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1 //===-- llvm/Value.h - Definition of the Value class ------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file declares the Value class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_VALUE_H
15 #define LLVM_VALUE_H
16 
17 #include "llvm/Use.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/Support/Casting.h"
20 #include <string>
21 
22 namespace llvm {
23 
24 class Constant;
25 class Argument;
26 class Instruction;
27 class BasicBlock;
28 class GlobalValue;
29 class Function;
30 class GlobalVariable;
31 class GlobalAlias;
32 class InlineAsm;
33 class ValueSymbolTable;
34 template<typename ValueTy> class StringMapEntry;
35 template <typename ValueTy = Value>
36 class AssertingVH;
37 typedef StringMapEntry<Value*> ValueName;
38 class raw_ostream;
39 class AssemblyAnnotationWriter;
40 class ValueHandleBase;
41 class LLVMContext;
42 class Twine;
43 class MDNode;
44 class Type;
45 
46 //===----------------------------------------------------------------------===//
47 //                                 Value Class
48 //===----------------------------------------------------------------------===//
49 
50 /// This is a very important LLVM class. It is the base class of all values
51 /// computed by a program that may be used as operands to other values. Value is
52 /// the super class of other important classes such as Instruction and Function.
53 /// All Values have a Type. Type is not a subclass of Value. Some values can
54 /// have a name and they belong to some Module.  Setting the name on the Value
55 /// automatically updates the module's symbol table.
56 ///
57 /// Every value has a "use list" that keeps track of which other Values are
58 /// using this Value.  A Value can also have an arbitrary number of ValueHandle
59 /// objects that watch it and listen to RAUW and Destroy events.  See
60 /// llvm/Support/ValueHandle.h for details.
61 ///
62 /// @brief LLVM Value Representation
63 class Value {
64   const unsigned char SubclassID;   // Subclass identifier (for isa/dyn_cast)
65   unsigned char HasValueHandle : 1; // Has a ValueHandle pointing to this?
66 protected:
67   /// SubclassOptionalData - This member is similar to SubclassData, however it
68   /// is for holding information which may be used to aid optimization, but
69   /// which may be cleared to zero without affecting conservative
70   /// interpretation.
71   unsigned char SubclassOptionalData : 7;
72 
73 private:
74   /// SubclassData - This member is defined by this class, but is not used for
75   /// anything.  Subclasses can use it to hold whatever state they find useful.
76   /// This field is initialized to zero by the ctor.
77   unsigned short SubclassData;
78 
79   Type *VTy;
80   Use *UseList;
81 
82   friend class ValueSymbolTable; // Allow ValueSymbolTable to directly mod Name.
83   friend class ValueHandleBase;
84   ValueName *Name;
85 
86   void operator=(const Value &);     // Do not implement
87   Value(const Value &);              // Do not implement
88 
89 protected:
90   /// printCustom - Value subclasses can override this to implement custom
91   /// printing behavior.
92   virtual void printCustom(raw_ostream &O) const;
93 
94   Value(Type *Ty, unsigned scid);
95 public:
96   virtual ~Value();
97 
98   /// dump - Support for debugging, callable in GDB: V->dump()
99   //
100   void dump() const;
101 
102   /// print - Implement operator<< on Value.
103   ///
104   void print(raw_ostream &O, AssemblyAnnotationWriter *AAW = 0) const;
105 
106   /// All values are typed, get the type of this value.
107   ///
getType()108   Type *getType() const { return VTy; }
109 
110   /// All values hold a context through their type.
111   LLVMContext &getContext() const;
112 
113   // All values can potentially be named...
hasName()114   bool hasName() const { return Name != 0; }
getValueName()115   ValueName *getValueName() const { return Name; }
116 
117   /// getName() - Return a constant reference to the value's name. This is cheap
118   /// and guaranteed to return the same reference as long as the value is not
119   /// modified.
120   ///
121   /// This is currently guaranteed to return a StringRef for which data() points
122   /// to a valid null terminated string. The use of StringRef.data() is
123   /// deprecated here, however, and clients should not rely on it. If such
124   /// behavior is needed, clients should use expensive getNameStr(), or switch
125   /// to an interface that does not depend on null termination.
