--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/llvm/lib/Analysis/CallGraphSCCPass.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,714 @@
+//===- CallGraphSCCPass.cpp - Pass that operates BU on call graph ---------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CallGraphSCCPass class, which is used for passes
+// which are implemented as bottom-up traversals on the call graph.  Because
+// there may be cycles in the call graph, passes of this type operate on the
+// call-graph in SCC order: that is, they process function bottom-up, except for
+// recursive functions, which they process all at once.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/CallGraphSCCPass.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SCCIterator.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/CallGraph.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRPrintingPasses.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/LegacyPassManagers.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/OptBisect.h"
+#include "llvm/IR/PassTimingInfo.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Timer.h"
+#include "llvm/Support/raw_ostream.h"
+#include <cassert>
+#include <string>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "cgscc-passmgr"
+
+static cl::opt<unsigned>
+MaxIterations("max-cg-scc-iterations", cl::ReallyHidden, cl::init(4));
+
+STATISTIC(MaxSCCIterations, "Maximum CGSCCPassMgr iterations on one SCC");
+
+//===----------------------------------------------------------------------===//
+// CGPassManager
+//
+/// CGPassManager manages FPPassManagers and CallGraphSCCPasses.
+
+namespace {
+
+class CGPassManager : public ModulePass, public PMDataManager {
+public:
+  static char ID;
+
+  explicit CGPassManager() : ModulePass(ID), PMDataManager() {}
+
+  /// Execute all of the passes scheduled for execution.  Keep track of
+  /// whether any of the passes modifies the module, and if so, return true.
+  bool runOnModule(Module &M) override;
+
+  using ModulePass::doInitialization;
+  using ModulePass::doFinalization;
+
+  bool doInitialization(CallGraph &CG);
+  bool doFinalization(CallGraph &CG);
+
+  /// Pass Manager itself does not invalidate any analysis info.
+  void getAnalysisUsage(AnalysisUsage &Info) const override {
+    // CGPassManager walks SCC and it needs CallGraph.
+    Info.addRequired<CallGraphWrapperPass>();
+    Info.setPreservesAll();
+  }
+
+  StringRef getPassName() const override { return "CallGraph Pass Manager"; }
+
+  PMDataManager *getAsPMDataManager() override { return this; }
+  Pass *getAsPass() override { return this; }
+
+  // Print passes managed by this manager
+  void dumpPassStructure(unsigned Offset) override {
+    errs().indent(Offset*2) << "Call Graph SCC Pass Manager\n";
+    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
+      Pass *P = getContainedPass(Index);
+      P->dumpPassStructure(Offset + 1);
+      dumpLastUses(P, Offset+1);
+    }
+  }
+
+  Pass *getContainedPass(unsigned N) {
+    assert(N < PassVector.size() && "Pass number out of range!");
+    return static_cast<Pass *>(PassVector[N]);
+  }
+
+  PassManagerType getPassManagerType() const override {
+    return PMT_CallGraphPassManager;
+  }
+
+private:
+  bool RunAllPassesOnSCC(CallGraphSCC &CurSCC, CallGraph &CG,
+                         bool &DevirtualizedCall);
+
+  bool RunPassOnSCC(Pass *P, CallGraphSCC &CurSCC,
+                    CallGraph &CG, bool &CallGraphUpToDate,
+                    bool &DevirtualizedCall);
+  bool RefreshCallGraph(const CallGraphSCC &CurSCC, CallGraph &CG,
+                        bool IsCheckingMode);
+};
+
+} // end anonymous namespace.
