lib/Analysis/LazyValueInfo.cpp

   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/Support/CFG.h"
  24 #include "llvm/Support/ConstantRange.h"
  25 #include "llvm/Support/Debug.h"
  26 #include "llvm/Support/raw_ostream.h"
  27 #include "llvm/Support/ValueHandle.h"
  28 #include "llvm/ADT/DenseMap.h"
  29 #include "llvm/ADT/DenseSet.h"
  30 #include "llvm/ADT/STLExtras.h"
  31 #include <map>
  32 #include <stack>
  33 using namespace llvm;
  34
  35 char LazyValueInfo::ID = 0;
  36 INITIALIZE_PASS(LazyValueInfo, "lazy-value-info",
  37                 "Lazy Value Information Analysis", false, true)
  38
  39 namespace llvm {
  40   FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
  41 }
  42
  43
  44 //===----------------------------------------------------------------------===//
  45 //                               LVILatticeVal
  46 //===----------------------------------------------------------------------===//
  47
  48 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
  49 /// value.
  50 ///
  51 /// FIXME: This is basically just for bringup, this can be made a lot more rich
  52 /// in the future.
  53 ///
  54 namespace {
  55 class LVILatticeVal {
  56   enum LatticeValueTy {
  57     /// undefined - This Value has no known value yet.
  58     undefined,
  59
  60     /// constant - This Value has a specific constant value.
  61     constant,
  62     /// notconstant - This Value is known to not have the specified value.
  63     notconstant,
  64
  65     /// constantrange - The Value falls within this range.
  66     constantrange,
  67
  68     /// overdefined - This value is not known to be constant, and we know that
  69     /// it has a value.
  70     overdefined
  71   };
  72
  73   /// Val: This stores the current lattice value along with the Constant* for
  74   /// the constant if this is a 'constant' or 'notconstant' value.
  75   LatticeValueTy Tag;
  76   Constant *Val;
  77   ConstantRange Range;
  78
  79 public:
  80   LVILatticeVal() : Tag(undefined), Val(0), Range(1, true) {}
  81
  82   static LVILatticeVal get(Constant *C) {
  83     LVILatticeVal Res;
  84     if (!isa<UndefValue>(C))
  85       Res.markConstant(C);
  86     return Res;
  87   }
  88   static LVILatticeVal getNot(Constant *C) {
  89     LVILatticeVal Res;
  90     if (!isa<UndefValue>(C))
  91       Res.markNotConstant(C);
  92     return Res;
  93   }
  94   static LVILatticeVal getRange(ConstantRange CR) {
  95     LVILatticeVal Res;
  96     Res.markConstantRange(CR);
  97     return Res;
  98   }
  99
 100   bool isUndefined() const     { return Tag == undefined; }
 101   bool isConstant() const      { return Tag == constant; }
 102   bool isNotConstant() const   { return Tag == notconstant; }
 103   bool isConstantRange() const { return Tag == constantrange; }
 104   bool isOverdefined() const   { return Tag == overdefined; }
 105
 106   Constant *getConstant() const {
 107     assert(isConstant() && "Cannot get the constant of a non-constant!");
 108     return Val;
 109   }
 110
 111   Constant *getNotConstant() const {
 112     assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
 113     return Val;
 114   }
 115
 116   ConstantRange getConstantRange() const {
 117     assert(isConstantRange() &&
 118            "Cannot get the constant-range of a non-constant-range!");
 119     return Range;
 120   }
 121
 122   /// markOverdefined - Return true if this is a change in status.
 123   bool markOverdefined() {
 124     if (isOverdefined())
 125       return false;
 126     Tag = overdefined;
 127     return true;
 128   }
 129
 130   /// markConstant - Return true if this is a change in status.
 131   bool markConstant(Constant *V) {
 132     assert(V && "Marking constant with NULL");
 133     if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
 134       return markConstantRange(ConstantRange(CI->getValue()));
 135     if (isa<UndefValue>(V))
 136       return false;
 137
 138     assert((!isConstant() || getConstant() == V) &&
 139            "Marking constant with different value");
 140     assert(isUndefined());
 141     Tag = constant;
 142     Val = V;
 143     return true;
 144   }
 145
 146   /// markNotConstant - Return true if this is a change in status.
 147   bool markNotConstant(Constant *V) {
 148     assert(V && "Marking constant with NULL");
 149     if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
 150       return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
 151     if (isa<UndefValue>(V))
 152       return false;
 153
 154     assert((!isConstant() || getConstant() != V) &&
 155            "Marking constant !constant with same value");
 156     assert((!isNotConstant() || getNotConstant() == V) &&
 157            "Marking !constant with different value");
 158     assert(isUndefined() || isConstant());
 159     Tag = notconstant;
 160     Val = V;
 161     return true;
 162   }
 163
 164   /// markConstantRange - Return true if this is a change in status.
