1 //===-- llvm/Constants.h - Constant class subclass definitions --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// This file contains the declarations for the subclasses of Constant,
12 /// which represent the different flavors of constant values that live in LLVM.
13 /// Note that Constants are immutable (once created they never change) and are
14 /// fully shared by structural equivalence. This means that two structurally
15 /// equivalent constants will always have the same address. Constants are
16 /// created on demand as needed and never deleted: thus clients don't have to
17 /// worry about the lifetime of the objects.
19 //===----------------------------------------------------------------------===//
21 #ifndef LLVM_IR_CONSTANTS_H
22 #define LLVM_IR_CONSTANTS_H
24 #include "llvm/ADT/APFloat.h"
25 #include "llvm/ADT/APInt.h"
26 #include "llvm/ADT/ArrayRef.h"
27 #include "llvm/IR/Constant.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/OperandTraits.h"
40 struct ConstantExprKeyType;
41 template <class ConstantClass> struct ConstantAggrKeyType;
43 //===----------------------------------------------------------------------===//
44 /// This is the shared class of boolean and integer constants. This class
45 /// represents both boolean and integral constants.
46 /// @brief Class for constant integers.
47 class ConstantInt : public Constant {
48 void anchor() override;
49 void *operator new(size_t, unsigned) = delete;
50 ConstantInt(const ConstantInt &) = delete;
51 ConstantInt(IntegerType *Ty, const APInt& V);
54 friend class Constant;
55 void destroyConstantImpl();
56 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
59 // allocate space for exactly zero operands
60 void *operator new(size_t s) {
61 return User::operator new(s, 0);
64 static ConstantInt *getTrue(LLVMContext &Context);
65 static ConstantInt *getFalse(LLVMContext &Context);
66 static Constant *getTrue(Type *Ty);
67 static Constant *getFalse(Type *Ty);
69 /// If Ty is a vector type, return a Constant with a splat of the given
70 /// value. Otherwise return a ConstantInt for the given value.
71 static Constant *get(Type *Ty, uint64_t V, bool isSigned = false);
73 /// Return a ConstantInt with the specified integer value for the specified
74 /// type. If the type is wider than 64 bits, the value will be zero-extended
75 /// to fit the type, unless isSigned is true, in which case the value will
76 /// be interpreted as a 64-bit signed integer and sign-extended to fit
78 /// @brief Get a ConstantInt for a specific value.
79 static ConstantInt *get(IntegerType *Ty, uint64_t V,
80 bool isSigned = false);
82 /// Return a ConstantInt with the specified value for the specified type. The
83 /// value V will be canonicalized to a an unsigned APInt. Accessing it with
84 /// either getSExtValue() or getZExtValue() will yield a correctly sized and
85 /// signed value for the type Ty.
86 /// @brief Get a ConstantInt for a specific signed value.
87 static ConstantInt *getSigned(IntegerType *Ty, int64_t V);
88 static Constant *getSigned(Type *Ty, int64_t V);
90 /// Return a ConstantInt with the specified value and an implied Type. The
91 /// type is the integer type that corresponds to the bit width of the value.
92 static ConstantInt *get(LLVMContext &Context, const APInt &V);
94 /// Return a ConstantInt constructed from the string strStart with the given
96 static ConstantInt *get(IntegerType *Ty, StringRef Str,
99 /// If Ty is a vector type, return a Constant with a splat of the given
100 /// value. Otherwise return a ConstantInt for the given value.
101 static Constant *get(Type* Ty, const APInt& V);
103 /// Return the constant as an APInt value reference. This allows clients to
104 /// obtain a copy of the value, with all its precision in tact.
105 /// @brief Return the constant's value.
106 inline const APInt &getValue() const {
110 /// getBitWidth - Return the bitwidth of this constant.
111 unsigned getBitWidth() const { return Val.getBitWidth(); }
113 /// Return the constant as a 64-bit unsigned integer value after it
114 /// has been zero extended as appropriate for the type of this constant. Note
115 /// that this method can assert if the value does not fit in 64 bits.
116 /// @brief Return the zero extended value.
117 inline uint64_t getZExtValue() const {
118 return Val.getZExtValue();
121 /// Return the constant as a 64-bit integer value after it has been sign
122 /// extended as appropriate for the type of this constant. Note that
123 /// this method can assert if the value does not fit in 64 bits.
124 /// @brief Return the sign extended value.
125 inline int64_t getSExtValue() const {
126 return Val.getSExtValue();
129 /// A helper method that can be used to determine if the constant contained
130 /// within is equal to a constant. This only works for very small values,
131 /// because this is all that can be represented with all types.
132 /// @brief Determine if this constant's value is same as an unsigned char.
133 bool equalsInt(uint64_t V) const {
137 /// getType - Specialize the getType() method to always return an IntegerType,
138 /// which reduces the amount of casting needed in parts of the compiler.
140 inline IntegerType *getType() const {
141 return cast<IntegerType>(Value::getType());
144 /// This static method returns true if the type Ty is big enough to
145 /// represent the value V. This can be used to avoid having the get method
146 /// assert when V is larger than Ty can represent. Note that there are two
147 /// versions of this method, one for unsigned and one for signed integers.
148 /// Although ConstantInt canonicalizes everything to an unsigned integer,
149 /// the signed version avoids callers having to convert a signed quantity
150 /// to the appropriate unsigned type before calling the method.
151 /// @returns true if V is a valid value for type Ty
152 /// @brief Determine if the value is in range for the given type.
153 static bool isValueValidForType(Type *Ty, uint64_t V);
154 static bool isValueValidForType(Type *Ty, int64_t V);
156 bool isNegative() const { return Val.isNegative(); }
158 /// This is just a convenience method to make client code smaller for a
159 /// common code. It also correctly performs the comparison without the
160 /// potential for an assertion from getZExtValue().
161 bool isZero() const {
165 /// This is just a convenience method to make client code smaller for a
166 /// common case. It also correctly performs the comparison without the
167 /// potential for an assertion from getZExtValue().
168 /// @brief Determine if the value is one.
173 /// This function will return true iff every bit in this constant is set
175 /// @returns true iff this constant's bits are all set to true.
176 /// @brief Determine if the value is all ones.
