C++ SmallVector::erase方法代码示例

/// removeDeadFunctions - Remove dead functions that are not included in
/// DNR (Do Not Remove) list.
bool Inliner::removeDeadFunctions(CallGraph &CG, bool AlwaysInlineOnly) {
  SmallVector<CallGraphNode*, 16> FunctionsToRemove;

  // Scan for all of the functions, looking for ones that should now be removed
  // from the program.  Insert the dead ones in the FunctionsToRemove set.
  for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
    CallGraphNode *CGN = I->second;
    Function *F = CGN->getFunction();
    if (!F || F->isDeclaration())
      continue;

    // Handle the case when this function is called and we only want to care
    // about always-inline functions. This is a bit of a hack to share code
    // between here and the InlineAlways pass.
    if (AlwaysInlineOnly &&
        !F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
                                         Attribute::AlwaysInline))
      continue;

    // If the only remaining users of the function are dead constants, remove
    // them.
    F->removeDeadConstantUsers();

    if (!F->isDefTriviallyDead())
      continue;
    
    // Remove any call graph edges from the function to its callees.
    CGN->removeAllCalledFunctions();

    // Remove any edges from the external node to the function's call graph
    // node.  These edges might have been made irrelegant due to
    // optimization of the program.
    CG.getExternalCallingNode()->removeAnyCallEdgeTo(CGN);

    // Removing the node for callee from the call graph and delete it.
    FunctionsToRemove.push_back(CGN);
  }
  if (FunctionsToRemove.empty())
    return false;

  // Now that we know which functions to delete, do so.  We didn't want to do
  // this inline, because that would invalidate our CallGraph::iterator
  // objects. :(
  //
  // Note that it doesn't matter that we are iterating over a non-stable order
  // here to do this, it doesn't matter which order the functions are deleted
  // in.
  array_pod_sort(FunctionsToRemove.begin(), FunctionsToRemove.end());
  FunctionsToRemove.erase(std::unique(FunctionsToRemove.begin(),
                                      FunctionsToRemove.end()),
                          FunctionsToRemove.end());
  for (SmallVectorImpl<CallGraphNode *>::iterator I = FunctionsToRemove.begin(),
                                                  E = FunctionsToRemove.end();
       I != E; ++I) {
    delete CG.removeFunctionFromModule(*I);
    ++NumDeleted;
  }
  return true;
}

 ArrayRef<Identifier> getNames() {
   llvm::array_pod_sort(names.begin(), names.end(),
                        [](const Identifier *lhs, const Identifier *rhs) {
     return lhs->compare(*rhs);
   });
   names.erase(std::unique(names.begin(), names.end()), names.end());
   return names;
 }

Counter CounterExpressionBuilder::simplify(Counter ExpressionTree) {
  // Gather constant terms.
  SmallVector<Term, 32> Terms;
  extractTerms(ExpressionTree, +1, Terms);

  // If there are no terms, this is just a zero. The algorithm below assumes at
  // least one term.
  if (Terms.size() == 0)
    return Counter::getZero();

  // Group the terms by counter ID.
  std::sort(Terms.begin(), Terms.end(), [](const Term &LHS, const Term &RHS) {
    return LHS.CounterID < RHS.CounterID;
  });

  // Combine terms by counter ID to eliminate counters that sum to zero.
  auto Prev = Terms.begin();
  for (auto I = Prev + 1, E = Terms.end(); I != E; ++I) {
    if (I->CounterID == Prev->CounterID) {
      Prev->Factor += I->Factor;
      continue;
    }
    ++Prev;
    *Prev = *I;
  }
  Terms.erase(++Prev, Terms.end());

  Counter C;
  // Create additions. We do this before subtractions to avoid constructs like
  // ((0 - X) + Y), as opposed to (Y - X).
  for (auto T : Terms) {
    if (T.Factor <= 0)
      continue;
    for (int I = 0; I < T.Factor; ++I)
      if (C.isZero())
        C = Counter::getCounter(T.CounterID);
      else
        C = get(CounterExpression(CounterExpression::Add, C,
                                  Counter::getCounter(T.CounterID)));
  }

  // Create subtractions.
  for (auto T : Terms) {
    if (T.Factor >= 0)
      continue;
    for (int I = 0; I < -T.Factor; ++I)
      C = get(CounterExpression(CounterExpression::Subtract, C,
                                Counter::getCounter(T.CounterID)));
  }
  return C;
}

