lib/Transforms/Utils/BasicBlockUtils.cpp

   1 //===- BasicBlockUtils.cpp - BasicBlock Utilities --------------------------==//
   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 family of functions perform manipulations on basic blocks, and
  10 // instructions contained within basic blocks.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  15 #include "llvm/ADT/ArrayRef.h"
  16 #include "llvm/ADT/SmallPtrSet.h"
  17 #include "llvm/ADT/SmallVector.h"
  18 #include "llvm/ADT/Twine.h"
  19 #include "llvm/Analysis/CFG.h"
  20 #include "llvm/Analysis/DomTreeUpdater.h"
  21 #include "llvm/Analysis/LoopInfo.h"
  22 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
  23 #include "llvm/Analysis/MemorySSAUpdater.h"
  24 #include "llvm/Analysis/PostDominators.h"
  25 #include "llvm/IR/BasicBlock.h"
  26 #include "llvm/IR/CFG.h"
  27 #include "llvm/IR/Constants.h"
  28 #include "llvm/IR/DebugInfoMetadata.h"
  29 #include "llvm/IR/Dominators.h"
  30 #include "llvm/IR/Function.h"
  31 #include "llvm/IR/InstrTypes.h"
  32 #include "llvm/IR/Instruction.h"
  33 #include "llvm/IR/Instructions.h"
  34 #include "llvm/IR/IntrinsicInst.h"
  35 #include "llvm/IR/LLVMContext.h"
  36 #include "llvm/IR/Type.h"
  37 #include "llvm/IR/User.h"
  38 #include "llvm/IR/Value.h"
  39 #include "llvm/IR/ValueHandle.h"
  40 #include "llvm/Support/Casting.h"
  41 #include "llvm/Support/Debug.h"
  42 #include "llvm/Support/raw_ostream.h"
  43 #include "llvm/Transforms/Utils/Local.h"
  44 #include <cassert>
  45 #include <cstdint>
  46 #include <string>
  47 #include <utility>
  48 #include <vector>
  49
  50 using namespace llvm;
  51
  52 #define DEBUG_TYPE "basicblock-utils"
  53
  54 void llvm::DetatchDeadBlocks(
  55     ArrayRef<BasicBlock *> BBs,
  56     SmallVectorImpl<DominatorTree::UpdateType> *Updates,
  57     bool KeepOneInputPHIs) {
  58   for (auto *BB : BBs) {
  59     // Loop through all of our successors and make sure they know that one
  60     // of their predecessors is going away.
  61     SmallPtrSet<BasicBlock *, 4> UniqueSuccessors;
  62     for (BasicBlock *Succ : successors(BB)) {
  63       Succ->removePredecessor(BB, KeepOneInputPHIs);
  64       if (Updates && UniqueSuccessors.insert(Succ).second)
  65         Updates->push_back({DominatorTree::Delete, BB, Succ});
  66     }
  67
  68     // Zap all the instructions in the block.
  69     while (!BB->empty()) {
  70       Instruction &I = BB->back();
  71       // If this instruction is used, replace uses with an arbitrary value.
  72       // Because control flow can't get here, we don't care what we replace the
  73       // value with.  Note that since this block is unreachable, and all values
  74       // contained within it must dominate their uses, that all uses will
  75       // eventually be removed (they are themselves dead).
  76       if (!I.use_empty())
  77         I.replaceAllUsesWith(UndefValue::get(I.getType()));
  78       BB->getInstList().pop_back();
  79     }
  80     new UnreachableInst(BB->getContext(), BB);
  81     assert(BB->getInstList().size() == 1 &&
  82            isa<UnreachableInst>(BB->getTerminator()) &&
  83            "The successor list of BB isn't empty before "
  84            "applying corresponding DTU updates.");
  85   }
  86 }
  87
  88 void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU,
  89                            bool KeepOneInputPHIs) {
  90   DeleteDeadBlocks({BB}, DTU, KeepOneInputPHIs);
  91 }
  92
  93 void llvm::DeleteDeadBlocks(ArrayRef <BasicBlock *> BBs, DomTreeUpdater *DTU,
  94                             bool KeepOneInputPHIs) {
  95 #ifndef NDEBUG
  96   // Make sure that all predecessors of each dead block is also dead.
