C++ BasicBlock::front方法代码示例

/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the location Loc.
///
bool AAResults::canBasicBlockModify(const BasicBlock &BB,
                                    const MemoryLocation &Loc) {
  return canInstructionRangeModRef(BB.front(), BB.back(), Loc, MRI_Mod);
}

//.........这里部分代码省略.........
    // FIXME: cross-block DSE would be fun. :)
    if (InstDep.isNonLocal() || 
        // Ignore self dependence, which happens in the entry block of the
        // function.
        InstDep.getInst() == Inst)
      continue;
     
    // If we're storing the same value back to a pointer that we just
    // loaded from, then the store can be removed.
    if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
      if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
        if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
            SI->getOperand(0) == DepLoad && !SI->isVolatile()) {
          DEBUG(dbgs() << "DSE: Remove Store Of Load from same pointer:\n  "
                       << "LOAD: " << *DepLoad << "\n  STORE: " << *SI << '\n');
          
          // DeleteDeadInstruction can delete the current instruction.  Save BBI
          // in case we need it.
          WeakVH NextInst(BBI);
          
          DeleteDeadInstruction(SI, *MD);
          
          if (NextInst == 0)  // Next instruction deleted.
            BBI = BB.begin();
          else if (BBI != BB.begin())  // Revisit this instruction if possible.
            --BBI;
          ++NumFastStores;
          MadeChange = true;
          continue;
        }
      }
    }
    
    // Figure out what location is being stored to.
    AliasAnalysis::Location Loc = getLocForWrite(Inst, *AA);

    // If we didn't get a useful location, fail.
    if (Loc.Ptr == 0)
      continue;
    
    while (!InstDep.isNonLocal()) {
      // Get the memory clobbered by the instruction we depend on.  MemDep will
      // skip any instructions that 'Loc' clearly doesn't interact with.  If we
      // end up depending on a may- or must-aliased load, then we can't optimize
      // away the store and we bail out.  However, if we depend on on something
      // that overwrites the memory location we *can* potentially optimize it.
      //
      // Find out what memory location the dependant instruction stores.
      Instruction *DepWrite = InstDep.getInst();
      AliasAnalysis::Location DepLoc = getLocForWrite(DepWrite, *AA);
      // If we didn't get a useful location, or if it isn't a size, bail out.
      if (DepLoc.Ptr == 0)
        break;

      // If we find a write that is a) removable (i.e., non-volatile), b) is
      // completely obliterated by the store to 'Loc', and c) which we know that
      // 'Inst' doesn't load from, then we can remove it.
      if (isRemovable(DepWrite) && isCompleteOverwrite(Loc, DepLoc, *AA) &&
          !isPossibleSelfRead(Inst, Loc, DepWrite, *AA)) {
        DEBUG(dbgs() << "DSE: Remove Dead Store:\n  DEAD: "
              << *DepWrite << "\n  KILLER: " << *Inst << '\n');
        
        // Delete the store and now-dead instructions that feed it.
        DeleteDeadInstruction(DepWrite, *MD);
        ++NumFastStores;
        MadeChange = true;
        
        // DeleteDeadInstruction can delete the current instruction in loop
        // cases, reset BBI.
        BBI = Inst;
        if (BBI != BB.begin())
          --BBI;
        break;
      }
      
      // If this is a may-aliased store that is clobbering the store value, we
      // can keep searching past it for another must-aliased pointer that stores
      // to the same location.  For example, in:
      //   store -> P
      //   store -> Q
      //   store -> P
      // we can remove the first store to P even though we don't know if P and Q
      // alias.
      if (DepWrite == &BB.front()) break;
      
      // Can't look past this instruction if it might read 'Loc'.
      if (AA->getModRefInfo(DepWrite, Loc) & AliasAnalysis::Ref)
        break;
        
      InstDep = MD->getPointerDependencyFrom(Loc, false, DepWrite, &BB);
    }
  }
  
  // If this block ends in a return, unwind, or unreachable, all allocas are
  // dead at its end, which means stores to them are also dead.
  if (BB.getTerminator()->getNumSuccessors() == 0)
    MadeChange |= handleEndBlock(BB);
  
  return MadeChange;
}

/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the value pointed to by Ptr.
///
bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
                                        const Value *Ptr, unsigned Size) {
  return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
}

  /// @brief Generate LLVM-IR for the SCoP @p S.
  bool runOnScop(Scop &S) override {
    AI = &getAnalysis<IslAstInfo>();

    // Check if we created an isl_ast root node, otherwise exit.
    isl_ast_node *AstRoot = AI->getAst();
    if (!AstRoot)
      return false;

    LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
    DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
    SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
    DL = &S.getRegion().getEntry()->getParent()->getParent()->getDataLayout();
    RI = &getAnalysis<RegionInfoPass>().getRegionInfo();
    Region *R = &S.getRegion();
    assert(!R->isTopLevelRegion() && "Top level regions are not supported");

    ScopAnnotator Annotator;
    Annotator.buildAliasScopes(S);

    simplifyRegion(R, DT, LI, RI);
    assert(R->isSimple());
    BasicBlock *EnteringBB = S.getRegion().getEnteringBlock();
    assert(EnteringBB);
    PollyIRBuilder Builder = createPollyIRBuilder(EnteringBB, Annotator);

    IslNodeBuilder NodeBuilder(Builder, Annotator, this, *DL, *LI, *SE, *DT, S);