126   StringRef getName() const;
127 
128   /// getNameStr() - Return the name of the specified value, *constructing a
129   /// string* to hold it.  This is guaranteed to construct a string and is very
130   /// expensive, clients should use getName() unless necessary.
131   std::string getNameStr() const;
132 
133   /// setName() - Change the name of the value, choosing a new unique name if
134   /// the provided name is taken.
135   ///
136   /// \arg Name - The new name; or "" if the value's name should be removed.
137   void setName(const Twine &Name);
138 
139 
140   /// takeName - transfer the name from V to this value, setting V's name to
141   /// empty.  It is an error to call V->takeName(V).
142   void takeName(Value *V);
143 
144   /// replaceAllUsesWith - Go through the uses list for this definition and make
145   /// each use point to "V" instead of "this".  After this completes, 'this's
146   /// use list is guaranteed to be empty.
147   ///
148   void replaceAllUsesWith(Value *V);
149 
150   //----------------------------------------------------------------------
151   // Methods for handling the chain of uses of this Value.
152   //
153   typedef value_use_iterator<User>       use_iterator;
154   typedef value_use_iterator<const User> const_use_iterator;
155 
use_empty()156   bool               use_empty() const { return UseList == 0; }
use_begin()157   use_iterator       use_begin()       { return use_iterator(UseList); }
use_begin()158   const_use_iterator use_begin() const { return const_use_iterator(UseList); }
use_end()159   use_iterator       use_end()         { return use_iterator(0);   }
use_end()160   const_use_iterator use_end()   const { return const_use_iterator(0);   }
use_back()161   User              *use_back()        { return *use_begin(); }
use_back()162   const User        *use_back()  const { return *use_begin(); }
163 
164   /// hasOneUse - Return true if there is exactly one user of this value.  This
165   /// is specialized because it is a common request and does not require
166   /// traversing the whole use list.
167   ///
hasOneUse()168   bool hasOneUse() const {
169     const_use_iterator I = use_begin(), E = use_end();
170     if (I == E) return false;
171     return ++I == E;
172   }
173 
174   /// hasNUses - Return true if this Value has exactly N users.
175   ///
176   bool hasNUses(unsigned N) const;
177 
178   /// hasNUsesOrMore - Return true if this value has N users or more.  This is
179   /// logically equivalent to getNumUses() >= N.
180   ///
181   bool hasNUsesOrMore(unsigned N) const;
182 
183   bool isUsedInBasicBlock(const BasicBlock *BB) const;
184 
185   /// getNumUses - This method computes the number of uses of this Value.  This
186   /// is a linear time operation.  Use hasOneUse, hasNUses, or hasNUsesOrMore
187   /// to check for specific values.
188   unsigned getNumUses() const;
189 
190   /// addUse - This method should only be used by the Use class.
191   ///
addUse(Use & U)192   void addUse(Use &U) { U.addToList(&UseList); }
193 
194   /// An enumeration for keeping track of the concrete subclass of Value that
195   /// is actually instantiated. Values of this enumeration are kept in the
196   /// Value classes SubclassID field. They are used for concrete type
197   /// identification.
198   enum ValueTy {
199     ArgumentVal,              // This is an instance of Argument
200     BasicBlockVal,            // This is an instance of BasicBlock
201     FunctionVal,              // This is an instance of Function
202     GlobalAliasVal,           // This is an instance of GlobalAlias
203     GlobalVariableVal,        // This is an instance of GlobalVariable
204     UndefValueVal,            // This is an instance of UndefValue
205     BlockAddressVal,          // This is an instance of BlockAddress
206     ConstantExprVal,          // This is an instance of ConstantExpr
207     ConstantAggregateZeroVal, // This is an instance of ConstantAggregateZero
208     ConstantIntVal,           // This is an instance of ConstantInt
209     ConstantFPVal,            // This is an instance of ConstantFP
210     ConstantArrayVal,         // This is an instance of ConstantArray
211     ConstantStructVal,        // This is an instance of ConstantStruct
212     ConstantVectorVal,        // This is an instance of ConstantVector
213     ConstantPointerNullVal,   // This is an instance of ConstantPointerNull
214     MDNodeVal,                // This is an instance of MDNode
215     MDStringVal,              // This is an instance of MDString
216     InlineAsmVal,             // This is an instance of InlineAsm
217     PseudoSourceValueVal,     // This is an instance of PseudoSourceValue
218     FixedStackPseudoSourceValueVal, // This is an instance of
219                                     // FixedStackPseudoSourceValue
220     InstructionVal,           // This is an instance of Instruction
221     // Enum values starting at InstructionVal are used for Instructions;
222     // don't add new values here!
