BasicBlock.cpp revision f8dfef74376dd85f37601855f7519d8256700dab
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 76 // Make sure that we get added to a function 77 LeakDetector::addGarbageObject(this); 78 79 if (InsertBefore) { 80 assert(NewParent && 81 "Cannot insert block before another block with no function!"); 82 NewParent->getBasicBlockList().insert(InsertBefore, this); 83 } else if (NewParent) { 84 NewParent->getBasicBlockList().push_back(this); 85 } 86 87 setName(Name); 88} 89 90 91BasicBlock::~BasicBlock() { 92 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 93 dropAllReferences(); 94 InstList.clear(); 95} 96 97void BasicBlock::setParent(Function *parent) { 98 if (getParent()) 99 LeakDetector::addGarbageObject(this); 100 101 // Set Parent=parent, updating instruction symtab entries as appropriate. 102 InstList.setSymTabObject(&Parent, parent); 103 104 if (getParent()) 105 LeakDetector::removeGarbageObject(this); 106} 107 108void BasicBlock::removeFromParent() { 109 getParent()->getBasicBlockList().remove(this); 110} 111 112void BasicBlock::eraseFromParent() { 113 getParent()->getBasicBlockList().erase(this); 114} 115 116/// moveBefore - Unlink this basic block from its current function and 117/// insert it into the function that MovePos lives in, right before MovePos. 118void BasicBlock::moveBefore(BasicBlock *MovePos) { 119 MovePos->getParent()->getBasicBlockList().splice(MovePos, 120 getParent()->getBasicBlockList(), this); 121} 122 123/// moveAfter - Unlink this basic block from its current function and 124/// insert it into the function that MovePos lives in, right after MovePos. 125void BasicBlock::moveAfter(BasicBlock *MovePos) { 126 Function::iterator I = MovePos; 127 MovePos->getParent()->getBasicBlockList().splice(++I, 128 getParent()->getBasicBlockList(), this); 129} 130 131 132TerminatorInst *BasicBlock::getTerminator() { 133 if (InstList.empty()) return 0; 134 return dyn_cast<TerminatorInst>(&InstList.back()); 135} 136 137const TerminatorInst *const BasicBlock::getTerminator() const { 138 if (InstList.empty()) return 0; 139 return dyn_cast<TerminatorInst>(&InstList.back()); 140} 141 142Instruction* BasicBlock::getFirstNonPHI() 143{ 144 BasicBlock::iterator i = begin(); 145 // All valid basic blocks should have a terminator, 146 // which is not a PHINode. If we have invalid basic 147 // block we'll get assert when dereferencing past-the-end 148 // iterator. 149 while (isa<PHINode>(i)) ++i; 150 return &*i; 151} 152 153void BasicBlock::dropAllReferences() { 154 for(iterator I = begin(), E = end(); I != E; ++I) 155 I->dropAllReferences(); 156} 157 158/// getSinglePredecessor - If this basic block has a single predecessor block, 159/// return the block, otherwise return a null pointer. 160BasicBlock *BasicBlock::getSinglePredecessor() { 161 pred_iterator PI = pred_begin(this), E = pred_end(this); 162 if (PI == E) return 0; // No preds. 163 BasicBlock *ThePred = *PI; 164 ++PI; 165 return (PI == E) ? ThePred : 0 /*multiple preds*/; 166} 167 168/// removePredecessor - This method is used to notify a BasicBlock that the 169/// specified Predecessor of the block is no longer able to reach it. This is 170/// actually not used to update the Predecessor list, but is actually used to 171/// update the PHI nodes that reside in the block. Note that this should be 172/// called while the predecessor still refers to this block. 173/// 174void BasicBlock::removePredecessor(BasicBlock *Pred, 175 bool DontDeleteUselessPHIs) { 176 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 177 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 178 "removePredecessor: BB is not a predecessor!"); 179 180 if (InstList.empty()) return; 181 PHINode *APN = dyn_cast<PHINode>(&front()); 182 if (!APN) return; // Quick exit. 183 184 // If there are exactly two predecessors, then we want to nuke the PHI nodes 185 // altogether. However, we cannot do this, if this in this case: 186 // 187 // Loop: 188 // %x = phi [X, Loop] 189 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 190 // br Loop ;; %x2 does not dominate all uses 191 // 192 // This is because the PHI node input is actually taken from the predecessor 193 // basic block. The only case this can happen is with a self loop, so we 194 // check for this case explicitly now. 195 // 196 unsigned max_idx = APN->getNumIncomingValues(); 197 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 198 if (max_idx == 2) { 199 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 200 201 // Disable PHI elimination! 202 if (this == Other) max_idx = 3; 203 } 204 205 // <= Two predecessors BEFORE I remove one? 206 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 207 // Yup, loop through and nuke the PHI nodes 208 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 209 // Remove the predecessor first. 210 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 211 212 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 213 if (max_idx == 2) { 214 if (PN->getOperand(0) != PN) 215 PN->replaceAllUsesWith(PN->getOperand(0)); 216 else 217 // We are left with an infinite loop with no entries: kill the PHI. 218 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 219 getInstList().pop_front(); // Remove the PHI node 220 } 221 222 // If the PHI node already only had one entry, it got deleted by 223 // removeIncomingValue. 224 } 225 } else { 226 // Okay, now we know that we need to remove predecessor #pred_idx from all 227 // PHI nodes. Iterate over each PHI node fixing them up 228 PHINode *PN; 229 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 230 ++II; 231 PN->removeIncomingValue(Pred, false); 232 // If all incoming values to the Phi are the same, we can replace the Phi 233 // with that value. 234 Value* PNV = 0; 235 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) { 236 PN->replaceAllUsesWith(PNV); 237 PN->eraseFromParent(); 238 } 239 } 240 } 241} 242 243 244/// splitBasicBlock - This splits a basic block into two at the specified 245/// instruction. Note that all instructions BEFORE the specified iterator stay 246/// as part of the original basic block, an unconditional branch is added to 247/// the new BB, and the rest of the instructions in the BB are moved to the new 248/// BB, including the old terminator. This invalidates the iterator. 249/// 250/// Note that this only works on well formed basic blocks (must have a 251/// terminator), and 'I' must not be the end of instruction list (which would 252/// cause a degenerate basic block to be formed, having a terminator inside of 253/// the basic block). 254/// 255BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 256 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 257 assert(I != InstList.end() && 258 "Trying to get me to create degenerate basic block!"); 259 260 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext()); 261 262 // Move all of the specified instructions from the original basic block into 263 // the new basic block. 264 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 265 266 // Add a branch instruction to the newly formed basic block. 267 new BranchInst(New, this); 268 269 // Now we must loop through all of the successors of the New block (which 270 // _were_ the successors of the 'this' block), and update any PHI nodes in 271 // successors. If there were PHI nodes in the successors, then they need to 272 // know that incoming branches will be from New, not from Old. 273 // 274 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 275 // Loop over any phi nodes in the basic block, updating the BB field of 276 // incoming values... 277 BasicBlock *Successor = *I; 278 PHINode *PN; 279 for (BasicBlock::iterator II = Successor->begin(); 280 (PN = dyn_cast<PHINode>(II)); ++II) { 281 int IDX = PN->getBasicBlockIndex(this); 282 while (IDX != -1) { 283 PN->setIncomingBlock((unsigned)IDX, New); 284 IDX = PN->getBasicBlockIndex(this); 285 } 286 } 287 } 288 return New; 289} 290