C++ SmallPtrSet::begin方法代码示例

void LTOCodeGenerator::applyScopeRestrictions() {
  if (ScopeRestrictionsDone || !shouldInternalize())
    return;
  Module *mergedModule = Linker.getModule();

  // Start off with a verification pass.
  PassManager passes;
  passes.add(createVerifierPass());

  // mark which symbols can not be internalized
  Mangler Mangler(TargetMach->getDataLayout());
  std::vector<const char*> MustPreserveList;
  SmallPtrSet<GlobalValue*, 8> AsmUsed;
  std::vector<StringRef> Libcalls;
  TargetLibraryInfo TLI(Triple(TargetMach->getTargetTriple()));
  accumulateAndSortLibcalls(Libcalls, TLI, TargetMach->getTargetLowering());

  for (Module::iterator f = mergedModule->begin(),
         e = mergedModule->end(); f != e; ++f)
    applyRestriction(*f, Libcalls, MustPreserveList, AsmUsed, Mangler);
  for (Module::global_iterator v = mergedModule->global_begin(),
         e = mergedModule->global_end(); v !=  e; ++v)
    applyRestriction(*v, Libcalls, MustPreserveList, AsmUsed, Mangler);
  for (Module::alias_iterator a = mergedModule->alias_begin(),
         e = mergedModule->alias_end(); a != e; ++a)
    applyRestriction(*a, Libcalls, MustPreserveList, AsmUsed, Mangler);

  GlobalVariable *LLVMCompilerUsed =
    mergedModule->getGlobalVariable("llvm.compiler.used");
  findUsedValues(LLVMCompilerUsed, AsmUsed);
  if (LLVMCompilerUsed)
    LLVMCompilerUsed->eraseFromParent();

  if (!AsmUsed.empty()) {
    llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(Context);
    std::vector<Constant*> asmUsed2;
    for (SmallPtrSet<GlobalValue*, 16>::const_iterator i = AsmUsed.begin(),
           e = AsmUsed.end(); i !=e; ++i) {
      GlobalValue *GV = *i;
      Constant *c = ConstantExpr::getBitCast(GV, i8PTy);
      asmUsed2.push_back(c);
    }

    llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, asmUsed2.size());
    LLVMCompilerUsed =
      new llvm::GlobalVariable(*mergedModule, ATy, false,
                               llvm::GlobalValue::AppendingLinkage,
                               llvm::ConstantArray::get(ATy, asmUsed2),
                               "llvm.compiler.used");

    LLVMCompilerUsed->setSection("llvm.metadata");
  }

  passes.add(
      createInternalizePass(MustPreserveList, shouldOnlyInternalizeHidden()));

  // apply scope restrictions
  passes.run(*mergedModule);

  ScopeRestrictionsDone = true;
}

/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
/// edge and spill them.
void SjLjEHPass::lowerAcrossUnwindEdges(Function &F,
                                        ArrayRef<InvokeInst*> Invokes) {
  // Finally, scan the code looking for instructions with bad live ranges.
  for (Function::iterator
         BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
    for (BasicBlock::iterator
           II = BB->begin(), IIE = BB->end(); II != IIE; ++II) {
      // Ignore obvious cases we don't have to handle. In particular, most
      // instructions either have no uses or only have a single use inside the
      // current block. Ignore them quickly.
      Instruction *Inst = II;
      if (Inst->use_empty()) continue;
      if (Inst->hasOneUse() &&
          cast<Instruction>(Inst->use_back())->getParent() == BB &&
          !isa<PHINode>(Inst->use_back())) continue;

      // If this is an alloca in the entry block, it's not a real register
      // value.
      if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
        if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
          continue;

      // Avoid iterator invalidation by copying users to a temporary vector.
      SmallVector<Instruction*, 16> Users;
      for (Value::use_iterator
             UI = Inst->use_begin(), E = Inst->use_end(); UI != E; ++UI) {
        Instruction *User = cast<Instruction>(*UI);
        if (User->getParent() != BB || isa<PHINode>(User))
          Users.push_back(User);
      }

      // Find all of the blocks that this value is live in.
      SmallPtrSet<BasicBlock*, 64> LiveBBs;
      LiveBBs.insert(Inst->getParent());
      while (!Users.empty()) {
        Instruction *U = Users.back();
        Users.pop_back();

        if (!isa<PHINode>(U)) {
          MarkBlocksLiveIn(U->getParent(), LiveBBs);
        } else {
          // Uses for a PHI node occur in their predecessor block.
          PHINode *PN = cast<PHINode>(U);
          for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
            if (PN->getIncomingValue(i) == Inst)
              MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
        }
      }

      // Now that we know all of the blocks that this thing is live in, see if
      // it includes any of the unwind locations.
      bool NeedsSpill = false;
      for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
        BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
        if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
          DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
                << UnwindBlock->getName() << "\n");
          NeedsSpill = true;
          break;
        }
      }

      // If we decided we need a spill, do it.
      // FIXME: Spilling this way is overkill, as it forces all uses of
      // the value to be reloaded from the stack slot, even those that aren't
      // in the unwind blocks. We should be more selective.
      if (NeedsSpill) {
        DemoteRegToStack(*Inst, true);
        ++NumSpilled;
      }
    }
  }

  // Go through the landing pads and remove any PHIs there.
  for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
    BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
    LandingPadInst *LPI = UnwindBlock->getLandingPadInst();

    // Place PHIs into a set to avoid invalidating the iterator.
    SmallPtrSet<PHINode*, 8> PHIsToDemote;
    for (BasicBlock::iterator
           PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
      PHIsToDemote.insert(cast<PHINode>(PN));
    if (PHIsToDemote.empty()) continue;

    // Demote the PHIs to the stack.
    for (SmallPtrSet<PHINode*, 8>::iterator
           I = PHIsToDemote.begin(), E = PHIsToDemote.end(); I != E; ++I)
      DemotePHIToStack(*I);

    // Move the landingpad instruction back to the top of the landing pad block.
    LPI->moveBefore(UnwindBlock->begin());
  }
}

