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"
32 template<> struct ilist_traits<Instruction>
33 : public SymbolTableListTraits<Instruction, BasicBlock> {
35 /// \brief Return a node that marks the end of a list.
37 /// The sentinel is relative to this instance, so we use a non-static
39 Instruction *createSentinel() const {
40 // Since i(p)lists always publicly derive from their corresponding traits,
41 // placing a data member in this class will augment the i(p)list. But since
42 // the NodeTy is expected to be publicly derive from ilist_node<NodeTy>,
43 // there is a legal viable downcast from it to NodeTy. We use this trick to
44 // superimpose an i(p)list with a "ghostly" NodeTy, which becomes the
45 // sentinel. Dereferencing the sentinel is forbidden (save the
46 // ilist_node<NodeTy>), so no one will ever notice the superposition.
47 return static_cast<Instruction*>(&Sentinel);
49 static void destroySentinel(Instruction*) {}
51 Instruction *provideInitialHead() const { return createSentinel(); }
52 Instruction *ensureHead(Instruction*) const { return createSentinel(); }
53 static void noteHead(Instruction*, Instruction*) {}
55 mutable ilist_half_node<Instruction> Sentinel;
58 /// \brief LLVM Basic Block Representation
60 /// This represents a single basic block in LLVM. A basic block is simply a
61 /// container of instructions that execute sequentially. Basic blocks are Values
62 /// because they are referenced by instructions such as branches and switch
63 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
64 /// represents a label to which a branch can jump.
66 /// A well formed basic block is formed of a list of non-terminating
67 /// instructions followed by a single TerminatorInst instruction.
68 /// TerminatorInst's may not occur in the middle of basic blocks, and must
69 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
70 /// occur because it may be useful in the intermediate stage of constructing or
71 /// modifying a program. However, the verifier will ensure that basic blocks
72 /// are "well formed".
73 class BasicBlock : public Value, // Basic blocks are data objects also
74 public ilist_node<BasicBlock> {
75 friend class BlockAddress;
77 typedef iplist<Instruction> InstListType;
79 InstListType InstList;
82 void setParent(Function *parent);
83 friend class SymbolTableListTraits<BasicBlock, Function>;
85 BasicBlock(const BasicBlock &) = delete;
86 void operator=(const BasicBlock &) = delete;
88 /// \brief Constructor.
90 /// If the function parameter is specified, the basic block is automatically
91 /// inserted at either the end of the function (if InsertBefore is null), or
92 /// before the specified basic block.
93 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
94 Function *Parent = nullptr,
95 BasicBlock *InsertBefore = nullptr);
97 /// \brief Get the context in which this basic block lives.
98 LLVMContext &getContext() const;
100 /// Instruction iterators...
101 typedef InstListType::iterator iterator;
102 typedef InstListType::const_iterator const_iterator;
103 typedef InstListType::reverse_iterator reverse_iterator;
104 typedef InstListType::const_reverse_iterator const_reverse_iterator;
106 /// \brief Creates a new BasicBlock.
108 /// If the Parent parameter is specified, the basic block is automatically
109 /// inserted at either the end of the function (if InsertBefore is 0), or
110 /// before the specified basic block.
111 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
112 Function *Parent = nullptr,
113 BasicBlock *InsertBefore = nullptr) {
114 return new BasicBlock(Context, Name, Parent, InsertBefore);
118 /// \brief Return the enclosing method, or null if none.
119 const Function *getParent() const { return Parent; }
120 Function *getParent() { return Parent; }
122 /// \brief Return the module owning the function this basic block belongs to,
123 /// or nullptr it the function does not have a module.
125 /// Note: this is undefined behavior if the block does not have a parent.
126 const Module *getModule() const;
128 /// \brief Returns the terminator instruction if the block is well formed or
129 /// null if the block is not well formed.
