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>
33using namespace llvm;
34
35char LazyValueInfo::ID = 0;
36INITIALIZE_PASS(LazyValueInfo, "lazy-value-info",
37                "Lazy Value Information Analysis", false, true)
38
39namespace 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///
54namespace {
55class 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
79public:
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
269namespace llvm {
270raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
271    LLVM_ATTRIBUTE_USED;
272raw_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
291namespace {
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
308namespace 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
352namespace {
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
447void 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
468void 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
485void 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
493bool 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
503LVILatticeVal 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
511bool 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
579static 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
608bool 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      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        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
678bool 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
714bool 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  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
796bool 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
907LVILatticeVal 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
919LVILatticeVal LazyValueInfoCache::
920getValueOnEdge(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
936void 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.
1001static LazyValueInfoCache &getCache(void *&PImpl) {
1002  if (!PImpl)
1003    PImpl = new LazyValueInfoCache();
1004  return *static_cast<LazyValueInfoCache*>(PImpl);
1005}
1006
1007bool LazyValueInfo::runOnFunction(Function &F) {
1008  if (PImpl)
1009    getCache(PImpl).clear();
1010
1011  TD = getAnalysisIfAvailable<TargetData>();
1012  // Fully lazy.
1013  return false;
1014}
1015
1016void LazyValueInfo::releaseMemory() {
1017  // If the cache was allocated, free it.
1018  if (PImpl) {
1019    delete &getCache(PImpl);
1020    PImpl = 0;
1021  }
1022}
1023
1024Constant *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.
1039Constant *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.
1056LazyValueInfo::Tristate
1057LazyValueInfo::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
1121void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1122                               BasicBlock *NewSucc) {
1123  if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
1124}
1125
1126void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1127  if (PImpl) getCache(PImpl).eraseBlock(BB);
1128}
1129