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_IR_BASICBLOCK_H
15 #define LLVM_IR_BASICBLOCK_H
17 #include "llvm/ADT/Twine.h"
18 #include "llvm/ADT/ilist.h"
19 #include "llvm/IR/Instruction.h"
20 #include "llvm/IR/SymbolTableListTraits.h"
21 #include "llvm/Support/DataTypes.h"
30 template<> struct ilist_traits<Instruction>
31 : public SymbolTableListTraits<Instruction, BasicBlock> {
33 /// \brief Return a node that marks the end of a list.
35 /// The sentinel is relative to this instance, so we use a non-static
37 Instruction *createSentinel() const {
38 // Since i(p)lists always publicly derive from their corresponding traits,
39 // placing a data member in this class will augment the i(p)list. But since
40 // the NodeTy is expected to be publicly derive from ilist_node<NodeTy>,
41 // there is a legal viable downcast from it to NodeTy. We use this trick to
42 // superimpose an i(p)list with a "ghostly" NodeTy, which becomes the
43 // sentinel. Dereferencing the sentinel is forbidden (save the
44 // ilist_node<NodeTy>), so no one will ever notice the superposition.
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 /// \brief LLVM Basic Block Representation
58 /// This represents a single basic block in LLVM. A basic block is simply a
59 /// container of instructions that execute sequentially. Basic blocks are Values
60 /// because they are referenced by instructions such as branches and switch
61 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
62 /// represents a label to which a branch can jump.
64 /// A well formed basic block is formed of a list of non-terminating
65 /// instructions followed by a single TerminatorInst instruction.
66 /// TerminatorInst's may not occur in the middle of basic blocks, and must
67 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
68 /// occur because it may be useful in the intermediate stage of constructing or
69 /// modifying a program. However, the verifier will ensure that basic blocks
70 /// are "well formed".
71 class BasicBlock : public Value, // Basic blocks are data objects also
72 public ilist_node<BasicBlock> {
73 friend class BlockAddress;
75 typedef iplist<Instruction> InstListType;
77 InstListType InstList;
80 void setParent(Function *parent);
81 friend class SymbolTableListTraits<BasicBlock, Function>;
83 BasicBlock(const BasicBlock &) LLVM_DELETED_FUNCTION;
84 void operator=(const BasicBlock &) LLVM_DELETED_FUNCTION;
86 /// \brief Constructor.
88 /// If the function parameter is specified, the basic block is automatically
89 /// inserted at either the end of the function (if InsertBefore is null), or
90 /// before the specified basic block.
91 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
92 Function *Parent = 0, BasicBlock *InsertBefore = 0);
94 /// \brief Get the context in which this basic block lives.
95 LLVMContext &getContext() const;
97 /// Instruction iterators...
98 typedef InstListType::iterator iterator;
99 typedef InstListType::const_iterator const_iterator;
100 typedef InstListType::reverse_iterator reverse_iterator;
101 typedef InstListType::const_reverse_iterator const_reverse_iterator;
103 /// \brief Creates a new BasicBlock.
105 /// If the Parent parameter is specified, the basic block is automatically
106 /// inserted at either the end of the function (if InsertBefore is 0), or
107 /// before the specified basic block.
108 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
109 Function *Parent = 0,BasicBlock *InsertBefore = 0) {
110 return new BasicBlock(Context, Name, Parent, InsertBefore);
114 /// \brief Return the enclosing method, or null if none.
115 const Function *getParent() const { return Parent; }
116 Function *getParent() { return Parent; }
118 /// \brief Returns the terminator instruction if the block is well formed or
119 /// null if the block is not well formed.
120 TerminatorInst *getTerminator();
121 const TerminatorInst *getTerminator() const;
123 /// \brief Returns a pointer to the first instruction in this block that is
124 /// not a PHINode instruction.
126 /// When adding instructions to the beginning of the basic block, they should
127 /// be added before the returned value, not before the first instruction,
128 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
129 Instruction* getFirstNonPHI();
130 const Instruction* getFirstNonPHI() const {
131 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
134 /// \brief Returns a pointer to the first instruction in this block that is not
135 /// a PHINode or a debug intrinsic.
136 Instruction* getFirstNonPHIOrDbg();
137 const Instruction* getFirstNonPHIOrDbg() const {
138 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
141 /// \brief Returns a pointer to the first instruction in this block that is not
142 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
143 Instruction* getFirstNonPHIOrDbgOrLifetime();
144 const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
145 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
148 /// \brief Returns an iterator to the first instruction in this block that is
149 /// suitable for inserting a non-PHI instruction.
151 /// In particular, it skips all PHIs and LandingPad instructions.
152 iterator getFirstInsertionPt();
153 const_iterator getFirstInsertionPt() const {
154 return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
157 /// \brief Unlink 'this' from the containing function, but do not delete it.
158 void removeFromParent();
160 /// \brief Unlink 'this' from the containing function and delete it.
161 void eraseFromParent();
163 /// \brief Unlink this basic block from its current function and insert it
164 /// into the function that \p MovePos lives in, right before \p MovePos.
