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 IR library. 11// 12//===----------------------------------------------------------------------===// 13 14#include "llvm/IR/BasicBlock.h" 15#include "SymbolTableListTraitsImpl.h" 16#include "llvm/ADT/STLExtras.h" 17#include "llvm/IR/CFG.h" 18#include "llvm/IR/Constants.h" 19#include "llvm/IR/Instructions.h" 20#include "llvm/IR/IntrinsicInst.h" 21#include "llvm/IR/LLVMContext.h" 22#include "llvm/IR/LeakDetector.h" 23#include "llvm/IR/Type.h" 24#include <algorithm> 25using namespace llvm; 26 27ValueSymbolTable *BasicBlock::getValueSymbolTable() { 28 if (Function *F = getParent()) 29 return &F->getValueSymbolTable(); 30 return nullptr; 31} 32 33const DataLayout *BasicBlock::getDataLayout() const { 34 return getParent()->getDataLayout(); 35} 36 37LLVMContext &BasicBlock::getContext() const { 38 return getType()->getContext(); 39} 40 41// Explicit instantiation of SymbolTableListTraits since some of the methods 42// are not in the public header file... 43template class llvm::SymbolTableListTraits<Instruction, BasicBlock>; 44 45 46BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent, 47 BasicBlock *InsertBefore) 48 : Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(nullptr) { 49 50 // Make sure that we get added to a function 51 LeakDetector::addGarbageObject(this); 52 53 if (InsertBefore) { 54 assert(NewParent && 55 "Cannot insert block before another block with no function!"); 56 NewParent->getBasicBlockList().insert(InsertBefore, this); 57 } else if (NewParent) { 58 NewParent->getBasicBlockList().push_back(this); 59 } 60 61 setName(Name); 62} 63 64 65BasicBlock::~BasicBlock() { 66 // If the address of the block is taken and it is being deleted (e.g. because 67 // it is dead), this means that there is either a dangling constant expr 68 // hanging off the block, or an undefined use of the block (source code 69 // expecting the address of a label to keep the block alive even though there 70 // is no indirect branch). Handle these cases by zapping the BlockAddress 71 // nodes. There are no other possible uses at this point. 72 if (hasAddressTaken()) { 73 assert(!use_empty() && "There should be at least one blockaddress!"); 74 Constant *Replacement = 75 ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1); 76 while (!use_empty()) { 77 BlockAddress *BA = cast<BlockAddress>(user_back()); 78 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, 79 BA->getType())); 80 BA->destroyConstant(); 81 } 82 } 83 84 assert(getParent() == nullptr && "BasicBlock still linked into the program!"); 85 dropAllReferences(); 86 InstList.clear(); 87} 88 89void BasicBlock::setParent(Function *parent) { 90 if (getParent()) 91 LeakDetector::addGarbageObject(this); 92 93 // Set Parent=parent, updating instruction symtab entries as appropriate. 94 InstList.setSymTabObject(&Parent, parent); 95 96 if (getParent()) 97 LeakDetector::removeGarbageObject(this); 98} 99 100void BasicBlock::removeFromParent() { 101 getParent()->getBasicBlockList().remove(this); 102} 103 104void BasicBlock::eraseFromParent() { 105 getParent()->getBasicBlockList().erase(this); 106} 107 108/// moveBefore - Unlink this basic block from its current function and 109/// insert it into the function that MovePos lives in, right before MovePos. 110void BasicBlock::moveBefore(BasicBlock *MovePos) { 111 MovePos->getParent()->getBasicBlockList().splice(MovePos, 112 getParent()->getBasicBlockList(), this); 113} 114 115/// moveAfter - Unlink this basic block from its current function and 116/// insert it into the function that MovePos lives in, right after MovePos. 117void BasicBlock::moveAfter(BasicBlock *MovePos) { 118 Function::iterator I = MovePos; 119 MovePos->getParent()->getBasicBlockList().splice(++I, 120 getParent()->getBasicBlockList(), this); 121} 122 123 124TerminatorInst *BasicBlock::getTerminator() { 125 if (InstList.empty()) return nullptr; 126 return dyn_cast<TerminatorInst>(&InstList.back()); 127} 128 129const TerminatorInst *BasicBlock::getTerminator() const { 130 if (InstList.empty()) return nullptr; 131 return dyn_cast<TerminatorInst>(&InstList.back()); 132} 133 134Instruction* BasicBlock::getFirstNonPHI() { 135 BasicBlock::iterator i = begin(); 136 // All valid basic blocks should have a terminator, 137 // which is not a PHINode. If we have an invalid basic 138 // block we'll get an assertion failure when dereferencing 139 // a past-the-end iterator. 