1//===-- llvm/Constant.h - Constant class definition -------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file contains the declaration of the Constant class.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_IR_CONSTANT_H
14#define LLVM_IR_CONSTANT_H
15
16#include "llvm/IR/User.h"
17#include "llvm/IR/Value.h"
18#include "llvm/Support/Casting.h"
19
20namespace llvm {
21
22class APInt;
23
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.
28///
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).
34///
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/// LLVM Constant Representation
41class Constant : public User {
42protected:
43 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
44 : User(ty, vty, Ops, NumOps) {}
45
46 ~Constant() = default;
47
48public:
49 void operator=(const Constant &) = delete;
50 Constant(const Constant &) = delete;
51
52 /// Return true if this is the value that would be returned by getNullValue.
53 bool isNullValue() const;
54
55 /// Returns true if the value is one.
56 bool isOneValue() const;
57
58 /// Return true if the value is not the one value, or,
59 /// for vectors, does not contain one value elements.
60 bool isNotOneValue() const;
61
62 /// Return true if this is the value that would be returned by
63 /// getAllOnesValue.
64 bool isAllOnesValue() const;
65
66 /// Return true if the value is what would be returned by
67 /// getZeroValueForNegation.
68 bool isNegativeZeroValue() const;
69
70 /// Return true if the value is negative zero or null value.
71 bool isZeroValue() const;
72
73 /// Return true if the value is not the smallest signed value, or,
74 /// for vectors, does not contain smallest signed value elements.
75 bool isNotMinSignedValue() const;
76
77 /// Return true if the value is the smallest signed value.
78 bool isMinSignedValue() const;
79
80 /// Return true if this is a finite and non-zero floating-point scalar
81 /// constant or a fixed width vector constant with all finite and non-zero
82 /// elements.
83 bool isFiniteNonZeroFP() const;
84
85 /// Return true if this is a normal (as opposed to denormal, infinity, nan,
86 /// or zero) floating-point scalar constant or a vector constant with all
87 /// normal elements. See APFloat::isNormal.
88 bool isNormalFP() const;
89
90 /// Return true if this scalar has an exact multiplicative inverse or this
91 /// vector has an exact multiplicative inverse for each element in the vector.
92 bool hasExactInverseFP() const;
93
94 /// Return true if this is a floating-point NaN constant or a vector
95 /// floating-point constant with all NaN elements.
96 bool isNaN() const;
97
98 /// Return true if this constant and a constant 'Y' are element-wise equal.
99 /// This is identical to just comparing the pointers, with the exception that
100 /// for vectors, if only one of the constants has an `undef` element in some
101 /// lane, the constants still match.
102 bool isElementWiseEqual(Value *Y) const;
103
104 /// Return true if this is a vector constant that includes any undef or
105 /// poison elements. Since it is impossible to inspect a scalable vector
106 /// element- wise at compile time, this function returns true only if the
107 /// entire vector is undef or poison.
108 bool containsUndefOrPoisonElement() const;
109
110 /// Return true if this is a vector constant that includes any poison
111 /// elements.
112 bool containsPoisonElement() const;
113
114 /// Return true if this is a fixed width vector constant that includes
115 /// any constant expressions.
116 bool containsConstantExpression() const;
117
118 /// Return true if evaluation of this constant could trap. This is true for
119 /// things like constant expressions that could divide by zero.
120 bool canTrap() const;
121
122 /// Return true if the value can vary between threads.
123 bool isThreadDependent() const;
124
125 /// Return true if the value is dependent on a dllimport variable.
126 bool isDLLImportDependent() const;
127
128 /// Return true if the constant has users other than constant expressions and
129 /// other dangling things.
130 bool isConstantUsed() const;
131
132 /// This method classifies the entry according to whether or not it may
133 /// generate a relocation entry (either static or dynamic). This must be
134 /// conservative, so if it might codegen to a relocatable entry, it should say
135 /// so.
136 ///
137 /// FIXME: This really should not be in IR.
138 bool needsRelocation() const;
139 bool needsDynamicRelocation() const;
140
141 /// For aggregates (struct/array/vector) return the constant that corresponds
142 /// to the specified element if possible, or null if not. This can return null
143 /// if the element index is a ConstantExpr, if 'this' is a constant expr or
144 /// if the constant does not fit into an uint64_t.
