//===- 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/Loads.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/OptimizationDiagnosticInfo.h" #include "llvm/Analysis/VectorUtils.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 #include #include using namespace llvm; using namespace llvm::PatternMatch; const unsigned MaxDepth = 6; // Controls the number of uses of the value searched for possible // dominating comparisons. static cl::opt DomConditionsMaxUses("dom-conditions-max-uses", cl::Hidden, cl::init(20)); // This optimization is known to cause performance regressions is some cases, // keep it under a temporary flag for now. static cl::opt DontImproveNonNegativePhiBits("dont-improve-non-negative-phi-bits", cl::Hidden, cl::init(true)); /// 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); } 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 { const DataLayout &DL; AssumptionCache *AC; const Instruction *CxtI; const DominatorTree *DT; // Unlike the other analyses, this may be a nullptr because not all clients // provide it currently. OptimizationRemarkEmitter *ORE; /// Set of assumptions that should be excluded from further queries. /// 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. std::array Excluded; unsigned NumExcluded; Query(const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, OptimizationRemarkEmitter *ORE = nullptr) : DL(DL), AC(AC), CxtI(CxtI), DT(DT), ORE(ORE), NumExcluded(0) {} Query(const Query &Q, const Value *NewExcl) : DL(Q.DL), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT), ORE(Q.ORE), NumExcluded(Q.NumExcluded) { Excluded = Q.Excluded; Excluded[NumExcluded++] = NewExcl; assert(NumExcluded <= Excluded.size()); } bool isExcluded(const Value *Value) const { if (NumExcluded == 0) return false; auto End = Excluded.begin() + NumExcluded; return std::find(Excluded.begin(), End, Value) != End; } }; } // end anonymous namespace // Given the provided Value and, potentially, a context instruction, return // the preferred context instruction (if any). static const Instruction *safeCxtI(const Value *V, const Instruction *CxtI) { // If we've been provided with a context instruction, then use that (provided // it has been inserted). if (CxtI && CxtI->getParent()) return CxtI; // If the value is really an already-inserted instruction, then use that. CxtI = dyn_cast(V); if (CxtI && CxtI->getParent()) return CxtI; return nullptr; } static void computeKnownBits(const Value *V, APInt &KnownZero, APInt &KnownOne, unsigned Depth, const Query &Q); void llvm::computeKnownBits(const Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, OptimizationRemarkEmitter *ORE) { ::computeKnownBits(V, KnownZero, KnownOne, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, ORE)); } bool llvm::haveNoCommonBitsSet(const Value *LHS, const 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(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(const Value *V, bool &KnownZero, bool &KnownOne, unsigned Depth, const Query &Q); void llvm::ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { ::ComputeSignBit(V, KnownZero, KnownOne, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT)); } static bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth, const Query &Q); bool llvm::isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL, bool OrZero, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::isKnownToBeAPowerOfTwo(V, OrZero, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT)); } static bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q); bool llvm::isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::isKnownNonZero(V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT)); } bool llvm::isKnownNonNegative(const 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; } bool llvm::isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { if (auto *CI = dyn_cast(V)) return CI->getValue().isStrictlyPositive(); // TODO: We'd doing two recursive queries here. We should factor this such // that only a single query is needed. return isKnownNonNegative(V, DL, Depth, AC, CxtI, DT) && isKnownNonZero(V, DL, Depth, AC, CxtI, DT); } bool llvm::isKnownNegative(const 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 Negative; } static bool isKnownNonEqual(const Value *V1, const Value *V2, const Query &Q); bool llvm::isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::isKnownNonEqual(V1, V2, Query(DL, AC, safeCxtI(V1, safeCxtI(V2, CxtI)), DT)); } static bool MaskedValueIsZero(const Value *V, const APInt &Mask, unsigned Depth, const Query &Q); bool llvm::MaskedValueIsZero(const Value *V, const APInt &Mask, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::MaskedValueIsZero(V, Mask, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT)); } static unsigned ComputeNumSignBits(const Value *V, unsigned Depth, const Query &Q); unsigned llvm::ComputeNumSignBits(const Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { return ::ComputeNumSignBits(V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT)); } static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1, bool NSW, APInt &KnownZero, APInt &KnownOne, APInt &KnownZero2, APInt &KnownOne2, unsigned Depth, const Query &Q) { 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, Depth + 1, Q); computeKnownBits(Op1, KnownZero2, KnownOne2, Depth + 1, Q); // Carry in a 1 for a subtract, rather than a 0. uint64_t CarryIn = 0; if (!Add) { // Sum = LHS + ~RHS + 1 std::swap(KnownZero2, KnownOne2); CarryIn = 1; } 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.setSignBit(); // 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.setSignBit(); } } } static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW, APInt &KnownZero, APInt &KnownOne, APInt &KnownZero2, APInt &KnownOne2, unsigned Depth, const Query &Q) { unsigned BitWidth = KnownZero.getBitWidth(); computeKnownBits(Op1, KnownZero, KnownOne, Depth + 1, Q); computeKnownBits(Op0, KnownZero2, KnownOne2, 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, Depth, Q)) || (isKnownNegativeOp0 && isKnownNonNegativeOp1 && isKnownNonZero(Op1, 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.clearAllBits(); KnownZero.setLowBits(TrailZ); KnownZero.setHighBits(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.setSignBit(); else if (isKnownNegative && !KnownZero.isNegative()) KnownOne.setSignBit(); } 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(Ranges.getOperand(2 * i + 0)); ConstantInt *Upper = mdconst::extract(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(const Instruction *I, const Value *E) { SmallVector WorkSet(1, I); SmallPtrSet Visited; SmallPtrSet 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 (is_contained(I->operands(), E)) 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 (all_of(V->users(), [&](const User *U) { return EphValues.count(U); })) { if (V == E) return true; EphValues.insert(V); if (const User *U = dyn_cast(V)) for (User::const_op_iterator J = U->op_begin(), JE = U->op_end(); J != JE; ++J) { if (isSafeToSpeculativelyExecute(*J)) WorkSet.push_back(*J); } } } return false; } // Is this an intrinsic that cannot be speculated but also cannot trap? static bool isAssumeLikeIntrinsic(const Instruction *I) { if (const CallInst *CI = dyn_cast(I)) if (Function *F = CI->getCalledFunction()) switch (F->getIntrinsicID()) { default: break; // FIXME: This list is repeated from NoTTI::getIntrinsicCost. case Intrinsic::assume: case Intrinsic::dbg_declare: case Intrinsic::dbg_value: case Intrinsic::invariant_start: case Intrinsic::invariant_end: case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: case Intrinsic::objectsize: case Intrinsic::ptr_annotation: case Intrinsic::var_annotation: return true; } return false; } bool llvm::isValidAssumeForContext(const Instruction *Inv, const Instruction *CxtI, const DominatorTree *DT) { // 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 (DT) { if (DT->dominates(Inv, CxtI)) return true; } else if (Inv->getParent() == CxtI->getParent()->getSinglePredecessor()) { // We don't have a DT, but this trivially dominates. return true; } // With or without a DT, the only remaining case we will check is if the // instructions are in the same BB. Give up if that is not the case. if (Inv->getParent() != CxtI->getParent()) return false; // If we have a dom tree, then we now know that the assume doens't dominate // the other instruction. If we don't have a dom tree then we can check if // the assume is first in the BB. if (!DT) { // 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 (auto I = std::next(BasicBlock::const_iterator(Inv)), IE = Inv->getParent()->end(); I != IE; ++I) if (&*I == CxtI) return true; } // 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(CxtI)), IE(Inv); I != IE; ++I) if (!isSafeToSpeculativelyExecute(&*I) && !isAssumeLikeIntrinsic(&*I)) return false; return !isEphemeralValueOf(Inv, CxtI); } static void computeKnownBitsFromAssume(const Value *V, APInt &KnownZero, APInt &KnownOne, 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(); // Note that the patterns below need to be kept in sync with the code // in AssumptionCache::updateAffectedValues. for (auto &AssumeVH : Q.AC->assumptionsFor(V)) { if (!AssumeVH) continue; CallInst *I = cast(AssumeVH); assert(I->getParent()->getParent() == Q.CxtI->getParent()->getParent() && "Got assumption for the wrong function!"); if (Q.isExcluded(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.CxtI, Q.DT)) { assert(BitWidth == 1 && "assume operand is not i1?"); KnownZero.clearAllBits(); KnownOne.setAllBits(); return; } if (match(Arg, m_Not(m_Specific(V))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { assert(BitWidth == 1 && "assume operand is not i1?"); KnownZero.setAllBits(); KnownOne.clearAllBits(); 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0); computeKnownBits(B, MaskKnownZero, MaskKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0); computeKnownBits(B, MaskKnownZero, MaskKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0); computeKnownBits(B, BKnownZero, BKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); if (RHSKnownZero.isNegative()) { // We know that the sign bit is zero. KnownZero.setSignBit(); } // 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); if (RHSKnownOne.isAllOnesValue() || RHSKnownZero.isNegative()) { // We know that the sign bit is zero. KnownZero.setSignBit(); } // 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); if (RHSKnownOne.isNegative()) { // We know that the sign bit is one. KnownOne.setSignBit(); } // 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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); if (RHSKnownZero.isAllOnesValue() || RHSKnownOne.isNegative()) { // We know that the sign bit is one. KnownOne.setSignBit(); } // assume(v <=_u c) } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) && Pred == ICmpInst::ICMP_ULE && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I)); // Whatever high bits in c are zero are known to be zero. KnownZero.setHighBits(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.CxtI, Q.DT)) { APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); computeKnownBits(A, RHSKnownZero, RHSKnownOne, 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))) KnownZero.setHighBits(RHSKnownZero.countLeadingOnes()+1); else KnownZero.setHighBits(RHSKnownZero.countLeadingOnes()); } } // If assumptions conflict with each other or previous known bits, then we // have a logical fallacy. It's possible that the assumption is not reachable, // so this isn't a real bug. On the other hand, the program may have undefined // behavior, or we might have a bug in the compiler. We can't assert/crash, so // clear out the known bits, try to warn the user, and hope for the best. if ((KnownZero & KnownOne) != 0) { KnownZero.clearAllBits(); KnownOne.clearAllBits(); if (Q.ORE) { auto *CxtI = const_cast(Q.CxtI); OptimizationRemarkAnalysis ORA("value-tracking", "BadAssumption", CxtI); Q.ORE->emit(ORA << "Detected conflicting code assumptions. Program may " "have undefined behavior, or compiler may have " "internal error."); } } } // 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. static void computeKnownBitsFromShiftOperator( const Operator *I, APInt &KnownZero, APInt &KnownOne, APInt &KnownZero2, APInt &KnownOne2, unsigned Depth, const Query &Q, function_ref KZF, function_ref KOF) { unsigned BitWidth = KnownZero.getBitWidth(); if (auto *SA = dyn_cast(I->getOperand(1))) { unsigned ShiftAmt = SA->getLimitedValue(BitWidth-1); computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q); KnownZero = KZF(KnownZero, ShiftAmt); KnownOne = KOF(KnownOne, ShiftAmt); // If there is conflict between KnownZero and KnownOne, this must be an // overflowing left shift, so the shift result is undefined. Clear KnownZero // and KnownOne bits so that other code could propagate this undef. if ((KnownZero & KnownOne) != 0) { KnownZero.clearAllBits(); KnownOne.clearAllBits(); } return; } computeKnownBits(I->getOperand(1), KnownZero, KnownOne, Depth + 1, Q); // If the shift amount could be greater than or equal to the bit-width of the LHS, the // value could be undef, so we don't know anything about it. if ((~KnownZero).uge(BitWidth)) { KnownZero.clearAllBits(); KnownOne.clearAllBits(); return; } // 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 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), Depth + 1, Q); if (!*ShifterOperandIsNonZero) return; } computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, 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), 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(const Operator *I, APInt &KnownZero, APInt &KnownOne, 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(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, Depth + 1, Q); computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, 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 (!KnownZero[0] && !KnownOne[0] && (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))))) { KnownZero2.clearAllBits(); KnownOne2.clearAllBits(); computeKnownBits(Y, KnownZero2, KnownOne2, Depth + 1, Q); if (KnownOne2.countTrailingOnes() > 0) KnownZero.setBit(0); } break; } case Instruction::Or: { computeKnownBits(I->getOperand(1), KnownZero, KnownOne, Depth + 1, Q); computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, 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, Depth + 1, Q); computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, 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 = std::move(KnownZeroOut); break; } case Instruction::Mul: { bool NSW = cast(I)->hasNoSignedWrap(); computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW, KnownZero, KnownOne, KnownZero2, KnownOne2, 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, Depth + 1, Q); unsigned LeadZ = KnownZero2.countLeadingOnes(); KnownOne2.clearAllBits(); KnownZero2.clearAllBits(); computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, Depth + 1, Q); unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros(); if (RHSUnknownLeadingOnes != BitWidth) LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSUnknownLeadingOnes - 1); KnownZero.setHighBits(LeadZ); break; } case Instruction::Select: { const Value *LHS, *RHS; SelectPatternFlavor SPF = matchSelectPattern(I, LHS, RHS).Flavor; if (SelectPatternResult::isMinOrMax(SPF)) { computeKnownBits(RHS, KnownZero, KnownOne, Depth + 1, Q); computeKnownBits(LHS, KnownZero2, KnownOne2, Depth + 1, Q); } else { computeKnownBits(I->getOperand(2), KnownZero, KnownOne, Depth + 1, Q); computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, Depth + 1, Q); } unsigned MaxHighOnes = 0; unsigned MaxHighZeros = 0; if (SPF == SPF_SMAX) { // If both sides are negative, the result is negative. if (KnownOne.isNegative() && KnownOne2.isNegative()) // We can derive a lower bound on the result by taking the max of the // leading one bits. MaxHighOnes = std::max(KnownOne.countLeadingOnes(), KnownOne2.countLeadingOnes()); // If either side is non-negative, the result is non-negative. else if (KnownZero.isNegative() || KnownZero2.isNegative()) MaxHighZeros = 1; } else if (SPF == SPF_SMIN) { // If both sides are non-negative, the result is non-negative. if (KnownZero.isNegative() && KnownZero2.isNegative()) // We can derive an upper bound on the result by taking the max of the // leading zero bits. MaxHighZeros = std::max(KnownZero.countLeadingOnes(), KnownZero2.countLeadingOnes()); // If either side is negative, the result is negative. else if (KnownOne.isNegative() || KnownOne2.isNegative()) MaxHighOnes = 1; } else if (SPF == SPF_UMAX) { // We can derive a lower bound on the result by taking the max of the // leading one bits. MaxHighOnes = std::max(KnownOne.countLeadingOnes(), KnownOne2.countLeadingOnes()); } else if (SPF == SPF_UMIN) { // We can derive an upper bound on the result by taking the max of the // leading zero bits. MaxHighZeros = std::max(KnownZero.countLeadingOnes(), KnownZero2.countLeadingOnes()); } // Only known if known in both the LHS and RHS. KnownOne &= KnownOne2; KnownZero &= KnownZero2; if (MaxHighOnes > 0) KnownOne.setHighBits(MaxHighOnes); if (MaxHighZeros > 0) KnownZero.setHighBits(MaxHighZeros); 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: // Fall through and handle them the same as zext/trunc. LLVM_FALLTHROUGH; 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 = Q.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, Depth + 1, Q); KnownZero = KnownZero.zextOrTrunc(BitWidth); KnownOne = KnownOne.zextOrTrunc(BitWidth); // Any top bits are known to be zero. if (BitWidth > SrcBitWidth) KnownZero.setBitsFrom(SrcBitWidth); break; } case Instruction::BitCast: { Type *SrcTy = I->getOperand(0)->getType(); if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && // TODO: For now, not handling conversions like: // (bitcast i64 %x to <2 x i32>) !I->getType()->isVectorTy()) { computeKnownBits(I->getOperand(0), KnownZero, KnownOne, 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, Depth + 1, Q); // If the sign bit of the input is known set or clear, then we know the // top bits of the result. KnownZero = KnownZero.sext(BitWidth); KnownOne = KnownOne.sext(BitWidth); break; } case Instruction::Shl: { // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 bool NSW = cast(I)->hasNoSignedWrap(); auto KZF = [NSW](const APInt &KnownZero, unsigned ShiftAmt) { APInt KZResult = KnownZero << ShiftAmt; KZResult.setLowBits(ShiftAmt); // Low bits known 0. // If this shift has "nsw" keyword, then the result is either a poison // value or has the same sign bit as the first operand. if (NSW && KnownZero.isNegative()) KZResult.setSignBit(); return KZResult; }; auto KOF = [NSW](const APInt &KnownOne, unsigned ShiftAmt) { APInt KOResult = KnownOne << ShiftAmt; if (NSW && KnownOne.isNegative()) KOResult.setSignBit(); return KOResult; }; computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne, KnownZero2, KnownOne2, 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 KnownZero.lshr(ShiftAmt) | // High bits known zero. APInt::getHighBitsSet(BitWidth, ShiftAmt); }; auto KOF = [](const APInt &KnownOne, unsigned ShiftAmt) { return KnownOne.lshr(ShiftAmt); }; computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne, KnownZero2, KnownOne2, Depth, Q, KZF, KOF); break; } case Instruction::AShr: { // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 auto KZF = [](const APInt &KnownZero, unsigned ShiftAmt) { return KnownZero.ashr(ShiftAmt); }; auto KOF = [](const APInt &KnownOne, unsigned ShiftAmt) { return KnownOne.ashr(ShiftAmt); }; computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne, KnownZero2, KnownOne2, Depth, Q, KZF, KOF); break; } case Instruction::Sub: { bool NSW = cast(I)->hasNoSignedWrap(); computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW, KnownZero, KnownOne, KnownZero2, KnownOne2, Depth, Q); break; } case Instruction::Add: { bool NSW = cast(I)->hasNoSignedWrap(); computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW, KnownZero, KnownOne, KnownZero2, KnownOne2, Depth, Q); break; } case Instruction::SRem: if (ConstantInt *Rem = dyn_cast(I->getOperand(1))) { APInt RA = Rem->getValue().abs(); if (RA.isPowerOf2()) { APInt LowBits = RA - 1; computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, 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.isNegative() || ((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.isNegative() && ((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, Depth + 1, Q); // If it's known zero, our sign bit is also zero. if (LHSKnownZero.isNegative()) KnownZero.setSignBit(); } break; case Instruction::URem: { if (ConstantInt *Rem = dyn_cast(I->getOperand(1))) { const APInt &RA = Rem->getValue(); if (RA.isPowerOf2()) { APInt LowBits = (RA - 1); computeKnownBits(I->getOperand(0), KnownZero, KnownOne, 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, Depth + 1, Q); computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, Depth + 1, Q); unsigned Leaders = std::max(KnownZero.countLeadingOnes(), KnownZero2.countLeadingOnes()); KnownOne.clearAllBits(); KnownZero.clearAllBits(); KnownZero.setHighBits(Leaders); break; } case Instruction::Alloca: { const AllocaInst *AI = cast(I); unsigned Align = AI->getAlignment(); if (Align == 0) Align = Q.DL.getABITypeAlignment(AI->getAllocatedType()); if (Align > 0) KnownZero.setLowBits(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, 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 = GTI.getStructTypeOrNull()) { // Handle struct member offset arithmetic. // Handle case when index is vector zeroinitializer Constant *CIndex = cast(Index); if (CIndex->isZeroValue()) continue; if (CIndex->getType()->isVectorTy()) Index = CIndex->getSplatValue(); unsigned Idx = cast(Index)->getZExtValue(); const StructLayout *SL = Q.DL.getStructLayout(STy); uint64_t Offset = SL->getElementOffset(Idx); TrailZ = std::min(TrailZ, countTrailingZeros(Offset)); } else { // Handle array index arithmetic. Type *IndexedTy = GTI.getIndexedType(); if (!IndexedTy->isSized()) { TrailZ = 0; break; } unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits(); uint64_t TypeSize = Q.DL.getTypeAllocSize(IndexedTy); LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0); computeKnownBits(Index, LocalKnownZero, LocalKnownOne, Depth + 1, Q); TrailZ = std::min(TrailZ, unsigned(countTrailingZeros(TypeSize) + LocalKnownZero.countTrailingOnes())); } } KnownZero.setLowBits(TrailZ); break; } case Instruction::PHI: { const PHINode *P = cast(I); // Handle the case of a simple two-predecessor recurrence PHI. // There's a lot more that could theoretically be done here, but // this is sufficient to catch some interesting cases. if (P->getNumIncomingValues() == 2) { for (unsigned i = 0; i != 2; ++i) { Value *L = P->getIncomingValue(i); Value *R = P->getIncomingValue(!i); Operator *LU = dyn_cast(L); if (!LU) continue; unsigned