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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229340 91177308-0d34-0410-b5e6-96231b3b80d8
174 lines
5.2 KiB
C++
174 lines
5.2 KiB
C++
//===-- llvm/Use.h - Definition of the Use class ----------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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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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//===----------------------------------------------------------------------===//
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/// \file
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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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///
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/// Pointer tagging is used to efficiently find the User corresponding to a Use
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/// without having to store a User pointer in every Use. A User is preceded in
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/// memory by all the Uses corresponding to its operands, and the low bits of
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/// one of the fields (Prev) of the Use class are used to encode offsets to be
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/// able to find that User given a pointer to any Use. For details, see:
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///
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/// http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_IR_USE_H
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#define LLVM_IR_USE_H
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#include "llvm-c/Core.h"
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#include "llvm/ADT/PointerIntPair.h"
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#include "llvm/Support/CBindingWrapping.h"
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#include "llvm/Support/Compiler.h"
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#include <cstddef>
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#include <iterator>
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namespace llvm {
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class Value;
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class User;
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class Use;
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template <typename> struct simplify_type;
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// Use** is only 4-byte aligned.
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template <> class PointerLikeTypeTraits<Use **> {
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public:
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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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}
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enum { NumLowBitsAvailable = 2 };
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};
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/// \brief A Use represents the edge between a Value definition and its users.
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///
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/// This is notionally a two-dimensional linked list. It supports traversing
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/// all of the uses for a particular value definition. It also supports jumping
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/// directly to the used value when we arrive from the User's operands, and
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/// jumping directly to the User when we arrive from the Value's uses.
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///
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/// The pointer to the used Value is explicit, and the pointer to the User is
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/// implicit. The implicit pointer is found via a waymarking algorithm
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/// described in the programmer's manual:
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///
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/// http://www.llvm.org/docs/ProgrammersManual.html#the-waymarking-algorithm
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///
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/// This is essentially the single most memory intensive object in LLVM because
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/// of the number of uses in the system. At the same time, the constant time
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/// operations it allows are essential to many optimizations having reasonable
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/// time complexity.
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class Use {
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public:
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/// \brief Provide a fast substitute to std::swap<Use>
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/// that also works with less standard-compliant compilers
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void swap(Use &RHS);
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// A type for the word following an array of hung-off Uses in memory, which is
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// a pointer back to their User with the bottom bit set.
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typedef PointerIntPair<User *, 1, unsigned> UserRef;
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private:
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Use(const Use &U) = delete;
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/// Destructor - Only for zap()
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~Use() {
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if (Val)
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removeFromList();
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}
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enum PrevPtrTag { zeroDigitTag, oneDigitTag, stopTag, fullStopTag };
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/// Constructor
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Use(PrevPtrTag tag) : Val(nullptr) { Prev.setInt(tag); }
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public:
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operator Value *() const { return Val; }
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Value *get() const { return Val; }
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/// \brief Returns the User that contains this Use.
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///
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/// For an instruction operand, for example, this will return the
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/// 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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set(RHS);
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return RHS;
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}
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const Use &operator=(const Use &RHS) {
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set(RHS.Val);
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return *this;
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}
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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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/// \brief Return the operand # of this use in its User.
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unsigned getOperandNo() const;
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/// \brief Initializes the waymarking tags on an array of Uses.
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///
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/// This sets up the array of Uses such that getUser() can find the User from
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/// any of those Uses.
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static Use *initTags(Use *Start, Use *Stop);
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/// \brief Destroys Use operands when the number of operands of
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/// a User changes.
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static void zap(Use *Start, const Use *Stop, bool del = false);
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private:
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const Use *getImpliedUser() const;
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Value *Val;
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Use *Next;
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PointerIntPair<Use **, 2, PrevPtrTag> Prev;
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void setPrev(Use **NewPrev) { Prev.setPointer(NewPrev); }
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void addToList(Use **List) {
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Next = *List;
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if (Next)
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Next->setPrev(&Next);
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setPrev(List);
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*List = this;
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}
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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)
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Next->setPrev(StrippedPrev);
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}
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friend class Value;
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};
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/// \brief 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(Use &Val) { return Val.get(); }
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};
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template <> struct simplify_type<const Use> {
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typedef /*const*/ Value *SimpleType;
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static SimpleType getSimplifiedValue(const Use &Val) { return Val.get(); }
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};
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// Create wrappers for C Binding types (see CBindingWrapping.h).
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DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Use, LLVMUseRef)
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}
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#endif
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