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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