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/Constant.h" 00016 #include "llvm/Instructions.h" 00017 #include "llvm/Type.h" 00018 #include "llvm/Support/CFG.h" 00019 #include "llvm/SymbolTable.h" 00020 #include "llvm/Support/LeakDetector.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 DummyInst : public Instruction { 00029 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd) { 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>::createNode() { 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 // Specialize setName to take care of symbol table majik 00099 void BasicBlock::setName(const std::string &name, SymbolTable *ST) { 00100 Function *P; 00101 assert((ST == 0 || (!getParent() || ST == &getParent()->getSymbolTable())) && 00102 "Invalid symtab argument!"); 00103 if ((P = getParent()) && hasName()) P->getSymbolTable().remove(this); 00104 Value::setName(name); 00105 if (P && hasName()) P->getSymbolTable().insert(this); 00106 } 00107 00108 void BasicBlock::removeFromParent() { 00109 getParent()->getBasicBlockList().remove(this); 00110 } 00111 00112 void BasicBlock::eraseFromParent() { 00113 getParent()->getBasicBlockList().erase(this); 00114 } 00115 00116 00117 TerminatorInst *BasicBlock::getTerminator() { 00118 if (InstList.empty()) return 0; 00119 return dyn_cast<TerminatorInst>(&InstList.back()); 00120 } 00121 00122 const TerminatorInst *const BasicBlock::getTerminator() const { 00123 if (InstList.empty()) return 0; 00124 return dyn_cast<TerminatorInst>(&InstList.back()); 00125 } 00126 00127 void BasicBlock::dropAllReferences() { 00128 for(iterator I = begin(), E = end(); I != E; ++I) 00129 I->dropAllReferences(); 00130 } 00131 00132 // removePredecessor - This method is used to notify a BasicBlock that the 00133 // specified Predecessor of the block is no longer able to reach it. This is 00134 // actually not used to update the Predecessor list, but is actually used to 00135 // update the PHI nodes that reside in the block. Note that this should be 00136 // called while the predecessor still refers to this block. 00137 // 00138 void BasicBlock::removePredecessor(BasicBlock *Pred) { 00139 assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) && 00140 "removePredecessor: BB is not a predecessor!"); 00141 PHINode *APN = dyn_cast<PHINode>(&front()); 00142 if (!APN) return; // Quick exit. 00143 00144 // If there are exactly two predecessors, then we want to nuke the PHI nodes 00145 // altogether. However, we cannot do this, if this in this case: 00146 // 00147 // Loop: 00148 // %x = phi [X, Loop] 00149 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 00150 // br Loop ;; %x2 does not dominate all uses 00151 // 00152 // This is because the PHI node input is actually taken from the predecessor 00153 // basic block. The only case this can happen is with a self loop, so we 00154 // check for this case explicitly now. 00155 // 00156 unsigned max_idx = APN->getNumIncomingValues(); 00157 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 00158 if (max_idx == 2) { 00159 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 00160 00161 // Disable PHI elimination! 00162 if (this == Other) max_idx = 3; 00163 } 00164 00165 if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one? 00166 // Yup, loop through and nuke the PHI nodes 00167 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 00168 PN->removeIncomingValue(Pred); // Remove the predecessor first... 00169 00170 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 00171 if (max_idx == 2) { 00172 if (PN->getOperand(0) != PN) 00173 PN->replaceAllUsesWith(PN->getOperand(0)); 00174 else 00175 // We are left with an infinite loop with no entries: kill the PHI. 00176 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); 00177 getInstList().pop_front(); // Remove the PHI node 00178 } 00179 00180 // If the PHI node already only had one entry, it got deleted by 00181 // removeIncomingValue. 00182 } 00183 } else { 00184 // Okay, now we know that we need to remove predecessor #pred_idx from all 00185 // PHI nodes. Iterate over each PHI node fixing them up 00186 PHINode *PN; 00187 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ++II) 00188 PN->removeIncomingValue(Pred); 00189 } 00190 } 00191 00192 00193 // splitBasicBlock - This splits a basic block into two at the specified 00194 // instruction. Note that all instructions BEFORE the specified iterator stay 00195 // as part of the original basic block, an unconditional branch is added to 00196 // the new BB, and the rest of the instructions in the BB are moved to the new 00197 // BB, including the old terminator. This invalidates the iterator. 00198 // 00199 // Note that this only works on well formed basic blocks (must have a 00200 // terminator), and 'I' must not be the end of instruction list (which would 00201 // cause a degenerate basic block to be formed, having a terminator inside of 00202 // the basic block). 00203 // 00204 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 00205 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 00206 assert(I != InstList.end() && 00207 "Trying to get me to create degenerate basic block!"); 00208 00209 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext()); 00210 00211 // Move all of the specified instructions from the original basic block into 00212 // the new basic block. 00213 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 00214 00215 // Add a branch instruction to the newly formed basic block. 00216 new BranchInst(New, this); 00217 00218 // Now we must loop through all of the successors of the New block (which 00219 // _were_ the successors of the 'this' block), and update any PHI nodes in 00220 // successors. If there were PHI nodes in the successors, then they need to 00221 // know that incoming branches will be from New, not from Old. 00222 // 00223 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 00224 // Loop over any phi nodes in the basic block, updating the BB field of 00225 // incoming values... 00226 BasicBlock *Successor = *I; 00227 PHINode *PN; 00228 for (BasicBlock::iterator II = Successor->begin(); 00229 (PN = dyn_cast<PHINode>(II)); ++II) { 00230 int IDX = PN->getBasicBlockIndex(this); 00231 while (IDX != -1) { 00232 PN->setIncomingBlock((unsigned)IDX, New); 00233 IDX = PN->getBasicBlockIndex(this); 00234 } 00235 } 00236 } 00237 return New; 00238 }