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
32namespace llvm {
33
34template <typename> struct simplify_type;
35class User;
36class 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.
44class Use {
45public:
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
52private:
53 /// Destructor - Only for zap()
54 ~Use() {
55 if (Val)
56 removeFromList();
57 }
58
59 /// Constructor
60 Use(User *Parent) : Parent(Parent) {}
61
62public:
63 friend class Value;
64 friend class User;
65
66 operator Value *() const { return Val; }
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.
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
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
92private:
93
94 Value *Val = nullptr;
95 Use *Next = nullptr;
96 Use **Prev = nullptr;
97 User *Parent = nullptr;
98
99 void addToList(Use **List) {
100 Next = *List;
101 if (Next)
102 Next->Prev = &Next;
103 Prev = List;
104 *Prev = this;
105 }
106
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.
116template <> struct simplify_type<Use> {
117 using SimpleType = Value *;
118
119 static SimpleType getSimplifiedValue(Use &Val) { return Val.get(); }
120};
121template <> 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).
128DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)
129
130} // end namespace llvm
131
132#endif // LLVM_IR_USE_H
133