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> 34using namespace llvm; 35using namespace PatternMatch; 36 37char LazyValueInfo::ID = 0; 38INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info", 39 "Lazy Value Information Analysis", false, true) 40INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 41INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info", 42 "Lazy Value Information Analysis", false, true) 43 44namespace 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/// 59namespace { 60class 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 84public: 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 274namespace llvm { 275raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) 276 LLVM_ATTRIBUTE_USED; 277raw_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 296namespace { 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 313namespace { 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 413void 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 434void 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 457void 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 467bool 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 479LVILatticeVal 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 488bool 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 557static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) { 558 if (LoadInst *L = dyn_cast<LoadInst>(I)) { 559 return L->getPointerAddressSpace() == 0 && 560 GetUnderlyingObject(L->getPointerOperand()) == 561 GetUnderlyingObject(Ptr); 562 } 563 if (StoreInst *S = dyn_cast<StoreInst>(I)) { 564 return S->getPointerAddressSpace() == 0 && 565 GetUnderlyingObject(S->getPointerOperand()) == 566 GetUnderlyingObject(Ptr); 567 } 568 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) { 569 if (MI->isVolatile()) return false; 570 571 // FIXME: check whether it has a valuerange that excludes zero? 572 ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength()); 573 if (!Len || Len->isZero()) return false; 574 575 if (MI->getDestAddressSpace() == 0) 576 if (MI->getRawDest() == Ptr || MI->getDest() == Ptr) 577 return true; 578 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) 579 if (MTI->getSourceAddressSpace() == 0) 580 if (MTI->getRawSource() == Ptr || MTI->getSource() == Ptr) 581 return true; 582 } 583 return false; 584} 585 586bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV, 587 Value *Val, BasicBlock *BB) { 588 LVILatticeVal Result; // Start Undefined. 589 590 // If this is a pointer, and there's a load from that pointer in this BB, 591 // then we know that the pointer can't be NULL. 592 bool NotNull = false; 593 if (Val->getType()->isPointerTy()) { 594 if (isa<AllocaInst>(Val)) { 595 NotNull = true; 596 } else { 597 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){ 598 if (InstructionDereferencesPointer(BI, Val)) { 599 NotNull = true; 600 break; 601 } 602 } 603 } 604 } 605 606 // If this is the entry block, we must be asking about an argument. The 607 // value is overdefined. 608 if (BB == &BB->getParent()->getEntryBlock()) { 609 assert(isa<Argument>(Val) && "Unknown live-in to the entry block"); 610 if (NotNull) { 611 PointerType *PTy = cast<PointerType>(Val->getType()); 612 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy)); 613 } else { 614 Result.markOverdefined(); 615 } 616 BBLV = Result; 617 return true; 618 } 619 620 // Loop over all of our predecessors, merging what we know from them into 621 // result. 622 bool EdgesMissing = false; 623 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 624 LVILatticeVal EdgeResult; 625 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult); 626 if (EdgesMissing) 627 continue; 628 629 Result.mergeIn(EdgeResult); 630 631 // If we hit overdefined, exit early. The BlockVals entry is already set 632 // to overdefined. 633 if (Result.isOverdefined()) { 634 DEBUG(dbgs() << " compute BB '" << BB->getName() 635 << "' - overdefined because of pred.\n"); 636 // If we previously determined that this is a pointer that can't be null 637 // then return that rather than giving up entirely. 