lib/IR/BasicBlock.cpp

   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/Type.h"
  23 #include <algorithm>
  24
  25 using namespace llvm;
  26
  27 ValueSymbolTable *BasicBlock::getValueSymbolTable() {
  28   if (Function *F = getParent())
  29     return F->getValueSymbolTable();
  30   return nullptr;
  31 }
  32
  33 LLVMContext &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...
  39 template class llvm::SymbolTableListTraits<Instruction>;
  40
  41 BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent,
  42                        BasicBlock *InsertBefore)
  43   : Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(nullptr) {
  44
  45   if (NewParent)
  46     insertInto(NewParent, InsertBefore);
  47   else
  48     assert(!InsertBefore &&
  49            "Cannot insert block before another block with no function!");
  50
  51   setName(Name);
  52 }
  53
  54 void BasicBlock::insertInto(Function *NewParent, BasicBlock *InsertBefore) {
  55   assert(NewParent && "Expected a parent");
  56   assert(!Parent && "Already has a parent");
  57
  58   if (InsertBefore)
  59     NewParent->getBasicBlockList().insert(InsertBefore->getIterator(), this);
  60   else
  61     NewParent->getBasicBlockList().push_back(this);
  62 }
  63
  64 BasicBlock::~BasicBlock() {
  65   // If the address of the block is taken and it is being deleted (e.g. because
  66   // it is dead), this means that there is either a dangling constant expr
  67   // hanging off the block, or an undefined use of the block (source code
  68   // expecting the address of a label to keep the block alive even though there
  69   // is no indirect branch).  Handle these cases by zapping the BlockAddress
  70   // nodes.  There are no other possible uses at this point.
  71   if (hasAddressTaken()) {
  72     assert(!use_empty() && "There should be at least one blockaddress!");
  73     Constant *Replacement =
  74       ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1);
  75     while (!use_empty()) {
  76       BlockAddress *BA = cast<BlockAddress>(user_back());
  77       BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
  78                                                        BA->getType()));
  79       BA->destroyConstant();
  80     }
  81   }
  82
  83   assert(getParent() == nullptr && "BasicBlock still linked into the program!");
  84   dropAllReferences();
  85   InstList.clear();
  86 }
  87
  88 void BasicBlock::setParent(Function *parent) {
  89   // Set Parent=parent, updating instruction symtab entries as appropriate.
  90   InstList.setSymTabObject(&Parent, parent);
  91 }
  92
  93 iterator_range<filter_iterator<BasicBlock::const_iterator,
  94                                std::function<bool(const Instruction &)>>>
  95 BasicBlock::instructionsWithoutDebug() const {
  96   std::function<bool(const Instruction &)> Fn = [](const Instruction &I) {
  97     return !isa<DbgInfoIntrinsic>(I);
  98   };
  99   return make_filter_range(*this, Fn);
 100 }
 101
 102 iterator_range<filter_iterator<BasicBlock::iterator,
 103                                std::function<bool(Instruction &)>>>
 104 BasicBlock::instructionsWithoutDebug() {
 105   std::function<bool(Instruction &)> Fn = [](Instruction &I) {
 106     return !isa<DbgInfoIntrinsic>(I);
 107   };
 108   return make_filter_range(*this, Fn);
 109 }
 110
 111 void BasicBlock::removeFromParent() {
 112   getParent()->getBasicBlockList().remove(getIterator());
 113 }
 114
 115 iplist<BasicBlock>::iterator BasicBlock::eraseFromParent() {
 116   return getParent()->getBasicBlockList().erase(getIterator());
 117 }
 118
 119 /// Unlink this basic block from its current function and
 120 /// insert it into the function that MovePos lives in, right before MovePos.
 121 void BasicBlock::moveBefore(BasicBlock *MovePos) {
 122   MovePos->getParent()->getBasicBlockList().splice(
 123       MovePos->getIterator(), getParent()->getBasicBlockList(), getIterator());
 124 }
 125
 126 /// Unlink this basic block from its current function and
 127 /// insert it into the function that MovePos lives in, right after MovePos.
 128 void BasicBlock::moveAfter(BasicBlock *MovePos) {
 129   MovePos->getParent()->getBasicBlockList().splice(
 130       ++MovePos->getIterator(), getParent()->getBasicBlockList(),
 131       getIterator());
 132 }
 133
 134 const Module *BasicBlock::getModule() const {
 135   return getParent()->getParent();
 136 }
 137
 138 const TerminatorInst *BasicBlock::getTerminator() const {
 139   if (InstList.empty()) return nullptr;
 140   return dyn_cast<TerminatorInst>(&InstList.back());
 141 }
 142
 143 const CallInst *BasicBlock::getTerminatingMustTailCall() const {
 144   if (InstList.empty())
 145     return nullptr;
 146   const ReturnInst *RI = dyn_cast<ReturnInst>(&InstList.back());
 147   if (!RI || RI == &InstList.front())
 148     return nullptr;
 149
 150   const Instruction *Prev = RI->getPrevNode();
 151   if (!Prev)
 152     return nullptr;
 153
 154   if (Value *RV = RI->getReturnValue()) {
 155     if (RV != Prev)
 156       return nullptr;
 157
 158     // Look through the optional bitcast.