    // Only build the run-time condition and parameters _after_ having
    // introduced the conditional branch. This is important as the conditional
    // branch will guard the original scop from new induction variables that
    // the SCEVExpander may introduce while code generating the parameters and
    // which may introduce scalar dependences that prevent us from correctly
    // code generating this scop.
    BasicBlock *StartBlock =
        executeScopConditionally(S, this, Builder.getTrue());
    auto SplitBlock = StartBlock->getSinglePredecessor();

    // First generate code for the hoisted invariant loads and transitively the
    // parameters they reference. Afterwards, for the remaining parameters that
    // might reference the hoisted loads. Finally, build the runtime check
    // that might reference both hoisted loads as well as parameters.
    // If the hoisting fails we have to bail and execute the original code.
    Builder.SetInsertPoint(SplitBlock->getTerminator());
    if (!NodeBuilder.preloadInvariantLoads()) {

      auto *FalseI1 = Builder.getFalse();
      auto *SplitBBTerm = Builder.GetInsertBlock()->getTerminator();
      SplitBBTerm->setOperand(0, FalseI1);
      auto *StartBBTerm = StartBlock->getTerminator();
      Builder.SetInsertPoint(StartBBTerm);
      Builder.CreateUnreachable();
      StartBBTerm->eraseFromParent();
      isl_ast_node_free(AstRoot);

    } else {

      NodeBuilder.addParameters(S.getContext());

      Value *RTC = buildRTC(Builder, NodeBuilder.getExprBuilder());
      Builder.GetInsertBlock()->getTerminator()->setOperand(0, RTC);
      Builder.SetInsertPoint(&StartBlock->front());

      NodeBuilder.create(AstRoot);

      NodeBuilder.finalizeSCoP(S);
      fixRegionInfo(EnteringBB->getParent(), R->getParent());
    }

    verifyGeneratedFunction(S, *EnteringBB->getParent());

    // Mark the function such that we run additional cleanup passes on this
    // function (e.g. mem2reg to rediscover phi nodes).
    Function *F = EnteringBB->getParent();
    F->addFnAttr("polly-optimized");

    return true;
  }

//.........这里部分代码省略.........
      Loads.push_back(LI);
      // Direct loads are equivalent to a GEP with a zero index and then a load.
      Operands.push_back(0);
    } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
      if (GEP->use_empty()) {
        // Dead GEP's cause trouble later.  Just remove them if we run into
        // them.
        getAnalysis<AliasAnalysis>().deleteValue(GEP);
        GEP->eraseFromParent();
        // TODO: This runs the above loop over and over again for dead GEPs
        // Couldn't we just do increment the UI iterator earlier and erase the
        // use?
        return isSafeToPromoteArgument(Arg, isByVal);
      }

      // Ensure that all of the indices are constants.
      for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end();
        i != e; ++i)
        if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
          Operands.push_back(C->getSExtValue());
        else
          return false;  // Not a constant operand GEP!

      // Ensure that the only users of the GEP are load instructions.
      for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end();
           UI != E; ++UI)
        if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
          // Don't hack volatile/atomic loads
          if (!LI->isSimple()) return false;
          Loads.push_back(LI);
        } else {
          // Other uses than load?
          return false;
        }
    } else {
      return false;  // Not a load or a GEP.
    }

    // Now, see if it is safe to promote this load / loads of this GEP. Loading
    // is safe if Operands, or a prefix of Operands, is marked as safe.
    if (!PrefixIn(Operands, SafeToUnconditionallyLoad))
      return false;

    // See if we are already promoting a load with these indices. If not, check
    // to make sure that we aren't promoting too many elements.  If so, nothing
    // to do.
    if (ToPromote.find(Operands) == ToPromote.end()) {
      if (maxElements > 0 && ToPromote.size() == maxElements) {
        DEBUG(dbgs() << "argpromotion not promoting argument '"
              << Arg->getName() << "' because it would require adding more "
              << "than " << maxElements << " arguments to the function.\n");
        // We limit aggregate promotion to only promoting up to a fixed number
        // of elements of the aggregate.
        return false;
      }
      ToPromote.insert(Operands);
    }
  }

  if (Loads.empty()) return true;  // No users, this is a dead argument.

  // Okay, now we know that the argument is only used by load instructions and
  // it is safe to unconditionally perform all of them. Use alias analysis to
  // check to see if the pointer is guaranteed to not be modified from entry of
  // the function to each of the load instructions.

  // Because there could be several/many load instructions, remember which
  // blocks we know to be transparent to the load.
  SmallPtrSet<BasicBlock*, 16> TranspBlocks;

  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();

  for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
    // Check to see if the load is invalidated from the start of the block to
    // the load itself.
    LoadInst *Load = Loads[i];
    BasicBlock *BB = Load->getParent();

    AliasAnalysis::Location Loc = AA.getLocation(Load);
    if (AA.canInstructionRangeModify(BB->front(), *Load, Loc))
      return false;  // Pointer is invalidated!

