| //===- 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/Optional.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/MemoryBuiltins.h" |
| #include "llvm/Analysis/LoopInfo.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/IR/Statepoint.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/MathExtras.h" |
| #include <cstring> |
| 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 chosen to be fairly aggressive. If you |
| /// run into compile time problems when testing, scale them back and report |
| /// your findings. |
| static cl::opt<bool> 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<unsigned> DomConditionsMaxDepth("dom-conditions-max-depth", |
| cl::Hidden, cl::init(1)); |
| |
| /// How many dominating blocks should be scanned looking for dominating |
| /// conditions? |
| static cl::opt<unsigned> DomConditionsMaxDomBlocks("dom-conditions-dom-blocks", |
| cl::Hidden, |
| cl::init(20)); |
| |
| // Controls the number of uses of the value searched for possible |
| // dominating comparisons. |
| static cl::opt<unsigned> DomConditionsMaxUses("dom-conditions-max-uses", |
| cl::Hidden, cl::init(20)); |
| |
| // If true, don't consider only compares whose only use is a branch. |
| static cl::opt<bool> 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<const Value *, 8> 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<Instruction>(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)); |
| } |
| |
| bool llvm::haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL, |
| AssumptionCache *AC, const Instruction *CxtI, |
| const DominatorTree *DT) { |
| assert(LHS->getType() == RHS->getType() && |
| "LHS and RHS should have the same type"); |
| assert(LHS->getType()->isIntOrIntVectorTy() && |
| "LHS and RHS should be integers"); |
| IntegerType *IT = cast<IntegerType>(LHS->getType()->getScalarType()); |
| APInt LHSKnownZero(IT->getBitWidth(), 0), LHSKnownOne(IT->getBitWidth(), 0); |
| APInt RHSKnownZero(IT->getBitWidth(), 0), RHSKnownOne(IT->getBitWidth(), 0); |
| computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, 0, AC, CxtI, DT); |
| computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, 0, AC, CxtI, DT); |
| return (LHSKnownZero | RHSKnownZero).isAllOnesValue(); |
| } |
| |
| 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)); |
| } |
| |
| bool llvm::isKnownNonNegative(Value *V, const DataLayout &DL, unsigned Depth, |
| AssumptionCache *AC, const Instruction *CxtI, |
| const DominatorTree *DT) { |
| bool NonNegative, Negative; |
| ComputeSignBit(V, NonNegative, Negative, DL, Depth, AC, CxtI, DT); |
| return NonNegative; |
| } |
| |
| static bool isKnownNonEqual(Value *V1, Value *V2, const DataLayout &DL, |
| const Query &Q); |
| |
| bool llvm::isKnownNonEqual(Value *V1, Value *V2, const DataLayout &DL, |
| AssumptionCache *AC, const Instruction *CxtI, |
| const DominatorTree *DT) { |
| return ::isKnownNonEqual(V1, V2, DL, Query(AC, |
| safeCxtI(V1, safeCxtI(V2, 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<ConstantInt>(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 conservative 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, |
| APInt &KnownOne) { |
| unsigned BitWidth = KnownZero.getBitWidth(); |
| unsigned NumRanges = Ranges.getNumOperands() / 2; |
| assert(NumRanges >= 1); |
| |
| KnownZero.setAllBits(); |
| KnownOne.setAllBits(); |
| |
| for (unsigned i = 0; i < NumRanges; ++i) { |
| ConstantInt *Lower = |
| mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0)); |
| ConstantInt *Upper = |
| mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1)); |
| ConstantRange Range(Lower->getValue(), Upper->getValue()); |
| |
| // The first CommonPrefixBits of all values in Range are equal. |
| unsigned CommonPrefixBits = |
| (Range.getUnsignedMax() ^ Range.getUnsignedMin()).countLeadingZeros(); |
| |
| APInt Mask = APInt::getHighBitsSet(BitWidth, CommonPrefixBits); |
| KnownOne &= Range.getUnsignedMax() & Mask; |
| KnownZero &= ~Range.getUnsignedMax() & Mask; |
| } |
| } |
| |
| static bool isEphemeralValueOf(Instruction *I, const Value *E) { |
| SmallVector<const Value *, 16> WorkSet(1, I); |
| SmallPtrSet<const Value *, 32> Visited; |
| SmallPtrSet<const Value *, 16> EphValues; |
| |
| // The instruction defining an assumption's condition itself is always |
| // considered ephemeral to that assumption (even if it has other |
| // non-ephemeral users). See r246696's test case for an example. |
| if (std::find(I->op_begin(), I->op_end(), E) != I->op_end()) |
| return true; |
| |
| 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. |
| if (std::all_of(V->user_begin(), V->user_end(), |
| [&](const User *U) { return EphValues.count(U); })) { |
| if (V == E) |
| return true; |
| |
| EphValues.insert(V); |
| if (const User *U = dyn_cast<User>(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<CallInst>(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<Instruction>(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<Instruction *>(I), |
| Query(nullptr, CxtI, DT)); |
| } |
| |
| template<typename LHS, typename RHS> |
| inline match_combine_or<CmpClass_match<LHS, RHS, ICmpInst, ICmpInst::Predicate>, |
| CmpClass_match<RHS, LHS, ICmpInst, ICmpInst::Predicate>> |
| 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<typename LHS, typename RHS> |
| inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::And>, |
| BinaryOp_match<RHS, LHS, Instruction::And>> |
| m_c_And(const LHS &L, const RHS &R) { |
| return m_CombineOr(m_And(L, R), m_And(R, L)); |
| } |
| |
| template<typename LHS, typename RHS> |
| inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Or>, |
| BinaryOp_match<RHS, LHS, Instruction::Or>> |
| m_c_Or(const LHS &L, const RHS &R) { |
| return m_CombineOr(m_Or(L, R), m_Or(R, L)); |
| } |
| |
| template<typename LHS, typename RHS> |
| inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Xor>, |
| BinaryOp_match<RHS, LHS, Instruction::Xor>> |
| 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: |
| { |
| APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0); |
| if (LHS == V) |
| computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q); |
| else if (RHS == V) |
| computeKnownBits(LHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q); |
| else |
| llvm_unreachable("missing use?"); |
| KnownZero |= KnownZeroTemp; |
| KnownOne |= KnownOneTemp; |
| } |
| 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<Instruction *>(Q.CxtI); |
| // The context instruction might be in a statically unreachable block. If |
| // so, asking dominator queries may yield suprising results. (e.g. the block |
| // may not have a dom tree node) |
| if (!Q.DT->isReachableFromEntry(Cxt->getParent())) |
| return; |
| |
| // Avoid useless work |
| if (auto VI = dyn_cast<Instruction>(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<BranchInst>(Current->getTerminator()); |
| if (!BI || BI->isUnconditional()) |
| continue; |
| ICmpInst *Cmp = dyn_cast<ICmpInst>(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. We |
| // know that the edge must be reachable since we started from a reachable |
| // block. |
| 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<ICmpInst>(U); |
| if (!Cmp) |
| continue; |
| |
| if (DomConditionsSingleCmpUse && !Cmp->hasOneUse()) |
| continue; |
| |
| for (auto *CmpU : Cmp->users()) { |
| BranchInst *BI = dyn_cast<BranchInst>(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<CallInst>(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()); |
| } |
| } |
| } |
| |
| // Compute known bits from a shift operator, including those with a |
| // non-constant shift amount. KnownZero and KnownOne are the outputs of this |
| // function. KnownZero2 and KnownOne2 are pre-allocated temporaries with the |
| // same bit width as KnownZero and KnownOne. KZF and KOF are operator-specific |
| // functors that, given the known-zero or known-one bits respectively, and a |
| // shift amount, compute the implied known-zero or known-one bits of the shift |
| // operator's result respectively for that shift amount. The results from calling |
| // KZF and KOF are conservatively combined for all permitted shift amounts. |
| template <typename KZFunctor, typename KOFunctor> |
| static void computeKnownBitsFromShiftOperator(Operator *I, |
| APInt &KnownZero, APInt &KnownOne, |
| APInt &KnownZero2, APInt &KnownOne2, |
| const DataLayout &DL, unsigned Depth, const Query &Q, |
