//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file contains routines that help analyze properties that chains of // computations have. // //===----------------------------------------------------------------------===// #ifndef LLVM_ANALYSIS_VALUETRACKING_H #define LLVM_ANALYSIS_VALUETRACKING_H #include "llvm/ADT/ArrayRef.h" #include "llvm/IR/ConstantRange.h" #include "llvm/IR/Instruction.h" #include "llvm/Support/DataTypes.h" namespace llvm { class APInt; class AddOperator; class AssumptionCache; class DataLayout; class DominatorTree; class Instruction; class Loop; class LoopInfo; class MDNode; class StringRef; class TargetLibraryInfo; class Value; /// Determine which bits of V are known to be either zero or one and return /// them in the KnownZero/KnownOne bit sets. /// /// 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 known zero and known one values are the /// same width as the vector element, and the bit is set only if it is true /// for all of the elements in the vector. void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// Compute known bits from the range metadata. /// \p KnownZero the set of bits that are known to be zero /// \p KnownOne the set of bits that are known to be one void computeKnownBitsFromRangeMetadata(const MDNode &Ranges, APInt &KnownZero, APInt &KnownOne); /// Return true if LHS and RHS have no common bits set. bool haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// ComputeSignBit - Determine whether the sign bit is known to be zero or /// one. Convenience wrapper around computeKnownBits. void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne, const DataLayout &DL, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// isKnownToBeAPowerOfTwo - 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 type and vectors of integers. If 'OrZero' is set then /// return true if the given value is either a power of two or zero. bool isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL, bool OrZero = false, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// isKnownNonZero - Return true if the given value is known to be non-zero /// when defined. For vectors return true if every element is known to be /// non-zero when defined. Supports values with integer or pointer type and /// vectors of integers. bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// Returns true if the give value is known to be non-negative. bool isKnownNonNegative(Value *V, const DataLayout &DL, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// isKnownNonEqual - Return true if the given values are known to be /// non-equal when defined. Supports scalar integer types only. bool isKnownNonEqual(Value *V1, Value *V2, const DataLayout &DL, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use /// this predicate to simplify operations downstream. Mask is known to be /// zero for bits that V cannot have. /// /// This function is defined on values with integer type, values with pointer /// type, and vectors of integers. In the case /// where V is a vector, the mask, known zero, and known one values are the /// same width as the vector element, and the bit is set only if it is true /// for all of the elements in the vector. bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// ComputeNumSignBits - Return the number of times the sign bit of the /// register is replicated into the other bits. We know that at least 1 bit /// is always equal to the sign bit (itself), but other cases can give us /// information. For example, immediately after an "ashr X, 2", we know that /// the top 3 bits are all equal to each other, so we return 3. /// /// 'Op' must have a scalar integer type. /// unsigned ComputeNumSignBits(Value *Op, const DataLayout &DL, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// ComputeMultiple - 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. Also, if V can be /// simplified to an integer, then the simplified V is returned in Val. Look /// through sext only if LookThroughSExt=true. bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, bool LookThroughSExt = false, unsigned Depth = 0); /// CannotBeNegativeZero - Return true if we can prove that the specified FP /// value is never equal to -0.0. /// bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI, unsigned Depth = 0); /// CannotBeOrderedLessThanZero - Return true if we can prove that the /// specified FP value is either a NaN or never less than 0.0. /// bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI, unsigned Depth = 0); /// isBytewiseValue - If the specified value can be set by repeating the same /// byte in memory, return the i8 value that it is represented with. This is /// true for all i8 values obviously, but is also true for i32 0, i32 -1, /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated /// byte store (e.g. i16 0x1234), return null. Value *isBytewiseValue(Value *V); /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if /// the scalar value indexed is already around as a register, for example if /// it were inserted directly into the aggregrate. /// /// If InsertBefore is not null, this function will duplicate (modified) /// insertvalues when a part of a nested struct is extracted. Value *FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range, Instruction *InsertBefore = nullptr); /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if /// it can be expressed as a base pointer plus a constant offset. Return the /// base and offset to the caller. Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, const DataLayout &DL); static inline const Value * GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, const DataLayout &DL) { return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset, DL); } /// getConstantStringInfo - 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. This /// does not include the trailing nul character by default. If TrimAtNul is /// set to false, then this returns any trailing nul characters as well as any /// other characters that come after it. bool getConstantStringInfo(const Value *V, StringRef &Str, uint64_t Offset = 0, bool TrimAtNul = true); /// GetStringLength - 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 GetStringLength(Value *V); /// GetUnderlyingObject - This method strips off any GEP address adjustments /// and pointer casts from the specified value, returning the original object /// being addressed. Note that the returned value has pointer type if the /// specified value does. If the MaxLookup value is non-zero, it limits the /// number of instructions to be stripped off. Value *GetUnderlyingObject(Value *V, const DataLayout &DL, unsigned MaxLookup = 6); static inline const Value *GetUnderlyingObject(const Value *V, const DataLayout &DL, unsigned MaxLookup = 6) { return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup); } /// \brief This method is similar to GetUnderlyingObject except that it can /// look through phi and select instructions and return multiple objects. /// /// If LoopInfo is passed, loop phis are further analyzed. If a pointer /// accesses different objects in each iteration, we don't look through the /// phi node. E.g. consider this loop nest: /// /// int **A; /// for (i) /// for (j) { /// A[i][j] = A[i-1][j] * B[j] /// } /// /// This is transformed by Load-PRE to stash away A[i] for the next iteration /// of the outer loop: /// /// Curr = A[0]; // Prev_0 /// for (i: 1..N) { /// Prev = Curr; // Prev = PHI (Prev_0, Curr) /// Curr = A[i]; /// for (j: 0..N) { /// Curr[j] = Prev[j] * B[j] /// } /// } /// /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects /// should not assume that Curr and Prev share the same underlying object thus /// it shouldn't look through the phi above. void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects, const DataLayout &DL, LoopInfo *LI = nullptr, unsigned MaxLookup = 6); /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer /// are lifetime markers. bool onlyUsedByLifetimeMarkers(const Value *V); /// isDereferenceablePointer - Return true if this is always a dereferenceable /// pointer. If the context instruction is specified perform context-sensitive /// analysis and return true if the pointer is dereferenceable at the /// specified instruction. bool isDereferenceablePointer(const Value *V, const DataLayout &DL, const Instruction *CtxI = nullptr, const DominatorTree *DT = nullptr, const TargetLibraryInfo *TLI = nullptr); /// Returns true if V is always a dereferenceable pointer with alignment /// greater or equal than requested. If the context instruction is specified /// performs context-sensitive analysis and returns true if the pointer is /// dereferenceable at the specified instruction. bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align, const DataLayout &DL, const Instruction *CtxI = nullptr, const DominatorTree *DT = nullptr, const TargetLibraryInfo *TLI = nullptr); /// isSafeToSpeculativelyExecute - Return true if the instruction does not /// have any effects besides calculating the result and does not have /// undefined behavior. /// /// This method never returns true for an instruction that returns true for /// mayHaveSideEffects; however, this method also does some other checks in /// addition. It checks for undefined behavior, like dividing by zero or /// loading from an invalid pointer (but not for undefined results, like a /// shift with a shift amount larger than the width of the result). It checks /// for malloc and alloca because speculatively executing them might cause a /// memory leak. It also returns false for instructions related to control /// flow, specifically terminators and PHI nodes. /// /// If the CtxI is specified this method performs context-sensitive analysis /// and returns true if it is safe to execute the instruction immediately /// before the CtxI. /// /// If the CtxI is NOT specified this method only looks at the instruction /// itself and its operands, so if this method returns true, it is safe to /// move the instruction as long as the correct dominance relationships for /// the operands and users hold. /// /// This method can return true for instructions that read memory; /// for such instructions, moving them may change the resulting value. bool isSafeToSpeculativelyExecute(const Value *V, const Instruction *CtxI = nullptr, const DominatorTree *DT = nullptr, const TargetLibraryInfo *TLI = nullptr); /// Returns true if the result or effects of the given instructions \p I /// depend on or influence global memory. /// Memory dependence arises for example if the instruction reads from /// memory or may produce effects or undefined behaviour. Memory dependent /// instructions generally cannot be reorderd with respect to other memory /// dependent instructions or moved into non-dominated basic blocks. /// Instructions which just compute a value based on the values of their /// operands are not memory dependent. bool mayBeMemoryDependent(const Instruction &I); /// isKnownNonNull - Return true if this pointer couldn't possibly be null by /// its definition. This returns true for allocas, non-extern-weak globals /// and byval arguments. bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI = nullptr); /// isKnownNonNullAt - Return true if this pointer couldn't possibly be null. /// If the context instruction is specified perform context-sensitive analysis /// and return true