1//===-- llvm/Use.h - Definition of the Use class ----------------*- 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 defines the Use class. The Use class represents the operand of an 11// instruction or some other User instance which refers to a Value. The Use 12// class keeps the "use list" of the referenced value up to date. 13// 14// Pointer tagging is used to efficiently find the User corresponding 15// to a Use without having to store a User pointer in every Use. A 16// User is preceded in memory by all the Uses corresponding to its 17// operands, and the low bits of one of the fields (Prev) of the Use 18// class are used to encode offsets to be able to find that User given 19// a pointer to any Use. For details, see: 20// 21// http://www.llvm.org/docs/ProgrammersManual.html#UserLayout 22// 23//===----------------------------------------------------------------------===// 24 25#ifndef LLVM_USE_H 26#define LLVM_USE_H 27 28#include "llvm/ADT/PointerIntPair.h" 29#include <cstddef> 30#include <iterator> 31 32namespace llvm { 33 34class Value; 35class User; 36class Use; 37template<typename> 38struct simplify_type; 39 40// Use** is only 4-byte aligned. 41template<> 42class PointerLikeTypeTraits<Use**> { 43public: 44 static inline void *getAsVoidPointer(Use** P) { return P; } 45 static inline Use **getFromVoidPointer(void *P) { 46 return static_cast<Use**>(P); 47 } 48 enum { NumLowBitsAvailable = 2 }; 49}; 50 51//===----------------------------------------------------------------------===// 52// Use Class 53//===----------------------------------------------------------------------===// 54 55/// Use is here to make keeping the "use" list of a Value up-to-date really 56/// easy. 57class Use { 58public: 59 /// swap - provide a fast substitute to std::swap<Use> 60 /// that also works with less standard-compliant compilers 61 void swap(Use &RHS); 62 63 // A type for the word following an array of hung-off Uses in memory, which is 64 // a pointer back to their User with the bottom bit set. 65 typedef PointerIntPair<User*, 1, unsigned> UserRef; 66 67private: 68 /// Copy ctor - do not implement 69 Use(const Use &U); 70 71 /// Destructor - Only for zap() 72 ~Use() { 73 if (Val) removeFromList(); 74 } 75 76 enum PrevPtrTag { zeroDigitTag 77 , oneDigitTag 78 , stopTag 79 , fullStopTag }; 80 81 /// Constructor 82 Use(PrevPtrTag tag) : Val(0) { 83 Prev.setInt(tag); 84 } 85 86public: 87 /// Normally Use will just implicitly convert to a Value* that it holds. 88 operator Value*() const { return Val; } 89 90 /// If implicit conversion to Value* doesn't work, the get() method returns 91 /// the Value*. 92 Value *get() const { return Val; } 93 94 /// getUser - This returns the User that contains this Use. For an 95 /// instruction operand, for example, this will return the instruction. 96 User *getUser() const; 97 98 inline void set(Value *Val); 99 100 Value *operator=(Value *RHS) { 101 set(RHS); 102 return RHS; 103 } 104 const Use &operator=(const Use &RHS) { 105 set(RHS.Val); 106 return *this; 107 } 108 109 Value *operator->() { return Val; } 110 const Value *operator->() const { return Val; } 111 112 Use *getNext() const { return Next; } 113 114 115 /// initTags - initialize the waymarking tags on an array of Uses, so that 116 /// getUser() can find the User from any of those Uses. 117 static Use *initTags(Use *Start, Use *Stop); 118 119 /// zap - This is used to destroy Use operands when the number of operands of 120 /// a User changes. 121 static void zap(Use *Start, const Use *Stop, bool del = false); 122 123private: 124 const Use* getImpliedUser() const; 125 126 Value *Val; 127 Use *Next; 128 PointerIntPair<Use**, 2, PrevPtrTag> Prev; 129 130 void setPrev(Use **NewPrev) { 131 Prev.setPointer(NewPrev); 132 } 133 void addToList(Use **List) { 134 Next = *List; 135 if (Next) Next->setPrev(&Next); 136 setPrev(List); 137 *List = this; 138 } 139 void removeFromList() { 140 Use **StrippedPrev = Prev.getPointer(); 141 *StrippedPrev = Next; 142 if (Next) Next->setPrev(StrippedPrev); 143 } 144 145 friend class Value; 146}; 147 148// simplify_type - Allow clients to treat uses just like values when using 149// casting operators. 150template<> struct simplify_type<Use> { 151 typedef Value* SimpleType; 152 static SimpleType getSimplifiedValue(const Use &Val) { 153 return static_cast<SimpleType>(Val.get()); 154 } 155}; 156template<> struct simplify_type<const Use> { 157 typedef Value* SimpleType; 158 static SimpleType getSimplifiedValue(const Use &Val) { 159 return static_cast<SimpleType>(Val.get()); 160 } 161}; 162 163 164 165template<typename UserTy> // UserTy == 'User' or 'const User' 166class value_use_iterator : public std::iterator<std::forward_iterator_tag, 167 UserTy*, ptrdiff_t> { 168 typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super; 169 typedef value_use_iterator<UserTy> _Self; 170 171 Use *U; 172 explicit value_use_iterator(Use *u) : U(u) {} 173 friend class Value; 174public: 175 typedef typename super::reference reference; 176 typedef typename super::pointer pointer; 177 178 value_use_iterator(const _Self &I) : U(I.U) {} 179 value_use_iterator() {} 180 181 bool operator==(const _Self &x) const { 182 return U == x.U; 183 } 184 bool operator!=(const _Self &x) const { 185 return !operator==(x); 186 } 187 188 /// atEnd - return true if this iterator is equal to use_end() on the value. 189 bool atEnd() const { return U == 0; } 190 191 // Iterator traversal: forward iteration only 192 _Self &operator++() { // Preincrement 193 assert(U && "Cannot increment end iterator!"); 194 U = U->getNext(); 195 return *this; 196 } 197 _Self operator++(int) { // Postincrement 198 _Self tmp = *this; ++*this; return tmp; 199 } 200 201 // Retrieve a pointer to the current User. 202 UserTy *operator*() const { 203 assert(U && "Cannot dereference end iterator!"); 204 return U->getUser(); 205 } 206 207 UserTy *operator->() const { return operator*(); } 208 209 Use &getUse() const { return *U; } 210 211 /// getOperandNo - Return the operand # of this use in its User. Defined in 212 /// User.h 213 /// 214 unsigned getOperandNo() const; 215}; 216 217} // End llvm namespace 218 219#endif 220