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