Ejemplo n.º 1
0
//------------------------------------------------------------------------------
void changeBlockTarget(BasicBlock *block, BasicBlock *newTarget,
                       unsigned int branchIndex) {
  TerminatorInst *terminator = block->getTerminator();
  assert(terminator->getNumSuccessors() &&
         "The target can be change only if it is unique");
  terminator->setSuccessor(branchIndex, newTarget);
}
Ejemplo n.º 2
0
void CheckInserter::insertCycleChecks(Function &F) {
  IdentifyBackEdges &IBE = getAnalysis<IdentifyBackEdges>();

  for (Function::iterator B1 = F.begin(); B1 != F.end(); ++B1) {
    TerminatorInst *TI = B1->getTerminator();
    for (unsigned j = 0; j < TI->getNumSuccessors(); ++j) {
      BasicBlock *B2 = TI->getSuccessor(j);
      unsigned BackEdgeID = IBE.getID(B1, B2);
      if (BackEdgeID != (unsigned)-1) {
        assert(BackEdgeID < MaxNumBackEdges);
        BasicBlock *BackEdgeBlock = BasicBlock::Create(
            F.getContext(),
            "backedge_" + B1->getName() + "_" + B2->getName(),
            &F);
        CallInst::Create(CycleCheck,
                         ConstantInt::get(IntType, BackEdgeID),
                         "",
                         BackEdgeBlock);
        // BackEdgeBlock -> B2
        // Fix the PHINodes in B2.
        BranchInst::Create(B2, BackEdgeBlock);
        for (BasicBlock::iterator I = B2->begin();
             B2->getFirstNonPHI() != I;
             ++I) {
          PHINode *PHI = cast<PHINode>(I);
          // Note: If B2 has multiple incoming edges from B1 (e.g. B1 terminates
          // with a SelectInst), its PHINodes must also have multiple incoming
          // edges from B1. However, after adding BackEdgeBlock and essentially
          // merging the multiple incoming edges from B1, there will be only one
          // edge from BackEdgeBlock to B2. Therefore, we need to remove the
          // redundant incoming edges from B2's PHINodes.
          bool FirstIncomingFromB1 = true;
          for (unsigned k = 0; k < PHI->getNumIncomingValues(); ++k) {
            if (PHI->getIncomingBlock(k) == B1) {
              if (FirstIncomingFromB1) {
                FirstIncomingFromB1 = false;
                PHI->setIncomingBlock(k, BackEdgeBlock);
              } else {
                PHI->removeIncomingValue(k, false);
                --k;
              }
            }
          }
        }
        // B1 -> BackEdgeBlock
        // There might be multiple back edges from B1 to B2. Need to replace
        // them all.
        for (unsigned j2 = j; j2 < TI->getNumSuccessors(); ++j2) {
          if (TI->getSuccessor(j2) == B2) {
            TI->setSuccessor(j2, BackEdgeBlock);
          }
        }
      }
    }
  }
}
Ejemplo n.º 3
0
  void JITInlineBlock::eraseBlockEmit() {
    if(!created_object_ && block_emit_loc_) {
      BasicBlock* before = block_emit_loc_->getSinglePredecessor();
      TerminatorInst* fromJump = before->getTerminator();
      TerminatorInst* toJump   = block_emit_loc_->getTerminator();

      fromJump->setSuccessor(0, toJump->getSuccessor(0));

      block_emit_loc_->eraseFromParent();
      block_emit_loc_ = NULL;
    }
  }
Ejemplo n.º 4
0
/// \brief This method is called when the specified loop has more than one
/// backedge in it.
///
/// If this occurs, revector all of these backedges to target a new basic block
/// and have that block branch to the loop header.  This ensures that loops
/// have exactly one backedge.
static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
                                             DominatorTree *DT, LoopInfo *LI) {
  assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");

  // Get information about the loop
  BasicBlock *Header = L->getHeader();
  Function *F = Header->getParent();

  // Unique backedge insertion currently depends on having a preheader.
  if (!Preheader)
    return nullptr;

  // The header is not a landing pad; preheader insertion should ensure this.
  assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");

  // Figure out which basic blocks contain back-edges to the loop header.
  std::vector<BasicBlock*> BackedgeBlocks;
  for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I){
    BasicBlock *P = *I;

