lib/Transforms/Utils/BasicBlockUtils.cpp

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