/// ProcessLoop - Walk the loop structure in depth first order, ensuring that
/// all loops have preheaders.
///
bool LoopSimplify::ProcessLoop(Loop *L, LPPassManager &LPM) {
  bool Changed = false;
ReprocessLoop:

  // Check to see that no blocks (other than the header) in this loop have
  // predecessors that are not in the loop.  This is not valid for natural
  // loops, but can occur if the blocks are unreachable.  Since they are
  // unreachable we can just shamelessly delete those CFG edges!
  for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
       BB != E; ++BB) {
    if (*BB == L->getHeader()) continue;

    SmallPtrSet<BasicBlock*, 4> BadPreds;
    for (pred_iterator PI = pred_begin(*BB),
         PE = pred_end(*BB); PI != PE; ++PI) {
      BasicBlock *P = *PI;
      if (!L->contains(P))
        BadPreds.insert(P);
    }

    // Delete each unique out-of-loop (and thus dead) predecessor.
    for (SmallPtrSet<BasicBlock*, 4>::iterator I = BadPreds.begin(),
         E = BadPreds.end(); I != E; ++I) {

      DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor "
                   << (*I)->getName() << "\n");

      // Inform each successor of each dead pred.
      for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
        (*SI)->removePredecessor(*I);
      // Zap the dead pred's terminator and replace it with unreachable.
      TerminatorInst *TI = (*I)->getTerminator();
       TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
      (*I)->getTerminator()->eraseFromParent();
      new UnreachableInst((*I)->getContext(), *I);
      Changed = true;
    }
  }

  // If there are exiting blocks with branches on undef, resolve the undef in
  // the direction which will exit the loop. This will help simplify loop
  // trip count computations.
  SmallVector<BasicBlock*, 8> ExitingBlocks;
  L->getExitingBlocks(ExitingBlocks);
  for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
       E = ExitingBlocks.end(); I != E; ++I)
    if (BranchInst *BI = dyn_cast<BranchInst>((*I)->getTerminator()))
      if (BI->isConditional()) {
        if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) {

          DEBUG(dbgs() << "LoopSimplify: Resolving \"br i1 undef\" to exit in "
                       << (*I)->getName() << "\n");

          BI->setCondition(ConstantInt::get(Cond->getType(),
                                            !L->contains(BI->getSuccessor(0))));
          Changed = true;
        }
      }

  // Does the loop already have a preheader?  If so, don't insert one.
  BasicBlock *Preheader = L->getLoopPreheader();
  if (!Preheader) {
    Preheader = InsertPreheaderForLoop(L);
    if (Preheader) {
      ++NumInserted;
      Changed = true;
    }
  }

  // Next, check to make sure that all exit nodes of the loop only have
  // predecessors that are inside of the loop.  This check guarantees that the
  // loop preheader/header will dominate the exit blocks.  If the exit block has
  // predecessors from outside of the loop, split the edge now.
  SmallVector<BasicBlock*, 8> ExitBlocks;
  L->getExitBlocks(ExitBlocks);

  SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
                                               ExitBlocks.end());
  for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(),
         E = ExitBlockSet.end(); I != E; ++I) {
    BasicBlock *ExitBlock = *I;
    for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
         PI != PE; ++PI)
      // Must be exactly this loop: no subloops, parent loops, or non-loop preds
      // allowed.
      if (!L->contains(*PI)) {
        if (RewriteLoopExitBlock(L, ExitBlock)) {
          ++NumInserted;
          Changed = true;
        }
        break;
      }
  }

  // If the header has more than two predecessors at this point (from the
  // preheader and from multiple backedges), we must adjust the loop.
  BasicBlock *LoopLatch = L->getLoopLatch();
//.........这里部分代码省略.........

bool CodeGenPrepare::runOnFunction(Function &F) {
  bool EverMadeChange = false;

  ModifiedDT = false;
  TLInfo = &getAnalysis<TargetLibraryInfo>();
  DT = getAnalysisIfAvailable<DominatorTree>();
  PFI = getAnalysisIfAvailable<ProfileInfo>();
  OptSize = F.hasFnAttr(Attribute::OptimizeForSize);

  // First pass, eliminate blocks that contain only PHI nodes and an
  // unconditional branch.
  EverMadeChange |= EliminateMostlyEmptyBlocks(F);

  // llvm.dbg.value is far away from the value then iSel may not be able
  // handle it properly. iSel will drop llvm.dbg.value if it can not
  // find a node corresponding to the value.
  EverMadeChange |= PlaceDbgValues(F);

  bool MadeChange = true;
  while (MadeChange) {
    MadeChange = false;
    for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
      BasicBlock *BB = I++;
      MadeChange |= OptimizeBlock(*BB);
    }
    EverMadeChange |= MadeChange;
  }

  SunkAddrs.clear();

  if (!DisableBranchOpts) {
    MadeChange = false;
    SmallPtrSet<BasicBlock*, 8> WorkList;
    for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
      SmallVector<BasicBlock*, 2> Successors(succ_begin(BB), succ_end(BB));
      MadeChange |= ConstantFoldTerminator(BB, true);
      if (!MadeChange) continue;

      for (SmallVectorImpl<BasicBlock*>::iterator
             II = Successors.begin(), IE = Successors.end(); II != IE; ++II)
        if (pred_begin(*II) == pred_end(*II))
          WorkList.insert(*II);
    }

    for (SmallPtrSet<BasicBlock*, 8>::iterator
           I = WorkList.begin(), E = WorkList.end(); I != E; ++I)
      DeleteDeadBlock(*I);