165 void moveBefore(BasicBlock *MovePos);
167 /// \brief Unlink this basic block from its current function and insert it
168 /// right after \p MovePos in the function \p MovePos lives in.
169 void moveAfter(BasicBlock *MovePos);
172 /// \brief Return this block if it has a single predecessor block. Otherwise
173 /// return a null pointer.
174 BasicBlock *getSinglePredecessor();
175 const BasicBlock *getSinglePredecessor() const {
176 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
179 /// \brief Return this block if it has a unique predecessor block. Otherwise return a null pointer.
181 /// Note that unique predecessor doesn't mean single edge, there can be
182 /// multiple edges from the unique predecessor to this block (for example a
183 /// switch statement with multiple cases having the same destination).
184 BasicBlock *getUniquePredecessor();
185 const BasicBlock *getUniquePredecessor() const {
186 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
189 //===--------------------------------------------------------------------===//
190 /// Instruction iterator methods
192 inline iterator begin() { return InstList.begin(); }
193 inline const_iterator begin() const { return InstList.begin(); }
194 inline iterator end () { return InstList.end(); }
195 inline const_iterator end () const { return InstList.end(); }
197 inline reverse_iterator rbegin() { return InstList.rbegin(); }
198 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
199 inline reverse_iterator rend () { return InstList.rend(); }
200 inline const_reverse_iterator rend () const { return InstList.rend(); }
202 inline size_t size() const { return InstList.size(); }
203 inline bool empty() const { return InstList.empty(); }
204 inline const Instruction &front() const { return InstList.front(); }
205 inline Instruction &front() { return InstList.front(); }
206 inline const Instruction &back() const { return InstList.back(); }
207 inline Instruction &back() { return InstList.back(); }
209 /// \brief Return the underlying instruction list container.
211 /// Currently you need to access the underlying instruction list container
212 /// directly if you want to modify it.
213 const InstListType &getInstList() const { return InstList; }
214 InstListType &getInstList() { return InstList; }
216 /// \brief Returns a pointer to a member of the instruction list.
217 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
218 return &BasicBlock::InstList;
221 /// \brief Returns a pointer to the symbol table if one exists.
222 ValueSymbolTable *getValueSymbolTable();
224 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
225 static inline bool classof(const Value *V) {
226 return V->getValueID() == Value::BasicBlockVal;
229 /// \brief Cause all subinstructions to "let go" of all the references that
230 /// said subinstructions are maintaining.
232 /// This allows one to 'delete' a whole class at a time, even though there may
233 /// be circular references... first all references are dropped, and all use
234 /// counts go to zero. Then everything is delete'd for real. Note that no
235 /// operations are valid on an object that has "dropped all references",
236 /// except operator delete.
237 void dropAllReferences();
239 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
240 /// able to reach it.
242 /// This is actually not used to update the Predecessor list, but is actually
243 /// used to update the PHI nodes that reside in the block. Note that this
244 /// should be called while the predecessor still refers to this block.
245 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
247 /// \brief Split the basic block into two basic blocks at the specified
250 /// Note that all instructions BEFORE the specified iterator stay as part of
251 /// the original basic block, an unconditional branch is added to the original
252 /// BB, and the rest of the instructions in the BB are moved to the new BB,
253 /// including the old terminator. The newly formed BasicBlock is returned.
254 /// This function invalidates the specified iterator.
256 /// Note that this only works on well formed basic blocks (must have a
257 /// terminator), and 'I' must not be the end of instruction list (which would
258 /// cause a degenerate basic block to be formed, having a terminator inside of
259 /// the basic block).
261 /// Also note that this doesn't preserve any passes. To split blocks while
262 /// keeping loop information consistent, use the SplitBlock utility function.
263 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
265 /// \brief Returns true if there are any uses of this basic block other than
266 /// direct branches, switches, etc. to it.
267 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
269 /// \brief Update all phi nodes in this basic block's successors to refer to
270 /// basic block \p New instead of to it.
271 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
273 /// \brief Return true if this basic block is a landing pad.
275 /// Being a ``landing pad'' means that the basic block is the destination of
276 /// the 'unwind' edge of an invoke instruction.
277 bool isLandingPad() const;
279 /// \brief Return the landingpad instruction associated with the landing pad.
280 LandingPadInst *getLandingPadInst();
281 const LandingPadInst *getLandingPadInst() const;
284 /// \brief Increment the internal refcount of the number of BlockAddresses
285 /// referencing this BasicBlock by \p Amt.
287 /// This is almost always 0, sometimes one possibly, but almost never 2, and
288 /// inconceivably 3 or more.
289 void AdjustBlockAddressRefCount(int Amt) {
290 setValueSubclassData(getSubclassDataFromValue()+Amt);
291 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
292 "Refcount wrap-around");
294 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
295 /// so that any future subclasses cannot accidentally use it.
296 void setValueSubclassData(unsigned short D) {
297 Value::setValueSubclassData(D);
301 } // End llvm namespace