177 bool isMinusOne() const {
178 return Val.isAllOnesValue();
181 /// This function will return true iff this constant represents the largest
182 /// value that may be represented by the constant's type.
183 /// @returns true iff this is the largest value that may be represented
185 /// @brief Determine if the value is maximal.
186 bool isMaxValue(bool isSigned) const {
188 return Val.isMaxSignedValue();
190 return Val.isMaxValue();
193 /// This function will return true iff this constant represents the smallest
194 /// value that may be represented by this constant's type.
195 /// @returns true if this is the smallest value that may be represented by
197 /// @brief Determine if the value is minimal.
198 bool isMinValue(bool isSigned) const {
200 return Val.isMinSignedValue();
202 return Val.isMinValue();
205 /// This function will return true iff this constant represents a value with
206 /// active bits bigger than 64 bits or a value greater than the given uint64_t
208 /// @returns true iff this constant is greater or equal to the given number.
209 /// @brief Determine if the value is greater or equal to the given number.
210 bool uge(uint64_t Num) const {
211 return Val.getActiveBits() > 64 || Val.getZExtValue() >= Num;
214 /// getLimitedValue - If the value is smaller than the specified limit,
215 /// return it, otherwise return the limit value. This causes the value
216 /// to saturate to the limit.
217 /// @returns the min of the value of the constant and the specified value
218 /// @brief Get the constant's value with a saturation limit
219 uint64_t getLimitedValue(uint64_t Limit = ~0ULL) const {
220 return Val.getLimitedValue(Limit);
223 /// @brief Methods to support type inquiry through isa, cast, and dyn_cast.
224 static bool classof(const Value *V) {
225 return V->getValueID() == ConstantIntVal;
230 //===----------------------------------------------------------------------===//
231 /// ConstantFP - Floating Point Values [float, double]
233 class ConstantFP : public Constant {
235 void anchor() override;
236 void *operator new(size_t, unsigned) = delete;
237 ConstantFP(const ConstantFP &) = delete;
238 friend class LLVMContextImpl;
240 friend class Constant;
241 void destroyConstantImpl();
242 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
245 ConstantFP(Type *Ty, const APFloat& V);
247 // allocate space for exactly zero operands
248 void *operator new(size_t s) {
249 return User::operator new(s, 0);
252 /// Floating point negation must be implemented with f(x) = -0.0 - x. This
253 /// method returns the negative zero constant for floating point or vector
254 /// floating point types; for all other types, it returns the null value.
255 static Constant *getZeroValueForNegation(Type *Ty);
257 /// get() - This returns a ConstantFP, or a vector containing a splat of a
258 /// ConstantFP, for the specified value in the specified type. This should
259 /// only be used for simple constant values like 2.0/1.0 etc, that are
260 /// known-valid both as host double and as the target format.
261 static Constant *get(Type* Ty, double V);
262 static Constant *get(Type* Ty, StringRef Str);
263 static ConstantFP *get(LLVMContext &Context, const APFloat &V);
264 static Constant *getNaN(Type *Ty, bool Negative = false, unsigned type = 0);
265 static Constant *getNegativeZero(Type *Ty);
266 static Constant *getInfinity(Type *Ty, bool Negative = false);
268 /// isValueValidForType - return true if Ty is big enough to represent V.
269 static bool isValueValidForType(Type *Ty, const APFloat &V);
270 inline const APFloat &getValueAPF() const { return Val; }
272 /// isZero - Return true if the value is positive or negative zero.
273 bool isZero() const { return Val.isZero(); }
275 /// isNegative - Return true if the sign bit is set.
276 bool isNegative() const { return Val.isNegative(); }
278 /// isInfinity - Return true if the value is infinity
279 bool isInfinity() const { return Val.isInfinity(); }
281 /// isNaN - Return true if the value is a NaN.
282 bool isNaN() const { return Val.isNaN(); }
284 /// isExactlyValue - We don't rely on operator== working on double values, as
285 /// it returns true for things that are clearly not equal, like -0.0 and 0.0.
286 /// As such, this method can be used to do an exact bit-for-bit comparison of
287 /// two floating point values. The version with a double operand is retained
288 /// because it's so convenient to write isExactlyValue(2.0), but please use
289 /// it only for simple constants.
290 bool isExactlyValue(const APFloat &V) const;
292 bool isExactlyValue(double V) const {
295 FV.convert(Val.getSemantics(), APFloat::rmNearestTiesToEven, &ignored);
296 return isExactlyValue(FV);
298 /// Methods for support type inquiry through isa, cast, and dyn_cast:
299 static bool classof(const Value *V) {
300 return V->getValueID() == ConstantFPVal;
304 //===----------------------------------------------------------------------===//
305 /// ConstantAggregateZero - All zero aggregate value
307 class ConstantAggregateZero : public Constant {
308 void *operator new(size_t, unsigned) = delete;
309 ConstantAggregateZero(const ConstantAggregateZero &) = delete;
311 friend class Constant;
312 void destroyConstantImpl();
313 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
316 explicit ConstantAggregateZero(Type *ty)
317 : Constant(ty, ConstantAggregateZeroVal, nullptr, 0) {}
319 // allocate space for exactly zero operands
320 void *operator new(size_t s) {
321 return User::operator new(s, 0);
324 static ConstantAggregateZero *get(Type *Ty);
326 /// getSequentialElement - If this CAZ has array or vector type, return a zero
327 /// with the right element type.
328 Constant *getSequentialElement() const;
330 /// getStructElement - If this CAZ has struct type, return a zero with the
331 /// right element type for the specified element.
332 Constant *getStructElement(unsigned Elt) const;
334 /// getElementValue - Return a zero of the right value for the specified GEP
336 Constant *getElementValue(Constant *C) const;
338 /// getElementValue - Return a zero of the right value for the specified GEP
340 Constant *getElementValue(unsigned Idx) const;
342 /// \brief Return the number of elements in the array, vector, or struct.
