1 //===-- llvm/Constant.h - Constant class definition -------------*- 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 file contains the declaration of the Constant class.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_CONSTANT_H
15 #define LLVM_CONSTANT_H
17 #include "llvm/User.h"
20 template<typename T> class SmallVectorImpl;
22 /// If object contains references to other objects, then relocations are
23 /// usually required for emission of such object (especially in PIC mode). One
24 /// usually distinguishes local and global relocations. Local relocations are
25 /// made wrt objects in the same module and these objects have local (internal
26 /// or private) linkage. Global relocations are made wrt externally visible
27 /// objects. In most cases local relocations can be resolved via so-called
28 /// 'pre-link' technique.
30 const unsigned None = 0;
31 const unsigned Local = 1 << 0; ///< Local relocations are required
32 const unsigned Global = 1 << 1; ///< Global relocations are required
33 const unsigned LocalOrGlobal = Local | Global;
36 /// This is an important base class in LLVM. It provides the common facilities
37 /// of all constant values in an LLVM program. A constant is a value that is
38 /// immutable at runtime. Functions are constants because their address is
39 /// immutable. Same with global variables.
41 /// All constants share the capabilities provided in this class. All constants
42 /// can have a null value. They can have an operand list. Constants can be
43 /// simple (integer and floating point values), complex (arrays and structures),
44 /// or expression based (computations yielding a constant value composed of
45 /// only certain operators and other constant values).
47 /// Note that Constants are immutable (once created they never change)
48 /// and are fully shared by structural equivalence. This means that two
49 /// structurally equivalent constants will always have the same address.
50 /// Constants are created on demand as needed and never deleted: thus clients
51 /// don't have to worry about the lifetime of the objects.
52 /// @brief LLVM Constant Representation
53 class Constant : public User {
54 void operator=(const Constant &); // Do not implement
55 Constant(const Constant &); // Do not implement
57 Constant(const Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
58 : User(ty, vty, Ops, NumOps) {}
60 void destroyConstantImpl();
62 /// Static constructor to get a '0' constant of arbitrary type...
64 static Constant *getNullValue(const Type *Ty);
66 /// Static constructor to get a '-1' constant. This supports integers and
69 static Constant *getAllOnesValue(const Type *Ty);
71 /// isNullValue - Return true if this is the value that would be returned by
73 virtual bool isNullValue() const = 0;
75 /// canTrap - Return true if evaluation of this constant could trap. This is
76 /// true for things like constant expressions that could divide by zero.
79 /// ContainsRelocations - Return true if the constant value contains
80 /// relocations which cannot be resolved at compile time. Note that answer is
81 /// not exclusive: there can be possibility that relocations of other kind are
83 bool ContainsRelocations(unsigned Kind = Reloc::LocalOrGlobal) const;
85 // Specialize get/setOperand for Constants as their operands are always
87 Constant *getOperand(unsigned i) {
88 return static_cast<Constant*>(User::getOperand(i));
90 const Constant *getOperand(unsigned i) const {
91 return static_cast<const Constant*>(User::getOperand(i));
93 void setOperand(unsigned i, Constant *C) {
94 User::setOperand(i, C);
97 /// getVectorElements - This method, which is only valid on constant of vector
98 /// type, returns the elements of the vector in the specified smallvector.
99 /// This handles breaking down a vector undef into undef elements, etc. For
100 /// constant exprs and other cases we can't handle, we return an empty vector.
101 void getVectorElements(SmallVectorImpl<Constant*> &Elts) const;
103 /// destroyConstant - Called if some element of this constant is no longer
104 /// valid. At this point only other constants may be on the use_list for this
105 /// constant. Any constants on our Use list must also be destroy'd. The
106 /// implementation must be sure to remove the constant from the list of
107 /// available cached constants. Implementations should call
108 /// destroyConstantImpl as the last thing they do, to destroy all users and
110 virtual void destroyConstant() { assert(0 && "Not reached!"); }
112 //// Methods for support type inquiry through isa, cast, and dyn_cast:
113 static inline bool classof(const Constant *) { return true; }
114 static inline bool classof(const GlobalValue *) { return true; }
115 static inline bool classof(const Value *V) {
116 return V->getValueID() >= ConstantFirstVal &&
117 V->getValueID() <= ConstantLastVal;
120 /// replaceUsesOfWithOnConstant - This method is a special form of
121 /// User::replaceUsesOfWith (which does not work on constants) that does work
122 /// on constants. Basically this method goes through the trouble of building
123 /// a new constant that is equivalent to the current one, with all uses of
124 /// From replaced with uses of To. After this construction is completed, all
125 /// of the users of 'this' are replaced to use the new constant, and then
126 /// 'this' is deleted. In general, you should not call this method, instead,
127 /// use Value::replaceAllUsesWith, which automatically dispatches to this
128 /// method as needed.
130 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
131 // Provide a default implementation for constants (like integers) that
132 // cannot use any other values. This cannot be called at runtime, but needs
133 // to be here to avoid link errors.
134 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
135 "implemented for all constants that have operands!");
136 assert(0 && "Constants that do not have operands cannot be using 'From'!");
140 } // End llvm namespace