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_IR_CONSTANT_H
15 #define LLVM_IR_CONSTANT_H
17 #include "llvm/IR/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 &) = delete;
43 Constant(const Constant &) = delete;
44 void anchor() override;
47 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
48 : User(ty, vty, Ops, NumOps) {}
50 void replaceUsesOfWithOnConstantImpl(Constant *Replacement);
53 /// isNullValue - Return true if this is the value that would be returned by
55 bool isNullValue() const;
57 /// \brief Returns true if the value is one.
58 bool isOneValue() const;
60 /// isAllOnesValue - Return true if this is the value that would be returned by
62 bool isAllOnesValue() const;
64 /// isNegativeZeroValue - Return true if the value is what would be returned
65 /// by getZeroValueForNegation.
66 bool isNegativeZeroValue() const;
68 /// Return true if the value is negative zero or null value.
69 bool isZeroValue() const;
71 /// \brief Return true if the value is not the smallest signed value.
72 bool isNotMinSignedValue() const;
74 /// \brief Return true if the value is the smallest signed value.
75 bool isMinSignedValue() const;
77 /// canTrap - Return true if evaluation of this constant could trap. This is
78 /// true for things like constant expressions that could divide by zero.
81 /// isThreadDependent - Return true if the value can vary between threads.
82 bool isThreadDependent() const;
84 /// Return true if the value is dependent on a dllimport variable.
85 bool isDLLImportDependent() const;
87 /// isConstantUsed - Return true if the constant has users other than constant
88 /// exprs and other dangling things.
89 bool isConstantUsed() const;
91 enum PossibleRelocationsTy {
97 /// getRelocationInfo - This method classifies the entry according to
98 /// whether or not it may generate a relocation entry. This must be
99 /// conservative, so if it might codegen to a relocatable entry, it should say
100 /// so. The return values are:
102 /// NoRelocation: This constant pool entry is guaranteed to never have a
103 /// relocation applied to it (because it holds a simple constant like
105 /// LocalRelocation: This entry has relocations, but the entries are
106 /// guaranteed to be resolvable by the static linker, so the dynamic
107 /// linker will never see them.
108 /// GlobalRelocations: This entry may have arbitrary relocations.
110 /// FIXME: This really should not be in VMCore.
111 PossibleRelocationsTy getRelocationInfo() const;
113 /// getAggregateElement - For aggregates (struct/array/vector) return the
114 /// constant that corresponds to the specified element if possible, or null if
115 /// not. This can return null if the element index is a ConstantExpr, or if
116 /// 'this' is a constant expr.
117 Constant *getAggregateElement(unsigned Elt) const;
118 Constant *getAggregateElement(Constant *Elt) const;
120 /// getSplatValue - If this is a splat vector constant, meaning that all of
121 /// the elements have the same value, return that value. Otherwise return 0.
122 Constant *getSplatValue() const;
124 /// If C is a constant integer then return its value, otherwise C must be a
125 /// vector of constant integers, all equal, and the common value is returned.
126 const APInt &getUniqueInteger() const;
128 /// Called if some element of this constant is no longer valid.
129 /// At this point only other constants may be on the use_list for this
130 /// constant. Any constants on our Use list must also be destroy'd. The
131 /// implementation must be sure to remove the constant from the list of
132 /// available cached constants. Implementations should implement
133 /// destroyConstantImpl to remove constants from any pools/maps they are
135 void destroyConstant();
137 //// Methods for support type inquiry through isa, cast, and dyn_cast:
138 static inline bool classof(const Value *V) {
139 return V->getValueID() >= ConstantFirstVal &&
140 V->getValueID() <= ConstantLastVal;
143 /// replaceUsesOfWithOnConstant - This method is a special form of
144 /// User::replaceUsesOfWith (which does not work on constants) that does work
145 /// on constants. Basically this method goes through the trouble of building
146 /// a new constant that is equivalent to the current one, with all uses of
147 /// From replaced with uses of To. After this construction is completed, all
148 /// of the users of 'this' are replaced to use the new constant, and then
149 /// 'this' is deleted. In general, you should not call this method, instead,
150 /// use Value::replaceAllUsesWith, which automatically dispatches to this
151 /// method as needed.
153 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
154 // Provide a default implementation for constants (like integers) that
155 // cannot use any other values. This cannot be called at runtime, but needs
156 // to be here to avoid link errors.
157 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
158 "implemented for all constants that have operands!");
159 llvm_unreachable("Constants that do not have operands cannot be using "
163 static Constant *getNullValue(Type* Ty);
165 /// @returns the value for an integer or vector of integer constant of the
166 /// given type that has all its bits set to true.
167 /// @brief Get the all ones value
168 static Constant *getAllOnesValue(Type* Ty);
170 /// getIntegerValue - Return the value for an integer or pointer constant,
171 /// or a vector thereof, with the given scalar value.
172 static Constant *getIntegerValue(Type* Ty, const APInt &V);
174 /// removeDeadConstantUsers - If there are any dead constant users dangling
175 /// off of this constant, remove them. This method is useful for clients
176 /// that want to check to see if a global is unused, but don't want to deal
177 /// with potentially dead constants hanging off of the globals.
178 void removeDeadConstantUsers() const;
180 Constant *stripPointerCasts() {
181 return cast<Constant>(Value::stripPointerCasts());
184 const Constant *stripPointerCasts() const {
185 return const_cast<Constant*>(this)->stripPointerCasts();
189 } // End llvm namespace