+
+char CGPassManager::ID = 0;
+
+bool CGPassManager::RunPassOnSCC(Pass *P, CallGraphSCC &CurSCC,
+                                 CallGraph &CG, bool &CallGraphUpToDate,
+                                 bool &DevirtualizedCall) {
+  bool Changed = false;
+  PMDataManager *PM = P->getAsPMDataManager();
+  Module &M = CG.getModule();
+
+  if (!PM) {
+    CallGraphSCCPass *CGSP = (CallGraphSCCPass *)P;
+    if (!CallGraphUpToDate) {
+      DevirtualizedCall |= RefreshCallGraph(CurSCC, CG, false);
+      CallGraphUpToDate = true;
+    }
+
+    {
+      unsigned InstrCount, SCCCount = 0;
+      StringMap<std::pair<unsigned, unsigned>> FunctionToInstrCount;
+      bool EmitICRemark = M.shouldEmitInstrCountChangedRemark();
+      TimeRegion PassTimer(getPassTimer(CGSP));
+      if (EmitICRemark)
+        InstrCount = initSizeRemarkInfo(M, FunctionToInstrCount);
+      Changed = CGSP->runOnSCC(CurSCC);
+
+      if (EmitICRemark) {
+        // FIXME: Add getInstructionCount to CallGraphSCC.
+        SCCCount = M.getInstructionCount();
+        // Is there a difference in the number of instructions in the module?
+        if (SCCCount != InstrCount) {
+          // Yep. Emit a remark and update InstrCount.
+          int64_t Delta =
+              static_cast<int64_t>(SCCCount) - static_cast<int64_t>(InstrCount);
+          emitInstrCountChangedRemark(P, M, Delta, InstrCount,
+                                      FunctionToInstrCount);
+          InstrCount = SCCCount;
+        }
+      }
+    }
+
+    // After the CGSCCPass is done, when assertions are enabled, use
+    // RefreshCallGraph to verify that the callgraph was correctly updated.
+#ifndef NDEBUG
+    if (Changed)
+      RefreshCallGraph(CurSCC, CG, true);
+#endif
+
+    return Changed;
+  }
+
+  assert(PM->getPassManagerType() == PMT_FunctionPassManager &&
+         "Invalid CGPassManager member");
+  FPPassManager *FPP = (FPPassManager*)P;
+
+  // Run pass P on all functions in the current SCC.
+  for (CallGraphNode *CGN : CurSCC) {
+    if (Function *F = CGN->getFunction()) {
+      dumpPassInfo(P, EXECUTION_MSG, ON_FUNCTION_MSG, F->getName());
+      {
+        TimeRegion PassTimer(getPassTimer(FPP));
+        Changed |= FPP->runOnFunction(*F);
+      }
+      F->getContext().yield();
+    }
+  }
+
+  // The function pass(es) modified the IR, they may have clobbered the
+  // callgraph.
+  if (Changed && CallGraphUpToDate) {
+    LLVM_DEBUG(dbgs() << "CGSCCPASSMGR: Pass Dirtied SCC: " << P->getPassName()
+                      << '\n');
+    CallGraphUpToDate = false;
+  }
+  return Changed;
+}
+
+/// Scan the functions in the specified CFG and resync the
+/// callgraph with the call sites found in it.  This is used after
+/// FunctionPasses have potentially munged the callgraph, and can be used after
+/// CallGraphSCC passes to verify that they correctly updated the callgraph.
+///
+/// This function returns true if it devirtualized an existing function call,
+/// meaning it turned an indirect call into a direct call.  This happens when
+/// a function pass like GVN optimizes away stuff feeding the indirect call.
+/// This never happens in checking mode.
+bool CGPassManager::RefreshCallGraph(const CallGraphSCC &CurSCC, CallGraph &CG,
+                                     bool CheckingMode) {
+  DenseMap<Value *, CallGraphNode *> Calls;
+
+  LLVM_DEBUG(dbgs() << "CGSCCPASSMGR: Refreshing SCC with " << CurSCC.size()
+                    << " nodes:\n";
+             for (CallGraphNode *CGN
+                  : CurSCC) CGN->dump(););
+
+  bool MadeChange = false;
+  bool DevirtualizedCall = false;
+
+  // Scan all functions in the SCC.