    // Now check every path from the entry block to the load for transparency.
    // To do this, we perform a depth first search on the inverse CFG from the
    // loading block.
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      BasicBlock *P = *PI;
      for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> >
             I = idf_ext_begin(P, TranspBlocks),
             E = idf_ext_end(P, TranspBlocks); I != E; ++I)
        if (AA.canBasicBlockModify(**I, Loc))
          return false;
    }
  }

  // If the path from the entry of the function to each load is free of
  // instructions that potentially invalidate the load, we can make the
  // transformation!
  return true;
}

/// Given an instruction in the loop, check to see if it has any uses that are
/// outside the current loop.  If so, insert LCSSA PHI nodes and rewrite the
/// uses.
static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
                               const SmallVectorImpl<BasicBlock *> &ExitBlocks,
                               PredIteratorCache &PredCache, LoopInfo *LI) {
  SmallVector<Use *, 16> UsesToRewrite;

  // Tokens cannot be used in PHI nodes, so we skip over them.
  // We can run into tokens which are live out of a loop with catchswitch
  // instructions in Windows EH if the catchswitch has one catchpad which
  // is inside the loop and another which is not.
  if (Inst.getType()->isTokenTy())
    return false;

  BasicBlock *InstBB = Inst.getParent();

  for (Use &U : Inst.uses()) {
    Instruction *User = cast<Instruction>(U.getUser());
    BasicBlock *UserBB = User->getParent();
    if (PHINode *PN = dyn_cast<PHINode>(User))
      UserBB = PN->getIncomingBlock(U);

    if (InstBB != UserBB && !L.contains(UserBB))
      UsesToRewrite.push_back(&U);
  }

  // If there are no uses outside the loop, exit with no change.
  if (UsesToRewrite.empty())
    return false;

  ++NumLCSSA; // We are applying the transformation

  // Invoke instructions are special in that their result value is not available
  // along their unwind edge. The code below tests to see whether DomBB
  // dominates the value, so adjust DomBB to the normal destination block,
  // which is effectively where the value is first usable.
  BasicBlock *DomBB = Inst.getParent();
  if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
    DomBB = Inv->getNormalDest();

  DomTreeNode *DomNode = DT.getNode(DomBB);

  SmallVector<PHINode *, 16> AddedPHIs;
  SmallVector<PHINode *, 8> PostProcessPHIs;

  SSAUpdater SSAUpdate;
  SSAUpdate.Initialize(Inst.getType(), Inst.getName());

  // Insert the LCSSA phi's into all of the exit blocks dominated by the
  // value, and add them to the Phi's map.
  for (BasicBlock *ExitBB : ExitBlocks) {
    if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
      continue;

    // If we already inserted something for this BB, don't reprocess it.
    if (SSAUpdate.HasValueForBlock(ExitBB))
      continue;

    PHINode *PN = PHINode::Create(Inst.getType(), PredCache.size(ExitBB),
                                  Inst.getName() + ".lcssa", &ExitBB->front());

    // Add inputs from inside the loop for this PHI.
    for (BasicBlock *Pred : PredCache.get(ExitBB)) {
      PN->addIncoming(&Inst, Pred);

      // If the exit block has a predecessor not within the loop, arrange for
      // the incoming value use corresponding to that predecessor to be
      // rewritten in terms of a different LCSSA PHI.
      if (!L.contains(Pred))
        UsesToRewrite.push_back(
            &PN->getOperandUse(PN->getOperandNumForIncomingValue(
                 PN->getNumIncomingValues() - 1)));
    }

    AddedPHIs.push_back(PN);

    // Remember that this phi makes the value alive in this block.
    SSAUpdate.AddAvailableValue(ExitBB, PN);

    // LoopSimplify might fail to simplify some loops (e.g. when indirect
    // branches are involved). In such situations, it might happen that an exit
    // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
    // PHIs in such an exit block, we are also inserting PHIs into L2's header.
    // This could break LCSSA form for L2 because these inserted PHIs can also
    // have uses outside of L2. Remember all PHIs in such situation as to
    // revisit than later on. FIXME: Remove this if indirectbr support into
    // LoopSimplify gets improved.
    if (auto *OtherLoop = LI->getLoopFor(ExitBB))
      if (!L.contains(OtherLoop))
        PostProcessPHIs.push_back(PN);
  }

  // Rewrite all uses outside the loop in terms of the new PHIs we just
  // inserted.
  for (Use *UseToRewrite : UsesToRewrite) {
    // If this use is in an exit block, rewrite to use the newly inserted PHI.
    // This is required for correctness because SSAUpdate doesn't handle uses in
    // the same block.  It assumes the PHI we inserted is at the end of the
    // block.
//.........这里部分代码省略.........

Function* PartialInliner::unswitchFunction(Function* F) {
  // First, verify that this function is an unswitching candidate...
  BasicBlock *entryBlock = &F->front();
  BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator());
  if (!BR || BR->isUnconditional())
    return nullptr;
  
  BasicBlock* returnBlock = nullptr;
  BasicBlock* nonReturnBlock = nullptr;
  unsigned returnCount = 0;
  for (BasicBlock *BB : successors(entryBlock)) {
    if (isa<ReturnInst>(BB->getTerminator())) {
      returnBlock = BB;
      returnCount++;
    } else
      nonReturnBlock = BB;
  }
  
  if (returnCount != 1)
    return nullptr;
  
  // Clone the function, so that we can hack away on it.
  ValueToValueMapTy VMap;
  Function* duplicateFunction = CloneFunction(F, VMap,
                                              /*ModuleLevelChanges=*/false);
  duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
  F->getParent()->getFunctionList().push_back(duplicateFunction);
  BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
  BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
  BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
  
  // Go ahead and update all uses to the duplicate, so that we can just
  // use the inliner functionality when we're done hacking.
  F->replaceAllUsesWith(duplicateFunction);
  
