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 const unsigned Local = 1 << 0; ///< Local relocations are required
24 const unsigned Global = 1 << 1; ///< Global relocations are required
25 const unsigned LocalOrGlobal = Local | Global;
28 /// This is an important base class in LLVM. It provides the common facilities
29 /// of all constant values in an LLVM program. A constant is a value that is
30 /// immutable at runtime. Functions are constants because their address is
31 /// immutable. Same with global variables.
33 /// All constants share the capabilities provided in this class. All constants
34 /// can have a null value. They can have an operand list. Constants can be
35 /// simple (integer and floating point values), complex (arrays and structures),
36 /// or expression based (computations yielding a constant value composed of
37 /// only certain operators and other constant values).
39 /// Note that Constants are immutable (once created they never change)
40 /// and are fully shared by structural equivalence. This means that two
41 /// structurally equivalent constants will always have the same address.
42 /// Constants are created on demand as needed and never deleted: thus clients
43 /// don't have to worry about the lifetime of the objects.
44 /// @brief LLVM Constant Representation
45 class Constant : public User {
46 void operator=(const Constant &); // Do not implement
47 Constant(const Constant &); // Do not implement
49 Constant(const Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
50 : User(ty, vty, Ops, NumOps) {}
52 void destroyConstantImpl();
54 /// Static constructor to get a '0' constant of arbitrary type...
56 static Constant *getNullValue(const Type *Ty);
58 /// Static constructor to get a '-1' constant. This supports integers and
61 static Constant *getAllOnesValue(const Type *Ty);
63 /// isNullValue - Return true if this is the value that would be returned by
65 virtual bool isNullValue() const = 0;
67 /// canTrap - Return true if evaluation of this constant could trap. This is
68 /// true for things like constant expressions that could divide by zero.
71 /// ContainsRelocations - Return true if the constant value contains
72 /// relocations which cannot be resolved at compile time.
73 bool ContainsRelocations(unsigned Kind = Reloc::LocalOrGlobal) const;
75 // Specialize get/setOperand for Constants as their operands are always
77 Constant *getOperand(unsigned i) {
78 return static_cast<Constant*>(User::getOperand(i));
80 const Constant *getOperand(unsigned i) const {
81 return static_cast<const Constant*>(User::getOperand(i));
83 void setOperand(unsigned i, Constant *C) {
84 User::setOperand(i, C);
87 /// getVectorElements - This method, which is only valid on constant of vector
88 /// type, returns the elements of the vector in the specified smallvector.
89 /// This handles breaking down a vector undef into undef elements, etc. For
90 /// constant exprs and other cases we can't handle, we return an empty vector.
91 void getVectorElements(SmallVectorImpl<Constant*> &Elts) const;
93 /// destroyConstant - Called if some element of this constant is no longer
94 /// valid. At this point only other constants may be on the use_list for this
95 /// constant. Any constants on our Use list must also be destroy'd. The
96 /// implementation must be sure to remove the constant from the list of
97 /// available cached constants. Implementations should call
98 /// destroyConstantImpl as the last thing they do, to destroy all users and
100 virtual void destroyConstant() { assert(0 && "Not reached!"); }
102 //// Methods for support type inquiry through isa, cast, and dyn_cast:
103 static inline bool classof(const Constant *) { return true; }
104 static inline bool classof(const GlobalValue *) { return true; }
105 static inline bool classof(const Value *V) {
106 return V->getValueID() >= ConstantFirstVal &&
107 V->getValueID() <= ConstantLastVal;
110 /// replaceUsesOfWithOnConstant - This method is a special form of
111 /// User::replaceUsesOfWith (which does not work on constants) that does work
112 /// on constants. Basically this method goes through the trouble of building
113 /// a new constant that is equivalent to the current one, with all uses of
114 /// From replaced with uses of To. After this construction is completed, all
115 /// of the users of 'this' are replaced to use the new constant, and then
116 /// 'this' is deleted. In general, you should not call this method, instead,
117 /// use Value::replaceAllUsesWith, which automatically dispatches to this
118 /// method as needed.
120 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
121 // Provide a default implementation for constants (like integers) that
122 // cannot use any other values. This cannot be called at runtime, but needs
123 // to be here to avoid link errors.
124 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
125 "implemented for all constants that have operands!");
126 assert(0 && "Constants that do not have operands cannot be using 'From'!");
130 } // End llvm namespace