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"
22 template<typename T> class SmallVectorImpl;
25 /// This is an important base class in LLVM. It provides the common facilities
26 /// of all constant values in an LLVM program. A constant is a value that is
27 /// immutable at runtime. Functions are constants because their address is
28 /// immutable. Same with global variables.
30 /// All constants share the capabilities provided in this class. All constants
31 /// can have a null value. They can have an operand list. Constants can be
32 /// simple (integer and floating point values), complex (arrays and structures),
33 /// or expression based (computations yielding a constant value composed of
34 /// only certain operators and other constant values).
36 /// Note that Constants are immutable (once created they never change)
37 /// and are fully shared by structural equivalence. This means that two
38 /// structurally equivalent constants will always have the same address.
39 /// Constants are created on demand as needed and never deleted: thus clients
40 /// don't have to worry about the lifetime of the objects.
41 /// @brief LLVM Constant Representation
42 class Constant : public User {
43 void operator=(const Constant &); // Do not implement
44 Constant(const Constant &); // Do not implement
47 Constant(const Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
48 : User(ty, vty, Ops, NumOps) {}
50 void destroyConstantImpl();
52 /// isNullValue - Return true if this is the value that would be returned by
54 virtual bool isNullValue() const = 0;
56 /// isNegativeZeroValue - Return true if the value is what would be returned
57 /// by getZeroValueForNegation.
58 virtual bool isNegativeZeroValue() const { return isNullValue(); }
60 /// canTrap - Return true if evaluation of this constant could trap. This is
61 /// true for things like constant expressions that could divide by zero.
64 enum PossibleRelocationsTy {
70 /// getRelocationInfo - This method classifies the entry according to
71 /// whether or not it may generate a relocation entry. This must be
72 /// conservative, so if it might codegen to a relocatable entry, it should say
73 /// so. The return values are:
75 /// NoRelocation: This constant pool entry is guaranteed to never have a
76 /// relocation applied to it (because it holds a simple constant like
78 /// LocalRelocation: This entry has relocations, but the entries are
79 /// guaranteed to be resolvable by the static linker, so the dynamic
80 /// linker will never see them.
81 /// GlobalRelocations: This entry may have arbitrary relocations.
83 /// FIXME: This really should not be in VMCore.
84 PossibleRelocationsTy getRelocationInfo() const;
86 // Specialize get/setOperand for Constants as their operands are always
88 Constant *getOperand(unsigned i) {
89 return static_cast<Constant*>(User::getOperand(i));
91 const Constant *getOperand(unsigned i) const {
92 return static_cast<const Constant*>(User::getOperand(i));
94 void setOperand(unsigned i, Constant *C) {
95 User::setOperand(i, C);
98 /// getVectorElements - This method, which is only valid on constant of vector
99 /// type, returns the elements of the vector in the specified smallvector.
100 /// This handles breaking down a vector undef into undef elements, etc. For
101 /// constant exprs and other cases we can't handle, we return an empty vector.
102 void getVectorElements(LLVMContext &Context,
103 SmallVectorImpl<Constant*> &Elts) const;
105 /// destroyConstant - Called if some element of this constant is no longer
106 /// valid. At this point only other constants may be on the use_list for this
107 /// constant. Any constants on our Use list must also be destroy'd. The
108 /// implementation must be sure to remove the constant from the list of
109 /// available cached constants. Implementations should call
110 /// destroyConstantImpl as the last thing they do, to destroy all users and
112 virtual void destroyConstant() { assert(0 && "Not reached!"); }
114 //// Methods for support type inquiry through isa, cast, and dyn_cast:
115 static inline bool classof(const Constant *) { return true; }
116 static inline bool classof(const GlobalValue *) { return true; }
117 static inline bool classof(const Value *V) {
118 return V->getValueID() >= ConstantFirstVal &&
119 V->getValueID() <= ConstantLastVal;
122 /// replaceUsesOfWithOnConstant - This method is a special form of
123 /// User::replaceUsesOfWith (which does not work on constants) that does work
124 /// on constants. Basically this method goes through the trouble of building
125 /// a new constant that is equivalent to the current one, with all uses of
126 /// From replaced with uses of To. After this construction is completed, all
127 /// of the users of 'this' are replaced to use the new constant, and then
128 /// 'this' is deleted. In general, you should not call this method, instead,
129 /// use Value::replaceAllUsesWith, which automatically dispatches to this
130 /// method as needed.
132 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
133 // Provide a default implementation for constants (like integers) that
134 // cannot use any other values. This cannot be called at runtime, but needs
135 // to be here to avoid link errors.
136 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
137 "implemented for all constants that have operands!");
138 assert(0 && "Constants that do not have operands cannot be using 'From'!");
141 static Constant* getNullValue(const Type* Ty);
143 /// @returns the value for an integer constant of the given type that has all
144 /// its bits set to true.
145 /// @brief Get the all ones value
146 static Constant* getAllOnesValue(const Type* Ty);
148 /// getIntegerValue - Return the value for an integer or pointer constant,
149 /// or a vector thereof, with the given scalar value.
150 static Constant* getIntegerValue(const Type* Ty, const APInt &V);
153 } // End llvm namespace