PreservedAnalyses AlwaysInlinerPass::run(Module &M, ModuleAnalysisManager &) {
  InlineFunctionInfo IFI;
  SmallSetVector<CallSite, 16> Calls;
  bool Changed = false;
  SmallVector<Function *, 16> InlinedFunctions;
  for (Function &F : M)
    if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
        isInlineViable(F)) {
      Calls.clear();

      for (User *U : F.users())
        if (auto CS = CallSite(U))
          if (CS.getCalledFunction() == &F)
            Calls.insert(CS);

      for (CallSite CS : Calls)
        // FIXME: We really shouldn't be able to fail to inline at this point!
        // We should do something to log or check the inline failures here.
        Changed |= InlineFunction(CS, IFI);

      // Remember to try and delete this function afterward. This both avoids
      // re-walking the rest of the module and avoids dealing with any iterator
      // invalidation issues while deleting functions.
      InlinedFunctions.push_back(&F);
    }

  // Remove any live functions.
  erase_if(InlinedFunctions, [&](Function *F) {
    F->removeDeadConstantUsers();
    return !F->isDefTriviallyDead();
  });

  // Delete the non-comdat ones from the module and also from our vector.
  auto NonComdatBegin = partition(
      InlinedFunctions, [&](Function *F) { return F->hasComdat(); });
  for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end()))
    M.getFunctionList().erase(F);
  InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end());

  if (!InlinedFunctions.empty()) {
    // Now we just have the comdat functions. Filter out the ones whose comdats
    // are not actually dead.
    filterDeadComdatFunctions(M, InlinedFunctions);
    // The remaining functions are actually dead.
    for (Function *F : InlinedFunctions)
      M.getFunctionList().erase(F);
  }

  return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
}

static void bindExtensions(SourceFile &SF, TypeChecker &TC) {
  // Utility function to try and resolve the extended type without diagnosing.
  // If we succeed, we go ahead and bind the extension. Otherwise, return false.
  auto tryBindExtension = [&](ExtensionDecl *ext) -> bool {
    if (auto nominal = ext->getExtendedNominal()) {
      bindExtensionToNominal(ext, nominal);
      return true;
    }

    return false;
  };

  // Phase 1 - try to bind each extension, adding those whose type cannot be
  // resolved to a worklist.
  SmallVector<ExtensionDecl *, 8> worklist;

  // FIXME: The current source file needs to be handled specially, because of
  // private extensions.
  SF.forAllVisibleModules([&](ModuleDecl::ImportedModule import) {
    // FIXME: Respect the access path?
    for (auto file : import.second->getFiles()) {
      auto SF = dyn_cast<SourceFile>(file);
      if (!SF)
        continue;

      for (auto D : SF->Decls) {
        if (auto ED = dyn_cast<ExtensionDecl>(D))
          if (!tryBindExtension(ED))
            worklist.push_back(ED);
      }
    }
  });

  // Phase 2 - repeatedly go through the worklist and attempt to bind each
  // extension there, removing it from the worklist if we succeed.
  bool changed;
  do {
    changed = false;

    auto last = std::remove_if(worklist.begin(), worklist.end(),
                               tryBindExtension);
    if (last != worklist.end()) {
      worklist.erase(last, worklist.end());
      changed = true;
    }
  } while(changed);

  // Any remaining extensions are invalid. They will be diagnosed later by
  // typeCheckDecl().
}

/// \brief Computes the set of declarations referenced by these base
/// paths.
void CXXBasePaths::ComputeDeclsFound() {
  assert(NumDeclsFound == 0 && !DeclsFound &&
         "Already computed the set of declarations");

  SmallVector<NamedDecl *, 8> Decls;
  for (paths_iterator Path = begin(), PathEnd = end(); Path != PathEnd; ++Path)
    Decls.push_back(*Path->Decls.first);

  // Eliminate duplicated decls.
  llvm::array_pod_sort(Decls.begin(), Decls.end());
  Decls.erase(std::unique(Decls.begin(), Decls.end()), Decls.end());

  NumDeclsFound = Decls.size();
  DeclsFound = new NamedDecl * [NumDeclsFound];
  std::copy(Decls.begin(), Decls.end(), DeclsFound);
}

/// Print only DIEs that have a certain name.
static void filterByAccelName(ArrayRef<std::string> Names, DWARFContext &DICtx,
                              raw_ostream &OS) {
  SmallVector<uint64_t, 4> Offsets;
  for (const auto &Name : Names) {
    getDIEOffset(DICtx.getAppleNames(), Name, Offsets);
    getDIEOffset(DICtx.getAppleTypes(), Name, Offsets);
    getDIEOffset(DICtx.getAppleNamespaces(), Name, Offsets);
    getDIEOffset(DICtx.getDebugNames(), Name, Offsets);
  }
  llvm::sort(Offsets.begin(), Offsets.end());
  Offsets.erase(std::unique(Offsets.begin(), Offsets.end()), Offsets.end());

  for (uint64_t Off: Offsets) {
    DWARFDie Die = DICtx.getDIEForOffset(Off);
    Die.dump(OS, 0, getDumpOpts());
  }
}

