lib/IR/BasicBlock.cpp

   1 //===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the BasicBlock class for the IR library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/IR/BasicBlock.h"
  14 #include "SymbolTableListTraitsImpl.h"
  15 #include "llvm/ADT/STLExtras.h"
  16 #include "llvm/IR/CFG.h"
  17 #include "llvm/IR/Constants.h"
  18 #include "llvm/IR/Instructions.h"
  19 #include "llvm/IR/IntrinsicInst.h"
  20 #include "llvm/IR/LLVMContext.h"
  21 #include "llvm/IR/Type.h"
  22 #include <algorithm>
  23
  24 using namespace llvm;
  25
  26 ValueSymbolTable *BasicBlock::getValueSymbolTable() {
  27   if (Function *F = getParent())
  28     return F->getValueSymbolTable();
  29   return nullptr;
  30 }
  31
  32 LLVMContext &BasicBlock::getContext() const {
  33   return getType()->getContext();
  34 }
  35
  36 // Explicit instantiation of SymbolTableListTraits since some of the methods
  37 // are not in the public header file...
  38 template class llvm::SymbolTableListTraits<Instruction>;
  39
  40 BasicBlock::BasicBlock(LLVMContext &C, const Twine &Name, Function *NewParent,
  41                        BasicBlock *InsertBefore)
  42   : Value(Type::getLabelTy(C), Value::BasicBlockVal), Parent(nullptr) {
  43
  44   if (NewParent)
  45     insertInto(NewParent, InsertBefore);
  46   else
  47     assert(!InsertBefore &&
  48            "Cannot insert block before another block with no function!");
  49
  50   setName(Name);
  51 }
  52
  53 void BasicBlock::insertInto(Function *NewParent, BasicBlock *InsertBefore) {
  54   assert(NewParent && "Expected a parent");
  55   assert(!Parent && "Already has a parent");
  56
  57   if (InsertBefore)
  58     NewParent->getBasicBlockList().insert(InsertBefore->getIterator(), this);
  59   else
  60     NewParent->getBasicBlockList().push_back(this);
  61 }
  62
  63 BasicBlock::~BasicBlock() {
  64   // If the address of the block is taken and it is being deleted (e.g. because
  65   // it is dead), this means that there is either a dangling constant expr
  66   // hanging off the block, or an undefined use of the block (source code
  67   // expecting the address of a label to keep the block alive even though there
  68   // is no indirect branch).  Handle these cases by zapping the BlockAddress
  69   // nodes.  There are no other possible uses at this point.
  70   if (hasAddressTaken()) {
  71     assert(!use_empty() && "There should be at least one blockaddress!");
  72     Constant *Replacement =
  73       ConstantInt::get(llvm::Type::getInt32Ty(getContext()), 1);
  74     while (!use_empty()) {
  75       BlockAddress *BA = cast<BlockAddress>(user_back());
  76       BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
  77                                                        BA->getType()));
  78       BA->destroyConstant();
  79     }
  80   }
  81
  82   assert(getParent() == nullptr && "BasicBlock still linked into the program!");
  83   dropAllReferences();
  84   InstList.clear();
  85 }
  86
  87 void BasicBlock::setParent(Function *parent) {
  88   // Set Parent=parent, updating instruction symtab entries as appropriate.
  89   InstList.setSymTabObject(&Parent, parent);
  90 }
  91
  92 iterator_range<filter_iterator<BasicBlock::const_iterator,
  93                                std::function<bool(const Instruction &)>>>
  94 BasicBlock::instructionsWithoutDebug() const {
  95   std::function<bool(const Instruction &)> Fn = [](const Instruction &I) {
  96     return !isa<DbgInfoIntrinsic>(I);
  97   };
  98   return make_filter_range(*this, Fn);
  99 }
 100
 101 iterator_range<filter_iterator<BasicBlock::iterator,
 102                                std::function<bool(Instruction &)>>>
 103 BasicBlock::instructionsWithoutDebug() {
 104   std::function<bool(Instruction &)> Fn = [](Instruction &I) {
 105     return !isa<DbgInfoIntrinsic>(I);
 106   };
 107   return make_filter_range(*this, Fn);
 108 }
 109
 110 void BasicBlock::removeFromParent() {
 111   getParent()->getBasicBlockList().remove(getIterator());
 112 }
 113
 114 iplist<BasicBlock>::iterator BasicBlock::eraseFromParent() {
 115   return getParent()->getBasicBlockList().erase(getIterator());
 116 }
 117
 118 /// Unlink this basic block from its current function and
 119 /// insert it into the function that MovePos lives in, right before MovePos.
