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_BASICBLOCK_H 15 #define LLVM_BASICBLOCK_H 16 17 #include "llvm/Instruction.h" 18 #include "llvm/SymbolTableListTraits.h" 19 #include "llvm/ADT/ilist.h" 20 #include "llvm/ADT/Twine.h" 21 #include "llvm/Support/DataTypes.h" 22 23 namespace llvm { 24 25 class TerminatorInst; 26 class LLVMContext; 27 class BlockAddress; 28 29 template<> struct ilist_traits<Instruction> 30 : public SymbolTableListTraits<Instruction, BasicBlock> { 31 // createSentinel is used to get hold of a node that marks the end of 32 // the list... 33 // The sentinel is relative to this instance, so we use a non-static 34 // method. 35 Instruction *createSentinel() const { 36 // since i(p)lists always publicly derive from the corresponding 37 // traits, placing a data member in this class will augment i(p)list. 38 // But since the NodeTy is expected to publicly derive from 39 // ilist_node<NodeTy>, there is a legal viable downcast from it 40 // to NodeTy. We use this trick to superpose i(p)list with a "ghostly" 41 // NodeTy, which becomes the sentinel. Dereferencing the sentinel is 42 // forbidden (save the ilist_node<NodeTy>) so no one will ever notice 43 // the superposition. 44 return static_cast<Instruction*>(&Sentinel); 45 } 46 static void destroySentinel(Instruction*) {} 47 48 Instruction *provideInitialHead() const { return createSentinel(); } 49 Instruction *ensureHead(Instruction*) const { return createSentinel(); } 50 static void noteHead(Instruction*, Instruction*) {} 51 private: 52 mutable ilist_half_node<Instruction> Sentinel; 53 }; 54 55 /// This represents a single basic block in LLVM. A basic block is simply a 56 /// container of instructions that execute sequentially. Basic blocks are Values 57 /// because they are referenced by instructions such as branches and switch 58 /// tables. The type of a BasicBlock is "Type::LabelTy" because the basic block 59 /// represents a label to which a branch can jump. 60 /// 61 /// A well formed basic block is formed of a list of non-terminating 62 /// instructions followed by a single TerminatorInst instruction. 63 /// TerminatorInst's may not occur in the middle of basic blocks, and must 64 /// terminate the blocks. The BasicBlock class allows malformed basic blocks to 65 /// occur because it may be useful in the intermediate stage of constructing or 66 /// modifying a program. However, the verifier will ensure that basic blocks 67 /// are "well formed". 68 /// @brief LLVM Basic Block Representation 69 class BasicBlock : public Value, // Basic blocks are data objects also 70 public ilist_node<BasicBlock> { 71 friend class BlockAddress; 72 public: 73 typedef iplist<Instruction> InstListType; 74 private: 75 InstListType InstList; 76 Function *Parent; 77 78 void setParent(Function *parent); 79 friend class SymbolTableListTraits<BasicBlock, Function>; 80 81 BasicBlock(const BasicBlock &); // Do not implement 82 void operator=(const BasicBlock &); // Do not implement 83 84 /// BasicBlock ctor - If the function parameter is specified, the basic block 85 /// is automatically inserted at either the end of the function (if 86 /// InsertBefore is null), or before the specified basic block. 87 /// 88 explicit BasicBlock(LLVMContext &C, const Twine &Name = "", 89 Function *Parent = 0, BasicBlock *InsertBefore = 0); 90 public: 91 /// getContext - Get the context in which this basic block lives. 92 LLVMContext &getContext() const; 93 94 /// Instruction iterators... 95 typedef InstListType::iterator iterator; 96 typedef InstListType::const_iterator const_iterator; 97 98 /// Create - Creates a new BasicBlock. If the Parent parameter is specified, 99 /// the basic block is automatically inserted at either the end of the 100 /// function (if InsertBefore is 0), or before the specified basic block. 101 static BasicBlock *Create(LLVMContext &Context, const Twine &Name = "", 102 Function *Parent = 0,BasicBlock *InsertBefore = 0) { 103 return new BasicBlock(Context, Name, Parent, InsertBefore); 104 } 105 ~BasicBlock(); 106 107 /// getParent - Return the enclosing method, or null if none 108 /// 109 const Function *getParent() const { return Parent; } 110 Function *getParent() { return Parent; } 111 112 /// use_back - Specialize the methods defined in Value, as we know that an 113 /// BasicBlock can only be used by Users (specifically terminators 114 /// and BlockAddress's). 115 User *use_back() { return cast<User>(*use_begin());} 116 const User *use_back() const { return cast<User>(*use_begin());} 117 118 /// getTerminator() - If this is a well formed basic block, then this returns 119 /// a pointer to the terminator instruction. If it is not, then you get a 120 /// null pointer back. 121 /// 122 TerminatorInst *getTerminator(); 123 const TerminatorInst *getTerminator() const; 124 125 /// Returns a pointer to the first instructon in this block that is not a 126 /// PHINode instruction. When adding instruction to the beginning of the 127 /// basic block, they should be added before the returned value, not before 128 /// the first instruction, which might be PHI. 129 /// 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 // Same as above, but also skip debug intrinsics. 136 Instruction* getFirstNonPHIOrDbg(); 137 const Instruction* getFirstNonPHIOrDbg() const { 138 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbg(); 139 } 140 141 // Same as above, but also skip lifetime intrinsics. 142 Instruction* getFirstNonPHIOrDbgOrLifetime(); 143 const Instruction* getFirstNonPHIOrDbgOrLifetime() const { 144 return const_cast<BasicBlock*>(this)->getFirstNonPHIOrDbgOrLifetime(); 145 } 146 147 /// removeFromParent - This method unlinks 'this' from the containing 148 /// function, but does not delete it. 149 /// 150 void removeFromParent(); 151 152 /// eraseFromParent - This method unlinks 'this' from the containing function 153 /// and deletes it. 154 /// 155 void eraseFromParent(); 156 157 /// moveBefore - Unlink this basic block from its current function and 158 /// insert it into the function that MovePos lives in, right before MovePos. 