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 //===----------------------------------------------------------------------===//
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.
14 // Pointer tagging is used to efficiently find the User corresponding
15 // to a Use without having to store a User pointer in every Use. A
16 // User is preceded in memory by all the Uses corresponding to its
17 // operands, and the low bits of one of the fields (Prev) of the Use
18 // class are used to encode offsets to be able to find that User given
19 // a pointer to any Use. For details, see:
21 // http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
23 //===----------------------------------------------------------------------===//
28 #include "llvm/Support/Casting.h"
29 #include "llvm/ADT/PointerIntPair.h"
39 /// Tag - generic tag type for (at least 32 bit) pointers
40 enum Tag { noTag, tagOne, tagTwo, tagThree };
42 // Use** is only 4-byte aligned.
44 class PointerLikeTypeTraits<Use**> {
46 static inline void *getAsVoidPointer(Use** P) { return P; }
47 static inline Use **getFromVoidPointer(void *P) {
48 return static_cast<Use**>(P);
50 enum { NumLowBitsAvailable = 2 };
53 //===----------------------------------------------------------------------===//
55 //===----------------------------------------------------------------------===//
57 /// Use is here to make keeping the "use" list of a Value up-to-date really
61 /// swap - provide a fast substitute to std::swap<Use>
62 /// that also works with less standard-compliant compilers
66 /// Copy ctor - do not implement
69 /// Destructor - Only for zap()
71 if (Val) removeFromList();
74 /// Default ctor - This leaves the Use completely uninitialized. The only
75 /// thing that is valid to do with this use is to call the "init" method.
77 enum PrevPtrTag { zeroDigitTag = noTag
78 , oneDigitTag = tagOne
80 , fullStopTag = tagThree };
83 /// Normally Use will just implicitly convert to a Value* that it holds.
84 operator Value*() const { return Val; }
86 /// If implicit conversion to Value* doesn't work, the get() method returns
88 Value *get() const { return Val; }
90 /// getUser - This returns the User that contains this Use. For an
91 /// instruction operand, for example, this will return the instruction.
92 User *getUser() const;
94 inline void set(Value *Val);
96 Value *operator=(Value *RHS) {
100 const Use &operator=(const Use &RHS) {
105 Value *operator->() { return Val; }
106 const Value *operator->() const { return Val; }
108 Use *getNext() const { return Next; }
111 /// zap - This is used to destroy Use operands when the number of operands of
113 static void zap(Use *Start, const Use *Stop, bool del = false);
115 /// getPrefix - Return deletable pointer if appropriate
118 const Use* getImpliedUser() const;
119 static Use *initTags(Use *Start, Use *Stop, ptrdiff_t Done = 0);
123 PointerIntPair<Use**, 2, PrevPtrTag> Prev;
125 void setPrev(Use **NewPrev) {
126 Prev.setPointer(NewPrev);
128 void addToList(Use **List) {
130 if (Next) Next->setPrev(&Next);
134 void removeFromList() {
135 Use **StrippedPrev = Prev.getPointer();
136 *StrippedPrev = Next;
137 if (Next) Next->setPrev(StrippedPrev);
144 // simplify_type - Allow clients to treat uses just like values when using
145 // casting operators.
146 template<> struct simplify_type<Use> {
147 typedef Value* SimpleType;
148 static SimpleType getSimplifiedValue(const Use &Val) {
149 return static_cast<SimpleType>(Val.get());
152 template<> struct simplify_type<const Use> {
153 typedef Value* SimpleType;
154 static SimpleType getSimplifiedValue(const Use &Val) {
155 return static_cast<SimpleType>(Val.get());
161 template<typename UserTy> // UserTy == 'User' or 'const User'
162 class value_use_iterator : public std::iterator<std::forward_iterator_tag,
163 UserTy*, ptrdiff_t> {
164 typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super;
165 typedef value_use_iterator<UserTy> _Self;
168 explicit value_use_iterator(Use *u) : U(u) {}
171 typedef typename super::reference reference;
172 typedef typename super::pointer pointer;
174 value_use_iterator(const _Self &I) : U(I.U) {}
175 value_use_iterator() {}
177 bool operator==(const _Self &x) const {
180 bool operator!=(const _Self &x) const {
181 return !operator==(x);
184 /// atEnd - return true if this iterator is equal to use_end() on the value.
185 bool atEnd() const { return U == 0; }
187 // Iterator traversal: forward iteration only
188 _Self &operator++() { // Preincrement
189 assert(U && "Cannot increment end iterator!");
193 _Self operator++(int) { // Postincrement
194 _Self tmp = *this; ++*this; return tmp;
197 // Retrieve a pointer to the current User.
198 UserTy *operator*() const {
199 assert(U && "Cannot dereference end iterator!");
203 UserTy *operator->() const { return operator*(); }
205 Use &getUse() const { return *U; }
207 /// getOperandNo - Return the operand # of this use in its User. Defined in
210 unsigned getOperandNo() const;
213 } // End llvm namespace