LazyValueInfo.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f 
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#include "llvm/Analysis/LazyValueInfo.h"
16#include "llvm/ADT/DenseSet.h"
17#include "llvm/ADT/STLExtras.h"
18#include "llvm/Analysis/ConstantFolding.h"
19#include "llvm/Analysis/ValueTracking.h"
20#include "llvm/IR/CFG.h"
21#include "llvm/IR/ConstantRange.h"
22#include "llvm/IR/Constants.h"
23#include "llvm/IR/DataLayout.h"
24#include "llvm/IR/Instructions.h"
25#include "llvm/IR/IntrinsicInst.h"
26#include "llvm/IR/PatternMatch.h"
27#include "llvm/IR/ValueHandle.h"
28#include "llvm/Support/Debug.h"
29#include "llvm/Support/raw_ostream.h"
30#include "llvm/Target/TargetLibraryInfo.h"
31#include <map>
32#include <stack>
33using namespace llvm;
34using namespace PatternMatch;
35
36#define DEBUG_TYPE "lazy-value-info"
37
38char LazyValueInfo::ID = 0;
39INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
40                "Lazy Value Information Analysis", false, true)
41INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
42INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
43                "Lazy Value Information Analysis", false, true)
44
45namespace llvm {
46  FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
47}
48
49
50//===----------------------------------------------------------------------===//
51//                               LVILatticeVal
52//===----------------------------------------------------------------------===//
53
54/// LVILatticeVal - This is the information tracked by LazyValueInfo for each
55/// value.
56///
57/// FIXME: This is basically just for bringup, this can be made a lot more rich
58/// in the future.
59///
60namespace {
61class LVILatticeVal {
62  enum LatticeValueTy {
63    /// undefined - This Value has no known value yet.
64    undefined,
65
66    /// constant - This Value has a specific constant value.
67    constant,
68    /// notconstant - This Value is known to not have the specified value.
69    notconstant,
70
71    /// constantrange - The Value falls within this range.
72    constantrange,
73
74    /// overdefined - This value is not known to be constant, and we know that
75    /// it has a value.
76    overdefined
77  };
78
79  /// Val: This stores the current lattice value along with the Constant* for
80  /// the constant if this is a 'constant' or 'notconstant' value.
81  LatticeValueTy Tag;
82  Constant *Val;
83  ConstantRange Range;
84
85public:
86  LVILatticeVal() : Tag(undefined), Val(nullptr), Range(1, true) {}
87
88  static LVILatticeVal get(Constant *C) {
89    LVILatticeVal Res;
90    if (!isa<UndefValue>(C))
91      Res.markConstant(C);
92    return Res;
93  }
94  static LVILatticeVal getNot(Constant *C) {
95    LVILatticeVal Res;
96    if (!isa<UndefValue>(C))
97      Res.markNotConstant(C);
98    return Res;
99  }
100  static LVILatticeVal getRange(ConstantRange CR) {
101    LVILatticeVal Res;
102    Res.markConstantRange(CR);
103    return Res;
104  }
105
106  bool isUndefined() const     { return Tag == undefined; }
107  bool isConstant() const      { return Tag == constant; }
108  bool isNotConstant() const   { return Tag == notconstant; }
109  bool isConstantRange() const { return Tag == constantrange; }
110  bool isOverdefined() const   { return Tag == overdefined; }
111
112  Constant *getConstant() const {
113    assert(isConstant() && "Cannot get the constant of a non-constant!");
114    return Val;
115  }
116
117  Constant *getNotConstant() const {
118    assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
119    return Val;
120  }
121
122  ConstantRange getConstantRange() const {
123    assert(isConstantRange() &&
124           "Cannot get the constant-range of a non-constant-range!");
125    return Range;
126  }
127
128  /// markOverdefined - Return true if this is a change in status.
129  bool markOverdefined() {
130    if (isOverdefined())
131      return false;
132    Tag = overdefined;
133    return true;
134  }
135
136  /// markConstant - Return true if this is a change in status.
137  bool markConstant(Constant *V) {
138    assert(V && "Marking constant with NULL");
139    if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
140      return markConstantRange(ConstantRange(CI->getValue()));
141    if (isa<UndefValue>(V))
142      return false;
143
144    assert((!isConstant() || getConstant() == V) &&
145           "Marking constant with different value");
146    assert(isUndefined());
147    Tag = constant;
148    Val = V;
149    return true;
150  }
151
152  /// markNotConstant - Return true if this is a change in status.
