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"
18 #include "llvm/IR/Value.h"
19 #include "llvm/Support/Casting.h"
25 /// This is an important base class in LLVM. It provides the common facilities
26 /// of all constant values in an LLVM program. A constant is a value that is
27 /// immutable at runtime. Functions are constants because their address is
28 /// immutable. Same with global variables.
30 /// All constants share the capabilities provided in this class. All constants
31 /// can have a null value. They can have an operand list. Constants can be
32 /// simple (integer and floating point values), complex (arrays and structures),
33 /// or expression based (computations yielding a constant value composed of
34 /// only certain operators and other constant values).
36 /// Note that Constants are immutable (once created they never change)
37 /// and are fully shared by structural equivalence. This means that two
38 /// structurally equivalent constants will always have the same address.
39 /// Constants are created on demand as needed and never deleted: thus clients
40 /// don't have to worry about the lifetime of the objects.
41 /// @brief LLVM Constant Representation
42 class Constant : public User {
44 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
45 : User(ty, vty, Ops, NumOps) {}
48 void operator=(const Constant &) = delete;
49 Constant(const Constant &) = delete;
51 /// Return true if this is the value that would be returned by getNullValue.
52 bool isNullValue() const;
54 /// Returns true if the value is one.
55 bool isOneValue() const;
57 /// Return true if this is the value that would be returned by
59 bool isAllOnesValue() const;
61 /// Return true if the value is what would be returned by
62 /// getZeroValueForNegation.
63 bool isNegativeZeroValue() const;
65 /// Return true if the value is negative zero or null value.
66 bool isZeroValue() const;
68 /// Return true if the value is not the smallest signed value.
69 bool isNotMinSignedValue() const;
71 /// Return true if the value is the smallest signed value.
72 bool isMinSignedValue() const;
74 /// Return true if evaluation of this constant could trap. This is true for
75 /// things like constant expressions that could divide by zero.
78 /// Return true if the value can vary between threads.
79 bool isThreadDependent() const;
81 /// Return true if the value is dependent on a dllimport variable.
82 bool isDLLImportDependent() const;
84 /// Return true if the constant has users other than constant expressions and
85 /// other dangling things.
86 bool isConstantUsed() const;
88 /// This method classifies the entry according to whether or not it may
89 /// generate a relocation entry. This must be conservative, so if it might
90 /// codegen to a relocatable entry, it should say so.
92 /// FIXME: This really should not be in IR.
93 bool needsRelocation() const;
95 /// For aggregates (struct/array/vector) return the constant that corresponds
96 /// to the specified element if possible, or null if not. This can return null
97 /// if the element index is a ConstantExpr, or if 'this' is a constant expr.
98 Constant *getAggregateElement(unsigned Elt) const;
99 Constant *getAggregateElement(Constant *Elt) const;
101 /// If this is a splat vector constant, meaning that all of the elements have
102 /// the same value, return that value. Otherwise return 0.
103 Constant *getSplatValue() const;
105 /// If C is a constant integer then return its value, otherwise C must be a
106 /// vector of constant integers, all equal, and the common value is returned.
107 const APInt &getUniqueInteger() const;
109 /// Called if some element of this constant is no longer valid.
110 /// At this point only other constants may be on the use_list for this
111 /// constant. Any constants on our Use list must also be destroy'd. The
112 /// implementation must be sure to remove the constant from the list of
113 /// available cached constants. Implementations should implement
114 /// destroyConstantImpl to remove constants from any pools/maps they are
116 void destroyConstant();
118 //// Methods for support type inquiry through isa, cast, and dyn_cast:
119 static bool classof(const Value *V) {
120 return V->getValueID() >= ConstantFirstVal &&
121 V->getValueID() <= ConstantLastVal;
124 /// This method is a special form of User::replaceUsesOfWith
125 /// (which does not work on constants) that does work
126 /// on constants. Basically this method goes through the trouble of building
127 /// a new constant that is equivalent to the current one, with all uses of
128 /// From replaced with uses of To. After this construction is completed, all
129 /// of the users of 'this' are replaced to use the new constant, and then
130 /// 'this' is deleted. In general, you should not call this method, instead,
131 /// use Value::replaceAllUsesWith, which automatically dispatches to this
132 /// method as needed.
134 void handleOperandChange(Value *, Value *);
136 static Constant *getNullValue(Type* Ty);
138 /// @returns the value for an integer or vector of integer constant of the
139 /// given type that has all its bits set to true.
140 /// @brief Get the all ones value
141 static Constant *getAllOnesValue(Type* Ty);
143 /// Return the value for an integer or pointer constant, or a vector thereof,
144 /// with the given scalar value.
145 static Constant *getIntegerValue(Type *Ty, const APInt &V);
147 /// If there are any dead constant users dangling off of this constant, remove
148 /// them. This method is useful for clients that want to check to see if a
149 /// global is unused, but don't want to deal with potentially dead constants
150 /// hanging off of the globals.
151 void removeDeadConstantUsers() const;
153 const Constant *stripPointerCasts() const {
154 return cast<Constant>(Value::stripPointerCasts());
157 Constant *stripPointerCasts() {
158 return const_cast<Constant*>(
159 static_cast<const Constant *>(this)->stripPointerCasts());
163 } // end namespace llvm
165 #endif // LLVM_IR_CONSTANT_H