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() ~Use()53 ~Use() { 54 if (Val) 55 removeFromList(); 56 } 57 58 /// Constructor Use(User * Parent)59 Use(User *Parent) : Parent(Parent) {} 60 61 public: 62 friend class Value; 63 friend class User; 64 65 operator Value *() const { return Val; } get()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. getUser()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 getNext()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 addToList(Use ** List)98 void addToList(Use **List) { 99 Next = *List; 100 if (Next) 101 Next->Prev = &Next; 102 Prev = List; 103 *Prev = this; 104 } 105 removeFromList()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