//===- ValueTracking.cpp - Walk computations to compute properties --------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file contains routines that help analyze properties that chains of // computations have. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/ValueTracking.h" #include "llvm/ADT/APFloat.h" #include "llvm/ADT/APInt.h" #include "llvm/ADT/ArrayRef.h" #include "llvm/ADT/None.h" #include "llvm/ADT/Optional.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallSet.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/StringRef.h" #include "llvm/ADT/iterator_range.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/GuardUtils.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/Loads.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/OptimizationRemarkEmitter.h" #include "llvm/Analysis/TargetLibraryInfo.h" #include "llvm/IR/Argument.h" #include "llvm/IR/Attributes.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/CallSite.h" #include "llvm/IR/Constant.h" #include "llvm/IR/ConstantRange.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/DiagnosticInfo.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/GetElementPtrTypeIterator.h" #include "llvm/IR/GlobalAlias.h" #include "llvm/IR/GlobalValue.h" #include "llvm/IR/GlobalVariable.h" #include "llvm/IR/InstrTypes.h" #include "llvm/IR/Instruction.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Intrinsics.h" #include "llvm/IR/IntrinsicsAArch64.h" #include "llvm/IR/IntrinsicsX86.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Metadata.h" #include "llvm/IR/Module.h" #include "llvm/IR/Operator.h" #include "llvm/IR/PatternMatch.h" #include "llvm/IR/Type.h" #include "llvm/IR/User.h" #include "llvm/IR/Value.h" #include "llvm/Support/Casting.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Compiler.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/KnownBits.h" #include "llvm/Support/MathExtras.h" #include #include #include #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)); /// Returns the bitwidth of the given scalar or pointer type. 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 isKnownToBeAPowerOfTwo /// (all of which can call computeKnownBits), and so on. std::array Excluded; /// If true, it is safe to use metadata during simplification. InstrInfoQuery IIQ; unsigned NumExcluded = 0; Query(const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo, OptimizationRemarkEmitter *ORE = nullptr) : DL(DL), AC(AC), CxtI(CxtI), DT(DT), ORE(ORE), IIQ(UseInstrInfo) {} Query(const Query &Q, const Value *NewExcl) : DL(Q.DL), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT), ORE(Q.ORE), IIQ(Q.IIQ), 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, KnownBits &Known, unsigned Depth, const Query &Q); void llvm::computeKnownBits(const Value *V, KnownBits &Known, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, OptimizationRemarkEmitter *ORE, bool UseInstrInfo) { ::computeKnownBits(V, Known, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo, ORE)); } static KnownBits computeKnownBits(const Value *V, unsigned Depth, const Query &Q); KnownBits llvm::computeKnownBits(const Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, OptimizationRemarkEmitter *ORE, bool UseInstrInfo) { return ::computeKnownBits( V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo, ORE)); } bool llvm::haveNoCommonBitsSet(const Value *LHS, const Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo) { assert(LHS->getType() == RHS->getType() && "LHS and RHS should have the same type"); assert(LHS->getType()->isIntOrIntVectorTy() && "LHS and RHS should be integers"); // Look for an inverted mask: (X & ~M) op (Y & M). Value *M; if (match(LHS, m_c_And(m_Not(m_Value(M)), m_Value())) && match(RHS, m_c_And(m_Specific(M), m_Value()))) return true; if (match(RHS, m_c_And(m_Not(m_Value(M)), m_Value())) && match(LHS, m_c_And(m_Specific(M), m_Value()))) return true; IntegerType *IT = cast(LHS->getType()->getScalarType()); KnownBits LHSKnown(IT->getBitWidth()); KnownBits RHSKnown(IT->getBitWidth()); computeKnownBits(LHS, LHSKnown, DL, 0, AC, CxtI, DT, nullptr, UseInstrInfo); computeKnownBits(RHS, RHSKnown, DL, 0, AC, CxtI, DT, nullptr, UseInstrInfo); return (LHSKnown.Zero | RHSKnown.Zero).isAllOnesValue(); } bool llvm::isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI) { for (const User *U : CxtI->users()) { if (const ICmpInst *IC = dyn_cast(U)) if (IC->isEquality()) if (Constant *C = dyn_cast(IC->getOperand(1))) if (C->isNullValue()) continue; return false; } return true; } 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, bool UseInstrInfo) { return ::isKnownToBeAPowerOfTwo( V, OrZero, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo)); } 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, bool UseInstrInfo) { return ::isKnownNonZero(V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo)); } bool llvm::isKnownNonNegative(const Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo) { KnownBits Known = computeKnownBits(V, DL, Depth, AC, CxtI, DT, nullptr, UseInstrInfo); return Known.isNonNegative(); } bool llvm::isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo) { 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, UseInstrInfo) && isKnownNonZero(V, DL, Depth, AC, CxtI, DT, UseInstrInfo); } bool llvm::isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo) { KnownBits Known = computeKnownBits(V, DL, Depth, AC, CxtI, DT, nullptr, UseInstrInfo); return Known.isNegative(); } 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, bool UseInstrInfo) { return ::isKnownNonEqual(V1, V2, Query(DL, AC, safeCxtI(V1, safeCxtI(V2, CxtI)), DT, UseInstrInfo, /*ORE=*/nullptr)); } 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, bool UseInstrInfo) { return ::MaskedValueIsZero( V, Mask, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo)); } 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, bool UseInstrInfo) { return ::ComputeNumSignBits( V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo)); } static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1, bool NSW, KnownBits &KnownOut, KnownBits &Known2, unsigned Depth, const Query &Q) { unsigned BitWidth = KnownOut.getBitWidth(); // If an initial sequence of bits in the result is not needed, the // corresponding bits in the operands are not needed. KnownBits LHSKnown(BitWidth); computeKnownBits(Op0, LHSKnown, Depth + 1, Q); computeKnownBits(Op1, Known2, Depth + 1, Q); KnownOut = KnownBits::computeForAddSub(Add, NSW, LHSKnown, Known2); } static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW, KnownBits &Known, KnownBits &Known2, unsigned Depth, const Query &Q) { unsigned BitWidth = Known.getBitWidth(); computeKnownBits(Op1, Known, Depth + 1, Q); computeKnownBits(Op0, Known2, 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 = Known.isNonNegative(); bool isKnownNonNegativeOp0 = Known2.isNonNegative(); bool isKnownNegativeOp1 = Known.isNegative(); bool isKnownNegativeOp0 = Known2.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)); } } assert(!Known.hasConflict() && !Known2.hasConflict()); // Compute a conservative estimate for high known-0 bits. unsigned LeadZ = std::max(Known.countMinLeadingZeros() + Known2.countMinLeadingZeros(), BitWidth) - BitWidth; LeadZ = std::min(LeadZ, BitWidth); // The result of the bottom bits of an integer multiply can be // inferred by looking at the bottom bits of both operands and // multiplying them together. // We can infer at least the minimum number of known trailing bits // of both operands. Depending on number of trailing zeros, we can // infer more bits, because (a*b) <=> ((a/m) * (b/n)) * (m*n) assuming // a and b are divisible by m and n respectively. // We then calculate how many of those bits are inferrable and set // the output. For example, the i8 mul: // a = XXXX1100 (12) // b = XXXX1110 (14) // We know the bottom 3 bits are zero since the first can be divided by // 4 and the second by 2, thus having ((12/4) * (14/2)) * (2*4). // Applying the multiplication to the trimmed arguments gets: // XX11 (3) // X111 (7) // ------- // XX11 // XX11 // XX11 // XX11 // ------- // XXXXX01 // Which allows us to infer the 2 LSBs. Since we're multiplying the result // by 8, the bottom 3 bits will be 0, so we can infer a total of 5 bits. // The proof for this can be described as: // Pre: (C1 >= 0) && (C1 < (1 << C5)) && (C2 >= 0) && (C2 < (1 << C6)) && // (C7 == (1 << (umin(countTrailingZeros(C1), C5) + // umin(countTrailingZeros(C2), C6) + // umin(C5 - umin(countTrailingZeros(C1), C5), // C6 - umin(countTrailingZeros(C2), C6)))) - 1) // %aa = shl i8 %a, C5 // %bb = shl i8 %b, C6 // %aaa = or i8 %aa, C1 // %bbb = or i8 %bb, C2 // %mul = mul i8 %aaa, %bbb // %mask = and i8 %mul, C7 // => // %mask = i8 ((C1*C2)&C7) // Where C5, C6 describe the known bits of %a, %b // C1, C2 describe the known bottom bits of %a, %b. // C7 describes the mask of the known bits of the result. APInt Bottom0 = Known.One; APInt Bottom1 = Known2.One; // How many times we'd be able to divide each argument by 2 (shr by 1). // This gives us the number of trailing zeros on the multiplication result. unsigned TrailBitsKnown0 = (Known.Zero | Known.One).countTrailingOnes(); unsigned TrailBitsKnown1 = (Known2.Zero | Known2.One).countTrailingOnes(); unsigned TrailZero0 = Known.countMinTrailingZeros(); unsigned TrailZero1 = Known2.countMinTrailingZeros(); unsigned TrailZ = TrailZero0 + TrailZero1; // Figure out the fewest known-bits operand. unsigned SmallestOperand = std::min(TrailBitsKnown0 - TrailZero0, TrailBitsKnown1 - TrailZero1); unsigned ResultBitsKnown = std::min(SmallestOperand + TrailZ, BitWidth); APInt BottomKnown = Bottom0.getLoBits(TrailBitsKnown0) * Bottom1.getLoBits(TrailBitsKnown1); Known.resetAll(); Known.Zero.setHighBits(LeadZ); Known.Zero |= (~BottomKnown).getLoBits(ResultBitsKnown); Known.One |= BottomKnown.getLoBits(ResultBitsKnown); // 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 && !Known.isNegative()) Known.makeNonNegative(); else if (isKnownNegative && !Known.isNonNegative()) Known.makeNegative(); } void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges, KnownBits &Known) { unsigned BitWidth = Known.getBitWidth(); unsigned NumRanges = Ranges.getNumOperands() / 2; assert(NumRanges >= 1); Known.Zero.setAllBits(); Known.One.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); Known.One &= Range.getUnsignedMax() & Mask; Known.Zero &= ~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 (llvm::all_of(V->users(), [&](const User *U) { return EphValues.count(U); })) { if (V == E) return true; if (V == I || isSafeToSpeculativelyExecute(V)) { 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) WorkSet.push_back(*J); } } } return false; } // Is this an intrinsic that cannot be speculated but also cannot trap? bool llvm::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::sideeffect: case Intrinsic::dbg_declare: case Intrinsic::dbg_value: case Intrinsic::dbg_label: 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 doesn'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; } // Don't let an assume affect itself - this would cause the problems // `isEphemeralValueOf` is trying to prevent, and it would also make // the loop below go out of bounds. if (Inv == CxtI) return false; // 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, not even CxtI itself. for (BasicBlock::const_iterator I(CxtI), IE(Inv); I != IE; ++I) if (!isGuaranteedToTransferExecutionToSuccessor(&*I)) return false; return !isEphemeralValueOf(Inv, CxtI); } static bool isKnownNonZeroFromAssume(const Value *V, 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 false; // Note that the patterns below need to be kept in sync with the code // in AssumptionCache::updateAffectedValues. auto CmpExcludesZero = [V](ICmpInst *Cmp) { auto m_V = m_CombineOr(m_Specific(V), m_PtrToInt(m_Specific(V))); Value *RHS; CmpInst::Predicate Pred; if (!match(Cmp, m_c_ICmp(Pred, m_V, m_Value(RHS)))) return false; // Canonicalize 'v' to be on the LHS of the comparison. if (Cmp->getOperand(1) != RHS) Pred = CmpInst::getSwappedPredicate(Pred); // assume(v u> y) -> assume(v != 0) if (Pred == ICmpInst::ICMP_UGT) return true; // assume(v != 0) // We special-case this one to ensure that we handle `assume(v != null)`. if (Pred == ICmpInst::ICMP_NE) return match(RHS, m_Zero()); // All other predicates - rely on generic ConstantRange handling. ConstantInt *CI; if (!match(RHS, m_ConstantInt(CI))) return false; ConstantRange RHSRange(CI->getValue()); ConstantRange TrueValues = ConstantRange::makeAllowedICmpRegion(Pred, RHSRange); return !TrueValues.contains(APInt::getNullValue(CI->getBitWidth())); }; for (auto &AssumeVH : Q.AC->assumptionsFor(V)) { if (!AssumeVH) continue; CallInst *I = cast(AssumeVH); assert(I->getFunction() == Q.CxtI->getFunction() && "Got assumption for the wrong function!"); if (Q.isExcluded(I)) continue; // Warning: This loop can end up being somewhat performance sensitive. // 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); ICmpInst *Cmp = dyn_cast(Arg); if (!Cmp) continue; if (CmpExcludesZero(Cmp) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) return true; } return false; } static void computeKnownBitsFromAssume(const Value *V, KnownBits &Known, 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 = Known.