 159     if (auto *BI = dyn_cast<BitCastInst>(Prev)) {
 160       RV = BI->getOperand(0);
 161       Prev = BI->getPrevNode();
 162       if (!Prev || RV != Prev)
 163         return nullptr;
 164     }
 165   }
 166
 167   if (auto *CI = dyn_cast<CallInst>(Prev)) {
 168     if (CI->isMustTailCall())
 169       return CI;
 170   }
 171   return nullptr;
 172 }
 173
 174 const CallInst *BasicBlock::getTerminatingDeoptimizeCall() const {
 175   if (InstList.empty())
 176     return nullptr;
 177   auto *RI = dyn_cast<ReturnInst>(&InstList.back());
 178   if (!RI || RI == &InstList.front())
 179     return nullptr;
 180
 181   if (auto *CI = dyn_cast_or_null<CallInst>(RI->getPrevNode()))
 182     if (Function *F = CI->getCalledFunction())
 183       if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize)
 184         return CI;
 185
 186   return nullptr;
 187 }
 188
 189 const Instruction* BasicBlock::getFirstNonPHI() const {
 190   for (const Instruction &I : *this)
 191     if (!isa<PHINode>(I))
 192       return &I;
 193   return nullptr;
 194 }
 195
 196 const Instruction* BasicBlock::getFirstNonPHIOrDbg() const {
 197   for (const Instruction &I : *this)
 198     if (!isa<PHINode>(I) && !isa<DbgInfoIntrinsic>(I))
 199       return &I;
 200   return nullptr;
 201 }
 202
 203 const Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() const {
 204   for (const Instruction &I : *this) {
 205     if (isa<PHINode>(I) || isa<DbgInfoIntrinsic>(I))
 206       continue;
 207
 208     if (auto *II = dyn_cast<IntrinsicInst>(&I))
 209       if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
 210           II->getIntrinsicID() == Intrinsic::lifetime_end)
 211         continue;
 212
 213     return &I;
 214   }
 215   return nullptr;
 216 }
 217
 218 BasicBlock::const_iterator BasicBlock::getFirstInsertionPt() const {
 219   const Instruction *FirstNonPHI = getFirstNonPHI();
 220   if (!FirstNonPHI)
 221     return end();
 222
 223   const_iterator InsertPt = FirstNonPHI->getIterator();
 224   if (InsertPt->isEHPad()) ++InsertPt;
 225   return InsertPt;
 226 }
 227
 228 void BasicBlock::dropAllReferences() {
 229   for (Instruction &I : *this)
 230     I.dropAllReferences();
 231 }
 232
 233 /// If this basic block has a single predecessor block,
 234 /// return the block, otherwise return a null pointer.
 235 const BasicBlock *BasicBlock::getSinglePredecessor() const {
 236   const_pred_iterator PI = pred_begin(this), E = pred_end(this);
 237   if (PI == E) return nullptr;         // No preds.
 238   const BasicBlock *ThePred = *PI;
 239   ++PI;
 240   return (PI == E) ? ThePred : nullptr /*multiple preds*/;
 241 }
 242
 243 /// If this basic block has a unique predecessor block,
 244 /// return the block, otherwise return a null pointer.
 245 /// Note that unique predecessor doesn't mean single edge, there can be
 246 /// multiple edges from the unique predecessor to this block (for example
 247 /// a switch statement with multiple cases having the same destination).
 248 const BasicBlock *BasicBlock::getUniquePredecessor() const {
 249   const_pred_iterator PI = pred_begin(this), E = pred_end(this);
 250   if (PI == E) return nullptr; // No preds.
 251   const BasicBlock *PredBB = *PI;
 252   ++PI;
 253   for (;PI != E; ++PI) {
 254     if (*PI != PredBB)
 255       return nullptr;
 256     // The same predecessor appears multiple times in the predecessor list.
 257     // This is OK.