130 TerminatorInst *getTerminator();
131 const TerminatorInst *getTerminator() const;
133 /// \brief Returns the call instruction marked 'musttail' prior to the
134 /// terminating return instruction of this basic block, if such a call is
135 /// present. Otherwise, returns null.
136 CallInst *getTerminatingMustTailCall();
137 const CallInst *getTerminatingMustTailCall() const {
138 return const_cast<BasicBlock *>(this)->getTerminatingMustTailCall();
141 /// \brief Returns a pointer to the first instruction in this block that is
142 /// not a PHINode instruction.
144 /// When adding instructions to the beginning of the basic block, they should
145 /// be added before the returned value, not before the first instruction,
146 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
147 Instruction* getFirstNonPHI();
148 const Instruction* getFirstNonPHI() const {
149 return const_cast<BasicBlock*>(this)->getFirstNonPHI();
152 /// \brief Returns a pointer to the first instruction in this block that is not
153 /// a PHINode or a debug intrinsic.
154 Instruction* getFirstNonPHIOrDbg();
155 const Instruction* getFirstNonPHIOrDbg() const {
156 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg();
159 /// \brief Returns a pointer to the first instruction in this block that is not
160 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
161 Instruction* getFirstNonPHIOrDbgOrLifetime();
162 const Instruction* getFirstNonPHIOrDbgOrLifetime() const {
163 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime();
166 /// \brief Returns an iterator to the first instruction in this block that is
167 /// suitable for inserting a non-PHI instruction.
169 /// In particular, it skips all PHIs and LandingPad instructions.
170 iterator getFirstInsertionPt();
171 const_iterator getFirstInsertionPt() const {
172 return const_cast<BasicBlock*>(this)->getFirstInsertionPt();
175 /// \brief Unlink 'this' from the containing function, but do not delete it.
176 void removeFromParent();
178 /// \brief Unlink 'this' from the containing function and delete it.
179 void eraseFromParent();
181 /// \brief Unlink this basic block from its current function and insert it
182 /// into the function that \p MovePos lives in, right before \p MovePos.
183 void moveBefore(BasicBlock *MovePos);
185 /// \brief Unlink this basic block from its current function and insert it
186 /// right after \p MovePos in the function \p MovePos lives in.
187 void moveAfter(BasicBlock *MovePos);
189 /// \brief Insert unlinked basic block into a function.
191 /// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
192 /// provided, inserts before that basic block, otherwise inserts at the end.
194 /// \pre \a getParent() is \c nullptr.
195 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
197 /// \brief Return the predecessor of this block if it has a single predecessor
198 /// block. Otherwise return a null pointer.
199 BasicBlock *getSinglePredecessor();
200 const BasicBlock *getSinglePredecessor() const {
201 return const_cast<BasicBlock*>(this)->getSinglePredecessor();
204 /// \brief Return the predecessor of this block if it has a unique predecessor
205 /// block. Otherwise return a null pointer.
207 /// Note that unique predecessor doesn't mean single edge, there can be
208 /// multiple edges from the unique predecessor to this block (for example a
209 /// switch statement with multiple cases having the same destination).
210 BasicBlock *getUniquePredecessor();
211 const BasicBlock *getUniquePredecessor() const {
212 return const_cast<BasicBlock*>(this)->getUniquePredecessor();
215 /// Return the successor of this block if it has a unique successor.
216 /// Otherwise return a null pointer. This method is analogous to
217 /// getUniquePredeccessor above.