153  bool markNotConstant(Constant *V) {
154    assert(V && "Marking constant with NULL");
155    if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
156      return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
157    if (isa<UndefValue>(V))
158      return false;
159
160    assert((!isConstant() || getConstant() != V) &&
161           "Marking constant !constant with same value");
162    assert((!isNotConstant() || getNotConstant() == V) &&
163           "Marking !constant with different value");
164    assert(isUndefined() || isConstant());
165    Tag = notconstant;
166    Val = V;
167    return true;
168  }
169
170  /// markConstantRange - Return true if this is a change in status.
171  bool markConstantRange(const ConstantRange NewR) {
172    if (isConstantRange()) {
173      if (NewR.isEmptySet())
174        return markOverdefined();
175
176      bool changed = Range != NewR;
177      Range = NewR;
178      return changed;
179    }
180
181    assert(isUndefined());
182    if (NewR.isEmptySet())
183      return markOverdefined();
184
185    Tag = constantrange;
186    Range = NewR;
187    return true;
188  }
189
190  /// mergeIn - Merge the specified lattice value into this one, updating this
191  /// one and returning true if anything changed.
192  bool mergeIn(const LVILatticeVal &RHS) {
193    if (RHS.isUndefined() || isOverdefined()) return false;
194    if (RHS.isOverdefined()) return markOverdefined();
195
196    if (isUndefined()) {
197      Tag = RHS.Tag;
198      Val = RHS.Val;
199      Range = RHS.Range;
200      return true;
201    }
202
203    if (isConstant()) {
204      if (RHS.isConstant()) {
205        if (Val == RHS.Val)
206          return false;
207        return markOverdefined();
208      }
209
210      if (RHS.isNotConstant()) {
211        if (Val == RHS.Val)
212          return markOverdefined();
213
214        // Unless we can prove that the two Constants are different, we must
215        // move to overdefined.
216        // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
217        if (ConstantInt *Res = dyn_cast<ConstantInt>(
218                ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
219                                                getConstant(),
220                                                RHS.getNotConstant())))
221          if (Res->isOne())
222            return markNotConstant(RHS.getNotConstant());
223
224        return markOverdefined();
225      }
226
227      // RHS is a ConstantRange, LHS is a non-integer Constant.
228
229      // FIXME: consider the case where RHS is a range [1, 0) and LHS is
230      // a function. The correct result is to pick up RHS.
231
232      return markOverdefined();
233    }
234
235    if (isNotConstant()) {
236      if (RHS.isConstant()) {
237        if (Val == RHS.Val)
238          return markOverdefined();
239
240        // Unless we can prove that the two Constants are different, we must
241        // move to overdefined.
242        // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
243        if (ConstantInt *Res = dyn_cast<ConstantInt>(
244                ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
245                                                getNotConstant(),
246                                                RHS.getConstant())))
247          if (Res->isOne())
248            return false;
249
250        return markOverdefined();
251      }
252
253      if (RHS.isNotConstant()) {
254        if (Val == RHS.Val)
255          return false;
256        return markOverdefined();
257      }
258
259      return markOverdefined();
260    }
261
262    assert(isConstantRange() && "New LVILattice type?");
263    if (!RHS.isConstantRange())
264      return markOverdefined();
265
266    ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
267    if (NewR.isFullSet())
268      return markOverdefined();
269    return markConstantRange(NewR);
270  }
271};
272
273} // end anonymous namespace.
274
275namespace llvm {
276raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
277    LLVM_ATTRIBUTE_USED;
278raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
279  if (Val.isUndefined())
280    return OS << "undefined";
281  if (Val.isOverdefined())
282    return OS << "overdefined";
283
284  if (Val.isNotConstant())
285    return OS << "notconstant<" << *Val.getNotConstant() << '>';
286  else if (Val.isConstantRange())
287    return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
288              << Val.getConstantRange().getUpper() << '>';
289  return OS << "constant<" << *Val.getConstant() << '>';
290}
291}
292
293//===----------------------------------------------------------------------===//
294//                          LazyValueInfoCache Decl
295//===----------------------------------------------------------------------===//
296
297namespace {
298  /// LVIValueHandle - A callback value handle updates the cache when
299  /// values are erased.
300  class LazyValueInfoCache;
301  struct LVIValueHandle : public CallbackVH {
302    LazyValueInfoCache *Parent;
303
304    LVIValueHandle(Value *V, LazyValueInfoCache *P)
305      : CallbackVH(V), Parent(P) { }
306
307    void deleted() override;
308    void allUsesReplacedWith(Value *V) override {
309      deleted();
310    }
311  };
312}
313
314namespace {
315  /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
316  /// maintains information about queries across the clients' queries.
