LLVM  9.0.0svn
Constant.h
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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 public:
47  void operator=(const Constant &) = delete;
48  Constant(const Constant &) = delete;
49 
50  /// Return true if this is the value that would be returned by getNullValue.
51  bool isNullValue() const;
52 
53  /// Returns true if the value is one.
54  bool isOneValue() const;
55 
56  /// Return true if this is the value that would be returned by
57  /// getAllOnesValue.
58  bool isAllOnesValue() const;
59 
60  /// Return true if the value is what would be returned by
61  /// getZeroValueForNegation.
62  bool isNegativeZeroValue() const;
63 
64  /// Return true if the value is negative zero or null value.
65  bool isZeroValue() const;
66 
67  /// Return true if the value is not the smallest signed value.
68  bool isNotMinSignedValue() const;
69 
70  /// Return true if the value is the smallest signed value.
71  bool isMinSignedValue() const;
72 
73  /// Return true if this is a finite and non-zero floating-point scalar
74  /// constant or a vector constant with all finite and non-zero elements.
75  bool isFiniteNonZeroFP() const;
76 
77  /// Return true if this is a normal (as opposed to denormal) floating-point
78  /// scalar constant or a vector constant with all normal elements.
79  bool isNormalFP() const;
80 
81  /// Return true if this scalar has an exact multiplicative inverse or this
82  /// vector has an exact multiplicative inverse for each element in the vector.
83  bool hasExactInverseFP() const;
84 
85  /// Return true if this is a floating-point NaN constant or a vector
86  /// floating-point constant with all NaN elements.
87  bool isNaN() const;
88 
89  /// Return true if this is a vector constant that includes any undefined
90  /// elements.
91  bool containsUndefElement() const;
92 
93  /// Return true if evaluation of this constant could trap. This is true for
94  /// things like constant expressions that could divide by zero.
95  bool canTrap() const;
96 
97  /// Return true if the value can vary between threads.
98  bool isThreadDependent() const;
99 
100  /// Return true if the value is dependent on a dllimport variable.
101  bool isDLLImportDependent() const;
102 
103  /// Return true if the constant has users other than constant expressions and
104  /// other dangling things.
105  bool isConstantUsed() const;
106 
107  /// This method classifies the entry according to whether or not it may
108  /// generate a relocation entry. This must be conservative, so if it might
109  /// codegen to a relocatable entry, it should say so.
110  ///
111  /// FIXME: This really should not be in IR.
112  bool needsRelocation() const;
113 
114  /// For aggregates (struct/array/vector) return the constant that corresponds
115  /// to the specified element if possible, or null if not. This can return null
116  /// if the element index is a ConstantExpr, if 'this' is a constant expr or
117  /// if the constant does not fit into an uint64_t.
118  Constant *getAggregateElement(unsigned Elt) const;
120 
121  /// If this is a splat vector constant, meaning that all of the elements have
122  /// the same value, return that value. Otherwise return 0.
123  Constant *getSplatValue() const;
124 
125  /// If C is a constant integer then return its value, otherwise C must be a
126  /// vector of constant integers, all equal, and the common value is returned.
127  const APInt &getUniqueInteger() const;
128 
129  /// Called if some element of this constant is no longer valid.
130  /// At this point only other constants may be on the use_list for this
131  /// constant. Any constants on our Use list must also be destroy'd. The
132  /// implementation must be sure to remove the constant from the list of
133  /// available cached constants. Implementations should implement
134  /// destroyConstantImpl to remove constants from any pools/maps they are
135  /// contained it.
136  void destroyConstant();
137 
138  //// Methods for support type inquiry through isa, cast, and dyn_cast:
139  static bool classof(const Value *V) {
140  static_assert(ConstantFirstVal == 0, "V->getValueID() >= ConstantFirstVal always succeeds");
141  return V->getValueID() <= ConstantLastVal;
142  }
143 
144  /// This method is a special form of User::replaceUsesOfWith
145  /// (which does not work on constants) that does work
146  /// on constants. Basically this method goes through the trouble of building
147  /// a new constant that is equivalent to the current one, with all uses of
148  /// From replaced with uses of To. After this construction is completed, all
149  /// of the users of 'this' are replaced to use the new constant, and then
150  /// 'this' is deleted. In general, you should not call this method, instead,
151  /// use Value::replaceAllUsesWith, which automatically dispatches to this
152  /// method as needed.
