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 "llvm/Support/Compiler.h"
30#include <cstddef>
31#include <iterator>
32
33namespace llvm {
34
35class Value;
36class User;
37class Use;
38template<typename>
39struct simplify_type;
40
41// Use** is only 4-byte aligned.
42template<>
43class PointerLikeTypeTraits<Use**> {
44public:
45  static inline void *getAsVoidPointer(Use** P) { return P; }
46  static inline Use **getFromVoidPointer(void *P) {
47    return static_cast<Use**>(P);
48  }
49  enum { NumLowBitsAvailable = 2 };
50};
51
52//===----------------------------------------------------------------------===//
53//                                  Use Class
54//===----------------------------------------------------------------------===//
55
56/// Use is here to make keeping the "use" list of a Value up-to-date really
57/// easy.
58class Use {
59public:
60  /// swap - provide a fast substitute to std::swap<Use>
61  /// that also works with less standard-compliant compilers
62  void swap(Use &RHS);
63
64  // A type for the word following an array of hung-off Uses in memory, which is
65  // a pointer back to their User with the bottom bit set.
66  typedef PointerIntPair<User*, 1, unsigned> UserRef;
67
68private:
69  /// Copy ctor - do not implement
70  Use(const Use &U) LLVM_DELETED_FUNCTION;
71
72  /// Destructor - Only for zap()
73  ~Use() {
74    if (Val) removeFromList();
75  }
76
77  enum PrevPtrTag { zeroDigitTag
78                  , oneDigitTag
79                  , stopTag
80                  , fullStopTag };
81
82  /// Constructor
83  Use(PrevPtrTag tag) : Val(0) {
84    Prev.setInt(tag);
85  }
86
87public:
88  /// Normally Use will just implicitly convert to a Value* that it holds.
89  operator Value*() const { return Val; }
90
91  /// If implicit conversion to Value* doesn't work, the get() method returns
92  /// the Value*.
93  Value *get() const { return Val; }
94
95  /// getUser - This returns the User that contains this Use.  For an
96  /// instruction operand, for example, this will return the instruction.
97  User *getUser() const;
98
99  inline void set(Value *Val);
100
101  Value *operator=(Value *RHS) {
102    set(RHS);
103    return RHS;
104  }
105  const Use &operator=(const Use &RHS) {
106    set(RHS.Val);
107    return *this;
108  }
109
110        Value *operator->()       { return Val; }
111  const Value *operator->() const { return Val; }
112
113  Use *getNext() const { return Next; }
114
115
116  /// initTags - initialize the waymarking tags on an array of Uses, so that
117  /// getUser() can find the User from any of those Uses.
118  static Use *initTags(Use *Start, Use *Stop);
119
120  /// zap - This is used to destroy Use operands when the number of operands of
121  /// a User changes.
122  static void zap(Use *Start, const Use *Stop, bool del = false);
123
124private:
125  const Use* getImpliedUser() const;
126
127  Value *Val;
128  Use *Next;
129  PointerIntPair<Use**, 2, PrevPtrTag> Prev;
130
131  void setPrev(Use **NewPrev) {
132    Prev.setPointer(NewPrev);
133  }
134  void addToList(Use **List) {
135    Next = *List;
136    if (Next) Next->setPrev(&Next);
137    setPrev(List);
138    *List = this;
139  }
140  void removeFromList() {
141    Use **StrippedPrev = Prev.getPointer();
142    *StrippedPrev = Next;
143    if (Next) Next->setPrev(StrippedPrev);
144  }
145
146  friend class Value;
147};
148
149// simplify_type - Allow clients to treat uses just like values when using
150// casting operators.
151template<> struct simplify_type<Use> {
152  typedef Value* SimpleType;
153  static SimpleType getSimplifiedValue(const Use &Val) {
154    return static_cast<SimpleType>(Val.get());
155  }
156};
157template<> struct simplify_type<const Use> {
158  typedef Value* SimpleType;
159  static SimpleType getSimplifiedValue(const Use &Val) {
160    return static_cast<SimpleType>(Val.get());
161  }
162};
163
164
165
166template<typename UserTy>  // UserTy == 'User' or 'const User'
167class value_use_iterator : public std::iterator<std::forward_iterator_tag,
168                                                UserTy*, ptrdiff_t> {
169  typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super;
170  typedef value_use_iterator<UserTy> _Self;
171
172  Use *U;
173  explicit value_use_iterator(Use *u) : U(u) {}
174  friend class Value;
175public:
176  typedef typename super::reference reference;
177  typedef typename super::pointer pointer;
178
179  value_use_iterator(const _Self &I) : U(I.U) {}
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} // End llvm namespace
219
220#endif
221