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