223 
224     // Markers:
225     ConstantFirstVal = FunctionVal,
226     ConstantLastVal  = ConstantPointerNullVal
227   };
228 
229   /// getValueID - Return an ID for the concrete type of this object.  This is
230   /// used to implement the classof checks.  This should not be used for any
231   /// other purpose, as the values may change as LLVM evolves.  Also, note that
232   /// for instructions, the Instruction's opcode is added to InstructionVal. So
233   /// this means three things:
234   /// # there is no value with code InstructionVal (no opcode==0).
235   /// # there are more possible values for the value type than in ValueTy enum.
236   /// # the InstructionVal enumerator must be the highest valued enumerator in
237   ///   the ValueTy enum.
getValueID()238   unsigned getValueID() const {
239     return SubclassID;
240   }
241 
242   /// getRawSubclassOptionalData - Return the raw optional flags value
243   /// contained in this value. This should only be used when testing two
244   /// Values for equivalence.
getRawSubclassOptionalData()245   unsigned getRawSubclassOptionalData() const {
246     return SubclassOptionalData;
247   }
248 
249   /// clearSubclassOptionalData - Clear the optional flags contained in
250   /// this value.
clearSubclassOptionalData()251   void clearSubclassOptionalData() {
252     SubclassOptionalData = 0;
253   }
254 
255   /// hasSameSubclassOptionalData - Test whether the optional flags contained
256   /// in this value are equal to the optional flags in the given value.
hasSameSubclassOptionalData(const Value * V)257   bool hasSameSubclassOptionalData(const Value *V) const {
258     return SubclassOptionalData == V->SubclassOptionalData;
259   }
260 
261   /// intersectOptionalDataWith - Clear any optional flags in this value
262   /// that are not also set in the given value.
intersectOptionalDataWith(const Value * V)263   void intersectOptionalDataWith(const Value *V) {
264     SubclassOptionalData &= V->SubclassOptionalData;
265   }
266 
267   /// hasValueHandle - Return true if there is a value handle associated with
268   /// this value.
hasValueHandle()269   bool hasValueHandle() const { return HasValueHandle; }
270 
271   // Methods for support type inquiry through isa, cast, and dyn_cast:
classof(const Value *)272   static inline bool classof(const Value *) {
273     return true; // Values are always values.
274   }
275 
276   /// stripPointerCasts - This method strips off any unneeded pointer
277   /// casts from the specified value, returning the original uncasted value.
278   /// Note that the returned value has pointer type if the specified value does.
279   Value *stripPointerCasts();
stripPointerCasts()280   const Value *stripPointerCasts() const {
281     return const_cast<Value*>(this)->stripPointerCasts();
282   }
283 
284   /// isDereferenceablePointer - Test if this value is always a pointer to
285   /// allocated and suitably aligned memory for a simple load or store.
286   bool isDereferenceablePointer() const;
287 
288   /// DoPHITranslation - If this value is a PHI node with CurBB as its parent,
289   /// return the value in the PHI node corresponding to PredBB.  If not, return
290   /// ourself.  This is useful if you want to know the value something has in a
291   /// predecessor block.