 258   }
 259   return PredBB;
 260 }
 261
 262 const BasicBlock *BasicBlock::getSingleSuccessor() const {
 263   succ_const_iterator SI = succ_begin(this), E = succ_end(this);
 264   if (SI == E) return nullptr; // no successors
 265   const BasicBlock *TheSucc = *SI;
 266   ++SI;
 267   return (SI == E) ? TheSucc : nullptr /* multiple successors */;
 268 }
 269
 270 const BasicBlock *BasicBlock::getUniqueSuccessor() const {
 271   succ_const_iterator SI = succ_begin(this), E = succ_end(this);
 272   if (SI == E) return nullptr; // No successors
 273   const BasicBlock *SuccBB = *SI;
 274   ++SI;
 275   for (;SI != E; ++SI) {
 276     if (*SI != SuccBB)
 277       return nullptr;
 278     // The same successor appears multiple times in the successor list.
 279     // This is OK.
 280   }
 281   return SuccBB;
 282 }
 283
 284 iterator_range<BasicBlock::phi_iterator> BasicBlock::phis() {
 285   PHINode *P = empty() ? nullptr : dyn_cast<PHINode>(&*begin());
 286   return make_range<phi_iterator>(P, nullptr);
 287 }
 288
 289 /// This method is used to notify a BasicBlock that the
 290 /// specified Predecessor of the block is no longer able to reach it.  This is
 291 /// actually not used to update the Predecessor list, but is actually used to
 292 /// update the PHI nodes that reside in the block.  Note that this should be
 293 /// called while the predecessor still refers to this block.
 294 ///
 295 void BasicBlock::removePredecessor(BasicBlock *Pred,
 296                                    bool DontDeleteUselessPHIs) {
 297   assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
 298           find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
 299          "removePredecessor: BB is not a predecessor!");
 300
 301   if (InstList.empty()) return;
 302   PHINode *APN = dyn_cast<PHINode>(&front());
 303   if (!APN) return;   // Quick exit.
 304
 305   // If there are exactly two predecessors, then we want to nuke the PHI nodes
 306   // altogether.  However, we cannot do this, if this in this case:
 307   //
 308   //  Loop:
 309   //    %x = phi [X, Loop]
 310   //    %x2 = add %x, 1         ;; This would become %x2 = add %x2, 1
 311   //    br Loop                 ;; %x2 does not dominate all uses
 312   //
 313   // This is because the PHI node input is actually taken from the predecessor
 314   // basic block.  The only case this can happen is with a self loop, so we
 315   // check for this case explicitly now.
 316   //
 317   unsigned max_idx = APN->getNumIncomingValues();
 318   assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
 319   if (max_idx == 2) {
 320     BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
 321
 322     // Disable PHI elimination!
 323     if (this == Other) max_idx = 3;
 324   }
 325
 326   // <= Two predecessors BEFORE I remove one?
 327   if (max_idx <= 2 && !DontDeleteUselessPHIs) {
 328     // Yup, loop through and nuke the PHI nodes
 329     while (PHINode *PN = dyn_cast<PHINode>(&front())) {
 330       // Remove the predecessor first.
 331       PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
 332
 333       // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
 334       if (max_idx == 2) {
 335         if (PN->getIncomingValue(0) != PN)
 336           PN->replaceAllUsesWith(PN->getIncomingValue(0));
 337         else
 338           // We are left with an infinite loop with no entries: kill the PHI.
 339           PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
 340         getInstList().pop_front();    // Remove the PHI node
 341       }
 342
 343       // If the PHI node already only had one entry, it got deleted by
 344       // removeIncomingValue.
 345     }
 346   } else {
 347     // Okay, now we know that we need to remove predecessor #pred_idx from all
 348     // PHI nodes.  Iterate over each PHI node fixing them up
 349     PHINode *PN;
 350     for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
 351       ++II;
 352       PN->removeIncomingValue(Pred, false);
 353       // If all incoming values to the Phi are the same, we can replace the Phi
 354       // with that value.
 355       Value* PNV = nullptr;
 356       if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue()))
 357         if (PNV != PN) {
 358           PN->replaceAllUsesWith(PNV);
 359           PN->eraseFromParent();
 360         }
 361     }
 362   }
 363 }
 364
 365 bool BasicBlock::canSplitPredecessors() const {
 366   const Instruction *FirstNonPHI = getFirstNonPHI();
 367   if (isa<LandingPadInst>(FirstNonPHI))
 368     return true;
 369   // This is perhaps a little conservative because constructs like
 370   // CleanupBlockInst are pretty easy to split.  However, SplitBlockPredecessors
 371   // cannot handle such things just yet.
 372   if (FirstNonPHI->isEHPad())
 373     return false;
 374   return true;
 375 }
 376
 377 bool BasicBlock::isLegalToHoistInto() const {
 378   auto *Term = getTerminator();
 379   // No terminator means the block is under construction.