    // Indirectbr edges cannot be split, so we must fail if we find one.
    if (isa<IndirectBrInst>(P->getTerminator()))
      return nullptr;

    if (P != Preheader) BackedgeBlocks.push_back(P);
  }

  // Create and insert the new backedge block...
  BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
                                           Header->getName() + ".backedge", F);
  BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
  BETerminator->setDebugLoc(Header->getFirstNonPHI()->getDebugLoc());

  DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
               << BEBlock->getName() << "\n");

  // Move the new backedge block to right after the last backedge block.
  Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
  F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);

  // Now that the block has been inserted into the function, create PHI nodes in
  // the backedge block which correspond to any PHI nodes in the header block.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PN = cast<PHINode>(I);
    PHINode *NewPN = PHINode::Create(PN->getType(), BackedgeBlocks.size(),
                                     PN->getName()+".be", BETerminator);

    // Loop over the PHI node, moving all entries except the one for the
    // preheader over to the new PHI node.
    unsigned PreheaderIdx = ~0U;
    bool HasUniqueIncomingValue = true;
    Value *UniqueValue = nullptr;
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *IBB = PN->getIncomingBlock(i);
      Value *IV = PN->getIncomingValue(i);
      if (IBB == Preheader) {
        PreheaderIdx = i;
      } else {
        NewPN->addIncoming(IV, IBB);
        if (HasUniqueIncomingValue) {
          if (!UniqueValue)
            UniqueValue = IV;
          else if (UniqueValue != IV)
            HasUniqueIncomingValue = false;
        }
      }
    }

    // Delete all of the incoming values from the old PN except the preheader's
    assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
    if (PreheaderIdx != 0) {
      PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
      PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
    }
    // Nuke all entries except the zero'th.
    for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
      PN->removeIncomingValue(e-i, false);

    // Finally, add the newly constructed PHI node as the entry for the BEBlock.
    PN->addIncoming(NewPN, BEBlock);

    // As an optimization, if all incoming values in the new PhiNode (which is a
    // subset of the incoming values of the old PHI node) have the same value,
    // eliminate the PHI Node.
    if (HasUniqueIncomingValue) {
      NewPN->replaceAllUsesWith(UniqueValue);
      BEBlock->getInstList().erase(NewPN);
    }
  }

  // Now that all of the PHI nodes have been inserted and adjusted, modify the
  // backedge blocks to just to the BEBlock instead of the header.
  for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
    TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
    for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
      if (TI->getSuccessor(Op) == Header)
        TI->setSuccessor(Op, BEBlock);
  }

  //===--- Update all analyses which we must preserve now -----------------===//

  // Update Loop Information - we know that this block is now in the current
  // loop and all parent loops.
  L->addBasicBlockToLoop(BEBlock, *LI);

  // Update dominator information
  DT->splitBlock(BEBlock);

  return BEBlock;
}
Ejemplo n.º 5
0
/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true
/// if unrolling was succesful, or false if the loop was unmodified. Unrolling
/// can only fail when the loop's latch block is not terminated by a conditional
/// branch instruction. However, if the trip count (and multiple) are not known,
/// loop unrolling will mostly produce more code that is no faster.
///
/// The LoopInfo Analysis that is passed will be kept consistent.
///
/// If a LoopPassManager is passed in, and the loop is fully removed, it will be
/// removed from the LoopPassManager as well. LPM can also be NULL.
bool llvm::UnrollLoop(Loop *L, unsigned Count, LoopInfo* LI, LPPassManager* LPM) {
  assert(L->isLCSSAForm());

  BasicBlock *Header = L->getHeader();
  BasicBlock *LatchBlock = L->getLoopLatch();
  BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
  
  if (!BI || BI->isUnconditional()) {
    // The loop-rotate pass can be helpful to avoid this in many cases.
    DOUT << "  Can't unroll; loop not terminated by a conditional branch.\n";
    return false;
  }

  // Find trip count
  unsigned TripCount = L->getSmallConstantTripCount();
  // Find trip multiple if count is not available
  unsigned TripMultiple = 1;
  if (TripCount == 0)
    TripMultiple = L->getSmallConstantTripMultiple();

  if (TripCount != 0)
    DOUT << "  Trip Count = " << TripCount << "\n";
  if (TripMultiple != 1)
    DOUT << "  Trip Multiple = " << TripMultiple << "\n";

  // Effectively "DCE" unrolled iterations that are beyond the tripcount
  // and will never be executed.
  if (TripCount != 0 && Count > TripCount)
    Count = TripCount;

  assert(Count > 0);
  assert(TripMultiple > 0);
  assert(TripCount == 0 || TripCount % TripMultiple == 0);

