LLVM  3.7.0
Use.h
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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 /// \file
10 ///
11 /// This defines the Use class. The Use class represents the operand of an
12 /// instruction or some other User instance which refers to a Value. The Use
13 /// class keeps the "use list" of the referenced value up to date.
14 ///
15 /// Pointer tagging is used to efficiently find the User corresponding to a Use
16 /// without having to store a User pointer in every Use. A User is preceded in
17 /// memory by all the Uses corresponding to its operands, and the low bits of
18 /// one of the fields (Prev) of the Use class are used to encode offsets to be
19 /// able to find that User given 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-c/Core.h"
31 #include "llvm/Support/Compiler.h"
32 #include <cstddef>
33 #include <iterator>
34 
35 namespace llvm {
36 
37 class Value;
38 class User;
39 class Use;
40 template <typename> struct simplify_type;
41 
42 // Use** is only 4-byte aligned.
43 template <> class PointerLikeTypeTraits<Use **> {
44 public:
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 /// \brief A Use represents the edge between a Value definition and its users.
53 ///
54 /// This is notionally a two-dimensional linked list. It supports traversing
55 /// all of the uses for a particular value definition. It also supports jumping
56 /// directly to the used value when we arrive from the User's operands, and
57 /// jumping directly to the User when we arrive from the Value's uses.
58 ///
59 /// The pointer to the used Value is explicit, and the pointer to the User is
60 /// implicit. The implicit pointer is found via a waymarking algorithm
61 /// described in the programmer's manual:
62 ///
63 /// http://www.llvm.org/docs/ProgrammersManual.html#the-waymarking-algorithm
64 ///
65 /// This is essentially the single most memory intensive object in LLVM because
66 /// of the number of uses in the system. At the same time, the constant time
67 /// operations it allows are essential to many optimizations having reasonable
68 /// time complexity.
69 class Use {
70 public:
71  /// \brief Provide a fast substitute to std::swap<Use>
72  /// that also works with less standard-compliant compilers
73  void swap(Use &RHS);
74 
75  // A type for the word following an array of hung-off Uses in memory, which is
76  // a pointer back to their User with the bottom bit set.
78 
79 private:
80  Use(const Use &U) = delete;
81 
82  /// Destructor - Only for zap()
83  ~Use() {
84  if (Val)
85  removeFromList();
86  }
87 
88  enum PrevPtrTag { zeroDigitTag, oneDigitTag, stopTag, fullStopTag };
89 
90  /// Constructor
91  Use(PrevPtrTag tag) : Val(nullptr) { Prev.setInt(tag); }
92 
93 public:
94  operator Value *() const { return Val; }
95  Value *get() const { return Val; }
96 
97  /// \brief Returns the User that contains this Use.
98  ///
99  /// For an instruction operand, for example, this will return the
100  /// instruction.
101  User *getUser() const;
102 
103  inline void set(Value *Val);
104 
106  set(RHS);
107  return RHS;
108  }
109  const Use &operator=(const Use &RHS) {
110  set(RHS.Val);
111  return *this;
112  }
113 
114  Value *operator->() { return Val; }
115  const Value *operator->() const { return Val; }
116 
117  Use *getNext() const { return Next; }
118 
119  /// \brief Return the operand # of this use in its User.
120  unsigned getOperandNo() const;
121 
122  /// \brief Initializes the waymarking tags on an array of Uses.
123  ///
124  /// This sets up the array of Uses such that getUser() can find the User from
125  /// any of those Uses.
126  static Use *initTags(Use *Start, Use *Stop);
127 
128  /// \brief Destroys Use operands when the number of operands of
129  /// a User changes.
130  static void zap(Use *Start, const Use *Stop, bool del = false);
131 
132 private:
133  const Use *getImpliedUser() const;
134 
135  Value *Val;
136  Use *Next;
138 
139  void setPrev(Use **NewPrev) { Prev.setPointer(NewPrev); }
140  void addToList(Use **List) {
141  Next = *List;
142  if (Next)
143  Next->setPrev(&Next);
144  setPrev(List);
145  *List = this;
146  }
147  void removeFromList() {
148  Use **StrippedPrev = Prev.getPointer();
149  *StrippedPrev = Next;
150  if (Next)
151  Next->setPrev(StrippedPrev);
152  }
153 
154  friend class Value;
155 };
156 
157 /// \brief Allow clients to treat uses just like values when using
158 /// casting operators.
159 template <> struct simplify_type<Use> {
160  typedef Value *SimpleType;
161  static SimpleType getSimplifiedValue(Use &Val) { return Val.get(); }
162 };
163 template <> struct simplify_type<const Use> {
164  typedef /*const*/ Value *SimpleType;
165  static SimpleType getSimplifiedValue(const Use &Val) { return Val.get(); }
166 };
167 
168 // Create wrappers for C Binding types (see CBindingWrapping.h).
170 
171 }
172 
173 #endif
const Value * operator->() const
Definition: Use.h:115
PointerLikeTypeTraits - This is a traits object that is used to handle pointer types and things that ...
#define DEFINE_SIMPLE_CONVERSION_FUNCTIONS(ty, ref)
A Use represents the edge between a Value definition and its users.
Definition: Use.h:69
Use * getNext() const
Definition: Use.h:117
const Use & operator=(const Use &RHS)
Definition: Use.h:109
#define P(N)
void set(Value *Val)
Definition: Value.h:516
unsigned getOperandNo() const
Return the operand # of this use in its User.
Definition: Use.cpp:48
PointerIntPair - This class implements a pair of a pointer and small integer.
static Use * initTags(Use *Start, Use *Stop)
Initializes the waymarking tags on an array of Uses.
Definition: Use.cpp:57
void swap(Use &RHS)
Provide a fast substitute to std::swap<Use> that also works with less standard-compliant compilers...
Definition: Use.cpp:17
Value * operator->()
Definition: Use.h:114
Value * get() const
Definition: Use.h:95
User * getUser() const
Returns the User that contains this Use.
Definition: Use.cpp:41
static void * getAsVoidPointer(Use **P)
Definition: Use.h:45
static SimpleType getSimplifiedValue(const Use &Val)
Definition: Use.h:165
PointerIntPair< User *, 1, unsigned > UserRef
Definition: Use.h:77
Value * operator=(Value *RHS)
Definition: Use.h:105
could "use" a pointer
struct LLVMOpaqueUse * LLVMUseRef
Used to get the users and usees of a Value.
Definition: Core.h:125
aarch64 promote const
LLVM Value Representation.
Definition: Value.h:69
static SimpleType getSimplifiedValue(Use &Val)
Definition: Use.h:161
static Use ** getFromVoidPointer(void *P)
Definition: Use.h:46
static void zap(Use *Start, const Use *Stop, bool del=false)
Destroys Use operands when the number of operands of a User changes.
Definition: Use.cpp:87