LLVM  14.0.0git
Constant.h
Go to the documentation of this file.
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 
20 namespace llvm {
21 
22 class 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
41 class Constant : public User {
42 protected:
43  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
44  : User(ty, vty, Ops, NumOps) {}
45 
46  ~Constant() = default;
47 
48 public:
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;
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  /// Return true if the constant has exactly one live use.
202  ///
203  /// This returns the same result as calling Value::hasOneUse after
204  /// Constant::removeDeadConstantUsers, but doesn't remove dead constants.
205  bool hasOneLiveUse() const;
206 
207  const Constant *stripPointerCasts() const {
208  return cast<Constant>(Value::stripPointerCasts());
209  }
210 
212  return const_cast<Constant*>(
213  static_cast<const Constant *>(this)->stripPointerCasts());
214  }
215 
216  /// Try to replace undefined constant C or undefined elements in C with
217  /// Replacement. If no changes are made, the constant C is returned.
218  static Constant *replaceUndefsWith(Constant *C, Constant *Replacement);
219 
220  /// Merges undefs of a Constant with another Constant, along with the
221  /// undefs already present. Other doesn't have to be the same type as C, but
222  /// both must either be scalars or vectors with the same element count. If no
223  /// changes are made, the constant C is returned.
224  static Constant *mergeUndefsWith(Constant *C, Constant *Other);
225 
226  /// Return true if a constant is ConstantData or a ConstantAggregate or
227  /// ConstantExpr that contain only ConstantData.
228  bool isManifestConstant() const;
229 
230 private:
231  enum PossibleRelocationsTy {
232  /// This constant requires no relocations. That is, it holds simple
233  /// constants (like integrals).
234  NoRelocation = 0,
235 
236  /// This constant holds static relocations that can be resolved by the
237  /// static linker.
238  LocalRelocation = 1,
239 
240  /// This constant holds dynamic relocations that the dynamic linker will
241  /// need to resolve.
242  GlobalRelocation = 2,
243  };
244 
245  /// Determine what potential relocations may be needed by this constant.
246  PossibleRelocationsTy getRelocationInfo() const;
247 };
248 
249 } // end namespace llvm
250 
251 #endif // LLVM_IR_CONSTANT_H
llvm::Constant::isAllOnesValue
bool isAllOnesValue() const
Return true if this is the value that would be returned by getAllOnesValue.
Definition: Constants.cpp:91
llvm::Constant::isFiniteNonZeroFP
bool isFiniteNonZeroFP() const
Return true if this is a finite and non-zero floating-point scalar constant or a fixed width vector c...
Definition: Constants.cpp:198
llvm
This file implements support for optimizing divisions by a constant.
Definition: AllocatorList.h:23
llvm::Constant::isNormalFP
bool isNormalFP() const
Return true if this is a normal (as opposed to denormal, infinity, nan, or zero) floating-point scala...
Definition: Constants.cpp:219
llvm::Constant::isNaN
bool isNaN() const
Return true if this is a floating-point NaN constant or a vector floating-point constant with all NaN...
Definition: Constants.cpp:261
llvm::Constant::containsPoisonElement
bool containsPoisonElement() const
Return true if this is a vector constant that includes any poison elements.
Definition: Constants.cpp:333
llvm::Type
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
llvm::Constant::isNotOneValue
bool isNotOneValue() const
Return true if the value is not the one value, or, for vectors, does not contain one value elements.
Definition: Constants.cpp:125
llvm::Constant::needsDynamicRelocation
bool needsDynamicRelocation() const
Definition: Constants.cpp:660
llvm::Constant::needsRelocation
bool needsRelocation() const
This method classifies the entry according to whether or not it may generate a relocation entry (eith...
Definition: Constants.cpp:664
llvm::Constant::classof
static bool classof(const Value *V)
Definition: Constant.h:167
llvm::Constant::~Constant
~Constant()=default
llvm::Constant::isOneValue
bool isOneValue() const
Returns true if the value is one.
Definition: Constants.cpp:108
llvm::Constant::isThreadDependent
bool isThreadDependent() const
Return true if the value can vary between threads.
Definition: Constants.cpp:634
llvm::Constant::containsConstantExpression
bool containsConstantExpression() const
Return true if this is a fixed width vector constant that includes any constant expressions.
Definition: Constants.cpp:338
llvm::Constant::isNullValue
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:74
llvm::User
Definition: User.h:44
C
(vector float) vec_cmpeq(*A, *B) C
Definition: README_ALTIVEC.txt:86
Y
static GCMetadataPrinterRegistry::Add< OcamlGCMetadataPrinter > Y("ocaml", "ocaml 3.10-compatible collector")
llvm::Value::getValueID
unsigned getValueID() const
Return an ID for the concrete type of this object.
