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-c/Core.h"
29 #include "llvm/ADT/PointerIntPair.h"
30 #include "llvm/Support/CBindingWrapping.h"
31 #include "llvm/Support/Compiler.h"
43 // Use** is only 4-byte aligned.
45 class PointerLikeTypeTraits<Use**> {
47 static inline void *getAsVoidPointer(Use** P) { return P; }
48 static inline Use **getFromVoidPointer(void *P) {
49 return static_cast<Use**>(P);
51 enum { NumLowBitsAvailable = 2 };
54 /// \brief A Use represents the edge between a Value definition and its users.
56 /// This is notionally a two-dimensional linked list. It supports traversing
57 /// all of the uses for a particular value definition. It also supports jumping
58 /// directly to the used value when we arrive from the User's operands, and
59 /// jumping directly to the User when we arrive from the Value's uses.
61 /// The pointer to the used Value is explicit, and the pointer to the User is
62 /// implicit. The implicit pointer is found via a waymarking algorithm
63 /// described in the programmer's manual:
65 /// http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
67 /// This is essentially the single most memory intensive object in LLVM because
68 /// of the number of uses in the system. At the same time, the constant time
69 /// operations it allows are essential to many optimizations having reasonable
73 /// \brief Provide a fast substitute to std::swap<Use>
74 /// that also works with less standard-compliant compilers
77 // A type for the word following an array of hung-off Uses in memory, which is
78 // a pointer back to their User with the bottom bit set.
79 typedef PointerIntPair<User*, 1, unsigned> UserRef;
82 Use(const Use &U) LLVM_DELETED_FUNCTION;
84 /// Destructor - Only for zap()
86 if (Val) removeFromList();
89 enum PrevPtrTag { zeroDigitTag
95 Use(PrevPtrTag tag) : Val(0) {
100 operator Value*() const { return Val; }
101 Value *get() const { return Val; }
103 /// \brief Returns the User that contains this Use.
105 /// For an instruction operand, for example, this will return the
107 User *getUser() const;
109 inline void set(Value *Val);
111 Value *operator=(Value *RHS) {
115 const Use &operator=(const Use &RHS) {
120 Value *operator->() { return Val; }
121 const Value *operator->() const { return Val; }
123 Use *getNext() const { return Next; }
125 /// \brief Initializes the waymarking tags on an array of Uses.
127 /// This sets up the array of Uses such that getUser() can find the User from
128 /// any of those Uses.
129 static Use *initTags(Use *Start, Use *Stop);
131 /// \brief Destroys Use operands when the number of operands of
133 static void zap(Use *Start, const Use *Stop, bool del = false);
136 const Use* getImpliedUser() const;
140 PointerIntPair<Use**, 2, PrevPtrTag> Prev;
142 void setPrev(Use **NewPrev) {
143 Prev.setPointer(NewPrev);
145 void addToList(Use **List) {
147 if (Next) Next->setPrev(&Next);
151 void removeFromList() {
152 Use **StrippedPrev = Prev.getPointer();
153 *StrippedPrev = Next;
154 if (Next) 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) {
168 template<> struct simplify_type<const Use> {
169 typedef /*const*/ Value* SimpleType;
170 static SimpleType getSimplifiedValue(const Use &Val) {
177 template<typename UserTy> // UserTy == 'User' or 'const User'
178 class value_use_iterator : public std::iterator<std::forward_iterator_tag,
179 UserTy*, ptrdiff_t> {
180 typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super;
181 typedef value_use_iterator<UserTy> _Self;
184 explicit value_use_iterator(Use *u) : U(u) {}
187 typedef typename super::reference reference;
188 typedef typename super::pointer pointer;
190 value_use_iterator() {}
192 bool operator==(const _Self &x) const {
195 bool operator!=(const _Self &x) const {
196 return !operator==(x);
199 /// \brief Returns true if this iterator is equal to use_end() on the value.
200 bool atEnd() const { return U == 0; }
202 // Iterator traversal: forward iteration only
203 _Self &operator++() { // Preincrement
204 assert(U && "Cannot increment end iterator!");
208 _Self operator++(int) { // Postincrement
209 _Self tmp = *this; ++*this; return tmp;
212 // Retrieve a pointer to the current User.
213 UserTy *operator*() const {
214 assert(U && "Cannot dereference end iterator!");
218 UserTy *operator->() const { return operator*(); }
220 Use &getUse() const { return *U; }
222 /// \brief Return the operand # of this use in its User.
224 /// Defined in User.h
225 unsigned getOperandNo() const;
228 // Create wrappers for C Binding types (see CBindingWrapping.h).
229 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)