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"
34 struct SymbolTableListSentinelTraits<BasicBlock>
35 : public ilist_half_embedded_sentinel_traits<BasicBlock> {};
37 /// \brief LLVM Basic Block Representation
39 /// This represents a single basic block in LLVM. A basic block is simply a
40 /// container of instructions that execute sequentially. Basic blocks are Values
41 /// because they are referenced by instructions such as branches and switch
42 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
43 /// represents a label to which a branch can jump.
45 /// A well formed basic block is formed of a list of non-terminating
46 /// instructions followed by a single TerminatorInst instruction.
47 /// TerminatorInst's may not occur in the middle of basic blocks, and must
48 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
49 /// occur because it may be useful in the intermediate stage of constructing or
50 /// modifying a program. However, the verifier will ensure that basic blocks
51 /// are "well formed".
52 class BasicBlock : public Value, // Basic blocks are data objects also
53 public ilist_node_with_parent<BasicBlock, Function> {
54 friend class BlockAddress;
56 typedef SymbolTableList<Instruction> InstListType;
59 InstListType InstList;
62 // XXX-update: A flag that checks whether we can eliminate this block.
63 bool canEliminateBlock;
65 void setParent(Function *parent);
66 friend class SymbolTableListTraits<BasicBlock>;
68 BasicBlock(const BasicBlock &) = delete;
69 void operator=(const BasicBlock &) = delete;
71 /// \brief Constructor.
73 /// If the function parameter is specified, the basic block is automatically
74 /// inserted at either the end of the function (if InsertBefore is null), or
75 /// before the specified basic block.
76 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
77 Function *Parent = nullptr,
78 BasicBlock *InsertBefore = nullptr);
81 void disableCanEliminateBlock() {
82 canEliminateBlock = false;
85 bool getCanEliminateBlock() {
86 return canEliminateBlock;
90 /// \brief Get the context in which this basic block lives.
91 LLVMContext &getContext() const;
93 /// Instruction iterators...
94 typedef InstListType::iterator iterator;
95 typedef InstListType::const_iterator const_iterator;
96 typedef InstListType::reverse_iterator reverse_iterator;
97 typedef InstListType::const_reverse_iterator const_reverse_iterator;
99 /// \brief Creates a new BasicBlock.
101 /// If the Parent parameter is specified, the basic block is automatically
102 /// inserted at either the end of the function (if InsertBefore is 0), or
103 /// before the specified basic block.
104 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
105 Function *Parent = nullptr,
106 BasicBlock *InsertBefore = nullptr) {
107 return new BasicBlock(Context, Name, Parent, InsertBefore);
109 ~BasicBlock() override;
111 /// \brief Return the enclosing method, or null if none.
112 const Function *getParent() const { return Parent; }
113 Function *getParent() { return Parent; }
115 /// \brief Return the module owning the function this basic block belongs to,
116 /// or nullptr it the function does not have a module.
118 /// Note: this is undefined behavior if the block does not have a parent.
119 const Module *getModule() const;
122 /// \brief Returns the terminator instruction if the block is well formed or
123 /// null if the block is not well formed.
124 TerminatorInst *getTerminator();
125 const TerminatorInst *getTerminator() const;
127 /// \brief Returns the call instruction marked 'musttail' prior to the
128 /// terminating return instruction of this basic block, if such a call is
129 /// present. Otherwise, returns null.
130 CallInst *getTerminatingMustTailCall();
131 const CallInst *getTerminatingMustTailCall() const {
132 return const_cast<BasicBlock *>(this)->getTerminatingMustTailCall();
135 /// \brief Returns a pointer to the first instruction in this block that is
136 /// not a PHINode instruction.
138 /// When adding instructions to the beginning of the basic block, they should
139 /// be added before the returned value, not before the first instruction,
140 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
141 Instruction* getFirstNonPHI();
142 const Instruction* getFirstNonPHI() const {
143 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
146 /// \brief Returns a pointer to the first instruction in this block that is not
147 /// a PHINode or a debug intrinsic.
148 Instruction* getFirstNonPHIOrDbg();
149 const Instruction* getFirstNonPHIOrDbg() const {
150 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
153 /// \brief Returns a pointer to the first instruction in this block that is not
154 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
155 Instruction* getFirstNonPHIOrDbgOrLifetime();
156 const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
157 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
160 /// \brief Returns an iterator to the first instruction in this block that is
161 /// suitable for inserting a non-PHI instruction.
163 /// In particular, it skips all PHIs and LandingPad instructions.
164 iterator getFirstInsertionPt();
165 const_iterator getFirstInsertionPt() const {
166 return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
169 /// \brief Unlink 'this' from the containing function, but do not delete it.
170 void removeFromParent();
172 /// \brief Unlink 'this' from the containing function and delete it.
174 // \returns an iterator pointing to the element after the erased one.
175 SymbolTableList<BasicBlock>::iterator eraseFromParent();
177 /// \brief Unlink this basic block from its current function and insert it
178 /// into the function that \p MovePos lives in, right before \p MovePos.
179 void moveBefore(BasicBlock *MovePos);
181 /// \brief Unlink this basic block from its current function and insert it
182 /// right after \p MovePos in the function \p MovePos lives in.
183 void moveAfter(BasicBlock *MovePos);
185 /// \brief Insert unlinked basic block into a function.
187 /// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
188 /// provided, inserts before that basic block, otherwise inserts at the end.
190 /// \pre \a getParent() is \c nullptr.
191 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
193 /// \brief Return the predecessor of this block if it has a single predecessor
194 /// block. Otherwise return a null pointer.
195 BasicBlock *getSinglePredecessor();
196 const BasicBlock *getSinglePredecessor() const {
197 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
200 /// \brief Return the predecessor of this block if it has a unique predecessor
201 /// block. Otherwise return a null pointer.