Opcode = LU->getOpcode(); // Check for operations that have the property that if // both their operands have low zero bits, the result // will have low zero bits. if (Opcode == Instruction::Add || Opcode == Instruction::Sub || Opcode == Instruction::And || Opcode == Instruction::Or || Opcode == Instruction::Mul) { Value *LL = LU->getOperand(0); Value *LR = LU->getOperand(1); // Find a recurrence. if (LL == I) L = LR; else if (LR == I) L = LL; else break; // Ok, we have a PHI of the form L op= R. Check for low // zero bits. computeKnownBits(R, KnownZero2, KnownOne2, Depth + 1, Q); // We need to take the minimum number of known bits APInt KnownZero3(KnownZero), KnownOne3(KnownOne); computeKnownBits(L, KnownZero3, KnownOne3, Depth + 1, Q); KnownZero.setLowBits(std::min(KnownZero2.countTrailingOnes(), KnownZero3.countTrailingOnes())); if (DontImproveNonNegativePhiBits) break; auto *OverflowOp = dyn_cast(LU); if (OverflowOp && OverflowOp->hasNoSignedWrap()) { // If initial value of recurrence is nonnegative, and we are adding // a nonnegative number with nsw, the result can only be nonnegative // or poison value regardless of the number of times we execute the // add in phi recurrence. If initial value is negative and we are // adding a negative number with nsw, the result can only be // negative or poison value. Similar arguments apply to sub and mul. // // (add non-negative, non-negative) --> non-negative // (add negative, negative) --> negative if (Opcode == Instruction::Add) { if (KnownZero2.isNegative() && KnownZero3.isNegative()) KnownZero.setSignBit(); else if (KnownOne2.isNegative() && KnownOne3.isNegative()) KnownOne.setSignBit(); } // (sub nsw non-negative, negative) --> non-negative // (sub nsw negative, non-negative) --> negative else if (Opcode == Instruction::Sub && LL == I) { if (KnownZero2.isNegative() && KnownOne3.isNegative()) KnownZero.setSignBit(); else if (KnownOne2.isNegative() && KnownZero3.isNegative()) KnownOne.setSignBit(); } // (mul nsw non-negative, non-negative) --> non-negative else if (Opcode == Instruction::Mul && KnownZero2.isNegative() && KnownZero3.isNegative()) KnownZero.setSignBit(); } break; } } } // Unreachable blocks may have zero-operand PHI nodes. if (P->getNumIncomingValues() == 0) break; // Otherwise take the unions of the known bit sets of the operands, // taking conservative care to avoid excessive recursion. if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) { // Skip if every incoming value references to ourself. if (dyn_cast_or_null(P->hasConstantValue())) break; KnownZero.setAllBits(); KnownOne.setAllBits(); 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, 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 range metadata is attached to this call, set known bits from that, // and then intersect with known bits based on other properties of the // function. if (MDNode *MD = cast(I)->getMetadata(LLVMContext::MD_range)) computeKnownBitsFromRangeMetadata(*MD, KnownZero, KnownOne); if (const Value *RV = ImmutableCallSite(I).getReturnedArgOperand()) { computeKnownBits(RV, KnownZero2, KnownOne2, Depth + 1, Q); KnownZero |= KnownZero2; KnownOne |= KnownOne2; } if (const IntrinsicInst *II = dyn_cast(I)) { switch (II->getIntrinsicID()) { default: break; case Intrinsic::bitreverse: computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q); KnownZero |= KnownZero2.reverseBits(); KnownOne |= KnownOne2.reverseBits(); break; case Intrinsic::bswap: computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, 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.setBitsFrom(LowBits); break; } case Intrinsic::ctpop: { computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, 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 LowBits = Log2_32(BitsPossiblySet)+1; KnownZero.setBitsFrom(LowBits); // 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::x86_sse42_crc32_64_64: KnownZero.setBitsFrom(32); break; } } break; case Instruction::ExtractElement: // Look through extract element. At the moment we keep this simple and skip // tracking the specific element. But at least we might find information // valid for all elements of the vector (for example if vector is sign // extended, shifted, etc). computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q); break; case Instruction::ExtractValue: if (IntrinsicInst *II = dyn_cast(I->getOperand(0))) { const ExtractValueInst *EVI = cast(I); if (EVI->getNumIndices() != 1) break; if (EVI->getIndices()[0] == 0) { switch (II->getIntrinsicID()) { default: break; case Intrinsic::uadd_with_overflow: case Intrinsic::sadd_with_overflow: computeKnownBitsAddSub(true, II->getArgOperand(0), II->getArgOperand(1), false, KnownZero, KnownOne, KnownZero2, KnownOne2, 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, 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, Depth, Q); break; } } } } } /// 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(const Value *V, APInt &KnownZero, APInt &KnownOne, unsigned Depth, const Query &Q) { assert(V && "No Value?"); assert(Depth <= MaxDepth && "Limit Search Depth"); unsigned BitWidth = KnownZero.getBitWidth(); assert((V->getType()->isIntOrIntVectorTy() || V->getType()->getScalarType()->isPointerTy()) && "Not integer or pointer type!"); assert((Q.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"); (void)BitWidth; const APInt *C; if (match(V, m_APInt(C))) { // We know all of the bits for a scalar constant or a splat vector constant! KnownOne = *C; KnownZero = ~KnownOne; return; } // Null and aggregate-zero are all-zeros. if (isa(V) || isa(V)) { KnownOne.clearAllBits(); KnownZero.setAllBits(); return; } // Handle a constant vector by taking the intersection of the known bits of // each element. if (const ConstantDataSequential *CDS = dyn_cast(V)) { // We know that CDS must be a vector of integers. Take the intersection of // each element. KnownZero.setAllBits(); KnownOne.setAllBits(); APInt Elt(KnownZero.getBitWidth(), 0); for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) { Elt = CDS->getElementAsInteger(i); KnownZero &= ~Elt; KnownOne &= Elt; } return; } if (const auto *CV = dyn_cast(V)) { // We know that CV 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 = CV->getNumOperands(); i != e; ++i) { Constant *Element = CV->getAggregateElement(i); auto *ElementCI = dyn_cast_or_null(Element); if (!ElementCI) { KnownZero.clearAllBits(); KnownOne.clearAllBits(); return; } Elt = ElementCI->getValue(); KnownZero &= ~Elt; KnownOne &= Elt; } return; } // Start out not knowing anything. KnownZero.clearAllBits(); KnownOne.clearAllBits(); // We can't imply anything about undefs. if (isa(V)) return; // There's no point in looking through other users of ConstantData for // assumptions. Confirm that we've handled them all. assert(!isa(V) && "Unhandled constant data!"); // 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 (const GlobalAlias *GA = dyn_cast(V)) { if (!GA->isInterposable()) computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, Depth + 1, Q); return; } if (const Operator *I = dyn_cast(V)) computeKnownBitsFromOperator(I, KnownZero, KnownOne, Depth, Q); // Aligned pointers have trailing zeros - refine KnownZero set if (V->getType()->isPointerTy()) { unsigned Align = V->getPointerAlignment(Q.DL); if (Align) KnownZero.setLowBits(countTrailingZeros(Align)); } // computeKnownBitsFromAssume 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, 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(const Value *V, bool &KnownZero, bool &KnownOne, unsigned Depth, const Query &Q) { unsigned BitWidth = getBitWidth(V->getType(), Q.DL); if (!BitWidth) { KnownZero = false; KnownOne = false; return; } APInt ZeroBits(BitWidth, 0); APInt OneBits(BitWidth, 0); computeKnownBits(V, ZeroBits, OneBits, Depth, Q); KnownOne = OneBits.isNegative(); KnownZero = ZeroBits.isNegative(); } /// 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(const Value *V, bool OrZero, unsigned Depth, const Query &Q) { if (const Constant *C = dyn_cast(V)) { if (C->isNullValue()) return OrZero; const APInt *ConstIntOrConstSplatInt; if (match(C, m_APInt(ConstIntOrConstSplatInt))) return ConstIntOrConstSplatInt->isPowerOf2(); } // 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); if (const ZExtInst *ZI = dyn_cast(V)) return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q); if (const SelectInst *SI = dyn_cast(V)) return isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth, Q) && isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth, Q); 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) || isKnownToBeAPowerOfTwo(Y, /*OrZero*/ true, Depth, Q)) 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)))) { const OverflowingBinaryOperator *VOBO = cast(V); if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) { if (match(X, m_And(m_Specific(Y), m_Value())) || match(X, m_And(m_Value(), m_Specific(Y)))) if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth, Q)) 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)) return true; unsigned BitWidth = V->getType()->getScalarSizeInBits(); APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0); computeKnownBits(X, LHSZeroBits, LHSOneBits, Depth, Q); APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0); computeKnownBits(Y, RHSZeroBits, RHSOneBits, Depth, Q); // If i8 V is a power of two or zero: // ZeroBits: 1 1 1 0 1 1 1 1 // ~ZeroBits: 0 0 0 1 0 0 0 0 if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2()) // If OrZero isn't set, we cannot give back a zero result. // Make sure either the LHS or RHS has a bit set. if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue()) return true; } } // An exact divide or right shift can only shift off zero bits, so the result // is a power of two only if the first operand is a power of two and not // copying a sign bit (sdiv int_min, 2). if (match(V, m_Exact(m_LShr(m_Value(), m_Value()))) || match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) { return isKnownToBeAPowerOfTwo(cast(V)->getOperand(0), OrZero, Depth, Q); } 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(const GEPOperator *GEP, 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(), 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 = GTI.getStructTypeOrNull()) { ConstantInt *OpC = cast(GTI.getOperand()); unsigned ElementIdx = OpC->getZExtValue(); const StructLayout *SL = Q.