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//===-- llvm/Use.h - Definition of the Use class ----------------*- C++ -*-===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This defines the Use class. The Use class represents the operand of an
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// instruction or some other User instance which refers to a Value. The Use
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// class keeps the "use list" of the referenced value up to date.
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// Pointer tagging is used to efficiently find the User corresponding
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// to a Use without having to store a User pointer in every Use. A
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// User is preceded in memory by all the Uses corresponding to its
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// operands, and the low bits of one of the fields (Prev) of the Use
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// class are used to encode offsets to be able to find that User given
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// a pointer to any Use. For details, see:
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// http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
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//===----------------------------------------------------------------------===//
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#include "llvm/Support/Casting.h"
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#include "llvm/ADT/PointerIntPair.h"
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/// Tag - generic tag type for (at least 32 bit) pointers
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enum Tag { noTag, tagOne, tagTwo, tagThree };
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// Use** is only 4-byte aligned.
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class PointerLikeTypeTraits<Use**> {
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static inline void *getAsVoidPointer(Use** P) { return P; }
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static inline Use **getFromVoidPointer(void *P) {
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return static_cast<Use**>(P);
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enum { NumLowBitsAvailable = 2 };
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//===----------------------------------------------------------------------===//
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//===----------------------------------------------------------------------===//
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/// Use is here to make keeping the "use" list of a Value up-to-date really
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/// swap - provide a fast substitute to std::swap<Use>
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/// that also works with less standard-compliant compilers
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/// Copy ctor - do not implement
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/// Destructor - Only for zap()
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if (Val) removeFromList();
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/// Default ctor - This leaves the Use completely uninitialized. The only
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/// thing that is valid to do with this use is to call the "init" method.
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enum PrevPtrTag { zeroDigitTag = noTag
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, oneDigitTag = tagOne
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, fullStopTag = tagThree };
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/// Normally Use will just implicitly convert to a Value* that it holds.
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operator Value*() const { return Val; }
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/// If implicit conversion to Value* doesn't work, the get() method returns
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Value *get() const { return Val; }
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/// getUser - This returns the User that contains this Use. For an
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/// instruction operand, for example, this will return the instruction.
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User *getUser() const;
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inline void set(Value *Val);
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Value *operator=(Value *RHS) {
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const Use &operator=(const Use &RHS) {
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Value *operator->() { return Val; }
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const Value *operator->() const { return Val; }
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Use *getNext() const { return Next; }
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/// zap - This is used to destroy Use operands when the number of operands of
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static void zap(Use *Start, const Use *Stop, bool del = false);
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/// getPrefix - Return deletable pointer if appropriate
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const Use* getImpliedUser() const;
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static Use *initTags(Use *Start, Use *Stop, ptrdiff_t Done = 0);
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PointerIntPair<Use**, 2, PrevPtrTag> Prev;
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void setPrev(Use **NewPrev) {
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Prev.setPointer(NewPrev);
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void addToList(Use **List) {
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if (Next) Next->setPrev(&Next);
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void removeFromList() {
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Use **StrippedPrev = Prev.getPointer();
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*StrippedPrev = Next;
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if (Next) Next->setPrev(StrippedPrev);
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// simplify_type - Allow clients to treat uses just like values when using
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// casting operators.
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template<> struct simplify_type<Use> {
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typedef Value* SimpleType;
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static SimpleType getSimplifiedValue(const Use &Val) {
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return static_cast<SimpleType>(Val.get());
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template<> struct simplify_type<const Use> {
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typedef Value* SimpleType;
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static SimpleType getSimplifiedValue(const Use &Val) {
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return static_cast<SimpleType>(Val.get());
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template<typename UserTy> // UserTy == 'User' or 'const User'
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class value_use_iterator : public std::iterator<std::forward_iterator_tag,
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UserTy*, ptrdiff_t> {
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typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super;
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typedef value_use_iterator<UserTy> _Self;
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explicit value_use_iterator(Use *u) : U(u) {}
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typedef typename super::reference reference;
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typedef typename super::pointer pointer;
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value_use_iterator(const _Self &I) : U(I.U) {}
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value_use_iterator() {}
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bool operator==(const _Self &x) const {
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bool operator!=(const _Self &x) const {
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return !operator==(x);
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/// atEnd - return true if this iterator is equal to use_end() on the value.
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bool atEnd() const { return U == 0; }
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// Iterator traversal: forward iteration only
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_Self &operator++() { // Preincrement
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assert(U && "Cannot increment end iterator!");
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_Self operator++(int) { // Postincrement
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_Self tmp = *this; ++*this; return tmp;
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// Retrieve a pointer to the current User.
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UserTy *operator*() const {
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assert(U && "Cannot dereference end iterator!");
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UserTy *operator->() const { return operator*(); }
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Use &getUse() const { return *U; }
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/// getOperandNo - Return the operand # of this use in its User. Defined in
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unsigned getOperandNo() const;
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} // End llvm namespace