    // Merge pairs of basic blocks with unconditional branches, connected by
    // a single edge.
    if (EverMadeChange || MadeChange)
      MadeChange |= EliminateFallThrough(F);

    if (MadeChange)
      ModifiedDT = true;
    EverMadeChange |= MadeChange;
  }

  if (ModifiedDT && DT)
    DT->DT->recalculate(F);

  return EverMadeChange;
}

// Sinks \p I from the loop \p L's preheader to its uses. Returns true if
// sinking is successful.
// \p LoopBlockNumber is used to sort the insertion blocks to ensure
// determinism.
static bool sinkInstruction(Loop &L, Instruction &I,
                            const SmallVectorImpl<BasicBlock *> &ColdLoopBBs,
                            const SmallDenseMap<BasicBlock *, int, 16> &LoopBlockNumber,
                            LoopInfo &LI, DominatorTree &DT,
                            BlockFrequencyInfo &BFI) {
  // Compute the set of blocks in loop L which contain a use of I.
  SmallPtrSet<BasicBlock *, 2> BBs;
  for (auto &U : I.uses()) {
    Instruction *UI = cast<Instruction>(U.getUser());
    // We cannot sink I to PHI-uses.
    if (dyn_cast<PHINode>(UI))
      return false;
    // We cannot sink I if it has uses outside of the loop.
    if (!L.contains(LI.getLoopFor(UI->getParent())))
      return false;
    BBs.insert(UI->getParent());
  }

  // findBBsToSinkInto is O(BBs.size() * ColdLoopBBs.size()). We cap the max
  // BBs.size() to avoid expensive computation.
  // FIXME: Handle code size growth for min_size and opt_size.
  if (BBs.size() > MaxNumberOfUseBBsForSinking)
    return false;

  // Find the set of BBs that we should insert a copy of I.
  SmallPtrSet<BasicBlock *, 2> BBsToSinkInto =
      findBBsToSinkInto(L, BBs, ColdLoopBBs, DT, BFI);
  if (BBsToSinkInto.empty())
    return false;

  // Copy the final BBs into a vector and sort them using the total ordering
  // of the loop block numbers as iterating the set doesn't give a useful
  // order. No need to stable sort as the block numbers are a total ordering.
  SmallVector<BasicBlock *, 2> SortedBBsToSinkInto;
  SortedBBsToSinkInto.insert(SortedBBsToSinkInto.begin(), BBsToSinkInto.begin(),
                             BBsToSinkInto.end());
  std::sort(SortedBBsToSinkInto.begin(), SortedBBsToSinkInto.end(),
            [&](BasicBlock *A, BasicBlock *B) {
              return *LoopBlockNumber.find(A) < *LoopBlockNumber.find(B);
            });

  BasicBlock *MoveBB = *SortedBBsToSinkInto.begin();
  // FIXME: Optimize the efficiency for cloned value replacement. The current
  //        implementation is O(SortedBBsToSinkInto.size() * I.num_uses()).
  for (BasicBlock *N : SortedBBsToSinkInto) {
    if (N == MoveBB)
      continue;
    // Clone I and replace its uses.
    Instruction *IC = I.clone();
    IC->setName(I.getName());
    IC->insertBefore(&*N->getFirstInsertionPt());
    // Replaces uses of I with IC in N
    for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); UI != UE;) {
      Use &U = *UI++;
      auto *I = cast<Instruction>(U.getUser());
      if (I->getParent() == N)
        U.set(IC);
    }
    // Replaces uses of I with IC in blocks dominated by N
    replaceDominatedUsesWith(&I, IC, DT, N);
    DEBUG(dbgs() << "Sinking a clone of " << I << " To: " << N->getName()
                 << '\n');
    NumLoopSunkCloned++;
  }
  DEBUG(dbgs() << "Sinking " << I << " To: " << MoveBB->getName() << '\n');
  NumLoopSunk++;
  I.moveBefore(&*MoveBB->getFirstInsertionPt());

  return true;
}

/// runOnLoop - Remove dead loops, by which we mean loops that do not impact the
/// observable behavior of the program other than finite running time.  Note
/// we do ensure that this never remove a loop that might be infinite, as doing
/// so could change the halting/non-halting nature of a program.
/// NOTE: This entire process relies pretty heavily on LoopSimplify and LCSSA
/// in order to make various safety checks work.
bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) {
  // We can only remove the loop if there is a preheader that we can
  // branch from after removing it.
  BasicBlock* preheader = L->getLoopPreheader();
  if (!preheader)
    return false;

  // If LoopSimplify form is not available, stay out of trouble.
  if (!L->hasDedicatedExits())
    return false;

  // We can't remove loops that contain subloops.  If the subloops were dead,
  // they would already have been removed in earlier executions of this pass.
  if (L->begin() != L->end())
    return false;

  SmallVector<BasicBlock*, 4> exitingBlocks;
  L->getExitingBlocks(exitingBlocks);

  SmallVector<BasicBlock*, 4> exitBlocks;
  L->getUniqueExitBlocks(exitBlocks);

  // We require that the loop only have a single exit block.  Otherwise, we'd
  // be in the situation of needing to be able to solve statically which exit
  // block will be branched to, or trying to preserve the branching logic in
  // a loop invariant manner.
  if (exitBlocks.size() != 1)
    return false;

  // Finally, we have to check that the loop really is dead.
  bool Changed = false;
  if (!IsLoopDead(L, exitingBlocks, exitBlocks, Changed, preheader))
    return Changed;

  // Don't remove loops for which we can't solve the trip count.
  // They could be infinite, in which case we'd be changing program behavior.
  ScalarEvolution& SE = getAnalysis<ScalarEvolution>();
  const SCEV *S = SE.getMaxBackedgeTakenCount(L);
  if (isa<SCEVCouldNotCompute>(S))
    return Changed;

  // Now that we know the removal is safe, remove the loop by changing the
  // branch from the preheader to go to the single exit block.
  BasicBlock* exitBlock = exitBlocks[0];

  // Because we're deleting a large chunk of code at once, the sequence in which
  // we remove things is very important to avoid invalidation issues.  Don't
  // mess with this unless you have good reason and know what you're doing.

