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"
30 template<> struct ilist_traits<Instruction>
31 : public SymbolTableListTraits<Instruction, BasicBlock> {
32 // createSentinel is used to get hold of a node that marks the end of
34 // The sentinel is relative to this instance, so we use a non-static
36 Instruction *createSentinel() const {
37 // since i(p)lists always publicly derive from the corresponding
38 // traits, placing a data member in this class will augment i(p)list.
39 // But since the NodeTy is expected to publicly derive from
40 // ilist_node<NodeTy>, there is a legal viable downcast from it
41 // to NodeTy. We use this trick to superpose i(p)list with a "ghostly"
42 // NodeTy, which becomes the sentinel. Dereferencing the sentinel is
43 // forbidden (save the ilist_node<NodeTy>) so no one will ever notice
45 return static_cast<Instruction*>(&Sentinel);
47 static void destroySentinel(Instruction*) {}
49 Instruction *provideInitialHead() const { return createSentinel(); }
50 Instruction *ensureHead(Instruction*) const { return createSentinel(); }
51 static void noteHead(Instruction*, Instruction*) {}
53 mutable ilist_half_node<Instruction> Sentinel;
56 /// This represents a single basic block in LLVM. A basic block is simply a
57 /// container of instructions that execute sequentially. Basic blocks are Values
58 /// because they are referenced by instructions such as branches and switch
59 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
60 /// represents a label to which a branch can jump.
62 /// A well formed basic block is formed of a list of non-terminating
63 /// instructions followed by a single TerminatorInst instruction.
64 /// TerminatorInst's may not occur in the middle of basic blocks, and must
65 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
66 /// occur because it may be useful in the intermediate stage of constructing or
67 /// modifying a program. However, the verifier will ensure that basic blocks
68 /// are "well formed".
69 /// @brief LLVM Basic Block Representation
70 class BasicBlock : public Value, // Basic blocks are data objects also
71 public ilist_node<BasicBlock> {
72 friend class BlockAddress;
74 typedef iplist<Instruction> InstListType;
76 InstListType InstList;
79 void setParent(Function *parent);
80 friend class SymbolTableListTraits<BasicBlock, Function>;
82 BasicBlock(const BasicBlock &); // Do not implement
83 void operator=(const BasicBlock &); // Do not implement
85 /// BasicBlock ctor - If the function parameter is specified, the basic block
86 /// is automatically inserted at either the end of the function (if
87 /// InsertBefore is null), or before the specified basic block.
89 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
90 Function *Parent = 0, BasicBlock *InsertBefore = 0);
92 /// getContext - Get the context in which this basic block lives.
93 LLVMContext &getContext() const;
95 /// Instruction iterators...
96 typedef InstListType::iterator iterator;
97 typedef InstListType::const_iterator const_iterator;
99 /// Create - Creates a new BasicBlock. If the Parent parameter is specified,
100 /// the basic block is automatically inserted at either the end of the
101 /// function (if InsertBefore is 0), or before the specified basic block.
102 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
103 Function *Parent = 0,BasicBlock *InsertBefore = 0) {
104 return new BasicBlock(Context, Name, Parent, InsertBefore);
108 /// getParent - Return the enclosing method, or null if none
110 const Function *getParent() const { return Parent; }
111 Function *getParent() { return Parent; }
113 /// use_back - Specialize the methods defined in Value, as we know that an
114 /// BasicBlock can only be used by Users (specifically terminators
115 /// and BlockAddress's).
116 User *use_back() { return cast<User>(*use_begin());}
117 const User *use_back() const { return cast<User>(*use_begin());}
119 /// getTerminator() - If this is a well formed basic block, then this returns
120 /// a pointer to the terminator instruction. If it is not, then you get a
121 /// null pointer back.
123 TerminatorInst *getTerminator();
124 const TerminatorInst *getTerminator() const;
126 /// Returns a pointer to the first instructon in this block that is not a
127 /// PHINode instruction. When adding instruction to the beginning of the
128 /// basic block, they should be added before the returned value, not before
129 /// the first instruction, which might be PHI.
130 /// Returns 0 is there's no non-PHI instruction.
131 Instruction* getFirstNonPHI();
132 const Instruction* getFirstNonPHI() const {
133 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
136 // Same as above, but also skip debug intrinsics.
137 Instruction* getFirstNonPHIOrDbg();
138 const Instruction* getFirstNonPHIOrDbg() const {
139 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
142 // Same as above, but also skip lifetime intrinsics.
143 Instruction* getFirstNonPHIOrDbgOrLifetime();
144 const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
145 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
148 /// getFirstInsertionPt - Returns an iterator to the first instruction in this
149 /// block that is suitable for inserting a non-PHI instruction. In particular,
150 /// it skips all PHIs and LandingPad instructions. Returns 0 if there are no
151 /// non-PHI instructions.
152 iterator getFirstInsertionPt();
153 const_iterator getFirstInsertionPt() const {
154 return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
157 /// removeFromParent - This method unlinks 'this' from the containing
158 /// function, but does not delete it.