317  class LazyValueInfoCache {
318    /// ValueCacheEntryTy - This is all of the cached block information for
319    /// exactly one Value*.  The entries are sorted by the BasicBlock* of the
320    /// entries, allowing us to do a lookup with a binary search.
321    typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
322
323    /// ValueCache - This is all of the cached information for all values,
324    /// mapped from Value* to key information.
325    std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
326
327    /// OverDefinedCache - This tracks, on a per-block basis, the set of
328    /// values that are over-defined at the end of that block.  This is required
329    /// for cache updating.
330    typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
331    DenseSet<OverDefinedPairTy> OverDefinedCache;
332
333    /// SeenBlocks - Keep track of all blocks that we have ever seen, so we
334    /// don't spend time removing unused blocks from our caches.
335    DenseSet<AssertingVH<BasicBlock> > SeenBlocks;
336
337    /// BlockValueStack - This stack holds the state of the value solver
338    /// during a query.  It basically emulates the callstack of the naive
339    /// recursive value lookup process.
340    std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
341
342    friend struct LVIValueHandle;
343
344    /// OverDefinedCacheUpdater - A helper object that ensures that the
345    /// OverDefinedCache is updated whenever solveBlockValue returns.
346    struct OverDefinedCacheUpdater {
347      LazyValueInfoCache *Parent;
348      Value *Val;
349      BasicBlock *BB;
350      LVILatticeVal &BBLV;
351
352      OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
353                       LazyValueInfoCache *P)
354        : Parent(P), Val(V), BB(B), BBLV(LV) { }
355
356      bool markResult(bool changed) {
357        if (changed && BBLV.isOverdefined())
358          Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
359        return changed;
360      }
361    };
362
363
364
365    LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
366    bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
367                      LVILatticeVal &Result);
368    bool hasBlockValue(Value *Val, BasicBlock *BB);
369
370    // These methods process one work item and may add more. A false value
371    // returned means that the work item was not completely processed and must
372    // be revisited after going through the new items.
373    bool solveBlockValue(Value *Val, BasicBlock *BB);
374    bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
375                                 Value *Val, BasicBlock *BB);
376    bool solveBlockValuePHINode(LVILatticeVal &BBLV,
377                                PHINode *PN, BasicBlock *BB);
378    bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
379                                      Instruction *BBI, BasicBlock *BB);
380
381    void solve();
382
383    ValueCacheEntryTy &lookup(Value *V) {
384      return ValueCache[LVIValueHandle(V, this)];
385    }
386
387  public:
388    /// getValueInBlock - This is the query interface to determine the lattice
389    /// value for the specified Value* at the end of the specified block.
390    LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
391
392    /// getValueOnEdge - This is the query interface to determine the lattice
393    /// value for the specified Value* that is true on the specified edge.
394    LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
395
396    /// threadEdge - This is the update interface to inform the cache that an
397    /// edge from PredBB to OldSucc has been threaded to be from PredBB to
398    /// NewSucc.
399    void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
400
401    /// eraseBlock - This is part of the update interface to inform the cache
402    /// that a block has been deleted.
403    void eraseBlock(BasicBlock *BB);
404
405    /// clear - Empty the cache.
406    void clear() {
407      SeenBlocks.clear();
408      ValueCache.clear();
409      OverDefinedCache.clear();
410    }
411  };
412} // end anonymous namespace
413
414void LVIValueHandle::deleted() {
415  typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
416
417  SmallVector<OverDefinedPairTy, 4> ToErase;
418  for (DenseSet<OverDefinedPairTy>::iterator
419       I = Parent->OverDefinedCache.begin(),
420       E = Parent->OverDefinedCache.end();
421       I != E; ++I) {
422    if (I->second == getValPtr())
423      ToErase.push_back(*I);
424  }
425
426  for (SmallVectorImpl<OverDefinedPairTy>::iterator I = ToErase.begin(),
427       E = ToErase.end(); I != E; ++I)
428    Parent->OverDefinedCache.erase(*I);
429
430  // This erasure deallocates *this, so it MUST happen after we're done
431  // using any and all members of *this.
432  Parent->ValueCache.erase(*this);
433}
434
435void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
436  // Shortcut if we have never seen this block.