  // Tell ScalarEvolution that the loop is deleted. Do this before
  // deleting the loop so that ScalarEvolution can look at the loop
  // to determine what it needs to clean up.
  SE.forgetLoop(L);

  // Connect the preheader directly to the exit block.
  TerminatorInst* TI = preheader->getTerminator();
  TI->replaceUsesOfWith(L->getHeader(), exitBlock);

  // Rewrite phis in the exit block to get their inputs from
  // the preheader instead of the exiting block.
  BasicBlock* exitingBlock = exitingBlocks[0];
  BasicBlock::iterator BI = exitBlock->begin();
  while (PHINode* P = dyn_cast<PHINode>(BI)) {
    int j = P->getBasicBlockIndex(exitingBlock);
    assert(j >= 0 && "Can't find exiting block in exit block's phi node!");
    P->setIncomingBlock(j, preheader);
    for (unsigned i = 1; i < exitingBlocks.size(); ++i)
      P->removeIncomingValue(exitingBlocks[i]);
    ++BI;
  }

  // Update the dominator tree and remove the instructions and blocks that will
  // be deleted from the reference counting scheme.
  DominatorTree& DT = getAnalysis<DominatorTree>();
  SmallVector<DomTreeNode*, 8> ChildNodes;
  for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end();
       LI != LE; ++LI) {
    // Move all of the block's children to be children of the preheader, which
    // allows us to remove the domtree entry for the block.
    ChildNodes.insert(ChildNodes.begin(), DT[*LI]->begin(), DT[*LI]->end());
    for (SmallVector<DomTreeNode*, 8>::iterator DI = ChildNodes.begin(),
         DE = ChildNodes.end(); DI != DE; ++DI) {
      DT.changeImmediateDominator(*DI, DT[preheader]);
    }

    ChildNodes.clear();
    DT.eraseNode(*LI);

    // Remove the block from the reference counting scheme, so that we can
    // delete it freely later.
    (*LI)->dropAllReferences();
  }

  // Erase the instructions and the blocks without having to worry
//.........这里部分代码省略.........

// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
// as taken, exiting edges as not-taken.
bool BranchProbabilityAnalysis::calcLoopBranchHeuristics(BasicBlock *BB) {
  uint32_t numSuccs = BB->getTerminator()->getNumSuccessors();

  Loop *L = LI->getLoopFor(BB);
  if (!L)
    return false;

  SmallPtrSet<BasicBlock *, 8> BackEdges;
  SmallPtrSet<BasicBlock *, 8> ExitingEdges;
  SmallPtrSet<BasicBlock *, 8> InEdges; // Edges from header to the loop.

  bool isHeader = BB == L->getHeader();

  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
    BasicBlock *Succ = *I;
    Loop *SuccL = LI->getLoopFor(Succ);
    if (SuccL != L)
      ExitingEdges.insert(Succ);
    else if (Succ == L->getHeader())
      BackEdges.insert(Succ);
    else if (isHeader)
      InEdges.insert(Succ);
  }

  if (uint32_t numBackEdges = BackEdges.size()) {
    uint32_t backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
    if (backWeight < NORMAL_WEIGHT)
      backWeight = NORMAL_WEIGHT;

    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = BackEdges.begin(),
         EE = BackEdges.end(); EI != EE; ++EI) {
      BasicBlock *Back = *EI;
      BP->setEdgeWeight(BB, Back, backWeight);
    }
  }

  if (uint32_t numInEdges = InEdges.size()) {
    uint32_t inWeight = LBH_TAKEN_WEIGHT / numInEdges;
    if (inWeight < NORMAL_WEIGHT)
      inWeight = NORMAL_WEIGHT;

    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = InEdges.begin(),
         EE = InEdges.end(); EI != EE; ++EI) {
      BasicBlock *Back = *EI;
      BP->setEdgeWeight(BB, Back, inWeight);
    }
  }

  uint32_t numExitingEdges = ExitingEdges.size();
  if (uint32_t numNonExitingEdges = numSuccs - numExitingEdges) {
    uint32_t exitWeight = LBH_NONTAKEN_WEIGHT / numNonExitingEdges;
    if (exitWeight < MIN_WEIGHT)
      exitWeight = MIN_WEIGHT;

    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
         EE = ExitingEdges.end(); EI != EE; ++EI) {
      BasicBlock *Exiting = *EI;
      BP->setEdgeWeight(BB, Exiting, exitWeight);
    }
  }

  return true;
}

/// handleEndBlock - Remove dead stores to stack-allocated locations in the
/// function end block.  Ex:
/// %A = alloca i32
/// ...
/// store i32 1, i32* %A
/// ret void
bool DSE::handleEndBlock(BasicBlock &BB) {
  bool MadeChange = false;
  
  // Keep track of all of the stack objects that are dead at the end of the
  // function.
  SmallPtrSet<Value*, 16> DeadStackObjects;
  
  // Find all of the alloca'd pointers in the entry block.
  BasicBlock *Entry = BB.getParent()->begin();
  for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
    if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
      DeadStackObjects.insert(AI);
  
  // Treat byval arguments the same, stores to them are dead at the end of the
  // function.
  for (Function::arg_iterator AI = BB.getParent()->arg_begin(),
       AE = BB.getParent()->arg_end(); AI != AE; ++AI)
    if (AI->hasByValAttr())
      DeadStackObjects.insert(AI);
  
  // Scan the basic block backwards
  for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
    --BBI;
    
    // If we find a store, check to see if it points into a dead stack value.
    if (hasMemoryWrite(BBI) && isRemovable(BBI)) {
      // See through pointer-to-pointer bitcasts
      Value *Pointer = GetUnderlyingObject(getStoredPointerOperand(BBI));

      // Stores to stack values are valid candidates for removal.
      if (DeadStackObjects.count(Pointer)) {
        Instruction *Dead = BBI++;
        
        DEBUG(dbgs() << "DSE: Dead Store at End of Block:\n  DEAD: "
                     << *Dead << "\n  Object: " << *Pointer << '\n');
        
        // DCE instructions only used to calculate that store.
        DeleteDeadInstruction(Dead, *MD, &DeadStackObjects);
        ++NumFastStores;
        MadeChange = true;
        continue;
      }
    }
    
    // Remove any dead non-memory-mutating instructions.
    if (isInstructionTriviallyDead(BBI)) {
      Instruction *Inst = BBI++;
      DeleteDeadInstruction(Inst, *MD, &DeadStackObjects);
      ++NumFastOther;
      MadeChange = true;
      continue;
    }
    
    if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
      DeadStackObjects.erase(A);
      continue;
    }
    
    if (CallSite CS = cast<Value>(BBI)) {
      // If this call does not access memory, it can't be loading any of our
      // pointers.
      if (AA->doesNotAccessMemory(CS))
        continue;
      
      unsigned NumModRef = 0, NumOther = 0;
      