 165   bool markConstantRange(const ConstantRange NewR) {
 166     if (isConstantRange()) {
 167       if (NewR.isEmptySet())
 168         return markOverdefined();
 169
 170       bool changed = Range == NewR;
 171       Range = NewR;
 172       return changed;
 173     }
 174
 175     assert(isUndefined());
 176     if (NewR.isEmptySet())
 177       return markOverdefined();
 178
 179     Tag = constantrange;
 180     Range = NewR;
 181     return true;
 182   }
 183
 184   /// mergeIn - Merge the specified lattice value into this one, updating this
 185   /// one and returning true if anything changed.
 186   bool mergeIn(const LVILatticeVal &RHS) {
 187     if (RHS.isUndefined() || isOverdefined()) return false;
 188     if (RHS.isOverdefined()) return markOverdefined();
 189
 190     if (isUndefined()) {
 191       Tag = RHS.Tag;
 192       Val = RHS.Val;
 193       Range = RHS.Range;
 194       return true;
 195     }
 196
 197     if (isConstant()) {
 198       if (RHS.isConstant()) {
 199         if (Val == RHS.Val)
 200           return false;
 201         return markOverdefined();
 202       }
 203
 204       if (RHS.isNotConstant()) {
 205         if (Val == RHS.Val)
 206           return markOverdefined();
 207
 208         // Unless we can prove that the two Constants are different, we must
 209         // move to overdefined.
 210         // FIXME: use TargetData for smarter constant folding.
 211         if (ConstantInt *Res = dyn_cast<ConstantInt>(
 212                 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
 213                                                 getConstant(),
 214                                                 RHS.getNotConstant())))
 215           if (Res->isOne())
 216             return markNotConstant(RHS.getNotConstant());
 217
 218         return markOverdefined();
 219       }
 220
 221       // RHS is a ConstantRange, LHS is a non-integer Constant.
 222
 223       // FIXME: consider the case where RHS is a range [1, 0) and LHS is
 224       // a function. The correct result is to pick up RHS.
 225
 226       return markOverdefined();
 227     }
 228
 229     if (isNotConstant()) {
 230       if (RHS.isConstant()) {
 231         if (Val == RHS.Val)
 232           return markOverdefined();
 233
 234         // Unless we can prove that the two Constants are different, we must
 235         // move to overdefined.
 236         // FIXME: use TargetData for smarter constant folding.
 237         if (ConstantInt *Res = dyn_cast<ConstantInt>(
 238                 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
 239                                                 getNotConstant(),
 240                                                 RHS.getConstant())))
 241           if (Res->isOne())
 242             return false;
 243
 244         return markOverdefined();
 245       }
 246
 247       if (RHS.isNotConstant()) {
 248         if (Val == RHS.Val)
 249           return false;
 250         return markOverdefined();
 251       }
 252
 253       return markOverdefined();
 254     }
 255
 256     assert(isConstantRange() && "New LVILattice type?");
 257     if (!RHS.isConstantRange())
 258       return markOverdefined();
 259
 260     ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
 261     if (NewR.isFullSet())
 262       return markOverdefined();
 263     return markConstantRange(NewR);
 264   }
 265 };
 266
 267 } // end anonymous namespace.
 268
 269 namespace llvm {
 270 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
 271     LLVM_ATTRIBUTE_USED;
 272 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
 273   if (Val.isUndefined())
 274     return OS << "undefined";
 275   if (Val.isOverdefined())
 276     return OS << "overdefined";
 277
 278   if (Val.isNotConstant())
 279     return OS << "notconstant<" << *Val.getNotConstant() << '>';
 280   else if (Val.isConstantRange())
 281     return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
 282               << Val.getConstantRange().getUpper() << '>';
 283   return OS << "constant<" << *Val.getConstant() << '>';
 284 }
 285 }
 286
 287 //===----------------------------------------------------------------------===//
 288 //                          LazyValueInfoCache Decl
 289 //===----------------------------------------------------------------------===//
 290
 291 namespace {
 292   /// LVIValueHandle - A callback value handle update the cache when
 293   /// values are erased.