void Job::printSummary(raw_ostream &os) const {
  // Deciding how to describe our inputs is a bit subtle; if we are a Job built
  // from a JobAction that itself has InputActions sources, then we collect
  // those up. Otherwise it's more correct to talk about our inputs as the
  // outputs of our input-jobs.
  SmallVector<std::string, 4> Inputs;

  for (const Action *A : getSource().getInputs())
    if (const InputAction *IA = dyn_cast<InputAction>(A))
      Inputs.push_back(IA->getInputArg().getValue());

  for (const Job *J : getInputs())
    for (const std::string &f : J->getOutput().getPrimaryOutputFilenames())
      Inputs.push_back(f);

  size_t limit = 3;
  size_t actual = Inputs.size();
  if (actual > limit) {
    Inputs.erase(Inputs.begin() + limit, Inputs.end());
  }

  os << "{" << getSource().getClassName() << ": ";
  interleave(getOutput().getPrimaryOutputFilenames(),
             [&](const std::string &Arg) {
               os << llvm::sys::path::filename(Arg);
             },
             [&] { os << ' '; });
  os << " <= ";
  interleave(Inputs,
             [&](const std::string &Arg) {
               os << llvm::sys::path::filename(Arg);
             },
             [&] { os << ' '; });
  if (actual > limit) {
    os << " ... " << (actual-limit) << " more";
  }
  os << "}";
}

bool CallingConvention_AnyArch_AnyCC::analyzeFunction(ParameterRegistry &registry, CallInformation &fillOut, llvm::Function &func)
{
	if (!isFullDisassembly() || md::isPrototype(func))
	{
		return false;
	}
	
	auto regs = &*func.arg_begin();
	unordered_map<const TargetRegisterInfo*, ModRefInfo> resultMap;
	
	// Find all GEPs
	const auto& target = registry.getTargetInfo();
	unordered_multimap<const TargetRegisterInfo*, User*> registerUsers;
	for (User* user : regs->users())
	{
		if (const TargetRegisterInfo* maybeRegister = target.registerInfo(*user))
		{
			const TargetRegisterInfo& registerInfo = target.largestOverlappingRegister(*maybeRegister);
			registerUsers.insert({&registerInfo, user});
		}
	}
	
	// Find all users of these GEPs
	DominatorsPerRegister gepUsers;
	for (auto iter = registerUsers.begin(); iter != registerUsers.end(); iter++)
	{
		addAllUsers(*iter->second, iter->first, gepUsers);
	}
	
	DominatorTree& preDom = registry.getAnalysis<DominatorTreeWrapperPass>(func).getDomTree();
	PostDominatorTree& postDom = registry.getAnalysis<PostDominatorTreeWrapperPass>(func).getPostDomTree();
	
	// Add calls
	SmallVector<CallInst*, 8> calls;
	CallGraph& cg = registry.getAnalysis<CallGraphWrapperPass>().getCallGraph();
	CallGraphNode* thisFunc = cg[&func];
	for (const auto& pair : *thisFunc)
	{
		Function* callee = pair.second->getFunction();
		if (const CallInformation* callInfo = registry.getCallInfo(*callee))
		if (callInfo->getStage() == CallInformation::Completed)
		{
			// pair.first is a weak value handle and has a cast operator to get the pointee
			CallInst* caller = cast<CallInst>((Value*)pair.first);
			calls.push_back(caller);
			
			for (const auto& vi : *callInfo)
			{
				if (vi.type == ValueInformation::IntegerRegister)
				{
					gepUsers[vi.registerInfo].insert(caller);
				}
			}
		}
	}
	
	// Start out resultMap based on call dominance. Weed out calls until dominant call set has been established.
	// This map will be refined by results from mod/ref instruction analysis. The purpose is mainly to define
	// mod/ref behavior for registers that are used in callees of this function, but not in this function
	// directly.
	while (calls.size() > 0)
	{
		unordered_map<const TargetRegisterInfo*, unsigned> callResult;
		auto dominant = findDominantValues(preDom, calls);
		for (CallInst* call : dominant)
		{
			Function* callee = call->getCalledFunction();
			for (const auto& pair : translateToModRef(*registry.getCallInfo(*callee)))
			{
				callResult[pair.first] |= pair.second;
			}
			
			calls.erase(find(calls.begin(), calls.end(), call));
		}
		
		for (const auto& pair : callResult)
		{
			resultMap[pair.first] = static_cast<ModRefInfo>(pair.second);
		}
	}
	
	// Find the dominant use(s)
	auto preDominatingUses = gepUsers;
	for (auto& pair : preDominatingUses)
	{
		pair.second = findDominantValues(preDom, pair.second);
	}
	
	// Fill out ModRef use dictionary
	// (Ref info is incomplete)
	for (auto& pair : preDominatingUses)
	{
		ModRefInfo& r = resultMap[pair.first];
		r = IncompleteRef;
		for (auto inst : pair.second)
		{
			if (isa<StoreInst>(inst))
			{
				// If we see a dominant store, then the register is modified.
				r = MRI_Mod;
//.........这里部分代码省略.........