343 unsigned getNumElements() const;
345 /// Methods for support type inquiry through isa, cast, and dyn_cast:
347 static bool classof(const Value *V) {
348 return V->getValueID() == ConstantAggregateZeroVal;
353 //===----------------------------------------------------------------------===//
354 /// ConstantArray - Constant Array Declarations
356 class ConstantArray : public Constant {
357 friend struct ConstantAggrKeyType<ConstantArray>;
358 ConstantArray(const ConstantArray &) = delete;
360 friend class Constant;
361 void destroyConstantImpl();
362 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
365 ConstantArray(ArrayType *T, ArrayRef<Constant *> Val);
367 // ConstantArray accessors
368 static Constant *get(ArrayType *T, ArrayRef<Constant*> V);
371 static Constant *getImpl(ArrayType *T, ArrayRef<Constant *> V);
374 /// Transparently provide more efficient getOperand methods.
375 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Constant);
377 /// getType - Specialize the getType() method to always return an ArrayType,
378 /// which reduces the amount of casting needed in parts of the compiler.
380 inline ArrayType *getType() const {
381 return cast<ArrayType>(Value::getType());
384 /// Methods for support type inquiry through isa, cast, and dyn_cast:
385 static bool classof(const Value *V) {
386 return V->getValueID() == ConstantArrayVal;
391 struct OperandTraits<ConstantArray> :
392 public VariadicOperandTraits<ConstantArray> {
395 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(ConstantArray, Constant)
397 //===----------------------------------------------------------------------===//
398 // ConstantStruct - Constant Struct Declarations
400 class ConstantStruct : public Constant {
401 friend struct ConstantAggrKeyType<ConstantStruct>;
402 ConstantStruct(const ConstantStruct &) = delete;
404 friend class Constant;
405 void destroyConstantImpl();
406 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
409 ConstantStruct(StructType *T, ArrayRef<Constant *> Val);
411 // ConstantStruct accessors
412 static Constant *get(StructType *T, ArrayRef<Constant*> V);
413 static Constant *get(StructType *T, ...) LLVM_END_WITH_NULL;
415 /// getAnon - Return an anonymous struct that has the specified
416 /// elements. If the struct is possibly empty, then you must specify a
418 static Constant *getAnon(ArrayRef<Constant*> V, bool Packed = false) {
419 return get(getTypeForElements(V, Packed), V);
421 static Constant *getAnon(LLVMContext &Ctx,
422 ArrayRef<Constant*> V, bool Packed = false) {
423 return get(getTypeForElements(Ctx, V, Packed), V);
426 /// getTypeForElements - Return an anonymous struct type to use for a constant
427 /// with the specified set of elements. The list must not be empty.
428 static StructType *getTypeForElements(ArrayRef<Constant*> V,
429 bool Packed = false);
430 /// getTypeForElements - This version of the method allows an empty list.
431 static StructType *getTypeForElements(LLVMContext &Ctx,
432 ArrayRef<Constant*> V,
433 bool Packed = false);
435 /// Transparently provide more efficient getOperand methods.
436 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Constant);
438 /// getType() specialization - Reduce amount of casting...
440 inline StructType *getType() const {
441 return cast<StructType>(Value::getType());
444 /// Methods for support type inquiry through isa, cast, and dyn_cast:
445 static bool classof(const Value *V) {
446 return V->getValueID() == ConstantStructVal;
451 struct OperandTraits<ConstantStruct> :
452 public VariadicOperandTraits<ConstantStruct> {
455 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(ConstantStruct, Constant)
458 //===----------------------------------------------------------------------===//
459 /// ConstantVector - Constant Vector Declarations
461 class ConstantVector : public Constant {
462 friend struct ConstantAggrKeyType<ConstantVector>;
463 ConstantVector(const ConstantVector &) = delete;
465 friend class Constant;
466 void destroyConstantImpl();
467 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
470 ConstantVector(VectorType *T, ArrayRef<Constant *> Val);
472 // ConstantVector accessors
473 static Constant *get(ArrayRef<Constant*> V);
476 static Constant *getImpl(ArrayRef<Constant *> V);
479 /// getSplat - Return a ConstantVector with the specified constant in each
481 static Constant *getSplat(unsigned NumElts, Constant *Elt);
483 /// Transparently provide more efficient getOperand methods.
484 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Constant);
486 /// getType - Specialize the getType() method to always return a VectorType,
487 /// which reduces the amount of casting needed in parts of the compiler.
489 inline VectorType *getType() const {
490 return cast<VectorType>(Value::getType());
493 /// getSplatValue - If this is a splat constant, meaning that all of the
494 /// elements have the same value, return that value. Otherwise return NULL.
495 Constant *getSplatValue() const;
497 /// Methods for support type inquiry through isa, cast, and dyn_cast:
498 static bool classof(const Value *V) {
499 return V->getValueID() == ConstantVectorVal;
504 struct OperandTraits<ConstantVector> :
505 public VariadicOperandTraits<ConstantVector> {
508 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(ConstantVector, Constant)
510 //===----------------------------------------------------------------------===//
511 /// ConstantPointerNull - a constant pointer value that points to null
513 class ConstantPointerNull : public Constant {
514 void *operator new(size_t, unsigned) = delete;
515 ConstantPointerNull(const ConstantPointerNull &) = delete;
517 friend class Constant;
518 void destroyConstantImpl();
519 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
522 explicit ConstantPointerNull(PointerType *T)
524 Value::ConstantPointerNullVal, nullptr, 0) {}
527 // allocate space for exactly zero operands
528 void *operator new(size_t s) {
529 return User::operator new(s, 0);
532 /// get() - Static factory methods - Return objects of the specified value
533 static ConstantPointerNull *get(PointerType *T);
535 /// getType - Specialize the getType() method to always return an PointerType,
536 /// which reduces the amount of casting needed in parts of the compiler.
538 inline PointerType *getType() const {
539 return cast<PointerType>(Value::getType());
542 /// Methods for support type inquiry through isa, cast, and dyn_cast:
543 static bool classof(const Value *V) {
544 return V->getValueID() == ConstantPointerNullVal;
548 //===----------------------------------------------------------------------===//
549 /// ConstantDataSequential - A vector or array constant whose element type is a
550 /// simple 1/2/4/8-byte integer or float/double, and whose elements are just
551 /// simple data values (i.e. ConstantInt/ConstantFP). This Constant node has no
552 /// operands because it stores all of the elements of the constant as densely
553 /// packed data, instead of as Value*'s.
