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
44 virtual void anchor();
47 Constant(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 bool isNullValue() const;
56 /// isAllOnesValue - Return true if this is the value that would be returned by
58 bool isAllOnesValue() const;
60 /// isNegativeZeroValue - Return true if the value is what would be returned
61 /// by getZeroValueForNegation.
62 bool isNegativeZeroValue() const;
64 /// canTrap - Return true if evaluation of this constant could trap. This is
65 /// true for things like constant expressions that could divide by zero.
68 /// isConstantUsed - Return true if the constant has users other than constant
69 /// exprs and other dangling things.
70 bool isConstantUsed() const;
72 enum PossibleRelocationsTy {
78 /// getRelocationInfo - This method classifies the entry according to
79 /// whether or not it may generate a relocation entry. This must be
80 /// conservative, so if it might codegen to a relocatable entry, it should say
81 /// so. The return values are:
83 /// NoRelocation: This constant pool entry is guaranteed to never have a
84 /// relocation applied to it (because it holds a simple constant like
86 /// LocalRelocation: This entry has relocations, but the entries are
87 /// guaranteed to be resolvable by the static linker, so the dynamic
88 /// linker will never see them.
89 /// GlobalRelocations: This entry may have arbitrary relocations.
91 /// FIXME: This really should not be in VMCore.
92 PossibleRelocationsTy getRelocationInfo() const;
94 /// getAggregateElement - For aggregates (struct/array/vector) return the
95 /// constant that corresponds to the specified element if possible, or null if
96 /// not. This can return null if the element index is a ConstantExpr, or if
97 /// 'this' is a constant expr.
98 Constant *getAggregateElement(unsigned Elt) const;
99 Constant *getAggregateElement(Constant *Elt) 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() { llvm_unreachable("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 llvm_unreachable("Constants that do not have operands cannot be using "
138 static Constant *getNullValue(Type* Ty);
140 /// @returns the value for an integer or vector of integer constant of the
141 /// given type that has all its bits set to true.
142 /// @brief Get the all ones value
143 static Constant *getAllOnesValue(Type* Ty);
145 /// getIntegerValue - Return the value for an integer or pointer constant,
146 /// or a vector thereof, with the given scalar value.
147 static Constant *getIntegerValue(Type* Ty, const APInt &V);
149 /// removeDeadConstantUsers - If there are any dead constant users dangling
150 /// off of this constant, remove them. This method is useful for clients
151 /// that want to check to see if a global is unused, but don't want to deal
152 /// with potentially dead constants hanging off of the globals.
153 void removeDeadConstantUsers() const;
156 } // End llvm namespace