BasicBlock.cpp revision 17fcdd5e1b78b829068ca657c97357a39d6e768b
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/Compiler.h" 21#include "SymbolTableListTraitsImpl.h" 22#include <algorithm> 23using namespace llvm; 24 25inline ValueSymbolTable * 26ilist_traits<Instruction>::getSymTab(BasicBlock *BB) { 27 if (BB) 28 if (Function *F = BB->getParent()) 29 return &F->getValueSymbolTable(); 30 return 0; 31} 32 33 34namespace { 35 /// DummyInst - An instance of this class is used to mark the end of the 36 /// instruction list. This is not a real instruction. 37 struct VISIBILITY_HIDDEN DummyInst : public Instruction { 38 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) { 39 // This should not be garbage monitored. 40 LeakDetector::removeGarbageObject(this); 41 } 42 43 virtual Instruction *clone() const { 44 assert(0 && "Cannot clone EOL");abort(); 45 return 0; 46 } 47 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; } 48 49 // Methods for support type inquiry through isa, cast, and dyn_cast... 50 static inline bool classof(const DummyInst *) { return true; } 51 static inline bool classof(const Instruction *I) { 52 return I->getOpcode() == OtherOpsEnd; 53 } 54 static inline bool classof(const Value *V) { 55 return isa<Instruction>(V) && classof(cast<Instruction>(V)); 56 } 57 }; 58} 59 60Instruction *ilist_traits<Instruction>::createSentinel() { 61 return new DummyInst(); 62} 63iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) { 64 return BB->getInstList(); 65} 66 67// Explicit instantiation of SymbolTableListTraits since some of the methods 68// are not in the public header file... 69template class SymbolTableListTraits<Instruction, BasicBlock>; 70 71 72BasicBlock::BasicBlock(const std::string &Name, Function *NewParent, 73 BasicBlock *InsertBefore) 74 : Value(Type::LabelTy, Value::BasicBlockVal), Parent(0) { 75 // Initialize the instlist. 76 InstList.setItemParent(this); 77 78 // Make sure that we get added to a function 79 LeakDetector::addGarbageObject(this); 80 81 if (InsertBefore) { 82 assert(NewParent && 83 "Cannot insert block before another block with no function!"); 84 NewParent->getBasicBlockList().insert(InsertBefore, this); 85 } else if (NewParent) { 86 NewParent->getBasicBlockList().push_back(this); 87 } 88 89 setName(Name); 90} 91 92 93BasicBlock::~BasicBlock() { 94 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 95 dropAllReferences(); 96 InstList.clear(); 97} 98 99void BasicBlock::setParent(Function *parent) { 100 if (getParent()) 101 LeakDetector::addGarbageObject(this); 102 103 // Set Parent=parent, updating instruction symtab entries as appropriate. 104 InstList.setSymTabObject(&Parent, parent); 105 106 if (getParent()) 107 LeakDetector::removeGarbageObject(this); 108} 109 110void BasicBlock::removeFromParent() { 111 getParent()->getBasicBlockList().remove(this); 112} 113 114void BasicBlock::eraseFromParent() { 115 getParent()->getBasicBlockList().erase(this); 116} 117 118/// moveBefore - Unlink this basic block from its current function and 119/// insert it into the function that MovePos lives in, right before MovePos. 120void BasicBlock::moveBefore(BasicBlock *MovePos) { 121 MovePos->getParent()->getBasicBlockList().splice(MovePos, 122 getParent()->getBasicBlockList(), this); 123} 124 125/// moveAfter - Unlink this basic block from its current function and 126/// insert it into the function that MovePos lives in, right after MovePos. 127void BasicBlock::moveAfter(BasicBlock *MovePos) { 128 Function::iterator I = MovePos; 129 MovePos->getParent()->getBasicBlockList().splice(++I, 130 getParent()->getBasicBlockList(), this); 131} 132 133 134TerminatorInst *BasicBlock::getTerminator() { 135 if (InstList.empty()) return 0; 136 return dyn_cast<TerminatorInst>(&InstList.back()); 137} 138 139const TerminatorInst *const BasicBlock::getTerminator() const { 140 if (InstList.empty()) return 0; 141 return dyn_cast<TerminatorInst>(&InstList.back()); 142} 143 144Instruction* BasicBlock::getFirstNonPHI() 145{ 146 BasicBlock::iterator i = begin(); 147 // All valid basic blocks should have a terminator, 148 // which is not a PHINode. If we have invalid basic 149 // block we'll get assert when dereferencing past-the-end 150 // iterator. 151 while (isa<PHINode>(i)) ++i; 152 return &*i; 153} 154 155void BasicBlock::dropAllReferences() { 156 for(iterator I = begin(), E = end(); I != E; ++I) 157 I->dropAllReferences(); 158} 159 160/// getSinglePredecessor - If this basic block has a single predecessor block, 161/// return the block, otherwise return a null pointer. 162BasicBlock *BasicBlock::getSinglePredecessor() { 163 pred_iterator PI = pred_begin(this), E = pred_end(this); 164 if (PI == E) return 0; // No preds. 