LLVM API Documentation

LazyValueInfo.cpp
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00001 //===- LazyValueInfo.cpp - Value constraint analysis ----------------------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This file defines the interface for lazy computation of value constraint
00011 // information.
00012 //
00013 //===----------------------------------------------------------------------===//
00014 
00015 #define DEBUG_TYPE "lazy-value-info"
00016 #include "llvm/Analysis/LazyValueInfo.h"
00017 #include "llvm/ADT/DenseSet.h"
00018 #include "llvm/ADT/STLExtras.h"
00019 #include "llvm/Analysis/ConstantFolding.h"
00020 #include "llvm/Analysis/ValueTracking.h"
00021 #include "llvm/IR/CFG.h"
00022 #include "llvm/IR/ConstantRange.h"
00023 #include "llvm/IR/Constants.h"
00024 #include "llvm/IR/DataLayout.h"
00025 #include "llvm/IR/Instructions.h"
00026 #include "llvm/IR/IntrinsicInst.h"
00027 #include "llvm/IR/PatternMatch.h"
00028 #include "llvm/IR/ValueHandle.h"
00029 #include "llvm/Support/Debug.h"
00030 #include "llvm/Support/raw_ostream.h"
00031 #include "llvm/Target/TargetLibraryInfo.h"
00032 #include <map>
00033 #include <stack>
00034 using namespace llvm;
00035 using namespace PatternMatch;
00036 
00037 char LazyValueInfo::ID = 0;
00038 INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
00039                 "Lazy Value Information Analysis", false, true)
00040 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
00041 INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
00042                 "Lazy Value Information Analysis", false, true)
00043 
00044 namespace llvm {
00045   FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
00046 }
00047 
00048 
00049 //===----------------------------------------------------------------------===//
00050 //                               LVILatticeVal
00051 //===----------------------------------------------------------------------===//
00052 
00053 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
00054 /// value.
00055 ///
00056 /// FIXME: This is basically just for bringup, this can be made a lot more rich
00057 /// in the future.
00058 ///
00059 namespace {
00060 class LVILatticeVal {
00061   enum LatticeValueTy {
00062     /// undefined - This Value has no known value yet.
00063     undefined,
00064     
00065     /// constant - This Value has a specific constant value.
00066     constant,
00067     /// notconstant - This Value is known to not have the specified value.
00068     notconstant,
00069 
00070     /// constantrange - The Value falls within this range.
00071     constantrange,
00072 
00073     /// overdefined - This value is not known to be constant, and we know that
00074     /// it has a value.
00075     overdefined
00076   };
00077   
00078   /// Val: This stores the current lattice value along with the Constant* for
00079   /// the constant if this is a 'constant' or 'notconstant' value.
00080   LatticeValueTy Tag;
00081   Constant *Val;
00082   ConstantRange Range;
00083   
00084 public:
00085   LVILatticeVal() : Tag(undefined), Val(nullptr), Range(1, true) {}
00086 
00087   static LVILatticeVal get(Constant *C) {
00088     LVILatticeVal Res;
00089     if (!isa<UndefValue>(C))
00090       Res.markConstant(C);
00091     return Res;
00092   }
00093   static LVILatticeVal getNot(Constant *C) {
00094     LVILatticeVal Res;
00095     if (!isa<UndefValue>(C))
00096       Res.markNotConstant(C);
00097     return Res;
00098   }
00099   static LVILatticeVal getRange(ConstantRange CR) {
00100     LVILatticeVal Res;
00101     Res.markConstantRange(CR);
00102     return Res;
00103   }
00104   
00105   bool isUndefined() const     { return Tag == undefined; }
00106   bool isConstant() const      { return Tag == constant; }
00107   bool isNotConstant() const   { return Tag == notconstant; }
00108   bool isConstantRange() const { return Tag == constantrange; }
00109   bool isOverdefined() const   { return Tag == overdefined; }
00110   
00111   Constant *getConstant() const {
00112     assert(isConstant() && "Cannot get the constant of a non-constant!");
00113     return Val;
00114   }
00115   
00116   Constant *getNotConstant() const {
00117     assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
00118     return Val;
00119   }
00120   
00121   ConstantRange getConstantRange() const {
00122     assert(isConstantRange() &&
00123            "Cannot get the constant-range of a non-constant-range!");
00124     return Range;
00125   }
00126   
00127   /// markOverdefined - Return true if this is a change in status.
00128   bool markOverdefined() {
00129     if (isOverdefined())
00130       return false;
00131     Tag = overdefined;
00132     return true;
00133   }
00134 
00135   /// markConstant - Return true if this is a change in status.
00136   bool markConstant(Constant *V) {
00137     assert(V && "Marking constant with NULL");
00138     if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
00139       return markConstantRange(ConstantRange(CI->getValue()));
00140     if (isa<UndefValue>(V))
00141       return false;
00142 
00143     assert((!isConstant() || getConstant() == V) &&
00144            "Marking constant with different value");
00145     assert(isUndefined());
00146     Tag = constant;
00147     Val = V;
00148     return true;
00149   }
00150   
00151   /// markNotConstant - Return true if this is a change in status.
