LLVM API Documentation
00001 //===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This file implements the BasicBlock class for the VMCore library. 00011 // 00012 //===----------------------------------------------------------------------===// 00013 00014 #include "llvm/BasicBlock.h" 00015 #include "llvm/Constants.h" 00016 #include "llvm/Instructions.h" 00017 #include "llvm/Type.h" 00018 #include "llvm/Support/CFG.h" 00019 #include "llvm/Support/LeakDetector.h" 00020 #include "llvm/Support/Visibility.h" 00021 #include "SymbolTableListTraitsImpl.h" 00022 #include <algorithm> 00023 using namespace llvm; 00024 00025 namespace { 00026 /// DummyInst - An instance of this class is used to mark the end of the 00027 /// instruction list. This is not a real instruction. 00028 struct VISIBILITY_HIDDEN DummyInst : public Instruction { 00029 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) { 00030 // This should not be garbage monitored. 00031 LeakDetector::removeGarbageObject(this); 00032 } 00033 00034 virtual Instruction *clone() const { 00035 assert(0 && "Cannot clone EOL");abort(); 00036 return 0; 00037 } 00038 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; } 00039 00040 // Methods for support type inquiry through isa, cast, and dyn_cast... 00041 static inline bool classof(const DummyInst *) { return true; } 00042 static inline bool classof(const Instruction *I) { 00043 return I->getOpcode() == OtherOpsEnd; 00044 } 00045 static inline bool classof(const Value *V) { 00046 return isa<Instruction>(V) && classof(cast<Instruction>(V)); 00047 } 00048 }; 00049 } 00050 00051 Instruction *ilist_traits<Instruction>::createSentinel() { 00052 return new DummyInst(); 00053 } 00054 iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) { 00055 return BB->getInstList(); 00056 } 00057 00058 // Explicit instantiation of SymbolTableListTraits since some of the methods 00059 // are not in the public header file... 00060 template class SymbolTableListTraits<Instruction, BasicBlock, Function>; 00061 00062 00063 BasicBlock::BasicBlock(const std::string &Name, Function *Parent, 00064 BasicBlock *InsertBefore) 00065 : Value(Type::LabelTy, Value::BasicBlockVal, Name) { 00066 // Initialize the instlist... 00067 InstList.setItemParent(this); 00068 00069 // Make sure that we get added to a function 00070 LeakDetector::addGarbageObject(this); 00071 00072 if (InsertBefore) { 00073 assert(Parent && 00074 "Cannot insert block before another block with no function!"); 00075 Parent->getBasicBlockList().insert(InsertBefore, this); 00076 } else if (Parent) { 00077 Parent->getBasicBlockList().push_back(this); 00078 } 00079 } 00080 00081 00082 BasicBlock::~BasicBlock() { 00083 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 00084 dropAllReferences(); 00085 InstList.clear(); 00086 } 00087 00088 void BasicBlock::setParent(Function *parent) { 00089 if (getParent()) 00090 LeakDetector::addGarbageObject(this); 00091 00092 InstList.setParent(parent); 00093 00094 if (getParent()) 00095 LeakDetector::removeGarbageObject(this); 00096 } 00097 00098 void BasicBlock::removeFromParent() { 00099 getParent()->getBasicBlockList().remove(this); 00100 } 00101 00102 void BasicBlock::eraseFromParent() { 00103 getParent()->getBasicBlockList().erase(this); 00104 } 00105 00106 /// moveBefore - Unlink this instruction from its current function and 00107 /// insert it into the function that MovePos lives in, right before 00108 /// MovePos. 00109 void BasicBlock::moveBefore(BasicBlock *MovePos) { 00110 MovePos->getParent()->getBasicBlockList().splice(MovePos, 00111 getParent()->getBasicBlockList(), this); 00112 } 00113 00114 00115 TerminatorInst *BasicBlock::getTerminator() { 00116 if (InstList.empty()) return 0; 00117 return dyn_cast<TerminatorInst>(&InstList.back()); 00118 } 00119 00120 const TerminatorInst *const BasicBlock::getTerminator() const { 00121 if (InstList.empty()) return 0; 00122 return dyn_cast<TerminatorInst>(&InstList.back()); 00123 } 00124 00125 Instruction* BasicBlock::getFirstNonPHI() 00126 { 00127 BasicBlock::iterator i = begin(); 00128 // All valid basic blocks should have a terminator, 00129 // which is not a PHINode. If we have invalid basic 00130 // block we'll get assert when dereferencing past-the-end 00131 // iterator. 00132 while (isa<PHINode>(i)) ++i; 00133 return &*i; 00134 } 00135 00136 void BasicBlock::dropAllReferences() { 00137 for(iterator I = begin(), E = end(); I != E; ++I) 00138 I->dropAllReferences(); 00139 } 00140 00141 /// getSinglePredecessor - If this basic block has a single predecessor block, 00142 /// return the block, otherwise return a null pointer. 00143 BasicBlock *BasicBlock::getSinglePredecessor() { 00144 pred_iterator PI = pred_begin(this), E = pred_end(this); 00145 if (PI == E) return 0; // No preds. 