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-c/Types.h"
18 #include "llvm/ADT/Twine.h"
19 #include "llvm/ADT/ilist.h"
20 #include "llvm/ADT/ilist_node.h"
21 #include "llvm/ADT/iterator.h"
22 #include "llvm/ADT/iterator_range.h"
23 #include "llvm/IR/Instruction.h"
24 #include "llvm/IR/SymbolTableListTraits.h"
25 #include "llvm/IR/Value.h"
26 #include "llvm/Support/CBindingWrapping.h"
27 #include "llvm/Support/Casting.h"
28 #include "llvm/Support/Compiler.h"
42 class ValueSymbolTable;
44 /// \brief LLVM Basic Block Representation
46 /// This represents a single basic block in LLVM. A basic block is simply a
47 /// container of instructions that execute sequentially. Basic blocks are Values
48 /// because they are referenced by instructions such as branches and switch
49 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block
50 /// represents a label to which a branch can jump.
52 /// A well formed basic block is formed of a list of non-terminating
53 /// instructions followed by a single TerminatorInst instruction.
54 /// TerminatorInst's may not occur in the middle of basic blocks, and must
55 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to
56 /// occur because it may be useful in the intermediate stage of constructing or
57 /// modifying a program. However, the verifier will ensure that basic blocks
58 /// are "well formed".
59 class BasicBlock final : public Value, // Basic blocks are data objects also
60 public ilist_node_with_parent<BasicBlock, Function> {
62 using InstListType = SymbolTableList<Instruction>;
65 friend class BlockAddress;
66 friend class SymbolTableListTraits<BasicBlock>;
68 InstListType InstList;
71 void setParent(Function *parent);
73 /// \brief Constructor.
75 /// If the function parameter is specified, the basic block is automatically
76 /// inserted at either the end of the function (if InsertBefore is null), or
77 /// before the specified basic block.
78 explicit BasicBlock(LLVMContext &C, const Twine &Name = "",
79 Function *Parent = nullptr,
80 BasicBlock *InsertBefore = nullptr);
83 BasicBlock(const BasicBlock &) = delete;
84 BasicBlock &operator=(const BasicBlock &) = delete;
87 /// \brief Get the context in which this basic block lives.
88 LLVMContext &getContext() const;
90 /// Instruction iterators...
91 using iterator = InstListType::iterator;
92 using const_iterator = InstListType::const_iterator;
93 using reverse_iterator = InstListType::reverse_iterator;
94 using const_reverse_iterator = InstListType::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);
107 /// \brief Return the enclosing method, or null if none.
108 const Function *getParent() const { return Parent; }
109 Function *getParent() { return Parent; }
111 /// \brief Return the module owning the function this basic block belongs to,
112 /// or nullptr it the function does not have a module.
114 /// Note: this is undefined behavior if the block does not have a parent.
115 const Module *getModule() const;
116 Module *getModule() {
117 return const_cast<Module *>(
118 static_cast<const BasicBlock *>(this)->getModule());
121 /// \brief Returns the terminator instruction if the block is well formed or
122 /// null if the block is not well formed.
123 const TerminatorInst *getTerminator() const LLVM_READONLY;
124 TerminatorInst *getTerminator() {
125 return const_cast<TerminatorInst *>(
126 static_cast<const BasicBlock *>(this)->getTerminator());
129 /// \brief Returns the call instruction calling @llvm.experimental.deoptimize
130 /// prior to the terminating return instruction of this basic block, if such a
131 /// call is present. Otherwise, returns null.
132 const CallInst *getTerminatingDeoptimizeCall() const;
133 CallInst *getTerminatingDeoptimizeCall() {
134 return const_cast<CallInst *>(
135 static_cast<const BasicBlock *>(this)->getTerminatingDeoptimizeCall());
138 /// \brief Returns the call instruction marked 'musttail' prior to the
139 /// terminating return instruction of this basic block, if such a call is
140 /// present. Otherwise, returns null.
141 const CallInst *getTerminatingMustTailCall() const;
142 CallInst *getTerminatingMustTailCall() {
143 return const_cast<CallInst *>(
144 static_cast<const BasicBlock *>(this)->getTerminatingMustTailCall());
147 /// \brief Returns a pointer to the first instruction in this block that is
148 /// not a PHINode instruction.
150 /// When adding instructions to the beginning of the basic block, they should
151 /// be added before the returned value, not before the first instruction,
152 /// which might be PHI. Returns 0 is there's no non-PHI instruction.
153 const Instruction* getFirstNonPHI() const;
154 Instruction* getFirstNonPHI() {
155 return const_cast<Instruction *>(
156 static_cast<const BasicBlock *>(this)->getFirstNonPHI());
159 /// \brief Returns a pointer to the first instruction in this block that is not
160 /// a PHINode or a debug intrinsic.
161 const Instruction* getFirstNonPHIOrDbg() const;
162 Instruction* getFirstNonPHIOrDbg() {
163 return const_cast<Instruction *>(
164 static_cast<const BasicBlock *>(this)->getFirstNonPHIOrDbg());
167 /// \brief Returns a pointer to the first instruction in this block that is not
168 /// a PHINode, a debug intrinsic, or a lifetime intrinsic.
