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/ADT/Twine.h"
21 #include "llvm/Support/DataTypes.h"
29 template<> struct ilist_traits<Instruction>
30 : public SymbolTableListTraits<Instruction, BasicBlock> {
31 // createSentinel is used to get hold of a node that marks the end of
33 // The sentinel is relative to this instance, so we use a non-static
35 Instruction *createSentinel() const {
36 // since i(p)lists always publicly derive from the corresponding
37 // traits, placing a data member in this class will augment i(p)list.
38 // But since the NodeTy is expected to publicly derive from
39 // ilist_node<NodeTy>, there is a legal viable downcast from it
40 // to NodeTy. We use this trick to superpose i(p)list with a "ghostly"
41 // NodeTy, which becomes the sentinel. Dereferencing the sentinel is
42 // forbidden (save the ilist_node<NodeTy>) so no one will ever notice
44 return static_cast<Instruction*>(&Sentinel);
46 static void destroySentinel(Instruction*) {}
48 Instruction *provideInitialHead() const { return createSentinel(); }
49 Instruction *ensureHead(Instruction*) const { return createSentinel(); }
50 static void noteHead(Instruction*, Instruction*) {}
52 mutable ilist_half_node<Instruction> Sentinel;
55 /// This represents a single basic block in LLVM. A basic block is simply a
56 /// container of instructions that execute sequentially. Basic blocks are Values
57 /// because they are referenced by instructions such as branches and switch
58 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
59 /// represents a label to which a branch can jump.
61 /// A well formed basic block is formed of a list of non-terminating
62 /// instructions followed by a single TerminatorInst instruction.
63 /// TerminatorInst's may not occur in the middle of basic blocks, and must
64 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
65 /// occur because it may be useful in the intermediate stage of constructing or
66 /// modifying a program. However, the verifier will ensure that basic blocks
67 /// are "well formed".
68 /// @brief LLVM Basic Block Representation
69 class BasicBlock : public Value, // Basic blocks are data objects also
70 public ilist_node<BasicBlock> {
71 friend class BlockAddress;
73 typedef iplist<Instruction> InstListType;
75 InstListType InstList;
78 void setParent(Function *parent);
79 friend class SymbolTableListTraits<BasicBlock, Function>;
81 BasicBlock(const BasicBlock &); // Do not implement
82 void operator=(const BasicBlock &); // Do not implement
84 /// BasicBlock ctor - If the function parameter is specified, the basic block
85 /// is automatically inserted at either the end of the function (if
86 /// InsertBefore is null), or before the specified basic block.
88 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
89 Function *Parent = 0, BasicBlock *InsertBefore = 0);
91 /// getContext - Get the context in which this basic block lives.
92 LLVMContext &getContext() const;
94 /// Instruction iterators...
95 typedef InstListType::iterator iterator;
96 typedef InstListType::const_iterator const_iterator;
98 /// Create - Creates a new BasicBlock. If the Parent parameter is specified,
99 /// the basic block is automatically inserted at either the end of the
100 /// function (if InsertBefore is 0), or before the specified basic block.
101 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
102 Function *Parent = 0,BasicBlock *InsertBefore = 0) {
103 return new BasicBlock(Context, Name, Parent, InsertBefore);
107 /// getParent - Return the enclosing method, or null if none
109 const Function *getParent() const { return Parent; }
110 Function *getParent() { return Parent; }
112 /// use_back - Specialize the methods defined in Value, as we know that an
113 /// BasicBlock can only be used by Users (specifically PHI nodes, terminators,
114 /// and BlockAddress's).
115 User *use_back() { return cast<User>(*use_begin());}
116 const User *use_back() const { return cast<User>(*use_begin());}
118 /// getTerminator() - If this is a well formed basic block, then this returns
119 /// a pointer to the terminator instruction. If it is not, then you get a
120 /// null pointer back.
122 TerminatorInst *getTerminator();
123 const TerminatorInst *getTerminator() const;
125 /// Returns a pointer to the first instructon in this block that is not a
126 /// PHINode instruction. When adding instruction to the beginning of the
127 /// basic block, they should be added before the returned value, not before
128 /// the first instruction, which might be PHI.
129 /// Returns 0 is there's no non-PHI instruction.
130 Instruction* getFirstNonPHI();
131 const Instruction* getFirstNonPHI() const {
132 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
135 // Same as above, but also skip debug intrinsics.
136 Instruction* getFirstNonPHIOrDbg();
137 const Instruction* getFirstNonPHIOrDbg() const {
138 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
141 /// removeFromParent - This method unlinks 'this' from the containing
142 /// function, but does not delete it.