  97   SmallPtrSet<BasicBlock *, 4> Dead(BBs.begin(), BBs.end());
  98   assert(Dead.size() == BBs.size() && "Duplicating blocks?");
  99   for (auto *BB : Dead)
 100     for (BasicBlock *Pred : predecessors(BB))
 101       assert(Dead.count(Pred) && "All predecessors must be dead!");
 102 #endif
 103
 104   SmallVector<DominatorTree::UpdateType, 4> Updates;
 105   DetatchDeadBlocks(BBs, DTU ? &Updates : nullptr, KeepOneInputPHIs);
 106
 107   if (DTU)
 108     DTU->applyUpdatesPermissive(Updates);
 109
 110   for (BasicBlock *BB : BBs)
 111     if (DTU)
 112       DTU->deleteBB(BB);
 113     else
 114       BB->eraseFromParent();
 115 }
 116
 117 bool llvm::EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU,
 118                                       bool KeepOneInputPHIs) {
 119   df_iterator_default_set<BasicBlock*> Reachable;
 120
 121   // Mark all reachable blocks.
 122   for (BasicBlock *BB : depth_first_ext(&F, Reachable))
 123     (void)BB/* Mark all reachable blocks */;
 124
 125   // Collect all dead blocks.
 126   std::vector<BasicBlock*> DeadBlocks;
 127   for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
 128     if (!Reachable.count(&*I)) {
 129       BasicBlock *BB = &*I;
 130       DeadBlocks.push_back(BB);
 131     }
 132
 133   // Delete the dead blocks.
 134   DeleteDeadBlocks(DeadBlocks, DTU, KeepOneInputPHIs);
 135
 136   return !DeadBlocks.empty();
 137 }
 138
 139 void llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
 140                                    MemoryDependenceResults *MemDep) {
 141   if (!isa<PHINode>(BB->begin())) return;
 142
 143   while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
 144     if (PN->getIncomingValue(0) != PN)
 145       PN->replaceAllUsesWith(PN->getIncomingValue(0));
 146     else
 147       PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
 148
 149     if (MemDep)
 150       MemDep->removeInstruction(PN);  // Memdep updates AA itself.
 151
 152     PN->eraseFromParent();
 153   }
 154 }
 155
 156 bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
 157   // Recursively deleting a PHI may cause multiple PHIs to be deleted
 158   // or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
 159   SmallVector<WeakTrackingVH, 8> PHIs;
 160   for (PHINode &PN : BB->phis())
 161     PHIs.push_back(&PN);
 162
 163   bool Changed = false;
 164   for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
 165     if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
 166       Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
 167
 168   return Changed;
 169 }
 170
 171 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
 172                                      LoopInfo *LI, MemorySSAUpdater *MSSAU,
 173                                      MemoryDependenceResults *MemDep) {
 174   if (BB->hasAddressTaken())
 175     return false;
 176
 177   // Can't merge if there are multiple predecessors, or no predecessors.
 178   BasicBlock *PredBB = BB->getUniquePredecessor();
 179   if (!PredBB) return false;
 180
 181   // Don't break self-loops.
 182   if (PredBB == BB) return false;
 183   // Don't break unwinding instructions.
 184   if (PredBB->getTerminator()->isExceptionalTerminator())
 185     return false;
 186
 187   // Can't merge if there are multiple distinct successors.
 188   if (PredBB->getUniqueSuccessor() != BB)
 189     return false;
 190
 191   // Can't merge if there is PHI loop.
 192   for (PHINode &PN : BB->phis())
 193     for (Value *IncValue : PN.incoming_values())
 194       if (IncValue == &PN)
 195         return false;
 196
 197   LLVM_DEBUG(dbgs() << "Merging: " << BB->getName() << " into "
 198                     << PredBB->getName() << "\n");
 199
 200   // Begin by getting rid of unneeded PHIs.
 201   SmallVector<AssertingVH<Value>, 4> IncomingValues;
 202   if (isa<PHINode>(BB->front())) {
 203     for (PHINode &PN : BB->phis())
 204       if (!isa<PHINode>(PN.getIncomingValue(0)) ||
 205           cast<PHINode>(PN.getIncomingValue(0))->getParent() != BB)
 206         IncomingValues.push_back(PN.getIncomingValue(0));
 207     FoldSingleEntryPHINodes(BB, MemDep);
 208   }
 209
 210   // DTU update: Collect all the edges that exit BB.
 211   // These dominator edges will be redirected from Pred.
 212   std::vector<DominatorTree::UpdateType> Updates;
 213   if (DTU) {
 214     Updates.reserve(1 + (2 * succ_size(BB)));
 215     // Add insert edges first. Experimentally, for the particular case of two
 216     // blocks that can be merged, with a single successor and single predecessor
 217     // respectively, it is beneficial to have all insert updates first. Deleting
 218     // edges first may lead to unreachable blocks, followed by inserting edges
 219     // making the blocks reachable again. Such DT updates lead to high compile
 220     // times. We add inserts before deletes here to reduce compile time.
 221     for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
 222       // This successor of BB may already have PredBB as a predecessor.
