 26 #include "llvm/Support/ConstantRange.h" 27 #include "llvm/Support/Debug.h" 28 #include "llvm/Support/PatternMatch.h" 29 #include "llvm/Support/ValueHandle.h" 30 #include "llvm/Support/raw_ostream.h" 31 #include "llvm/Target/TargetLibraryInfo.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 DataLayout/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 DataLayout/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 updates 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 assert(BlockValueStack.top() == e); 462 BlockValueStack.pop(); 463 } 464 } 465 } 466 467 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) { 468 // If already a constant, there is nothing to compute. 469 if (isa<Constant>(Val)) 470 return true; 471 472 LVIValueHandle ValHandle(Val, this); 473 std::map<LVIValueHandle, ValueCacheEntryTy>::iterator I = 474 ValueCache.find(ValHandle); 475 if (I == ValueCache.end()) return false; 476 return I->second.count(BB); 477 } 478 479 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) { 480 // If already a constant, there is nothing to compute. 481 if (Constant *VC = dyn_cast<Constant>(Val)) 482 return LVILatticeVal::get(VC); 483 484 SeenBlocks.insert(BB); 485 return lookup(Val)[BB]; 486 } 487 488 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) { 489 if (isa<Constant>(Val)) 490 return true; 491 492 ValueCacheEntryTy &Cache = lookup(Val); 493 SeenBlocks.insert(BB); 494 LVILatticeVal &BBLV = Cache[BB]; 495 496 // OverDefinedCacheUpdater is a helper object that will update 497 // the OverDefinedCache for us when this method exits. Make sure to 498 // call markResult on it as we exist, passing a bool to indicate if the 499 // cache needs updating, i.e. if we have solve a new value or not. 500 OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this); 501 502 // If we've already computed this block's value, return it. 503 if (!BBLV.isUndefined()) { 504 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n'); 505 506 // Since we're reusing a cached value here, we don't need to update the 507 // OverDefinedCahce. The cache will have been properly updated 508 // whenever the cached value was inserted. 509 ODCacheUpdater.markResult(false); 510 return true; 511 } 512 513 // Otherwise, this is the first time we're seeing this block. Reset the 514 // lattice value to overdefined, so that cycles will terminate and be 515 // conservatively correct. 516 BBLV.markOverdefined(); 517 518 Instruction *BBI = dyn_cast<Instruction>(Val); 519 if (BBI == 0 || BBI->getParent() != BB) { 520 return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB)); 521 } 522 523 if (PHINode *PN = dyn_cast<PHINode>(BBI)) { 524 return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB)); 525 } 526 527 if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) { 528 BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType())); 529 return ODCacheUpdater.markResult(true); 530 } 531 532 // We can only analyze the definitions of certain classes of instructions 533 // (integral binops and casts at the moment), so bail if this isn't one. 534 LVILatticeVal Result; 535 if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) || 536 !BBI->getType()->isIntegerTy()) { 537 DEBUG(dbgs() << " compute BB '" << BB->getName() 538 << "' - overdefined because inst def found.\n"); 539 BBLV.markOverdefined(); 540 return ODCacheUpdater.markResult(true); 541 } 542 543 // FIXME: We're currently limited to binops with a constant RHS. This should 544 // be improved. 545 BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI); 546 if (BO && !isa<ConstantInt>(BO->getOperand(1))) { 547 DEBUG(dbgs() << " compute BB '" << BB->getName() 548 << "' - overdefined because inst def found.