555 /// This is the common base class of ConstantDataArray and ConstantDataVector.
557 class ConstantDataSequential : public Constant {
558 friend class LLVMContextImpl;
559 /// DataElements - A pointer to the bytes underlying this constant (which is
560 /// owned by the uniquing StringMap).
561 const char *DataElements;
563 /// Next - This forms a link list of ConstantDataSequential nodes that have
564 /// the same value but different type. For example, 0,0,0,1 could be a 4
565 /// element array of i8, or a 1-element array of i32. They'll both end up in
566 /// the same StringMap bucket, linked up.
567 ConstantDataSequential *Next;
568 void *operator new(size_t, unsigned) = delete;
569 ConstantDataSequential(const ConstantDataSequential &) = delete;
571 friend class Constant;
572 void destroyConstantImpl();
573 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
576 explicit ConstantDataSequential(Type *ty, ValueTy VT, const char *Data)
577 : Constant(ty, VT, nullptr, 0), DataElements(Data), Next(nullptr) {}
578 ~ConstantDataSequential() override { delete Next; }
580 static Constant *getImpl(StringRef Bytes, Type *Ty);
583 // allocate space for exactly zero operands.
584 void *operator new(size_t s) {
585 return User::operator new(s, 0);
589 /// isElementTypeCompatible - Return true if a ConstantDataSequential can be
590 /// formed with a vector or array of the specified element type.
591 /// ConstantDataArray only works with normal float and int types that are
592 /// stored densely in memory, not with things like i42 or x86_f80.
593 static bool isElementTypeCompatible(Type *Ty);
595 /// getElementAsInteger - If this is a sequential container of integers (of
596 /// any size), return the specified element in the low bits of a uint64_t.
597 uint64_t getElementAsInteger(unsigned i) const;
599 /// getElementAsAPFloat - If this is a sequential container of floating point
600 /// type, return the specified element as an APFloat.
601 APFloat getElementAsAPFloat(unsigned i) const;
603 /// getElementAsFloat - If this is an sequential container of floats, return
604 /// the specified element as a float.
605 float getElementAsFloat(unsigned i) const;
607 /// getElementAsDouble - If this is an sequential container of doubles, return
608 /// the specified element as a double.
609 double getElementAsDouble(unsigned i) const;
611 /// getElementAsConstant - Return a Constant for a specified index's element.
612 /// Note that this has to compute a new constant to return, so it isn't as
613 /// efficient as getElementAsInteger/Float/Double.
614 Constant *getElementAsConstant(unsigned i) const;
616 /// getType - Specialize the getType() method to always return a
617 /// SequentialType, which reduces the amount of casting needed in parts of the
619 inline SequentialType *getType() const {
620 return cast<SequentialType>(Value::getType());
623 /// getElementType - Return the element type of the array/vector.
624 Type *getElementType() const;
626 /// getNumElements - Return the number of elements in the array or vector.
627 unsigned getNumElements() const;
629 /// getElementByteSize - Return the size (in bytes) of each element in the
630 /// array/vector. The size of the elements is known to be a multiple of one
632 uint64_t getElementByteSize() const;
635 /// isString - This method returns true if this is an array of i8.
636 bool isString() const;
638 /// isCString - This method returns true if the array "isString", ends with a
639 /// nul byte, and does not contains any other nul bytes.
640 bool isCString() const;
642 /// getAsString - If this array is isString(), then this method returns the
643 /// array as a StringRef. Otherwise, it asserts out.
645 StringRef getAsString() const {
646 assert(isString() && "Not a string");
647 return getRawDataValues();
650 /// getAsCString - If this array is isCString(), then this method returns the
651 /// array (without the trailing null byte) as a StringRef. Otherwise, it
654 StringRef getAsCString() const {
655 assert(isCString() && "Isn't a C string");
656 StringRef Str = getAsString();
657 return Str.substr(0, Str.size()-1);
660 /// getRawDataValues - Return the raw, underlying, bytes of this data. Note
661 /// that this is an extremely tricky thing to work with, as it exposes the
662 /// host endianness of the data elements.
663 StringRef getRawDataValues() const;
665 /// Methods for support type inquiry through isa, cast, and dyn_cast:
667 static bool classof(const Value *V) {
668 return V->getValueID() == ConstantDataArrayVal ||
669 V->getValueID() == ConstantDataVectorVal;
672 const char *getElementPointer(unsigned Elt) const;
675 //===----------------------------------------------------------------------===//
676 /// ConstantDataArray - An array constant whose element type is a simple
677 /// 1/2/4/8-byte integer or float/double, and whose elements are just simple
678 /// data values (i.e. ConstantInt/ConstantFP). This Constant node has no
679 /// operands because it stores all of the elements of the constant as densely
680 /// packed data, instead of as Value*'s.
681 class ConstantDataArray : public ConstantDataSequential {
682 void *operator new(size_t, unsigned) = delete;
683 ConstantDataArray(const ConstantDataArray &) = delete;
684 void anchor() override;
685 friend class ConstantDataSequential;
686 explicit ConstantDataArray(Type *ty, const char *Data)
687 : ConstantDataSequential(ty, ConstantDataArrayVal, Data) {}
689 // allocate space for exactly zero operands.
690 void *operator new(size_t s) {
691 return User::operator new(s, 0);
695 /// get() constructors - Return a constant with array type with an element
696 /// count and element type matching the ArrayRef passed in. Note that this
697 /// can return a ConstantAggregateZero object.
698 static Constant *get(LLVMContext &Context, ArrayRef<uint8_t> Elts);
699 static Constant *get(LLVMContext &Context, ArrayRef<uint16_t> Elts);
700 static Constant *get(LLVMContext &Context, ArrayRef<uint32_t> Elts);
701 static Constant *get(LLVMContext &Context, ArrayRef<uint64_t> Elts);
702 static Constant *get(LLVMContext &Context, ArrayRef<float> Elts);
703 static Constant *get(LLVMContext &Context, ArrayRef<double> Elts);
705 /// getFP() constructors - Return a constant with array type with an element
706 /// count and element type of float with precision matching the number of
707 /// bits in the ArrayRef passed in. (i.e. half for 16bits, float for 32bits,
708 /// double for 64bits) Note that this can return a ConstantAggregateZero
710 static Constant *getFP(LLVMContext &Context, ArrayRef<uint16_t> Elts);
711 static Constant *getFP(LLVMContext &Context, ArrayRef<uint32_t> Elts);
712 static Constant *getFP(LLVMContext &Context, ArrayRef<uint64_t> Elts);
714 /// getString - This method constructs a CDS and initializes it with a text
715 /// string. The default behavior (AddNull==true) causes a null terminator to
716 /// be placed at the end of the array (increasing the length of the string by
717 /// one more than the StringRef would normally indicate. Pass AddNull=false
718 /// to disable this behavior.