00152   bool markNotConstant(Constant *V) {
00153     assert(V && "Marking constant with NULL");
00154     if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
00155       return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
00156     if (isa<UndefValue>(V))
00157       return false;
00158 
00159     assert((!isConstant() || getConstant() != V) &&
00160            "Marking constant !constant with same value");
00161     assert((!isNotConstant() || getNotConstant() == V) &&
00162            "Marking !constant with different value");
00163     assert(isUndefined() || isConstant());
00164     Tag = notconstant;
00165     Val = V;
00166     return true;
00167   }
00168   
00169   /// markConstantRange - Return true if this is a change in status.
00170   bool markConstantRange(const ConstantRange NewR) {
00171     if (isConstantRange()) {
00172       if (NewR.isEmptySet())
00173         return markOverdefined();
00174       
00175       bool changed = Range != NewR;
00176       Range = NewR;
00177       return changed;
00178     }
00179     
00180     assert(isUndefined());
00181     if (NewR.isEmptySet())
00182       return markOverdefined();
00183     
00184     Tag = constantrange;
00185     Range = NewR;
00186     return true;
00187   }
00188   
00189   /// mergeIn - Merge the specified lattice value into this one, updating this
00190   /// one and returning true if anything changed.
00191   bool mergeIn(const LVILatticeVal &RHS) {
00192     if (RHS.isUndefined() || isOverdefined()) return false;
00193     if (RHS.isOverdefined()) return markOverdefined();
00194 
00195     if (isUndefined()) {
00196       Tag = RHS.Tag;
00197       Val = RHS.Val;
00198       Range = RHS.Range;
00199       return true;
00200     }
00201 
00202     if (isConstant()) {
00203       if (RHS.isConstant()) {
00204         if (Val == RHS.Val)
00205           return false;
00206         return markOverdefined();
00207       }
00208 
00209       if (RHS.isNotConstant()) {
00210         if (Val == RHS.Val)
00211           return markOverdefined();
00212 
00213         // Unless we can prove that the two Constants are different, we must
00214         // move to overdefined.
00215         // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
00216         if (ConstantInt *Res = dyn_cast<ConstantInt>(
00217                 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
00218                                                 getConstant(),
00219                                                 RHS.getNotConstant())))
00220           if (Res->isOne())
00221             return markNotConstant(RHS.getNotConstant());
00222 
00223         return markOverdefined();
00224       }
00225 
00226       // RHS is a ConstantRange, LHS is a non-integer Constant.
00227 
00228       // FIXME: consider the case where RHS is a range [1, 0) and LHS is
00229       // a function. The correct result is to pick up RHS.
00230 
00231       return markOverdefined();
00232     }
00233 
00234     if (isNotConstant()) {
00235       if (RHS.isConstant()) {
00236         if (Val == RHS.Val)
00237           return markOverdefined();
00238 
00239         // Unless we can prove that the two Constants are different, we must
00240         // move to overdefined.
00241         // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
00242         if (ConstantInt *Res = dyn_cast<ConstantInt>(
00243                 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
00244                                                 getNotConstant(),
00245                                                 RHS.getConstant())))
00246           if (Res->isOne())
00247             return false;
00248 
00249         return markOverdefined();
00250       }
00251 
00252       if (RHS.isNotConstant()) {
00253         if (Val == RHS.Val)
00254           return false;
00255         return markOverdefined();
00256       }
00257 
00258       return markOverdefined();
00259     }
00260 
00261     assert(isConstantRange() && "New LVILattice type?");
00262     if (!RHS.isConstantRange())
00263       return markOverdefined();
00264 
00265     ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
00266     if (NewR.isFullSet())
00267       return markOverdefined();
00268     return markConstantRange(NewR);
00269   }
00270 };
00271   
00272 } // end anonymous namespace.
00273 
00274 namespace llvm {
00275 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
00276     LLVM_ATTRIBUTE_USED;
00277 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
00278   if (Val.isUndefined())
00279     return OS << "undefined";
00280   if (Val.isOverdefined())
00281     return OS << "overdefined";
00282 
00283   if (Val.isNotConstant())
00284     return OS << "notconstant<" << *Val.getNotConstant() << '>';
00285   else if (Val.isConstantRange())
00286     return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
00287               << Val.getConstantRange().getUpper() << '>';
00288   return OS << "constant<" << *Val.getConstant() << '>';
00289 }
00290 }
00291 
00292 //===----------------------------------------------------------------------===//
00293 //                          LazyValueInfoCache Decl
00294 //===----------------------------------------------------------------------===//
00295 
00296 namespace {
00297   /// LVIValueHandle - A callback value handle updates the cache when
00298   /// values are erased.
