BasicBlock.cpp revision d7bb295d223e028aa9ba7fbeafc8928db4a74972
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/IntrinsicInst.h" 18#include "llvm/LLVMContext.h" 19#include "llvm/Type.h" 20#include "llvm/ADT/STLExtras.h" 21#include "llvm/Support/CFG.h" 22#include "llvm/Support/LeakDetector.h" 23#include "SymbolTableListTraitsImpl.h" 24#include <algorithm> 25using namespace llvm; 26 27ValueSymbolTable *BasicBlock::getValueSymbolTable() { 28 if (Function *F = getParent()) 29 return &F->getValueSymbolTable(); 30 return 0; 31} 32 33LLVMContext &BasicBlock::getContext() const { 34 return getType()->getContext(); 35} 36 37// Explicit instantiation of SymbolTableListTraits since some of the methods 38// are not in the public header file... 39template class llvm::SymbolTableListTraits<Instruction, BasicBlock>; 40 41BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent, 42 BasicBlock *InsertBefore) 43 : Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(0), 44 IsLandingPad(false) { 45 46 // Make sure that we get added to a function 47 LeakDetector::addGarbageObject(this); 48 49 if (InsertBefore) { 50 assert(NewParent && 51 "Cannot insert block before another block with no function!"); 52 NewParent->getBasicBlockList().insert(InsertBefore, this); 53 } else if (NewParent) { 54 NewParent->getBasicBlockList().push_back(this); 55 } 56 57 setName(Name); 58} 59 60BasicBlock::~BasicBlock() { 61 // If the address of the block is taken and it is being deleted (e.g. because 62 // it is dead), this means that there is either a dangling constant expr 63 // hanging off the block, or an undefined use of the block (source code 64 // expecting the address of a label to keep the block alive even though there 65 // is no indirect branch). Handle these cases by zapping the BlockAddress 66 // nodes. There are no other possible uses at this point. 67 if (hasAddressTaken()) { 68 assert(!use_empty() && "There should be at least one blockaddress!"); 69 Constant *Replacement = 70 ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1); 71 while (!use_empty()) { 72 BlockAddress *BA = cast<BlockAddress>(use_back()); 73 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 74 BA->getType())); 75 BA->destroyConstant(); 76 } 77 } 78 79 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 80 dropAllReferences(); 81 InstList.clear(); 82} 83 84void BasicBlock::setParent(Function *parent) { 85 if (getParent()) 86 LeakDetector::addGarbageObject(this); 87 88 // Set Parent=parent, updating instruction symtab entries as appropriate. 89 InstList.setSymTabObject(&Parent, parent); 90 91 if (getParent()) 92 LeakDetector::removeGarbageObject(this); 93} 94 95void BasicBlock::removeFromParent() { 96 getParent()->getBasicBlockList().remove(this); 97} 98 99void BasicBlock::eraseFromParent() { 100 getParent()->getBasicBlockList().erase(this); 101} 102 103/// moveBefore - Unlink this basic block from its current function and 104/// insert it into the function that MovePos lives in, right before MovePos. 105void BasicBlock::moveBefore(BasicBlock *MovePos) { 106 MovePos->getParent()->getBasicBlockList().splice(MovePos, 107 getParent()->getBasicBlockList(), this); 108} 109 110/// moveAfter - Unlink this basic block from its current function and 111/// insert it into the function that MovePos lives in, right after MovePos. 112void BasicBlock::moveAfter(BasicBlock *MovePos) { 113 Function::iterator I = MovePos; 114 MovePos->getParent()->getBasicBlockList().splice(++I, 115 getParent()->getBasicBlockList(), this); 116} 117 118 119TerminatorInst *BasicBlock::getTerminator() { 120 if (InstList.empty()) return 0; 121 return dyn_cast<TerminatorInst>(&InstList.back()); 122} 123 124const TerminatorInst *BasicBlock::getTerminator() const { 125 if (InstList.empty()) return 0; 126 return dyn_cast<TerminatorInst>(&InstList.back()); 127} 128 129Instruction* BasicBlock::getFirstNonPHI() { 130 BasicBlock::iterator i = begin(); 131 // All valid basic blocks should have a terminator, 132 // which is not a PHINode. If we have an invalid basic 133 // block we'll get an assertion failure when dereferencing 134 // a past-the-end iterator. 135 while (isa<PHINode>(i)) ++i; 136 return &*i; 137} 138 139Instruction* BasicBlock::getFirstNonPHIOrDbg() { 140 BasicBlock::iterator i = begin(); 141 // All valid basic blocks should have a terminator, 142 // which is not a PHINode. If we have an invalid basic 143 // block we'll get an assertion failure when dereferencing 144 // a past-the-end iterator. 145 while (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i)) ++i; 146 return &*i; 147} 148 149void BasicBlock::dropAllReferences() { 150 for(iterator I = begin(), E = end(); I != E; ++I) 151 I->dropAllReferences(); 152} 153 154/// getSinglePredecessor - If this basic block has a single predecessor block, 155/// return the block, otherwise return a null pointer. 156BasicBlock *BasicBlock::getSinglePredecessor() { 157 pred_iterator PI = pred_begin(this), E = pred_end(this); 158 if (PI == E) return 0; // No preds. 159 BasicBlock *ThePred = *PI; 160 ++PI; 161 return (PI == E) ? ThePred : 0 /*multiple preds*/; 162} 163 164/// getUniquePredecessor - If this basic block has a unique predecessor block, 165/// return the block, otherwise return a null pointer. 166/// Note that unique predecessor doesn't mean single edge, there can be 167/// multiple edges from the unique predecessor to this block (for example 168/// a switch statement with multiple cases having the same destination). 