638 if (NotNull) { 639 PointerType *PTy = cast<PointerType>(Val->getType()); 640 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy)); 641 } 642 643 BBLV = Result; 644 return true; 645 } 646 } 647 if (EdgesMissing) 648 return false; 649 650 // Return the merged value, which is more precise than 'overdefined'. 651 assert(!Result.isOverdefined()); 652 BBLV = Result; 653 return true; 654} 655 656bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV, 657 PHINode *PN, BasicBlock *BB) { 658 LVILatticeVal Result; // Start Undefined. 659 660 // Loop over all of our predecessors, merging what we know from them into 661 // result. 662 bool EdgesMissing = false; 663 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 664 BasicBlock *PhiBB = PN->getIncomingBlock(i); 665 Value *PhiVal = PN->getIncomingValue(i); 666 LVILatticeVal EdgeResult; 667 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult); 668 if (EdgesMissing) 669 continue; 670 671 Result.mergeIn(EdgeResult); 672 673 // If we hit overdefined, exit early. The BlockVals entry is already set 674 // to overdefined. 675 if (Result.isOverdefined()) { 676 DEBUG(dbgs() << " compute BB '" << BB->getName() 677 << "' - overdefined because of pred.\n"); 678 679 BBLV = Result; 680 return true; 681 } 682 } 683 if (EdgesMissing) 684 return false; 685 686 // Return the merged value, which is more precise than 'overdefined'. 687 assert(!Result.isOverdefined() && "Possible PHI in entry block?"); 688 BBLV = Result; 689 return true; 690} 691 692bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV, 693 Instruction *BBI, 694 BasicBlock *BB) { 695 // Figure out the range of the LHS. If that fails, bail. 696 if (!hasBlockValue(BBI->getOperand(0), BB)) { 697 BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0))); 698 return false; 699 } 700 701 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB); 702 if (!LHSVal.isConstantRange()) { 703 BBLV.markOverdefined(); 704 return true; 705 } 706 707 ConstantRange LHSRange = LHSVal.getConstantRange(); 708 ConstantRange RHSRange(1); 709 IntegerType *ResultTy = cast<IntegerType>(BBI->getType()); 710 if (isa<BinaryOperator>(BBI)) { 711 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) { 712 RHSRange = ConstantRange(RHS->getValue()); 713 } else { 714 BBLV.markOverdefined(); 715 return true; 716 } 717 } 718 719 // NOTE: We're currently limited by the set of operations that ConstantRange 720 // can evaluate symbolically. Enhancing that set will allows us to analyze 721 // more definitions. 722 LVILatticeVal Result; 723 switch (BBI->getOpcode()) { 724 case Instruction::Add: 725 Result.markConstantRange(LHSRange.add(RHSRange)); 726 break; 727 case Instruction::Sub: 728 Result.markConstantRange(LHSRange.sub(RHSRange)); 729 break; 730 case Instruction::Mul: 731 Result.markConstantRange(LHSRange.multiply(RHSRange)); 732 break; 733 case Instruction::UDiv: 734 Result.markConstantRange(LHSRange.udiv(RHSRange)); 735 break; 736 case Instruction::Shl: 737 Result.markConstantRange(LHSRange.shl(RHSRange)); 738 break; 739 case Instruction::LShr: 740 Result.markConstantRange(LHSRange.lshr(RHSRange)); 741 break; 742 case Instruction::Trunc: 743 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth())); 744 break; 745 case Instruction::SExt: 746 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth())); 747 break; 748 case Instruction::ZExt: 749 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth())); 750 break; 751 case Instruction::BitCast: 752 Result.markConstantRange(LHSRange); 753 break; 754 case Instruction::And: 755 Result.markConstantRange(LHSRange.binaryAnd(RHSRange)); 756 break; 757 case Instruction::Or: 758 Result.markConstantRange(LHSRange.binaryOr(RHSRange)); 759 break; 760 761 // Unhandled instructions are overdefined. 762 default: 763 DEBUG(dbgs() << " compute BB '" << BB->getName() 764 << "' - overdefined because inst def found.\n"); 765 Result.markOverdefined(); 766 break; 767 } 768 769 BBLV = Result; 770 return true; 771} 772 773/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if 774/// Val is not constrained on the edge. 775static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom, 776 BasicBlock *BBTo, LVILatticeVal &Result) { 777 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we 778 // know that v != 0. 