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/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" 23 24 namespace llvm { 25 26 class LandingPadInst; 27 class TerminatorInst; 28 class LLVMContext; 29 class BlockAddress; 30 31 template<> struct ilist_traits<Instruction> 32 : public SymbolTableListTraits<Instruction, BasicBlock> { 33 34 /// \brief Return a node that marks the end of a list. 35 /// 36 /// The sentinel is relative to this instance, so we use a non-static 37 /// method. 38 Instruction *createSentinel() const { 39 // Since i(p)lists always publicly derive from their corresponding traits, 40 // placing a data member in this class will augment the i(p)list. But since 41 // the NodeTy is expected to be publicly derive from ilist_node<NodeTy>, 42 // there is a legal viable downcast from it to NodeTy. We use this trick to 43 // superimpose an i(p)list with a "ghostly" NodeTy, which becomes the 44 // sentinel. Dereferencing the sentinel is forbidden (save the 45 // ilist_node<NodeTy>), so no one will ever notice the superposition. 46 return static_cast<Instruction*>(&Sentinel); 47 } 48 static void destroySentinel(Instruction*) {} 49 50 Instruction *provideInitialHead() const { return createSentinel(); } 51 Instruction *ensureHead(Instruction*) const { return createSentinel(); } 52 static void noteHead(Instruction*, Instruction*) {} 53 private: 54 mutable ilist_half_node<Instruction> Sentinel; 55 }; 56 57 /// \brief LLVM Basic Block Representation 58 /// 59 /// This represents a single basic block in LLVM. A basic block is simply a 60 /// container of instructions that execute sequentially. Basic blocks are Values 61 /// because they are referenced by instructions such as branches and switch 62 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block 63 /// represents a label to which a branch can jump. 64 /// 65 /// A well formed basic block is formed of a list of non-terminating 66 /// instructions followed by a single TerminatorInst instruction. 67 /// TerminatorInst's may not occur in the middle of basic blocks, and must 68 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to 69 /// occur because it may be useful in the intermediate stage of constructing or 70 /// modifying a program. However, the verifier will ensure that basic blocks 71 /// are "well formed". 72 class BasicBlock : public Value, // Basic blocks are data objects also 73 public ilist_node<BasicBlock> { 74 friend class BlockAddress; 75 public: 76 typedef iplist<Instruction> InstListType; 77 private: 78 InstListType InstList; 79 Function *Parent; 80 81 void setParent(Function *parent); 82 friend class SymbolTableListTraits<BasicBlock, Function>; 83 84 BasicBlock(const BasicBlock &) LLVM_DELETED_FUNCTION; 85 void operator=(const BasicBlock &) LLVM_DELETED_FUNCTION; 86 87 /// \brief Constructor. 88 /// 89 /// If the function parameter is specified, the basic block is automatically 90 /// inserted at either the end of the function (if InsertBefore is null), or 91 /// before the specified basic block. 92 explicit BasicBlock(LLVMContext &C, const Twine &Name = "", 93 Function *Parent = nullptr, 94 BasicBlock *InsertBefore = nullptr); 95 public: 96 /// \brief Get the context in which this basic block lives. 97 LLVMContext &getContext() const; 98 99 /// Instruction iterators... 100 typedef InstListType::iterator iterator; 101 typedef InstListType::const_iterator const_iterator; 102 typedef InstListType::reverse_iterator reverse_iterator; 103 typedef InstListType::const_reverse_iterator const_reverse_iterator; 104 105 /// \brief Creates a new BasicBlock. 106 /// 107 /// If the Parent parameter is specified, the basic block is automatically 108 /// inserted at either the end of the function (if InsertBefore is 0), or 109 /// before the specified basic block. 110 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "", 111 Function *Parent = nullptr, 112 BasicBlock *InsertBefore = nullptr) { 113 return new BasicBlock(Context, Name, Parent, InsertBefore); 114 } 115 ~BasicBlock(); 116 117 /// \brief Return the enclosing method, or null if none. 118 const Function *getParent() const { return Parent; } 119 Function *getParent() { return Parent; } 120 121 const DataLayout *getDataLayout() const; 122 123 /// \brief Returns the terminator instruction if the block is well formed or 124 /// null if the block is not well formed. 