  // Special hackery is needed with PHI nodes that have inputs from more than
  // one extracted block.  For simplicity, just split the PHIs into a two-level
  // sequence of PHIs, some of which will go in the extracted region, and some
  // of which will go outside.
  BasicBlock* preReturn = newReturnBlock;
  newReturnBlock = newReturnBlock->splitBasicBlock(
      newReturnBlock->getFirstNonPHI()->getIterator());
  BasicBlock::iterator I = preReturn->begin();
  Instruction *Ins = &newReturnBlock->front();
  while (I != preReturn->end()) {
    PHINode* OldPhi = dyn_cast<PHINode>(I);
    if (!OldPhi) break;

    PHINode *retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins);
    OldPhi->replaceAllUsesWith(retPhi);
    Ins = newReturnBlock->getFirstNonPHI();

    retPhi->addIncoming(&*I, preReturn);
    retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
                        newEntryBlock);
    OldPhi->removeIncomingValue(newEntryBlock);
    
    ++I;
  }
  newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
  
  // Gather up the blocks that we're going to extract.
  std::vector<BasicBlock*> toExtract;
  toExtract.push_back(newNonReturnBlock);
  for (Function::iterator FI = duplicateFunction->begin(),
       FE = duplicateFunction->end(); FI != FE; ++FI)
    if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
        &*FI != newNonReturnBlock)
      toExtract.push_back(&*FI);

  // The CodeExtractor needs a dominator tree.
  DominatorTree DT;
  DT.recalculate(*duplicateFunction);

  // Extract the body of the if.
  Function* extractedFunction
    = CodeExtractor(toExtract, &DT).extractCodeRegion();
  
  InlineFunctionInfo IFI;
  
  // Inline the top-level if test into all callers.
  std::vector<User *> Users(duplicateFunction->user_begin(),
                            duplicateFunction->user_end());
  for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
       UI != UE; ++UI)
    if (CallInst *CI = dyn_cast<CallInst>(*UI))
      InlineFunction(CI, IFI);
    else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
      InlineFunction(II, IFI);
  
  // Ditch the duplicate, since we're done with it, and rewrite all remaining
  // users (function pointers, etc.) back to the original function.
  duplicateFunction->replaceAllUsesWith(F);
  duplicateFunction->eraseFromParent();
  
  ++NumPartialInlined;
  
  return extractedFunction;
}

/// \brief Recursively handle the condition leading to a loop
Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
                                                  llvm::Loop *L) {

  // Only search through PHI nodes which are inside the loop.  If we try this
  // with PHI nodes that are outside of the loop, we end up inserting new PHI
  // nodes outside of the loop which depend on values defined inside the loop.
  // This will break the module with
  // 'Instruction does not dominate all users!' errors.
  PHINode *Phi = nullptr;
  if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {

    BasicBlock *Parent = Phi->getParent();
    PHINode *NewPhi = PHINode::Create(Int64, 0, "", &Parent->front());
    Value *Ret = NewPhi;

    // Handle all non-constant incoming values first
    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
      Value *Incoming = Phi->getIncomingValue(i);
      BasicBlock *From = Phi->getIncomingBlock(i);
      if (isa<ConstantInt>(Incoming)) {
        NewPhi->addIncoming(Broken, From);
        continue;
      }

      Phi->setIncomingValue(i, BoolFalse);
      Value *PhiArg = handleLoopCondition(Incoming, Broken, L);
      NewPhi->addIncoming(PhiArg, From);
    }

    BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();

    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {

      Value *Incoming = Phi->getIncomingValue(i);
      if (Incoming != BoolTrue)
        continue;

      BasicBlock *From = Phi->getIncomingBlock(i);
      if (From == IDom) {
        CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
        if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
          Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
          Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
          continue;
        }
      }
      TerminatorInst *Insert = From->getTerminator();
      Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
      NewPhi->setIncomingValue(i, PhiArg);
    }
    eraseIfUnused(Phi);
    return Ret;

  } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
    BasicBlock *Parent = Inst->getParent();
    Instruction *Insert;
    if (L->contains(Inst)) {
      Insert = Parent->getTerminator();
    } else {
      Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
    }
    Value *Args[] = { Cond, Broken };
    return CallInst::Create(IfBreak, Args, "", Insert);

  } else {
    llvm_unreachable("Unhandled loop condition!");
  }
  return 0;
}

/// \brief Recursively handle the condition leading to a loop
Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
                                             llvm::Loop *L, BranchInst *Term) {

  // Only search through PHI nodes which are inside the loop.  If we try this
  // with PHI nodes that are outside of the loop, we end up inserting new PHI
  // nodes outside of the loop which depend on values defined inside the loop.
  // This will break the module with
  // 'Instruction does not dominate all users!' errors.
  PHINode *Phi = nullptr;
  if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {

    BasicBlock *Parent = Phi->getParent();
    PHINode *NewPhi = PHINode::Create(Int64, 0, "", &Parent->front());
    Value *Ret = NewPhi;

    // Handle all non-constant incoming values first
    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
      Value *Incoming = Phi->getIncomingValue(i);
      BasicBlock *From = Phi->getIncomingBlock(i);
      if (isa<ConstantInt>(Incoming)) {
        NewPhi->addIncoming(Broken, From);
        continue;
      }

      Phi->setIncomingValue(i, BoolFalse);
      Value *PhiArg = handleLoopCondition(Incoming, Broken, L, Term);
      NewPhi->addIncoming(PhiArg, From);
    }

    BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();

    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {

      Value *Incoming = Phi->getIncomingValue(i);
      if (Incoming != BoolTrue)
        continue;

      BasicBlock *From = Phi->getIncomingBlock(i);
      if (From == IDom) {
        // We're in the following situation:
        //   IDom/From
        //      |   \
        //      |   If-block
        //      |   /
        //     Parent
        // where we want to break out of the loop if the If-block is not taken.
        // Due to the depth-first traversal, there should be an end.cf
        // intrinsic in Parent, and we insert an else.break before it.
        //
        // Note that the end.cf need not be the first non-phi instruction
        // of parent, particularly when we're dealing with a multi-level
        // break, but it should occur within a group of intrinsic calls
        // at the beginning of the block.
        CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
        while (OldEnd && OldEnd->getCalledFunction() != EndCf)
          OldEnd = dyn_cast<CallInst>(OldEnd->getNextNode());
        if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
          Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
          Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
          continue;
        }
      }
      TerminatorInst *Insert = From->getTerminator();
      Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
      NewPhi->setIncomingValue(i, PhiArg);
    }
    eraseIfUnused(Phi);
    return Ret;

  } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
    BasicBlock *Parent = Inst->getParent();
    Instruction *Insert;
    if (L->contains(Inst)) {
      Insert = Parent->getTerminator();
    } else {
      Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
    }
    Value *Args[] = { Cond, Broken };
    return CallInst::Create(IfBreak, Args, "", Insert);

  // Insert IfBreak before TERM for constant COND.
  } else if (isa<ConstantInt>(Cond)) {
    Value *Args[] = { Cond, Broken };
    return CallInst::Create(IfBreak, Args, "", Term);

  } else {
    llvm_unreachable("Unhandled loop condition!");
  }
  return nullptr;
}

//.........这里部分代码省略.........
    exn = findExceptionInBlock(exnBlock);
  } while (!exn);

  // Look for a selector call for the exception we found.
  EHSelectorInst *selector = findSelectorForException(exn);
  if (!selector) return 0;

  // The easy case is when the landing pad still dominates the
  // exception call, in which case we can just move both calls back to
  // the landing pad.
  if (dominates) {
    selector->moveBefore(lpad->getFirstNonPHI());
    exn->moveBefore(selector);
    return selector;
  }

  // Otherwise, we have to split at the first non-dominating block.
  // The CFG looks basically like this:
  //    lpad:
  //      phis_0
  //      insnsAndBranches_1
  //      br label %nonDominated
  //    nonDominated:
  //      phis_2
  //      insns_3
  //      %exn = call i8* @llvm.eh.exception()
  //      insnsAndBranches_4
  //      %selector = call @llvm.eh.selector(i8* %exn, ...
  // We need to turn this into:
  //    lpad:
  //      phis_0
  //      %exn0 = call i8* @llvm.eh.exception()
  //      %selector0 = call @llvm.eh.selector(i8* %exn0, ...
  //      insnsAndBranches_1
  //      br label %split // from lastDominated
  //    nonDominated:
  //      phis_2 (without edge from lastDominated)
  //      %exn1 = call i8* @llvm.eh.exception()
  //      %selector1 = call i8* @llvm.eh.selector(i8* %exn1, ...
  //      br label %split
  //    split:
  //      phis_2 (edge from lastDominated, edge from split)
  //      %exn = phi ...
  //      %selector = phi ...
  //      insns_3
  //      insnsAndBranches_4

  assert(nonDominated);
  assert(lastDominated);

  // First, make clones of the intrinsics to go in lpad.
  EHExceptionInst *lpadExn = cast<EHExceptionInst>(exn->clone());
  EHSelectorInst *lpadSelector = cast<EHSelectorInst>(selector->clone());
  lpadSelector->setArgOperand(0, lpadExn);
  lpadSelector->insertBefore(lpad->getFirstNonPHI());
  lpadExn->insertBefore(lpadSelector);

  // Split the non-dominated block.
  BasicBlock *split =
    nonDominated->splitBasicBlock(nonDominated->getFirstNonPHI(),
                                  nonDominated->getName() + ".lpad-fix");

  // Redirect the last dominated branch there.
  cast<BranchInst>(lastDominated->back()).setSuccessor(0, split);

  // Move the existing intrinsics to the end of the old block.
  selector->moveBefore(&nonDominated->back());
  exn->moveBefore(selector);

  Instruction *splitIP = &split->front();

  // For all the phis in nonDominated, make a new phi in split to join
  // that phi with the edge from lastDominated.
  for (BasicBlock::iterator
         i = nonDominated->begin(), e = nonDominated->end(); i != e; ++i) {
    PHINode *phi = dyn_cast<PHINode>(i);
    if (!phi) break;

    PHINode *splitPhi = PHINode::Create(phi->getType(), 2, phi->getName(),
                                        splitIP);
    phi->replaceAllUsesWith(splitPhi);
    splitPhi->addIncoming(phi, nonDominated);
    splitPhi->addIncoming(phi->removeIncomingValue(lastDominated),
                          lastDominated);
  }

  // Make new phis for the exception and selector.
  PHINode *exnPhi = PHINode::Create(exn->getType(), 2, "", splitIP);
  exn->replaceAllUsesWith(exnPhi);
  selector->setArgOperand(0, exn); // except for this use
  exnPhi->addIncoming(exn, nonDominated);
  exnPhi->addIncoming(lpadExn, lastDominated);