140 while (isa<PHINode>(i)) ++i; 141 return &*i; 142} 143 144Instruction* BasicBlock::getFirstNonPHIOrDbg() { 145 BasicBlock::iterator i = begin(); 146 // All valid basic blocks should have a terminator, 147 // which is not a PHINode. If we have an invalid basic 148 // block we'll get an assertion failure when dereferencing 149 // a past-the-end iterator. 150 while (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i)) ++i; 151 return &*i; 152} 153 154Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() { 155 // All valid basic blocks should have a terminator, 156 // which is not a PHINode. If we have an invalid basic 157 // block we'll get an assertion failure when dereferencing 158 // a past-the-end iterator. 159 BasicBlock::iterator i = begin(); 160 for (;; ++i) { 161 if (isa<PHINode>(i) || isa<DbgInfoIntrinsic>(i)) 162 continue; 163 164 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(i); 165 if (!II) 166 break; 167 if (II->getIntrinsicID() != Intrinsic::lifetime_start && 168 II->getIntrinsicID() != Intrinsic::lifetime_end) 169 break; 170 } 171 return &*i; 172} 173 174BasicBlock::iterator BasicBlock::getFirstInsertionPt() { 175 iterator InsertPt = getFirstNonPHI(); 176 if (isa<LandingPadInst>(InsertPt)) ++InsertPt; 177 return InsertPt; 178} 179 180void BasicBlock::dropAllReferences() { 181 for(iterator I = begin(), E = end(); I != E; ++I) 182 I->dropAllReferences(); 183} 184 185/// getSinglePredecessor - If this basic block has a single predecessor block, 186/// return the block, otherwise return a null pointer. 187BasicBlock *BasicBlock::getSinglePredecessor() { 188 pred_iterator PI = pred_begin(this), E = pred_end(this); 189 if (PI == E) return nullptr; // No preds. 190 BasicBlock *ThePred = *PI; 191 ++PI; 192 return (PI == E) ? ThePred : nullptr /*multiple preds*/; 193} 194 195/// getUniquePredecessor - If this basic block has a unique predecessor block, 196/// return the block, otherwise return a null pointer. 197/// Note that unique predecessor doesn't mean single edge, there can be 198/// multiple edges from the unique predecessor to this block (for example 199/// a switch statement with multiple cases having the same destination). 200BasicBlock *BasicBlock::getUniquePredecessor() { 201 pred_iterator PI = pred_begin(this), E = pred_end(this); 202 if (PI == E) return nullptr; // No preds. 203 BasicBlock *PredBB = *PI; 204 ++PI; 205 for (;PI != E; ++PI) { 206 if (*PI != PredBB) 207 return nullptr; 208 // The same predecessor appears multiple times in the predecessor list. 209 // This is OK. 210 } 211 return PredBB; 212} 213 214/// removePredecessor - This method is used to notify a BasicBlock that the 215/// specified Predecessor of the block is no longer able to reach it. This is 216/// actually not used to update the Predecessor list, but is actually used to 217/// update the PHI nodes that reside in the block. Note that this should be 218/// called while the predecessor still refers to this block. 219/// 220void BasicBlock::removePredecessor(BasicBlock *Pred, 221 bool DontDeleteUselessPHIs) { 222 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs. 223 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) && 224 "removePredecessor: BB is not a predecessor!"); 225 226 if (InstList.empty()) return; 227 PHINode *APN = dyn_cast<PHINode>(&front()); 228 if (!APN) return; // Quick exit. 229 230 // If there are exactly two predecessors, then we want to nuke the PHI nodes 231 // altogether. However, we cannot do this, if this in this case: 232 // 233 // Loop: 234 // %x = phi [X, Loop] 235 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1 236 // br Loop ;; %x2 does not dominate all uses 237 // 238 // This is because the PHI node input is actually taken from the predecessor 239 // basic block. The only case this can happen is with a self loop, so we 240 // check for this case explicitly now. 241 // 242 unsigned max_idx = APN->getNumIncomingValues(); 243 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!"); 244 if (max_idx == 2) { 245 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred); 246 247 // Disable PHI elimination! 248 if (this == Other) max_idx = 3; 249 } 250 251 // <= Two predecessors BEFORE I remove one? 252 if (max_idx <= 2 && !DontDeleteUselessPHIs) { 253 // Yup, loop through and nuke the PHI nodes 254 while (PHINode *PN = dyn_cast<PHINode>(&front())) { 255 // Remove the predecessor first. 