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/CBindingWrapping.h"
22 #include "llvm/Support/DataTypes.h"
33 // Traits for intrusive list of basic blocks...
34 template<> struct ilist_traits<BasicBlock>
35 : public SymbolTableListTraits<BasicBlock, Function> {
37 BasicBlock *createSentinel() const;
38 static void destroySentinel(BasicBlock*) {}
40 BasicBlock *provideInitialHead() const { return createSentinel(); }
41 BasicBlock *ensureHead(BasicBlock*) const { return createSentinel(); }
42 static void noteHead(BasicBlock*, BasicBlock*) {}
44 static ValueSymbolTable *getSymTab(Function *ItemParent);
46 mutable ilist_half_node<BasicBlock> Sentinel;
50 /// \brief LLVM Basic Block Representation
52 /// This represents a single basic block in LLVM. A basic block is simply a
53 /// container of instructions that execute sequentially. Basic blocks are Values
54 /// because they are referenced by instructions such as branches and switch
55 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
56 /// represents a label to which a branch can jump.
58 /// A well formed basic block is formed of a list of non-terminating
59 /// instructions followed by a single TerminatorInst instruction.
60 /// TerminatorInst's may not occur in the middle of basic blocks, and must
61 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
62 /// occur because it may be useful in the intermediate stage of constructing or
63 /// modifying a program. However, the verifier will ensure that basic blocks
64 /// are "well formed".
65 class BasicBlock : public Value, // Basic blocks are data objects also
66 public ilist_node<BasicBlock> {
67 friend class BlockAddress;
69 typedef iplist<Instruction> InstListType;
71 InstListType InstList;
74 void setParent(Function *parent);
75 friend class SymbolTableListTraits<BasicBlock, Function>;
77 BasicBlock(const BasicBlock &) = delete;
78 void operator=(const BasicBlock &) = delete;
80 /// \brief Constructor.
82 /// If the function parameter is specified, the basic block is automatically
83 /// inserted at either the end of the function (if InsertBefore is null), or
84 /// before the specified basic block.
85 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
86 Function *Parent = nullptr,
87 BasicBlock *InsertBefore = nullptr);
89 /// \brief 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;
95 typedef InstListType::reverse_iterator reverse_iterator;
96 typedef InstListType::const_reverse_iterator const_reverse_iterator;
98 /// \brief Creates a new BasicBlock.
100 /// If the Parent parameter is specified, the basic block is automatically
101 /// inserted at either the end of the function (if InsertBefore is 0), or
102 /// before the specified basic block.
103 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
104 Function *Parent = nullptr,
105 BasicBlock *InsertBefore = nullptr) {
106 return new BasicBlock(Context, Name, Parent, InsertBefore);
108 ~BasicBlock() override;
110 /// \brief Return the enclosing method, or null if none.
111 const Function *getParent() const { return Parent; }
112 Function *getParent() { return Parent; }
114 /// \brief Return the module owning the function this basic block belongs to,
115 /// or nullptr it the function does not have a module.
117 /// Note: this is undefined behavior if the block does not have a parent.
118 const Module *getModule() const;
120 /// \brief Returns the terminator instruction if the block is well formed or
121 /// null if the block is not well formed.
122 TerminatorInst *getTerminator();
123 const TerminatorInst *getTerminator() const;
125 /// \brief Returns the call instruction marked 'musttail' prior to the
126 /// terminating return instruction of this basic block, if such a call is
127 /// present. Otherwise, returns null.
128 CallInst *getTerminatingMustTailCall();
129 const CallInst *getTerminatingMustTailCall() const {
130 return const_cast<BasicBlock *>(this)->getTerminatingMustTailCall();
133 /// \brief Returns a pointer to the first instruction in this block that is
134 /// not a PHINode instruction.
136 /// When adding instructions to the beginning of the basic block, they should
137 /// be added before the returned value, not before the first instruction,
138 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
139 Instruction* getFirstNonPHI();
140 const Instruction* getFirstNonPHI() const {
141 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
144 /// \brief Returns a pointer to the first instruction in this block that is not
145 /// a PHINode or a debug intrinsic.
146 Instruction* getFirstNonPHIOrDbg();
147 const Instruction* getFirstNonPHIOrDbg() const {
148 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
151 /// \brief Returns a pointer to the first instruction in this block that is not
152 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
153 Instruction* getFirstNonPHIOrDbgOrLifetime();
154 const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
155 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
158 /// \brief Returns an iterator to the first instruction in this block that is
159 /// suitable for inserting a non-PHI instruction.
161 /// In particular, it skips all PHIs and LandingPad instructions.
162 iterator getFirstInsertionPt();
163 const_iterator getFirstInsertionPt() const {
164 return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
167 /// \brief Unlink 'this' from the containing function, but do not delete it.
168 void removeFromParent();
170 /// \brief Unlink 'this' from the containing function and delete it.
172 // \returns an iterator pointing to the element after the erased one.
173 iplist<BasicBlock>::iterator eraseFromParent();
175 /// \brief Unlink this basic block from its current function and insert it
176 /// into the function that \p MovePos lives in, right before \p MovePos.
177 void moveBefore(BasicBlock *MovePos);
179 /// \brief Unlink this basic block from its current function and insert it
180 /// right after \p MovePos in the function \p MovePos lives in.
181 void moveAfter(BasicBlock *MovePos);
183 /// \brief Insert unlinked basic block into a function.
185 /// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
186 /// provided, inserts before that basic block, otherwise inserts at the end.
188 /// \pre \a getParent() is \c nullptr.
189 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
191 /// \brief Return the predecessor of this block if it has a single predecessor
192 /// block. Otherwise return a null pointer.
