1 //===- llvm/BasicBlock.h - Represent a basic block in the VM ----*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file contains the declaration of the BasicBlock class. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_IR_BASICBLOCK_H 15 #define LLVM_IR_BASICBLOCK_H 16 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" 29 #include <cassert> 30 #include <cstddef> 31 #include <iterator> 32 33 namespace llvm { 34 35 class CallInst; 36 class Function; 37 class LandingPadInst; 38 class LLVMContext; 39 class Module; 40 class PHINode; 41 class TerminatorInst; 42 class ValueSymbolTable; 43 44 /// \brief LLVM Basic Block Representation 45 /// 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. 51 /// 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> { 61 public: 62 using InstListType = SymbolTableList<Instruction>; 63 64 private: 65 friend class BlockAddress; 66 friend class SymbolTableListTraits<BasicBlock>; 67 68 InstListType InstList; 69 Function *Parent; 70 71 void setParent(Function *parent); 72 73 /// \brief Constructor. 74 /// 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); 81 82 public: 83 BasicBlock(const BasicBlock &) = delete; 84 BasicBlock &operator=(const BasicBlock &) = delete; 85 ~BasicBlock(); 86 87 /// \brief Get the context in which this basic block lives. 88 LLVMContext &getContext() const; 89 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; 95 96 /// \brief Creates a new BasicBlock. 97 /// 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); 105 } 106 107 /// \brief Return the enclosing method, or null if none. 108 const Function *getParent() const { return Parent; } 109 Function *getParent() { return Parent; } 110 111 /// \brief Return the module owning the function this basic block belongs to, 112 /// or nullptr it the function does not have a module. 113 /// 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()); 119 } 120 121 /// \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()); 127 } 128 129 /// \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()); 136 } 137 138 /// \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()); 145 } 146 147 /// \brief Returns a pointer to the first instruction in this block that is 148 /// not a PHINode instruction. 149 /// 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()); 157 } 158 159 /// \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()); 165 } 166 167 /// \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()); 173 } 174 175 /// \brief Returns an iterator to the first instruction in this block that is 176 /// suitable for inserting a non-PHI instruction. 177 /// 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(); 183 } 184 185 /// \brief Unlink 'this' from the containing function, but do not delete it. 186 void removeFromParent(); 187 188 /// \brief Unlink 'this' from the containing function and delete it. 189 /// 190 // \returns an iterator pointing to the element after the erased one. 191 SymbolTableList<BasicBlock>::iterator eraseFromParent(); 192 193 /// \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); 196 197 /// \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); 200 201 /// \brief Insert unlinked basic block into a function. 202 /// 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. 205 /// 206 /// \pre \a getParent() is \c nullptr. 207 void insertInto(Function *Parent, BasicBlock *InsertBefore = nullptr); 208 209 /// \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()); 215 } 216 217 /// \brief Return the predecessor of this block if it has a unique predecessor 218 /// block. Otherwise return a null pointer. 219 /// 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()); 227 } 228 229 /// \brief Return the successor of this block if it has a single successor. 230 /// Otherwise return a null pointer. 231 /// 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()); 237 } 238 239 /// \brief Return the successor of this block if it has a unique successor. 240 /// Otherwise return a null pointer. 241 /// 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()); 247 } 248 249 //===--------------------------------------------------------------------===// 250 /// Instruction iterator methods 251 /// 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(); } 256 257 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(); } 261 262 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(); } 268 269 /// 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> { 274 friend BasicBlock; 275 276 PHINodeT *PN; 277 278 phi_iterator_impl(PHINodeT *PN) : PN(PN) {} 279 280 public: 281 // Allow default construction to build variables, but this doesn't build 282 // a useful iterator. 283 phi_iterator_impl() = default; 284 285 // Allow conversion between instantiations where valid. 286 template <typename PHINodeU, typename BBIteratorU> 287 phi_iterator_impl(const phi_iterator_impl<PHINodeU, BBIteratorU> &Arg) 288 : PN(Arg.PN) {} 289 290 bool operator==(const phi_iterator_impl &Arg) const { return PN == Arg.PN; } 291 292 PHINodeT &operator*() const { return *PN; } 293 294 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))); 298 return *this; 299 } 300 }; 301 using phi_iterator = phi_iterator_impl<>; 302 using const_phi_iterator = 303 phi_iterator_impl<const PHINode, BasicBlock::const_iterator>; 304 305 /// Returns a range that iterates over the phis in the basic block. 306 /// 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(); 310 } 311 iterator_range<phi_iterator> phis(); 312 313 /// \brief Return the underlying instruction list container. 314 /// 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; } 319 320 /// \brief Returns a pointer to a member of the instruction list. 321 static InstListType BasicBlock::*getSublistAccess(Instruction*) { 322 return &BasicBlock::InstList; 323 } 324 325 /// \brief Returns a pointer to the symbol table if one exists. 326 ValueSymbolTable *getValueSymbolTable(); 327 328 /// \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; 331 } 332 333 /// \brief Cause all subinstructions to "let go" of all the references that 334 /// said subinstructions are maintaining. 335 /// 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(); 342 343 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer 344 /// able to reach it. 345 /// 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); 350 351 bool canSplitPredecessors() const; 352 353 /// \brief Split the basic block into two basic blocks at the specified 354 /// instruction. 355 /// 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. 361 /// 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). 366 /// 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); 372 } 373 374 /// \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; } 377 378 /// \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); 381 382 /// \brief Return true if this basic block is an exception handling block. 383 bool isEHPad() const { return getFirstNonPHI()->isEHPad(); } 384 385 /// \brief Return true if this basic block is a landing pad. 386 /// 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; 390 391 /// \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()); 396 } 397 398 /// \brief Return true if it is legal to hoist instructions into this block. 399 bool isLegalToHoistInto() const; 400 401 private: 402 /// \brief Increment the internal refcount of the number of BlockAddresses 403 /// referencing this BasicBlock by \p Amt. 404 /// 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"); 411 } 412 413 /// \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); 417 } 418 }; 419 420 // Create wrappers for C Binding types (see CBindingWrapping.h). 421 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef) 422 423 } // end namespace llvm 424 425 #endif // LLVM_IR_BASICBLOCK_H 426
