//===- ValueTracking.cpp - Walk computations to compute properties --------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file contains routines that help analyze properties that chains of // computations have. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/ValueTracking.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/IR/CallSite.h" #include "llvm/IR/ConstantRange.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/GetElementPtrTypeIterator.h" #include "llvm/IR/GlobalAlias.h" #include "llvm/IR/GlobalVariable.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Metadata.h" #include "llvm/IR/Operator.h" #include "llvm/IR/PatternMatch.h" #include "llvm/Support/Debug.h" #include "llvm/Support/MathExtras.h" #include using namespace llvm; using namespace llvm::PatternMatch; const unsigned MaxDepth = 6; /// Enable an experimental feature to leverage information about dominating /// conditions to compute known bits. The individual options below control how /// hard we search. The defaults are choosen to be fairly aggressive. If you /// run into compile time problems when testing, scale them back and report /// your findings. static cl::opt EnableDomConditions("value-tracking-dom-conditions", cl::Hidden, cl::init(false)); // This is expensive, so we only do it for the top level query value. // (TODO: evaluate cost vs profit, consider higher thresholds) static cl::opt DomConditionsMaxDepth("dom-conditions-max-depth", cl::Hidden, cl::init(1)); /// How many dominating blocks should be scanned looking for dominating /// conditions? static cl::opt DomConditionsMaxDomBlocks("dom-conditions-dom-blocks", cl::Hidden, cl::init(20000)); // Controls the number of uses of the value searched for possible // dominating comparisons. static cl::opt DomConditionsMaxUses("dom-conditions-max-uses", cl::Hidden, cl::init(2000)); // If true, don't consider only compares whose only use is a branch. static cl::opt DomConditionsSingleCmpUse("dom-conditions-single-cmp-use", cl::Hidden, cl::init(false)); /// Returns the bitwidth of the given scalar or pointer type (if unknown returns /// 0). For vector types, returns the element type's bitwidth. static unsigned getBitWidth(Type *Ty, const DataLayout &DL) { if (unsigned BitWidth = Ty->getScalarSizeInBits()) return BitWidth; return DL.getPointerTypeSizeInBits(Ty); } // Many of these functions have internal versions that take an assumption // exclusion set. This is because of the potential for mutual recursion to // cause computeKnownBits to repeatedly visit the same assume intrinsic. The // classic case of this is assume(x = y), which will attempt to determine // bits in x from bits in y, which will attempt to determine bits in y from // bits in x, etc. Regarding the mutual recursion, computeKnownBits can call // isKnownNonZero, which calls computeKnownBits and ComputeSignBit and // isKnownToBeAPowerOfTwo (all of which can call computeKnownBits), and so on. typedef SmallPtrSet ExclInvsSet; namespace { // Simplifying using an assume can only be done in a particular control-flow // context (the context instruction provides that context). If an assume and // the context instruction are not in the same block then the DT helps in // figuring out if we can use it. struct Query { ExclInvsSet ExclInvs; AssumptionCache *AC; const Instruction *CxtI; const DominatorTree *DT; Query(AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr) : AC(AC), CxtI(CxtI), DT(DT) {} Query(const Query &Q, const Value *NewExcl) : ExclInvs(Q.ExclInvs), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT) { ExclInvs.insert(NewExcl); } }; } // end anonymous namespace // Given the provided Value and, potentially, a context instruction, return // the preferred context instruction (if any). static const Instruction *safeCxtI(const Value *V, const Instruction *CxtI) { // If we've been provided with a context instruction, then use that (provided // it has been inserted). if (CxtI && CxtI->getParent()) return CxtI; // If the value is really an already-inserted instruction, then use that. CxtI = dyn_cast(V); if (CxtI && CxtI->getParent()) return CxtI; return nullptr; } static void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth, const Query &Q); void llvm::computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { ::computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT)); } static void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne, const DataLayout &DL, unsigned Depth, const Query &Q); void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { ::ComputeSignBit(V, KnownZero, KnownOne, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT)); } static bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth, const Query &Q, const DataLayout &DL); bool llvm::isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL, bool OrZero, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::isKnownToBeAPowerOfTwo(V, OrZero, Depth, Query(AC, safeCxtI(V, CxtI), DT), DL); } static bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth, const Query &Q); bool llvm::isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::isKnownNonZero(V, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT)); } static bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL, unsigned Depth, const Query &Q); bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::MaskedValueIsZero(V, Mask, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT)); } static unsigned ComputeNumSignBits(Value *V, const DataLayout &DL, unsigned Depth, const Query &Q); unsigned llvm::ComputeNumSignBits(Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::ComputeNumSignBits(V, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT)); } static void computeKnownBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW, APInt &KnownZero, APInt &KnownOne, APInt &KnownZero2, APInt &KnownOne2, const DataLayout &DL, unsigned Depth, const Query &Q) { if (!Add) { if (ConstantInt *CLHS = dyn_cast(Op0)) { // We know that the top bits of C-X are clear if X contains less bits // than C (i.e. no wrap-around can happen). For example, 20-X is // positive if we can prove that X is >= 0 and < 16. if (!CLHS->getValue().isNegative()) { unsigned BitWidth = KnownZero.getBitWidth(); unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros(); // NLZ can't be BitWidth with no sign bit APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1); computeKnownBits(Op1, KnownZero2, KnownOne2, DL, Depth + 1, Q); // If all of the MaskV bits are known to be zero, then we know the // output top bits are zero, because we now know that the output is // from [0-C]. if ((KnownZero2 & MaskV) == MaskV) { unsigned NLZ2 = CLHS->getValue().countLeadingZeros(); // Top bits known zero. KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2); } } } } unsigned BitWidth = KnownZero.getBitWidth(); // If an initial sequence of bits in the result is not needed, the // corresponding bits in the operands are not needed. APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); computeKnownBits(Op0, LHSKnownZero, LHSKnownOne, DL, Depth + 1, Q); computeKnownBits(Op1, KnownZero2, KnownOne2, DL, Depth + 1, Q); // Carry in a 1 for a subtract, rather than a 0. APInt CarryIn(BitWidth, 0); if (!Add) { // Sum = LHS + ~RHS + 1 std::swap(KnownZero2, KnownOne2); CarryIn.setBit(0); } APInt PossibleSumZero = ~LHSKnownZero + ~KnownZero2 + CarryIn; APInt PossibleSumOne = LHSKnownOne + KnownOne2 + CarryIn; // Compute known bits of the carry. APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ KnownZero2); APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ KnownOne2; // Compute set of known bits (where all three relevant bits are known). APInt LHSKnown = LHSKnownZero | LHSKnownOne; APInt RHSKnown = KnownZero2 | KnownOne2; APInt CarryKnown = CarryKnownZero | CarryKnownOne; APInt Known = LHSKnown & RHSKnown & CarryKnown; assert((PossibleSumZero & Known) == (PossibleSumOne & Known) && "known bits of sum differ"); // Compute known bits of the result. KnownZero = ~PossibleSumOne & Known; KnownOne = PossibleSumOne & Known; // Are we still trying to solve for the sign bit? if (!Known.isNegative()) { if (NSW) { // Adding two non-negative numbers, or subtracting a negative number from // a non-negative one, can't wrap into negative. if (LHSKnownZero.isNegative() && KnownZero2.isNegative()) KnownZero |= APInt::getSignBit(BitWidth); // Adding two negative numbers, or subtracting a non-negative number from // a negative one, can't wrap into non-negative. else if (LHSKnownOne.isNegative() && KnownOne2.isNegative()) KnownOne |= APInt::getSignBit(BitWidth); } } } static void computeKnownBitsMul(Value *Op0, Value *Op1, bool NSW, APInt &KnownZero, APInt &KnownOne, APInt &KnownZero2, APInt &KnownOne2, const DataLayout &DL, unsigned Depth, const Query &Q) { unsigned BitWidth = KnownZero.getBitWidth(); computeKnownBits(Op1, KnownZero, KnownOne, DL, Depth + 1, Q); computeKnownBits(Op0, KnownZero2, KnownOne2, DL, Depth + 1, Q); bool isKnownNegative = false; bool isKnownNonNegative = false; // If the multiplication is known not to overflow, compute the sign bit. if (NSW) { if (Op0 == Op1) { // The product of a number with itself is non-negative. isKnownNonNegative = true; } else { bool isKnownNonNegativeOp1 = KnownZero.isNegative(); bool isKnownNonNegativeOp0 = KnownZero2.isNegative(); bool isKnownNegativeOp1 = KnownOne.isNegative(); bool isKnownNegativeOp0 = KnownOne2.isNegative(); // The product of two numbers with the same sign is non-negative. isKnownNonNegative = (isKnownNegativeOp1 && isKnownNegativeOp0) || (isKnownNonNegativeOp1 && isKnownNonNegativeOp0); // The product of a negative number and a non-negative number is either // negative or zero. if (!isKnownNonNegative) isKnownNegative = (isKnownNegativeOp1 && isKnownNonNegativeOp0 && isKnownNonZero(Op0, DL, Depth, Q)) || (isKnownNegativeOp0 && isKnownNonNegativeOp1 && isKnownNonZero(Op1, DL, Depth, Q)); } } // If low bits are zero in either operand, output low known-0 bits. // Also compute a conserative estimate for high known-0 bits. // More trickiness is possible, but this is sufficient for the // interesting case of alignment computation. KnownOne.clearAllBits(); unsigned TrailZ = KnownZero.countTrailingOnes() + KnownZero2.countTrailingOnes(); unsigned LeadZ = std::max(KnownZero.countLeadingOnes() + KnownZero2.countLeadingOnes(), BitWidth) - BitWidth; TrailZ = std::min(TrailZ, BitWidth); LeadZ = std::min(LeadZ, BitWidth); KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) | APInt::getHighBitsSet(BitWidth, LeadZ); // Only make use of no-wrap flags if we failed to compute the sign bit // directly. This matters if the multiplication always overflows, in // which case we prefer to follow the result of the direct computation, // though as the program is invoking undefined behaviour we can choose // whatever we like here. if (isKnownNonNegative && !KnownOne.isNegative()) KnownZero.setBit(BitWidth - 1); else if (isKnownNegative && !KnownZero.isNegative()) KnownOne.setBit(BitWidth - 1); } void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges, APInt &KnownZero) { unsigned BitWidth = KnownZero.getBitWidth(); unsigned NumRanges = Ranges.getNumOperands() / 2; assert(NumRanges >= 1); // Use the high end of the ranges to find leading zeros. unsigned MinLeadingZeros = BitWidth; for (unsigned i = 0; i < NumRanges; ++i) { ConstantInt *Lower = mdconst::extract(Ranges.getOperand(2 * i + 0)); ConstantInt *Upper = mdconst::extract(Ranges.getOperand(2 * i + 1)); ConstantRange Range(Lower->getValue(), Upper->getValue()); if (Range.isWrappedSet()) MinLeadingZeros = 0; // -1 has no zeros unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros(); MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros); } KnownZero = APInt::getHighBitsSet(BitWidth, MinLeadingZeros); } static bool isEphemeralValueOf(Instruction *I, const Value *E) { SmallVector WorkSet(1, I); SmallPtrSet Visited; SmallPtrSet EphValues; while (!WorkSet.empty()) { const Value *V = WorkSet.pop_back_val(); if (!Visited.insert(V).second) continue; // If all uses of this value are ephemeral, then so is this value. bool FoundNEUse = false; for (const User *I : V->users()) if (!EphValues.count(I)) { FoundNEUse = true; break; } if (!FoundNEUse) { if (V == E) return true; EphValues.insert(V); if (const User *U = dyn_cast(V)) for (User::const_op_iterator J = U->op_begin(), JE = U->op_end(); J != JE; ++J) { if (isSafeToSpeculativelyExecute(*J)) WorkSet.push_back(*J); } } } return false; } // Is this an intrinsic that cannot be speculated but also cannot trap? static bool isAssumeLikeIntrinsic(const Instruction *I) { if (const CallInst *CI = dyn_cast(I)) if (Function *F = CI->getCalledFunction()) switch (F->getIntrinsicID()) { default: break; // FIXME: This list is repeated from NoTTI::getIntrinsicCost. case Intrinsic::assume: case Intrinsic::dbg_declare: case Intrinsic::dbg_value: case Intrinsic::invariant_start: case Intrinsic::invariant_end: case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: case Intrinsic::objectsize: case Intrinsic::ptr_annotation: case Intrinsic::var_annotation: return true; } return false; } static bool isValidAssumeForContext(Value *V, const Query &Q) { Instruction *Inv = cast(V); // There are two restrictions on the use of an assume: // 1. The assume must dominate the context (or the control flow must // reach the assume whenever it reaches the context). // 2. The context must not be in the assume's set of ephemeral values // (otherwise we will use the assume to prove that the condition // feeding the assume is trivially true, thus causing the removal of // the assume). if (Q.DT) { if (Q.DT->dominates(Inv, Q.CxtI)) { return true; } else if (Inv->getParent() == Q.CxtI->getParent()) { // The context comes first, but they're both in the same block. Make sure // there is nothing in between that might interrupt the control flow. for (BasicBlock::const_iterator I = std::next(BasicBlock::const_iterator(Q.CxtI)), IE(Inv); I != IE; ++I) if (!isSafeToSpeculativelyExecute(I) && !isAssumeLikeIntrinsic(I)) return false; return !isEphemeralValueOf(Inv, Q.CxtI); } return false; } // When we don't have a DT, we do a limited search... if (Inv->getParent() == Q.CxtI->getParent()->getSinglePredecessor()) { return true; } else if (Inv->getParent() == Q.CxtI->getParent()) { // Search forward from the assume until we reach the context (or the end // of the block); the common case is that the assume will come first. for (BasicBlock::iterator I = std::next(BasicBlock::iterator(Inv)), IE = Inv->getParent()->end(); I != IE; ++I) if (I == Q.CxtI) return true; // The context must come first... for (BasicBlock::const_iterator I = std::next(BasicBlock::const_iterator(Q.CxtI)), IE(Inv); I != IE; ++I) if (!isSafeToSpeculativelyExecute(I) && !isAssumeLikeIntrinsic(I)) return false; return !isEphemeralValueOf(Inv, Q.CxtI); } return false; } bool llvm::isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, const DominatorTree *DT) { return ::isValidAssumeForContext(const_cast(I), Query(nullptr, CxtI, DT)); } template inline match_combine_or, CmpClass_match> m_c_ICmp(ICmpInst::Predicate &Pred, const LHS &L, const RHS &R) { return m_CombineOr(m_ICmp(Pred, L, R), m_ICmp(Pred, R, L)); } template inline match_combine_or, BinaryOp_match> m_c_And(const LHS &L, const RHS &R) { return m_CombineOr(m_And(L, R), m_And(R, L)); } template inline match_combine_or, BinaryOp_match> m_c_Or(const LHS &L, const RHS &R) { return m_CombineOr(m_Or(L, R), m_Or(R, L)); } template inline match_combine_or, BinaryOp_match> m_c_Xor(const LHS &L, const RHS &R) { return m_CombineOr(m_Xor(L, R), m_Xor(R, L)); } /// Compute known bits in 'V' under the assumption that the condition 'Cmp' is /// true (at the context instruction.) This is mostly a utility function for /// the prototype dominating conditions reasoning below. static void computeKnownBitsFromTrueCondition(Value *V, ICmpInst *Cmp, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth, const Query &Q) { Value *LHS = Cmp->getOperand(0); Value *RHS = Cmp->getOperand(1); // TODO: We could potentially be more aggressive here. This would be worth // evaluating. If we can, explore commoning this code with the assume // handling logic. if (LHS != V && RHS != V) return; const unsigned BitWidth = KnownZero.getBitWidth(); switch (Cmp->getPredicate()) { default: // We know nothing from this condition break; // TODO: implement unsigned bound from below (known one bits) // TODO: common condition check implementations with assumes // TODO: implement other patterns from assume (e.g. V & B == A) case ICmpInst::ICMP_SGT: if (LHS == V) { APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0); computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q); if (KnownOneTemp.isAllOnesValue() || KnownZeroTemp.isNegative()) { // We know that the sign bit is zero. KnownZero |= APInt::getSignBit(BitWidth); } } break; case ICmpInst::ICMP_EQ: if (LHS == V) computeKnownBits(RHS, KnownZero, KnownOne, DL, Depth + 1, Q); else if (RHS == V) computeKnownBits(LHS, KnownZero, KnownOne, DL, Depth + 1, Q); else llvm_unreachable("missing use?"); break; case ICmpInst::ICMP_ULE: if (LHS == V) { APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0); computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q); // The known zero bits carry over unsigned SignBits = KnownZeroTemp.countLeadingOnes(); KnownZero |= APInt::getHighBitsSet(BitWidth, SignBits); } break; case ICmpInst::ICMP_ULT: if (LHS == V) { APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0); computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q); // Whatever high bits in rhs are zero are known to be zero (if rhs is a // power of 2, then one more). unsigned SignBits = KnownZeroTemp.countLeadingOnes(); if (isKnownToBeAPowerOfTwo(RHS, false, Depth + 1, Query(Q, Cmp), DL)) SignBits++; KnownZero |= APInt::getHighBitsSet(BitWidth, SignBits); } break; }; } /// Compute known bits in 'V' from conditions which are known to be true along /// all paths leading to the context instruction. In particular, look for /// cases where one branch of an interesting condition dominates the context /// instruction. This does not do general dataflow. /// NOTE: This code is EXPERIMENTAL and currently off by default. static void computeKnownBitsFromDominatingCondition(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth, const Query &Q) { // Need both the dominator tree and the query location to do anything useful if (!Q.DT || !Q.CxtI) return; Instruction *Cxt = const_cast(Q.CxtI); // Avoid useless work if (auto VI = dyn_cast(V)) if (VI->getParent() == Cxt->getParent()) return; // Note: We currently implement two options. It's not clear which of these // will survive long term, we need data for that. // Option 1 - Try walking the dominator tree looking for conditions which // might apply. This works well for local conditions (loop guards, etc..), // but not as well for things far from the context instruction (presuming a // low max blocks explored). If we can set an high enough limit, this would // be all we need. // Option 2 - We restrict out search to those conditions which are uses of // the value we're interested in. This is independent of dom structure, // but is slightly less powerful without looking through lots of use chains. // It does handle conditions far from the context instruction (e.g. early // function exits on entry) really well though. // Option 1 - Search the dom tree unsigned NumBlocksExplored = 0; BasicBlock *Current = Cxt->getParent(); while (true) { // Stop searching if we've gone too far up the chain if (NumBlocksExplored >= DomConditionsMaxDomBlocks) break; NumBlocksExplored++; if (!Q.DT->getNode(Current)->getIDom()) break; Current = Q.DT->getNode(Current)->getIDom()->getBlock(); if (!Current) // found function entry break; BranchInst *BI = dyn_cast(Current->getTerminator()); if (!BI || BI->isUnconditional()) continue; ICmpInst *Cmp = dyn_cast(BI->getCondition()); if (!Cmp) continue; // We're looking for conditions that are guaranteed to hold at the context // instruction. Finding a condition where one path dominates the context // isn't enough because both the true and false cases could merge before // the context instruction we're actually interested in. Instead, we need // to ensure that the taken *edge* dominates the context instruction. BasicBlock *BB0 = BI->getSuccessor(0); BasicBlockEdge Edge(BI->getParent(), BB0); if (!Edge.isSingleEdge() || !Q.DT->dominates(Edge, Q.CxtI->getParent())) continue; computeKnownBitsFromTrueCondition(V, Cmp, KnownZero, KnownOne, DL, Depth, Q); } // Option 2 - Search the other uses of V unsigned NumUsesExplored = 0; for (auto U : V->users()) { // Avoid massive lists if (NumUsesExplored >= DomConditionsMaxUses) break; NumUsesExplored++; // Consider only compare instructions uniquely controlling a branch ICmpInst *Cmp = dyn_cast(U); if (!Cmp) continue; if (DomConditionsSingleCmpUse && !Cmp->hasOneUse()) continue; for (auto *CmpU : Cmp->users()) { BranchInst *BI = dyn_cast(CmpU); if (!BI || BI->isUnconditional()) continue; // We're looking for conditions that are guaranteed to hold at the // context instruction. Finding a condition where one path dominates // the context isn't enough because both the true and false cases could // merge before the context instruction we're actually interested in. // Instead, we need to ensure that the taken *edge* dominates the context // instruction. BasicBlock *BB0 = BI->getSuccessor(0); BasicBlockEdge Edge(BI->getParent(), BB0); if (!Edge.isSingleEdge() || !Q.DT->dominates(Edge, Q.CxtI->getParent())) continue; computeKnownBitsFromTrueCondition(V, Cmp, KnownZero, KnownOne, DL, Depth, Q); } } } static void computeKnownBitsFromAssume(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth, const Query &Q) { // Use of assumptions is context-sensitive. If we don't have a context, we // cannot use them! if (!Q.AC || !Q.CxtI) return; unsigned BitWidth = KnownZero.getBitWidth(); for (auto &AssumeVH : Q.AC->assumptions()) { if (!AssumeVH) continue; CallInst *I = cast(AssumeVH); assert(I->getParent()->getParent() == Q.CxtI->getParent()->getParent() && "Got assumption for the wrong function!"); if (Q.ExclInvs.count(I)) continue; // Warning: This loop can end up being somewhat performance sensetive. // We're running this loop for once for each value queried resulting in a // runtime of ~O(#assumes * #values). assert(I->getCalledFunction()->getIntrinsicID() == Intrinsic::assume && "must be an assume intrinsic"); Value *Arg = I->getArgOperand(0); if (Arg == V && isValidAssumeForContext(I, Q)) { assert(BitWidth == 1 && "assume operand is not i1?"); KnownZero.clearAllBits(); KnownOne.setAllBits(); return; } // The remaining tests are all recursive, so bail out if we hit the limit. if (Depth == MaxDepth) continue; Value *A, *B; auto m_V = m_CombineOr(m_Specific(V), m_CombineOr(m_PtrToInt(m_Specific(V)), m_BitCast(m_Specific(V)))); CmpInst::Predicate Pred; ConstantInt *C; // assume(v = a) if (match(Arg, m_c_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); KnownZero |= RHSKnownZero; KnownOne |= RHSKnownOne; // assume(v & b = a) } else if (match(Arg, m_c_ICmp(Pred, m_c_And(m_V, m_Value(B)), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0); computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in the mask that are known to be one, we can propagate // known bits from the RHS to V. KnownZero |= RHSKnownZero & MaskKnownOne; KnownOne |= RHSKnownOne & MaskKnownOne; // assume(~(v & b) = a) } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_And(m_V, m_Value(B))), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0); computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in the mask that are known to be one, we can propagate // inverted known bits from the RHS to V. KnownZero |= RHSKnownOne & MaskKnownOne; KnownOne |= RHSKnownZero & MaskKnownOne; // assume(v | b = a) } else if (match(Arg, m_c_ICmp(Pred, m_c_Or(m_V, m_Value(B)), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in B that are known to be zero, we