BasicBlock.cpp revision 9ef7e06ccef062dfa5df516913b12b7c3ca17805
1//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements the BasicBlock class for the VMCore library. 11// 12//===----------------------------------------------------------------------===// 13 14#include "llvm/BasicBlock.h" 15#include "llvm/Constants.h" 16#include "llvm/Instructions.h" 17#include "llvm/Type.h" 18#include "llvm/Support/CFG.h" 19#include "llvm/Support/LeakDetector.h" 20#include "llvm/Support/Visibility.h" 21#include "SymbolTableListTraitsImpl.h" 22#include <algorithm> 23using namespace llvm; 24 25namespace { 26 /// DummyInst - An instance of this class is used to mark the end of the 27 /// instruction list. This is not a real instruction. 28 struct VISIBILITY_HIDDEN DummyInst : public Instruction { 29 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) { 30 // This should not be garbage monitored. 31 LeakDetector::removeGarbageObject(this); 32 } 33 34 virtual Instruction *clone() const { 35 assert(0 && "Cannot clone EOL");abort(); 36 return 0; 37 } 38 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; } 39 40 // Methods for support type inquiry through isa, cast, and dyn_cast... 41 static inline bool classof(const DummyInst *) { return true; } 42 static inline bool classof(const Instruction *I) { 43 return I->getOpcode() == OtherOpsEnd; 44 } 45 static inline bool classof(const Value *V) { 46 return isa<Instruction>(V) && classof(cast<Instruction>(V)); 47 } 48 }; 49} 50 51Instruction *ilist_traits<Instruction>::createSentinel() { 52 return new DummyInst(); 53} 54iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) { 55 return BB->getInstList(); 56} 57 58// Explicit instantiation of SymbolTableListTraits since some of the methods 59// are not in the public header file... 60template class SymbolTableListTraits<Instruction, BasicBlock, Function>; 61 62 63BasicBlock::BasicBlock(const std::string &Name, Function *Parent, 64 BasicBlock *InsertBefore) 65 : Value(Type::LabelTy, Value::BasicBlockVal, Name) { 66 // Initialize the instlist... 67 InstList.setItemParent(this); 68 69 // Make sure that we get added to a function 70 LeakDetector::addGarbageObject(this); 71 72 if (InsertBefore) { 73 assert(Parent && 74 "Cannot insert block before another block with no function!"); 75 Parent->getBasicBlockList().insert(InsertBefore, this); 76 } else if (Parent) { 77 Parent->getBasicBlockList().push_back(this); 78 } 79} 80 81 82BasicBlock::~BasicBlock() { 83 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 84 dropAllReferences(); 85 InstList.clear(); 86} 87 88void BasicBlock::setParent(Function *parent) { 89 if (getParent()) 90 LeakDetector::addGarbageObject(this); 91 92 InstList.setParent(parent); 93 94 if (getParent()) 95 LeakDetector::removeGarbageObject(this); 96} 97 98void BasicBlock::removeFromParent() { 99 getParent()->getBasicBlockList().remove(this); 100} 101 102void BasicBlock::eraseFromParent() { 103 getParent()->getBasicBlockList().erase(this); 104} 105 106/// moveBefore - Unlink this instruction from its current function and 107/// insert it into the function that MovePos lives in, right before 108/// MovePos. 109void BasicBlock::moveBefore(BasicBlock *MovePos) { 110 MovePos->getParent()->getBasicBlockList().splice(MovePos, 111 getParent()->getBasicBlockList(), this); 112} 113 114 115TerminatorInst *BasicBlock::getTerminator() { 116 if (InstList.empty()) return 0; 117 return dyn_cast<TerminatorInst>(&InstList.back()); 118} 119 120const TerminatorInst *const BasicBlock::getTerminator() const { 121 if (InstList.empty()) return 0; 122 return dyn_cast<TerminatorInst>(&InstList.back()); 123} 124 125Instruction* BasicBlock::getFirstNonPHI() 126{ 127 BasicBlock::iterator i = begin(); 128 // All valid basic blocks should have a terminator, 129 // which is not a PHINode. If we have invalid basic 130 // block we'll get assert when dereferencing past-the-end 131 // iterator. 132 while (isa<PHINode>(i)) ++i; 133 return &*i; 134} 135 136void BasicBlock::dropAllReferences() { 137 for(iterator I = begin(), E = end(); I != E; ++I) 138 I->dropAllReferences(); 139} 140 141/// getSinglePredecessor - If this basic block has a single predecessor block, 142/// return the block, otherwise return a null pointer. 143BasicBlock *BasicBlock::getSinglePredecessor() { 144 pred_iterator PI = pred_begin(this), E = pred_end(this); 145 if (PI == E) return 0; // No preds. 146 BasicBlock *ThePred = *PI; 147 ++PI; 148 return (PI == E) ? ThePred : 0 /*multiple preds*/; 149} 150 151/// removePredecessor - This method is used to notify a BasicBlock that the 152/// specified Predecessor of the block is no longer able to reach it. This is 153/// actually not used to update the Predecessor list, but is actually used to 154/// update the PHI nodes that reside in the block. Note that this should be 155/// called while the predecessor still refers to this block. 