\n"); 549 550 BBLV.markOverdefined(); 551 return ODCacheUpdater.markResult(true); 552 } 553 554 return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB)); 555 } 556 557 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) { 558 if (LoadInst *L = dyn_cast<LoadInst>(I)) { 559 return L->getPointerAddressSpace() == 0 && 560 GetUnderlyingObject(L->getPointerOperand()) == Ptr; 561 } 562 if (StoreInst *S = dyn_cast<StoreInst>(I)) { 563 return S->getPointerAddressSpace() == 0 && 564 GetUnderlyingObject(S->getPointerOperand()) == Ptr; 565 } 566 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) { 567 if (MI->isVolatile()) return false; 568 569 // FIXME: check whether it has a valuerange that excludes zero? 570 ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength()); 571 if (!Len || Len->isZero()) return false; 572 573 if (MI->getDestAddressSpace() == 0) 574 if (GetUnderlyingObject(MI->getRawDest()) == Ptr) 575 return true; 576 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) 577 if (MTI->getSourceAddressSpace() == 0) 578 if (GetUnderlyingObject(MTI->getRawSource()) == Ptr) 579 return true; 580 } 581 return false; 582 } 583 584 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV, 585 Value *Val, BasicBlock *BB) { 586 LVILatticeVal Result; // Start Undefined. 587 588 // If this is a pointer, and there's a load from that pointer in this BB, 589 // then we know that the pointer can't be NULL. 590 bool NotNull = false; 591 if (Val->getType()->isPointerTy()) { 592 if (isKnownNonNull(Val)) { 593 NotNull = true; 594 } else { 595 Value *UnderlyingVal = GetUnderlyingObject(Val); 596 // If 'GetUnderlyingObject' didn't converge, skip it. It won't converge 597 // inside InstructionDereferencesPointer either. 598 if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, NULL, 1)) { 599 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 600 BI != BE; ++BI) { 601 if (InstructionDereferencesPointer(BI, UnderlyingVal)) { 602 NotNull = true; 603 break; 604 } 605 } 606 } 607 } 608 } 609 610 // If this is the entry block, we must be asking about an argument. The 611 // value is overdefined. 612 if (BB == &BB->getParent()->getEntryBlock()) { 613 assert(isa<Argument>(Val) && "Unknown live-in to the entry block"); 614 if (NotNull) { 615 PointerType *PTy = cast<PointerType>(Val->getType()); 616 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy)); 617 } else { 618 Result.markOverdefined(); 619 } 620 BBLV = Result; 621 return true; 622 } 623 624 // Loop over all of our predecessors, merging what we know from them into 625 // result. 626 bool EdgesMissing = false; 627 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 628 LVILatticeVal EdgeResult; 629 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult); 630 if (EdgesMissing) 631 continue; 632 633 Result.mergeIn(EdgeResult); 634 635 // If we hit overdefined, exit early. The BlockVals entry is already set 636 // to overdefined. 637 if (Result.isOverdefined()) { 638 DEBUG(dbgs() << " compute BB '" << BB->getName() 639 << "' - overdefined because of pred.\n"); 640 // If we previously determined that this is a pointer that can't be null 641 // then return that rather than giving up entirely. 642 if (NotNull) { 643 PointerType *PTy = cast<PointerType>(Val->getType()); 644 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy)); 645 } 646 647 BBLV = Result; 648 return true; 649 } 650 } 651 if (EdgesMissing) 652 return false; 653 654 // Return the merged value, which is more precise than 'overdefined'. 655 assert(!Result.isOverdefined()); 656 BBLV = Result; 657 return true; 658 } 659 660 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV, 661 PHINode *PN, BasicBlock *BB) { 662 LVILatticeVal Result; // Start Undefined. 663 664 // Loop over all of our predecessors, merging what we know from them into 665 // result. 666 bool EdgesMissing = false; 667 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 668 BasicBlock *PhiBB = PN->getIncomingBlock(i); 669 Value *PhiVal = PN->getIncomingValue(i); 670 LVILatticeVal EdgeResult; 671 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult); 672 if (EdgesMissing) 673 continue; 674 675 Result.mergeIn(EdgeResult); 676 677 // If we hit overdefined, exit early. The BlockVals entry is already set 678 // to overdefined. 