 380   if (!Term)
 381     return true;
 382
 383   // If the block has no successors, there can be no instructions to hoist.
 384   assert(Term->getNumSuccessors() > 0);
 385
 386   // Instructions should not be hoisted across exception handling boundaries.
 387   return !Term->isExceptionalTerminator();
 388 }
 389
 390 /// This splits a basic block into two at the specified
 391 /// instruction.  Note that all instructions BEFORE the specified iterator stay
 392 /// as part of the original basic block, an unconditional branch is added to
 393 /// the new BB, and the rest of the instructions in the BB are moved to the new
 394 /// BB, including the old terminator.  This invalidates the iterator.
 395 ///
 396 /// Note that this only works on well formed basic blocks (must have a
 397 /// terminator), and 'I' must not be the end of instruction list (which would
 398 /// cause a degenerate basic block to be formed, having a terminator inside of
 399 /// the basic block).
 400 ///
 401 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
 402   assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
 403   assert(I != InstList.end() &&
 404          "Trying to get me to create degenerate basic block!");
 405
 406   BasicBlock *New = BasicBlock::Create(getContext(), BBName, getParent(),
 407                                        this->getNextNode());
 408
 409   // Save DebugLoc of split point before invalidating iterator.
 410   DebugLoc Loc = I->getDebugLoc();
 411   // Move all of the specified instructions from the original basic block into
 412   // the new basic block.
 413   New->getInstList().splice(New->end(), this->getInstList(), I, end());
 414
 415   // Add a branch instruction to the newly formed basic block.
 416   BranchInst *BI = BranchInst::Create(New, this);
 417   BI->setDebugLoc(Loc);
 418
 419   // Now we must loop through all of the successors of the New block (which
 420   // _were_ the successors of the 'this' block), and update any PHI nodes in
 421   // successors.  If there were PHI nodes in the successors, then they need to
 422   // know that incoming branches will be from New, not from Old.
 423   //
 424   for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
 425     // Loop over any phi nodes in the basic block, updating the BB field of
 426     // incoming values...
 427     BasicBlock *Successor = *I;
 428     for (auto &PN : Successor->phis()) {
 429       int Idx = PN.getBasicBlockIndex(this);
 430       while (Idx != -1) {
 431         PN.setIncomingBlock((unsigned)Idx, New);
 432         Idx = PN.getBasicBlockIndex(this);
 433       }
 434     }
 435   }
 436   return New;
 437 }
 438
 439 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
 440   TerminatorInst *TI = getTerminator();
 441   if (!TI)
 442     // Cope with being called on a BasicBlock that doesn't have a terminator
 443     // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
 444     return;
 445   for (BasicBlock *Succ : successors(TI)) {
 446     // N.B. Succ might not be a complete BasicBlock, so don't assume
 447     // that it ends with a non-phi instruction.
 448     for (iterator II = Succ->begin(), IE = Succ->end(); II != IE; ++II) {
 449       PHINode *PN = dyn_cast<PHINode>(II);
 450       if (!PN)
 451         break;
 452       int i;
 453       while ((i = PN->getBasicBlockIndex(this)) >= 0)
 454         PN->setIncomingBlock(i, New);
 455     }
 456   }
 457 }
 458
 459 /// Return true if this basic block is a landing pad. I.e., it's
 460 /// the destination of the 'unwind' edge of an invoke instruction.
 461 bool BasicBlock::isLandingPad() const {
 462   return isa<LandingPadInst>(getFirstNonPHI());
 463 }
 464
 465 /// Return the landingpad instruction associated with the landing pad.
 466 const LandingPadInst *BasicBlock::getLandingPadInst() const {
 467   return dyn_cast<LandingPadInst>(getFirstNonPHI());
 468 }
 469
 470 Optional<uint64_t> BasicBlock::getIrrLoopHeaderWeight() const {
 471   const TerminatorInst *TI = getTerminator();
 472   if (MDNode *MDIrrLoopHeader =
 473       TI->getMetadata(LLVMContext::MD_irr_loop)) {
 474     MDString *MDName = cast<MDString>(MDIrrLoopHeader->getOperand(0));
 475     if (MDName->getString().equals("loop_header_weight")) {
 476       auto *CI = mdconst::extract<ConstantInt>(MDIrrLoopHeader->getOperand(1));
 477       return Optional<uint64_t>(CI->getValue().getZExtValue());
 478     }
 479   }
 480   return Optional<uint64_t>();
 481 }
 482
 483 BasicBlock::iterator llvm::skipDebugIntrinsics(BasicBlock::iterator It) {
 484   while (isa<DbgInfoIntrinsic>(It))
 485     ++It;
 486   return It;
 487 }