BasicBlock.cpp revision dd49dbfe44098eb53b1ac29f017e422147572bbb
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 "SymbolTableListTraitsImpl.h" 21#include <algorithm> 22using namespace llvm; 23 24namespace { 25 /// DummyInst - An instance of this class is used to mark the end of the 26 /// instruction list. This is not a real instruction. 27 struct DummyInst : public Instruction { 28 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) { 29 // This should not be garbage monitored. 30 LeakDetector::removeGarbageObject(this); 31 } 32 33 virtual Instruction *clone() const { 34 assert(0 && "Cannot clone EOL");abort(); 35 return 0; 36 } 37 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; } 38 39 // Methods for support type inquiry through isa, cast, and dyn_cast... 40 static inline bool classof(const DummyInst *) { return true; } 41 static inline bool classof(const Instruction *I) { 42 return I->getOpcode() == OtherOpsEnd; 43 } 44 static inline bool classof(const Value *V) { 45 return isa<Instruction>(V) && classof(cast<Instruction>(V)); 46 } 47 }; 48} 49 50Instruction *ilist_traits<Instruction>::createSentinel() { 51 return new DummyInst(); 52} 53iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) { 54 return BB->getInstList(); 55} 56 57// Explicit instantiation of SymbolTableListTraits since some of the methods 58// are not in the public header file... 59template class SymbolTableListTraits<Instruction, BasicBlock, Function>; 60 61 62BasicBlock::BasicBlock(const std::string &Name, Function *Parent, 63 BasicBlock *InsertBefore) 64 : Value(Type::LabelTy, Value::BasicBlockVal, Name) { 65 // Initialize the instlist... 66 InstList.setItemParent(this); 67 68 // Make sure that we get added to a function 69 LeakDetector::addGarbageObject(this); 70 71 if (InsertBefore) { 72 assert(Parent && 73 "Cannot insert block before another block with no function!"); 74 Parent->getBasicBlockList().insert(InsertBefore, this); 75 } else if (Parent) { 76 Parent->getBasicBlockList().push_back(this); 77 } 78} 79 80 81BasicBlock::~BasicBlock() { 82 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 83 dropAllReferences(); 84 InstList.clear(); 85} 86 87void BasicBlock::setParent(Function *parent) { 88 if (getParent()) 89 LeakDetector::addGarbageObject(this); 90 91 InstList.setParent(parent); 92 93 if (getParent()) 94 LeakDetector::removeGarbageObject(this); 95} 96 97void BasicBlock::removeFromParent() { 98 getParent()->getBasicBlockList().remove(this); 99} 100 101void BasicBlock::eraseFromParent() { 102 getParent()->getBasicBlockList().erase(this); 103} 104 105/// moveBefore - Unlink this instruction from its current function and 106/// insert it into the function that MovePos lives in, right before 107/// MovePos. 108void BasicBlock::moveBefore(BasicBlock *MovePos) { 109 MovePos->getParent()->getBasicBlockList().splice(MovePos, 110 getParent()->getBasicBlockList(), this); 111} 112 113 114TerminatorInst *BasicBlock::getTerminator() { 115 if (InstList.empty()) return 0; 116 return dyn_cast<TerminatorInst>(&InstList.back()); 117} 118 119const TerminatorInst *const BasicBlock::getTerminator() const { 120 if (InstList.empty()) return 0; 121 return dyn_cast<TerminatorInst>(&InstList.back()); 122} 123 124Instruction* BasicBlock::getFirstNonPHI() 125{ 126 BasicBlock::iterator i = begin(), e = end(); 127 // All valid basic blocks should have a terminator, 128 // which is not a PHINode. If we have invalid basic 129 // block we'll get assert when dereferencing past-the-end 130 // iterator. 131 while (isa<PHINode>(i)) ++i; 132 return &*i; 133} 134 135void BasicBlock::dropAllReferences() { 136 for(iterator I = begin(), E = end(); I != E; ++I) 137 I->dropAllReferences(); 138} 139 140/// getSinglePredecessor - If this basic block has a single predecessor block, 141/// return the block, otherwise return a null pointer. 142BasicBlock *BasicBlock::getSinglePredecessor() { 143 pred_iterator PI = pred_begin(this), E = pred_end(this); 144 if (PI == E) return 0; // No preds. 145 BasicBlock *ThePred = *PI; 146 ++PI; 147 return (PI == E) ? ThePred : 0 /*multiple preds*/; 148} 149 150/// removePredecessor - This method is used to notify a BasicBlock that the 151/// specified Predecessor of the block is no longer able to reach it. This is 152/// actually not used to update the Predecessor list, but is actually used to 153/// update the PHI nodes that reside in the block. Note that this should be 154/// called while the predecessor still refers to this block. 