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1 //===-- llvm/BasicBlock.h - Represent a basic block in the VM ---*- 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 contains the declaration of the BasicBlock class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_IR_BASICBLOCK_H
15 #define LLVM_IR_BASICBLOCK_H
16 
17 #include "llvm/ADT/ilist.h"
18 #include "llvm/ADT/ilist_node.h"
19 #include "llvm/ADT/Twine.h"
20 #include "llvm/IR/Instruction.h"
21 #include "llvm/IR/SymbolTableListTraits.h"
22 #include "llvm/IR/Value.h"
23 #include "llvm/Support/CBindingWrapping.h"
24 #include "llvm-c/Types.h"
25 #include <cassert>
26 #include <cstddef>
27 
28 namespace llvm {
29 
30 class CallInst;
31 class Function;
32 class LandingPadInst;
33 class LLVMContext;
34 class TerminatorInst;
35 
36 /// \brief LLVM Basic Block Representation
37 ///
38 /// This represents a single basic block in LLVM. A basic block is simply a
39 /// container of instructions that execute sequentially. Basic blocks are Values
40 /// because they are referenced by instructions such as branches and switch
41 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
42 /// represents a label to which a branch can jump.
43 ///
44 /// A well formed basic block is formed of a list of non-terminating
45 /// instructions followed by a single TerminatorInst instruction.
46 /// TerminatorInst's may not occur in the middle of basic blocks, and must
47 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
48 /// occur because it may be useful in the intermediate stage of constructing or
49 /// modifying a program. However, the verifier will ensure that basic blocks
50 /// are "well formed".
51 class BasicBlock : public Value, // Basic blocks are data objects also
52                    public ilist_node_with_parent<BasicBlock, Function> {
53 public:
54   typedef SymbolTableList<Instruction> InstListType;
55 
56 private:
57   friend class BlockAddress;
58   friend class SymbolTableListTraits<BasicBlock>;
59 
60   InstListType InstList;
61   Function *Parent;
62 
63   void setParent(Function *parent);
64 
65   /// \brief Constructor.
66   ///
67   /// If the function parameter is specified, the basic block is automatically
68   /// inserted at either the end of the function (if InsertBefore is null), or
69   /// before the specified basic block.
70   explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
71                       Function *Parent = nullptr,
72                       BasicBlock *InsertBefore = nullptr);
73 
74 public:
75   BasicBlock(const BasicBlock &) = delete;
76   BasicBlock &operator=(const BasicBlock &) = delete;
77   ~BasicBlock() override;
78 
79   /// \brief Get the context in which this basic block lives.
80   LLVMContext &getContext() const;
81 
82   /// Instruction iterators...
83   typedef InstListType::iterator iterator;
84   typedef InstListType::const_iterator const_iterator;
85   typedef InstListType::reverse_iterator reverse_iterator;
86   typedef InstListType::const_reverse_iterator const_reverse_iterator;
87 
88   /// \brief Creates a new BasicBlock.
89   ///
90   /// If the Parent parameter is specified, the basic block is automatically
91   /// inserted at either the end of the function (if InsertBefore is 0), or
92   /// before the specified basic block.
93   static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
94                             Function *Parent = nullptr,
95                             BasicBlock *InsertBefore = nullptr) {
96     return new BasicBlock(Context, Name, Parent, InsertBefore);
97   }
98 
99   /// \brief Return the enclosing method, or null if none.
getParent()100   const Function *getParent() const { return Parent; }
getParent()101         Function *getParent()       { return Parent; }
102 
103   /// \brief Return the module owning the function this basic block belongs to,
104   /// or nullptr it the function does not have a module.
105   ///
106   /// Note: this is undefined behavior if the block does not have a parent.
107   const Module *getModule() const;
108   Module *getModule();
109 
110   /// \brief Returns the terminator instruction if the block is well formed or
111   /// null if the block is not well formed.
112   TerminatorInst *getTerminator();
113   const TerminatorInst *getTerminator() const;
114 
115   /// \brief Returns the call instruction calling @llvm.experimental.deoptimize
116   /// prior to the terminating return instruction of this basic block, if such a
117   /// call is present.  Otherwise, returns null.
118   CallInst *getTerminatingDeoptimizeCall();
getTerminatingDeoptimizeCall()119   const CallInst *getTerminatingDeoptimizeCall() const {
120     return const_cast<BasicBlock *>(this)->getTerminatingDeoptimizeCall();
121   }
122 
123   /// \brief Returns the call instruction marked 'musttail' prior to the
124   /// terminating return instruction of this basic block, if such a call is
125   /// present.  Otherwise, returns null.
126   CallInst *getTerminatingMustTailCall();
getTerminatingMustTailCall()127   const CallInst *getTerminatingMustTailCall() const {
128     return const_cast<BasicBlock *>(this)->getTerminatingMustTailCall();
129   }
130 
131   /// \brief Returns a pointer to the first instruction in this block that is
132   /// not a PHINode instruction.
