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"
27 template<> struct ilist_traits<Instruction>
28 : public SymbolTableListTraits<Instruction, BasicBlock> {
29 // createSentinel is used to get hold of a node that marks the end of
31 // The sentinel is relative to this instance, so we use a non-static
33 Instruction *createSentinel() const {
34 // since i(p)lists always publicly derive from the corresponding
35 // traits, placing a data member in this class will augment i(p)list.
36 // But since the NodeTy is expected to publicly derive from
37 // ilist_node<NodeTy>, there is a legal viable downcast from it
38 // to NodeTy. We use this trick to superpose i(p)list with a "ghostly"
39 // NodeTy, which becomes the sentinel. Dereferencing the sentinel is
40 // forbidden (save the ilist_node<NodeTy>) so no one will ever notice
42 return static_cast<Instruction*>(&Sentinel);
44 static void destroySentinel(Instruction*) {}
46 Instruction *provideInitialHead() const { return createSentinel(); }
47 Instruction *ensureHead(Instruction*) const { return createSentinel(); }
48 static void noteHead(Instruction*, Instruction*) {}
50 mutable ilist_half_node<Instruction> Sentinel;
53 /// This represents a single basic block in LLVM. A basic block is simply a
54 /// container of instructions that execute sequentially. Basic blocks are Values
55 /// because they are referenced by instructions such as branches and switch
56 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
57 /// represents a label to which a branch can jump.
59 /// A well formed basic block is formed of a list of non-terminating
60 /// instructions followed by a single TerminatorInst instruction.
61 /// TerminatorInst's may not occur in the middle of basic blocks, and must
62 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
63 /// occur because it may be useful in the intermediate stage of constructing or
64 /// modifying a program. However, the verifier will ensure that basic blocks
65 /// are "well formed".
66 /// @brief LLVM Basic Block Representation
67 class BasicBlock : public Value, // Basic blocks are data objects also
68 public ilist_node<BasicBlock> {
71 typedef iplist<Instruction> InstListType;
73 InstListType InstList;
76 void setParent(Function *parent);
77 friend class SymbolTableListTraits<BasicBlock, Function>;
79 BasicBlock(const BasicBlock &); // Do not implement
80 void operator=(const BasicBlock &); // Do not implement
82 /// BasicBlock ctor - If the function parameter is specified, the basic block
83 /// is automatically inserted at either the end of the function (if
84 /// InsertBefore is null), or before the specified basic block.
86 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
87 Function *Parent = 0, BasicBlock *InsertBefore = 0);
89 /// getContext - Get the context in which this basic block lives.
90 LLVMContext &getContext() const;
92 /// Instruction iterators...
93 typedef InstListType::iterator iterator;
94 typedef InstListType::const_iterator const_iterator;
96 /// Create - Creates a new BasicBlock. If the Parent parameter is specified,
97 /// the basic block is automatically inserted at either the end of the
98 /// function (if InsertBefore is 0), or before the specified basic block.
99 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
100 Function *Parent = 0,BasicBlock *InsertBefore = 0) {
101 return new BasicBlock(Context, Name, Parent, InsertBefore);
105 /// getParent - Return the enclosing method, or null if none
107 const Function *getParent() const { return Parent; }
108 Function *getParent() { return Parent; }
110 /// use_back - Specialize the methods defined in Value, as we know that an
111 /// BasicBlock can only be used by Instructions (specifically PHI nodes and
113 Instruction *use_back() { return cast<Instruction>(*use_begin());}
114 const Instruction *use_back() const { return cast<Instruction>(*use_begin());}
116 /// getTerminator() - If this is a well formed basic block, then this returns
117 /// a pointer to the terminator instruction. If it is not, then you get a
118 /// null pointer back.
120 TerminatorInst *getTerminator();
121 const TerminatorInst *getTerminator() const;
123 /// Returns a pointer to the first instructon in this block that is not a
124 /// PHINode instruction. When adding instruction to the beginning of the
125 /// basic block, they should be added before the returned value, not before
126 /// the first instruction, which might be PHI.
127 /// Returns 0 is there's no non-PHI instruction.
