LLVM  4.0.0
Use.h
Go to the documentation of this file.
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 
30 #include "llvm-c/Types.h"
31 
32 namespace llvm {
33 
34 class Value;
35 class User;
36 class Use;
37 template <typename> struct simplify_type;
38 
39 /// \brief A Use represents the edge between a Value definition and its users.
40 ///
41 /// This is notionally a two-dimensional linked list. It supports traversing
42 /// all of the uses for a particular value definition. It also supports jumping
43 /// directly to the used value when we arrive from the User's operands, and
44 /// jumping directly to the User when we arrive from the Value's uses.
45 ///
46 /// The pointer to the used Value is explicit, and the pointer to the User is
47 /// implicit. The implicit pointer is found via a waymarking algorithm
48 /// described in the programmer's manual:
49 ///
50 /// http://www.llvm.org/docs/ProgrammersManual.html#the-waymarking-algorithm
51 ///
52 /// This is essentially the single most memory intensive object in LLVM because
53 /// of the number of uses in the system. At the same time, the constant time
54 /// operations it allows are essential to many optimizations having reasonable
55 /// time complexity.
56 class Use {
57 public:
58  Use(const Use &U) = delete;
59 
60  /// \brief 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.
67 
68 private:
69  /// Destructor - Only for zap()
70  ~Use() {
71  if (Val)
72  removeFromList();
73  }
74 
75  enum PrevPtrTag { zeroDigitTag, oneDigitTag, stopTag, fullStopTag };
76 
77  /// Constructor
78  Use(PrevPtrTag tag) : Val(nullptr) { Prev.setInt(tag); }
79 
80 public:
81  operator Value *() const { return Val; }
82  Value *get() const { return Val; }
83 
84  /// \brief Returns the User that contains this Use.
85  ///
86  /// For an instruction operand, for example, this will return the
87  /// instruction.
88  User *getUser() const;
89 
90  inline void set(Value *Val);
91 
92  inline Value *operator=(Value *RHS);
93  inline const Use &operator=(const Use &RHS);
94 
95  Value *operator->() { return Val; }
96  const Value *operator->() const { return Val; }
97 
98  Use *getNext() const { return Next; }
99 
100  /// \brief Return the operand # of this use in its User.
101  unsigned getOperandNo() const;
102 
103  /// \brief Initializes the waymarking tags on an array of Uses.
104  ///
105  /// This sets up the array of Uses such that getUser() can find the User from
106  /// any of those Uses.
107  static Use *initTags(Use *Start, Use *Stop);
108 
109  /// \brief Destroys Use operands when the number of operands of
110  /// a User changes.
111  static void zap(Use *Start, const Use *Stop, bool del = false);
112 
113 private:
114  const Use *getImpliedUser() const;
115 
116  Value *Val;
117  Use *Next;
119 
120  void setPrev(Use **NewPrev) { Prev.setPointer(NewPrev); }
121 
122  void addToList(Use **List) {
123  Next = *List;
124  if (Next)
125  Next->setPrev(&Next);
126  setPrev(List);
127  *List = this;
128  }
129 
130  void removeFromList() {
131  Use **StrippedPrev = Prev.getPointer();
132  *StrippedPrev = Next;
133  if (Next)
134  Next->setPrev(StrippedPrev);
135  }
136 
137  friend class Value;
138 };
139 
140 /// \brief Allow clients to treat uses just like values when using
141 /// casting operators.
142 template <> struct simplify_type<Use> {
143  typedef Value *SimpleType;
144  static SimpleType getSimplifiedValue(Use &Val) { return Val.get(); }
145 };
146 template <> struct simplify_type<const Use> {
147  typedef /*const*/ Value *SimpleType;
148  static SimpleType getSimplifiedValue(const Use &Val) { return Val.get(); }
149 };
150 
151 // Create wrappers for C Binding types (see CBindingWrapping.h).
153 
154 } // end namespace llvm
155 
156 #endif // LLVM_IR_USE_H
const Value * operator->() const
Definition: Use.h:96
Use(const Use &U)=delete
#define DEFINE_SIMPLE_CONVERSION_FUNCTIONS(ty, ref)
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
Use * getNext() const
Definition: Use.h:98
struct LLVMOpaqueUse * LLVMUseRef
Used to get the users and usees of a Value.
Definition: c/Types.h:109
void set(Value *Val)
Definition: Value.h:624
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:95
Value * get() const
Definition: Use.h:82
User * getUser() const
Returns the User that contains this Use.
Definition: Use.cpp:41
static SimpleType getSimplifiedValue(const Use &Val)
Definition: Use.h:148
PointerIntPair< User *, 1, unsigned > UserRef
Definition: Use.h:66
could "use" a pointer
const NodeList & List
Definition: RDFGraph.cpp:205
aarch64 promote const
LLVM Value Representation.
Definition: Value.h:71
static SimpleType getSimplifiedValue(Use &Val)
Definition: Use.h:144
Value * operator=(Value *RHS)
Definition: Value.h:630
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