| KZFunctor KZF, KOFunctor KOF) { |
| unsigned BitWidth = KnownZero.getBitWidth(); |
| |
| if (auto *SA = dyn_cast<ConstantInt>(I->getOperand(1))) { |
| unsigned ShiftAmt = SA->getLimitedValue(BitWidth-1); |
| |
| computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q); |
| KnownZero = KZF(KnownZero, ShiftAmt); |
| KnownOne = KOF(KnownOne, ShiftAmt); |
| return; |
| } |
| |
| computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q); |
| |
| // Note: We cannot use KnownZero.getLimitedValue() here, because if |
| // BitWidth > 64 and any upper bits are known, we'll end up returning the |
| // limit value (which implies all bits are known). |
| uint64_t ShiftAmtKZ = KnownZero.zextOrTrunc(64).getZExtValue(); |
| uint64_t ShiftAmtKO = KnownOne.zextOrTrunc(64).getZExtValue(); |
| |
| // It would be more-clearly correct to use the two temporaries for this |
| // calculation. Reusing the APInts here to prevent unnecessary allocations. |
| KnownZero.clearAllBits(), KnownOne.clearAllBits(); |
| |
| // If we know the shifter operand is nonzero, we can sometimes infer more |
| // known bits. However this is expensive to compute, so be lazy about it and |
| // only compute it when absolutely necessary. |
| Optional<bool> ShifterOperandIsNonZero; |
| |
| // Early exit if we can't constrain any well-defined shift amount. |
| if (!(ShiftAmtKZ & (BitWidth - 1)) && !(ShiftAmtKO & (BitWidth - 1))) { |
| ShifterOperandIsNonZero = |
| isKnownNonZero(I->getOperand(1), DL, Depth + 1, Q); |
| if (!*ShifterOperandIsNonZero) |
| return; |
| } |
| |
| computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q); |
| |
| KnownZero = KnownOne = APInt::getAllOnesValue(BitWidth); |
| for (unsigned ShiftAmt = 0; ShiftAmt < BitWidth; ++ShiftAmt) { |
| // Combine the shifted known input bits only for those shift amounts |
| // compatible with its known constraints. |
| if ((ShiftAmt & ~ShiftAmtKZ) != ShiftAmt) |
| continue; |
| if ((ShiftAmt | ShiftAmtKO) != ShiftAmt) |
| continue; |
| // If we know the shifter is nonzero, we may be able to infer more known |
| // bits. This check is sunk down as far as possible to avoid the expensive |
| // call to isKnownNonZero if the cheaper checks above fail. |
| if (ShiftAmt == 0) { |
| if (!ShifterOperandIsNonZero.hasValue()) |
| ShifterOperandIsNonZero = |
| isKnownNonZero(I->getOperand(1), DL, Depth + 1, Q); |
| if (*ShifterOperandIsNonZero) |
| continue; |
| } |
| |
| KnownZero &= KZF(KnownZero2, ShiftAmt); |
| KnownOne &= KOF(KnownOne2, ShiftAmt); |
| } |
| |
| // If there are no compatible shift amounts, then we've proven that the shift |
| // amount must be >= the BitWidth, and the result is undefined. We could |
| // return anything we'd like, but we need to make sure the sets of known bits |
| // stay disjoint (it should be better for some other code to actually |
| // propagate the undef than to pick a value here using known bits). |
| if ((KnownZero & KnownOne) != 0) |
| KnownZero.clearAllBits(), KnownOne.clearAllBits(); |
| } |
| |
| static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero, |
| APInt &KnownOne, const DataLayout &DL, |
| unsigned Depth, const Query &Q) { |
| unsigned BitWidth = KnownZero.getBitWidth(); |
| |
| APInt KnownZero2(KnownZero), KnownOne2(KnownOne); |
| switch (I->getOpcode()) { |
| default: break; |
| case Instruction::Load: |
| if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range)) |
| computeKnownBitsFromRangeMetadata(*MD, KnownZero, KnownOne); |
| 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; |
| |
| // and(x, add (x, -1)) is a common idiom that always clears the low bit; |
| // here we handle the more general case of adding any odd number by |
| // matching the form add(x, add(x, y)) where y is odd. |
| // TODO: This could be generalized to clearing any bit set in y where the |
| // following bit is known to be unset in y. |
| Value *Y = nullptr; |
| if (match(I->getOperand(0), m_Add(m_Specific(I->getOperand(1)), |
| m_Value(Y))) || |
| match(I->getOperand(1), m_Add(m_Specific(I->getOperand(0)), |
| m_Value(Y)))) { |
| APInt KnownZero3(BitWidth, 0), KnownOne3(BitWidth, 0); |
| computeKnownBits(Y, KnownZero3, KnownOne3, DL, Depth + 1, Q); |
| if (KnownOne3.countTrailingOnes() > 0) |
| KnownZero |= APInt::getLowBitsSet(BitWidth, 1); |
| } |
| 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<OverflowingBinaryOperator>(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() || |
| SrcTy->isFloatingPointTy()) && |
| // 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 |
| auto KZF = [BitWidth](const APInt &KnownZero, unsigned ShiftAmt) { |
| return (KnownZero << ShiftAmt) | |
| APInt::getLowBitsSet(BitWidth, ShiftAmt); // Low bits known 0. |
| }; |
| |
| auto KOF = [BitWidth](const APInt &KnownOne, unsigned ShiftAmt) { |
| return KnownOne << ShiftAmt; |
| }; |
| |
| computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne, |
| KnownZero2, KnownOne2, DL, Depth, Q, |
| KZF, KOF); |
| break; |
| } |
| case Instruction::LShr: { |
| // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 |
| auto KZF = [BitWidth](const APInt &KnownZero, unsigned ShiftAmt) { |
| return APIntOps::lshr(KnownZero, ShiftAmt) | |
| // High bits known zero. |
| APInt::getHighBitsSet(BitWidth, ShiftAmt); |
| }; |
| |
| auto KOF = [BitWidth](const APInt &KnownOne, unsigned ShiftAmt) { |
| return APIntOps::lshr(KnownOne, ShiftAmt); |
| }; |
| |
| computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne, |
| KnownZero2, KnownOne2, DL, Depth, Q, |
| KZF, KOF); |
| break; |
| } |
| case Instruction::AShr: { |
| // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 |
| auto KZF = [BitWidth](const APInt &KnownZero, unsigned ShiftAmt) { |
| return APIntOps::ashr(KnownZero, ShiftAmt); |
| }; |
| |
| auto KOF = [BitWidth](const APInt &KnownOne, unsigned ShiftAmt) { |
| return APIntOps::ashr(KnownOne, ShiftAmt); |
| }; |
| |
| computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne, |
| KnownZero2, KnownOne2, DL, Depth, Q, |
| KZF, KOF); |
| break; |
| } |
| case Instruction::Sub: { |
| bool NSW = cast<OverflowingBinaryOperator>(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<OverflowingBinaryOperator>(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<ConstantInt>(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<ConstantInt>(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<AllocaInst>(I); |
| 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<StructType>(*GTI)) { |
| // Handle struct member offset arithmetic. |
| |
| // Handle case when index is vector zeroinitializer |
| Constant *CIndex = cast<Constant>(Index); |
| if (CIndex->isZeroValue()) |
| continue; |
| |
| if (CIndex->getType()->isVectorTy()) |
| Index = CIndex->getSplatValue(); |
| |
| unsigned Idx = cast<ConstantInt>(Index)->getZExtValue(); |
| const StructLayout *SL = DL.getStructLayout(STy); |
| uint64_t Offset = SL->getElementOffset(Idx); |
| TrailZ = std::min<unsigned>(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<PHINode>(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<Operator>(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<UndefValue>(P->hasConstantValue())) |
| break; |
| |
| KnownZero = APInt::getAllOnesValue(BitWidth); |
| KnownOne = APInt::getAllOnesValue(BitWidth); |
| for (Value *IncValue : P->incoming_values()) { |
| // Skip direct self references. |
| if (IncValue == 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(IncValue, 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<Instruction>(I)->getMetadata(LLVMContext::MD_range)) |
| computeKnownBitsFromRangeMetadata(*MD, KnownZero, KnownOne); |
| // 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<IntrinsicInst>(I)) { |
| switch (II->getIntrinsicID()) { |
| default: break; |
| case Intrinsic::bswap: |
| computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, |
| Depth + 1, Q); |
| KnownZero |= KnownZero2.byteSwap(); |
| KnownOne |= KnownOne2.byteSwap(); |
| 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: { |
| computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, |
| Depth + 1, Q); |
| // We can bound the space the count needs. Also, bits known to be zero |
| // can't contribute to the population. |
| unsigned BitsPossiblySet = BitWidth - KnownZero2.countPopulation(); |
| unsigned LeadingZeros = |
| APInt(BitWidth, BitsPossiblySet).countLeadingZeros(); |
| assert(LeadingZeros <= BitWidth); |