//.........这里部分代码省略.........
        else {
          R << " with cost=" << NV("Cost", OIC->getCost());
          R << " (threshold=" << NV("Threshold", OIC->getThreshold());
          R << ")";
        }
        return R;
      });

      // Add any new callsites to defined functions to the worklist.
      if (!IFI.InlinedCallSites.empty()) {
        int NewHistoryID = InlineHistory.size();
        InlineHistory.push_back({&Callee, InlineHistoryID});
        for (CallSite &CS : reverse(IFI.InlinedCallSites))
          if (Function *NewCallee = CS.getCalledFunction())
            if (!NewCallee->isDeclaration())
              Calls.push_back({CS, NewHistoryID});
      }

      if (InlinerFunctionImportStats != InlinerFunctionImportStatsOpts::No)
        ImportedFunctionsStats->recordInline(F, Callee);

      // Merge the attributes based on the inlining.
      AttributeFuncs::mergeAttributesForInlining(F, Callee);

      // For local functions, check whether this makes the callee trivially
      // dead. In that case, we can drop the body of the function eagerly
      // which may reduce the number of callers of other functions to one,
      // changing inline cost thresholds.
      if (Callee.hasLocalLinkage()) {
        // To check this we also need to nuke any dead constant uses (perhaps
        // made dead by this operation on other functions).
        Callee.removeDeadConstantUsers();
        if (Callee.use_empty() && !CG.isLibFunction(Callee)) {
          Calls.erase(
              std::remove_if(Calls.begin() + i + 1, Calls.end(),
                             [&Callee](const std::pair<CallSite, int> &Call) {
                               return Call.first.getCaller() == &Callee;
                             }),
              Calls.end());
          // Clear the body and queue the function itself for deletion when we
          // finish inlining and call graph updates.
          // Note that after this point, it is an error to do anything other
          // than use the callee's address or delete it.
          Callee.dropAllReferences();
          assert(find(DeadFunctions, &Callee) == DeadFunctions.end() &&
                 "Cannot put cause a function to become dead twice!");
          DeadFunctions.push_back(&Callee);
        }
      }
    }

    // Back the call index up by one to put us in a good position to go around
    // the outer loop.
    --i;

    if (!DidInline)
      continue;
    Changed = true;

    // Add all the inlined callees' edges as ref edges to the caller. These are
    // by definition trivial edges as we always have *some* transitive ref edge
    // chain. While in some cases these edges are direct calls inside the
    // callee, they have to be modeled in the inliner as reference edges as
    // there may be a reference edge anywhere along the chain from the current
    // caller to the callee that causes the whole thing to appear like
    // a (transitive) reference edge that will require promotion to a call edge

/// \brief Recursively emit notes for each macro expansion and caret
/// diagnostics where appropriate.
///
/// Walks up the macro expansion stack printing expansion notes, the code
/// snippet, caret, underlines and FixItHint display as appropriate at each
/// level.
///
/// \param Loc The location for this caret.
/// \param Level The diagnostic level currently being emitted.
/// \param Ranges The underlined ranges for this code snippet.
/// \param Hints The FixIt hints active for this diagnostic.
void DiagnosticRenderer::emitMacroExpansions(SourceLocation Loc,
                                             DiagnosticsEngine::Level Level,
                                             ArrayRef<CharSourceRange> Ranges,
                                             ArrayRef<FixItHint> Hints,
                                             const SourceManager &SM) {
  assert(!Loc.isInvalid() && "must have a valid source location here");

  // Produce a stack of macro backtraces.
  SmallVector<SourceLocation, 8> LocationStack;
  unsigned IgnoredEnd = 0;
  while (Loc.isMacroID()) {
    // If this is the expansion of a macro argument, point the caret at the
    // use of the argument in the definition of the macro, not the expansion.
    if (SM.isMacroArgExpansion(Loc))
      LocationStack.push_back(SM.getImmediateExpansionRange(Loc).first);
    else
      LocationStack.push_back(Loc);

    if (checkRangesForMacroArgExpansion(Loc, Ranges, SM))
      IgnoredEnd = LocationStack.size();

    Loc = SM.getImmediateMacroCallerLoc(Loc);