can propagate known // bits from the RHS to V. KnownZero |= RHSKnownZero & BKnownZero; KnownOne |= RHSKnownOne & BKnownZero; // assume(~(v | b) = a) } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Or(m_V, m_Value(B))), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in B that are known to be zero, we can propagate // inverted known bits from the RHS to V. KnownZero |= RHSKnownOne & BKnownZero; KnownOne |= RHSKnownZero & BKnownZero; // assume(v ^ b = a) } else if (match(Arg, m_c_ICmp(Pred, m_c_Xor(m_V, m_Value(B)), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in B that are known to be zero, we can propagate known // bits from the RHS to V. For those bits in B that are known to be one, // we can propagate inverted known bits from the RHS to V. KnownZero |= RHSKnownZero & BKnownZero; KnownOne |= RHSKnownOne & BKnownZero; KnownZero |= RHSKnownOne & BKnownOne; KnownOne |= RHSKnownZero & BKnownOne; // assume(~(v ^ b) = a) } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Xor(m_V, m_Value(B))), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in B that are known to be zero, we can propagate // inverted known bits from the RHS to V. For those bits in B that are // known to be one, we can propagate known bits from the RHS to V. KnownZero |= RHSKnownOne & BKnownZero; KnownOne |= RHSKnownZero & BKnownZero; KnownZero |= RHSKnownZero & BKnownOne; KnownOne |= RHSKnownOne & BKnownOne; // assume(v << c = a) } else if (match(Arg, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in RHS that are known, we can propagate them to known // bits in V shifted to the right by C. KnownZero |= RHSKnownZero.lshr(C->getZExtValue()); KnownOne |= RHSKnownOne.lshr(C->getZExtValue()); // assume(~(v << c) = a) } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in RHS that are known, we can propagate them inverted // to known bits in V shifted to the right by C. KnownZero |= RHSKnownOne.lshr(C->getZExtValue()); KnownOne |= RHSKnownZero.lshr(C->getZExtValue()); // assume(v >> c = a) } else if (match(Arg, m_c_ICmp(Pred, m_CombineOr(m_LShr(m_V, m_ConstantInt(C)), m_AShr(m_V, m_ConstantInt(C))), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in RHS that are known, we can propagate them to known // bits in V shifted to the right by C. KnownZero |= RHSKnownZero << C->getZExtValue(); KnownOne |= RHSKnownOne << C->getZExtValue(); // assume(~(v >> c) = a) } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_CombineOr( m_LShr(m_V, m_ConstantInt(C)), m_AShr(m_V, m_ConstantInt(C)))), m_Value(A))) && Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); // For those bits in RHS that are known, we can propagate them inverted // to known bits in V shifted to the right by C. KnownZero |= RHSKnownOne << C->getZExtValue(); KnownOne |= RHSKnownZero << C->getZExtValue(); // assume(v >=_s c) where c is non-negative } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_SGE && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); if (RHSKnownZero.isNegative()) { // We know that the sign bit is zero. KnownZero |= APInt::getSignBit(BitWidth); } // assume(v >_s c) where c is at least -1. } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_SGT && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); if (RHSKnownOne.isAllOnesValue() || RHSKnownZero.isNegative()) { // We know that the sign bit is zero. KnownZero |= APInt::getSignBit(BitWidth); } // assume(v <=_s c) where c is negative } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_SLE && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); if (RHSKnownOne.isNegative()) { // We know that the sign bit is one. KnownOne |= APInt::getSignBit(BitWidth); } // assume(v <_s c) where c is non-positive } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_SLT && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); if (RHSKnownZero.isAllOnesValue() || RHSKnownOne.isNegative()) { // We know that the sign bit is one. KnownOne |= APInt::getSignBit(BitWidth); } // assume(v <=_u c) } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_ULE && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); // Whatever high bits in c are zero are known to be zero. KnownZero |= APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes()); // assume(v <_u c) } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_ULT && isValidAssumeForContext(I, Q)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I)); // Whatever high bits in c are zero are known to be zero (if c is a power // of 2, then one more). if (isKnownToBeAPowerOfTwo(A, false, Depth + 1, Query(Q, I), DL)) KnownZero |= APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes()+1); else KnownZero |= APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes()); } } } /// Determine which bits of V are known to be either zero or one and return /// them in the KnownZero/KnownOne bit sets. /// /// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that /// we cannot optimize based on the assumption that it is zero without changing /// it to be an explicit zero. If we don't change it to zero, other code could /// optimized based on the contradictory assumption that it is non-zero. /// Because instcombine aggressively folds operations with undef args anyway, /// this won't lose us code quality. /// /// This function is defined on values with integer type, values with pointer /// type, and vectors of integers. In the case /// where V is a vector, known zero, and known one values are the /// same width as the vector element, and the bit is set only if it is true /// for all of the elements in the vector. void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth, const Query &Q) { assert(V && "No Value?"); assert(Depth <= MaxDepth && "Limit Search Depth"); unsigned BitWidth = KnownZero.getBitWidth(); assert((V->getType()->isIntOrIntVectorTy() || V->getType()->getScalarType()->isPointerTy()) && "Not integer or pointer type!"); assert((DL.getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) && (!V->getType()->isIntOrIntVectorTy() || V->getType()->getScalarSizeInBits() == BitWidth) && KnownZero.getBitWidth() == BitWidth && KnownOne.getBitWidth() == BitWidth && "V, KnownOne and KnownZero should have same BitWidth"); if (ConstantInt *CI = dyn_cast(V)) { // We know all of the bits for a constant! KnownOne = CI->getValue(); KnownZero = ~KnownOne; return; } // Null and aggregate-zero are all-zeros. if (isa(V) || isa(V)) { KnownOne.clearAllBits(); KnownZero = APInt::getAllOnesValue(BitWidth); return; } // Handle a constant vector by taking the intersection of the known bits of // each element. There is no real need to handle ConstantVector here, because // we don't handle undef in any particularly useful way. if (ConstantDataSequential *CDS = dyn_cast(V)) { // We know that CDS must be a vector of integers. Take the intersection of // each element. KnownZero.setAllBits(); KnownOne.setAllBits(); APInt Elt(KnownZero.getBitWidth(), 0); for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) { Elt = CDS->getElementAsInteger(i); KnownZero &= ~Elt; KnownOne &= Elt; } return; } // The address of an aligned GlobalValue has trailing zeros. if (auto *GO = dyn_cast(V)) { unsigned Align = GO->getAlignment(); if (Align == 0) { if (auto *GVar = dyn_cast(GO)) { Type *ObjectType = GVar->getType()->getElementType(); if (ObjectType->isSized()) { // If the object is defined in the current Module, we'll be giving // it the preferred alignment. Otherwise, we have to assume that it // may only have the minimum ABI alignment. if (!GVar->isDeclaration() && !GVar->isWeakForLinker()) Align = DL.getPreferredAlignment(GVar); else Align = DL.getABITypeAlignment(ObjectType); } } } if (Align > 0) KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align)); else KnownZero.clearAllBits(); KnownOne.clearAllBits(); return; } if (Argument *A = dyn_cast(V)) { unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0; if (!Align && A->hasStructRetAttr()) { // An sret parameter has at least the ABI alignment of the return type. Type *EltTy = cast(A->getType())->getElementType(); if (EltTy->isSized()) Align = DL.getABITypeAlignment(EltTy); } if (Align) KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align)); else KnownZero.clearAllBits(); KnownOne.clearAllBits(); // Don't give up yet... there might be an assumption that provides more // information... computeKnownBitsFromAssume(V, KnownZero, KnownOne, DL, Depth, Q); // Or a dominating condition for that matter if (EnableDomConditions && Depth <= DomConditionsMaxDepth) computeKnownBitsFromDominatingCondition(V, KnownZero, KnownOne, DL, Depth, Q); return; } // Start out not knowing anything. KnownZero.clearAllBits(); KnownOne.clearAllBits(); // Limit search depth. // All recursive calls that increase depth must come after this. if (Depth == MaxDepth) return; // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has // the bits of its aliasee. if (GlobalAlias *GA = dyn_cast(V)) { if (!GA->mayBeOverridden()) computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, DL, Depth + 1, Q); return; } // Check whether a nearby assume intrinsic can determine some known bits. computeKnownBitsFromAssume(V, KnownZero, KnownOne, DL, Depth, Q); // Check whether there's a dominating condition which implies something about // this value at the given context. if (EnableDomConditions && Depth <= DomConditionsMaxDepth) computeKnownBitsFromDominatingCondition(V, KnownZero, KnownOne, DL, Depth, Q); Operator *I = dyn_cast(V); if (!I) return; APInt KnownZero2(KnownZero), KnownOne2(KnownOne); switch (I->getOpcode()) { default: break; case Instruction::Load: if (MDNode *MD = cast(I)->getMetadata(LLVMContext::MD_range)) computeKnownBitsFromRangeMetadata(*MD, KnownZero); break; case Instruction::And: { // If either the LHS or the RHS are Zero, the result is zero. computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q); computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q); // Output known-1 bits are only known if set in both the LHS & RHS. KnownOne &= KnownOne2; // Output known-0 are known to be clear if zero in either the LHS | RHS. KnownZero |= KnownZero2; break; } case Instruction::Or: { computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q); computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q); // Output known-0 bits are only known if clear in both the LHS & RHS. KnownZero &= KnownZero2; // Output known-1 are known to be set if set in either the LHS | RHS. KnownOne |= KnownOne2; break; } case Instruction::Xor: { computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q); computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q); // Output known-0 bits are known if clear or set in both the LHS & RHS. APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2); // Output known-1 are known to be set if set in only one of the LHS, RHS. KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2); KnownZero = KnownZeroOut; break; } case Instruction::Mul: { bool NSW = cast(I)->hasNoSignedWrap(); computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW, KnownZero, KnownOne, KnownZero2, KnownOne2, DL, Depth, Q); break; } case Instruction::UDiv: { // For the purposes of computing leading zeros we can conservatively // treat a udiv as a logical right shift by the power of 2 known to // be less than the denominator. computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q); unsigned LeadZ = KnownZero2.countLeadingOnes(); KnownOne2.clearAllBits(); KnownZero2.clearAllBits(); computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q); unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros(); if (RHSUnknownLeadingOnes != BitWidth) LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSUnknownLeadingOnes - 1); KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ); break; } case Instruction::Select: computeKnownBits(I->getOperand(2), KnownZero, KnownOne, DL, Depth + 1, Q); computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q); // Only known if known in both the LHS and RHS. KnownOne &= KnownOne2; KnownZero &= KnownZero2; break; case