 223       if (llvm::find(successors(PredBB), *I) == succ_end(PredBB))
 224         Updates.push_back({DominatorTree::Insert, PredBB, *I});
 225     for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
 226       Updates.push_back({DominatorTree::Delete, BB, *I});
 227     Updates.push_back({DominatorTree::Delete, PredBB, BB});
 228   }
 229
 230   if (MSSAU)
 231     MSSAU->moveAllAfterMergeBlocks(BB, PredBB, &*(BB->begin()));
 232
 233   // Delete the unconditional branch from the predecessor...
 234   PredBB->getInstList().pop_back();
 235
 236   // Make all PHI nodes that referred to BB now refer to Pred as their
 237   // source...
 238   BB->replaceAllUsesWith(PredBB);
 239
 240   // Move all definitions in the successor to the predecessor...
 241   PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
 242   new UnreachableInst(BB->getContext(), BB);
 243
 244   // Eliminate duplicate dbg.values describing the entry PHI node post-splice.
 245   for (auto Incoming : IncomingValues) {
 246     if (isa<Instruction>(*Incoming)) {
 247       SmallVector<DbgValueInst *, 2> DbgValues;
 248       SmallDenseSet<std::pair<DILocalVariable *, DIExpression *>, 2>
 249           DbgValueSet;
 250       llvm::findDbgValues(DbgValues, Incoming);
 251       for (auto &DVI : DbgValues) {
 252         auto R = DbgValueSet.insert({DVI->getVariable(), DVI->getExpression()});
 253         if (!R.second)
 254           DVI->eraseFromParent();
 255       }
 256     }
 257   }
 258
 259   // Inherit predecessors name if it exists.
 260   if (!PredBB->hasName())
 261     PredBB->takeName(BB);
 262
 263   if (LI)
 264     LI->removeBlock(BB);
 265
 266   if (MemDep)
 267     MemDep->invalidateCachedPredecessors();
 268
 269   // Finally, erase the old block and update dominator info.
 270   if (DTU) {
 271     assert(BB->getInstList().size() == 1 &&
 272            isa<UnreachableInst>(BB->getTerminator()) &&
 273            "The successor list of BB isn't empty before "
 274            "applying corresponding DTU updates.");
 275     DTU->applyUpdatesPermissive(Updates);
 276     DTU->deleteBB(BB);
 277   }
 278
 279   else {
 280     BB->eraseFromParent(); // Nuke BB if DTU is nullptr.
 281   }
 282   return true;
 283 }
 284
 285 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
 286                                 BasicBlock::iterator &BI, Value *V) {
 287   Instruction &I = *BI;
 288   // Replaces all of the uses of the instruction with uses of the value
 289   I.replaceAllUsesWith(V);
 290
 291   // Make sure to propagate a name if there is one already.
 292   if (I.hasName() && !V->hasName())
 293     V->takeName(&I);
 294
 295   // Delete the unnecessary instruction now...
 296   BI = BIL.erase(BI);
 297 }
 298
 299 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
 300                                BasicBlock::iterator &BI, Instruction *I) {
 301   assert(I->getParent() == nullptr &&
 302          "ReplaceInstWithInst: Instruction already inserted into basic block!");
 303
 304   // Copy debug location to newly added instruction, if it wasn't already set
 305   // by the caller.
 306   if (!I->getDebugLoc())
 307     I->setDebugLoc(BI->getDebugLoc());
 308
 309   // Insert the new instruction into the basic block...
 310   BasicBlock::iterator New = BIL.insert(BI, I);
 311
 312   // Replace all uses of the old instruction, and delete it.
 313   ReplaceInstWithValue(BIL, BI, I);
 314
 315   // Move BI back to point to the newly inserted instruction
 316   BI = New;
 317 }
 318
 319 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
 320   BasicBlock::iterator BI(From);
 321   ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
 322 }
 323
 324 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
 325                             LoopInfo *LI, MemorySSAUpdater *MSSAU) {
 326   unsigned SuccNum = GetSuccessorNumber(BB, Succ);
 327
 328   // If this is a critical edge, let SplitCriticalEdge do it.
 329   Instruction *LatchTerm = BB->getTerminator();
 330   if (SplitCriticalEdge(
 331           LatchTerm, SuccNum,
 332           CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA()))
 333     return LatchTerm->getSuccessor(SuccNum);
 334
 335   // If the edge isn't critical, then BB has a single successor or Succ has a
 336   // single pred.  Split the block.
 337   if (BasicBlock *SP = Succ->getSinglePredecessor()) {
 338     // If the successor only has a single pred, split the top of the successor
 339     // block.
