1 //===-- llvm/BasicBlock.h - Represent a basic block in the VM ---*- 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 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"
20 #include "llvm/Support/DataTypes.h"
25 template <class Term, class BB> class SuccIterator; // Successor Iterator
26 template <class Ptr, class USE_iterator> class PredIterator;
28 template<> struct ilist_traits<Instruction>
29 : public SymbolTableListTraits<Instruction, BasicBlock> {
30 // createSentinel is used to create a node that marks the end of the list...
31 static Instruction *createSentinel();
32 static void destroySentinel(Instruction *I) { delete I; }
33 static iplist<Instruction> &getList(BasicBlock *BB);
34 static ValueSymbolTable *getSymTab(BasicBlock *ItemParent);
35 static int getListOffset();
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.
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 /// @brief LLVM Basic Block Representation
52 class BasicBlock : public User { // Basic blocks are data objects also
54 typedef iplist<Instruction> InstListType;
56 InstListType InstList;
57 BasicBlock *Prev, *Next; // Next and Prev links for our intrusive linked list
61 void setParent(Function *parent);
62 void setNext(BasicBlock *N) { Next = N; }
63 void setPrev(BasicBlock *N) { Prev = N; }
64 friend class SymbolTableListTraits<BasicBlock, Function>;
66 BasicBlock(const BasicBlock &); // Do not implement
67 void operator=(const BasicBlock &); // Do not implement
70 /// Instruction iterators...
71 typedef InstListType::iterator iterator;
72 typedef InstListType::const_iterator const_iterator;
74 /// BasicBlock ctor - If the function parameter is specified, the basic block
75 /// is automatically inserted at either the end of the function (if
76 /// InsertBefore is null), or before the specified basic block.
78 explicit BasicBlock(const std::string &Name = "", Function *Parent = 0,
79 BasicBlock *InsertBefore = 0, BasicBlock *unwindDest = 0);
82 /// getUnwindDest - Returns the BasicBlock that flow will enter if an unwind
83 /// instruction occurs in this block. May be null, in which case unwinding
84 /// is undefined in this block.
85 const BasicBlock *getUnwindDest() const;
86 BasicBlock *getUnwindDest();
88 /// setUnwindDest - Set which BasicBlock flow will enter if an unwind is
89 /// executed within this block. It may be set to null if unwinding is not
90 /// permitted in this block.
91 void setUnwindDest(BasicBlock *unwindDest);
93 /// getParent - Return the enclosing method, or null if none
95 const Function *getParent() const { return Parent; }
96 Function *getParent() { return Parent; }
98 /// use_back - Specialize the methods defined in Value, as we know that an
99 /// BasicBlock can only be used by Instructions (specifically PHI and terms).
100 Instruction *use_back() { return cast<Instruction>(*use_begin());}
101 const Instruction *use_back() const { return cast<Instruction>(*use_begin());}
103 /// getTerminator() - If this is a well formed basic block, then this returns
104 /// a pointer to the terminator instruction. If it is not, then you get a
105 /// null pointer back.
107 TerminatorInst *getTerminator();
108 const TerminatorInst *getTerminator() const;
110 /// Returns a pointer to the first instructon in this block that is not a
111 /// PHINode instruction. When adding instruction to the beginning of the
112 /// basic block, they should be added before the returned value, not before
113 /// the first instruction, which might be PHI.
114 /// Returns 0 is there's no non-PHI instruction.
115 Instruction* getFirstNonPHI();
117 /// removeFromParent - This method unlinks 'this' from the containing
118 /// function, but does not delete it.
120 void removeFromParent();
122 /// eraseFromParent - This method unlinks 'this' from the containing function
125 void eraseFromParent();
127 /// moveBefore - Unlink this basic block from its current function and
128 /// insert it into the function that MovePos lives in, right before MovePos.
129 void moveBefore(BasicBlock *MovePos);
131 /// moveAfter - Unlink this basic block from its current function and
132 /// insert it into the function that MovePos lives in, right after MovePos.
133 void moveAfter(BasicBlock *MovePos);
136 /// getSinglePredecessor - If this basic block has a single predecessor block,
137 /// return the block, otherwise return a null pointer.
138 BasicBlock *getSinglePredecessor();
139 const BasicBlock *getSinglePredecessor() const {
140 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
143 //===--------------------------------------------------------------------===//
144 /// Instruction iterator methods
146 inline iterator begin() { return InstList.begin(); }
147 inline const_iterator begin() const { return InstList.begin(); }
148 inline iterator end () { return InstList.end(); }
149 inline const_iterator end () const { return InstList.end(); }
151 inline size_t size() const { return InstList.size(); }
152 inline bool empty() const { return InstList.empty(); }
153 inline const Instruction &front() const { return InstList.front(); }
154 inline Instruction &front() { return InstList.front(); }
155 inline const Instruction &back() const { return InstList.back(); }
156 inline Instruction &back() { return InstList.back(); }
158 /// getInstList() - Return the underlying instruction list container. You
159 /// need to access it directly if you want to modify it currently.
161 const InstListType &getInstList() const { return InstList; }
162 InstListType &getInstList() { return InstList; }
164 virtual void print(std::ostream &OS) const { print(OS, 0); }
165 void print(std::ostream *OS) const { if (OS) print(*OS); }
166 void print(std::ostream &OS, AssemblyAnnotationWriter *AAW) const;
168 /// Methods for support type inquiry through isa, cast, and dyn_cast:
169 static inline bool classof(const BasicBlock *) { return true; }
170 static inline bool classof(const Value *V) {
171 return V->getValueID() == Value::BasicBlockVal;
174 /// dropAllReferences() - This function causes all the subinstructions to "let
175 /// go" of all references that they are maintaining. This allows one to
176 /// 'delete' a whole class at a time, even though there may be circular
177 /// references... first all references are dropped, and all use counts go to
178 /// zero. Then everything is delete'd for real. Note that no operations are
179 /// valid on an object that has "dropped all references", except operator
182 void dropAllReferences();
184 /// removePredecessor - This method is used to notify a BasicBlock that the
185 /// specified Predecessor of the block is no longer able to reach it. This is
186 /// actually not used to update the Predecessor list, but is actually used to
187 /// update the PHI nodes that reside in the block. Note that this should be
188 /// called while the predecessor still refers to this block.
190 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
192 /// splitBasicBlock - This splits a basic block into two at the specified
193 /// instruction. Note that all instructions BEFORE the specified iterator
194 /// stay as part of the original basic block, an unconditional branch is added
195 /// to the original BB, and the rest of the instructions in the BB are moved
196 /// to the new BB, including the old terminator. The newly formed BasicBlock
197 /// is returned. This function invalidates the specified iterator.
199 /// Note that this only works on well formed basic blocks (must have a
200 /// terminator), and 'I' must not be the end of instruction list (which would
201 /// cause a degenerate basic block to be formed, having a terminator inside of
202 /// the basic block).
204 BasicBlock *splitBasicBlock(iterator I, const std::string &BBName = "");
207 static unsigned getInstListOffset() {
209 return unsigned(reinterpret_cast<uintptr_t>(&Obj->InstList));
213 // getNext/Prev - Return the next or previous basic block in the list. Access
214 // these with Function::iterator.
215 BasicBlock *getNext() { return Next; }
216 const BasicBlock *getNext() const { return Next; }
217 BasicBlock *getPrev() { return Prev; }
218 const BasicBlock *getPrev() const { return Prev; }
222 ilist_traits<Instruction>::getListOffset() {
223 return BasicBlock::getInstListOffset();
226 } // End llvm namespace