779 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) { 780 // If this is a conditional branch and only one successor goes to BBTo, then 781 // we maybe able to infer something from the condition. 782 if (BI->isConditional() && 783 BI->getSuccessor(0) != BI->getSuccessor(1)) { 784 bool isTrueDest = BI->getSuccessor(0) == BBTo; 785 assert(BI->getSuccessor(!isTrueDest) == BBTo && 786 "BBTo isn't a successor of BBFrom"); 787 788 // If V is the condition of the branch itself, then we know exactly what 789 // it is. 790 if (BI->getCondition() == Val) { 791 Result = LVILatticeVal::get(ConstantInt::get( 792 Type::getInt1Ty(Val->getContext()), isTrueDest)); 793 return true; 794 } 795 796 // If the condition of the branch is an equality comparison, we may be 797 // able to infer the value. 798 ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()); 799 if (ICI && isa<Constant>(ICI->getOperand(1))) { 800 if (ICI->isEquality() && ICI->getOperand(0) == Val) { 801 // We know that V has the RHS constant if this is a true SETEQ or 802 // false SETNE. 803 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ)) 804 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1))); 805 else 806 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1))); 807 return true; 808 } 809 810 // Recognize the range checking idiom that InstCombine produces. 811 // (X-C1) u< C2 --> [C1, C1+C2) 812 ConstantInt *NegOffset = 0; 813 if (ICI->getPredicate() == ICmpInst::ICMP_ULT) 814 match(ICI->getOperand(0), m_Add(m_Specific(Val), 815 m_ConstantInt(NegOffset))); 816 817 ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1)); 818 if (CI && (ICI->getOperand(0) == Val || NegOffset)) { 819 // Calculate the range of values that would satisfy the comparison. 820 ConstantRange CmpRange(CI->getValue()); 821 ConstantRange TrueValues = 822 ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange); 823 824 if (NegOffset) // Apply the offset from above. 825 TrueValues = TrueValues.subtract(NegOffset->getValue()); 826 827 // If we're interested in the false dest, invert the condition. 828 if (!isTrueDest) TrueValues = TrueValues.inverse(); 829 830 Result = LVILatticeVal::getRange(TrueValues); 831 return true; 832 } 833 } 834 } 835 } 836 837 // If the edge was formed by a switch on the value, then we may know exactly 838 // what it is. 839 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) { 840 if (SI->getCondition() != Val) 841 return false; 842 843 bool DefaultCase = SI->getDefaultDest() == BBTo; 844 unsigned BitWidth = Val->getType()->getIntegerBitWidth(); 845 ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/); 846 847 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 848 i != e; ++i) { 849 ConstantRange EdgeVal(i.getCaseValue()->getValue()); 850 if (DefaultCase) { 851 // It is possible that the default destination is the destination of 852 // some cases. There is no need to perform difference for those cases. 853 if (i.getCaseSuccessor() != BBTo) 854 EdgesVals = EdgesVals.difference(EdgeVal); 855 } else if (i.getCaseSuccessor() == BBTo) 856 EdgesVals = EdgesVals.unionWith(EdgeVal); 857 } 858 Result = LVILatticeVal::getRange(EdgesVals); 859 return true; 860 } 861 return false; 862} 863 864/// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at 865/// the basic block if the edge does not constraint Val. 866bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom, 867 BasicBlock *BBTo, LVILatticeVal &Result) { 868 // If already a constant, there is nothing to compute. 869 if (Constant *VC = dyn_cast<Constant>(Val)) { 870 Result = LVILatticeVal::get(VC); 871 return true; 872 } 873 874 if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) { 875 if (!Result.isConstantRange() || 876 Result.getConstantRange().getSingleElement()) 877 return true; 878 879 // FIXME: this check should be moved to the beginning of the function when 880 // LVI better supports recursive values. Even for the single value case, we 881 // can intersect to detect dead code (an empty range). 