 294   class LazyValueInfoCache;
 295   struct LVIValueHandle : public CallbackVH {
 296     LazyValueInfoCache *Parent;
 297
 298     LVIValueHandle(Value *V, LazyValueInfoCache *P)
 299       : CallbackVH(V), Parent(P) { }
 300
 301     void deleted();
 302     void allUsesReplacedWith(Value *V) {
 303       deleted();
 304     }
 305   };
 306 }
 307
 308 namespace llvm {
 309   template<>
 310   struct DenseMapInfo<LVIValueHandle> {
 311     typedef DenseMapInfo<Value*> PointerInfo;
 312     static inline LVIValueHandle getEmptyKey() {
 313       return LVIValueHandle(PointerInfo::getEmptyKey(),
 314                             static_cast<LazyValueInfoCache*>(0));
 315     }
 316     static inline LVIValueHandle getTombstoneKey() {
 317       return LVIValueHandle(PointerInfo::getTombstoneKey(),
 318                             static_cast<LazyValueInfoCache*>(0));
 319     }
 320     static unsigned getHashValue(const LVIValueHandle &Val) {
 321       return PointerInfo::getHashValue(Val);
 322     }
 323     static bool isEqual(const LVIValueHandle &LHS, const LVIValueHandle &RHS) {
 324       return LHS == RHS;
 325     }
 326   };
 327
 328   template<>
 329   struct DenseMapInfo<std::pair<AssertingVH<BasicBlock>, Value*> > {
 330     typedef std::pair<AssertingVH<BasicBlock>, Value*> PairTy;
 331     typedef DenseMapInfo<AssertingVH<BasicBlock> > APointerInfo;
 332     typedef DenseMapInfo<Value*> BPointerInfo;
 333     static inline PairTy getEmptyKey() {
 334       return std::make_pair(APointerInfo::getEmptyKey(),
 335                             BPointerInfo::getEmptyKey());
 336     }
 337     static inline PairTy getTombstoneKey() {
 338       return std::make_pair(APointerInfo::getTombstoneKey(),
 339                             BPointerInfo::getTombstoneKey());
 340     }
 341     static unsigned getHashValue( const PairTy &Val) {
 342       return APointerInfo::getHashValue(Val.first) ^
 343              BPointerInfo::getHashValue(Val.second);
 344     }
 345     static bool isEqual(const PairTy &LHS, const PairTy &RHS) {
 346       return APointerInfo::isEqual(LHS.first, RHS.first) &&
 347              BPointerInfo::isEqual(LHS.second, RHS.second);
 348     }
 349   };
 350 }
 351
 352 namespace {
 353   /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
 354   /// maintains information about queries across the clients' queries.
 355   class LazyValueInfoCache {
 356     /// ValueCacheEntryTy - This is all of the cached block information for
 357     /// exactly one Value*.  The entries are sorted by the BasicBlock* of the
 358     /// entries, allowing us to do a lookup with a binary search.
 359     typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
 360
 361     /// ValueCache - This is all of the cached information for all values,
 362     /// mapped from Value* to key information.
 363     DenseMap<LVIValueHandle, ValueCacheEntryTy> ValueCache;
 364
 365     /// OverDefinedCache - This tracks, on a per-block basis, the set of
 366     /// values that are over-defined at the end of that block.  This is required
 367     /// for cache updating.
 368     typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
 369     DenseSet<OverDefinedPairTy> OverDefinedCache;
 370
 371     /// BlockValueStack - This stack holds the state of the value solver
 372     /// during a query.  It basically emulates the callstack of the naive
 373     /// recursive value lookup process.
 374     std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
 375
 376     friend struct LVIValueHandle;
 377
 378     /// OverDefinedCacheUpdater - A helper object that ensures that the
 379     /// OverDefinedCache is updated whenever solveBlockValue returns.
 380     struct OverDefinedCacheUpdater {
 381       LazyValueInfoCache *Parent;
 382       Value *Val;
 383       BasicBlock *BB;
 384       LVILatticeVal &BBLV;
 385
 386       OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
 387                        LazyValueInfoCache *P)
 388         : Parent(P), Val(V), BB(B), BBLV(LV) { }
 389
 390       bool markResult(bool changed) {
 391         if (changed && BBLV.isOverdefined())
 392           Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
 393         return changed;
 394       }
 395     };
 396
 397
 398
 399     LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
 400     bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
 401                       LVILatticeVal &Result);
 402     bool hasBlockValue(Value *Val, BasicBlock *BB);
 403
 404     // These methods process one work item and may add more. A false value
 405     // returned means that the work item was not completely processed and must
 406     // be revisited after going through the new items.
 407     bool solveBlockValue(Value *Val, BasicBlock *BB);
 408     bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
 409                                  Value *Val, BasicBlock *BB);
 410     bool solveBlockValuePHINode(LVILatticeVal &BBLV,
 411                                 PHINode *PN, BasicBlock *BB);
 412     bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
 413                                       Instruction *BBI, BasicBlock *BB);
 414
 415     void solve();
 416
 417     ValueCacheEntryTy &lookup(Value *V) {
 418       return ValueCache[LVIValueHandle(V, this)];
 419     }
 420
 421   public:
 422     /// getValueInBlock - This is the query interface to determine the lattice
 423     /// value for the specified Value* at the end of the specified block.
 424     LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
 425
 426     /// getValueOnEdge - This is the query interface to determine the lattice
 427     /// value for the specified Value* that is true on the specified edge.