719 static Constant *getString(LLVMContext &Context, StringRef Initializer,
720 bool AddNull = true);
722 /// getType - Specialize the getType() method to always return an ArrayType,
723 /// which reduces the amount of casting needed in parts of the compiler.
725 inline ArrayType *getType() const {
726 return cast<ArrayType>(Value::getType());
729 /// Methods for support type inquiry through isa, cast, and dyn_cast:
731 static bool classof(const Value *V) {
732 return V->getValueID() == ConstantDataArrayVal;
736 //===----------------------------------------------------------------------===//
737 /// ConstantDataVector - A vector constant whose element type is a simple
738 /// 1/2/4/8-byte integer or float/double, and whose elements are just simple
739 /// data values (i.e. ConstantInt/ConstantFP). This Constant node has no
740 /// operands because it stores all of the elements of the constant as densely
741 /// packed data, instead of as Value*'s.
742 class ConstantDataVector : public ConstantDataSequential {
743 void *operator new(size_t, unsigned) = delete;
744 ConstantDataVector(const ConstantDataVector &) = delete;
745 void anchor() override;
746 friend class ConstantDataSequential;
747 explicit ConstantDataVector(Type *ty, const char *Data)
748 : ConstantDataSequential(ty, ConstantDataVectorVal, Data) {}
750 // allocate space for exactly zero operands.
751 void *operator new(size_t s) {
752 return User::operator new(s, 0);
756 /// get() constructors - Return a constant with vector type with an element
757 /// count and element type matching the ArrayRef passed in. Note that this
758 /// can return a ConstantAggregateZero object.
759 static Constant *get(LLVMContext &Context, ArrayRef<uint8_t> Elts);
760 static Constant *get(LLVMContext &Context, ArrayRef<uint16_t> Elts);
761 static Constant *get(LLVMContext &Context, ArrayRef<uint32_t> Elts);
762 static Constant *get(LLVMContext &Context, ArrayRef<uint64_t> Elts);
763 static Constant *get(LLVMContext &Context, ArrayRef<float> Elts);
764 static Constant *get(LLVMContext &Context, ArrayRef<double> Elts);
766 /// getFP() constructors - Return a constant with vector type with an element
767 /// count and element type of float with the precision matching the number of
768 /// bits in the ArrayRef passed in. (i.e. half for 16bits, float for 32bits,
769 /// double for 64bits) Note that this can return a ConstantAggregateZero
771 static Constant *getFP(LLVMContext &Context, ArrayRef<uint16_t> Elts);
772 static Constant *getFP(LLVMContext &Context, ArrayRef<uint32_t> Elts);
773 static Constant *getFP(LLVMContext &Context, ArrayRef<uint64_t> Elts);
775 /// getSplat - Return a ConstantVector with the specified constant in each
776 /// element. The specified constant has to be a of a compatible type (i8/i16/
777 /// i32/i64/float/double) and must be a ConstantFP or ConstantInt.
778 static Constant *getSplat(unsigned NumElts, Constant *Elt);
780 /// getSplatValue - If this is a splat constant, meaning that all of the
781 /// elements have the same value, return that value. Otherwise return NULL.
782 Constant *getSplatValue() const;
784 /// getType - Specialize the getType() method to always return a VectorType,
785 /// which reduces the amount of casting needed in parts of the compiler.
787 inline VectorType *getType() const {
788 return cast<VectorType>(Value::getType());
791 /// Methods for support type inquiry through isa, cast, and dyn_cast:
793 static bool classof(const Value *V) {
794 return V->getValueID() == ConstantDataVectorVal;
800 /// BlockAddress - The address of a basic block.
802 class BlockAddress : public Constant {
803 void *operator new(size_t, unsigned) = delete;
804 void *operator new(size_t s) { return User::operator new(s, 2); }
805 BlockAddress(Function *F, BasicBlock *BB);
807 friend class Constant;
808 void destroyConstantImpl();
809 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
812 /// get - Return a BlockAddress for the specified function and basic block.
813 static BlockAddress *get(Function *F, BasicBlock *BB);
815 /// get - Return a BlockAddress for the specified basic block. The basic
816 /// block must be embedded into a function.
817 static BlockAddress *get(BasicBlock *BB);
819 /// \brief Lookup an existing \c BlockAddress constant for the given
822 /// \returns 0 if \c !BB->hasAddressTaken(), otherwise the \c BlockAddress.
823 static BlockAddress *lookup(const BasicBlock *BB);
825 /// Transparently provide more efficient getOperand methods.
826 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
828 Function *getFunction() const { return (Function*)Op<0>().get(); }
829 BasicBlock *getBasicBlock() const { return (BasicBlock*)Op<1>().get(); }
831 /// Methods for support type inquiry through isa, cast, and dyn_cast:
832 static inline bool classof(const Value *V) {
833 return V->getValueID() == BlockAddressVal;
838 struct OperandTraits<BlockAddress> :
839 public FixedNumOperandTraits<BlockAddress, 2> {
842 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(BlockAddress, Value)
845 //===----------------------------------------------------------------------===//
846 /// ConstantExpr - a constant value that is initialized with an expression using
847 /// other constant values.
849 /// This class uses the standard Instruction opcodes to define the various
850 /// constant expressions. The Opcode field for the ConstantExpr class is
851 /// maintained in the Value::SubclassData field.