882 if (!hasBlockValue(Val, BBFrom)) { 883 BlockValueStack.push(std::make_pair(BBFrom, Val)); 884 return false; 885 } 886 887 // Try to intersect ranges of the BB and the constraint on the edge. 888 LVILatticeVal InBlock = getBlockValue(Val, BBFrom); 889 if (!InBlock.isConstantRange()) 890 return true; 891 892 ConstantRange Range = 893 Result.getConstantRange().intersectWith(InBlock.getConstantRange()); 894 Result = LVILatticeVal::getRange(Range); 895 return true; 896 } 897 898 if (!hasBlockValue(Val, BBFrom)) { 899 BlockValueStack.push(std::make_pair(BBFrom, Val)); 900 return false; 901 } 902 903 // if we couldn't compute the value on the edge, use the value from the BB 904 Result = getBlockValue(Val, BBFrom); 905 return true; 906} 907 908LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) { 909 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '" 910 << BB->getName() << "'\n"); 911 912 BlockValueStack.push(std::make_pair(BB, V)); 913 solve(); 914 LVILatticeVal Result = getBlockValue(V, BB); 915 916 DEBUG(dbgs() << " Result = " << Result << "\n"); 917 return Result; 918} 919 920LVILatticeVal LazyValueInfoCache:: 921getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) { 922 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '" 923 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n"); 924 925 LVILatticeVal Result; 926 if (!getEdgeValue(V, FromBB, ToBB, Result)) { 927 solve(); 928 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result); 929 (void)WasFastQuery; 930 assert(WasFastQuery && "More work to do after problem solved?"); 931 } 932 933 DEBUG(dbgs() << " Result = " << Result << "\n"); 934 return Result; 935} 936 937void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, 938 BasicBlock *NewSucc) { 939 // When an edge in the graph has been threaded, values that we could not 940 // determine a value for before (i.e. were marked overdefined) may be possible 941 // to solve now. We do NOT try to proactively update these values. Instead, 942 // we clear their entries from the cache, and allow lazy updating to recompute 943 // them when needed. 944 945 // The updating process is fairly simple: we need to dropped cached info 946 // for all values that were marked overdefined in OldSucc, and for those same 947 // values in any successor of OldSucc (except NewSucc) in which they were 948 // also marked overdefined. 949 std::vector<BasicBlock*> worklist; 950 worklist.push_back(OldSucc); 951 952 DenseSet<Value*> ClearSet; 953 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(), 954 E = OverDefinedCache.end(); I != E; ++I) { 955 if (I->first == OldSucc) 956 ClearSet.insert(I->second); 957 } 958 959 // Use a worklist to perform a depth-first search of OldSucc's successors. 960 // NOTE: We do not need a visited list since any blocks we have already 961 // visited will have had their overdefined markers cleared already, and we 962 // thus won't loop to their successors. 963 while (!worklist.empty()) { 964 BasicBlock *ToUpdate = worklist.back(); 965 worklist.pop_back(); 966 967 // Skip blocks only accessible through NewSucc. 968 if (ToUpdate == NewSucc) continue; 969 970 bool changed = false; 971 for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end(); 972 I != E; ++I) { 973 // If a value was marked overdefined in OldSucc, and is here too... 974 DenseSet<OverDefinedPairTy>::iterator OI = 975 OverDefinedCache.find(std::make_pair(ToUpdate, *I)); 976 if (OI == OverDefinedCache.end()) continue; 977 978 // Remove it from the caches. 979 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)]; 980 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate); 981 982 assert(CI != Entry.end() && "Couldn't find entry to update?"); 983 Entry.erase(CI); 984 OverDefinedCache.erase(OI); 985 986 // If we removed anything, then we potentially need to update 987 // blocks successors too. 988 changed = true; 989 } 990 991 if (!changed) continue; 992 993 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate)); 994 } 995} 996 997//===----------------------------------------------------------------------===// 998// LazyValueInfo Impl 999//===----------------------------------------------------------------------===// 1000 1001/// getCache - This lazily constructs the LazyValueInfoCache. 