 428     LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
 429
 430     /// threadEdge - This is the update interface to inform the cache that an
 431     /// edge from PredBB to OldSucc has been threaded to be from PredBB to
 432     /// NewSucc.
 433     void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
 434
 435     /// eraseBlock - This is part of the update interface to inform the cache
 436     /// that a block has been deleted.
 437     void eraseBlock(BasicBlock *BB);
 438
 439     /// clear - Empty the cache.
 440     void clear() {
 441       ValueCache.clear();
 442       OverDefinedCache.clear();
 443     }
 444   };
 445 } // end anonymous namespace
 446
 447 void LVIValueHandle::deleted() {
 448   typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
 449
 450   SmallVector<OverDefinedPairTy, 4> ToErase;
 451   for (DenseSet<OverDefinedPairTy>::iterator
 452        I = Parent->OverDefinedCache.begin(),
 453        E = Parent->OverDefinedCache.end();
 454        I != E; ++I) {
 455     if (I->second == getValPtr())
 456       ToErase.push_back(*I);
 457   }
 458
 459   for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
 460        E = ToErase.end(); I != E; ++I)
 461     Parent->OverDefinedCache.erase(*I);
 462
 463   // This erasure deallocates *this, so it MUST happen after we're done
 464   // using any and all members of *this.
 465   Parent->ValueCache.erase(*this);
 466 }
 467
 468 void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
 469   SmallVector<OverDefinedPairTy, 4> ToErase;
 470   for (DenseSet<OverDefinedPairTy>::iterator  I = OverDefinedCache.begin(),
 471        E = OverDefinedCache.end(); I != E; ++I) {
 472     if (I->first == BB)
 473       ToErase.push_back(*I);
 474   }
 475
 476   for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
 477        E = ToErase.end(); I != E; ++I)
 478     OverDefinedCache.erase(*I);
 479
 480   for (DenseMap<LVIValueHandle, ValueCacheEntryTy>::iterator
 481        I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
 482     I->second.erase(BB);
 483 }
 484
 485 void LazyValueInfoCache::solve() {
 486   while (!BlockValueStack.empty()) {
 487     std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
 488     if (solveBlockValue(e.second, e.first))
 489       BlockValueStack.pop();
 490   }
 491 }
 492
 493 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
 494   // If already a constant, there is nothing to compute.
 495   if (isa<Constant>(Val))
 496     return true;
 497
 498   LVIValueHandle ValHandle(Val, this);
 499   if (!ValueCache.count(ValHandle)) return false;
 500   return ValueCache[ValHandle].count(BB);
 501 }
 502
 503 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
 504   // If already a constant, there is nothing to compute.
 505   if (Constant *VC = dyn_cast<Constant>(Val))
 506     return LVILatticeVal::get(VC);
 507
 508   return lookup(Val)[BB];
 509 }
 510
 511 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
 512   if (isa<Constant>(Val))
 513     return true;
 514
 515   ValueCacheEntryTy &Cache = lookup(Val);
 516   LVILatticeVal &BBLV = Cache[BB];
 517
 518   // OverDefinedCacheUpdater is a helper object that will update
 519   // the OverDefinedCache for us when this method exits.  Make sure to
 520   // call markResult on it as we exist, passing a bool to indicate if the
 521   // cache needs updating, i.e. if we have solve a new value or not.
 522   OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
 523
 524   // If we've already computed this block's value, return it.
 525   if (!BBLV.isUndefined()) {
 526     DEBUG(dbgs() << "  reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
 527
 528     // Since we're reusing a cached value here, we don't need to update the
 529     // OverDefinedCahce.  The cache will have been properly updated
 530     // whenever the cached value was inserted.
 531     ODCacheUpdater.markResult(false);
 532     return true;
 533   }
 534
 535   // Otherwise, this is the first time we're seeing this block.  Reset the
 536   // lattice value to overdefined, so that cycles will terminate and be
 537   // conservatively correct.
 538   BBLV.markOverdefined();
 539
 540   Instruction *BBI = dyn_cast<Instruction>(Val);
 541   if (BBI == 0 || BBI->getParent() != BB) {
 542     return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
 543   }
 544
 545   if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
 546     return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
 547   }
 548
 549   if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
 550     BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
 551     return ODCacheUpdater.markResult(true);
 552   }
 553
 554   // We can only analyze the definitions of certain classes of instructions
 555   // (integral binops and casts at the moment), so bail if this isn't one.
 556   LVILatticeVal Result;
 557   if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
 558      !BBI->getType()->isIntegerTy()) {
 559     DEBUG(dbgs() << " compute BB '" << BB->getName()
 560                  << "' - overdefined because inst def found.\n");
 561     BBLV.markOverdefined();
 562     return ODCacheUpdater.markResult(true);
 563   }
 564
 565   // FIXME: We're currently limited to binops with a constant RHS.  This should
 566   // be improved.