437  DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
438  if (I == SeenBlocks.end())
439    return;
440  SeenBlocks.erase(I);
441
442  SmallVector<OverDefinedPairTy, 4> ToErase;
443  for (DenseSet<OverDefinedPairTy>::iterator  I = OverDefinedCache.begin(),
444       E = OverDefinedCache.end(); I != E; ++I) {
445    if (I->first == BB)
446      ToErase.push_back(*I);
447  }
448
449  for (SmallVectorImpl<OverDefinedPairTy>::iterator I = ToErase.begin(),
450       E = ToErase.end(); I != E; ++I)
451    OverDefinedCache.erase(*I);
452
453  for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator
454       I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
455    I->second.erase(BB);
456}
457
458void LazyValueInfoCache::solve() {
459  while (!BlockValueStack.empty()) {
460    std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
461    if (solveBlockValue(e.second, e.first)) {
462      assert(BlockValueStack.top() == e);
463      BlockValueStack.pop();
464    }
465  }
466}
467
468bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
469  // If already a constant, there is nothing to compute.
470  if (isa<Constant>(Val))
471    return true;
472
473  LVIValueHandle ValHandle(Val, this);
474  std::map<LVIValueHandle, ValueCacheEntryTy>::iterator I =
475    ValueCache.find(ValHandle);
476  if (I == ValueCache.end()) return false;
477  return I->second.count(BB);
478}
479
480LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
481  // If already a constant, there is nothing to compute.
482  if (Constant *VC = dyn_cast<Constant>(Val))
483    return LVILatticeVal::get(VC);
484
485  SeenBlocks.insert(BB);
486  return lookup(Val)[BB];
487}
488
489bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
490  if (isa<Constant>(Val))
491    return true;
492
493  ValueCacheEntryTy &Cache = lookup(Val);
494  SeenBlocks.insert(BB);
495  LVILatticeVal &BBLV = Cache[BB];
496
497  // OverDefinedCacheUpdater is a helper object that will update
498  // the OverDefinedCache for us when this method exits.  Make sure to
499  // call markResult on it as we exist, passing a bool to indicate if the
500  // cache needs updating, i.e. if we have solve a new value or not.
501  OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
502
503  // If we've already computed this block's value, return it.
504  if (!BBLV.isUndefined()) {
505    DEBUG(dbgs() << "  reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
506
507    // Since we're reusing a cached value here, we don't need to update the
508    // OverDefinedCahce.  The cache will have been properly updated
509    // whenever the cached value was inserted.
510    ODCacheUpdater.markResult(false);
511    return true;
512  }
513
514  // Otherwise, this is the first time we're seeing this block.  Reset the
515  // lattice value to overdefined, so that cycles will terminate and be
516  // conservatively correct.
517  BBLV.markOverdefined();
518
519  Instruction *BBI = dyn_cast<Instruction>(Val);
520  if (!BBI || BBI->getParent() != BB) {
521    return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
522  }
523
524  if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
525    return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
526  }
527
528  if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
529    BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
530    return ODCacheUpdater.markResult(true);
531  }
532
533  // We can only analyze the definitions of certain classes of instructions
534  // (integral binops and casts at the moment), so bail if this isn't one.
535  LVILatticeVal Result;
536  if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
537     !BBI->getType()->isIntegerTy()) {
538    DEBUG(dbgs() << " compute BB '" << BB->getName()
539                 << "' - overdefined because inst def found.\n");
540    BBLV.markOverdefined();
541    return ODCacheUpdater.markResult(true);
542  }
543
544  // FIXME: We're currently limited to binops with a constant RHS.  This should
545  // be improved.
546  BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
547  if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
548    DEBUG(dbgs() << " compute BB '" << BB->getName()
549                 << "' - overdefined because inst def found.\n");
550
551    BBLV.markOverdefined();
552    return ODCacheUpdater.markResult(true);
553  }
554
555  return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
556}
557
558static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
559  if (LoadInst *L = dyn_cast<LoadInst>(I)) {
560    return L->getPointerAddressSpace() == 0 &&
561        GetUnderlyingObject(L->getPointerOperand()) == Ptr;
562  }
563  if (StoreInst *S = dyn_cast<StoreInst>(I)) {
564    return S->getPointerAddressSpace() == 0 &&
565        GetUnderlyingObject(S->getPointerOperand()) == Ptr;
566  }
567  if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
568    if (MI->isVolatile()) return false;
569
570    // FIXME: check whether it has a valuerange that excludes zero?
571    ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
572    if (!Len || Len->isZero()) return false;
573
574    if (MI->getDestAddressSpace() == 0)
575      if (GetUnderlyingObject(MI->getRawDest()) == Ptr)
576        return true;
577    if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
578      if (MTI->getSourceAddressSpace() == 0)
579        if (GetUnderlyingObject(MTI->getRawSource()) == Ptr)
580          return true;
581  }
582  return false;
583}
584
585bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
586                                                 Value *Val, BasicBlock *BB) {
587  LVILatticeVal Result;  // Start Undefined.
588
589  // If this is a pointer, and there's a load from that pointer in this BB,
590  // then we know that the pointer can't be NULL.