00299   class LazyValueInfoCache;
00300   struct LVIValueHandle : public CallbackVH {
00301     LazyValueInfoCache *Parent;
00302       
00303     LVIValueHandle(Value *V, LazyValueInfoCache *P)
00304       : CallbackVH(V), Parent(P) { }
00305 
00306     void deleted() override;
00307     void allUsesReplacedWith(Value *V) override {
00308       deleted();
00309     }
00310   };
00311 }
00312 
00313 namespace { 
00314   /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
00315   /// maintains information about queries across the clients' queries.
00316   class LazyValueInfoCache {
00317     /// ValueCacheEntryTy - This is all of the cached block information for
00318     /// exactly one Value*.  The entries are sorted by the BasicBlock* of the
00319     /// entries, allowing us to do a lookup with a binary search.
00320     typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
00321 
00322     /// ValueCache - This is all of the cached information for all values,
00323     /// mapped from Value* to key information.
00324     std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
00325     
00326     /// OverDefinedCache - This tracks, on a per-block basis, the set of 
00327     /// values that are over-defined at the end of that block.  This is required
00328     /// for cache updating.
00329     typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
00330     DenseSet<OverDefinedPairTy> OverDefinedCache;
00331 
00332     /// SeenBlocks - Keep track of all blocks that we have ever seen, so we
00333     /// don't spend time removing unused blocks from our caches.
00334     DenseSet<AssertingVH<BasicBlock> > SeenBlocks;
00335 
00336     /// BlockValueStack - This stack holds the state of the value solver
00337     /// during a query.  It basically emulates the callstack of the naive
00338     /// recursive value lookup process.
00339     std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
00340     
00341     friend struct LVIValueHandle;
00342     
00343     /// OverDefinedCacheUpdater - A helper object that ensures that the
00344     /// OverDefinedCache is updated whenever solveBlockValue returns.
00345     struct OverDefinedCacheUpdater {
00346       LazyValueInfoCache *Parent;
00347       Value *Val;
00348       BasicBlock *BB;
00349       LVILatticeVal &BBLV;
00350       
00351       OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
00352                        LazyValueInfoCache *P)
00353         : Parent(P), Val(V), BB(B), BBLV(LV) { }
00354       
00355       bool markResult(bool changed) { 
00356         if (changed && BBLV.isOverdefined())
00357           Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
00358         return changed;
00359       }
00360     };
00361     
00362 
00363 
00364     LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
00365     bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
00366                       LVILatticeVal &Result);
00367     bool hasBlockValue(Value *Val, BasicBlock *BB);
00368 
00369     // These methods process one work item and may add more. A false value
00370     // returned means that the work item was not completely processed and must
00371     // be revisited after going through the new items.
00372     bool solveBlockValue(Value *Val, BasicBlock *BB);
00373     bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
00374                                  Value *Val, BasicBlock *BB);
00375     bool solveBlockValuePHINode(LVILatticeVal &BBLV,
00376                                 PHINode *PN, BasicBlock *BB);
00377     bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
00378                                       Instruction *BBI, BasicBlock *BB);
00379 
00380     void solve();
00381     
00382     ValueCacheEntryTy &lookup(Value *V) {
00383       return ValueCache[LVIValueHandle(V, this)];
00384     }
00385 
00386   public:
00387     /// getValueInBlock - This is the query interface to determine the lattice
00388     /// value for the specified Value* at the end of the specified block.
00389     LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
00390 
00391     /// getValueOnEdge - This is the query interface to determine the lattice
00392     /// value for the specified Value* that is true on the specified edge.
00393     LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
00394     
00395     /// threadEdge - This is the update interface to inform the cache that an
00396     /// edge from PredBB to OldSucc has been threaded to be from PredBB to
00397     /// NewSucc.
00398     void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
00399     
00400     /// eraseBlock - This is part of the update interface to inform the cache
00401     /// that a block has been deleted.
00402     void eraseBlock(BasicBlock *BB);
00403     
00404     /// clear - Empty the cache.
00405     void clear() {
00406       SeenBlocks.clear();
00407       ValueCache.clear();
00408       OverDefinedCache.clear();
00409     }
00410   };
00411 } // end anonymous namespace
00412 
00413 void LVIValueHandle::deleted() {
00414   typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
00415   
00416   SmallVector<OverDefinedPairTy, 4> ToErase;
00417   for (DenseSet<OverDefinedPairTy>::iterator 
00418        I = Parent->OverDefinedCache.begin(),
00419        E = Parent->OverDefinedCache.end();
00420        I != E; ++I) {
00421     if (I->second == getValPtr())
00422       ToErase.push_back(*I);
00423   }
00424 
00425   for (SmallVectorImpl<OverDefinedPairTy>::iterator I = ToErase.begin(),
00426        E = ToErase.end(); I != E; ++I)
00427     Parent->OverDefinedCache.erase(*I);
00428   
00429   // This erasure deallocates *this, so it MUST happen after we're done
00430   // using any and all members of *this.
00431   Parent->ValueCache.erase(*this);
00432 }
00433 
00434 void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
00435   // Shortcut if we have never seen this block.
