C++ BranchInst::setDebugLoc方法代码示例

BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
                                         ArrayRef<BasicBlock *> Preds,
                                         const char *Suffix, DominatorTree *DT,
                                         LoopInfo *LI, bool PreserveLCSSA) {
  // Do not attempt to split that which cannot be split.
  if (!BB->canSplitPredecessors())
    return nullptr;

  // For the landingpads we need to act a bit differently.
  // Delegate this work to the SplitLandingPadPredecessors.
  if (BB->isLandingPad()) {
    SmallVector<BasicBlock*, 2> NewBBs;
    std::string NewName = std::string(Suffix) + ".split-lp";

    SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs, DT,
                                LI, PreserveLCSSA);
    return NewBBs[0];
  }

  // Create new basic block, insert right before the original block.
  BasicBlock *NewBB = BasicBlock::Create(
      BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);

  // The new block unconditionally branches to the old block.
  BranchInst *BI = BranchInst::Create(BB, NewBB);
  BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->getDebugLoc());

  // Move the edges from Preds to point to NewBB instead of BB.
  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
    // This is slightly more strict than necessary; the minimum requirement
    // is that there be no more than one indirectbr branching to BB. And
    // all BlockAddress uses would need to be updated.
    assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
           "Cannot split an edge from an IndirectBrInst");
    Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
  }

  // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
  // node becomes an incoming value for BB's phi node.  However, if the Preds
  // list is empty, we need to insert dummy entries into the PHI nodes in BB to
  // account for the newly created predecessor.
  if (Preds.empty()) {
    // Insert dummy values as the incoming value.
    for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
      cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
    return NewBB;
  }

  // Update DominatorTree, LoopInfo, and LCCSA analysis information.
  bool HasLoopExit = false;
  UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, PreserveLCSSA,
                            HasLoopExit);

  // Update the PHI nodes in BB with the values coming from NewBB.
  UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
  return NewBB;
}

/// This splits a basic block into two at the specified
/// instruction.  Note that all instructions BEFORE the specified iterator stay
/// as part of the original basic block, an unconditional branch is added to
/// the new BB, and the rest of the instructions in the BB are moved to the new
/// BB, including the old terminator.  This invalidates the iterator.
///
/// Note that this only works on well formed basic blocks (must have a
/// terminator), and 'I' must not be the end of instruction list (which would
/// cause a degenerate basic block to be formed, having a terminator inside of
/// the basic block).
///
BasicBlock *BasicBlock::splitBasicBlock(iterator I, const Twine &BBName) {
  assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
  assert(I != InstList.end() &&
         "Trying to get me to create degenerate basic block!");

  BasicBlock *InsertBefore = std::next(Function::iterator(this))
                               .getNodePtrUnchecked();
  BasicBlock *New = BasicBlock::Create(getContext(), BBName,
                                       getParent(), InsertBefore);

  // Save DebugLoc of split point before invalidating iterator.
  DebugLoc Loc = I->getDebugLoc();
  // Move all of the specified instructions from the original basic block into
  // the new basic block.
  New->getInstList().splice(New->end(), this->getInstList(), I, end());

  // Add a branch instruction to the newly formed basic block.
  BranchInst *BI = BranchInst::Create(New, this);
  BI->setDebugLoc(Loc);

  // Now we must loop through all of the successors of the New block (which
  // _were_ the successors of the 'this' block), and update any PHI nodes in
  // successors.  If there were PHI nodes in the successors, then they need to
  // know that incoming branches will be from New, not from Old.
  //
  for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
    // Loop over any phi nodes in the basic block, updating the BB field of
    // incoming values...
    BasicBlock *Successor = *I;
    PHINode *PN;
    for (BasicBlock::iterator II = Successor->begin();
         (PN = dyn_cast<PHINode>(II)); ++II) {
      int IDX = PN->getBasicBlockIndex(this);
      while (IDX != -1) {
        PN->setIncomingBlock((unsigned)IDX, New);
        IDX = PN->getBasicBlockIndex(this);
      }
    }
  }
  return New;
}

