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 filter_iterator<BasicBlock::const_iterator,
 111                 std::function<bool(const Instruction &)>>::difference_type
 112 BasicBlock::sizeWithoutDebug() const {
 113   return std::distance(instructionsWithoutDebug().begin(),
 114                        instructionsWithoutDebug().end());
 115 }
 116
 117 void BasicBlock::removeFromParent() {
 118   getParent()->getBasicBlockList().remove(getIterator());
 119 }
 120
 121 iplist<BasicBlock>::iterator BasicBlock::eraseFromParent() {
 122   return getParent()->getBasicBlockList().erase(getIterator());
 123 }
 124
 125 /// Unlink this basic block from its current function and
 126 /// insert it into the function that MovePos lives in, right before MovePos.
 127 void BasicBlock::moveBefore(BasicBlock *MovePos) {
 128   MovePos->getParent()->getBasicBlockList().splice(
 129       MovePos->getIterator(), getParent()->getBasicBlockList(), getIterator());
 130 }
 131
 132 /// Unlink this basic block from its current function and
 133 /// insert it into the function that MovePos lives in, right after MovePos.
 134 void BasicBlock::moveAfter(BasicBlock *MovePos) {
 135   MovePos->getParent()->getBasicBlockList().splice(
 136       ++MovePos->getIterator(), getParent()->getBasicBlockList(),
 137       getIterator());
 138 }
 139
 140 const Module *BasicBlock::getModule() const {
 141   return getParent()->getParent();
 142 }
 143
 144 const Instruction *BasicBlock::getTerminator() const {
 145   if (InstList.empty() || !InstList.back().isTerminator())
 146     return nullptr;
 147   return &InstList.back();
 148 }
 149
 150 const CallInst *BasicBlock::getTerminatingMustTailCall() const {
 151   if (InstList.empty())
 152     return nullptr;
 153   const ReturnInst *RI = dyn_cast<ReturnInst>(&InstList.back());
 154   if (!RI || RI == &InstList.front())
 155     return nullptr;
 156
 157   const Instruction *Prev = RI->getPrevNode();
 158   if (!Prev)
 159     return nullptr;
 160
 161   if (Value *RV = RI->getReturnValue()) {
 162     if (RV != Prev)
 163       return nullptr;
 164
 165     // Look through the optional bitcast.
 166     if (auto *BI = dyn_cast<BitCastInst>(Prev)) {
 167       RV = BI->getOperand(0);
 168       Prev = BI->getPrevNode();
 169       if (!Prev || RV != Prev)
 170         return nullptr;
 171     }
 172   }
 173
 174   if (auto *CI = dyn_cast<CallInst>(Prev)) {
 175     if (CI->isMustTailCall())
 176       return CI;
 177   }
 178   return nullptr;
 179 }
 180
 181 const CallInst *BasicBlock::getTerminatingDeoptimizeCall() const {
 182   if (InstList.empty())
 183     return nullptr;
 184   auto *RI = dyn_cast<ReturnInst>(&InstList.back());
 185   if (!RI || RI == &InstList.front())
 186     return nullptr;
 187
 188   if (auto *CI = dyn_cast_or_null<CallInst>(RI->getPrevNode()))
 189     if (Function *F = CI->getCalledFunction())
 190       if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize)
 191         return CI;
 192
 193   return nullptr;
 194 }
 195
 196 const Instruction* BasicBlock::getFirstNonPHI() const {
 197   for (const Instruction &I : *this)
 198     if (!isa<PHINode>(I))
 199       return &I;
 200   return nullptr;
 201 }
 202
 203 const Instruction* BasicBlock::getFirstNonPHIOrDbg() const {
 204   for (const Instruction &I : *this)
 205     if (!isa<PHINode>(I) && !isa<DbgInfoIntrinsic>(I))
 206       return &I;
 207   return nullptr;
 208 }
 209
 210 const Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() const {
 211   for (const Instruction &I : *this) {
 212     if (isa<PHINode>(I) || isa<DbgInfoIntrinsic>(I))
 213       continue;
 214
 215     if (I.isLifetimeStartOrEnd())
 216       continue;
 217
 218     return &I;
 219   }
 220   return nullptr;
 221 }
 222
 223 BasicBlock::const_iterator BasicBlock::getFirstInsertionPt() const {
 224   const Instruction *FirstNonPHI = getFirstNonPHI();
 225   if (!FirstNonPHI)
 226     return end();
 227
 228   const_iterator InsertPt = FirstNonPHI->getIterator();
 229   if (InsertPt->isEHPad()) ++InsertPt;
 230   return InsertPt;
 231 }
 232
 233 void BasicBlock::dropAllReferences() {
 234   for (Instruction &I : *this)
 235     I.dropAllReferences();
 236 }
 237
 238 /// If this basic block has a single predecessor block,
 239 /// return the block, otherwise return a null pointer.