00436   DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
00437   if (I == SeenBlocks.end())
00438     return;
00439   SeenBlocks.erase(I);
00440 
00441   SmallVector<OverDefinedPairTy, 4> ToErase;
00442   for (DenseSet<OverDefinedPairTy>::iterator  I = OverDefinedCache.begin(),
00443        E = OverDefinedCache.end(); I != E; ++I) {
00444     if (I->first == BB)
00445       ToErase.push_back(*I);
00446   }
00447 
00448   for (SmallVectorImpl<OverDefinedPairTy>::iterator I = ToErase.begin(),
00449        E = ToErase.end(); I != E; ++I)
00450     OverDefinedCache.erase(*I);
00451 
00452   for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator
00453        I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
00454     I->second.erase(BB);
00455 }
00456 
00457 void LazyValueInfoCache::solve() {
00458   while (!BlockValueStack.empty()) {
00459     std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
00460     if (solveBlockValue(e.second, e.first)) {
00461       assert(BlockValueStack.top() == e);
00462       BlockValueStack.pop();
00463     }
00464   }
00465 }
00466 
00467 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
00468   // If already a constant, there is nothing to compute.
00469   if (isa<Constant>(Val))
00470     return true;
00471 
00472   LVIValueHandle ValHandle(Val, this);
00473   std::map<LVIValueHandle, ValueCacheEntryTy>::iterator I =
00474     ValueCache.find(ValHandle);
00475   if (I == ValueCache.end()) return false;
00476   return I->second.count(BB);
00477 }
00478 
00479 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
00480   // If already a constant, there is nothing to compute.
00481   if (Constant *VC = dyn_cast<Constant>(Val))
00482     return LVILatticeVal::get(VC);
00483 
00484   SeenBlocks.insert(BB);
00485   return lookup(Val)[BB];
00486 }
00487 
00488 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
00489   if (isa<Constant>(Val))
00490     return true;
00491 
00492   ValueCacheEntryTy &Cache = lookup(Val);
00493   SeenBlocks.insert(BB);
00494   LVILatticeVal &BBLV = Cache[BB];
00495   
00496   // OverDefinedCacheUpdater is a helper object that will update
00497   // the OverDefinedCache for us when this method exits.  Make sure to
00498   // call markResult on it as we exist, passing a bool to indicate if the
00499   // cache needs updating, i.e. if we have solve a new value or not.
00500   OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
00501 
00502   // If we've already computed this block's value, return it.
00503   if (!BBLV.isUndefined()) {
00504     DEBUG(dbgs() << "  reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
00505     
00506     // Since we're reusing a cached value here, we don't need to update the 
00507     // OverDefinedCahce.  The cache will have been properly updated 
00508     // whenever the cached value was inserted.
00509     ODCacheUpdater.markResult(false);
00510     return true;
00511   }
00512 
00513   // Otherwise, this is the first time we're seeing this block.  Reset the
00514   // lattice value to overdefined, so that cycles will terminate and be
00515   // conservatively correct.
00516   BBLV.markOverdefined();
00517   
00518   Instruction *BBI = dyn_cast<Instruction>(Val);
00519   if (!BBI || BBI->getParent() != BB) {
00520     return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
00521   }
00522 
00523   if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
00524     return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
00525   }
00526 
00527   if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
00528     BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
00529     return ODCacheUpdater.markResult(true);
00530   }
00531 
00532   // We can only analyze the definitions of certain classes of instructions
00533   // (integral binops and casts at the moment), so bail if this isn't one.
00534   LVILatticeVal Result;
00535   if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
00536      !BBI->getType()->isIntegerTy()) {
00537     DEBUG(dbgs() << " compute BB '" << BB->getName()
00538                  << "' - overdefined because inst def found.\n");
00539     BBLV.markOverdefined();
00540     return ODCacheUpdater.markResult(true);
00541   }
00542 
00543   // FIXME: We're currently limited to binops with a constant RHS.  This should
00544   // be improved.
00545   BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
00546   if (BO && !isa<ConstantInt>(BO->getOperand(1))) { 
00547     DEBUG(dbgs() << " compute BB '" << BB->getName()
00548                  << "' - overdefined because inst def found.\n");
00549 
00550     BBLV.markOverdefined();
00551     return ODCacheUpdater.markResult(true);
00552   }
00553 
00554   return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
00555 }
00556 
00557 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
00558   if (LoadInst *L = dyn_cast<LoadInst>(I)) {
00559     return L->getPointerAddressSpace() == 0 &&
00560         GetUnderlyingObject(L->getPointerOperand()) == Ptr;
00561   }
00562   if (StoreInst *S = dyn_cast<StoreInst>(I)) {
00563     return S->getPointerAddressSpace() == 0 &&
00564         GetUnderlyingObject(S->getPointerOperand()) == Ptr;
00565   }
00566   if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
00567     if (MI->isVolatile()) return false;
00568 
00569     // FIXME: check whether it has a valuerange that excludes zero?