  // Are we eliminating the loop control altogether?
  bool CompletelyUnroll = Count == TripCount;

  // If we know the trip count, we know the multiple...
  unsigned BreakoutTrip = 0;
  if (TripCount != 0) {
    BreakoutTrip = TripCount % Count;
    TripMultiple = 0;
  } else {
    // Figure out what multiple to use.
    BreakoutTrip = TripMultiple =
      (unsigned)GreatestCommonDivisor64(Count, TripMultiple);
  }

  if (CompletelyUnroll) {
    DEBUG(errs() << "COMPLETELY UNROLLING loop %" << Header->getName()
          << " with trip count " << TripCount << "!\n");
  } else {
    DEBUG(errs() << "UNROLLING loop %" << Header->getName()
          << " by " << Count);
    if (TripMultiple == 0 || BreakoutTrip != TripMultiple) {
      DOUT << " with a breakout at trip " << BreakoutTrip;
    } else if (TripMultiple != 1) {
      DOUT << " with " << TripMultiple << " trips per branch";
    }
    DOUT << "!\n";
  }

  std::vector<BasicBlock*> LoopBlocks = L->getBlocks();

  bool ContinueOnTrue = L->contains(BI->getSuccessor(0));
  BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue);

  // For the first iteration of the loop, we should use the precloned values for
  // PHI nodes.  Insert associations now.
  typedef DenseMap<const Value*, Value*> ValueMapTy;
  ValueMapTy LastValueMap;
  std::vector<PHINode*> OrigPHINode;
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PN = cast<PHINode>(I);
    OrigPHINode.push_back(PN);
    if (Instruction *I = 
                dyn_cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock)))
      if (L->contains(I->getParent()))
        LastValueMap[I] = I;
  }

  std::vector<BasicBlock*> Headers;
  std::vector<BasicBlock*> Latches;
  Headers.push_back(Header);
  Latches.push_back(LatchBlock);

  for (unsigned It = 1; It != Count; ++It) {
    char SuffixBuffer[100];
    sprintf(SuffixBuffer, ".%d", It);
    
    std::vector<BasicBlock*> NewBlocks;
    
    for (std::vector<BasicBlock*>::iterator BB = LoopBlocks.begin(),
         E = LoopBlocks.end(); BB != E; ++BB) {
      ValueMapTy ValueMap;
      BasicBlock *New = CloneBasicBlock(*BB, ValueMap, SuffixBuffer);
      Header->getParent()->getBasicBlockList().push_back(New);

      // Loop over all of the PHI nodes in the block, changing them to use the
      // incoming values from the previous block.
      if (*BB == Header)
        for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
          PHINode *NewPHI = cast<PHINode>(ValueMap[OrigPHINode[i]]);
          Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock);
          if (Instruction *InValI = dyn_cast<Instruction>(InVal))
            if (It > 1 && L->contains(InValI->getParent()))
              InVal = LastValueMap[InValI];
          ValueMap[OrigPHINode[i]] = InVal;
          New->getInstList().erase(NewPHI);
        }

      // Update our running map of newest clones
      LastValueMap[*BB] = New;
      for (ValueMapTy::iterator VI = ValueMap.begin(), VE = ValueMap.end();
           VI != VE; ++VI)
        LastValueMap[VI->first] = VI->second;

      L->addBasicBlockToLoop(New, LI->getBase());

      // Add phi entries for newly created values to all exit blocks except
      // the successor of the latch block.  The successor of the exit block will
      // be updated specially after unrolling all the way.
      if (*BB != LatchBlock)
        for (Value::use_iterator UI = (*BB)->use_begin(), UE = (*BB)->use_end();
             UI != UE;) {
          Instruction *UseInst = cast<Instruction>(*UI);
          ++UI;
          if (isa<PHINode>(UseInst) && !L->contains(UseInst->getParent())) {
            PHINode *phi = cast<PHINode>(UseInst);
            Value *Incoming = phi->getIncomingValueForBlock(*BB);
            phi->addIncoming(Incoming, New);
          }
        }

      // Keep track of new headers and latches as we create them, so that
      // we can insert the proper branches later.
      if (*BB == Header)
        Headers.push_back(New);
      if (*BB == LatchBlock) {
        Latches.push_back(New);