 240 const BasicBlock *BasicBlock::getSinglePredecessor() const {
 241   const_pred_iterator PI = pred_begin(this), E = pred_end(this);
 242   if (PI == E) return nullptr;         // No preds.
 243   const BasicBlock *ThePred = *PI;
 244   ++PI;
 245   return (PI == E) ? ThePred : nullptr /*multiple preds*/;
 246 }
 247
 248 /// If this basic block has a unique predecessor block,
 249 /// return the block, otherwise return a null pointer.
 250 /// Note that unique predecessor doesn't mean single edge, there can be
 251 /// multiple edges from the unique predecessor to this block (for example
 252 /// a switch statement with multiple cases having the same destination).
 253 const BasicBlock *BasicBlock::getUniquePredecessor() const {
 254   const_pred_iterator PI = pred_begin(this), E = pred_end(this);
 255   if (PI == E) return nullptr; // No preds.
 256   const BasicBlock *PredBB = *PI;
 257   ++PI;
 258   for (;PI != E; ++PI) {
 259     if (*PI != PredBB)
 260       return nullptr;
 261     // The same predecessor appears multiple times in the predecessor list.
 262     // This is OK.
 263   }
 264   return PredBB;
 265 }
 266
 267 bool BasicBlock::hasNPredecessors(unsigned N) const {
 268   return hasNItems(pred_begin(this), pred_end(this), N);
 269 }
 270
 271 bool BasicBlock::hasNPredecessorsOrMore(unsigned N) const {
 272   return hasNItemsOrMore(pred_begin(this), pred_end(this), N);
 273 }
 274
 275 const BasicBlock *BasicBlock::getSingleSuccessor() const {
 276   succ_const_iterator SI = succ_begin(this), E = succ_end(this);
 277   if (SI == E) return nullptr; // no successors
 278   const BasicBlock *TheSucc = *SI;
 279   ++SI;
 280   return (SI == E) ? TheSucc : nullptr /* multiple successors */;
 281 }
 282
 283 const BasicBlock *BasicBlock::getUniqueSuccessor() const {
 284   succ_const_iterator SI = succ_begin(this), E = succ_end(this);
 285   if (SI == E) return nullptr; // No successors
 286   const BasicBlock *SuccBB = *SI;
 287   ++SI;
 288   for (;SI != E; ++SI) {
 289     if (*SI != SuccBB)
 290       return nullptr;
 291     // The same successor appears multiple times in the successor list.
 292     // This is OK.
 293   }
 294   return SuccBB;
 295 }
 296
 297 iterator_range<BasicBlock::phi_iterator> BasicBlock::phis() {
 298   PHINode *P = empty() ? nullptr : dyn_cast<PHINode>(&*begin());
 299   return make_range<phi_iterator>(P, nullptr);
 300 }
 301
 302 /// This method is used to notify a BasicBlock that the
 303 /// specified Predecessor of the block is no longer able to reach it.  This is
 304 /// actually not used to update the Predecessor list, but is actually used to
 305 /// update the PHI nodes that reside in the block.  Note that this should be
 306 /// called while the predecessor still refers to this block.