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 (Q.DL.getTypeAllocSize(GTI.getIndexedType()) == 0) continue; // Fast path the constant operand case both for efficiency and so we don't // increment Depth when just zipping down an all-constant GEP. if (ConstantInt *OpC = dyn_cast(GTI.getOperand())) { if (!OpC->isZero()) return true; continue; } // We post-increment Depth here because while isKnownNonZero increments it // as well, when we pop back up that increment won't persist. We don't want // to recurse 10k times just because we have 10k GEP operands. We don't // bail completely out because we want to handle constant GEPs regardless // of depth. if (Depth++ >= MaxDepth) continue; if (isKnownNonZero(GTI.getOperand(), 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(const MDNode* Ranges, const APInt& Value) { const unsigned NumRanges = Ranges->getNumOperands() / 2; assert(NumRanges >= 1); for (unsigned i = 0; i < NumRanges; ++i) { ConstantInt *Lower = mdconst::extract(Ranges->getOperand(2 * i + 0)); ConstantInt *Upper = mdconst::extract(Ranges->getOperand(2 * i + 1)); ConstantRange Range(Lower->getValue(), Upper->getValue()); if (Range.contains(Value)) return false; } return true; } /// Return true if the given value is known to be non-zero when defined. For /// vectors, return true if every element is known to be non-zero when /// defined. For pointers, if the context instruction and dominator tree are /// specified, perform context-sensitive analysis and return true if the /// pointer couldn't possibly be null at the specified instruction. /// Supports values with integer or pointer type and vectors of integers. bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q) { if (auto *C = dyn_cast(V)) { if (C->isNullValue()) return false; if (isa(C)) // Must be non-zero due to null test above. return true; // For constant vectors, check that all elements are undefined or known // non-zero to determine that the whole vector is known non-zero. if (auto *VecTy = dyn_cast(C->getType())) { for (unsigned i = 0, e = VecTy->getNumElements(); i != e; ++i) { Constant *Elt = C->getAggregateElement(i); if (!Elt || Elt->isNullValue()) return false; if (!isa(Elt) && !isa(Elt)) return false; } return true; } return false; } if (auto *I = dyn_cast(V)) { if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) { // If the possible ranges don't contain zero, then the value is // definitely non-zero. if (auto *Ty = dyn_cast(V->getType())) { const APInt ZeroValue(Ty->getBitWidth(), 0); if (rangeMetadataExcludesValue(Ranges, ZeroValue)) return true; } } } // The remaining tests are all recursive, so bail out if we hit the limit. if (Depth++ >= MaxDepth) return false; // Check for pointer simplifications. if (V->getType()->isPointerTy()) { if (isKnownNonNullAt(V, Q.CxtI, Q.DT)) return true; if (const GEPOperator *GEP = dyn_cast(V)) if (isGEPKnownNonNull(GEP, Depth, Q)) return true; } unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), Q.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, Depth, Q) || isKnownNonZero(Y, Depth, Q); // ext X != 0 if X != 0. if (isa(V) || isa(V)) return isKnownNonZero(cast(V)->getOperand(0), 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. const OverflowingBinaryOperator *BO = cast(V); if (BO->hasNoUnsignedWrap()) return isKnownNonZero(X, Depth, Q); APInt KnownZero(BitWidth, 0); APInt KnownOne(BitWidth, 0); computeKnownBits(X, KnownZero, KnownOne, 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. const PossiblyExactOperator *BO = cast(V); if (BO->isExact()) return isKnownNonZero(X, Depth, Q); bool XKnownNonNegative, XKnownNegative; ComputeSignBit(X, XKnownNonNegative, XKnownNegative, 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(Y)) { APInt KnownZero(BitWidth, 0); APInt KnownOne(BitWidth, 0); computeKnownBits(X, KnownZero, KnownOne, 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, 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, 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, Depth, Q); ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, 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, Depth, Q) || isKnownNonZero(Y, 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, 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, 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)) return true; if (YKnownNonNegative && isKnownToBeAPowerOfTwo(X, /*OrZero*/ false, Depth, Q)) return true; } // X * Y. else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) { const OverflowingBinaryOperator *BO = cast(V); // If X and Y are non-zero then so is X * Y as long as the multiplication // does not overflow. if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) && isKnownNonZero(X, Depth, Q) && isKnownNonZero(Y, Depth, Q)) return true; } // (C ? X : Y) != 0 if X != 0 and Y != 0. else if (const SelectInst *SI = dyn_cast(V)) { if (isKnownNonZero(SI->getTrueValue(), Depth, Q) && isKnownNonZero(SI->getFalseValue(), Depth, Q)) return true; } // PHI else if (const PHINode *PN = dyn_cast(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(Induction) && !isa(Start)) std::swap(Start, Induction); if (ConstantInt *C = dyn_cast(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; } } } // Check if all incoming values are non-zero constant. bool AllNonZeroConstants = all_of(PN->operands(), [](Value *V) { return isa(V) && !cast(V)->isZeroValue(); }); if (AllNonZeroConstants) return true; } if (!BitWidth) return false; APInt KnownZero(BitWidth, 0); APInt KnownOne(BitWidth, 0); computeKnownBits(V, KnownZero, KnownOne, Depth, Q); return KnownOne != 0; } /// Return true if V2 == V1 + X, where X is known non-zero. static bool isAddOfNonZero(const Value *V1, const Value *V2, const Query &Q) { const BinaryOperator *BO = dyn_cast(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, 0, Q); } /// Return true if it is known that V1 != V2. static bool isKnownNonEqual(const Value *V1, const Value *V2, 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, Q) || isAddOfNonZero(V2, V1, Q)) return true; if (IntegerType *Ty = dyn_cast(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, 0, Q); APInt KnownZero2(BitWidth, 0); APInt KnownOne2(BitWidth, 0); computeKnownBits(V2, KnownZero2, KnownOne2, 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(const Value *V, const APInt &Mask, unsigned Depth, const Query &Q) { APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0); computeKnownBits(V, KnownZero, KnownOne, Depth, Q); return (KnownZero & Mask) == Mask; } /// For vector constants, loop over the elements and find the constant with the /// minimum number of sign bits. Return 0 if the value is not a vector constant /// or if any element was not analyzed; otherwise, return the count for the /// element with the minimum number of sign bits. static unsigned computeNumSignBitsVectorConstant(const Value *V, unsigned TyBits) { const auto *CV = dyn_cast(V); if (!CV || !CV->getType()->isVectorTy()) return 0; unsigned MinSignBits = TyBits; unsigned NumElts = CV->getType()->getVectorNumElements(); for (unsigned i = 0; i != NumElts; ++i) { // If we find a non-ConstantInt, bail out. auto *Elt = dyn_cast_or_null(CV->getAggregateElement(i)); if (!Elt) return 0; // If the sign bit is 1, flip the bits, so we always count leading zeros. APInt EltVal = Elt->getValue(); if (EltVal.isNegative()) EltVal = ~EltVal; MinSignBits = std::min(MinSignBits, EltVal.countLeadingZeros()); } return MinSignBits; } static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth, const Query &Q); static unsigned ComputeNumSignBits(const Value *V, unsigned Depth, const Query &Q) { unsigned Result = ComputeNumSignBitsImpl(V, Depth, Q); assert(Result > 0 && "At least one sign bit needs to be present!"); return Result; } /// 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. For vectors, return the number of sign bits for the /// vector element with the mininum number of known sign bits. static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth, const Query &Q) { // We return the minimum number of sign bits that are guaranteed to be present // in V, so for undef we have to conservatively return 1. We don't have the // same behavior for poison though -- that's a FIXME today. unsigned TyBits = Q.DL.getTypeSizeInBits(V->getType()->getScalarType()); unsigned Tmp, Tmp2; unsigned FirstAnswer = 1; // Note that ConstantInt is handled by the general computeKnownBits case // below. if (Depth == MaxDepth) return 1; // Limit search depth. const Operator *U = dyn_cast(V); switch (Operator::getOpcode(V)) { default: break; case Instruction::SExt: Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits(); return ComputeNumSignBits(U->getOperand(0), 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), 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), 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), Depth + 1, Q); // ashr X, C -> adds C sign bits. Vectors too. const APInt *ShAmt; if (match(U->getOperand(1), m_APInt(ShAmt))) { unsigned ShAmtLimited = ShAmt->getZExtValue(); if (ShAmtLimited >= TyBits) break; // Bad shift. Tmp += ShAmtLimited; 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), 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), Depth + 1, Q); if (Tmp != 1) { Tmp2 = ComputeNumSignBits(U->getOperand(1), 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), Depth + 1, Q); if (Tmp == 1) return 1; // Early out. Tmp2 = ComputeNumSignBits(U->getOperand(2), 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), Depth + 1, Q); if (Tmp == 1) return 1; // Early out. // Special case decrementing a value (ADD X, -1): if (const auto *CRHS = dyn_cast(U->getOperand(1))) if (CRHS->isAllOnesValue()) { APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); computeKnownBits(U->getOperand(0), KnownZero, KnownOne, 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), Depth + 1, Q); if (Tmp2 == 1) return 1; return std::min(Tmp, Tmp2)-1; case Instruction::Sub: Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q); if (Tmp2 == 1) return 1; // Handle NEG. if (const auto *CLHS = dyn_cast(U->getOperand(0))) if (CLHS->isNullValue()) { APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); computeKnownBits(U->getOperand(1), KnownZero, KnownOne, 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), Depth + 1, Q); if (Tmp == 1) return 1; // Early out. return std::min(Tmp, Tmp2)-1; case Instruction::PHI: { const PHINode *PN = cast(U); unsigned NumIncomingValues = PN->getNumIncomingValues(); // Don't analyze large in-degree PHIs. if (NumIncomingValues > 4) break; // Unreachable blocks may have zero-operand PHI nodes. if (NumIncomingValues == 0) break; // Take the minimum of all incoming values. This can't infinitely loop // because of our depth threshold. Tmp = ComputeNumSignBits(PN->getIncomingValue(0), 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), 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; case Instruction::ExtractElement: // Look through extract element. At the moment we keep this simple and skip // tracking the specific element. But at least we might find information // valid for all elements of the vector (for example if vector is sign // extended, shifted, etc). return ComputeNumSignBits(U->getOperand(0), Depth + 1, Q); } // Finally, if we can prove that the top bits of the result are 0's or 1's, // use this information. // If we can examine all elements of a vector constant successfully, we're // done (we can't do any better than that). If not, keep trying. if (unsigned VecSignBits = computeNumSignBitsVectorConstant(V, TyBits)) return VecSignBits; APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0); computeKnownBits(V, KnownZero, KnownOne, Depth, Q); // If we know that the sign bit is either zero or one, determine the number of // identical bits in the top of the input value. if (KnownZero.isNegative()) return std::max(FirstAnswer, KnownZero.countLeadingOnes()); if (KnownOne.isNegative()) return std::max(FirstAnswer, KnownOne.countLeadingOnes()); // computeKnownBits gave us no extra information about the top bits. return FirstAnswer; } /// This function computes the integer multiple of Base that equals V. /// If successful, it returns true and returns the multiple in /// Multiple. If unsuccessful, it returns false. It looks /// through SExt instructions only if LookThroughSExt is true. bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, bool LookThroughSExt, unsigned Depth) { const unsigned MaxDepth = 6; assert(V && "No Value?"); assert(Depth <= MaxDepth && "Limit Search