145 Constant *getAggregateElement(unsigned Elt) const;
146 Constant *getAggregateElement(Constant *Elt) const;
147
148 /// If all elements of the vector constant have the same value, return that
149 /// value. Otherwise, return nullptr. Ignore undefined elements by setting
150 /// AllowUndefs to true.
151 Constant *getSplatValue(bool AllowUndefs = false) const;
152
153 /// If C is a constant integer then return its value, otherwise C must be a
154 /// vector of constant integers, all equal, and the common value is returned.
155 const APInt &getUniqueInteger() const;
156
157 /// Called if some element of this constant is no longer valid.
158 /// At this point only other constants may be on the use_list for this
159 /// constant. Any constants on our Use list must also be destroy'd. The
160 /// implementation must be sure to remove the constant from the list of
161 /// available cached constants. Implementations should implement
162 /// destroyConstantImpl to remove constants from any pools/maps they are
163 /// contained it.
164 void destroyConstant();
165
166 //// Methods for support type inquiry through isa, cast, and dyn_cast:
167 static bool classof(const Value *V) {
168 static_assert(ConstantFirstVal == 0, "V->getValueID() >= ConstantFirstVal always succeeds");
169 return V->getValueID() <= ConstantLastVal;
170 }
171
172 /// This method is a special form of User::replaceUsesOfWith
173 /// (which does not work on constants) that does work
174 /// on constants. Basically this method goes through the trouble of building
175 /// a new constant that is equivalent to the current one, with all uses of
176 /// From replaced with uses of To. After this construction is completed, all
177 /// of the users of 'this' are replaced to use the new constant, and then
178 /// 'this' is deleted. In general, you should not call this method, instead,
179 /// use Value::replaceAllUsesWith, which automatically dispatches to this
180 /// method as needed.
181 ///
182 void handleOperandChange(Value *, Value *);
183
184 static Constant *getNullValue(Type* Ty);
185
186 /// @returns the value for an integer or vector of integer constant of the
187 /// given type that has all its bits set to true.
188 /// Get the all ones value
189 static Constant *getAllOnesValue(Type* Ty);
190
191 /// Return the value for an integer or pointer constant, or a vector thereof,
192 /// with the given scalar value.
193 static Constant *getIntegerValue(Type *Ty, const APInt &V);
194
195 /// If there are any dead constant users dangling off of this constant, remove
196 /// them. This method is useful for clients that want to check to see if a
197 /// global is unused, but don't want to deal with potentially dead constants
198 /// hanging off of the globals.
199 void removeDeadConstantUsers() const;
200
201 const Constant *stripPointerCasts() const {
202 return cast<Constant>(Value::stripPointerCasts());
203 }
204
205 Constant *stripPointerCasts() {
206 return const_cast<Constant*>(
207 static_cast<const Constant *>(this)->stripPointerCasts());
208 }
209
210 /// Try to replace undefined constant C or undefined elements in C with
211 /// Replacement. If no changes are made, the constant C is returned.
212 static Constant *replaceUndefsWith(Constant *C, Constant *Replacement);
213
214 /// Merges undefs of a Constant with another Constant, along with the
215 /// undefs already present. Other doesn't have to be the same type as C, but
216 /// both must either be scalars or vectors with the same element count. If no
217 /// changes are made, the constant C is returned.
218 static Constant *mergeUndefsWith(Constant *C, Constant *Other);
219
220private:
221 enum PossibleRelocationsTy {
222 /// This constant requires no relocations. That is, it holds simple
223 /// constants (like integrals).
224 NoRelocation = 0,
225
226 /// This constant holds static relocations that can be resolved by the
227 /// static linker.
228 LocalRelocation = 1,
229
230 /// This constant holds dynamic relocations that the dynamic linker will
231 /// need to resolve.
232 GlobalRelocation = 2,
233 };
234
235 /// Determine what potential relocations may be needed by this constant.
236 PossibleRelocationsTy getRelocationInfo() const;
237};
238
239} // end namespace llvm
240
241#endif // LLVM_IR_CONSTANT_H
242