        // Also, clear out the new latch's back edge so that it doesn't look
        // like a new loop, so that it's amenable to being merged with adjacent
        // blocks later on.
        TerminatorInst *Term = New->getTerminator();
        assert(L->contains(Term->getSuccessor(!ContinueOnTrue)));
        assert(Term->getSuccessor(ContinueOnTrue) == LoopExit);
        Term->setSuccessor(!ContinueOnTrue, NULL);
      }

      NewBlocks.push_back(New);
    }
    
    // Remap all instructions in the most recent iteration
    for (unsigned i = 0; i < NewBlocks.size(); ++i)
      for (BasicBlock::iterator I = NewBlocks[i]->begin(),
           E = NewBlocks[i]->end(); I != E; ++I)
        RemapInstruction(I, LastValueMap);
  }
  
  // The latch block exits the loop.  If there are any PHI nodes in the
  // successor blocks, update them to use the appropriate values computed as the
  // last iteration of the loop.
  if (Count != 1) {
    SmallPtrSet<PHINode*, 8> Users;
    for (Value::use_iterator UI = LatchBlock->use_begin(),
         UE = LatchBlock->use_end(); UI != UE; ++UI)
      if (PHINode *phi = dyn_cast<PHINode>(*UI))
        Users.insert(phi);
    
    BasicBlock *LastIterationBB = cast<BasicBlock>(LastValueMap[LatchBlock]);
    for (SmallPtrSet<PHINode*,8>::iterator SI = Users.begin(), SE = Users.end();
         SI != SE; ++SI) {
      PHINode *PN = *SI;
      Value *InVal = PN->removeIncomingValue(LatchBlock, false);
      // If this value was defined in the loop, take the value defined by the
      // last iteration of the loop.
      if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
        if (L->contains(InValI->getParent()))
          InVal = LastValueMap[InVal];
      }
      PN->addIncoming(InVal, LastIterationBB);
    }
  }

  // Now, if we're doing complete unrolling, loop over the PHI nodes in the
  // original block, setting them to their incoming values.
  if (CompletelyUnroll) {
    BasicBlock *Preheader = L->getLoopPreheader();
    for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
      PHINode *PN = OrigPHINode[i];
      PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
      Header->getInstList().erase(PN);
    }
  }

  // Now that all the basic blocks for the unrolled iterations are in place,
  // set up the branches to connect them.
  for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
    // The original branch was replicated in each unrolled iteration.
    BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator());

    // The branch destination.
    unsigned j = (i + 1) % e;
    BasicBlock *Dest = Headers[j];
    bool NeedConditional = true;

    // For a complete unroll, make the last iteration end with a branch
    // to the exit block.
    if (CompletelyUnroll && j == 0) {
      Dest = LoopExit;
      NeedConditional = false;
    }

    // If we know the trip count or a multiple of it, we can safely use an
    // unconditional branch for some iterations.
    if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) {
      NeedConditional = false;
    }

    if (NeedConditional) {
      // Update the conditional branch's successor for the following
      // iteration.
      Term->setSuccessor(!ContinueOnTrue, Dest);
    } else {
      Term->setUnconditionalDest(Dest);
      // Merge adjacent basic blocks, if possible.
      if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI)) {
        std::replace(Latches.begin(), Latches.end(), Dest, Fold);
        std::replace(Headers.begin(), Headers.end(), Dest, Fold);
      }
    }
  }
  
  // At this point, the code is well formed.  We now do a quick sweep over the
  // inserted code, doing constant propagation and dead code elimination as we
  // go.
  const std::vector<BasicBlock*> &NewLoopBlocks = L->getBlocks();
  for (std::vector<BasicBlock*>::const_iterator BB = NewLoopBlocks.begin(),
       BBE = NewLoopBlocks.end(); BB != BBE; ++BB)
    for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ) {
      Instruction *Inst = I++;

      if (isInstructionTriviallyDead(Inst))
        (*BB)->getInstList().erase(Inst);
      else if (Constant *C = ConstantFoldInstruction(Inst, 
                                                     Header->getContext())) {
        Inst->replaceAllUsesWith(C);
        (*BB)->getInstList().erase(Inst);
      }
    }

  NumCompletelyUnrolled += CompletelyUnroll;
  ++NumUnrolled;
  // Remove the loop from the LoopPassManager if it's completely removed.
  if (CompletelyUnroll && LPM != NULL)
    LPM->deleteLoopFromQueue(L);