Depth"); assert(V->getType()->isIntegerTy() && "Not integer or pointer type!"); Type *T = V->getType(); ConstantInt *CI = dyn_cast(V); if (Base == 0) return false; if (Base == 1) { Multiple = V; return true; } ConstantExpr *CO = dyn_cast(V); Constant *BaseVal = ConstantInt::get(T, Base); if (CO && CO == BaseVal) { // Multiple is 1. Multiple = ConstantInt::get(T, 1); return true; } if (CI && CI->getZExtValue() % Base == 0) { Multiple = ConstantInt::get(T, CI->getZExtValue() / Base); return true; } if (Depth == MaxDepth) return false; // Limit search depth. Operator *I = dyn_cast(V); if (!I) return false; switch (I->getOpcode()) { default: break; case Instruction::SExt: if (!LookThroughSExt) return false; // otherwise fall through to ZExt case Instruction::ZExt: return ComputeMultiple(I->getOperand(0), Base, Multiple, LookThroughSExt, Depth+1); case Instruction::Shl: case Instruction::Mul: { Value *Op0 = I->getOperand(0); Value *Op1 = I->getOperand(1); if (I->getOpcode() == Instruction::Shl) { ConstantInt *Op1CI = dyn_cast(Op1); if (!Op1CI) return false; // Turn Op0 << Op1 into Op0 * 2^Op1 APInt Op1Int = Op1CI->getValue(); uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1); APInt API(Op1Int.getBitWidth(), 0); API.setBit(BitToSet); Op1 = ConstantInt::get(V->getContext(), API); } Value *Mul0 = nullptr; if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) { if (Constant *Op1C = dyn_cast(Op1)) if (Constant *MulC = dyn_cast(Mul0)) { if (Op1C->getType()->getPrimitiveSizeInBits() < MulC->getType()->getPrimitiveSizeInBits()) Op1C = ConstantExpr::getZExt(Op1C, MulC->getType()); if (Op1C->getType()->getPrimitiveSizeInBits() > MulC->getType()->getPrimitiveSizeInBits()) MulC = ConstantExpr::getZExt(MulC, Op1C->getType()); // V == Base * (Mul0 * Op1), so return (Mul0 * Op1) Multiple = ConstantExpr::getMul(MulC, Op1C); return true; } if (ConstantInt *Mul0CI = dyn_cast(Mul0)) if (Mul0CI->getValue() == 1) { // V == Base * Op1, so return Op1 Multiple = Op1; return true; } } Value *Mul1 = nullptr; if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) { if (Constant *Op0C = dyn_cast(Op0)) if (Constant *MulC = dyn_cast(Mul1)) { if (Op0C->getType()->getPrimitiveSizeInBits() < MulC->getType()->getPrimitiveSizeInBits()) Op0C = ConstantExpr::getZExt(Op0C, MulC->getType()); if (Op0C->getType()->getPrimitiveSizeInBits() > MulC->getType()->getPrimitiveSizeInBits()) MulC = ConstantExpr::getZExt(MulC, Op0C->getType()); // V == Base * (Mul1 * Op0), so return (Mul1 * Op0) Multiple = ConstantExpr::getMul(MulC, Op0C); return true; } if (ConstantInt *Mul1CI = dyn_cast(Mul1)) if (Mul1CI->getValue() == 1) { // V == Base * Op0, so return Op0 Multiple = Op0; return true; } } } } // We could not determine if V is a multiple of Base. return false; } Intrinsic::ID llvm::getIntrinsicForCallSite(ImmutableCallSite ICS, const TargetLibraryInfo *TLI) { const Function *F = ICS.getCalledFunction(); if (!F) return Intrinsic::not_intrinsic; if (F->isIntrinsic()) return F->getIntrinsicID(); if (!TLI) return Intrinsic::not_intrinsic; LibFunc Func; // We're going to make assumptions on the semantics of the functions, check // that the target knows that it's available in this environment and it does // not have local linkage. if (!F || F->hasLocalLinkage() || !TLI->getLibFunc(*F, Func)) return Intrinsic::not_intrinsic; if (!ICS.onlyReadsMemory()) return Intrinsic::not_intrinsic; // Otherwise check if we have a call to a function that can be turned into a // vector intrinsic. switch (Func) { default: break; case LibFunc_sin: case LibFunc_sinf: case LibFunc_sinl: return Intrinsic::sin; case LibFunc_cos: case LibFunc_cosf: case LibFunc_cosl: return Intrinsic::cos; case LibFunc_exp: case LibFunc_expf: case LibFunc_expl: return Intrinsic::exp; case LibFunc_exp2: case LibFunc_exp2f: case LibFunc_exp2l: return Intrinsic::exp2; case LibFunc_log: case LibFunc_logf: case LibFunc_logl: return Intrinsic::log; case LibFunc_log10: case LibFunc_log10f: case LibFunc_log10l: return Intrinsic::log10; case LibFunc_log2: case LibFunc_log2f: case LibFunc_log2l: return Intrinsic::log2; case LibFunc_fabs: case LibFunc_fabsf: case LibFunc_fabsl: return Intrinsic::fabs; case LibFunc_fmin: case LibFunc_fminf: case LibFunc_fminl: return Intrinsic::minnum; case LibFunc_fmax: case LibFunc_fmaxf: case LibFunc_fmaxl: return Intrinsic::maxnum; case LibFunc_copysign: case LibFunc_copysignf: case LibFunc_copysignl: return Intrinsic::copysign; case LibFunc_floor: case LibFunc_floorf: case LibFunc_floorl: return Intrinsic::floor; case LibFunc_ceil: case LibFunc_ceilf: case LibFunc_ceill: return Intrinsic::ceil; case LibFunc_trunc: case LibFunc_truncf: case LibFunc_truncl: return Intrinsic::trunc; case LibFunc_rint: case LibFunc_rintf: case LibFunc_rintl: return Intrinsic::rint; case LibFunc_nearbyint: case LibFunc_nearbyintf: case LibFunc_nearbyintl: return Intrinsic::nearbyint; case LibFunc_round: case LibFunc_roundf: case LibFunc_roundl: return Intrinsic::round; case LibFunc_pow: case LibFunc_powf: case LibFunc_powl: return Intrinsic::pow; case LibFunc_sqrt: case LibFunc_sqrtf: case LibFunc_sqrtl: if (ICS->hasNoNaNs()) return Intrinsic::sqrt; return Intrinsic::not_intrinsic; } return Intrinsic::not_intrinsic; } /// 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, const TargetLibraryInfo *TLI, unsigned Depth) { if (const ConstantFP *CFP = dyn_cast(V)) return !CFP->getValueAPF().isNegZero(); if (Depth == MaxDepth) return false; // Limit search depth. const Operator *I = dyn_cast(V); if (!I) return false; // Check if the nsz fast-math flag is set if (const FPMathOperator *FPO = dyn_cast(I)) if (FPO->hasNoSignedZeros()) return true; // (add x, 0.0) is guaranteed to return +0.0, not -0.0. if (I->getOpcode() == Instruction::FAdd) if (ConstantFP *CFP = dyn_cast(I->getOperand(1))) if (CFP->isNullValue()) return true; // sitofp and uitofp turn into +0.0 for zero. if (isa(I) || isa(I)) return true; if (const CallInst *CI = dyn_cast(I)) { Intrinsic::ID IID = getIntrinsicForCallSite(CI, TLI); switch (IID) { default: break; // sqrt(-0.0) = -0.0, no other negative results are possible. case Intrinsic::sqrt: return CannotBeNegativeZero(CI->getArgOperand(0), TLI, Depth + 1); // fabs(x) != -0.0 case Intrinsic::fabs: return true; } } return false; } /// If \p SignBitOnly is true, test for a known 0 sign bit rather than a /// standard ordered compare. e.g. make -0.0 olt 0.0 be true because of the sign /// bit despite comparing equal. static bool cannotBeOrderedLessThanZeroImpl(const Value *V, const TargetLibraryInfo *TLI, bool SignBitOnly, unsigned Depth) { // TODO: This function does not do the right thing when SignBitOnly is true // and we're lowering to a hypothetical IEEE 754-compliant-but-evil platform // which flips the sign bits of NaNs. See // https://llvm.org/bugs/show_bug.cgi?id=31702. if (const ConstantFP *CFP = dyn_cast(V)) { return !CFP->getValueAPF().isNegative() || (!SignBitOnly && CFP->getValueAPF().isZero()); } if (Depth == MaxDepth) return false; // Limit search depth. const Operator *I = dyn_cast(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) && (!SignBitOnly || cast(I)->hasNoNaNs())) return true; LLVM_FALLTHROUGH; case Instruction::FAdd: case Instruction::FDiv: case Instruction::FRem: return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly, Depth + 1) && cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly, Depth + 1); case Instruction::Select: return cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly, Depth + 1) && cannotBeOrderedLessThanZeroImpl(I->getOperand(2), TLI, SignBitOnly, Depth + 1); case Instruction::FPExt: case Instruction::FPTrunc: // Widening/narrowing never change sign. return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly, Depth + 1); case Instruction::Call: const auto *CI = cast(I); Intrinsic::ID IID = getIntrinsicForCallSite(CI, TLI); switch (IID) { default: break; case Intrinsic::maxnum: return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly, Depth + 1) || cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly, Depth + 1); case Intrinsic::minnum: return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly, Depth + 1) && cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly, Depth + 1); case Intrinsic::exp: case Intrinsic::exp2: case Intrinsic::fabs: return true; case Intrinsic::sqrt: // sqrt(x) is always >= -0 or NaN. Moreover, sqrt(x) == -0 iff x == -0. if (!SignBitOnly) return true; return CI->hasNoNaNs() && (CI->hasNoSignedZeros() || CannotBeNegativeZero(CI->getOperand(0), TLI)); case Intrinsic::powi: if (ConstantInt *Exponent = dyn_cast(I->getOperand(1))) { // powi(x,n) is non-negative if n is even. if (Exponent->getBitWidth() <= 64 && Exponent->getSExtValue() % 2u == 0) return true; } // TODO: This is not correct. Given that exp is an integer, here are the // ways that pow can return a negative value: // // pow(x, exp) --> negative if exp is odd and x is negative. // pow(-0, exp) --> -inf if exp is negative odd. // pow(-0, exp) --> -0 if exp is positive odd. // pow(-inf, exp) --> -0 if exp is negative odd. // pow(-inf, exp) --> -inf if exp is positive odd. // // Therefore, if !SignBitOnly, we can return true if x >= +0 or x is NaN, // but we must return false if x == -0. Unfortunately we do not currently // have a way of expressing this constraint. See details in // https://llvm.org/bugs/show_bug.cgi?id=31702. return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly, 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) && (!SignBitOnly || cast(I)->hasNoNaNs()) && cannotBeOrderedLessThanZeroImpl(I->getOperand(2), TLI, SignBitOnly, Depth + 1); } break; } return false; } bool llvm::CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI) { return cannotBeOrderedLessThanZeroImpl(V, TLI, false, 0); } bool llvm::SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI) { return cannotBeOrderedLessThanZeroImpl(V, TLI, true, 0); } /// If the specified value can be set by repeating the same byte in memory, /// return the i8 value that it is represented with. This is /// true for all i8 values obviously, but is also true for i32 0, i32 -1, /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated /// byte store (e.g. i16 0x1234), return null. Value *llvm::isBytewiseValue(Value *V) { // All byte-wide stores are splatable, even of arbitrary variables. if (V->getType()->isIntegerTy(8)) return V; // Handle 'null' ConstantArrayZero etc. if (Constant *C = dyn_cast(V)) if (C->isNullValue()) return Constant::getNullValue(Type::getInt8Ty(V->getContext())); // Constant float and double values can be handled as integer values if the // corresponding integer value is "byteable". An important case is 0.0. if (ConstantFP *CFP = dyn_cast(V)) { if (CFP->getType()->isFloatTy()) V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext())); if (CFP->getType()->isDoubleTy()) V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext())); // Don't handle long double formats, which have strange constraints. } // We can handle constant integers that are multiple of 8 bits. if (ConstantInt *CI = dyn_cast(V)) { if (CI->getBitWidth() % 8 == 0) { assert(CI->getBitWidth() > 8 && "8 bits should be handled above!"); if (!CI->getValue().isSplat(8)) return nullptr; return ConstantInt::get(V->getContext(), CI->getValue().trunc(8)); } } // A ConstantDataArray/Vector is splatable if all its members are equal and // also splatable. if (ConstantDataSequential *CA = dyn_cast(V)) { Value *Elt = CA->getElementAsConstant(0); Value *Val = isBytewiseValue(Elt); if (!Val) return nullptr; for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I) if (CA->getElementAsConstant(I) != Elt) return nullptr; return Val; } // Conceptually, we could handle things like: // %a = zext i8 %X to i16 // %b = shl i16 %a, 8 // %c = or i16 %a, %b // but until there is an example that actually needs this, it doesn't seem // worth worrying about. return nullptr; } // This is the recursive version of BuildSubAggregate. It takes a few different // arguments. Idxs is the index within the nested struct From that we are // looking at now (which is of type IndexedType). IdxSkip is the number of // indices from Idxs that should be left out when inserting into the resulting // struct. To is the result struct built so far, new insertvalue instructions // build on that. static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType, SmallVectorImpl &Idxs, unsigned IdxSkip, Instruction *InsertBefore) { llvm::StructType *STy = dyn_cast(IndexedType); if (STy) { // Save the original To argument so we can modify it Value *OrigTo = To; // General case, the type indexed by Idxs is a struct for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { // Process each struct element recursively Idxs.push_back(i); Value *PrevTo = To; To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip, InsertBefore); Idxs.pop_back(); if (!To) { // Couldn't find any inserted value for this index? Cleanup while (PrevTo != OrigTo) { InsertValueInst* Del = cast(PrevTo); PrevTo = Del->getAggregateOperand(); Del->eraseFromParent(); } // Stop processing elements break; } } // If we successfully found a value for each of our subaggregates if (To) return To; } // Base case, the type indexed by SourceIdxs is not a struct, or not all of // the struct's elements had a value that was inserted directly. In the latter // case, perhaps we can't determine each of the subelements individually, but // we might be able to find the complete struct somewhere. // Find the value that is at that particular spot Value *V = FindInsertedValue(From, Idxs); if (!V) return nullptr; // Insert the value in the new (sub) aggregrate return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip), "tmp", InsertBefore); } // This helper takes a nested struct and extracts a part of it (which is again a // struct) into a new value. For example, given the struct: // { a, { b, { c, d }, e } } // and the indices "1, 1" this returns // { c, d }. // // It does this by inserting an insertvalue for each element in the resulting // struct, as opposed to just inserting a single struct. This will only work if // each of the elements of the substruct are known (ie, inserted into From by an // insertvalue instruction somewhere). // // All inserted insertvalue instructions are inserted before InsertBefore static Value *BuildSubAggregate(Value *From, ArrayRef idx_range, Instruction *InsertBefore) { assert(InsertBefore && "Must have someplace to insert!"); Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(), idx_range); Value *To = UndefValue::get(IndexedType); SmallVector Idxs(idx_range.begin(), idx_range.end()); unsigned IdxSkip = Idxs.size(); return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore); } /// Given an aggregrate and an sequence of indices, see if /// the scalar value indexed is already around as a register, for example if it /// were inserted directly into the aggregrate. /// /// If InsertBefore is not null, this function will duplicate (modified) /// insertvalues when a part of a nested struct is extracted. Value *llvm::FindInsertedValue(Value *V, ArrayRef idx_range, Instruction *InsertBefore) { // Nothing to index? Just return V then (this is useful at the end of our // recursion). if (idx_range.empty()) return V; // We have indices, so V should have an indexable type. assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) && "Not looking at a struct or array?"); assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) && "Invalid indices for type?"); if (Constant *C = dyn_cast(V)) { C = C->getAggregateElement(idx_range[0]); if (!C) return nullptr; return FindInsertedValue(C, idx_range.slice(1), InsertBefore); } if (InsertValueInst *I = dyn_cast(V)) { // Loop the indices for the insertvalue instruction in parallel with the // requested indices const unsigned *req_idx = idx_range.begin(); for (const unsigned *i = I->idx_begin(), *e = I->idx_end(); i != e; ++i, ++req_idx) { if (req_idx == idx_range.end()) { // We can't handle this without inserting insertvalues if (!InsertBefore) return nullptr; // The requested index identifies a part of a nested aggregate. Handle // this specially. For example, // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0 // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1 // %C = extractvalue {i32, { i32, i32 } } %B, 1 // This can be changed into // %A = insertvalue {i32, i32 } undef, i32 10, 0 // %C = insertvalue {i32, i32 } %A, i32 11, 1 // which allows the unused 0,0 element from the nested struct to be // removed. return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx), InsertBefore); } // This insert value inserts something else than what we are looking for. // See if the (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(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 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 Visited; while (Visited.insert(Ptr).second) { if (Ptr->getType()->isVectorTy()) break; if (GEPOperator *GEP = dyn_cast(Ptr)) { // If one of the values we have visited is an addrspacecast, then // the pointer type of this GEP may be different from the type // of the Ptr parameter which was passed to this function. This // means when we construct GEPOffset, we need to use the size // of GEP's pointer type rather than the size of the original // pointer type. APInt GEPOffset(DL.getPointerTypeSizeInBits(Ptr->getType()), 0); if (!GEP->accumulateConstantOffset(DL, GEPOffset)) break; ByteOffset += GEPOffset.getSExtValue(); Ptr = GEP->getPointerOperand(); } else if (Operator::getOpcode(Ptr) == Instruction::BitCast || Operator::getOpcode(Ptr) == Instruction::AddrSpaceCast) { Ptr = cast(Ptr)->getOperand(0); } else if (GlobalAlias *GA = dyn_cast(Ptr)) { if (GA->isInterposable()) break; Ptr = GA->getAliasee(); } else { break; } } Offset = ByteOffset.getSExtValue(); return Ptr; } bool llvm::isGEPBasedOnPointerToString(const GEPOperator *GEP) { // 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. ArrayType *AT = dyn_cast(GEP->getSourceElementType()); if (!AT || !AT->getElementType()->isIntegerTy(8)) return false; // Check to make sure that the first operand of the GEP is an integer and // has value 0 so that we are sure we're indexing into the initializer. const ConstantInt *FirstIdx = dyn_cast(GEP->getOperand(1)); if (!FirstIdx || !FirstIdx->isZero()) return false; return true; } /// This function computes the length of a null-terminated C string pointed to /// by V. If successful, it returns true and returns the string in Str. /// If unsuccessful, it returns false. bool llvm::getConstantStringInfo(const Value *V, StringRef &Str, uint64_t Offset, bool TrimAtNul) { assert(V); // Look through bitcast instructions and geps. V = V->stripPointerCasts(); // If the value is a GEP instruction or constant expression, treat it as an // offset. if (const GEPOperator *GEP = dyn_cast(V)) { // The GEP operator should be based on a pointer to string constant, and is // indexing into the string constant. if (!isGEPBasedOnPointerToString(GEP)) return false; // If the second index isn't a ConstantInt, then this is a variable index // into the array. If this occurs, we can't say anything meaningful about // the string. uint64_t StartIdx = 0; if (const ConstantInt *CI = dyn_cast(GEP->getOperand(2))) StartIdx = CI->getZExtValue(); else return false; return getConstantStringInfo(GEP->getOperand(0), Str, StartIdx + Offset, TrimAtNul); } // The GEP instruction, constant or instruction, must reference a global // variable that is a constant and is initialized. The referenced constant // initializer is the array that we'll use for optimization. const GlobalVariable *GV = dyn_cast(V); if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer()) return false; // Handle the all-zeros case. if (GV->getInitializer()->isNullValue()) { // This is a degenerate case. The initializer is constant zero so the // length of the string must be zero. Str = ""; return true; } // This must be a ConstantDataArray. const auto *Array = dyn_cast(GV->getInitializer()); if (!Array || !Array->isString()) return false; // Get the number of elements in the array. uint64_t NumElts = Array->getType()->getArrayNumElements(); // Start out with the entire array in the StringRef. Str = Array->getAsString(); if (Offset > NumElts) return false; // Skip over 'offset' bytes. Str = Str.substr(Offset); if (TrimAtNul) { // Trim off the \0 and anything after it. If the array is not nul // terminated, we just return the whole end of string. The client may know // some other way that the string is length-bound. Str = Str.substr(0, Str.find('\0')); } return true; } // These next two are very similar to the above, but also look through PHI // nodes. // TODO: See if we can integrate these two together. /// If we can compute the length of the string pointed to by /// the specified pointer, return 'len+1'. If we can't, return 0. static uint64_t GetStringLengthH(const Value *V, SmallPtrSetImpl &PHIs) { // Look through noop bitcast instructions. V = V->stripPointerCasts(); // If this is a PHI node, there are two cases: either we have already seen it // or we haven't. if (const PHINode *PN = dyn_cast(V)) { if (!PHIs.insert(PN).second) return ~0ULL; // already in the set. // If it was new, see if all the input strings are the same length. uint64_t LenSoFar = ~0ULL; for (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 (const SelectInst *SI = dyn_cast(V)) { uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs); if (Len1 == 0) return 0; uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs); if (Len2 == 0) return 0; if (Len1 == ~0ULL) return Len2; if (Len2 == ~0ULL) return Len1; if (Len1 != Len2) return 0; return Len1; } // Otherwise, see if we can read the string. StringRef StrData; if (!getConstantStringInfo(V, StrData)) return 0; return StrData.size()+1; } /// If we can compute the length of the string pointed to by /// the specified pointer, return 'len+1'. If we can't, return 0. uint64_t llvm::GetStringLength(const Value *V) { if (!V->getType()->isPointerTy()) return 0; SmallPtrSet PHIs; uint64_t Len = GetStringLengthH(V, PHIs); // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return // an empty string as a length. return Len == ~0ULL ? 