00570     ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
00571     if (!Len || Len->isZero()) return false;
00572 
00573     if (MI->getDestAddressSpace() == 0)
00574       if (GetUnderlyingObject(MI->getRawDest()) == Ptr)
00575         return true;
00576     if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
00577       if (MTI->getSourceAddressSpace() == 0)
00578         if (GetUnderlyingObject(MTI->getRawSource()) == Ptr)
00579           return true;
00580   }
00581   return false;
00582 }
00583 
00584 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
00585                                                  Value *Val, BasicBlock *BB) {
00586   LVILatticeVal Result;  // Start Undefined.
00587 
00588   // If this is a pointer, and there's a load from that pointer in this BB,
00589   // then we know that the pointer can't be NULL.
00590   bool NotNull = false;
00591   if (Val->getType()->isPointerTy()) {
00592     if (isKnownNonNull(Val)) {
00593       NotNull = true;
00594     } else {
00595       Value *UnderlyingVal = GetUnderlyingObject(Val);
00596       // If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
00597       // inside InstructionDereferencesPointer either.
00598       if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, nullptr, 1)) {
00599         for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
00600              BI != BE; ++BI) {
00601           if (InstructionDereferencesPointer(BI, UnderlyingVal)) {
00602             NotNull = true;
00603             break;
00604           }
00605         }
00606       }
00607     }
00608   }
00609 
00610   // If this is the entry block, we must be asking about an argument.  The
00611   // value is overdefined.
00612   if (BB == &BB->getParent()->getEntryBlock()) {
00613     assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
00614     if (NotNull) {
00615       PointerType *PTy = cast<PointerType>(Val->getType());
00616       Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
00617     } else {
00618       Result.markOverdefined();
00619     }
00620     BBLV = Result;
00621     return true;
00622   }
00623 
00624   // Loop over all of our predecessors, merging what we know from them into
00625   // result.
00626   bool EdgesMissing = false;
00627   for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
00628     LVILatticeVal EdgeResult;
00629     EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
00630     if (EdgesMissing)
00631       continue;
00632 
00633     Result.mergeIn(EdgeResult);
00634 
00635     // If we hit overdefined, exit early.  The BlockVals entry is already set
00636     // to overdefined.
00637     if (Result.isOverdefined()) {
00638       DEBUG(dbgs() << " compute BB '" << BB->getName()
00639             << "' - overdefined because of pred.\n");
00640       // If we previously determined that this is a pointer that can't be null
00641       // then return that rather than giving up entirely.
00642       if (NotNull) {
00643         PointerType *PTy = cast<PointerType>(Val->getType());
00644         Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
00645       }
00646       
00647       BBLV = Result;
00648       return true;
00649     }
00650   }
00651   if (EdgesMissing)
00652     return false;
00653 
00654   // Return the merged value, which is more precise than 'overdefined'.
00655   assert(!Result.isOverdefined());
00656   BBLV = Result;
00657   return true;
00658 }
00659   
00660 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
00661                                                 PHINode *PN, BasicBlock *BB) {
00662   LVILatticeVal Result;  // Start Undefined.
00663 
00664   // Loop over all of our predecessors, merging what we know from them into
00665   // result.
00666   bool EdgesMissing = false;
00667   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
00668     BasicBlock *PhiBB = PN->getIncomingBlock(i);
00669     Value *PhiVal = PN->getIncomingValue(i);
00670     LVILatticeVal EdgeResult;
00671     EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
00672     if (EdgesMissing)
00673       continue;
00674 
00675     Result.mergeIn(EdgeResult);
00676 
00677     // If we hit overdefined, exit early.  The BlockVals entry is already set
00678     // to overdefined.
00679     if (Result.isOverdefined()) {
00680       DEBUG(dbgs() << " compute BB '" << BB->getName()
00681             << "' - overdefined because of pred.\n");
00682       
00683       BBLV = Result;
00684       return true;
00685     }
00686   }
00687   if (EdgesMissing)
00688     return false;
00689 
00690   // Return the merged value, which is more precise than 'overdefined'.
00691   assert(!Result.isOverdefined() && "Possible PHI in entry block?");
00692   BBLV = Result;
00693   return true;
00694 }
00695 
00696 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
00697                                                       Instruction *BBI,
00698                                                       BasicBlock *BB) {
00699   // Figure out the range of the LHS.  If that fails, bail.
00700   if (!hasBlockValue(BBI->getOperand(0), BB)) {
00701     BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
00702     return false;
00703   }
00704 
00705   LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
00706   if (!LHSVal.isConstantRange()) {
00707     BBLV.markOverdefined();
00708     return true;
00709   }
00710   
00711   ConstantRange LHSRange = LHSVal.getConstantRange();
00712   ConstantRange RHSRange(1);
00713   IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
00714   if (isa<BinaryOperator>(BBI)) {
00715     if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
00716       RHSRange = ConstantRange(RHS->getValue());
00717     } else {
00718       BBLV.markOverdefined();
00719       return true;
00720     }
00721   }
00722 
00723   // NOTE: We're currently limited by the set of operations that ConstantRange
00724   // can evaluate symbolically.  Enhancing that set will allows us to analyze
00725   // more definitions.