292   Value *DoPHITranslation(const BasicBlock *CurBB, const BasicBlock *PredBB);
293 
DoPHITranslation(const BasicBlock * CurBB,const BasicBlock * PredBB)294   const Value *DoPHITranslation(const BasicBlock *CurBB,
295                                 const BasicBlock *PredBB) const{
296     return const_cast<Value*>(this)->DoPHITranslation(CurBB, PredBB);
297   }
298 
299   /// MaximumAlignment - This is the greatest alignment value supported by
300   /// load, store, and alloca instructions, and global values.
301   static const unsigned MaximumAlignment = 1u << 29;
302 
303   /// mutateType - Mutate the type of this Value to be of the specified type.
304   /// Note that this is an extremely dangerous operation which can create
305   /// completely invalid IR very easily.  It is strongly recommended that you
306   /// recreate IR objects with the right types instead of mutating them in
307   /// place.
mutateType(Type * Ty)308   void mutateType(Type *Ty) {
309     VTy = Ty;
310   }
311 
312 protected:
getSubclassDataFromValue()313   unsigned short getSubclassDataFromValue() const { return SubclassData; }
setValueSubclassData(unsigned short D)314   void setValueSubclassData(unsigned short D) { SubclassData = D; }
315 };
316 
317 inline raw_ostream &operator<<(raw_ostream &OS, const Value &V) {
318   V.print(OS);
319   return OS;
320 }
321 
set(Value * V)322 void Use::set(Value *V) {
323   if (Val) removeFromList();
324   Val = V;
325   if (V) V->addUse(*this);
326 }
327 
328 
329 // isa - Provide some specializations of isa so that we don't have to include
330 // the subtype header files to test to see if the value is a subclass...
331 //
332 template <> struct isa_impl<Constant, Value> {
333   static inline bool doit(const Value &Val) {
334     return Val.getValueID() >= Value::ConstantFirstVal &&
335       Val.getValueID() <= Value::ConstantLastVal;
336   }
337 };
338 
339 template <> struct isa_impl<Argument, Value> {
340   static inline bool doit (const Value &Val) {
341     return Val.getValueID() == Value::ArgumentVal;
342   }
343 };
344 
345 template <> struct isa_impl<InlineAsm, Value> {
346   static inline bool doit(const Value &Val) {
347     return Val.getValueID() == Value::InlineAsmVal;
348   }
349 };
350 
351 template <> struct isa_impl<Instruction, Value> {
352   static inline bool doit(const Value &Val) {
353     return Val.getValueID() >= Value::InstructionVal;
354   }
355 };
356 
357 template <> struct isa_impl<BasicBlock, Value> {
358   static inline bool doit(const Value &Val) {
359     return Val.getValueID() == Value::BasicBlockVal;
360   }
361 };
362 
363 template <> struct isa_impl<Function, Value> {
364   static inline bool doit(const Value &Val) {
365     return Val.getValueID() == Value::FunctionVal;
366   }
367 };
368 
369 template <> struct isa_impl<GlobalVariable, Value> {
370   static inline bool doit(const Value &Val) {
371     return Val.getValueID() == Value::GlobalVariableVal;
372   }
373 };
374 
375 template <> struct isa_impl<GlobalAlias, Value> {
376   static inline bool doit(const Value &Val) {
377     return Val.getValueID() == Value::GlobalAliasVal;
378   }
379 };
380 
381 template <> struct isa_impl<GlobalValue, Value> {
382   static inline bool doit(const Value &Val) {
383     return isa<GlobalVariable>(Val) || isa<Function>(Val) ||
384       isa<GlobalAlias>(Val);
385   }
386 };
387 
388 template <> struct isa_impl<MDNode, Value> {
389   static inline bool doit(const Value &Val) {
390     return Val.getValueID() == Value::MDNodeVal;
391   }
392 };
393 
394 // Value* is only 4-byte aligned.
395 template<>
396 class PointerLikeTypeTraits<Value*> {
397   typedef Value* PT;
398 public:
399   static inline void *getAsVoidPointer(PT P) { return P; }
400   static inline PT getFromVoidPointer(void *P) {
401     return static_cast<PT>(P);
402   }
403   enum { NumLowBitsAvailable = 2 };
404 };
405 
406 } // End llvm namespace
407 
408 #endif
409