591  bool NotNull = false;
592  if (Val->getType()->isPointerTy()) {
593    if (isKnownNonNull(Val)) {
594      NotNull = true;
595    } else {
596      Value *UnderlyingVal = GetUnderlyingObject(Val);
597      // If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
598      // inside InstructionDereferencesPointer either.
599      if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, nullptr, 1)) {
600        for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
601             BI != BE; ++BI) {
602          if (InstructionDereferencesPointer(BI, UnderlyingVal)) {
603            NotNull = true;
604            break;
605          }
606        }
607      }
608    }
609  }
610
611  // If this is the entry block, we must be asking about an argument.  The
612  // value is overdefined.
613  if (BB == &BB->getParent()->getEntryBlock()) {
614    assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
615    if (NotNull) {
616      PointerType *PTy = cast<PointerType>(Val->getType());
617      Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
618    } else {
619      Result.markOverdefined();
620    }
621    BBLV = Result;
622    return true;
623  }
624
625  // Loop over all of our predecessors, merging what we know from them into
626  // result.
627  bool EdgesMissing = false;
628  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
629    LVILatticeVal EdgeResult;
630    EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
631    if (EdgesMissing)
632      continue;
633
634    Result.mergeIn(EdgeResult);
635
636    // If we hit overdefined, exit early.  The BlockVals entry is already set
637    // to overdefined.
638    if (Result.isOverdefined()) {
639      DEBUG(dbgs() << " compute BB '" << BB->getName()
640            << "' - overdefined because of pred.\n");
641      // If we previously determined that this is a pointer that can't be null
642      // then return that rather than giving up entirely.
643      if (NotNull) {
644        PointerType *PTy = cast<PointerType>(Val->getType());
645        Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
646      }
647
648      BBLV = Result;
649      return true;
650    }
651  }
652  if (EdgesMissing)
653    return false;
654
655  // Return the merged value, which is more precise than 'overdefined'.
656  assert(!Result.isOverdefined());
657  BBLV = Result;
658  return true;
659}
660
661bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
662                                                PHINode *PN, BasicBlock *BB) {
663  LVILatticeVal Result;  // Start Undefined.
664
665  // Loop over all of our predecessors, merging what we know from them into
666  // result.
667  bool EdgesMissing = false;
668  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
669    BasicBlock *PhiBB = PN->getIncomingBlock(i);
670    Value *PhiVal = PN->getIncomingValue(i);
671    LVILatticeVal EdgeResult;
672    EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
673    if (EdgesMissing)
674      continue;
675
676    Result.mergeIn(EdgeResult);
677
678    // If we hit overdefined, exit early.  The BlockVals entry is already set
679    // to overdefined.
680    if (Result.isOverdefined()) {
681      DEBUG(dbgs() << " compute BB '" << BB->getName()
682            << "' - overdefined because of pred.\n");
683
684      BBLV = Result;
685      return true;
686    }
687  }
688  if (EdgesMissing)
689    return false;
690
691  // Return the merged value, which is more precise than 'overdefined'.
692  assert(!Result.isOverdefined() && "Possible PHI in entry block?");
693  BBLV = Result;
694  return true;
695}
696
697bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
698                                                      Instruction *BBI,
699                                                      BasicBlock *BB) {
700  // Figure out the range of the LHS.  If that fails, bail.
701  if (!hasBlockValue(BBI->getOperand(0), BB)) {
702    BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
703    return false;
704  }
705
706  LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
707  if (!LHSVal.isConstantRange()) {
708    BBLV.markOverdefined();
709    return true;
710  }
711
712  ConstantRange LHSRange = LHSVal.getConstantRange();
713  ConstantRange RHSRange(1);
714  IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
715  if (isa<BinaryOperator>(BBI)) {
716    if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
717      RHSRange = ConstantRange(RHS->getValue());
718    } else {
719      BBLV.markOverdefined();
720      return true;
721    }
722  }
723
724  // NOTE: We're currently limited by the set of operations that ConstantRange
725  // can evaluate symbolically.  Enhancing that set will allows us to analyze
726  // more definitions.