Instruction::FPTrunc: case Instruction::FPExt: case Instruction::FPToUI: case Instruction::FPToSI: case Instruction::SIToFP: case Instruction::UIToFP: break; // Can't work with floating point. case Instruction::PtrToInt: case Instruction::IntToPtr: case Instruction::AddrSpaceCast: // Pointers could be different sizes. // FALL THROUGH and handle them the same as zext/trunc. case Instruction::ZExt: case Instruction::Trunc: { Type *SrcTy = I->getOperand(0)->getType(); unsigned SrcBitWidth; // Note that we handle pointer operands here because of inttoptr/ptrtoint // which fall through here. SrcBitWidth = DL.getTypeSizeInBits(SrcTy->getScalarType()); assert(SrcBitWidth && "SrcBitWidth can't be zero"); KnownZero = KnownZero.zextOrTrunc(SrcBitWidth); KnownOne = KnownOne.zextOrTrunc(SrcBitWidth); computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); KnownZero = KnownZero.zextOrTrunc(BitWidth); KnownOne = KnownOne.zextOrTrunc(BitWidth); // Any top bits are known to be zero. if (BitWidth > SrcBitWidth) KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); break; } case Instruction::BitCast: { Type *SrcTy = I->getOperand(0)->getType(); if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && // TODO: For now, not handling conversions like: // (bitcast i64 %x to <2 x i32>) !I->getType()->isVectorTy()) { computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); break; } break; } case Instruction::SExt: { // Compute the bits in the result that are not present in the input. unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits(); KnownZero = KnownZero.trunc(SrcBitWidth); KnownOne = KnownOne.trunc(SrcBitWidth); computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); KnownZero = KnownZero.zext(BitWidth); KnownOne = KnownOne.zext(BitWidth); // If the sign bit of the input is known set or clear, then we know the // top bits of the result. if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); break; } case Instruction::Shl: // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 if (ConstantInt *SA = dyn_cast(I->getOperand(1))) { uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); KnownZero <<= ShiftAmt; KnownOne <<= ShiftAmt; KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0 } break; case Instruction::LShr: // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 if (ConstantInt *SA = dyn_cast(I->getOperand(1))) { // Compute the new bits that are at the top now. uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); // Unsigned shift right. computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); // high bits known zero. KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt); } break; case Instruction::AShr: // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 if (ConstantInt *SA = dyn_cast(I->getOperand(1))) { // Compute the new bits that are at the top now. uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1); // Signed shift right. computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt)); if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero. KnownZero |= HighBits; else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one. KnownOne |= HighBits; } break; case Instruction::Sub: { bool NSW = cast(I)->hasNoSignedWrap(); computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW, KnownZero, KnownOne, KnownZero2, KnownOne2, DL, Depth, Q); break; } case Instruction::Add: { bool NSW = cast(I)->hasNoSignedWrap(); computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW, KnownZero, KnownOne, KnownZero2, KnownOne2, DL, Depth, Q); break; } case Instruction::SRem: if (ConstantInt *Rem = dyn_cast(I->getOperand(1))) { APInt RA = Rem->getValue().abs(); if (RA.isPowerOf2()) { APInt LowBits = RA - 1; computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q); // The low bits of the first operand are unchanged by the srem. KnownZero = KnownZero2 & LowBits; KnownOne = KnownOne2 & LowBits; // If the first operand is non-negative or has all low bits zero, then // the upper bits are all zero. if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits)) KnownZero |= ~LowBits; // If the first operand is negative and not all low bits are zero, then // the upper bits are all one. if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0)) KnownOne |= ~LowBits; assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); } } // The sign bit is the LHS's sign bit, except when the result of the // remainder is zero. if (KnownZero.isNonNegative()) { APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, DL, Depth + 1, Q); // If it's known zero, our sign bit is also zero. if (LHSKnownZero.isNegative()) KnownZero.setBit(BitWidth - 1); } break; case Instruction::URem: { if (ConstantInt *Rem = dyn_cast(I->getOperand(1))) { APInt RA = Rem->getValue(); if (RA.isPowerOf2()) { APInt LowBits = (RA - 1); computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); KnownZero |= ~LowBits; KnownOne &= LowBits; break; } } // Since the result is less than or equal to either operand, any leading // zero bits in either operand must also exist in the result. computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q); unsigned Leaders = std::max(KnownZero.countLeadingOnes(), KnownZero2.countLeadingOnes()); KnownOne.clearAllBits(); KnownZero = APInt::getHighBitsSet(BitWidth, Leaders); break; } case Instruction::Alloca: { AllocaInst *AI = cast(V); unsigned Align = AI->getAlignment(); if (Align == 0) Align = DL.getABITypeAlignment(AI->getType()->getElementType()); if (Align > 0) KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align)); break; } case Instruction::GetElementPtr: { // Analyze all of the subscripts of this getelementptr instruction // to determine if we can prove known low zero bits. APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0); computeKnownBits(I->getOperand(0), LocalKnownZero, LocalKnownOne, DL, Depth + 1, Q); unsigned TrailZ = LocalKnownZero.countTrailingOnes(); gep_type_iterator GTI = gep_type_begin(I); for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) { Value *Index = I->getOperand(i); if (StructType *STy = dyn_cast(*GTI)) { // Handle struct member offset arithmetic. // Handle case when index is vector zeroinitializer Constant *CIndex = cast(Index); if (CIndex->isZeroValue()) continue; if (CIndex->getType()->isVectorTy()) Index = CIndex->getSplatValue(); unsigned Idx = cast(Index)->getZExtValue(); const StructLayout *SL = DL.getStructLayout(STy); uint64_t Offset = SL->getElementOffset(Idx); TrailZ = std::min(TrailZ, countTrailingZeros(Offset)); } else { // Handle array index arithmetic. Type *IndexedTy = GTI.getIndexedType(); if (!IndexedTy->isSized()) { TrailZ = 0; break; } unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits(); uint64_t TypeSize = DL.getTypeAllocSize(IndexedTy); LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0); computeKnownBits(Index, LocalKnownZero, LocalKnownOne, DL, Depth + 1, Q); TrailZ = std::min(TrailZ, unsigned(countTrailingZeros(TypeSize) + LocalKnownZero.countTrailingOnes())); } } KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ); break; } case Instruction::PHI: { PHINode *P = cast(I); // Handle the case of a simple two-predecessor recurrence PHI. // There's a lot more that could theoretically be done here, but // this is sufficient to catch some interesting cases. if (P->getNumIncomingValues() == 2) { for (unsigned i = 0; i != 2; ++i) { Value *L = P->getIncomingValue(i); Value *R = P->getIncomingValue(!i); Operator *LU = dyn_cast(L); if (!LU) continue; unsigned Opcode = LU->getOpcode(); // Check for operations that have the property that if // both their operands have low zero bits, the result // will have low zero bits. if (Opcode == Instruction::Add || Opcode == Instruction::Sub || Opcode == Instruction::And || Opcode == Instruction::Or || Opcode == Instruction::Mul) { Value *LL = LU->getOperand(0); Value *LR = LU->getOperand(1); // Find a recurrence. if (LL == I) L = LR; else if (LR == I) L = LL; else break; // Ok, we have a PHI of the form L op= R. Check for low // zero bits. computeKnownBits(R, KnownZero2, KnownOne2, DL, Depth + 1, Q); // We need to take the minimum number of known bits APInt KnownZero3(KnownZero), KnownOne3(KnownOne); computeKnownBits(L, KnownZero3, KnownOne3, DL, Depth + 1, Q); KnownZero = APInt::getLowBitsSet(BitWidth, std::min(KnownZero2.countTrailingOnes(), KnownZero3.countTrailingOnes())); break; } } } // Unreachable blocks may have zero-operand PHI nodes. if (P->getNumIncomingValues() == 0) break; // Otherwise take the unions of the known bit sets of the operands, // taking conservative care to avoid excessive recursion. if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) { // Skip if every incoming value references to ourself. if (dyn_cast_or_null(P->hasConstantValue())) break; KnownZero = APInt::getAllOnesValue(BitWidth); KnownOne = APInt::getAllOnesValue(BitWidth); for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) { // Skip direct self references. if (P->getIncomingValue(i) == P) continue; KnownZero2 = APInt(BitWidth, 0); KnownOne2 = APInt(BitWidth, 0); // Recurse, but cap the recursion to one level, because we don't // want to waste time spinning around in loops. computeKnownBits(P->getIncomingValue(i), KnownZero2, KnownOne2, DL, MaxDepth - 1, Q); KnownZero &= KnownZero2; KnownOne &= KnownOne2; // If all bits have been ruled out, there's no need to check // more operands. if (!KnownZero && !KnownOne) break; } } break; } case Instruction::Call: case Instruction::Invoke: if (MDNode *MD = cast(I)->getMetadata(LLVMContext::MD_range)) computeKnownBitsFromRangeMetadata(*MD, KnownZero); // If a range metadata is attached to this IntrinsicInst, intersect the // explicit range specified by the metadata and the implicit range of // the intrinsic. if (IntrinsicInst *II = dyn_cast(I)) { switch (II->getIntrinsicID()) { default: break; case Intrinsic::ctlz: case Intrinsic::cttz: { unsigned LowBits = Log2_32(BitWidth)+1; // If this call is undefined for 0, the result will be less than 2^n. if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext())) LowBits -= 1; KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits); break; } case Intrinsic::ctpop: { unsigned LowBits = Log2_32(BitWidth)+1; KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits); break; } case Intrinsic::x86_sse42_crc32_64_64: KnownZero |= APInt::getHighBitsSet(64, 32); break; } } break; case Instruction::ExtractValue: if (IntrinsicInst *II = dyn_cast(I->getOperand(0))) { ExtractValueInst *EVI = cast(I); if (EVI->getNumIndices() != 1) break; if (EVI->getIndices()[0] == 0) { switch (II->getIntrinsicID()) { default: break; case Intrinsic::uadd_with_overflow: case Intrinsic::sadd_with_overflow: computeKnownBitsAddSub(true, II->getArgOperand(0), II->getArgOperand(1), false, KnownZero, KnownOne, KnownZero2, KnownOne2, DL, Depth, Q); break; case Intrinsic::usub_with_overflow: case Intrinsic::ssub_with_overflow: computeKnownBitsAddSub(false, II->getArgOperand(0), II->getArgOperand(1), false, KnownZero, KnownOne, KnownZero2, KnownOne2, DL, Depth, Q); break; case Intrinsic::umul_with_overflow: case Intrinsic::smul_with_overflow: computeKnownBitsMul(II->getArgOperand(0), II->getArgOperand(1), false, KnownZero, KnownOne, KnownZero2, KnownOne2, DL, Depth, Q); break; } } } } assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); } /// Determine whether the sign bit is known to be zero or one. /// Convenience wrapper around computeKnownBits. void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne, const DataLayout &DL, unsigned Depth, const Query &Q) { unsigned BitWidth = getBitWidth(V->getType(), DL); if (!BitWidth) { KnownZero = false; KnownOne = false; return; } APInt ZeroBits(BitWidth, 0); APInt OneBits(BitWidth, 0); computeKnownBits(V, ZeroBits, OneBits, DL, Depth, Q); KnownOne = OneBits[BitWidth - 1]; KnownZero = ZeroBits[BitWidth - 1]; } /// Return true if the given value is known to have exactly one /// bit set when defined. For vectors return true if every element is known to /// be a power of two when