169BasicBlock *BasicBlock::getUniquePredecessor() { 170 pred_iterator PI = pred_begin(this), E = pred_end(this); 171 if (PI == E) return 0; // No preds. 172 BasicBlock *PredBB = *PI; 173 ++PI; 174 for (;PI != E; ++PI) { 175 if (*PI != PredBB) 176 return 0; 177 // The same predecessor appears multiple times in the predecessor list. 178 // This is OK. 179 } 180 return PredBB; 181} 182 183/// removePredecessor - This method is used to notify a BasicBlock that the 184/// specified Predecessor of the block is no longer able to reach it. This is 185/// actually not used to update the Predecessor list, but is actually used to 186/// update the PHI nodes that reside in the block. Note that this should be 187/// called while the predecessor still refers to this block. 188/// 189void BasicBlock::removePredecessor(BasicBlock *Pred, 190 bool DontDeleteUselessPHIs) { 191 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 192 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 193 "removePredecessor: BB is not a predecessor!"); 194 195 if (InstList.empty()) return; 196 PHINode *APN = dyn_cast<PHINode>(&front()); 197 if (!APN) return; // Quick exit. 198 199 // If there are exactly two predecessors, then we want to nuke the PHI nodes 200 // altogether. However, we cannot do this, if this in this case: 201 // 202 // Loop: 203 // %x = phi [X, Loop] 204 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 205 // br Loop ;; %x2 does not dominate all uses 206 // 207 // This is because the PHI node input is actually taken from the predecessor 208 // basic block. The only case this can happen is with a self loop, so we 209 // check for this case explicitly now. 210 // 211 unsigned max_idx = APN->getNumIncomingValues(); 212 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 213 if (max_idx == 2) { 214 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 215 216 // Disable PHI elimination! 217 if (this == Other) max_idx = 3; 218 } 219 220 // <= Two predecessors BEFORE I remove one? 221 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 222 // Yup, loop through and nuke the PHI nodes 223 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 224 // Remove the predecessor first. 225 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 226 227 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 228 if (max_idx == 2) { 229 if (PN->getOperand(0) != PN) 230 PN->replaceAllUsesWith(PN->getOperand(0)); 231 else 232 // We are left with an infinite loop with no entries: kill the PHI. 233 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 234 getInstList().pop_front(); // Remove the PHI node 235 } 236 237 // If the PHI node already only had one entry, it got deleted by 238 // removeIncomingValue. 239 } 240 } else { 241 // Okay, now we know that we need to remove predecessor #pred_idx from all 242 // PHI nodes. Iterate over each PHI node fixing them up 243 PHINode *PN; 244 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 245 ++II; 246 PN->removeIncomingValue(Pred, false); 247 // If all incoming values to the Phi are the same, we can replace the Phi 248 // with that value. 249 Value* PNV = 0; 250 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) 251 if (PNV != PN) { 252 PN->replaceAllUsesWith(PNV); 253 PN->eraseFromParent(); 254 } 255 } 256 } 257} 258 259 260/// splitBasicBlock - This splits a basic block into two at the specified 261/// instruction. Note that all instructions BEFORE the specified iterator stay 262/// as part of the original basic block, an unconditional branch is added to 263/// the new BB, and the rest of the instructions in the BB are moved to the new 264/// BB, including the old terminator. This invalidates the iterator. 265/// 266/// Note that this only works on well formed basic blocks (must have a 267/// terminator), and 'I' must not be the end of instruction list (which would 268/// cause a degenerate basic block to be formed, having a terminator inside of 269/// the basic block). 270/// 271BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) { 272 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 273 assert(I != InstList.end() && 274 "Trying to get me to create degenerate basic block!"); 275 276 BasicBlock *InsertBefore = llvm::next(Function::iterator(this)) 277 .getNodePtrUnchecked(); 278 BasicBlock *New = BasicBlock::Create(getContext(), BBName, 279 getParent(), InsertBefore); 280 281 // Move all of the specified instructions from the original basic block into 282 // the new basic block. 283 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 284 285 // Add a branch instruction to the newly formed basic block. 286 BranchInst::Create(New, this); 287 288 // Now we must loop through all of the successors of the New block (which 289 // _were_ the successors of the 'this' block), and update any PHI nodes in 290 // successors. If there were PHI nodes in the successors, then they need to 291 // know that incoming branches will be from New, not from Old. 292 // 293 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 294 // Loop over any phi nodes in the basic block, updating the BB field of 295 // incoming values... 296 BasicBlock *Successor = *I; 297 PHINode *PN; 298 for (BasicBlock::iterator II = Successor->begin(); 299 (PN = dyn_cast<PHINode>(II)); ++II) { 300 int IDX = PN->getBasicBlockIndex(this); 301 while (IDX != -1) { 302 PN->setIncomingBlock((unsigned)IDX, New); 303 IDX = PN->getBasicBlockIndex(this); 304 } 305 } 306 } 307 return New; 308} 309 310