727  LVILatticeVal Result;
728  switch (BBI->getOpcode()) {
729  case Instruction::Add:
730    Result.markConstantRange(LHSRange.add(RHSRange));
731    break;
732  case Instruction::Sub:
733    Result.markConstantRange(LHSRange.sub(RHSRange));
734    break;
735  case Instruction::Mul:
736    Result.markConstantRange(LHSRange.multiply(RHSRange));
737    break;
738  case Instruction::UDiv:
739    Result.markConstantRange(LHSRange.udiv(RHSRange));
740    break;
741  case Instruction::Shl:
742    Result.markConstantRange(LHSRange.shl(RHSRange));
743    break;
744  case Instruction::LShr:
745    Result.markConstantRange(LHSRange.lshr(RHSRange));
746    break;
747  case Instruction::Trunc:
748    Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
749    break;
750  case Instruction::SExt:
751    Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
752    break;
753  case Instruction::ZExt:
754    Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
755    break;
756  case Instruction::BitCast:
757    Result.markConstantRange(LHSRange);
758    break;
759  case Instruction::And:
760    Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
761    break;
762  case Instruction::Or:
763    Result.markConstantRange(LHSRange.binaryOr(RHSRange));
764    break;
765
766  // Unhandled instructions are overdefined.
767  default:
768    DEBUG(dbgs() << " compute BB '" << BB->getName()
769                 << "' - overdefined because inst def found.\n");
770    Result.markOverdefined();
771    break;
772  }
773
774  BBLV = Result;
775  return true;
776}
777
778/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
779/// Val is not constrained on the edge.
780static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
781                              BasicBlock *BBTo, LVILatticeVal &Result) {
782  // TODO: Handle more complex conditionals.  If (v == 0 || v2 < 1) is false, we
783  // know that v != 0.
784  if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
785    // If this is a conditional branch and only one successor goes to BBTo, then
786    // we maybe able to infer something from the condition.
787    if (BI->isConditional() &&
788        BI->getSuccessor(0) != BI->getSuccessor(1)) {
789      bool isTrueDest = BI->getSuccessor(0) == BBTo;
790      assert(BI->getSuccessor(!isTrueDest) == BBTo &&
791             "BBTo isn't a successor of BBFrom");
792
793      // If V is the condition of the branch itself, then we know exactly what
794      // it is.
795      if (BI->getCondition() == Val) {
796        Result = LVILatticeVal::get(ConstantInt::get(
797                              Type::getInt1Ty(Val->getContext()), isTrueDest));
798        return true;
799      }
800
801      // If the condition of the branch is an equality comparison, we may be
802      // able to infer the value.
803      ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
804      if (ICI && isa<Constant>(ICI->getOperand(1))) {
805        if (ICI->isEquality() && ICI->getOperand(0) == Val) {
806          // We know that V has the RHS constant if this is a true SETEQ or
807          // false SETNE.
808          if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
809            Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
810          else
811            Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
812          return true;
813        }
814
815        // Recognize the range checking idiom that InstCombine produces.
816        // (X-C1) u< C2 --> [C1, C1+C2)
817        ConstantInt *NegOffset = nullptr;
818        if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
819          match(ICI->getOperand(0), m_Add(m_Specific(Val),
820                                          m_ConstantInt(NegOffset)));
821
822        ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
823        if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
824          // Calculate the range of values that would satisfy the comparison.
825          ConstantRange CmpRange(CI->getValue());
826          ConstantRange TrueValues =
827            ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
828
829          if (NegOffset) // Apply the offset from above.
830            TrueValues = TrueValues.subtract(NegOffset->getValue());
831
832          // If we're interested in the false dest, invert the condition.
833          if (!isTrueDest) TrueValues = TrueValues.inverse();
834
835          Result = LVILatticeVal::getRange(TrueValues);
836          return true;
837        }
838      }
839    }
840  }
841
842  // If the edge was formed by a switch on the value, then we may know exactly
843  // what it is.
844  if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
845    if (SI->getCondition() != Val)
846      return false;
847
848    bool DefaultCase = SI->getDefaultDest() == BBTo;
849    unsigned BitWidth = Val->getType()->getIntegerBitWidth();
850    ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
851
852    for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
853         i != e; ++i) {
854      ConstantRange EdgeVal(i.getCaseValue()->getValue());
855      if (DefaultCase) {
856        // It is possible that the default destination is the destination of
857        // some cases. There is no need to perform difference for those cases.
858        if (i.getCaseSuccessor() != BBTo)
859          EdgesVals = EdgesVals.difference(EdgeVal);
860      } else if (i.getCaseSuccessor() == BBTo)
861        EdgesVals = EdgesVals.unionWith(EdgeVal);
862    }
863    Result = LVILatticeVal::getRange(EdgesVals);
864    return true;
865  }
866  return false;
867}
868
869/// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
870/// the basic block if the edge does not constraint Val.
871bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
872                                      BasicBlock *BBTo, LVILatticeVal &Result) {
873  // If already a constant, there is nothing to compute.
874  if (Constant *VC = dyn_cast<Constant>(Val)) {
875    Result = LVILatticeVal::get(VC);
876    return true;
877  }
878
879  if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
880    if (!Result.isConstantRange() ||
881      Result.getConstantRange().getSingleElement())
882      return true;
883
884    // FIXME: this check should be moved to the beginning of the function when
885    // LVI better supports recursive values. Even for the single value case, we
886    // can intersect to detect dead code (an empty range).
887    if (!hasBlockValue(Val, BBFrom)) {
888      BlockValueStack.push(std::make_pair(BBFrom, Val));
889      return false;
890    }
891
892    // Try to intersect ranges of the BB and the constraint on the edge.
893    LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
894    if (!InBlock.isConstantRange())
895      return true;
896
897    ConstantRange Range =
898      Result.getConstantRange().intersectWith(InBlock.getConstantRange());
899    Result = LVILatticeVal::getRange(Range);
900    return true;
901  }
902
903  if (!hasBlockValue(Val, BBFrom)) {
904    BlockValueStack.push(std::make_pair(BBFrom, Val));
905    return false;
906  }
907
908  // if we couldn't compute the value on the edge, use the value from the BB
909  Result = getBlockValue(Val, BBFrom);
910  return true;
911}
912
913LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
914  DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
915        << BB->getName() << "'\n");
916
917  BlockValueStack.push(std::make_pair(BB, V));
918  solve();
919  LVILatticeVal Result = getBlockValue(V, BB);
920
921  DEBUG(dbgs() << "  Result = " << Result << "\n");
922  return Result;
923}
924
925LVILatticeVal LazyValueInfoCache::
926getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
927  DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
928        << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
929
930  LVILatticeVal Result;
931  if (!getEdgeValue(V, FromBB, ToBB, Result)) {
932    solve();
933    bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result);
934    (void)WasFastQuery;
935    assert(WasFastQuery && "More work to do after problem solved?");
936  }
937
938  DEBUG(dbgs() << "  Result = " << Result << "\n");
939  return Result;
940}
941
942void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
943                                    BasicBlock *NewSucc) {
944  // When an edge in the graph has been threaded, values that we could not
945  // determine a value for before (i.e. were marked overdefined) may be possible
946  // to solve now.  We do NOT try to proactively update these values.  Instead,
947  // we clear their entries from the cache, and allow lazy updating to recompute
948  // them when needed.
949
950  // The updating process is fairly simple: we need to dropped cached info
951  // for all values that were marked overdefined in OldSucc, and for those same
952  // values in any successor of OldSucc (except NewSucc) in which they were
953  // also marked overdefined.
954  std::vector<BasicBlock*> worklist;
955  worklist.push_back(OldSucc);
956
957  DenseSet<Value*> ClearSet;
958  for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
959       E = OverDefinedCache.end(); I != E; ++I) {
960    if (I->first == OldSucc)
961      ClearSet.insert(I->second);
962  }
963
964  // Use a worklist to perform a depth-first search of OldSucc's successors.
965  // NOTE: We do not need a visited list since any blocks we have already
966  // visited will have had their overdefined markers cleared already, and we
967  // thus won't loop to their successors.
968  while (!worklist.empty()) {
969    BasicBlock *ToUpdate = worklist.back();
970    worklist.pop_back();
971
972    // Skip blocks only accessible through NewSucc.
973    if (ToUpdate == NewSucc) continue;
974
975    bool changed = false;
976    for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
977         I != E; ++I) {
978      // If a value was marked overdefined in OldSucc, and is here too...
979      DenseSet<OverDefinedPairTy>::iterator OI =
980        OverDefinedCache.find(std::make_pair(ToUpdate, *I));
981      if (OI == OverDefinedCache.end()) continue;
982
983      // Remove it from the caches.
984      ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
985      ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
986
987      assert(CI != Entry.end() && "Couldn't find entry to update?");
988      Entry.erase(CI);
989      OverDefinedCache.erase(OI);
990
991      // If we removed anything, then we potentially need to update
992      // blocks successors too.
993      changed = true;
994    }
995
996    if (!changed) continue;
997
998    worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
999  }
1000}
1001
1002//===----------------------------------------------------------------------===//
1003//                            LazyValueInfo Impl
1004//===----------------------------------------------------------------------===//
1005
1006/// getCache - This lazily constructs the LazyValueInfoCache.
