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 ConstantRange;
23class APInt;
24
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.
29///
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).
35///
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/// LLVM Constant Representation
42class Constant : public User {
43protected:
44 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
45 : User(ty, vty, Ops, NumOps) {}
46
47 ~Constant() = default;
48
49public:
50 void operator=(const Constant &) = delete;
51 Constant(const Constant &) = delete;
52
53 /// Return true if this is the value that would be returned by getNullValue.
54 bool isNullValue() const;
55
56 /// Returns true if the value is one.
57 bool isOneValue() const;
58
59 /// Return true if the value is not the one value, or,
60 /// for vectors, does not contain one value elements.
61 bool isNotOneValue() const;
62
63 /// Return true if this is the value that would be returned by
64 /// getAllOnesValue.
65 bool isAllOnesValue() const;
66
67 /// Return true if the value is what would be returned by
68 /// getZeroValueForNegation.
69 bool isNegativeZeroValue() const;
70
71 /// Return true if the value is negative zero or null value.
72 bool isZeroValue() const;
73
74 /// Return true if the value is not the smallest signed value, or,
75 /// for vectors, does not contain smallest signed value elements.
76 bool isNotMinSignedValue() const;
77
78 /// Return true if the value is the smallest signed value.
79 bool isMinSignedValue() const;
80
81 /// Return true if this is a finite and non-zero floating-point scalar
82 /// constant or a fixed width vector constant with all finite and non-zero
83 /// elements.
84 bool isFiniteNonZeroFP() const;
85
86 /// Return true if this is a normal (as opposed to denormal, infinity, nan,
87 /// or zero) floating-point scalar constant or a vector constant with all
88 /// normal elements. See APFloat::isNormal.
89 bool isNormalFP() const;
90
91 /// Return true if this scalar has an exact multiplicative inverse or this
92 /// vector has an exact multiplicative inverse for each element in the vector.
93 bool hasExactInverseFP() const;
94
95 /// Return true if this is a floating-point NaN constant or a vector
96 /// floating-point constant with all NaN elements.
97 bool isNaN() const;
98
99 /// Return true if this constant and a constant 'Y' are element-wise equal.
100 /// This is identical to just comparing the pointers, with the exception that
101 /// for vectors, if only one of the constants has an `undef` element in some
102 /// lane, the constants still match.
103 bool isElementWiseEqual(Value *Y) const;
104
105 /// Return true if this is a vector constant that includes any undef or
106 /// poison elements. Since it is impossible to inspect a scalable vector
107 /// element- wise at compile time, this function returns true only if the
108 /// entire vector is undef or poison.
109 bool containsUndefOrPoisonElement() const;
110
111 /// Return true if this is a vector constant that includes any poison
112 /// elements.
113 bool containsPoisonElement() const;
114
115 /// Return true if this is a vector constant that includes any strictly undef
116 /// (not poison) elements.
117 bool containsUndefElement() const;
118
119 /// Return true if this is a fixed width vector constant that includes
120 /// any constant expressions.
121 bool containsConstantExpression() const;
122
123 /// Return true if the value can vary between threads.
124 bool isThreadDependent() const;
125
126 /// Return true if the value is dependent on a dllimport variable.
127 bool isDLLImportDependent() const;
128
129 /// Return true if the constant has users other than constant expressions and
130 /// other dangling things.
131 bool isConstantUsed() const;
132
133 /// This method classifies the entry according to whether or not it may
134 /// generate a relocation entry (either static or dynamic). This must be
135 /// conservative, so if it might codegen to a relocatable entry, it should say
136 /// so.
137 ///
138 /// FIXME: This really should not be in IR.
139 bool needsRelocation() const;
140 bool needsDynamicRelocation() const;
141
142 /// For aggregates (struct/array/vector) return the constant that corresponds
143 /// to the specified element if possible, or null if not. This can return null
144 /// if the element index is a ConstantExpr, if 'this' is a constant expr or
145 /// if the constant does not fit into an uint64_t.
146 Constant *getAggregateElement(unsigned Elt) const;
147 Constant *getAggregateElement(Constant *Elt) const;
148
149 /// If all elements of the vector constant have the same value, return that
150 /// value. Otherwise, return nullptr. Ignore poison elements by setting
151 /// AllowPoison to true.
152 Constant *getSplatValue(bool AllowPoison = false) const;
153
154 /// If C is a constant integer then return its value, otherwise C must be a
155 /// vector of constant integers, all equal, and the common value is returned.
