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 mutable ilist_half_node<BasicBlock> Sentinel;
48 /// \brief LLVM Basic Block Representation
50 /// This represents a single basic block in LLVM. A basic block is simply a
51 /// container of instructions that execute sequentially. Basic blocks are Values
52 /// because they are referenced by instructions such as branches and switch
53 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
54 /// represents a label to which a branch can jump.
56 /// A well formed basic block is formed of a list of non-terminating
57 /// instructions followed by a single TerminatorInst instruction.
58 /// TerminatorInst's may not occur in the middle of basic blocks, and must
59 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
60 /// occur because it may be useful in the intermediate stage of constructing or
61 /// modifying a program. However, the verifier will ensure that basic blocks
62 /// are "well formed".
63 class BasicBlock : public Value, // Basic blocks are data objects also
64 public ilist_node<BasicBlock> {
65 friend class BlockAddress;
67 typedef iplist<Instruction> InstListType;
69 InstListType InstList;
72 void setParent(Function *parent);
73 friend class SymbolTableListTraits<BasicBlock, Function>;
75 BasicBlock(const BasicBlock &) = delete;
76 void operator=(const BasicBlock &) = delete;
78 /// \brief Constructor.
80 /// If the function parameter is specified, the basic block is automatically
81 /// inserted at either the end of the function (if InsertBefore is null), or
82 /// before the specified basic block.
83 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
84 Function *Parent = nullptr,
85 BasicBlock *InsertBefore = nullptr);
87 /// \brief Get the context in which this basic block lives.
88 LLVMContext &getContext() const;
90 /// Instruction iterators...
91 typedef InstListType::iterator iterator;
92 typedef InstListType::const_iterator const_iterator;
93 typedef InstListType::reverse_iterator reverse_iterator;
94 typedef InstListType::const_reverse_iterator const_reverse_iterator;
96 /// \brief Creates a new BasicBlock.
98 /// If the Parent parameter is specified, the basic block is automatically
99 /// inserted at either the end of the function (if InsertBefore is 0), or
100 /// before the specified basic block.
101 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
102 Function *Parent = nullptr,
103 BasicBlock *InsertBefore = nullptr) {
104 return new BasicBlock(Context, Name, Parent, InsertBefore);
106 ~BasicBlock() override;
108 /// \brief Return the enclosing method, or null if none.
109 const Function *getParent() const { return Parent; }
110 Function *getParent() { return Parent; }
112 /// \brief Return the module owning the function this basic block belongs to,
113 /// or nullptr it the function does not have a module.
115 /// Note: this is undefined behavior if the block does not have a parent.
116 const Module *getModule() const;
119 /// \brief Returns the terminator instruction if the block is well formed or
120 /// null if the block is not well formed.
121 TerminatorInst *getTerminator();
122 const TerminatorInst *getTerminator() const;
124 /// \brief Returns the call instruction marked 'musttail' prior to the
125 /// terminating return instruction of this basic block, if such a call is
126 /// present. Otherwise, returns null.
127 CallInst *getTerminatingMustTailCall();
128 const CallInst *getTerminatingMustTailCall() const {
129 return const_cast<BasicBlock *>(this)->getTerminatingMustTailCall();
132 /// \brief Returns a pointer to the first instruction in this block that is
133 /// not a PHINode instruction.
135 /// When adding instructions to the beginning of the basic block, they should
136 /// be added before the returned value, not before the first instruction,
137 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
138 Instruction* getFirstNonPHI();
139 const Instruction* getFirstNonPHI() const {
140 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
143 /// \brief Returns a pointer to the first instruction in this block that is not
144 /// a PHINode or a debug intrinsic.
145 Instruction* getFirstNonPHIOrDbg();
146 const Instruction* getFirstNonPHIOrDbg() const {
147 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
150 /// \brief Returns a pointer to the first instruction in this block that is not
151 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
152 Instruction* getFirstNonPHIOrDbgOrLifetime();
153 const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
154 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
157 /// \brief Returns an iterator to the first instruction in this block that is
158 /// suitable for inserting a non-PHI instruction.
160 /// In particular, it skips all PHIs and LandingPad instructions.
161 iterator getFirstInsertionPt();
162 const_iterator getFirstInsertionPt() const {
163 return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
166 /// \brief Unlink 'this' from the containing function, but do not delete it.
167 void removeFromParent();
169 /// \brief Unlink 'this' from the containing function and delete it.
171 // \returns an iterator pointing to the element after the erased one.
172 iplist<BasicBlock>::iterator eraseFromParent();
174 /// \brief Unlink this basic block from its current function and insert it
175 /// into the function that \p MovePos lives in, right before \p MovePos.
176 void moveBefore(BasicBlock *MovePos);
178 /// \brief Unlink this basic block from its current function and insert it
179 /// right after \p MovePos in the function \p MovePos lives in.
180 void moveAfter(BasicBlock *MovePos);
182 /// \brief Insert unlinked basic block into a function.
184 /// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
185 /// provided, inserts before that basic block, otherwise inserts at the end.
187 /// \pre \a getParent() is \c nullptr.