 307 ///
 308 void BasicBlock::removePredecessor(BasicBlock *Pred,
 309                                    bool KeepOneInputPHIs) {
 310   assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
 311           find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
 312          "removePredecessor: BB is not a predecessor!");
 313
 314   if (InstList.empty()) return;
 315   PHINode *APN = dyn_cast<PHINode>(&front());
 316   if (!APN) return;   // Quick exit.
 317
 318   // If there are exactly two predecessors, then we want to nuke the PHI nodes
 319   // altogether.  However, we cannot do this, if this in this case:
 320   //
 321   //  Loop:
 322   //    %x = phi [X, Loop]
 323   //    %x2 = add %x, 1         ;; This would become %x2 = add %x2, 1
 324   //    br Loop                 ;; %x2 does not dominate all uses
 325   //
 326   // This is because the PHI node input is actually taken from the predecessor
 327   // basic block.  The only case this can happen is with a self loop, so we
 328   // check for this case explicitly now.
 329   //
 330   unsigned max_idx = APN->getNumIncomingValues();
 331   assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
 332   if (max_idx == 2) {
 333     BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
 334
 335     // Disable PHI elimination!
 336     if (this == Other) max_idx = 3;
 337   }
 338
 339   // <= Two predecessors BEFORE I remove one?
 340   if (max_idx <= 2 && !KeepOneInputPHIs) {
 341     // Yup, loop through and nuke the PHI nodes
 342     while (PHINode *PN = dyn_cast<PHINode>(&front())) {
 343       // Remove the predecessor first.
 344       PN->removeIncomingValue(Pred, !KeepOneInputPHIs);
 345
 346       // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
 347       if (max_idx == 2) {
 348         if (PN->getIncomingValue(0) != PN)
 349           PN->replaceAllUsesWith(PN->getIncomingValue(0));
 350         else
 351           // We are left with an infinite loop with no entries: kill the PHI.
 352           PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
 353         getInstList().pop_front();    // Remove the PHI node
 354       }
 355
 356       // If the PHI node already only had one entry, it got deleted by
 357       // removeIncomingValue.
 358     }
 359   } else {
 360     // Okay, now we know that we need to remove predecessor #pred_idx from all
 361     // PHI nodes.  Iterate over each PHI node fixing them up
 362     PHINode *PN;
 363     for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
 364       ++II;
 365       PN->removeIncomingValue(Pred, false);
 366       // If all incoming values to the Phi are the same, we can replace the Phi
 367       // with that value.
 368       Value* PNV = nullptr;
 369       if (!KeepOneInputPHIs && (PNV = PN->hasConstantValue()))
 370         if (PNV != PN) {
 371           PN->replaceAllUsesWith(PNV);
 372           PN->eraseFromParent();
 373         }
 374     }
 375   }
 376 }
 377
 378 bool BasicBlock::canSplitPredecessors() const {
 379   const Instruction *FirstNonPHI = getFirstNonPHI();
 380   if (isa<LandingPadInst>(FirstNonPHI))
 381     return true;
 382   // This is perhaps a little conservative because constructs like
 383   // CleanupBlockInst are pretty easy to split.  However, SplitBlockPredecessors
 384   // cannot handle such things just yet.
 385   if (FirstNonPHI->isEHPad())
 386     return false;
 387   return true;
 388 }
 389
 390 bool BasicBlock::isLegalToHoistInto() const {
 391   auto *Term = getTerminator();
 392   // No terminator means the block is under construction.
 393   if (!Term)
 394     return true;
 395
 396   // If the block has no successors, there can be no instructions to hoist.
 397   assert(Term->getNumSuccessors() > 0);
 398
 399   // Instructions should not be hoisted across exception handling boundaries.
 400   return !Term->isExceptionalTerminator();
 401 }
 402
 403 /// This splits a basic block into two at the specified
 404 /// instruction.  Note that all instructions BEFORE the specified iterator stay
 405 /// as part of the original basic block, an unconditional branch is added to
 406 /// the new BB, and the rest of the instructions in the BB are moved to the new
 407 /// BB, including the old terminator.  This invalidates the iterator.
