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 = 0, BasicBlock *InsertBefore = 0); 94 public: 95 /// \brief Get the context in which this basic block lives. 96 LLVMContext &getContext() const; 97 98 /// Instruction iterators... 99 typedef InstListType::iterator iterator; 100 typedef InstListType::const_iterator const_iterator; 101 typedef InstListType::reverse_iterator reverse_iterator; 102 typedef InstListType::const_reverse_iterator const_reverse_iterator; 103 104 /// \brief Creates a new BasicBlock. 105 /// 106 /// If the Parent parameter is specified, the basic block is automatically 107 /// inserted at either the end of the function (if InsertBefore is 0), or 108 /// before the specified basic block. 109 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "", 110 Function *Parent = 0,BasicBlock *InsertBefore = 0) { 111 return new BasicBlock(Context, Name, Parent, InsertBefore); 112 } 113 ~BasicBlock(); 114 115 /// \brief Return the enclosing method, or null if none. 116 const Function *getParent() const { return Parent; } 117 Function *getParent() { return Parent; } 118 119 /// \brief Returns the terminator instruction if the block is well formed or 120 /// null if the block is not well formed. 121 TerminatorInst *getTerminator(); 122 const TerminatorInst *getTerminator() const; 123 124 /// \brief Returns a pointer to the first instruction in this block that is 125 /// not a PHINode instruction. 126 /// 127 /// When adding instructions to the beginning of the basic block, they should 128 /// be added before the returned value, not before the first instruction, 129 /// which might be PHI. Returns 0 is there's no non-PHI instruction. 130 Instruction* getFirstNonPHI(); 131 const Instruction* getFirstNonPHI() const { 132 return const_cast<BasicBlock*>(this)->getFirstNonPHI(); 133 } 134 135 /// \brief Returns a pointer to the first instruction in this block that is not 136 /// a PHINode or a debug intrinsic. 137 Instruction* getFirstNonPHIOrDbg(); 138 const Instruction* getFirstNonPHIOrDbg() const { 139 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg(); 140 } 141 142 /// \brief Returns a pointer to the first instruction in this block that is not 143 /// a PHINode, a debug intrinsic, or a lifetime intrinsic. 144 Instruction* getFirstNonPHIOrDbgOrLifetime(); 145 const Instruction* getFirstNonPHIOrDbgOrLifetime() const { 146 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime(); 147 } 148 149 /// \brief Returns an iterator to the first instruction in this block that is 150 /// suitable for inserting a non-PHI instruction. 151 /// 152 /// In particular, it skips all PHIs and LandingPad instructions. 153 iterator getFirstInsertionPt(); 154 const_iterator getFirstInsertionPt() const { 155 return const_cast<BasicBlock*>(this)->getFirstInsertionPt(); 156 } 157 158 /// \brief Unlink 'this' from the containing function, but do not delete it. 159 void removeFromParent(); 160 161 /// \brief Unlink 'this' from the containing function and delete it. 162 void eraseFromParent(); 163 164 /// \brief Unlink this basic block from its current function and insert it 165 /// into the function that \p MovePos lives in, right before \p MovePos. 166 void moveBefore(BasicBlock *MovePos); 167 168 /// \brief Unlink this basic block from its current function and insert it 169 /// right after \p MovePos in the function \p MovePos lives in. 170 void moveAfter(BasicBlock *MovePos); 171 172 173 /// \brief Return this block if it has a single predecessor block. Otherwise 174 /// return a null pointer. 175 BasicBlock *getSinglePredecessor(); 176 const BasicBlock *getSinglePredecessor() const { 177 return const_cast<BasicBlock*>(this)->getSinglePredecessor(); 178 } 179 180 /// \brief Return this block if it has a unique predecessor block. Otherwise return a null pointer. 181 /// 182 /// Note that unique predecessor doesn't mean single edge, there can be 183 /// multiple edges from the unique predecessor to this block (for example a 184 /// switch statement with multiple cases having the same destination). 185 BasicBlock *getUniquePredecessor(); 186 const BasicBlock *getUniquePredecessor() const { 187 return const_cast<BasicBlock*>(this)->getUniquePredecessor(); 188 } 189 190 //===--------------------------------------------------------------------===// 191 /// Instruction iterator methods 192 /// 193 inline iterator begin() { return InstList.begin(); } 194 inline const_iterator begin() const { return InstList.begin(); } 195 inline iterator end () { return InstList.end(); } 196 inline const_iterator end () const { return InstList.end(); } 197 198 inline reverse_iterator rbegin() { return InstList.rbegin(); } 199 inline const_reverse_iterator rbegin() const { return InstList.rbegin(); } 200 inline reverse_iterator rend () { return InstList.rend(); } 201 inline const_reverse_iterator rend () const { return InstList.rend(); } 202 203 inline size_t size() const { return InstList.size(); } 204 inline bool empty() const { return InstList.empty(); } 205 inline const Instruction &front() const { return InstList.front(); } 206 inline Instruction &front() { return InstList.front(); } 207 inline const Instruction &back() const { return InstList.back(); } 208 inline Instruction &back() { return InstList.back(); } 209 210 /// \brief Return the underlying instruction list container. 