 567   BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
 568   if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
 569     DEBUG(dbgs() << " compute BB '" << BB->getName()
 570                  << "' - overdefined because inst def found.\n");
 571
 572     BBLV.markOverdefined();
 573     return ODCacheUpdater.markResult(true);
 574   }
 575
 576   return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
 577 }
 578
 579 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
 580   if (LoadInst *L = dyn_cast<LoadInst>(I)) {
 581     return L->getPointerAddressSpace() == 0 &&
 582         GetUnderlyingObject(L->getPointerOperand()) ==
 583         GetUnderlyingObject(Ptr);
 584   }
 585   if (StoreInst *S = dyn_cast<StoreInst>(I)) {
 586     return S->getPointerAddressSpace() == 0 &&
 587         GetUnderlyingObject(S->getPointerOperand()) ==
 588         GetUnderlyingObject(Ptr);
 589   }
 590   if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
 591     if (MI->isVolatile()) return false;
 592
 593     // FIXME: check whether it has a valuerange that excludes zero?
 594     ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
 595     if (!Len || Len->isZero()) return false;
 596
 597     if (MI->getDestAddressSpace() == 0)
 598       if (MI->getRawDest() == Ptr || MI->getDest() == Ptr)
 599         return true;
 600     if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
 601       if (MTI->getSourceAddressSpace() == 0)
 602         if (MTI->getRawSource() == Ptr || MTI->getSource() == Ptr)
 603           return true;
 604   }
 605   return false;
 606 }
 607
 608 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
 609                                                  Value *Val, BasicBlock *BB) {
 610   LVILatticeVal Result;  // Start Undefined.
 611
 612   // If this is a pointer, and there's a load from that pointer in this BB,
 613   // then we know that the pointer can't be NULL.
 614   bool NotNull = false;
 615   if (Val->getType()->isPointerTy()) {
 616     if (isa<AllocaInst>(Val)) {
 617       NotNull = true;
 618     } else {
 619       for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){
 620         if (InstructionDereferencesPointer(BI, Val)) {
 621           NotNull = true;
 622           break;
 623         }
 624       }
 625     }
 626   }
 627
 628   // If this is the entry block, we must be asking about an argument.  The
 629   // value is overdefined.
 630   if (BB == &BB->getParent()->getEntryBlock()) {
 631     assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
 632     if (NotNull) {
 633       const PointerType *PTy = cast<PointerType>(Val->getType());
 634       Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
 635     } else {
 636       Result.markOverdefined();
 637     }
 638     BBLV = Result;
 639     return true;
 640   }
 641
 642   // Loop over all of our predecessors, merging what we know from them into
 643   // result.
 644   bool EdgesMissing = false;
 645   for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
 646     LVILatticeVal EdgeResult;
 647     EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
 648     if (EdgesMissing)
 649       continue;
 650
 651     Result.mergeIn(EdgeResult);
 652
 653     // If we hit overdefined, exit early.  The BlockVals entry is already set
 654     // to overdefined.
 655     if (Result.isOverdefined()) {
 656       DEBUG(dbgs() << " compute BB '" << BB->getName()
 657             << "' - overdefined because of pred.\n");
 658       // If we previously determined that this is a pointer that can't be null
 659       // then return that rather than giving up entirely.
 660       if (NotNull) {
 661         const PointerType *PTy = cast<PointerType>(Val->getType());
 662         Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
 663       }
 664
 665       BBLV = Result;
 666       return true;
 667     }
 668   }
 669   if (EdgesMissing)
 670     return false;
 671
 672   // Return the merged value, which is more precise than 'overdefined'.
 673   assert(!Result.isOverdefined());
 674   BBLV = Result;
 675   return true;
 676 }
 677
 678 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
 679                                                 PHINode *PN, BasicBlock *BB) {
 680   LVILatticeVal Result;  // Start Undefined.
 681
 682   // Loop over all of our predecessors, merging what we know from them into
 683   // result.
 684   bool EdgesMissing = false;
 685   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
 686     BasicBlock *PhiBB = PN->getIncomingBlock(i);
 687     Value *PhiVal = PN->getIncomingValue(i);
 688     LVILatticeVal EdgeResult;
 689     EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
 690     if (EdgesMissing)
 691       continue;
 692
 693     Result.mergeIn(EdgeResult);
 694
 695     // If we hit overdefined, exit early.  The BlockVals entry is already set
 696     // to overdefined.
 697     if (Result.isOverdefined()) {
 698       DEBUG(dbgs() << " compute BB '" << BB->getName()
 699             << "' - overdefined because of pred.\n");
 700
 701       BBLV = Result;
 702       return true;
 703     }
 704   }
 705   if (EdgesMissing)
 706     return false;
 707
 708   // Return the merged value, which is more precise than 'overdefined'.
