1 //===- llvm/Use.h - Definition of the Use class -----------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 /// \file
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 to a Use
15 /// without having to store a User pointer in every Use. A User is preceded in
16 /// memory by all the Uses corresponding to its operands, and the low bits of
17 /// one of the fields (Prev) of the Use class are used to encode offsets to be
18 /// able to find that User given a pointer to any Use. For details, see:
19 ///
20 ///   http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
21 ///
22 //===----------------------------------------------------------------------===//
23 
24 #ifndef LLVM_IR_USE_H
25 #define LLVM_IR_USE_H
26 
27 #include "llvm-c/Types.h"
28 #include "llvm/Support/CBindingWrapping.h"
29 #include "llvm/Support/Compiler.h"
30 
31 namespace llvm {
32 
33 template <typename> struct simplify_type;
34 class User;
35 class Value;
36 
37 /// A Use represents the edge between a Value definition and its users.
38 ///
39 /// This is notionally a two-dimensional linked list. It supports traversing
40 /// all of the uses for a particular value definition. It also supports jumping
41 /// directly to the used value when we arrive from the User's operands, and
42 /// jumping directly to the User when we arrive from the Value's uses.
43 class Use {
44 public:
45   Use(const Use &U) = delete;
46 
47   /// Provide a fast substitute to std::swap<Use>
48   /// that also works with less standard-compliant compilers
49   void swap(Use &RHS);
50 
51 private:
52   /// Destructor - Only for zap()
53   ~Use() {
54     if (Val)
55       removeFromList();
56   }
57 
58   /// Constructor
59   Use(User *Parent) : Parent(Parent) {}
60 
61 public:
62   friend class Value;
63   friend class User;
64 
65   operator Value *() const { return Val; }
66   Value *get() const { return Val; }
67 
68   /// Returns the User that contains this Use.
69   ///
70   /// For an instruction operand, for example, this will return the
71   /// instruction.
72   User *getUser() const { return Parent; };
73 
74   inline void set(Value *Val);
75 
76   inline Value *operator=(Value *RHS);
77   inline const Use &operator=(const Use &RHS);
78 
79   Value *operator->() { return Val; }
80   const Value *operator->() const { return Val; }
81 
82   Use *getNext() const { return Next; }
83 
84   /// Return the operand # of this use in its User.
85   unsigned getOperandNo() const;
86 
87   /// Destroys Use operands when the number of operands of
88   /// a User changes.
89   static void zap(Use *Start, const Use *Stop, bool del = false);
90 
91 private:
92 
93   Value *Val = nullptr;
94   Use *Next = nullptr;
95   Use **Prev = nullptr;
96   User *Parent = nullptr;
97 
98   void addToList(Use **List) {
99     Next = *List;
100     if (Next)
101       Next->Prev = &Next;
102     Prev = List;
103     *Prev = this;
104   }
105 
106   void removeFromList() {
107     *Prev = Next;
108     if (Next)
109       Next->Prev = Prev;
110   }
111 };
112 
113 /// Allow clients to treat uses just like values when using
114 /// casting operators.
115 template <> struct simplify_type<Use> {
116   using SimpleType = Value *;
117 
118   static SimpleType getSimplifiedValue(Use &Val) { return Val.get(); }
119 };
120 template <> struct simplify_type<const Use> {
121   using SimpleType = /*const*/ Value *;
122 
123   static SimpleType getSimplifiedValue(const Use &Val) { return Val.get(); }
124 };
125 
126 // Create wrappers for C Binding types (see CBindingWrapping.h).
127 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)
128 
129 } // end namespace llvm
130 
131 #endif // LLVM_IR_USE_H
132