  PHINode *selectorPhi = PHINode::Create(selector->getType(), 2, "", splitIP);
  selector->replaceAllUsesWith(selectorPhi);
  selectorPhi->addIncoming(selector, nonDominated);
  selectorPhi->addIncoming(lpadSelector, lastDominated);

  return lpadSelector;
}

/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
/// edge and spill them.
void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
                                           ArrayRef<InvokeInst *> Invokes) {
  // Finally, scan the code looking for instructions with bad live ranges.
  for (BasicBlock &BB : F) {
    for (Instruction &Inst : BB) {
      // 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.
      if (Inst.use_empty())
        continue;
      if (Inst.hasOneUse() &&
          cast<Instruction>(Inst.user_back())->getParent() == &BB &&
          !isa<PHINode>(Inst.user_back()))
        continue;

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

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

      // Find all of the blocks that this value is live in.
      SmallPtrSet<BasicBlock *, 32> LiveBBs;
      LiveBBs.insert(&BB);
      while (!Users.empty()) {
        Instruction *U = Users.pop_back_val();

        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 (InvokeInst *Invoke : Invokes) {
        BasicBlock *UnwindBlock = Invoke->getUnwindDest();
        if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
          LLVM_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 (InvokeInst *Invoke : Invokes) {
    BasicBlock *UnwindBlock = Invoke->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 (PHINode *PN : PHIsToDemote)
      DemotePHIToStack(PN);

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

Function *PartialInlinerImpl::unswitchFunction(Function *F) {
  // First, verify that this function is an unswitching candidate...
  BasicBlock *EntryBlock = &F->front();
  BranchInst *BR = dyn_cast<BranchInst>(EntryBlock->getTerminator());
  if (!BR || BR->isUnconditional())
    return nullptr;

  BasicBlock *ReturnBlock = nullptr;
  BasicBlock *NonReturnBlock = nullptr;
  unsigned ReturnCount = 0;
  for (BasicBlock *BB : successors(EntryBlock)) {
    if (isa<ReturnInst>(BB->getTerminator())) {
      ReturnBlock = BB;
      ReturnCount++;
    } else
      NonReturnBlock = BB;
  }

  if (ReturnCount != 1)
    return nullptr;

  // Clone the function, so that we can hack away on it.
  ValueToValueMapTy VMap;
  Function *DuplicateFunction = CloneFunction(F, VMap);
  DuplicateFunction->setLinkage(GlobalValue::InternalLinkage);
  BasicBlock *NewEntryBlock = cast<BasicBlock>(VMap[EntryBlock]);
  BasicBlock *NewReturnBlock = cast<BasicBlock>(VMap[ReturnBlock]);
  BasicBlock *NewNonReturnBlock = cast<BasicBlock>(VMap[NonReturnBlock]);

  // Go ahead and update all uses to the duplicate, so that we can just
  // use the inliner functionality when we're done hacking.
  F->replaceAllUsesWith(DuplicateFunction);

  // Special hackery is needed with PHI nodes that have inputs from more than
  // one extracted block.  For simplicity, just split the PHIs into a two-level
  // sequence of PHIs, some of which will go in the extracted region, and some
  // of which will go outside.
  BasicBlock *PreReturn = NewReturnBlock;
  NewReturnBlock = NewReturnBlock->splitBasicBlock(
      NewReturnBlock->getFirstNonPHI()->getIterator());
  BasicBlock::iterator I = PreReturn->begin();
  Instruction *Ins = &NewReturnBlock->front();
  while (I != PreReturn->end()) {
    PHINode *OldPhi = dyn_cast<PHINode>(I);
    if (!OldPhi)
      break;

    PHINode *RetPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins);
    OldPhi->replaceAllUsesWith(RetPhi);
    Ins = NewReturnBlock->getFirstNonPHI();

    RetPhi->addIncoming(&*I, PreReturn);
    RetPhi->addIncoming(OldPhi->getIncomingValueForBlock(NewEntryBlock),
                        NewEntryBlock);
    OldPhi->removeIncomingValue(NewEntryBlock);

    ++I;
  }
  NewEntryBlock->getTerminator()->replaceUsesOfWith(PreReturn, NewReturnBlock);

  // Gather up the blocks that we're going to extract.
  std::vector<BasicBlock *> ToExtract;
  ToExtract.push_back(NewNonReturnBlock);
  for (BasicBlock &BB : *DuplicateFunction)
    if (&BB != NewEntryBlock && &BB != NewReturnBlock &&
        &BB != NewNonReturnBlock)
      ToExtract.push_back(&BB);

  // The CodeExtractor needs a dominator tree.
  DominatorTree DT;
  DT.recalculate(*DuplicateFunction);

  // Extract the body of the if.
  Function *ExtractedFunction =
      CodeExtractor(ToExtract, &DT).extractCodeRegion();

  // Inline the top-level if test into all callers.
  std::vector<User *> Users(DuplicateFunction->user_begin(),
                            DuplicateFunction->user_end());
  for (User *User : Users)
    if (CallInst *CI = dyn_cast<CallInst>(User))
      InlineFunction(CI, IFI);
    else if (InvokeInst *II = dyn_cast<InvokeInst>(User))
      InlineFunction(II, IFI);

