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) {}
51 /// isNullValue - Return true if this is the value that would be returned by
53 bool isNullValue() const;
55 /// \brief Returns true if the value is one.
56 bool isOneValue() const;
58 /// isAllOnesValue - Return true if this is the value that would be returned by
60 bool isAllOnesValue() const;
62 /// isNegativeZeroValue - Return true if the value is what would be returned
63 /// by getZeroValueForNegation.
64 bool isNegativeZeroValue() const;
66 /// Return true if the value is negative zero or null value.
67 bool isZeroValue() const;
69 /// \brief Return true if the value is not the smallest signed value.
70 bool isNotMinSignedValue() const;
72 /// \brief Return true if the value is the smallest signed value.
73 bool isMinSignedValue() const;
75 /// canTrap - Return true if evaluation of this constant could trap. This is
76 /// true for things like constant expressions that could divide by zero.
79 /// isThreadDependent - Return true if the value can vary between threads.
80 bool isThreadDependent() const;
82 /// Return true if the value is dependent on a dllimport variable.
83 bool isDLLImportDependent() const;
85 /// isConstantUsed - Return true if the constant has users other than constant
86 /// exprs and other dangling things.
87 bool isConstantUsed() const;
89 enum PossibleRelocationsTy {
95 /// getRelocationInfo - This method classifies the entry according to
96 /// whether or not it may generate a relocation entry. This must be
97 /// conservative, so if it might codegen to a relocatable entry, it should say
98 /// so. The return values are:
100 /// NoRelocation: This constant pool entry is guaranteed to never have a
101 /// relocation applied to it (because it holds a simple constant like
103 /// LocalRelocation: This entry has relocations, but the entries are
104 /// guaranteed to be resolvable by the static linker, so the dynamic
105 /// linker will never see them.
106 /// GlobalRelocations: This entry may have arbitrary relocations.
108 /// FIXME: This really should not be in VMCore.
109 PossibleRelocationsTy getRelocationInfo() const;
111 /// getAggregateElement - For aggregates (struct/array/vector) return the
112 /// constant that corresponds to the specified element if possible, or null if
113 /// not. This can return null if the element index is a ConstantExpr, or if
114 /// 'this' is a constant expr.
115 Constant *getAggregateElement(unsigned Elt) const;
116 Constant *getAggregateElement(Constant *Elt) const;
118 /// getSplatValue - If this is a splat vector constant, meaning that all of
119 /// the elements have the same value, return that value. Otherwise return 0.
120 Constant *getSplatValue() const;
122 /// If C is a constant integer then return its value, otherwise C must be a
123 /// vector of constant integers, all equal, and the common value is returned.
124 const APInt &getUniqueInteger() const;
126 /// Called if some element of this constant is no longer valid.
127 /// At this point only other constants may be on the use_list for this
128 /// constant. Any constants on our Use list must also be destroy'd. The
129 /// implementation must be sure to remove the constant from the list of
130 /// available cached constants. Implementations should implement
131 /// destroyConstantImpl to remove constants from any pools/maps they are
133 void destroyConstant();
135 //// Methods for support type inquiry through isa, cast, and dyn_cast:
136 static inline bool classof(const Value *V) {
137 return V->getValueID() >= ConstantFirstVal &&
138 V->getValueID() <= ConstantLastVal;
141 /// This method is a special form of User::replaceUsesOfWith
142 /// (which does not work on constants) that does work
143 /// on constants. Basically this method goes through the trouble of building
144 /// a new constant that is equivalent to the current one, with all uses of
145 /// From replaced with uses of To. After this construction is completed, all
146 /// of the users of 'this' are replaced to use the new constant, and then
147 /// 'this' is deleted. In general, you should not call this method, instead,
148 /// use Value::replaceAllUsesWith, which automatically dispatches to this
149 /// method as needed.
151 void handleOperandChange(Value *, Value *, Use *);
153 static Constant *getNullValue(Type* Ty);
155 /// @returns the value for an integer or vector of integer constant of the
156 /// given type that has all its bits set to true.
157 /// @brief Get the all ones value
158 static Constant *getAllOnesValue(Type* Ty);
160 /// getIntegerValue - Return the value for an integer or pointer constant,
161 /// or a vector thereof, with the given scalar value.
162 static Constant *getIntegerValue(Type* Ty, const APInt &V);
164 /// removeDeadConstantUsers - If there are any dead constant users dangling
165 /// off of this constant, remove them. This method is useful for clients
166 /// that want to check to see if a global is unused, but don't want to deal
167 /// with potentially dead constants hanging off of the globals.
168 void removeDeadConstantUsers() const;
170 Constant *stripPointerCasts() {
171 return cast<Constant>(Value::stripPointerCasts());
174 const Constant *stripPointerCasts() const {
175 return const_cast<Constant*>(this)->stripPointerCasts();
179 } // End llvm namespace