679 if (Result.isOverdefined()) { 680 DEBUG(dbgs() << " compute BB '" << BB->getName() 681 << "' - overdefined because of pred.\n"); 682 683 BBLV = Result; 684 return true; 685 } 686 } 687 if (EdgesMissing) 688 return false; 689 690 // Return the merged value, which is more precise than 'overdefined'. 691 assert(!Result.isOverdefined() && "Possible PHI in entry block?"); 692 BBLV = Result; 693 return true; 694 } 695 696 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV, 697 Instruction *BBI, 698 BasicBlock *BB) { 699 // Figure out the range of the LHS. If that fails, bail. 700 if (!hasBlockValue(BBI->getOperand(0), BB)) { 701 BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0))); 702 return false; 703 } 704 705 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB); 706 if (!LHSVal.isConstantRange()) { 707 BBLV.markOverdefined(); 708 return true; 709 } 710 711 ConstantRange LHSRange = LHSVal.getConstantRange(); 712 ConstantRange RHSRange(1); 713 IntegerType *ResultTy = cast<IntegerType>(BBI->getType()); 714 if (isa<BinaryOperator>(BBI)) { 715 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) { 716 RHSRange = ConstantRange(RHS->getValue()); 717 } else { 718 BBLV.markOverdefined(); 719 return true; 720 } 721 } 722 723 // NOTE: We're currently limited by the set of operations that ConstantRange 724 // can evaluate symbolically. Enhancing that set will allows us to analyze 725 // more definitions. 726 LVILatticeVal Result; 727 switch (BBI->getOpcode()) { 728 case Instruction::Add: 729 Result.markConstantRange(LHSRange.add(RHSRange)); 730 break; 731 case Instruction::Sub: 732 Result.markConstantRange(LHSRange.sub(RHSRange)); 733 break; 734 case Instruction::Mul: 735 Result.markConstantRange(LHSRange.multiply(RHSRange)); 736 break; 737 case Instruction::UDiv: 738 Result.markConstantRange(LHSRange.udiv(RHSRange)); 739 break; 740 case Instruction::Shl: 741 Result.markConstantRange(LHSRange.shl(RHSRange)); 742 break; 743 case Instruction::LShr: 744 Result.markConstantRange(LHSRange.lshr(RHSRange)); 745 break; 746 case Instruction::Trunc: 747 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth())); 748 break; 749 case Instruction::SExt: 750 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth())); 751 break; 752 case Instruction::ZExt: 753 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth())); 754 break; 755 case Instruction::BitCast: 756 Result.markConstantRange(LHSRange); 757 break; 758 case Instruction::And: 759 Result.markConstantRange(LHSRange.binaryAnd(RHSRange)); 760 break; 761 case Instruction::Or: 762 Result.markConstantRange(LHSRange.binaryOr(RHSRange)); 763 break; 764 765 // Unhandled instructions are overdefined. 766 default: 767 DEBUG(dbgs() << " compute BB '" << BB->getName() 768 << "' - overdefined because inst def found.\n"); 769 Result.markOverdefined(); 770 break; 771 } 772 773 BBLV = Result; 774 return true; 775 } 776 777 /// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if 778 /// Val is not constrained on the edge. 779 static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom, 780 BasicBlock *BBTo, LVILatticeVal &Result) { 781 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we 782 // know that v != 0. 783 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) { 784 // If this is a conditional branch and only one successor goes to BBTo, then 785 // we maybe able to infer something from the condition. 786 if (BI->isConditional() && 787 BI->getSuccessor(0) != BI->getSuccessor(1)) { 788 bool isTrueDest = BI->getSuccessor(0) == BBTo; 789 assert(BI->getSuccessor(!isTrueDest) == BBTo && 790 "BBTo isn't a successor of BBFrom"); 791 792 // If V is the condition of the branch itself, then we know exactly what 793 // it is. 794 if (BI->getCondition() == Val) { 795 Result = LVILatticeVal::get(ConstantInt::get( 796 Type::getInt1Ty(Val->getContext()), isTrueDest)); 797 return true; 798 } 799 800 // If the condition of the branch is an equality comparison, we may be 801 // able to infer the value. 