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