      // If the call might load from any of our allocas, then any store above
      // the call is live.
      SmallVector<Value*, 8> LiveAllocas;
      for (SmallPtrSet<Value*, 16>::iterator I = DeadStackObjects.begin(),
           E = DeadStackObjects.end(); I != E; ++I) {
        // If we detect that our AA is imprecise, it's not worth it to scan the
        // rest of the DeadPointers set.  Just assume that the AA will return
        // ModRef for everything, and go ahead and bail out.
        if (NumModRef >= 16 && NumOther == 0)
          return MadeChange;

        // See if the call site touches it.
        AliasAnalysis::ModRefResult A = 
          AA->getModRefInfo(CS, *I, getPointerSize(*I, *AA));
        
        if (A == AliasAnalysis::ModRef)
          ++NumModRef;
        else
          ++NumOther;
        
        if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
          LiveAllocas.push_back(*I);
      }
      
      for (SmallVector<Value*, 8>::iterator I = LiveAllocas.begin(),
           E = LiveAllocas.end(); I != E; ++I)
        DeadStackObjects.erase(*I);
      
//.........这里部分代码省略.........

/*
  This method performs Unroll and Jam. For a simple loop like:
  for (i = ..)
    Fore(i)
    for (j = ..)
      SubLoop(i, j)
    Aft(i)

  Instead of doing normal inner or outer unrolling, we do:
  for (i = .., i+=2)
    Fore(i)
    Fore(i+1)
    for (j = ..)
      SubLoop(i, j)
      SubLoop(i+1, j)
    Aft(i)
    Aft(i+1)

  So the outer loop is essetially unrolled and then the inner loops are fused
  ("jammed") together into a single loop. This can increase speed when there
  are loads in SubLoop that are invariant to i, as they become shared between
  the now jammed inner loops.

  We do this by spliting the blocks in the loop into Fore, Subloop and Aft.
  Fore blocks are those before the inner loop, Aft are those after. Normal
  Unroll code is used to copy each of these sets of blocks and the results are
  combined together into the final form above.

  isSafeToUnrollAndJam should be used prior to calling this to make sure the
  unrolling will be valid. Checking profitablility is also advisable.
*/
LoopUnrollResult
llvm::UnrollAndJamLoop(Loop *L, unsigned Count, unsigned TripCount,
                       unsigned TripMultiple, bool UnrollRemainder,
                       LoopInfo *LI, ScalarEvolution *SE, DominatorTree *DT,
                       AssumptionCache *AC, OptimizationRemarkEmitter *ORE) {

  // When we enter here we should have already checked that it is safe
  BasicBlock *Header = L->getHeader();
  assert(L->getSubLoops().size() == 1);
  Loop *SubLoop = *L->begin();

  // Don't enter the unroll code if there is nothing to do.
  if (TripCount == 0 && Count < 2) {
    LLVM_DEBUG(dbgs() << "Won't unroll; almost nothing to do\n");
    return LoopUnrollResult::Unmodified;
  }

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

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

  // We use the runtime remainder in cases where we don't know trip multiple
  if (TripMultiple == 1 || TripMultiple % Count != 0) {
    if (!UnrollRuntimeLoopRemainder(L, Count, /*AllowExpensiveTripCount*/ false,
                                    /*UseEpilogRemainder*/ true,
                                    UnrollRemainder, LI, SE, DT, AC, true)) {
      LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; remainder loop could not be "
                           "generated when assuming runtime trip count\n");
      return LoopUnrollResult::Unmodified;
    }
  }

  // Notify ScalarEvolution that the loop will be substantially changed,
  // if not outright eliminated.
  if (SE) {
    SE->forgetLoop(L);
    SE->forgetLoop(SubLoop);
  }

  using namespace ore;
  // Report the unrolling decision.
  if (CompletelyUnroll) {
    LLVM_DEBUG(dbgs() << "COMPLETELY UNROLL AND JAMMING loop %"
                      << Header->getName() << " with trip count " << TripCount
                      << "!\n");
    ORE->emit(OptimizationRemark(DEBUG_TYPE, "FullyUnrolled", L->getStartLoc(),
                                 L->getHeader())
              << "completely unroll and jammed loop with "
              << NV("UnrollCount", TripCount) << " iterations");
  } else {
    auto DiagBuilder = [&]() {
      OptimizationRemark Diag(DEBUG_TYPE, "PartialUnrolled", L->getStartLoc(),
                              L->getHeader());
      return Diag << "unroll and jammed loop by a factor of "
                  << NV("UnrollCount", Count);
    };

    LLVM_DEBUG(dbgs() << "UNROLL AND JAMMING loop %" << Header->getName()
                      << " by " << Count);
    if (TripMultiple != 1) {
      LLVM_DEBUG(dbgs() << " with " << TripMultiple << " trips per branch");
      ORE->emit([&]() {
        return DiagBuilder() << " with " << NV("TripMultiple", TripMultiple)
                             << " trips per branch";
      });
    } else {
//.........这里部分代码省略.........