    // Once the location no longer points into a macro, try stepping through
    // the last found location.  This sometimes produces additional useful
    // backtraces.
    if (Loc.isFileID())
      Loc = SM.getImmediateMacroCallerLoc(LocationStack.back());
    assert(!Loc.isInvalid() && "must have a valid source location here");
  }

  LocationStack.erase(LocationStack.begin(),
                      LocationStack.begin() + IgnoredEnd);

  unsigned MacroDepth = LocationStack.size();
  unsigned MacroLimit = DiagOpts->MacroBacktraceLimit;
  if (MacroDepth <= MacroLimit || MacroLimit == 0) {
    for (auto I = LocationStack.rbegin(), E = LocationStack.rend();
         I != E; ++I)
      emitSingleMacroExpansion(*I, Level, Ranges, SM);
    return;
  }

  unsigned MacroStartMessages = MacroLimit / 2;
  unsigned MacroEndMessages = MacroLimit / 2 + MacroLimit % 2;

  for (auto I = LocationStack.rbegin(),
            E = LocationStack.rbegin() + MacroStartMessages;
       I != E; ++I)
    emitSingleMacroExpansion(*I, Level, Ranges, SM);

  SmallString<200> MessageStorage;
  llvm::raw_svector_ostream Message(MessageStorage);
  Message << "(skipping " << (MacroDepth - MacroLimit)
          << " expansions in backtrace; use -fmacro-backtrace-limit=0 to "
             "see all)";
  emitBasicNote(Message.str());

  for (auto I = LocationStack.rend() - MacroEndMessages,
            E = LocationStack.rend();
       I != E; ++I)
    emitSingleMacroExpansion(*I, Level, Ranges, SM);
}

/// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
/// information, and remove any dead successors it has.
///
void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
                                     std::vector<Instruction*> &Worklist,
                                     Loop *L) {
  if (pred_begin(BB) != pred_end(BB)) {
    // This block isn't dead, since an edge to BB was just removed, see if there
    // are any easy simplifications we can do now.
    if (BasicBlock *Pred = BB->getSinglePredecessor()) {
      // If it has one pred, fold phi nodes in BB.
      while (isa<PHINode>(BB->begin()))
        ReplaceUsesOfWith(BB->begin(), 
                          cast<PHINode>(BB->begin())->getIncomingValue(0), 
                          Worklist, L, LPM);
      
      // If this is the header of a loop and the only pred is the latch, we now
      // have an unreachable loop.
      if (Loop *L = LI->getLoopFor(BB))
        if (loopHeader == BB && L->contains(Pred)) {
          // Remove the branch from the latch to the header block, this makes
          // the header dead, which will make the latch dead (because the header
          // dominates the latch).
          LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
          Pred->getTerminator()->eraseFromParent();
          new UnreachableInst(BB->getContext(), Pred);
          
          // The loop is now broken, remove it from LI.
          RemoveLoopFromHierarchy(L);
          
          // Reprocess the header, which now IS dead.
          RemoveBlockIfDead(BB, Worklist, L);
          return;
        }
      
      // If pred ends in a uncond branch, add uncond branch to worklist so that
      // the two blocks will get merged.
      if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
        if (BI->isUnconditional())
          Worklist.push_back(BI);
    }
    return;
  }

  DEBUG(dbgs() << "Nuking dead block: " << *BB);
  
  // Remove the instructions in the basic block from the worklist.
  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
    RemoveFromWorklist(I, Worklist);
    
    // Anything that uses the instructions in this basic block should have their
    // uses replaced with undefs.
    // If I is not void type then replaceAllUsesWith undef.
    // This allows ValueHandlers and custom metadata to adjust itself.
    if (!I->getType()->isVoidTy())
      I->replaceAllUsesWith(UndefValue::get(I->getType()));
  }
  
  // If this is the edge to the header block for a loop, remove the loop and
  // promote all subloops.
  if (Loop *BBLoop = LI->getLoopFor(BB)) {
    if (BBLoop->getLoopLatch() == BB)
      RemoveLoopFromHierarchy(BBLoop);
  }

  // Remove the block from the loop info, which removes it from any loops it
  // was in.
  LI->removeBlock(BB);
  
  
  // Remove phi node entries in successors for this block.
  TerminatorInst *TI = BB->getTerminator();
  SmallVector<BasicBlock*, 4> Succs;
  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
    Succs.push_back(TI->getSuccessor(i));
    TI->getSuccessor(i)->removePredecessor(BB);
  }
  
  // Unique the successors, remove anything with multiple uses.
  array_pod_sort(Succs.begin(), Succs.end());
  Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
  
  // Remove the basic block, including all of the instructions contained in it.
  LPM->deleteSimpleAnalysisValue(BB, L);  
  BB->eraseFromParent();
  // Remove successor blocks here that are not dead, so that we know we only
  // have dead blocks in this list.  Nondead blocks have a way of becoming dead,
  // then getting removed before we revisit them, which is badness.
  //
  for (unsigned i = 0; i != Succs.size(); ++i)
    if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
      // One exception is loop headers.  If this block was the preheader for a
      // loop, then we DO want to visit the loop so the loop gets deleted.
      // We know that if the successor is a loop header, that this loop had to
      // be the preheader: the case where this was the latch block was handled
      // above and headers can only have two predecessors.
      if (!LI->isLoopHeader(Succs[i])) {
        Succs.erase(Succs.begin()+i);
        --i;
      }
//.........这里部分代码省略.........