125 TerminatorInst *getTerminator(); 126 const TerminatorInst *getTerminator() const; 127 128 /// \brief Returns a pointer to the first instruction in this block that is 129 /// not a PHINode instruction. 130 /// 131 /// When adding instructions to the beginning of the basic block, they should 132 /// be added before the returned value, not before the first instruction, 133 /// which might be PHI. Returns 0 is there's no non-PHI instruction. 134 Instruction* getFirstNonPHI(); 135 const Instruction* getFirstNonPHI() const { 136 return const_cast<BasicBlock*>(this)->getFirstNonPHI(); 137 } 138 139 /// \brief Returns a pointer to the first instruction in this block that is not 140 /// a PHINode or a debug intrinsic. 141 Instruction* getFirstNonPHIOrDbg(); 142 const Instruction* getFirstNonPHIOrDbg() const { 143 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg(); 144 } 145 146 /// \brief Returns a pointer to the first instruction in this block that is not 147 /// a PHINode, a debug intrinsic, or a lifetime intrinsic. 148 Instruction* getFirstNonPHIOrDbgOrLifetime(); 149 const Instruction* getFirstNonPHIOrDbgOrLifetime() const { 150 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime(); 151 } 152 153 /// \brief Returns an iterator to the first instruction in this block that is 154 /// suitable for inserting a non-PHI instruction. 155 /// 156 /// In particular, it skips all PHIs and LandingPad instructions. 157 iterator getFirstInsertionPt(); 158 const_iterator getFirstInsertionPt() const { 159 return const_cast<BasicBlock*>(this)->getFirstInsertionPt(); 160 } 161 162 /// \brief Unlink 'this' from the containing function, but do not delete it. 163 void removeFromParent(); 164 165 /// \brief Unlink 'this' from the containing function and delete it. 166 void eraseFromParent(); 167 168 /// \brief Unlink this basic block from its current function and insert it 169 /// into the function that \p MovePos lives in, right before \p MovePos. 170 void moveBefore(BasicBlock *MovePos); 171 172 /// \brief Unlink this basic block from its current function and insert it 173 /// right after \p MovePos in the function \p MovePos lives in. 174 void moveAfter(BasicBlock *MovePos); 175 176 177 /// \brief Return the predecessor of this block if it has a single predecessor 178 /// block. Otherwise return a null pointer. 179 BasicBlock *getSinglePredecessor(); 180 const BasicBlock *getSinglePredecessor() const { 181 return const_cast<BasicBlock*>(this)->getSinglePredecessor(); 182 } 183 184 /// \brief Return the predecessor of this block if it has a unique predecessor 185 /// block. Otherwise return a null pointer. 186 /// 187 /// Note that unique predecessor doesn't mean single edge, there can be 188 /// multiple edges from the unique predecessor to this block (for example a 189 /// switch statement with multiple cases having the same destination). 190 BasicBlock *getUniquePredecessor(); 191 const BasicBlock *getUniquePredecessor() const { 192 return const_cast<BasicBlock*>(this)->getUniquePredecessor(); 193 } 194 195 //===--------------------------------------------------------------------===// 196 /// Instruction iterator methods 197 /// 198 inline iterator begin() { return InstList.begin(); } 199 inline const_iterator begin() const { return InstList.begin(); } 200 inline iterator end () { return InstList.end(); } 201 inline const_iterator end () const { return InstList.end(); } 202 203 inline reverse_iterator rbegin() { return InstList.rbegin(); } 204 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); } 205 inline reverse_iterator rend () { return InstList.rend(); } 206 inline const_reverse_iterator rend () const { return InstList.rend(); } 207 208 inline size_t size() const { return InstList.size(); } 209 inline bool empty() const { return InstList.empty(); } 210 inline const Instruction &front() const { return InstList.front(); } 211 inline Instruction &front() { return InstList.front(); } 212 inline const Instruction &back() const { return InstList.back(); } 213 inline Instruction &back() { return InstList.back(); } 214 215 /// \brief Return the underlying instruction list container. 