LLVM API Documentation

BasicBlock.h

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00001 //===-- llvm/BasicBlock.h - Represent a basic block in the VM ---*- C++ -*-===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 //
00011 // This file contains the declaration of the BasicBlock class.
00012 //===----------------------------------------------------------------------===//
00013 
00014 #ifndef LLVM_BASICBLOCK_H
00015 #define LLVM_BASICBLOCK_H
00016 
00017 #include "llvm/Instruction.h"
00018 #include "llvm/SymbolTableListTraits.h"
00019 #include "llvm/ADT/ilist"
00020 
00021 namespace llvm {
00022 
00023 class TerminatorInst;
00024 template <class Term, class BB> class SuccIterator;  // Successor Iterator
00025 template <class Ptr, class USE_iterator> class PredIterator;
00026 
00027 template<> struct ilist_traits<Instruction>
00028   : public SymbolTableListTraits<Instruction, BasicBlock, Function> {
00029   // createSentinel is used to create a node that marks the end of the list...
00030   static Instruction *createSentinel();
00031   static void destroySentinel(Instruction *I) { delete I; }
00032   static iplist<Instruction> &getList(BasicBlock *BB);
00033 };
00034 
00035 /// This represents a single basic block in LLVM. A basic block is simply a
00036 /// container of instructions that execute sequentially. Basic blocks are Values
00037 /// because they are referenced by instructions such as branches and switch
00038 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
00039 /// represents a label to which a branch can jump.
00040 ///
00041 /// A well formed basic block is formed of a list of non-terminating 
00042 /// instructions followed by a single TerminatorInst instruction.  
00043 /// TerminatorInst's may not occur in the middle of basic blocks, and must 
00044 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
00045 /// occur because it may be useful in the intermediate stage of constructing or
00046 /// modifying a program. However, the verifier will ensure that basic blocks
00047 /// are "well formed".
00048 /// @brief LLVM Basic Block Representation
00049 class BasicBlock : public Value {       // Basic blocks are data objects also
00050 public:
00051   typedef iplist<Instruction> InstListType;
00052 private :
00053   InstListType InstList;
00054   BasicBlock *Prev, *Next; // Next and Prev links for our intrusive linked list
00055 
00056   void setParent(Function *parent);
00057   void setNext(BasicBlock *N) { Next = N; }
00058   void setPrev(BasicBlock *N) { Prev = N; }
00059   friend class SymbolTableListTraits<BasicBlock, Function, Function>;
00060 
00061   BasicBlock(const BasicBlock &);     // Do not implement
00062   void operator=(const BasicBlock &); // Do not implement
00063 
00064 public:
00065   /// Instruction iterators...
00066   typedef InstListType::iterator                              iterator;
00067   typedef InstListType::const_iterator                  const_iterator;
00068 
00069   /// BasicBlock ctor - If the function parameter is specified, the basic block
00070   /// is automatically inserted at either the end of the function (if
00071   /// InsertBefore is null), or before the specified basic block.
00072   ///
00073   BasicBlock(const std::string &Name = "", Function *Parent = 0,
00074              BasicBlock *InsertBefore = 0);
00075   ~BasicBlock();
00076 
00077   /// getParent - Return the enclosing method, or null if none
00078   ///
00079   const Function *getParent() const { return InstList.getParent(); }
00080         Function *getParent()       { return InstList.getParent(); }
00081 
00082   // getNext/Prev - Return the next or previous basic block in the list.
00083         BasicBlock *getNext()       { return Next; }
00084   const BasicBlock *getNext() const { return Next; }
00085         BasicBlock *getPrev()       { return Prev; }
00086   const BasicBlock *getPrev() const { return Prev; }
00087 
00088   /// getTerminator() - If this is a well formed basic block, then this returns
00089   /// a pointer to the terminator instruction.  If it is not, then you get a
00090   /// null pointer back.
00091   ///
00092   TerminatorInst *getTerminator();
00093   const TerminatorInst *const getTerminator() const;
00094   
00095   /// Returns a pointer to the first instructon in this block that is not a 
00096   /// PHINode instruction. When adding instruction to the beginning of the
00097   /// basic block, they should be added before the returned value, not before
00098   /// the first instruction, which might be PHI.