153  ///
154  void handleOperandChange(Value *, Value *);
155 
156  static Constant *getNullValue(Type* Ty);
157 
158  /// @returns the value for an integer or vector of integer constant of the
159  /// given type that has all its bits set to true.
160  /// Get the all ones value
161  static Constant *getAllOnesValue(Type* Ty);
162 
163  /// Return the value for an integer or pointer constant, or a vector thereof,
164  /// with the given scalar value.
165  static Constant *getIntegerValue(Type *Ty, const APInt &V);
166 
167  /// If there are any dead constant users dangling off of this constant, remove
168  /// them. This method is useful for clients that want to check to see if a
169  /// global is unused, but don't want to deal with potentially dead constants
170  /// hanging off of the globals.
171  void removeDeadConstantUsers() const;
172 
173  const Constant *stripPointerCasts() const {
174  return cast<Constant>(Value::stripPointerCasts());
175  }
176 
178  return const_cast<Constant*>(
179  static_cast<const Constant *>(this)->stripPointerCasts());
180  }
181 };
182 
183 } // end namespace llvm
184 
185 #endif // LLVM_IR_CONSTANT_H
bool isAllOnesValue() const
Return true if this is the value that would be returned by getAllOnesValue.
Definition: Constants.cpp:99
unsigned getValueID() const
Return an ID for the concrete type of this object.
Definition: Value.h:463
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:240
This class represents lattice values for constants.
Definition: AllocatorList.h:23
bool needsRelocation() const
This method classifies the entry according to whether or not it may generate a relocation entry...
Definition: Constants.cpp:488
bool isConstantUsed() const
Return true if the constant has users other than constant expressions and other dangling things...
Definition: Constants.cpp:476
static bool classof(const Value *V)
Definition: Constant.h:139
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:1388
static Constant * getNullValue(Type *Ty)
Constructor to create a &#39;0&#39; constant of arbitrary type.
Definition: Constants.cpp:264
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:84
bool canTrap() const
Return true if evaluation of this constant could trap.
Definition: Constants.cpp:432
bool isFiniteNonZeroFP() const
Return true if this is a finite and non-zero floating-point scalar constant or a vector constant with...
Definition: Constants.cpp:201
Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
Definition: Constant.h:43
bool isMinSignedValue() const
Return true if the value is the smallest signed value.
Definition: Constants.cpp:151
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:536
Constant * getAggregateElement(unsigned Elt) const
For aggregates (struct/array/vector) return the constant that corresponds to the specified element if...
Definition: Constants.cpp:334
bool isZeroValue() const
Return true if the value is negative zero or null value.
Definition: Constants.cpp:64
bool isThreadDependent() const
Return true if the value can vary between threads.
Definition: Constants.cpp:462
Constant * stripPointerCasts()
Definition: Constant.h:177
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
This is an important base class in LLVM.
Definition: Constant.h:41
bool isDLLImportDependent() const
Return true if the value is dependent on a dllimport variable.
Definition: Constants.cpp:469
bool isNegativeZeroValue() const
Return true if the value is what would be returned by getZeroValueForNegation.
Definition: Constants.cpp:38
static Constant * getAllOnesValue(Type *Ty)
Definition: Constants.cpp:318
const Constant * stripPointerCasts() const
Definition: Constant.h:173
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:529
Constant * getSplatValue() const
If this is a splat vector constant, meaning that all of the elements have the same value...
Definition: Constants.cpp:1367
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:301
bool isNormalFP() const
Return true if this is a normal (as opposed to denormal) floating-point scalar constant or a vector c...
Definition: Constants.cpp:214
bool containsUndefElement() const
Return true if this is a vector constant that includes any undefined elements.
Definition: Constants.cpp:253
ValueTy
Concrete subclass of this.
Definition: Value.h:444
void handleOperandChange(Value *, Value *)
This method is a special form of User::replaceUsesOfWith (which does not work on constants) that does...
Definition: Constants.cpp:2816
Class for arbitrary precision integers.
Definition: APInt.h:69
void destroyConstant()
Called if some element of this constant is no longer valid.
Definition: Constants.cpp:361
bool isOneValue() const
Returns true if the value is one.
Definition: Constants.cpp:125
LLVM Value Representation.
Definition: Value.h:72
void operator=(const Constant &)=delete
bool hasExactInverseFP() const
Return true if this scalar has an exact multiplicative inverse or this vector has an exact multiplica...
Definition: Constants.cpp:227
bool isNotMinSignedValue() const
Return true if the value is not the smallest signed value.
Definition: Constants.cpp:177