| KnownZero |= APInt::getHighBitsSet(BitWidth, LeadingZeros); |
| KnownOne &= ~KnownZero; |
| // TODO: we could bound KnownOne using the lower bound on the number |
| // of bits which might be set provided by popcnt KnownOne2. |
| break; |
| } |
| case Intrinsic::fabs: { |
| Type *Ty = II->getType(); |
| APInt SignBit = APInt::getSignBit(Ty->getScalarSizeInBits()); |
| KnownZero |= APInt::getSplat(Ty->getPrimitiveSizeInBits(), SignBit); |
| break; |
| } |
| case Intrinsic::x86_sse42_crc32_64_64: |
| KnownZero |= APInt::getHighBitsSet(64, 32); |
| break; |
| } |
| } |
| break; |
| case Instruction::ExtractValue: |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) { |
| ExtractValueInst *EVI = cast<ExtractValueInst>(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; |
| } |
| } |
| } |
| } |
| } |
| |
| static unsigned getAlignment(const Value *V, const DataLayout &DL) { |
| unsigned Align = 0; |
| if (auto *GO = dyn_cast<GlobalObject>(V)) { |
| Align = GO->getAlignment(); |
| if (Align == 0) { |
| if (auto *GVar = dyn_cast<GlobalVariable>(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->isStrongDefinitionForLinker()) |
| Align = DL.getPreferredAlignment(GVar); |
| else |
| Align = DL.getABITypeAlignment(ObjectType); |
| } |
| } |
| } |
| } else if (const Argument *A = dyn_cast<Argument>(V)) { |
| 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<PointerType>(A->getType())->getElementType(); |
| if (EltTy->isSized()) |
| Align = DL.getABITypeAlignment(EltTy); |
| } |
| } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(V)) |
| Align = AI->getAlignment(); |
| else if (auto CS = ImmutableCallSite(V)) |
| Align = CS.getAttributes().getParamAlignment(AttributeSet::ReturnIndex); |
| else if (const LoadInst *LI = dyn_cast<LoadInst>(V)) |
| if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) { |
| ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0)); |
| Align = CI->getLimitedValue(); |
| } |
| |
| return Align; |
| } |
| |
| /// 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()->isFPOrFPVectorTy() || |
| V->getType()->getScalarType()->isPointerTy()) && |
| "Not integer, floating point, 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<ConstantInt>(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<ConstantPointerNull>(V) || |
| isa<ConstantAggregateZero>(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<ConstantDataSequential>(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; |
| } |
| |
| // 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<GlobalAlias>(V)) { |
| if (!GA->mayBeOverridden()) |
| computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, DL, Depth + 1, Q); |
| return; |
| } |
| |
| if (Operator *I = dyn_cast<Operator>(V)) |
| computeKnownBitsFromOperator(I, KnownZero, KnownOne, DL, Depth, Q); |
| |
| // Aligned pointers have trailing zeros - refine KnownZero set |
| if (V->getType()->isPointerTy()) { |
| unsigned Align = getAlignment(V, DL); |
| if (Align) |
| KnownZero |= APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align)); |
| } |
| |
| // computeKnownBitsFromAssume and computeKnownBitsFromDominatingCondition |
| // strictly refines KnownZero and KnownOne. Therefore, we run them after |
| // computeKnownBitsFromOperator. |
| |
| // 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); |
| |
| 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<Constant>(V)) { |
| if (C->isNullValue()) |
| return OrZero; |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(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 left or a logical shift right 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_LShr(m_Value(X), m_Value())))) |
| return isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q, DL); |
| |
| if (ZExtInst *ZI = dyn_cast<ZExtInst>(V)) |
| return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q, DL); |
| |
| if (SelectInst *SI = dyn_cast<SelectInst>(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<OverflowingBinaryOperator>(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<Operator>(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<StructType>(*GTI)) { |
| ConstantInt *OpC = cast<ConstantInt>(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<ConstantInt>(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<ConstantInt>(Ranges->getOperand(2 * i + 0)); |
| ConstantInt *Upper = |
| mdconst::extract<ConstantInt>(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<Constant>(V)) { |
| if (C->isNullValue()) |
| return false; |
| if (isa<ConstantInt>(C)) |
| // Must be non-zero due to null test above. |
| return true; |
| // TODO: Handle vectors |
| return false; |
| } |
| |
| if (Instruction* I = dyn_cast<Instruction>(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<IntegerType>(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<GEPOperator>(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<SExtInst>(V) || isa<ZExtInst>(V)) |
| return isKnownNonZero(cast<Instruction>(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<OverflowingBinaryOperator>(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<PossiblyExactOperator>(V); |
| if (BO->isExact()) |
| return isKnownNonZero(X, DL, Depth, Q); |
| |
| bool XKnownNonNegative, XKnownNegative; |
| ComputeSignBit(X, XKnownNonNegative, XKnownNegative, DL, Depth, Q); |
| if (XKnownNegative) |
| return true; |
| |
| // If the shifter operand is a constant, and all of the bits shifted |
| // out are known to be zero, and X is known non-zero then at least one |
| // non-zero bit must remain. |
| if (ConstantInt *Shift = dyn_cast<ConstantInt>(Y)) { |
| APInt KnownZero(BitWidth, 0); |
| APInt KnownOne(BitWidth, 0); |
| computeKnownBits(X, KnownZero, KnownOne, DL, Depth, Q); |
| |
| auto ShiftVal = Shift->getLimitedValue(BitWidth - 1); |
| // Is there a known one in the portion not shifted out? |
| if (KnownOne.countLeadingZeros() < BitWidth - ShiftVal) |
| return true; |
| // Are all the bits to be shifted out known zero? |
| if (KnownZero.countTrailingOnes() >= ShiftVal) |
| return isKnownNonZero(X, DL, Depth, Q); |
| } |
| } |
| // 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<OverflowingBinaryOperator>(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<SelectInst>(V)) { |
| if (isKnownNonZero(SI->getTrueValue(), DL, Depth, Q) && |
| isKnownNonZero(SI->getFalseValue(), DL, Depth, Q)) |
| return true; |
| } |
| // PHI |
| else if (PHINode *PN = dyn_cast<PHINode>(V)) { |
| // Try and detect a recurrence that monotonically increases from a |
| // starting value, as these are common as induction variables. |
| if (PN->getNumIncomingValues() == 2) { |
| Value *Start = PN->getIncomingValue(0); |
| Value *Induction = PN->getIncomingValue(1); |
| if (isa<ConstantInt>(Induction) && !isa<ConstantInt>(Start)) |
| std::swap(Start, Induction); |
| if (ConstantInt *C = dyn_cast<ConstantInt>(Start)) { |
| if (!C->isZero() && !C->isNegative()) { |
| ConstantInt *X; |
| if ((match(Induction, m_NSWAdd(m_Specific(PN), m_ConstantInt(X))) || |
| match(Induction, m_NUWAdd(m_Specific(PN), m_ConstantInt(X)))) && |
| !X->isNegative()) |
| 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 V2 == V1 + X, where X is known non-zero. |
| static bool isAddOfNonZero(Value *V1, Value *V2, const DataLayout &DL, |
| const Query &Q) { |
| BinaryOperator *BO = dyn_cast<BinaryOperator>(V1); |
| if (!BO || BO->getOpcode() != Instruction::Add) |
| return false; |
| Value *Op = nullptr; |
| if (V2 == BO->getOperand(0)) |
| Op = BO->getOperand(1); |
| else if (V2 == BO->getOperand(1)) |
| Op = BO->getOperand(0); |
| else |
| return false; |
| return isKnownNonZero(Op, DL, 0, Q); |
| } |
| |
| /// Return true if it is known that V1 != V2. |
| static bool isKnownNonEqual(Value *V1, Value *V2, const DataLayout &DL, |
| const Query &Q) { |
| if (V1->getType()->isVectorTy() || V1 == V2) |
| return false; |
| if (V1->getType() != V2->getType()) |
| // We can't look through casts yet. |
| return false; |
| if (isAddOfNonZero(V1, V2, DL, Q) || isAddOfNonZero(V2, V1, DL, Q)) |
| return true; |
| |
| if (IntegerType *Ty = dyn_cast<IntegerType>(V1->getType())) { |
| // Are any known bits in V1 contradictory to known bits in V2? If V1 |
| // has a known zero where V2 has a known one, they must not be equal. |
| auto BitWidth = Ty->getBitWidth(); |
| APInt KnownZero1(BitWidth, 0); |
| APInt KnownOne1(BitWidth, 0); |
| computeKnownBits(V1, KnownZero1, KnownOne1, DL, 0, Q); |