+  unsigned FunctionNo = 0;
+  for (CallGraphSCC::iterator SCCIdx = CurSCC.begin(), E = CurSCC.end();
+       SCCIdx != E; ++SCCIdx, ++FunctionNo) {
+    CallGraphNode *CGN = *SCCIdx;
+    Function *F = CGN->getFunction();
+    if (!F || F->isDeclaration()) continue;
+
+    // Walk the function body looking for call sites.  Sync up the call sites in
+    // CGN with those actually in the function.
+
+    // Keep track of the number of direct and indirect calls that were
+    // invalidated and removed.
+    unsigned NumDirectRemoved = 0, NumIndirectRemoved = 0;
+
+    // Get the set of call sites currently in the function.
+    for (CallGraphNode::iterator I = CGN->begin(), E = CGN->end(); I != E; ) {
+      // If this call site is null, then the function pass deleted the call
+      // entirely and the WeakTrackingVH nulled it out.
+      auto *Call = dyn_cast_or_null<CallBase>(I->first);
+      if (!I->first ||
+          // If we've already seen this call site, then the FunctionPass RAUW'd
+          // one call with another, which resulted in two "uses" in the edge
+          // list of the same call.
+          Calls.count(I->first) ||
+
+          // If the call edge is not from a call or invoke, or it is a
+          // instrinsic call, then the function pass RAUW'd a call with
+          // another value. This can happen when constant folding happens
+          // of well known functions etc.
+          !Call ||
+          (Call->getCalledFunction() &&
+           Call->getCalledFunction()->isIntrinsic() &&
+           Intrinsic::isLeaf(Call->getCalledFunction()->getIntrinsicID()))) {
+        assert(!CheckingMode &&
+               "CallGraphSCCPass did not update the CallGraph correctly!");
+
+        // If this was an indirect call site, count it.
+        if (!I->second->getFunction())
+          ++NumIndirectRemoved;
+        else
+          ++NumDirectRemoved;
+
+        // Just remove the edge from the set of callees, keep track of whether
+        // I points to the last element of the vector.
+        bool WasLast = I + 1 == E;
+        CGN->removeCallEdge(I);
+
+        // If I pointed to the last element of the vector, we have to bail out:
+        // iterator checking rejects comparisons of the resultant pointer with
+        // end.
+        if (WasLast)
+          break;
+        E = CGN->end();
+        continue;
+      }
+
+      assert(!Calls.count(I->first) &&
+             "Call site occurs in node multiple times");
+
+      if (Call) {
+        Function *Callee = Call->getCalledFunction();
+        // Ignore intrinsics because they're not really function calls.
+        if (!Callee || !(Callee->isIntrinsic()))
+          Calls.insert(std::make_pair(I->first, I->second));
+      }
+      ++I;
+    }
+
+    // Loop over all of the instructions in the function, getting the callsites.
+    // Keep track of the number of direct/indirect calls added.
+    unsigned NumDirectAdded = 0, NumIndirectAdded = 0;
+
+    for (BasicBlock &BB : *F)
+      for (Instruction &I : BB) {
+        auto *Call = dyn_cast<CallBase>(&I);
+        if (!Call)
+          continue;
+        Function *Callee = Call->getCalledFunction();
+        if (Callee && Callee->isIntrinsic())
+          continue;
+
+        // If this call site already existed in the callgraph, just verify it
+        // matches up to expectations and remove it from Calls.
+        DenseMap<Value *, CallGraphNode *>::iterator ExistingIt =
+            Calls.find(Call);
+        if (ExistingIt != Calls.end()) {
+          CallGraphNode *ExistingNode = ExistingIt->second;
+
+          // Remove from Calls since we have now seen it.
+          Calls.erase(ExistingIt);
+
+          // Verify that the callee is right.
+          if (ExistingNode->getFunction() == Call->getCalledFunction())
+            continue;
+
+          // If we are in checking mode, we are not allowed to actually mutate
+          // the callgraph.  If this is a case where we can infer that the
+          // callgraph is less precise than it could be (e.g. an indirect call
+          // site could be turned direct), don't reject it in checking mode, and
+          // don't tweak it to be more precise.