133   ///
134   /// When adding instructions to the beginning of the basic block, they should
135   /// be added before the returned value, not before the first instruction,
136   /// which might be PHI. Returns 0 is there's no non-PHI instruction.
137   Instruction* getFirstNonPHI();
getFirstNonPHI()138   const Instruction* getFirstNonPHI() const {
139     return const_cast<BasicBlock*>(this)->getFirstNonPHI();
140   }
141 
142   /// \brief Returns a pointer to the first instruction in this block that is not
143   /// a PHINode or a debug intrinsic.
144   Instruction* getFirstNonPHIOrDbg();
getFirstNonPHIOrDbg()145   const Instruction* getFirstNonPHIOrDbg() const {
146     return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
147   }
148 
149   /// \brief Returns a pointer to the first instruction in this block that is not
150   /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
151   Instruction* getFirstNonPHIOrDbgOrLifetime();
getFirstNonPHIOrDbgOrLifetime()152   const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
153     return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
154   }
155 
156   /// \brief Returns an iterator to the first instruction in this block that is
157   /// suitable for inserting a non-PHI instruction.
158   ///
159   /// In particular, it skips all PHIs and LandingPad instructions.
160   iterator getFirstInsertionPt();
getFirstInsertionPt()161   const_iterator getFirstInsertionPt() const {
162     return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
163   }
164 
165   /// \brief Unlink 'this' from the containing function, but do not delete it.
166   void removeFromParent();
167 
168   /// \brief Unlink 'this' from the containing function and delete it.
169   ///
170   // \returns an iterator pointing to the element after the erased one.
171   SymbolTableList<BasicBlock>::iterator eraseFromParent();
172 
173   /// \brief Unlink this basic block from its current function and insert it
174   /// into the function that \p MovePos lives in, right before \p MovePos.
175   void moveBefore(BasicBlock *MovePos);
176 
177   /// \brief Unlink this basic block from its current function and insert it
178   /// right after \p MovePos in the function \p MovePos lives in.
179   void moveAfter(BasicBlock *MovePos);
180 
181   /// \brief Insert unlinked basic block into a function.
182   ///
183   /// Inserts an unlinked basic block into \c Parent.  If \c InsertBefore is
184   /// provided, inserts before that basic block, otherwise inserts at the end.
185   ///
186   /// \pre \a getParent() is \c nullptr.
187   void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
188 
189   /// \brief Return the predecessor of this block if it has a single predecessor
190   /// block. Otherwise return a null pointer.
191   BasicBlock *getSinglePredecessor();
getSinglePredecessor()192   const BasicBlock *getSinglePredecessor() const {
193     return const_cast<BasicBlock*>(this)->getSinglePredecessor();
194   }
195 
196   /// \brief Return the predecessor of this block if it has a unique predecessor
197   /// block. Otherwise return a null pointer.
198   ///
199   /// Note that unique predecessor doesn't mean single edge, there can be
200   /// multiple edges from the unique predecessor to this block (for example a
201   /// switch statement with multiple cases having the same destination).
202   BasicBlock *getUniquePredecessor();
getUniquePredecessor()203   const BasicBlock *getUniquePredecessor() const {
204     return const_cast<BasicBlock*>(this)->getUniquePredecessor();
205   }
206 
207   /// \brief Return the successor of this block if it has a single successor.
208   /// Otherwise return a null pointer.
209   ///
210   /// This method is analogous to getSinglePredecessor above.
211   BasicBlock *getSingleSuccessor();
getSingleSuccessor()212   const BasicBlock *getSingleSuccessor() const {
213     return const_cast<BasicBlock*>(this)->getSingleSuccessor();
214   }
215 
216   /// \brief Return the successor of this block if it has a unique successor.
217   /// Otherwise return a null pointer.
218   ///
219   /// This method is analogous to getUniquePredecessor above.
220   BasicBlock *getUniqueSuccessor();
getUniqueSuccessor()221   const BasicBlock *getUniqueSuccessor() const {
222     return const_cast<BasicBlock*>(this)->getUniqueSuccessor();
223   }
224 
225   //===--------------------------------------------------------------------===//
226   /// Instruction iterator methods
227   ///
begin()228   inline iterator                begin()       { return InstList.begin(); }
begin()229   inline const_iterator          begin() const { return InstList.begin(); }
end()230   inline iterator                end  ()       { return InstList.end();   }
end()231   inline const_iterator          end  () const { return InstList.end();   }
232 
rbegin()233   inline reverse_iterator        rbegin()       { return InstList.rbegin(); }
rbegin()234   inline const_reverse_iterator  rbegin() const { return InstList.rbegin(); }
rend()235   inline reverse_iterator        rend  ()       { return InstList.rend();   }
rend()236   inline const_reverse_iterator  rend  () const { return InstList.rend();   }
237 
size()238   inline size_t                   size() const { return InstList.size();  }
empty()239   inline bool                    empty() const { return InstList.empty(); }
front()240   inline const Instruction      &front() const { return InstList.front(); }
front()241   inline       Instruction      &front()       { return InstList.front(); }
back()242   inline const Instruction       &back() const { return InstList.back();  }
back()243   inline       Instruction       &back()       { return InstList.back();  }
244 
245   /// \brief Return the underlying instruction list container.