// This is basically the split basic block function but it does not create
// a new basic block.
void Decompiler::splitBasicBlockIntoBlock(Function::iterator Src,
  BasicBlock::iterator FirstInst, BasicBlock *Tgt) {
  assert(Src->getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
  assert(FirstInst != Src->end() &&
         "Trying to get me to create degenerate basic block!");

  Tgt->moveAfter(Src);

  // Move all of the specified instructions from the original basic block into
  // the new basic block.
  Tgt->getInstList().splice(Tgt->end(), Src->getInstList(),
    FirstInst, Src->end());

  // Add a branch instruction to the newly formed basic block.
  BranchInst *BI = BranchInst::Create(Tgt, Src);
  // Set debugLoc to the instruction before the terminator's DebugLoc.
  // Note the pre-inc which can confuse folks.
  BI->setDebugLoc((++Src->rbegin())->getDebugLoc());

  // Now we must loop through all of the successors of the New block (which
  // _were_ the successors of the 'this' block), and update any PHI nodes in
  // successors.  If there were PHI nodes in the successors, then they need to
  // know that incoming branches will be from New, not from Old.
  //
  for (succ_iterator I = succ_begin(Tgt), E = succ_end(Tgt); I != E; ++I) {
    // Loop over any phi nodes in the basic block, updating the BB field of
    // incoming values...
    BasicBlock *Successor = *I;
    PHINode *PN;
    for (BasicBlock::iterator II = Successor->begin();
         (PN = dyn_cast<PHINode>(II)); ++II) {
      int IDX = PN->getBasicBlockIndex(Src);
      while (IDX != -1) {
        PN->setIncomingBlock((unsigned)IDX, Tgt);
        IDX = PN->getBasicBlockIndex(Src);
      }
    }
  }
}

/// \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();
//.........这里部分代码省略.........

/// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
/// split the critical edge.  This will update DominatorTree information if it
/// is available, thus calling this pass will not invalidate either of them.
/// This returns the new block if the edge was split, null otherwise.
///
/// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the
/// specified successor will be merged into the same critical edge block.
/// This is most commonly interesting with switch instructions, which may
/// have many edges to any one destination.  This ensures that all edges to that
/// dest go to one block instead of each going to a different block, but isn't
/// the standard definition of a "critical edge".
///
/// It is invalid to call this function on a critical edge that starts at an
/// IndirectBrInst.  Splitting these edges will almost always create an invalid
/// program because the address of the new block won't be the one that is jumped
/// to.
///
BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
                                    Pass *P, bool MergeIdenticalEdges,
                                    bool DontDeleteUselessPhis,
                                    bool SplitLandingPads) {
  if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0;

  assert(!isa<IndirectBrInst>(TI) &&
         "Cannot split critical edge from IndirectBrInst");

  BasicBlock *TIBB = TI->getParent();
  BasicBlock *DestBB = TI->getSuccessor(SuccNum);

  // Splitting the critical edge to a landing pad block is non-trivial. Don't do
  // it in this generic function.
  if (DestBB->isLandingPad()) return 0;

  // Create a new basic block, linking it into the CFG.
  BasicBlock *NewBB = BasicBlock::Create(TI->getContext(),
                      TIBB->getName() + "." + DestBB->getName() + "_crit_edge");
  // Create our unconditional branch.
  BranchInst *NewBI = BranchInst::Create(DestBB, NewBB);
  NewBI->setDebugLoc(TI->getDebugLoc());

  // Branch to the new block, breaking the edge.
  TI->setSuccessor(SuccNum, NewBB);

  // Insert the block into the function... right after the block TI lives in.
  Function &F = *TIBB->getParent();
  Function::iterator FBBI = TIBB;
  F.getBasicBlockList().insert(++FBBI, NewBB);

  // If there are any PHI nodes in DestBB, we need to update them so that they
  // merge incoming values from NewBB instead of from TIBB.
  {
    unsigned BBIdx = 0;
    for (BasicBlock::iterator I = DestBB->begin(); isa<PHINode>(I); ++I) {
      // We no longer enter through TIBB, now we come in through NewBB.
      // Revector exactly one entry in the PHI node that used to come from
      // TIBB to come from NewBB.
      PHINode *PN = cast<PHINode>(I);