 709   assert(!Result.isOverdefined() && "Possible PHI in entry block?");
 710   BBLV = Result;
 711   return true;
 712 }
 713
 714 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
 715                                                       Instruction *BBI,
 716                                                       BasicBlock *BB) {
 717   // Figure out the range of the LHS.  If that fails, bail.
 718   if (!hasBlockValue(BBI->getOperand(0), BB)) {
 719     BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
 720     return false;
 721   }
 722
 723   LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
 724   if (!LHSVal.isConstantRange()) {
 725     BBLV.markOverdefined();
 726     return true;
 727   }
 728
 729   ConstantRange LHSRange = LHSVal.getConstantRange();
 730   ConstantRange RHSRange(1);
 731   const IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
 732   if (isa<BinaryOperator>(BBI)) {
 733     if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
 734       RHSRange = ConstantRange(RHS->getValue());
 735     } else {
 736       BBLV.markOverdefined();
 737       return true;
 738     }
 739   }
 740
 741   // NOTE: We're currently limited by the set of operations that ConstantRange
 742   // can evaluate symbolically.  Enhancing that set will allows us to analyze
 743   // more definitions.
 744   LVILatticeVal Result;
 745   switch (BBI->getOpcode()) {
 746   case Instruction::Add:
 747     Result.markConstantRange(LHSRange.add(RHSRange));
 748     break;
 749   case Instruction::Sub:
 750     Result.markConstantRange(LHSRange.sub(RHSRange));
 751     break;
 752   case Instruction::Mul:
 753     Result.markConstantRange(LHSRange.multiply(RHSRange));
 754     break;
 755   case Instruction::UDiv:
 756     Result.markConstantRange(LHSRange.udiv(RHSRange));
 757     break;
 758   case Instruction::Shl:
 759     Result.markConstantRange(LHSRange.shl(RHSRange));
 760     break;
 761   case Instruction::LShr:
 762     Result.markConstantRange(LHSRange.lshr(RHSRange));
 763     break;
 764   case Instruction::Trunc:
 765     Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
 766     break;
 767   case Instruction::SExt:
 768     Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
 769     break;
 770   case Instruction::ZExt:
 771     Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
 772     break;
 773   case Instruction::BitCast:
 774     Result.markConstantRange(LHSRange);
 775     break;
 776   case Instruction::And:
 777     Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
 778     break;
 779   case Instruction::Or:
 780     Result.markConstantRange(LHSRange.binaryOr(RHSRange));
 781     break;
 782
 783   // Unhandled instructions are overdefined.
 784   default:
 785     DEBUG(dbgs() << " compute BB '" << BB->getName()
 786                  << "' - overdefined because inst def found.\n");
 787     Result.markOverdefined();
 788     break;
 789   }
 790
 791   BBLV = Result;
 792   return true;
 793 }
 794
 795 /// getEdgeValue - This method attempts to infer more complex
 796 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
 797                                       BasicBlock *BBTo, LVILatticeVal &Result) {
 798   // If already a constant, there is nothing to compute.
 799   if (Constant *VC = dyn_cast<Constant>(Val)) {
 800     Result = LVILatticeVal::get(VC);
 801     return true;
 802   }
 803
 804   // TODO: Handle more complex conditionals.  If (v == 0 || v2 < 1) is false, we
 805   // know that v != 0.
 806   if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
 807     // If this is a conditional branch and only one successor goes to BBTo, then
 808     // we maybe able to infer something from the condition.
 809     if (BI->isConditional() &&
 810         BI->getSuccessor(0) != BI->getSuccessor(1)) {
 811       bool isTrueDest = BI->getSuccessor(0) == BBTo;
 812       assert(BI->getSuccessor(!isTrueDest) == BBTo &&
 813              "BBTo isn't a successor of BBFrom");
 814
 815       // If V is the condition of the branch itself, then we know exactly what
 816       // it is.
 817       if (BI->getCondition() == Val) {
 818         Result = LVILatticeVal::get(ConstantInt::get(
 819                               Type::getInt1Ty(Val->getContext()), isTrueDest));
 820         return true;
 821       }
 822
 823       // If the condition of the branch is an equality comparison, we may be
 824       // able to infer the value.
 825       ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
 826       if (ICI && ICI->getOperand(0) == Val &&
 827           isa<Constant>(ICI->getOperand(1))) {
 828         if (ICI->isEquality()) {
 829           // We know that V has the RHS constant if this is a true SETEQ or
 830           // false SETNE.
 831           if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
 832             Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
 833           else
 834             Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
 835           return true;
 836         }
 837
 838         if (ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
 839           // Calculate the range of values that would satisfy the comparison.
 840           ConstantRange CmpRange(CI->getValue(), CI->getValue()+1);
 841           ConstantRange TrueValues =
 842             ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
 843
 844           // If we're interested in the false dest, invert the condition.