 120 void BasicBlock::moveBefore(BasicBlock *MovePos) {
 121   MovePos->getParent()->getBasicBlockList().splice(
 122       MovePos->getIterator(), getParent()->getBasicBlockList(), getIterator());
 123 }
 124
 125 /// Unlink this basic block from its current function and
 126 /// insert it into the function that MovePos lives in, right after MovePos.
 127 void BasicBlock::moveAfter(BasicBlock *MovePos) {
 128   MovePos->getParent()->getBasicBlockList().splice(
 129       ++MovePos->getIterator(), getParent()->getBasicBlockList(),
 130       getIterator());
 131 }
 132
 133 const Module *BasicBlock::getModule() const {
 134   return getParent()->getParent();
 135 }
 136
 137 const Instruction *BasicBlock::getTerminator() const {
 138   if (InstList.empty() || !InstList.back().isTerminator())
 139     return nullptr;
 140   return &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 (I.isLifetimeStartOrEnd())
 209       continue;
 210
 211     return &I;
 212   }
 213   return nullptr;
 214 }
 215
 216 BasicBlock::const_iterator BasicBlock::getFirstInsertionPt() const {
 217   const Instruction *FirstNonPHI = getFirstNonPHI();
 218   if (!FirstNonPHI)
 219     return end();
 220
 221   const_iterator InsertPt = FirstNonPHI->getIterator();
 222   if (InsertPt->isEHPad()) ++InsertPt;
 223   return InsertPt;
 224 }
 225
 226 void BasicBlock::dropAllReferences() {
 227   for (Instruction &I : *this)
 228     I.dropAllReferences();
 229 }
 230
 231 /// If this basic block has a single predecessor block,
 232 /// return the block, otherwise return a null pointer.
 233 const BasicBlock *BasicBlock::getSinglePredecessor() const {
 234   const_pred_iterator PI = pred_begin(this), E = pred_end(this);
 235   if (PI == E) return nullptr;         // No preds.
 236   const BasicBlock *ThePred = *PI;
 237   ++PI;
 238   return (PI == E) ? ThePred : nullptr /*multiple preds*/;
 239 }
 240
 241 /// If this basic block has a unique predecessor block,
 242 /// return the block, otherwise return a null pointer.
 243 /// Note that unique predecessor doesn't mean single edge, there can be
 244 /// multiple edges from the unique predecessor to this block (for example
 245 /// a switch statement with multiple cases having the same destination).
 246 const BasicBlock *BasicBlock::getUniquePredecessor() const {
 247   const_pred_iterator PI = pred_begin(this), E = pred_end(this);
 248   if (PI == E) return nullptr; // No preds.
 249   const BasicBlock *PredBB = *PI;
 250   ++PI;
 251   for (;PI != E; ++PI) {
 252     if (*PI != PredBB)
 253       return nullptr;
 254     // The same predecessor appears multiple times in the predecessor list.
 255     // This is OK.
 256   }
 257   return PredBB;
 258 }
 259
 260 bool BasicBlock::hasNPredecessors(unsigned N) const {
 261   return hasNItems(pred_begin(this), pred_end(this), N);
 262 }
 263
 264 bool BasicBlock::hasNPredecessorsOrMore(unsigned N) const {
 265   return hasNItemsOrMore(pred_begin(this), pred_end(this), N);
 266 }
 267
 268 const BasicBlock *BasicBlock::getSingleSuccessor() const {
 269   succ_const_iterator SI = succ_begin(this), E = succ_end(this);
 270   if (SI == E) return nullptr; // no successors
 271   const BasicBlock *TheSucc = *SI;
 272   ++SI;
 273   return (SI == E) ? TheSucc : nullptr /* multiple successors */;
 274 }
 275
 276 const BasicBlock *BasicBlock::getUniqueSuccessor() const {
 277   succ_const_iterator SI = succ_begin(this), E = succ_end(this);
 278   if (SI == E) return nullptr; // No successors
 279   const BasicBlock *SuccBB = *SI;
 280   ++SI;
 281   for (;SI != E; ++SI) {
 282     if (*SI != SuccBB)
 283       return nullptr;
 284     // The same successor appears multiple times in the successor list.
