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/ADT/PointerIntPair.h"
29 #include "llvm/Support/CBindingWrapping.h"
30 #include "llvm/Support/Compiler.h"
31 
32 namespace llvm {
33 
34 template <typename> struct simplify_type;
35 class User;
36 class Value;
37 
38 /// A Use represents the edge between a Value definition and its users.
39 ///
40 /// This is notionally a two-dimensional linked list. It supports traversing
41 /// all of the uses for a particular value definition. It also supports jumping
42 /// directly to the used value when we arrive from the User's operands, and
43 /// jumping directly to the User when we arrive from the Value's uses.
44 class Use {
45 public:
46   Use(const Use &U) = delete;
47 
48   /// Provide a fast substitute to std::swap<Use>
49   /// that also works with less standard-compliant compilers
50   void swap(Use &RHS);
51 
52 private:
53   /// Destructor - Only for zap()
~Use()54   ~Use() {
55     if (Val)
56       removeFromList();
57   }
58 
59   /// Constructor
Use(User * Parent)60   Use(User *Parent) : Parent(Parent) {}
61 
62 public:
63   friend class Value;
64   friend class User;
65 
66   operator Value *() const { return Val; }
get()67   Value *get() const { return Val; }
68 
69   /// Returns the User that contains this Use.
70   ///
71   /// For an instruction operand, for example, this will return the
72   /// instruction.
getUser()73   User *getUser() const { return Parent; };
74 
75   inline void set(Value *Val);
76 
77   inline Value *operator=(Value *RHS);
78   inline const Use &operator=(const Use &RHS);
79 
80   Value *operator->() { return Val; }
81   const Value *operator->() const { return Val; }
82 
getNext()83   Use *getNext() const { return Next; }
84 
85   /// Return the operand # of this use in its User.
86   unsigned getOperandNo() const;
87 
88   /// Destroys Use operands when the number of operands of
89   /// a User changes.
90   static void zap(Use *Start, const Use *Stop, bool del = false);
91 
92 private:
93 
94   Value *Val = nullptr;
95   Use *Next = nullptr;
96   Use **Prev = nullptr;
97   User *Parent = nullptr;
98 
addToList(Use ** List)99   void addToList(Use **List) {
100     Next = *List;
101     if (Next)
102       Next->Prev = &Next;
103     Prev = List;
104     *Prev = this;
105   }
106 
removeFromList()107   void removeFromList() {
108     *Prev = Next;
109     if (Next)
110       Next->Prev = Prev;
111   }
112 };
113 
114 /// Allow clients to treat uses just like values when using
115 /// casting operators.
116 template <> struct simplify_type<Use> {
117   using SimpleType = Value *;
118 
119   static SimpleType getSimplifiedValue(Use &Val) { return Val.get(); }
120 };
121 template <> struct simplify_type<const Use> {
122   using SimpleType = /*const*/ Value *;
123 
124   static SimpleType getSimplifiedValue(const Use &Val) { return Val.get(); }
125 };
126 
127 // Create wrappers for C Binding types (see CBindingWrapping.h).
128 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)
129 
130 } // end namespace llvm
131 
132 #endif // LLVM_IR_USE_H
133