203 /// Note that unique predecessor doesn't mean single edge, there can be
204 /// multiple edges from the unique predecessor to this block (for example a
205 /// switch statement with multiple cases having the same destination).
206 BasicBlock *getUniquePredecessor();
207 const BasicBlock *getUniquePredecessor() const {
208 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
211 /// \brief Return the successor of this block if it has a single successor.
212 /// Otherwise return a null pointer.
214 /// This method is analogous to getSinglePredecessor above.
215 BasicBlock *getSingleSuccessor();
216 const BasicBlock *getSingleSuccessor() const {
217 return const_cast<BasicBlock*>(this)->getSingleSuccessor();
220 /// \brief Return the successor of this block if it has a unique successor.
221 /// Otherwise return a null pointer.
223 /// This method is analogous to getUniquePredecessor above.
224 BasicBlock *getUniqueSuccessor();
225 const BasicBlock *getUniqueSuccessor() const {
226 return const_cast<BasicBlock*>(this)->getUniqueSuccessor();
229 //===--------------------------------------------------------------------===//
230 /// Instruction iterator methods
232 inline iterator begin() { return InstList.begin(); }
233 inline const_iterator begin() const { return InstList.begin(); }
234 inline iterator end () { return InstList.end(); }
235 inline const_iterator end () const { return InstList.end(); }
237 inline reverse_iterator rbegin() { return InstList.rbegin(); }
238 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
239 inline reverse_iterator rend () { return InstList.rend(); }
240 inline const_reverse_iterator rend () const { return InstList.rend(); }
242 inline size_t size() const { return InstList.size(); }
243 inline bool empty() const { return InstList.empty(); }
244 inline const Instruction &front() const { return InstList.front(); }
245 inline Instruction &front() { return InstList.front(); }
246 inline const Instruction &back() const { return InstList.back(); }
247 inline Instruction &back() { return InstList.back(); }
249 /// \brief Return the underlying instruction list container.
251 /// Currently you need to access the underlying instruction list container
252 /// directly if you want to modify it.
253 const InstListType &getInstList() const { return InstList; }
254 InstListType &getInstList() { return InstList; }
256 /// \brief Returns a pointer to a member of the instruction list.
257 static InstListType BasicBlock::*getSublistAccess(Instruction*) {
258 return &BasicBlock::InstList;
261 /// \brief Returns a pointer to the symbol table if one exists.
262 ValueSymbolTable *getValueSymbolTable();
264 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
265 static inline bool classof(const Value *V) {
266 return V->getValueID() == Value::BasicBlockVal;
269 /// \brief Cause all subinstructions to "let go" of all the references that
270 /// said subinstructions are maintaining.
272 /// This allows one to 'delete' a whole class at a time, even though there may
273 /// be circular references... first all references are dropped, and all use
274 /// counts go to zero. Then everything is delete'd for real. Note that no
275 /// operations are valid on an object that has "dropped all references",
276 /// except operator delete.
277 void dropAllReferences();
279 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
280 /// able to reach it.
282 /// This is actually not used to update the Predecessor list, but is actually
283 /// used to update the PHI nodes that reside in the block. Note that this
284 /// should be called while the predecessor still refers to this block.
285 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
287 bool canSplitPredecessors() const;
289 /// \brief Split the basic block into two basic blocks at the specified
292 /// Note that all instructions BEFORE the specified iterator stay as part of
293 /// the original basic block, an unconditional branch is added to the original
294 /// BB, and the rest of the instructions in the BB are moved to the new BB,
295 /// including the old terminator. The newly formed BasicBlock is returned.
296 /// This function invalidates the specified iterator.
298 /// Note that this only works on well formed basic blocks (must have a
299 /// terminator), and 'I' must not be the end of instruction list (which would
300 /// cause a degenerate basic block to be formed, having a terminator inside of
301 /// the basic block).
303 /// Also note that this doesn't preserve any passes. To split blocks while
304 /// keeping loop information consistent, use the SplitBlock utility function.
305 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
306 BasicBlock *splitBasicBlock(Instruction *I, const Twine &BBName = "") {
307 return splitBasicBlock(I->getIterator(), BBName);
310 /// \brief Returns true if there are any uses of this basic block other than
311 /// direct branches, switches, etc. to it.
312 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
314 /// \brief Update all phi nodes in this basic block's successors to refer to
315 /// basic block \p New instead of to it.
316 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
318 /// \brief Return true if this basic block is an exception handling block.
319 bool isEHPad() const { return getFirstNonPHI()->isEHPad(); }
321 /// \brief Return true if this basic block is a landing pad.
323 /// Being a ``landing pad'' means that the basic block is the destination of
324 /// the 'unwind' edge of an invoke instruction.
325 bool isLandingPad() const;
327 /// \brief Return the landingpad instruction associated with the landing pad.
328 LandingPadInst *getLandingPadInst();
329 const LandingPadInst *getLandingPadInst() const;
332 /// \brief Increment the internal refcount of the number of BlockAddresses
333 /// referencing this BasicBlock by \p Amt.
335 /// This is almost always 0, sometimes one possibly, but almost never 2, and
336 /// inconceivably 3 or more.
337 void AdjustBlockAddressRefCount(int Amt) {
338 setValueSubclassData(getSubclassDataFromValue()+Amt);
339 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
340 "Refcount wrap-around");
342 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
343 /// so that any future subclasses cannot accidentally use it.
344 void setValueSubclassData(unsigned short D) {
345 Value::setValueSubclassData(D);
349 // Create wrappers for C Binding types (see CBindingWrapping.h).
350 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
352 } // End llvm namespace