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