128 Instruction* getFirstNonPHI();
129 const Instruction* getFirstNonPHI() const {
130 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
133 /// removeFromParent - This method unlinks 'this' from the containing
134 /// function, but does not delete it.
136 void removeFromParent();
138 /// eraseFromParent - This method unlinks 'this' from the containing function
141 void eraseFromParent();
143 /// moveBefore - Unlink this basic block from its current function and
144 /// insert it into the function that MovePos lives in, right before MovePos.
145 void moveBefore(BasicBlock *MovePos);
147 /// moveAfter - Unlink this basic block from its current function and
148 /// insert it into the function that MovePos lives in, right after MovePos.
149 void moveAfter(BasicBlock *MovePos);
152 /// getSinglePredecessor - If this basic block has a single predecessor block,
153 /// return the block, otherwise return a null pointer.
154 BasicBlock *getSinglePredecessor();
155 const BasicBlock *getSinglePredecessor() const {
156 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
159 /// getUniquePredecessor - If this basic block has a unique predecessor block,
160 /// return the block, otherwise return a null pointer.
161 /// Note that unique predecessor doesn't mean single edge, there can be
162 /// multiple edges from the unique predecessor to this block (for example
163 /// a switch statement with multiple cases having the same destination).
164 BasicBlock *getUniquePredecessor();
165 const BasicBlock *getUniquePredecessor() const {
166 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
169 //===--------------------------------------------------------------------===//
170 /// Instruction iterator methods
172 inline iterator begin() { return InstList.begin(); }
173 inline const_iterator begin() const { return InstList.begin(); }
174 inline iterator end () { return InstList.end(); }
175 inline const_iterator end () const { return InstList.end(); }
177 inline size_t size() const { return InstList.size(); }
178 inline bool empty() const { return InstList.empty(); }
179 inline const Instruction &front() const { return InstList.front(); }
180 inline Instruction &front() { return InstList.front(); }
181 inline const Instruction &back() const { return InstList.back(); }
182 inline Instruction &back() { return InstList.back(); }
184 /// getInstList() - Return the underlying instruction list container. You
185 /// need to access it directly if you want to modify it currently.
187 const InstListType &getInstList() const { return InstList; }
188 InstListType &getInstList() { return InstList; }
190 /// getSublistAccess() - returns pointer to member of instruction list
191 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
192 return &BasicBlock::InstList;
195 /// getValueSymbolTable() - returns pointer to symbol table (if any)
196 ValueSymbolTable *getValueSymbolTable();
198 /// Methods for support type inquiry through isa, cast, and dyn_cast:
199 static inline bool classof(const BasicBlock *) { return true; }
200 static inline bool classof(const Value *V) {
201 return V->getValueID() == Value::BasicBlockVal;
204 /// dropAllReferences() - This function causes all the subinstructions to "let
205 /// go" of all references that they are maintaining. This allows one to
206 /// 'delete' a whole class at a time, even though there may be circular
207 /// references... first all references are dropped, and all use counts go to
208 /// zero. Then everything is delete'd for real. Note that no operations are
209 /// valid on an object that has "dropped all references", except operator
212 void dropAllReferences();
214 /// removePredecessor - This method is used to notify a BasicBlock that the
215 /// specified Predecessor of the block is no longer able to reach it. This is
216 /// actually not used to update the Predecessor list, but is actually used to
217 /// update the PHI nodes that reside in the block. Note that this should be
218 /// called while the predecessor still refers to this block.
220 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
222 /// splitBasicBlock - This splits a basic block into two at the specified
223 /// instruction. Note that all instructions BEFORE the specified iterator
224 /// stay as part of the original basic block, an unconditional branch is added
225 /// to the original BB, and the rest of the instructions in the BB are moved
226 /// to the new BB, including the old terminator. The newly formed BasicBlock
227 /// is returned. This function invalidates the specified iterator.
229 /// Note that this only works on well formed basic blocks (must have a
230 /// terminator), and 'I' must not be the end of instruction list (which would
231 /// cause a degenerate basic block to be formed, having a terminator inside of
232 /// the basic block).
234 /// Also note that this doesn't preserve any passes. To split blocks while
235 /// keeping loop information consistent, use the SplitBlock utility function.
237 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
240 } // End llvm namespace