Value* LoopTripCount::insertTripCount(Loop* L, Instruction* InsertPos)
{
	// inspired from Loop::getCanonicalInductionVariable
	BasicBlock *H = L->getHeader();
	BasicBlock* LoopPred = L->getLoopPredecessor();
	BasicBlock* startBB = NULL;//which basicblock stores start value
	int OneStep = 0;// the extra add or plus step for calc

   Assert(LoopPred, "Require Loop has a Pred");
	DEBUG(errs()<<"loop  depth:"<<L->getLoopDepth()<<"\n");
	/** whats difference on use of predecessor and preheader??*/
	//RET_ON_FAIL(self->getLoopLatch()&&self->getLoopPreheader());
	//assert(self->getLoopLatch() && self->getLoopPreheader() && "need loop simplify form" );
	ret_null_fail(L->getLoopLatch(), "need loop simplify form");

	BasicBlock* TE = NULL;//True Exit
	SmallVector<BasicBlock*,4> Exits;
	L->getExitingBlocks(Exits);

	if(Exits.size()==1) TE = Exits.front();
	else{
		if(std::find(Exits.begin(),Exits.end(),L->getLoopLatch())!=Exits.end()) TE = L->getLoopLatch();
		else{
			SmallVector<llvm::Loop::Edge,4> ExitEdges;
			L->getExitEdges(ExitEdges);
			//stl 用法,先把所有满足条件的元素(出口的结束符是不可到达)移动到数组的末尾,再统一删除
			ExitEdges.erase(std::remove_if(ExitEdges.begin(), ExitEdges.end(), 
						[](llvm::Loop::Edge& I){
						return isa<UnreachableInst>(I.second->getTerminator());
						}), ExitEdges.end());
			if(ExitEdges.size()==1) TE = const_cast<BasicBlock*>(ExitEdges.front().first);
		}
	}

	//process true exit
	ret_null_fail(TE, "need have a true exit");

	Instruction* IndOrNext = NULL;
	Value* END = NULL;
   //终止块的终止指令：分情况讨论branchinst,switchinst;
   //跳转指令br bool a1,a2;condition<-->bool
	if(isa<BranchInst>(TE->getTerminator())){
		const BranchInst* EBR = cast<BranchInst>(TE->getTerminator());
		Assert(EBR->isConditional(), "end branch is not conditional");
		ICmpInst* EC = dyn_cast<ICmpInst>(EBR->getCondition());
		if(EC->getPredicate() == EC->ICMP_SGT){
         Assert(!L->contains(EBR->getSuccessor(0)), *EBR<<":abnormal exit with great than");//终止块的终止指令---->跳出执行循环外的指令
         OneStep += 1;
      } else if(EC->getPredicate() == EC->ICMP_EQ)
         Assert(!L->contains(EBR->getSuccessor(0)), *EBR<<":abnormal exit with great than");
      else if(EC->getPredicate() == EC->ICMP_SLT) {
         ret_null_fail(!L->contains(EBR->getSuccessor(1)), *EBR<<":abnormal exit with less than");
      } else {
         ret_null_fail(0, *EC<<" unknow combination of end condition");
      }
		IndOrNext = dyn_cast<Instruction>(castoff(EC->getOperand(0)));//去掉类型转化
		END = EC->getOperand(1);
		DEBUG(errs()<<"end   value:"<<*EC<<"\n");
	}else if(isa<SwitchInst>(TE->getTerminator())){
		SwitchInst* ESW = const_cast<SwitchInst*>(cast<SwitchInst>(TE->getTerminator()));
		IndOrNext = dyn_cast<Instruction>(castoff(ESW->getCondition()));
		for(auto I = ESW->case_begin(),E = ESW->case_end();I!=E;++I){
			if(!L->contains(I.getCaseSuccessor())){
				ret_null_fail(!END,"");
				assert(!END && "shouldn't have two ends");
				END = I.getCaseValue();
			}
		}
		DEBUG(errs()<<"end   value:"<<*ESW<<"\n");
	}else{
		assert(0 && "unknow terminator type");
	}

	ret_null_fail(L->isLoopInvariant(END), "end value should be loop invariant");//至此得END值