  // Ditch the duplicate, since we're done with it, and rewrite all remaining
  // users (function pointers, etc.) back to the original function.
  DuplicateFunction->replaceAllUsesWith(F);
  DuplicateFunction->eraseFromParent();

  ++NumPartialInlined;

  return ExtractedFunction;
}

/// Check whether \param BB is the merge block of a if-region.  If yes, check
/// whether there exists an adjacent if-region upstream, the two if-regions
/// contain identical instructions and can be legally merged.  \returns true if
/// the two if-regions are merged.
///
/// From:
/// if (a)
///   statement;
/// if (b)
///   statement;
///
/// To:
/// if (a || b)
///   statement;
bool FlattenCFGOpt::MergeIfRegion(BasicBlock *BB, IRBuilder<> &Builder) {
  BasicBlock *IfTrue2, *IfFalse2;
  Value *IfCond2 = GetIfCondition(BB, IfTrue2, IfFalse2);
  Instruction *CInst2 = dyn_cast_or_null<Instruction>(IfCond2);
  if (!CInst2)
    return false;

  BasicBlock *SecondEntryBlock = CInst2->getParent();
  if (SecondEntryBlock->hasAddressTaken())
    return false;

  BasicBlock *IfTrue1, *IfFalse1;
  Value *IfCond1 = GetIfCondition(SecondEntryBlock, IfTrue1, IfFalse1);
  Instruction *CInst1 = dyn_cast_or_null<Instruction>(IfCond1);
  if (!CInst1)
    return false;

  BasicBlock *FirstEntryBlock = CInst1->getParent();

  // Either then-path or else-path should be empty.
  if ((IfTrue1 != FirstEntryBlock) && (IfFalse1 != FirstEntryBlock))
    return false;
  if ((IfTrue2 != SecondEntryBlock) && (IfFalse2 != SecondEntryBlock))
    return false;

  TerminatorInst *PTI2 = SecondEntryBlock->getTerminator();
  Instruction *PBI2 = &SecondEntryBlock->front();

  if (!CompareIfRegionBlock(FirstEntryBlock, SecondEntryBlock, IfTrue1,
                            IfTrue2))
    return false;

  if (!CompareIfRegionBlock(FirstEntryBlock, SecondEntryBlock, IfFalse1,
                            IfFalse2))
    return false;

  // Check whether \param SecondEntryBlock has side-effect and is safe to
  // speculate.
  for (BasicBlock::iterator BI(PBI2), BE(PTI2); BI != BE; ++BI) {
    Instruction *CI = &*BI;
    if (isa<PHINode>(CI) || CI->mayHaveSideEffects() ||
        !isSafeToSpeculativelyExecute(CI))
      return false;
  }

  // Merge \param SecondEntryBlock into \param FirstEntryBlock.
  FirstEntryBlock->getInstList().pop_back();
  FirstEntryBlock->getInstList()
      .splice(FirstEntryBlock->end(), SecondEntryBlock->getInstList());
  BranchInst *PBI = dyn_cast<BranchInst>(FirstEntryBlock->getTerminator());
  Value *CC = PBI->getCondition();
  BasicBlock *SaveInsertBB = Builder.GetInsertBlock();
  BasicBlock::iterator SaveInsertPt = Builder.GetInsertPoint();
  Builder.SetInsertPoint(PBI);
  Value *NC = Builder.CreateOr(CInst1, CC);
  PBI->replaceUsesOfWith(CC, NC);
  Builder.SetInsertPoint(SaveInsertBB, SaveInsertPt);

  // Remove IfTrue1
  if (IfTrue1 != FirstEntryBlock) {
    IfTrue1->dropAllReferences();
    IfTrue1->eraseFromParent();
  }

  // Remove IfFalse1
  if (IfFalse1 != FirstEntryBlock) {
    IfFalse1->dropAllReferences();
    IfFalse1->eraseFromParent();
  }

  // Remove \param SecondEntryBlock
  SecondEntryBlock->dropAllReferences();
  SecondEntryBlock->eraseFromParent();
  LLVM_DEBUG(dbgs() << "If conditions merged into:\n" << *FirstEntryBlock);
  return true;
}

/// mergeEmptyReturnBlocks - If we have more than one empty (other than phi
/// node) return blocks, merge them together to promote recursive block merging.
static bool mergeEmptyReturnBlocks(Function &F) {
  bool Changed = false;

  BasicBlock *RetBlock = nullptr;

  // Scan all the blocks in the function, looking for empty return blocks.
  for (Function::iterator BBI = F.begin(), E = F.end(); BBI != E; ) {
    BasicBlock &BB = *BBI++;

    // Only look at return blocks.
    ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator());
    if (!Ret) continue;

    // Only look at the block if it is empty or the only other thing in it is a
    // single PHI node that is the operand to the return.
    if (Ret != &BB.front()) {
      // Check for something else in the block.
      BasicBlock::iterator I = Ret;
      --I;
      // Skip over debug info.
      while (isa<DbgInfoIntrinsic>(I) && I != BB.begin())
        --I;
      if (!isa<DbgInfoIntrinsic>(I) &&
          (!isa<PHINode>(I) || I != BB.begin() ||
           Ret->getNumOperands() == 0 ||
           Ret->getOperand(0) != I))
        continue;
    }

    // If this is the first returning block, remember it and keep going.
    if (!RetBlock) {
      RetBlock = &BB;
      continue;
    }

    // Otherwise, we found a duplicate return block.  Merge the two.
    Changed = true;