193 BasicBlock *getSinglePredecessor();
194 const BasicBlock *getSinglePredecessor() const {
195 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
198 /// \brief Return the predecessor of this block if it has a unique predecessor
199 /// block. Otherwise return a null pointer.
201 /// Note that unique predecessor doesn't mean single edge, there can be
202 /// multiple edges from the unique predecessor to this block (for example a
203 /// switch statement with multiple cases having the same destination).
204 BasicBlock *getUniquePredecessor();
205 const BasicBlock *getUniquePredecessor() const {
206 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
209 /// \brief Return the successor of this block if it has a single successor.
210 /// Otherwise return a null pointer.
212 /// This method is analogous to getSinglePredecessor above.
213 BasicBlock *getSingleSuccessor();
214 const BasicBlock *getSingleSuccessor() const {
215 return const_cast<BasicBlock*>(this)->getSingleSuccessor();
218 /// \brief Return the successor of this block if it has a unique successor.
219 /// Otherwise return a null pointer.
221 /// This method is analogous to getUniquePredecessor above.
222 BasicBlock *getUniqueSuccessor();
223 const BasicBlock *getUniqueSuccessor() const {
224 return const_cast<BasicBlock*>(this)->getUniqueSuccessor();
227 //===--------------------------------------------------------------------===//
228 /// Instruction iterator methods
230 inline iterator begin() { return InstList.begin(); }
231 inline const_iterator begin() const { return InstList.begin(); }
232 inline iterator end () { return InstList.end(); }
233 inline const_iterator end () const { return InstList.end(); }
235 inline reverse_iterator rbegin() { return InstList.rbegin(); }
236 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
237 inline reverse_iterator rend () { return InstList.rend(); }
238 inline const_reverse_iterator rend () const { return InstList.rend(); }
240 inline size_t size() const { return InstList.size(); }
241 inline bool empty() const { return InstList.empty(); }
242 inline const Instruction &front() const { return InstList.front(); }
243 inline Instruction &front() { return InstList.front(); }
244 inline const Instruction &back() const { return InstList.back(); }
245 inline Instruction &back() { return InstList.back(); }
247 /// \brief Return the underlying instruction list container.
249 /// Currently you need to access the underlying instruction list container
250 /// directly if you want to modify it.
251 const InstListType &getInstList() const { return InstList; }
252 InstListType &getInstList() { return InstList; }
254 /// \brief Returns a pointer to a member of the instruction list.
255 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
256 return &BasicBlock::InstList;
259 /// \brief Returns a pointer to the symbol table if one exists.
260 ValueSymbolTable *getValueSymbolTable();
262 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
263 static inline bool classof(const Value *V) {
264 return V->getValueID() == Value::BasicBlockVal;
267 /// \brief Cause all subinstructions to "let go" of all the references that
268 /// said subinstructions are maintaining.
270 /// This allows one to 'delete' a whole class at a time, even though there may
271 /// be circular references... first all references are dropped, and all use
272 /// counts go to zero. Then everything is delete'd for real. Note that no
273 /// operations are valid on an object that has "dropped all references",
274 /// except operator delete.
275 void dropAllReferences();
277 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
278 /// able to reach it.
280 /// This is actually not used to update the Predecessor list, but is actually
281 /// used to update the PHI nodes that reside in the block. Note that this
282 /// should be called while the predecessor still refers to this block.
283 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
285 /// \brief Split the basic block into two basic blocks at the specified
288 /// Note that all instructions BEFORE the specified iterator stay as part of
289 /// the original basic block, an unconditional branch is added to the original
290 /// BB, and the rest of the instructions in the BB are moved to the new BB,
291 /// including the old terminator. The newly formed BasicBlock is returned.
292 /// This function invalidates the specified iterator.
294 /// Note that this only works on well formed basic blocks (must have a
295 /// terminator), and 'I' must not be the end of instruction list (which would
296 /// cause a degenerate basic block to be formed, having a terminator inside of
297 /// the basic block).
299 /// Also note that this doesn't preserve any passes. To split blocks while
300 /// keeping loop information consistent, use the SplitBlock utility function.
301 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
303 /// \brief Returns true if there are any uses of this basic block other than
304 /// direct branches, switches, etc. to it.
305 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
307 /// \brief Update all phi nodes in this basic block's successors to refer to
308 /// basic block \p New instead of to it.
309 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
311 /// \brief Return true if this basic block is a landing pad.
313 /// Being a ``landing pad'' means that the basic block is the destination of
314 /// the 'unwind' edge of an invoke instruction.
315 bool isLandingPad() const;
317 /// \brief Return the landingpad instruction associated with the landing pad.
318 LandingPadInst *getLandingPadInst();
319 const LandingPadInst *getLandingPadInst() const;
322 /// \brief Increment the internal refcount of the number of BlockAddresses
323 /// referencing this BasicBlock by \p Amt.
325 /// This is almost always 0, sometimes one possibly, but almost never 2, and
326 /// inconceivably 3 or more.
327 void AdjustBlockAddressRefCount(int Amt) {
328 setValueSubclassData(getSubclassDataFromValue()+Amt);
329 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
330 "Refcount wrap-around");
332 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
333 /// so that any future subclasses cannot accidentally use it.
334 void setValueSubclassData(unsigned short D) {
335 Value::setValueSubclassData(D);
339 // createSentinel is used to get hold of the node that marks the end of the
340 // list... (same trick used here as in ilist_traits<Instruction>)
341 inline BasicBlock *ilist_traits<BasicBlock>::createSentinel() const {
342 return static_cast<BasicBlock*>(&Sentinel);
345 // Create wrappers for C Binding types (see CBindingWrapping.h).
346 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
348 } // End llvm namespace