+          if (CheckingMode && Call->getCalledFunction() &&
+              ExistingNode->getFunction() == nullptr)
+            continue;
+
+          assert(!CheckingMode &&
+                 "CallGraphSCCPass did not update the CallGraph correctly!");
+
+          // If not, we either went from a direct call to indirect, indirect to
+          // direct, or direct to different direct.
+          CallGraphNode *CalleeNode;
+          if (Function *Callee = Call->getCalledFunction()) {
+            CalleeNode = CG.getOrInsertFunction(Callee);
+            // Keep track of whether we turned an indirect call into a direct
+            // one.
+            if (!ExistingNode->getFunction()) {
+              DevirtualizedCall = true;
+              LLVM_DEBUG(dbgs() << "  CGSCCPASSMGR: Devirtualized call to '"
+                                << Callee->getName() << "'\n");
+            }
+          } else {
+            CalleeNode = CG.getCallsExternalNode();
+          }
+
+          // Update the edge target in CGN.
+          CGN->replaceCallEdge(*Call, *Call, CalleeNode);
+          MadeChange = true;
+          continue;
+        }
+
+        assert(!CheckingMode &&
+               "CallGraphSCCPass did not update the CallGraph correctly!");
+
+        // If the call site didn't exist in the CGN yet, add it.
+        CallGraphNode *CalleeNode;
+        if (Function *Callee = Call->getCalledFunction()) {
+          CalleeNode = CG.getOrInsertFunction(Callee);
+          ++NumDirectAdded;
+        } else {
+          CalleeNode = CG.getCallsExternalNode();
+          ++NumIndirectAdded;
+        }
+
+        CGN->addCalledFunction(Call, CalleeNode);
+        MadeChange = true;
+      }
+
+    // We scanned the old callgraph node, removing invalidated call sites and
+    // then added back newly found call sites.  One thing that can happen is
+    // that an old indirect call site was deleted and replaced with a new direct
+    // call.  In this case, we have devirtualized a call, and CGSCCPM would like
+    // to iteratively optimize the new code.  Unfortunately, we don't really
+    // have a great way to detect when this happens.  As an approximation, we
+    // just look at whether the number of indirect calls is reduced and the
+    // number of direct calls is increased.  There are tons of ways to fool this
+    // (e.g. DCE'ing an indirect call and duplicating an unrelated block with a
+    // direct call) but this is close enough.
+    if (NumIndirectRemoved > NumIndirectAdded &&
+        NumDirectRemoved < NumDirectAdded)
+      DevirtualizedCall = true;
+
+    // After scanning this function, if we still have entries in callsites, then
+    // they are dangling pointers.  WeakTrackingVH should save us for this, so
+    // abort if
+    // this happens.
+    assert(Calls.empty() && "Dangling pointers found in call sites map");
+
+    // Periodically do an explicit clear to remove tombstones when processing
+    // large scc's.
+    if ((FunctionNo & 15) == 15)
+      Calls.clear();
+  }
+
+  LLVM_DEBUG(if (MadeChange) {
+    dbgs() << "CGSCCPASSMGR: Refreshed SCC is now:\n";
+    for (CallGraphNode *CGN : CurSCC)
+      CGN->dump();
+    if (DevirtualizedCall)
+      dbgs() << "CGSCCPASSMGR: Refresh devirtualized a call!\n";
+  } else {
+    dbgs() << "CGSCCPASSMGR: SCC Refresh didn't change call graph.\n";
+  });
+  (void)MadeChange;
+
+  return DevirtualizedCall;
+}
+
+/// Execute the body of the entire pass manager on the specified SCC.
+/// This keeps track of whether a function pass devirtualizes
+/// any calls and returns it in DevirtualizedCall.
+bool CGPassManager::RunAllPassesOnSCC(CallGraphSCC &CurSCC, CallGraph &CG,
+                                      bool &DevirtualizedCall) {
+  bool Changed = false;
+
+  // Keep track of whether the callgraph is known to be up-to-date or not.