216 /// 217 /// Currently you need to access the underlying instruction list container 218 /// directly if you want to modify it. 219 const InstListType &getInstList() const { return InstList; } 220 InstListType &getInstList() { return InstList; } 221 222 /// \brief Returns a pointer to a member of the instruction list. 223 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) { 224 return &BasicBlock::InstList; 225 } 226 227 /// \brief Returns a pointer to the symbol table if one exists. 228 ValueSymbolTable *getValueSymbolTable(); 229 230 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast. 231 static inline bool classof(const Value *V) { 232 return V->getValueID() == Value::BasicBlockVal; 233 } 234 235 /// \brief Cause all subinstructions to "let go" of all the references that 236 /// said subinstructions are maintaining. 237 /// 238 /// This allows one to 'delete' a whole class at a time, even though there may 239 /// be circular references... first all references are dropped, and all use 240 /// counts go to zero. Then everything is delete'd for real. Note that no 241 /// operations are valid on an object that has "dropped all references", 242 /// except operator delete. 243 void dropAllReferences(); 244 245 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer 246 /// able to reach it. 247 /// 248 /// This is actually not used to update the Predecessor list, but is actually 249 /// used to update the PHI nodes that reside in the block. Note that this 250 /// should be called while the predecessor still refers to this block. 251 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false); 252 253 /// \brief Split the basic block into two basic blocks at the specified 254 /// instruction. 255 /// 256 /// Note that all instructions BEFORE the specified iterator stay as part of 257 /// the original basic block, an unconditional branch is added to the original 258 /// BB, and the rest of the instructions in the BB are moved to the new BB, 259 /// including the old terminator. The newly formed BasicBlock is returned. 260 /// This function invalidates the specified iterator. 261 /// 262 /// Note that this only works on well formed basic blocks (must have a 263 /// terminator), and 'I' must not be the end of instruction list (which would 264 /// cause a degenerate basic block to be formed, having a terminator inside of 265 /// the basic block). 266 /// 267 /// Also note that this doesn't preserve any passes. To split blocks while 268 /// keeping loop information consistent, use the SplitBlock utility function. 269 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = ""); 270 271 /// \brief Returns true if there are any uses of this basic block other than 272 /// direct branches, switches, etc. to it. 273 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; } 274 275 /// \brief Update all phi nodes in this basic block's successors to refer to 276 /// basic block \p New instead of to it. 277 void replaceSuccessorsPhiUsesWith(BasicBlock *New); 278 279 /// \brief Return true if this basic block is a landing pad. 280 /// 281 /// Being a ``landing pad'' means that the basic block is the destination of 282 /// the 'unwind' edge of an invoke instruction. 283 bool isLandingPad() const; 284 285 /// \brief Return the landingpad instruction associated with the landing pad. 286 LandingPadInst *getLandingPadInst(); 287 const LandingPadInst *getLandingPadInst() const; 288 289 private: 290 /// \brief Increment the internal refcount of the number of BlockAddresses 291 /// referencing this BasicBlock by \p Amt. 292 /// 293 /// This is almost always 0, sometimes one possibly, but almost never 2, and 294 /// inconceivably 3 or more. 295 void AdjustBlockAddressRefCount(int Amt) { 296 setValueSubclassData(getSubclassDataFromValue()+Amt); 297 assert((int)(signed char)getSubclassDataFromValue() >= 0 && 298 "Refcount wrap-around"); 299 } 300 /// \brief Shadow Value::setValueSubclassData with a private forwarding method 301 /// so that any future subclasses cannot accidentally use it. 302 void setValueSubclassData(unsigned short D) { 303 Value::setValueSubclassData(D); 304 } 305 }; 306 307 // Create wrappers for C Binding types (see CBindingWrapping.h). 308 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef) 309 310 } // End llvm namespace 311 312 #endif 313