 845           if (!isTrueDest) TrueValues = TrueValues.inverse();
 846
 847           // Figure out the possible values of the query BEFORE this branch.
 848           if (!hasBlockValue(Val, BBFrom)) {
 849             BlockValueStack.push(std::make_pair(BBFrom, Val));
 850             return false;
 851           }
 852
 853           LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
 854           if (!InBlock.isConstantRange()) {
 855             Result = LVILatticeVal::getRange(TrueValues);
 856             return true;
 857           }
 858
 859           // Find all potential values that satisfy both the input and output
 860           // conditions.
 861           ConstantRange PossibleValues =
 862             TrueValues.intersectWith(InBlock.getConstantRange());
 863
 864           Result = LVILatticeVal::getRange(PossibleValues);
 865           return true;
 866         }
 867       }
 868     }
 869   }
 870
 871   // If the edge was formed by a switch on the value, then we may know exactly
 872   // what it is.
 873   if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
 874     if (SI->getCondition() == Val) {
 875       // We don't know anything in the default case.
 876       if (SI->getDefaultDest() == BBTo) {
 877         Result.markOverdefined();
 878         return true;
 879       }
 880
 881       // We only know something if there is exactly one value that goes from
 882       // BBFrom to BBTo.
 883       unsigned NumEdges = 0;
 884       ConstantInt *EdgeVal = 0;
 885       for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
 886         if (SI->getSuccessor(i) != BBTo) continue;
 887         if (NumEdges++) break;
 888         EdgeVal = SI->getCaseValue(i);
 889       }
 890       assert(EdgeVal && "Missing successor?");
 891       if (NumEdges == 1) {
 892         Result = LVILatticeVal::get(EdgeVal);
 893         return true;
 894       }
 895     }
 896   }
 897
 898   // Otherwise see if the value is known in the block.
 899   if (hasBlockValue(Val, BBFrom)) {
 900     Result = getBlockValue(Val, BBFrom);
 901     return true;
 902   }
 903   BlockValueStack.push(std::make_pair(BBFrom, Val));
 904   return false;
 905 }
 906
 907 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
 908   DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
 909         << BB->getName() << "'\n");
 910
 911   BlockValueStack.push(std::make_pair(BB, V));
 912   solve();
 913   LVILatticeVal Result = getBlockValue(V, BB);
 914
 915   DEBUG(dbgs() << "  Result = " << Result << "\n");
 916   return Result;
 917 }
 918
 919 LVILatticeVal LazyValueInfoCache::
 920 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
 921   DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
 922         << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
 923
 924   LVILatticeVal Result;
 925   if (!getEdgeValue(V, FromBB, ToBB, Result)) {
 926     solve();
 927     bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result);
 928     (void)WasFastQuery;
 929     assert(WasFastQuery && "More work to do after problem solved?");
 930   }
 931
 932   DEBUG(dbgs() << "  Result = " << Result << "\n");
 933   return Result;
 934 }
 935
 936 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
 937                                     BasicBlock *NewSucc) {
 938   // When an edge in the graph has been threaded, values that we could not
 939   // determine a value for before (i.e. were marked overdefined) may be possible
 940   // to solve now.  We do NOT try to proactively update these values.  Instead,
 941   // we clear their entries from the cache, and allow lazy updating to recompute
 942   // them when needed.
 943
 944   // The updating process is fairly simple: we need to dropped cached info
 945   // for all values that were marked overdefined in OldSucc, and for those same
 946   // values in any successor of OldSucc (except NewSucc) in which they were
 947   // also marked overdefined.
 948   std::vector<BasicBlock*> worklist;
 949   worklist.push_back(OldSucc);
 950
 951   DenseSet<Value*> ClearSet;
 952   for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
 953        E = OverDefinedCache.end(); I != E; ++I) {
 954     if (I->first == OldSucc)
 955       ClearSet.insert(I->second);
 956   }
 957
 958   // Use a worklist to perform a depth-first search of OldSucc's successors.
 959   // NOTE: We do not need a visited list since any blocks we have already
 960   // visited will have had their overdefined markers cleared already, and we
 961   // thus won't loop to their successors.
 962   while (!worklist.empty()) {
 963     BasicBlock *ToUpdate = worklist.back();
 964     worklist.pop_back();
 965
 966     // Skip blocks only accessible through NewSucc.
 967     if (ToUpdate == NewSucc) continue;
 968
 969     bool changed = false;
 970     for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
 971          I != E; ++I) {
 972       // If a value was marked overdefined in OldSucc, and is here too...
 973       DenseSet<OverDefinedPairTy>::iterator OI =
 974         OverDefinedCache.find(std::make_pair(ToUpdate, *I));
 975       if (OI == OverDefinedCache.end()) continue;
 976
 977       // Remove it from the caches.