+  // The CGSSC pass manager runs two types of passes:
+  // CallGraphSCC Passes and other random function passes.  Because other
+  // random function passes are not CallGraph aware, they may clobber the
+  // call graph by introducing new calls or deleting other ones.  This flag
+  // is set to false when we run a function pass so that we know to clean up
+  // the callgraph when we need to run a CGSCCPass again.
+  bool CallGraphUpToDate = true;
+
+  // Run all passes on current SCC.
+  for (unsigned PassNo = 0, e = getNumContainedPasses();
+       PassNo != e; ++PassNo) {
+    Pass *P = getContainedPass(PassNo);
+
+    // If we're in -debug-pass=Executions mode, construct the SCC node list,
+    // otherwise avoid constructing this string as it is expensive.
+    if (isPassDebuggingExecutionsOrMore()) {
+      std::string Functions;
+  #ifndef NDEBUG
+      raw_string_ostream OS(Functions);
+      for (CallGraphSCC::iterator I = CurSCC.begin(), E = CurSCC.end();
+           I != E; ++I) {
+        if (I != CurSCC.begin()) OS << ", ";
+        (*I)->print(OS);
+      }
+      OS.flush();
+  #endif
+      dumpPassInfo(P, EXECUTION_MSG, ON_CG_MSG, Functions);
+    }
+    dumpRequiredSet(P);
+
+    initializeAnalysisImpl(P);
+
+    // Actually run this pass on the current SCC.
+    Changed |= RunPassOnSCC(P, CurSCC, CG,
+                            CallGraphUpToDate, DevirtualizedCall);
+
+    if (Changed)
+      dumpPassInfo(P, MODIFICATION_MSG, ON_CG_MSG, "");
+    dumpPreservedSet(P);
+
+    verifyPreservedAnalysis(P);
+    removeNotPreservedAnalysis(P);
+    recordAvailableAnalysis(P);
+    removeDeadPasses(P, "", ON_CG_MSG);
+  }
+
+  // If the callgraph was left out of date (because the last pass run was a
+  // functionpass), refresh it before we move on to the next SCC.
+  if (!CallGraphUpToDate)
+    DevirtualizedCall |= RefreshCallGraph(CurSCC, CG, false);
+  return Changed;
+}
+
+/// Execute all of the passes scheduled for execution.  Keep track of
+/// whether any of the passes modifies the module, and if so, return true.
+bool CGPassManager::runOnModule(Module &M) {
+  CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
+  bool Changed = doInitialization(CG);
+
+  // Walk the callgraph in bottom-up SCC order.
+  scc_iterator<CallGraph*> CGI = scc_begin(&CG);
+
+  CallGraphSCC CurSCC(CG, &CGI);
+  while (!CGI.isAtEnd()) {
+    // Copy the current SCC and increment past it so that the pass can hack
+    // on the SCC if it wants to without invalidating our iterator.
+    const std::vector<CallGraphNode *> &NodeVec = *CGI;
+    CurSCC.initialize(NodeVec);
+    ++CGI;
+
+    // At the top level, we run all the passes in this pass manager on the
+    // functions in this SCC.  However, we support iterative compilation in the
+    // case where a function pass devirtualizes a call to a function.  For
+    // example, it is very common for a function pass (often GVN or instcombine)
+    // to eliminate the addressing that feeds into a call.  With that improved
+    // information, we would like the call to be an inline candidate, infer
+    // mod-ref information etc.
+    //
+    // Because of this, we allow iteration up to a specified iteration count.
+    // This only happens in the case of a devirtualized call, so we only burn
+    // compile time in the case that we're making progress.  We also have a hard
+    // iteration count limit in case there is crazy code.