246   ///
247   /// Currently you need to access the underlying instruction list container
248   /// directly if you want to modify it.
getInstList()249   const InstListType &getInstList() const { return InstList; }
getInstList()250         InstListType &getInstList()       { return InstList; }
251 
252   /// \brief Returns a pointer to a member of the instruction list.
getSublistAccess(Instruction *)253   static InstListType BasicBlock::*getSublistAccess(Instruction*) {
254     return &BasicBlock::InstList;
255   }
256 
257   /// \brief Returns a pointer to the symbol table if one exists.
258   ValueSymbolTable *getValueSymbolTable();
259 
260   /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
classof(const Value * V)261   static inline bool classof(const Value *V) {
262     return V->getValueID() == Value::BasicBlockVal;
263   }
264 
265   /// \brief Cause all subinstructions to "let go" of all the references that
266   /// said subinstructions are maintaining.
267   ///
268   /// This allows one to 'delete' a whole class at a time, even though there may
269   /// be circular references... first all references are dropped, and all use
270   /// counts go to zero.  Then everything is delete'd for real.  Note that no
271   /// operations are valid on an object that has "dropped all references",
272   /// except operator delete.
273   void dropAllReferences();
274 
275   /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
276   /// able to reach it.
277   ///
278   /// This is actually not used to update the Predecessor list, but is actually
279   /// used to update the PHI nodes that reside in the block.  Note that this
280   /// should be called while the predecessor still refers to this block.
281   void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
282 
283   bool canSplitPredecessors() const;
284 
285   /// \brief Split the basic block into two basic blocks at the specified
286   /// instruction.
287   ///
288   /// Note that all instructions BEFORE the specified iterator stay as part of
289   /// the original basic block, an unconditional branch is added to the original
290   /// BB, and the rest of the instructions in the BB are moved to the new BB,
291   /// including the old terminator.  The newly formed BasicBlock is returned.
292   /// This function invalidates the specified iterator.
293   ///
294   /// Note that this only works on well formed basic blocks (must have a
295   /// terminator), and 'I' must not be the end of instruction list (which would
296   /// cause a degenerate basic block to be formed, having a terminator inside of
297   /// the basic block).
298   ///
299   /// Also note that this doesn't preserve any passes. To split blocks while
300   /// keeping loop information consistent, use the SplitBlock utility function.
301   BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
302   BasicBlock *splitBasicBlock(Instruction *I, const Twine &BBName = "") {
303     return splitBasicBlock(I->getIterator(), BBName);
304   }
305 
306   /// \brief Returns true if there are any uses of this basic block other than
307   /// direct branches, switches, etc. to it.
hasAddressTaken()308   bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
309 
310   /// \brief Update all phi nodes in this basic block's successors to refer to
311   /// basic block \p New instead of to it.
312   void replaceSuccessorsPhiUsesWith(BasicBlock *New);
313 
314   /// \brief Return true if this basic block is an exception handling block.
isEHPad()315   bool isEHPad() const { return getFirstNonPHI()->isEHPad(); }
316 
317   /// \brief Return true if this basic block is a landing pad.
318   ///
319   /// Being a ``landing pad'' means that the basic block is the destination of
320   /// the 'unwind' edge of an invoke instruction.
321   bool isLandingPad() const;
322 
323   /// \brief Return the landingpad instruction associated with the landing pad.
324   LandingPadInst *getLandingPadInst();
325   const LandingPadInst *getLandingPadInst() const;
326 
327 private:
328   /// \brief Increment the internal refcount of the number of BlockAddresses
329   /// referencing this BasicBlock by \p Amt.
330   ///
331   /// This is almost always 0, sometimes one possibly, but almost never 2, and
332   /// inconceivably 3 or more.
AdjustBlockAddressRefCount(int Amt)333   void AdjustBlockAddressRefCount(int Amt) {
334     setValueSubclassData(getSubclassDataFromValue()+Amt);
335     assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
336            "Refcount wrap-around");
337   }
338 
339   /// \brief Shadow Value::setValueSubclassData with a private forwarding method
340   /// so that any future subclasses cannot accidentally use it.
setValueSubclassData(unsigned short D)341   void setValueSubclassData(unsigned short D) {
342     Value::setValueSubclassData(D);
343   }
344 };
345 
346 // Create wrappers for C Binding types (see CBindingWrapping.h).
347 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
348 
349 } // end namespace llvm
350 
351 #endif // LLVM_IR_BASICBLOCK_H
352