 340     assert(SP == BB && "CFG broken");
 341     SP = nullptr;
 342     return SplitBlock(Succ, &Succ->front(), DT, LI, MSSAU);
 343   }
 344
 345   // Otherwise, if BB has a single successor, split it at the bottom of the
 346   // block.
 347   assert(BB->getTerminator()->getNumSuccessors() == 1 &&
 348          "Should have a single succ!");
 349   return SplitBlock(BB, BB->getTerminator(), DT, LI, MSSAU);
 350 }
 351
 352 unsigned
 353 llvm::SplitAllCriticalEdges(Function &F,
 354                             const CriticalEdgeSplittingOptions &Options) {
 355   unsigned NumBroken = 0;
 356   for (BasicBlock &BB : F) {
 357     Instruction *TI = BB.getTerminator();
 358     if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
 359       for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
 360         if (SplitCriticalEdge(TI, i, Options))
 361           ++NumBroken;
 362   }
 363   return NumBroken;
 364 }
 365
 366 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
 367                              DominatorTree *DT, LoopInfo *LI,
 368                              MemorySSAUpdater *MSSAU, const Twine &BBName) {
 369   BasicBlock::iterator SplitIt = SplitPt->getIterator();
 370   while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
 371     ++SplitIt;
 372   std::string Name = BBName.str();
 373   BasicBlock *New = Old->splitBasicBlock(
 374       SplitIt, Name.empty() ? Old->getName() + ".split" : Name);
 375
 376   // The new block lives in whichever loop the old one did. This preserves
 377   // LCSSA as well, because we force the split point to be after any PHI nodes.
 378   if (LI)
 379     if (Loop *L = LI->getLoopFor(Old))
 380       L->addBasicBlockToLoop(New, *LI);
 381
 382   if (DT)
 383     // Old dominates New. New node dominates all other nodes dominated by Old.
 384     if (DomTreeNode *OldNode = DT->getNode(Old)) {
 385       std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
 386
 387       DomTreeNode *NewNode = DT->addNewBlock(New, Old);
 388       for (DomTreeNode *I : Children)
 389         DT->changeImmediateDominator(I, NewNode);
 390     }
 391
 392   // Move MemoryAccesses still tracked in Old, but part of New now.
 393   // Update accesses in successor blocks accordingly.
 394   if (MSSAU)
 395     MSSAU->moveAllAfterSpliceBlocks(Old, New, &*(New->begin()));
 396
 397   return New;
 398 }
 399
 400 /// Update DominatorTree, LoopInfo, and LCCSA analysis information.
 401 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
 402                                       ArrayRef<BasicBlock *> Preds,
 403                                       DominatorTree *DT, LoopInfo *LI,
 404                                       MemorySSAUpdater *MSSAU,
 405                                       bool PreserveLCSSA, bool &HasLoopExit) {
 406   // Update dominator tree if available.
 407   if (DT) {
 408     if (OldBB == DT->getRootNode()->getBlock()) {
 409       assert(NewBB == &NewBB->getParent()->getEntryBlock());
 410       DT->setNewRoot(NewBB);
 411     } else {
 412       // Split block expects NewBB to have a non-empty set of predecessors.
 413       DT->splitBlock(NewBB);
 414     }
 415   }
 416
 417   // Update MemoryPhis after split if MemorySSA is available
 418   if (MSSAU)
 419     MSSAU->wireOldPredecessorsToNewImmediatePredecessor(OldBB, NewBB, Preds);
 420
 421   // The rest of the logic is only relevant for updating the loop structures.
 422   if (!LI)
 423     return;
 424
 425   assert(DT && "DT should be available to update LoopInfo!");
 426   Loop *L = LI->getLoopFor(OldBB);
 427
 428   // If we need to preserve loop analyses, collect some information about how
 429   // this split will affect loops.
 430   bool IsLoopEntry = !!L;
 431   bool SplitMakesNewLoopHeader = false;
 432   for (BasicBlock *Pred : Preds) {
 433     // Preds that are not reachable from entry should not be used to identify if
 434     // OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
 435     // are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
 436     // as true and make the NewBB the header of some loop. This breaks LI.
 437     if (!DT->isReachableFromEntry(Pred))
 438       continue;
 439     // If we need to preserve LCSSA, determine if any of the preds is a loop
 440     // exit.
 441     if (PreserveLCSSA)
 442       if (Loop *PL = LI->getLoopFor(Pred))
 443         if (!PL->contains(OldBB))
 444           HasLoopExit = true;
 445
 446     // If we need to preserve LoopInfo, note whether any of the preds crosses
 447     // an interesting loop boundary.