	Value* start = NULL;
	Value* ind = NULL;
	Instruction* next = NULL;
	bool addfirst = false;//add before icmp ed

	DISABLE(errs()<<*IndOrNext<<"\n");
	if(isa<LoadInst>(IndOrNext)){
		//memory depend analysis
		Value* PSi = IndOrNext->getOperand(0);//point type Step.i

		int SICount[2] = {0};//store in predecessor count,store in loop body count
		for( auto I = PSi->use_begin(),E = PSi->use_end();I!=E;++I){
			DISABLE(errs()<<**I<<"\n");
			StoreInst* SI = dyn_cast<StoreInst>(*I);
			if(!SI || SI->getOperand(1) != PSi) continue;
			if(!start&&L->isLoopInvariant(SI->getOperand(0))) {
				if(SI->getParent() != LoopPred)
					if(std::find(pred_begin(LoopPred),pred_end(LoopPred),SI->getParent()) == pred_end(LoopPred)) continue;
				start = SI->getOperand(0);
				startBB = SI->getParent();
				++SICount[0];
			}
			Instruction* SI0 = dyn_cast<Instruction>(SI->getOperand(0));
			if(L->contains(SI) && SI0 && SI0->getOpcode() == Instruction::Add){
				next = SI0;
//.........这里部分代码省略.........

//.........这里部分代码省略.........
  assert(!LBraceLocs.empty() && "Should have at least one location here");

  // If we don't support assembly, or the assembly is empty, we don't
  // need to instantiate the AsmParser, etc.
  if (!TheTarget || AsmToks.empty()) {
    return Actions.ActOnMSAsmStmt(AsmLoc, LBraceLocs[0], AsmToks, StringRef(),
                                  /*NumOutputs*/ 0, /*NumInputs*/ 0,
                                  ConstraintRefs, ClobberRefs, Exprs, EndLoc);
  }

  // Expand the tokens into a string buffer.
  SmallString<512> AsmString;
  SmallVector<unsigned, 8> TokOffsets;
  if (buildMSAsmString(PP, AsmLoc, AsmToks, TokOffsets, AsmString))
    return StmtError();

  std::unique_ptr<llvm::MCRegisterInfo> MRI(TheTarget->createMCRegInfo(TT));
  std::unique_ptr<llvm::MCAsmInfo> MAI(TheTarget->createMCAsmInfo(*MRI, TT));
  // Get the instruction descriptor.
  std::unique_ptr<llvm::MCInstrInfo> MII(TheTarget->createMCInstrInfo());
  std::unique_ptr<llvm::MCObjectFileInfo> MOFI(new llvm::MCObjectFileInfo());
  std::unique_ptr<llvm::MCSubtargetInfo> STI(
      TheTarget->createMCSubtargetInfo(TT, "", ""));

  llvm::SourceMgr TempSrcMgr;
  llvm::MCContext Ctx(MAI.get(), MRI.get(), MOFI.get(), &TempSrcMgr);
  MOFI->InitMCObjectFileInfo(TheTriple, llvm::Reloc::Default,
                             llvm::CodeModel::Default, Ctx);
  std::unique_ptr<llvm::MemoryBuffer> Buffer =
      llvm::MemoryBuffer::getMemBuffer(AsmString, "<MS inline asm>");

  // Tell SrcMgr about this buffer, which is what the parser will pick up.
  TempSrcMgr.AddNewSourceBuffer(std::move(Buffer), llvm::SMLoc());

  std::unique_ptr<llvm::MCStreamer> Str(createNullStreamer(Ctx));
  std::unique_ptr<llvm::MCAsmParser> Parser(
      createMCAsmParser(TempSrcMgr, Ctx, *Str.get(), *MAI));

  // FIXME: init MCOptions from sanitizer flags here.
  llvm::MCTargetOptions MCOptions;
  std::unique_ptr<llvm::MCTargetAsmParser> TargetParser(
      TheTarget->createMCAsmParser(*STI, *Parser, *MII, MCOptions));

  std::unique_ptr<llvm::MCInstPrinter> IP(
      TheTarget->createMCInstPrinter(llvm::Triple(TT), 1, *MAI, *MII, *MRI));

  // Change to the Intel dialect.
  Parser->setAssemblerDialect(1);
  Parser->setTargetParser(*TargetParser.get());
  Parser->setParsingInlineAsm(true);
  TargetParser->setParsingInlineAsm(true);

