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/ilist.h"
18 #include "llvm/ADT/ilist_node.h"
19 #include "llvm/ADT/Twine.h"
20 #include "llvm/IR/Instruction.h"
21 #include "llvm/IR/SymbolTableListTraits.h"
22 #include "llvm/IR/Value.h"
23 #include "llvm/Support/CBindingWrapping.h"
24 #include "llvm/Support/Compiler.h"
25 #include "llvm-c/Types.h"
37 class ValueSymbolTable;
39 /// \brief LLVM Basic Block Representation
41 /// This represents a single basic block in LLVM. A basic block is simply a
42 /// container of instructions that execute sequentially. Basic blocks are Values
43 /// because they are referenced by instructions such as branches and switch
44 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
45 /// represents a label to which a branch can jump.
47 /// A well formed basic block is formed of a list of non-terminating
48 /// instructions followed by a single TerminatorInst instruction.
49 /// TerminatorInst's may not occur in the middle of basic blocks, and must
50 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
51 /// occur because it may be useful in the intermediate stage of constructing or
52 /// modifying a program. However, the verifier will ensure that basic blocks
53 /// are "well formed".
54 class BasicBlock : public Value, // Basic blocks are data objects also
55 public ilist_node_with_parent<BasicBlock, Function> {
57 using InstListType = SymbolTableList<Instruction>;
60 friend class BlockAddress;
61 friend class SymbolTableListTraits<BasicBlock>;
63 InstListType InstList;
66 void setParent(Function *parent);
68 /// \brief Constructor.
70 /// If the function parameter is specified, the basic block is automatically
71 /// inserted at either the end of the function (if InsertBefore is null), or
72 /// before the specified basic block.
73 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
74 Function *Parent = nullptr,
75 BasicBlock *InsertBefore = nullptr);
78 BasicBlock(const BasicBlock &) = delete;
79 BasicBlock &operator=(const BasicBlock &) = delete;
80 ~BasicBlock() override;
82 /// \brief Get the context in which this basic block lives.
83 LLVMContext &getContext() const;
85 /// Instruction iterators...
86 using iterator = InstListType::iterator;
87 using const_iterator = InstListType::const_iterator;
88 using reverse_iterator = InstListType::reverse_iterator;
89 using const_reverse_iterator = InstListType::const_reverse_iterator;
91 /// \brief Creates a new BasicBlock.
93 /// If the Parent parameter is specified, the basic block is automatically
94 /// inserted at either the end of the function (if InsertBefore is 0), or
95 /// before the specified basic block.
96 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "",
97 Function *Parent = nullptr,
98 BasicBlock *InsertBefore = nullptr) {
99 return new BasicBlock(Context, Name, Parent, InsertBefore);
102 /// \brief Return the enclosing method, or null if none.
103 const Function *getParent() const { return Parent; }
104 Function *getParent() { return Parent; }
106 /// \brief Return the module owning the function this basic block belongs to,
107 /// or nullptr it the function does not have a module.
109 /// Note: this is undefined behavior if the block does not have a parent.
110 const Module *getModule() const;
111 Module *getModule() {
112 return const_cast<Module *>(
113 static_cast<const BasicBlock *>(this)->getModule());
116 /// \brief Returns the terminator instruction if the block is well formed or
117 /// null if the block is not well formed.
118 const TerminatorInst *getTerminator() const LLVM_READONLY;
119 TerminatorInst *getTerminator() {
120 return const_cast<TerminatorInst *>(
121 static_cast<const BasicBlock *>(this)->getTerminator());
124 /// \brief Returns the call instruction calling @llvm.experimental.deoptimize
125 /// prior to the terminating return instruction of this basic block, if such a
126 /// call is present. Otherwise, returns null.
127 const CallInst *getTerminatingDeoptimizeCall() const;
128 CallInst *getTerminatingDeoptimizeCall() {
129 return const_cast<CallInst *>(
130 static_cast<const BasicBlock *>(this)->getTerminatingDeoptimizeCall());
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 const CallInst *getTerminatingMustTailCall() const;
137 CallInst *getTerminatingMustTailCall() {
138 return const_cast<CallInst *>(
139 static_cast<const BasicBlock *>(this)->getTerminatingMustTailCall());
142 /// \brief Returns a pointer to the first instruction in this block that is
143 /// not a PHINode instruction.