 448     if (!L)
 449       continue;
 450     if (L->contains(Pred))
 451       IsLoopEntry = false;
 452     else
 453       SplitMakesNewLoopHeader = true;
 454   }
 455
 456   // Unless we have a loop for OldBB, nothing else to do here.
 457   if (!L)
 458     return;
 459
 460   if (IsLoopEntry) {
 461     // Add the new block to the nearest enclosing loop (and not an adjacent
 462     // loop). To find this, examine each of the predecessors and determine which
 463     // loops enclose them, and select the most-nested loop which contains the
 464     // loop containing the block being split.
 465     Loop *InnermostPredLoop = nullptr;
 466     for (BasicBlock *Pred : Preds) {
 467       if (Loop *PredLoop = LI->getLoopFor(Pred)) {
 468         // Seek a loop which actually contains the block being split (to avoid
 469         // adjacent loops).
 470         while (PredLoop && !PredLoop->contains(OldBB))
 471           PredLoop = PredLoop->getParentLoop();
 472
 473         // Select the most-nested of these loops which contains the block.
 474         if (PredLoop && PredLoop->contains(OldBB) &&
 475             (!InnermostPredLoop ||
 476              InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
 477           InnermostPredLoop = PredLoop;
 478       }
 479     }
 480
 481     if (InnermostPredLoop)
 482       InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
 483   } else {
 484     L->addBasicBlockToLoop(NewBB, *LI);
 485     if (SplitMakesNewLoopHeader)
 486       L->moveToHeader(NewBB);
 487   }
 488 }
 489
 490 /// Update the PHI nodes in OrigBB to include the values coming from NewBB.
 491 /// This also updates AliasAnalysis, if available.
 492 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
 493                            ArrayRef<BasicBlock *> Preds, BranchInst *BI,
 494                            bool HasLoopExit) {
 495   // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
 496   SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
 497   for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
 498     PHINode *PN = cast<PHINode>(I++);
 499
 500     // Check to see if all of the values coming in are the same.  If so, we
 501     // don't need to create a new PHI node, unless it's needed for LCSSA.
 502     Value *InVal = nullptr;
 503     if (!HasLoopExit) {
 504       InVal = PN->getIncomingValueForBlock(Preds[0]);
 505       for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
 506         if (!PredSet.count(PN->getIncomingBlock(i)))
 507           continue;
 508         if (!InVal)
 509           InVal = PN->getIncomingValue(i);
 510         else if (InVal != PN->getIncomingValue(i)) {
 511           InVal = nullptr;
 512           break;
 513         }
 514       }
 515     }
 516
 517     if (InVal) {
 518       // If all incoming values for the new PHI would be the same, just don't
 519       // make a new PHI.  Instead, just remove the incoming values from the old
 520       // PHI.
 521
 522       // NOTE! This loop walks backwards for a reason! First off, this minimizes
 523       // the cost of removal if we end up removing a large number of values, and
 524       // second off, this ensures that the indices for the incoming values
 525       // aren't invalidated when we remove one.
 526       for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
 527         if (PredSet.count(PN->getIncomingBlock(i)))
 528           PN->removeIncomingValue(i, false);
 529
 530       // Add an incoming value to the PHI node in the loop for the preheader
 531       // edge.
 532       PN->addIncoming(InVal, NewBB);
 533       continue;
 534     }
 535
 536     // If the values coming into the block are not the same, we need a new
 537     // PHI.
 538     // Create the new PHI node, insert it into NewBB at the end of the block
 539     PHINode *NewPHI =
 540         PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
 541
 542     // NOTE! This loop walks backwards for a reason! First off, this minimizes
 543     // the cost of removal if we end up removing a large number of values, and
 544     // second off, this ensures that the indices for the incoming values aren't
 545     // invalidated when we remove one.
 546     for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
 547       BasicBlock *IncomingBB = PN->getIncomingBlock(i);
 548       if (PredSet.count(IncomingBB)) {
 549         Value *V = PN->removeIncomingValue(i, false);
 550         NewPHI->addIncoming(V, IncomingBB);
 551       }
 552     }
 553
 554     PN->addIncoming(NewPHI, NewBB);
 555   }
 556 }
 557
 558 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
 559                                          ArrayRef<BasicBlock *> Preds,
 560                                          const char *Suffix, DominatorTree *DT,
 561                                          LoopInfo *LI, MemorySSAUpdater *MSSAU,
 562                                          bool PreserveLCSSA) {
 563   // Do not attempt to split that which cannot be split.
 564   if (!BB->canSplitPredecessors())
 565     return nullptr;
 566
 567   // For the landingpads we need to act a bit differently.
 568   // Delegate this work to the SplitLandingPadPredecessors.
