1 //===-- llvm/Use.h - Definition of the Use class ----------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// This defines the Use class. The Use class represents the operand of an
12 /// instruction or some other User instance which refers to a Value. The Use
13 /// class keeps the "use list" of the referenced value up to date.
15 /// Pointer tagging is used to efficiently find the User corresponding to a Use
16 /// without having to store a User pointer in every Use. A User is preceded in
17 /// memory by all the Uses corresponding to its operands, and the low bits of
18 /// one of the fields (Prev) of the Use class are used to encode offsets to be
19 /// able to find that User given a pointer to any Use. For details, see:
21 /// http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
23 //===----------------------------------------------------------------------===//
28 #include "llvm/ADT/PointerIntPair.h"
29 #include "llvm/Support/CBindingWrapping.h"
30 #include "llvm-c/Types.h"
37 template <typename> struct simplify_type;
39 /// \brief A Use represents the edge between a Value definition and its users.
41 /// This is notionally a two-dimensional linked list. It supports traversing
42 /// all of the uses for a particular value definition. It also supports jumping
43 /// directly to the used value when we arrive from the User's operands, and
44 /// jumping directly to the User when we arrive from the Value's uses.
46 /// The pointer to the used Value is explicit, and the pointer to the User is
47 /// implicit. The implicit pointer is found via a waymarking algorithm
48 /// described in the programmer's manual:
50 /// http://www.llvm.org/docs/ProgrammersManual.html#the-waymarking-algorithm
52 /// This is essentially the single most memory intensive object in LLVM because
53 /// of the number of uses in the system. At the same time, the constant time
54 /// operations it allows are essential to many optimizations having reasonable
58 Use(const Use &U) = delete;
60 /// \brief Provide a fast substitute to std::swap<Use>
61 /// that also works with less standard-compliant compilers
64 /// Pointer traits for the UserRef PointerIntPair. This ensures we always
65 /// use the LSB regardless of pointer alignment on different targets.
66 struct UserRefPointerTraits {
67 static inline void *getAsVoidPointer(User *P) { return P; }
68 static inline User *getFromVoidPointer(void *P) {
71 enum { NumLowBitsAvailable = 1 };
74 // A type for the word following an array of hung-off Uses in memory, which is
75 // a pointer back to their User with the bottom bit set.
76 typedef PointerIntPair<User *, 1, unsigned, UserRefPointerTraits> UserRef;
78 /// Pointer traits for the Prev PointerIntPair. This ensures we always use
79 /// the two LSBs regardless of pointer alignment on different targets.
80 struct PrevPointerTraits {
81 static inline void *getAsVoidPointer(Use **P) { return P; }
82 static inline Use **getFromVoidPointer(void *P) {
85 enum { NumLowBitsAvailable = 2 };
89 /// Destructor - Only for zap()
95 enum PrevPtrTag { zeroDigitTag, oneDigitTag, stopTag, fullStopTag };
98 Use(PrevPtrTag tag) : Val(nullptr) { Prev.setInt(tag); }
101 operator Value *() const { return Val; }
102 Value *get() const { return Val; }
104 /// \brief Returns the User that contains this Use.
106 /// For an instruction operand, for example, this will return the
108 User *getUser() const LLVM_READONLY;
110 inline void set(Value *Val);
112 inline Value *operator=(Value *RHS);
113 inline const Use &operator=(const Use &RHS);
115 Value *operator->() { return Val; }
116 const Value *operator->() const { return Val; }
118 Use *getNext() const { return Next; }
120 /// \brief Return the operand # of this use in its User.
121 unsigned getOperandNo() const;
123 /// \brief Initializes the waymarking tags on an array of Uses.
125 /// This sets up the array of Uses such that getUser() can find the User from
126 /// any of those Uses.
127 static Use *initTags(Use *Start, Use *Stop);
129 /// \brief Destroys Use operands when the number of operands of
131 static void zap(Use *Start, const Use *Stop, bool del = false);
134 const Use *getImpliedUser() const LLVM_READONLY;
138 PointerIntPair<Use **, 2, PrevPtrTag, PrevPointerTraits> Prev;
140 void setPrev(Use **NewPrev) { Prev.setPointer(NewPrev); }
142 void addToList(Use **List) {
145 Next->setPrev(&Next);
150 void removeFromList() {
151 Use **StrippedPrev = Prev.getPointer();
152 *StrippedPrev = Next;
154 Next->setPrev(StrippedPrev);
160 /// \brief Allow clients to treat uses just like values when using
161 /// casting operators.
162 template <> struct simplify_type<Use> {
163 typedef Value *SimpleType;
164 static SimpleType getSimplifiedValue(Use &Val) { return Val.get(); }
166 template <> struct simplify_type<const Use> {
167 typedef /*const*/ Value *SimpleType;
168 static SimpleType getSimplifiedValue(const Use &Val) { return Val.get(); }
171 // Create wrappers for C Binding types (see CBindingWrapping.h).
172 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)
174 } // end namespace llvm
176 #endif // LLVM_IR_USE_H