defined. Supports values with integer or pointer /// types and vectors of integers. bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth, const Query &Q, const DataLayout &DL) { if (Constant *C = dyn_cast(V)) { if (C->isNullValue()) return OrZero; if (ConstantInt *CI = dyn_cast(C)) return CI->getValue().isPowerOf2(); // TODO: Handle vector constants. } // 1 << X is clearly a power of two if the one is not shifted off the end. If // it is shifted off the end then the result is undefined. if (match(V, m_Shl(m_One(), m_Value()))) return true; // (signbit) >>l X is clearly a power of two if the one is not shifted off the // bottom. If it is shifted off the bottom then the result is undefined. if (match(V, m_LShr(m_SignBit(), m_Value()))) return true; // The remaining tests are all recursive, so bail out if we hit the limit. if (Depth++ == MaxDepth) return false; Value *X = nullptr, *Y = nullptr; // A shift of a power of two is a power of two or zero. if (OrZero && (match(V, m_Shl(m_Value(X), m_Value())) || match(V, m_Shr(m_Value(X), m_Value())))) return isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q, DL); if (ZExtInst *ZI = dyn_cast(V)) return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q, DL); if (SelectInst *SI = dyn_cast(V)) return isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth, Q, DL) && isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth, Q, DL); if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) { // A power of two and'd with anything is a power of two or zero. if (isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q, DL) || isKnownToBeAPowerOfTwo(Y, /*OrZero*/ true, Depth, Q, DL)) return true; // X & (-X) is always a power of two or zero. if (match(X, m_Neg(m_Specific(Y))) || match(Y, m_Neg(m_Specific(X)))) return true; return false; } // Adding a power-of-two or zero to the same power-of-two or zero yields // either the original power-of-two, a larger power-of-two or zero. if (match(V, m_Add(m_Value(X), m_Value(Y)))) { OverflowingBinaryOperator *VOBO = cast(V); if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) { if (match(X, m_And(m_Specific(Y), m_Value())) || match(X, m_And(m_Value(), m_Specific(Y)))) if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth, Q, DL)) return true; if (match(Y, m_And(m_Specific(X), m_Value())) || match(Y, m_And(m_Value(), m_Specific(X)))) if (isKnownToBeAPowerOfTwo(X, OrZero, Depth, Q, DL)) return true; unsigned BitWidth = V->getType()->getScalarSizeInBits(); APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0); computeKnownBits(X, LHSZeroBits, LHSOneBits, DL, Depth, Q); APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0); computeKnownBits(Y, RHSZeroBits, RHSOneBits, DL, Depth, Q); // If i8 V is a power of two or zero: // ZeroBits: 1 1 1 0 1 1 1 1 // ~ZeroBits: 0 0 0 1 0 0 0 0 if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2()) // If OrZero isn't set, we cannot give back a zero result. // Make sure either the LHS or RHS has a bit set. if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue()) return true; } } // An exact divide or right shift can only shift off zero bits, so the result // is a power of two only if the first operand is a power of two and not // copying a sign bit (sdiv int_min, 2). if (match(V, m_Exact(m_LShr(m_Value(), m_Value()))) || match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) { return isKnownToBeAPowerOfTwo(cast(V)->getOperand(0), OrZero, Depth, Q, DL); } return false; } /// \brief Test whether a GEP's result is known to be non-null. /// /// Uses properties inherent in a GEP to try to determine whether it is known /// to be non-null. /// /// Currently this routine does not support vector GEPs. static bool isGEPKnownNonNull(GEPOperator *GEP, const DataLayout &DL, unsigned Depth, const Query &Q) { if (!GEP->isInBounds() || GEP->getPointerAddressSpace() != 0) return false; // FIXME: Support vector-GEPs. assert(GEP->getType()->isPointerTy() && "We only support plain pointer GEP"); // If the base pointer is non-null, we cannot walk to a null address with an // inbounds GEP in address space zero. if (isKnownNonZero(GEP->getPointerOperand(), DL, Depth, Q)) return true; // Walk the GEP operands and see if any operand introduces a non-zero offset. // If so, then the GEP cannot produce a null pointer, as doing so would // inherently violate the inbounds contract within address space zero. for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP); GTI != GTE; ++GTI) { // Struct types are easy -- they must always be indexed by a constant. if (StructType *STy = dyn_cast(*GTI)) { ConstantInt *OpC = cast(GTI.getOperand()); unsigned ElementIdx = OpC->getZExtValue(); const StructLayout *SL = DL.getStructLayout(STy); uint64_t ElementOffset = SL->getElementOffset(ElementIdx); if (ElementOffset > 0) return true; continue; } // If we have a zero-sized type, the index doesn't matter. Keep looping. if (DL.getTypeAllocSize(GTI.getIndexedType()) == 0) continue; // Fast path the constant operand case both for efficiency and so we don't // increment Depth when just zipping down an all-constant GEP. if (ConstantInt *OpC = dyn_cast(GTI.getOperand())) { if (!OpC->isZero()) return true; continue; } // We post-increment Depth here because while isKnownNonZero increments it // as well, when we pop back up that increment won't persist. We don't want // to recurse 10k times just because we have 10k GEP operands. We don't // bail completely out because we want to handle constant GEPs regardless // of depth. if (Depth++ >= MaxDepth) continue; if (isKnownNonZero(GTI.getOperand(), DL, Depth, Q)) return true; } return false; } /// Does the 'Range' metadata (which must be a valid MD_range operand list) /// ensure that the value it's attached to is never Value? 'RangeType' is /// is the type of the value described by the range. static bool rangeMetadataExcludesValue(MDNode* Ranges, const APInt& Value) { const unsigned NumRanges = Ranges->getNumOperands() / 2; assert(NumRanges >= 1); for (unsigned i = 0; i < NumRanges; ++i) { ConstantInt *Lower = mdconst::extract(Ranges->getOperand(2 * i + 0)); ConstantInt *Upper = mdconst::extract(Ranges->getOperand(2 * i + 1)); ConstantRange Range(Lower->getValue(), Upper->getValue()); if (Range.contains(Value)) return false; } return true; } /// Return true if the given value is known to be non-zero when defined. /// For vectors return true if every element is known to be non-zero when /// defined. Supports values with integer or pointer type and vectors of /// integers. bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth, const Query &Q) { if (Constant *C = dyn_cast(V)) { if (C->isNullValue()) return false; if (isa(C)) // Must be non-zero due to null test above. return true; // TODO: Handle vectors return false; } if (Instruction* I = dyn_cast(V)) { if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) { // If the possible ranges don't contain zero, then the value is // definitely non-zero. if (IntegerType* Ty = dyn_cast(V->getType())) { const APInt ZeroValue(Ty->getBitWidth(), 0); if (rangeMetadataExcludesValue(Ranges, ZeroValue)) return true; } } } // The remaining tests are all recursive, so bail out if we hit the limit. if (Depth++ >= MaxDepth) return false; // Check for pointer simplifications. if (V->getType()->isPointerTy()) { if (isKnownNonNull(V)) return true; if (GEPOperator *GEP = dyn_cast(V)) if (isGEPKnownNonNull(GEP, DL, Depth, Q)) return true; } unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), DL); // X | Y != 0 if X != 0 or Y != 0. Value *X = nullptr, *Y = nullptr; if (match(V, m_Or(m_Value(X), m_Value(Y)))) return isKnownNonZero(X, DL, Depth, Q) || isKnownNonZero(Y, DL, Depth, Q); // ext X != 0 if X != 0. if (isa(V) || isa(V)) return isKnownNonZero(cast(V)->getOperand(0), DL, Depth, Q); // shl X, Y != 0 if X is odd. Note that the value of the shift is undefined // if the lowest bit is shifted off the end. if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) { // shl nuw can't remove any non-zero bits. OverflowingBinaryOperator *BO = cast(V); if (BO->hasNoUnsignedWrap()) return isKnownNonZero(X, DL, Depth, Q); APInt KnownZero(BitWidth, 0); APInt KnownOne(BitWidth, 0); computeKnownBits(X, KnownZero, KnownOne, DL, Depth, Q); if (KnownOne[0]) return true; } // shr X, Y != 0 if X is negative. Note that the value of the shift is not // defined if the sign bit is shifted off the end. else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) { // shr exact can only shift out zero bits. PossiblyExactOperator *BO = cast(V); if (BO->isExact()) return isKnownNonZero(X, DL, Depth, Q); bool XKnownNonNegative, XKnownNegative; ComputeSignBit(X, XKnownNonNegative, XKnownNegative, DL, Depth, Q); if (XKnownNegative) return true; } // div exact can only produce a zero if the dividend is zero. else if (match(V, m_Exact(m_IDiv(m_Value(X), m_Value())))) { return isKnownNonZero(X, DL, Depth, Q); } // X + Y. else if (match(V, m_Add(m_Value(X), m_Value(Y)))) { bool XKnownNonNegative, XKnownNegative; bool YKnownNonNegative, YKnownNegative; ComputeSignBit(X, XKnownNonNegative, XKnownNegative, DL, Depth, Q); ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, DL, Depth, Q); // If X and Y are both non-negative (as signed values) then their sum is not // zero unless both X and Y are zero. if (XKnownNonNegative && YKnownNonNegative) if (isKnownNonZero(X, DL, Depth, Q) || isKnownNonZero(Y, DL, Depth, Q)) return true; // If X and Y are both negative (as signed values) then their sum is not // zero unless both X and Y equal INT_MIN. if (BitWidth && XKnownNegative && YKnownNegative) { APInt KnownZero(BitWidth, 0); APInt KnownOne(BitWidth, 0); APInt Mask = APInt::getSignedMaxValue(BitWidth); // The sign bit of X is set. If some other bit is set then X is not equal // to INT_MIN. computeKnownBits(X, KnownZero, KnownOne, DL, Depth, Q); if ((KnownOne & Mask) != 0) return true; // The sign bit of Y is set. If some other bit is set then Y is not equal // to INT_MIN. computeKnownBits(Y, KnownZero, KnownOne, DL, Depth, Q); if ((KnownOne & Mask) != 0) return true; } // The sum of a non-negative number and a power of two is not zero. if (XKnownNonNegative && isKnownToBeAPowerOfTwo(Y, /*OrZero*/ false, Depth, Q, DL)) return true; if (YKnownNonNegative && isKnownToBeAPowerOfTwo(X, /*OrZero*/ false, Depth, Q, DL)) return true; } // X * Y. else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) { OverflowingBinaryOperator *BO = cast(V); // If X and Y are non-zero then so is X * Y as long as the multiplication // does not overflow. if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) && isKnownNonZero(X, DL, Depth, Q) && isKnownNonZero(Y, DL, Depth, Q)) return true; } // (C ? X : Y) != 0 if X != 0 and Y != 0. else if (SelectInst *SI = dyn_cast(V)) { if (isKnownNonZero(SI->getTrueValue(), DL, Depth, Q) && isKnownNonZero(SI->getFalseValue(), DL, Depth, Q)) return true; } if (!BitWidth) return false; APInt KnownZero(BitWidth, 0); APInt KnownOne(BitWidth, 0); computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q); return KnownOne != 0; } /// Return true if 'V & Mask' is known to be zero. We use this predicate to /// simplify operations downstream. Mask is known to be zero for bits that V /// cannot have. /// /// This function is defined on values with integer type, values with pointer /// type, and vectors of integers. In the case /// where V is a vector, the mask, known zero, and known one values are the /// same width as the vector element, and the bit is set only if it is true /// for all of the elements in the vector. bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL, unsigned Depth, const Query &Q) { APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0); computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q); return (KnownZero & Mask) == Mask; } /// Return the number of times the sign bit of the register is replicated into /// the other bits. We know that at least 1 bit is always equal to the sign bit /// (itself), but other cases can give us information. For