 569   if (BB->isLandingPad()) {
 570     SmallVector<BasicBlock*, 2> NewBBs;
 571     std::string NewName = std::string(Suffix) + ".split-lp";
 572
 573     SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs, DT,
 574                                 LI, MSSAU, PreserveLCSSA);
 575     return NewBBs[0];
 576   }
 577
 578   // Create new basic block, insert right before the original block.
 579   BasicBlock *NewBB = BasicBlock::Create(
 580       BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
 581
 582   // The new block unconditionally branches to the old block.
 583   BranchInst *BI = BranchInst::Create(BB, NewBB);
 584   // Splitting the predecessors of a loop header creates a preheader block.
 585   if (LI && LI->isLoopHeader(BB))
 586     // Using the loop start line number prevents debuggers stepping into the
 587     // loop body for this instruction.
 588     BI->setDebugLoc(LI->getLoopFor(BB)->getStartLoc());
 589   else
 590     BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->getDebugLoc());
 591
 592   // Move the edges from Preds to point to NewBB instead of BB.
 593   for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
 594     // This is slightly more strict than necessary; the minimum requirement
 595     // is that there be no more than one indirectbr branching to BB. And
 596     // all BlockAddress uses would need to be updated.
 597     assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
 598            "Cannot split an edge from an IndirectBrInst");
 599     assert(!isa<CallBrInst>(Preds[i]->getTerminator()) &&
 600            "Cannot split an edge from a CallBrInst");
 601     Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
 602   }
 603
 604   // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
 605   // node becomes an incoming value for BB's phi node.  However, if the Preds
 606   // list is empty, we need to insert dummy entries into the PHI nodes in BB to
 607   // account for the newly created predecessor.
 608   if (Preds.empty()) {
 609     // Insert dummy values as the incoming value.
 610     for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
 611       cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
 612   }
 613
 614   // Update DominatorTree, LoopInfo, and LCCSA analysis information.
 615   bool HasLoopExit = false;
 616   UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, MSSAU, PreserveLCSSA,
 617                             HasLoopExit);
 618
 619   if (!Preds.empty()) {
 620     // Update the PHI nodes in BB with the values coming from NewBB.
 621     UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
 622   }
 623
 624   return NewBB;
 625 }
 626
 627 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
 628                                        ArrayRef<BasicBlock *> Preds,
 629                                        const char *Suffix1, const char *Suffix2,
 630                                        SmallVectorImpl<BasicBlock *> &NewBBs,
 631                                        DominatorTree *DT, LoopInfo *LI,
 632                                        MemorySSAUpdater *MSSAU,
 633                                        bool PreserveLCSSA) {
 634   assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
 635
 636   // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
 637   // it right before the original block.
 638   BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
 639                                           OrigBB->getName() + Suffix1,
 640                                           OrigBB->getParent(), OrigBB);
 641   NewBBs.push_back(NewBB1);
 642
 643   // The new block unconditionally branches to the old block.
 644   BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
 645   BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
 646
 647   // Move the edges from Preds to point to NewBB1 instead of OrigBB.
 648   for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
 649     // This is slightly more strict than necessary; the minimum requirement
 650     // is that there be no more than one indirectbr branching to BB. And
 651     // all BlockAddress uses would need to be updated.
 652     assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
 653            "Cannot split an edge from an IndirectBrInst");
 654     Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
 655   }
 656
 657   bool HasLoopExit = false;
 658   UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, MSSAU, PreserveLCSSA,
 659                             HasLoopExit);
 660
 661   // Update the PHI nodes in OrigBB with the values coming from NewBB1.
 662   UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, HasLoopExit);
 663
 664   // Move the remaining edges from OrigBB to point to NewBB2.
 665   SmallVector<BasicBlock*, 8> NewBB2Preds;
 666   for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
 667        i != e; ) {
 668     BasicBlock *Pred = *i++;
 669     if (Pred == NewBB1) continue;
 670     assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
 671            "Cannot split an edge from an IndirectBrInst");
 672     NewBB2Preds.push_back(Pred);
 673     e = pred_end(OrigBB);
 674   }
 675
 676   BasicBlock *NewBB2 = nullptr;
 677   if (!NewBB2Preds.empty()) {
 678     // Create another basic block for the rest of OrigBB's predecessors.
 679     NewBB2 = BasicBlock::Create(OrigBB->getContext(),
 680                                 OrigBB->getName() + Suffix2,
 681                                 OrigBB->getParent(), OrigBB);
 682     NewBBs.push_back(NewBB2);
 683
 684     // The new block unconditionally branches to the old block.
 685     BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
 686     BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
 687
 688     // Move the remaining edges from OrigBB to point to NewBB2.