 285     // This is OK.
 286   }
 287   return SuccBB;
 288 }
 289
 290 iterator_range<BasicBlock::phi_iterator> BasicBlock::phis() {
 291   PHINode *P = empty() ? nullptr : dyn_cast<PHINode>(&*begin());
 292   return make_range<phi_iterator>(P, nullptr);
 293 }
 294
 295 /// This method is used to notify a BasicBlock that the
 296 /// specified Predecessor of the block is no longer able to reach it.  This is
 297 /// actually not used to update the Predecessor list, but is actually used to
 298 /// update the PHI nodes that reside in the block.  Note that this should be
 299 /// called while the predecessor still refers to this block.
 300 ///
 301 void BasicBlock::removePredecessor(BasicBlock *Pred,
 302                                    bool KeepOneInputPHIs) {
 303   assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
 304           find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
 305          "removePredecessor: BB is not a predecessor!");
 306
 307   if (InstList.empty()) return;
 308   PHINode *APN = dyn_cast<PHINode>(&front());
 309   if (!APN) return;   // Quick exit.
 310
 311   // If there are exactly two predecessors, then we want to nuke the PHI nodes
 312   // altogether.  However, we cannot do this, if this in this case:
 313   //
 314   //  Loop:
 315   //    %x = phi [X, Loop]
 316   //    %x2 = add %x, 1         ;; This would become %x2 = add %x2, 1
 317   //    br Loop                 ;; %x2 does not dominate all uses
 318   //
 319   // This is because the PHI node input is actually taken from the predecessor
 320   // basic block.  The only case this can happen is with a self loop, so we
 321   // check for this case explicitly now.
 322   //
 323   unsigned max_idx = APN->getNumIncomingValues();
 324   assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
 325   if (max_idx == 2) {
 326     BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
 327
 328     // Disable PHI elimination!
 329     if (this == Other) max_idx = 3;
 330   }
 331
 332   // <= Two predecessors BEFORE I remove one?
 333   if (max_idx <= 2 && !KeepOneInputPHIs) {
 334     // Yup, loop through and nuke the PHI nodes
 335     while (PHINode *PN = dyn_cast<PHINode>(&front())) {
 336       // Remove the predecessor first.
 337       PN->removeIncomingValue(Pred, !KeepOneInputPHIs);
 338
 339       // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
 340       if (max_idx == 2) {
 341         if (PN->getIncomingValue(0) != PN)
 342           PN->replaceAllUsesWith(PN->getIncomingValue(0));
 343         else
 344           // We are left with an infinite loop with no entries: kill the PHI.
 345           PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
 346         getInstList().pop_front();    // Remove the PHI node
 347       }
 348
 349       // If the PHI node already only had one entry, it got deleted by
 350       // removeIncomingValue.
 351     }
 352   } else {
 353     // Okay, now we know that we need to remove predecessor #pred_idx from all
 354     // PHI nodes.  Iterate over each PHI node fixing them up
 355     PHINode *PN;
 356     for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
 357       ++II;
 358       PN->removeIncomingValue(Pred, false);
 359       // If all incoming values to the Phi are the same, we can replace the Phi
 360       // with that value.
 361       Value* PNV = nullptr;
 362       if (!KeepOneInputPHIs && (PNV = PN->hasConstantValue()))
 363         if (PNV != PN) {
 364           PN->replaceAllUsesWith(PNV);
 365           PN->eraseFromParent();
 366         }
 367     }
 368   }
 369 }
 370
 371 bool BasicBlock::canSplitPredecessors() const {
 372   const Instruction *FirstNonPHI = getFirstNonPHI();
 373   if (isa<LandingPadInst>(FirstNonPHI))
 374     return true;
 375   // This is perhaps a little conservative because constructs like
 376   // CleanupBlockInst are pretty easy to split.  However, SplitBlockPredecessors
 377   // cannot handle such things just yet.
 378   if (FirstNonPHI->isEHPad())
 379     return false;
 380   return true;
 381 }
 382
 383 bool BasicBlock::isLegalToHoistInto() const {
 384   auto *Term = getTerminator();
 385   // No terminator means the block is under construction.
 386   if (!Term)
 387     return true;
 388
 389   // If the block has no successors, there can be no instructions to hoist.