802 ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()); 803 if (ICI && isa<Constant>(ICI->getOperand(1))) { 804 if (ICI->isEquality() && ICI->getOperand(0) == Val) { 805 // We know that V has the RHS constant if this is a true SETEQ or 806 // false SETNE. 807 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ)) 808 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1))); 809 else 810 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1))); 811 return true; 812 } 813 814 // Recognize the range checking idiom that InstCombine produces. 815 // (X-C1) u< C2 --> [C1, C1+C2) 816 ConstantInt *NegOffset = 0; 817 if (ICI->getPredicate() == ICmpInst::ICMP_ULT) 818 match(ICI->getOperand(0), m_Add(m_Specific(Val), 819 m_ConstantInt(NegOffset))); 820 821 ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1)); 822 if (CI && (ICI->getOperand(0) == Val || NegOffset)) { 823 // Calculate the range of values that would satisfy the comparison. 824 ConstantRange CmpRange(CI->getValue()); 825 ConstantRange TrueValues = 826 ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange); 827 828 if (NegOffset) // Apply the offset from above. 829 TrueValues = TrueValues.subtract(NegOffset->getValue()); 830 831 // If we're interested in the false dest, invert the condition. 832 if (!isTrueDest) TrueValues = TrueValues.inverse(); 833 834 Result = LVILatticeVal::getRange(TrueValues); 835 return true; 836 } 837 } 838 } 839 } 840 841 // If the edge was formed by a switch on the value, then we may know exactly 842 // what it is. 843 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) { 844 if (SI->getCondition() != Val) 845 return false; 846 847 bool DefaultCase = SI->getDefaultDest() == BBTo; 848 unsigned BitWidth = Val->getType()->getIntegerBitWidth(); 849 ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/); 850 851 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 852 i != e; ++i) { 853 ConstantRange EdgeVal(i.getCaseValue()->getValue()); 854 if (DefaultCase) { 855 // It is possible that the default destination is the destination of 856 // some cases. There is no need to perform difference for those cases. 857 if (i.getCaseSuccessor() != BBTo) 858 EdgesVals = EdgesVals.difference(EdgeVal); 859 } else if (i.getCaseSuccessor() == BBTo) 860 EdgesVals = EdgesVals.unionWith(EdgeVal); 861 } 862 Result = LVILatticeVal::getRange(EdgesVals); 863 return true; 864 } 865 return false; 866 } 867 868 /// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at 869 /// the basic block if the edge does not constraint Val. 870 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom, 871 BasicBlock *BBTo, LVILatticeVal &Result) { 872 // If already a constant, there is nothing to compute. 873 if (Constant *VC = dyn_cast<Constant>(Val)) { 874 Result = LVILatticeVal::get(VC); 875 return true; 876 } 877 878 if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) { 879 if (!Result.isConstantRange() || 880 Result.getConstantRange().getSingleElement()) 881 return true; 882 883 // FIXME: this check should be moved to the beginning of the function when 884 // LVI better supports recursive values. Even for the single value case, we 885 // can intersect to detect dead code (an empty range). 886 if (!hasBlockValue(Val, BBFrom)) { 887 BlockValueStack.push(std::make_pair(BBFrom, Val)); 888 return false; 889 } 890 891 // Try to intersect ranges of the BB and the constraint on the edge. 892 LVILatticeVal InBlock = getBlockValue(Val, BBFrom); 893 if (!InBlock.isConstantRange()) 894 return true; 895 896 ConstantRange Range = 897 Result.getConstantRange().intersectWith(InBlock.getConstantRange()); 898 Result = LVILatticeVal::getRange(Range); 899 return true; 900 } 901 902 if (!hasBlockValue(Val, BBFrom)) { 903 BlockValueStack.push(std::make_pair(BBFrom, Val)); 904 return false; 905 } 906 907 // if we couldn't compute the value on the