852 class ConstantExpr : public Constant {
853 friend struct ConstantExprKeyType;
855 friend class Constant;
856 void destroyConstantImpl();
857 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
860 ConstantExpr(Type *ty, unsigned Opcode, Use *Ops, unsigned NumOps)
861 : Constant(ty, ConstantExprVal, Ops, NumOps) {
862 // Operation type (an Instruction opcode) is stored as the SubclassData.
863 setValueSubclassData(Opcode);
867 // Static methods to construct a ConstantExpr of different kinds. Note that
868 // these methods may return a object that is not an instance of the
869 // ConstantExpr class, because they will attempt to fold the constant
870 // expression into something simpler if possible.
872 /// getAlignOf constant expr - computes the alignment of a type in a target
873 /// independent way (Note: the return type is an i64).
874 static Constant *getAlignOf(Type *Ty);
876 /// getSizeOf constant expr - computes the (alloc) size of a type (in
877 /// address-units, not bits) in a target independent way (Note: the return
880 static Constant *getSizeOf(Type *Ty);
882 /// getOffsetOf constant expr - computes the offset of a struct field in a
883 /// target independent way (Note: the return type is an i64).
885 static Constant *getOffsetOf(StructType *STy, unsigned FieldNo);
887 /// getOffsetOf constant expr - This is a generalized form of getOffsetOf,
888 /// which supports any aggregate type, and any Constant index.
890 static Constant *getOffsetOf(Type *Ty, Constant *FieldNo);
892 static Constant *getNeg(Constant *C, bool HasNUW = false, bool HasNSW =false);
893 static Constant *getFNeg(Constant *C);
894 static Constant *getNot(Constant *C);
895 static Constant *getAdd(Constant *C1, Constant *C2,
896 bool HasNUW = false, bool HasNSW = false);
897 static Constant *getFAdd(Constant *C1, Constant *C2);
898 static Constant *getSub(Constant *C1, Constant *C2,
899 bool HasNUW = false, bool HasNSW = false);
900 static Constant *getFSub(Constant *C1, Constant *C2);
901 static Constant *getMul(Constant *C1, Constant *C2,
902 bool HasNUW = false, bool HasNSW = false);
903 static Constant *getFMul(Constant *C1, Constant *C2);
904 static Constant *getUDiv(Constant *C1, Constant *C2, bool isExact = false);
905 static Constant *getSDiv(Constant *C1, Constant *C2, bool isExact = false);
906 static Constant *getFDiv(Constant *C1, Constant *C2);
907 static Constant *getURem(Constant *C1, Constant *C2);
908 static Constant *getSRem(Constant *C1, Constant *C2);
909 static Constant *getFRem(Constant *C1, Constant *C2);
910 static Constant *getAnd(Constant *C1, Constant *C2);
911 static Constant *getOr(Constant *C1, Constant *C2);
912 static Constant *getXor(Constant *C1, Constant *C2);
913 static Constant *getShl(Constant *C1, Constant *C2,
914 bool HasNUW = false, bool HasNSW = false);
915 static Constant *getLShr(Constant *C1, Constant *C2, bool isExact = false);
916 static Constant *getAShr(Constant *C1, Constant *C2, bool isExact = false);
917 static Constant *getTrunc(Constant *C, Type *Ty, bool OnlyIfReduced = false);
918 static Constant *getSExt(Constant *C, Type *Ty, bool OnlyIfReduced = false);
919 static Constant *getZExt(Constant *C, Type *Ty, bool OnlyIfReduced = false);
920 static Constant *getFPTrunc(Constant *C, Type *Ty,
921 bool OnlyIfReduced = false);
922 static Constant *getFPExtend(Constant *C, Type *Ty,
923 bool OnlyIfReduced = false);
924 static Constant *getUIToFP(Constant *C, Type *Ty, bool OnlyIfReduced = false);
925 static Constant *getSIToFP(Constant *C, Type *Ty, bool OnlyIfReduced = false);
926 static Constant *getFPToUI(Constant *C, Type *Ty, bool OnlyIfReduced = false);
927 static Constant *getFPToSI(Constant *C, Type *Ty, bool OnlyIfReduced = false);
928 static Constant *getPtrToInt(Constant *C, Type *Ty,
929 bool OnlyIfReduced = false);
930 static Constant *getIntToPtr(Constant *C, Type *Ty,
931 bool OnlyIfReduced = false);
932 static Constant *getBitCast(Constant *C, Type *Ty,
933 bool OnlyIfReduced = false);
934 static Constant *getAddrSpaceCast(Constant *C, Type *Ty,
935 bool OnlyIfReduced = false);
937 static Constant *getNSWNeg(Constant *C) { return getNeg(C, false, true); }
938 static Constant *getNUWNeg(Constant *C) { return getNeg(C, true, false); }
939 static Constant *getNSWAdd(Constant *C1, Constant *C2) {
940 return getAdd(C1, C2, false, true);
942 static Constant *getNUWAdd(Constant *C1, Constant *C2) {
943 return getAdd(C1, C2, true, false);
945 static Constant *getNSWSub(Constant *C1, Constant *C2) {
946 return getSub(C1, C2, false, true);
948 static Constant *getNUWSub(Constant *C1, Constant *C2) {
949 return getSub(C1, C2, true, false);
951 static Constant *getNSWMul(Constant *C1, Constant *C2) {
952 return getMul(C1, C2, false, true);
954 static Constant *getNUWMul(Constant *C1, Constant *C2) {
955 return getMul(C1, C2, true, false);
957 static Constant *getNSWShl(Constant *C1, Constant *C2) {
958 return getShl(C1, C2, false, true);
960 static Constant *getNUWShl(Constant *C1, Constant *C2) {
961 return getShl(C1, C2, true, false);
963 static Constant *getExactSDiv(Constant *C1, Constant *C2) {
964 return getSDiv(C1, C2, true);
966 static Constant *getExactUDiv(Constant *C1, Constant *C2) {
967 return getUDiv(C1, C2, true);
969 static Constant *getExactAShr(Constant *C1, Constant *C2) {
970 return getAShr(C1, C2, true);
972 static Constant *getExactLShr(Constant *C1, Constant *C2) {
973 return getLShr(C1, C2, true);
976 /// getBinOpIdentity - Return the identity for the given binary operation,
977 /// i.e. a constant C such that X op C = X and C op X = X for every X. It
978 /// returns null if the operator doesn't have an identity.