1 : Len; } /// \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(const PHINode *PN, const 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(PN->getIncomingValue(0)); if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L) PrevValue = dyn_cast(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(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(V)) { V = GEP->getPointerOperand(); } else if (Operator::getOpcode(V) == Instruction::BitCast || Operator::getOpcode(V) == Instruction::AddrSpaceCast) { V = cast(V)->getOperand(0); } else if (GlobalAlias *GA = dyn_cast(V)) { if (GA->isInterposable()) return V; V = GA->getAliasee(); } else if (isa(V)) { // An alloca can't be further simplified. return V; } else { if (auto CS = CallSite(V)) if (Value *RV = CS.getReturnedArgOperand()) { V = RV; continue; } // See if InstructionSimplify knows any relevant tricks. if (Instruction *I = dyn_cast(V)) // TODO: Acquire a DominatorTree and AssumptionCache and use them. if (Value *Simplified = SimplifyInstruction(I, DL, nullptr)) { V = Simplified; continue; } return V; } assert(V->getType()->isPointerTy() && "Unexpected operand type!"); } return V; } void llvm::GetUnderlyingObjects(Value *V, SmallVectorImpl &Objects, const DataLayout &DL, LoopInfo *LI, unsigned MaxLookup) { SmallPtrSet Visited; SmallVector Worklist; Worklist.push_back(V); do { Value *P = Worklist.pop_back_val(); P = GetUnderlyingObject(P, DL, MaxLookup); if (!Visited.insert(P).second) continue; if (SelectInst *SI = dyn_cast(P)) { Worklist.push_back(SI->getTrueValue()); Worklist.push_back(SI->getFalseValue()); continue; } if (PHINode *PN = dyn_cast(P)) { // 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(U); if (!II) return false; if (II->getIntrinsicID() != Intrinsic::lifetime_start && II->getIntrinsicID() != Intrinsic::lifetime_end) return false; } return true; } bool llvm::isSafeToSpeculativelyExecute(const Value *V, const Instruction *CtxI, const DominatorTree *DT) { const Operator *Inst = dyn_cast(V); if (!Inst) return false; for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i) if (Constant *C = dyn_cast(Inst->getOperand(i))) if (C->canTrap()) return false; switch (Inst->getOpcode()) { default: return true; case Instruction::UDiv: case Instruction::URem: { // x / y is undefined if y == 0. const APInt *V; if (match(Inst->getOperand(1), m_APInt(V))) return *V != 0; return false; } case Instruction::SDiv: case Instruction::SRem: { // x / y is undefined if y == 0 or x == INT_MIN and y == -1 const APInt *Numerator, *Denominator; if (!match(Inst->getOperand(1), m_APInt(Denominator))) return false; // We cannot hoist this division if the denominator is 0. if (*Denominator == 0) return false; // It's safe to hoist if the denominator is not 0 or -1. if (*Denominator != -1) return true; // At this point we know that the denominator is -1. It is safe to hoist as // long we know that the numerator is not INT_MIN. if (match(Inst->getOperand(0), m_APInt(Numerator))) return !Numerator->isMinSignedValue(); // The numerator *might* be MinSignedValue. return false; } case Instruction::Load: { const LoadInst *LI = cast(Inst); if (!LI->isUnordered() || // Speculative load may create a race that did not exist in the source. LI->getFunction()->hasFnAttribute(Attribute::SanitizeThread) || // Speculative load may load data from dirty regions. LI->getFunction()->hasFnAttribute(Attribute::SanitizeAddress)) return false; const DataLayout &DL = LI->getModule()->getDataLayout(); return isDereferenceableAndAlignedPointer(LI->getPointerOperand(), LI->getAlignment(), DL, CtxI, DT); } case Instruction::Call: { if (const IntrinsicInst *II = dyn_cast(Inst)) { switch (II->getIntrinsicID()) { // These synthetic intrinsics have no side-effects and just mark // information about their operands. // FIXME: There are other no-op synthetic instructions that potentially // should be considered at least *safe* to speculate... case Intrinsic::dbg_declare: case Intrinsic::dbg_value: return true; case Intrinsic::bitreverse: 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; // These intrinsics are defined to have the same behavior as libm // functions except for setting errno. case Intrinsic::sqrt: case Intrinsic::fma: case Intrinsic::fmuladd: return true; // These intrinsics are defined to have the same behavior as libm // functions, and the corresponding libm functions never set errno. case Intrinsic::trunc: case Intrinsic::copysign: case Intrinsic::fabs: case Intrinsic::minnum: case Intrinsic::maxnum: return true; // These intrinsics are defined to have the same behavior as libm // functions, which never overflow when operating on the IEEE754 types // that we support, and never set errno otherwise. case Intrinsic::ceil: case Intrinsic::floor: case Intrinsic::nearbyint: case Intrinsic::rint: case Intrinsic::round: return true; // These intrinsics do not correspond to any libm function, and // do not set errno. case Intrinsic::powi: return true; // 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) { assert(V->getType()->isPointerTy() && "V must be pointer type"); // Alloca never returns null, malloc might. if (isa(V)) return true; // A byval, inalloca, or nonnull argument is never null. if (const Argument *A = dyn_cast(V)) return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr(); // A global variable in address space 0 is non null unless extern weak // or an absolute symbol reference. 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(V)) return !GV->isAbsoluteSymbolRef() && !GV->hasExternalWeakLinkage() && GV->getType()->getAddressSpace() == 0; // A Load tagged with nonnull metadata is never null. if (const LoadInst *LI = dyn_cast(V)) return LI->getMetadata(LLVMContext::MD_nonnull); if (auto CS = ImmutableCallSite(V)) if (CS.isReturnNonNull()) return true; return false; } static bool isKnownNonNullFromDominatingCondition(const Value *V, const Instruction *CtxI, const DominatorTree *DT) { assert(V->getType()->isPointerTy() && "V must be pointer type"); assert(!isa(V) && "Did not expect ConstantPointerNull"); assert(CtxI && "Context instruction required for analysis"); assert(DT && "Dominator tree required for analysis"); unsigned NumUsesExplored = 0; for (auto *U : V->users()) { // Avoid massive lists if (NumUsesExplored >= DomConditionsMaxUses) break; NumUsesExplored++; // If the value is used as an argument to a call or invoke, then argument // attributes may provide an answer about null-ness. if (auto CS = ImmutableCallSite(U)) if (auto *CalledFunc = CS.getCalledFunction()) for (const Argument &Arg : CalledFunc->args()) if (CS.getArgOperand(Arg.getArgNo()) == V && Arg.hasNonNullAttr() && DT->dominates(CS.getInstruction(), CtxI)) return true; // Consider only compare instructions uniquely controlling a branch CmpInst::Predicate Pred; if (!match(const_cast(U), m_c_ICmp(Pred, m_Specific(V), m_Zero())) || (Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE)) continue; for (auto *CmpU : U->users()) { if (const BranchInst *BI = dyn_cast(CmpU)) { assert(BI->isConditional() && "uses a comparison!"); BasicBlock *NonNullSuccessor = BI->getSuccessor(Pred == ICmpInst::ICMP_EQ ? 1 : 0); BasicBlockEdge Edge(BI->getParent(), NonNullSuccessor); if (Edge.isSingleEdge() && DT->dominates(Edge, CtxI->getParent())) return true; } else if (Pred == ICmpInst::ICMP_NE && match(CmpU, m_Intrinsic()) && DT->dominates(cast(CmpU), CtxI)) { return true; } } } return false; } bool llvm::isKnownNonNullAt(const Value *V, const Instruction *CtxI, const DominatorTree *DT) { if (isa(V) || isa(V)) return false; if (isKnownNonNull(V)) return true; if (!CtxI || !DT) return false; return ::isKnownNonNullFromDominatingCondition(V, CtxI, DT); } OverflowResult llvm::computeOverflowForUnsignedMul(const Value *LHS, const 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(const Value *LHS, const 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(const Value *LHS, const Value *RHS, const 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; } bool llvm::isOverflowIntrinsicNoWrap(const IntrinsicInst *II, const DominatorTree &DT) { #ifndef NDEBUG auto IID = II->getIntrinsicID(); assert((IID == Intrinsic::sadd_with_overflow || IID == Intrinsic::uadd_with_overflow || IID == Intrinsic::ssub_with_overflow || IID == Intrinsic::usub_with_overflow || IID == Intrinsic::smul_with_overflow || IID == Intrinsic::umul_with_overflow) && "Not an overflow intrinsic!"); #endif SmallVector GuardingBranches; SmallVector Results; for (const User *U : II->users()) { if (const auto *EVI = dyn_cast(U)) { assert(EVI->getNumIndices() == 1 && "Obvious from CI's type"); if (EVI->getIndices()[0] == 0) Results.push_back(EVI); else { assert(EVI->getIndices()[0] == 1 && "Obvious from CI's type"); for (const auto *U : EVI->users()) if (const auto *B = dyn_cast(U)) { assert(B->isConditional() && "How else is it using an i1?"); GuardingBranches.push_back(B); } } } else { // We are using the aggregate directly in a way we don't want to analyze // here (storing it to a global, say). return false; } } auto AllUsesGuardedByBranch = [&](const BranchInst *BI) { BasicBlockEdge NoWrapEdge(BI->getParent(), BI->getSuccessor(1)); if (!NoWrapEdge.isSingleEdge()) return false; // Check if all users of the add are provably no-wrap. for (const auto *Result : Results) { // If the extractvalue itself is not executed on overflow, the we don't // need to check each use separately, since domination is transitive. if (DT.dominates(NoWrapEdge, Result->getParent())) continue; for (auto &RU : Result->uses()) if (!DT.dominates(NoWrapEdge, RU)) return false; } return true; }; return any_of(GuardingBranches, AllUsesGuardedByBranch); } OverflowResult llvm::computeOverflowForSignedAdd(const 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(const Value *LHS, const 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) { // A memory operation returns normally if it isn't volatile. A volatile // operation is allowed to trap. // // An atomic operation isn't guaranteed to return in a reasonable amount of // time because it's possible for another thread to interfere with it for an // arbitrary length of time, but programs aren't allowed to rely on that. if (const LoadInst *LI = dyn_cast(I)) return !LI->isVolatile(); if (const StoreInst *SI = dyn_cast(I)) return !SI->isVolatile(); if (const AtomicCmpXchgInst *CXI = dyn_cast(I)) return !CXI->isVolatile(); if (const AtomicRMWInst *RMWI = dyn_cast(I)) return !RMWI->isVolatile(); if (const MemIntrinsic *MII = dyn_cast(I)) return !MII->isVolatile(); // If there is no successor, then execution can't transfer to it. if (const auto *CRI = dyn_cast(I)) return !CRI->unwindsToCaller(); if (const auto *CatchSwitch = dyn_cast(I)) return !CatchSwitch->unwindsToCaller(); if (isa(I)) return false; if (isa(I)) return false; if (isa(I)) return false; // Calls can throw, or contain an infinite loop, or kill the process. if (auto CS = ImmutableCallSite(I)) { // Call sites that throw have implicit non-local control flow. if (!CS.doesNotThrow()) return false; // Non-throwing call sites can loop infinitely, call exit/pthread_exit // etc. and thus not return. However, LLVM already assumes that // // - Thread exiting actions are modeled as writes to memory invisible to // the program. // // - Loops that don't have side effects (side effects are volatile/atomic // stores and IO) always terminate (see http://llvm.org/PR965). // Furthermore IO itself is also modeled as writes to memory invisible to // the program. // // We rely on those assumptions here, and use the memory effects of the call // target as a proxy for checking that it always returns. // FIXME: This isn't aggressive enough; a call which only writes to a global // is guaranteed to return. return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory() || match(I, m_Intrinsic()); } // Other instructions return normally. return true; } 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: case Instruction::Mul: case Instruction::Shl: case Instruction::GetElementPtr: // 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::ICmp: // Comparing poison with any value yields poison. This is why, for // instance, x s< (x +nsw 1) can