      // Reuse the previous value of BBIdx if it lines up.  In cases where we
      // have multiple phi nodes with *lots* of predecessors, this is a speed
      // win because we don't have to scan the PHI looking for TIBB.  This
      // happens because the BB list of PHI nodes are usually in the same
      // order.
      if (PN->getIncomingBlock(BBIdx) != TIBB)
        BBIdx = PN->getBasicBlockIndex(TIBB);
      PN->setIncomingBlock(BBIdx, NewBB);
    }
  }

  // If there are any other edges from TIBB to DestBB, update those to go
  // through the split block, making those edges non-critical as well (and
  // reducing the number of phi entries in the DestBB if relevant).
  if (MergeIdenticalEdges) {
    for (unsigned i = SuccNum+1, e = TI->getNumSuccessors(); i != e; ++i) {
      if (TI->getSuccessor(i) != DestBB) continue;

      // Remove an entry for TIBB from DestBB phi nodes.
      DestBB->removePredecessor(TIBB, DontDeleteUselessPhis);

      // We found another edge to DestBB, go to NewBB instead.
      TI->setSuccessor(i, NewBB);
    }
  }



  // If we don't have a pass object, we can't update anything...
  if (P == 0) return NewBB;

  DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
  LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();

  // If we have nothing to update, just return.
  if (DT == 0 && LI == 0)
    return NewBB;

  // Now update analysis information.  Since the only predecessor of NewBB is
  // the TIBB, TIBB clearly dominates NewBB.  TIBB usually doesn't dominate
  // anything, as there are other successors of DestBB.  However, if all other
  // predecessors of DestBB are already dominated by DestBB (e.g. DestBB is a
//.........这里部分代码省略.........

//.........这里部分代码省略.........
    TailCallsAreMarkedTail = CI->isTailCall();
    if (TailCallsAreMarkedTail)
      // Move all fixed sized allocas from OldEntry to NewEntry.
      for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(),
             NEBI = NewEntry->begin(); OEBI != E; )
        if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++))
          if (isa<ConstantInt>(AI->getArraySize()))
            AI->moveBefore(&*NEBI);

    // Now that we have created a new block, which jumps to the entry
    // block, insert a PHI node for each argument of the function.
    // For now, we initialize each PHI to only have the real arguments
    // which are passed in.
    Instruction *InsertPos = &OldEntry->front();
    for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
         I != E; ++I) {
      PHINode *PN = PHINode::Create(I->getType(), 2,
                                    I->getName() + ".tr", InsertPos);
      I->replaceAllUsesWith(PN); // Everyone use the PHI node now!
      PN->addIncoming(&*I, NewEntry);
      ArgumentPHIs.push_back(PN);
    }
  }

  // If this function has self recursive calls in the tail position where some
  // are marked tail and some are not, only transform one flavor or another.  We
  // have to choose whether we move allocas in the entry block to the new entry
  // block or not, so we can't make a good choice for both.  NOTE: We could do
  // slightly better here in the case that the function has no entry block
  // allocas.
  if (TailCallsAreMarkedTail && !CI->isTailCall())
    return false;

  // Ok, now that we know we have a pseudo-entry block WITH all of the
  // required PHI nodes, add entries into the PHI node for the actual
  // parameters passed into the tail-recursive call.
  for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i)
    ArgumentPHIs[i]->addIncoming(CI->getArgOperand(i), BB);

  // If we are introducing an accumulator variable to eliminate the recursion,
  // do so now.  Note that we _know_ that no subsequent tail recursion
  // eliminations will happen on this function because of the way the
  // accumulator recursion predicate is set up.
  //
  if (AccumulatorRecursionEliminationInitVal) {
    Instruction *AccRecInstr = AccumulatorRecursionInstr;
    // Start by inserting a new PHI node for the accumulator.
    pred_iterator PB = pred_begin(OldEntry), PE = pred_end(OldEntry);
    PHINode *AccPN = PHINode::Create(
        AccumulatorRecursionEliminationInitVal->getType(),
        std::distance(PB, PE) + 1, "accumulator.tr", &OldEntry->front());