  // If we didn't completely unroll the loop, it should still be in LCSSA form.
  if (!CompletelyUnroll)
    assert(L->isLCSSAForm());

  return true;
}
Ejemplo n.º 6
0
/// NormalizeLandingPads - Normalize and discover landing pads, noting them
/// in the LandingPads set.  A landing pad is normal if the only CFG edges
/// that end at it are unwind edges from invoke instructions. If we inlined
/// through an invoke we could have a normal branch from the previous
/// unwind block through to the landing pad for the original invoke.
/// Abnormal landing pads are fixed up by redirecting all unwind edges to
/// a new basic block which falls through to the original.
bool DwarfEHPrepare::NormalizeLandingPads() {
  bool Changed = false;

  for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
    TerminatorInst *TI = I->getTerminator();
    if (!isa<InvokeInst>(TI))
      continue;
    BasicBlock *LPad = TI->getSuccessor(1);
    // Skip landing pads that have already been normalized.
    if (LandingPads.count(LPad))
      continue;

    // Check that only invoke unwind edges end at the landing pad.
    bool OnlyUnwoundTo = true;
    for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad);
         PI != PE; ++PI) {
      TerminatorInst *PT = (*PI)->getTerminator();
      if (!isa<InvokeInst>(PT) || LPad == PT->getSuccessor(0)) {
        OnlyUnwoundTo = false;
        break;
      }
    }

    if (OnlyUnwoundTo) {
      // Only unwind edges lead to the landing pad.  Remember the landing pad.
      LandingPads.insert(LPad);
      continue;
    }

    // At least one normal edge ends at the landing pad.  Redirect the unwind
    // edges to a new basic block which falls through into this one.

    // Create the new basic block.
    BasicBlock *NewBB = BasicBlock::Create(F->getContext(),
                                           LPad->getName() + "_unwind_edge");

    // Insert it into the function right before the original landing pad.
    LPad->getParent()->getBasicBlockList().insert(LPad, NewBB);

    // Redirect unwind edges from the original landing pad to NewBB.
    for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ) {
      TerminatorInst *PT = (*PI++)->getTerminator();
      if (isa<InvokeInst>(PT) && PT->getSuccessor(1) == LPad)
        // Unwind to the new block.
        PT->setSuccessor(1, NewBB);
    }

    // If there are any PHI nodes in LPad, we need to update them so that they
    // merge incoming values from NewBB instead.
    for (BasicBlock::iterator II = LPad->begin(); isa<PHINode>(II); ++II) {
      PHINode *PN = cast<PHINode>(II);
      pred_iterator PB = pred_begin(NewBB), PE = pred_end(NewBB);

      // Check to see if all of the values coming in via unwind edges are the
      // same.  If so, we don't need to create a new PHI node.
      Value *InVal = PN->getIncomingValueForBlock(*PB);
      for (pred_iterator PI = PB; PI != PE; ++PI) {
        if (PI != PB && InVal != PN->getIncomingValueForBlock(*PI)) {
          InVal = 0;
          break;
        }
      }

      if (InVal == 0) {
        // Different unwind edges have different values.  Create a new PHI node
        // in NewBB.
        PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".unwind",
                                         NewBB);
        // Add an entry for each unwind edge, using the value from the old PHI.
        for (pred_iterator PI = PB; PI != PE; ++PI)
          NewPN->addIncoming(PN->getIncomingValueForBlock(*PI), *PI);

        // Now use this new PHI as the common incoming value for NewBB in PN.
        InVal = NewPN;
      }

      // Revector exactly one entry in the PHI node to come from NewBB
      // and delete all other entries that come from unwind edges.  If
      // there are both normal and unwind edges from the same predecessor,
      // this leaves an entry for the normal edge.
      for (pred_iterator PI = PB; PI != PE; ++PI)
        PN->removeIncomingValue(*PI);
      PN->addIncoming(InVal, NewBB);
    }

    // Add a fallthrough from NewBB to the original landing pad.
    BranchInst::Create(LPad, NewBB);

    // Now update DominatorTree and DominanceFrontier analysis information.
    if (DT)
      DT->splitBlock(NewBB);
    if (DF)
      DF->splitBlock(NewBB);

    // Remember the newly constructed landing pad.  The original landing pad
    // LPad is no longer a landing pad now that all unwind edges have been
    // revectored to NewBB.
    LandingPads.insert(NewBB);
    ++NumLandingPadsSplit;
    Changed = true;
  }

  return Changed;
}