be folded to true. return true; default: return false; } } const Value *llvm::getGuaranteedNonFullPoisonOp(const Instruction *I) { switch (I->getOpcode()) { case Instruction::Store: return cast(I)->getPointerOperand(); case Instruction::Load: return cast(I)->getPointerOperand(); case Instruction::AtomicCmpXchg: return cast(I)->getPointerOperand(); case Instruction::AtomicRMW: return cast(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 YieldsPoison; SmallSet Visited; YieldsPoison.insert(PoisonI); Visited.insert(PoisonI->getParent()); BasicBlock::const_iterator Begin = PoisonI->getIterator(), End = BB->end(); unsigned Iter = 0; while (Iter++ < MaxDepth) { for (auto &I : make_range(Begin, End)) { 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(User); if (propagatesFullPoison(UserI)) YieldsPoison.insert(User); } } } if (auto *NextBB = BB->getSingleSuccessor()) { if (Visited.insert(NextBB).second) { BB = NextBB; Begin = BB->getFirstNonPHI()->getIterator(); End = BB->end(); continue; } } break; }; return false; } static bool isKnownNonNaN(const Value *V, FastMathFlags FMF) { if (FMF.noNaNs()) return true; if (auto *C = dyn_cast(V)) return !C->isNaN(); return false; } static bool isKnownNonZero(const Value *V) { if (auto *C = dyn_cast(V)) return !C->isZero(); return false; } /// Match non-obvious integer minimum and maximum sequences. static SelectPatternResult matchMinMax(CmpInst::Predicate Pred, Value *CmpLHS, Value *CmpRHS, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS) { // Assume success. If there's no match, callers should not use these anyway. LHS = TrueVal; RHS = FalseVal; // Recognize variations of: // CLAMP(v,l,h) ==> ((v) < (l) ? (l) : ((v) > (h) ? (h) : (v))) const APInt *C1; if (CmpRHS == TrueVal && match(CmpRHS, m_APInt(C1))) { const APInt *C2; // (X SMAX(SMIN(X, C2), C1) if (match(FalseVal, m_SMin(m_Specific(CmpLHS), m_APInt(C2))) && C1->slt(*C2) && Pred == CmpInst::ICMP_SLT) return {SPF_SMAX, SPNB_NA, false}; // (X >s C1) ? C1 : SMAX(X, C2) ==> SMIN(SMAX(X, C2), C1) if (match(FalseVal, m_SMax(m_Specific(CmpLHS), m_APInt(C2))) && C1->sgt(*C2) && Pred == CmpInst::ICMP_SGT) return {SPF_SMIN, SPNB_NA, false}; // (X UMAX(UMIN(X, C2), C1) if (match(FalseVal, m_UMin(m_Specific(CmpLHS), m_APInt(C2))) && C1->ult(*C2) && Pred == CmpInst::ICMP_ULT) return {SPF_UMAX, SPNB_NA, false}; // (X >u C1) ? C1 : UMAX(X, C2) ==> UMIN(UMAX(X, C2), C1) if (match(FalseVal, m_UMax(m_Specific(CmpLHS), m_APInt(C2))) && C1->ugt(*C2) && Pred == CmpInst::ICMP_UGT) return {SPF_UMIN, SPNB_NA, false}; } if (Pred != CmpInst::ICMP_SGT && Pred != CmpInst::ICMP_SLT) return {SPF_UNKNOWN, SPNB_NA, false}; // Z = X -nsw Y // (X >s Y) ? 0 : Z ==> (Z >s 0) ? 0 : Z ==> SMIN(Z, 0) // (X (Z SMAX(Z, 0) if (match(TrueVal, m_Zero()) && match(FalseVal, m_NSWSub(m_Specific(CmpLHS), m_Specific(CmpRHS)))) return {Pred == CmpInst::ICMP_SGT ? SPF_SMIN : SPF_SMAX, SPNB_NA, false}; // Z = X -nsw Y // (X >s Y) ? Z : 0 ==> (Z >s 0) ? Z : 0 ==> SMAX(Z, 0) // (X (Z SMIN(Z, 0) if (match(FalseVal, m_Zero()) && match(TrueVal, m_NSWSub(m_Specific(CmpLHS), m_Specific(CmpRHS)))) return {Pred == CmpInst::ICMP_SGT ? SPF_SMAX : SPF_SMIN, SPNB_NA, false}; if (!match(CmpRHS, m_APInt(C1))) return {SPF_UNKNOWN, SPNB_NA, false}; // An unsigned min/max can be written with a signed compare. const APInt *C2; if ((CmpLHS == TrueVal && match(FalseVal, m_APInt(C2))) || (CmpLHS == FalseVal && match(TrueVal, m_APInt(C2)))) { // Is the sign bit set? // (X (X >u MAXVAL) ? X : MAXVAL ==> UMAX // (X (X >u MAXVAL) ? MAXVAL : X ==> UMIN if (Pred == CmpInst::ICMP_SLT && *C1 == 0 && C2->isMaxSignedValue()) return {CmpLHS == TrueVal ? SPF_UMAX : SPF_UMIN, SPNB_NA, false}; // Is the sign bit clear? // (X >s -1) ? MINVAL : X ==> (X UMAX // (X >s -1) ? X : MINVAL ==> (X UMIN if (Pred == CmpInst::ICMP_SGT && C1->isAllOnesValue() && C2->isMinSignedValue()) return {CmpLHS == FalseVal ? SPF_UMAX : SPF_UMIN, SPNB_NA, false}; } // Look through 'not' ops to find disguised signed min/max. // (X >s C) ? ~X : ~C ==> (~X SMIN(~X, ~C) // (X (~X >s ~C) ? ~X : ~C ==> SMAX(~X, ~C) if (match(TrueVal, m_Not(m_Specific(CmpLHS))) && match(FalseVal, m_APInt(C2)) && ~(*C1) == *C2) return {Pred == CmpInst::ICMP_SGT ? SPF_SMIN : SPF_SMAX, SPNB_NA, false}; // (X >s C) ? ~C : ~X ==> (~X SMAX(~C, ~X) // (X (~X >s ~C) ? ~C : ~X ==> SMIN(~C, ~X) if (match(FalseVal, m_Not(m_Specific(CmpLHS))) && match(TrueVal, m_APInt(C2)) && ~(*C1) == *C2) return {Pred == CmpInst::ICMP_SGT ? SPF_SMAX : SPF_SMIN, SPNB_NA, false}; return {SPF_UNKNOWN, SPNB_NA, 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}; } } const APInt *C1; if (match(CmpRHS, m_APInt(C1))) { 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 == 0 || C1->isAllOnesValue())) { return {(CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false}; } // ABS(X) ==> (X (X (V1); if (!Cast1) return nullptr; *CastOp = Cast1->getOpcode(); Type *SrcTy = Cast1->getSrcTy(); if (auto *Cast2 = dyn_cast(V2)) { // If V1 and V2 are both the same cast from the same type, look through V1. if (*CastOp == Cast2->getOpcode() && SrcTy == Cast2->getSrcTy()) return Cast2->getOperand(0); return nullptr; } auto *C = dyn_cast(V2); if (!C) return nullptr; Constant *CastedTo = nullptr; switch (*CastOp) { case Instruction::ZExt: if (CmpI->isUnsigned()) CastedTo = ConstantExpr::getTrunc(C, SrcTy); break; case Instruction::SExt: if (CmpI->isSigned()) CastedTo = ConstantExpr::getTrunc(C, SrcTy, true); break; case Instruction::Trunc: CastedTo = ConstantExpr::getIntegerCast(C, SrcTy, CmpI->isSigned()); break; case Instruction::FPTrunc: CastedTo = ConstantExpr::getFPExtend(C, SrcTy, true); break; case Instruction::FPExt: CastedTo = ConstantExpr::getFPTrunc(C, SrcTy, true); break; case Instruction::FPToUI: CastedTo = ConstantExpr::getUIToFP(C, SrcTy, true); break; case Instruction::FPToSI: CastedTo = ConstantExpr::getSIToFP(C, SrcTy, true); break; case Instruction::UIToFP: CastedTo = ConstantExpr::getFPToUI(C, SrcTy, true); break; case Instruction::SIToFP: CastedTo = ConstantExpr::getFPToSI(C, SrcTy, true); break; default: break; } if (!CastedTo) return nullptr; // Make sure the cast doesn't lose any information. Constant *CastedBack = ConstantExpr::getCast(*CastOp, CastedTo, C->getType(), true); if (CastedBack != C) return nullptr; return CastedTo; } SelectPatternResult llvm::matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, Instruction::CastOps *CastOp) { SelectInst *SI = dyn_cast(V); if (!SI) return {SPF_UNKNOWN, SPNB_NA, false}; CmpInst *CmpI = dyn_cast(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(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(TrueVal)->getOperand(0), C, LHS, RHS); if (Value *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp)) return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, C, cast(FalseVal)->getOperand(0), LHS, RHS); } return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, TrueVal, FalseVal, LHS, RHS); } /// Return true if "icmp Pred LHS RHS" is always true. static bool isTruePredicate(CmpInst::Predicate Pred, const Value *LHS, const 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 = [&](const Value *A, const Value *B, const 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; }; const 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. Otherwise, return None. static Optional isImpliedCondOperands(CmpInst::Predicate Pred, const Value *ALHS, const Value *ARHS, const Value *BLHS, const Value *BRHS, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { switch (Pred) { default: return None; case CmpInst::ICMP_SLT: case CmpInst::ICMP_SLE: if (isTruePredicate(CmpInst::ICMP_SLE, BLHS, ALHS, DL, Depth, AC, CxtI, DT) && isTruePredicate(CmpInst::ICMP_SLE, ARHS, BRHS, DL, Depth, AC, CxtI, DT)) return true; return None; case CmpInst::ICMP_ULT: case CmpInst::ICMP_ULE: if (isTruePredicate(CmpInst::ICMP_ULE, BLHS, ALHS, DL, Depth, AC, CxtI, DT) && isTruePredicate(CmpInst::ICMP_ULE, ARHS, BRHS, DL, Depth, AC, CxtI, DT)) return true; return None; } } /// Return true if the operands of the two compares match. IsSwappedOps is true /// when the operands match, but are swapped. static bool isMatchingOps(const Value *ALHS, const Value *ARHS, const Value *BLHS, const Value *BRHS, bool &IsSwappedOps) { bool IsMatchingOps = (ALHS == BLHS && ARHS == BRHS); IsSwappedOps = (ALHS == BRHS && ARHS == BLHS); return IsMatchingOps || IsSwappedOps; } /// Return true if "icmp1 APred ALHS ARHS" implies "icmp2 BPred BLHS BRHS" is /// true. Return false if "icmp1 APred ALHS ARHS" implies "icmp2 BPred BLHS /// BRHS" is false. Otherwise, return None if we can't infer anything. static Optional isImpliedCondMatchingOperands(CmpInst::Predicate APred, const Value *ALHS, const Value *ARHS, CmpInst::Predicate BPred, const Value *BLHS, const Value *BRHS, bool IsSwappedOps) { // Canonicalize the operands so they're matching. if (IsSwappedOps) { std::swap(BLHS, BRHS); BPred = ICmpInst::getSwappedPredicate(BPred); } if (CmpInst::isImpliedTrueByMatchingCmp(APred, BPred)) return true; if (CmpInst::isImpliedFalseByMatchingCmp(APred, BPred)) return false; return None; } /// Return true if "icmp1 APred ALHS C1" implies "icmp2 BPred BLHS C2" is /// true. Return false if "icmp1 APred ALHS C1" implies "icmp2 BPred BLHS /// C2" is false. Otherwise, return None if we can't infer anything. static Optional isImpliedCondMatchingImmOperands(CmpInst::Predicate APred, const Value *ALHS, const ConstantInt *C1, CmpInst::Predicate BPred, const Value *BLHS, const ConstantInt *C2) { assert(ALHS == BLHS && "LHS operands must match."); ConstantRange DomCR = ConstantRange::makeExactICmpRegion(APred, C1->getValue()); ConstantRange CR = ConstantRange::makeAllowedICmpRegion(BPred, C2->getValue()); ConstantRange Intersection = DomCR.intersectWith(CR); ConstantRange Difference = DomCR.difference(CR); if (Intersection.isEmptySet()) return false; if (Difference.isEmptySet()) return true; return None; } Optional llvm::isImpliedCondition(const Value *LHS, const Value *RHS, const DataLayout &DL, bool InvertAPred, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { // A mismatch occurs when we compare a scalar cmp to a vector cmp, for example. if (LHS->getType() != RHS->getType()) return None; Type *OpTy = LHS->getType(); assert(OpTy->getScalarType()->isIntegerTy(1)); // LHS ==> RHS by definition if (!InvertAPred && LHS == RHS) return true; if (OpTy->isVectorTy()) // TODO: extending the code below to handle vectors return None; 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 None; if (InvertAPred) APred = CmpInst::getInversePredicate(APred); // Can we infer anything when the two compares have matching operands? bool IsSwappedOps; if (isMatchingOps(ALHS, ARHS, BLHS, BRHS, IsSwappedOps)) { if (Optional Implication = isImpliedCondMatchingOperands( APred, ALHS, ARHS, BPred, BLHS, BRHS, IsSwappedOps)) return Implication; // No amount of additional analysis will infer the second condition, so // early exit. return None; } // Can we infer anything when the LHS operands match and the RHS operands are // constants (not necessarily matching)? if (ALHS == BLHS && isa(ARHS) && isa(BRHS)) { if (Optional Implication = isImpliedCondMatchingImmOperands( APred, ALHS, cast(ARHS), BPred, BLHS, cast(BRHS))) return Implication; // No amount of additional analysis will infer the second condition, so // early exit. return None; } if (APred == BPred) return isImpliedCondOperands(APred, ALHS, ARHS, BLHS, BRHS, DL, Depth, AC, CxtI, DT); return None; }