example, immediately /// after an "ashr X, 2", we know that the top 3 bits are all equal to each /// other, so we return 3. /// /// 'Op' must have a scalar integer type. /// unsigned ComputeNumSignBits(Value *V, const DataLayout &DL, unsigned Depth, const Query &Q) { unsigned TyBits = DL.getTypeSizeInBits(V->getType()->getScalarType()); unsigned Tmp, Tmp2; unsigned FirstAnswer = 1; // Note that ConstantInt is handled by the general computeKnownBits case // below. if (Depth == 6) return 1; // Limit search depth. Operator *U = dyn_cast(V); switch (Operator::getOpcode(V)) { default: break; case Instruction::SExt: Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits(); return ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q) + Tmp; case Instruction::SDiv: { const APInt *Denominator; // sdiv X, C -> adds log(C) sign bits. if (match(U->getOperand(1), m_APInt(Denominator))) { // Ignore non-positive denominator. if (!Denominator->isStrictlyPositive()) break; // Calculate the incoming numerator bits. unsigned NumBits = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q); // Add floor(log(C)) bits to the numerator bits. return std::min(TyBits, NumBits + Denominator->logBase2()); } break; } case Instruction::SRem: { const APInt *Denominator; // srem X, C -> we know that the result is within [-C+1,C) when C is a // positive constant. This let us put a lower bound on the number of sign // bits. if (match(U->getOperand(1), m_APInt(Denominator))) { // Ignore non-positive denominator. if (!Denominator->isStrictlyPositive()) break; // Calculate the incoming numerator bits. SRem by a positive constant // can't lower the number of sign bits. unsigned NumrBits = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q); // Calculate the leading sign bit constraints by examining the // denominator. Given that the denominator is positive, there are two // cases: // // 1. the numerator is positive. The result range is [0,C) and [0,C) u< // (1 << ceilLogBase2(C)). // // 2. the numerator is negative. Then the result range is (-C,0] and // integers in (-C,0] are either 0 or >u (-1 << ceilLogBase2(C)). // // Thus a lower bound on the number of sign bits is `TyBits - // ceilLogBase2(C)`. unsigned ResBits = TyBits - Denominator->ceilLogBase2(); return std::max(NumrBits, ResBits); } break; } case Instruction::AShr: { Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q); // ashr X, C -> adds C sign bits. Vectors too. const APInt *ShAmt; if (match(U->getOperand(1), m_APInt(ShAmt))) { Tmp += ShAmt->getZExtValue(); if (Tmp > TyBits) Tmp = TyBits; } return Tmp; } case Instruction::Shl: { const APInt *ShAmt; if (match(U->getOperand(1), m_APInt(ShAmt))) { // shl destroys sign bits. Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q); Tmp2 = ShAmt->getZExtValue(); if (Tmp2 >= TyBits || // Bad shift. Tmp2 >= Tmp) break; // Shifted all sign bits out. return Tmp - Tmp2; } break; } case Instruction::And: case Instruction::Or: case Instruction::Xor: // NOT is handled here. // Logical binary ops preserve the number of sign bits at the worst. Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q); if (Tmp != 1) { Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q); FirstAnswer = std::min(Tmp, Tmp2); // We computed what we know about the sign bits as our first // answer. Now proceed to the generic code that uses // computeKnownBits, and pick whichever answer is better. } break; case Instruction::Select: Tmp = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q); if (Tmp == 1) return 1; // Early out. Tmp2 = ComputeNumSignBits(U->getOperand(2), DL, Depth + 1, Q); return std::min(Tmp, Tmp2); case Instruction::Add: // Add can have at most one carry bit. Thus we know that the output // is, at worst, one more bit than the inputs. Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q); if (Tmp == 1) return 1; // Early out. // Special case decrementing a value (ADD X, -1): if (const auto *CRHS = dyn_cast(U->getOperand(1))) if (CRHS->isAllOnesValue()) { APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); computeKnownBits(U->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); // If the input is known to be 0 or 1, the output is 0/-1, which is all // sign bits set. if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue()) return TyBits; // If we are subtracting one from a positive number, there is no carry // out of the result. if (KnownZero.isNegative()) return Tmp; } Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q); if (Tmp2 == 1) return 1; return std::min(Tmp, Tmp2)-1; case Instruction::Sub: Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q); if (Tmp2 == 1) return 1; // Handle NEG. if (const auto *CLHS = dyn_cast(U->getOperand(0))) if (CLHS->isNullValue()) { APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); computeKnownBits(U->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q); // If the input is known to be 0 or 1, the output is 0/-1, which is all // sign bits set. if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue()) return TyBits; // If the input is known to be positive (the sign bit is known clear), // the output of the NEG has the same number of sign bits as the input. if (KnownZero.isNegative()) return Tmp2; // Otherwise, we treat this like a SUB. } // Sub can have at most one carry bit. Thus we know that the output // is, at worst, one more bit than the inputs. Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q); if (Tmp == 1) return 1; // Early out. return std::min(Tmp, Tmp2)-1; case Instruction::PHI: { PHINode *PN = cast(U); unsigned NumIncomingValues = PN->getNumIncomingValues(); // Don't analyze large in-degree PHIs. if (NumIncomingValues > 4) break; // Unreachable blocks may have zero-operand PHI nodes. if (NumIncomingValues == 0) break; // Take the minimum of all incoming values. This can't infinitely loop // because of our depth threshold. Tmp = ComputeNumSignBits(PN->getIncomingValue(0), DL, Depth + 1, Q); for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) { if (Tmp == 1) return Tmp; Tmp = std::min( Tmp, ComputeNumSignBits(PN->getIncomingValue(i), DL, Depth + 1, Q)); } return Tmp; } case Instruction::Trunc: // FIXME: it's tricky to do anything useful for this, but it is an important // case for targets like X86. break; } // Finally, if we can prove that the top bits of the result are 0's or 1's, // use this information. APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); APInt Mask; computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q); if (KnownZero.isNegative()) { // sign bit is 0 Mask = KnownZero; } else if (KnownOne.isNegative()) { // sign bit is 1; Mask = KnownOne; } else { // Nothing known. return FirstAnswer; } // Okay, we know that the sign bit in Mask is set. Use CLZ to determine // the number of identical bits in the top of the input value. Mask = ~Mask; Mask <<= Mask.getBitWidth()-TyBits; // Return # leading zeros. We use 'min' here in case Val was zero before // shifting. We don't want to return '64' as for an i32 "0". return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros())); } /// This function computes the integer multiple of Base that equals V. /// If successful, it returns true and returns the multiple in /// Multiple. If unsuccessful, it returns false. It looks /// through SExt instructions only if LookThroughSExt is true. bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, bool LookThroughSExt, unsigned Depth) { const unsigned MaxDepth = 6; assert(V && "No Value?"); assert(Depth <= MaxDepth && "Limit Search Depth"); assert(V->getType()->isIntegerTy() && "Not integer or pointer type!"); Type *T = V->getType(); ConstantInt *CI = dyn_cast(V); if (Base == 0) return false; if (Base == 1) { Multiple = V; return true; } ConstantExpr *CO = dyn_cast(V); Constant *BaseVal = ConstantInt::get(T, Base); if (CO && CO == BaseVal) { // Multiple is 1. Multiple = ConstantInt::get(T, 1); return true; } if (CI && CI->getZExtValue() % Base == 0) { Multiple = ConstantInt::get(T, CI->getZExtValue() / Base); return true; } if (Depth == MaxDepth) return false; // Limit search depth. Operator *I = dyn_cast(V); if (!I) return false; switch (I->getOpcode()) { default: break; case Instruction::SExt: if (!LookThroughSExt) return false; // otherwise fall through to ZExt case Instruction::ZExt: return ComputeMultiple(I->getOperand(0), Base, Multiple, LookThroughSExt, Depth+1); case Instruction::Shl: case Instruction::Mul: { Value *Op0 = I->getOperand(0); Value *Op1 = I->getOperand(1); if (I->getOpcode() == Instruction::Shl) { ConstantInt *Op1CI = dyn_cast(Op1); if (!Op1CI) return false; // Turn Op0 << Op1 into Op0 * 2^Op1 APInt Op1Int = Op1CI->getValue(); uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1); APInt API(Op1Int.getBitWidth(), 0); API.setBit(BitToSet); Op1 = ConstantInt::get(V->getContext(), API); } Value *Mul0 = nullptr; if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) { if (Constant *Op1C = dyn_cast(Op1)) if (Constant *MulC = dyn_cast(Mul0)) { if (Op1C->getType()->getPrimitiveSizeInBits() < MulC->getType()->getPrimitiveSizeInBits()) Op1C = ConstantExpr::getZExt(Op1C, MulC->getType()); if (Op1C->getType()->getPrimitiveSizeInBits() > MulC->getType()->getPrimitiveSizeInBits()) MulC = ConstantExpr::getZExt(MulC, Op1C->getType()); // V == Base * (Mul0 * Op1), so return (Mul0 * Op1) Multiple = ConstantExpr::getMul(MulC, Op1C); return true; } if (ConstantInt *Mul0CI = dyn_cast(Mul0)) if (Mul0CI->getValue() == 1) { // V == Base * Op1, so return Op1 Multiple = Op1; return true; } } Value *Mul1 = nullptr; if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) { if (Constant *Op0C = dyn_cast(Op0)) if (Constant *MulC = dyn_cast(Mul1)) { if (Op0C->getType()->getPrimitiveSizeInBits() < MulC->getType()->getPrimitiveSizeInBits()) Op0C = ConstantExpr::getZExt(Op0C, MulC->getType()); if (Op0C->getType()->getPrimitiveSizeInBits() > MulC->getType()->getPrimitiveSizeInBits()) MulC = ConstantExpr::getZExt(MulC, Op0C->getType()); // V == Base * (Mul1 * Op0), so return (Mul1 * Op0) Multiple = ConstantExpr::getMul(MulC, Op0C); return true; } if (ConstantInt *Mul1CI = dyn_cast(Mul1)) if (Mul1CI->getValue() == 1) { // V == Base * Op0, so return Op0 Multiple = Op0; return true; } } } } // We could not determine if V is a multiple of Base. return false; } /// Return true if we can prove that the specified FP value is never equal to /// -0.0. /// /// NOTE: this function will need to be revisited when we support non-default /// rounding modes! /// bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) { if (const ConstantFP *CFP = dyn_cast(V)) return !CFP->getValueAPF().isNegZero(); // FIXME: Magic number! At the least, this should be given a name because it's // used similarly in CannotBeOrderedLessThanZero(). A better fix may be to // expose it as a parameter, so it can be used for testing / experimenting. if (Depth == 6) return false; // Limit search depth. const Operator *I = dyn_cast(V); if (!I) return false; // Check if the nsz fast-math flag is set if (const FPMathOperator *FPO = dyn_cast(I)) if (FPO->hasNoSignedZeros()) return true; // (add x, 0.0) is guaranteed to return +0.0, not -0.0. if (I->getOpcode() == Instruction::FAdd) if (ConstantFP *CFP = dyn_cast(I->getOperand(1))) if (CFP->isNullValue()) return true; // sitofp and uitofp turn into +0.0 for zero. if (isa(I) || isa(I)) return true; if (const IntrinsicInst *II = dyn_cast(I)) // sqrt(-0.0) = -0.0, no other negative results are possible. if (II->getIntrinsicID() == Intrinsic::sqrt) return CannotBeNegativeZero(II->getArgOperand(0), Depth+1); if (const CallInst *CI = dyn_cast(I)) if (const Function *F = CI->getCalledFunction()) { if (F->isDeclaration()) { // abs(x) != -0.0 if (F->getName() == "abs") return true; // fabs[lf](x) != -0.0 if (F->getName() == "fabs") return true; if (F->getName() == "fabsf") return true; if (F->getName() == "fabsl") return true; if (F->getName() == "sqrt" || F->getName() == "sqrtf" || F->getName() == "sqrtl") return CannotBeNegativeZero(CI->getArgOperand(0), Depth+1); } } return