ValueTracking.h revision bd1801b5553c8be3960255a92738464e0010b6f6
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 /// isBytewiseValue - If the specified value can be set by repeating the same 81 /// byte in memory, return the i8 value that it is represented with. This is 82 /// true for all i8 values obviously, but is also true for i32 0, i32 -1, 83 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated 84 /// byte store (e.g. i16 0x1234), return null. 85 Value *isBytewiseValue(Value *V); 86 87 /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if 88 /// the scalar value indexed is already around as a register, for example if 89 /// it were inserted directly into the aggregrate. 90 /// 91 /// If InsertBefore is not null, this function will duplicate (modified) 92 /// insertvalues when a part of a nested struct is extracted. 93 Value *FindInsertedValue(Value *V, 94 const unsigned *idx_begin, 95 const unsigned *idx_end, 96 Instruction *InsertBefore = 0); 97 98 /// This is a convenience wrapper for finding values indexed by a single index 99 /// only. 100 inline Value *FindInsertedValue(Value *V, const unsigned Idx, 101 Instruction *InsertBefore = 0) { 102 const unsigned Idxs[1] = { Idx }; 103 return FindInsertedValue(V, &Idxs[0], &Idxs[1], InsertBefore); 104 } 105 106 /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if 107 /// it can be expressed as a base pointer plus a constant offset. Return the 108 /// base and offset to the caller. 109 Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 110 const TargetData &TD); 111 static inline const Value * 112 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, 113 const TargetData &TD) { 114 return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD); 115 } 116 117 /// GetConstantStringInfo - This function computes the length of a 118 /// null-terminated C string pointed to by V. If successful, it returns true 119 /// and returns the string in Str. If unsuccessful, it returns false. If 120 /// StopAtNul is set to true (the default), the returned string is truncated 121 /// by a nul character in the global. If StopAtNul is false, the nul 122 /// character is included in the result string. 123 bool GetConstantStringInfo(const Value *V, std::string &Str, 124 uint64_t Offset = 0, 125 bool StopAtNul = true); 126 127 /// GetStringLength - If we can compute the length of the string pointed to by 128 /// the specified pointer, return 'len+1'. If we can't, return 0. 129 uint64_t GetStringLength(Value *V); 130 131 /// GetUnderlyingObject - This method strips off any GEP address adjustments 132 /// and pointer casts from the specified value, returning the original object 133 /// being addressed. Note that the returned value has pointer type if the 134 /// specified value does. If the MaxLookup value is non-zero, it limits the 135 /// number of instructions to be stripped off. 136 Value *GetUnderlyingObject(Value *V, const TargetData *TD = 0, 137 unsigned MaxLookup = 6); 138 static inline const Value * 139 GetUnderlyingObject(const Value *V, const TargetData *TD = 0, 140 unsigned MaxLookup = 6) { 141 return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup); 142 } 143 144} // end namespace llvm 145 146#endif 147