144 void removeFromParent();
146 /// eraseFromParent - This method unlinks 'this' from the containing function
149 void eraseFromParent();
151 /// moveBefore - Unlink this basic block from its current function and
152 /// insert it into the function that MovePos lives in, right before MovePos.
153 void moveBefore(BasicBlock *MovePos);
155 /// moveAfter - Unlink this basic block from its current function and
156 /// insert it into the function that MovePos lives in, right after MovePos.
157 void moveAfter(BasicBlock *MovePos);
160 /// getSinglePredecessor - If this basic block has a single predecessor block,
161 /// return the block, otherwise return a null pointer.
162 BasicBlock *getSinglePredecessor();
163 const BasicBlock *getSinglePredecessor() const {
164 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
167 /// getUniquePredecessor - If this basic block has a unique predecessor block,
168 /// return the block, otherwise return a null pointer.
169 /// Note that unique predecessor doesn't mean single edge, there can be
170 /// multiple edges from the unique predecessor to this block (for example
171 /// a switch statement with multiple cases having the same destination).
172 BasicBlock *getUniquePredecessor();
173 const BasicBlock *getUniquePredecessor() const {
174 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
177 //===--------------------------------------------------------------------===//
178 /// Instruction iterator methods
180 inline iterator begin() { return InstList.begin(); }
181 inline const_iterator begin() const { return InstList.begin(); }
182 inline iterator end () { return InstList.end(); }
183 inline const_iterator end () const { return InstList.end(); }
185 inline size_t size() const { return InstList.size(); }
186 inline bool empty() const { return InstList.empty(); }
187 inline const Instruction &front() const { return InstList.front(); }
188 inline Instruction &front() { return InstList.front(); }
189 inline const Instruction &back() const { return InstList.back(); }
190 inline Instruction &back() { return InstList.back(); }
192 /// getInstList() - Return the underlying instruction list container. You
193 /// need to access it directly if you want to modify it currently.
195 const InstListType &getInstList() const { return InstList; }
196 InstListType &getInstList() { return InstList; }
198 /// getSublistAccess() - returns pointer to member of instruction list
199 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
200 return &BasicBlock::InstList;
203 /// getValueSymbolTable() - returns pointer to symbol table (if any)
204 ValueSymbolTable *getValueSymbolTable();
206 /// Methods for support type inquiry through isa, cast, and dyn_cast:
207 static inline bool classof(const BasicBlock *) { return true; }
208 static inline bool classof(const Value *V) {
209 return V->getValueID() == Value::BasicBlockVal;
212 /// dropAllReferences() - This function causes all the subinstructions to "let
213 /// go" of all references that they are maintaining. This allows one to
214 /// 'delete' a whole class at a time, even though there may be circular
215 /// references... first all references are dropped, and all use counts go to
216 /// zero. Then everything is delete'd for real. Note that no operations are
217 /// valid on an object that has "dropped all references", except operator
220 void dropAllReferences();
222 /// removePredecessor - This method is used to notify a BasicBlock that the
223 /// specified Predecessor of the block is no longer able to reach it. This is
224 /// actually not used to update the Predecessor list, but is actually used to
225 /// update the PHI nodes that reside in the block. Note that this should be
226 /// called while the predecessor still refers to this block.
228 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
230 /// splitBasicBlock - This splits a basic block into two at the specified
231 /// instruction. Note that all instructions BEFORE the specified iterator
232 /// stay as part of the original basic block, an unconditional branch is added
233 /// to the original BB, and the rest of the instructions in the BB are moved
234 /// to the new BB, including the old terminator. The newly formed BasicBlock
235 /// is returned. This function invalidates the specified iterator.
237 /// Note that this only works on well formed basic blocks (must have a
238 /// terminator), and 'I' must not be the end of instruction list (which would
239 /// cause a degenerate basic block to be formed, having a terminator inside of
240 /// the basic block).
242 /// Also note that this doesn't preserve any passes. To split blocks while
243 /// keeping loop information consistent, use the SplitBlock utility function.
245 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
247 /// hasAddressTaken - returns true if there are any uses of this basic block
248 /// other than direct branches, switches, etc. to it.
249 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
252 /// AdjustBlockAddressRefCount - BasicBlock stores the number of BlockAddress
253 /// objects using it. This is almost always 0, sometimes one, possibly but
254 /// almost never 2, and inconceivably 3 or more.
255 void AdjustBlockAddressRefCount(int Amt) {
256 setValueSubclassData(getSubclassDataFromValue()+Amt);
257 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
258 "Refcount wrap-around");
260 // Shadow Value::setValueSubclassData with a private forwarding method so that
261 // any future subclasses cannot accidentally use it.
262 void setValueSubclassData(unsigned short D) {
263 Value::setValueSubclassData(D);
267 } // End llvm namespace