false; } bool llvm::CannotBeOrderedLessThanZero(const Value *V, unsigned Depth) { if (const ConstantFP *CFP = dyn_cast(V)) return !CFP->getValueAPF().isNegative() || CFP->getValueAPF().isZero(); // FIXME: Magic number! At the least, this should be given a name because it's // used similarly in CannotBeNegativeZero(). A better fix may be to // expose it as a parameter, so it can be used for testing / experimenting. if (Depth == 6) return false; // Limit search depth. const Operator *I = dyn_cast(V); if (!I) return false; switch (I->getOpcode()) { default: break; case Instruction::FMul: // x*x is always non-negative or a NaN. if (I->getOperand(0) == I->getOperand(1)) return true; // Fall through case Instruction::FAdd: case Instruction::FDiv: case Instruction::FRem: return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1) && CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1); case Instruction::FPExt: case Instruction::FPTrunc: // Widening/narrowing never change sign. return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1); case Instruction::Call: if (const IntrinsicInst *II = dyn_cast(I)) switch (II->getIntrinsicID()) { default: break; case Intrinsic::exp: case Intrinsic::exp2: case Intrinsic::fabs: case Intrinsic::sqrt: return true; case Intrinsic::powi: if (ConstantInt *CI = dyn_cast(I->getOperand(1))) { // powi(x,n) is non-negative if n is even. if (CI->getBitWidth() <= 64 && CI->getSExtValue() % 2u == 0) return true; } return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1); case Intrinsic::fma: case Intrinsic::fmuladd: // x*x+y is non-negative if y is non-negative. return I->getOperand(0) == I->getOperand(1) && CannotBeOrderedLessThanZero(I->getOperand(2), Depth+1); } break; } return false; } /// If the specified value can be set by repeating the same byte in memory, /// return the i8 value that it is represented with. This is /// true for all i8 values obviously, but is also true for i32 0, i32 -1, /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated /// byte store (e.g. i16 0x1234), return null. Value *llvm::isBytewiseValue(Value *V) { // All byte-wide stores are splatable, even of arbitrary variables. if (V->getType()->isIntegerTy(8)) return V; // Handle 'null' ConstantArrayZero etc. if (Constant *C = dyn_cast(V)) if (C->isNullValue()) return Constant::getNullValue(Type::getInt8Ty(V->getContext())); // Constant float and double values can be handled as integer values if the // corresponding integer value is "byteable". An important case is 0.0. if (ConstantFP *CFP = dyn_cast(V)) { if (CFP->getType()->isFloatTy()) V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext())); if (CFP->getType()->isDoubleTy()) V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext())); // Don't handle long double formats, which have strange constraints. } // We can handle constant integers that are multiple of 8 bits. if (ConstantInt *CI = dyn_cast(V)) { if (CI->getBitWidth() % 8 == 0) { assert(CI->getBitWidth() > 8 && "8 bits should be handled above!"); if (!CI->getValue().isSplat(8)) return nullptr; return ConstantInt::get(V->getContext(), CI->getValue().trunc(8)); } } // A ConstantDataArray/Vector is splatable if all its members are equal and // also splatable. if (ConstantDataSequential *CA = dyn_cast(V)) { Value *Elt = CA->getElementAsConstant(0); Value *Val = isBytewiseValue(Elt); if (!Val) return nullptr; for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I) if (CA->getElementAsConstant(I) != Elt) return nullptr; return Val; } // Conceptually, we could handle things like: // %a = zext i8 %X to i16 // %b = shl i16 %a, 8 // %c = or i16 %a, %b // but until there is an example that actually needs this, it doesn't seem // worth worrying about. return nullptr; } // This is the recursive version of BuildSubAggregate. It takes a few different // arguments. Idxs is the index within the nested struct From that we are // looking at now (which is of type IndexedType). IdxSkip is the number of // indices from Idxs that should be left out when inserting into the resulting // struct. To is the result struct built so far, new insertvalue instructions // build on that. static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType, SmallVectorImpl &Idxs, unsigned IdxSkip, Instruction *InsertBefore) { llvm::StructType *STy = dyn_cast(IndexedType); if (STy) { // Save the original To argument so we can modify it Value *OrigTo = To; // General case, the type indexed by Idxs is a struct for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { // Process each struct element recursively Idxs.push_back(i); Value *PrevTo = To; To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip, InsertBefore); Idxs.pop_back(); if (!To) { // Couldn't find any inserted value for this index? Cleanup while (PrevTo != OrigTo) { InsertValueInst* Del = cast(PrevTo); PrevTo = Del->getAggregateOperand(); Del->eraseFromParent(); } // Stop processing elements break; } } // If we successfully found a value for each of our subaggregates if (To) return To; } // Base case, the type indexed by SourceIdxs is not a struct, or not all of // the struct's elements had a value that was inserted directly. In the latter // case, perhaps we can't determine each of the subelements individually, but // we might be able to find the complete struct somewhere. // Find the value that is at that particular spot Value *V = FindInsertedValue(From, Idxs); if (!V) return nullptr; // Insert the value in the new (sub) aggregrate return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip), "tmp", InsertBefore); } // This helper takes a nested struct and extracts a part of it (which is again a // struct) into a new value. For example, given the struct: // { a, { b, { c, d }, e } } // and the indices "1, 1" this returns // { c, d }. // // It does this by inserting an insertvalue for each element in the resulting // struct, as opposed to just inserting a single struct. This will only work if // each of the elements of the substruct are known (ie, inserted into From by an // insertvalue instruction somewhere). // // All inserted insertvalue instructions are inserted before InsertBefore static Value *BuildSubAggregate(Value *From, ArrayRef idx_range, Instruction *InsertBefore) { assert(InsertBefore && "Must have someplace to insert!"); Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(), idx_range); Value *To = UndefValue::get(IndexedType); SmallVector Idxs(idx_range.begin(), idx_range.end()); unsigned IdxSkip = Idxs.size(); return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore); } /// Given an aggregrate and an sequence of indices, see if /// the scalar value indexed is already around as a register, for example if it /// were inserted directly into the aggregrate. /// /// If InsertBefore is not null, this function will duplicate (modified) /// insertvalues when a part of a nested struct is extracted. Value *llvm::FindInsertedValue(Value *V, ArrayRef idx_range, Instruction *InsertBefore) { // Nothing to index? Just return V then (this is useful at the end of our // recursion). if (idx_range.empty()) return V; // We have indices, so V should have an indexable type. assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) && "Not looking at a struct or array?"); assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) && "Invalid indices for type?"); if (Constant *C = dyn_cast(V)) { C = C->getAggregateElement(idx_range[0]); if (!C) return nullptr; return FindInsertedValue(C, idx_range.slice(1), InsertBefore); } if (InsertValueInst *I = dyn_cast(V)) { // Loop the indices for the insertvalue instruction in parallel with the // requested indices const unsigned *req_idx = idx_range.begin(); for (const unsigned *i = I->idx_begin(), *e = I->idx_end(); i != e; ++i, ++req_idx) { if (req_idx == idx_range.end()) { // We can't handle this without inserting insertvalues if (!InsertBefore) return nullptr; // The requested index identifies a part of a nested aggregate. Handle // this specially. For example, // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0 // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1 // %C = extractvalue {i32, { i32, i32 } } %B, 1 // This can be changed into // %A = insertvalue {i32, i32 } undef, i32 10, 0 // %C = insertvalue {i32, i32 } %A, i32 11, 1 // which allows the unused 0,0 element from the nested struct to be // removed. return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx), InsertBefore); } // This insert value inserts something else than what we are looking for. // See if the (aggregrate) value inserted into has the value we are // looking for, then. if (*req_idx != *i) return FindInsertedValue(I->getAggregateOperand(), idx_range, InsertBefore); } // If we end up here, the indices of the insertvalue match with those // requested (though possibly only partially). Now we recursively look at // the inserted value, passing any remaining indices. return FindInsertedValue(I->getInsertedValueOperand(), makeArrayRef(req_idx, idx_range.end()), InsertBefore); } if (ExtractValueInst *I = dyn_cast(V)) { // If we're extracting a value from an aggregrate that was extracted from // something else, we can extract from that something else directly instead. // However, we will need to chain I's indices with the requested indices. // Calculate the number of indices required unsigned size = I->getNumIndices() + idx_range.size(); // Allocate some space to put the new indices in SmallVector Idxs; Idxs.reserve(size); // Add indices from the extract value instruction Idxs.append(I->idx_begin(), I->idx_end()); // Add requested indices Idxs.append(idx_range.begin(), idx_range.end()); assert(Idxs.size() == size && "Number of indices added not correct?"); return FindInsertedValue(I->getAggregateOperand(), Idxs, InsertBefore); } // Otherwise, we don't know (such as, extracting from a function return value // or load instruction) return nullptr; } /// Analyze the specified pointer to see if it can be expressed as a base /// pointer plus a constant offset. Return the base and offset to the caller. Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, const DataLayout &DL) { unsigned BitWidth = DL.getPointerTypeSizeInBits(Ptr->getType()); APInt ByteOffset(BitWidth, 0); while (1) { if (Ptr->getType()->isVectorTy()) break; if (GEPOperator *GEP = dyn_cast(Ptr)) { APInt GEPOffset(BitWidth, 0); if (!GEP->accumulateConstantOffset(DL, GEPOffset)) break; ByteOffset += GEPOffset; Ptr = GEP->getPointerOperand(); } else if (Operator::getOpcode(Ptr) == Instruction::BitCast || Operator::getOpcode(Ptr) == Instruction::AddrSpaceCast) { Ptr = cast(Ptr)->getOperand(0); } else if (GlobalAlias *GA = dyn_cast(Ptr)) { if (GA->mayBeOverridden()) break; Ptr = GA->getAliasee(); } else { break; } } Offset = ByteOffset.getSExtValue(); return Ptr; } /// This function computes the length of a null-terminated C string pointed to /// by V. If successful, it returns true and returns the string in Str. /// If unsuccessful, it returns false. bool llvm::getConstantStringInfo(const Value *V, StringRef &Str, uint64_t Offset, bool TrimAtNul) { assert(V); // Look through bitcast instructions and geps. V = V->stripPointerCasts(); // If the value is a GEP instruction or constant expression, treat it as an // offset. if (const GEPOperator *GEP = dyn_cast(V)) { // Make sure the GEP has exactly three arguments. if (GEP->getNumOperands() != 3) return false; // Make sure the index-ee is a pointer to array of i8. PointerType *PT = cast(GEP->getOperand(0)->getType()); ArrayType *AT = dyn_cast(PT->getElementType()); if (!AT || !AT->getElementType()->isIntegerTy(8)) return false; // Check to make sure that the first operand of the GEP is an integer and // has value 0 so that we are sure we're indexing into the initializer. const ConstantInt *FirstIdx = dyn_cast(GEP->getOperand(1)); if (!FirstIdx || !FirstIdx->isZero()) return false; // If the second index isn't a ConstantInt, then this is a variable index // into the array. If this occurs, we can't say anything meaningful about // the