/// HandleURoRInvokes - Handle invokes of "_Unwind_Resume_or_Rethrow" calls. The
/// "unwind" part of these invokes jump to a landing pad within the current
/// function. This is a candidate to merge the selector associated with the URoR
/// invoke with the one from the URoR's landing pad.
bool DwarfEHPrepare::HandleURoRInvokes() {
  if (!EHCatchAllValue) {
    EHCatchAllValue =
      F->getParent()->getNamedGlobal("llvm.eh.catch.all.value");
    if (!EHCatchAllValue) return false;
  }

  if (!SelectorIntrinsic) {
    SelectorIntrinsic =
      Intrinsic::getDeclaration(F->getParent(), Intrinsic::eh_selector);
    if (!SelectorIntrinsic) return false;
  }

  SmallPtrSet<IntrinsicInst*, 32> Sels;
  SmallPtrSet<IntrinsicInst*, 32> CatchAllSels;
  FindAllCleanupSelectors(Sels, CatchAllSels);

  if (!DT)
    // We require DominatorTree information.
    return CleanupSelectors(CatchAllSels);

  if (!URoR) {
    URoR = F->getParent()->getFunction("_Unwind_Resume_or_Rethrow");
    if (!URoR) return CleanupSelectors(CatchAllSels);
  }

  SmallPtrSet<InvokeInst*, 32> URoRInvokes;
  FindAllURoRInvokes(URoRInvokes);

  SmallPtrSet<IntrinsicInst*, 32> SelsToConvert;

  for (SmallPtrSet<IntrinsicInst*, 32>::iterator
         SI = Sels.begin(), SE = Sels.end(); SI != SE; ++SI) {
    const BasicBlock *SelBB = (*SI)->getParent();
    for (SmallPtrSet<InvokeInst*, 32>::iterator
           UI = URoRInvokes.begin(), UE = URoRInvokes.end(); UI != UE; ++UI) {
      const BasicBlock *URoRBB = (*UI)->getParent();
      if (DT->dominates(SelBB, URoRBB)) {
        SelsToConvert.insert(*SI);
        break;
      }
    }
  }

  bool Changed = false;

  if (Sels.size() != SelsToConvert.size()) {
    // If we haven't been able to convert all of the clean-up selectors, then
    // loop through the slow way to see if they still need to be converted.
    if (!ExceptionValueIntrinsic) {
      ExceptionValueIntrinsic =
        Intrinsic::getDeclaration(F->getParent(), Intrinsic::eh_exception);
      if (!ExceptionValueIntrinsic)
        return CleanupSelectors(CatchAllSels);
    }

    for (Value::use_iterator
           I = ExceptionValueIntrinsic->use_begin(),
           E = ExceptionValueIntrinsic->use_end(); I != E; ++I) {
      IntrinsicInst *EHPtr = dyn_cast<IntrinsicInst>(*I);
      if (!EHPtr || EHPtr->getParent()->getParent() != F) continue;

      Changed |= PromoteEHPtrStore(EHPtr);

      bool URoRInvoke = false;
      SmallPtrSet<IntrinsicInst*, 8> SelCalls;
      Changed |= FindSelectorAndURoR(EHPtr, URoRInvoke, SelCalls);

      if (URoRInvoke) {
        // This EH pointer is being used by an invoke of an URoR instruction and
        // an eh.selector intrinsic call. If the eh.selector is a 'clean-up', we
        // need to convert it to a 'catch-all'.
        for (SmallPtrSet<IntrinsicInst*, 8>::iterator
               SI = SelCalls.begin(), SE = SelCalls.end(); SI != SE; ++SI)
          if (!HasCatchAllInSelector(*SI))
              SelsToConvert.insert(*SI);
      }
    }
  }

  if (!SelsToConvert.empty()) {
    // Convert all clean-up eh.selectors, which are associated with "invokes" of
    // URoR calls, into catch-all eh.selectors.
    Changed = true;

    for (SmallPtrSet<IntrinsicInst*, 8>::iterator
           SI = SelsToConvert.begin(), SE = SelsToConvert.end();
         SI != SE; ++SI) {
      IntrinsicInst *II = *SI;

      // Use the exception object pointer and the personality function
      // from the original selector.
      CallSite CS(II);
      IntrinsicInst::op_iterator I = CS.arg_begin();
      IntrinsicInst::op_iterator E = CS.arg_end();
      IntrinsicInst::op_iterator B = prior(E);
//.........这里部分代码省略.........

void moduleDepGraph::matchParametersAndReturnValues(Function &F) {

        // Only do the matching if F has any use
        if (F.isVarArg() || !F.hasNUsesOrMore(1)) {
                return;
        }

        // Data structure which contains the matches between formal and real parameters
        // First: formal parameter
        // Second: real parameter
        SmallVector<std::pair<GraphNode*, GraphNode*>, 4> Parameters(F.arg_size());

        // Fetch the function arguments (formal parameters) into the data structure
        Function::arg_iterator argptr;
        Function::arg_iterator e;
        unsigned i;

        //Create the PHI nodes for the formal parameters
        for (i = 0, argptr = F.arg_begin(), e = F.arg_end(); argptr != e; ++i, ++argptr) {

                OpNode* argPHI = new OpNode(Instruction::PHI);
                GraphNode* argNode = NULL;
                argNode = depGraph->addInst(argptr);

                if (argNode != NULL)
                        depGraph->addEdge(argPHI, argNode);

                Parameters[i].first = argPHI;
        }

        // Check if the function returns a supported value type. If not, no return value matching is done
        bool noReturn = F.getReturnType()->isVoidTy();

        // Creates the data structure which receives the return values of the function, if there is any
        SmallPtrSet<llvm::Value*, 8> ReturnValues;

        if (!noReturn) {
                // Iterate over the basic blocks to fetch all possible return values
                for (Function::iterator bb = F.begin(), bbend = F.end(); bb != bbend; ++bb) {
                        // Get the terminator instruction of the basic block and check if it's
                        // a return instruction: if it's not, continue to next basic block
                        Instruction *terminator = bb->getTerminator();

                        ReturnInst *RI = dyn_cast<ReturnInst> (terminator);

                        if (!RI)
                                continue;

                        // Get the return value and insert in the data structure
                        ReturnValues.insert(RI->getReturnValue());
                }
        }

        for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
                User *U = *UI;

                // Ignore blockaddress uses
                if (isa<BlockAddress> (U))
                        continue;

                // Used by a non-instruction, or not the callee of a function, do not
                // match.
                if (!isa<CallInst> (U) && !isa<InvokeInst> (U))
                        continue;

                Instruction *caller = cast<Instruction> (U);

                CallSite CS(caller);
                if (!CS.isCallee(UI))
                        continue;

