ValueTracking.h revision 43ea505fb07e303721d92f2b2bdda6e601868523
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/System/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 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose 81 /// it into a base pointer with a constant offset and a number of scaled 82 /// symbolic offsets. 83 /// 84 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale 85 /// in the VarIndices vector) are Value*'s that are known to be scaled by the 86 /// specified amount, but which may have other unrepresented high bits. As 87 /// such, the gep cannot necessarily be reconstructed from its decomposed 88 /// form. 89 /// 90 /// When TargetData is around, this function is capable of analyzing 91 /// everything that Value::getUnderlyingObject() can look through. When not, 92 /// it just looks through pointer casts. 93 /// 94 const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, 95 SmallVectorImpl<std::pair<const Value*, int64_t> > &VarIndices, 96 const TargetData *TD); 97 98 99 100 /// FindScalarValue - Given an aggregrate and an sequence of indices, see if 101 /// the scalar value indexed is already around as a register, for example if 102 /// it were inserted directly into the aggregrate. 103 /// 104 /// If InsertBefore is not null, this function will duplicate (modified) 105 /// insertvalues when a part of a nested struct is extracted. 106 Value *FindInsertedValue(Value *V, 107 const unsigned *idx_begin, 108 const unsigned *idx_end, 109 Instruction *InsertBefore = 0); 110 111 /// This is a convenience wrapper for finding values indexed by a single index 112 /// only. 113 inline Value *FindInsertedValue(Value *V, const unsigned Idx, 114 Instruction *InsertBefore = 0) { 115 const unsigned Idxs[1] = { Idx }; 116 return FindInsertedValue(V, &Idxs[0], &Idxs[1], InsertBefore); 117 } 118 119 /// GetConstantStringInfo - This function computes the length of a 120 /// null-terminated C string pointed to by V. If successful, it returns true 121 /// and returns the string in Str. If unsuccessful, it returns false. If 122 /// StopAtNul is set to true (the default), the returned string is truncated 123 /// by a nul character in the global. If StopAtNul is false, the nul 124 /// character is included in the result string. 125 bool GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset = 0, 126 bool StopAtNul = true); 127} // end namespace llvm 128 129#endif 130