156 const APInt &getUniqueInteger() const;
157
158 /// Convert constant to an approximate constant range. For vectors, the
159 /// range is the union over the element ranges. Poison elements are ignored.
160 ConstantRange toConstantRange() const;
161
162 /// Called if some element of this constant is no longer valid.
163 /// At this point only other constants may be on the use_list for this
164 /// constant. Any constants on our Use list must also be destroy'd. The
165 /// implementation must be sure to remove the constant from the list of
166 /// available cached constants. Implementations should implement
167 /// destroyConstantImpl to remove constants from any pools/maps they are
168 /// contained it.
169 void destroyConstant();
170
171 //// Methods for support type inquiry through isa, cast, and dyn_cast:
172 static bool classof(const Value *V) {
173 static_assert(ConstantFirstVal == 0, "V->getValueID() >= ConstantFirstVal always succeeds");
174 return V->getValueID() <= ConstantLastVal;
175 }
176
177 /// This method is a special form of User::replaceUsesOfWith
178 /// (which does not work on constants) that does work
179 /// on constants. Basically this method goes through the trouble of building
180 /// a new constant that is equivalent to the current one, with all uses of
181 /// From replaced with uses of To. After this construction is completed, all
182 /// of the users of 'this' are replaced to use the new constant, and then
183 /// 'this' is deleted. In general, you should not call this method, instead,
184 /// use Value::replaceAllUsesWith, which automatically dispatches to this
185 /// method as needed.
186 ///
187 void handleOperandChange(Value *, Value *);
188
189 static Constant *getNullValue(Type* Ty);
190
191 /// @returns the value for an integer or vector of integer constant of the
192 /// given type that has all its bits set to true.
193 /// Get the all ones value
194 static Constant *getAllOnesValue(Type* Ty);
195
196 /// Return the value for an integer or pointer constant, or a vector thereof,
197 /// with the given scalar value.
198 static Constant *getIntegerValue(Type *Ty, const APInt &V);
199
200 /// If there are any dead constant users dangling off of this constant, remove
201 /// them. This method is useful for clients that want to check to see if a
202 /// global is unused, but don't want to deal with potentially dead constants
203 /// hanging off of the globals.
204 void removeDeadConstantUsers() const;
205
206 /// Return true if the constant has exactly one live use.
207 ///
208 /// This returns the same result as calling Value::hasOneUse after
209 /// Constant::removeDeadConstantUsers, but doesn't remove dead constants.
210 bool hasOneLiveUse() const;
211
212 /// Return true if the constant has no live uses.
213 ///
214 /// This returns the same result as calling Value::use_empty after
215 /// Constant::removeDeadConstantUsers, but doesn't remove dead constants.
216 bool hasZeroLiveUses() const;
217
218 const Constant *stripPointerCasts() const {
219 return cast<Constant>(Val: Value::stripPointerCasts());
220 }
221
222 Constant *stripPointerCasts() {
223 return const_cast<Constant*>(
224 static_cast<const Constant *>(this)->stripPointerCasts());
225 }
226
227 /// Try to replace undefined constant C or undefined elements in C with
228 /// Replacement. If no changes are made, the constant C is returned.
229 static Constant *replaceUndefsWith(Constant *C, Constant *Replacement);
230
231 /// Merges undefs of a Constant with another Constant, along with the
232 /// undefs already present. Other doesn't have to be the same type as C, but
233 /// both must either be scalars or vectors with the same element count. If no
234 /// changes are made, the constant C is returned.
235 static Constant *mergeUndefsWith(Constant *C, Constant *Other);
236
237 /// Return true if a constant is ConstantData or a ConstantAggregate or
238 /// ConstantExpr that contain only ConstantData.
239 bool isManifestConstant() const;
240
241private:
242 enum PossibleRelocationsTy {
243 /// This constant requires no relocations. That is, it holds simple
244 /// constants (like integrals).
245 NoRelocation = 0,
246
247 /// This constant holds static relocations that can be resolved by the
248 /// static linker.
249 LocalRelocation = 1,
250
251 /// This constant holds dynamic relocations that the dynamic linker will
252 /// need to resolve.
253 GlobalRelocation = 2,
254 };
255
256 /// Determine what potential relocations may be needed by this constant.
257 PossibleRelocationsTy getRelocationInfo() const;
258
259 bool hasNLiveUses(unsigned N) const;
260};
261
262} // end namespace llvm
263
264#endif // LLVM_IR_CONSTANT_H
265