211 /// 212 /// Currently you need to access the underlying instruction list container 213 /// directly if you want to modify it. 214 const InstListType &getInstList() const { return InstList; } 215 InstListType &getInstList() { return InstList; } 216 217 /// \brief Returns a pointer to a member of the instruction list. 218 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) { 219 return &BasicBlock::InstList; 220 } 221 222 /// \brief Returns a pointer to the symbol table if one exists. 223 ValueSymbolTable *getValueSymbolTable(); 224 225 /// \brief Methods for support type inquiry through isa, cast, and dyn_cast. 226 static inline bool classof(const Value *V) { 227 return V->getValueID() == Value::BasicBlockVal; 228 } 229 230 /// \brief Cause all subinstructions to "let go" of all the references that 231 /// said subinstructions are maintaining. 232 /// 233 /// This allows one to 'delete' a whole class at a time, even though there may 234 /// be circular references... first all references are dropped, and all use 235 /// counts go to zero. Then everything is delete'd for real. Note that no 236 /// operations are valid on an object that has "dropped all references", 237 /// except operator delete. 238 void dropAllReferences(); 239 240 /// \brief Notify the BasicBlock that the predecessor \p Pred is no longer 241 /// able to reach it. 242 /// 243 /// This is actually not used to update the Predecessor list, but is actually 244 /// used to update the PHI nodes that reside in the block. Note that this 245 /// should be called while the predecessor still refers to this block. 246 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false); 247 248 /// \brief Split the basic block into two basic blocks at the specified 249 /// instruction. 250 /// 251 /// Note that all instructions BEFORE the specified iterator stay as part of 252 /// the original basic block, an unconditional branch is added to the original 253 /// BB, and the rest of the instructions in the BB are moved to the new BB, 254 /// including the old terminator. The newly formed BasicBlock is returned. 255 /// This function invalidates the specified iterator. 256 /// 257 /// Note that this only works on well formed basic blocks (must have a 258 /// terminator), and 'I' must not be the end of instruction list (which would 259 /// cause a degenerate basic block to be formed, having a terminator inside of 260 /// the basic block). 261 /// 262 /// Also note that this doesn't preserve any passes. To split blocks while 263 /// keeping loop information consistent, use the SplitBlock utility function. 264 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = ""); 265 266 /// \brief Returns true if there are any uses of this basic block other than 267 /// direct branches, switches, etc. to it. 268 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; } 269 270 /// \brief Update all phi nodes in this basic block's successors to refer to 271 /// basic block \p New instead of to it. 272 void replaceSuccessorsPhiUsesWith(BasicBlock *New); 273 274 /// \brief Return true if this basic block is a landing pad. 275 /// 276 /// Being a ``landing pad'' means that the basic block is the destination of 277 /// the 'unwind' edge of an invoke instruction. 278 bool isLandingPad() const; 279 280 /// \brief Return the landingpad instruction associated with the landing pad. 281 LandingPadInst *getLandingPadInst(); 282 const LandingPadInst *getLandingPadInst() const; 283 284 private: 285 /// \brief Increment the internal refcount of the number of BlockAddresses 286 /// referencing this BasicBlock by \p Amt. 287 /// 288 /// This is almost always 0, sometimes one possibly, but almost never 2, and 289 /// inconceivably 3 or more. 290 void AdjustBlockAddressRefCount(int Amt) { 291 setValueSubclassData(getSubclassDataFromValue()+Amt); 292 assert((int)(signed char)getSubclassDataFromValue() >= 0 && 293 "Refcount wrap-around"); 294 } 295 /// \brief Shadow Value::setValueSubclassData with a private forwarding method 296 /// so that any future subclasses cannot accidentally use it. 297 void setValueSubclassData(unsigned short D) { 298 Value::setValueSubclassData(D); 299 } 300 }; 301 302 // Create wrappers for C Binding types (see CBindingWrapping.h). 303 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(BasicBlock, LLVMBasicBlockRef) 304 305 } // End llvm namespace 306 307 #endif 308