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 sensitive. // 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?"); Known.setAllOnes(); return; } if (match(Arg, m_Not(m_Specific(V))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { assert(BitWidth == 1 && "assume operand is not i1?"); Known.setAllZero(); return; } // The remaining tests are all recursive, so bail out if we hit the limit. if (Depth == MaxDepth) continue; ICmpInst *Cmp = dyn_cast(Arg); if (!Cmp) continue; Value *A, *B; auto m_V = m_CombineOr(m_Specific(V), m_PtrToInt(m_Specific(V))); CmpInst::Predicate Pred; uint64_t C; switch (Cmp->getPredicate()) { default: break; case ICmpInst::ICMP_EQ: // assume(v = a) if (match(Cmp, m_c_ICmp(Pred, m_V, m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); Known.Zero |= RHSKnown.Zero; Known.One |= RHSKnown.One; // assume(v & b = a) } else if (match(Cmp, m_c_ICmp(Pred, m_c_And(m_V, m_Value(B)), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); KnownBits MaskKnown(BitWidth); computeKnownBits(B, MaskKnown, 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. Known.Zero |= RHSKnown.Zero & MaskKnown.One; Known.One |= RHSKnown.One & MaskKnown.One; // assume(~(v & b) = a) } else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_c_And(m_V, m_Value(B))), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); KnownBits MaskKnown(BitWidth); computeKnownBits(B, MaskKnown, 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. Known.Zero |= RHSKnown.One & MaskKnown.One; Known.One |= RHSKnown.Zero & MaskKnown.One; // assume(v | b = a) } else if (match(Cmp, m_c_ICmp(Pred, m_c_Or(m_V, m_Value(B)), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); KnownBits BKnown(BitWidth); computeKnownBits(B, BKnown, 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. Known.Zero |= RHSKnown.Zero & BKnown.Zero; Known.One |= RHSKnown.One & BKnown.Zero; // assume(~(v | b) = a) } else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_c_Or(m_V, m_Value(B))), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); KnownBits BKnown(BitWidth); computeKnownBits(B, BKnown, 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. Known.Zero |= RHSKnown.One & BKnown.Zero; Known.One |= RHSKnown.Zero & BKnown.Zero; // assume(v ^ b = a) } else if (match(Cmp, m_c_ICmp(Pred, m_c_Xor(m_V, m_Value(B)), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); KnownBits BKnown(BitWidth); computeKnownBits(B, BKnown, 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. Known.Zero |= RHSKnown.Zero & BKnown.Zero; Known.One |= RHSKnown.One & BKnown.Zero; Known.Zero |= RHSKnown.One & BKnown.One; Known.One |= RHSKnown.Zero & BKnown.One; // assume(~(v ^ b) = a) } else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_c_Xor(m_V, m_Value(B))), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); KnownBits BKnown(BitWidth); computeKnownBits(B, BKnown, 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. Known.Zero |= RHSKnown.One & BKnown.Zero; Known.One |= RHSKnown.Zero & BKnown.Zero; Known.Zero |= RHSKnown.Zero & BKnown.One; Known.One |= RHSKnown.One & BKnown.One; // assume(v << c = a) } else if (match(Cmp, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, 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. RHSKnown.Zero.lshrInPlace(C); Known.Zero |= RHSKnown.Zero; RHSKnown.One.lshrInPlace(C); Known.One |= RHSKnown.One; // assume(~(v << c) = a) } else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, 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. RHSKnown.One.lshrInPlace(C); Known.Zero |= RHSKnown.One; RHSKnown.Zero.lshrInPlace(C); Known.One |= RHSKnown.Zero; // assume(v >> c = a) } else if (match(Cmp, m_c_ICmp(Pred, m_Shr(m_V, m_ConstantInt(C)), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, 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. Known.Zero |= RHSKnown.Zero << C; Known.One |= RHSKnown.One << C; // assume(~(v >> c) = a) } else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_Shr(m_V, m_ConstantInt(C))), m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, 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. Known.Zero |= RHSKnown.One << C; Known.One |= RHSKnown.Zero << C; } break; case ICmpInst::ICMP_SGE: // assume(v >=_s c) where c is non-negative if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth + 1, Query(Q, I)); if (RHSKnown.isNonNegative()) { // We know that the sign bit is zero. Known.makeNonNegative(); } } break; case ICmpInst::ICMP_SGT: // assume(v >_s c) where c is at least -1. if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth + 1, Query(Q, I)); if (RHSKnown.isAllOnes() || RHSKnown.isNonNegative()) { // We know that the sign bit is zero. Known.makeNonNegative(); } } break; case ICmpInst::ICMP_SLE: // assume(v <=_s c) where c is negative if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth + 1, Query(Q, I)); if (RHSKnown.isNegative()) { // We know that the sign bit is one. Known.makeNegative(); } } break; case ICmpInst::ICMP_SLT: // assume(v <_s c) where c is non-positive if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); if (RHSKnown.isZero() || RHSKnown.isNegative()) { // We know that the sign bit is one. Known.makeNegative(); } } break; case ICmpInst::ICMP_ULE: // assume(v <=_u c) if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); // Whatever high bits in c are zero are known to be zero. Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros()); } break; case ICmpInst::ICMP_ULT: // assume(v <_u c) if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) && isValidAssumeForContext(I, Q.CxtI, Q.DT)) { KnownBits RHSKnown(BitWidth); computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I)); // If the RHS is known zero, then this assumption must be wrong (nothing // is unsigned less than zero). Signal a conflict and get out of here. if (RHSKnown.isZero()) { Known.Zero.setAllBits(); Known.One.setAllBits(); break; } // 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))) Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros() + 1); else Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros()); } break; } } // 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 (Known.Zero.intersects(Known.One)) { Known.resetAll(); if (Q.ORE) Q.ORE->emit([&]() { auto *CxtI = const_cast(Q.CxtI); return OptimizationRemarkAnalysis("value-tracking", "BadAssumption", CxtI) << "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. Known is the output of this function. Known2 is a /// pre-allocated temporary with the same bit width as Known. KZF and KOF are /// operator-specific functions 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, KnownBits &Known, KnownBits &Known2, unsigned Depth, const Query &Q, function_ref KZF, function_ref KOF) { unsigned BitWidth = Known.getBitWidth(); if (auto *SA = dyn_cast(I->getOperand(1))) { unsigned ShiftAmt = SA->getLimitedValue(BitWidth-1); computeKnownBits(I->getOperand(0), Known, Depth + 1, Q); Known.Zero = KZF(Known.Zero, ShiftAmt); Known.One = KOF(Known.One, ShiftAmt); // If the known bits conflict, this must be an overflowing left shift, so // the shift result is poison. We can return anything we want. Choose 0 for // the best folding opportunity. if (Known.hasConflict()) Known.setAllZero(); return; } computeKnownBits(I->getOperand(1), Known, Depth + 1, Q); // If the shift amount could be greater than or equal to the bit-width of the // LHS, the value could be poison, but bail out because the check below is // expensive. TODO: Should we just carry on? if (Known.getMaxValue().uge(BitWidth)) { Known.resetAll(); return; } // Note: We cannot use Known.Zero.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 = Known.Zero.zextOrTrunc(64).getZExtValue(); uint64_t ShiftAmtKO = Known.One.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. Known.resetAll(); // 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 & (PowerOf2Ceil(BitWidth) - 1)) && !(ShiftAmtKO & (PowerOf2Ceil(BitWidth) - 1))) { ShifterOperandIsNonZero = isKnownNonZero(I->getOperand(1), Depth + 1, Q); if (!*ShifterOperandIsNonZero) return; } computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); Known.Zero.setAllBits(); Known.One.setAllBits(); 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; } Known.Zero &= KZF(Known2.Zero, ShiftAmt); Known.One &= KOF(Known2.One, ShiftAmt); } // If the known bits conflict, the result is poison. Return a 0 and hope the // caller can further optimize that. if (Known.hasConflict()) Known.setAllZero(); } static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known, unsigned Depth, const Query &Q) { unsigned BitWidth = Known.getBitWidth(); KnownBits Known2(Known); switch (I->getOpcode()) { default: break; case Instruction::Load: if (MDNode *MD = Q.IIQ.getMetadata(cast(I), LLVMContext::MD_range)) computeKnownBitsFromRangeMetadata(*MD, Known); break; case Instruction::And: { // If either the LHS or the RHS are Zero, the result is zero. computeKnownBits(I->getOperand(1), Known, Depth + 1, Q); computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); // Output known-1 bits are only known if set in both the LHS & RHS. Known.One &= Known2.One; // Output known-0 are known to be clear if zero in either the LHS | RHS. Known.Zero |= Known2.Zero; // 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 *X = nullptr, *Y = nullptr; if (!Known.Zero[0] && !Known.One[0] && match(I, m_c_BinOp(m_Value(X), m_Add(m_Deferred(X), m_Value(Y))))) { Known2.resetAll(); computeKnownBits(Y, Known2, Depth + 1, Q); if (Known2.countMinTrailingOnes() > 0) Known.Zero.setBit(0); } break; } case Instruction::Or: computeKnownBits(I->getOperand(1), Known, Depth + 1, Q); computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); // Output known-0 bits are only known if clear in both the LHS & RHS. Known.Zero &= Known2.Zero; // Output known-1 are known to be set if set in either the LHS | RHS. Known.One |= Known2.One; break; case Instruction::Xor: { computeKnownBits(I->getOperand(1), Known, Depth + 1, Q); computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); // Output known-0 bits are known if clear or set in both the LHS & RHS. APInt KnownZeroOut = (Known.Zero & Known2.Zero) | (Known.One & Known2.One); // Output known-1 are known to be set if set in only one of the LHS, RHS. Known.One = (Known.Zero & Known2.One) | (Known.One & Known2.Zero); Known.Zero = std::move(KnownZeroOut); break; } case Instruction::Mul: { bool NSW = Q.IIQ.hasNoSignedWrap(cast(I)); computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW, Known, Known2, 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), Known2, Depth + 1, Q); unsigned LeadZ = Known2.countMinLeadingZeros(); Known2.resetAll(); computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q); unsigned RHSMaxLeadingZeros = Known2.countMaxLeadingZeros(); if (RHSMaxLeadingZeros != BitWidth) LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSMaxLeadingZeros - 1); Known.Zero.setHighBits(LeadZ); break; } case Instruction::Select: { const Value *LHS = nullptr, *RHS = nullptr; SelectPatternFlavor SPF = matchSelectPattern(I, LHS, RHS).Flavor; if (SelectPatternResult::isMinOrMax(SPF)) { computeKnownBits(RHS, Known, Depth + 1, Q); computeKnownBits(LHS, Known2, Depth + 1, Q); } else { computeKnownBits(I->getOperand(2), Known, Depth + 1, Q); computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q); } unsigned MaxHighOnes = 0; unsigned MaxHighZeros = 0; if (SPF == SPF_SMAX) { // If both sides are negative, the result is negative. if (Known.isNegative() && Known2.isNegative()) // We can derive a lower bound on the result by taking the max of the // leading one bits. MaxHighOnes = std::max(Known.countMinLeadingOnes(), Known2.countMinLeadingOnes()); // If either side is non-negative, the result is non-negative. else if (Known.isNonNegative() || Known2.isNonNegative()) MaxHighZeros = 1; } else if (SPF == SPF_SMIN) { // If both sides are non-negative, the result is non-negative. if (Known.isNonNegative() && Known2.isNonNegative()) // We can derive an upper bound on the result by taking the max of the // leading zero bits. MaxHighZeros = std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros()); // If either side is negative, the result is negative. else if (Known.isNegative() || Known2.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(Known.countMinLeadingOnes(), Known2.countMinLeadingOnes()); } 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(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros()); } else if (SPF == SPF_ABS) { // RHS from matchSelectPattern returns the negation part of abs pattern. // If the negate has an NSW flag we can assume the sign bit of the result // will be 0 because that makes abs(INT_MIN) undefined. if (match(RHS, m_Neg(m_Specific(LHS))) && Q.IIQ.hasNoSignedWrap(cast(RHS))) MaxHighZeros = 1; } // Only known if known in both the LHS and RHS. Known.One &= Known2.One; Known.Zero &= Known2.Zero; if (MaxHighOnes > 0) Known.One.setHighBits(MaxHighOnes); if (MaxHighZeros > 0) Known.Zero.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. Type *ScalarTy = SrcTy->getScalarType(); SrcBitWidth = ScalarTy->isPointerTy() ? Q.DL.getPointerTypeSizeInBits(ScalarTy) : Q.DL.getTypeSizeInBits(ScalarTy); assert(SrcBitWidth && "SrcBitWidth can't be zero"); Known = Known.zextOrTrunc(SrcBitWidth, false); computeKnownBits(I->getOperand(0), Known, Depth + 1, Q); Known = Known.zextOrTrunc(BitWidth, true /* ExtendedBitsAreKnownZero */); break; } case Instruction::BitCast: { Type *SrcTy = I->getOperand(0)->getType(); if (SrcTy->isIntOrPtrTy() && // TODO: For now, not handling conversions like: // (bitcast i64 %x to <2 x i32>) !I->getType()->isVectorTy()) { computeKnownBits(I->getOperand(0), Known, 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(); Known = Known.trunc(SrcBitWidth); computeKnownBits(I->getOperand(0), Known, Depth + 1, Q); // If the sign bit of the input is known set or clear, then we know the // top bits of the result. Known = Known.sext(BitWidth); break; } case Instruction::Shl: { // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 bool NSW = Q.IIQ.hasNoSignedWrap(cast(I)); 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.isSignBitSet()) KZResult.setSignBit(); return KZResult; }; auto KOF = [NSW](const APInt &KnownOne, unsigned ShiftAmt) { APInt KOResult = KnownOne << ShiftAmt; if (NSW && KnownOne.isSignBitSet()) KOResult.setSignBit(); return KOResult; }; computeKnownBitsFromShiftOperator(I, Known, Known2, Depth, Q, KZF, KOF); break; } case Instruction::LShr: { // (lshr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 auto KZF = [](const APInt &KnownZero, unsigned ShiftAmt) { APInt KZResult = KnownZero.lshr(ShiftAmt); // High bits known zero. KZResult.setHighBits(ShiftAmt); return KZResult; }; auto KOF = [](const APInt &KnownOne, unsigned ShiftAmt) { return KnownOne.lshr(ShiftAmt); }; computeKnownBitsFromShiftOperator(I, Known, Known2, 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, Known, Known2, Depth, Q, KZF, KOF); break; } case Instruction::Sub: { bool NSW = Q.IIQ.hasNoSignedWrap(cast(I)); computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW, Known, Known2, Depth, Q); break; } case Instruction::Add: { bool NSW = Q.IIQ.hasNoSignedWrap(cast(I)); computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW, Known, Known2, 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), Known2, Depth + 1, Q); // The low bits of the first operand are unchanged by the srem. Known.Zero = Known2.Zero & LowBits; Known.One = Known2.One & LowBits; // If the first operand is non-negative or has all low bits zero, then // the upper bits are all zero. if (Known2.isNonNegative() || LowBits.isSubsetOf(Known2.Zero)) Known.Zero |= ~LowBits; // If the first operand is negative and not all low bits are zero, then // the upper bits are all one. if (Known2.isNegative() && LowBits.intersects(Known2.One)) Known.One |= ~LowBits; assert((Known.Zero & Known.One) == 0 && "Bits known to be one AND zero?"); break; } } // The sign bit is the LHS's sign bit, except when the result of the // remainder is zero. computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); // If it's known zero, our sign bit is also zero. if (Known2.isNonNegative()) Known.makeNonNegative(); 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), Known, Depth + 1, Q); Known.Zero |= ~LowBits; Known.One &= 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), Known, Depth + 1, Q); computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q); unsigned Leaders = std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros()); Known.resetAll(); Known.Zero.