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 &) LLVM_DELETED_FUNCTION;
43 Constant(const Constant &) LLVM_DELETED_FUNCTION;
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 /// isThreadDependent - Return true if the value can vary between threads.
69 bool isThreadDependent() const;
71 /// isConstantUsed - Return true if the constant has users other than constant
72 /// exprs and other dangling things.
73 bool isConstantUsed() const;
75 enum PossibleRelocationsTy {
81 /// getRelocationInfo - This method classifies the entry according to
82 /// whether or not it may generate a relocation entry. This must be
83 /// conservative, so if it might codegen to a relocatable entry, it should say
84 /// so. The return values are:
86 /// NoRelocation: This constant pool entry is guaranteed to never have a
87 /// relocation applied to it (because it holds a simple constant like
89 /// LocalRelocation: This entry has relocations, but the entries are
90 /// guaranteed to be resolvable by the static linker, so the dynamic
91 /// linker will never see them.
92 /// GlobalRelocations: This entry may have arbitrary relocations.
94 /// FIXME: This really should not be in VMCore.
95 PossibleRelocationsTy getRelocationInfo() const;
97 /// getAggregateElement - For aggregates (struct/array/vector) return the
98 /// constant that corresponds to the specified element if possible, or null if
99 /// not. This can return null if the element index is a ConstantExpr, or if
100 /// 'this' is a constant expr.
101 Constant *getAggregateElement(unsigned Elt) const;
102 Constant *getAggregateElement(Constant *Elt) const;
104 /// destroyConstant - Called if some element of this constant is no longer
105 /// valid. At this point only other constants may be on the use_list for this
106 /// constant. Any constants on our Use list must also be destroy'd. The
107 /// implementation must be sure to remove the constant from the list of
108 /// available cached constants. Implementations should call
109 /// destroyConstantImpl as the last thing they do, to destroy all users and
111 virtual void destroyConstant() { llvm_unreachable("Not reached!"); }
113 //// Methods for support type inquiry through isa, cast, and dyn_cast:
114 static inline bool classof(const Value *V) {
115 return V->getValueID() >= ConstantFirstVal &&
116 V->getValueID() <= ConstantLastVal;
119 /// replaceUsesOfWithOnConstant - This method is a special form of
120 /// User::replaceUsesOfWith (which does not work on constants) that does work
121 /// on constants. Basically this method goes through the trouble of building
122 /// a new constant that is equivalent to the current one, with all uses of
123 /// From replaced with uses of To. After this construction is completed, all
124 /// of the users of 'this' are replaced to use the new constant, and then
125 /// 'this' is deleted. In general, you should not call this method, instead,
126 /// use Value::replaceAllUsesWith, which automatically dispatches to this
127 /// method as needed.
129 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
130 // Provide a default implementation for constants (like integers) that
131 // cannot use any other values. This cannot be called at runtime, but needs
132 // to be here to avoid link errors.
133 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
134 "implemented for all constants that have operands!");
135 llvm_unreachable("Constants that do not have operands cannot be using "
139 static Constant *getNullValue(Type* Ty);
141 /// @returns the value for an integer or vector of integer constant of the
142 /// given type that has all its bits set to true.
143 /// @brief Get the all ones value
144 static Constant *getAllOnesValue(Type* Ty);
146 /// getIntegerValue - Return the value for an integer or pointer constant,
147 /// or a vector thereof, with the given scalar value.
148 static Constant *getIntegerValue(Type* Ty, const APInt &V);
150 /// removeDeadConstantUsers - If there are any dead constant users dangling
151 /// off of this constant, remove them. This method is useful for clients
152 /// that want to check to see if a global is unused, but don't want to deal
153 /// with potentially dead constants hanging off of the globals.
154 void removeDeadConstantUsers() const;
157 } // End llvm namespace