00146 BasicBlock *ThePred = *PI; 00147 ++PI; 00148 return (PI == E) ? ThePred : 0 /*multiple preds*/; 00149 } 00150 00151 /// removePredecessor - This method is used to notify a BasicBlock that the 00152 /// specified Predecessor of the block is no longer able to reach it. This is 00153 /// actually not used to update the Predecessor list, but is actually used to 00154 /// update the PHI nodes that reside in the block. Note that this should be 00155 /// called while the predecessor still refers to this block. 00156 /// 00157 void BasicBlock::removePredecessor(BasicBlock *Pred, 00158 bool DontDeleteUselessPHIs) { 00159 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 00160 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 00161 "removePredecessor: BB is not a predecessor!"); 00162 00163 if (InstList.empty()) return; 00164 PHINode *APN = dyn_cast<PHINode>(&front()); 00165 if (!APN) return; // Quick exit. 00166 00167 // If there are exactly two predecessors, then we want to nuke the PHI nodes 00168 // altogether. However, we cannot do this, if this in this case: 00169 // 00170 // Loop: 00171 // %x = phi [X, Loop] 00172 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 00173 // br Loop ;; %x2 does not dominate all uses 00174 // 00175 // This is because the PHI node input is actually taken from the predecessor 00176 // basic block. The only case this can happen is with a self loop, so we 00177 // check for this case explicitly now. 00178 // 00179 unsigned max_idx = APN->getNumIncomingValues(); 00180 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 00181 if (max_idx == 2) { 00182 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 00183 00184 // Disable PHI elimination! 00185 if (this == Other) max_idx = 3; 00186 } 00187 00188 // <= Two predecessors BEFORE I remove one? 00189 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 00190 // Yup, loop through and nuke the PHI nodes 00191 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 00192 // Remove the predecessor first. 00193 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 00194 00195 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 00196 if (max_idx == 2) { 00197 if (PN->getOperand(0) != PN) 00198 PN->replaceAllUsesWith(PN->getOperand(0)); 00199 else 00200 // We are left with an infinite loop with no entries: kill the PHI. 00201 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 00202 getInstList().pop_front(); // Remove the PHI node 00203 } 00204 00205 // If the PHI node already only had one entry, it got deleted by 00206 // removeIncomingValue. 00207 } 00208 } else { 00209 // Okay, now we know that we need to remove predecessor #pred_idx from all 00210 // PHI nodes. Iterate over each PHI node fixing them up 00211 PHINode *PN; 00212 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 00213 ++II; 00214 PN->removeIncomingValue(Pred, false); 00215 // If all incoming values to the Phi are the same, we can replace the Phi 00216 // with that value. 00217 Value* PNV = 0; 00218 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) { 00219 PN->replaceAllUsesWith(PNV); 00220 PN->eraseFromParent(); 00221 } 00222 } 00223 } 00224 } 00225 00226 00227 /// splitBasicBlock - This splits a basic block into two at the specified 00228 /// instruction. Note that all instructions BEFORE the specified iterator stay 00229 /// as part of the original basic block, an unconditional branch is added to 00230 /// the new BB, and the rest of the instructions in the BB are moved to the new 00231 /// BB, including the old terminator. This invalidates the iterator. 00232 /// 00233 /// Note that this only works on well formed basic blocks (must have a 00234 /// terminator), and 'I' must not be the end of instruction list (which would 00235 /// cause a degenerate basic block to be formed, having a terminator inside of 00236 /// the basic block). 00237 /// 00238 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 00239 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 00240 assert(I != InstList.end() && 00241 "Trying to get me to create degenerate basic block!"); 00242 00243 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext()); 00244 00245 // Move all of the specified instructions from the original basic block into 00246 // the new basic block. 00247 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 00248 00249 // Add a branch instruction to the newly formed basic block. 00250 new BranchInst(New, this); 00251 00252 // Now we must loop through all of the successors of the New block (which 00253 // _were_ the successors of the 'this' block), and update any PHI nodes in 00254 // successors. If there were PHI nodes in the successors, then they need to 00255 // know that incoming branches will be from New, not from Old. 00256 // 00257 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 00258 // Loop over any phi nodes in the basic block, updating the BB field of 00259 // incoming values... 00260 BasicBlock *Successor = *I; 00261 PHINode *PN; 00262 for (BasicBlock::iterator II = Successor->begin(); 00263 (PN = dyn_cast<PHINode>(II)); ++II) { 00264 int IDX = PN->getBasicBlockIndex(this); 00265 while (IDX != -1) { 00266 PN->setIncomingBlock((unsigned)IDX, New); 00267 IDX = PN->getBasicBlockIndex(this); 00268 } 00269 } 00270 } 00271 return New; 00272 }