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) Known.Zero.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. KnownBits LocalKnown(BitWidth); computeKnownBits(I->getOperand(0), LocalKnown, Depth + 1, Q); unsigned TrailZ = LocalKnown.countMinTrailingZeros(); 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); LocalKnown.Zero = LocalKnown.One = APInt(GEPOpiBits, 0); computeKnownBits(Index, LocalKnown, Depth + 1, Q); TrailZ = std::min(TrailZ, unsigned(countTrailingZeros(TypeSize) + LocalKnown.countMinTrailingZeros())); } } Known.Zero.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); Instruction *RInst = P->getIncomingBlock(!i)->getTerminator(); Instruction *LInst = P->getIncomingBlock(i)->getTerminator(); 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 continue; // Check for recurrence with L and R flipped. // Change the context instruction to the "edge" that flows into the // phi. This is important because that is where the value is actually // "evaluated" even though it is used later somewhere else. (see also // D69571). Query RecQ = Q; // Ok, we have a PHI of the form L op= R. Check for low // zero bits. RecQ.CxtI = RInst; computeKnownBits(R, Known2, Depth + 1, RecQ); // We need to take the minimum number of known bits KnownBits Known3(Known); RecQ.CxtI = LInst; computeKnownBits(L, Known3, Depth + 1, RecQ); Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(), Known3.countMinTrailingZeros())); auto *OverflowOp = dyn_cast(LU); if (OverflowOp && Q.IIQ.hasNoSignedWrap(OverflowOp)) { // 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 (Known2.isNonNegative() && Known3.isNonNegative()) Known.makeNonNegative(); else if (Known2.isNegative() && Known3.isNegative()) Known.makeNegative(); } // (sub nsw non-negative, negative) --> non-negative // (sub nsw negative, non-negative) --> negative else if (Opcode == Instruction::Sub && LL == I) { if (Known2.isNonNegative() && Known3.isNegative()) Known.makeNonNegative(); else if (Known2.isNegative() && Known3.isNonNegative()) Known.makeNegative(); } // (mul nsw non-negative, non-negative) --> non-negative else if (Opcode == Instruction::Mul && Known2.isNonNegative() && Known3.isNonNegative()) Known.makeNonNegative(); } 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 && !Known.Zero && !Known.One) { // Skip if every incoming value references to ourself. if (dyn_cast_or_null(P->hasConstantValue())) break; Known.Zero.setAllBits(); Known.One.setAllBits(); for (unsigned u = 0, e = P->getNumIncomingValues(); u < e; ++u) { Value *IncValue = P->getIncomingValue(u); // Skip direct self references. if (IncValue == P) continue; // Change the context instruction to the "edge" that flows into the // phi. This is important because that is where the value is actually // "evaluated" even though it is used later somewhere else. (see also // D69571). Query RecQ = Q; RecQ.CxtI = P->getIncomingBlock(u)->getTerminator(); Known2 = KnownBits(BitWidth); // Recurse, but cap the recursion to one level, because we don't // want to waste time spinning around in loops. computeKnownBits(IncValue, Known2, MaxDepth - 1, RecQ); Known.Zero &= Known2.Zero; Known.One &= Known2.One; // If all bits have been ruled out, there's no need to check // more operands. if (!Known.Zero && !Known.One) 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 = Q.IIQ.getMetadata(cast(I), LLVMContext::MD_range)) computeKnownBitsFromRangeMetadata(*MD, Known); if (const Value *RV = ImmutableCallSite(I).getReturnedArgOperand()) { computeKnownBits(RV, Known2, Depth + 1, Q); Known.Zero |= Known2.Zero; Known.One |= Known2.One; } if (const IntrinsicInst *II = dyn_cast(I)) { switch (II->getIntrinsicID()) { default: break; case Intrinsic::bitreverse: computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); Known.Zero |= Known2.Zero.reverseBits(); Known.One |= Known2.One.reverseBits(); break; case Intrinsic::bswap: computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); Known.Zero |= Known2.Zero.byteSwap(); Known.One |= Known2.One.byteSwap(); break; case Intrinsic::ctlz: { computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); // If we have a known 1, its position is our upper bound. unsigned PossibleLZ = Known2.One.countLeadingZeros(); // If this call is undefined for 0, the result will be less than 2^n. if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext())) PossibleLZ = std::min(PossibleLZ, BitWidth - 1); unsigned LowBits = Log2_32(PossibleLZ)+1; Known.Zero.setBitsFrom(LowBits); break; } case Intrinsic::cttz: { computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); // If we have a known 1, its position is our upper bound. unsigned PossibleTZ = Known2.One.countTrailingZeros(); // If this call is undefined for 0, the result will be less than 2^n. if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext())) PossibleTZ = std::min(PossibleTZ, BitWidth - 1); unsigned LowBits = Log2_32(PossibleTZ)+1; Known.Zero.setBitsFrom(LowBits); break; } case Intrinsic::ctpop: { computeKnownBits(I->getOperand(0), Known2, 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 = Known2.countMaxPopulation(); unsigned LowBits = Log2_32(BitsPossiblySet)+1; Known.Zero.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::fshr: case Intrinsic::fshl: { const APInt *SA; if (!match(I->getOperand(2), m_APInt(SA))) break; // Normalize to funnel shift left. uint64_t ShiftAmt = SA->urem(BitWidth); if (II->getIntrinsicID() == Intrinsic::fshr) ShiftAmt = BitWidth - ShiftAmt; KnownBits Known3(Known); computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q); computeKnownBits(I->getOperand(1), Known3, Depth + 1, Q); Known.Zero = Known2.Zero.shl(ShiftAmt) | Known3.Zero.lshr(BitWidth - ShiftAmt); Known.One = Known2.One.shl(ShiftAmt) | Known3.One.lshr(BitWidth - ShiftAmt); break; } case Intrinsic::uadd_sat: case Intrinsic::usub_sat: { bool IsAdd = II->getIntrinsicID() == Intrinsic::uadd_sat; computeKnownBits(I->getOperand(0), Known, Depth + 1, Q); computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q); // Add: Leading ones of either operand are preserved. // Sub: Leading zeros of LHS and leading ones of RHS are preserved // as leading zeros in the result. unsigned LeadingKnown; if (IsAdd) LeadingKnown = std::max(Known.countMinLeadingOnes(), Known2.countMinLeadingOnes()); else LeadingKnown = std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingOnes()); Known = KnownBits::computeForAddSub( IsAdd, /* NSW */ false, Known, Known2); // We select between the operation result and all-ones/zero // respectively, so we can preserve known ones/zeros. if (IsAdd) { Known.One.setHighBits(LeadingKnown); Known.Zero.clearAllBits(); } else { Known.Zero.setHighBits(LeadingKnown); Known.One.clearAllBits(); } break; } case Intrinsic::x86_sse42_crc32_64_64: Known.Zero.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), Known, 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, Known, Known2, Depth, Q); break; case Intrinsic::usub_with_overflow: case Intrinsic::ssub_with_overflow: computeKnownBitsAddSub(false, II->getArgOperand(0), II->getArgOperand(1), false, Known, Known2, Depth, Q); break; case Intrinsic::umul_with_overflow: case Intrinsic::smul_with_overflow: computeKnownBitsMul(II->getArgOperand(0), II->getArgOperand(1), false, Known, Known2, Depth, Q); break; } } } } } /// Determine which bits of V are known to be either zero or one and return /// them. KnownBits computeKnownBits(const Value *V, unsigned Depth, const Query &Q) { KnownBits Known(getBitWidth(V->getType(), Q.DL)); computeKnownBits(V, Known, Depth, Q); return Known; } /// Determine which bits of V are known to be either zero or one and return /// them in the Known bit set. /// /// 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, KnownBits &Known, unsigned Depth, const Query &Q) { assert(V && "No Value?"); assert(Depth <= MaxDepth && "Limit Search Depth"); unsigned BitWidth = Known.getBitWidth(); assert((V->getType()->isIntOrIntVectorTy(BitWidth) || V->getType()->isPtrOrPtrVectorTy()) && "Not integer or pointer type!"); Type *ScalarTy = V->getType()->getScalarType(); unsigned ExpectedWidth = ScalarTy->isPointerTy() ? Q.DL.getPointerTypeSizeInBits(ScalarTy) : Q.DL.getTypeSizeInBits(ScalarTy); assert(ExpectedWidth == BitWidth && "V and Known should have same BitWidth"); (void)BitWidth; (void)ExpectedWidth; const APInt *C; if (match(V, m_APInt(C))) { // We know all of the bits for a scalar constant or a splat vector constant! Known.One = *C; Known.Zero = ~Known.One; return; } // Null and aggregate-zero are all-zeros. if (isa(V) || isa(V)) { Known.setAllZero(); 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. Known.Zero.setAllBits(); Known.One.setAllBits(); for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) { APInt Elt = CDS->getElementAsAPInt(i); Known.Zero &= ~Elt; Known.One &= 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. Known.Zero.setAllBits(); Known.One.setAllBits(); for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) { Constant *Element = CV->getAggregateElement(i); auto *ElementCI = dyn_cast_or_null(Element); if (!ElementCI) { Known.resetAll(); return; } const APInt &Elt = ElementCI->getValue(); Known.Zero &= ~Elt; Known.One &= Elt; } return; } // Start out not knowing anything. Known.resetAll(); // 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(), Known, Depth + 1, Q); return; } if (const Operator *I = dyn_cast(V)) computeKnownBitsFromOperator(I, Known, Depth, Q); // Aligned pointers have trailing zeros - refine Known.Zero set if (V->getType()->isPointerTy()) { const MaybeAlign Align = V->getPointerAlignment(Q.DL); if (Align) Known.Zero.setLowBits(countTrailingZeros(Align->value())); } // computeKnownBitsFromAssume strictly refines Known. // Therefore, we run them after computeKnownBitsFromOperator. // Check whether a nearby assume intrinsic can determine some known bits. computeKnownBitsFromAssume(V, Known, Depth, Q); assert((Known.Zero & Known.One) == 0 && "Bits known to be one AND zero?"); } /// 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) { assert(Depth <= MaxDepth && "Limit Search Depth"); // Attempt to match against constants. if (OrZero && match(V, m_Power2OrZero())) return true; if (match(V, m_Power2())) return true; // 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; // (signmask) >>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_SignMask(), 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 || Q.IIQ.hasNoUnsignedWrap(VOBO) || Q.IIQ.hasNoSignedWrap(VOBO)) { 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(); KnownBits LHSBits(BitWidth); computeKnownBits(X, LHSBits, Depth, Q); KnownBits RHSBits(BitWidth); computeKnownBits(Y, RHSBits, 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 ((~(LHSBits.Zero & RHSBits.Zero)).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 || RHSBits.One.getBoolValue() || LHSBits.One.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; } /// 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) { const Function *F = nullptr; if (const Instruction *I = dyn_cast(GEP)) F = I->getFunction(); if (!GEP->isInBounds() || NullPointerIsDefined(F, GEP->getPointerAddressSpace())) 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; } static bool isKnownNonNullFromDominatingCondition(const Value *V, const Instruction *CtxI, const DominatorTree *DT) { if (isa(V)) return false; if (!CtxI || !DT) return false; 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; // If the value is used as a load/store, then the pointer must be non null. if (V == getLoadStorePointerOperand(U)) { const Instruction *I = cast(U); if (!NullPointerIsDefined(I->getFunction(), V->getType()->getPointerAddressSpace()) && DT->dominates(I, 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; SmallVector WorkList; SmallPtrSet Visited; for (auto *CmpU : U->users()) { assert(WorkList.empty() && "Should be!"); if (Visited.insert(CmpU).second) WorkList.push_back(CmpU); while (!WorkList.empty()) { auto *Curr = WorkList.pop_back_val(); // If a user is an AND, add all its users to the work list. We only // propagate "pred != null" condition through AND because it is only // correct to assume that all conditions of AND are met in true branch. // TODO: Support similar logic of OR and EQ predicate? if (Pred == ICmpInst::ICMP_NE) if (auto *BO = dyn_cast(Curr)) if (BO->getOpcode() == Instruction::And) { for (auto *BOU : BO->users()) if (Visited.insert(BOU).second) WorkList.push_back(BOU); continue; } if (const BranchInst *BI = dyn_cast(Curr)) { 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 && isGuard(Curr) && DT->dominates(cast(Curr), CtxI)) { 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; if (auto *CE = dyn_cast(C)) { // See the comment for IntToPtr/PtrToInt instructions below. if (CE->getOpcode() == Instruction::IntToPtr || CE->getOpcode() == Instruction::PtrToInt) if (Q.DL.getTypeSizeInBits(CE->getOperand(0)->getType()) <= Q.DL.getTypeSizeInBits(CE->getType())) return isKnownNonZero(CE->getOperand(0), Depth, Q); } // 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; } // 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)) { if (!GV->isAbsoluteSymbolRef() && !GV->hasExternalWeakLinkage() && GV->getType()->getAddressSpace() == 0) return true; } else return false; } if (auto *I = dyn_cast(V)) { if (MDNode *Ranges = Q.IIQ.getMetadata(I, 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; } } } if (isKnownNonZeroFromAssume(V, Q)) return true; // Some of the tests below are