                // Iterate over the real parameters and put them in the data structure
                CallSite::arg_iterator AI;
                CallSite::arg_iterator EI;

                for (i = 0, AI = CS.arg_begin(), EI = CS.arg_end(); AI != EI; ++i, ++AI) {
                        Parameters[i].second = depGraph->addInst(*AI);
                }

                // Match formal and real parameters
                for (i = 0; i < Parameters.size(); ++i) {

                        depGraph->addEdge(Parameters[i].second, Parameters[i].first);
                }

                // Match return values
                if (!noReturn) {

                        OpNode* retPHI = new OpNode(Instruction::PHI);
                        GraphNode* callerNode = depGraph->addInst(caller);
                        depGraph->addEdge(retPHI, callerNode);

                        for (SmallPtrSetIterator<llvm::Value*> ri = ReturnValues.begin(),
                                        re = ReturnValues.end(); ri != re; ++ri) {
                                GraphNode* retNode = depGraph->addInst(*ri);
                                depGraph->addEdge(retNode, retPHI);
                        }

                }

//.........这里部分代码省略.........

/// Given \p BBs as input, find another set of BBs which collectively
/// dominates \p BBs and have the minimal sum of frequencies. Return the BB
/// set found in \p BBs.
static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
                                 BasicBlock *Entry,
                                 SmallPtrSet<BasicBlock *, 8> &BBs) {
  assert(!BBs.count(Entry) && "Assume Entry is not in BBs");
  // Nodes on the current path to the root.
  SmallPtrSet<BasicBlock *, 8> Path;
  // Candidates includes any block 'BB' in set 'BBs' that is not strictly
  // dominated by any other blocks in set 'BBs', and all nodes in the path
  // in the dominator tree from Entry to 'BB'.
  SmallPtrSet<BasicBlock *, 16> Candidates;
  for (auto BB : BBs) {
    // Ignore unreachable basic blocks.
    if (!DT.isReachableFromEntry(BB))
      continue;
    Path.clear();
    // Walk up the dominator tree until Entry or another BB in BBs
    // is reached. Insert the nodes on the way to the Path.
    BasicBlock *Node = BB;
    // The "Path" is a candidate path to be added into Candidates set.
    bool isCandidate = false;
    do {
      Path.insert(Node);
      if (Node == Entry || Candidates.count(Node)) {
        isCandidate = true;
        break;
      }
      assert(DT.getNode(Node)->getIDom() &&
             "Entry doens't dominate current Node");
      Node = DT.getNode(Node)->getIDom()->getBlock();
    } while (!BBs.count(Node));

    // If isCandidate is false, Node is another Block in BBs dominating
    // current 'BB'. Drop the nodes on the Path.
    if (!isCandidate)
      continue;

    // Add nodes on the Path into Candidates.
    Candidates.insert(Path.begin(), Path.end());
  }

  // Sort the nodes in Candidates in top-down order and save the nodes
  // in Orders.
  unsigned Idx = 0;
  SmallVector<BasicBlock *, 16> Orders;
  Orders.push_back(Entry);
  while (Idx != Orders.size()) {
    BasicBlock *Node = Orders[Idx++];
    for (auto ChildDomNode : DT.getNode(Node)->getChildren()) {
      if (Candidates.count(ChildDomNode->getBlock()))
        Orders.push_back(ChildDomNode->getBlock());
    }
  }

  // Visit Orders in bottom-up order.
  using InsertPtsCostPair =
      std::pair<SmallPtrSet<BasicBlock *, 16>, BlockFrequency>;

  // InsertPtsMap is a map from a BB to the best insertion points for the
  // subtree of BB (subtree not including the BB itself).
  DenseMap<BasicBlock *, InsertPtsCostPair> InsertPtsMap;
  InsertPtsMap.reserve(Orders.size() + 1);
  for (auto RIt = Orders.rbegin(); RIt != Orders.rend(); RIt++) {
    BasicBlock *Node = *RIt;
    bool NodeInBBs = BBs.count(Node);
    SmallPtrSet<BasicBlock *, 16> &InsertPts = InsertPtsMap[Node].first;
    BlockFrequency &InsertPtsFreq = InsertPtsMap[Node].second;

    // Return the optimal insert points in BBs.
    if (Node == Entry) {
      BBs.clear();
      if (InsertPtsFreq > BFI.getBlockFreq(Node) ||
          (InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1))
        BBs.insert(Entry);
      else
        BBs.insert(InsertPts.begin(), InsertPts.end());
      break;
    }

    BasicBlock *Parent = DT.getNode(Node)->getIDom()->getBlock();
    // Initially, ParentInsertPts is empty and ParentPtsFreq is 0. Every child
    // will update its parent's ParentInsertPts and ParentPtsFreq.
    SmallPtrSet<BasicBlock *, 16> &ParentInsertPts = InsertPtsMap[Parent].first;
    BlockFrequency &ParentPtsFreq = InsertPtsMap[Parent].second;
    // Choose to insert in Node or in subtree of Node.
    // Don't hoist to EHPad because we may not find a proper place to insert
    // in EHPad.
    // If the total frequency of InsertPts is the same as the frequency of the
    // target Node, and InsertPts contains more than one nodes, choose hoisting
    // to reduce code size.
    if (NodeInBBs ||
        (!Node->isEHPad() &&
         (InsertPtsFreq > BFI.getBlockFreq(Node) ||
          (InsertPtsFreq == BFI.getBlockFreq(Node) && InsertPts.size() > 1)))) {
      ParentInsertPts.insert(Node);
      ParentPtsFreq += BFI.getBlockFreq(Node);
    } else {
      ParentInsertPts.insert(InsertPts.begin(), InsertPts.end());
//.........这里部分代码省略.........