+    unsigned Iteration = 0;
+    bool DevirtualizedCall = false;
+    do {
+      LLVM_DEBUG(if (Iteration) dbgs()
+                 << "  SCCPASSMGR: Re-visiting SCC, iteration #" << Iteration
+                 << '\n');
+      DevirtualizedCall = false;
+      Changed |= RunAllPassesOnSCC(CurSCC, CG, DevirtualizedCall);
+    } while (Iteration++ < MaxIterations && DevirtualizedCall);
+
+    if (DevirtualizedCall)
+      LLVM_DEBUG(dbgs() << "  CGSCCPASSMGR: Stopped iteration after "
+                        << Iteration
+                        << " times, due to -max-cg-scc-iterations\n");
+
+    MaxSCCIterations.updateMax(Iteration);
+  }
+  Changed |= doFinalization(CG);
+  return Changed;
+}
+
+/// Initialize CG
+bool CGPassManager::doInitialization(CallGraph &CG) {
+  bool Changed = false;
+  for (unsigned i = 0, e = getNumContainedPasses(); i != e; ++i) {
+    if (PMDataManager *PM = getContainedPass(i)->getAsPMDataManager()) {
+      assert(PM->getPassManagerType() == PMT_FunctionPassManager &&
+             "Invalid CGPassManager member");
+      Changed |= ((FPPassManager*)PM)->doInitialization(CG.getModule());
+    } else {
+      Changed |= ((CallGraphSCCPass*)getContainedPass(i))->doInitialization(CG);
+    }
+  }
+  return Changed;
+}
+
+/// Finalize CG
+bool CGPassManager::doFinalization(CallGraph &CG) {
+  bool Changed = false;
+  for (unsigned i = 0, e = getNumContainedPasses(); i != e; ++i) {
+    if (PMDataManager *PM = getContainedPass(i)->getAsPMDataManager()) {
+      assert(PM->getPassManagerType() == PMT_FunctionPassManager &&
+             "Invalid CGPassManager member");
+      Changed |= ((FPPassManager*)PM)->doFinalization(CG.getModule());
+    } else {
+      Changed |= ((CallGraphSCCPass*)getContainedPass(i))->doFinalization(CG);
+    }
+  }
+  return Changed;
+}
+
+//===----------------------------------------------------------------------===//
+// CallGraphSCC Implementation
+//===----------------------------------------------------------------------===//
+
+/// This informs the SCC and the pass manager that the specified
+/// Old node has been deleted, and New is to be used in its place.
+void CallGraphSCC::ReplaceNode(CallGraphNode *Old, CallGraphNode *New) {
+  assert(Old != New && "Should not replace node with self");
+  for (unsigned i = 0; ; ++i) {
+    assert(i != Nodes.size() && "Node not in SCC");
+    if (Nodes[i] != Old) continue;
+    if (New)
+      Nodes[i] = New;
+    else
+      Nodes.erase(Nodes.begin() + i);
+    break;
+  }
+
+  // Update the active scc_iterator so that it doesn't contain dangling
+  // pointers to the old CallGraphNode.
+  scc_iterator<CallGraph*> *CGI = (scc_iterator<CallGraph*>*)Context;
+  CGI->ReplaceNode(Old, New);
+}
+
+//===----------------------------------------------------------------------===//
+// CallGraphSCCPass Implementation
+//===----------------------------------------------------------------------===//
+
+/// Assign pass manager to manage this pass.
+void CallGraphSCCPass::assignPassManager(PMStack &PMS,
+                                         PassManagerType PreferredType) {
+  // Find CGPassManager
+  while (!PMS.empty() &&
+         PMS.top()->getPassManagerType() > PMT_CallGraphPassManager)
+    PMS.pop();
+
+  assert(!PMS.empty() && "Unable to handle Call Graph Pass");
+  CGPassManager *CGP;
+
+  if (PMS.top()->getPassManagerType() == PMT_CallGraphPassManager)
+    CGP = (CGPassManager*)PMS.top();
+  else {
+    // Create new Call Graph SCC Pass Manager if it does not exist.