 978       ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
 979       ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
 980
 981       assert(CI != Entry.end() && "Couldn't find entry to update?");
 982       Entry.erase(CI);
 983       OverDefinedCache.erase(OI);
 984
 985       // If we removed anything, then we potentially need to update
 986       // blocks successors too.
 987       changed = true;
 988     }
 989
 990     if (!changed) continue;
 991
 992     worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
 993   }
 994 }
 995
 996 //===----------------------------------------------------------------------===//
 997 //                            LazyValueInfo Impl
 998 //===----------------------------------------------------------------------===//
 999
1000 /// getCache - This lazily constructs the LazyValueInfoCache.
1001 static LazyValueInfoCache &getCache(void *&PImpl) {
1002   if (!PImpl)
1003     PImpl = new LazyValueInfoCache();
1004   return *static_cast<LazyValueInfoCache*>(PImpl);
1005 }
1006
1007 bool LazyValueInfo::runOnFunction(Function &F) {
1008   if (PImpl)
1009     getCache(PImpl).clear();
1010
1011   TD = getAnalysisIfAvailable<TargetData>();
1012   // Fully lazy.
1013   return false;
1014 }
1015
1016 void LazyValueInfo::releaseMemory() {
1017   // If the cache was allocated, free it.
1018   if (PImpl) {
1019     delete &getCache(PImpl);
1020     PImpl = 0;
1021   }
1022 }
1023
1024 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
1025   LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
1026
1027   if (Result.isConstant())
1028     return Result.getConstant();
1029   if (Result.isConstantRange()) {
1030     ConstantRange CR = Result.getConstantRange();
1031     if (const APInt *SingleVal = CR.getSingleElement())
1032       return ConstantInt::get(V->getContext(), *SingleVal);
1033   }
1034   return 0;
1035 }
1036
1037 /// getConstantOnEdge - Determine whether the specified value is known to be a
1038 /// constant on the specified edge.  Return null if not.
1039 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
1040                                            BasicBlock *ToBB) {
1041   LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1042
1043   if (Result.isConstant())
1044     return Result.getConstant();
1045   if (Result.isConstantRange()) {
1046     ConstantRange CR = Result.getConstantRange();
1047     if (const APInt *SingleVal = CR.getSingleElement())
1048       return ConstantInt::get(V->getContext(), *SingleVal);
1049   }
1050   return 0;
1051 }
1052
1053 /// getPredicateOnEdge - Determine whether the specified value comparison
1054 /// with a constant is known to be true or false on the specified CFG edge.
1055 /// Pred is a CmpInst predicate.
1056 LazyValueInfo::Tristate
1057 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
1058                                   BasicBlock *FromBB, BasicBlock *ToBB) {
1059   LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1060
1061   // If we know the value is a constant, evaluate the conditional.
1062   Constant *Res = 0;
1063   if (Result.isConstant()) {
1064     Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
1065     if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
1066       return ResCI->isZero() ? False : True;
1067     return Unknown;
1068   }
1069
1070   if (Result.isConstantRange()) {
1071     ConstantInt *CI = dyn_cast<ConstantInt>(C);
1072     if (!CI) return Unknown;
1073
1074     ConstantRange CR = Result.getConstantRange();
1075     if (Pred == ICmpInst::ICMP_EQ) {
1076       if (!CR.contains(CI->getValue()))
1077         return False;
1078
1079       if (CR.isSingleElement() && CR.contains(CI->getValue()))
1080         return True;
1081     } else if (Pred == ICmpInst::ICMP_NE) {
1082       if (!CR.contains(CI->getValue()))
1083         return True;
1084
1085       if (CR.isSingleElement() && CR.contains(CI->getValue()))
1086         return False;
1087     }
1088
1089     // Handle more complex predicates.
1090     ConstantRange TrueValues =
1091         ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
1092     if (TrueValues.contains(CR))
1093       return True;
1094     if (TrueValues.inverse().contains(CR))
1095       return False;
1096     return Unknown;
1097   }
1098
1099   if (Result.isNotConstant()) {
1100     // If this is an equality comparison, we can try to fold it knowing that
1101     // "V != C1".
1102     if (Pred == ICmpInst::ICMP_EQ) {
1103       // !C1 == C -> false iff C1 == C.
1104       Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1105                                             Result.getNotConstant(), C, TD);
1106       if (Res->isNullValue())
1107         return False;
1108     } else if (Pred == ICmpInst::ICMP_NE) {
1109       // !C1 != C -> true iff C1 == C.
1110       Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1111                                             Result.getNotConstant(), C, TD);
1112       if (Res->isNullValue())
1113         return True;
1114     }
1115     return Unknown;
1116   }
1117
1118   return Unknown;
1119 }
1120
1121 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1122                                BasicBlock *NewSucc) {
1123   if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
1124 }
1125
1126 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1127   if (PImpl) getCache(PImpl).eraseBlock(BB);
1128 }