| APInt KnownZero2(BitWidth, 0); |
| APInt KnownOne2(BitWidth, 0); |
| computeKnownBits(V2, KnownZero2, KnownOne2, DL, 0, Q); |
| |
| auto OppositeBits = (KnownZero1 & KnownOne2) | (KnownZero2 & KnownOne1); |
| if (OppositeBits.getBoolValue()) |
| return true; |
| } |
| return false; |
| } |
| |
| /// 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<Operator>(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<Constant>(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<Constant>(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<PHINode>(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<ConstantInt>(V); |
| |
| if (Base == 0) |
| return false; |
| |
| if (Base == 1) { |
| Multiple = V; |
| return true; |
| } |
| |
| ConstantExpr *CO = dyn_cast<ConstantExpr>(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<Operator>(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<ConstantInt>(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<Constant>(Op1)) |
| if (Constant *MulC = dyn_cast<Constant>(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<ConstantInt>(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<Constant>(Op0)) |
| if (Constant *MulC = dyn_cast<Constant>(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<ConstantInt>(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<ConstantFP>(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<Operator>(V); |
| if (!I) return false; |
| |
| // Check if the nsz fast-math flag is set |
| if (const FPMathOperator *FPO = dyn_cast<FPMathOperator>(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<ConstantFP>(I->getOperand(1))) |
| if (CFP->isNullValue()) |
| return true; |
| |
| // sitofp and uitofp turn into +0.0 for zero. |
| if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I)) |
| return true; |
| |
| if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(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<CallInst>(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<ConstantFP>(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<Operator>(V); |
| if (!I) return false; |
| |
| switch (I->getOpcode()) { |
| default: break; |
| // Unsigned integers are always nonnegative. |
| case Instruction::UIToFP: |
| return true; |
| 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::Select: |
| return CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1) && |
| CannotBeOrderedLessThanZero(I->getOperand(2), 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<IntrinsicInst>(I)) |
| switch (II->getIntrinsicID()) { |
| default: break; |
| case Intrinsic::maxnum: |
| return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1) || |
| CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1); |
| case Intrinsic::minnum: |
| return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1) && |
| CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1); |
| case Intrinsic::exp: |
| case Intrinsic::exp2: |
| case Intrinsic::fabs: |
| case Intrinsic::sqrt: |
| return true; |
| case Intrinsic::powi: |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(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<Constant>(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<ConstantFP>(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<ConstantInt>(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<ConstantDataSequential>(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<unsigned> &Idxs, |
| unsigned IdxSkip, |
| Instruction *InsertBefore) { |
| llvm::StructType *STy = dyn_cast<llvm::StructType>(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<InsertValueInst>(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<unsigned> 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<unsigned, 10> 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<unsigned> 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<Constant>(V)) { |
| C = C->getAggregateElement(idx_range[0]); |
| if (!C) return nullptr; |
| return FindInsertedValue(C, idx_range.slice(1), InsertBefore); |
| } |
| |
| if (InsertValueInst *I = dyn_cast<InsertValueInst>(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 (aggregate) 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<ExtractValueInst>(V)) { |
| // If we're extracting a value from an aggregate 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<unsigned, 5> 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); |
| |
| // We walk up the defs but use a visited set to handle unreachable code. In |
| // that case, we stop after accumulating the cycle once (not that it |
| // matters). |
| SmallPtrSet<Value *, 16> Visited; |
| while (Visited.insert(Ptr).second) { |
| if (Ptr->getType()->isVectorTy()) |
| break; |
| |
| if (GEPOperator *GEP = dyn_cast<GEPOperator>(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<Operator>(Ptr)->getOperand(0); |
| } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(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<GEPOperator>(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<PointerType>(GEP->getOperand(0)->getType()); |
| ArrayType *AT = dyn_cast<ArrayType>(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<ConstantInt>(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<ConstantInt>(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<GlobalVariable>(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<ConstantDataArray>(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<PHINode*> &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<PHINode>(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 (Value *IncValue : PN->incoming_values()) { |
| uint64_t Len = GetStringLengthH(IncValue, 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<SelectInst>(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<PHINode*, 32> 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; |
| } |
| |
| /// \brief \p PN defines a loop-variant pointer to an object. Check if the |
| /// previous iteration of the loop was referring to the same object as \p PN. |
| static bool isSameUnderlyingObjectInLoop(PHINode *PN, LoopInfo *LI) { |
| // Find the loop-defined value. |
| Loop *L = LI->getLoopFor(PN->getParent()); |
| if (PN->getNumIncomingValues() != 2) |
| return true; |
| |
| // Find the value from previous iteration. |
| auto *PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(0)); |
| if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L) |
| PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(1)); |
| if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L) |
| return true; |
| |
| // If a new pointer is loaded in the loop, the pointer references a different |
| // object in every iteration. E.g.: |
| // for (i) |
| // int *p = a[i]; |
| // ... |
| if (auto *Load = dyn_cast<LoadInst>(PrevValue)) |
| if (!L->isLoopInvariant(Load->getPointerOperand())) |
| return false; |
| return true; |
| } |
| |
| 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<GEPOperator>(V)) { |
| V = GEP->getPointerOperand(); |
| } else if (Operator::getOpcode(V) == Instruction::BitCast || |
| Operator::getOpcode(V) == Instruction::AddrSpaceCast) { |
| V = cast<Operator>(V)->getOperand(0); |
| } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { |
| if (GA->mayBeOverridden()) |
| return V; |
| V = GA->getAliasee(); |
| } else { |
| // See if InstructionSimplify knows any relevant tricks. |
| if (Instruction *I = dyn_cast<Instruction>(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<Value *> &Objects, |
| const DataLayout &DL, LoopInfo *LI, |
| unsigned MaxLookup) { |
| SmallPtrSet<Value *, 4> Visited; |
| SmallVector<Value *, 4> 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<SelectInst>(P)) { |
| Worklist.push_back(SI->getTrueValue()); |
| Worklist.push_back(SI->getFalseValue()); |
| continue; |
| } |
| |
| if (PHINode *PN = dyn_cast<PHINode>(P)) { |
| // If this PHI changes the underlying object in every iteration of the |
| // loop, don't look through it. Consider: |
| // int **A; |
| // for (i) { |
| // Prev = Curr; // Prev = PHI (Prev_0, Curr) |
| // Curr = A[i]; |
| // *Prev, *Curr; |
| // |
| // Prev is tracking Curr one iteration behind so they refer to different |
| // underlying objects. |
| if (!LI || !LI->isLoopHeader(PN->getParent()) || |
| isSameUnderlyingObjectInLoop(PN, LI)) |
| for (Value *IncValue : PN->incoming_values()) |
| Worklist.push_back(IncValue); |
