BasicBlock.cpp revision 87f1e7796d02ea991bdbf084f312879988732a26
1//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// 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/ADT/STLExtras.h" 19#include "llvm/Support/CFG.h" 20#include "llvm/Support/LeakDetector.h" 21#include "llvm/Support/Compiler.h" 22#include "SymbolTableListTraitsImpl.h" 23#include <algorithm> 24using namespace llvm; 25 26inline ValueSymbolTable * 27ilist_traits<Instruction>::getSymTab(BasicBlock *BB) { 28 if (BB) 29 if (Function *F = BB->getParent()) 30 return &F->getValueSymbolTable(); 31 return 0; 32} 33 34 35namespace { 36 /// DummyInst - An instance of this class is used to mark the end of the 37 /// instruction list. This is not a real instruction. 38 struct VISIBILITY_HIDDEN DummyInst : public Instruction { 39 // allocate space for exactly zero operands 40 void *operator new(size_t s) { 41 return User::operator new(s, 0); 42 } 43 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) { 44 // This should not be garbage monitored. 45 LeakDetector::removeGarbageObject(this); 46 } 47 48 Instruction *clone() const { 49 assert(0 && "Cannot clone EOL");abort(); 50 return 0; 51 } 52 const char *getOpcodeName() const { return "*end-of-list-inst*"; } 53 54 // Methods for support type inquiry through isa, cast, and dyn_cast... 55 static inline bool classof(const DummyInst *) { return true; } 56 static inline bool classof(const Instruction *I) { 57 return I->getOpcode() == OtherOpsEnd; 58 } 59 static inline bool classof(const Value *V) { 60 return isa<Instruction>(V) && classof(cast<Instruction>(V)); 61 } 62 }; 63} 64 65Instruction *ilist_traits<Instruction>::createSentinel() { 66 return new DummyInst(); 67} 68iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) { 69 return BB->getInstList(); 70} 71 72// Explicit instantiation of SymbolTableListTraits since some of the methods 73// are not in the public header file... 74template class SymbolTableListTraits<Instruction, BasicBlock>; 75 76 77BasicBlock::BasicBlock(const std::string &Name, Function *NewParent, 78 BasicBlock *InsertBefore) 79 : Value(Type::LabelTy, Value::BasicBlockVal), Parent(0) { 80 81 // Make sure that we get added to a function 82 LeakDetector::addGarbageObject(this); 83 84 if (InsertBefore) { 85 assert(NewParent && 86 "Cannot insert block before another block with no function!"); 87 NewParent->getBasicBlockList().insert(InsertBefore, this); 88 } else if (NewParent) { 89 NewParent->getBasicBlockList().push_back(this); 90 } 91 92 setName(Name); 93} 94 95 96BasicBlock::~BasicBlock() { 97 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 98 dropAllReferences(); 99 InstList.clear(); 100} 101 102void BasicBlock::setParent(Function *parent) { 103 if (getParent()) 104 LeakDetector::addGarbageObject(this); 105 106 // Set Parent=parent, updating instruction symtab entries as appropriate. 107 InstList.setSymTabObject(&Parent, parent); 108 109 if (getParent()) 110 LeakDetector::removeGarbageObject(this); 111} 112 113void BasicBlock::removeFromParent() { 114 getParent()->getBasicBlockList().remove(this); 115} 116 117void BasicBlock::eraseFromParent() { 118 getParent()->getBasicBlockList().erase(this); 119} 120 121/// moveBefore - Unlink this basic block from its current function and 122/// insert it into the function that MovePos lives in, right before MovePos. 123void BasicBlock::moveBefore(BasicBlock *MovePos) { 124 MovePos->getParent()->getBasicBlockList().splice(MovePos, 125 getParent()->getBasicBlockList(), this); 126} 127 128/// moveAfter - Unlink this basic block from its current function and 129/// insert it into the function that MovePos lives in, right after MovePos. 130void BasicBlock::moveAfter(BasicBlock *MovePos) { 131 Function::iterator I = MovePos; 132 MovePos->getParent()->getBasicBlockList().splice(++I, 133 getParent()->getBasicBlockList(), this); 134} 135 136 137TerminatorInst *BasicBlock::getTerminator() { 138 if (InstList.empty()) return 0; 139 return dyn_cast<TerminatorInst>(&InstList.back()); 140} 141 142const TerminatorInst *BasicBlock::getTerminator() const { 143 if (InstList.empty()) return 0; 144 return dyn_cast<TerminatorInst>(&InstList.back()); 145} 146 147Instruction* BasicBlock::getFirstNonPHI() { 148 BasicBlock::iterator i = begin(); 149 // All valid basic blocks should have a terminator, 150 // which is not a PHINode. If we have an invalid basic 151 // block we'll get an assertion failure when dereferencing 152 // a past-the-end iterator. 153 while (isa<PHINode>(i)) ++i; 154 return &*i; 155} 156 157void BasicBlock::dropAllReferences() { 158 for(iterator I = begin(), E = end(); I != E; ++I) 159 I->dropAllReferences(); 160} 161 162/// getSinglePredecessor - If this basic block has a single predecessor block, 163/// return the block, otherwise return a null pointer. 164BasicBlock *BasicBlock::getSinglePredecessor() { 165 pred_iterator PI = pred_begin(this), E = pred_end(this); 166 if (PI == E) return 0; // No preds. 167 BasicBlock *ThePred = *PI; 168 ++PI; 169 return (PI == E) ? ThePred : 0 /*multiple preds*/; 170} 171 172/// getUniquePredecessor - If this basic block has a unique predecessor block, 173/// return the block, otherwise return a null pointer. 174/// Note that unique predecessor doesn't mean single edge, there can be 175/// multiple edges from the unique predecessor to this block (for example in 176/// case of a switch statement with multiple cases having same destination). 