00726   LVILatticeVal Result;
00727   switch (BBI->getOpcode()) {
00728   case Instruction::Add:
00729     Result.markConstantRange(LHSRange.add(RHSRange));
00730     break;
00731   case Instruction::Sub:
00732     Result.markConstantRange(LHSRange.sub(RHSRange));
00733     break;
00734   case Instruction::Mul:
00735     Result.markConstantRange(LHSRange.multiply(RHSRange));
00736     break;
00737   case Instruction::UDiv:
00738     Result.markConstantRange(LHSRange.udiv(RHSRange));
00739     break;
00740   case Instruction::Shl:
00741     Result.markConstantRange(LHSRange.shl(RHSRange));
00742     break;
00743   case Instruction::LShr:
00744     Result.markConstantRange(LHSRange.lshr(RHSRange));
00745     break;
00746   case Instruction::Trunc:
00747     Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
00748     break;
00749   case Instruction::SExt:
00750     Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
00751     break;
00752   case Instruction::ZExt:
00753     Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
00754     break;
00755   case Instruction::BitCast:
00756     Result.markConstantRange(LHSRange);
00757     break;
00758   case Instruction::And:
00759     Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
00760     break;
00761   case Instruction::Or:
00762     Result.markConstantRange(LHSRange.binaryOr(RHSRange));
00763     break;
00764   
00765   // Unhandled instructions are overdefined.
00766   default:
00767     DEBUG(dbgs() << " compute BB '" << BB->getName()
00768                  << "' - overdefined because inst def found.\n");
00769     Result.markOverdefined();
00770     break;
00771   }
00772   
00773   BBLV = Result;
00774   return true;
00775 }
00776 
00777 /// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
00778 /// Val is not constrained on the edge.
00779 static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
00780                               BasicBlock *BBTo, LVILatticeVal &Result) {
00781   // TODO: Handle more complex conditionals.  If (v == 0 || v2 < 1) is false, we
00782   // know that v != 0.
00783   if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
00784     // If this is a conditional branch and only one successor goes to BBTo, then
00785     // we maybe able to infer something from the condition. 
00786     if (BI->isConditional() &&
00787         BI->getSuccessor(0) != BI->getSuccessor(1)) {
00788       bool isTrueDest = BI->getSuccessor(0) == BBTo;
00789       assert(BI->getSuccessor(!isTrueDest) == BBTo &&
00790              "BBTo isn't a successor of BBFrom");
00791       
00792       // If V is the condition of the branch itself, then we know exactly what
00793       // it is.
00794       if (BI->getCondition() == Val) {
00795         Result = LVILatticeVal::get(ConstantInt::get(
00796                               Type::getInt1Ty(Val->getContext()), isTrueDest));
00797         return true;
00798       }
00799       
00800       // If the condition of the branch is an equality comparison, we may be
00801       // able to infer the value.
00802       ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
00803       if (ICI && isa<Constant>(ICI->getOperand(1))) {
00804         if (ICI->isEquality() && ICI->getOperand(0) == Val) {
00805           // We know that V has the RHS constant if this is a true SETEQ or
00806           // false SETNE. 
00807           if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
00808             Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
00809           else
00810             Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
00811           return true;
00812         }
00813 
00814         // Recognize the range checking idiom that InstCombine produces.
00815         // (X-C1) u< C2 --> [C1, C1+C2)
00816         ConstantInt *NegOffset = nullptr;
00817         if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
00818           match(ICI->getOperand(0), m_Add(m_Specific(Val),
00819                                           m_ConstantInt(NegOffset)));
00820 
00821         ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
00822         if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
00823           // Calculate the range of values that would satisfy the comparison.
00824           ConstantRange CmpRange(CI->getValue());
00825           ConstantRange TrueValues =
00826             ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
00827 
00828           if (NegOffset) // Apply the offset from above.
00829             TrueValues = TrueValues.subtract(NegOffset->getValue());
00830 
00831           // If we're interested in the false dest, invert the condition.
00832           if (!isTrueDest) TrueValues = TrueValues.inverse();
00833 
00834           Result = LVILatticeVal::getRange(TrueValues);
00835           return true;
00836         }
00837       }
00838     }
00839   }
00840 
00841   // If the edge was formed by a switch on the value, then we may know exactly
00842   // what it is.
00843   if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
00844     if (SI->getCondition() != Val)
00845       return false;
00846 
00847     bool DefaultCase = SI->getDefaultDest() == BBTo;
00848     unsigned BitWidth = Val->getType()->getIntegerBitWidth();
00849     ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
00850 
00851     for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
00852          i != e; ++i) {
00853       ConstantRange EdgeVal(i.getCaseValue()->getValue());
00854       if (DefaultCase) {
00855         // It is possible that the default destination is the destination of
00856         // some cases. There is no need to perform difference for those cases.