155/// 156void BasicBlock::removePredecessor(BasicBlock *Pred, 157 bool DontDeleteUselessPHIs) { 158 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 159 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 160 "removePredecessor: BB is not a predecessor!"); 161 162 if (InstList.empty()) return; 163 PHINode *APN = dyn_cast<PHINode>(&front()); 164 if (!APN) return; // Quick exit. 165 166 // If there are exactly two predecessors, then we want to nuke the PHI nodes 167 // altogether. However, we cannot do this, if this in this case: 168 // 169 // Loop: 170 // %x = phi [X, Loop] 171 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 172 // br Loop ;; %x2 does not dominate all uses 173 // 174 // This is because the PHI node input is actually taken from the predecessor 175 // basic block. The only case this can happen is with a self loop, so we 176 // check for this case explicitly now. 177 // 178 unsigned max_idx = APN->getNumIncomingValues(); 179 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 180 if (max_idx == 2) { 181 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 182 183 // Disable PHI elimination! 184 if (this == Other) max_idx = 3; 185 } 186 187 // <= Two predecessors BEFORE I remove one? 188 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 189 // Yup, loop through and nuke the PHI nodes 190 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 191 // Remove the predecessor first. 192 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 193 194 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 195 if (max_idx == 2) { 196 if (PN->getOperand(0) != PN) 197 PN->replaceAllUsesWith(PN->getOperand(0)); 198 else 199 // We are left with an infinite loop with no entries: kill the PHI. 200 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 201 getInstList().pop_front(); // Remove the PHI node 202 } 203 204 // If the PHI node already only had one entry, it got deleted by 205 // removeIncomingValue. 206 } 207 } else { 208 // Okay, now we know that we need to remove predecessor #pred_idx from all 209 // PHI nodes. Iterate over each PHI node fixing them up 210 PHINode *PN; 211 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 212 ++II; 213 PN->removeIncomingValue(Pred, false); 214 // If all incoming values to the Phi are the same, we can replace the Phi 215 // with that value. 216 if (Value *PNV = PN->hasConstantValue()) { 217 PN->replaceAllUsesWith(PNV); 218 PN->eraseFromParent(); 219 } 220 } 221 } 222} 223 224 225/// splitBasicBlock - This splits a basic block into two at the specified 226/// instruction. Note that all instructions BEFORE the specified iterator stay 227/// as part of the original basic block, an unconditional branch is added to 228/// the new BB, and the rest of the instructions in the BB are moved to the new 229/// BB, including the old terminator. This invalidates the iterator. 230/// 231/// Note that this only works on well formed basic blocks (must have a 232/// terminator), and 'I' must not be the end of instruction list (which would 233/// cause a degenerate basic block to be formed, having a terminator inside of 234/// the basic block). 235/// 236BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 237 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 238 assert(I != InstList.end() && 239 "Trying to get me to create degenerate basic block!"); 240 241 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext()); 242 243 // Move all of the specified instructions from the original basic block into 244 // the new basic block. 245 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 246 247 // Add a branch instruction to the newly formed basic block. 248 new BranchInst(New, this); 249 250 // Now we must loop through all of the successors of the New block (which 251 // _were_ the successors of the 'this' block), and update any PHI nodes in 252 // successors. If there were PHI nodes in the successors, then they need to 253 // know that incoming branches will be from New, not from Old. 254 // 255 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 256 // Loop over any phi nodes in the basic block, updating the BB field of 257 // incoming values... 258 BasicBlock *Successor = *I; 259 PHINode *PN; 260 for (BasicBlock::iterator II = Successor->begin(); 261 (PN = dyn_cast<PHINode>(II)); ++II) { 262 int IDX = PN->getBasicBlockIndex(this); 263 while (IDX != -1) { 264 PN->setIncomingBlock((unsigned)IDX, New); 265 IDX = PN->getBasicBlockIndex(this); 266 } 267 } 268 } 269 return New; 270} 271