    // Loop over all of the predecessors of the tail recursion block.  For the
    // real entry into the function we seed the PHI with the initial value,
    // computed earlier.  For any other existing branches to this block (due to
    // other tail recursions eliminated) the accumulator is not modified.
    // Because we haven't added the branch in the current block to OldEntry yet,
    // it will not show up as a predecessor.
    for (pred_iterator PI = PB; PI != PE; ++PI) {
      BasicBlock *P = *PI;
      if (P == &F->getEntryBlock())
        AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, P);
      else
        AccPN->addIncoming(AccPN, P);
    }

    if (AccRecInstr) {
      // Add an incoming argument for the current block, which is computed by
      // our associative and commutative accumulator instruction.
      AccPN->addIncoming(AccRecInstr, BB);

      // Next, rewrite the accumulator recursion instruction so that it does not
      // use the result of the call anymore, instead, use the PHI node we just
      // inserted.
      AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN);
    } else {
      // Add an incoming argument for the current block, which is just the
      // constant returned by the current return instruction.
      AccPN->addIncoming(Ret->getReturnValue(), BB);
    }

    // Finally, rewrite any return instructions in the program to return the PHI
    // node instead of the "initval" that they do currently.  This loop will
    // actually rewrite the return value we are destroying, but that's ok.
    for (BasicBlock &BBI : *F)
      if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI.getTerminator()))
        RI->setOperand(0, AccPN);
    ++NumAccumAdded;
  }

  // Now that all of the PHI nodes are in place, remove the call and
  // ret instructions, replacing them with an unconditional branch.
  BranchInst *NewBI = BranchInst::Create(OldEntry, Ret);
  NewBI->setDebugLoc(CI->getDebugLoc());

  BB->getInstList().erase(Ret);  // Remove return.
  BB->getInstList().erase(CI);   // Remove call.
  ++NumEliminated;
  return true;
}

//.........这里部分代码省略.........
  // 'nounwind'.
  if (InlinedFunctionInfo.ContainsCalls &&
      (MustClearTailCallFlags || MarkNoUnwind)) {
    for (Function::iterator BB = FirstNewBlock, E = Caller->end();
         BB != E; ++BB)
      for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
        if (CallInst *CI = dyn_cast<CallInst>(I)) {
          if (MustClearTailCallFlags)
            CI->setTailCall(false);
          if (MarkNoUnwind)
            CI->setDoesNotThrow();
        }
  }

  // If we are inlining for an invoke instruction, we must make sure to rewrite
  // any call instructions into invoke instructions.
  if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall))
    HandleInlinedInvoke(II, FirstNewBlock, InlinedFunctionInfo);

  // If we cloned in _exactly one_ basic block, and if that block ends in a
  // return instruction, we splice the body of the inlined callee directly into
  // the calling basic block.
  if (Returns.size() == 1 && std::distance(FirstNewBlock, Caller->end()) == 1) {
    // Move all of the instructions right before the call.
    OrigBB->getInstList().splice(TheCall, FirstNewBlock->getInstList(),
                                 FirstNewBlock->begin(), FirstNewBlock->end());
    // Remove the cloned basic block.
    Caller->getBasicBlockList().pop_back();

    // If the call site was an invoke instruction, add a branch to the normal
    // destination.
    if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) {
      BranchInst *NewBr = BranchInst::Create(II->getNormalDest(), TheCall);
      NewBr->setDebugLoc(Returns[0]->getDebugLoc());
    }

    // If the return instruction returned a value, replace uses of the call with
    // uses of the returned value.
    if (!TheCall->use_empty()) {
      ReturnInst *R = Returns[0];
      if (TheCall == R->getReturnValue())
        TheCall->replaceAllUsesWith(UndefValue::get(TheCall->getType()));
      else
        TheCall->replaceAllUsesWith(R->getReturnValue());
    }
    // Since we are now done with the Call/Invoke, we can delete it.
    TheCall->eraseFromParent();

    // Since we are now done with the return instruction, delete it also.
    Returns[0]->eraseFromParent();

    // We are now done with the inlining.
    return true;
  }

  // Otherwise, we have the normal case, of more than one block to inline or
  // multiple return sites.

  // We want to clone the entire callee function into the hole between the
  // "starter" and "ender" blocks.  How we accomplish this depends on whether
  // this is an invoke instruction or a call instruction.
  BasicBlock *AfterCallBB;
  BranchInst *CreatedBranchToNormalDest = NULL;
  if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) {

    // Add an unconditional branch to make this look like the CallInst case...