188 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
190 /// \brief Return the predecessor of this block if it has a single predecessor
191 /// block. Otherwise return a null pointer.
192 BasicBlock *getSinglePredecessor();
193 const BasicBlock *getSinglePredecessor() const {
194 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
197 /// \brief Return the predecessor of this block if it has a unique predecessor
198 /// block. Otherwise return a null pointer.
200 /// Note that unique predecessor doesn't mean single edge, there can be
201 /// multiple edges from the unique predecessor to this block (for example a
202 /// switch statement with multiple cases having the same destination).
203 BasicBlock *getUniquePredecessor();
204 const BasicBlock *getUniquePredecessor() const {
205 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
208 /// \brief Return the successor of this block if it has a single successor.
209 /// Otherwise return a null pointer.
211 /// This method is analogous to getSinglePredecessor above.
212 BasicBlock *getSingleSuccessor();
213 const BasicBlock *getSingleSuccessor() const {
214 return const_cast<BasicBlock*>(this)->getSingleSuccessor();
217 /// \brief Return the successor of this block if it has a unique successor.
218 /// Otherwise return a null pointer.
220 /// This method is analogous to getUniquePredecessor above.
221 BasicBlock *getUniqueSuccessor();
222 const BasicBlock *getUniqueSuccessor() const {
223 return const_cast<BasicBlock*>(this)->getUniqueSuccessor();
226 //===--------------------------------------------------------------------===//
227 /// Instruction iterator methods
229 inline iterator begin() { return InstList.begin(); }
230 inline const_iterator begin() const { return InstList.begin(); }
231 inline iterator end () { return InstList.end(); }
232 inline const_iterator end () const { return InstList.end(); }
234 inline reverse_iterator rbegin() { return InstList.rbegin(); }
235 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
236 inline reverse_iterator rend () { return InstList.rend(); }
237 inline const_reverse_iterator rend () const { return InstList.rend(); }
239 inline size_t size() const { return InstList.size(); }
240 inline bool empty() const { return InstList.empty(); }
241 inline const Instruction &front() const { return InstList.front(); }
242 inline Instruction &front() { return InstList.front(); }
243 inline const Instruction &back() const { return InstList.back(); }
244 inline Instruction &back() { return InstList.back(); }
246 /// \brief Return the underlying instruction list container.
248 /// Currently you need to access the underlying instruction list container
249 /// directly if you want to modify it.
250 const InstListType &getInstList() const { return InstList; }
251 InstListType &getInstList() { return InstList; }
253 /// \brief Returns a pointer to a member of the instruction list.
254 static InstListType BasicBlock::*getSublistAccess(Instruction*) {
255 return &BasicBlock::InstList;
258 /// \brief Returns a pointer to the symbol table if one exists.
259 ValueSymbolTable *getValueSymbolTable();
261 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
262 static inline bool classof(const Value *V) {
263 return V->getValueID() == Value::BasicBlockVal;
266 /// \brief Cause all subinstructions to "let go" of all the references that
267 /// said subinstructions are maintaining.
269 /// This allows one to 'delete' a whole class at a time, even though there may
270 /// be circular references... first all references are dropped, and all use
271 /// counts go to zero. Then everything is delete'd for real. Note that no
272 /// operations are valid on an object that has "dropped all references",
273 /// except operator delete.
274 void dropAllReferences();
276 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
277 /// able to reach it.
279 /// This is actually not used to update the Predecessor list, but is actually
280 /// used to update the PHI nodes that reside in the block. Note that this
281 /// should be called while the predecessor still refers to this block.
282 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
284 bool canSplitPredecessors() const;
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 an exception handling block.
313 bool isEHPad() const { return getFirstNonPHI()->isEHPad(); }
315 /// \brief Return true if this basic block is a landing pad.
317 /// Being a ``landing pad'' means that the basic block is the destination of
318 /// the 'unwind' edge of an invoke instruction.
319 bool isLandingPad() const;
321 /// \brief Return the landingpad instruction associated with the landing pad.
322 LandingPadInst *getLandingPadInst();
323 const LandingPadInst *getLandingPadInst() const;
326 /// \brief Increment the internal refcount of the number of BlockAddresses
327 /// referencing this BasicBlock by \p Amt.
329 /// This is almost always 0, sometimes one possibly, but almost never 2, and
330 /// inconceivably 3 or more.
331 void AdjustBlockAddressRefCount(int Amt) {
332 setValueSubclassData(getSubclassDataFromValue()+Amt);
333 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
334 "Refcount wrap-around");
336 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
337 /// so that any future subclasses cannot accidentally use it.
338 void setValueSubclassData(unsigned short D) {
339 Value::setValueSubclassData(D);
343 // createSentinel is used to get hold of the node that marks the end of the
344 // list... (same trick used here as in ilist_traits<Instruction>)
345 inline BasicBlock *ilist_traits<BasicBlock>::createSentinel() const {
346 return static_cast<BasicBlock*>(&Sentinel);
349 // Create wrappers for C Binding types (see CBindingWrapping.h).
350 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
352 } // End llvm namespace