string. uint64_t StartIdx = 0; if (const ConstantInt *CI = dyn_cast(GEP->getOperand(2))) StartIdx = CI->getZExtValue(); else return false; return getConstantStringInfo(GEP->getOperand(0), Str, StartIdx + Offset, TrimAtNul); } // The GEP instruction, constant or instruction, must reference a global // variable that is a constant and is initialized. The referenced constant // initializer is the array that we'll use for optimization. const GlobalVariable *GV = dyn_cast(V); if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer()) return false; // Handle the all-zeros case if (GV->getInitializer()->isNullValue()) { // This is a degenerate case. The initializer is constant zero so the // length of the string must be zero. Str = ""; return true; } // Must be a Constant Array const ConstantDataArray *Array = dyn_cast(GV->getInitializer()); if (!Array || !Array->isString()) return false; // Get the number of elements in the array uint64_t NumElts = Array->getType()->getArrayNumElements(); // Start out with the entire array in the StringRef. Str = Array->getAsString(); if (Offset > NumElts) return false; // Skip over 'offset' bytes. Str = Str.substr(Offset); if (TrimAtNul) { // Trim off the \0 and anything after it. If the array is not nul // terminated, we just return the whole end of string. The client may know // some other way that the string is length-bound. Str = Str.substr(0, Str.find('\0')); } return true; } // These next two are very similar to the above, but also look through PHI // nodes. // TODO: See if we can integrate these two together. /// If we can compute the length of the string pointed to by /// the specified pointer, return 'len+1'. If we can't, return 0. static uint64_t GetStringLengthH(Value *V, SmallPtrSetImpl &PHIs) { // Look through noop bitcast instructions. V = V->stripPointerCasts(); // If this is a PHI node, there are two cases: either we have already seen it // or we haven't. if (PHINode *PN = dyn_cast(V)) { if (!PHIs.insert(PN).second) return ~0ULL; // already in the set. // If it was new, see if all the input strings are the same length. uint64_t LenSoFar = ~0ULL; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { uint64_t Len = GetStringLengthH(PN->getIncomingValue(i), PHIs); if (Len == 0) return 0; // Unknown length -> unknown. if (Len == ~0ULL) continue; if (Len != LenSoFar && LenSoFar != ~0ULL) return 0; // Disagree -> unknown. LenSoFar = Len; } // Success, all agree. return LenSoFar; } // strlen(select(c,x,y)) -> strlen(x) ^ strlen(y) if (SelectInst *SI = dyn_cast(V)) { uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs); if (Len1 == 0) return 0; uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs); if (Len2 == 0) return 0; if (Len1 == ~0ULL) return Len2; if (Len2 == ~0ULL) return Len1; if (Len1 != Len2) return 0; return Len1; } // Otherwise, see if we can read the string. StringRef StrData; if (!getConstantStringInfo(V, StrData)) return 0; return StrData.size()+1; } /// If we can compute the length of the string pointed to by /// the specified pointer, return 'len+1'. If we can't, return 0. uint64_t llvm::GetStringLength(Value *V) { if (!V->getType()->isPointerTy()) return 0; SmallPtrSet PHIs; uint64_t Len = GetStringLengthH(V, PHIs); // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return // an empty string as a length. return Len == ~0ULL ? 1 : Len; } Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL, unsigned MaxLookup) { if (!V->getType()->isPointerTy()) return V; for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) { if (GEPOperator *GEP = dyn_cast(V)) { V = GEP->getPointerOperand(); } else if (Operator::getOpcode(V) == Instruction::BitCast || Operator::getOpcode(V) == Instruction::AddrSpaceCast) { V = cast(V)->getOperand(0); } else if (GlobalAlias *GA = dyn_cast(V)) { if (GA->mayBeOverridden()) return V; V = GA->getAliasee(); } else { // See if InstructionSimplify knows any relevant tricks. if (Instruction *I = dyn_cast(V)) // TODO: Acquire a DominatorTree and AssumptionCache and use them. if (Value *Simplified = SimplifyInstruction(I, DL, nullptr)) { V = Simplified; continue; } return V; } assert(V->getType()->isPointerTy() && "Unexpected operand type!"); } return V; } void llvm::GetUnderlyingObjects(Value *V, SmallVectorImpl &Objects, const DataLayout &DL, unsigned MaxLookup) { SmallPtrSet Visited; SmallVector Worklist; Worklist.push_back(V); do { Value *P = Worklist.pop_back_val(); P = GetUnderlyingObject(P, DL, MaxLookup); if (!Visited.insert(P).second) continue; if (SelectInst *SI = dyn_cast(P)) { Worklist.push_back(SI->getTrueValue()); Worklist.push_back(SI->getFalseValue()); continue; } if (PHINode *PN = dyn_cast(P)) { for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) Worklist.push_back(PN->getIncomingValue(i)); continue; } Objects.push_back(P); } while (!Worklist.empty()); } /// Return true if the only users of this pointer are lifetime markers. bool llvm::onlyUsedByLifetimeMarkers(const Value *V) { for (const User *U : V->users()) { const IntrinsicInst *II = dyn_cast(U); if (!II) return false; if (II->getIntrinsicID() != Intrinsic::lifetime_start && II->getIntrinsicID() != Intrinsic::lifetime_end) return false; } return true; } bool llvm::isSafeToSpeculativelyExecute(const Value *V) { const Operator *Inst = dyn_cast(V); if (!Inst) return false; for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) if (Constant *C = dyn_cast(Inst->getOperand(i))) if (C->canTrap()) return false; switch (Inst->getOpcode()) { default: return true; case Instruction::UDiv: case Instruction::URem: { // x / y is undefined if y == 0. const APInt *V; if (match(Inst->getOperand(1), m_APInt(V))) return *V != 0; return false; } case Instruction::SDiv: case Instruction::SRem: { // x / y is undefined if y == 0 or x == INT_MIN and y == -1 const APInt *Numerator, *Denominator; if (!match(Inst->getOperand(1), m_APInt(Denominator))) return false; // We cannot hoist this division if the denominator is 0. if (*Denominator == 0) return false; // It's safe to hoist if the denominator is not 0 or -1. if (*Denominator != -1) return true; // At this point we know that the denominator is -1. It is safe to hoist as // long we know that the numerator is not INT_MIN. if (match(Inst->getOperand(0), m_APInt(Numerator))) return !Numerator->isMinSignedValue(); // The numerator *might* be MinSignedValue. return false; } case Instruction::Load: { const LoadInst *LI = cast(Inst); if (!LI->isUnordered() || // Speculative load may create a race that did not exist in the source. LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread)) return false; const DataLayout &DL = LI->getModule()->getDataLayout(); return LI->getPointerOperand()->isDereferenceablePointer(DL); } case Instruction::Call: { if (const IntrinsicInst *II = dyn_cast(Inst)) { switch (II->getIntrinsicID()) { // These synthetic intrinsics have no side-effects and just mark // information about their operands. // FIXME: There are other no-op synthetic instructions that potentially // should be considered at least *safe* to speculate... case Intrinsic::dbg_declare: case Intrinsic::dbg_value: return true; case Intrinsic::bswap: case Intrinsic::ctlz: case Intrinsic::ctpop: case Intrinsic::cttz: case Intrinsic::objectsize: case Intrinsic::sadd_with_overflow: case Intrinsic::smul_with_overflow: case Intrinsic::ssub_with_overflow: case Intrinsic::uadd_with_overflow: case Intrinsic::umul_with_overflow: case Intrinsic::usub_with_overflow: return true; // Sqrt should be OK, since the llvm sqrt intrinsic isn't defined to set // errno like libm sqrt would. case Intrinsic::sqrt: case Intrinsic::fma: case Intrinsic::fmuladd: case Intrinsic::fabs: case Intrinsic::minnum: case Intrinsic::maxnum: return true; // TODO: some fp intrinsics are marked as having the same error handling // as libm. They're safe to speculate when they won't error. // TODO: are convert_{from,to}_fp16 safe? // TODO: can we list target-specific intrinsics here? default: break; } } return false; // The called function could have undefined behavior or // side-effects, even if marked readnone nounwind. } case Instruction::VAArg: case Instruction::Alloca: case Instruction::Invoke: case Instruction::PHI: case Instruction::Store: case Instruction::Ret: case Instruction::Br: case Instruction::IndirectBr: case Instruction::Switch: case Instruction::Unreachable: case Instruction::Fence: case Instruction::LandingPad: case Instruction::AtomicRMW: case Instruction::AtomicCmpXchg: case Instruction::Resume: return false; // Misc instructions which have effects } } /// Return true if we know that the specified value is never null. bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) { // Alloca never returns null, malloc might. if (isa(V)) return true; // A byval, inalloca, or nonnull argument is never null. if (const Argument *A = dyn_cast(V)) return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr(); // Global values are not null unless extern weak. if (const GlobalValue *GV = dyn_cast(V)) return !GV->hasExternalWeakLinkage(); // A Load tagged w/nonnull metadata is never null. if (const LoadInst *LI = dyn_cast(V)) return LI->getMetadata(LLVMContext::MD_nonnull); if (auto CS = ImmutableCallSite(V)) if (CS.isReturnNonNull()) return true; // operator new never returns null. if (isOperatorNewLikeFn(V, TLI, /*LookThroughBitCast=*/true)) return true; return false; } OverflowResult llvm::computeOverflowForUnsignedMul(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { // Multiplying n * m significant bits yields a result of n + m significant // bits. If the total number of significant bits does not exceed the // result bit width (minus 1), there is no overflow. // This means if we have enough leading zero bits in the operands // we can guarantee that the result does not overflow. // Ref: "Hacker's Delight" by Henry Warren unsigned BitWidth = LHS->getType()->getScalarSizeInBits(); APInt LHSKnownZero(BitWidth, 0); APInt LHSKnownOne(BitWidth, 0); APInt RHSKnownZero(BitWidth, 0); APInt RHSKnownOne(BitWidth, 0); computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, /*Depth=*/0, AC, CxtI, DT); computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, /*Depth=*/0, AC, CxtI, DT); // Note that underestimating the number of zero bits gives a more // conservative answer. unsigned ZeroBits = LHSKnownZero.countLeadingOnes() + RHSKnownZero.countLeadingOnes(); // First handle the easy case: if we have enough zero bits there's // definitely no overflow. if (ZeroBits >= BitWidth) return OverflowResult::NeverOverflows; // Get the largest possible values for each operand. APInt LHSMax = ~LHSKnownZero; APInt RHSMax = ~RHSKnownZero; // We know the multiply operation doesn't overflow if the maximum values for // each operand will not overflow after we multiply them together. bool MaxOverflow; LHSMax.umul_ov(RHSMax, MaxOverflow); if (!MaxOverflow) return OverflowResult::NeverOverflows; // We know it always overflows if multiplying the smallest possible values for // the operands also results in overflow. bool MinOverflow; LHSKnownOne.umul_ov(RHSKnownOne, MinOverflow); if (MinOverflow) return OverflowResult::AlwaysOverflows; return OverflowResult::MayOverflow; } OverflowResult llvm::computeOverflowForUnsignedAdd(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { bool LHSKnownNonNegative, LHSKnownNegative; ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0, AC, CxtI, DT); if (LHSKnownNonNegative || LHSKnownNegative) { bool RHSKnownNonNegative, RHSKnownNegative; ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0, AC, CxtI, DT); if (LHSKnownNegative && RHSKnownNegative) { // The sign bit is set in both cases: this MUST overflow. // Create a simple add instruction, and insert it into the struct. return OverflowResult::AlwaysOverflows; } if (LHSKnownNonNegative && RHSKnownNonNegative) { // The sign bit is clear in both cases: this CANNOT overflow. // Create a simple add instruction, and insert it into the struct. return OverflowResult::NeverOverflows; } } return OverflowResult::MayOverflow; }