979 static Constant *getBinOpIdentity(unsigned Opcode, Type *Ty);
981 /// getBinOpAbsorber - Return the absorbing element for the given binary
982 /// operation, i.e. a constant C such that X op C = C and C op X = C for
983 /// every X. For example, this returns zero for integer multiplication.
984 /// It returns null if the operator doesn't have an absorbing element.
985 static Constant *getBinOpAbsorber(unsigned Opcode, Type *Ty);
987 /// Transparently provide more efficient getOperand methods.
988 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Constant);
990 /// \brief Convenience function for getting a Cast operation.
992 /// \param ops The opcode for the conversion
993 /// \param C The constant to be converted
994 /// \param Ty The type to which the constant is converted
995 /// \param OnlyIfReduced see \a getWithOperands() docs.
996 static Constant *getCast(unsigned ops, Constant *C, Type *Ty,
997 bool OnlyIfReduced = false);
999 // @brief Create a ZExt or BitCast cast constant expression
1000 static Constant *getZExtOrBitCast(
1001 Constant *C, ///< The constant to zext or bitcast
1002 Type *Ty ///< The type to zext or bitcast C to
1005 // @brief Create a SExt or BitCast cast constant expression
1006 static Constant *getSExtOrBitCast(
1007 Constant *C, ///< The constant to sext or bitcast
1008 Type *Ty ///< The type to sext or bitcast C to
1011 // @brief Create a Trunc or BitCast cast constant expression
1012 static Constant *getTruncOrBitCast(
1013 Constant *C, ///< The constant to trunc or bitcast
1014 Type *Ty ///< The type to trunc or bitcast C to
1017 /// @brief Create a BitCast, AddrSpaceCast, or a PtrToInt cast constant
1019 static Constant *getPointerCast(
1020 Constant *C, ///< The pointer value to be casted (operand 0)
1021 Type *Ty ///< The type to which cast should be made
1024 /// @brief Create a BitCast or AddrSpaceCast for a pointer type depending on
1025 /// the address space.
1026 static Constant *getPointerBitCastOrAddrSpaceCast(
1027 Constant *C, ///< The constant to addrspacecast or bitcast
1028 Type *Ty ///< The type to bitcast or addrspacecast C to
1031 /// @brief Create a ZExt, Bitcast or Trunc for integer -> integer casts
1032 static Constant *getIntegerCast(
1033 Constant *C, ///< The integer constant to be casted
1034 Type *Ty, ///< The integer type to cast to
1035 bool isSigned ///< Whether C should be treated as signed or not
1038 /// @brief Create a FPExt, Bitcast or FPTrunc for fp -> fp casts
1039 static Constant *getFPCast(
1040 Constant *C, ///< The integer constant to be casted
1041 Type *Ty ///< The integer type to cast to
1044 /// @brief Return true if this is a convert constant expression
1045 bool isCast() const;
1047 /// @brief Return true if this is a compare constant expression
1048 bool isCompare() const;
1050 /// @brief Return true if this is an insertvalue or extractvalue expression,
1051 /// and the getIndices() method may be used.
1052 bool hasIndices() const;
1054 /// @brief Return true if this is a getelementptr expression and all
1055 /// the index operands are compile-time known integers within the
1056 /// corresponding notional static array extents. Note that this is
1057 /// not equivalant to, a subset of, or a superset of the "inbounds"
1059 bool isGEPWithNoNotionalOverIndexing() const;
1061 /// Select constant expr
1063 /// \param OnlyIfReducedTy see \a getWithOperands() docs.
1064 static Constant *getSelect(Constant *C, Constant *V1, Constant *V2,
1065 Type *OnlyIfReducedTy = nullptr);
1067 /// get - Return a binary or shift operator constant expression,
1068 /// folding if possible.
1070 /// \param OnlyIfReducedTy see \a getWithOperands() docs.
1071 static Constant *get(unsigned Opcode, Constant *C1, Constant *C2,
1072 unsigned Flags = 0, Type *OnlyIfReducedTy = nullptr);
1074 /// \brief Return an ICmp or FCmp comparison operator constant expression.
1076 /// \param OnlyIfReduced see \a getWithOperands() docs.
1077 static Constant *getCompare(unsigned short pred, Constant *C1, Constant *C2,
1078 bool OnlyIfReduced = false);
1080 /// get* - Return some common constants without having to
1081 /// specify the full Instruction::OPCODE identifier.
1083 static Constant *getICmp(unsigned short pred, Constant *LHS, Constant *RHS,
1084 bool OnlyIfReduced = false);
1085 static Constant *getFCmp(unsigned short pred, Constant *LHS, Constant *RHS,
1086 bool OnlyIfReduced = false);
1088 /// Getelementptr form. Value* is only accepted for convenience;
1089 /// all elements must be Constants.
1091 /// \param OnlyIfReducedTy see \a getWithOperands() docs.
1092 static Constant *getGetElementPtr(Type *Ty, Constant *C,
1093 ArrayRef<Constant *> IdxList,
1094 bool InBounds = false,
1095 Type *OnlyIfReducedTy = nullptr) {
1096 return getGetElementPtr(
1097 Ty, C, makeArrayRef((Value * const *)IdxList.data(), IdxList.size()),
1098 InBounds, OnlyIfReducedTy);
1100 static Constant *getGetElementPtr(Type *Ty, Constant *C, Constant *Idx,
1101 bool InBounds = false,
1102 Type *OnlyIfReducedTy = nullptr) {
1103 // This form of the function only exists to avoid ambiguous overload
1104 // warnings about whether to convert Idx to ArrayRef<Constant *> or
1105 // ArrayRef<Value *>.
1106 return getGetElementPtr(Ty, C, cast<Value>(Idx), InBounds, OnlyIfReducedTy);
1108 static Constant *getGetElementPtr(Type *Ty, Constant *C,
1109 ArrayRef<Value *> IdxList,
1110 bool InBounds = false,
1111 Type *OnlyIfReducedTy = nullptr);
1113 /// Create an "inbounds" getelementptr. See the documentation for the
1114 /// "inbounds" flag in LangRef.html for details.
