//===- 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/Support/DataTypes.h" namespace llvm { class Value; class Instruction; class APInt; class DataLayout; class StringRef; class MDNode; class TargetLibraryInfo; /// ComputeMaskedBits - Determine which of the bits specified in Mask are /// known to be either zero or one and return them in the KnownZero/KnownOne /// bit sets. This code only analyzes bits in Mask, in order to short-circuit /// processing. /// /// This function is defined on values with integer type, values with pointer /// type (but only if TD is non-null), 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. void ComputeMaskedBits(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout *TD = 0, unsigned Depth = 0); void computeMaskedBitsLoad(const MDNode &Ranges, APInt &KnownZero); /// ComputeSignBit - Determine whether the sign bit is known to be zero or /// one. Convenience wrapper around ComputeMaskedBits. void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne, const DataLayout *TD = 0, unsigned Depth = 0); /// 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 /// returns true if the given value is either a power of two or zero. bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero = false, unsigned Depth = 0); /// 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 *TD = 0, unsigned Depth = 0); /// 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 (but only if TD is non-null), 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 *TD = 0, unsigned Depth = 0); /// 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 *TD = 0, unsigned Depth = 0); /// 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, 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 = 0); /// 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 *TD); static inline const Value * GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, const DataLayout *TD) { return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD); } /// 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 *TD = 0, unsigned MaxLookup = 6); static inline const Value * GetUnderlyingObject(const Value *V, const DataLayout *TD = 0, unsigned MaxLookup = 6) { return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup); } /// GetUnderlyingObjects - This method is similar to GetUnderlyingObject /// except that it can look through phi and select instructions and return /// multiple objects. void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects, const DataLayout *TD = 0, unsigned MaxLookup = 6); /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer /// are lifetime markers. bool onlyUsedByLifetimeMarkers(const Value *V); /// 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. /// /// 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. /// However, 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 DataLayout *TD = 0); /// 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 = 0); } // end namespace llvm #endif