 689     for (BasicBlock *NewBB2Pred : NewBB2Preds)
 690       NewBB2Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
 691
 692     // Update DominatorTree, LoopInfo, and LCCSA analysis information.
 693     HasLoopExit = false;
 694     UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI, MSSAU,
 695                               PreserveLCSSA, HasLoopExit);
 696
 697     // Update the PHI nodes in OrigBB with the values coming from NewBB2.
 698     UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, HasLoopExit);
 699   }
 700
 701   LandingPadInst *LPad = OrigBB->getLandingPadInst();
 702   Instruction *Clone1 = LPad->clone();
 703   Clone1->setName(Twine("lpad") + Suffix1);
 704   NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
 705
 706   if (NewBB2) {
 707     Instruction *Clone2 = LPad->clone();
 708     Clone2->setName(Twine("lpad") + Suffix2);
 709     NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
 710
 711     // Create a PHI node for the two cloned landingpad instructions only
 712     // if the original landingpad instruction has some uses.
 713     if (!LPad->use_empty()) {
 714       assert(!LPad->getType()->isTokenTy() &&
 715              "Split cannot be applied if LPad is token type. Otherwise an "
 716              "invalid PHINode of token type would be created.");
 717       PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
 718       PN->addIncoming(Clone1, NewBB1);
 719       PN->addIncoming(Clone2, NewBB2);
 720       LPad->replaceAllUsesWith(PN);
 721     }
 722     LPad->eraseFromParent();
 723   } else {
 724     // There is no second clone. Just replace the landing pad with the first
 725     // clone.
 726     LPad->replaceAllUsesWith(Clone1);
 727     LPad->eraseFromParent();
 728   }
 729 }
 730
 731 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
 732                                              BasicBlock *Pred,
 733                                              DomTreeUpdater *DTU) {
 734   Instruction *UncondBranch = Pred->getTerminator();
 735   // Clone the return and add it to the end of the predecessor.
 736   Instruction *NewRet = RI->clone();
 737   Pred->getInstList().push_back(NewRet);
 738
 739   // If the return instruction returns a value, and if the value was a
 740   // PHI node in "BB", propagate the right value into the return.
 741   for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
 742        i != e; ++i) {
 743     Value *V = *i;
 744     Instruction *NewBC = nullptr;
 745     if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
 746       // Return value might be bitcasted. Clone and insert it before the
 747       // return instruction.
 748       V = BCI->getOperand(0);
 749       NewBC = BCI->clone();
 750       Pred->getInstList().insert(NewRet->getIterator(), NewBC);
 751       *i = NewBC;
 752     }
 753     if (PHINode *PN = dyn_cast<PHINode>(V)) {
 754       if (PN->getParent() == BB) {
 755         if (NewBC)
 756           NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
 757         else
 758           *i = PN->getIncomingValueForBlock(Pred);
 759       }
 760     }
 761   }
 762
 763   // Update any PHI nodes in the returning block to realize that we no
 764   // longer branch to them.
 765   BB->removePredecessor(Pred);
 766   UncondBranch->eraseFromParent();
 767
 768   if (DTU)
 769     DTU->applyUpdates({{DominatorTree::Delete, Pred, BB}});
 770
 771   return cast<ReturnInst>(NewRet);
 772 }
 773
 774 Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
 775                                              Instruction *SplitBefore,
 776                                              bool Unreachable,
 777                                              MDNode *BranchWeights,
 778                                              DominatorTree *DT, LoopInfo *LI,
 779                                              BasicBlock *ThenBlock) {
 780   BasicBlock *Head = SplitBefore->getParent();
 781   BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
 782   Instruction *HeadOldTerm = Head->getTerminator();
 783   LLVMContext &C = Head->getContext();
 784   Instruction *CheckTerm;
 785   bool CreateThenBlock = (ThenBlock == nullptr);
 786   if (CreateThenBlock) {
 787     ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
 788     if (Unreachable)
 789       CheckTerm = new UnreachableInst(C, ThenBlock);
 790     else
 791       CheckTerm = BranchInst::Create(Tail, ThenBlock);
 792     CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
 793   } else
 794     CheckTerm = ThenBlock->getTerminator();
 795   BranchInst *HeadNewTerm =
 796     BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
 797   HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
 798   ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
 799
 800   if (DT) {
 801     if (DomTreeNode *OldNode = DT->getNode(Head)) {
 802       std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
 803
 804       DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
 805       for (DomTreeNode *Child : Children)
 806         DT->changeImmediateDominator(Child, NewNode);
 807
 808       // Head dominates ThenBlock.
