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_IR_USE_H 26 #define LLVM_IR_USE_H 27 28 #include "llvm/ADT/PointerIntPair.h" 29 #include "llvm/Support/CBindingWrapping.h" 30 #include "llvm/Support/Compiler.h" 31 #include "llvm-c/Core.h" 32 #include <cstddef> 33 #include <iterator> 34 35 namespace llvm { 36 37 class Value; 38 class User; 39 class Use; 40 template<typename> 41 struct simplify_type; 42 43 // Use** is only 4-byte aligned. 44 template<> 45 class PointerLikeTypeTraits<Use**> { 46 public: getAsVoidPointer(Use ** P)47 static inline void *getAsVoidPointer(Use** P) { return P; } getFromVoidPointer(void * P)48 static inline Use **getFromVoidPointer(void *P) { 49 return static_cast<Use**>(P); 50 } 51 enum { NumLowBitsAvailable = 2 }; 52 }; 53 54 //===----------------------------------------------------------------------===// 55 // Use Class 56 //===----------------------------------------------------------------------===// 57 58 /// Use is here to make keeping the "use" list of a Value up-to-date really 59 /// easy. 60 class Use { 61 public: 62 /// swap - provide a fast substitute to std::swap<Use> 63 /// that also works with less standard-compliant compilers 64 void swap(Use &RHS); 65 66 // A type for the word following an array of hung-off Uses in memory, which is 67 // a pointer back to their User with the bottom bit set. 68 typedef PointerIntPair<User*, 1, unsigned> UserRef; 69 70 private: 71 Use(const Use &U) LLVM_DELETED_FUNCTION; 72 73 /// Destructor - Only for zap() ~Use()74 ~Use() { 75 if (Val) removeFromList(); 76 } 77 78 enum PrevPtrTag { zeroDigitTag 79 , oneDigitTag 80 , stopTag 81 , fullStopTag }; 82 83 /// Constructor Use(PrevPtrTag tag)84 Use(PrevPtrTag tag) : Val(0) { 85 Prev.setInt(tag); 86 } 87 88 public: 89 /// Normally Use will just implicitly convert to a Value* that it holds. 90 operator Value*() const { return Val; } 91 92 /// If implicit conversion to Value* doesn't work, the get() method returns 93 /// the Value*. get()94 Value *get() const { return Val; } 95 96 /// getUser - This returns the User that contains this Use. For an 97 /// instruction operand, for example, this will return the instruction. 98 User *getUser() const; 99 100 inline void set(Value *Val); 101 102 Value *operator=(Value *RHS) { 103 set(RHS); 104 return RHS; 105 } 106 const Use &operator=(const Use &RHS) { 107 set(RHS.Val); 108 return *this; 109 } 110 111 Value *operator->() { return Val; } 112 const Value *operator->() const { return Val; } 113 getNext()114 Use *getNext() const { return Next; } 115 116 117 /// initTags - initialize the waymarking tags on an array of Uses, so that 118 /// getUser() can find the User from any of those Uses. 119 static Use *initTags(Use *Start, Use *Stop); 120 121 /// zap - This is used to destroy Use operands when the number of operands of 122 /// a User changes. 123 static void zap(Use *Start, const Use *Stop, bool del = false); 124 125 private: 126 const Use* getImpliedUser() const; 127 128 Value *Val; 129 Use *Next; 130 PointerIntPair<Use**, 2, PrevPtrTag> Prev; 131 setPrev(Use ** NewPrev)132 void setPrev(Use **NewPrev) { 133 Prev.setPointer(NewPrev); 134 } addToList(Use ** List)135 void addToList(Use **List) { 136 Next = *List; 137 if (Next) Next->setPrev(&Next); 138 setPrev(List); 139 *List = this; 140 } removeFromList()141 void removeFromList() { 142 Use **StrippedPrev = Prev.getPointer(); 143 *StrippedPrev = Next; 144 if (Next) Next->setPrev(StrippedPrev); 145 } 146 147 friend class Value; 148 }; 149 150 // simplify_type - Allow clients to treat uses just like values when using 151 // casting operators. 152 template<> struct simplify_type<Use> { 153 typedef Value* SimpleType; 154 static SimpleType getSimplifiedValue(Use &Val) { 155 return Val.get(); 156 } 157 }; 158 template<> struct simplify_type<const Use> { 159 typedef /*const*/ Value* SimpleType; 160 static SimpleType getSimplifiedValue(const Use &Val) { 161 return Val.get(); 162 } 163 }; 164 165 166 167 template<typename UserTy> // UserTy == 'User' or 'const User' 168 class value_use_iterator : public std::iterator<std::forward_iterator_tag, 169 UserTy*, ptrdiff_t> { 170 typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super; 171 typedef value_use_iterator<UserTy> _Self; 172 173 Use *U; 174 explicit value_use_iterator(Use *u) : U(u) {} 175 friend class Value; 176 public: 177 typedef typename super::reference reference; 178 typedef typename super::pointer pointer; 179 180 value_use_iterator() {} 181 182 bool operator==(const _Self &x) const { 183 return U == x.U; 184 } 185 bool operator!=(const _Self &x) const { 186 return !operator==(x); 187 } 188 189 /// atEnd - return true if this iterator is equal to use_end() on the value. 190 bool atEnd() const { return U == 0; } 191 192 // Iterator traversal: forward iteration only 193 _Self &operator++() { // Preincrement 194 assert(U && "Cannot increment end iterator!"); 195 U = U->getNext(); 196 return *this; 197 } 198 _Self operator++(int) { // Postincrement 199 _Self tmp = *this; ++*this; return tmp; 200 } 201 202 // Retrieve a pointer to the current User. 203 UserTy *operator*() const { 204 assert(U && "Cannot dereference end iterator!"); 205 return U->getUser(); 206 } 207 208 UserTy *operator->() const { return operator*(); } 209 210 Use &getUse() const { return *U; } 211 212 /// getOperandNo - Return the operand # of this use in its User. Defined in 213 /// User.h 214 /// 215 unsigned getOperandNo() const; 216 }; 217 218 // Create wrappers for C Binding types (see CBindingWrapping.h). 219 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef) 220 221 } // End llvm namespace 222 223 #endif 224