1115 static Constant *getInBoundsGetElementPtr(Type *Ty, Constant *C,
1116 ArrayRef<Constant *> IdxList) {
1117 return getGetElementPtr(Ty, C, IdxList, true);
1119 static Constant *getInBoundsGetElementPtr(Type *Ty, Constant *C,
1121 // This form of the function only exists to avoid ambiguous overload
1122 // warnings about whether to convert Idx to ArrayRef<Constant *> or
1123 // ArrayRef<Value *>.
1124 return getGetElementPtr(Ty, C, Idx, true);
1126 static Constant *getInBoundsGetElementPtr(Type *Ty, Constant *C,
1127 ArrayRef<Value *> IdxList) {
1128 return getGetElementPtr(Ty, C, IdxList, true);
1131 static Constant *getExtractElement(Constant *Vec, Constant *Idx,
1132 Type *OnlyIfReducedTy = nullptr);
1133 static Constant *getInsertElement(Constant *Vec, Constant *Elt, Constant *Idx,
1134 Type *OnlyIfReducedTy = nullptr);
1135 static Constant *getShuffleVector(Constant *V1, Constant *V2, Constant *Mask,
1136 Type *OnlyIfReducedTy = nullptr);
1137 static Constant *getExtractValue(Constant *Agg, ArrayRef<unsigned> Idxs,
1138 Type *OnlyIfReducedTy = nullptr);
1139 static Constant *getInsertValue(Constant *Agg, Constant *Val,
1140 ArrayRef<unsigned> Idxs,
1141 Type *OnlyIfReducedTy = nullptr);
1143 /// getOpcode - Return the opcode at the root of this constant expression
1144 unsigned getOpcode() const { return getSubclassDataFromValue(); }
1146 /// getPredicate - Return the ICMP or FCMP predicate value. Assert if this is
1147 /// not an ICMP or FCMP constant expression.
1148 unsigned getPredicate() const;
1150 /// getIndices - Assert that this is an insertvalue or exactvalue
1151 /// expression and return the list of indices.
1152 ArrayRef<unsigned> getIndices() const;
1154 /// getOpcodeName - Return a string representation for an opcode.
1155 const char *getOpcodeName() const;
1157 /// getWithOperandReplaced - Return a constant expression identical to this
1158 /// one, but with the specified operand set to the specified value.
1159 Constant *getWithOperandReplaced(unsigned OpNo, Constant *Op) const;
1161 /// getWithOperands - This returns the current constant expression with the
1162 /// operands replaced with the specified values. The specified array must
1163 /// have the same number of operands as our current one.
1164 Constant *getWithOperands(ArrayRef<Constant*> Ops) const {
1165 return getWithOperands(Ops, getType());
1168 /// \brief Get the current expression with the operands replaced.
1170 /// Return the current constant expression with the operands replaced with \c
1171 /// Ops and the type with \c Ty. The new operands must have the same number
1172 /// as the current ones.
1174 /// If \c OnlyIfReduced is \c true, nullptr will be returned unless something
1175 /// gets constant-folded, the type changes, or the expression is otherwise
1176 /// canonicalized. This parameter should almost always be \c false.
1177 Constant *getWithOperands(ArrayRef<Constant *> Ops, Type *Ty,
1178 bool OnlyIfReduced = false,
1179 Type *SrcTy = nullptr) const;
1181 /// getAsInstruction - Returns an Instruction which implements the same
1182 /// operation as this ConstantExpr. The instruction is not linked to any basic
1185 /// A better approach to this could be to have a constructor for Instruction
1186 /// which would take a ConstantExpr parameter, but that would have spread
1187 /// implementation details of ConstantExpr outside of Constants.cpp, which
1188 /// would make it harder to remove ConstantExprs altogether.
1189 Instruction *getAsInstruction();
1191 /// Methods for support type inquiry through isa, cast, and dyn_cast:
1192 static inline bool classof(const Value *V) {
1193 return V->getValueID() == ConstantExprVal;
1197 // Shadow Value::setValueSubclassData with a private forwarding method so that
1198 // subclasses cannot accidentally use it.
1199 void setValueSubclassData(unsigned short D) {
1200 Value::setValueSubclassData(D);
1205 struct OperandTraits<ConstantExpr> :
1206 public VariadicOperandTraits<ConstantExpr, 1> {
1209 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(ConstantExpr, Constant)
1211 //===----------------------------------------------------------------------===//
1212 /// UndefValue - 'undef' values are things that do not have specified contents.
1213 /// These are used for a variety of purposes, including global variable
1214 /// initializers and operands to instructions. 'undef' values can occur with
1215 /// any first-class type.
1217 /// Undef values aren't exactly constants; if they have multiple uses, they
1218 /// can appear to have different bit patterns at each use. See
1219 /// LangRef.html#undefvalues for details.
1221 class UndefValue : public Constant {
1222 void *operator new(size_t, unsigned) = delete;
1223 UndefValue(const UndefValue &) = delete;
1225 friend class Constant;
1226 void destroyConstantImpl();
1227 Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
1230 explicit UndefValue(Type *T) : Constant(T, UndefValueVal, nullptr, 0) {}
1232 // allocate space for exactly zero operands
1233 void *operator new(size_t s) {
1234 return User::operator new(s, 0);
1237 /// get() - Static factory methods - Return an 'undef' object of the specified
1240 static UndefValue *get(Type *T);
1242 /// getSequentialElement - If this Undef has array or vector type, return a
1243 /// undef with the right element type.
1244 UndefValue *getSequentialElement() const;
1246 /// getStructElement - If this undef has struct type, return a undef with the
1247 /// right element type for the specified element.
1248 UndefValue *getStructElement(unsigned Elt) const;
1250 /// getElementValue - Return an undef of the right value for the specified GEP
1252 UndefValue *getElementValue(Constant *C) const;
1254 /// getElementValue - Return an undef of the right value for the specified GEP
1256 UndefValue *getElementValue(unsigned Idx) const;
1258 /// \brief Return the number of elements in the array, vector, or struct.
1259 unsigned getNumElements() const;
1261 /// Methods for support type inquiry through isa, cast, and dyn_cast:
1262 static bool classof(const Value *V) {
1263 return V->getValueID() == UndefValueVal;
1267 } // End llvm namespace