159 void moveBefore(BasicBlock *MovePos); 160 161 /// moveAfter - Unlink this basic block from its current function and 162 /// insert it into the function that MovePos lives in, right after MovePos. 163 void moveAfter(BasicBlock *MovePos); 164 165 166 /// getSinglePredecessor - If this basic block has a single predecessor block, 167 /// return the block, otherwise return a null pointer. 168 BasicBlock *getSinglePredecessor(); 169 const BasicBlock *getSinglePredecessor() const { 170 return const_cast<BasicBlock*>(this)->getSinglePredecessor(); 171 } 172 173 /// getUniquePredecessor - If this basic block has a unique predecessor block, 174 /// return the block, otherwise return a null pointer. 175 /// Note that unique predecessor doesn't mean single edge, there can be 176 /// multiple edges from the unique predecessor to this block (for example 177 /// a switch statement with multiple cases having the same destination). 178 BasicBlock *getUniquePredecessor(); 179 const BasicBlock *getUniquePredecessor() const { 180 return const_cast<BasicBlock*>(this)->getUniquePredecessor(); 181 } 182 183 //===--------------------------------------------------------------------===// 184 /// Instruction iterator methods 185 /// 186 inline iterator begin() { return InstList.begin(); } 187 inline const_iterator begin() const { return InstList.begin(); } 188 inline iterator end () { return InstList.end(); } 189 inline const_iterator end () const { return InstList.end(); } 190 191 inline size_t size() const { return InstList.size(); } 192 inline bool empty() const { return InstList.empty(); } 193 inline const Instruction &front() const { return InstList.front(); } 194 inline Instruction &front() { return InstList.front(); } 195 inline const Instruction &back() const { return InstList.back(); } 196 inline Instruction &back() { return InstList.back(); } 197 198 /// getInstList() - Return the underlying instruction list container. You 199 /// need to access it directly if you want to modify it currently. 200 /// 201 const InstListType &getInstList() const { return InstList; } 202 InstListType &getInstList() { return InstList; } 203 204 /// getSublistAccess() - returns pointer to member of instruction list 205 static iplist<Instruction> BasicBlock::*getSublistAccess(Instruction*) { 206 return &BasicBlock::InstList; 207 } 208 209 /// getValueSymbolTable() - returns pointer to symbol table (if any) 210 ValueSymbolTable *getValueSymbolTable(); 211 212 /// Methods for support type inquiry through isa, cast, and dyn_cast: 213 static inline bool classof(const BasicBlock *) { return true; } 214 static inline bool classof(const Value *V) { 215 return V->getValueID() == Value::BasicBlockVal; 216 } 217 218 /// dropAllReferences() - This function causes all the subinstructions to "let 219 /// go" of all references that they are maintaining. This allows one to 220 /// 'delete' a whole class at a time, even though there may be circular 221 /// references... first all references are dropped, and all use counts go to 222 /// zero. Then everything is delete'd for real. Note that no operations are 223 /// valid on an object that has "dropped all references", except operator 224 /// delete. 225 /// 226 void dropAllReferences(); 227 228 /// removePredecessor - This method is used to notify a BasicBlock that the 229 /// specified Predecessor of the block is no longer able to reach it. This is 230 /// actually not used to update the Predecessor list, but is actually used to 231 /// update the PHI nodes that reside in the block. Note that this should be 232 /// called while the predecessor still refers to this block. 233 /// 234 void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false); 235 236 /// splitBasicBlock - This splits a basic block into two at the specified 237 /// instruction. Note that all instructions BEFORE the specified iterator 238 /// stay as part of the original basic block, an unconditional branch is added 239 /// to the original BB, and the rest of the instructions in the BB are moved 240 /// to the new BB, including the old terminator. The newly formed BasicBlock 241 /// is returned. This function invalidates the specified iterator. 242 /// 243 /// Note that this only works on well formed basic blocks (must have a 244 /// terminator), and 'I' must not be the end of instruction list (which would 245 /// cause a degenerate basic block to be formed, having a terminator inside of 246 /// the basic block). 247 /// 248 /// Also note that this doesn't preserve any passes. To split blocks while 249 /// keeping loop information consistent, use the SplitBlock utility function. 250 /// 251 BasicBlock *splitBasicBlock(iterator I, const Twine &BBName = ""); 252 253 /// hasAddressTaken - returns true if there are any uses of this basic block 254 /// other than direct branches, switches, etc. to it. 255 bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; } 256 257 /// replaceSuccessorsPhiUsesWith - Update all phi nodes in all our successors 258 /// to refer to basic block New instead of to us. 259 void replaceSuccessorsPhiUsesWith(BasicBlock *New); 260 261 private: 262 /// AdjustBlockAddressRefCount - BasicBlock stores the number of BlockAddress 263 /// objects using it. This is almost always 0, sometimes one, possibly but 264 /// almost never 2, and inconceivably 3 or more. 265 void AdjustBlockAddressRefCount(int Amt) { 266 setValueSubclassData(getSubclassDataFromValue()+Amt); 267 assert((int)(signed char)getSubclassDataFromValue() >= 0 && 268 "Refcount wrap-around"); 269 } 270 // Shadow Value::setValueSubclassData with a private forwarding method so that 271 // any future subclasses cannot accidentally use it. 272 void setValueSubclassData(unsigned short D) { 273 Value::setValueSubclassData(D); 274 } 275 }; 276 277 } // End llvm namespace 278 279 #endif 280