| 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<IntrinsicInst>(U); |
| if (!II) return false; |
| |
| if (II->getIntrinsicID() != Intrinsic::lifetime_start && |
| II->getIntrinsicID() != Intrinsic::lifetime_end) |
| return false; |
| } |
| return true; |
| } |
| |
| static bool isDereferenceableFromAttribute(const Value *BV, APInt Offset, |
| Type *Ty, const DataLayout &DL, |
| const Instruction *CtxI, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| assert(Offset.isNonNegative() && "offset can't be negative"); |
| assert(Ty->isSized() && "must be sized"); |
| |
| APInt DerefBytes(Offset.getBitWidth(), 0); |
| bool CheckForNonNull = false; |
| if (const Argument *A = dyn_cast<Argument>(BV)) { |
| DerefBytes = A->getDereferenceableBytes(); |
| if (!DerefBytes.getBoolValue()) { |
| DerefBytes = A->getDereferenceableOrNullBytes(); |
| CheckForNonNull = true; |
| } |
| } else if (auto CS = ImmutableCallSite(BV)) { |
| DerefBytes = CS.getDereferenceableBytes(0); |
| if (!DerefBytes.getBoolValue()) { |
| DerefBytes = CS.getDereferenceableOrNullBytes(0); |
| CheckForNonNull = true; |
| } |
| } else if (const LoadInst *LI = dyn_cast<LoadInst>(BV)) { |
| if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) { |
| ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0)); |
| DerefBytes = CI->getLimitedValue(); |
| } |
| if (!DerefBytes.getBoolValue()) { |
| if (MDNode *MD = |
| LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) { |
| ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0)); |
| DerefBytes = CI->getLimitedValue(); |
| } |
| CheckForNonNull = true; |
| } |
| } |
| |
| if (DerefBytes.getBoolValue()) |
| if (DerefBytes.uge(Offset + DL.getTypeStoreSize(Ty))) |
| if (!CheckForNonNull || isKnownNonNullAt(BV, CtxI, DT, TLI)) |
| return true; |
| |
| return false; |
| } |
| |
| static bool isDereferenceableFromAttribute(const Value *V, const DataLayout &DL, |
| const Instruction *CtxI, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| Type *VTy = V->getType(); |
| Type *Ty = VTy->getPointerElementType(); |
| if (!Ty->isSized()) |
| return false; |
| |
| APInt Offset(DL.getTypeStoreSizeInBits(VTy), 0); |
| return isDereferenceableFromAttribute(V, Offset, Ty, DL, CtxI, DT, TLI); |
| } |
| |
| static bool isAligned(const Value *Base, APInt Offset, unsigned Align, |
| const DataLayout &DL) { |
| APInt BaseAlign(Offset.getBitWidth(), getAlignment(Base, DL)); |
| |
| if (!BaseAlign) { |
| Type *Ty = Base->getType()->getPointerElementType(); |
| if (!Ty->isSized()) |
| return false; |
| BaseAlign = DL.getABITypeAlignment(Ty); |
| } |
| |
| APInt Alignment(Offset.getBitWidth(), Align); |
| |
| assert(Alignment.isPowerOf2() && "must be a power of 2!"); |
| return BaseAlign.uge(Alignment) && !(Offset & (Alignment-1)); |
| } |
| |
| static bool isAligned(const Value *Base, unsigned Align, const DataLayout &DL) { |
| Type *Ty = Base->getType(); |
| assert(Ty->isSized() && "must be sized"); |
| APInt Offset(DL.getTypeStoreSizeInBits(Ty), 0); |
| return isAligned(Base, Offset, Align, DL); |
| } |
| |
| /// Test if V is always a pointer to allocated and suitably aligned memory for |
| /// a simple load or store. |
| static bool isDereferenceableAndAlignedPointer( |
| const Value *V, unsigned Align, const DataLayout &DL, |
| const Instruction *CtxI, const DominatorTree *DT, |
| const TargetLibraryInfo *TLI, SmallPtrSetImpl<const Value *> &Visited) { |
| // Note that it is not safe to speculate into a malloc'd region because |
| // malloc may return null. |
| |
| // These are obviously ok if aligned. |
| if (isa<AllocaInst>(V)) |
| return isAligned(V, Align, DL); |
| |
| // It's not always safe to follow a bitcast, for example: |
| // bitcast i8* (alloca i8) to i32* |
| // would result in a 4-byte load from a 1-byte alloca. However, |
| // if we're casting from a pointer from a type of larger size |
| // to a type of smaller size (or the same size), and the alignment |
| // is at least as large as for the resulting pointer type, then |
| // we can look through the bitcast. |
| if (const BitCastOperator *BC = dyn_cast<BitCastOperator>(V)) { |
| Type *STy = BC->getSrcTy()->getPointerElementType(), |
| *DTy = BC->getDestTy()->getPointerElementType(); |
| if (STy->isSized() && DTy->isSized() && |
| (DL.getTypeStoreSize(STy) >= DL.getTypeStoreSize(DTy)) && |
| (DL.getABITypeAlignment(STy) >= DL.getABITypeAlignment(DTy))) |
| return isDereferenceableAndAlignedPointer(BC->getOperand(0), Align, DL, |
| CtxI, DT, TLI, Visited); |
| } |
| |
| // Global variables which can't collapse to null are ok. |
| if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) |
| if (!GV->hasExternalWeakLinkage()) |
| return isAligned(V, Align, DL); |
| |
| // byval arguments are okay. |
| if (const Argument *A = dyn_cast<Argument>(V)) |
| if (A->hasByValAttr()) |
| return isAligned(V, Align, DL); |
| |
| if (isDereferenceableFromAttribute(V, DL, CtxI, DT, TLI)) |
| return isAligned(V, Align, DL); |
| |
| // For GEPs, determine if the indexing lands within the allocated object. |
| if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) { |
| Type *VTy = GEP->getType(); |
| Type *Ty = VTy->getPointerElementType(); |
| const Value *Base = GEP->getPointerOperand(); |
| |
| // Conservatively require that the base pointer be fully dereferenceable |
| // and aligned. |
| if (!Visited.insert(Base).second) |
| return false; |
| if (!isDereferenceableAndAlignedPointer(Base, Align, DL, CtxI, DT, TLI, |
| Visited)) |
| return false; |
| |
| APInt Offset(DL.getPointerTypeSizeInBits(VTy), 0); |
| if (!GEP->accumulateConstantOffset(DL, Offset)) |
| return false; |
| |
| // Check if the load is within the bounds of the underlying object |
| // and offset is aligned. |
| uint64_t LoadSize = DL.getTypeStoreSize(Ty); |
| Type *BaseType = Base->getType()->getPointerElementType(); |
| assert(isPowerOf2_32(Align) && "must be a power of 2!"); |
| return (Offset + LoadSize).ule(DL.getTypeAllocSize(BaseType)) && |
| !(Offset & APInt(Offset.getBitWidth(), Align-1)); |
| } |
| |
| // For gc.relocate, look through relocations |
| if (const GCRelocateInst *RelocateInst = dyn_cast<GCRelocateInst>(V)) |
| return isDereferenceableAndAlignedPointer( |
| RelocateInst->getDerivedPtr(), Align, DL, CtxI, DT, TLI, Visited); |
| |
| if (const AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(V)) |
| return isDereferenceableAndAlignedPointer(ASC->getOperand(0), Align, DL, |
| CtxI, DT, TLI, Visited); |
| |
| // If we don't know, assume the worst. |
| return false; |
| } |
| |
| bool llvm::isDereferenceableAndAlignedPointer(const Value *V, unsigned Align, |
| const DataLayout &DL, |
| const Instruction *CtxI, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| // When dereferenceability information is provided by a dereferenceable |
| // attribute, we know exactly how many bytes are dereferenceable. If we can |
| // determine the exact offset to the attributed variable, we can use that |
| // information here. |
| Type *VTy = V->getType(); |
| Type *Ty = VTy->getPointerElementType(); |
| |
| // Require ABI alignment for loads without alignment specification |
| if (Align == 0) |
| Align = DL.getABITypeAlignment(Ty); |
| |
| if (Ty->isSized()) { |
| APInt Offset(DL.getTypeStoreSizeInBits(VTy), 0); |
| const Value *BV = V->stripAndAccumulateInBoundsConstantOffsets(DL, Offset); |
| |
| if (Offset.isNonNegative()) |
| if (isDereferenceableFromAttribute(BV, Offset, Ty, DL, CtxI, DT, TLI) && |
| isAligned(BV, Offset, Align, DL)) |
| return true; |
| } |
| |
| SmallPtrSet<const Value *, 32> Visited; |
| return ::isDereferenceableAndAlignedPointer(V, Align, DL, CtxI, DT, TLI, |
| Visited); |
| } |
| |
| bool llvm::isDereferenceablePointer(const Value *V, const DataLayout &DL, |
| const Instruction *CtxI, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| return isDereferenceableAndAlignedPointer(V, 1, DL, CtxI, DT, TLI); |
| } |
| |
| bool llvm::isSafeToSpeculativelyExecute(const Value *V, |
| const Instruction *CtxI, |
| const DominatorTree *DT, |
| const TargetLibraryInfo *TLI) { |
| const Operator *Inst = dyn_cast<Operator>(V); |
| if (!Inst) |
| return false; |
| |
| for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) |
| if (Constant *C = dyn_cast<Constant>(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<LoadInst>(Inst); |
| if (!LI->isUnordered() || |
| // Speculative load may create a race that did not exist in the source. |