165 BasicBlock *ThePred = *PI; 166 ++PI; 167 return (PI == E) ? ThePred : 0 /*multiple preds*/; 168} 169 170/// removePredecessor - This method is used to notify a BasicBlock that the 171/// specified Predecessor of the block is no longer able to reach it. This is 172/// actually not used to update the Predecessor list, but is actually used to 173/// update the PHI nodes that reside in the block. Note that this should be 174/// called while the predecessor still refers to this block. 175/// 176void BasicBlock::removePredecessor(BasicBlock *Pred, 177 bool DontDeleteUselessPHIs) { 178 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 179 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 180 "removePredecessor: BB is not a predecessor!"); 181 182 if (InstList.empty()) return; 183 PHINode *APN = dyn_cast<PHINode>(&front()); 184 if (!APN) return; // Quick exit. 185 186 // If there are exactly two predecessors, then we want to nuke the PHI nodes 187 // altogether. However, we cannot do this, if this in this case: 188 // 189 // Loop: 190 // %x = phi [X, Loop] 191 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 192 // br Loop ;; %x2 does not dominate all uses 193 // 194 // This is because the PHI node input is actually taken from the predecessor 195 // basic block. The only case this can happen is with a self loop, so we 196 // check for this case explicitly now. 197 // 198 unsigned max_idx = APN->getNumIncomingValues(); 199 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 200 if (max_idx == 2) { 201 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 202 203 // Disable PHI elimination! 204 if (this == Other) max_idx = 3; 205 } 206 207 // <= Two predecessors BEFORE I remove one? 208 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 209 // Yup, loop through and nuke the PHI nodes 210 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 211 // Remove the predecessor first. 212 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 213 214 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 215 if (max_idx == 2) { 216 if (PN->getOperand(0) != PN) 217 PN->replaceAllUsesWith(PN->getOperand(0)); 218 else 219 // We are left with an infinite loop with no entries: kill the PHI. 220 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 221 getInstList().pop_front(); // Remove the PHI node 222 } 223 224 // If the PHI node already only had one entry, it got deleted by 225 // removeIncomingValue. 226 } 227 } else { 228 // Okay, now we know that we need to remove predecessor #pred_idx from all 229 // PHI nodes. Iterate over each PHI node fixing them up 230 PHINode *PN; 231 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 232 ++II; 233 PN->removeIncomingValue(Pred, false); 234 // If all incoming values to the Phi are the same, we can replace the Phi 235 // with that value. 236 Value* PNV = 0; 237 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) { 238 PN->replaceAllUsesWith(PNV); 239 PN->eraseFromParent(); 240 } 241 } 242 } 243} 244 245 246/// splitBasicBlock - This splits a basic block into two at the specified 247/// instruction. Note that all instructions BEFORE the specified iterator stay 248/// as part of the original basic block, an unconditional branch is added to 249/// the new BB, and the rest of the instructions in the BB are moved to the new 250/// BB, including the old terminator. This invalidates the iterator. 251/// 252/// Note that this only works on well formed basic blocks (must have a 253/// terminator), and 'I' must not be the end of instruction list (which would 254/// cause a degenerate basic block to be formed, having a terminator inside of 255/// the basic block). 256/// 257BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 258 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 259 assert(I != InstList.end() && 260 "Trying to get me to create degenerate basic block!"); 261 262 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext()); 263 264 // Move all of the specified instructions from the original basic block into 265 // the new basic block. 266 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 267 268 // Add a branch instruction to the newly formed basic block. 269 new BranchInst(New, this); 270 271 // Now we must loop through all of the successors of the New block (which 272 // _were_ the successors of the 'this' block), and update any PHI nodes in 273 // successors. If there were PHI nodes in the successors, then they need to 274 // know that incoming branches will be from New, not from Old. 275 // 276 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 277 // Loop over any phi nodes in the basic block, updating the BB field of 278 // incoming values... 279 BasicBlock *Successor = *I; 280 PHINode *PN; 281 for (BasicBlock::iterator II = Successor->begin(); 282 (PN = dyn_cast<PHINode>(II)); ++II) { 283 int IDX = PN->getBasicBlockIndex(this); 284 while (IDX != -1) { 285 PN->setIncomingBlock((unsigned)IDX, New); 286 IDX = PN->getBasicBlockIndex(this); 287 } 288 } 289 } 290 return New; 291} 292