//.........这里部分代码省略.........
    Value *V = SimplifyInstruction(C);
    if (V && LI->replacementPreservesLCSSAForm(C, V)) {
      // If so, then delete the temporary instruction and stick the folded value
      // in the map.
      delete C;
      ValueMap[Inst] = V;
    } else {
      // Otherwise, stick the new instruction into the new block!
      C->setName(Inst->getName());
      C->insertBefore(LoopEntryBranch);
      ValueMap[Inst] = C;
    }
  }

  // Along with all the other instructions, we just cloned OrigHeader's
  // terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
  // successors by duplicating their incoming values for OrigHeader.
  TerminatorInst *TI = OrigHeader->getTerminator();
  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
    for (BasicBlock::iterator BI = TI->getSuccessor(i)->begin();
         PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
      PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);

  // Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
  // OrigPreHeader's old terminator (the original branch into the loop), and
  // remove the corresponding incoming values from the PHI nodes in OrigHeader.
  LoopEntryBranch->eraseFromParent();

  // If there were any uses of instructions in the duplicated block outside the
  // loop, update them, inserting PHI nodes as required
  RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap);

  // NewHeader is now the header of the loop.
  L->moveToHeader(NewHeader);
  assert(L->getHeader() == NewHeader && "Latch block is our new header");


  // At this point, we've finished our major CFG changes.  As part of cloning
  // the loop into the preheader we've simplified instructions and the
  // duplicated conditional branch may now be branching on a constant.  If it is
  // branching on a constant and if that constant means that we enter the loop,
  // then we fold away the cond branch to an uncond branch.  This simplifies the
  // loop in cases important for nested loops, and it also means we don't have
  // to split as many edges.
  BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator());
  assert(PHBI->isConditional() && "Should be clone of BI condbr!");
  if (!isa<ConstantInt>(PHBI->getCondition()) ||
      PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero())
          != NewHeader) {
    // The conditional branch can't be folded, handle the general case.
    // Update DominatorTree to reflect the CFG change we just made.  Then split
    // edges as necessary to preserve LoopSimplify form.
    if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) {
      // Since OrigPreheader now has the conditional branch to Exit block, it is
      // the dominator of Exit.
      DT->changeImmediateDominator(Exit, OrigPreheader);
      DT->changeImmediateDominator(NewHeader, OrigPreheader);

      // Update OrigHeader to be dominated by the new header block.
      DT->changeImmediateDominator(OrigHeader, OrigLatch);
    }

    // Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
    // thus is not a preheader anymore.
    // Split the edge to form a real preheader.
    BasicBlock *NewPH = SplitCriticalEdge(OrigPreheader, NewHeader, this);
    NewPH->setName(NewHeader->getName() + ".lr.ph");

    // Preserve canonical loop form, which means that 'Exit' should have only
    // one predecessor.
    BasicBlock *ExitSplit = SplitCriticalEdge(L->getLoopLatch(), Exit, this);
    ExitSplit->moveBefore(Exit);
  } else {
    // We can fold the conditional branch in the preheader, this makes things
    // simpler. The first step is to remove the extra edge to the Exit block.
    Exit->removePredecessor(OrigPreheader, true /*preserve LCSSA*/);
    BranchInst *NewBI = BranchInst::Create(NewHeader, PHBI);
    NewBI->setDebugLoc(PHBI->getDebugLoc());
    PHBI->eraseFromParent();

    // With our CFG finalized, update DomTree if it is available.
    if (DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>()) {
      // Update OrigHeader to be dominated by the new header block.
      DT->changeImmediateDominator(NewHeader, OrigPreheader);
      DT->changeImmediateDominator(OrigHeader, OrigLatch);
    }
  }

  assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
  assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");

  // Now that the CFG and DomTree are in a consistent state again, try to merge
  // the OrigHeader block into OrigLatch.  This will succeed if they are
  // connected by an unconditional branch.  This is just a cleanup so the
  // emitted code isn't too gross in this common case.
  MergeBlockIntoPredecessor(OrigHeader, this);

