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; 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); 219 220 /// Return true if a constant is ConstantData or a ConstantAggregate or 221 /// ConstantExpr that contain only ConstantData. 222 bool isManifestConstant() const; 223 224 private: 225 enum PossibleRelocationsTy { 226 /// This constant requires no relocations. That is, it holds simple 227 /// constants (like integrals). 228 NoRelocation = 0, 229 230 /// This constant holds static relocations that can be resolved by the 231 /// static linker. 232 LocalRelocation = 1, 233 234 /// This constant holds dynamic relocations that the dynamic linker will 235 /// need to resolve. 236 GlobalRelocation = 2, 237 }; 238 239 /// Determine what potential relocations may be needed by this constant. 240 PossibleRelocationsTy getRelocationInfo() const; 241 }; 242 243 } // end namespace llvm 244 245 #endif // LLVM_IR_CONSTANT_H 246
Indexes created Tue Jun 16 00:25:01 UTC 2026