177BasicBlock *BasicBlock::getUniquePredecessor() { 178 pred_iterator PI = pred_begin(this), E = pred_end(this); 179 if (PI == E) return 0; // No preds. 180 BasicBlock *PredBB = *PI; 181 ++PI; 182 for (;PI != E; ++PI) { 183 if (*PI != PredBB) 184 return 0; 185 // same predecessor appears multiple times in predecessor list, 186 // this is ok 187 } 188 return PredBB; 189} 190 191/// removePredecessor - This method is used to notify a BasicBlock that the 192/// specified Predecessor of the block is no longer able to reach it. This is 193/// actually not used to update the Predecessor list, but is actually used to 194/// update the PHI nodes that reside in the block. Note that this should be 195/// called while the predecessor still refers to this block. 196/// 197void BasicBlock::removePredecessor(BasicBlock *Pred, 198 bool DontDeleteUselessPHIs) { 199 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 200 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 201 "removePredecessor: BB is not a predecessor!"); 202 203 if (InstList.empty()) return; 204 PHINode *APN = dyn_cast<PHINode>(&front()); 205 if (!APN) return; // Quick exit. 206 207 // If there are exactly two predecessors, then we want to nuke the PHI nodes 208 // altogether. However, we cannot do this, if this in this case: 209 // 210 // Loop: 211 // %x = phi [X, Loop] 212 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 213 // br Loop ;; %x2 does not dominate all uses 214 // 215 // This is because the PHI node input is actually taken from the predecessor 216 // basic block. The only case this can happen is with a self loop, so we 217 // check for this case explicitly now. 218 // 219 unsigned max_idx = APN->getNumIncomingValues(); 220 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 221 if (max_idx == 2) { 222 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 223 224 // Disable PHI elimination! 225 if (this == Other) max_idx = 3; 226 } 227 228 // <= Two predecessors BEFORE I remove one? 229 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 230 // Yup, loop through and nuke the PHI nodes 231 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 232 // Remove the predecessor first. 233 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 234 235 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 236 if (max_idx == 2) { 237 if (PN->getOperand(0) != PN) 238 PN->replaceAllUsesWith(PN->getOperand(0)); 239 else 240 // We are left with an infinite loop with no entries: kill the PHI. 241 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 242 getInstList().pop_front(); // Remove the PHI node 243 } 244 245 // If the PHI node already only had one entry, it got deleted by 246 // removeIncomingValue. 247 } 248 } else { 249 // Okay, now we know that we need to remove predecessor #pred_idx from all 250 // PHI nodes. Iterate over each PHI node fixing them up 251 PHINode *PN; 252 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 253 ++II; 254 PN->removeIncomingValue(Pred, false); 255 // If all incoming values to the Phi are the same, we can replace the Phi 256 // with that value. 257 Value* PNV = 0; 258 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) { 259 PN->replaceAllUsesWith(PNV); 260 PN->eraseFromParent(); 261 } 262 } 263 } 264} 265 266 267/// splitBasicBlock - This splits a basic block into two at the specified 268/// instruction. Note that all instructions BEFORE the specified iterator stay 269/// as part of the original basic block, an unconditional branch is added to 270/// the new BB, and the rest of the instructions in the BB are moved to the new 271/// BB, including the old terminator. This invalidates the iterator. 272/// 273/// Note that this only works on well formed basic blocks (must have a 274/// terminator), and 'I' must not be the end of instruction list (which would 275/// cause a degenerate basic block to be formed, having a terminator inside of 276/// the basic block). 277/// 278BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 279 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 280 assert(I != InstList.end() && 281 "Trying to get me to create degenerate basic block!"); 282 283 BasicBlock *InsertBefore = next(Function::iterator(this)) 284 .getNodePtrUnchecked(); 285 BasicBlock *New = BasicBlock::Create(BBName, getParent(), InsertBefore); 286 287 // Move all of the specified instructions from the original basic block into 288 // the new basic block. 289 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 290 291 // Add a branch instruction to the newly formed basic block. 292 BranchInst::Create(New, this); 293 294 // Now we must loop through all of the successors of the New block (which 295 // _were_ the successors of the 'this' block), and update any PHI nodes in 296 // successors. If there were PHI nodes in the successors, then they need to 297 // know that incoming branches will be from New, not from Old. 298 // 299 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 300 // Loop over any phi nodes in the basic block, updating the BB field of 301 // incoming values... 302 BasicBlock *Successor = *I; 303 PHINode *PN; 304 for (BasicBlock::iterator II = Successor->begin(); 305 (PN = dyn_cast<PHINode>(II)); ++II) { 306 int IDX = PN->getBasicBlockIndex(this); 307 while (IDX != -1) { 308 PN->setIncomingBlock((unsigned)IDX, New); 309 IDX = PN->getBasicBlockIndex(this); 310 } 311 } 312 } 313 return New; 314} 315