| LI->getParent()->getParent()->hasFnAttribute( |
| Attribute::SanitizeThread) || |
| // Speculative load may load data from dirty regions. |
| LI->getParent()->getParent()->hasFnAttribute( |
| Attribute::SanitizeAddress)) |
| return false; |
| const DataLayout &DL = LI->getModule()->getDataLayout(); |
| return isDereferenceableAndAlignedPointer( |
| LI->getPointerOperand(), LI->getAlignment(), DL, CtxI, DT, TLI); |
| } |
| case Instruction::Call: { |
| if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(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::AtomicRMW: |
| case Instruction::AtomicCmpXchg: |
| case Instruction::LandingPad: |
| case Instruction::Resume: |
| case Instruction::CatchSwitch: |
| case Instruction::CatchPad: |
| case Instruction::CatchRet: |
| case Instruction::CleanupPad: |
| case Instruction::CleanupRet: |
| return false; // Misc instructions which have effects |
| } |
| } |
| |
| bool llvm::mayBeMemoryDependent(const Instruction &I) { |
| return I.mayReadOrWriteMemory() || !isSafeToSpeculativelyExecute(&I); |
| } |
| |
| /// Return true if we know that the specified value is never null. |
| bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) { |
| assert(V->getType()->isPointerTy() && "V must be pointer type"); |
| |
| // Alloca never returns null, malloc might. |
| if (isa<AllocaInst>(V)) return true; |
| |
| // A byval, inalloca, or nonnull argument is never null. |
| if (const Argument *A = dyn_cast<Argument>(V)) |
| return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr(); |
| |
| // A global variable in address space 0 is non null unless extern weak. |
| // Other address spaces may have null as a valid address for a global, |
| // so we can't assume anything. |
| if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) |
| return !GV->hasExternalWeakLinkage() && |
| GV->getType()->getAddressSpace() == 0; |
| |
| // A Load tagged w/nonnull metadata is never null. |
| if (const LoadInst *LI = dyn_cast<LoadInst>(V)) |
| return LI->getMetadata(LLVMContext::MD_nonnull); |
| |
| if (auto CS = ImmutableCallSite(V)) |
| if (CS.isReturnNonNull()) |
| return true; |
| |
| return false; |
| } |
| |
| static bool isKnownNonNullFromDominatingCondition(const Value *V, |
| const Instruction *CtxI, |
| const DominatorTree *DT) { |
| assert(V->getType()->isPointerTy() && "V must be pointer type"); |
| |
| unsigned NumUsesExplored = 0; |
| for (auto U : V->users()) { |
| // Avoid massive lists |
| if (NumUsesExplored >= DomConditionsMaxUses) |
| break; |
| NumUsesExplored++; |
| // Consider only compare instructions uniquely controlling a branch |
| const ICmpInst *Cmp = dyn_cast<ICmpInst>(U); |
| if (!Cmp) |
| continue; |
| |
| if (DomConditionsSingleCmpUse && !Cmp->hasOneUse()) |
| continue; |
| |
| for (auto *CmpU : Cmp->users()) { |
| const BranchInst *BI = dyn_cast<BranchInst>(CmpU); |
| if (!BI) |
| continue; |
| |
| assert(BI->isConditional() && "uses a comparison!"); |
| |
| BasicBlock *NonNullSuccessor = nullptr; |
| CmpInst::Predicate Pred; |
| |
| if (match(const_cast<ICmpInst*>(Cmp), |
| m_c_ICmp(Pred, m_Specific(V), m_Zero()))) { |
| if (Pred == ICmpInst::ICMP_EQ) |
| NonNullSuccessor = BI->getSuccessor(1); |
| else if (Pred == ICmpInst::ICMP_NE) |
| NonNullSuccessor = BI->getSuccessor(0); |
| } |
| |
| if (NonNullSuccessor) { |
| BasicBlockEdge Edge(BI->getParent(), NonNullSuccessor); |
| if (Edge.isSingleEdge() && DT->dominates(Edge, CtxI->getParent())) |
| return true; |
| } |
| } |
| } |
| |
| return false; |
| } |
| |
| bool llvm::isKnownNonNullAt(const Value *V, const Instruction *CtxI, |
| const DominatorTree *DT, const TargetLibraryInfo *TLI) { |
| if (isKnownNonNull(V, TLI)) |
| return true; |
| |
| return CtxI ? ::isKnownNonNullFromDominatingCondition(V, CtxI, DT) : 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; |
| } |
| |
| static OverflowResult computeOverflowForSignedAdd( |
| Value *LHS, Value *RHS, AddOperator *Add, const DataLayout &DL, |
| AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { |
| if (Add && Add->hasNoSignedWrap()) { |
| return OverflowResult::NeverOverflows; |
| } |
| |
| bool LHSKnownNonNegative, LHSKnownNegative; |
| bool RHSKnownNonNegative, RHSKnownNegative; |
| ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0, |
| AC, CxtI, DT); |
| ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0, |
| AC, CxtI, DT); |
| |
| if ((LHSKnownNonNegative && RHSKnownNegative) || |
| (LHSKnownNegative && RHSKnownNonNegative)) { |
| // The sign bits are opposite: this CANNOT overflow. |
| return OverflowResult::NeverOverflows; |
| } |
| |
| // The remaining code needs Add to be available. Early returns if not so. |
| if (!Add) |
| return OverflowResult::MayOverflow; |
| |
| // If the sign of Add is the same as at least one of the operands, this add |
| // CANNOT overflow. This is particularly useful when the sum is |
| // @llvm.assume'ed non-negative rather than proved so from analyzing its |
| // operands. |
| bool LHSOrRHSKnownNonNegative = |
| (LHSKnownNonNegative || RHSKnownNonNegative); |
| bool LHSOrRHSKnownNegative = (LHSKnownNegative || RHSKnownNegative); |
| if (LHSOrRHSKnownNonNegative || LHSOrRHSKnownNegative) { |
| bool AddKnownNonNegative, AddKnownNegative; |
| ComputeSignBit(Add, AddKnownNonNegative, AddKnownNegative, DL, |
| /*Depth=*/0, AC, CxtI, DT); |
| if ((AddKnownNonNegative && LHSOrRHSKnownNonNegative) || |
| (AddKnownNegative && LHSOrRHSKnownNegative)) { |
| return OverflowResult::NeverOverflows; |
| } |
| } |
| |
| return OverflowResult::MayOverflow; |
| } |
| |
| OverflowResult llvm::computeOverflowForSignedAdd(AddOperator *Add, |
| const DataLayout &DL, |
| AssumptionCache *AC, |
| const Instruction *CxtI, |
| const DominatorTree *DT) { |
| return ::computeOverflowForSignedAdd(Add->getOperand(0), Add->getOperand(1), |
| Add, DL, AC, CxtI, DT); |
| } |
| |
| OverflowResult llvm::computeOverflowForSignedAdd(Value *LHS, Value *RHS, |
| const DataLayout &DL, |
| AssumptionCache *AC, |
| const Instruction *CxtI, |
| const DominatorTree *DT) { |
| return ::computeOverflowForSignedAdd(LHS, RHS, nullptr, DL, AC, CxtI, DT); |
| } |
| |
| bool llvm::isGuaranteedToTransferExecutionToSuccessor(const Instruction *I) { |
| // FIXME: This conservative implementation can be relaxed. E.g. most |
| // atomic operations are guaranteed to terminate on most platforms |
| // and most functions terminate. |
| |
| return !I->isAtomic() && // atomics may never succeed on some platforms |
| !isa<CallInst>(I) && // could throw and might not terminate |
| !isa<InvokeInst>(I) && // might not terminate and could throw to |
| // non-successor (see bug 24185 for details). |
| !isa<ResumeInst>(I) && // has no successors |
| !isa<ReturnInst>(I); // has no successors |
| } |
| |
| bool llvm::isGuaranteedToExecuteForEveryIteration(const Instruction *I, |
| const Loop *L) { |
| // The loop header is guaranteed to be executed for every iteration. |
| // |
| // FIXME: Relax this constraint to cover all basic blocks that are |
| // guaranteed to be executed at every iteration. |
| if (I->getParent() != L->getHeader()) return false; |
| |
| for (const Instruction &LI : *L->getHeader()) { |
| if (&LI == I) return true; |
| if (!isGuaranteedToTransferExecutionToSuccessor(&LI)) return false; |
| } |
| llvm_unreachable("Instruction not contained in its own parent basic block."); |
| } |
| |
| bool llvm::propagatesFullPoison(const Instruction *I) { |
| switch (I->getOpcode()) { |
| case Instruction::Add: |
| case Instruction::Sub: |
| case Instruction::Xor: |
| case Instruction::Trunc: |
| case Instruction::BitCast: |
| case Instruction::AddrSpaceCast: |
| // These operations all propagate poison unconditionally. Note that poison |
| // is not any particular value, so xor or subtraction of poison with |
| // itself still yields poison, not zero. |
| return true; |
| |
| case Instruction::AShr: |
| case Instruction::SExt: |
| // For these operations, one bit of the input is replicated across |
| // multiple output bits. A replicated poison bit is still poison. |
| return true; |
| |
| case Instruction::Shl: { |
| // Left shift *by* a poison value is poison. The number of |
| // positions to shift is unsigned, so no negative values are |
| // possible there. Left shift by zero places preserves poison. So |
| // it only remains to consider left shift of poison by a positive |
| // number of places. |
| // |