    // Case when there is no input to the return or when the returned values
    // agree is trivial.  Note that they can't agree if there are phis in the
    // blocks.
    if (Ret->getNumOperands() == 0 ||
        Ret->getOperand(0) ==
          cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0)) {
      BB.replaceAllUsesWith(RetBlock);
      BB.eraseFromParent();
      continue;
    }

    // If the canonical return block has no PHI node, create one now.
    PHINode *RetBlockPHI = dyn_cast<PHINode>(RetBlock->begin());
    if (!RetBlockPHI) {
      Value *InVal = cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0);
      pred_iterator PB = pred_begin(RetBlock), PE = pred_end(RetBlock);
      RetBlockPHI = PHINode::Create(Ret->getOperand(0)->getType(),
                                    std::distance(PB, PE), "merge",
                                    &RetBlock->front());

      for (pred_iterator PI = PB; PI != PE; ++PI)
        RetBlockPHI->addIncoming(InVal, *PI);
      RetBlock->getTerminator()->setOperand(0, RetBlockPHI);
    }

    // Turn BB into a block that just unconditionally branches to the return
    // block.  This handles the case when the two return blocks have a common
    // predecessor but that return different things.
    RetBlockPHI->addIncoming(Ret->getOperand(0), &BB);
    BB.getTerminator()->eraseFromParent();
    BranchInst::Create(RetBlock, &BB);
  }

  return Changed;
}

/// For every instruction from the worklist, check to see if it has any uses
/// that are outside the current loop.  If so, insert LCSSA PHI nodes and
/// rewrite the uses.
bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
                                    DominatorTree &DT, LoopInfo &LI) {
  SmallVector<Use *, 16> UsesToRewrite;
  SmallVector<BasicBlock *, 8> ExitBlocks;
  SmallSetVector<PHINode *, 16> PHIsToRemove;
  PredIteratorCache PredCache;
  bool Changed = false;

  while (!Worklist.empty()) {
    UsesToRewrite.clear();
    ExitBlocks.clear();

    Instruction *I = Worklist.pop_back_val();
    BasicBlock *InstBB = I->getParent();
    Loop *L = LI.getLoopFor(InstBB);
    L->getExitBlocks(ExitBlocks);

    if (ExitBlocks.empty())
      continue;

    // Tokens cannot be used in PHI nodes, so we skip over them.
    // We can run into tokens which are live out of a loop with catchswitch
    // instructions in Windows EH if the catchswitch has one catchpad which
    // is inside the loop and another which is not.
    if (I->getType()->isTokenTy())
      continue;

    for (Use &U : I->uses()) {
      Instruction *User = cast<Instruction>(U.getUser());
      BasicBlock *UserBB = User->getParent();
      if (PHINode *PN = dyn_cast<PHINode>(User))
        UserBB = PN->getIncomingBlock(U);

      if (InstBB != UserBB && !L->contains(UserBB))
        UsesToRewrite.push_back(&U);
    }

    // If there are no uses outside the loop, exit with no change.
    if (UsesToRewrite.empty())
      continue;

    ++NumLCSSA; // We are applying the transformation

    // Invoke instructions are special in that their result value is not
    // available along their unwind edge. The code below tests to see whether
    // DomBB dominates the value, so adjust DomBB to the normal destination
    // block, which is effectively where the value is first usable.
    BasicBlock *DomBB = InstBB;
    if (InvokeInst *Inv = dyn_cast<InvokeInst>(I))
      DomBB = Inv->getNormalDest();

    DomTreeNode *DomNode = DT.getNode(DomBB);

    SmallVector<PHINode *, 16> AddedPHIs;
    SmallVector<PHINode *, 8> PostProcessPHIs;

    SmallVector<PHINode *, 4> InsertedPHIs;
    SSAUpdater SSAUpdate(&InsertedPHIs);
    SSAUpdate.Initialize(I->getType(), I->getName());

    // Insert the LCSSA phi's into all of the exit blocks dominated by the
    // value, and add them to the Phi's map.
    for (BasicBlock *ExitBB : ExitBlocks) {
      if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
        continue;

      // If we already inserted something for this BB, don't reprocess it.
      if (SSAUpdate.HasValueForBlock(ExitBB))
        continue;

      PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB),
                                    I->getName() + ".lcssa", &ExitBB->front());

      // Add inputs from inside the loop for this PHI.
      for (BasicBlock *Pred : PredCache.get(ExitBB)) {
        PN->addIncoming(I, Pred);

        // If the exit block has a predecessor not within the loop, arrange for
        // the incoming value use corresponding to that predecessor to be
        // rewritten in terms of a different LCSSA PHI.
        if (!L->contains(Pred))
          UsesToRewrite.push_back(
              &PN->getOperandUse(PN->getOperandNumForIncomingValue(
                  PN->getNumIncomingValues() - 1)));
      }

      AddedPHIs.push_back(PN);

      // Remember that this phi makes the value alive in this block.
      SSAUpdate.AddAvailableValue(ExitBB, PN);

      // LoopSimplify might fail to simplify some loops (e.g. when indirect
      // branches are involved). In such situations, it might happen that an
      // exit for Loop L1 is the header of a disjoint Loop L2. Thus, when we
      // create PHIs in such an exit block, we are also inserting PHIs into L2's
      // header. This could break LCSSA form for L2 because these inserted PHIs
      // can also have uses outside of L2. Remember all PHIs in such situation
//.........这里部分代码省略.........