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