| // A left shift by a positive number of places leaves the lowest order bit |
| // non-poisoned. However, if such a shift has a no-wrap flag, then we can |
| // make the poison operand violate that flag, yielding a fresh full-poison |
| // value. |
| auto *OBO = cast<OverflowingBinaryOperator>(I); |
| return OBO->hasNoUnsignedWrap() || OBO->hasNoSignedWrap(); |
| } |
| |
| case Instruction::Mul: { |
| // A multiplication by zero yields a non-poison zero result, so we need to |
| // rule out zero as an operand. Conservatively, multiplication by a |
| // non-zero constant is not multiplication by zero. |
| // |
| // Multiplication by a non-zero constant can leave some bits |
| // non-poisoned. For example, a multiplication by 2 leaves the lowest |
| // order bit unpoisoned. So we need to consider that. |
| // |
| // Multiplication by 1 preserves poison. If the multiplication has a |
| // no-wrap flag, then we can make the poison operand violate that flag |
| // when multiplied by any integer other than 0 and 1. |
| auto *OBO = cast<OverflowingBinaryOperator>(I); |
| if (OBO->hasNoUnsignedWrap() || OBO->hasNoSignedWrap()) { |
| for (Value *V : OBO->operands()) { |
| if (auto *CI = dyn_cast<ConstantInt>(V)) { |
| // A ConstantInt cannot yield poison, so we can assume that it is |
| // the other operand that is poison. |
| return !CI->isZero(); |
| } |
| } |
| } |
| return false; |
| } |
| |
| case Instruction::GetElementPtr: |
| // A GEP implicitly represents a sequence of additions, subtractions, |
| // truncations, sign extensions and multiplications. The multiplications |
| // are by the non-zero sizes of some set of types, so we do not have to be |
| // concerned with multiplication by zero. If the GEP is in-bounds, then |
| // these operations are implicitly no-signed-wrap so poison is propagated |
| // by the arguments above for Add, Sub, Trunc, SExt and Mul. |
| return cast<GEPOperator>(I)->isInBounds(); |
| |
| default: |
| return false; |
| } |
| } |
| |
| const Value *llvm::getGuaranteedNonFullPoisonOp(const Instruction *I) { |
| switch (I->getOpcode()) { |
| case Instruction::Store: |
| return cast<StoreInst>(I)->getPointerOperand(); |
| |
| case Instruction::Load: |
| return cast<LoadInst>(I)->getPointerOperand(); |
| |
| case Instruction::AtomicCmpXchg: |
| return cast<AtomicCmpXchgInst>(I)->getPointerOperand(); |
| |
| case Instruction::AtomicRMW: |
| return cast<AtomicRMWInst>(I)->getPointerOperand(); |
| |
| case Instruction::UDiv: |
| case Instruction::SDiv: |
| case Instruction::URem: |
| case Instruction::SRem: |
| return I->getOperand(1); |
| |
| default: |
| return nullptr; |
| } |
| } |
| |
| bool llvm::isKnownNotFullPoison(const Instruction *PoisonI) { |
| // We currently only look for uses of poison values within the same basic |
| // block, as that makes it easier to guarantee that the uses will be |
| // executed given that PoisonI is executed. |
| // |
| // FIXME: Expand this to consider uses beyond the same basic block. To do |
| // this, look out for the distinction between post-dominance and strong |
| // post-dominance. |
| const BasicBlock *BB = PoisonI->getParent(); |
| |
| // Set of instructions that we have proved will yield poison if PoisonI |
| // does. |
| SmallSet<const Value *, 16> YieldsPoison; |
| YieldsPoison.insert(PoisonI); |
| |
| for (BasicBlock::const_iterator I = PoisonI->getIterator(), E = BB->end(); |
| I != E; ++I) { |
| if (&*I != PoisonI) { |
| const Value *NotPoison = getGuaranteedNonFullPoisonOp(&*I); |
| if (NotPoison != nullptr && YieldsPoison.count(NotPoison)) return true; |
| if (!isGuaranteedToTransferExecutionToSuccessor(&*I)) |
| return false; |
| } |
| |
| // Mark poison that propagates from I through uses of I. |
| if (YieldsPoison.count(&*I)) { |
| for (const User *User : I->users()) { |
| const Instruction *UserI = cast<Instruction>(User); |
| if (UserI->getParent() == BB && propagatesFullPoison(UserI)) |
| YieldsPoison.insert(User); |
| } |
| } |
| } |
| return false; |
| } |
| |
| static bool isKnownNonNaN(Value *V, FastMathFlags FMF) { |
| if (FMF.noNaNs()) |
| return true; |
| |
| if (auto *C = dyn_cast<ConstantFP>(V)) |
| return !C->isNaN(); |
| return false; |
| } |
| |
| static bool isKnownNonZero(Value *V) { |
| if (auto *C = dyn_cast<ConstantFP>(V)) |
| return !C->isZero(); |
| return false; |
| } |
| |
| static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred, |
| FastMathFlags FMF, |
| Value *CmpLHS, Value *CmpRHS, |
| Value *TrueVal, Value *FalseVal, |
| Value *&LHS, Value *&RHS) { |
| LHS = CmpLHS; |
| RHS = CmpRHS; |
| |
| // If the predicate is an "or-equal" (FP) predicate, then signed zeroes may |
| // return inconsistent results between implementations. |
| // (0.0 <= -0.0) ? 0.0 : -0.0 // Returns 0.0 |
| // minNum(0.0, -0.0) // May return -0.0 or 0.0 (IEEE 754-2008 5.3.1) |
| // Therefore we behave conservatively and only proceed if at least one of the |
| // operands is known to not be zero, or if we don't care about signed zeroes. |
| switch (Pred) { |
| default: break; |
| case CmpInst::FCMP_OGE: case CmpInst::FCMP_OLE: |
| case CmpInst::FCMP_UGE: case CmpInst::FCMP_ULE: |
| if (!FMF.noSignedZeros() && !isKnownNonZero(CmpLHS) && |
| !isKnownNonZero(CmpRHS)) |
| return {SPF_UNKNOWN, SPNB_NA, false}; |
| } |
| |
| SelectPatternNaNBehavior NaNBehavior = SPNB_NA; |
| bool Ordered = false; |
| |
| // When given one NaN and one non-NaN input: |
| // - maxnum/minnum (C99 fmaxf()/fminf()) return the non-NaN input. |
| // - A simple C99 (a < b ? a : b) construction will return 'b' (as the |
| // ordered comparison fails), which could be NaN or non-NaN. |
| // so here we discover exactly what NaN behavior is required/accepted. |
| if (CmpInst::isFPPredicate(Pred)) { |
| bool LHSSafe = isKnownNonNaN(CmpLHS, FMF); |
| bool RHSSafe = isKnownNonNaN(CmpRHS, FMF); |
| |
| if (LHSSafe && RHSSafe) { |
| // Both operands are known non-NaN. |
| NaNBehavior = SPNB_RETURNS_ANY; |
| } else if (CmpInst::isOrdered(Pred)) { |
| // An ordered comparison will return false when given a NaN, so it |
| // returns the RHS. |
| Ordered = true; |
| if (LHSSafe) |
| // LHS is non-NaN, so if RHS is NaN then NaN will be returned. |
| NaNBehavior = SPNB_RETURNS_NAN; |
| else if (RHSSafe) |
| NaNBehavior = SPNB_RETURNS_OTHER; |
| else |
| // Completely unsafe. |
| return {SPF_UNKNOWN, SPNB_NA, false}; |
| } else { |
| Ordered = false; |
| // An unordered comparison will return true when given a NaN, so it |
| // returns the LHS. |
| if (LHSSafe) |
| // LHS is non-NaN, so if RHS is NaN then non-NaN will be returned. |
| NaNBehavior = SPNB_RETURNS_OTHER; |
| else if (RHSSafe) |
| NaNBehavior = SPNB_RETURNS_NAN; |
| else |
| // Completely unsafe. |
| return {SPF_UNKNOWN, SPNB_NA, false}; |
| } |
| } |
| |
| if (TrueVal == CmpRHS && FalseVal == CmpLHS) { |
| std::swap(CmpLHS, CmpRHS); |
| Pred = CmpInst::getSwappedPredicate(Pred); |
| if (NaNBehavior == SPNB_RETURNS_NAN) |
| NaNBehavior = SPNB_RETURNS_OTHER; |
| else if (NaNBehavior == SPNB_RETURNS_OTHER) |
| NaNBehavior = SPNB_RETURNS_NAN; |
| Ordered = !Ordered; |
| } |
| |
| // ([if]cmp X, Y) ? X : Y |
| if (TrueVal == CmpLHS && FalseVal == CmpRHS) { |
| switch (Pred) { |
| default: return {SPF_UNKNOWN, SPNB_NA, false}; // Equality. |
| case ICmpInst::ICMP_UGT: |
| case ICmpInst::ICMP_UGE: return {SPF_UMAX, SPNB_NA, false}; |
| case ICmpInst::ICMP_SGT: |
| case ICmpInst::ICMP_SGE: return {SPF_SMAX, SPNB_NA, false}; |
| case ICmpInst::ICMP_ULT: |
| case ICmpInst::ICMP_ULE: return {SPF_UMIN, SPNB_NA, false}; |
| case ICmpInst::ICMP_SLT: |
| case ICmpInst::ICMP_SLE: return {SPF_SMIN, SPNB_NA, false}; |
| case FCmpInst::FCMP_UGT: |
| case FCmpInst::FCMP_UGE: |
| case FCmpInst::FCMP_OGT: |
| case FCmpInst::FCMP_OGE: return {SPF_FMAXNUM, NaNBehavior, Ordered}; |
| case FCmpInst::FCMP_ULT: |
| case FCmpInst::FCMP_ULE: |
| case FCmpInst::FCMP_OLT: |
| case FCmpInst::FCMP_OLE: return {SPF_FMINNUM, NaNBehavior, Ordered}; |
| } |
| } |
| |
| if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) { |
| if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) || |
| (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) { |
| |
| // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X |
| // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X |
| if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) { |
| return {(CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false}; |
| } |