 390   assert(Term->getNumSuccessors() > 0);
 391
 392   // Instructions should not be hoisted across exception handling boundaries.
 393   return !Term->isExceptionalTerminator();
 394 }
 395
 396 /// This splits a basic block into two at the specified
 397 /// instruction.  Note that all instructions BEFORE the specified iterator stay
 398 /// as part of the original basic block, an unconditional branch is added to
 399 /// the new BB, and the rest of the instructions in the BB are moved to the new
 400 /// BB, including the old terminator.  This invalidates the iterator.
 401 ///
 402 /// Note that this only works on well formed basic blocks (must have a
 403 /// terminator), and 'I' must not be the end of instruction list (which would
 404 /// cause a degenerate basic block to be formed, having a terminator inside of
 405 /// the basic block).
 406 ///
 407 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
 408   assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
 409   assert(I != InstList.end() &&
 410          "Trying to get me to create degenerate basic block!");
 411
 412   BasicBlock *New = BasicBlock::Create(getContext(), BBName, getParent(),
 413                                        this->getNextNode());
 414
 415   // Save DebugLoc of split point before invalidating iterator.
 416   DebugLoc Loc = I->getDebugLoc();
 417   // Move all of the specified instructions from the original basic block into
 418   // the new basic block.
 419   New->getInstList().splice(New->end(), this->getInstList(), I, end());
 420
 421   // Add a branch instruction to the newly formed basic block.
 422   BranchInst *BI = BranchInst::Create(New, this);
 423   BI->setDebugLoc(Loc);
 424
 425   // Now we must loop through all of the successors of the New block (which
 426   // _were_ the successors of the 'this' block), and update any PHI nodes in
 427   // successors.  If there were PHI nodes in the successors, then they need to
 428   // know that incoming branches will be from New, not from Old (this).
 429   //
 430   New->replaceSuccessorsPhiUsesWith(this, New);
 431   return New;
 432 }
 433
 434 void BasicBlock::replacePhiUsesWith(BasicBlock *Old, BasicBlock *New) {
 435   // N.B. This might not be a complete BasicBlock, so don't assume
 436   // that it ends with a non-phi instruction.
 437   for (iterator II = begin(), IE = end(); II != IE; ++II) {
 438     PHINode *PN = dyn_cast<PHINode>(II);
 439     if (!PN)
 440       break;
 441     PN->replaceIncomingBlockWith(Old, New);
 442   }
 443 }
 444
 445 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *Old,
 446                                               BasicBlock *New) {
 447   Instruction *TI = getTerminator();
 448   if (!TI)
 449     // Cope with being called on a BasicBlock that doesn't have a terminator
 450     // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
 451     return;
 452   llvm::for_each(successors(TI), [Old, New](BasicBlock *Succ) {
 453     Succ->replacePhiUsesWith(Old, New);
 454   });
 455 }
 456
 457 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
 458   this->replaceSuccessorsPhiUsesWith(this, New);
 459 }
 460
 461 /// Return true if this basic block is a landing pad. I.e., it's
 462 /// the destination of the 'unwind' edge of an invoke instruction.
 463 bool BasicBlock::isLandingPad() const {
 464   return isa<LandingPadInst>(getFirstNonPHI());
 465 }
 466
 467 /// Return the landingpad instruction associated with the landing pad.
 468 const LandingPadInst *BasicBlock::getLandingPadInst() const {
 469   return dyn_cast<LandingPadInst>(getFirstNonPHI());
 470 }
 471
 472 Optional<uint64_t> BasicBlock::getIrrLoopHeaderWeight() const {
 473   const Instruction *TI = getTerminator();
 474   if (MDNode *MDIrrLoopHeader =
 475       TI->getMetadata(LLVMContext::MD_irr_loop)) {
 476     MDString *MDName = cast<MDString>(MDIrrLoopHeader->getOperand(0));
 477     if (MDName->getString().equals("loop_header_weight")) {
 478       auto *CI = mdconst::extract<ConstantInt>(MDIrrLoopHeader->getOperand(1));
 479       return Optional<uint64_t>(CI->getValue().getZExtValue());
 480     }
 481   }
 482   return Optional<uint64_t>();
 483 }
 484
 485 BasicBlock::iterator llvm::skipDebugIntrinsics(BasicBlock::iterator It) {
 486   while (isa<DbgInfoIntrinsic>(It))
 487     ++It;
 488   return It;
 489 }