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 vector constant with all finite and non-zero elements. 82 bool isFiniteNonZeroFP() const; 83 84 /// Return true if this is a normal (as opposed to denormal) floating-point 85 /// scalar constant or a vector constant with all normal elements. 86 bool isNormalFP() const; 87 88 /// Return true if this scalar has an exact multiplicative inverse or this 89 /// vector has an exact multiplicative inverse for each element in the vector. 90 bool hasExactInverseFP() const; 91 92 /// Return true if this is a floating-point NaN constant or a vector 93 /// floating-point constant with all NaN elements. 94 bool isNaN() const; 95 96 /// Return true if this constant and a constant 'Y' are element-wise equal. 97 /// This is identical to just comparing the pointers, with the exception that 98 /// for vectors, if only one of the constants has an `undef` element in some 99 /// lane, the constants still match. 100 bool isElementWiseEqual(Value *Y) const; 101 102 /// Return true if this is a vector constant that includes any undefined 103 /// elements. 104 bool containsUndefElement() const; 105 106 /// Return true if this is a vector constant that includes any constant 107 /// expressions. 108 bool containsConstantExpression() const; 109 110 /// Return true if evaluation of this constant could trap. This is true for 111 /// things like constant expressions that could divide by zero. 112 bool canTrap() const; 113 114 /// Return true if the value can vary between threads. 115 bool isThreadDependent() const; 116 117 /// Return true if the value is dependent on a dllimport variable. 118 bool isDLLImportDependent() const; 119 120 /// Return true if the constant has users other than constant expressions and 121 /// other dangling things. 122 bool isConstantUsed() const; 123 124 /// This method classifies the entry according to whether or not it may 125 /// generate a relocation entry. This must be conservative, so if it might 126 /// codegen to a relocatable entry, it should say so. 127 /// 128 /// FIXME: This really should not be in IR. 129 bool needsRelocation() const; 130 131 /// For aggregates (struct/array/vector) return the constant that corresponds 132 /// to the specified element if possible, or null if not. This can return null 133 /// if the element index is a ConstantExpr, if 'this' is a constant expr or 134 /// if the constant does not fit into an uint64_t. 135 Constant *getAggregateElement(unsigned Elt) const; 136 Constant *getAggregateElement(Constant *Elt) const; 137 138 /// If all elements of the vector constant have the same value, return that 139 /// value. Otherwise, return nullptr. Ignore undefined elements by setting 140 /// AllowUndefs to true. 141 Constant *getSplatValue(bool AllowUndefs = false) const; 142 143 /// If C is a constant integer then return its value, otherwise C must be a 144 /// vector of constant integers, all equal, and the common value is returned. 145 const APInt &getUniqueInteger() const; 146 147 /// Called if some element of this constant is no longer valid. 148 /// At this point only other constants may be on the use_list for this 149 /// constant. Any constants on our Use list must also be destroy'd. The 150 /// implementation must be sure to remove the constant from the list of 151 /// available cached constants. Implementations should implement 152 /// destroyConstantImpl to remove constants from any pools/maps they are 153 /// contained it. 154 void destroyConstant(); 155 156 //// Methods for support type inquiry through isa, cast, and dyn_cast: 157 static bool classof(const Value *V) { 158 static_assert(ConstantFirstVal == 0, "V->getValueID() >= ConstantFirstVal always succeeds"); 159 return V->getValueID() <= ConstantLastVal; 160 } 161 162 /// This method is a special form of User::replaceUsesOfWith 163 /// (which does not work on constants) that does work 164 /// on constants. Basically this method goes through the trouble of building 165 /// a new constant that is equivalent to the current one, with all uses of 166 /// From replaced with uses of To. After this construction is completed, all 167 /// of the users of 'this' are replaced to use the new constant, and then 168 /// 'this' is deleted. In general, you should not call this method, instead, 169 /// use Value::replaceAllUsesWith, which automatically dispatches to this 170 /// method as needed. 171 /// 172 void handleOperandChange(Value *, Value *); 173 174 static Constant *getNullValue(Type* Ty); 175 176 /// @returns the value for an integer or vector of integer constant of the 177 /// given type that has all its bits set to true. 178 /// Get the all ones value 179 static Constant *getAllOnesValue(Type* Ty); 180 181 /// Return the value for an integer or pointer constant, or a vector thereof, 182 /// with the given scalar value. 183 static Constant *getIntegerValue(Type *Ty, const APInt &V); 184 185 /// If there are any dead constant users dangling off of this constant, remove 186 /// them. This method is useful for clients that want to check to see if a 187 /// global is unused, but don't want to deal with potentially dead constants 188 /// hanging off of the globals. 189 void removeDeadConstantUsers() const; 190 191 const Constant *stripPointerCasts() const { 192 return cast<Constant>(Value::stripPointerCasts()); 193 } 194 195 Constant *stripPointerCasts() { 196 return const_cast<Constant*>( 197 static_cast<const Constant *>(this)->stripPointerCasts()); 198 } 199 200 /// Try to replace undefined constant C or undefined elements in C with 201 /// Replacement. If no changes are made, the constant C is returned. 202 static Constant *replaceUndefsWith(Constant *C, Constant *Replacement); 203 }; 204 205 } // end namespace llvm 206 207 #endif // LLVM_IR_CONSTANT_H 208