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  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()
  53.   ~Use() {
  54.     if (Val)
  55.       removeFromList();
  56.   }
  57.  
  58.   /// Constructor
  59.   Use(User *Parent) : Parent(Parent) {}
  60.  
  61. public:
  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.  
  91. private:
  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.
  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.