 809       if (CreateThenBlock)
 810         DT->addNewBlock(ThenBlock, Head);
 811       else
 812         DT->changeImmediateDominator(ThenBlock, Head);
 813     }
 814   }
 815
 816   if (LI) {
 817     if (Loop *L = LI->getLoopFor(Head)) {
 818       L->addBasicBlockToLoop(ThenBlock, *LI);
 819       L->addBasicBlockToLoop(Tail, *LI);
 820     }
 821   }
 822
 823   return CheckTerm;
 824 }
 825
 826 void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
 827                                          Instruction **ThenTerm,
 828                                          Instruction **ElseTerm,
 829                                          MDNode *BranchWeights) {
 830   BasicBlock *Head = SplitBefore->getParent();
 831   BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
 832   Instruction *HeadOldTerm = Head->getTerminator();
 833   LLVMContext &C = Head->getContext();
 834   BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
 835   BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
 836   *ThenTerm = BranchInst::Create(Tail, ThenBlock);
 837   (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
 838   *ElseTerm = BranchInst::Create(Tail, ElseBlock);
 839   (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
 840   BranchInst *HeadNewTerm =
 841     BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
 842   HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
 843   ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
 844 }
 845
 846 Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
 847                              BasicBlock *&IfFalse) {
 848   PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
 849   BasicBlock *Pred1 = nullptr;
 850   BasicBlock *Pred2 = nullptr;
 851
 852   if (SomePHI) {
 853     if (SomePHI->getNumIncomingValues() != 2)
 854       return nullptr;
 855     Pred1 = SomePHI->getIncomingBlock(0);
 856     Pred2 = SomePHI->getIncomingBlock(1);
 857   } else {
 858     pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
 859     if (PI == PE) // No predecessor
 860       return nullptr;
 861     Pred1 = *PI++;
 862     if (PI == PE) // Only one predecessor
 863       return nullptr;
 864     Pred2 = *PI++;
 865     if (PI != PE) // More than two predecessors
 866       return nullptr;
 867   }
 868
 869   // We can only handle branches.  Other control flow will be lowered to
 870   // branches if possible anyway.
 871   BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
 872   BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
 873   if (!Pred1Br || !Pred2Br)
 874     return nullptr;
 875
 876   // Eliminate code duplication by ensuring that Pred1Br is conditional if
 877   // either are.
 878   if (Pred2Br->isConditional()) {
 879     // If both branches are conditional, we don't have an "if statement".  In
 880     // reality, we could transform this case, but since the condition will be
 881     // required anyway, we stand no chance of eliminating it, so the xform is
 882     // probably not profitable.
 883     if (Pred1Br->isConditional())
 884       return nullptr;
 885
 886     std::swap(Pred1, Pred2);
 887     std::swap(Pred1Br, Pred2Br);
 888   }
 889
 890   if (Pred1Br->isConditional()) {
 891     // The only thing we have to watch out for here is to make sure that Pred2
 892     // doesn't have incoming edges from other blocks.  If it does, the condition
 893     // doesn't dominate BB.
 894     if (!Pred2->getSinglePredecessor())
 895       return nullptr;
 896
 897     // If we found a conditional branch predecessor, make sure that it branches
 898     // to BB and Pred2Br.  If it doesn't, this isn't an "if statement".
 899     if (Pred1Br->getSuccessor(0) == BB &&
 900         Pred1Br->getSuccessor(1) == Pred2) {
 901       IfTrue = Pred1;
 902       IfFalse = Pred2;
 903     } else if (Pred1Br->getSuccessor(0) == Pred2 &&
 904                Pred1Br->getSuccessor(1) == BB) {
 905       IfTrue = Pred2;
 906       IfFalse = Pred1;
 907     } else {
 908       // We know that one arm of the conditional goes to BB, so the other must
 909       // go somewhere unrelated, and this must not be an "if statement".
 910       return nullptr;
 911     }
 912
 913     return Pred1Br->getCondition();
 914   }
 915
 916   // Ok, if we got here, both predecessors end with an unconditional branch to
 917   // BB.  Don't panic!  If both blocks only have a single (identical)
 918   // predecessor, and THAT is a conditional branch, then we're all ok!
 919   BasicBlock *CommonPred = Pred1->getSinglePredecessor();
 920   if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
 921     return nullptr;
 922
 923   // Otherwise, if this is a conditional branch, then we can use it!
 924   BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
 925   if (!BI) return nullptr;
 926
 927   assert(BI->isConditional() && "Two successors but not conditional?");
 928   if (BI->getSuccessor(0) == Pred1) {
 929     IfTrue = Pred1;
 930     IfFalse = Pred2;
 931   } else {
 932     IfTrue = Pred2;
 933     IfFalse = Pred1;
 934   }
 935   return BI->getCondition();
 936 }