+    assert(!PMS.empty() && "Unable to create Call Graph Pass Manager");
+    PMDataManager *PMD = PMS.top();
+
+    // [1] Create new Call Graph Pass Manager
+    CGP = new CGPassManager();
+
+    // [2] Set up new manager's top level manager
+    PMTopLevelManager *TPM = PMD->getTopLevelManager();
+    TPM->addIndirectPassManager(CGP);
+
+    // [3] Assign manager to manage this new manager. This may create
+    // and push new managers into PMS
+    Pass *P = CGP;
+    TPM->schedulePass(P);
+
+    // [4] Push new manager into PMS
+    PMS.push(CGP);
+  }
+
+  CGP->add(this);
+}
+
+/// For this class, we declare that we require and preserve the call graph.
+/// If the derived class implements this method, it should
+/// always explicitly call the implementation here.
+void CallGraphSCCPass::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<CallGraphWrapperPass>();
+  AU.addPreserved<CallGraphWrapperPass>();
+}
+
+//===----------------------------------------------------------------------===//
+// PrintCallGraphPass Implementation
+//===----------------------------------------------------------------------===//
+
+namespace {
+
+  /// PrintCallGraphPass - Print a Module corresponding to a call graph.
+  ///
+  class PrintCallGraphPass : public CallGraphSCCPass {
+    std::string Banner;
+    raw_ostream &OS;       // raw_ostream to print on.
+
+  public:
+    static char ID;
+
+    PrintCallGraphPass(const std::string &B, raw_ostream &OS)
+      : CallGraphSCCPass(ID), Banner(B), OS(OS) {}
+
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.setPreservesAll();
+    }
+
+    bool runOnSCC(CallGraphSCC &SCC) override {
+      bool BannerPrinted = false;
+      auto PrintBannerOnce = [&]() {
+        if (BannerPrinted)
+          return;
+        OS << Banner;
+        BannerPrinted = true;
+      };
+
+      bool NeedModule = llvm::forcePrintModuleIR();
+      if (isFunctionInPrintList("*") && NeedModule) {
+        PrintBannerOnce();
+        OS << "\n";
+        SCC.getCallGraph().getModule().print(OS, nullptr);
+        return false;
+      }
+      bool FoundFunction = false;
+      for (CallGraphNode *CGN : SCC) {
+        if (Function *F = CGN->getFunction()) {
+          if (!F->isDeclaration() && isFunctionInPrintList(F->getName())) {
+            FoundFunction = true;
+            if (!NeedModule) {
+              PrintBannerOnce();
+              F->print(OS);
+            }
+          }
+        } else if (isFunctionInPrintList("*")) {
+          PrintBannerOnce();
+          OS << "\nPrinting <null> Function\n";
+        }
+      }
+      if (NeedModule && FoundFunction) {
+        PrintBannerOnce();
+        OS << "\n";
+        SCC.getCallGraph().getModule().print(OS, nullptr);
+      }
+      return false;
+    }
+
+    StringRef getPassName() const override { return "Print CallGraph IR"; }
+  };
+
+} // end anonymous namespace.
+
+char PrintCallGraphPass::ID = 0;
+
+Pass *CallGraphSCCPass::createPrinterPass(raw_ostream &OS,
+                                          const std::string &Banner) const {
+  return new PrintCallGraphPass(Banner, OS);
+}
+
+static std::string getDescription(const CallGraphSCC &SCC) {
+  std::string Desc = "SCC (";
+  bool First = true;
+  for (CallGraphNode *CGN : SCC) {
+    if (First)
+      First = false;
+    else
+      Desc += ", ";
+    Function *F = CGN->getFunction();
+    if (F)
+      Desc += F->getName();
+    else
+      Desc += "<<null function>>";
+  }
+  Desc += ")";
+  return Desc;
+}
+
+bool CallGraphSCCPass::skipSCC(CallGraphSCC &SCC) const {
+  OptPassGate &Gate =
+      SCC.getCallGraph().getModule().getContext().getOptPassGate();
+  return Gate.isEnabled() && !Gate.shouldRunPass(this, getDescription(SCC));
+}
+
+char DummyCGSCCPass::ID = 0;
+
+INITIALIZE_PASS(DummyCGSCCPass, "DummyCGSCCPass", "DummyCGSCCPass", false,
+                false)