recursive, so bail out if we hit the limit. if (Depth++ >= MaxDepth) return false; // Check for pointer simplifications. if (V->getType()->isPointerTy()) { // Alloca never returns null, malloc might. if (isa(V) && Q.DL.getAllocaAddrSpace() == 0) return true; // A byval, inalloca, or nonnull argument is never null. if (const Argument *A = dyn_cast(V)) if (A->hasByValOrInAllocaAttr() || A->hasNonNullAttr()) return true; // A Load tagged with nonnull metadata is never null. if (const LoadInst *LI = dyn_cast(V)) if (Q.IIQ.getMetadata(LI, LLVMContext::MD_nonnull)) return true; if (const auto *Call = dyn_cast(V)) { if (Call->isReturnNonNull()) return true; if (const auto *RP = getArgumentAliasingToReturnedPointer(Call, true)) return isKnownNonZero(RP, Depth, Q); } } if (isKnownNonNullFromDominatingCondition(V, Q.CxtI, Q.DT)) return true; // Check for recursive pointer simplifications. if (V->getType()->isPointerTy()) { // Look through bitcast operations, GEPs, and int2ptr instructions as they // do not alter the value, or at least not the nullness property of the // value, e.g., int2ptr is allowed to zero/sign extend the value. // // Note that we have to take special care to avoid looking through // truncating casts, e.g., int2ptr/ptr2int with appropriate sizes, as well // as casts that can alter the value, e.g., AddrSpaceCasts. if (const GEPOperator *GEP = dyn_cast(V)) if (isGEPKnownNonNull(GEP, Depth, Q)) return true; if (auto *BCO = dyn_cast(V)) return isKnownNonZero(BCO->getOperand(0), Depth, Q); if (auto *I2P = dyn_cast(V)) if (Q.DL.getTypeSizeInBits(I2P->getSrcTy()) <= Q.DL.getTypeSizeInBits(I2P->getDestTy())) return isKnownNonZero(I2P->getOperand(0), Depth, Q); } // Similar to int2ptr above, we can look through ptr2int here if the cast // is a no-op or an extend and not a truncate. if (auto *P2I = dyn_cast(V)) if (Q.DL.getTypeSizeInBits(P2I->getSrcTy()) <= Q.DL.getTypeSizeInBits(P2I->getDestTy())) return isKnownNonZero(P2I->getOperand(0), Depth, Q); 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 (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 (Q.IIQ.hasNoUnsignedWrap(BO)) return isKnownNonZero(X, Depth, Q); KnownBits Known(BitWidth); computeKnownBits(X, Known, Depth, Q); if (Known.One[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); KnownBits Known = computeKnownBits(X, Depth, Q); if (Known.isNegative()) 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)) { auto ShiftVal = Shift->getLimitedValue(BitWidth - 1); // Is there a known one in the portion not shifted out? if (Known.countMaxLeadingZeros() < BitWidth - ShiftVal) return true; // Are all the bits to be shifted out known zero? if (Known.countMinTrailingZeros() >= 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)))) { KnownBits XKnown = computeKnownBits(X, Depth, Q); KnownBits YKnown = computeKnownBits(Y, 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 (XKnown.isNonNegative() && YKnown.isNonNegative()) 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 (XKnown.isNegative() && YKnown.isNegative()) { 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. if (XKnown.One.intersects(Mask)) return true; // The sign bit of Y is set. If some other bit is set then Y is not equal // to INT_MIN. if (YKnown.One.intersects(Mask)) return true; } // The sum of a non-negative number and a power of two is not zero. if (XKnown.isNonNegative() && isKnownToBeAPowerOfTwo(Y, /*OrZero*/ false, Depth, Q)) return true; if (YKnown.isNonNegative() && 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 ((Q.IIQ.hasNoSignedWrap(BO) || Q.IIQ.hasNoUnsignedWrap(BO)) && 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 (Q.IIQ.UseInstrInfo && (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 = llvm::all_of(PN->operands(), [](Value *V) { return isa(V) && !cast(V)->isZero(); }); if (AllNonZeroConstants) return true; } KnownBits Known(BitWidth); computeKnownBits(V, Known, Depth, Q); return Known.One != 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 == 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 (V1->getType()->isIntOrIntVectorTy()) { // 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. KnownBits Known1 = computeKnownBits(V1, 0, Q); KnownBits Known2 = computeKnownBits(V2, 0, Q); if (Known1.Zero.intersects(Known2.One) || Known2.Zero.intersects(Known1.One)) 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) { KnownBits Known(Mask.getBitWidth()); computeKnownBits(V, Known, Depth, Q); return Mask.isSubsetOf(Known.Zero); } // Match a signed min+max clamp pattern like smax(smin(In, CHigh), CLow). // Returns the input and lower/upper bounds. static bool isSignedMinMaxClamp(const Value *Select, const Value *&In, const APInt *&CLow, const APInt *&CHigh) { assert(isa(Select) && cast(Select)->getOpcode() == Instruction::Select && "Input should be a Select!"); const Value *LHS = nullptr, *RHS = nullptr; SelectPatternFlavor SPF = matchSelectPattern(Select, LHS, RHS).Flavor; if (SPF != SPF_SMAX && SPF != SPF_SMIN) return false; if (!match(RHS, m_APInt(CLow))) return false; const Value *LHS2 = nullptr, *RHS2 = nullptr; SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2).Flavor; if (getInverseMinMaxFlavor(SPF) != SPF2) return false; if (!match(RHS2, m_APInt(CHigh))) return false; if (SPF == SPF_SMIN) std::swap(CLow, CHigh); In = LHS2; return CLow->sle(*CHigh); } /// 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; MinSignBits = std::min(MinSignBits, Elt->getValue().getNumSignBits()); } 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 minimum number of known sign bits. static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth, const Query &Q) { assert(Depth <= MaxDepth && "Limit Search Depth"); // 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. Type *ScalarTy = V->getType()->getScalarType(); unsigned TyBits = ScalarTy->isPointerTy() ? Q.DL.getPointerTypeSizeInBits(ScalarTy) : Q.DL.getTypeSizeInBits(ScalarTy); 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. if (auto *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))) { if (ShAmt->uge(TyBits)) break; // Bad shift. unsigned ShAmtLimited = ShAmt->getZExtValue(); 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); if (ShAmt->uge(TyBits) || // Bad shift. ShAmt->uge(Tmp)) break; // Shifted all sign bits out. Tmp2 = ShAmt->getZExtValue(); 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: { // If we have a clamp pattern, we know that the number of sign bits will // be the minimum of the clamp min/max range. const Value *X; const APInt *CLow, *CHigh; if (isSignedMinMaxClamp(U, X, CLow, CHigh)) return std::min(CLow->getNumSignBits(), CHigh->getNumSignBits()); Tmp = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q); if (Tmp == 1) break; 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) break; // Special case decrementing a value (ADD X, -1): if (const auto *CRHS = dyn_cast(U->getOperand(1))) if (CRHS->isAllOnesValue()) { KnownBits Known(TyBits); computeKnownBits(U->getOperand(0), Known, 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 ((Known.Zero | 1).isAllOnesValue()) return TyBits; // If we are subtracting one from a positive number, there is no carry // out of the result. if (Known.isNonNegative()) return Tmp; } Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q); if (Tmp2 == 1) break; return std::min(Tmp, Tmp2) - 1; case Instruction::Sub: Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q); if (Tmp2 == 1) break; // Handle NEG. if (const auto *CLHS = dyn_cast(U->getOperand(0))) if (CLHS->isNullValue()) { KnownBits Known(TyBits); computeKnownBits(U->getOperand(1), Known, 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 ((Known.Zero | 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 (Known.isNonNegative()) 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) break; return std::min(Tmp, Tmp2) - 1; case Instruction::Mul: { // The output of the Mul can be at most twice the valid bits in the // inputs. unsigned SignBitsOp0 = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q); if (SignBitsOp0 == 1) break; unsigned SignBitsOp1 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q); if (SignBitsOp1 == 1) break; unsigned OutValidBits = (TyBits - SignBitsOp0 + 1) + (TyBits - SignBitsOp1 + 1); return OutValidBits > TyBits ? 1 : TyBits - OutValidBits + 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); case Instruction::ShuffleVector: { // TODO: This is copied almost directly from the SelectionDAG version of // ComputeNumSignBits. It would be better if we could share common // code. If not, make sure that changes are translated to the DAG. // Collect the minimum number of sign bits that are shared by every vector // element referenced by the shuffle. auto *Shuf = cast(U); int NumElts = Shuf->getOperand(0)->getType()->getVectorNumElements(); int NumMaskElts = Shuf->getMask()->getType()->getVectorNumElements(); APInt DemandedLHS(NumElts, 0), DemandedRHS(NumElts, 0); for (int i = 0; i != NumMaskElts; ++i) { int M = Shuf->getMaskValue(i); assert(M < NumElts * 2 && "Invalid shuffle mask constant"); // For undef elements, we don't know anything about the common state of // the shuffle result. if (M == -1) return 1; if (M < NumElts) DemandedLHS.setBit(M % NumElts); else DemandedRHS.setBit(M % NumElts); } Tmp = std::numeric_limits::max(); if (!!DemandedLHS) Tmp = ComputeNumSignBits(Shuf->getOperand(0), Depth + 1, Q); if (!!DemandedRHS) { Tmp2 = ComputeNumSignBits(Shuf->getOperand(1), Depth + 1, Q); Tmp = std::min(Tmp, Tmp2); } // If we don't know anything, early out and try computeKnownBits // fall-back. if (Tmp == 1) break; assert(Tmp <= V->getType()->getScalarSizeInBits() && "Failed to determine minimum sign bits"); return Tmp; } } } // 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; KnownBits Known(TyBits); computeKnownBits(V, Known, 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. return std::max(FirstAnswer, Known.countMinSignBits()); } /// 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) { 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 LLVM_FALLTHROUGH; 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: return Intrinsic::sqrt; } 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 (auto *CFP = dyn_cast(V)) return !CFP->getValueAPF().isNegZero(); // Limit search depth. if (Depth == MaxDepth) return false; auto *Op = dyn_cast(V); if (!Op) return false; // Check if the nsz fast-math flag is set. if (auto *FPO = dyn_cast(Op)) if (FPO->hasNoSignedZeros()) return true; // (fadd x, 0.0) is guaranteed to return +0.0, not -0.0. if (match(Op, m_FAdd(m_Value(), m_PosZeroFP()))) return true; // sitofp and uitofp turn into +0.0 for zero. if (isa(Op) || isa(Op)) return true; if (auto *Call = dyn_cast(Op)) { Intrinsic::ID IID = getIntrinsicForCallSite(Call, TLI); switch (IID) { default: break; // sqrt(-0.0) = -0.0, no other negative results are possible. case Intrinsic::sqrt: case Intrinsic::canonicalize: return CannotBeNegativeZero(Call->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()); } // Handle vector of constants. if (auto *CV = dyn_cast(V)) { if (CV->getType()->isVectorTy()) { unsigned NumElts = CV->getType()->getVectorNumElements(); for (unsigned i = 0; i != NumElts; ++i) { auto *CFP = dyn_cast_or_null(CV->getAggregateElement(i)); if (!CFP) return false; if (CFP->getValueAPF().isNegative() && (SignBitOnly || !CFP->getValueAPF().isZero())) return false; } // All non-negative ConstantFPs. return true; } } 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::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. 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 (isKnownNeverNaN(I->getOperand(0), TLI) && cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly, Depth + 1)) || (isKnownNeverNaN(I->getOperand(1), TLI) && cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly, Depth + 1)); case Intrinsic::maximum: return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly, Depth + 1) || cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly, Depth + 1); case Intrinsic::minnum: case Intrinsic::minimum: 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); } bool llvm::isKnownNeverInfinity(const Value *V, const TargetLibraryInfo *TLI, unsigned Depth) { assert(V->getType()->isFPOrFPVectorTy() && "Querying for Inf on non-FP type"); // If we're told that infinities won't happen, assume they won't. if (auto *FPMathOp = dyn_cast(V)) if (FPMathOp->hasNoInfs()) return true; // Handle scalar constants. if (auto *CFP = dyn_cast(V)) return !CFP->isInfinity(); if (Depth == MaxDepth) return false; if (auto *Inst = dyn_cast(V)) { switch (Inst->getOpcode()) { case Instruction::Select: { return isKnownNeverInfinity(Inst->getOperand(1), TLI, Depth + 1) && isKnownNeverInfinity(Inst->getOperand(2), TLI, Depth + 1); } case Instruction::UIToFP: // If the input type fits into the floating type the result is finite. return ilogb(APFloat::getLargest( Inst->getType()->getScalarType()->getFltSemantics())) >= (int)Inst->getOperand(0)->getType()->getScalarSizeInBits(); default: break; } } // Bail out for constant expressions, but try to handle vector constants. if (!V->getType()->isVectorTy() || !isa(V)) return false; // For vectors, verify that each element is not infinity. unsigned NumElts = V->getType()->getVectorNumElements(); for (unsigned i = 0; i != NumElts; ++i) { Constant *Elt = cast(V)->getAggregateElement(i); if (!Elt) return false; if (isa(Elt)) continue; auto *CElt = dyn_cast(Elt); if (!CElt || CElt->isInfinity()) return false; } // All elements were confirmed non-infinity or undefined. return true; } bool llvm::isKnownNeverNaN(const Value *V, const TargetLibraryInfo *TLI, unsigned Depth) { assert(V->getType()->isFPOrFPVectorTy() && "Querying for NaN on non-FP type"); // If we're told that NaNs won't happen, assume they won't. if (auto *FPMathOp = dyn_cast(V)) if (FPMathOp->hasNoNaNs()) return true; // Handle scalar constants. if (auto *CFP = dyn_cast(V)) return !CFP->isNaN(); if (Depth == MaxDepth) return false; if (auto *Inst = dyn_cast(V)) { switch (Inst->getOpcode()) { case Instruction::FAdd: case Instruction::FSub: // Adding positive and negative infinity produces NaN. return isKnownNeverNaN(Inst->getOperand(0), TLI, Depth + 1) && isKnownNeverNaN(Inst->getOperand(1), TLI, Depth + 1) && (isKnownNeverInfinity(Inst->getOperand(0), TLI, Depth + 1) || isKnownNeverInfinity(Inst->getOperand(1), TLI, Depth + 1)); case Instruction::FMul: // Zero multiplied with infinity produces NaN. // FIXME: If neither side can be zero fmul never produces NaN. return isKnownNeverNaN(Inst->getOperand(0), TLI, Depth + 1) && isKnownNeverInfinity(Inst->getOperand(0), TLI, Depth + 1) && isKnownNeverNaN(Inst->getOperand(1), TLI, Depth + 1) && isKnownNeverInfinity(Inst->getOperand(1), TLI, Depth + 1); case Instruction::FDiv: case Instruction::FRem: // FIXME: Only 0/0, Inf/Inf, Inf REM x and x REM 0 produce NaN. return false; case Instruction::Select: { return isKnownNeverNaN(Inst->getOperand(1), TLI, Depth + 1) && isKnownNeverNaN(Inst->getOperand(2), TLI, Depth + 1); } case Instruction::SIToFP: case Instruction::UIToFP: return true; case Instruction::FPTrunc: case Instruction::FPExt: return isKnownNeverNaN(Inst->getOperand(0), TLI, Depth + 1); default: break; } } if (const auto *II = dyn_cast(V)) { switch (II->getIntrinsicID()) { case Intrinsic::canonicalize: case Intrinsic::fabs: case Intrinsic::copysign: case Intrinsic::exp: case Intrinsic::exp2: case Intrinsic::floor: case Intrinsic::ceil: case Intrinsic::trunc: case Intrinsic::rint: case Intrinsic::nearbyint: case Intrinsic::round: return isKnownNeverNaN(II->getArgOperand(0), TLI, Depth + 1); case Intrinsic::sqrt: return isKnownNeverNaN(II->getArgOperand(0), TLI, Depth + 1) && CannotBeOrderedLessThanZero(II->getArgOperand(0), TLI); case Intrinsic::minnum: case Intrinsic::maxnum: // If either operand is not NaN, the result is not NaN. return isKnownNeverNaN(II->getArgOperand(0), TLI, Depth + 1) || isKnownNeverNaN(II->getArgOperand(1), TLI, Depth + 1); default: return false; } } // Bail out for constant expressions, but try to handle vector constants. if (!V->getType()->isVectorTy() || !isa(V)) return false; // For vectors, verify that each element is not NaN. unsigned NumElts = V->getType()->getVectorNumElements(); for (unsigned i = 0; i != NumElts; ++i) { Constant *Elt = cast(V)->getAggregateElement(i); if (!Elt) return false; if (isa(Elt)) continue; auto *CElt = dyn_cast(Elt); if (!CElt || CElt->isNaN()) return false; } // All elements were confirmed not-NaN or undefined. return true; } Value *llvm::isBytewiseValue(Value *V, const DataLayout &DL) { // All byte-wide stores are splatable, even of arbitrary variables. if (V->getType()->isIntegerTy(8)) return V; LLVMContext &Ctx = V->getContext(); // Undef don't care. auto *UndefInt8 = UndefValue::get(Type::getInt8Ty(Ctx)); if (isa(V)) return UndefInt8; const uint64_t Size = DL.getTypeStoreSize(V->getType()); if (!Size) return UndefInt8; Constant *C = dyn_cast(V); if (!C) { // 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; } // Handle 'null' ConstantArrayZero etc. if (C->isNullValue()) return Constant::getNullValue(Type::getInt8Ty(Ctx)); // Constant floating-point 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(C)) { Type *Ty = nullptr; if (CFP->getType()->isHalfTy()) Ty = Type::getInt16Ty(Ctx); else if (CFP->getType()->isFloatTy()) Ty = Type::getInt32Ty(Ctx); else if (CFP->getType()->isDoubleTy()) Ty = Type::getInt64Ty(Ctx); // Don't handle long double formats, which have strange constraints. return Ty ? isBytewiseValue(ConstantExpr::getBitCast(CFP, Ty), DL) : nullptr; } // We can handle constant integers that are multiple of 8 bits. if (ConstantInt *CI = dyn_cast(C)) { 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(Ctx, CI->getValue().trunc(8)); } } if (auto *CE = dyn_cast(C)) { if (CE->getOpcode() == Instruction::IntToPtr) { auto PS = DL.getPointerSizeInBits( cast(CE->getType())->getAddressSpace()); return isBytewiseValue( ConstantExpr::getIntegerCast(CE->getOperand(0), Type::getIntNTy(Ctx, PS), false), DL); } } auto Merge = [&](Value *LHS, Value *RHS) -> Value * { if (LHS == RHS) return LHS; if (!LHS || !RHS) return nullptr; if (LHS == UndefInt8) return RHS; if (RHS == UndefInt8) return LHS; return nullptr; }; if (ConstantDataSequential *CA = dyn_cast(C)) { Value *Val = UndefInt8; for (unsigned I = 0, E = CA->getNumElements(); I != E; ++I) if (!(Val = Merge(Val, isBytewiseValue(CA->getElementAsConstant(I), DL)))) return nullptr; return Val; } if (isa(C)) { Value *Val = UndefInt8; for (unsigned I = 0, E = C->getNumOperands(); I != E; ++I) if (!(Val = Merge(Val, isBytewiseValue(C->getOperand(I), DL)))) return nullptr; return Val; } // Don't try to handle the handful of other constants. 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) { 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) aggregate return 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 aggregate and a sequence of indices, see if the scalar value /// indexed is already around as a register, for example if it was inserted /// directly into the aggregate. /// /// 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; } bool llvm::isGEPBasedOnPointerToString(const GEPOperator *GEP, unsigned CharSize) { // 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 \p CharSize integers. // CharSize. ArrayType *AT = dyn_cast(GEP->getSourceElementType()); if (!AT || !AT->getElementType()->isIntegerTy(CharSize)) 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; } bool llvm::getConstantDataArrayInfo(const Value *V, ConstantDataArraySlice &Slice, unsigned ElementSize, uint64_t Offset) { 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, ElementSize)) 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 getConstantDataArrayInfo(GEP->getOperand(0), Slice, ElementSize, StartIdx + Offset); } // 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; const ConstantDataArray *Array; ArrayType *ArrayTy; if (GV->getInitializer()->isNullValue()) { Type *GVTy = GV->getValueType(); if ( (ArrayTy = dyn_cast(GVTy)) ) { // A zeroinitializer for the array; there is no ConstantDataArray. Array = nullptr; } else { const DataLayout &DL = GV->getParent()->getDataLayout(); uint64_t SizeInBytes = DL.getTypeStoreSize(GVTy); uint64_t Length = SizeInBytes / (ElementSize / 8); if (Length <= Offset) return false; Slice.Array = nullptr; Slice.Offset = 0; Slice.Length = Length - Offset; return true; } } else { // This must be a ConstantDataArray. Array = dyn_cast(GV->getInitializer()); if (!Array) return false; ArrayTy = Array->getType(); } if (!ArrayTy->getElementType()->isIntegerTy(ElementSize)) return false; uint64_t NumElts = ArrayTy->getArrayNumElements(); if (Offset > NumElts) return false; Slice.Array = Array; Slice.Offset = Offset; Slice.Length = NumElts - Offset; 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) { ConstantDataArraySlice Slice; if (!getConstantDataArrayInfo(V, Slice, 8, Offset)) return false; if (Slice.Array == nullptr) { if (TrimAtNul) { Str = StringRef(); return true; } if (Slice.Length == 1) { Str = StringRef("", 1); return true; } // We cannot instantiate a StringRef as we do not have an appropriate string // of 0s at hand. return false; } // Start out with the entire array in the StringRef. Str = Slice.Array->getAsString(); // Skip over 'offset' bytes. Str = Str.substr(Slice.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, unsigned CharSize) { // 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, CharSize); 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, CharSize); if (Len1 == 0) return 0; uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs, CharSize); 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. ConstantDataArraySlice Slice; if (!getConstantDataArrayInfo(V, Slice, CharSize)) return 0; if (Slice.Array == nullptr) return 1; // Search for nul characters unsigned NullIndex = 0; for (unsigned E = Slice.Length; NullIndex < E; ++NullIndex) { if (Slice.Array->getElementAsInteger(Slice.Offset + NullIndex) == 0) break; } return NullIndex + 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, unsigned CharSize) { if (!V->getType()->isPointerTy()) return 0; SmallPtrSet PHIs; uint64_t Len = GetStringLengthH(V, PHIs, CharSize); // 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; } const Value * llvm::getArgumentAliasingToReturnedPointer(const CallBase *Call, bool MustPreserveNullness) { assert(Call && "getArgumentAliasingToReturnedPointer only works on nonnull calls"); if (const Value *RV = Call->getReturnedArgOperand()) return RV; // This can be used only as a aliasing property. if (isIntrinsicReturningPointerAliasingArgumentWithoutCapturing( Call, MustPreserveNullness)) return Call->getArgOperand(0); return nullptr; } bool llvm::isIntrinsicReturningPointerAliasingArgumentWithoutCapturing( const CallBase *Call, bool MustPreserveNullness) { return Call->getIntrinsicID() == Intrinsic::launder_invariant_group || Call->getIntrinsicID() == Intrinsic::strip_invariant_group || Call->getIntrinsicID() == Intrinsic::aarch64_irg || Call->getIntrinsicID() == Intrinsic::aarch64_tagp || (!MustPreserveNullness && Call->getIntrinsicID() == Intrinsic::ptrmask); } /// \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 *Call = dyn_cast(V)) { // CaptureTracking can know about special capturing properties of some // intrinsics like launder.invariant.group, that can't be expressed with // the attributes, but have properties like returning aliasing pointer. // Because some analysis may assume that nocaptured pointer is not // returned from some special intrinsic (because function would have to // be marked with returns attribute), it is crucial to use this function // because it should be in sync with CaptureTracking. Not using it may // cause weird miscompilations where 2 aliasing pointers are assumed to // noalias. if (auto *RP = getArgumentAliasingToReturnedPointer(Call, false)) { V = RP; 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, I})) { V = Simplified; continue; } return V; } assert(V->getType()->isPointerTy() && "Unexpected operand type!"); } return V; } void llvm::GetUnderlyingObjects(const Value *V, SmallVectorImpl &Objects, const DataLayout &DL, LoopInfo *LI, unsigned MaxLookup) { SmallPtrSet Visited; SmallVector Worklist; Worklist.push_back(V); do { const Value *P = Worklist.pop_back_val(); P = GetUnderlyingObject(P, DL, MaxLookup); if (!Visited.insert(P).second) continue; if (auto *SI = dyn_cast(P)) { Worklist.push_back(SI->getTrueValue()); Worklist.push_back(SI->getFalseValue()); continue; } if (auto *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()); } /// This is the function that does the work of looking through basic /// ptrtoint+arithmetic+inttoptr sequences. static const Value *getUnderlyingObjectFromInt(const Value *V) { do { if (const Operator *U = dyn_cast(V)) { // If we find a ptrtoint, we can transfer control back to the // regular getUnderlyingObjectFromInt. if (U->getOpcode() == Instruction::PtrToInt) return U->getOperand(0); // If we find an add of a constant, a multiplied value, or a phi, it's // likely that the other operand will lead us to the base // object. We don't have to worry about the case where the // object address is somehow being computed by the multiply, // because our callers only care when the result is an // identifiable object. if (U->getOpcode() != Instruction::Add || (!isa(U->getOperand(1)) && Operator::getOpcode(U->getOperand(1)) != Instruction::Mul && !isa(U->getOperand(1)))) return V; V = U->getOperand(0); } else { return V; } assert(V->getType()->isIntegerTy() && "Unexpected operand type!"); } while (true); } /// This is a wrapper around GetUnderlyingObjects and adds support for basic /// ptrtoint+arithmetic+inttoptr sequences. /// It returns false if unidentified object is found in GetUnderlyingObjects. bool llvm::getUnderlyingObjectsForCodeGen(const Value *V, SmallVectorImpl &Objects, const DataLayout &DL) { SmallPtrSet Visited; SmallVector Working(1, V); do { V = Working.pop_back_val(); SmallVector Objs; GetUnderlyingObjects(V, Objs, DL); for (const Value *V : Objs) { if (!Visited.insert(V).second) continue; if (Operator::getOpcode(V) == Instruction::IntToPtr) { const Value *O = getUnderlyingObjectFromInt(cast(V)->getOperand(0)); if (O->getType()->isPointerTy()) { Working.push_back(O); continue; } } // If GetUnderlyingObjects fails to find an identifiable object, // getUnderlyingObjectsForCodeGen also fails for safety. if (!isIdentifiedObject(V)) { Objects.clear(); return false; } Objects.push_back(const_cast(V)); } } while (!Working.empty()); return true; } /// 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->isLifetimeStartOrEnd()) return false; } return true; } bool llvm::mustSuppressSpeculation(const LoadInst &LI) { if (!LI.isUnordered()) return true; const Function &F = *LI.getFunction(); // Speculative load may create a race that did not exist in the source. return F.hasFnAttribute(Attribute::SanitizeThread) || // Speculative load may load data from dirty regions. F.hasFnAttribute(Attribute::SanitizeAddress) || F.hasFnAttribute(Attribute::SanitizeHWAddress); } 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 (mustSuppressSpeculation(*LI)) return false; const DataLayout &DL = LI->getModule()->getDataLayout(); return isDereferenceableAndAlignedPointer( LI->getPointerOperand(), LI->getType(), MaybeAlign(LI->getAlignment()), DL, CtxI, DT); } case Instruction::Call: { auto *CI = cast(Inst); const Function *Callee = CI->getCalledFunction(); // The called function could have undefined behavior or side-effects, even // if marked readnone nounwind. return Callee && Callee->isSpeculatable(); } case Instruction::VAArg: case Instruction::Alloca: case Instruction::Invoke: case Instruction::CallBr: 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); } /// Convert ConstantRange OverflowResult into ValueTracking OverflowResult. static OverflowResult mapOverflowResult(ConstantRange::OverflowResult OR) { switch (OR) { case ConstantRange::OverflowResult::MayOverflow: return OverflowResult::MayOverflow; case ConstantRange::OverflowResult::AlwaysOverflowsLow: return OverflowResult::AlwaysOverflowsLow; case ConstantRange::OverflowResult::AlwaysOverflowsHigh: return OverflowResult::AlwaysOverflowsHigh; case ConstantRange::OverflowResult::NeverOverflows: return OverflowResult::NeverOverflows; } llvm_unreachable("Unknown OverflowResult"); } /// Combine constant ranges from computeConstantRange() and computeKnownBits(). static ConstantRange computeConstantRangeIncludingKnownBits( const Value *V, bool ForSigned, const DataLayout &DL, unsigned Depth, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, OptimizationRemarkEmitter *ORE = nullptr, bool UseInstrInfo = true) { KnownBits Known = computeKnownBits( V, DL, Depth, AC, CxtI, DT, ORE, UseInstrInfo); ConstantRange CR1 = ConstantRange::fromKnownBits(Known, ForSigned); ConstantRange CR2 = computeConstantRange(V, UseInstrInfo); ConstantRange::PreferredRangeType RangeType = ForSigned ? ConstantRange::Signed : ConstantRange::Unsigned; return CR1.intersectWith(CR2, RangeType); } OverflowResult llvm::computeOverflowForUnsignedMul( const Value *LHS, const Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo) { KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT, nullptr, UseInstrInfo); KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT, nullptr, UseInstrInfo); ConstantRange LHSRange = ConstantRange::fromKnownBits(LHSKnown, false); ConstantRange RHSRange = ConstantRange::fromKnownBits(RHSKnown, false); return mapOverflowResult(LHSRange.unsignedMulMayOverflow(RHSRange)); } OverflowResult llvm::computeOverflowForSignedMul(const Value *LHS, const Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo) { // 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 sign 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(); // Note that underestimating the number of sign bits gives a more // conservative answer. unsigned SignBits = ComputeNumSignBits(LHS, DL, 0, AC, CxtI, DT) + ComputeNumSignBits(RHS, DL, 0, AC, CxtI, DT); // First handle the easy case: if we have enough sign bits there's // definitely no overflow. if (SignBits > BitWidth + 1) return OverflowResult::NeverOverflows; // There are two ambiguous cases where there can be no overflow: // SignBits == BitWidth + 1 and // SignBits == BitWidth // The second case is difficult to check, therefore we only handle the // first case. if (SignBits == BitWidth + 1) { // It overflows only when both arguments are negative and the true // product is exactly the minimum negative number. // E.g. mul i16 with 17 sign bits: 0xff00 * 0xff80 = 0x8000 // For simplicity we just check if at least one side is not negative. KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT, nullptr, UseInstrInfo); KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT, nullptr, UseInstrInfo); if (LHSKnown.isNonNegative() || RHSKnown.isNonNegative()) return OverflowResult::NeverOverflows; } return OverflowResult::MayOverflow; } OverflowResult llvm::computeOverflowForUnsignedAdd( const Value *LHS, const Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT, bool UseInstrInfo) { ConstantRange LHSRange = computeConstantRangeIncludingKnownBits( LHS, /*ForSigned=*/false, DL, /*Depth=*/0, AC, CxtI, DT, nullptr, UseInstrInfo); ConstantRange RHSRange = computeConstantRangeIncludingKnownBits( RHS, /*ForSigned=*/false, DL, /*Depth=*/0, AC, CxtI, DT, nullptr, UseInstrInfo); return mapOverflowResult(LHSRange.unsignedAddMayOverflow(RHSRange)); } 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; } // If LHS and RHS each have at least two sign bits, the addition will look // like // // XX..... + // YY..... // // If the carry into the most significant position is 0, X and Y can't both // be 1 and therefore the carry out of the addition is also 0. // // If the carry into the most significant position is 1, X and Y can't both // be 0 and therefore the carry out of the addition is also 1. // // Since the carry into the most significant position is always equal to // the carry out of the addition, there is no signed overflow. if (ComputeNumSignBits(LHS, DL, 0, AC, CxtI, DT) > 1 && ComputeNumSignBits(RHS, DL, 0, AC, CxtI, DT) > 1) return OverflowResult::NeverOverflows; ConstantRange LHSRange = computeConstantRangeIncludingKnownBits( LHS, /*ForSigned=*/true, DL, /*Depth=*/0, AC, CxtI, DT); ConstantRange RHSRange = computeConstantRangeIncludingKnownBits( RHS, /*ForSigned=*/true, DL, /*Depth=*/0, AC, CxtI, DT); OverflowResult OR = mapOverflowResult(LHSRange.signedAddMayOverflow(RHSRange)); if (OR != OverflowResult::MayOverflow) return OR; // 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. If this can be determined from the known bits of the // operands the above signedAddMayOverflow() check will have already done so. // The only other way to improve on the known bits is from an assumption, so // call computeKnownBitsFromAssume() directly. bool LHSOrRHSKnownNonNegative = (LHSRange.isAllNonNegative() || RHSRange.isAllNonNegative()); bool LHSOrRHSKnownNegative = (LHSRange.isAllNegative() || RHSRange.isAllNegative()); if (LHSOrRHSKnownNonNegative || LHSOrRHSKnownNegative) { KnownBits AddKnown(LHSRange.getBitWidth()); computeKnownBitsFromAssume( Add, AddKnown, /*Depth=*/0, Query(DL, AC, CxtI, DT, true)); if ((AddKnown.isNonNegative() && LHSOrRHSKnownNonNegative) || (AddKnown.isNegative() && LHSOrRHSKnownNegative)) return OverflowResult::NeverOverflows; } return OverflowResult::MayOverflow; } OverflowResult llvm::computeOverflowForUnsignedSub(const Value *LHS, const Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { ConstantRange LHSRange = computeConstantRangeIncludingKnownBits( LHS, /*ForSigned=*/false, DL, /*Depth=*/0, AC, CxtI, DT); ConstantRange RHSRange = computeConstantRangeIncludingKnownBits( RHS, /*ForSigned=*/false, DL, /*Depth=*/0, AC, CxtI, DT); return mapOverflowResult(LHSRange.unsignedSubMayOverflow(RHSRange)); } OverflowResult llvm::computeOverflowForSignedSub(const Value *LHS, const Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) { // If LHS and RHS each have at least two sign bits, the subtraction // cannot overflow. if (ComputeNumSignBits(LHS, DL, 0, AC, CxtI, DT) > 1 && ComputeNumSignBits(RHS, DL, 0, AC, CxtI, DT) > 1) return OverflowResult::NeverOverflows; ConstantRange LHSRange = computeConstantRangeIncludingKnownBits( LHS, /*ForSigned=*/true, DL, /*Depth=*/0, AC, CxtI, DT); ConstantRange RHSRange = computeConstantRangeIncludingKnownBits( RHS, /*ForSigned=*/true, DL, /*Depth=*/0, AC, CxtI, DT); return mapOverflowResult(LHSRange.signedSubMayOverflow(RHSRange)); } bool llvm::isOverflowIntrinsicNoWrap(const WithOverflowInst *WO, const DominatorTree &DT) { SmallVector GuardingBranches; SmallVector Results; for (const User *U : WO->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 llvm::any_of(GuardingBranches, AllUsesGuardedByBranch); } bool llvm::isGuaranteedNotToBeUndefOrPoison(const Value *V) { // If the value is a freeze instruction, then it can never // be undef or poison. if (isa(V)) return true; // TODO: Some instructions are guaranteed to return neither undef // nor poison if their arguments are not poison/undef. // TODO: Deal with other Constant subclasses. if (isa(V) || isa(V)) return true; return false; } 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) { // Note: 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 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; // A function which doens't throw and has "willreturn" attribute will // always return. if (CS.hasFnAttr(Attribute::WillReturn)) return true; // 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(); } // Other instructions return normally. return true; } bool llvm::isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB) { // TODO: This is slightly conservative for invoke instruction since exiting // via an exception *is* normal control for them. for (auto I = BB->begin(), E = BB->end(); I != E; ++I) if (!isGuaranteedToTransferExecutionToSuccessor(&*I)) return false; 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) { // TODO: This should include all instructions apart from phis, selects and // call-like instructions. 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: // Note: It's really tempting to think that a conditional branch or // switch should be listed here, but that's incorrect. It's not // branching off of poison which is UB, it is executing a side effecting // instruction which follows the branch. return nullptr; } } bool llvm::mustTriggerUB(const Instruction *I, const SmallSet& KnownPoison) { auto *NotPoison = getGuaranteedNonFullPoisonOp(I); return (NotPoison && KnownPoison.count(NotPoison)); } bool llvm::programUndefinedIfFullPoison(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) { if (mustTriggerUB(&I, YieldsPoison)) 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(); if (auto *C = dyn_cast(V)) { if (!C->getElementType()->isFloatingPointTy()) return false; for (unsigned I = 0, E = C->getNumElements(); I < E; ++I) { if (C->getElementAsAPFloat(I).isNaN()) return false; } return true; } return false; } static bool isKnownNonZero(const Value *V) { if (auto *C = dyn_cast(V)) return !C->isZero(); if (auto *C = dyn_cast(V)) { if (!C->getElementType()->isFloatingPointTy()) return false; for (unsigned I = 0, E = C->getNumElements(); I < E; ++I) { if (C->getElementAsAPFloat(I).isZero()) return false; } return true; } return false; } /// Match clamp pattern for float types without care about NaNs or signed zeros. /// Given non-min/max outer cmp/select from the clamp pattern this /// function recognizes if it can be substitued by a "canonical" min/max /// pattern. static SelectPatternResult matchFastFloatClamp(CmpInst::Predicate Pred, Value *CmpLHS, Value *CmpRHS, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS) { // Try to match // X < C1 ? C1 : Min(X, C2) --> Max(C1, Min(X, C2)) // X > C1 ? C1 : Max(X, C2) --> Min(C1, Max(X, C2)) // and return description of the outer Max/Min. // First, check if select has inverse order: if (CmpRHS == FalseVal) { std::swap(TrueVal, FalseVal); Pred = CmpInst::getInversePredicate(Pred); } // Assume success now. If there's no match, callers should not use these anyway. LHS = TrueVal; RHS = FalseVal; const APFloat *FC1; if (CmpRHS != TrueVal || !match(CmpRHS, m_APFloat(FC1)) || !FC1->isFinite()) return {SPF_UNKNOWN, SPNB_NA, false}; const APFloat *FC2; switch (Pred) { case CmpInst::FCMP_OLT: case CmpInst::FCMP_OLE: case CmpInst::FCMP_ULT: case CmpInst::FCMP_ULE: if (match(FalseVal, m_CombineOr(m_OrdFMin(m_Specific(CmpLHS), m_APFloat(FC2)), m_UnordFMin(m_Specific(CmpLHS), m_APFloat(FC2)))) && FC1->compare(*FC2) == APFloat::cmpResult::cmpLessThan) return {SPF_FMAXNUM, SPNB_RETURNS_ANY, false}; break; case CmpInst::FCMP_OGT: case CmpInst::FCMP_OGE: case CmpInst::FCMP_UGT: case CmpInst::FCMP_UGE: if (match(FalseVal, m_CombineOr(m_OrdFMax(m_Specific(CmpLHS), m_APFloat(FC2)), m_UnordFMax(m_Specific(CmpLHS), m_APFloat(FC2)))) && FC1->compare(*FC2) == APFloat::cmpResult::cmpGreaterThan) return {SPF_FMINNUM, SPNB_RETURNS_ANY, false}; break; default: break; } return {SPF_UNKNOWN, SPNB_NA, false}; } /// Recognize variations of: /// CLAMP(v,l,h) ==> ((v) < (l) ? (l) : ((v) > (h) ? (h) : (v))) static SelectPatternResult matchClamp(CmpInst::Predicate Pred, Value *CmpLHS, Value *CmpRHS, Value *TrueVal, Value *FalseVal) { // Swap the select operands and predicate to match the patterns below. if (CmpRHS != TrueVal) { Pred = ICmpInst::getSwappedPredicate(Pred); std::swap(TrueVal, FalseVal); } 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}; } return {SPF_UNKNOWN, SPNB_NA, false}; } /// Recognize variations of: /// a < c ? min(a,b) : min(b,c) ==> min(min(a,b),min(b,c)) static SelectPatternResult matchMinMaxOfMinMax(CmpInst::Predicate Pred, Value *CmpLHS, Value *CmpRHS, Value *TVal, Value *FVal, unsigned Depth) { // TODO: Allow FP min/max with nnan/nsz. assert(CmpInst::isIntPredicate(Pred) && "Expected integer comparison"); Value *A = nullptr, *B = nullptr; SelectPatternResult L = matchSelectPattern(TVal, A, B, nullptr, Depth + 1); if (!SelectPatternResult::isMinOrMax(L.Flavor)) return {SPF_UNKNOWN, SPNB_NA, false}; Value *C = nullptr, *D = nullptr; SelectPatternResult R = matchSelectPattern(FVal, C, D, nullptr, Depth + 1); if (L.Flavor != R.Flavor) return {SPF_UNKNOWN, SPNB_NA, false}; // We have something like: x Pred y ? min(a, b) : min(c, d). // Try to match the compare to the min/max operations of the select operands. // First, make sure we have the right compare predicate. switch (L.Flavor) { case SPF_SMIN: if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE) { Pred = ICmpInst::getSwappedPredicate(Pred); std::swap(CmpLHS, CmpRHS); } if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE) break; return {SPF_UNKNOWN, SPNB_NA, false}; case SPF_SMAX: if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE) { Pred = ICmpInst::getSwappedPredicate(Pred); std::swap(CmpLHS, CmpRHS); } if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE) break; return {SPF_UNKNOWN, SPNB_NA, false}; case SPF_UMIN: if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) { Pred = ICmpInst::getSwappedPredicate(Pred); std::swap(CmpLHS, CmpRHS); } if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) break; return {SPF_UNKNOWN, SPNB_NA, false}; case SPF_UMAX: if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) { Pred = ICmpInst::getSwappedPredicate(Pred); std::swap(CmpLHS, CmpRHS); } if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) break; return {SPF_UNKNOWN, SPNB_NA, false}; default: return {SPF_UNKNOWN, SPNB_NA, false}; } // If there is a common operand in the already matched min/max and the other // min/max operands match the compare operands (either directly or inverted), // then this is min/max of the same flavor. // a pred c ? m(a, b) : m(c, b) --> m(m(a, b), m(c, b)) // ~c pred ~a ? m(a, b) : m(c, b) --> m(m(a, b), m(c, b)) if (D == B) { if ((CmpLHS == A && CmpRHS == C) || (match(C, m_Not(m_Specific(CmpLHS))) && match(A, m_Not(m_Specific(CmpRHS))))) return {L.Flavor, SPNB_NA, false}; } // a pred d ? m(a, b) : m(b, d) --> m(m(a, b), m(b, d)) // ~d pred ~a ? m(a, b) : m(b, d) --> m(m(a, b), m(b, d)) if (C == B) { if ((CmpLHS == A && CmpRHS == D) || (match(D, m_Not(m_Specific(CmpLHS))) && match(A, m_Not(m_Specific(CmpRHS))))) return {L.Flavor, SPNB_NA, false}; } // b pred c ? m(a, b) : m(c, a) --> m(m(a, b), m(c, a)) // ~c pred ~b ? m(a, b) : m(c, a) --> m(m(a, b), m(c, a)) if (D == A) { if ((CmpLHS == B && CmpRHS == C) || (match(C, m_Not(m_Specific(CmpLHS))) && match(B, m_Not(m_Specific(CmpRHS))))) return {L.Flavor, SPNB_NA, false}; } // b pred d ? m(a, b) : m(a, d) --> m(m(a, b), m(a, d)) // ~d pred ~b ? m(a, b) : m(a, d) --> m(m(a, b), m(a, d)) if (C == A) { if ((CmpLHS == B && CmpRHS == D) || (match(D, m_Not(m_Specific(CmpLHS))) && match(B, m_Not(m_Specific(CmpRHS))))) return {L.Flavor, SPNB_NA, false}; } return {SPF_UNKNOWN, SPNB_NA, 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, unsigned Depth) { // Assume success. If there's no match, callers should not use these anyway. LHS = TrueVal; RHS = FalseVal; SelectPatternResult SPR = matchClamp(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal); if (SPR.Flavor != SelectPatternFlavor::SPF_UNKNOWN) return SPR; SPR = matchMinMaxOfMinMax(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal, Depth); if (SPR.Flavor != SelectPatternFlavor::SPF_UNKNOWN) return SPR; 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}; const APInt *C1; 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->isNullValue() && 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}; } bool llvm::isKnownNegation(const Value *X, const Value *Y, bool NeedNSW) { assert(X && Y && "Invalid operand"); // X = sub (0, Y) || X = sub nsw (0, Y) if ((!NeedNSW && match(X, m_Sub(m_ZeroInt(), m_Specific(Y)))) || (NeedNSW && match(X, m_NSWSub(m_ZeroInt(), m_Specific(Y))))) return true; // Y = sub (0, X) || Y = sub nsw (0, X) if ((!NeedNSW && match(Y, m_Sub(m_ZeroInt(), m_Specific(X)))) || (NeedNSW && match(Y, m_NSWSub(m_ZeroInt(), m_Specific(X))))) return true; // X = sub (A, B), Y = sub (B, A) || X = sub nsw (A, B), Y = sub nsw (B, A) Value *A, *B; return (!NeedNSW && (match(X, m_Sub(m_Value(A), m_Value(B))) && match(Y, m_Sub(m_Specific(B), m_Specific(A))))) || (NeedNSW && (match(X, m_NSWSub(m_Value(A), m_Value(B))) && match(Y, m_NSWSub(m_Specific(B), m_Specific(A))))); } static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred, FastMathFlags FMF, Value *CmpLHS, Value *CmpRHS, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS, unsigned Depth) { if (CmpInst::isFPPredicate(Pred)) { // IEEE-754 ignores the sign of 0.0 in comparisons. So if the select has one // 0.0 operand, set the compare's 0.0 operands to that same value for the // purpose of identifying min/max. Disregard vector constants with undefined // elements because those can not be back-propagated for analysis. Value *OutputZeroVal = nullptr; if (match(TrueVal, m_AnyZeroFP()) && !match(FalseVal, m_AnyZeroFP()) && !cast(TrueVal)->containsUndefElement()) OutputZeroVal = TrueVal; else if (match(FalseVal, m_AnyZeroFP()) && !match(TrueVal, m_AnyZeroFP()) && !cast(FalseVal)->containsUndefElement()) OutputZeroVal = FalseVal; if (OutputZeroVal) { if (match(CmpLHS, m_AnyZeroFP())) CmpLHS = OutputZeroVal; if (match(CmpRHS, m_AnyZeroFP())) CmpRHS = OutputZeroVal; } } LHS = CmpLHS; RHS = CmpRHS; // Signed zero 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 zero. switch (Pred) { default: break; // FIXME: Include OGT/OLT/UGT/ULT. case CmpInst::FCMP_OGE: case CmpInst::FCMP_OLE: case CmpInst::FCMP_UGE: case CmpInst::FCMP_ULE: if (!FMF.noSignedZeros() && !isKnownNonZero(CmpLHS) && !isKnownNonZero(CmpRHS)) return {SPF_UNKNOWN, SPNB_NA, false}; } SelectPatternNaNBehavior NaNBehavior = SPNB_NA; bool Ordered = false; // When given one NaN and one non-NaN input: // - maxnum/minnum (C99 fmaxf()/fminf()) return the non-NaN input. // - A simple C99 (a < b ? a : b) construction will return 'b' (as the // ordered comparison fails), which could be NaN or non-NaN. // so here we discover exactly what NaN behavior is required/accepted. if (CmpInst::isFPPredicate(Pred)) { bool LHSSafe = isKnownNonNaN(CmpLHS, FMF); bool RHSSafe = isKnownNonNaN(CmpRHS, FMF); if (LHSSafe && RHSSafe) { // Both operands are known non-NaN. NaNBehavior = SPNB_RETURNS_ANY; } else if (CmpInst::isOrdered(Pred)) { // An ordered comparison will return false when given a NaN, so it // returns the RHS. Ordered = true; if (LHSSafe) // LHS is non-NaN, so if RHS is NaN then NaN will be returned. NaNBehavior = SPNB_RETURNS_NAN; else if (RHSSafe) NaNBehavior = SPNB_RETURNS_OTHER; else // Completely unsafe. return {SPF_UNKNOWN, SPNB_NA, false}; } else { Ordered = false; // An unordered comparison will return true when given a NaN, so it // returns the LHS. if (LHSSafe) // LHS is non-NaN, so if RHS is NaN then non-NaN will be returned. NaNBehavior = SPNB_RETURNS_OTHER; else if (RHSSafe) NaNBehavior = SPNB_RETURNS_NAN; else // Completely unsafe. return {SPF_UNKNOWN, SPNB_NA, false}; } } if (TrueVal == CmpRHS && FalseVal == CmpLHS) { std::swap(CmpLHS, CmpRHS); Pred = CmpInst::getSwappedPredicate(Pred); if (NaNBehavior == SPNB_RETURNS_NAN) NaNBehavior = SPNB_RETURNS_OTHER; else if (NaNBehavior == SPNB_RETURNS_OTHER) NaNBehavior = SPNB_RETURNS_NAN; Ordered = !Ordered; } // ([if]cmp X, Y) ? X : Y if (TrueVal == CmpLHS && FalseVal == CmpRHS) { switch (Pred) { default: return {SPF_UNKNOWN, SPNB_NA, false}; // Equality. case ICmpInst::ICMP_UGT: case ICmpInst::ICMP_UGE: return {SPF_UMAX, SPNB_NA, false}; case ICmpInst::ICMP_SGT: case ICmpInst::ICMP_SGE: return {SPF_SMAX, SPNB_NA, false}; case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_ULE: return {SPF_UMIN, SPNB_NA, false}; case ICmpInst::ICMP_SLT: case ICmpInst::ICMP_SLE: return {SPF_SMIN, SPNB_NA, false}; case FCmpInst::FCMP_UGT: case FCmpInst::FCMP_UGE: case FCmpInst::FCMP_OGT: case FCmpInst::FCMP_OGE: return {SPF_FMAXNUM, NaNBehavior, Ordered}; case FCmpInst::FCMP_ULT: case FCmpInst::FCMP_ULE: case FCmpInst::FCMP_OLT: case FCmpInst::FCMP_OLE: return {SPF_FMINNUM, NaNBehavior, Ordered}; } } if (isKnownNegation(TrueVal, FalseVal)) { // Sign-extending LHS does not change its sign, so TrueVal/FalseVal can // match against either LHS or sext(LHS). auto MaybeSExtCmpLHS = m_CombineOr(m_Specific(CmpLHS), m_SExt(m_Specific(CmpLHS))); auto ZeroOrAllOnes = m_CombineOr(m_ZeroInt(), m_AllOnes()); auto ZeroOrOne = m_CombineOr(m_ZeroInt(), m_One()); if (match(TrueVal, MaybeSExtCmpLHS)) { // Set the return values. If the compare uses the negated value (-X >s 0), // swap the return values because the negated value is always 'RHS'. LHS = TrueVal; RHS = FalseVal; if (match(CmpLHS, m_Neg(m_Specific(FalseVal)))) std::swap(LHS, RHS); // (X >s 0) ? X : -X or (X >s -1) ? X : -X --> ABS(X) // (-X >s 0) ? -X : X or (-X >s -1) ? -X : X --> ABS(X) if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, ZeroOrAllOnes)) return {SPF_ABS, SPNB_NA, false}; // (X >=s 0) ? X : -X or (X >=s 1) ? X : -X --> ABS(X) if (Pred == ICmpInst::ICMP_SGE && match(CmpRHS, ZeroOrOne)) return {SPF_ABS, SPNB_NA, false}; // (X NABS(X) // (-X NABS(X) if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, ZeroOrOne)) return {SPF_NABS, SPNB_NA, false}; } else if (match(FalseVal, MaybeSExtCmpLHS)) { // Set the return values. If the compare uses the negated value (-X >s 0), // swap the return values because the negated value is always 'RHS'. LHS = FalseVal; RHS = TrueVal; if (match(CmpLHS, m_Neg(m_Specific(TrueVal)))) std::swap(LHS, RHS); // (X >s 0) ? -X : X or (X >s -1) ? -X : X --> NABS(X) // (-X >s 0) ? X : -X or (-X >s -1) ? X : -X --> NABS(X) if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, ZeroOrAllOnes)) return {SPF_NABS, SPNB_NA, false}; // (X ABS(X) // (-X ABS(X) if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, ZeroOrOne)) return {SPF_ABS, SPNB_NA, false}; } } if (CmpInst::isIntPredicate(Pred)) return matchMinMax(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal, LHS, RHS, Depth); // According to (IEEE 754-2008 5.3.1), minNum(0.0, -0.0) and similar // may return either -0.0 or 0.0, so fcmp/select pair has stricter // semantics than minNum. Be conservative in such case. if (NaNBehavior != SPNB_RETURNS_ANY || (!FMF.noSignedZeros() && !isKnownNonZero(CmpLHS) && !isKnownNonZero(CmpRHS))) return {SPF_UNKNOWN, SPNB_NA, false}; return matchFastFloatClamp(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal, LHS, RHS); } /// Helps to match a select pattern in case of a type mismatch. /// /// The function processes the case when type of true and false values of a /// select instruction differs from type of the cmp instruction operands because /// of a cast instruction. The function checks if it is legal to move the cast /// operation after "select". If yes, it returns the new second value of /// "select" (with the assumption that cast is moved): /// 1. As operand of cast instruction when both values of "select" are same cast /// instructions. /// 2. As restored constant (by applying reverse cast operation) when the first /// value of the "select" is a cast operation and the second value is a /// constant. /// NOTE: We return only the new second value because the first value could be /// accessed as operand of cast instruction. static Value *lookThroughCast(CmpInst *CmpI, Value *V1, Value *V2, Instruction::CastOps *CastOp) { auto *Cast1 = dyn_cast(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: Constant *CmpConst; if (match(CmpI->getOperand(1), m_Constant(CmpConst)) && CmpConst->getType() == SrcTy) { // Here we have the following case: // // %cond = cmp iN %x, CmpConst // %tr = trunc iN %x to iK // %narrowsel = select i1 %cond, iK %t, iK C // // We can always move trunc after select operation: // // %cond = cmp iN %x, CmpConst // %widesel = select i1 %cond, iN %x, iN CmpConst // %tr = trunc iN %widesel to iK // // Note that C could be extended in any way because we don't care about // upper bits after truncation. It can't be abs pattern, because it would // look like: // // select i1 %cond, x, -x. // // So only min/max pattern could be matched. Such match requires widened C // == CmpConst. That is why set widened C = CmpConst, condition trunc // CmpConst == C is checked below. CastedTo = CmpConst; } else { 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, unsigned Depth) { if (Depth >= MaxDepth) return {SPF_UNKNOWN, SPNB_NA, false}; 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}; Value *TrueVal = SI->getTrueValue(); Value *FalseVal = SI->getFalseValue(); return llvm::matchDecomposedSelectPattern(CmpI, TrueVal, FalseVal, LHS, RHS, CastOp, Depth); } SelectPatternResult llvm::matchDecomposedSelectPattern( CmpInst *CmpI, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS, Instruction::CastOps *CastOp, unsigned Depth) { CmpInst::Predicate Pred = CmpI->getPredicate(); Value *CmpLHS = CmpI->getOperand(0); Value *CmpRHS = CmpI->getOperand(1); 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)) { // If this is a potential fmin/fmax with a cast to integer, then ignore // -0.0 because there is no corresponding integer value. if (*CastOp == Instruction::FPToSI || *CastOp == Instruction::FPToUI) FMF.setNoSignedZeros(); return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, cast(TrueVal)->getOperand(0), C, LHS, RHS, Depth); } if (Value *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp)) { // If this is a potential fmin/fmax with a cast to integer, then ignore // -0.0 because there is no corresponding integer value. if (*CastOp == Instruction::FPToSI || *CastOp == Instruction::FPToUI) FMF.setNoSignedZeros(); return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, C, cast(FalseVal)->getOperand(0), LHS, RHS, Depth); } } return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, TrueVal, FalseVal, LHS, RHS, Depth); } CmpInst::Predicate llvm::getMinMaxPred(SelectPatternFlavor SPF, bool Ordered) { if (SPF == SPF_SMIN) return ICmpInst::ICMP_SLT; if (SPF == SPF_UMIN) return ICmpInst::ICMP_ULT; if (SPF == SPF_SMAX) return ICmpInst::ICMP_SGT; if (SPF == SPF_UMAX) return ICmpInst::ICMP_UGT; if (SPF == SPF_FMINNUM) return Ordered ? FCmpInst::FCMP_OLT : FCmpInst::FCMP_ULT; if (SPF == SPF_FMAXNUM) return Ordered ? FCmpInst::FCMP_OGT : FCmpInst::FCMP_UGT; llvm_unreachable("unhandled!"); } SelectPatternFlavor llvm::getInverseMinMaxFlavor(SelectPatternFlavor SPF) { if (SPF == SPF_SMIN) return SPF_SMAX; if (SPF == SPF_UMIN) return SPF_UMAX; if (SPF == SPF_SMAX) return SPF_SMIN; if (SPF == SPF_UMAX) return SPF_UMIN; llvm_unreachable("unhandled!"); } CmpInst::Predicate llvm::getInverseMinMaxPred(SelectPatternFlavor SPF) { return getMinMaxPred(getInverseMinMaxFlavor(SPF)); } /// 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) { 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)))) { KnownBits Known(CA->getBitWidth()); computeKnownBits(X, Known, DL, Depth + 1, /*AC*/ nullptr, /*CxtI*/ nullptr, /*DT*/ nullptr); if (CA->isSubsetOf(Known.Zero) && CB->isSubsetOf(Known.Zero)) 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) { switch (Pred) { default: return None; case CmpInst::ICMP_SLT: case CmpInst::ICMP_SLE: if (isTruePredicate(CmpInst::ICMP_SLE, BLHS, ALHS, DL, Depth) && isTruePredicate(CmpInst::ICMP_SLE, ARHS, BRHS, DL, Depth)) return true; return None; case CmpInst::ICMP_ULT: case CmpInst::ICMP_ULE: if (isTruePredicate(CmpInst::ICMP_ULE, BLHS, ALHS, DL, Depth) && isTruePredicate(CmpInst::ICMP_ULE, ARHS, BRHS, DL, Depth)) 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 X, Y" implies "icmp2 BPred X, Y" is true. /// Return false if "icmp1 APred X, Y" implies "icmp2 BPred X, Y" is false. /// Otherwise, return None if we can't infer anything. static Optional isImpliedCondMatchingOperands(CmpInst::Predicate APred, CmpInst::Predicate BPred, bool AreSwappedOps) { // Canonicalize the predicate as if the operands were not commuted. if (AreSwappedOps) BPred = ICmpInst::getSwappedPredicate(BPred); if (CmpInst::isImpliedTrueByMatchingCmp(APred, BPred)) return true; if (CmpInst::isImpliedFalseByMatchingCmp(APred, BPred)) return false; return None; } /// Return true if "icmp APred X, C1" implies "icmp BPred X, C2" is true. /// Return false if "icmp APred X, C1" implies "icmp BPred X, C2" is false. /// Otherwise, return None if we can't infer anything. static Optional isImpliedCondMatchingImmOperands(CmpInst::Predicate APred, const ConstantInt *C1, CmpInst::Predicate BPred, const ConstantInt *C2) { 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; } /// Return true if LHS implies RHS is true. Return false if LHS implies RHS is /// false. Otherwise, return None if we can't infer anything. static Optional isImpliedCondICmps(const ICmpInst *LHS, const ICmpInst *RHS, const DataLayout &DL, bool LHSIsTrue, unsigned Depth) { Value *ALHS = LHS->getOperand(0); Value *ARHS = LHS->getOperand(1); // The rest of the logic assumes the LHS condition is true. If that's not the // case, invert the predicate to make it so. ICmpInst::Predicate APred = LHSIsTrue ? LHS->getPredicate() : LHS->getInversePredicate(); Value *BLHS = RHS->getOperand(0); Value *BRHS = RHS->getOperand(1); ICmpInst::Predicate BPred = RHS->getPredicate(); // Can we infer anything when the two compares have matching operands? bool AreSwappedOps; if (isMatchingOps(ALHS, ARHS, BLHS, BRHS, AreSwappedOps)) { if (Optional Implication = isImpliedCondMatchingOperands( APred, BPred, AreSwappedOps)) 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, cast(ARHS), BPred, 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); return None; } /// Return true if LHS implies RHS is true. Return false if LHS implies RHS is /// false. Otherwise, return None if we can't infer anything. We