1 //===-- llvm/BasicBlock.h - Represent a basic block in the VM ---*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 // This file contains the declaration of the BasicBlock class.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_BASICBLOCK_H
15 #define LLVM_BASICBLOCK_H
17 #include "llvm/Instruction.h"
18 #include "llvm/SymbolTableListTraits.h"
19 #include "llvm/ADT/ilist"
24 template <class Term, class BB> class SuccIterator; // Successor Iterator
25 template <class Ptr, class USE_iterator> class PredIterator;
27 template<> struct ilist_traits<Instruction>
28 : public SymbolTableListTraits<Instruction, BasicBlock> {
29 // createSentinel is used to create a node that marks the end of the list...
30 static Instruction *createSentinel();
31 static void destroySentinel(Instruction *I) { delete I; }
32 static iplist<Instruction> &getList(BasicBlock *BB);
33 static ValueSymbolTable *getSymTab(BasicBlock *ItemParent);
34 static int getListOffset();
37 /// This represents a single basic block in LLVM. A basic block is simply a
38 /// container of instructions that execute sequentially. Basic blocks are Values
39 /// because they are referenced by instructions such as branches and switch
40 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
41 /// represents a label to which a branch can jump.
43 /// A well formed basic block is formed of a list of non-terminating
44 /// instructions followed by a single TerminatorInst instruction.
45 /// TerminatorInst's may not occur in the middle of basic blocks, and must
46 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
47 /// occur because it may be useful in the intermediate stage of constructing or
48 /// modifying a program. However, the verifier will ensure that basic blocks
49 /// are "well formed".
50 /// @brief LLVM Basic Block Representation
51 class BasicBlock : public Value { // Basic blocks are data objects also
53 typedef iplist<Instruction> InstListType;
55 InstListType InstList;
56 BasicBlock *Prev, *Next; // Next and Prev links for our intrusive linked list
59 void setParent(Function *parent);
60 void setNext(BasicBlock *N) { Next = N; }
61 void setPrev(BasicBlock *N) { Prev = N; }
62 friend class SymbolTableListTraits<BasicBlock, Function>;
64 BasicBlock(const BasicBlock &); // Do not implement
65 void operator=(const BasicBlock &); // Do not implement
68 /// Instruction iterators...
69 typedef InstListType::iterator iterator;
70 typedef InstListType::const_iterator const_iterator;
72 /// BasicBlock ctor - If the function parameter is specified, the basic block
73 /// is automatically inserted at either the end of the function (if
74 /// InsertBefore is null), or before the specified basic block.
76 explicit BasicBlock(const std::string &Name = "", Function *Parent = 0,
77 BasicBlock *InsertBefore = 0);
80 /// getParent - Return the enclosing method, or null if none
82 const Function *getParent() const { return Parent; }
83 Function *getParent() { return Parent; }
85 /// use_back - Specialize the methods defined in Value, as we know that an
86 /// BasicBlock can only be used by Instructions (specifically PHI and terms).
87 Instruction *use_back() { return cast<Instruction>(*use_begin());}
88 const Instruction *use_back() const { return cast<Instruction>(*use_begin());}
90 /// getTerminator() - If this is a well formed basic block, then this returns
91 /// a pointer to the terminator instruction. If it is not, then you get a
92 /// null pointer back.
94 TerminatorInst *getTerminator();
95 const TerminatorInst *const getTerminator() const;
97 /// Returns a pointer to the first instructon in this block that is not a
98 /// PHINode instruction. When adding instruction to the beginning of the
99 /// basic block, they should be added before the returned value, not before
100 /// the first instruction, which might be PHI.
101 /// Returns 0 is there's no non-PHI instruction.
102 Instruction* getFirstNonPHI();
104 /// removeFromParent - This method unlinks 'this' from the containing
105 /// function, but does not delete it.
107 void removeFromParent();
109 /// eraseFromParent - This method unlinks 'this' from the containing function
112 void eraseFromParent();
114 /// moveBefore - Unlink this basic block from its current function and
115 /// insert it into the function that MovePos lives in, right before MovePos.
