BasicBlock.cpp revision f81b57694b3c34a79b1464ffd21e6768c8d22662
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/LLVMContext.h" 18#include "llvm/Type.h" 19#include "llvm/ADT/STLExtras.h" 20#include "llvm/Support/CFG.h" 21#include "llvm/Support/LeakDetector.h" 22#include "llvm/Support/Compiler.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 Parent ? Parent->getContext() : 0; 35} 36 37// Explicit instantiation of SymbolTableListTraits since some of the methods 38// are not in the public header file... 39template class SymbolTableListTraits<Instruction, BasicBlock>; 40 41 42BasicBlock::BasicBlock(const std::string &Name, Function *NewParent, 43 BasicBlock *InsertBefore) 44 : Value(Type::LabelTy, Value::BasicBlockVal), Parent(0) { 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 60 61BasicBlock::~BasicBlock() { 62 assert(getParent() == 0 && "BasicBlock still linked into the program!"); 63 dropAllReferences(); 64 InstList.clear(); 65} 66 67void BasicBlock::setParent(Function *parent) { 68 if (getParent()) 69 LeakDetector::addGarbageObject(this); 70 71 // Set Parent=parent, updating instruction symtab entries as appropriate. 72 InstList.setSymTabObject(&Parent, parent); 73 74 if (getParent()) 75 LeakDetector::removeGarbageObject(this); 76} 77 78void BasicBlock::removeFromParent() { 79 getParent()->getBasicBlockList().remove(this); 80} 81 82void BasicBlock::eraseFromParent() { 83 getParent()->getBasicBlockList().erase(this); 84} 85 86/// moveBefore - Unlink this basic block from its current function and 87/// insert it into the function that MovePos lives in, right before MovePos. 88void BasicBlock::moveBefore(BasicBlock *MovePos) { 89 MovePos->getParent()->getBasicBlockList().splice(MovePos, 90 getParent()->getBasicBlockList(), this); 91} 92 93/// moveAfter - Unlink this basic block from its current function and 94/// insert it into the function that MovePos lives in, right after MovePos. 95void BasicBlock::moveAfter(BasicBlock *MovePos) { 96 Function::iterator I = MovePos; 97 MovePos->getParent()->getBasicBlockList().splice(++I, 98 getParent()->getBasicBlockList(), this); 99} 100 101 102TerminatorInst *BasicBlock::getTerminator() { 103 if (InstList.empty()) return 0; 104 return dyn_cast<TerminatorInst>(&InstList.back()); 105} 106 107const TerminatorInst *BasicBlock::getTerminator() const { 108 if (InstList.empty()) return 0; 109 return dyn_cast<TerminatorInst>(&InstList.back()); 110} 111 112Instruction* BasicBlock::getFirstNonPHI() { 113 BasicBlock::iterator i = begin(); 114 // All valid basic blocks should have a terminator, 115 // which is not a PHINode. If we have an invalid basic 116 // block we'll get an assertion failure when dereferencing 117 // a past-the-end iterator. 118 while (isa<PHINode>(i)) ++i; 119 return &*i; 120} 121 122void BasicBlock::dropAllReferences() { 123 for(iterator I = begin(), E = end(); I != E; ++I) 124 I->dropAllReferences(); 125} 126 127/// getSinglePredecessor - If this basic block has a single predecessor block, 128/// return the block, otherwise return a null pointer. 129BasicBlock *BasicBlock::getSinglePredecessor() { 130 pred_iterator PI = pred_begin(this), E = pred_end(this); 131 if (PI == E) return 0; // No preds. 132 BasicBlock *ThePred = *PI; 133 ++PI; 134 return (PI == E) ? ThePred : 0 /*multiple preds*/; 135} 136 137/// getUniquePredecessor - If this basic block has a unique predecessor block, 138/// return the block, otherwise return a null pointer. 139/// Note that unique predecessor doesn't mean single edge, there can be 140/// multiple edges from the unique predecessor to this block (for example 141/// a switch statement with multiple cases having the same destination). 142BasicBlock *BasicBlock::getUniquePredecessor() { 143 pred_iterator PI = pred_begin(this), E = pred_end(this); 144 if (PI == E) return 0; // No preds. 145 BasicBlock *PredBB = *PI; 146 ++PI; 147 for (;PI != E; ++PI) { 148 if (*PI != PredBB) 149 return 0; 150 // The same predecessor appears multiple times in the predecessor list. 151 // This is OK. 152 } 153 return PredBB; 154} 155 156/// removePredecessor - This method is used to notify a BasicBlock that the 157/// specified Predecessor of the block is no longer able to reach it. This is 158/// actually not used to update the Predecessor list, but is actually used to 159/// update the PHI nodes that reside in the block. Note that this should be 160/// called while the predecessor still refers to this block. 