00099   /// Returns 0 is there's no non-PHI instruction.
00100   Instruction* getFirstNonPHI();
00101   
00102   /// removeFromParent - This method unlinks 'this' from the containing
00103   /// function, but does not delete it.
00104   ///
00105   void removeFromParent();
00106 
00107   /// eraseFromParent - This method unlinks 'this' from the containing function
00108   /// and deletes it.
00109   ///
00110   void eraseFromParent();
00111   
00112   /// moveBefore - Unlink this instruction from its current function and
00113   /// insert it into the function that MovePos lives in, right before
00114   /// MovePos.
00115   void moveBefore(BasicBlock *MovePos);
00116 
00117   /// getSinglePredecessor - If this basic block has a single predecessor block,
00118   /// return the block, otherwise return a null pointer.
00119   BasicBlock *getSinglePredecessor();
00120   const BasicBlock *getSinglePredecessor() const {
00121     return const_cast<BasicBlock*>(this)->getSinglePredecessor();
00122   }
00123 
00124   //===--------------------------------------------------------------------===//
00125   /// Instruction iterator methods
00126   ///
00127   inline iterator                begin()       { return InstList.begin(); }
00128   inline const_iterator          begin() const { return InstList.begin(); }
00129   inline iterator                end  ()       { return InstList.end();   }
00130   inline const_iterator          end  () const { return InstList.end();   }
00131 
00132   inline size_t                   size() const { return InstList.size();  }
00133   inline bool                    empty() const { return InstList.empty(); }
00134   inline const Instruction      &front() const { return InstList.front(); }
00135   inline       Instruction      &front()       { return InstList.front(); }
00136   inline const Instruction       &back() const { return InstList.back();  }
00137   inline       Instruction       &back()       { return InstList.back();  }
00138 
00139   /// getInstList() - Return the underlying instruction list container.  You
00140   /// need to access it directly if you want to modify it currently.
00141   ///
00142   const InstListType &getInstList() const { return InstList; }
00143         InstListType &getInstList()       { return InstList; }
00144 
00145   virtual void print(std::ostream &OS) const { print(OS, 0); }
00146   void print(std::ostream &OS, AssemblyAnnotationWriter *AAW) const;
00147 
00148   /// Methods for support type inquiry through isa, cast, and dyn_cast:
00149   static inline bool classof(const BasicBlock *) { return true; }
00150   static inline bool classof(const Value *V) {
00151     return V->getValueType() == Value::BasicBlockVal;
00152   }
00153 
00154   /// dropAllReferences() - This function causes all the subinstructions to "let
00155   /// go" of all references that they are maintaining.  This allows one to
00156   /// 'delete' a whole class at a time, even though there may be circular
00157   /// references... first all references are dropped, and all use counts go to
00158   /// zero.  Then everything is delete'd for real.  Note that no operations are
00159   /// valid on an object that has "dropped all references", except operator
00160   /// delete.
00161   ///
00162   void dropAllReferences();
00163 
00164   /// removePredecessor - This method is used to notify a BasicBlock that the
00165   /// specified Predecessor of the block is no longer able to reach it.  This is
00166   /// actually not used to update the Predecessor list, but is actually used to
00167   /// update the PHI nodes that reside in the block.  Note that this should be
00168   /// called while the predecessor still refers to this block.
00169   ///
00170   void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
00171 
00172   /// splitBasicBlock - This splits a basic block into two at the specified
00173   /// instruction.  Note that all instructions BEFORE the specified iterator
00174   /// stay as part of the original basic block, an unconditional branch is added
00175   /// to the original BB, and the rest of the instructions in the BB are moved
00176   /// to the new BB, including the old terminator.  The newly formed BasicBlock
00177   /// is returned.  This function invalidates the specified iterator.
00178   ///
00179   /// Note that this only works on well formed basic blocks (must have a
00180   /// terminator), and 'I' must not be the end of instruction list (which would
00181   /// cause a degenerate basic block to be formed, having a terminator inside of
00182   /// the basic block).
00183   ///
00184   BasicBlock *splitBasicBlock(iterator I, const std::string &BBName = "");
00185 };
00186 
00187 } // End llvm namespace
00188 
00189 #endif