145 /// When adding instructions to the beginning of the basic block, they should
146 /// be added before the returned value, not before the first instruction,
147 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
148 const Instruction* getFirstNonPHI() const;
149 Instruction* getFirstNonPHI() {
150 return const_cast<Instruction *>(
151 static_cast<const BasicBlock *>(this)->getFirstNonPHI());
154 /// \brief Returns a pointer to the first instruction in this block that is not
155 /// a PHINode or a debug intrinsic.
156 const Instruction* getFirstNonPHIOrDbg() const;
157 Instruction* getFirstNonPHIOrDbg() {
158 return const_cast<Instruction *>(
159 static_cast<const BasicBlock *>(this)->getFirstNonPHIOrDbg());
162 /// \brief Returns a pointer to the first instruction in this block that is not
163 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
164 const Instruction* getFirstNonPHIOrDbgOrLifetime() const;
165 Instruction* getFirstNonPHIOrDbgOrLifetime() {
166 return const_cast<Instruction *>(
167 static_cast<const BasicBlock *>(this)->getFirstNonPHIOrDbgOrLifetime());
170 /// \brief Returns an iterator to the first instruction in this block that is
171 /// suitable for inserting a non-PHI instruction.
173 /// In particular, it skips all PHIs and LandingPad instructions.
174 const_iterator getFirstInsertionPt() const;
175 iterator getFirstInsertionPt() {
176 return static_cast<const BasicBlock *>(this)
177 ->getFirstInsertionPt().getNonConst();
180 /// \brief Unlink 'this' from the containing function, but do not delete it.
181 void removeFromParent();
183 /// \brief Unlink 'this' from the containing function and delete it.
185 // \returns an iterator pointing to the element after the erased one.
186 SymbolTableList<BasicBlock>::iterator eraseFromParent();
188 /// \brief Unlink this basic block from its current function and insert it
189 /// into the function that \p MovePos lives in, right before \p MovePos.
190 void moveBefore(BasicBlock *MovePos);
192 /// \brief Unlink this basic block from its current function and insert it
193 /// right after \p MovePos in the function \p MovePos lives in.
194 void moveAfter(BasicBlock *MovePos);
196 /// \brief Insert unlinked basic block into a function.
198 /// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
199 /// provided, inserts before that basic block, otherwise inserts at the end.
201 /// \pre \a getParent() is \c nullptr.
202 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
204 /// \brief Return the predecessor of this block if it has a single predecessor
205 /// block. Otherwise return a null pointer.
206 const BasicBlock *getSinglePredecessor() const;
207 BasicBlock *getSinglePredecessor() {
208 return const_cast<BasicBlock *>(
209 static_cast<const BasicBlock *>(this)->getSinglePredecessor());
212 /// \brief Return the predecessor of this block if it has a unique predecessor
213 /// block. Otherwise return a null pointer.
215 /// Note that unique predecessor doesn't mean single edge, there can be
216 /// multiple edges from the unique predecessor to this block (for example a
217 /// switch statement with multiple cases having the same destination).
218 const BasicBlock *getUniquePredecessor() const;
219 BasicBlock *getUniquePredecessor() {
220 return const_cast<BasicBlock *>(
221 static_cast<const BasicBlock *>(this)->getUniquePredecessor());
224 /// \brief Return the successor of this block if it has a single successor.
225 /// Otherwise return a null pointer.
227 /// This method is analogous to getSinglePredecessor above.
228 const BasicBlock *getSingleSuccessor() const;
229 BasicBlock *getSingleSuccessor() {
230 return const_cast<BasicBlock *>(
231 static_cast<const BasicBlock *>(this)->getSingleSuccessor());
234 /// \brief Return the successor of this block if it has a unique successor.
235 /// Otherwise return a null pointer.
237 /// This method is analogous to getUniquePredecessor above.
238 const BasicBlock *getUniqueSuccessor() const;
239 BasicBlock *getUniqueSuccessor() {
240 return const_cast<BasicBlock *>(
241 static_cast<const BasicBlock *>(this)->getUniqueSuccessor());
244 //===--------------------------------------------------------------------===//
245 /// Instruction iterator methods
247 inline iterator begin() { return InstList.begin(); }
248 inline const_iterator begin() const { return InstList.begin(); }
249 inline iterator end () { return InstList.end(); }
250 inline const_iterator end () const { return InstList.end(); }
252 inline reverse_iterator rbegin() { return InstList.rbegin(); }
253 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
254 inline reverse_iterator rend () { return InstList.rend(); }
255 inline const_reverse_iterator rend () const { return InstList.rend(); }
257 inline size_t size() const { return InstList.size(); }
258 inline bool empty() const { return InstList.empty(); }
259 inline const Instruction &front() const { return InstList.front(); }
260 inline Instruction &front() { return InstList.front(); }
261 inline const Instruction &back() const { return InstList.back(); }
262 inline Instruction &back() { return InstList.back(); }
264 /// \brief Return the underlying instruction list container.
