ValueTracking.h revision 5034dd318a9dfa0dc45a3ac01e58e60f2aa2498d
1//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file contains routines that help analyze properties that chains of 11// computations have. 12// 13//===----------------------------------------------------------------------===// 14 15#ifndef LLVM_ANALYSIS_VALUETRACKING_H 16#define LLVM_ANALYSIS_VALUETRACKING_H 17 18#include "llvm/Support/DataTypes.h" 19#include <string> 20 21namespace llvm { 22 template <typename T> class SmallVectorImpl; 23 class Value; 24 class Instruction; 25 class APInt; 26 class TargetData; 27 28 /// ComputeMaskedBits - Determine which of the bits specified in Mask are 29 /// known to be either zero or one and return them in the KnownZero/KnownOne 30 /// bit sets. This code only analyzes bits in Mask, in order to short-circuit 31 /// processing. 32 /// 33 /// This function is defined on values with integer type, values with pointer 34 /// type (but only if TD is non-null), and vectors of integers. In the case 35 /// where V is a vector, the mask, known zero, and known one values are the 36 /// same width as the vector element, and the bit is set only if it is true 37 /// for all of the elements in the vector. 38 void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero, 39 APInt &KnownOne, const TargetData *TD = 0, 40 unsigned Depth = 0); 41 42 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use 43 /// this predicate to simplify operations downstream. Mask is known to be 44 /// zero for bits that V cannot have. 45 /// 46 /// This function is defined on values with integer type, values with pointer 47 /// type (but only if TD is non-null), and vectors of integers. In the case 48 /// where V is a vector, the mask, known zero, and known one values are the 49 /// same width as the vector element, and the bit is set only if it is true 50 /// for all of the elements in the vector. 51 bool MaskedValueIsZero(Value *V, const APInt &Mask, 52 const TargetData *TD = 0, unsigned Depth = 0); 53 54 55 /// ComputeNumSignBits - Return the number of times the sign bit of the 56 /// register is replicated into the other bits. We know that at least 1 bit 57 /// is always equal to the sign bit (itself), but other cases can give us 58 /// information. For example, immediately after an "ashr X, 2", we know that 59 /// the top 3 bits are all equal to each other, so we return 3. 60 /// 61 /// 'Op' must have a scalar integer type. 62 /// 63 unsigned ComputeNumSignBits(Value *Op, const TargetData *TD = 0, 64 unsigned Depth = 0); 65 66 /// ComputeMultiple - This function computes the integer multiple of Base that 67 /// equals V. If successful, it returns true and returns the multiple in 68 /// Multiple. If unsuccessful, it returns false. Also, if V can be 69 /// simplified to an integer, then the simplified V is returned in Val. Look 70 /// through sext only if LookThroughSExt=true. 71 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, 72 bool LookThroughSExt = false, 73 unsigned Depth = 0); 74 75 /// CannotBeNegativeZero - Return true if we can prove that the specified FP 76 /// value is never equal to -0.0. 77 /// 78 bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0); 79 80 81 /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if 82 /// the scalar value indexed is already around as a register, for example if 83 /// it were inserted directly into the aggregrate. 84 /// 85 /// If InsertBefore is not null, this function will duplicate (modified) 86 /// insertvalues when a part of a nested struct is extracted. 87 Value *FindInsertedValue(Value *V, 88 const unsigned *idx_begin, 89 const unsigned *idx_end, 90 Instruction *InsertBefore = 0); 91 92 /// This is a convenience wrapper for finding values indexed by a single index 93 /// only. 94 inline Value *FindInsertedValue(Value *V, const unsigned Idx, 95 Instruction *InsertBefore = 0) { 96 const unsigned Idxs[1] = { Idx }; 97 return FindInsertedValue(V, &Idxs[0], &Idxs[1], InsertBefore); 98 } 99 100 /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if 101 /// it can be expressed as a base pointer plus a constant offset. Return the 102 /// base and offset to the caller. 103 Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 104 const TargetData &TD); 105 static inline const Value * 106 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, 107 const TargetData &TD) { 108 return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD); 109 } 110 111 /// GetConstantStringInfo - This function computes the length of a 112 /// null-terminated C string pointed to by V. If successful, it returns true 113 /// and returns the string in Str. If unsuccessful, it returns false. If 114 /// StopAtNul is set to true (the default), the returned string is truncated 115 /// by a nul character in the global. If StopAtNul is false, the nul 116 /// character is included in the result string. 117 bool GetConstantStringInfo(const Value *V, std::string &Str, 118 uint64_t Offset = 0, 119 bool StopAtNul = true); 120 121 /// GetStringLength - If we can compute the length of the string pointed to by 122 /// the specified pointer, return 'len+1'. If we can't, return 0. 123 uint64_t GetStringLength(Value *V); 124 125 /// GetUnderlyingObject - This method strips off any GEP address adjustments 126 /// and pointer casts from the specified value, returning the original object 127 /// being addressed. Note that the returned value has pointer type if the 128 /// specified value does. If the MaxLookup value is non-zero, it limits the 129 /// number of instructions to be stripped off. 130 Value *GetUnderlyingObject(Value *V, unsigned MaxLookup = 6); 131 static inline const Value * 132 GetUnderlyingObject(const Value *V, unsigned MaxLookup = 6) { 133 return GetUnderlyingObject(const_cast<Value *>(V), MaxLookup); 134 } 135 136} // end namespace llvm 137 138#endif 139