expect the /// RHS to be an icmp and the LHS to be an 'and' or an 'or' instruction. static Optional isImpliedCondAndOr(const BinaryOperator *LHS, const ICmpInst *RHS, const DataLayout &DL, bool LHSIsTrue, unsigned Depth) { // The LHS must be an 'or' or an 'and' instruction. assert((LHS->getOpcode() == Instruction::And || LHS->getOpcode() == Instruction::Or) && "Expected LHS to be 'and' or 'or'."); assert(Depth <= MaxDepth && "Hit recursion limit"); // If the result of an 'or' is false, then we know both legs of the 'or' are // false. Similarly, if the result of an 'and' is true, then we know both // legs of the 'and' are true. Value *ALHS, *ARHS; if ((!LHSIsTrue && match(LHS, m_Or(m_Value(ALHS), m_Value(ARHS)))) || (LHSIsTrue && match(LHS, m_And(m_Value(ALHS), m_Value(ARHS))))) { // FIXME: Make this non-recursion. if (Optional Implication = isImpliedCondition(ALHS, RHS, DL, LHSIsTrue, Depth + 1)) return Implication; if (Optional Implication = isImpliedCondition(ARHS, RHS, DL, LHSIsTrue, Depth + 1)) return Implication; return None; } return None; } Optional llvm::isImpliedCondition(const Value *LHS, const Value *RHS, const DataLayout &DL, bool LHSIsTrue, unsigned Depth) { // Bail out when we hit the limit. if (Depth == MaxDepth) return None; // 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->isIntOrIntVectorTy(1) && "Expected integer type only!"); // LHS ==> RHS by definition if (LHS == RHS) return LHSIsTrue; // FIXME: Extending the code below to handle vectors. if (OpTy->isVectorTy()) return None; assert(OpTy->isIntegerTy(1) && "implied by above"); // Both LHS and RHS are icmps. const ICmpInst *LHSCmp = dyn_cast(LHS); const ICmpInst *RHSCmp = dyn_cast(RHS); if (LHSCmp && RHSCmp) return isImpliedCondICmps(LHSCmp, RHSCmp, DL, LHSIsTrue, Depth); // The LHS should be an 'or' or an 'and' instruction. We expect the RHS to be // an icmp. FIXME: Add support for and/or on the RHS. const BinaryOperator *LHSBO = dyn_cast(LHS); if (LHSBO && RHSCmp) { if ((LHSBO->getOpcode() == Instruction::And || LHSBO->getOpcode() == Instruction::Or)) return isImpliedCondAndOr(LHSBO, RHSCmp, DL, LHSIsTrue, Depth); } return None; } Optional llvm::isImpliedByDomCondition(const Value *Cond, const Instruction *ContextI, const DataLayout &DL) { assert(Cond->getType()->isIntOrIntVectorTy(1) && "Condition must be bool"); if (!ContextI || !ContextI->getParent()) return None; // TODO: This is a poor/cheap way to determine dominance. Should we use a // dominator tree (eg, from a SimplifyQuery) instead? const BasicBlock *ContextBB = ContextI->getParent(); const BasicBlock *PredBB = ContextBB->getSinglePredecessor(); if (!PredBB) return None; // We need a conditional branch in the predecessor. Value *PredCond; BasicBlock *TrueBB, *FalseBB; if (!match(PredBB->getTerminator(), m_Br(m_Value(PredCond), TrueBB, FalseBB))) return None; // The branch should get simplified. Don't bother simplifying this condition. if (TrueBB == FalseBB) return None; assert((TrueBB == ContextBB || FalseBB == ContextBB) && "Predecessor block does not point to successor?"); // Is this condition implied by the predecessor condition? bool CondIsTrue = TrueBB == ContextBB; return isImpliedCondition(PredCond, Cond, DL, CondIsTrue); } static void setLimitsForBinOp(const BinaryOperator &BO, APInt &Lower, APInt &Upper, const InstrInfoQuery &IIQ) { unsigned Width = Lower.getBitWidth(); const APInt *C; switch (BO.getOpcode()) { case Instruction::Add: if (match(BO.getOperand(1), m_APInt(C)) && !C->isNullValue()) { // FIXME: If we have both nuw and nsw, we should reduce the range further. if (IIQ.hasNoUnsignedWrap(cast(&BO))) { // 'add nuw x, C' produces [C, UINT_MAX]. Lower = *C; } else if (IIQ.hasNoSignedWrap(cast(&BO))) { if (C->isNegative()) { // 'add nsw x, -C' produces [SINT_MIN, SINT_MAX - C]. Lower = APInt::getSignedMinValue(Width); Upper = APInt::getSignedMaxValue(Width) + *C + 1; } else { // 'add nsw x, +C' produces [SINT_MIN + C, SINT_MAX]. Lower = APInt::getSignedMinValue(Width) + *C; Upper = APInt::getSignedMaxValue(Width) + 1; } } } break; case Instruction::And: if (match(BO.getOperand(1), m_APInt(C))) // 'and x, C' produces [0, C]. Upper = *C + 1; break; case Instruction::Or: if (match(BO.getOperand(1), m_APInt(C))) // 'or x, C' produces [C, UINT_MAX]. Lower = *C; break; case Instruction::AShr: if (match(BO.getOperand(1), m_APInt(C)) && C->ult(Width)) { // 'ashr x, C' produces [INT_MIN >> C, INT_MAX >> C]. Lower = APInt::getSignedMinValue(Width).ashr(*C); Upper = APInt::getSignedMaxValue(Width).ashr(*C) + 1; } else if (match(BO.getOperand(0), m_APInt(C))) { unsigned ShiftAmount = Width - 1; if (!C->isNullValue() && IIQ.isExact(&BO)) ShiftAmount = C->countTrailingZeros(); if (C->isNegative()) { // 'ashr C, x' produces [C, C >> (Width-1)] Lower = *C; Upper = C->ashr(ShiftAmount) + 1; } else { // 'ashr C, x' produces [C >> (Width-1), C] Lower = C->ashr(ShiftAmount); Upper = *C + 1; } } break; case Instruction::LShr: if (match(BO.getOperand(1), m_APInt(C)) && C->ult(Width)) { // 'lshr x, C' produces [0, UINT_MAX >> C]. Upper = APInt::getAllOnesValue(Width).lshr(*C) + 1; } else if (match(BO.getOperand(0), m_APInt(C))) { // 'lshr C, x' produces [C >> (Width-1), C]. unsigned ShiftAmount = Width - 1; if (!C->isNullValue() && IIQ.isExact(&BO)) ShiftAmount = C->countTrailingZeros(); Lower = C->lshr(ShiftAmount); Upper = *C + 1; } break; case Instruction::Shl: if (match(BO.getOperand(0), m_APInt(C))) { if (IIQ.hasNoUnsignedWrap(&BO)) { // 'shl nuw C, x' produces [C, C << CLZ(C)] Lower = *C; Upper = Lower.shl(Lower.countLeadingZeros()) + 1; } else if (BO.hasNoSignedWrap()) { // TODO: What if both nuw+nsw? if (C->isNegative()) { // 'shl nsw C, x' produces [C << CLO(C)-1, C] unsigned ShiftAmount = C->countLeadingOnes() - 1; Lower = C->shl(ShiftAmount); Upper = *C + 1; } else { // 'shl nsw C, x' produces [C, C << CLZ(C)-1] unsigned ShiftAmount = C->countLeadingZeros() - 1; Lower = *C; Upper = C->shl(ShiftAmount) + 1; } } } break; case Instruction::SDiv: if (match(BO.getOperand(1), m_APInt(C))) { APInt IntMin = APInt::getSignedMinValue(Width); APInt IntMax = APInt::getSignedMaxValue(Width); if (C->isAllOnesValue()) { // 'sdiv x, -1' produces [INT_MIN + 1, INT_MAX] // where C != -1 and C != 0 and C != 1 Lower = IntMin + 1; Upper = IntMax + 1; } else if (C->countLeadingZeros() < Width - 1) { // 'sdiv x, C' produces [INT_MIN / C, INT_MAX / C] // where C != -1 and C != 0 and C != 1 Lower = IntMin.sdiv(*C); Upper = IntMax.sdiv(*C); if (Lower.sgt(Upper)) std::swap(Lower, Upper); Upper = Upper + 1; assert(Upper != Lower && "Upper part of range has wrapped!"); } } else if (match(BO.getOperand(0), m_APInt(C))) { if (C->isMinSignedValue()) { // 'sdiv INT_MIN, x' produces [INT_MIN, INT_MIN / -2]. Lower = *C; Upper = Lower.lshr(1) + 1; } else { // 'sdiv C, x' produces [-|C|, |C|]. Upper = C->abs() + 1; Lower = (-Upper) + 1; } } break; case Instruction::UDiv: if (match(BO.getOperand(1), m_APInt(C)) && !C->isNullValue()) { // 'udiv x, C' produces [0, UINT_MAX / C]. Upper = APInt::getMaxValue(Width).udiv(*C) + 1; } else if (match(BO.getOperand(0), m_APInt(C))) { // 'udiv C, x' produces [0, C]. Upper = *C + 1; } break; case Instruction::SRem: if (match(BO.getOperand(1), m_APInt(C))) { // 'srem x, C' produces (-|C|, |C|). Upper = C->abs(); Lower = (-Upper) + 1; } break; case Instruction::URem: if (match(BO.getOperand(1), m_APInt(C))) // 'urem x, C' produces [0, C). Upper = *C; break; default: break; } } static void setLimitsForIntrinsic(const IntrinsicInst &II, APInt &Lower, APInt &Upper) { unsigned Width = Lower.getBitWidth(); const APInt *C; switch (II.getIntrinsicID()) { case Intrinsic::uadd_sat: // uadd.sat(x, C) produces [C, UINT_MAX]. if (match(II.getOperand(0), m_APInt(C)) || match(II.getOperand(1), m_APInt(C))) Lower = *C; break; case Intrinsic::sadd_sat: if (match(II.getOperand(0), m_APInt(C)) || match(II.getOperand(1), m_APInt(C))) { if (C->isNegative()) { // sadd.sat(x, -C) produces [SINT_MIN, SINT_MAX + (-C)]. Lower = APInt::getSignedMinValue(Width); Upper = APInt::getSignedMaxValue(Width) + *C + 1; } else { // sadd.sat(x, +C) produces [SINT_MIN + C, SINT_MAX]. Lower = APInt::getSignedMinValue(Width) + *C; Upper = APInt::getSignedMaxValue(Width) + 1; } } break; case Intrinsic::usub_sat: // usub.sat(C, x) produces [0, C]. if (match(II.getOperand(0), m_APInt(C))) Upper = *C + 1; // usub.sat(x, C) produces [0, UINT_MAX - C]. else if (match(II.getOperand(1), m_APInt(C))) Upper = APInt::getMaxValue(Width) - *C + 1; break; case Intrinsic::ssub_sat: if (match(II.getOperand(0), m_APInt(C))) { if (C->isNegative()) { // ssub.sat(-C, x) produces [SINT_MIN, -SINT_MIN + (-C)]. Lower = APInt::getSignedMinValue(Width); Upper = *C - APInt::getSignedMinValue(Width) + 1; } else { // ssub.sat(+C, x) produces [-SINT_MAX + C, SINT_MAX]. Lower = *C - APInt::getSignedMaxValue(Width); Upper = APInt::getSignedMaxValue(Width) + 1; } } else if (match(II.getOperand(1), m_APInt(C))) { if (C->isNegative()) { // ssub.sat(x, -C) produces [SINT_MIN - (-C), SINT_MAX]: Lower = APInt::getSignedMinValue(Width) - *C; Upper = APInt::getSignedMaxValue(Width) + 1; } else { // ssub.sat(x, +C) produces [SINT_MIN, SINT_MAX - C]. Lower = APInt::getSignedMinValue(Width); Upper = APInt::getSignedMaxValue(Width) - *C + 1; } } break; default: break; } } static void setLimitsForSelectPattern(const SelectInst &SI, APInt &Lower, APInt &Upper, const InstrInfoQuery &IIQ) { const Value *LHS = nullptr, *RHS = nullptr; SelectPatternResult R = matchSelectPattern(&SI, LHS, RHS); if (R.Flavor == SPF_UNKNOWN) return; unsigned BitWidth = SI.getType()->getScalarSizeInBits(); if (R.Flavor == SelectPatternFlavor::SPF_ABS) { // If the negation part of the abs (in RHS) has the NSW flag, // then the result of abs(X) is [0..SIGNED_MAX], // otherwise it is [0..SIGNED_MIN], as -SIGNED_MIN == SIGNED_MIN. Lower = APInt::getNullValue(BitWidth); if (match(RHS, m_Neg(m_Specific(LHS))) && IIQ.hasNoSignedWrap(cast(RHS))) Upper = APInt::getSignedMaxValue(BitWidth) + 1; else Upper = APInt::getSignedMinValue(BitWidth) + 1; return; } if (R.Flavor == SelectPatternFlavor::SPF_NABS) { // The result of -abs(X) is <= 0. Lower = APInt::getSignedMinValue(BitWidth); Upper = APInt(BitWidth, 1); return; } const APInt *C; if (!match(LHS, m_APInt(C)) && !match(RHS, m_APInt(C))) return; switch (R.Flavor) { case SPF_UMIN: Upper = *C + 1; break; case SPF_UMAX: Lower = *C; break; case SPF_SMIN: Lower = APInt::getSignedMinValue(BitWidth); Upper = *C + 1; break; case SPF_SMAX: Lower = *C; Upper = APInt::getSignedMaxValue(BitWidth) + 1; break; default: break; } } ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo) { assert(V->getType()->isIntOrIntVectorTy() && "Expected integer instruction"); const APInt *C; if (match(V, m_APInt(C))) return ConstantRange(*C); InstrInfoQuery IIQ(UseInstrInfo); unsigned BitWidth = V->getType()->getScalarSizeInBits(); APInt Lower = APInt(BitWidth, 0); APInt Upper = APInt(BitWidth, 0); if (auto *BO = dyn_cast(V)) setLimitsForBinOp(*BO, Lower, Upper, IIQ); else if (auto *II = dyn_cast(V)) setLimitsForIntrinsic(*II, Lower, Upper); else if (auto *SI = dyn_cast(V)) setLimitsForSelectPattern(*SI, Lower, Upper, IIQ); ConstantRange CR = ConstantRange::getNonEmpty(Lower, Upper); if (auto *I = dyn_cast(V)) if (auto *Range = IIQ.getMetadata(I, LLVMContext::MD_range)) CR = CR.intersectWith(getConstantRangeFromMetadata(*Range)); return CR; } static Optional getOffsetFromIndex(const GEPOperator *GEP, unsigned Idx, const DataLayout &DL) { // Skip over the first indices. gep_type_iterator GTI = gep_type_begin(GEP); for (unsigned i = 1; i != Idx; ++i, ++GTI) /*skip along*/; // Compute the offset implied by the rest of the indices. int64_t Offset = 0; for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) { ConstantInt *OpC = dyn_cast(GEP->getOperand(i)); if (!OpC) return None; if (OpC->isZero()) continue; // No offset. // Handle struct indices, which add their field offset to the pointer. if (StructType *STy = GTI.getStructTypeOrNull()) { Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue()); continue; } // Otherwise, we have a sequential type like an array or vector. Multiply // the index by the ElementSize. uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType()); Offset += Size * OpC->getSExtValue(); } return Offset; } Optional llvm::isPointerOffset(const Value *Ptr1, const Value *Ptr2, const DataLayout &DL) { Ptr1 = Ptr1->stripPointerCasts(); Ptr2 = Ptr2->stripPointerCasts(); // Handle the trivial case first. if (Ptr1 == Ptr2) { return 0; } const GEPOperator *GEP1 = dyn_cast(Ptr1); const GEPOperator *GEP2 = dyn_cast(Ptr2); // If one pointer is a GEP see if the GEP is a constant offset from the base, // as in "P" and "gep P, 1". // Also do this iteratively to handle the the following case: // Ptr_t1 = GEP Ptr1, c1 // Ptr_t2 = GEP Ptr_t1, c2 // Ptr2 = GEP Ptr_t2, c3 // where we will return c1+c2+c3. // TODO: Handle the case when both Ptr1 and Ptr2 are GEPs of some common base // -- replace getOffsetFromBase with getOffsetAndBase, check that the bases // are the same, and return the difference between offsets. auto getOffsetFromBase = [&DL](const GEPOperator *GEP, const Value *Ptr) -> Optional { const GEPOperator *GEP_T = GEP; int64_t OffsetVal = 0; bool HasSameBase = false; while (GEP_T) { auto Offset = getOffsetFromIndex(GEP_T, 1, DL); if (!Offset) return None; OffsetVal += *Offset; auto Op0 = GEP_T->getOperand(0)->stripPointerCasts(); if (Op0 == Ptr) { HasSameBase = true; break; } GEP_T = dyn_cast(Op0); } if (!HasSameBase) return None; return OffsetVal; }; if (GEP1) { auto Offset = getOffsetFromBase(GEP1, Ptr2); if (Offset) return -*Offset; } if (GEP2) { auto Offset = getOffsetFromBase(GEP2, Ptr1); if (Offset) return Offset; } // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical // base. After that base, they may have some number of common (and // potentially variable) indices. After that they handle some constant // offset, which determines their offset from each other. At this point, we // handle no other case. if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0)) return None; // Skip any common indices and track the GEP types. unsigned Idx = 1; for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx) if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx)) break; auto Offset1 = getOffsetFromIndex(GEP1, Idx, DL); auto Offset2 = getOffsetFromIndex(GEP2, Idx, DL); if (!Offset1 || !Offset2) return None; return *Offset2 - *Offset1; }