266 /// Currently you need to access the underlying instruction list container
267 /// directly if you want to modify it.
268 const InstListType &getInstList() const { return InstList; }
269 InstListType &getInstList() { return InstList; }
271 /// \brief Returns a pointer to a member of the instruction list.
272 static InstListType BasicBlock::*getSublistAccess(Instruction*) {
273 return &BasicBlock::InstList;
276 /// \brief Returns a pointer to the symbol table if one exists.
277 ValueSymbolTable *getValueSymbolTable();
279 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
280 static inline bool classof(const Value *V) {
281 return V->getValueID() == Value::BasicBlockVal;
284 /// \brief Cause all subinstructions to "let go" of all the references that
285 /// said subinstructions are maintaining.
287 /// This allows one to 'delete' a whole class at a time, even though there may
288 /// be circular references... first all references are dropped, and all use
289 /// counts go to zero. Then everything is delete'd for real. Note that no
290 /// operations are valid on an object that has "dropped all references",
291 /// except operator delete.
292 void dropAllReferences();
294 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
295 /// able to reach it.
297 /// This is actually not used to update the Predecessor list, but is actually
298 /// used to update the PHI nodes that reside in the block. Note that this
299 /// should be called while the predecessor still refers to this block.
300 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
302 bool canSplitPredecessors() const;
304 /// \brief Split the basic block into two basic blocks at the specified
307 /// Note that all instructions BEFORE the specified iterator stay as part of
308 /// the original basic block, an unconditional branch is added to the original
309 /// BB, and the rest of the instructions in the BB are moved to the new BB,
310 /// including the old terminator. The newly formed BasicBlock is returned.
311 /// This function invalidates the specified iterator.
313 /// Note that this only works on well formed basic blocks (must have a
314 /// terminator), and 'I' must not be the end of instruction list (which would
315 /// cause a degenerate basic block to be formed, having a terminator inside of
316 /// the basic block).
318 /// Also note that this doesn't preserve any passes. To split blocks while
319 /// keeping loop information consistent, use the SplitBlock utility function.
320 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
321 BasicBlock *splitBasicBlock(Instruction *I, const Twine &BBName = "") {
322 return splitBasicBlock(I->getIterator(), BBName);
325 /// \brief Returns true if there are any uses of this basic block other than
326 /// direct branches, switches, etc. to it.
327 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
329 /// \brief Update all phi nodes in this basic block's successors to refer to
330 /// basic block \p New instead of to it.
331 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
333 /// \brief Return true if this basic block is an exception handling block.
334 bool isEHPad() const { return getFirstNonPHI()->isEHPad(); }
336 /// \brief Return true if this basic block is a landing pad.
338 /// Being a ``landing pad'' means that the basic block is the destination of
339 /// the 'unwind' edge of an invoke instruction.
340 bool isLandingPad() const;
342 /// \brief Return the landingpad instruction associated with the landing pad.
343 const LandingPadInst *getLandingPadInst() const;
344 LandingPadInst *getLandingPadInst() {
345 return const_cast<LandingPadInst *>(
346 static_cast<const BasicBlock *>(this)->getLandingPadInst());
350 /// \brief Increment the internal refcount of the number of BlockAddresses
351 /// referencing this BasicBlock by \p Amt.
353 /// This is almost always 0, sometimes one possibly, but almost never 2, and
354 /// inconceivably 3 or more.
355 void AdjustBlockAddressRefCount(int Amt) {
356 setValueSubclassData(getSubclassDataFromValue()+Amt);
357 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
358 "Refcount wrap-around");
361 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
362 /// so that any future subclasses cannot accidentally use it.
363 void setValueSubclassData(unsigned short D) {
364 Value::setValueSubclassData(D);
368 // Create wrappers for C Binding types (see CBindingWrapping.h).
369 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
371 } // end namespace llvm
373 #endif // LLVM_IR_BASICBLOCK_H