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 //===----------------------------------------------------------------------===//
10 // 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.h"
20 #include "llvm/Support/DataTypes.h"
26 template<> struct ilist_traits<Instruction>
27 : public SymbolTableListTraits<Instruction, BasicBlock> {
28 // createSentinel is used to create a node that marks the end of the list...
29 static Instruction *createSentinel();
30 static void destroySentinel(Instruction *I) { delete I; }
31 static iplist<Instruction> &getList(BasicBlock *BB);
32 static ValueSymbolTable *getSymTab(BasicBlock *ItemParent);
33 static int getListOffset();
36 /// This represents a single basic block in LLVM. A basic block is simply a
37 /// container of instructions that execute sequentially. Basic blocks are Values
38 /// because they are referenced by instructions such as branches and switch
39 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
40 /// represents a label to which a branch can jump.
42 /// A well formed basic block is formed of a list of non-terminating
43 /// instructions followed by a single TerminatorInst instruction.
44 /// TerminatorInst's may not occur in the middle of basic blocks, and must
45 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
46 /// occur because it may be useful in the intermediate stage of constructing or
47 /// modifying a program. However, the verifier will ensure that basic blocks
48 /// are "well formed".
49 /// @brief LLVM Basic Block Representation
50 class BasicBlock : public Value, // Basic blocks are data objects also
51 public ilist_node<BasicBlock> {
53 typedef iplist<Instruction> InstListType;
55 InstListType InstList;
58 void setParent(Function *parent);
59 friend class SymbolTableListTraits<BasicBlock, Function>;
61 BasicBlock(const BasicBlock &); // Do not implement
62 void operator=(const BasicBlock &); // Do not implement
64 /// BasicBlock ctor - If the function parameter is specified, the basic block
65 /// is automatically inserted at either the end of the function (if
66 /// InsertBefore is null), or before the specified basic block.
68 explicit BasicBlock(const std::string &Name = "", Function *Parent = 0,
69 BasicBlock *InsertBefore = 0);
71 /// Instruction iterators...
72 typedef InstListType::iterator iterator;
73 typedef InstListType::const_iterator const_iterator;
75 /// Create - Creates a new BasicBlock. If the Parent parameter is specified,
76 /// the basic block is automatically inserted at either the end of the
77 /// function (if InsertBefore is 0), or before the specified basic block.
78 static BasicBlock *Create(const std::string &Name = "", Function *Parent = 0,
79 BasicBlock *InsertBefore = 0) {
80 return new BasicBlock(Name, Parent, InsertBefore);
84 /// getParent - Return the enclosing method, or null if none
86 const Function *getParent() const { return Parent; }
87 Function *getParent() { return Parent; }
89 /// use_back - Specialize the methods defined in Value, as we know that an
90 /// BasicBlock can only be used by Instructions (specifically PHI and terms).
91 Instruction *use_back() { return cast<Instruction>(*use_begin());}
92 const Instruction *use_back() const { return cast<Instruction>(*use_begin());}
94 /// getTerminator() - If this is a well formed basic block, then this returns
95 /// a pointer to the terminator instruction. If it is not, then you get a
96 /// null pointer back.
98 TerminatorInst *getTerminator();
99 const TerminatorInst *getTerminator() const;
101 /// Returns a pointer to the first instructon in this block that is not a
102 /// PHINode instruction. When adding instruction to the beginning of the
103 /// basic block, they should be added before the returned value, not before
104 /// the first instruction, which might be PHI.
105 /// Returns 0 is there's no non-PHI instruction.
106 Instruction* getFirstNonPHI();
107 const Instruction* getFirstNonPHI() const {
108 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
111 /// removeFromParent - This method unlinks 'this' from the containing
112 /// function, but does not delete it.
114 void removeFromParent();
116 /// eraseFromParent - This method unlinks 'this' from the containing function
119 void eraseFromParent();
121 /// moveBefore - Unlink this basic block from its current function and
122 /// insert it into the function that MovePos lives in, right before MovePos.
123 void moveBefore(BasicBlock *MovePos);
125 /// moveAfter - Unlink this basic block from its current function and
126 /// insert it into the function that MovePos lives in, right after MovePos.
127 void moveAfter(BasicBlock *MovePos);
130 /// getSinglePredecessor - If this basic block has a single predecessor block,
131 /// return the block, otherwise return a null pointer.
132 BasicBlock *getSinglePredecessor();
133 const BasicBlock *getSinglePredecessor() const {
134 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
137 /// getUniquePredecessor - If this basic block has a unique predecessor block,
138 /// return the block, otherwise return a null pointer.
139 /// Note that unique predecessor doesn't mean single edge, there can be
140 /// multiple edges from the unique predecessor to this block (for example
141 /// a switch statement with multiple cases having the same destination).
142 BasicBlock *getUniquePredecessor();
143 const BasicBlock *getUniquePredecessor() const {
144 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
147 //===--------------------------------------------------------------------===//
148 /// Instruction iterator methods
150 inline iterator begin() { return InstList.begin(); }
151 inline const_iterator begin() const { return InstList.begin(); }
152 inline iterator end () { return InstList.end(); }
153 inline const_iterator end () const { return InstList.end(); }
155 inline size_t size() const { return InstList.size(); }
156 inline bool empty() const { return InstList.empty(); }
157 inline const Instruction &front() const { return InstList.front(); }
158 inline Instruction &front() { return InstList.front(); }
159 inline const Instruction &back() const { return InstList.back(); }
160 inline Instruction &back() { return InstList.back(); }
162 /// getInstList() - Return the underlying instruction list container. You
163 /// need to access it directly if you want to modify it currently.
165 const InstListType &getInstList() const { return InstList; }
166 InstListType &getInstList() { return InstList; }
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));
214 ilist_traits<Instruction>::getListOffset() {
215 return BasicBlock::getInstListOffset();
218 } // End llvm namespace