169 const Instruction* getFirstNonPHIOrDbgOrLifetime() const;
170 Instruction* getFirstNonPHIOrDbgOrLifetime() {
171 return const_cast<Instruction *>(
172 static_cast<const BasicBlock *>(this)->getFirstNonPHIOrDbgOrLifetime());
175 /// \brief Returns an iterator to the first instruction in this block that is
176 /// suitable for inserting a non-PHI instruction.
178 /// In particular, it skips all PHIs and LandingPad instructions.
179 const_iterator getFirstInsertionPt() const;
180 iterator getFirstInsertionPt() {
181 return static_cast<const BasicBlock *>(this)
182 ->getFirstInsertionPt().getNonConst();
185 /// \brief Unlink 'this' from the containing function, but do not delete it.
186 void removeFromParent();
188 /// \brief Unlink 'this' from the containing function and delete it.
190 // \returns an iterator pointing to the element after the erased one.
191 SymbolTableList<BasicBlock>::iterator eraseFromParent();
193 /// \brief Unlink this basic block from its current function and insert it
194 /// into the function that \p MovePos lives in, right before \p MovePos.
195 void moveBefore(BasicBlock *MovePos);
197 /// \brief Unlink this basic block from its current function and insert it
198 /// right after \p MovePos in the function \p MovePos lives in.
199 void moveAfter(BasicBlock *MovePos);
201 /// \brief Insert unlinked basic block into a function.
203 /// Inserts an unlinked basic block into \c Parent. If \c InsertBefore is
204 /// provided, inserts before that basic block, otherwise inserts at the end.
206 /// \pre \a getParent() is \c nullptr.
207 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr);
209 /// \brief Return the predecessor of this block if it has a single predecessor
210 /// block. Otherwise return a null pointer.
211 const BasicBlock *getSinglePredecessor() const;
212 BasicBlock *getSinglePredecessor() {
213 return const_cast<BasicBlock *>(
214 static_cast<const BasicBlock *>(this)->getSinglePredecessor());
217 /// \brief Return the predecessor of this block if it has a unique predecessor
218 /// block. Otherwise return a null pointer.
220 /// Note that unique predecessor doesn't mean single edge, there can be
221 /// multiple edges from the unique predecessor to this block (for example a
222 /// switch statement with multiple cases having the same destination).
223 const BasicBlock *getUniquePredecessor() const;
224 BasicBlock *getUniquePredecessor() {
225 return const_cast<BasicBlock *>(
226 static_cast<const BasicBlock *>(this)->getUniquePredecessor());
229 /// \brief Return the successor of this block if it has a single successor.
230 /// Otherwise return a null pointer.
232 /// This method is analogous to getSinglePredecessor above.
233 const BasicBlock *getSingleSuccessor() const;
234 BasicBlock *getSingleSuccessor() {
235 return const_cast<BasicBlock *>(
236 static_cast<const BasicBlock *>(this)->getSingleSuccessor());
239 /// \brief Return the successor of this block if it has a unique successor.
240 /// Otherwise return a null pointer.
242 /// This method is analogous to getUniquePredecessor above.
243 const BasicBlock *getUniqueSuccessor() const;
244 BasicBlock *getUniqueSuccessor() {
245 return const_cast<BasicBlock *>(
246 static_cast<const BasicBlock *>(this)->getUniqueSuccessor());
249 //===--------------------------------------------------------------------===//
250 /// Instruction iterator methods
252 inline iterator begin() { return InstList.begin(); }
253 inline const_iterator begin() const { return InstList.begin(); }
254 inline iterator end () { return InstList.end(); }
255 inline const_iterator end () const { return InstList.end(); }
257 inline reverse_iterator rbegin() { return InstList.rbegin(); }
258 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); }
259 inline reverse_iterator rend () { return InstList.rend(); }
260 inline const_reverse_iterator rend () const { return InstList.rend(); }
262 inline size_t size() const { return InstList.size(); }
263 inline bool empty() const { return InstList.empty(); }
264 inline const Instruction &front() const { return InstList.front(); }
265 inline Instruction &front() { return InstList.front(); }
266 inline const Instruction &back() const { return InstList.back(); }
267 inline Instruction &back() { return InstList.back(); }
269 /// Iterator to walk just the phi nodes in the basic block.
270 template <typename PHINodeT = PHINode, typename BBIteratorT = iterator>
271 class phi_iterator_impl
272 : public iterator_facade_base<phi_iterator_impl<PHINodeT, BBIteratorT>,
273 std::forward_iterator_tag, PHINodeT> {
278 phi_iterator_impl(PHINodeT *PN) : PN(PN) {}
281 // Allow default construction to build variables, but this doesn't build
282 // a useful iterator.
283 phi_iterator_impl() = default;
285 // Allow conversion between instantiations where valid.