256 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs); 257 258 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value 259 if (max_idx == 2) { 260 if (PN->getIncomingValue(0) != PN) 261 PN->replaceAllUsesWith(PN->getIncomingValue(0)); 262 else 263 // We are left with an infinite loop with no entries: kill the PHI. 264 PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 265 getInstList().pop_front(); // Remove the PHI node 266 } 267 268 // If the PHI node already only had one entry, it got deleted by 269 // removeIncomingValue. 270 } 271 } else { 272 // Okay, now we know that we need to remove predecessor #pred_idx from all 273 // PHI nodes. Iterate over each PHI node fixing them up 274 PHINode *PN; 275 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) { 276 ++II; 277 PN->removeIncomingValue(Pred, false); 278 // If all incoming values to the Phi are the same, we can replace the Phi 279 // with that value. 280 Value* PNV = nullptr; 281 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) 282 if (PNV != PN) { 283 PN->replaceAllUsesWith(PNV); 284 PN->eraseFromParent(); 285 } 286 } 287 } 288} 289 290 291/// splitBasicBlock - This splits a basic block into two at the specified 292/// instruction. Note that all instructions BEFORE the specified iterator stay 293/// as part of the original basic block, an unconditional branch is added to 294/// the new BB, and the rest of the instructions in the BB are moved to the new 295/// BB, including the old terminator. This invalidates the iterator. 296/// 297/// Note that this only works on well formed basic blocks (must have a 298/// terminator), and 'I' must not be the end of instruction list (which would 299/// cause a degenerate basic block to be formed, having a terminator inside of 300/// the basic block). 301/// 302BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) { 303 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!"); 304 assert(I != InstList.end() && 305 "Trying to get me to create degenerate basic block!"); 306 307 BasicBlock *InsertBefore = std::next(Function::iterator(this)) 308 .getNodePtrUnchecked(); 309 BasicBlock *New = BasicBlock::Create(getContext(), BBName, 310 getParent(), InsertBefore); 311 312 // Move all of the specified instructions from the original basic block into 313 // the new basic block. 314 New->getInstList().splice(New->end(), this->getInstList(), I, end()); 315 316 // Add a branch instruction to the newly formed basic block. 317 BranchInst::Create(New, this); 318 319 // Now we must loop through all of the successors of the New block (which 320 // _were_ the successors of the 'this' block), and update any PHI nodes in 321 // successors. If there were PHI nodes in the successors, then they need to 322 // know that incoming branches will be from New, not from Old. 323 // 324 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) { 325 // Loop over any phi nodes in the basic block, updating the BB field of 326 // incoming values... 327 BasicBlock *Successor = *I; 328 PHINode *PN; 329 for (BasicBlock::iterator II = Successor->begin(); 330 (PN = dyn_cast<PHINode>(II)); ++II) { 331 int IDX = PN->getBasicBlockIndex(this); 332 while (IDX != -1) { 333 PN->setIncomingBlock((unsigned)IDX, New); 334 IDX = PN->getBasicBlockIndex(this); 335 } 336 } 337 } 338 return New; 339} 340 341void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) { 342 TerminatorInst *TI = getTerminator(); 343 if (!TI) 344 // Cope with being called on a BasicBlock that doesn't have a terminator 345 // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this. 346 return; 347 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { 348 BasicBlock *Succ = TI->getSuccessor(i); 349 // N.B. Succ might not be a complete BasicBlock, so don't assume 350 // that it ends with a non-phi instruction. 351 for (iterator II = Succ->begin(), IE = Succ->end(); II != IE; ++II) { 352 PHINode *PN = dyn_cast<PHINode>(II); 353 if (!PN) 354 break; 355 int i; 356 while ((i = PN->getBasicBlockIndex(this)) >= 0) 357 PN->setIncomingBlock(i, New); 358 } 359 } 360} 361 362/// isLandingPad - Return true if this basic block is a landing pad. I.e., it's 363/// the destination of the 'unwind' edge of an invoke instruction. 364bool BasicBlock::isLandingPad() const { 365 return isa<LandingPadInst>(getFirstNonPHI()); 366} 367 368/// getLandingPadInst() - Return the landingpad instruction associated with 369/// the landing pad. 370LandingPadInst *BasicBlock::getLandingPadInst() { 371 return dyn_cast<LandingPadInst>(getFirstNonPHI()); 372} 373const LandingPadInst *BasicBlock::getLandingPadInst() const { 374 return dyn_cast<LandingPadInst>(getFirstNonPHI()); 375} 376