00857         if (i.getCaseSuccessor() != BBTo)
00858           EdgesVals = EdgesVals.difference(EdgeVal);
00859       } else if (i.getCaseSuccessor() == BBTo)
00860         EdgesVals = EdgesVals.unionWith(EdgeVal);
00861     }
00862     Result = LVILatticeVal::getRange(EdgesVals);
00863     return true;
00864   }
00865   return false;
00866 }
00867 
00868 /// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
00869 /// the basic block if the edge does not constraint Val.
00870 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
00871                                       BasicBlock *BBTo, LVILatticeVal &Result) {
00872   // If already a constant, there is nothing to compute.
00873   if (Constant *VC = dyn_cast<Constant>(Val)) {
00874     Result = LVILatticeVal::get(VC);
00875     return true;
00876   }
00877 
00878   if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
00879     if (!Result.isConstantRange() ||
00880       Result.getConstantRange().getSingleElement())
00881       return true;
00882 
00883     // FIXME: this check should be moved to the beginning of the function when
00884     // LVI better supports recursive values. Even for the single value case, we
00885     // can intersect to detect dead code (an empty range).
00886     if (!hasBlockValue(Val, BBFrom)) {
00887       BlockValueStack.push(std::make_pair(BBFrom, Val));
00888       return false;
00889     }
00890 
00891     // Try to intersect ranges of the BB and the constraint on the edge.
00892     LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
00893     if (!InBlock.isConstantRange())
00894       return true;
00895 
00896     ConstantRange Range =
00897       Result.getConstantRange().intersectWith(InBlock.getConstantRange());
00898     Result = LVILatticeVal::getRange(Range);
00899     return true;
00900   }
00901 
00902   if (!hasBlockValue(Val, BBFrom)) {
00903     BlockValueStack.push(std::make_pair(BBFrom, Val));
00904     return false;
00905   }
00906 
00907   // if we couldn't compute the value on the edge, use the value from the BB
00908   Result = getBlockValue(Val, BBFrom);
00909   return true;
00910 }
00911 
00912 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
00913   DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
00914         << BB->getName() << "'\n");
00915   
00916   BlockValueStack.push(std::make_pair(BB, V));
00917   solve();
00918   LVILatticeVal Result = getBlockValue(V, BB);
00919 
00920   DEBUG(dbgs() << "  Result = " << Result << "\n");
00921   return Result;
00922 }
00923 
00924 LVILatticeVal LazyValueInfoCache::
00925 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
00926   DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
00927         << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
00928   
00929   LVILatticeVal Result;
00930   if (!getEdgeValue(V, FromBB, ToBB, Result)) {
00931     solve();
00932     bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result);
00933     (void)WasFastQuery;
00934     assert(WasFastQuery && "More work to do after problem solved?");
00935   }
00936 
00937   DEBUG(dbgs() << "  Result = " << Result << "\n");
00938   return Result;
00939 }
00940 
00941 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
00942                                     BasicBlock *NewSucc) {
00943   // When an edge in the graph has been threaded, values that we could not 
00944   // determine a value for before (i.e. were marked overdefined) may be possible
00945   // to solve now.  We do NOT try to proactively update these values.  Instead,
00946   // we clear their entries from the cache, and allow lazy updating to recompute
00947   // them when needed.
00948   
00949   // The updating process is fairly simple: we need to dropped cached info
00950   // for all values that were marked overdefined in OldSucc, and for those same
00951   // values in any successor of OldSucc (except NewSucc) in which they were
00952   // also marked overdefined.
00953   std::vector<BasicBlock*> worklist;
00954   worklist.push_back(OldSucc);
00955   
00956   DenseSet<Value*> ClearSet;
00957   for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
00958        E = OverDefinedCache.end(); I != E; ++I) {
00959     if (I->first == OldSucc)
00960       ClearSet.insert(I->second);
00961   }
00962   
00963   // Use a worklist to perform a depth-first search of OldSucc's successors.
00964   // NOTE: We do not need a visited list since any blocks we have already
00965   // visited will have had their overdefined markers cleared already, and we
00966   // thus won't loop to their successors.
00967   while (!worklist.empty()) {
00968     BasicBlock *ToUpdate = worklist.back();
00969     worklist.pop_back();
00970     
00971     // Skip blocks only accessible through NewSucc.
00972     if (ToUpdate == NewSucc) continue;
00973     
00974     bool changed = false;
00975     for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
00976          I != E; ++I) {
00977       // If a value was marked overdefined in OldSucc, and is here too...
00978       DenseSet<OverDefinedPairTy>::iterator OI =
00979         OverDefinedCache.find(std::make_pair(ToUpdate, *I));
00980       if (OI == OverDefinedCache.end()) continue;
00981 
00982       // Remove it from the caches.
00983       ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
00984       ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
00985 
00986       assert(CI != Entry.end() && "Couldn't find entry to update?");
00987       Entry.erase(CI);
00988       OverDefinedCache.erase(OI);
00989 
00990       // If we removed anything, then we potentially need to update 
00991       // blocks successors too.
