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