edge, use the value from the BB 908 Result = getBlockValue(Val, BBFrom); 909 return true; 910 } 911 912 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) { 913 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '" 914 << BB->getName() << "'\n"); 915 916 BlockValueStack.push(std::make_pair(BB, V)); 917 solve(); 918 LVILatticeVal Result = getBlockValue(V, BB); 919 920 DEBUG(dbgs() << " Result = " << Result << "\n"); 921 return Result; 922 } 923 924 LVILatticeVal LazyValueInfoCache:: 925 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) { 926 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '" 927 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n"); 928 929 LVILatticeVal Result; 930 if (!getEdgeValue(V, FromBB, ToBB, Result)) { 931 solve(); 932 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result); 933 (void)WasFastQuery; 934 assert(WasFastQuery && "More work to do after problem solved?"); 935 } 936 937 DEBUG(dbgs() << " Result = " << Result << "\n"); 938 return Result; 939 } 940 941 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, 942 BasicBlock *NewSucc) { 943 // When an edge in the graph has been threaded, values that we could not 944 // determine a value for before (i.e. were marked overdefined) may be possible 945 // to solve now. We do NOT try to proactively update these values. Instead, 946 // we clear their entries from the cache, and allow lazy updating to recompute 947 // them when needed. 948 949 // The updating process is fairly simple: we need to dropped cached info 950 // for all values that were marked overdefined in OldSucc, and for those same 951 // values in any successor of OldSucc (except NewSucc) in which they were 952 // also marked overdefined. 953 std::vector<BasicBlock*> worklist; 954 worklist.push_back(OldSucc); 955 956 DenseSet<Value*> ClearSet; 957 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(), 958 E = OverDefinedCache.end(); I != E; ++I) { 959 if (I->first == OldSucc) 960 ClearSet.insert(I->second); 961 } 962 963 // Use a worklist to perform a depth-first search of OldSucc's successors. 964 // NOTE: We do not need a visited list since any blocks we have already 965 // visited will have had their overdefined markers cleared already, and we 966 // thus won't loop to their successors. 967 while (!worklist.empty()) { 968 BasicBlock *ToUpdate = worklist.back(); 969 worklist.pop_back(); 970 971 // Skip blocks only accessible through NewSucc. 972 if (ToUpdate == NewSucc) continue; 973 974 bool changed = false; 975 for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end(); 976 I != E; ++I) { 977 // If a value was marked overdefined in OldSucc, and is here too... 978 DenseSet<OverDefinedPairTy>::iterator OI = 979 OverDefinedCache.find(std::make_pair(ToUpdate, *I)); 980 if (OI == OverDefinedCache.end()) continue; 981 982 // Remove it from the caches. 983 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)]; 984 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate); 985 986 assert(CI != Entry.end() && "Couldn't find entry to update?"); 987 Entry.erase(CI); 988 OverDefinedCache.erase(OI); 989 990 // If we removed anything, then we potentially need to update 991 // blocks successors too. 992 changed = true; 993 } 994 995 if (!changed) continue; 996 997 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate)); 998 } 999 } 1000 1001 //===----------------------------------------------------------------------===// 1002 // LazyValueInfo Impl 1003 //===----------------------------------------------------------------------===// 1004 1005 /// getCache - This lazily constructs the LazyValueInfoCache. 