1007static LazyValueInfoCache &getCache(void *&PImpl) {
1008  if (!PImpl)
1009    PImpl = new LazyValueInfoCache();
1010  return *static_cast<LazyValueInfoCache*>(PImpl);
1011}
1012
1013bool LazyValueInfo::runOnFunction(Function &F) {
1014  if (PImpl)
1015    getCache(PImpl).clear();
1016
1017  DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
1018  DL = DLP ? &DLP->getDataLayout() : nullptr;
1019  TLI = &getAnalysis<TargetLibraryInfo>();
1020
1021  // Fully lazy.
1022  return false;
1023}
1024
1025void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
1026  AU.setPreservesAll();
1027  AU.addRequired<TargetLibraryInfo>();
1028}
1029
1030void LazyValueInfo::releaseMemory() {
1031  // If the cache was allocated, free it.
1032  if (PImpl) {
1033    delete &getCache(PImpl);
1034    PImpl = nullptr;
1035  }
1036}
1037
1038Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
1039  LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
1040
1041  if (Result.isConstant())
1042    return Result.getConstant();
1043  if (Result.isConstantRange()) {
1044    ConstantRange CR = Result.getConstantRange();
1045    if (const APInt *SingleVal = CR.getSingleElement())
1046      return ConstantInt::get(V->getContext(), *SingleVal);
1047  }
1048  return nullptr;
1049}
1050
1051/// getConstantOnEdge - Determine whether the specified value is known to be a
1052/// constant on the specified edge.  Return null if not.
1053Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
1054                                           BasicBlock *ToBB) {
1055  LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1056
1057  if (Result.isConstant())
1058    return Result.getConstant();
1059  if (Result.isConstantRange()) {
1060    ConstantRange CR = Result.getConstantRange();
1061    if (const APInt *SingleVal = CR.getSingleElement())
1062      return ConstantInt::get(V->getContext(), *SingleVal);
1063  }
1064  return nullptr;
1065}
1066
1067/// getPredicateOnEdge - Determine whether the specified value comparison
1068/// with a constant is known to be true or false on the specified CFG edge.
1069/// Pred is a CmpInst predicate.
1070LazyValueInfo::Tristate
1071LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
1072                                  BasicBlock *FromBB, BasicBlock *ToBB) {
1073  LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1074
1075  // If we know the value is a constant, evaluate the conditional.
1076  Constant *Res = nullptr;
1077  if (Result.isConstant()) {
1078    Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, DL,
1079                                          TLI);
1080    if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
1081      return ResCI->isZero() ? False : True;
1082    return Unknown;
1083  }
1084
1085  if (Result.isConstantRange()) {
1086    ConstantInt *CI = dyn_cast<ConstantInt>(C);
1087    if (!CI) return Unknown;
1088
1089    ConstantRange CR = Result.getConstantRange();
1090    if (Pred == ICmpInst::ICMP_EQ) {
1091      if (!CR.contains(CI->getValue()))
1092        return False;
1093
1094      if (CR.isSingleElement() && CR.contains(CI->getValue()))
1095        return True;
1096    } else if (Pred == ICmpInst::ICMP_NE) {
1097      if (!CR.contains(CI->getValue()))
1098        return True;
1099
1100      if (CR.isSingleElement() && CR.contains(CI->getValue()))
1101        return False;
1102    }
1103
1104    // Handle more complex predicates.
1105    ConstantRange TrueValues =
1106        ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
1107    if (TrueValues.contains(CR))
1108      return True;
1109    if (TrueValues.inverse().contains(CR))
1110      return False;
1111    return Unknown;
1112  }
1113
1114  if (Result.isNotConstant()) {
1115    // If this is an equality comparison, we can try to fold it knowing that
1116    // "V != C1".
1117    if (Pred == ICmpInst::ICMP_EQ) {
1118      // !C1 == C -> false iff C1 == C.
1119      Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1120                                            Result.getNotConstant(), C, DL,
1121                                            TLI);
1122      if (Res->isNullValue())
1123        return False;
1124    } else if (Pred == ICmpInst::ICMP_NE) {
1125      // !C1 != C -> true iff C1 == C.
1126      Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1127                                            Result.getNotConstant(), C, DL,
1128                                            TLI);
1129      if (Res->isNullValue())
1130        return True;
1131    }
1132    return Unknown;
1133  }
1134
1135  return Unknown;
1136}
1137
1138void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1139                               BasicBlock *NewSucc) {
1140  if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
1141}
1142
1143void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1144  if (PImpl) getCache(PImpl).eraseBlock(BB);
1145}
1146