| |
| // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X |
| // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X |
| if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) { |
| return {(CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false}; |
| } |
| } |
| |
| // Y >s C ? ~Y : ~C == ~Y <s ~C ? ~Y : ~C = SMIN(~Y, ~C) |
| if (const auto *C2 = dyn_cast<ConstantInt>(FalseVal)) { |
| if (C1->getType() == C2->getType() && ~C1->getValue() == C2->getValue() && |
| (match(TrueVal, m_Not(m_Specific(CmpLHS))) || |
| match(CmpLHS, m_Not(m_Specific(TrueVal))))) { |
| LHS = TrueVal; |
| RHS = FalseVal; |
| return {SPF_SMIN, SPNB_NA, false}; |
| } |
| } |
| } |
| |
| // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5) |
| |
| return {SPF_UNKNOWN, SPNB_NA, false}; |
| } |
| |
| static Value *lookThroughCast(CmpInst *CmpI, Value *V1, Value *V2, |
| Instruction::CastOps *CastOp) { |
| CastInst *CI = dyn_cast<CastInst>(V1); |
| Constant *C = dyn_cast<Constant>(V2); |
| CastInst *CI2 = dyn_cast<CastInst>(V2); |
| if (!CI) |
| return nullptr; |
| *CastOp = CI->getOpcode(); |
| |
| if (CI2) { |
| // If V1 and V2 are both the same cast from the same type, we can look |
| // through V1. |
| if (CI2->getOpcode() == CI->getOpcode() && |
| CI2->getSrcTy() == CI->getSrcTy()) |
| return CI2->getOperand(0); |
| return nullptr; |
| } else if (!C) { |
| return nullptr; |
| } |
| |
| if (isa<SExtInst>(CI) && CmpI->isSigned()) { |
| Constant *T = ConstantExpr::getTrunc(C, CI->getSrcTy()); |
| // This is only valid if the truncated value can be sign-extended |
| // back to the original value. |
| if (ConstantExpr::getSExt(T, C->getType()) == C) |
| return T; |
| return nullptr; |
| } |
| if (isa<ZExtInst>(CI) && CmpI->isUnsigned()) |
| return ConstantExpr::getTrunc(C, CI->getSrcTy()); |
| |
| if (isa<TruncInst>(CI)) |
| return ConstantExpr::getIntegerCast(C, CI->getSrcTy(), CmpI->isSigned()); |
| |
| if (isa<FPToUIInst>(CI)) |
| return ConstantExpr::getUIToFP(C, CI->getSrcTy(), true); |
| |
| if (isa<FPToSIInst>(CI)) |
| return ConstantExpr::getSIToFP(C, CI->getSrcTy(), true); |
| |
| if (isa<UIToFPInst>(CI)) |
| return ConstantExpr::getFPToUI(C, CI->getSrcTy(), true); |
| |
| if (isa<SIToFPInst>(CI)) |
| return ConstantExpr::getFPToSI(C, CI->getSrcTy(), true); |
| |
| if (isa<FPTruncInst>(CI)) |
| return ConstantExpr::getFPExtend(C, CI->getSrcTy(), true); |
| |
| if (isa<FPExtInst>(CI)) |
| return ConstantExpr::getFPTrunc(C, CI->getSrcTy(), true); |
| |
| return nullptr; |
| } |
| |
| SelectPatternResult llvm::matchSelectPattern(Value *V, |
| Value *&LHS, Value *&RHS, |
| Instruction::CastOps *CastOp) { |
| SelectInst *SI = dyn_cast<SelectInst>(V); |
| if (!SI) return {SPF_UNKNOWN, SPNB_NA, false}; |
| |
| CmpInst *CmpI = dyn_cast<CmpInst>(SI->getCondition()); |
| if (!CmpI) return {SPF_UNKNOWN, SPNB_NA, false}; |
| |
| CmpInst::Predicate Pred = CmpI->getPredicate(); |
| Value *CmpLHS = CmpI->getOperand(0); |
| Value *CmpRHS = CmpI->getOperand(1); |
| Value *TrueVal = SI->getTrueValue(); |
| Value *FalseVal = SI->getFalseValue(); |
| FastMathFlags FMF; |
| if (isa<FPMathOperator>(CmpI)) |
| FMF = CmpI->getFastMathFlags(); |
| |
| // Bail out early. |
| if (CmpI->isEquality()) |
| return {SPF_UNKNOWN, SPNB_NA, false}; |
| |
| // Deal with type mismatches. |
| if (CastOp && CmpLHS->getType() != TrueVal->getType()) { |
| if (Value *C = lookThroughCast(CmpI, TrueVal, FalseVal, CastOp)) |
| return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, |
| cast<CastInst>(TrueVal)->getOperand(0), C, |
| LHS, RHS); |
| if (Value *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp)) |
| return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, |
| C, cast<CastInst>(FalseVal)->getOperand(0), |
| LHS, RHS); |
| } |
| return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, TrueVal, FalseVal, |
| LHS, RHS); |
| } |
| |
| ConstantRange llvm::getConstantRangeFromMetadata(MDNode &Ranges) { |
| const unsigned NumRanges = Ranges.getNumOperands() / 2; |
| assert(NumRanges >= 1 && "Must have at least one range!"); |
| assert(Ranges.getNumOperands() % 2 == 0 && "Must be a sequence of pairs"); |
| |
| auto *FirstLow = mdconst::extract<ConstantInt>(Ranges.getOperand(0)); |
| auto *FirstHigh = mdconst::extract<ConstantInt>(Ranges.getOperand(1)); |
| |
| ConstantRange CR(FirstLow->getValue(), FirstHigh->getValue()); |
| |
| for (unsigned i = 1; i < NumRanges; ++i) { |
| auto *Low = mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0)); |
| auto *High = mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1)); |
| |
| // Note: unionWith will potentially create a range that contains values not |
| // contained in any of the original N ranges. |
| CR = CR.unionWith(ConstantRange(Low->getValue(), High->getValue())); |
| } |
| |
| return CR; |
| } |
| |
| /// Return true if "icmp Pred LHS RHS" is always true. |
| static bool isTruePredicate(CmpInst::Predicate Pred, Value *LHS, Value *RHS, |
| const DataLayout &DL, unsigned Depth, |
| AssumptionCache *AC, const Instruction *CxtI, |
| const DominatorTree *DT) { |
| assert(!LHS->getType()->isVectorTy() && "TODO: extend to handle vectors!"); |
| if (ICmpInst::isTrueWhenEqual(Pred) && LHS == RHS) |
| return true; |
| |
| switch (Pred) { |
| default: |
| return false; |
| |
| case CmpInst::ICMP_SLE: { |
| const APInt *C; |
| |
| // LHS s<= LHS +_{nsw} C if C >= 0 |
| if (match(RHS, m_NSWAdd(m_Specific(LHS), m_APInt(C)))) |
| return !C->isNegative(); |
| return false; |
| } |
| |
| case CmpInst::ICMP_ULE: { |
| const APInt *C; |
| |
| // LHS u<= LHS +_{nuw} C for any C |
| if (match(RHS, m_NUWAdd(m_Specific(LHS), m_APInt(C)))) |
| return true; |
| |
| // Match A to (X +_{nuw} CA) and B to (X +_{nuw} CB) |
| auto MatchNUWAddsToSameValue = [&](Value *A, Value *B, Value *&X, |
| const APInt *&CA, const APInt *&CB) { |
| if (match(A, m_NUWAdd(m_Value(X), m_APInt(CA))) && |
| match(B, m_NUWAdd(m_Specific(X), m_APInt(CB)))) |
| return true; |
| |
| // If X & C == 0 then (X | C) == X +_{nuw} C |
| if (match(A, m_Or(m_Value(X), m_APInt(CA))) && |
| match(B, m_Or(m_Specific(X), m_APInt(CB)))) { |
| unsigned BitWidth = CA->getBitWidth(); |
| APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); |
| computeKnownBits(X, KnownZero, KnownOne, DL, Depth + 1, AC, CxtI, DT); |
| |
| if ((KnownZero & *CA) == *CA && (KnownZero & *CB) == *CB) |
| return true; |
| } |
| |
| return false; |
| }; |
| |
| Value *X; |
| const APInt *CLHS, *CRHS; |
| if (MatchNUWAddsToSameValue(LHS, RHS, X, CLHS, CRHS)) |
| return CLHS->ule(*CRHS); |
| |
| return false; |
| } |
| } |
| } |
| |
| /// Return true if "icmp Pred BLHS BRHS" is true whenever "icmp Pred |
| /// ALHS ARHS" is true. |
| static bool isImpliedCondOperands(CmpInst::Predicate Pred, Value *ALHS, |
| Value *ARHS, Value *BLHS, Value *BRHS, |
| const DataLayout &DL, unsigned Depth, |
| AssumptionCache *AC, const Instruction *CxtI, |
| const DominatorTree *DT) { |
| switch (Pred) { |
| default: |
| return false; |
| |
| case CmpInst::ICMP_SLT: |
| case CmpInst::ICMP_SLE: |
| return isTruePredicate(CmpInst::ICMP_SLE, BLHS, ALHS, DL, Depth, AC, CxtI, |
| DT) && |
| isTruePredicate(CmpInst::ICMP_SLE, ARHS, BRHS, DL, Depth, AC, CxtI, |
| DT); |
| |
| case CmpInst::ICMP_ULT: |
| case CmpInst::ICMP_ULE: |
| return isTruePredicate(CmpInst::ICMP_ULE, BLHS, ALHS, DL, Depth, AC, CxtI, |
| DT) && |
| isTruePredicate(CmpInst::ICMP_ULE, ARHS, BRHS, DL, Depth, AC, CxtI, |
| DT); |
| } |
| } |
| |
| bool llvm::isImpliedCondition(Value *LHS, Value *RHS, const DataLayout &DL, |
| unsigned Depth, AssumptionCache *AC, |
| const Instruction *CxtI, |
| const DominatorTree *DT) { |
| assert(LHS->getType() == RHS->getType() && "mismatched type"); |
| Type *OpTy = LHS->getType(); |
| assert(OpTy->getScalarType()->isIntegerTy(1)); |
| |
| // LHS ==> RHS by definition |
| if (LHS == RHS) return true; |
| |
| if (OpTy->isVectorTy()) |
| // TODO: extending the code below to handle vectors |
| return false; |
| assert(OpTy->isIntegerTy(1) && "implied by above"); |
| |
| ICmpInst::Predicate APred, BPred; |
| Value *ALHS, *ARHS; |
| Value *BLHS, *BRHS; |
| |
| if (!match(LHS, m_ICmp(APred, m_Value(ALHS), m_Value(ARHS))) || |
| !match(RHS, m_ICmp(BPred, m_Value(BLHS), m_Value(BRHS)))) |
| return false; |
| |
| if (APred == BPred) |
| return isImpliedCondOperands(APred, ALHS, ARHS, BLHS, BRHS, DL, Depth, AC, |
| CxtI, DT); |
| |
| return false; |
| } |