  ClangAsmParserCallback Callback(*this, AsmLoc, AsmString, AsmToks,
                                  TokOffsets);
  TargetParser->setSemaCallback(&Callback);
  TempSrcMgr.setDiagHandler(ClangAsmParserCallback::DiagHandlerCallback,
                            &Callback);

  unsigned NumOutputs;
  unsigned NumInputs;
  std::string AsmStringIR;
  SmallVector<std::pair<void *, bool>, 4> OpExprs;
  SmallVector<std::string, 4> Constraints;
  SmallVector<std::string, 4> Clobbers;
  if (Parser->parseMSInlineAsm(AsmLoc.getPtrEncoding(), AsmStringIR, NumOutputs,
                               NumInputs, OpExprs, Constraints, Clobbers,
                               MII.get(), IP.get(), Callback))
    return StmtError();

  // Filter out "fpsw".  Clang doesn't accept it, and it always lists flags and
  // fpsr as clobbers.
  auto End = std::remove(Clobbers.begin(), Clobbers.end(), "fpsw");
  Clobbers.erase(End, Clobbers.end());

  // Build the vector of clobber StringRefs.
  ClobberRefs.insert(ClobberRefs.end(), Clobbers.begin(), Clobbers.end());

  // Recast the void pointers and build the vector of constraint StringRefs.
  unsigned NumExprs = NumOutputs + NumInputs;
  ConstraintRefs.resize(NumExprs);
  Exprs.resize(NumExprs);
  for (unsigned i = 0, e = NumExprs; i != e; ++i) {
    Expr *OpExpr = static_cast<Expr *>(OpExprs[i].first);
    if (!OpExpr)
      return StmtError();

    // Need address of variable.
    if (OpExprs[i].second)
      OpExpr =
          Actions.BuildUnaryOp(getCurScope(), AsmLoc, UO_AddrOf, OpExpr).get();

    ConstraintRefs[i] = StringRef(Constraints[i]);
    Exprs[i] = OpExpr;
  }

  // FIXME: We should be passing source locations for better diagnostics.
  return Actions.ActOnMSAsmStmt(AsmLoc, LBraceLocs[0], AsmToks, AsmStringIR,
                                NumOutputs, NumInputs, ConstraintRefs,
                                ClobberRefs, Exprs, EndLoc);
}

//.........这里部分代码省略.........

  // Include synthetic reference edges to known, defined lib functions.
  for (auto *F : G.getLibFunctions())
    // While the list of lib functions doesn't have repeats, don't re-visit
    // anything handled above.
    if (!Visited.count(F))
      VisitRef(*F);

  // First remove all of the edges that are no longer present in this function.
  // The first step makes these edges uniformly ref edges and accumulates them
  // into a separate data structure so removal doesn't invalidate anything.
  SmallVector<Node *, 4> DeadTargets;
  for (Edge &E : *N) {
    if (RetainedEdges.count(&E.getNode()))
      continue;

    SCC &TargetC = *G.lookupSCC(E.getNode());
    RefSCC &TargetRC = TargetC.getOuterRefSCC();
    if (&TargetRC == RC && E.isCall()) {
      if (C != &TargetC) {
        // For separate SCCs this is trivial.
        RC->switchTrivialInternalEdgeToRef(N, E.getNode());
      } else {
        // Now update the call graph.
        C = incorporateNewSCCRange(RC->switchInternalEdgeToRef(N, E.getNode()),
                                   G, N, C, AM, UR);
      }
    }

    // Now that this is ready for actual removal, put it into our list.
    DeadTargets.push_back(&E.getNode());
  }
  // Remove the easy cases quickly and actually pull them out of our list.
  DeadTargets.erase(
      llvm::remove_if(DeadTargets,
                      [&](Node *TargetN) {
                        SCC &TargetC = *G.lookupSCC(*TargetN);
                        RefSCC &TargetRC = TargetC.getOuterRefSCC();

                        // We can't trivially remove internal targets, so skip
                        // those.
                        if (&TargetRC == RC)
                          return false;

                        RC->removeOutgoingEdge(N, *TargetN);
                        LLVM_DEBUG(dbgs() << "Deleting outgoing edge from '"
                                          << N << "' to '" << TargetN << "'\n");
                        return true;
                      }),
      DeadTargets.end());

  // Now do a batch removal of the internal ref edges left.
  auto NewRefSCCs = RC->removeInternalRefEdge(N, DeadTargets);
  if (!NewRefSCCs.empty()) {
    // The old RefSCC is dead, mark it as such.
    UR.InvalidatedRefSCCs.insert(RC);

    // Note that we don't bother to invalidate analyses as ref-edge
    // connectivity is not really observable in any way and is intended
    // exclusively to be used for ordering of transforms rather than for
    // analysis conclusions.

    // Update RC to the "bottom".
    assert(G.lookupSCC(N) == C && "Changed the SCC when splitting RefSCCs!");
    RC = &C->getOuterRefSCC();
    assert(G.lookupRefSCC(N) == RC && "Failed to update current RefSCC!");