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
31namespace llvm {
32
33template <typename> struct simplify_type;
34class User;
35class 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.
43class Use {
44public:
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
51private:
52 /// Destructor - Only for zap()
53 ~Use() {
54 if (Val)
55 removeFromList();
56 }
57
58 /// Constructor
59 Use(User *Parent) : Parent(Parent) {}
60
61public:
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
91private:
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.
115template <> struct simplify_type<Use> {
116 using SimpleType = Value *;
117
118 static SimpleType getSimplifiedValue(Use &Val) { return Val.get(); }
119};
120template <> 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).
127DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)
128
129} // end namespace llvm
130
131#endif // LLVM_IR_USE_H
132

source code of llvm/include/llvm/IR/Use.h