161/// 162void BasicBlock::removePredecessor(BasicBlock *Pred, 163 bool DontDeleteUselessPHIs) { 164 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 165 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 166 "removePredecessor: BB is not a predecessor!"); 167 168 if (InstList.empty()) return; 169 PHINode *APN = dyn_cast<PHINode>(&front()); 170 if (!APN) return; // Quick exit. 171 172 // If there are exactly two predecessors, then we want to nuke the PHI nodes 173 // altogether. However, we cannot do this, if this in this case: 174 // 175 // Loop: 176 // %x = phi [X, Loop] 177 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 178 // br Loop ;; %x2 does not dominate all uses 179 // 180 // This is because the PHI node input is actually taken from the predecessor 181 // basic block. The only case this can happen is with a self loop, so we 182 // check for this case explicitly now. 183 // 184 unsigned max_idx = APN->getNumIncomingValues(); 185 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 186 if (max_idx == 2) { 187 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 188 189 // Disable PHI elimination! 190 if (this == Other) max_idx = 3; 191 } 192 193 // <= Two predecessors BEFORE I remove one? 194 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 195 // Yup, loop through and nuke the PHI nodes 196 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 197 // Remove the predecessor first. 198 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 199 200 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 201 if (max_idx == 2) { 202 if (PN->getOperand(0) != PN) 203 PN->replaceAllUsesWith(PN->getOperand(0)); 204 else 205 // We are left with an infinite loop with no entries: kill the PHI. 206 PN->replaceAllUsesWith(getContext()->getUndef(PN->getType())); 207 getInstList().pop_front(); // Remove the PHI node 208 } 209 210 // If the PHI node already only had one entry, it got deleted by 211 // removeIncomingValue. 212 } 213 } else { 214 // Okay, now we know that we need to remove predecessor #pred_idx from all 215 // PHI nodes. Iterate over each PHI node fixing them up 216 PHINode *PN; 217 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 218 ++II; 219 PN->removeIncomingValue(Pred, false); 220 // If all incoming values to the Phi are the same, we can replace the Phi 221 // with that value. 222 Value* PNV = 0; 223 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) { 224 PN->replaceAllUsesWith(PNV); 225 PN->eraseFromParent(); 226 } 227 } 228 } 229} 230 231 232/// splitBasicBlock - This splits a basic block into two at the specified 233/// instruction. Note that all instructions BEFORE the specified iterator stay 234/// as part of the original basic block, an unconditional branch is added to 235/// the new BB, and the rest of the instructions in the BB are moved to the new 236/// BB, including the old terminator. This invalidates the iterator. 237/// 238/// Note that this only works on well formed basic blocks (must have a 239/// terminator), and 'I' must not be the end of instruction list (which would 240/// cause a degenerate basic block to be formed, having a terminator inside of 241/// the basic block). 242/// 243BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) { 244 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 245 assert(I != InstList.end() && 246 "Trying to get me to create degenerate basic block!"); 247 248 BasicBlock *InsertBefore = next(Function::iterator(this)) 249 .getNodePtrUnchecked(); 250 BasicBlock *New = BasicBlock::Create(BBName, getParent(), InsertBefore); 251 252 // Move all of the specified instructions from the original basic block into 253 // the new basic block. 254 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 255 256 // Add a branch instruction to the newly formed basic block. 257 BranchInst::Create(New, this); 258 259 // Now we must loop through all of the successors of the New block (which 260 // _were_ the successors of the 'this' block), and update any PHI nodes in 261 // successors. If there were PHI nodes in the successors, then they need to 262 // know that incoming branches will be from New, not from Old. 263 // 264 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 265 // Loop over any phi nodes in the basic block, updating the BB field of 266 // incoming values... 267 BasicBlock *Successor = *I; 268 PHINode *PN; 269 for (BasicBlock::iterator II = Successor->begin(); 270 (PN = dyn_cast<PHINode>(II)); ++II) { 271 int IDX = PN->getBasicBlockIndex(this); 272 while (IDX != -1) { 273 PN->setIncomingBlock((unsigned)IDX, New); 274 IDX = PN->getBasicBlockIndex(this); 275 } 276 } 277 } 278 return New; 279} 280