116 void moveBefore(BasicBlock *MovePos);
118 /// moveAfter - Unlink this basic block from its current function and
119 /// insert it into the function that MovePos lives in, right after MovePos.
120 void moveAfter(BasicBlock *MovePos);
123 /// getSinglePredecessor - If this basic block has a single predecessor block,
124 /// return the block, otherwise return a null pointer.
125 BasicBlock *getSinglePredecessor();
126 const BasicBlock *getSinglePredecessor() const {
127 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
130 //===--------------------------------------------------------------------===//
131 /// Instruction iterator methods
133 inline iterator begin() { return InstList.begin(); }
134 inline const_iterator begin() const { return InstList.begin(); }
135 inline iterator end () { return InstList.end(); }
136 inline const_iterator end () const { return InstList.end(); }
138 inline size_t size() const { return InstList.size(); }
139 inline bool empty() const { return InstList.empty(); }
140 inline const Instruction &front() const { return InstList.front(); }
141 inline Instruction &front() { return InstList.front(); }
142 inline const Instruction &back() const { return InstList.back(); }
143 inline Instruction &back() { return InstList.back(); }
145 /// getInstList() - Return the underlying instruction list container. You
146 /// need to access it directly if you want to modify it currently.
148 const InstListType &getInstList() const { return InstList; }
149 InstListType &getInstList() { return InstList; }
151 virtual void print(std::ostream &OS) const { print(OS, 0); }
152 void print(std::ostream *OS) const { if (OS) print(*OS); }
153 void print(std::ostream &OS, AssemblyAnnotationWriter *AAW) const;
155 /// Methods for support type inquiry through isa, cast, and dyn_cast:
156 static inline bool classof(const BasicBlock *) { return true; }
157 static inline bool classof(const Value *V) {
158 return V->getValueID() == Value::BasicBlockVal;
161 /// dropAllReferences() - This function causes all the subinstructions to "let
162 /// go" of all references that they are maintaining. This allows one to
163 /// 'delete' a whole class at a time, even though there may be circular
164 /// references... first all references are dropped, and all use counts go to
165 /// zero. Then everything is delete'd for real. Note that no operations are
166 /// valid on an object that has "dropped all references", except operator
169 void dropAllReferences();
171 /// removePredecessor - This method is used to notify a BasicBlock that the
172 /// specified Predecessor of the block is no longer able to reach it. This is
173 /// actually not used to update the Predecessor list, but is actually used to
174 /// update the PHI nodes that reside in the block. Note that this should be
175 /// called while the predecessor still refers to this block.
177 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
179 /// splitBasicBlock - This splits a basic block into two at the specified
180 /// instruction. Note that all instructions BEFORE the specified iterator
181 /// stay as part of the original basic block, an unconditional branch is added
182 /// to the original BB, and the rest of the instructions in the BB are moved
183 /// to the new BB, including the old terminator. The newly formed BasicBlock
184 /// is returned. This function invalidates the specified iterator.
186 /// Note that this only works on well formed basic blocks (must have a
187 /// terminator), and 'I' must not be the end of instruction list (which would
188 /// cause a degenerate basic block to be formed, having a terminator inside of
189 /// the basic block).
191 BasicBlock *splitBasicBlock(iterator I, const std::string &BBName = "");
194 static unsigned getInstListOffset() {
196 return unsigned(reinterpret_cast<uintptr_t>(&Obj->InstList));
200 // getNext/Prev - Return the next or previous basic block in the list. Access
201 // these with Function::iterator.
202 BasicBlock *getNext() { return Next; }
203 const BasicBlock *getNext() const { return Next; }
204 BasicBlock *getPrev() { return Prev; }
205 const BasicBlock *getPrev() const { return Prev; }
209 ilist_traits<Instruction>::getListOffset() {
210 return BasicBlock::getInstListOffset();
213 } // End llvm namespace