00992       changed = true;
00993     }
00994 
00995     if (!changed) continue;
00996     
00997     worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
00998   }
00999 }
01000 
01001 //===----------------------------------------------------------------------===//
01002 //                            LazyValueInfo Impl
01003 //===----------------------------------------------------------------------===//
01004 
01005 /// getCache - This lazily constructs the LazyValueInfoCache.
01006 static LazyValueInfoCache &getCache(void *&PImpl) {
01007   if (!PImpl)
01008     PImpl = new LazyValueInfoCache();
01009   return *static_cast<LazyValueInfoCache*>(PImpl);
01010 }
01011 
01012 bool LazyValueInfo::runOnFunction(Function &F) {
01013   if (PImpl)
01014     getCache(PImpl).clear();
01015 
01016   DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
01017   DL = DLP ? &DLP->getDataLayout() : nullptr;
01018   TLI = &getAnalysis<TargetLibraryInfo>();
01019 
01020   // Fully lazy.
01021   return false;
01022 }
01023 
01024 void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
01025   AU.setPreservesAll();
01026   AU.addRequired<TargetLibraryInfo>();
01027 }
01028 
01029 void LazyValueInfo::releaseMemory() {
01030   // If the cache was allocated, free it.
01031   if (PImpl) {
01032     delete &getCache(PImpl);
01033     PImpl = nullptr;
01034   }
01035 }
01036 
01037 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
01038   LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
01039   
01040   if (Result.isConstant())
01041     return Result.getConstant();
01042   if (Result.isConstantRange()) {
01043     ConstantRange CR = Result.getConstantRange();
01044     if (const APInt *SingleVal = CR.getSingleElement())
01045       return ConstantInt::get(V->getContext(), *SingleVal);
01046   }
01047   return nullptr;
01048 }
01049 
01050 /// getConstantOnEdge - Determine whether the specified value is known to be a
01051 /// constant on the specified edge.  Return null if not.
01052 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
01053                                            BasicBlock *ToBB) {
01054   LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
01055   
01056   if (Result.isConstant())
01057     return Result.getConstant();
01058   if (Result.isConstantRange()) {
01059     ConstantRange CR = Result.getConstantRange();
01060     if (const APInt *SingleVal = CR.getSingleElement())
01061       return ConstantInt::get(V->getContext(), *SingleVal);
01062   }
01063   return nullptr;
01064 }
01065 
01066 /// getPredicateOnEdge - Determine whether the specified value comparison
01067 /// with a constant is known to be true or false on the specified CFG edge.
01068 /// Pred is a CmpInst predicate.
01069 LazyValueInfo::Tristate
01070 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
01071                                   BasicBlock *FromBB, BasicBlock *ToBB) {
01072   LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
01073   
01074   // If we know the value is a constant, evaluate the conditional.
01075   Constant *Res = nullptr;
01076   if (Result.isConstant()) {
01077     Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, DL,
01078                                           TLI);
01079     if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
01080       return ResCI->isZero() ? False : True;
01081     return Unknown;
01082   }
01083   
01084   if (Result.isConstantRange()) {
01085     ConstantInt *CI = dyn_cast<ConstantInt>(C);
01086     if (!CI) return Unknown;
01087     
01088     ConstantRange CR = Result.getConstantRange();
01089     if (Pred == ICmpInst::ICMP_EQ) {
01090       if (!CR.contains(CI->getValue()))
01091         return False;
01092       
01093       if (CR.isSingleElement() && CR.contains(CI->getValue()))
01094         return True;
01095     } else if (Pred == ICmpInst::ICMP_NE) {
01096       if (!CR.contains(CI->getValue()))
01097         return True;
01098       
01099       if (CR.isSingleElement() && CR.contains(CI->getValue()))
01100         return False;
01101     }
01102     
01103     // Handle more complex predicates.
01104     ConstantRange TrueValues =
01105         ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
01106     if (TrueValues.contains(CR))
01107       return True;
01108     if (TrueValues.inverse().contains(CR))
01109       return False;
01110     return Unknown;
01111   }
01112   
01113   if (Result.isNotConstant()) {
01114     // If this is an equality comparison, we can try to fold it knowing that
01115     // "V != C1".
01116     if (Pred == ICmpInst::ICMP_EQ) {
01117       // !C1 == C -> false iff C1 == C.
01118       Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
01119                                             Result.getNotConstant(), C, DL,
01120                                             TLI);
01121       if (Res->isNullValue())
01122         return False;
01123     } else if (Pred == ICmpInst::ICMP_NE) {
01124       // !C1 != C -> true iff C1 == C.
01125       Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
01126                                             Result.getNotConstant(), C, DL,
01127                                             TLI);
01128       if (Res->isNullValue())
01129         return True;
01130     }
01131     return Unknown;
01132   }
01133   
01134   return Unknown;
01135 }
01136 
01137 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
01138                                BasicBlock *NewSucc) {
01139   if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
01140 }
01141 
01142 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
01143   if (PImpl) getCache(PImpl).eraseBlock(BB);
01144 }