160 void removeFromParent();
162 /// eraseFromParent - This method unlinks 'this' from the containing function
165 void eraseFromParent();
167 /// moveBefore - Unlink this basic block from its current function and
168 /// insert it into the function that MovePos lives in, right before MovePos.
169 void moveBefore(BasicBlock *MovePos);
171 /// moveAfter - Unlink this basic block from its current function and
172 /// insert it into the function that MovePos lives in, right after MovePos.
173 void moveAfter(BasicBlock *MovePos);
176 /// getSinglePredecessor - If this basic block has a single predecessor block,
177 /// return the block, otherwise return a null pointer.
178 BasicBlock *getSinglePredecessor();
179 const BasicBlock *getSinglePredecessor() const {
180 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
183 /// getUniquePredecessor - If this basic block has a unique predecessor block,
184 /// return the block, otherwise return a null pointer.
185 /// Note that unique predecessor doesn't mean single edge, there can be
186 /// multiple edges from the unique predecessor to this block (for example
187 /// a switch statement with multiple cases having the same destination).
188 BasicBlock *getUniquePredecessor();
189 const BasicBlock *getUniquePredecessor() const {
190 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
193 //===--------------------------------------------------------------------===//
194 /// Instruction iterator methods
196 inline iterator begin() { return InstList.begin(); }
197 inline const_iterator begin() const { return InstList.begin(); }
198 inline iterator end () { return InstList.end(); }
199 inline const_iterator end () const { return InstList.end(); }
201 inline size_t size() const { return InstList.size(); }
202 inline bool empty() const { return InstList.empty(); }
203 inline const Instruction &front() const { return InstList.front(); }
204 inline Instruction &front() { return InstList.front(); }
205 inline const Instruction &back() const { return InstList.back(); }
206 inline Instruction &back() { return InstList.back(); }
208 /// getInstList() - Return the underlying instruction list container. You
209 /// need to access it directly if you want to modify it currently.
211 const InstListType &getInstList() const { return InstList; }
212 InstListType &getInstList() { return InstList; }
214 /// getSublistAccess() - returns pointer to member of instruction list
215 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
216 return &BasicBlock::InstList;
219 /// getValueSymbolTable() - returns pointer to symbol table (if any)
220 ValueSymbolTable *getValueSymbolTable();
222 /// Methods for support type inquiry through isa, cast, and dyn_cast:
223 static inline bool classof(const BasicBlock *) { return true; }
224 static inline bool classof(const Value *V) {
225 return V->getValueID() == Value::BasicBlockVal;
228 /// dropAllReferences() - This function causes all the subinstructions to "let
229 /// go" of all references that they are maintaining. This allows one to
230 /// 'delete' a whole class at a time, even though there may be circular
231 /// references... first all references are dropped, and all use counts go to
232 /// zero. Then everything is delete'd for real. Note that no operations are
233 /// valid on an object that has "dropped all references", except operator
236 void dropAllReferences();
238 /// removePredecessor - This method is used to notify a BasicBlock that the
239 /// specified Predecessor of the block is no longer able to reach it. This is
240 /// actually not used to update the Predecessor list, but is actually used to
241 /// update the PHI nodes that reside in the block. Note that this should be
242 /// called while the predecessor still refers to this block.
244 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
246 /// splitBasicBlock - This splits a basic block into two at the specified
247 /// instruction. Note that all instructions BEFORE the specified iterator
248 /// stay as part of the original basic block, an unconditional branch is added
249 /// to the original BB, and the rest of the instructions in the BB are moved
250 /// to the new BB, including the old terminator. The newly formed BasicBlock
251 /// is returned. This function invalidates the specified iterator.
253 /// Note that this only works on well formed basic blocks (must have a
254 /// terminator), and 'I' must not be the end of instruction list (which would
255 /// cause a degenerate basic block to be formed, having a terminator inside of
256 /// the basic block).
258 /// Also note that this doesn't preserve any passes. To split blocks while
259 /// keeping loop information consistent, use the SplitBlock utility function.
261 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
263 /// hasAddressTaken - returns true if there are any uses of this basic block
264 /// other than direct branches, switches, etc. to it.
265 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
267 /// replaceSuccessorsPhiUsesWith - Update all phi nodes in all our successors
268 /// to refer to basic block New instead of to us.
269 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
271 /// isLandingPad - Return true if this basic block is a landing pad. I.e.,
272 /// it's the destination of the 'unwind' edge of an invoke instruction.
273 bool isLandingPad() const;
275 /// getLandingPadInst() - Return the landingpad instruction associated with
277 LandingPadInst *getLandingPadInst();
280 /// AdjustBlockAddressRefCount - BasicBlock stores the number of BlockAddress
281 /// objects using it. This is almost always 0, sometimes one, possibly but
282 /// almost never 2, and inconceivably 3 or more.
283 void AdjustBlockAddressRefCount(int Amt) {
284 setValueSubclassData(getSubclassDataFromValue()+Amt);
285 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
286 "Refcount wrap-around");
288 // Shadow Value::setValueSubclassData with a private forwarding method so that
289 // any future subclasses cannot accidentally use it.
290 void setValueSubclassData(unsigned short D) {
291 Value::setValueSubclassData(D);
295 } // End llvm namespace