 408 ///
 409 /// Note that this only works on well formed basic blocks (must have a
 410 /// terminator), and 'I' must not be the end of instruction list (which would
 411 /// cause a degenerate basic block to be formed, having a terminator inside of
 412 /// the basic block).
 413 ///
 414 BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
 415   assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
 416   assert(I != InstList.end() &&
 417          "Trying to get me to create degenerate basic block!");
 418
 419   BasicBlock *New = BasicBlock::Create(getContext(), BBName, getParent(),
 420                                        this->getNextNode());
 421
 422   // Save DebugLoc of split point before invalidating iterator.
 423   DebugLoc Loc = I->getDebugLoc();
 424   // Move all of the specified instructions from the original basic block into
 425   // the new basic block.
 426   New->getInstList().splice(New->end(), this->getInstList(), I, end());
 427
 428   // Add a branch instruction to the newly formed basic block.
 429   BranchInst *BI = BranchInst::Create(New, this);
 430   BI->setDebugLoc(Loc);
 431
 432   // Now we must loop through all of the successors of the New block (which
 433   // _were_ the successors of the 'this' block), and update any PHI nodes in
 434   // successors.  If there were PHI nodes in the successors, then they need to
 435   // know that incoming branches will be from New, not from Old (this).
 436   //
 437   New->replaceSuccessorsPhiUsesWith(this, New);
 438   return New;
 439 }
 440
 441 void BasicBlock::replacePhiUsesWith(BasicBlock *Old, BasicBlock *New) {
 442   // N.B. This might not be a complete BasicBlock, so don't assume
 443   // that it ends with a non-phi instruction.
 444   for (iterator II = begin(), IE = end(); II != IE; ++II) {
 445     PHINode *PN = dyn_cast<PHINode>(II);
 446     if (!PN)
 447       break;
 448     PN->replaceIncomingBlockWith(Old, New);
 449   }
 450 }
 451
 452 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *Old,
 453                                               BasicBlock *New) {
 454   Instruction *TI = getTerminator();
 455   if (!TI)
 456     // Cope with being called on a BasicBlock that doesn't have a terminator
 457     // yet. Clang's CodeGenFunction::EmitReturnBlock() likes to do this.
 458     return;
 459   llvm::for_each(successors(TI), [Old, New](BasicBlock *Succ) {
 460     Succ->replacePhiUsesWith(Old, New);
 461   });
 462 }
 463
 464 void BasicBlock::replaceSuccessorsPhiUsesWith(BasicBlock *New) {
 465   this->replaceSuccessorsPhiUsesWith(this, New);
 466 }
 467
 468 /// Return true if this basic block is a landing pad. I.e., it's
 469 /// the destination of the 'unwind' edge of an invoke instruction.
 470 bool BasicBlock::isLandingPad() const {
 471   return isa<LandingPadInst>(getFirstNonPHI());
 472 }
 473
 474 /// Return the landingpad instruction associated with the landing pad.
 475 const LandingPadInst *BasicBlock::getLandingPadInst() const {
 476   return dyn_cast<LandingPadInst>(getFirstNonPHI());
 477 }
 478
 479 Optional<uint64_t> BasicBlock::getIrrLoopHeaderWeight() const {
 480   const Instruction *TI = getTerminator();
 481   if (MDNode *MDIrrLoopHeader =
 482       TI->getMetadata(LLVMContext::MD_irr_loop)) {
 483     MDString *MDName = cast<MDString>(MDIrrLoopHeader->getOperand(0));
 484     if (MDName->getString().equals("loop_header_weight")) {
 485       auto *CI = mdconst::extract<ConstantInt>(MDIrrLoopHeader->getOperand(1));
 486       return Optional<uint64_t>(CI->getValue().getZExtValue());
 487     }
 488   }
 489   return Optional<uint64_t>();
 490 }
 491
 492 BasicBlock::iterator llvm::skipDebugIntrinsics(BasicBlock::iterator It) {
 493   while (isa<DbgInfoIntrinsic>(It))
 494     ++It;
 495   return It;
 496 }