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;
121 /// \brief Returns the terminator instruction if the block is well formed or
122 /// null if the block is not well formed.
123 TerminatorInst *getTerminator();
124 const TerminatorInst *getTerminator() const;
126 /// \brief Returns the call instruction marked 'musttail' prior to the
127 /// terminating return instruction of this basic block, if such a call is
128 /// present. Otherwise, returns null.
129 CallInst *getTerminatingMustTailCall();
130 const CallInst *getTerminatingMustTailCall() const {
131 return const_cast<BasicBlock *>(this)->getTerminatingMustTailCall();
134 /// \brief Returns a pointer to the first instruction in this block that is
135 /// not a PHINode instruction.
137 /// When adding instructions to the beginning of the basic block, they should
138 /// be added before the returned value, not before the first instruction,
139 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
140 Instruction* getFirstNonPHI();
141 const Instruction* getFirstNonPHI() const {
142 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
145 /// \brief Returns a pointer to the first instruction in this block that is not
146 /// a PHINode or a debug intrinsic.
147 Instruction* getFirstNonPHIOrDbg();
148 const Instruction* getFirstNonPHIOrDbg() const {
149 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
152 /// \brief Returns a pointer to the first instruction in this block that is not
153 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
154 Instruction* getFirstNonPHIOrDbgOrLifetime();
155 const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
156 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
159 /// \brief Returns an iterator to the first instruction in this block that is
160 /// suitable for inserting a non-PHI instruction.
162 /// In particular, it skips all PHIs and LandingPad instructions.
163 iterator getFirstInsertionPt();
164 const_iterator getFirstInsertionPt() const {
165 return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
168 /// \brief Unlink 'this' from the containing function, but do not delete it.
169 void removeFromParent();
171 /// \brief Unlink 'this' from the containing function and delete it.
173 // \returns an iterator pointing to the element after the erased one.
174 iplist<BasicBlock>::iterator eraseFromParent();
176 /// \brief Unlink this basic block from its current function and insert it
177 /// into the function that \p MovePos lives in, right before \p MovePos.
178 void moveBefore(BasicBlock *MovePos);
180 /// \brief Unlink this basic block from its current function and insert it
181 /// right after \p MovePos in the function \p MovePos lives in.
182 void moveAfter(BasicBlock *MovePos);
184 /// \brief Insert unlinked basic block into a function.
186 /// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
187 /// provided, inserts before that basic block, otherwise inserts at the end.
189 /// \pre \a getParent() is \c nullptr.
190 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
192 /// \brief Return the predecessor of this block if it has a single predecessor
193 /// block. Otherwise return a null pointer.
194 BasicBlock *getSinglePredecessor();
195 const BasicBlock *getSinglePredecessor() const {
196 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
199 /// \brief Return the predecessor of this block if it has a unique predecessor
200 /// block. Otherwise return a null pointer.
202 /// Note that unique predecessor doesn't mean single edge, there can be
203 /// multiple edges from the unique predecessor to this block (for example a
204 /// switch statement with multiple cases having the same destination).
205 BasicBlock *getUniquePredecessor();
206 const BasicBlock *getUniquePredecessor() const {
207 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
210 /// \brief Return the successor of this block if it has a single successor.
211 /// Otherwise return a null pointer.
213 /// This method is analogous to getSinglePredecessor above.
214 BasicBlock *getSingleSuccessor();
215 const BasicBlock *getSingleSuccessor() const {
216 return const_cast<BasicBlock*>(this)->getSingleSuccessor();
219 /// \brief Return the successor of this block if it has a unique successor.
220 /// Otherwise return a null pointer.
222 /// This method is analogous to getUniquePredecessor above.