if the pointer couldn't possibly be null at the specified /// instruction. bool isKnownNonNullAt(const Value *V, const Instruction *CtxI = nullptr, const DominatorTree *DT = nullptr, const TargetLibraryInfo *TLI = nullptr); /// Return true if it is valid to use the assumptions provided by an /// assume intrinsic, I, at the point in the control-flow identified by the /// context instruction, CxtI. bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, const DominatorTree *DT = nullptr); enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows }; OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT); OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT); OverflowResult computeOverflowForSignedAdd(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// This version also leverages the sign bit of Add if known. OverflowResult computeOverflowForSignedAdd(AddOperator *Add, const DataLayout &DL, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); /// Return true if this function can prove that the instruction I will /// always transfer execution to one of its successors (including the next /// instruction that follows within a basic block). E.g. this is not /// guaranteed for function calls that could loop infinitely. /// /// In other words, this function returns false for instructions that may /// transfer execution or fail to transfer execution in a way that is not /// captured in the CFG nor in the sequence of instructions within a basic /// block. /// /// Undefined behavior is assumed not to happen, so e.g. division is /// guaranteed to transfer execution to the following instruction even /// though division by zero might cause undefined behavior. bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I); /// Return true if this function can prove that the instruction I /// is executed for every iteration of the loop L. /// /// Note that this currently only considers the loop header. bool isGuaranteedToExecuteForEveryIteration(const Instruction *I, const Loop *L); /// Return true if this function can prove that I is guaranteed to yield /// full-poison (all bits poison) if at least one of its operands are /// full-poison (all bits poison). /// /// The exact rules for how poison propagates through instructions have /// not been settled as of 2015-07-10, so this function is conservative /// and only considers poison to be propagated in uncontroversial /// cases. There is no attempt to track values that may be only partially /// poison. bool propagatesFullPoison(const Instruction *I); /// Return either nullptr or an operand of I such that I will trigger /// undefined behavior if I is executed and that operand has a full-poison /// value (all bits poison). const Value *getGuaranteedNonFullPoisonOp(const Instruction *I); /// Return true if this function can prove that if PoisonI is executed /// and yields a full-poison value (all bits poison), then that will /// trigger undefined behavior. /// /// Note that this currently only considers the basic block that is /// the parent of I. bool isKnownNotFullPoison(const Instruction *PoisonI); /// \brief Specific patterns of select instructions we can match. enum SelectPatternFlavor { SPF_UNKNOWN = 0, SPF_SMIN, /// Signed minimum SPF_UMIN, /// Unsigned minimum SPF_SMAX, /// Signed maximum SPF_UMAX, /// Unsigned maximum SPF_FMINNUM, /// Floating point minnum SPF_FMAXNUM, /// Floating point maxnum SPF_ABS, /// Absolute value SPF_NABS /// Negated absolute value }; /// \brief Behavior when a floating point min/max is given one NaN and one /// non-NaN as input. enum SelectPatternNaNBehavior { SPNB_NA = 0, /// NaN behavior not applicable. SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN. SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN. SPNB_RETURNS_ANY /// Given one NaN input, can return either (or /// it has been determined that no operands can /// be NaN). }; struct SelectPatternResult { SelectPatternFlavor Flavor; SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is /// SPF_FMINNUM or SPF_FMAXNUM. bool Ordered; /// When implementing this min/max pattern as /// fcmp; select, does the fcmp have to be /// ordered? /// \brief Return true if \p SPF is a min or a max pattern. static bool isMinOrMax(SelectPatternFlavor SPF) { return !(SPF == SPF_UNKNOWN || SPF == SPF_ABS || SPF == SPF_NABS); } }; /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind /// and providing the out parameter results if we successfully match. /// /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does /// not match that of the original select. If this is the case, the cast /// operation (one of Trunc,SExt,Zext) that must be done to transform the /// type of LHS and RHS into the type of V is returned in CastOp. /// /// For example: /// %1 = icmp slt i32 %a, i32 4 /// %2 = sext i32 %a to i64 /// %3 = select i1 %1, i64 %2, i64 4 /// /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt /// SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, Instruction::CastOps *CastOp = nullptr); /// Parse out a conservative ConstantRange from !range metadata. /// /// E.g. if RangeMD is !{i32 0, i32 10, i32 15, i32 20} then return [0, 20). ConstantRange getConstantRangeFromMetadata(MDNode &RangeMD); /// Return true if RHS is known to be implied by LHS. A & B must be i1 /// (boolean) values or a vector of such values. Note that the truth table for /// implication is the same as <=u on i1 values (but not <=s!). The truth /// table for both is: /// | T | F (B) /// T | T | F /// F | T | T /// (A) bool isImpliedCondition(Value *LHS, Value *RHS, const DataLayout &DL, unsigned Depth = 0, AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr); } // end namespace llvm #endif