156/// 157void BasicBlock::removePredecessor(BasicBlock *Pred, 158 bool DontDeleteUselessPHIs) { 159 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 160 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 161 "removePredecessor: BB is not a predecessor!"); 162 163 if (InstList.empty()) return; 164 PHINode *APN = dyn_cast<PHINode>(&front()); 165 if (!APN) return; // Quick exit. 166 167 // If there are exactly two predecessors, then we want to nuke the PHI nodes 168 // altogether. However, we cannot do this, if this in this case: 169 // 170 // Loop: 171 // %x = phi [X, Loop] 172 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 173 // br Loop ;; %x2 does not dominate all uses 174 // 175 // This is because the PHI node input is actually taken from the predecessor 176 // basic block. The only case this can happen is with a self loop, so we 177 // check for this case explicitly now. 178 // 179 unsigned max_idx = APN->getNumIncomingValues(); 180 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 181 if (max_idx == 2) { 182 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 183 184 // Disable PHI elimination! 185 if (this == Other) max_idx = 3; 186 } 187 188 // <= Two predecessors BEFORE I remove one? 189 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 190 // Yup, loop through and nuke the PHI nodes 191 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 192 // Remove the predecessor first. 193 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 194 195 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 196 if (max_idx == 2) { 197 if (PN->getOperand(0) != PN) 198 PN->replaceAllUsesWith(PN->getOperand(0)); 199 else 200 // We are left with an infinite loop with no entries: kill the PHI. 201 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 202 getInstList().pop_front(); // Remove the PHI node 203 } 204 205 // If the PHI node already only had one entry, it got deleted by 206 // removeIncomingValue. 207 } 208 } else { 209 // Okay, now we know that we need to remove predecessor #pred_idx from all 210 // PHI nodes. Iterate over each PHI node fixing them up 211 PHINode *PN; 212 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 213 ++II; 214 PN->removeIncomingValue(Pred, false); 215 // If all incoming values to the Phi are the same, we can replace the Phi 216 // with that value. 217 Value* PNV = 0; 218 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) { 219 PN->replaceAllUsesWith(PNV); 220 PN->eraseFromParent(); 221 } 222 } 223 } 224} 225 226 227/// splitBasicBlock - This splits a basic block into two at the specified 228/// instruction. Note that all instructions BEFORE the specified iterator stay 229/// as part of the original basic block, an unconditional branch is added to 230/// the new BB, and the rest of the instructions in the BB are moved to the new 231/// BB, including the old terminator. This invalidates the iterator. 232/// 233/// Note that this only works on well formed basic blocks (must have a 234/// terminator), and 'I' must not be the end of instruction list (which would 235/// cause a degenerate basic block to be formed, having a terminator inside of 236/// the basic block). 237/// 238BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 239 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 240 assert(I != InstList.end() && 241 "Trying to get me to create degenerate basic block!"); 242 243 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext()); 244 245 // Move all of the specified instructions from the original basic block into 246 // the new basic block. 247 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 248 249 // Add a branch instruction to the newly formed basic block. 250 new BranchInst(New, this); 251 252 // Now we must loop through all of the successors of the New block (which 253 // _were_ the successors of the 'this' block), and update any PHI nodes in 254 // successors. If there were PHI nodes in the successors, then they need to 255 // know that incoming branches will be from New, not from Old. 256 // 257 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 258 // Loop over any phi nodes in the basic block, updating the BB field of 259 // incoming values... 260 BasicBlock *Successor = *I; 261 PHINode *PN; 262 for (BasicBlock::iterator II = Successor->begin(); 263 (PN = dyn_cast<PHINode>(II)); ++II) { 264 int IDX = PN->getBasicBlockIndex(this); 265 while (IDX != -1) { 266 PN->setIncomingBlock((unsigned)IDX, New); 267 IDX = PN->getBasicBlockIndex(this); 268 } 269 } 270 } 271 return New; 272} 273