1006 static LazyValueInfoCache &getCache(void *&PImpl) { 1007 if (!PImpl) 1008 PImpl = new LazyValueInfoCache(); 1009 return *static_cast<LazyValueInfoCache*>(PImpl); 1010 } 1011 1012 bool LazyValueInfo::runOnFunction(Function &F) { 1013 if (PImpl) 1014 getCache(PImpl).clear(); 1015 1016 TD = getAnalysisIfAvailable<DataLayout>(); 1017 TLI = &getAnalysis<TargetLibraryInfo>(); 1018 1019 // Fully lazy. 1020 return false; 1021 } 1022 1023 void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const { 1024 AU.setPreservesAll(); 1025 AU.addRequired<TargetLibraryInfo>(); 1026 } 1027 1028 void LazyValueInfo::releaseMemory() { 1029 // If the cache was allocated, free it. 1030 if (PImpl) { 1031 delete &getCache(PImpl); 1032 PImpl = 0; 1033 } 1034 } 1035 1036 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) { 1037 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB); 1038 1039 if (Result.isConstant()) 1040 return Result.getConstant(); 1041 if (Result.isConstantRange()) { 1042 ConstantRange CR = Result.getConstantRange(); 1043 if (const APInt *SingleVal = CR.getSingleElement()) 1044 return ConstantInt::get(V->getContext(), *SingleVal); 1045 } 1046 return 0; 1047 } 1048 1049 /// getConstantOnEdge - Determine whether the specified value is known to be a 1050 /// constant on the specified edge. Return null if not. 1051 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB, 1052 BasicBlock *ToBB) { 1053 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB); 1054 1055 if (Result.isConstant()) 1056 return Result.getConstant(); 1057 if (Result.isConstantRange()) { 1058 ConstantRange CR = Result.getConstantRange(); 1059 if (const APInt *SingleVal = CR.getSingleElement()) 1060 return ConstantInt::get(V->getContext(), *SingleVal); 1061 } 1062 return 0; 1063 } 1064 1065 /// getPredicateOnEdge - Determine whether the specified value comparison 1066 /// with a constant is known to be true or false on the specified CFG edge. 1067 /// Pred is a CmpInst predicate. 1068 LazyValueInfo::Tristate 1069 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C, 1070 BasicBlock *FromBB, BasicBlock *ToBB) { 1071 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB); 1072 1073 // If we know the value is a constant, evaluate the conditional. 1074 Constant *Res = 0; 1075 if (Result.isConstant()) { 1076 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD, 1077 TLI); 1078 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res)) 1079 return ResCI->isZero() ? False : True; 1080 return Unknown; 1081 } 1082 1083 if (Result.isConstantRange()) { 1084 ConstantInt *CI = dyn_cast<ConstantInt>(C); 1085 if (!CI) return Unknown; 1086 1087 ConstantRange CR = Result.getConstantRange(); 1088 if (Pred == ICmpInst::ICMP_EQ) { 1089 if (!CR.contains(CI->getValue())) 1090 return False; 1091 1092 if (CR.isSingleElement() && CR.contains(CI->getValue())) 1093 return True; 1094 } else if (Pred == ICmpInst::ICMP_NE) { 1095 if (!CR.contains(CI->getValue())) 1096 return True; 1097 1098 if (CR.isSingleElement() && CR.contains(CI->getValue())) 1099 return False; 1100 } 1101 1102 // Handle more complex predicates. 1103 ConstantRange TrueValues = 1104 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue()); 1105 if (TrueValues.contains(CR)) 1106 return True; 1107 if (TrueValues.inverse().contains(CR)) 1108 return False; 1109 return Unknown; 1110 } 1111 1112 if (Result.isNotConstant()) { 1113 // If this is an equality comparison, we can try to fold it knowing that 1114 // "V != C1". 1115 if (Pred == ICmpInst::ICMP_EQ) { 1116 // !C1 == C -> false iff C1 == C. 1117 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE, 1118 Result.getNotConstant(), C, TD, 1119 TLI); 1120 if (Res->isNullValue()) 1121 return False; 1122 } else if (Pred == ICmpInst::ICMP_NE) { 1123 // !C1 != C -> true iff C1 == C. 1124 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE, 1125 Result.getNotConstant(), C, TD, 1126 TLI); 1127 if (Res->isNullValue()) 1128 return True; 1129 } 1130 return Unknown; 1131 } 1132 1133 return Unknown; 1134 } 1135 1136 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, 1137 BasicBlock *NewSucc) { 1138 if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc); 1139 } 1140 1141 void LazyValueInfo::eraseBlock(BasicBlock *BB) { 1142 if (PImpl) getCache(PImpl).eraseBlock(BB); 1143 } 1144