/// inlineFuctions - Walk all call sites in all functions supplied by
/// client. Inline as many call sites as possible. Delete completely
/// inlined functions.
void BasicInlinerImpl::inlineFunctions() {

    // Scan through and identify all call sites ahead of time so that we only
    // inline call sites in the original functions, not call sites that result
    // from inlining other functions.
    std::vector<CallSite> CallSites;

    for (std::vector<Function *>::iterator FI = Functions.begin(),
            FE = Functions.end(); FI != FE; ++FI) {
        Function *F = *FI;
        for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
            for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
                CallSite CS(cast<Value>(I));
                if (CS && CS.getCalledFunction()
                        && !CS.getCalledFunction()->isDeclaration())
                    CallSites.push_back(CS);
            }
    }

    DEBUG(dbgs() << ": " << CallSites.size() << " call sites.\n");

    // Inline call sites.
    bool Changed = false;
    do {
        Changed = false;
        for (unsigned index = 0; index != CallSites.size() && !CallSites.empty();
                ++index) {
            CallSite CS = CallSites[index];
            if (Function *Callee = CS.getCalledFunction()) {

                // Eliminate calls that are never inlinable.
                if (Callee->isDeclaration() ||
                        CS.getInstruction()->getParent()->getParent() == Callee) {
                    CallSites.erase(CallSites.begin() + index);
                    --index;
                    continue;
                }
                InlineCost IC = CA.getInlineCost(CS, NeverInline);
                if (IC.isAlways()) {
                    DEBUG(dbgs() << "  Inlining: cost=always"
                          <<", call: " << *CS.getInstruction());
                } else if (IC.isNever()) {
                    DEBUG(dbgs() << "  NOT Inlining: cost=never"
                          <<", call: " << *CS.getInstruction());
                    continue;
                } else {
                    int Cost = IC.getValue();

                    if (Cost >= (int) BasicInlineThreshold) {
                        DEBUG(dbgs() << "  NOT Inlining: cost = " << Cost
                              << ", call: " <<  *CS.getInstruction());
                        continue;
                    } else {
                        DEBUG(dbgs() << "  Inlining: cost = " << Cost
                              << ", call: " <<  *CS.getInstruction());
                    }
                }

                // Inline
                InlineFunctionInfo IFI(0, TD);
                if (InlineFunction(CS, IFI)) {
                    Callee->removeDeadConstantUsers();
                    if (Callee->isDefTriviallyDead())
                        DeadFunctions.insert(Callee);
                    Changed = true;
                    CallSites.erase(CallSites.begin() + index);
                    --index;
                }
            }
        }
    } while (Changed);

    // Remove completely inlined functions from module.
    for(SmallPtrSet<Function *, 8>::iterator I = DeadFunctions.begin(),
            E = DeadFunctions.end(); I != E; ++I) {
        Function *D = *I;
        Module *M = D->getParent();
        M->getFunctionList().remove(D);
    }
}

/// Some initialization for the rename part
///
void SSI::renameInit(SmallPtrSet<Instruction*, 4> &value) {
  for (SmallPtrSet<Instruction*, 4>::iterator I = value.begin(),
       E = value.end(); I != E; ++I)
    value_stack[*I].push_back(*I);
}

bool ReduceCrashingBlocks::TestBlocks(std::vector<const BasicBlock*> &BBs) {
  // Clone the program to try hacking it apart...
  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap);

  // Convert list to set for fast lookup...
  SmallPtrSet<BasicBlock*, 8> Blocks;
  for (unsigned i = 0, e = BBs.size(); i != e; ++i)
    Blocks.insert(cast<BasicBlock>(VMap[BBs[i]]));

  outs() << "Checking for crash with only these blocks:";
  unsigned NumPrint = Blocks.size();
  if (NumPrint > 10) NumPrint = 10;
  for (unsigned i = 0, e = NumPrint; i != e; ++i)
    outs() << " " << BBs[i]->getName();
  if (NumPrint < Blocks.size())
    outs() << "... <" << Blocks.size() << " total>";
  outs() << ": ";

  // Loop over and delete any hack up any blocks that are not listed...
  for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
    for (Function::iterator BB = I->begin(), E = I->end(); BB != E; ++BB)
      if (!Blocks.count(BB) && BB->getTerminator()->getNumSuccessors()) {
        // Loop over all of the successors of this block, deleting any PHI nodes
        // that might include it.
        for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
          (*SI)->removePredecessor(BB);

        TerminatorInst *BBTerm = BB->getTerminator();
        
        if (!BB->getTerminator()->getType()->isVoidTy())
          BBTerm->replaceAllUsesWith(Constant::getNullValue(BBTerm->getType()));

        // Replace the old terminator instruction.
        BB->getInstList().pop_back();
        new UnreachableInst(BB->getContext(), BB);
      }

  // The CFG Simplifier pass may delete one of the basic blocks we are
  // interested in.  If it does we need to take the block out of the list.  Make
  // a "persistent mapping" by turning basic blocks into <function, name> pairs.
  // This won't work well if blocks are unnamed, but that is just the risk we
  // have to take.
  std::vector<std::pair<std::string, std::string> > BlockInfo;

  for (SmallPtrSet<BasicBlock*, 8>::iterator I = Blocks.begin(),
         E = Blocks.end(); I != E; ++I)
    BlockInfo.push_back(std::make_pair((*I)->getParent()->getName(),
                                       (*I)->getName()));

  // Now run the CFG simplify pass on the function...
  std::vector<std::string> Passes;
  Passes.push_back("simplifycfg");
  Passes.push_back("verify");
  Module *New = BD.runPassesOn(M, Passes);
  delete M;
  if (!New) {
    errs() << "simplifycfg failed!\n";
    exit(1);
  }
  M = New;

  // Try running on the hacked up program...
  if (TestFn(BD, M)) {
    BD.setNewProgram(M);      // It crashed, keep the trimmed version...

    // Make sure to use basic block pointers that point into the now-current
    // module, and that they don't include any deleted blocks.
    BBs.clear();
    const ValueSymbolTable &GST = M->getValueSymbolTable();
    for (unsigned i = 0, e = BlockInfo.size(); i != e; ++i) {
      Function *F = cast<Function>(GST.lookup(BlockInfo[i].first));
      ValueSymbolTable &ST = F->getValueSymbolTable();
      Value* V = ST.lookup(BlockInfo[i].second);
      if (V && V->getType() == Type::getLabelTy(V->getContext()))
        BBs.push_back(cast<BasicBlock>(V));
    }
    return true;
  }
  delete M;  // It didn't crash, try something else.
  return false;
}