218 BasicBlock *getUniqueSuccessor();
219 const BasicBlock *getUniqueSuccessor() const {
220 return const_cast<BasicBlock*>(this)->getUniqueSuccessor();
223 //===--------------------------------------------------------------------===//
224 /// Instruction iterator methods
226 inline iterator begin() { return InstList.begin(); }
227 inline const_iterator begin() const { return InstList.begin(); }
228 inline iterator end () { return InstList.end(); }
229 inline const_iterator end () const { return InstList.end(); }
231 inline reverse_iterator rbegin() { return InstList.rbegin(); }
232 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
233 inline reverse_iterator rend () { return InstList.rend(); }
234 inline const_reverse_iterator rend () const { return InstList.rend(); }
236 inline size_t size() const { return InstList.size(); }
237 inline bool empty() const { return InstList.empty(); }
238 inline const Instruction &front() const { return InstList.front(); }
239 inline Instruction &front() { return InstList.front(); }
240 inline const Instruction &back() const { return InstList.back(); }
241 inline Instruction &back() { return InstList.back(); }
243 /// \brief Return the underlying instruction list container.
245 /// Currently you need to access the underlying instruction list container
246 /// directly if you want to modify it.
247 const InstListType &getInstList() const { return InstList; }
248 InstListType &getInstList() { return InstList; }
250 /// \brief Returns a pointer to a member of the instruction list.
251 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) {
252 return &BasicBlock::InstList;
255 /// \brief Returns a pointer to the symbol table if one exists.
256 ValueSymbolTable *getValueSymbolTable();
258 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
259 static inline bool classof(const Value *V) {
260 return V->getValueID() == Value::BasicBlockVal;
263 /// \brief Cause all subinstructions to "let go" of all the references that
264 /// said subinstructions are maintaining.
266 /// This allows one to 'delete' a whole class at a time, even though there may
267 /// be circular references... first all references are dropped, and all use
268 /// counts go to zero. Then everything is delete'd for real. Note that no
269 /// operations are valid on an object that has "dropped all references",
270 /// except operator delete.
271 void dropAllReferences();
273 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
274 /// able to reach it.
276 /// This is actually not used to update the Predecessor list, but is actually
277 /// used to update the PHI nodes that reside in the block. Note that this
278 /// should be called while the predecessor still refers to this block.
279 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
281 /// \brief Split the basic block into two basic blocks at the specified
284 /// Note that all instructions BEFORE the specified iterator stay as part of
285 /// the original basic block, an unconditional branch is added to the original
286 /// BB, and the rest of the instructions in the BB are moved to the new BB,
287 /// including the old terminator. The newly formed BasicBlock is returned.
288 /// This function invalidates the specified iterator.
290 /// Note that this only works on well formed basic blocks (must have a
291 /// terminator), and 'I' must not be the end of instruction list (which would
292 /// cause a degenerate basic block to be formed, having a terminator inside of
293 /// the basic block).
295 /// Also note that this doesn't preserve any passes. To split blocks while
296 /// keeping loop information consistent, use the SplitBlock utility function.
297 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
299 /// \brief Returns true if there are any uses of this basic block other than
300 /// direct branches, switches, etc. to it.
301 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
303 /// \brief Update all phi nodes in this basic block's successors to refer to
304 /// basic block \p New instead of to it.
305 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
307 /// \brief Return true if this basic block is a landing pad.
309 /// Being a ``landing pad'' means that the basic block is the destination of
310 /// the 'unwind' edge of an invoke instruction.
311 bool isLandingPad() const;
313 /// \brief Return the landingpad instruction associated with the landing pad.
314 LandingPadInst *getLandingPadInst();
315 const LandingPadInst *getLandingPadInst() const;
318 /// \brief Increment the internal refcount of the number of BlockAddresses
319 /// referencing this BasicBlock by \p Amt.
321 /// This is almost always 0, sometimes one possibly, but almost never 2, and
322 /// inconceivably 3 or more.
323 void AdjustBlockAddressRefCount(int Amt) {
324 setValueSubclassData(getSubclassDataFromValue()+Amt);
325 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
326 "Refcount wrap-around");
328 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
329 /// so that any future subclasses cannot accidentally use it.
330 void setValueSubclassData(unsigned short D) {
331 Value::setValueSubclassData(D);
335 // Create wrappers for C Binding types (see CBindingWrapping.h).
336 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
338 } // End llvm namespace