223 BasicBlock *getUniqueSuccessor();
224 const BasicBlock *getUniqueSuccessor() const {
225 return const_cast<BasicBlock*>(this)->getUniqueSuccessor();
228 //===--------------------------------------------------------------------===//
229 /// Instruction iterator methods
231 inline iterator begin() { return InstList.begin(); }
232 inline const_iterator begin() const { return InstList.begin(); }
233 inline iterator end () { return InstList.end(); }
234 inline const_iterator end () const { return InstList.end(); }
236 inline reverse_iterator rbegin() { return InstList.rbegin(); }
237 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
238 inline reverse_iterator rend () { return InstList.rend(); }
239 inline const_reverse_iterator rend () const { return InstList.rend(); }
241 inline size_t size() const { return InstList.size(); }
242 inline bool empty() const { return InstList.empty(); }
243 inline const Instruction &front() const { return InstList.front(); }
244 inline Instruction &front() { return InstList.front(); }
245 inline const Instruction &back() const { return InstList.back(); }
246 inline Instruction &back() { return InstList.back(); }
248 /// \brief Return the underlying instruction list container.
250 /// Currently you need to access the underlying instruction list container
251 /// directly if you want to modify it.
252 const InstListType &getInstList() const { return InstList; }
253 InstListType &getInstList() { return InstList; }
255 /// \brief Returns a pointer to a member of the instruction list.
256 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
257 return &BasicBlock::InstList;
260 /// \brief Returns a pointer to the symbol table if one exists.
261 ValueSymbolTable *getValueSymbolTable();
263 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
264 static inline bool classof(const Value *V) {
265 return V->getValueID() == Value::BasicBlockVal;
268 /// \brief Cause all subinstructions to "let go" of all the references that
269 /// said subinstructions are maintaining.
271 /// This allows one to 'delete' a whole class at a time, even though there may
272 /// be circular references... first all references are dropped, and all use
273 /// counts go to zero. Then everything is delete'd for real. Note that no
274 /// operations are valid on an object that has "dropped all references",
275 /// except operator delete.
276 void dropAllReferences();
278 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
279 /// able to reach it.
281 /// This is actually not used to update the Predecessor list, but is actually
282 /// used to update the PHI nodes that reside in the block. Note that this
283 /// should be called while the predecessor still refers to this block.
284 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
286 /// \brief Split the basic block into two basic blocks at the specified
289 /// Note that all instructions BEFORE the specified iterator stay as part of
290 /// the original basic block, an unconditional branch is added to the original
291 /// BB, and the rest of the instructions in the BB are moved to the new BB,
292 /// including the old terminator. The newly formed BasicBlock is returned.
293 /// This function invalidates the specified iterator.
295 /// Note that this only works on well formed basic blocks (must have a
296 /// terminator), and 'I' must not be the end of instruction list (which would
297 /// cause a degenerate basic block to be formed, having a terminator inside of
298 /// the basic block).
300 /// Also note that this doesn't preserve any passes. To split blocks while
301 /// keeping loop information consistent, use the SplitBlock utility function.
302 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
304 /// \brief Returns true if there are any uses of this basic block other than
305 /// direct branches, switches, etc. to it.
306 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
308 /// \brief Update all phi nodes in this basic block's successors to refer to
309 /// basic block \p New instead of to it.
310 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
312 /// \brief Return true if this basic block is a landing pad.
314 /// Being a ``landing pad'' means that the basic block is the destination of
315 /// the 'unwind' edge of an invoke instruction.
316 bool isLandingPad() const;
318 /// \brief Return the landingpad instruction associated with the landing pad.
319 LandingPadInst *getLandingPadInst();
320 const LandingPadInst *getLandingPadInst() const;
323 /// \brief Increment the internal refcount of the number of BlockAddresses
324 /// referencing this BasicBlock by \p Amt.
326 /// This is almost always 0, sometimes one possibly, but almost never 2, and
327 /// inconceivably 3 or more.
328 void AdjustBlockAddressRefCount(int Amt) {
329 setValueSubclassData(getSubclassDataFromValue()+Amt);
330 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
331 "Refcount wrap-around");
333 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
334 /// so that any future subclasses cannot accidentally use it.
335 void setValueSubclassData(unsigned short D) {
336 Value::setValueSubclassData(D);
340 // createSentinel is used to get hold of the node that marks the end of the
341 // list... (same trick used here as in ilist_traits<Instruction>)
342 inline BasicBlock *ilist_traits<BasicBlock>::createSentinel() const {
343 return static_cast<BasicBlock*>(&Sentinel);
346 // Create wrappers for C Binding types (see CBindingWrapping.h).
347 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
349 } // End llvm namespace