286 template <typename PHINodeU, typename BBIteratorU>
287 phi_iterator_impl(const phi_iterator_impl<PHINodeU, BBIteratorU> &Arg)
290 bool operator==(const phi_iterator_impl &Arg) const { return PN == Arg.PN; }
292 PHINodeT &operator*() const { return *PN; }
294 using phi_iterator_impl::iterator_facade_base::operator++;
295 phi_iterator_impl &operator++() {
296 assert(PN && "Cannot increment the end iterator!");
297 PN = dyn_cast<PHINodeT>(std::next(BBIteratorT(PN)));
301 using phi_iterator = phi_iterator_impl<>;
302 using const_phi_iterator =
303 phi_iterator_impl<const PHINode, BasicBlock::const_iterator>;
305 /// Returns a range that iterates over the phis in the basic block.
307 /// Note that this cannot be used with basic blocks that have no terminator.
308 iterator_range<const_phi_iterator> phis() const {
309 return const_cast<BasicBlock *>(this)->phis();
311 iterator_range<phi_iterator> phis();
313 /// \brief Return the underlying instruction list container.
315 /// Currently you need to access the underlying instruction list container
316 /// directly if you want to modify it.
317 const InstListType &getInstList() const { return InstList; }
318 InstListType &getInstList() { return InstList; }
320 /// \brief Returns a pointer to a member of the instruction list.
321 static InstListType BasicBlock::*getSublistAccess(Instruction*) {
322 return &BasicBlock::InstList;
325 /// \brief Returns a pointer to the symbol table if one exists.
326 ValueSymbolTable *getValueSymbolTable();
328 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
329 static bool classof(const Value *V) {
330 return V->getValueID() == Value::BasicBlockVal;
333 /// \brief Cause all subinstructions to "let go" of all the references that
334 /// said subinstructions are maintaining.
336 /// This allows one to 'delete' a whole class at a time, even though there may
337 /// be circular references... first all references are dropped, and all use
338 /// counts go to zero. Then everything is delete'd for real. Note that no
339 /// operations are valid on an object that has "dropped all references",
340 /// except operator delete.
341 void dropAllReferences();
343 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer
344 /// able to reach it.
346 /// This is actually not used to update the Predecessor list, but is actually
347 /// used to update the PHI nodes that reside in the block. Note that this
348 /// should be called while the predecessor still refers to this block.
349 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
351 bool canSplitPredecessors() const;
353 /// \brief Split the basic block into two basic blocks at the specified
356 /// Note that all instructions BEFORE the specified iterator stay as part of
357 /// the original basic block, an unconditional branch is added to the original
358 /// BB, and the rest of the instructions in the BB are moved to the new BB,
359 /// including the old terminator. The newly formed BasicBlock is returned.
360 /// This function invalidates the specified iterator.
362 /// Note that this only works on well formed basic blocks (must have a
363 /// terminator), and 'I' must not be the end of instruction list (which would
364 /// cause a degenerate basic block to be formed, having a terminator inside of
365 /// the basic block).
367 /// Also note that this doesn't preserve any passes. To split blocks while
368 /// keeping loop information consistent, use the SplitBlock utility function.
369 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = "");
370 BasicBlock *splitBasicBlock(Instruction *I, const Twine &BBName = "") {
371 return splitBasicBlock(I->getIterator(), BBName);
374 /// \brief Returns true if there are any uses of this basic block other than
375 /// direct branches, switches, etc. to it.
376 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
378 /// \brief Update all phi nodes in this basic block's successors to refer to
379 /// basic block \p New instead of to it.
380 void replaceSuccessorsPhiUsesWith(BasicBlock *New);
382 /// \brief Return true if this basic block is an exception handling block.
383 bool isEHPad() const { return getFirstNonPHI()->isEHPad(); }
385 /// \brief Return true if this basic block is a landing pad.
387 /// Being a ``landing pad'' means that the basic block is the destination of
388 /// the 'unwind' edge of an invoke instruction.
389 bool isLandingPad() const;
391 /// \brief Return the landingpad instruction associated with the landing pad.
392 const LandingPadInst *getLandingPadInst() const;
393 LandingPadInst *getLandingPadInst() {
394 return const_cast<LandingPadInst *>(
395 static_cast<const BasicBlock *>(this)->getLandingPadInst());
398 /// \brief Return true if it is legal to hoist instructions into this block.
399 bool isLegalToHoistInto() const;
402 /// \brief Increment the internal refcount of the number of BlockAddresses
403 /// referencing this BasicBlock by \p Amt.
405 /// This is almost always 0, sometimes one possibly, but almost never 2, and
406 /// inconceivably 3 or more.
407 void AdjustBlockAddressRefCount(int Amt) {
408 setValueSubclassData(getSubclassDataFromValue()+Amt);
409 assert((int)(signed char)getSubclassDataFromValue() >= 0 &&
410 "Refcount wrap-around");
413 /// \brief Shadow Value::setValueSubclassData with a private forwarding method
414 /// so that any future subclasses cannot accidentally use it.
415 void setValueSubclassData(unsigned short D) {
416 Value::setValueSubclassData(D);
420 // Create wrappers for C Binding types (see CBindingWrapping.h).
421 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef)
423 } // end namespace llvm
425 #endif // LLVM_IR_BASICBLOCK_H