  ++NumRotated;
  return true;
}

BasicBlock *
llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
                        const CriticalEdgeSplittingOptions &Options) {
  if (!isCriticalEdge(TI, SuccNum, Options.MergeIdenticalEdges))
    return nullptr;

  assert(!isa<IndirectBrInst>(TI) &&
         "Cannot split critical edge from IndirectBrInst");

  BasicBlock *TIBB = TI->getParent();
  BasicBlock *DestBB = TI->getSuccessor(SuccNum);

  // Splitting the critical edge to a pad block is non-trivial. Don't do
  // it in this generic function.
  if (DestBB->isEHPad()) return nullptr;

  // Create a new basic block, linking it into the CFG.
  BasicBlock *NewBB = BasicBlock::Create(TI->getContext(),
                      TIBB->getName() + "." + DestBB->getName() + "_crit_edge");
  // Create our unconditional branch.
  BranchInst *NewBI = BranchInst::Create(DestBB, NewBB);
  NewBI->setDebugLoc(TI->getDebugLoc());

  // Branch to the new block, breaking the edge.
  TI->setSuccessor(SuccNum, NewBB);

  // Insert the block into the function... right after the block TI lives in.
  Function &F = *TIBB->getParent();
  Function::iterator FBBI = TIBB->getIterator();
  F.getBasicBlockList().insert(++FBBI, NewBB);

  // If there are any PHI nodes in DestBB, we need to update them so that they
  // merge incoming values from NewBB instead of from TIBB.
  {
    unsigned BBIdx = 0;
    for (BasicBlock::iterator I = DestBB->begin(); isa<PHINode>(I); ++I) {
      // We no longer enter through TIBB, now we come in through NewBB.
      // Revector exactly one entry in the PHI node that used to come from
      // TIBB to come from NewBB.
      PHINode *PN = cast<PHINode>(I);

      // Reuse the previous value of BBIdx if it lines up.  In cases where we
      // have multiple phi nodes with *lots* of predecessors, this is a speed
      // win because we don't have to scan the PHI looking for TIBB.  This
      // happens because the BB list of PHI nodes are usually in the same
      // order.
      if (PN->getIncomingBlock(BBIdx) != TIBB)
        BBIdx = PN->getBasicBlockIndex(TIBB);
      PN->setIncomingBlock(BBIdx, NewBB);
    }
  }

  // If there are any other edges from TIBB to DestBB, update those to go
  // through the split block, making those edges non-critical as well (and
  // reducing the number of phi entries in the DestBB if relevant).
  if (Options.MergeIdenticalEdges) {
    for (unsigned i = SuccNum+1, e = TI->getNumSuccessors(); i != e; ++i) {
      if (TI->getSuccessor(i) != DestBB) continue;

      // Remove an entry for TIBB from DestBB phi nodes.
      DestBB->removePredecessor(TIBB, Options.DontDeleteUselessPHIs);

      // We found another edge to DestBB, go to NewBB instead.
      TI->setSuccessor(i, NewBB);
    }
  }

  // If we have nothing to update, just return.
  auto *DT = Options.DT;
  auto *LI = Options.LI;
  if (!DT && !LI)
    return NewBB;

  // Now update analysis information.  Since the only predecessor of NewBB is
  // the TIBB, TIBB clearly dominates NewBB.  TIBB usually doesn't dominate
  // anything, as there are other successors of DestBB.  However, if all other
  // predecessors of DestBB are already dominated by DestBB (e.g. DestBB is a
  // loop header) then NewBB dominates DestBB.
  SmallVector<BasicBlock*, 8> OtherPreds;

  // If there is a PHI in the block, loop over predecessors with it, which is
  // faster than iterating pred_begin/end.
  if (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
      if (PN->getIncomingBlock(i) != NewBB)
        OtherPreds.push_back(PN->getIncomingBlock(i));
  } else {
    for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB);
         I != E; ++I) {
      BasicBlock *P = *I;
      if (P != NewBB)
        OtherPreds.push_back(P);
    }
  }

  bool NewBBDominatesDestBB = true;

  // Should we update DominatorTree information?
  if (DT) {
    DomTreeNode *TINode = DT->getNode(TIBB);
//.........这里部分代码省略.........