1002static LazyValueInfoCache &getCache(void *&PImpl) { 1003 if (!PImpl) 1004 PImpl = new LazyValueInfoCache(); 1005 return *static_cast<LazyValueInfoCache*>(PImpl); 1006} 1007 1008bool LazyValueInfo::runOnFunction(Function &F) { 1009 if (PImpl) 1010 getCache(PImpl).clear(); 1011 1012 TD = getAnalysisIfAvailable<TargetData>(); 1013 TLI = &getAnalysis<TargetLibraryInfo>(); 1014 1015 // Fully lazy. 1016 return false; 1017} 1018 1019void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const { 1020 AU.setPreservesAll(); 1021 AU.addRequired<TargetLibraryInfo>(); 1022} 1023 1024void LazyValueInfo::releaseMemory() { 1025 // If the cache was allocated, free it. 1026 if (PImpl) { 1027 delete &getCache(PImpl); 1028 PImpl = 0; 1029 } 1030} 1031 1032Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) { 1033 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB); 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/// getConstantOnEdge - Determine whether the specified value is known to be a 1046/// constant on the specified edge. Return null if not. 1047Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB, 1048 BasicBlock *ToBB) { 1049 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB); 1050 1051 if (Result.isConstant()) 1052 return Result.getConstant(); 1053 if (Result.isConstantRange()) { 1054 ConstantRange CR = Result.getConstantRange(); 1055 if (const APInt *SingleVal = CR.getSingleElement()) 1056 return ConstantInt::get(V->getContext(), *SingleVal); 1057 } 1058 return 0; 1059} 1060 1061/// getPredicateOnEdge - Determine whether the specified value comparison 1062/// with a constant is known to be true or false on the specified CFG edge. 1063/// Pred is a CmpInst predicate. 1064LazyValueInfo::Tristate 1065LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C, 1066 BasicBlock *FromBB, BasicBlock *ToBB) { 1067 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB); 1068 1069 // If we know the value is a constant, evaluate the conditional. 1070 Constant *Res = 0; 1071 if (Result.isConstant()) { 1072 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD, 1073 TLI); 1074 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res)) 1075 return ResCI->isZero() ? False : True; 1076 return Unknown; 1077 } 1078 1079 if (Result.isConstantRange()) { 1080 ConstantInt *CI = dyn_cast<ConstantInt>(C); 1081 if (!CI) return Unknown; 1082 1083 ConstantRange CR = Result.getConstantRange(); 1084 if (Pred == ICmpInst::ICMP_EQ) { 1085 if (!CR.contains(CI->getValue())) 1086 return False; 1087 1088 if (CR.isSingleElement() && CR.contains(CI->getValue())) 1089 return True; 1090 } else if (Pred == ICmpInst::ICMP_NE) { 1091 if (!CR.contains(CI->getValue())) 1092 return True; 1093 1094 if (CR.isSingleElement() && CR.contains(CI->getValue())) 1095 return False; 1096 } 1097 1098 // Handle more complex predicates. 1099 ConstantRange TrueValues = 1100 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue()); 1101 if (TrueValues.contains(CR)) 1102 return True; 1103 if (TrueValues.inverse().contains(CR)) 1104 return False; 1105 return Unknown; 1106 } 1107 1108 if (Result.isNotConstant()) { 1109 // If this is an equality comparison, we can try to fold it knowing that 1110 // "V != C1". 1111 if (Pred == ICmpInst::ICMP_EQ) { 1112 // !C1 == C -> false iff C1 == C. 1113 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE, 1114 Result.getNotConstant(), C, TD, 1115 TLI); 1116 if (Res->isNullValue()) 1117 return False; 1118 } else if (Pred == ICmpInst::ICMP_NE) { 1119 // !C1 != C -> true iff C1 == C. 1120 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE, 1121 Result.getNotConstant(), C, TD, 1122 TLI); 1123 if (Res->isNullValue()) 1124 return True; 1125 } 1126 return Unknown; 1127 } 1128 1129 return Unknown; 1130} 1131 1132void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, 1133 BasicBlock *NewSucc) { 1134 if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc); 1135} 1136 1137void LazyValueInfo::eraseBlock(BasicBlock *BB) { 1138 if (PImpl) getCache(PImpl).eraseBlock(BB); 1139} 1140