Definition: Value.h:532
llvm::Constant::getAllOnesValue
static Constant * getAllOnesValue(Type *Ty)
Definition: Constants.cpp:405
llvm::Constant::Constant
Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
Definition: Constant.h:43
llvm::Constant::stripPointerCasts
Constant * stripPointerCasts()
Definition: Constant.h:211
llvm::Constant::isMinSignedValue
bool isMinSignedValue() const
Return true if the value is the smallest signed value.
Definition: Constants.cpp:153
llvm::Constant::isDLLImportDependent
bool isDLLImportDependent() const
Return true if the value is dependent on a dllimport variable.
Definition: Constants.cpp:641
llvm::Constant
This is an important base class in LLVM.
Definition: Constant.h:41
llvm::Constant::isElementWiseEqual
bool isElementWiseEqual(Value *Y) const
Return true if this constant and a constant 'Y' are element-wise equal.
Definition: Constants.cpp:282
llvm::Constant::replaceUndefsWith
static Constant * replaceUndefsWith(Constant *C, Constant *Replacement)
Try to replace undefined constant C or undefined elements in C with Replacement.
Definition: Constants.cpp:793
llvm::Constant::hasOneLiveUse
bool hasOneLiveUse() const
Return true if the constant has exactly one live use.
Definition: Constants.cpp:779
llvm::Constant::isNegativeZeroValue
bool isNegativeZeroValue() const
Return true if the value is what would be returned by getZeroValueForNegation.
Definition: Constants.cpp:40
llvm::Constant::isManifestConstant
bool isManifestConstant() const
Return true if a constant is ConstantData or a ConstantAggregate or ConstantExpr that contain only Co...
Definition: Constants.cpp:852
llvm::Constant::handleOperandChange
void handleOperandChange(Value *, Value *)
This method is a special form of User::replaceUsesOfWith (which does not work on constants) that does...
Definition: Constants.cpp:3339
llvm::APInt
Class for arbitrary precision integers.
Definition: APInt.h:75
llvm::Value::ValueTy
ValueTy
Concrete subclass of this.
Definition: Value.h:513
llvm::Constant::removeDeadConstantUsers
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:752
llvm::Constant::getAggregateElement
Constant * getAggregateElement(unsigned Elt) const
For aggregates (struct/array/vector) return the constant that corresponds to the specified element if...
Definition: Constants.cpp:420
llvm::Constant::stripPointerCasts
const Constant * stripPointerCasts() const
Definition: Constant.h:207
llvm::Value::stripPointerCasts
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs and address space casts.
Definition: Value.cpp:687
llvm::Constant::getNullValue
static Constant * getNullValue(Type *Ty)
Constructor to create a '0' constant of arbitrary type.
Definition: Constants.cpp:348
llvm::Constant::operator=
void operator=(const Constant &)=delete
llvm::Constant::isZeroValue
bool isZeroValue() const
Return true if the value is negative zero or null value.
Definition: Constants.cpp:60
Casting.h
llvm::Constant::mergeUndefsWith
static Constant * mergeUndefsWith(Constant *C, Constant *Other)
Merges undefs of a Constant with another Constant, along with the undefs already present.
Definition: Constants.cpp:817
llvm::Constant::getIntegerValue
static Constant * getIntegerValue(Type *Ty, const APInt &V)
Return the value for an integer or pointer constant, or a vector thereof, with the given scalar value...
Definition: Constants.cpp:388
llvm::Constant::hasExactInverseFP
bool hasExactInverseFP() const
Return true if this scalar has an exact multiplicative inverse or this vector has an exact multiplica...
Definition: Constants.cpp:240
User.h
llvm::Constant::getUniqueInteger
const APInt & getUniqueInteger() const
If C is a constant integer then return its value, otherwise C must be a vector of constant integers,...
Definition: Constants.cpp:1770
llvm::Constant::containsUndefOrPoisonElement
bool containsUndefOrPoisonElement() const
Return true if this is a vector constant that includes any undef or poison elements.
Definition: Constants.cpp:328
llvm::Constant::canTrap
bool canTrap() const
Return true if evaluation of this constant could trap.
Definition: Constants.cpp:604
llvm::Constant::getSplatValue
Constant * getSplatValue(bool AllowUndefs=false) const
If all elements of the vector constant have the same value, return that value.
Definition: Constants.cpp:1711
llvm::Constant::isNotMinSignedValue
bool isNotMinSignedValue() const
Return true if the value is not the smallest signed value, or, for vectors, does not contain smallest...
Definition: Constants.cpp:170
llvm::Constant::isConstantUsed
bool isConstantUsed() const
Return true if the constant has users other than constant expressions and other dangling things.
Definition: Constants.cpp:648
Value.h
llvm::Value
LLVM Value Representation.
Definition: Value.h:74
llvm::Constant::destroyConstant
void destroyConstant()
Called if some element of this constant is no longer valid.
Definition: Constants.cpp:460
llvm::Use
A Use represents the edge between a Value definition and its users.
Definition: Use.h:44